Note: Descriptions are shown in the official language in which they were submitted.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
NONWOVEN COMPOSITES AND RELATED PRODUCTS
AND METHODS
Background Of The Invention
Field of the Invention
[0002] This invention relates to substrates useful for catalyzing particular
reactions and for filtering particulate matter, and to embodiments related
thereto, such as but not limited to the treatment of emissions from internal
combustion engines, and more specifically to catalyst/substrate combinations
useful in emissions control and related processes and to related products and
methods of manufacture. It is believed that embodiments of the invention
described herein materially enhances the quality of the environment of
mankind by contributing to the restoration or maintenance of one or more
basic life-sustaining natural elements, including air, water, and/or soil. The
invention and embodiments thereof are more fully described below in the
Brief Summary of the Invention and Detailed Description sections.
-1-
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Exhaust, Industsy, and Pollution
[0003] Engines produce much of the power and mechanical work used across
the globe. The internal combustion engine is perhaps the most widespread
device, as it is more efficient than an external combustion engine, such as
those that existed on old-fashioned trains and steamboats. With internal
combustion engines, combustion of the fuel takes place internally. Such
engines produce motion and power used for any number of purposes.
Examples include motor vehicles, locomotives, marine applications,
recreational vehicles, tractors, construction equipment, generators, power
plants, manufacturing facilities, and industrial equipment. Fuels used to
power internal combustion engines include, but are not limited to gasoline,
compressed gas, diesel, ethanol, and vegetable oil. Inherent inefficiencies in
engine mechanics and the fuels used to power the them result in emissions of
various pollutants. Thus, while they are a great innovation and convenience,
the millions of engines used throughout the world today represent a
substantial
source of air pollution.
[0004] There are two main types of pollutants produced by internal
combustion engines: particulate and nonparticulate. Particulate pollution is
generally small solids and liquid particles. Examples include carbonaceous
soot and ash, dust, and other related particles. Nonparticulate pollutants
include gases and small molecules, such as carbon monoxide, nitrogen oxides,
sulfur oxides, unburned hydrocarbons, and volatile organic compounds.
Particulate pollutants can be filtered from the exhaust and, in certain
situations, further burned off. Nonparticulate pollutants are converted to
nonpollutants. Both kinds of pollutants can also be produced from non-engine
sources, such as "off-gas" chemical reactions and evaporative emissions.
[0005] Air pollution can cause serious health problems for people and the
environment. Ground-level ozone and airborne particles are the two pollutants
that pose one of the greatest threats to human health in this country. Ozone
(03), can irritate the respiratory system, causing coughing, irritation in the
throat, and/or a burning sensation in the respiratory airways. Ozone
contributes to the formation of smog. Ozone can also reduce lung function,
causing feelings of chest tightness, wheezing and shortness of breath, and can
2
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
aggravate asthma. Particle pollution, is composed of microscopic solids or
liquid droplets that are small enough to get deep into the lungs and cause
serious health problems. When exposed to these small particles, people may
experience nose and throat irritation, lung damage and bronchitis, and can
increase their risk of heart or lung disease. Short-term effects of air
pollutants
include irritation to the eyes, nose, and throat. Upper respiratory infections
such as bronchitis and pneumonia may also result. Other symptoms can
include headaches, nausea, and allergic reactions. Long-term health effects
can
include chronic respiratory disease, lung cancer, heart disease, and even
damage to the brain, nerves, liver, or kidneys. Continual exposure to air
pollution affects the lungs of growing children and may aggravate or
complicate medical conditions in the elderly.
[0006] Medical conditions arising from air pollution can be very expensive.
Healthcare costs, lost productivity in the workplace, and human welfare
impacts cost billions of dollars each year. Understanding the health effects
of
pollution and finding means to ameliorate, prevent, or eliminate pollution
would not only enhance the overall respiratory health of the population but
would also decrease the substantial burden and cost borne by the healthcare
system.
[0007] For all of these reasons, governments, environmental agencies, and
various industries have committed to reducing the level of air pollution
emitted from various sources. Government agencies are the principal bodies
setting emissions standards and implementing regulations. In the European
Union (EU), regulations stem from European Community legislation;
individual countries enforce the regulations. For instance, most EU states
have taxes on sources that produce excessive air pollution. A recent
development was the Kyoto Protocol, which called for worldwide reductions
in greenhouse gases. Many nations, including the EU, ratified the protocol.
The EU, Japan, and U.S. have enacted some of the most stringent standards
worldwide, but many other countries, including Argentina, Brazil, Mexico,
Korea, Thailand, India, Singapore, and Australia, have all enacted regulations
on air pollution. In the U.S., there are many different groups that affect
regulations in certain geographies, such as: state environmental agencies
(e.g.,
California Air Resources Board (CARB)), national parks, forest agencies, and
3
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the Mine Safety and Health Administration. Some states and metropolitan
areas that have failed national ambient air quality standards (NAAQS) have
been designated as "non-attainment areas" and implement standards of their
own. CARB has historically been one of the strictest agencies regulating air
pollution in the U.S.. The chief U.S. regulatory agency, however, is the
Environmental Protection Agency (EPA). It was created by the Nixon
administration in the 1970 amendments to the Clean Air Act (CAA) of 1963.
The Clean Air Act is the comprehensive Federal law that regulates air
emissions from area, stationary, and mobile sources. (See, e.g., 42 U.S.C. SS
7401 et seq. (1970) of the Clean Air Act). The Clean Air Act has had five
major amendments, the most recent of which was in 1990. The 1990
amendments to the Clean Air Act in large part were intended to meet
unaddressed or insufficiently addressed problems such as acid rain, ground-
level ozone, stratospheric ozone depletion, and air toxics. These amendments
required the EPA to issue 175 new regulations, including automotive
emissions, gasoline reformation, uses of ozone depleting chemicals, etc.
[0008] Following the Clean Air Act legislation, the EPA set regulations for
pollutants that are or could be harmful to people. This set of "criteria
pollutants" includes: (1) ozone (03); (2) lead (Pb); (3) nitrogen dioxide
(NO2);
(4) carbon monoxide (CO); (5) particulate matter (PM); and (6) sulfur dioxide
(SOa). Each criteria pollutant is described in turn.
[0009] Ground-level ozone (a primary constituent of smog) continues to be a
pollution problem in the U.S. Ozone is not emitted directly into the air but
is
formed by the reaction of volatile organic compounds (VOCs) or reactive
organic gases (ROGs) and nitrogen oxides (NOx) in the presence of heat and
sunlight. VOCs/ROGs are emitted from a various sources including burning
fuels, and from solvents, petroleum processing, and pesticides, which come
from sources such as motor vehicles, chemical plants, refineries, factories,
consumer and commercial products, and other industrial sources. Nitrogen
oxides are emitted from motor vehicles, power plants, and other sources of
combustion. Ozone and the precursor pollutants that cause ozone also can be
carried miles from their original sources by wind. In 1997, the EPA revised
the national ambient air quality standards for ozone by replacing the 1-hour
4
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
ozone 0.12 parts per million (ppm) standard with a new 8-hour 0.08 ppm
standard.
[0010] Nitrogen dioxide (NOZ) is a reactive gas that can be formed by the
oxidation of nitric oxide (NO). Nitrogen oxides (NOx), the term used to
describe NO, NO2, and other oxides of nitrogen, play a major role in the
formation of ozone and smog. The major sources of man-made NOx
emissions include high-temperature combustion processes, such as those
occurring in automobiles, heavy construction equipment, and power plants.
Home heaters and gas stoves also produce substantial amounts of NO2.
[0011] Carbon monoxide (CO) is a colorless, odorless, and poisonous gas that
can be formed by incomplete combustion of carbon in fuels. Motor vehicle
exhaust contributes about 60% of CO emissions in the U.S. In cities, as much
as 95% of CO emissions may come from automobile exhaust. Other sources
of CO emissions include industrial processes, non-transportation fuel
combustion, and natural sources such as wildfires.
[0012] Particulate matter (PM) is a term used for a mixture of solid particles
and liquid droplets found in the air. Some particles are large or dark enough
to
be seen as soot or smoke. Others are so small they can be detected only with
an electron microscope. These particles, which come in a wide range of sizes
("fine" particles are less than 2.5 micrometers in diameter and coarser
particles
are larger than 2.5 micrometers), originate from many different stationary and
mobile sources as well as from natural sources. Fine particles (PM-2.5) result
from fuel combustion from motor vehicles, power generation, and industrial
facilities, as well as from residential fireplaces and wood stoves. Coarse
particles (PM-10) are generally emitted from sources such as vehicles
traveling on unpaved roads, materials handling equipment, and crushing and
grinding operations, as well as windblown dust. Some particles are emitted
directly from their sources, such as smokestacks and cars. In other cases,
gases such as sulfur oxide, SO2, NOx, and VOC interact with other
compounds in the air to form fine particles. Their chemical and physical
compositions vary depending on location, time of year, and weather. In 1997,
the EPA added two new PM-2.5 standards, set at 15 micrograms per cubic
meter ( GA) and 65 ghn3, respectively, for the annual and 24-hour
standards.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0013] Sulfur dioxide can be formed when fuel containing sulfur (such as coal
and oil) is burned, for example, during metal smelting and other industrial
processes.
[0014] The last criteria pollutant, lead, was historically produced from use
of
leaded fuel in automobiles. As a result of regulatory efforts to reduce the
content of Pb in gasoline, the contribution from the transportation sector has
declined over the past decade. Today, metals processing is the major source of
Pb emissions to the atmosphere.
[0015] The Clean Air Act requires to EPA and states to develop plans to meet
national ambient air quality standards for these six criteria pollutants.
Outside
of the six is a separate list of 188 "toxic air pollutants." Examples of toxic
air
pollutants include benzene, found in gasoline; perchloroethylene, emitted from
some dry cleaning facilities; and methylene chloride, used as a solvent and
paint stripper by a number of industries. Some air toxics are released from
natural sources, but most originate from anthropogenic sources, including both
mobile sources (e.g., cars, trucks, and buses) and stationary sources (e.g.,
factories, refineries, and power plants). The CAA required the EPA to have a
two-phased program for these 188 pollutants. The first phase consists of
identifying the sources of toxic pollutants and developing technology-based
standards to significantly reduce them. The EPA determined a list of over 900
stationary sources, which resulted in new air toxics emissions standards,
affecting many industrial sources, including: chemical plants, oil refineries,
aerospace manufacturers, and steel mills, as well as smaller sources, such as
dry cleaners, commercial sterilizers, secondary lead smelters, and chromium
electroplating facilities. The second phase consists of strategies and
programs
for evaluating the remaining risks and ensuring that the overall program has
achieved substantial reductions; this phase is still in progress.
[0016] Internal combustion engines are directly affected by these regulations
since they emit criteria pollutants. These engines run on two fuel. The most
common types of fuel used are: gasoline and diesel. Each type of fuel
contains complex mixtures of hydrocarbon compounds as well as traces of
many other materials, including sulfur. Even when burned completely, these
fuels produce pollutants. Moreover, because no engine is capable of "perfect"
combustion, some fuel is incompletely oxidized and therefore produces
6
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
additional pollutants. Other types of fuel can also be used, for example,
ethanol mixtures, vegetable oils, and other fuels known in the art.
[0017] In gasoline engines, in order to reduce emissions, modern car engines
carefully control the amount of fuel they burn. They try to keep the air-to-
fuel
ratio very close to the stoichiometric point, which is the calculated ideal
ratio
of air to fuel. Theoretically, at this ratio, all of the fuel will be burned
using all
of the oxygen in the air. The fuel mixture actually varies from the ideal
ratio
quite a bit during driving. Sometimes the mixture can be lean (e.g., an air-to-
fuel ratio higher than the typical value of 14.7), and other times the mixture
can be rich (e.g., an air-to-fuel ratio lower than 14.7). These deviations
result
in various air emissions.
[0018] Significant emissions of a gasoline car engine include: nitrogen gas
(N2) (air is 78% N2); carbon dioxide (CO2), a combustion product; and water
vapor (HZO), another combustion product. These emissions are mostly benign
to humans (although excess levels of atmospheric CO2 are believed to
contribute to global warming). Gasoline engines, however, also produce
carbon monoxide, nitrogen oxides, and unburned hydrocarbons, all of which
are included in the EPA's criteria pollutants (unburned hydrocarbons form part
of the ozone formation mechanism, along with NOx).
[0019] Diesel engines also contribute to the criteria pollutants. These
engines
use hydrocarbon fractions that auto-ignite when compressed sufficiently in the
presence of oxygen. In general, diesel combusting within a cylinder produce
greater amounts of particulate matter and the pollutants nitrogen and sulfur
oxides (NOx and SO,t respectively) than does gasoline. Even so, diesel
mixtures are generally lean, with relatively abundant amounts of oxygen
present. Consequently, the combustion of smaller hydrocarbons is usually
more complete, producing less carbon monoxide than gasoline. Longer chain
hydrocarbons are more difficult to burn completely and can result in the
formation of particulate residues such as carbon "soot."
[0020] Despite these drawbacks, fossil fuels are relatively abundant, easy to
handle, and economical. Thus, these fuels will continue to represent a
significant source of mechanical power and pollution for years to come.
Moreover, the pervasiveness of the internal combustion engine indicates how
fossil fuels will continue to be a necessary source of energy.
7
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0021] There are at least three markets of internal combustion engines that
produce air significant pollution: 1) mobile, on-road engines, equipment, and
vehicles 2) mobile, non-road engines, equipment, and vehicles and 3)
stationary or "point" sources. In each of these markets, government agencies
and other organizations have dictated restrictions on levels of air pollution.
These restrictions have become increasingly stringent as the number of
internal combustion engines in use proliferates and more is learned about the
harm caused by air pollution. The ever-tightening regulations have required
industries to continuously research, develop, and invest in new emissions
control technologies, from fuel formulations to engine redesign, to after
treatment devices. These technologies vary in both effectiveness and cost but
have become essential in order for companies to comply with regulations. No
single emissions control technology has been able to remove all relevant
pollutants, so multiple technologies often have to be used together in order
to
enable a particular type of vehicle or equipment to meet regulatory emission
limits. These markets, their regulations, and the technologies on which they
rely are described in the following paragraphs. The technologies, including
their benefits and drawbacks, are described in more detail following this
section. While the sections focus on U.S. engines, equipment, and vehicles,
other geographies have similar products and regulations. For instance, the EU
has similar market sizes but focuses more on selective catalytic reduction
than
exhaust gas recirculation as a diesel emission control technology, uses
catalytic converters in a greater percentage of its small, off-road engines,
and
has a much larger percentage of diesel engines in light duty vehicles. Other
geographies have their own characteristic differences from the U.S., but
essentially use the same types of equipment and restrict the same types of air
pollutants.
[0022] The mobile, on-road engines, equipment, and vehicles include, but are
not limited to, passenger cars, pickup trucks, minivans, sport-utility
vehicles
(SUVs), buses, delivery trucks, semi-trucks, passenger vans, and two or three-
wheeled motorcycles designed for on-road use. These markets historically
have lead the way in emissions control and continue to do so today by
following regulations that dictate lower levels of air pollutants.
8
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0023] The car and truck markets are divided by weights. Those under 8,500
pounds Gross Vehicle Weight Rating (GVWR) are considered light duty
vehicles. Vehicles between 8,500 and 10,000 lbs GVWR that are designed for
passenger transport are considered medium duty vehicles. Vehicles over
8,500 lbs GVWR that are not designed for personal use are labeled as heavy-
duty vehicles.
[0024] Passenger cars and light-duty vehicles were previously regulated by
vehicle weight and fuel type but will be regulated in one group in future
standards. Less than 1% of -17 million new passenger cars and light-duty
vehicles produced in the United States use diesel engines. Passenger cars and
light-duty vehicles includes those made by manufacturers such as Ford,
General Motors (GM), DaimlerChrysler, BMW, Honda, Hyundai, Daewoo,
First Automobile Group, Toyota, Nissan, SAIC-Chevy and Subaru.
[0025] Regulations on passenger cars and light-duty vehicles have existed for
decades but have recently become much more stringent. The Tier 2 standards,
phasing in from model year (MY) 2004-2009, require original equipment
manufacturers (OEMs) to certify their fleet into certain "bins" of standards
and to maintain a corporate average for NOx emissions. Vehicles under
6,000lbs GVWR must be fully compliant by 2007, those from 6,000-8,500 lbs
and MDVs must be compliant by 2009. Pollutants included in the standards
include: NOx, formaldehyde (HCHO), CO, PM, and non-methane organic
gases. California has historically had tighter regulations than the EPA, and
other states, including New Jersey, New York, Vermont, Maine, and
Massachusetts, have joined in California's even lower emissions levels for new
and used vehicles. Manufacturers who do not meet the standards are
essentially prohibited from producing their vehicles in these markets, and are
fined for ones discovered on the market. In the aftermarket, states regulate
cars and light duty vehicles' emissions through inspection and maintenance
(I/M) programs. These programs are often created from state implementation
plans (SIPs) required in national ambient air quality (NAAQ) non-attainment
areas. Meeting both new vehicle and aftermarket standards requires the use of
emission control technologies, often in parallel.
[0026] Historically, three-way catalytic converters have had widespread use in
cars and light-duty vehicles. Recent improvements in these converters (such
9
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
as increased substrate porosity, an optimized washcoat, reduced catalyst
loading, etc), have yielded incremental improvements in emissions control. To
meet the newest set of U.S. regulations, manufacturers will likely increase
catalyst loading or the number of substrates per vehicle. Cars in use that do
not meet inspection/maintenance standards have to replace the faulty
technology or purchase additional devices. Other emission control devices
include, but are not limited to, advanced injection systems (such as injection
timing, injection pressure, rate shaping, common rail injection, and
electronic
controls), changed combustion chamber design (such as higher compression
ratios, piston geometry, and injector location), variable valve timing,
catalytic
converters, and filters.
[0027] Heavy-duty vehicles (HDV) include both private and commercial
trucks and buses over 8,500 lbs GVWR. The vast majority of these engines
run on diesel fuel; over 300,000 are produced each year in the U.S..
Manufacturers and engine suppliers include, but are not limited to, Cummins,
Caterpillar, Detroit Diesel, GM, Mack/Volvo, International/Navistar, Sterling,
Western Star, Kenworth, and Peterbilt. Other companies offering other
emission control technologies for the aftermarket include, but are not limited
to, Donaldson, Engelhard, Johnson Matthey, Lubrizol, Fleetguard, Cleaire,
Clean Air Partners, and Engine Control Systems.
[0028] Heavy-duty trucks are facing rigorous eniissions-reducing standards
for PM, NOx, CO, and non-methane hydrocarbons (NMHC). The PM
standard takes effect in 2007, while NOx and NMHC standards phase-in from
2007-2010. Similar to light duty vehicles, California, along with certain
other
states and metropolitan areas, has often enacted tighter emissions standards
than the EPA. For vehicles that do not meet standards, the manufacturers are
prohibited from selling them. Non-compliance penalties for NOx range up to
$12,000 per vehicle, based on size and compliance effort. While other
industries, such as locomotive, marine, agriculture, and construction use
highly similar engines to those in heavy-duty vehicles, the HDV market has
faced the tightest emission standards. Meanwhile, some states and
metropolitan areas (such as Califomia, New York City, and Seattle) require
additional retrofits or offer incentives for retrofits to further bring down
pollution levels. These areas have certified technologies that meet the
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
approved levels and qualifications. Examples include Donaldson's diesel
oxidation catalyst muffler and diesel particulate filter, Cleaire's diesel
oxidation catalyst and diesel particulate filter, and Johnson Matthey's
continuously regenerating technology particulate filter.
[0029] Emissions control technologies used to meet these standards and for
retrofits include, but are not limited to, advanced injection systems
(injection
timing, injection pressure, rate shaping, common rail injection, electronic
controls), exhaust gas recirculation, changes in combustion chamber design
(higher compression ratios, piston geometry, and injector location), advanced
turbocharging, ACERT, diesel particulate filters, NOx adsorbers, selective
catalytic reduction, conventional catalytic converters, catalytic exhaust
mufflers, and diesel oxidation catalysts. Meeting the 2007 standards has
initiated new research and development on many of these emission control
technologies. There has been tremendous cost and effort put into determining
an emissions control solution for 2007 HDVs.
[0030] Motorcycles are another type of mobile, on-road vehicle and include
both two and three-wheeled motorcycles designed for on-road use.
Motorcycles primarily use gasoline fuel. Manufacturers include, but are not
limited to: Harley Davidson, BMW, Honda, Kawasaki, Triumph, Tianjin
Gangtian, Lifan Motorcycle, and Yamaha. Regulations for on-road
motorcycles were adopted in 1978 and then left unrevised through 2003, when
new standards following those in California were agreed upon. Pollutants
monitored in the new standards include HC, NOx, and CO.
[0031] Emissions control technologies for motorcycles include, but are not
limited to, conversion of 2-stroke engines to 4-stroke, advanced injection
systems (injection timing, injection pressure, rate shaping, common rail
injection, and electronic controls), pulse air systems, changed combustion
chamber design (higher compression ratios, piston geometry, and injector
location), and use of catalytic converters. Limitations in motorcycles'
emissions control technologies are different than those in light or heavy-duty
vehicles. Motorcycles focus more on the appearance, placement, and heat of
aftertreatment devices, as there are fewer places to "hide" the device and the
passenger is in much closer proximity to the exothermic oxidation reaction.
11
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0032] The mobile, non-road engines, equipment, and vehicles category
includes, but is not limited to, engines for agriculture, construction,
mining,
lawn and garden, personal watercraft, boats, commercial ships, locomotives,
aircraft, snowmobiles, off-road motorcycles, and ATVs.
[0033] Small engines emit significant levels of air pollution for their size;
they
are the largest single contributor to nonroad HC inventories. Small engine
equipment includes, but is not limited to, leaf blowers, trimmers, brush
cutters,
chainsaws, lawn mowers, engine riding mowers, wood splitters, snowblowers,
and chippers. Engine and equipment manufacturers include, but are not
limited to, John Deere, Komatsu, Honda, Ryobi, Electrolux (Husqvarna and
Poulan, also supplies Craftsman), Fuji, Tecumseh, Stihl, American Yard
Products, and Briggs and Stratton.
[0034] The EPA began regulating small engines in 1993 (Phase I) with
standards that went into effect in 1997 and continued to reduce emission
levels
with new standards in 2002 (Phase II). The standards divide the equipment
into handheld and non-handheld categories and categorize it based on different
engine displacements. The regulations focus on hydrocarbons and nitrogen
oxides emissions.
[0035] Emissions control technologies include, but are not limited to, use of
a
catalyst (i.e., John Deere's LE technology and Komatsu's "Stratified
Scavenged" design), converting 2-stroke engines to 4-stroke, advanced
injection systems (injection timing, injection pressure, rate shaping, common
rail injection, electronic controls), or changing combustion chamber design
(higher compression ratios, piston geometry, and injector location).
[0036] The recreational vehicle markets include off-highway motorcycles,
snowmobiles, and all-terrain vehicles (ATVs). These are made by
manufacturers and engine suppliers such as:
[0037] Honda, John Deere, Kawasaki, Mitsubishi Motors, Nissan, Toyota,
Yanmar, Arctic Cat, Bombardier, Brunswisk, International Powercraft,
Polaris, Suzuki, and Yamaha.
[0038] The EPA began regulating recreational vehicles later than many other
markets, though California had regulations in place beforehand. EPA has
phase-ins from 2006-2009 for snowmobiles, and 2006-2007 for off-highway
motorcycles and ATVs. The regulated pollutants include HC, CO, and NOx.
12
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Emission control technologies for recreational vehicles include, but are not
limited to, converting 2-stroke engines to 4-stroke, advanced injection
systems
(injection timing, injection pressure, rate shaping, common rail injection,
electronic controls), pulse air, or changing combustion chamber design (higher
compression ratios, piston geometry, and injector location).
[0038] In mining, regulations are established by the Mine Safety and Health
Administration. Mining is often considered one of the most taxing
environments for equipment, due to the high levels of vibration, impact, and
dust. Temperature and flammability are also larger concerns in mining.
Diesel oxidation catalyst have been retrofitted on some mining equipment,
while diesel particulate filters are becoming more common.
[0039] In the agriculture and construction markets, the EPA regulates both
spark-ignition and compression-ignition engines. These can be used in
tractors, forklifts, bulldozers, electric generators, pavers, rollers,
trenchers,
drill rigs, mixers, cranes, balers, compressors, etc. Manufacturers of engines
and equipment include, but are not limited to: Agco, Komatsu, CNH Global,
Caterpillar, Cummins, Daewoo, John Deere & Co, Dueutz, Detroit Diesel, and
Kubota.
[0040] The EPA began regulating the diesel portion of these engines in 1994
(Tier 1) and has more recently increased the standards with Tier 2 (phased in
from 2001-2006). The standards are slated to increase again with Tier 3 levels
from 2006-2008. The Tier 3 levels will likely require the use of emissions
control devices similar to those used on heavy-duty vehicles (such as tractor-
trailers). The gasoline, liquid propane gas, or compressed natural gas (CNG)
engines used in agriculture and construction applications have also had recent
changes in regulations. Tier 1 levels began in 2004 and match those adopted
earlier by CARB; Tier 2 levels are expected to start in 2007. A voluntary
program for vehicles with lower emissions than the standards exists, named
"Blue Skies Series." Based on engine size and fuel type, the levels of
particulates, carbon monoxide, nitrogen oxides, and non-methane
hydrocarbons all must be significantly reduced for current phase-ins and for
shortly forthcoming standards.
[0041] Emissions control technologies are similar to those used on heavy-duty
vehicles and includes, but is not limited to, advanced injection systems
13
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
(injection timing, injection pressure, rate shaping, common rail injection,
electronic controls), exhaust gas recirculation, changes in combustion chamber
design (higher compression ratios, piston geometry, and injector location),
advanced turbocharging, ACERT, diesel particulate filters, NOx adsorbers,
selective catalytic reduction, conventional catalytic converters, catalytic
exhaust mufflers, and diesel oxidation catalysts. Exhaust gas recirculation
(EGR) has been problematic due to its tendency to create sulfuric acid
formation in the engine's intake. It also requires cooling, which necessitates
a
larger radiator, and thus a larger nose on the vehicle, creating aerodynamic
and
fuel economy constraints.
[0042] In marine applications, engines can generally be divided by use of
gasoline or diesel fuel, personal or commercial use, or by engine size. Marine
units range from personal watercraft, to yachts, to ferries, to tugs and ocean-
going ships. Manufacturers and engine suppliers include, but are not limited
to: Bombardier (Evinrude, Johnson, Ski Doo, Rotax, etc), Caterpillar,
Cummins, Detroit Diesel, GM, Isuzu, Yanmar, Alaska Diesel, Daytona
Marine, Marine Power, Atlantic Marine, Bender Shipbuilding, Bollinger
Shipyards, VT Halter Marine, Eastern Shipbuilding, Gladding-Hearn,
JeffBoat, Main Iron Works, Master Boat, Patti Shipyard, Quality shipyards,
and Verret Shipyard, MAN B&W Diesel, Wartsila, Mitsubishi, Bath Iron
Works, Electric Boat, Northrop Grumman (includes Avondale, Ingalls, and
Newport News Shipyards).
[0043] The EPA regulates boats whether they are recreational, private, or
commercial. The major category divisions are based on engine displacement,
from recreational vehicles to tankers. Diesel marine non-recreational boats
under thirty liter (30L) displacement, including fishing boats, tugboats,
towboats, dredgers, and cargo vessels, have new standards for NOx and PM
going into effect between 2004 and 2007, depending on engine size. Diesel
marine non-recreational boats over 30L, including container ships, tankers,
bulk carriers, and cruise ships, have NOx standards going into effect in 2004
(Tier 1) and additional HC, PM, and CO standards in 2007 (Tier 2). Diesel
marine recreational boats, including yachts, cruisers, and other types of
pleasure craft, have standards matching those of diesel marine non-
recreational boats under 30L displacement, but have later implementation
14
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
dates, ranging from 2006-2009 based on engine size. Gasoline and diesel
boats only have regulations currently applying HC emissions in outboard
engines, personal watercraft, and jetboats. Sterndrive and inboard engines are
inherently cleaner and are not yet regulated.
[0044] Emissions control technologies are similar to those used on heavy-duty
vehicles and include, but are not limited to, using "green terminals" when the
boat is at dock, conversion from 2-stroke to 4-stroke engines, water
aftercooling, exhaust gas recirculation, diesel particulate filters, selective
catalytic reduction, diesel oxidation catalyst, catalytic converters, advanced
fuel injection (injection timing, injection pressure, rate shaping, common
rail
injection, electronic controls), advanced turbocharging, variable valve
timing,
and changing the combustion chamber design (higher compression ratios,
piston geometry, and injector location). Using smaller engines for auxiliary
power (e.g., auxiliary power unit, APU) also helps to control emissions.
While salt water and its associated pollutants and cooling effect on boats
present difficulties in aftertreatment, the APU may work well with an
aftertreatment device.
[0045] The locomotive market relies principally on diesel fuel (coal and
wood-fired have limited use) and includes trains used in freight and passenger
rail, line-haul, local, and switch yard service. There are over 600 trains
produced each year in the U.S. Manufacturers and engine suppliers include,
but are not limited to, GM's Electromotive Division, GE Transportation
Systems, Caterpillar, Detroit Diesel, Cummins, MotovePower, Peoria
Locomotive Works, Republic Locomotives, Trinity, Greenbrier, and CSX.
[0046] Regulations on trains began in 2000 and largely imitated those of
heavy-duty vehicles. The standards include levels for newly produced
engines, as well as for engines that are remanufactured (which occurs
approximately ever 4-8 years) and vary based on whether the engine is for
switch or line-haul purposes. Tier 0 applies to engine model years (MY) from
1973-2001, Tier 1 to MY2002-2004, and Tier 2 to MY2005 and later. A non-
compliance penalty can range up to $25,000 per engine per day. The
pollutants regulated include particulate matter, NOx, HC, CO, and smoke
opacity.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0047] Emissions control technologies are similar to those used on heavy-duty
vehicles and include, but are not limited to, advanced injection systems
(injection timing, injection pressure, rate shaping, common rail injection,
electronic controls), exhaust gas recirculation, changes to combustion chamber
design (higher compression ratios, piston geometry, and injector location),
selective catalytic reduction, diesel oxidation catalysts, and aftercoolers,
split
cooling, zeolite sieves, and NOx reduction catalysts. Using a smaller,
auxiliary power unit is also becoming an emissions control strategy, one which
has fewer restrictions around the use of an aftertreatment device
[0048] The aircraft market includes all types of aircraft, including planes
made by Boeing, Airbus, Cessna, Gulfstream, and Lockheed Martin, among
others. Both the EPA and European Union follow the International Civil
Aviation Organization's (ICAO) emissions standards. The EPA adopted
ICAO's current standards for CO and NOx in gas turbine engines in 1997,
having adopted their HC levels in 1984. In the U.S., the FAA monitors and
enforces these standards. Much of the emissions control is done through
engine technologies and fuel changes.
[0049] Stationary sources include those sources of pollution that are non-
mobile. The EPA has issued rules covering over 80 categories of major
industrial sources, including power plants, chemical plants, oil refineries,
aerospace manufacturers, and steel mills, as well as categories of smaller
sources, such as dry cleaners, commercial sterilizers, secondary lead
smelters,
and chromium electroplating facilities. Power plants can use stationary diesel
engines, stationary gas turbines, and nuclear power, among other sources.
Each of these sources produces different pollutants; for instance, nuclear
power plants produce iodine and hydrogen, gas turbines produce NOx, CO,
SOx, CH4, and VOCs, and refineries produce gaseous vapors, CO, NOx,
VOCs, CO2, CH4, and PM. Each industry requires different control
technologies to reduce air emissions.
[0050] EPA regulations cover the six criteria pollutants and the additional
188
toxic air pollutants. Specific programs implemented include the Acid Rain
Program, designed to reduce sulfur emissions and the Ozone Transport
Commission's NOx Budget Program, designed to reduce NOx emissions.
RECLAIM is a program established for trading NOx and SOx credits. In
16
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
addition, cap and trade programs have been implemented in some industries
and geographies, allowing companies to trade their emission credits.
[0051] The technology used to control emissions from stationary sources
varies widely, but examples include filters, scrubbers, sorbents, selective
catalytic reduction (SCR), precipitators, zero-slip catalysts, catalysts for
turbines, or oxidation catalysts. Some of the suppliers of emissions control
systems to stationary markets include: M+W Zander, Crystall, Jacobs E.,
Takasogo, IDC, ADP, Marshall, Bechtel, Megte, Angui, Adwest, Eisenmann,
Catalytic Products, LTG, Durr, Siemens, Alston. Catalyst suppliers include:
Nikki, BASF, Cormetech, W.R. Grace, Johnson Matthey, UOP, and Sud
Chemie.
[0052] Due to the importance of improving air quality and complying with
relevant laws and regulations, substantial time, money, and effort have been
invested in technologies capable of reducing emissions. Three general areas
of technology include, a) engine improvements, b) fuel improvements, and c)
after-treatments. These approaches are typically not mutually exclusive or
stand-alone solutions. Engine improvements include, but are not limited to,
such technologies as: advanced injection systems, exhaust gas recirculation,
electronic sensors and fuel controls, combustion chamber designs, advanced
turbocharging, and variable valve timing. Fuel improvements include, but are
not limited to, such formulations as: high cetane, low aromatics, low sulfur
fuel, fuel borne catalysts, liquefied petroleum gas (LPG), oxygenation of
fuels,
compressed natural gas (CNG) and biodiesels. After-treatment technologies
include, but are not limited to: catalytic converters (2, 3, and 4-way),
particulate traps, selective catalytic reduction, NOx adsorbers, HC adsorbers,
NOx reduction catalysts, and many others. Some systems incorporate various
pieces of these and other technologies; ACERT by Caterpillar or catalyzed
diesel particulate traps are examples of combination systems and devices.
There are also some technologies that are currently limited in use, either by
technological or commercial restrictions.
[0053] Advanced injection systems include changes in injection timing,
injection pressure, rate shaping, air-assisted fuel injection, sequential
multi-
point injection, common rail injection, resizing or moving the injector holes,
and some electronic controls. In the common-rail system, a
17
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
microcomputerized fuel pump controls the flow and timing of fuel (e.g., the
Mercedes-Benz E320 uses this system). Secondary air injection can promote
HC and CO combustion in the manifold. Changing the injection system can
reduce a variety of emissions and can also increase fuel economy; however,
this requires significant work on the engine to ensure efficiency.
[0054] Exhaust gas recirculation (EGR) directs some of the exhaust gases
back into the intake of the engine. By mixing the exhaust gases with the fresh
intake air, the amount of oxygen entering the engine is reduced, resulting in
lower nitrogen oxide emissions. EGR does not require regular maintenance
and works well in combination with high swirl, high turbulence combustion
chambers. EGR also has drawbacks, such as reduced fuel efficiency and
engine life, greater demands on the vehicle's cooling system, limited to no
effect on pollutants other than NOx, and it requires control algorithms and
sensors. For these reasons, EGR is often used in parallel with another control
technology. Companies involved in EGR technology include Doubletree
Technologies, ETC, STT Emtec, Cummins, Detroit Diesel, Mack, and Volvo.
[0055] Optimizing the combustion chamber, or making incremental
improvements to it, is another way manufacturers and developers are
controlling emissions. Reducing the crevice volumes can limit trapping of
unburned fuel (and thus HC formation), while reducing the amount of
lubricating oil can also reduce HC formation and can limit catalyst poisoning.
Other measures include: improving the surface finishes of cylinders and
pistons, improving piston ring design and material, and improving exhaust
valve stem seals. Also, a "fast burn" combustion chamber can be made by:
increasing the rate of combustion, reducing the spark advance, adding a
dilutent to the air-fuel mixture, and/or increasing turbulence in the chamber.
While optimizing the combustion chamber can lead to reduced emissions, it is
another technology that requires reworking of the engine, which can be an
expensive process.
[0056] Variable valve timing involves calibrating the engine valves to open
and close for maximum fuel and engine efficiency. Often, a sensor is used to
detect the engine's speed and to adjust the valve openings and closings
accordingly. This technology can increase engine torque and horsepower and
can improve swirl and intake charge velocity, thus improving the efficiency of
18
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
combustion. Variable valve technology does not reduce emissions as much as
some other technologies and often leads to reductions in fuel efficiency.
[0057] Reformulating or using different fuels is another emissions control
technique, as some fuels naturally pollute more than others, while some tend
to poison the catalysts that would otherwise clean the exhaust air. For
instance, the shift from leaded to unleaded fuel in the U.S. greatly decreased
lead emissions. Lowering the sulfur content in fuel reduces SOx emissions
and increases the efficiency of many catalytic converters, as sulfur can
poison
catalysts. Another type of fuel, natural gas, typically produces less
particulate
pollution than diesel fuel and also can reduce NOx and combustion noise.
Conversely, natural gas also can increase vehicle weight (due to the need for
high pressure tanks) and has refueling limitations.
[0058] Using an aftertreatment device-equipment that is used after the fuel is
combusted-is very common in certain industries affected by emissions
control regulations. One example of an aftertreatment device is a catalytic
converter. Catalytic converters can vary widely and can have different
functions, but the general description is a device that treats exhaust with
the
use of catalysts. The composition of the substrates and the catalysts that are
on it have changed throughout the years, as has the placement and the number
of converters.
[0059] A two-way catalytic converter performs oxidation of gas-phase
pollution, such as the oxidation of HC and CO to COZ and H2O. Diesel
oxidation catalysts (DOCs) are another type of two-way catalytic converter
used with diesel engines. While these converters are effective at controlling
HC and CO and require little maintenance, they can increase NOx emissions
and are sensitive to sulfur.
[0060] A three-way catalytic converter perform.s both oxidation (conversion of
CO and HC to CO2 and H2O) and reduction (conversion of NOx to N2 gas)
reactions. Since the 1970s, three-way catalytic converters have reduced
vehicle emissions. Further performance improvements by these devices are
limited by a number of factors, such as the temperature range and surface area
of their substrates and by catalyst poisoning. To meet increasingly stringent
regulations, some cars require multiple catalytic converters.
19
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0061] A four-way catalytic converter performs oxidation and reduction
reactions, and traps particulates to burn them off (regeneration can occur in
active or passive mode).
[0062] Suppliers of catalytic converters and their associated parts include,
but
are not limited to, Corning, NGK, Denso, Ibiden, Emitec, Johnson Matthey,
Engelhard, Catalytic Solutions, Delphi, Umicore, 3M, Schwabische Hutten-
Werke GmbH (SHW); Hermann J. Schulte(HJS), Clean Diesel Technology,
Cleaire, Clean Air Systems, ArvinMeritor, Tenneco, Eberspacher, Faurecia,
Donaldson, and Fleetguard.
[0063] Particulate traps or filters are another type of aftertreatment device
commonly used in diesel applications, as diesel fuel generates more
particulate
matter than gasoline or some alternative fuels. In a diesel particulate trap
(DPT), particles in the exhaust stream pass through a filter that collects
them.
The removal of particulate matter that is collected on the trap is referred to
as
"regeneration" and can occur in multiple ways. One method uses external
heaters to raise the temperature of the filter to a level necessary for the PM
to
"burn off." Another method releases small amounts of diesel fuel in the
exhaust stream. When the fuel particles come in contact with the filter, the
fuel burns off at an elevated temperature. This higher temperature burns the
PM off the filter as well. Yet another means is to use fuel borne catalysts to
facilitate regeneration. In another approach, called a "catalyzed diesel
particulate trap," a catalyst is applied directly to the filter itself, which
reduces
the temperature necessary for the PM to burn off. Finally, an oxidation
catalyst can be used in front of the filter to facilitate burn off of the PM.
Johnson Matthey's Continuously Regenerating Trap (CRT) is such a system.
Diesel particulate traps can reduce PM by as much as 85% in some
applications. Traps utilizing a catalyst can also reduce other pollutants
besides
PM (e.g., HC, CO, and PM) with use of a catalyst (as mentioned earlier).
Conversely, these traps can become clogged with PM, soot, and ash and
catalyzed versions can be poisoned. They also add cost and weight to
vehicles.
[0064] Diesel particulate traps can use a number of different types of
filters,
including: ceramic monolithic cell fiber (Corning, NGK), fiber-wound filter
(3M), knitted fiber (BUCK), woven fiber (HUG, 3M), sintered metal fiber
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
(SHW, HJS) or filter paper, among others. Suppliers of these devices and
their related technologies -include, but are not limited to, Donaldson,
Engelhard, Johnson Matthey, HJS, Eminos, Deutz, Coming, ETG, Paas, and
Engine Control Systems.
[0065] Selective catalytic reduction (SCR) is another example of an
aftertreatment system. In this technology, a chemical capable of acting as a
reducing agent, such as urea, is added before the exhaust reaches the catalyst
chamber. Urea hydrolyzes to form ammonia. The ammonia then reacts with
the NOx of the exhaust gas to yield N2 gas, thereby decreasing NOx
emissions. The ammonia may be directly injected or be held in the form of
solid urea, urea solution or in crystalline form. An oxidation catalyst is
often
used in parallel with SCR to reduce CO and HC. Unfortunately, while SCR is
effective in reducing NOx and has low catalyst deterioration with good fuel
economy, it requires an additional tank on the vehicle and an infrastructure
for
refilling the tank. It is also dependent on end user compliance; companies and
drivers are required to refill the tank in order to maintain the emissions
control. Suppliers of SCR or its components include, but are not limited to,
Engelhard, Johnson Matthey, Miratech Corporation, McDermott, ICT, Sud
Chemie, SK Catalysts, and PE Systems,. While only used in the U.S. on a
limited basis, SCR is expected to be widely used in Europe to reduce
emissions, particularly in the heavy duty truck market.
[0066] NOx adsorbers are materials that store NOx under lean conditions and
release and catalytically reduce it under fuel rich conditions (typically
every
few minutes). This technology can work in both gas and diesel applications,
though gas provides a better fuel rich, high temperature environment. NOx
adsorbers reduce the levels of HC, NOx, and CO, but have little to no effect
on
PM. They can function under a wide range of temperatures. Conversely, NOx
adsorbing capacity decreases based on temperature, requires engine controls
and sensors, and is functionally hindered or disabled by the sulfur content in
fuel. In diesel applications, there are additional constraints, including the
quantity of oxygen present in the exhaust, the HC utilization rate, the
temperature range, and smoke or particulate formation.
[0067] A NOx reduction catalyst can also be used to control emissions by
1) actively injecting reductant into the system ahead of the catalyst and/or
21
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
2) using a washcoat with a zeolite that adsorbs HC, thus creating an oxidizing
region conducive to reducing NOx. While this technology can reduce NOx
and PM, it is more expensive than many other technologies and can lead to
poor fuel economy or sulfate particulates.
[0068] HC adsorbers are designed to trap VOCs while the catalyst is cold and
then release them once the catalyst is heated. This can be done by 1) coating
the adsorber directly onto the catalytic converter substrate, which allows for
minimal changes but less control, 2) locating the adsorber in a separate, but
connected exhaust pipe before the catalytic converter and having the air
switch
channels once the converter is heated, and/or 3) placing the adsorber after
the
catalyst. The last two options require a cleaning option for the adsorber.
While this technology reduces cold start emissions, it is difficult to control
and
adds cost.
[0069] Since emissions have proven difficult to control, emissions control
technologies are often combined in a system. Examples of combination
systems include: a DeNOx and DPT (such as HJS' SCRT system), a catalytic
converter placed in the muffler, SCR integrated with the muffler, or a
catalyzed diesel particulate filter.
[0070] ACERT is another example of a system incorporating multiple
emissions control technologies. ACERT, from Caterpillar, targets four areas -
intake air handling, combustion, electronics, and exhaust aftertreament. Key
components include single and series turbocharging for cooling intake air;
variable valve actuation for improving fuel burns; electronic multiplexing for
integrating computer control; and catalytic conversion for reducing tailpipe
particulate emissions. Working in concert, these subsystems allow the
company to increase fuel savings. A significant weakness of this technology
is the high volume of catalyst needed.
[0071] There are many other emissions control technologies, some of which
are not yet technically feasible.
Catalytic Converters
[0072] The concerns of pollution caused partly by the automobile led to the
Clean Air Act of 1970 which required 90 percent reductions in auto exhaust.
22
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
The mandatory reduction was considered controversial by some but generally
recognized as an advance for clean air and better health.
[0073] The automobile industry initially offered resistance to the new
proposed regulations. Part of the resistance may have stemmed from the
industries' development of improved fuels. From the mid 1920's until the mid
1980's, motor gasoline fuel contained an additive, tetraethyllead (TEL). TEL
improved fuel performance by preventing pre-ignition in the cylinders of the
engine. Pre-ignition results when the fuel/air mixture ignites prematurely in
the combustion chamber of an engine. This results in damage to the engine
and efficiency and power reducing caused by knocking.
[0074] To attain the reduced emission standards set by the government,
engineers invented the catalytic converter. The catalytic converter was added
to vehicle exhaust systems starting about 1976. The catalytic converter was
effective in reducing emissions to a certain degree. However, the common
gasoline formulations containing TEL interfered with the function of the
catalytic converter. Because the TEL in the fuel poisoned the metal catalysts
of the catalytic converter, TEL was eventually removed from fuel.
[0075] While many people may be aware that many vehicles have a catalytic
converter, it is generally an unappreciated piece of technology. The purpose
of the catalytic converter is to convert, or change, exhaust gases that are
pollutants to less harmful compounds, such as nitrogen (N2, which makes up
about 78% of the atmosphere), water (H20), and carbon dioxide (C02, a
product of photosynthesis in plants).
[0076] The catalytic converter is used to facilitate the conversion of the
unwanted pollutants to relatively harmless molecules such as N2, H20, and
CO2. Basically, the catalytic converter provides a surface on which the
pollutants are converted into the relatively harmless products. A catalyst
allows the reaction to proceed faster (or at a lower temperature) by lowering
the activation energy required. However, a catalyst is not used up in the
reaction and can be used again (unless the catalyst is poisoned).
[0077] Typical pollutants in exhaust include nitrogen oxides (NOx), unburned
hydrocarbons, carbon monoxide, and particulate matter. The nitrogen oxides
can be reduced to form nitrogen. When an NO or NO2 molecule contacts the
catalyst, the catalyst facilitates removal of nitrogen from the molecule,
freeing
23
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
oxygen in the form of 02. Nitrogen atoms adhering to the catalyst then react
to form NZ gas: 2 N0 => N2 + O2 and 2 NO2 => N2 + 2 02.
[0078] The carbon monoxide, unburned hydrocarbons, and particulate matter
can be further oxidized to form nonpollutants. For example, carbon monoxide
is processed as shown: 2 CO + 02 => 2 COZ.
[0079] The overall result of the catalytic converter is to complete the
combustion of fuel into nonpollutants.
[0080] Conventional catalytic converters have a number of limitations on their
effectiveness of eliminating pollutants. For example, if they are located too
close to an engine, they can crack from overheating or a quick change in
temperature. As such, the filters of the conventional catalytic converters
cannot be placed immediately next to or inside an engine exhaust manifold,
which is an optimal location to take advantage of the in situ high
temperatures
before the temperature decreases due to radiant cooling from the high thermal
conducting properties of exhaust pipe material. Engine vibration and the
quick change in temperatures that exist near and within the exhaust manifold
would cause conventional filter material to fatigue and dramatically shorten
the life of the filters. In addition, some catalysts applied to conventional
filters
work less efficiently or even cease to function at high temperatures, i.e.,
above
500 degrees Celsius. Accordingly, the conventional catalytic converter filters
are usually placed in the exhaust path in a location away from the engine.
Structures of Catalytic Converter and Particulate Filter
[0081] The components and materials of a catalytic converter are shown
schematically in Figures 4a and 4b. The catalyst substrate is held within the
converter shell (also called a canister) using packaging mat (most often made
of ceramic fibers). The converter is connected to the vehicle's exhaust system
through the end cones, which can be either welded to the shell or be formed as
one part together with the shell, depending on converter packaging
technology. The other components shown in the schematic-end seals and/or
steel support rings-are optional; they are usually not present in modern
passenger car converters, but may be required in more demanding
applications, such as close-coupled converters, large converters for heavy-
duty
24
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
engines, or diesel particulate filters. Catalytic converters, especially those
in
gasoline applications, can be also equipped with steel heat shields (not shown
in the schematic) to protect adjacent vehicle components from exposure to
excessive temperatures.
[0082] Generally, a catalytic converter is composed of at least five main
components: 1) a substrate; 2) a catalytic coating; 3) a wash-coat; 4) a
matting;
and 5) a canister. A general catalytic converter is shown in Figure X. In
certain applications, as discussed in more detail below, the catalytic coating
is
optional.
Substrate
[0083] The substrate is a solid surface on which the pollutants can be
converted to the nonpollutants. Physically, a substrate provides the interface
for several molecular species, in any physical state such as solid, liquid, or
gas, to react with each other. The substrate generally has a large surface
area
to provide a large area on which the pollutants can be converted to
nonpollutants.
[0084] Over the past decades, many different materials and designs have been
tested to act as the substrate for chemical reactions. For example, main
physical structures include honeycomb monoliths and beads. (See Figure 1).
The honeycomb structure contains numerous channels, usually running
parallel to each other along the length of the substrate. The substrate has
channels that run the length of the substrate. The width of channels varies,
often depending on the substrate material and applications for which it is
used.
These channels allow the exhaust gas to flow from the engine through the
catalytic converter and out through exhaust pipe. While the exhaust gas flows
through the channels of the substrate, the pollutant molecules are converted
into nonpollutant molecules via chemical reactions and physical changes.
[0085] In the bead structure, the substrate is made of a collection of small
beads (sinular to putting a bunch of jelly beans in a tube). The exhaust can
flow around the beads (through the channels and crevices). The pollutants are
converted to nonpollutants as the exhaust gas hits the beads. The bead
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
structure was one of the early attempts to maximize the surface area of
substrate to which the exhaust molecules were exposed.
[0086] A number of different materials have been used as the substrate. These
include ceramic, Fiber Reinforced Ceramic Matrix Composites (FRCMC),
foam, powder ceramic, nanocomposite, metals, and fiber mat-type substrates.
The most commonly used is a ceramic called cordierite, which is produced by
Corning. Cordierite is a ceramic formed from refractory powders. FRCMC is
an open celled foam wherein catalyst is disposed on the walls of the cells,
the
foam being disposed within a catalytic chamber such that exhaust gas must
pass through a cell path of the foam to exit. Foams are solids containing
numerous pores that are formed by bubbles from gas and burned-off voids.
Powder ceramic substrates are different than cordierite and related ceramics
in
that the powder ceramic is formed from sintered ceramic powders.
Nanocomposites are materials that use nano-powders and/or nano-fibers.
Metals can also be used as a substrate. Generally, thin sheets of corrugated
metal foil, such as steel, are rolled into a honeycomb-like structure. Fiber
mat-
type substrates are materials that are woven on a small scale. Certain fiber
mat-type substrates utilize NEXTEL fibers, produced by 3M. Additionally,
"two-dimensional" non-woven fibrous composites have also been tried where
honeycomb structures were formed using rolled up pleating and/or
corrugation. For example, see U.S. Patent Nos. 4,894,070; 5,196,120; and
6,444,006 B 1.
Catalytic Coatirag
[0087] The third component of current catalytic converters is a catalytic
coating. As the name implies, the catalytic coating is the component which
actually catalyzes the conversion of pollutants to non-pollutants.
[0088] A catalyst is usually defined as a substance which influences the rate
of
a chemical reaction but is not one of the original reactants or final
products,
i.e., it is not consumed or altered in the reaction. In several known
catalytic
reaction mechanisms, the catalyst forms intermediate compounds with
reactants but is recovered in the course of the reaction. Many other catalytic
processes are not explained fully or understood in their entirety. Neither are
26
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the principles governing the selection and preparation of catalysts for
specific
purposes. Many of the developments in this field are achieved through
elaborate exploration programs involving trials of countless materials.
Catalysts are widely used in chemical and petrochemical processing to
facilitate reactions which otherwise are too slow, or which require high
temperatures to yield good efficiencies. Catalysts are also used to convert
harmful components of engine exhaust gases, such as hydrocarbons and
carbon monoxide, into harmless substances, such as carbon dioxide and water
vapor.
[0089] Catalysts are substances that have the ability to accelerate certain
chemical reactions between exhaust gas components. In emission control
catalysis, solid catalysts are used to catalyze gas phase reactions. The
catalytic
effect and the observed reaction rates are maximized by providing good
contact between the gas phase and the solid catalyst. In catalytic reactors,
this
is usually realized by providing high catalytic surface area through finely
dispersing the catalyst on high specific surface area carrier (support).
[0090] The catalytic coating is added to the substrate after the substrate is
formed. The coating forms a layer on the surface of the substrate, the layer
containing the catalyst. Different types of catalysts are needed depending,
for
example, on the chemical reaction, application needed, temperature
conditions, economic factors, etc. A number of metal catalysts are known in
the art. For example, the most commonly used are platinum, palladium and
rhodium. Significant research has been done to develop new catalysts. See,
for example,
[0091] The rate of chemical reactions, including catalytic reactions,
generally
increases with temperature. A strong dependency of conversion efficiency on
temperature is a characteristic feature of all emission control catalysts. A
typical relationship between the catalytic conversion rate of a pollutant and
the
temperature is shown as the solid line (A) in Figure 4. The conversion, near-
zero at low temperatures, increases slowly at first and then more rapidly, to
reach a plateau at high gas temperatures. When discussing combustion
reactions, the term light-off temperature is commonly used to characterize
this
behavior. The catalyst light-off is the minimum temperature necessary to
initiate the catalytic reaction. Due to the gradual increase of the reaction
rate,
27
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the above definition is not very precise. By a more precise definition, the
light-off temperature is the temperature at which conversion reaches 50%.
That temperature is frequently denoted T50. When comparing activities of
different catalysts, the most active catalyst will be characterized by the
lowest
light-off temperature for a given reaction.
[0092] In some catalyst systems, increasing the temperature may increase the
conversion efficiency only up to a certain point, as illustrated by the dashed
line (B) in Figure 4. Further temperature increase, despite increasing
reaction
rates, causes "a decrease in the catalyst conversion efficiency. The declining
efficiency is usually explained by other competing reactions which deplete the
concentrations of reactants or by thermodynamic reaction equilibrium
constrains.
[0093] The temperature range corresponding to the high conversion efficiency
is frequently called the catalyst temperature window. This type of conversion
curve is typical for selective catalytic processes. Good examples include
selective reduction of NO by hydrocarbons or ammonia.
[0094] Another important variable influencing the conversion efficiency is the
size of the reactor. The gas flow rate through a catalytic reactor is commonly
expressed, relative to the size of the reactor, as space velocity (SV). The
space
velocity is defined as the volume of gas, measured at standard conditions
(STP), per unit time per unit volume of the reactor, as follows: (3)SV = V/Vr
where V is the volumetric gas flow rate at STP, m3/h; Vr is the reactor
volume,
m3, and SV has the dimension of reciprocal time which is commonly
expressed in 1/h or h-1.
[0095] In various catalytic emission control applications, the space
velocities
range from 10,000 1/h to 300,000 1/h. Space velocities for monolithic
reactors are calculated on the basis of their outside dimensions, e.g.,
diameter
and length of a cylindrical ceramic catalyst substrate. Since this method does
not take into account the geometric surface area of the substrate, cell
density,
wall thickness, or catalyst loading, it is not always appropriate for catalyst
comparisons. Nevertheless, it is a commonly used and widely accepted
industry standard.
[0096] Typical platinum loadings in filters used for off-road engines through
the 1990's were between 35 and 50 g/ft3. These filters, installed on
relatively
28
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
high polluting engines, required minimum temperatures of nearly 400 C for
regeneration. Later, when catalyzed filters were applied to much cleaner urban
bus and other highway vehicle engines, it was found that they were able to
regenerate at much lower temperatures. However, higher platinum loadings
were needed to support the low temperature regeneration. Filters used in clean
engine, low temperature applications have typically platinum loadings of
50-75 g/ft3.
Wash Coat
[0097] In most cases, the catalytic coating includes a wash coat as a fourth
component. The washcoat is applied to the surface of the substrate, thereby
increasing surface area of the substrate. The washcoat also provides a surface
to which the catalyst adheres. The metal catalyst may be impregnated on this
porous, high surface area layer of inorganic carrier, (i.e., washcoat - the
term
"catalyst support" may be used to denote the ceramic/metallic substrate, as
well as the carrier/washcoat material).
[0098] A number of substances can be used as a washcoat. Substances which
are widely used for catalyst carriers include activated aluminum oxide and
silicone oxide (silica).
[0099] The washcoat is a porous, high surface area layer bonded to the surface
of the support. Its exact role, which is certainly very complex, is not
clearly
understood or explained. The main function of the washcoat is to provide very
high surface area, which is needed for the dispersion of catalytic metals.
Additionally, the washcoat can physically separate and prevent undesired
reactions between components of a complex catalytic system.
[0100] Washcoat materials include inorganic base metal oxides such as A1203
(aluminum oxide or alumina), Si02, Ti02, CeO2, Zr02, V205, La203 and
zeolites. Some of them are used as catalyst carriers. Others are added to the
washcoat as promoters or stabilizers. Still others exhibit catalytic activity
of
their own. Good washcoat materials are characterized by high specific surface
area and thermal stability. The specific surface area is determined by
nitrogen
adsorption measurement technique in conjunction with mathematical
modeling known as the BET (Brunauer, Emmet, and Teller) method. Thermal
29
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
stability is evaluated by exposing samples of given material to high
temperatures in a controlled atmosphere, usually in the presence of oxygen
and water vapor. The loss of BET surface area, which is remeasured at
different time intervals during the test, indicates the degree of thermal
deterioration of the tested material.
[0101] The washcoat can be applied to the catalyst support from a water based
slurry. The wet washcoated parts are then dried and calcined at high
temperatures. The quality of the catalyst washcoat can significantly influence
the performance and durability of the finished catalyst. Since the noble metal
is subsequently applied to the washcoated parts by impregnation, i.e.,
"soaking" the washcoat porosity with the catalyst solution, the washcoat
loading will determine the noble metal catalyst loading in the finished
product.
Therefore, it is extremely important that the washcoating process produces a
very repeatable and uniform washcoat layer. The details on the washcoating
process and its parameters are guarded as trade secrets by all catalyst
makers.
Canister
[0102] The substrate is packaged into a canister, e.g., a steel shell, to form
a
catalytic converter. The canister performs a number of functions. It holds the
catalyzed substrate and protects the substrate from the external environment.
Additionally, the canister forces exhaust gas to flow through and/or over the
catalyzed substrate.
[0103] The catalyzed substrate can be also packaged inside mufflers, which
are then referred to as "catalyst mufflers" or "catalytic mufflers." In this
case,
one steel canister holds both the catalyst and the noise attenuation
components, such as baffles and perforated tubing. Catalyst mufflers can offer
more space saving design compared to the combination of a catalytic
converter and a muffler.
[0104] The catalyzed substrate is usually placed inside the canister having a
configuration made according to one of several methods, including: clamshell,
tourniquet, shoebox, stuffing, and swaging, as shown in Figure 28.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Matting
[0105] In addition to the canister, a matting material is often used to
package
the catalytic substrate in the canister. The packaging mats, usually made of
ceramic fibers can be used to protect the substrate and to distribute evenly
the
pressure from the shell. The mats often include vermiculite, which expands at
high temperatures, thus compensating for the thermal expansion of the shell
and providing adequate holding force under all operating conditions.
[0106] For example, ceramic monoliths are wrapped in a special packaging
material which holds them securely in the steel housing, uniformly
distributing
pressure and preventing cracking. Ceramic fiber mats are most commonly
used for packaging of catalytic converters for both gasoline and diesel
applications. These packaging mats can be classified as follows: intumescent
(heat-expandable) mats; conventional (high vermiculite); reduced vermiculite;
non-intumescent mats; or hybrid mats.
Heat Insulation
[0107] In many applications, the catalytic converter must be heat insulated to
avoid damage to surrounding vehicle components (e.g., plastic parts, fluid
hoses) or-in converters mounted closer the engine-to prevent an increase of
engine compartment temperature. One of the methods of converter thermal
management is to employ a steel heat shield positioned around the converter
body. An alternative method is to provide an insulation layer inside the shell
by either (1) increasing the thickness of the mounting mat, or (2) providing
an
additional layer of dedicated, low thermal conductivity insulation. While heat
shields have been traditionally used in the underfloor location, it has been
suggested that increased mat thickness offers the best solution for converters
installed in the engine compartment (Said Zidat and Michael Parmentier,
"Heat Insulation Methods for Manifold Mounted Converters," Delphi
Automotive Systems, Technical Centre Luxembourg, SAE Technical Paper
Series 2000-01-0215). One of the advantages of using thicker mat rather than
the heat shield is the lower average mat temperature, which minimizes the risk
of destroying vermiculite mats in close-coupled gasoline engine applications.
31
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Particulate Trap
[0108] Another device for removing pollutants from an exhaust gas is a
particulate trap. A common particulate trap used on diesel engines is a diesel
particulate trap (DPT). A main purpose of a particulate trap is to filter and
trap particulate matter of various sizes from a stream of fluid, such as an
exhaust gas flow. The effectiveness of a particulate filter is generally
measured in its ability of filtering PM of different size, e.g., PM-2.5 and
PM-10.
[0109] Diesel traps are relatively effective at removing carbon soot from the
exhaust of diesel engines. The most widely used diesel trap is the wall-flow
filter which filters the diesel exhaust by capturing the soot on the porous
walls
of the filter body. The wall-flow filter is designed to provide for nearly
complete filtration of soot without significantly hindering the exhaust flow.
[0110] As the layer of soot collects on the surfaces of the inlet channels of
the
filter, the lower permeability of the soot layer causes a pressure drop across
the filter and a gradual rise in the back pressure of the filter against the
engine,
causing the engine to work harder, thus affecting engine operating efficiency.
Eventually, the pressure drop becomes unacceptable and regeneration of the
filter becomes necessary. In conventional systems, the regeneration process
involves heating the filter to initiate combustion of the carbon soot. In
certain
circumstances, the regeneration is accomplished under controlled conditions
of engine management whereby a slow burn is initiated and lasts a number of
minutes, during which the temperature in the filter rises from about 400-600 C
to a maximum of about 800-1000 C.
[0111] In certain applications, the highest temperatures during regeneration
tend to occur near the exit end of the filter due to the cumulative effects of
the
wave of soot combustion that progresses from the entrance face to the exit
face of the filter as the exhaust flow carries the combustion heat down the
filter. Under certain circumstances, a so-called "uncontrolled regeneration"
can occur when the onset of combustion coincides with, or is immediately
followed by, high oxygen content and low flow rates in the exhaust gas (such
as engine idling conditions). During an uncontrolled regeneration, the
combustion of the soot may produce temperature spikes within the filter which
32
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
can thermally shock and crack, or even melt, the filter. The most common
temperature gradients observed are radial temperature gradients where the
temperature of the center of the filter is hotter than the rest of the
substrate and
axial temperature gradients where the exit end of the filter is hotter than
the
rest of the substrate.
[0112] In addition to capturing the carbon soot, the filter also traps metal
oxide "ash" particles that are carried by the exhaust gas. Usually, these ash
deposits are derived from unburnt lubrication oil that accompanies the exhaust
gas under certain conditions. These particles are not combustible and,
therefore, are not removed during regeneration. However, if temperatures
during uncontrolled regenerations are sufficiently high, the ash may
eventually
sinter to the filter or even react with the filter resulting in partial
melting.
[0113] It would be considered an advancement in the art to obtain a filter
which offers improved resistance to melting and thermal shock damage so that
the filter not only survives the numerous controlled regenerations over its
lifetime, but also the much less frequent but more severe uncontrolled
regenerations.
Continuous Regeneration Trap
[0114] One conventional method for catalytic conversion is a diesel
particulate trap ("DPT"). A DPT is a filter that collects particulate matter
in
the exhaust. The collected particulate matter must then be burned off before
the filter becomes clogged. Burning off the particulate matter is referred to
as
"regeneration." Several conventional methods exist for regeneration of DPTs.
First, an application of precious metal catalysts or base-metal catalyst to
the
surface of the filter can reduce the temperature needed for oxidation of
particulate matter. Second, the filter can be preceded with a chamber
containing oxidation catalyst that creates NO2, which helps to burn off
particulate matter. Third, the system can utilize fuel-born catalysts.
Finally,
external source of heat may be employed, wherein soot burns at 550 degrees
Celsius without catalysts or approximately 260 degrees Celsius with precious
metal catalysts. Regeneration leaves behind ash residue as the carbon burns,
requiring constant maintenance to clean the filter.
33
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0115] Yet another conventional method utilizes diesel oxidation catalysts
("DOCs"). DOCs are catalytic converters that oxidize CO and hydrocarbons.
Hydrocarbon activity extends to the polynuclear aromatic hydrocarbons
("PAHs") and the soluble organic fraction ("SOF") of particulate matter.
Catalyst formulations have been developed that selectively oxidize the SOF
while minimizing oxidation of sulfur dioxide or nitric oxide. However, DOCs
may produce sulfuric acid and increase the emission of NOZ.
[0116] The function of the catalyst in the catalyzed diesel particulate filter
(CDPF) is to lower the soot combustion temperature to facilitate regeneration
of the filter by oxidation of diesel particulate matter (DPM) under exhaust
temperatures experienced during regular operation of the engine/vehicle,
typically in the 300-400 C range. In the absence of the catalyst, DPM can be
oxidized at appreciable rates at temperatures in excess of 500 C, which are
rarely seen in diesel engines during real-life operation. Reported substrates
used in these catalyst applications include cordierite and silicon carbide
wall-
flow monoliths, wire mesh, ceramic foams, ceramic fiber media, and more.
The most common type of a CDPF is the catalyzed ceramic wall-flow
monolith.
[0117] Catalyzed ceramic traps were developed in early 1980's. Their first
applications included diesel powered cars and, later, underground mining
machinery. Catalyzed filters were commercially introduced for Mercedes cars
sold in California in 1985. Mercedes models 300SD and 300D with
turbocharged engines were equipped with 5.66" diameter x 6" filters fitted
between the engine and the turbocharger.
[0118] The use of diesel traps on cars was later abandoned, due to such issues
as insufficient durability, increased pressure drop, and filter clogging.
Today,
even though not all of these problems have been solved, catalyzed ceramic
traps remain one of the most important diesel filter technologies. CDPFs are
increasingly used in a number of heavy-duty applications, such as urban buses
and municipal diesel trucks. For a number of years, limited quantities of
catalyzed filters have been also used in underground mining (North America
and Australia) and in certain stationary engine applications.
[0119] Catalyzed ceramic filters are commercially available for a number of
highway, off-road, and stationary engine applications as both OEM and
34
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
aftermarket (retrofit) product. The list of suppliers includes Engelhard, OMG
dmc2, as well as several smaller emission control manufacturers who
specialize primarily in the off-road markets.
[0120] The main component of conventional filters is a ceramic (typically
cordierite or SiC) wall-flow monolith. The porous walls of the monolith are
coated with an active catalyst. As the diesel exhaust aerosol permeates
through the walls, the soot particles are deposited within the wall pore
network, as well as over the inlet channel surface. The catalyst facilitates
DPM oxidation by the oxygen present in exhaust gas.
Pressure Drop
[0121] The flow of exhaust gas through a conventional catalytic converter
creates a substantial amount of backpressure. The backpressure buildup in a
catalytic converter is an important attribute to catalytic converter success.
If
the catalytic converter is partially or wholly clogged, it will create a
restriction
in the exhaust system. The subsequent buildup of backpressure will cause a
drastic drop in engine performance (e.g., horsepower and torque) and fuel
economy, and may even cause the engine to stall after it starts if the
blockage
is severe. Conventional attempts to reduce pollutant emissions are very
expensive, due to both the cost of materials and retrofitting or manufacturing
an original engine with the appropriate filter.
[0122] High filtration efficiencies of wall-flow filters are obtained at the
expense of relatively high pressure drop which increases with the filter soot
load. Initially, the filter is clean. As the particulate start depositing
within the
pores in monolith walls (depth filtration), the pressure drop starts
increasing
with time in a non-linear manner. This phase is called the initial loading
phase, during which pore attributes like permeability and filter porosity
continuously change due to the increasing soot deposit inside the pore
network. After the filtration capacity of the pores becomes saturated, soot
starts depositing as a layer inside the inlet monolith channels (cake
filtration
phase). A linear increase in pressure drop with time (and with soot load) is
observed during this period. One property that changes is the thickness of the
soot layer. Some authors also distinguish an intermediate short transition
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
phase, from the moment the particulates start depositing on the channel
surface until the soot layer is fully established (Tan, J.C., et al., 1996, "A
Study on the Regeneration Process in Diesel Particulate Traps Using a Copper
Fuel Additive", SAE 960136; Versaevel, P., et al., 2000, "Some Empirical
Observations on Diesel Particulate Filter Modeling and Comparison Between
Simulations and Experiments", SAE 2000-01-0477).
[0123] Pressure drop modeling in clean filter substrates has been done.
Relatively simple models that have been developed show excellent agreement
with experimental results (Masoudi, M., et al., 2000, "Predicting Pressure
Drop of Wall-Flow Diesel Particulate Filters - Theory and Experiment", SAE
2000-01-0184; Masoudi, M., et al., 2001, "Validation of a Model and
Development of a Simulator for Predicting the Pressure Drop of Diesel
Particulate Filters," SAE 2001-01-0911). Most of the filter pressure drop in
real applications, however, is created by the soot deposit. In practical
applications, the pressure drop of the clean wall-flow filter can be in the
range
of 1 to 2 kPa, while a loaded filter pressure drop of 10 kPa can be considered
in certain circumstances low to moderate.
[0124] The total pressure drop of the particulate loaded filter, can be
divided
into the following four components: pressure drop due to sudden contraction
and expansion at the inlet and outlet from the filter; pressure drop due to
channel wall friction; pressure drop due to permeability of particulate layer;
and pressure drop due to wall permeability.
[0125] Pressure drop due to sudden contraction and expansion at the inlet and
outlet from the filter is similar to the same component in the clean filter,
except that the effective channel size (hydraulic diameter) is now smaller due
to the soot layer, resulting in more gas contraction.
[0126] Pressure drop due to channel wall friction also increases relative to
the
clean filter scenario, due to the decrease in the channel hydraulic diameter.
With thick soot layers, APchannel can become a very significant contributor to
the total pressure drop.
[0127] Pressure drop due to permeability of particulate layer (APparticulate)
is
can be a signficant contributor to the total pressure drop.
[0128] Pressure drop due to wall permeability (APwall) is now also higher
than in the clean filter, because the wall pores are partly filled with soot.
The
36
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
increase in APwall that can be attributed to the initial soot loading phase in
the
pores is represented by API in Figure 3.
[0129] The total pressure drop can be expressed as follows:
AP = APin/out + APchannel + APparticulate + APwall
[0130] Mathematical modeling of the pressure drop in soot loaded diesel
filters becomes a complex and difficult task. Important properties of soot,
such
as the permeability and packing density, depend on the application, engine
operating conditions, and other parameters. There is an ongoing effort to
simulate pressure drop in wall-flow filters and increasingly more
sophisticated
models are being developed. Predicting the actual soot loading may require a
theoretical model of the regeneration process itself.
Types of Catalytic Converters and Particulate Filters
[0131] Catalytic converters can be classified based on a number of factors
including: a) the type of engine on which the converter is used, b) its
location
relative to the engine, c) the number and type of catalysts used in the
converter, and d) the type and structure of the substrate used. In addition
each
of these catalytic converters are often used in conjunction with other
emission-
control devices, such as CRT, EGR, SCR, ACERT, and other devices and
methods.
Engine
[0132] Catalytic converters are used on at least two types of engines:
gasoline
and diesel. Within these two general classes, there are numerous types of
specific gasoline and diesel engines. For example, gasoline and diesel engines
are manufactured having varying displacements and horsepower. Certain
engines are equipped with a turbocharger and/or an intercooler. Most car and
truck engines are water-cooled, while many motorcycle engines are air-cooled.
Certain utilities require high available horsepower, while others maximize
fuel
economy. All of these variables, in addition to others, may affect the level
of
pollutants produced during combustion of the fuel. Moreover, depending on
37
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the use of the engine, e.g., on-road, off-road, or stationary, there are
different
regulatory requirements with respect to emissions standards.
Location
[0133] The catalytic converter can theoretically be placed anywhere along the
exhaust stream of an engine. However, physical characteristics of
conventional catalytic converters limit their location. Most commonly in
vehicles, the catalytic converter is placed some distance from the engine
block, closer to the muffler and underneath the body of the car. The catalytic
converter is usually not placed close to the engine because the catalytic
converter can fail for several reasons. Such reasons include extreme
temperatures, thermal shock, mechanical vibration, mechanical stress, and
space limitations near the engine. Also, physical setups of stationary engines
may limit the location of a catalytic converter or particular filter. ,
[0134] For example, in its 2004 FOCU.S.TM, Ford Motor Company managed
to deploy a mani-cat as did Honda Motor Corporation in one of its offerings.
These systems are in actuality adjacent to, rather than part of, the manifold.
The higher temperatures and the extreme vibrational energy generated by
cylinder explosions and moving parts would subject current catalytic
converters, if placed in a manifold, to extremes in thermal and physical
shock.
Additionally, a design for a mani-cat was proposed by Northup Grumman
Corporation in U.S. Patent No. 5,692,373. It is believed that even the current
cordierite substrate would find such an environment challenging to endure.
[0135] In other applications, for example such as motorcycles (e.g., Harley-
Davidson), the presence of a catalytic converter in certain locations can
cause
serious injury to the user. Because of the high operating temperatures of a
catalytic converter, it would be preferable to use a catalytic converter that
is
less prone to causing injury to a user, e.g., a smaller catalytic converter, a
converter that does not get as hot, etc.
[0136] In certain instances, the exhaust system (for example, in a car) may
contain more than one catalytic converter or particular filter along its
exhaust
flow. (See Figure 4). For example, an exhaust system may have an additional
catalytic converter between the engine and the main catalytic converter. This
38
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
configuration is referred to as a pre-cat. The pre-cat may have denser
configuration. Another set-up is a back-cat, which has second catalytic
converter behind (or after) the main catalytic converter. The back-cat is also
sometimes used for a retrofit catalytic converter.
Two way vs. Three way vs. Four way
[0137] Catalytic converters can generally be classified as being a two-way,
three-way, or four-way converter. There are at least the following types of
converters commercially available: oxidation converters, three-way converters
(no air), three-way-plus oxidation converters, and four-way converters.
[0138] Oxidation (two-way) converters represent the early generation of
converters that were designed to oxidize hydrocarbons (HC) and carbon
monoxide (CO). Although these units represent the most basic fozm of
catalytic converter technology, they remain a viable pollution reduction
option
in some areas. Oxidation converters usually contain platinum or palladium.
However, other non-noble metals can be used as well.
[0139] In the early 1980s, most vehicle manufacturers began using converters
designed to reduce NOx, in addition to oxidizing HC and CO. These three-
way converters, which were used in conjunction with computer controlled
engine systems and oxygen sensors, were employed to more precisely control
the air to fuel ratio. These converters are referred to as three-way
converters
because they deal with three compounds: HC, CO and NOx.
[0140] Most modern cars are equipped with "three-way" catalytic converters
typically having one or more substrates in tandem using Corning's clay
extrusion technology. "Three-way" refers to the three regulated emissions the
converter helps to reduce: carbon monoxide, volatile organic compounds
(VOCs, e.g., unburned hydrocarbons), and NOx molecules. Such converters
use two different types of catalysts, a reduction catalyst and an oxidization
catalyst.
[0141] In a three-way catalytic converter, the reduction catalyst is usually
found in the first stage of the catalytic converter and serves to reverse the
oxidation of nitrogen that occurred in the combustion chamber. It commonly
uses platinum and rhodium to help reduce NOx emissions. The oxidation
39
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
catalyst, which can be composed of metals such as platinum and/or palladium,
is commonly located in a second region of the catalytic converter.
[0142] Three-way converters that have a reduction and an oxidation catalyst
together in one housing are sometimes called three-way-plus-oxidation
converters. These converters use air injection between the two substrates.
This air injection aids the oxidation chemical reaction.
[0143] Four-way converters process carbon monoxide, nitrogen oxide,
unburnt hydrocarbons, and particulate matter. These include, for example, the
QuadCAT Four-Way Catalytic Converter manufactured by Ceryx. It is a
catalytic converter that that, according to its manufacturer, reduces four of
the
major sources of air pollution - NOx, hydrocarbons, carbon monoxide and
particulate matter - to levels that will allow diesel engines to meet
2002/2004
emissions standards. Others include those described in U.S. Patent Nos.
4,329,162; and 5,253,476.
[0144] The catalytic converter, like other catalysts, facilitates reactions by
lowering the activation energy required to accomplish the desired reaction.
For example, if particulates require a temperature of 550 C before reacting
with oxygen in the presence of catalysts, to bum off, this same reaction might
require a temperature of only 260 C. This lower energy threshold permits one
physically to locate a catalytic system downstream from the engine where
space is more abundant, even though temperatures are cooler. Otherwise, the
catalytic system will need to be placed upstream where temperatures are
higher. However, this is impractical with current technology because there is
more potential to damage the substrate when it is placed closer to the engine.
[0145] Diesel engines produce emissions that are high in NOx and particulate
matter due to the high temperature and pressure, while relatively low CO and
hydrocarbon production. The compression combustion is less complete than
with a spark of a gasoline engine. However, because of the relatively lean
mixture with high air content, diesel is able to provide better gas mileage
than
a gasoline engine. Three-way catalysts do not work well in diesel exhaust due
to the excess air. NOx reduction catalysts typically require a well-maintained
stoichiometric ratio of fuel-to-air which cannot be easily done in diesel
combustion engines.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0146] Catalytic converter technology may be applied to various applications,
including internal combustion engines and stationary combustion engines.
The internal combustion engine is the most common engine used for vehicles.
A catalytic converter is installed as a device in the vehicle's exhaust
system,
so the entire exhaust gas stream passes through the substrate, contacting the
catalyst before being discharged from the tailpipe. However, catalytic
converters can be also part of fairly complex systems involving various active
strategies, such as injection of reactants in front of the catalyst or
sophisticated
engine control algorithms. Examples include a number of diesel catalyst
systems being developed for the reduction of NOx. The attributes of
simplicity and passive character which have been listed among the advantages
of catalysts may no longer apply to those systems.
[0147] Conventional attempts to reduce pollutant emissions can be very
expensive, due partly to both the cost of materials and, in certain
applications,
to retrofitting or manufacturing an original engine with the appropriate
filter.
Advances in Catalytic Converter and Particulate Filter Technology
[0148] An invention that lead to progress in catalytic converters was Coming's
development of extruded cordierite honeycomb monoliths. (See U.S. Patent
No. 4,033,779). Since the 1970's, more than a billion pounds of pollutants
have been removed from exhaust streams using this approach which employs
catalysts (platinum, palladium, rhodium, etc.) from the noble and base metal
families firnIy lodged in a washcoat on the surface of a rugged substrate
(generally cordierite) that can withstand the extreme environment of an engine
exhaust system. Variations and improvements to this core technology have
evolved in the years since, including variations in the placement of catalytic
converters as well as in their composition and methods of manufacture. Still,
however, there remain fundamental inadequacies that, to date, have not been
overcome. Currently, the state of technology is reaching physical and
economical limits with only minor improvements being made at great
expense.
41
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Limitations of Current Substrates
[0149] While the present state of catalytic converter and particulate matter
filter technology is useful to some degree for reducing emission pollution,
there are certainly drawbacks to the current technology. There are also
characteristics that are not met by the present catalytic converters. Some
inadequacies are inherent to the type of substrate used. Accordingly, an
improved substrate for use in a catalytic converter or particulate filter
would
be a significant advance in the fundamental physical and chemical attributes
of
the materials used as catalyst substrates in the catalytic converter.
Moreover,
an improved substrate would dramatically enhance the quality and would
enable manufacturers and users to meet more easily the emissions standards of
2007, and 2010, and later years.
[0150] The conventional monolithic catalytic converter substrate is generally
formed through an extrusion process. This process, which is both complicated
and relatively expensive, has been used for the past twenty-five years.
However, there are limitations to the extrusion process. There is a limit as
to
how small channels can be created within the material and still maintain
quality control. The extrusion process also limits the shapes of the catalytic
converters to cylinders or parallelograms, or shapes that have sides parallel
to
the extrusion axis. This shape limitation has not been an issue with previous
emission standards. However, the need to design a catalytic converter and
particulate filter able to reach near-zero emissions performance may require
non-linear and/or non-cylindrical filter design and vehicle integration.
[0151] Decreasing the wall thickness increases the surface area, e.g., in
certain
instances, decreasing wall thickness from 0.006 inches to 0.002 inches
increases surface area by 54%. By increasing the surface area, more
particulate matter may be deposited in less volume. Figure 1 shows a prior art
honeycomb configuration 102 formed within a ceramic filter element 100
configured to increase the surface area for a catalytic converter. The
honeycomb configuration 102 is formed using an extrusion process in which
long channels with their major axis parallel to the extrusion action are
created.
The opening of these channels faces the incoming exhaust airflow.
42
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0152] Progress in technology has allowed the manufacture of ceramic
cordierite substrates with decreased wall thickness. The once standard
configuration for passenger car applications, 400/6.5, of 400 cpsi cell
density
and of 0.0065" (or about 0.17 mm) was gradually replaced with substrates of
thinner walls (0.0055 to 0.004 mil). However, the physical limitations of this
material have been approached. Because of the physical characteristics of
ceramics, in particular cordierite, using substrates made of cordierite
ceramics
with even thinner walls is not practical. The thinner-walled material is not
able to meet other necessary characteristics (e.g., durability, heat
resistance).
[0153] Diesel catalysts, in part because of their larger sizes, often have
thicker
walls than their automotive counterparts. Because diesel wall flow filters
generally have thicker walls, there are physical limitations on the channels
per
square inch these filters can have. Generally, there are no commercially
available diesel wall flow filters having more than 200 channels per square
inch.
[0154] Another limitation of currently available substrates is their decreased
catalytic efficiency at lower temperatures. When a converter system is cold,
such as at engine start up, temperatures are not sufficiently high to commence
the catalytic reactions. The cordierite, silicon carbide, and various metal
substrates employed in catalytic converters and marketed by Corning, NGK,
Denso, and other companies today are fashioned from very tough, dense
materials with excellent mechanical strength and tolerances for thermal shock
and vibration. However, these materials require time to absorb heat after
start
up to reach temperatures sufficient for catalytic reactions. Due to the delay
in
the catalysis reaction start-up, it is estimated that approximately 50% of all
of
the emissions from modem engines are released to the atmosphere during the
first 25 seconds of engine operation. Even a small improvement during these
critical "cold start" seconds could drastically improve the amount of
pollutants
successfully treated annually. While effort has been invested to address this
problem, there remains a need for a catalytic converter that can reduce
emissions during this critical cold start period. Even the most advanced and
expensive state of the art, cordierite-based catalytic converter requires
approximately 20 seconds to start up.
43
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0155] To more quickly achieve reaction temperatures, attempts have been
made to move the converters closer to the engine exhaust manifold where
higher temperatures are more quickly available and also serve to drive
reactions more vigorously during operation. Because usable space under the
hood of a vehicle is limited, the size of converter systems, and therefore the
amount of throughput that can be successfully treated, is limited. Current
substrates cannot be effectively used in the engine compartment of vehicles.
Moreover, adding additional weight to the engine compartment is undesirable,
and many current substrates are dense and have limited porosity (roughly 50%
or less), requiring systems that are both weighty and voluminous to treat
large
scale exhaust output. Additionally, substrates such as cordierite are
susceptible to melting under many operating conditions, thereby causing clogs
and increased back pressure.
[0156] Other methods of compensating for cold starts include elaborate
adsorption systems to store NOx and/or hydrocarbons temporarily so that they
might be treated once the converter has reached critical temperatures. Some
of these systems require parallel piping and elaborate adsorption surfaces,
additional valves and control mechanisms, or multiple layers of differing
washcoats used to adhere catalysts to substrates and to segregate reaction
environments. This problem is especially challenging in diesel engines where
large volumes of soot particulates, NOx, and SOx may need to be trapped. In
some large, industrial diesel engines, rotating banks of diesel particulate
traps
are used to collect, store, and subsequently treat particles. (In still other
systems, NOx is stored and used as an oxidizing agent to convert CO into CO2
while it is reduced to N2.)
[0157] Given regulatory restrictions on total emissions, a system that could
readily curtail even some of the 50% of emissions that occur during cold start
might obviate the need for some of the expensive and elaborate work-arounds
described above. Used in conjunction with these worlc arounds, such a system
could result it in substantially decreased emissions. However, as explained
above, conventional systems are generally complicated and expensive and also
tend to misfire and/or work unpredictably.
[0158] Another inherent limitation of conventional systems is the typical
"residence time" required to burn off particulates. When one considers the
44
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
large volume of exhaust gas throughput during operation and the speed at
which the gas must flow, it is important that a converter be capable of rapid
light off. Thus, a catalytic converter capable of rapid light off, of enduring
extreme thermal and vibrational shocks, and capable of rapid internal
temperature build up during cold starts, would greatly enhance the capability
of industry to reduce emissions, meet upcoming environmental standards for
2007 and 2010, and produce cleaner operating cars, trucks, buses, and heavy
industrial engines.
[0159] If the substrate were also lightweight, it would also result in
improved
mileage statistics on new vehicles. To date, however, no substrate has been
identified capable of addressing many or all of these problems.
Design Considerations for a Substrate for a Catalytic Converter or
Particulate Filter
[0160] Catalyst substrate is a crucial component influencing performance,
robustness, and durability of catalytic converter systems. Furthermore,
filtering substrates significantly affect the operating performance of
particulate
filters. Ideally, the substrate used in a catalytic converter or particulate
filter
should have a number of attributes. These attributes include, but are not
necessarily limited to, one or more of the following aspects: a) surface area;
b)
porosity/permeability; c) emissivity; d) heat conductance; f) thermal
attributes
such as shock resistance, expansion, and conductance; g) density; h)
structural
integrity; i) efficiency of pollutant treatment; j) amount of catalyst
required;
and k) weight of the system. A catalytic or filtering substrate that optimizes
one or more attributes would be an advance in the field of filtering fluids
and
catalyzing reactions.
Brief Summary of the Invention
[0161] Various embodiments are described in this summary. These, as well as
other embodiments of the invention, are described in the following Detailed
Description section.
[0162] The inventor has discovered that a non-woven Sintered Refractory
Fibrous Ceramic (nSiRF-C) composite, as described herein, can be used as
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
and shaped into an improved substrate for catalytic converters, particulate
filters, and related devices.
[0163] The inventor has also discovered that an improved catalytic substrate
and improved filtering substrate can be prepared from a material having
particular attributes as described herein. For example, suitable attributes
include high melting point, low heat conductance, low coefficient of thermal
expansion, ability to withstand thermal and vibrational shock, low density,
and
very high porosity and permeability. An exemplary material in one
embodiment that has these attributes is a nSiRF-C.
[0164] One example of a material having suitable attributes is a nSiRF-C
composite. An example of a nSiRF-C is an alumina enhanced thermal barrier
("AETB") material or a like material, which can be used in accordance with
embodiments of the present invention as a catalytic substrate or a filtering
substrate. AETB materials are known in the art and comprise
aluminaboriasilica (also known as alumina-boria-silica, aluminoborosilicate,
and aluminoboriasilicate) fibers, silica fibers, and alumina fibers. One
commonly known application for AETB is as an exterior tile on the Space
Shuttle, ideal for shuttle re-entry. AETB has not been used as a filtering
substrate or a catalytic converter substrate.
[0165] It has been realized by the present inventor that the attributes that
make
AETB desirable to the space industry are also preferred in combustion
technology. Among other attributes, AETB has a high melting point, low heat
conductance, low coefficient of thermal expansion, ability to withstand
thermal and vibrational shock, low density, and very high porosity and
permeability. This combination of desired attributes is lacking in current
filtering and catalytic converter substrates.
[0166] It has also been discovered that nSiRF-C composites, such as AETB
and similar suitable substrates, can be prepared, shaped, molded, cut, and/or
fashioned (or otherwise modified physically) into new forms suitable for use
as particulate filter and catalytic converter substrates.
[0167] The present invention has a number of advantages over current
technology. First, the present invention will lead to improved air quality and
respiratory health. The present invention may substantially reduce the
potential for carbon monoxide poisoning.
46
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0168] Embodiments of the present invention can be used as a direct substitute
for currently used catalytic and filtering substrates, as well as catalytic
converters and particulate filters, and exhaust and engine systems. As
described in fine detail below, the substrates of the present invention
provides
a number of advantages over prior art substrates and further solves a number
of problems left unsolved by the prior art substrates. This can translate into
significant cost savings on the part of the manufacturers. Because it is
possible to use the present invention as a direct substitute for current
technology, there is no need to redesign exhaust systems. Thus, enhanced
exhaust filtering and cleaning can be obtained without the need to retool
manufacturing plants and lines and with only minimal investment in time.
[0169] The improved catalytic and filtering characteristics of the present
invention require, in certain embodiments, the use of less catalyst. Because
most catalysts used for the relevant applications are expensive, this
advantage
leads to another cost-saving.
[0170] The preferred thermal attributes of some embodiments of the present
invention reduce and/or eliminate the need for certain parts of the exhaust
system that deal with the heat build-up associated with current catalytic
converters and particulate filters. Heat shields and insulation may not be
needed in certain embodiments of the present invention. Elimination of these
components from exhaust systems and vehicles reduces cost only directly
(components are not used, thus lower costs of production) but also indirectly
(the weight of a vehicle is reduced, thus reducing fuel costs). Other benefits
may include better performance, better mileage, and/or better horsepower.
[0171] In certain embodiments, a conventional catalytic converter or
particulate filter can be replaced with the present invention that is smaller
but
has the same or better efficiency of removing pollutants. With a smaller
catalytic converter or particulate filter, more space is available on the
vehicle
for other purposes. Furthermore, because the filter or converter of the
present
invention is smaller, the overall weight of the vehicle is reduced.
[0172] Another aspect of some embodiments of the present invention is a
catalytic substrate suitable for use in a catalytic converter that is placed,
either
wholly or in part, in the head of an engine Said catalytic converter, referred
to
herein as head cat, has numerous advantages over the prior art. For example,
47
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
conventionally such a head cat is not practical because of the limitations of
currently available catalytic substrates. The common substrate cordierite
would absorb too much heat. Because of the preferred thermal characteristics
of the substrate of the present invention, a head cat comprising said
substrate
would reduce turbo thermal stress on a turbocharger and/or intercooler if
present.
[0173] Also a head cat does not require additional external hardware such as
heat shields. The use of a head cat permits the maintenance of prefelTed
appearances of engines and products, such as in motorcycles. In certain
embodiments, the use of a head cat also reduces external discoloration of the
exhaust system, such as mufflers and header pipes. A number of additional
advantages of the head cat in certain embodiments include one or more of the
following: increased safety; filters particles that intercooler would
otherwise
pick up, hence improving life of inter-cooler and providing a cost saving; no
matting required in certain embodiments; rattling sounds in heat shields can
be
reduced or eliminated with the use of a head-cat; and the head cat can reduce
the size of the requisite muffler.
[0174] In other embodiments of the head cat; smaller particulate matter is
more efficiently burnt off. In case of failure of a head-cat, only one small
cat
may need replacement. Head-cats are also provide these advantages to for
boats, watercraft, motorcycles, leaf-blowers etc.
[0175] More, different embodiments of the present invention provide one or
more of the following advantages over the prior art: improved appearance;
avoidance of additional hardware; additional hardware (that might be required
due to tighter regulations) would not be necessary with the present invention;
decreased or eliminated discoloration of muffler and exhaust pipes due to
exothermic chemical reactions. The present invention allows in certain
embodiments a smaller substrate, and thus a smaller muffler or canister in
certain systems. The substrate of the present invention provides increased
safety for systems using a catalytic converter or particulate filter because
the
substrate of the present invention has improved thermal properties and does
not absorb as much heat as certain conventional substrates. Moreover, the
substrate of the present invention cools off faster than many conventional
substrates, leading to increased safety. Certain embodiments of the present
48
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
invention provide for improved resistance to temperature change and therefore
will not crack, fracture, or become damaged as much as certain conventional
substrates if there is a sudden temperature change. In certain embodiments,
the substrate is easier to manufacture than conventional substrates (e.g., a
nSiRF-C wall flow substrate can be manufactured from a single piece of
material rather than plugging channels). This attribute saves not only time
but
also money.
[0176] In other embodiments, a nSiRF-C weighs less than conventional
aftertreatment devices. This attribute is not only important for cars, but
also
crucial in markets where weight is a factor (e.g., small engines, motorcycles,
personal watercraft, and performance cars).
[0177] In some embodiments, the substrate of the present invention exhibits a
less backpressure than competing aftertreatment devices. This lower
backpressure can results in increased vehicle performance, increased
horsepower, and increases fuel economy.
[0178] Other embodiments of the invention are directed to, for example, a
method catalyzing reaction, a method of filtering a fluid, a process of
preparing a catalytic substrate, a process of preparing a filtering substrate,
a
substrate prepared according to said processes, and others as described in
more
detail below.
Brief Description Of The Drawings
[0179] Figure 1 is a cross-sectional view of a conventional cordierite
substrate incorporating a honeycomb structure. The honeycomb configuration
302 is formed within the cordierite filter element 300. The honeycomb
structure 302 is formed using an extrusion process in which long channels (or
tubes) with their major axis parallel to the extrusion action are created. The
openings of these channels face the incoming exhaust airflow. As the
emissions enter the channels, the particulate will deposit along the interior
septum of the tubes.
[0180] Figures 2a and 2b show micrographs of. In Figure 2b, sphere 210
represents a PM-10 sized particle and sphere 225 represents a PM-2.5 sized
particle.
49
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0181] Figure 3 is a micrograph of cordierite 205 along with a sphere 210
representing a PM10 particle and a second sphere 225 represent a PM2.5
particle.
[0182] Figure 4 is a longitudinal cross-sectional view of a typical catalytic
converter schematic diagram. The catalytic converter 400 includes a reduction
catalyst 402 and an oxidation catalyst 404. As exhaust flow 406 enters the
catalytic converter 400 it is filtered and exposed to the reduction catalyst
102
and then to the oxidation catalyst 404. The exhaust flow 406 is then treated
by
the oxidation catalyst 404 which causes unburned hydro-carbons and carbon
monoxide to burn further.
[0183] Figure 4b shows a schematic diagram of a catalytic converter.
[0184] Figure 5 is a cross-sectional view of a schematic of three substrates
of
having three different frontal surface shapes.
[0185] Figure 6 is an example schematic diagram of a flow-through
configuration of a catalytic or filtering substrate. The substrate has a
plurality
of channels 610 formed by channel walls 620. The fluid flow 630 enters the
frontal surface and travels through the channels 610 and exits the rear
surface.
[0186] Figure 7 is an example schematic diagram of a wall-through
configuration of a catalytic or filtering substrate. A wall-flow pattern is
composed of the same substrate material 720 and channels 710, except the
channels 710 do not connect completely to the other side. Instead, the
channels 710 are formed as blind holes, leaving an undrilled portion 740 of
substrate 720 at the end of the channel 710. The fluid flow 730 than passes
through a channel wal1720 befor exiting the substrate at the rear surface. One
particular advantage of the present invention is that fluid flow 730 in the
wall-
flow pattern has substantially the same characteristics as the flow-through
pattern.
[0187] Figure 8 is an example schematic diagram of a wall-through
configuration of a catalytic or filtering substrate. In this instance, fluid
flow
830 enters the substrate at the frontal surface. Some of the fluid exits the
substrate at the rear surface by flowing through an undrilled portion 845.
Some channels
[0188] Figure 9 is an end view of an embodiment of a substrate 900 that
employs wall flow channels. Alternating channels have an undrilled portion
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
920 at either the ingress or egress. Drilled channels 910 alternate with
undrilled portions 920 of channels drilled from the opposing side. As a
result,
the substrate appears to have a "checkerboard" pattern of channels..
[0189] FIGS. l0a-10d show a comparison of frontal surface area 1020, 1021,
1022, 1023 and number of cells 1010, 1011, 1012, 1012 is shown. In a
comparison of FIGS. l0a and lOc, each embodiment has the same cell density,
i.e., number of channels or cells. However, FIG. lOc has a much higher
frontal surface area. Ideally, the frontal surface area is minimized such that
structural integrity still remains. A similar comparison may be made between
the embodiments of FIGS. lOb and lOd. Regarding FIGS. l0a-lOd, the
embodiment of FIG. 10b has the preferable structure; cell density is
maximized and frontal surface area is minimized.
[0190] FIG. 11 shows an embodiment of square channels to scale. In this
embodiment, the cell void 1110 to cell wall 1120 ratio is 31.83:1.5, or
approximately 20:1.
[0191] FIG. 12 shows an embodiment of a substrate 1210 having an
exemplified cell void to cell wall ratio shown to scale. The substrate 1210 is
four square inches in length and width and comprises four squares 1220, 1221,
1222, 1223 of 1 1/8 inches by 1 1/8 inches. Each of the four squares 1220,
1221, 1222, 1223 is drilled to have a cell density of 900, for a total
substrate
cell density of 3600. The wall thickness between the cells is 1.5 mil. The
spacing between each square 1220, 1221, 1222, 1223 on the substrate 1210 is
7/8 inches and the squares 1220, 1221, 1222, 1223 are each approximately
7/16 inches from the closest edge of substrate 1210.
[0192] Figures 13a-c is show several embodiments of the channels structure
FIGS. 13a-13c show hexagonal channels 1310, triangular 1320, and square
channels 1330, respectively. These embodiments are all successful in carrying
out the present invention because the walls 1315, 1325, 1335 of the channels
1310, 1320, 1320 are substantially parallel to each other.
[0193] Figure 14 shows an embodiment of the present invention. The
microscopic view shows the substantially similar dimensions of rectangular-
shaped channels 1410, 1411, 1412, 1413 in a substrate 1415, 1416, 1417,
1418. FIGS. 14c and 14d illustrate the fibers 1420, 1421 present in the
51
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
material. These fibers show the porosity, which is superior to the platelets
of
cordierite in conventional systems.
[0194] Figure 15 is a two-dimensional diagram of a comb 1500 that can be
used in a combing method of preparing a catalytic or filtering substrate of
the
present invention.
[0195] Figure 16 shows various views of a comb 1600 (or portion thereof) that
can be used in certain embodiments of the present invention. Figure 16 also
provides exemplary physical dimensions in inches of comb 1600.
[0196] Figure 17 is a schematic diagram of the surface area enhancements and
entry and exit tubes which can be formed in the filter element of embodiments
of the present invention. Figure 17 provides fluid flow 1704 entering channel
openings 1702 on the frontal surface. Fluid exits the rear surface of the
substrate at 1704 on the right hand side. The substrate shown in Figure 17
exemplifies a substrate having a wall-flow configuration, wherein the channels
gradually decrease in size as the channel extends from the channel opening
through the substrate to the channel terminus.
[0197] Figure 18 is a longitudinal view (photograph) of an embodiment
substrate embodiment of the present invention. A filter substrate 1800 of the
present invention is shown. The substrate 1800 has a hard coating 1804 on the
outside wall 1802. For the sample shown in Figure 18, the hard coating
consists of finely crushed cordierite and inorganic fibers. A powder was also
painted on the filter foundation 1800 and cured as described herein. The hard
coating protects and insulates the filter foundation while not changing the
dimensions.
[0198] Figure 19 is a graphical display of the residence time required to burn
particulate matter at varying temperatures. It provides the residence time
required to combust or burn particulate matter (soot mass) at various
temperatures. As seen, the residence time to combust or burn soot mass
having an initial 0.9 soot mass at 600 Kelvin is much longer than the
residence
time at 1200 Kelvin.
[0199] Figure 20 provides an exhaust substrate system 2000 including a
substrate 2002 combined with a wire mesh heating element 2004. The
substrate 2002 and wire mesh heating element 2004 are inserted into the
exhaust casing 2006 at an angle compared to the exhaust flow. Since the wire
52
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
mesh heating element 2004 is placed behind and below the substrate 2002 as a
result of the angle, the substrate 2002 can be heated more efficiently and
uniformly taking advantage of the known principal that heat rises. As
previously discussed, more uniform and efficient heating enables the substrate
2002 to more completely combust or flash off the particulates resulting in
cleaner exhaust.
[0200] Figure 21 is a diagram of a frontal view of the filter element 2102 and
wire mesh heating element 2104 described and discussed in relation to
Figure 9. As can be seen the filter element 2102 and wire mesh heating
element 2104 are oval shaped so as to fit in the casing at an angle. The shape
of the casing, shape of the filter element 2102, type of heating element 2104
and angle can all be modified to fit the requirements and restrictions of the
intended exhaust system application.
[0201] Figure 22a is a photomicrograph of a substrate of the present
invention, specifically AETB. -
[0202] Figure 22b is a photomicrograph of a substrate of the present
invention, specifically AETB. Fiber 2205 can be seen. Sphere 2210
illustrates a PM-10 sized particle, and Sphere 2225 illustrates a PM-2.5 sized
particle.
[0203] Figure 23 is a graph showing pressure drop (delta P) as a function of
gas hourly space velocity (hr 1) for seven tested materials: Corning 200/12
DPT 932 F (2340); AETB-11 having 600 cpsi; 6 mil wall thickness and
11 lb/ft3; 1100 F(2310); AETB-11 having 600 cpsi; 6 mil wall thickness and
11 lb/ft3; 932 F (2320); AETB-11 having 600 cpsi; 6 mil wall thickness and
11 lb/ft3; 662 F (2330); cordierite having 1100 F (2350); cordierite having
932 F (2360); and cordierite having 662 F (2370);
[0204] Figure 24 is a graph showing the % destruction versus temperature. A
substrate of the present invention 2410 shows a greater percentage of
destruction of material at lower temperatures than a coridierite substrate
2420.
[0205] Figure 25 is a diagram of a cross sectional view of an embodiment of
an improved catalytic converter of the present invention. In this embodiment,
the catalytic converter comprises a durable and heat resistant casing 2502.
The casing 2502 has an intake 2504 and an exhaust port 2506. The improved
substrate 2510 has one or a plurality of zones 2512, 2514. The improved
53
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
substrate 2510 is wrapped or enclosed in one or more layers of
matting/insulation 2515. The matting layer 2515 may be applied to the filter
foundation 2510 to shield the foundation 2510 from engine and mobile
environment vibrational shock as well as to insulate the exterior environment
from internal thermal temperatures of the filter foundation 2510.
[0206] Figure 26 is a shows a schematic of a catalytic converter or particular
filter 2600 having four substrates 2601a, 2601b, 2601c, and 2601d arranged in
a parallel fashion. The filter or converter has a frontal opening 2604 and an
rear exit 2605.
[0207] Figures 27a-c shows a catalytic converter or particulate filter 2700
having stacked membrane configuration substrates 2710. The inlet port 2720
and outlet port 2730 are fashioned at different heights. Figs. 27b and 27c
show alternative embodiments.
Detailed Description Of Embodiments Of The Invention
Overview
[0208] The present invention in certain embodiments is directed to a catalytic
substrate suitable for use in a number of applications, including as a
substrate
in a catalytic converter. Another aspect of the present invention is a
filtering
substrate suitable for use in a number of applications, including as a
substrate
in a particulate filter, such as a diesel particulate filter (DPF), or diesel
particulate trap (DPT). The invention also provides an improved substrate for
removing and/or eliminating pollutants from the exhaust of combustion
engines. The catalytic substrate and filtering substrate provide, in certain
embodiments, improvements in removing pollutants from an exhaust gas. The
improvements include, but not limited to, one or more of the following: faster
light-off period, increased depth filtration of PM, less back pressure, lower
probability of clogging, increased ability to be placed in multiple locations
in
the exhaust system including the manifold or the head itself, high probability
of catalytic reaction, high conversion ratios of NOx, HC, and CO, a faster
54
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
burnoff of PM, minimization of catalyst material use, reduced weight of the
after-treatment exhaust system, and the like.
[0209] Other embodiments of the invention include catalytic converters,
particulate filters, diesel particulate filters, diesel particulate traps, and
the like.
The present invention also provides a process of making or preparing the
catalytic and filtering substrates, catalytic converters, particulate filters,
catalytic mufflers, and exhaust systems. Other embodiments of the present
invention include a pre-cat, a back-cat, a head-cat, and a mani-cat, each of
which comprises a substrate of the present invention. Additionally, the
present invention, in alternative embodiments, is directed to a substrate made
according to the process described herein.
[0210] In another aspect, the present invention includes a catalytic substrate
or
filtering substrate that offers one or more of the following attributes: a
faster
light-off period, increased depth filtration of PM, a lower backpressure, a
lower probability of clogging up, an ability to be placed in multiple
locations
in the exhaust system including the manifold or the head itself, a higher
probability of catalytic reaction, a higher conversion ratios of pollutants
such
as NOx, HC, CO, faster burnoff of PM, a lower amount of catalyst material
needed, faster light-off in for cold starts, lower external wall temperature
of
the substrate, and the like.
[0211] Using a substrate, catalytic converter, particulate filter, or exhaust
system of the present invention provides a number of advantages and
improvements over the prior art. In certain embodiments, these improved
catalytic converters and/or particulate filters are able to remove and/or
eliminate pollutants from the exhaust of combustion engines with a number of
specific advantages, as described in more detail below. Improved exhaust
systems are likewise an additional aspect of the invention described herein.
The improved exhaust system reduces the amount of pollutants emitted from
the operated engine.
[0212] The present invention, including nonlimiting embodiments and
examples, are described in more detail below. The embodiments discussed
herein are provided for illustrative purposes only. The invention is not
limited
to these embodiments.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Catalytic Substrate
[0213] The present invention is directed to a catalytic substrate comprising,
or
alternatively consisting of or consisting essentially of, a non-woven Sintered
Refractory Fibrous Ceramic (nSiRF-C) composite, as described herein, that
can be used in catalytic converters, particulate filters, and related devices;
and
optionally further comprising an effective amount of a catalyst, such as a
catalytic metal. Preferably, the catalytic substrate comprises a catalyst. The
nSiRF-C composite can be shaped into configurations suitable for uses
described herein.
[0214] The nSiRF-C composite is non-woven. In certain embodiments, the
nSiRF-C composite is a material having a definitive, rigid three-dimensional
shape. The fibers of the nSiRF-C composite are not arranged in an organized
pattern but are arranged three-dimensionally in a random, haphazard, or
omnidirectional fashion. In some embodiments, the nSiRF-C is in the form of
a matrix.
[0215] The nSiRF-C is a sintered composite. In one embodiment, a sintered
composite is a cohesive mass formed by heating without melting. However,
the process of sintering a ceramic material is well-known in the art, and thus
the scope of the present invention is not necessarily limited to specific
embodiments and descriptions described herein. Sintering creates bonds
without resin residue. With reference to the present invention, the sintered
ceramic is a cohesive mass of dispersed fibers formed by heating without
melting.
[0216] The nSiRF-C is a refractory fibrous ceramic composite. The nSiRF-C
of certain embodiments is composed of high grade refractory fibers of various
lengths and compositions as exemplified in nonlimiting embodiments herein..
[0217] In one embodiment, the present invention is directed to a catalytic
substrate suitable for use in a number of applications as described herein.
Such a substrate includes a number of materials which have one or more,
preferably a plurality of attributes as described herein. The substrate of the
present invention is made of a non-woven, fibrous ceramic composite made
from refractory grade fibers. Such a material is disclosed in U.S. Patent No.
56
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
4,148,962, which is incorporated herein by reference in its entirety. Other
suitable materials are disclosed in U.S. Patent Nos. 3,953,083.
[0218] In one embodiment, the catalytic substrate of the present invention
comprises, or alternatively consists or consists essentially of, an alumina
enhanced thermal barrier ("AETB") material or a like material known to one
of ordinary skill in the art. AETB material is known in the art and more fully
described in Leiser et al., "Options for Improving Rigidized Ceramic
Heatshields", Ceramic Engineering and Science Proceedings, 6, No. 7-8, pp.
757-768 (1985) and Leiser et al., "Effect of Fiber Size and Composition on
Mechanical and Thermal Properties of Low Density Ceramic Composite
Insulation Materials", NASA CP 2357, pp. 231-244 (1984), both of which are
hereby incorporated by reference.
[0219] In another embodiment, the catalytic substrate comprises Ceramic tiles,
such as alumina enhanced thermal barrier (AETB) with toughened unipiece
fibrous insulation (TUFI) and/or reaction cured glass (RCG) coatings. Such
materials are known in the art.
[0220] Another suitable material is Fibrous Refractory Ceramic Insulation
(FRCI). In one embodiment, AETB is made from aluminaboriasilica (also
known as alumina-boria-silica, aluminoborosilicate, and aluminoboriasilicate)
fibers, silica fibers, and alumina fibers. One commonly known application for
AETB is as an exterior tile on the Space Shuttle, ideal for shuttle re-entry.
AETB has a high melting point, low heat conductance, and coefficient of
thermal expansion, ability to withstand thermal and vibrational shock, low
density, and very high porosity and permeability. Thus, in a preferred
embodiment, the catalytic substrate has a high melting point, low heat
conductance, coefficient of thermal expansion, an ability to withstand thermal
and vibrational shock, a low density, a high porosity, and a high
permeability.
[0221] In one embodiment, a first component of AETB is alumina fibers. In
preferred instances of the present invention, the alumina (A1203 or aluminum
oxide, e.g., SAFFIL), is typically about 95 to about 97 weight percent alumina
and about 3 to about 5 weight percent silica in commercial form. In other
embodiments, alumina having a lower purity are also useful, e.g., 90%, 92%,
and 94%. In other embodiments, alumina having a higher purity are also
useful. Alumina can be produced by extruding or spinning. First, a solution
57
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
of precursor species is prepared. A slow and gradual polymerization process
is initiated, for example, by manipulation of pH, whereby individual precursor
molecules combine to form larger molecules. As this process proceeds, the
average molecular weight/size increases, thereby causing the viscosity of the
solution to increase with time. At a viscosity of about ten centipoise, the
solution becomes slightly adhesive, allowing fiber to be drawn or spun. In
this
state, the fiber may also be extruded through a die. In certain embodiments,
the average fiber diameter ranges from about one to six microns, although
larger and smaller diameter fibers are also suitable for the present
invention.
For example, the fiber diameters in other embodiments range from 1-50
microns, preferably 1-25 microns, more preferably 1-10 microns.
[0222] In one embodiment, a second component of an AETB is silica fiber.
Silica (Si02, e.g., Q-fiber or quartz fiber), in certain embodiments, contains
over 99.5 weight percent amorphous silica with very low impurity levels.
Silica of lower purities, e.g., 90%, 95%, and 97%, are also useful for the
invention. In certain embodiments, an amorphous silica is used that has a
low density (e.g., 2.1 to 2.2 g/cm), high refractoriness (1600 degrees
Celsius),
low thermal conductivity (about 0.1 W/m-K), and near zero thermal
expansion.
[0223] In one embodiment, a third component of an AETB is
aluminaboriasilica fibers. In certain instances, aluminaboriasilica fiber
(3A12O3=2SiO2=B2O3, e.g., NEXTEL 312) is typically 62.5 weight percent
alumina, 24.5 weight percent silica, and 13 weight percent boria. Of course,
the exact percentages of the constituents of the aluminaboriasilca may vary.
It
is largely an amorphous product but may contain crystalline mullite. Suitable
aluminaboriasilica fibers and methods of making the same are disclosed, for
example, in U.S. Patent No. 3,795,524, the teachings of which are herein
incorporated by reference in their entirety.
[0224] Another suitable material for use as a substrate of the present
invention
includes Orbital Ceramics Thermal Barrier (OCTB), available from Orbital
Ceramics (Valencia, CA).
[0225] Other suitable materials for use as a nSiRF-C in the present invention
include: AETB-12 (having a composition of about 20% A12O3, about 12%
(14% B2O3, 72% A12O3, 14% Si02; NEXTELTM fiber), and about 68% Si02);
58
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
AETB-8 (having a composition of about 20% A1203, aboutl2% (14% B203,
72% A1203, 14% Si02 NEXTELTM fiber), 68% Si02); FRCI-12 (having a
composition of about 78% wt. silica (SiOZ), and 22% wt. aluminoborosilicate
(62% A1203, 24% Si02, 14% B203); and FRCI-20 (having a composition of
about 78% wt. silica (Si02) and about 22% wt. aluminoborosilicate (62%
A1203, 24% Si02, 14% B203).
[0226] In a preferred embodiment, the components of the inorganic fibers
consists, or consists essentially of, fibrous silica, alumina fiber, and
aluminoborosilicate fiber. In this embodiment, the fibrous silica comprises
approximately 50-90 (%) percent of the inorganic fiber mix, the alumina fiber
comprises approximately 5-50 (%) percent of the inorganic fiber, and the
aluminoborosilicate fiber comprises approximately 10-25 (%) percent of the
inorganic fiber mix. The fibers used to prepare the substrate of the present
invention may have both crystalline and glassy phases in certain embodiments.
[0227] Other suitable fibers include aluminoborosilicate fibers preferably
comprising aluminum oxide in the range from about 55 to about 75 percent by
weight, silicon oxide in the range from less than about 45 to greater than
zero
(preferably, less than 44 to greater than zero) percent by weight, and boron
oxide in the range from less than 25 to greater than zero (preferably, about 1
to
about 5) percent by weight (calculated on a theoretical oxide basis as A1203,
Si02, and B203, respectively). The aluminoborosilicate fibers preferably are
at least 50 percent by weight crystalline, more preferably, at least 75
percent,
and most preferably, about 100% (i.e., crystalline fibers). Sized
aluminoborosilicate fibers are commercially available, for example, under the
trade designations "NEXTEL 312" and "NEXTEL 440" from the 3M
Company. Further, suitable aluminoborosilicate fibers can be made as
disclosed, for example, in U.S. Patent No. 3,795,524, which is incorporated
herein by reference in its entirety.
[0228] Additional suitable fibers include aluminosilicate fibers, which are
typically crystalline, comprising aluminum oxide in the range from about 67 to
about 77, e.g., 69, 71, 73 and 75, percent by weight and silicon oxide in the
range from about 33 to about 23, e.g., 31, 29, 27, and 25, percent by weight.
Sized aluminosilicate fibers are commercially available, for example, under
the trade designation "NEXTEL 550" from the 3M Company. Further,
59
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
suitable aluminosilicate fibers can be made as disclosed, for example, in U.S.
Patent No. 4,047,965 (Karst et al.), the disclosure of which is incorporated
herein by reference.
[0229] In other embodiments, the fibers used to prepare the substrate of the
present invention comprise a-A1203 with Y203 and Zr02 additions, and/or
a-A1203 with Si02 added (forming a-A1203/mullite)
[0230] Various specific materials can be used to prepare the catalytic
substrate. In one embodiment, the material used to prepare a substrate of the
present invention comprises, or alternatively consists or consists essentially
of,
refractory silica fibers and refractory aluminumborosilicate fibers. In
another
embodiment, the material used to prepare the catalytic substrate comprises
refractory silica fibers, refractory grade alumina fibers, and a binding
agent,
preferably a boronoxide or a boron nitride powder. In another embodiment
the fibers are high grade.
[0231] In another embodiment, the substrate comprises a refractory composite
consisting essentially of aluminosilicate fibers and silica fibers in a weight
ratio within the range of about 19:1 to 1:19, and about 0.5 to 30% boron
oxide,
based on the total weight of the fibers. Alternatively, the weight ratio of
aluminosilicate fibers to silica fibers is selected from 16:1, 14:1, 12:1,
10:1,
8:1; 6:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, and 1:16. The
boron
oxide is present in other embodiments in about 5%, 10%, 15%, 20%, 25%, or
30%. In a further embodiment, the boron oxide and aluminosilicate fibers are
present in the form of aluminoborosilicate fibers. In a further embodiment,
the
catalytic substrate comprises a nSiRF-C composite wherein the
aluminosilicate fiber to silica fiber ratio ranges from 1:9 to 2:3 and the
boron
oxide content is about 1 to 6% of the fiber weight.
[0232] In another embodiment, fibers suitable for preparing the substrate of
the present invention include the refractory fibers produced by 3M such as
NEXTELTM Ceramic Fiber 312, NEXTELTM Ceramic Fiber 440, NEXTELTM
Ceramic Fiber 550, NEXTELTM Ceramic Fiber 610, and NEXTELTM Ceramic
Fiber 720. The composite grade fibers NextelTM Fibers 610, 650, and 720 have
more refined crystal structures based on alpha-A1203 and do not contain any
glassy phases. This allows them to retain strength to higher temperatures than
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the industrial fibers. NextelTM Fiber 610 has essentially a single-phase
composition of a-A1203. It has the lowest strength retention at temperature
even though it starts with the highest strength at room temperature. Both
NextelTM Fiber 650, which is a-A1203 with Y203 and Zr02 additions, and
NextelTM Fiber 720 which is alpha-A1203 with Si02 added (forming
(x-A1203/mullite) have better strength retention at temperature and lower
creep.
[02331 In another suitable embodiment, a nSiRF-C is made from or comprises
(or alternatively, consists of or consists essentially of) ceramic fibers
comprising A1203, Si02, and B203, having the following attributes: 1) melting
point of about 1600 C to about 2000 C, preferably about 1800 C; 2) a density
of about 2 to about 4 g/cc, preferably about 2.7 to about 3 g/cc; 3) a
refractive
index of about 1.5 to about 1.8, more preferably selected from 1.56, 1.60,
1.61,
1.67, and 1.74; 4) a filament tensile strength (25.4 mm gauge) of about 100 to
about 3500 MPa, more preferably from about 150 to about 200 or from about
2000 to about 3000, or selected from 150, 190, 193, 2100, or 3100; 5) a
thermal expansion (100-1100 C) from about 2 to about 10, preferably about 3
to about 9, more preferably selected from 3, 4, 5.3, 6, and 8; 6) and a
surface
area of less than about 0.4 m2/g, more preferably less than about 0.2 m2 /g.
In
other embodiments, the crystal phase of the fibers are mullite and amorphous,
substantially amorphous, y-A1203, or amorphous Si02. In still other
embodiments, the dielectric constant of a fiber that is suitable for use in
preparing a substrate according to the present invention is about 5 to about 9
(at 9.375 GHz), or preferably selected from the group consisting of 5.2, 5.4,
5.6, 5.7, 5.8, 6, 7, 8, and 9.
[0234] In certain embodiments, the substrate of the present invention is
substantially "shot-free" meaning free of particulate ceramic (i.e.,
crystalline
ceramic, glass, or glass-ceramic) from the fiber manufacture process.
[0235] In certain embodiments, the nSiRF C composite is "nonflexible." In
one embodiment, nonflexible refers to a substrate that cannot be bent more to
an angle of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, or 25 degrees (with respect
to the
point of bending) without breaking, cracking, or becoming permanently
deformed or misshaped.
61
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0236] The diameter of the fibers used different embodiments of the invention
may vary. In certain embodiments, the average diameter is from about 1 to
about 50 microns, preferably 1 to about 20 microns. In other embodiments,
the average diameter is about 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 microns.
In
other embodiments, the average fiber diameter for aluminiaboriasilica fibers
is
from about ten to about twelve microns.
[0237] In another embodiment, the catalytic substrate of the present invention
further comprises a binding agent such as boron nitride. In another
embodiment of the present invention, boron nitride is added to replace the
aluminaboriasilica fiber when it is not used. That is, in some embodiments,
the substrate comprises (or consists of or consists essentially of or is made
from) silica fiber, alumina fiber, and boron nitride in similar weight
percentage as described above. In a further embodiment, the substrate
comprises silica fiber, alumina fiber, and a boron binder. Each of these may,
in certain embodiments, contain small amounts of other material such as
organic binders, inorganic binders and some fibrous or non-fibrous impurities.
In other embodiments, the substrate does not contain an organic binder.
Furthermore, in other instances, the binder that is used to create the nSiRF-C
is materially changed during the process of making, as is known in the art.
[0238] Additional suitable materials for use in preparing the substrate of the
present invention are disclosed in U.S. Patent No. 5,629,186 which describes
low density fused fibrous ceramic composites prepared from amorphous silica
and/or alumina fibers with 2 to 12% boron nitride by weight of fibers. In
another embodiment, a thickening agent is added. Suitable thickening agents
are known in the art.
[0239] In other embodiments, the ceramic fibers used to prepare the nSiRF-C
have an average tensile strength greater than about 700 MPa (100,000 psi),
preferably greater than about 1200 MPa (200,000 psi), more preferably,
greater than about 1800 MPa (300,000 psi), and most preferably, greater than
about 2100 MPa (350,000 psi).
[0240] In another embodiment, a dispersant is added. Suitable dispersants are
known in the art.
62
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0241] In other embodiments, the catalytic substrate is treated with, altered,
modified, and/or enhanced in one or more aspects as described herein and/or
as is known in the art.
[0242] In still other embodiments, minor impurities of various sources are
present. In these cases, the impurities do not substantially affect the nSiRF-
C
and/or its attributes.
[0243] A substrate according to the present invention does not include a
NEXTELTM woven fabrics or mat.
Catalyst
[0244] In another aspect, the present invention is directed to a substrate as
described above comprising a catalyst. Any number of catalysts can be used
with the substrate to form a catalytic substrate. The catalyst may be coated
onto the surface of the substrate. That is, the catalyst, in one embodiment,
is
adsorbed onto the surface (e.g., the walls of the channels) of the catalytic
substrate. Catalyst could also reside on the inside of the core of the
substrate
and attached to the individual fibers of the substrate. In certain
embodiments,
the present invention can function at the same or better levels compared to
current technology but require a smaller amount of catalyst.
[0245] In another embodiment, the catalyst is deposited only on the channel
wall surfaces and not inside the channel walls. In another embodiment, the
catalyst is deposited on the ingress channel walls, on the egress channel
walls,
within the walls, or combinations thereof. In yet a further embodiment, a
first
catalyst lines, coats, or permeates a beginning, or proximal, portion of the
channel wall; a second catalyst lines, coats, or permeates a middle portion of
the channel wall; and yet a third catalyst at a terminal section of the
channel
wall.
[0246] In one embodiment, the catalytic substrate of the present invention
preferably contains a catalytic metal. In another metal, the catalytic
substrate
does not contain a catalytic metal. However, under certain conditions, the
substrate is able to catalyze suitable reactions without the need for a
separate
catalytic metal, for example, in certain embodiments, a washcoat as described
below may function as a catalyst.
63
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0247] Any catalyst capable of being applied to the substrate can be used.
Such a catalyst includes but is not limited to platinum, palladium (such as
palladium oxide), rhodium, derivatives thereof including oxides, and mixtures
thereof. In addition, the catalysts are not restricted to noble metals,
combinations of noble metals, or only to oxidation catalysts. Other suitable
catalysts include chromium, nickel, rhenium, ruthenium, silver, osmium,
iridium, platinum, and gold, iridium, derivatives thereof, and mixtures
thereof.
Other suitable catalysts include binary oxides of palladium and rare earth
metals as disclosed in U.S. Pat. Nos. 5,378,142 and 5,102,639, the disclosures
of which are hereby incorporated herein by reference. These binary oxides
may result from the solid state reaction of palladium oxide with the rare
earth
metal oxides, to produce, e.g., Sm4PdO7, Nd4PdO7, Pr4PdO7 or La4PdO7.
Other catalysts that can be used in the present invention include those
disclosed in U.S. Patent No. 6,090,744 (assigned to Mazda Motor
Corporation). Other suitable catalysts include non-metallic catalysts, organic
catalysts, base metal catalysts, precious metal catalysts, and noble metal
catalysts.
[0248] Other suitable catalysts are disclosed in 6,692,712 (assigned to
Johnson Matthey Public Limited Company). Catalysts that do not comprise
precious metals may be used in the present invention. Such catalysts are
shown in U.S. Patent No. 5,182,249.
[0249] Another suitable platinum catalyst developed by Engelhard is
composed of Pt/Rh at 5:1 ratio (applied in an amount of about 5-150 g/ft3) and
MgO (applied in an amount of about 30-1500 g/ft).
[0250] In other embodiments, vanadium and derivates thereof, e.g., VZO5, are
useful catalysts, in particular for diesel particulate filters. Such catalysts
have
been used in commercially available in diesel particulate filters.
[0251] Catalysts were developed that utilized vanadium compounds other than
V205, for example silver or copper vanadates. An example copper vanadate
base metal catalyst was developed by Heraeus (Strutz 1989). The catalyst can
be prepared by doping and calcining copper vanadate Cu3VzO8 with potassium
carbonate in the molar ratio Cu:V:K about 3:2:0.13. The catalyst loading was
between 10 and 80 g/m2 of the filtration surface area. Another suitable
catalyst is Cu/ZSM5, which can be used as a DeNox catalyst.
64
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0252] Precious metals such as platinum, palladium, and rhodium are the most
common and are preferred, although other catalysts known in the art can be
used. These three precious metals have been known as excellent and highly
efficient catalysts with internal combustion engine emissions. In over twenty-
five years of catalytic converters, there has not really been a meaningful
substitute for this trinity. However, there are thousands of combinations of
these catalysts configured according to the original equipment manufacturer,
vehicle, vehicle load, environmental regulations, engine, transmission, etc.
Throughout the truck and automotive manufacturing industry, various
combinations and formulations of catalysts are employed. A catalytic
substrate according to the present invention comprises any one or more of
these catalyst combinations. Many combinations are considered proprietary
material. Manufacturers such as Ford, GM, and Toyota have a unique catalyst
formula for each vehicle, due to the varying vehicle weights and engine
performance demands. Manufacturers also have different catalyst formulas
for the same vehicle depending upon where the vehicle will be sold or
licensed, e.g., Canada, United States, California, Mexico. Currently, these
formulations may change two to three times per vehicle per model year, due to
the strict governmental regulations. For these reasons, most manufacturers
handle the application of the catalytic coatings themselves.
[0253] In a further embodiment, the catalytic substrate comprises a nSiRF C
and a catalyst that is used in a commercially available catalytic environment.
[0254] In one aspect, once the substrate has been shaped to its final
dimensions and a washcoat is applied and cured, one or more catalysts are
applied using known techniques and methods, such as the manner of applying
a palladium-platinum based catalyst as disclosed in U.S. Patent Nos.
5,224,852 and 5,272,125, the teachings of which are both incorporated herein
by reference in their entirety.
[0255] In one embodiment, the catalyst is in an amount sufficient for the
catalytic action to take place effectively. For example, the amount
sufficient,
in one embodiment, refers to an amount of catalyst, e.g., a precious metal,
interacting with and in the path of the emi.ssion sufficient to react with as
much of the emission as possible, such as 80%, 85%, 90%, 95%, 97%, 98%,
and 99%, and the like.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0256] In one embodiment, the catalyst is deposited on or impregnated into
the washcoat, preferably as individual crystals. In this embodiment, the
catalysts are not applied as a veneer-like coating over the washcoat (like
paint
on a wall). When the catalysts are impregnated onto the washcoat, they are
applied so the end product is partially or substantially a colony of
individual
crystals. This can be visualized as salt crystals on a pretzel. It is
preferable
that sufficient spacing is provided between the catalysts. At the same time,
there should be enough precious metals in the fluid path, e.g., the exhaust
path,
at the optimum catalytic activity operating temperature, i.e., light off, and
the
precious metals must fit within the physical restraints, i.e., space,
permitted by
the functionality and design of a vehicle and engine.
[0257] A manufacturing goal is to maximize the pollutants removed while
minimizing the amount of catalyst required on the substrate. Each vehicle
produces a different amount of pollutant, and as such, the substrate is in
some
embodiments customized to address that level of pollutants and minimize the
amount of precious metals.
[0258] In another embodiment, the catalyst addition to the catalytic substrate
can occur during the slurry process when making of the substrate, or it can
occur after the machining process (as described below). In this case, the
catalyst is mixed with the slurry of fibers prior to any heating step.
[0259] Single and multiple catalyst formulations can be applied to a single
substrate, or due to the small size of the filter relative to the existing
catalytic
converters and exhaust systems, the placement of multiple substrates is
possible. Thus, the catalytic substrate of the present invention in one
embodiment comprises or consists of or consists essentially of one or more
zones, wherein each zone has a different catalyst. Alternatively, one or more
of the zones may be uncatalyzed. For example, a catalytic substrate of the
present invention may include an oxidation catalyst in one zone which
contains the front surface of the substrate, and a reducing catalyst in
another
zone which contain the rear surface.
[0260] If the substrate is to be used as a flow through configuration, then it
is
preferable, although not required, for the catalysts, or the majority of the
catalysts, to reside along the surface of the channels. If the substrate is
machined into a wall flow configuration, then it is preferable for the
catalysts
66
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
to be evenly distributed throughout the substrate as the gases are going to be
traveling through all of the substrate and not just passing through.
[0261] For example, the substrate of the present invention can be used in a
catalyzed diesel particulate filters (CDPF). A CDPF utilizes catalysts
deposited directly on the substrate. Both precious and base metal catalysts
can
be used, such as platinum, silver, copper, vanadium, iron, molybdenum,
manganese, chromium, nickel, derivatives thereof (such as oxides) and others.
Depending on the type of filter, the catalyst can be impregnated directly into
the media or an intermediate washcoat layer can be used. A CDPF can
utilize exhaust temperatures of about 325-420 C for regeneration, depending
on engine technology (PM emissions) and fuel quality (sulfur content).
[0262] Platinum is one of the most active and most commonly used noble
metal catalysts, but palladium, rhodium, or ruthenium catalysts, usually in
mixtures, are also suitable for use in the present invention. The list of
common non platinum-group metals used in catalytic converters includes
vanadium, magnesium, calcium, strontium, barium, copper and silver. In one
embodiment, platinum is the preferred catalyst for use with diesel engines. In
another embodiment, palladium and rhodium suitable for use with a gasoline
engine.
[0263] Catalysts are typically quite expensive. It is therefore desirable to
achieve the maximum reduction in pollution with the minimum amount of
catalyst used. Platinum and palladium, two common catalysts, are both
expensive precious metals. A substrate having a porous, permeable nature
with a large surface area on which catalysts can reside as evenly distributed
crystals or layer allow for achieving that objective. An advantage of the
present invention is a lower amount of catalyst needed compared to
conventional substrates.
[0264] Typical platinum loadings in filters used for off-road engines through
the 1990's were between 35 and 50 g/ft3. These filters, installed on
relatively
high polluting engines, required minimum temperatures of nearly 400 C for
regeneration. Later, when catalyzed filters were applied to much cleaner
urban bus and other highway vehicle engines, it was found that the catalyzed
filters were able to regenerate at much lower temperatures. However, higher
platinum loadings were needed to support the low temperature regeneration.
67
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Filters used in clean engine, low temperature applications have typically
platinum loadings of 50-75 g/ft3.
[0265] In one embodiment, the catalytic substrate comprises a catalyst in the
amount of about 1 to about 100, about 1 to about 50, about 1 to about 30, or
about 10 to about 40 g/ft3.
[0266] In another embodiment, the catalytic substrate, preferably an nSiRF-C
such as AETB, OCTB, and FRCI, comprises catalyst of platinum and rhodium
in a ratio of about 5:1 and an amount of about 30 g/ft3.
Filtering Substrate
[0267] The present invention is directed to a catalytic substrate comprising a
non-woven Sintered Refractory Fibrous Ceramic (nSiRF-C) composite, as
described herein, that can be used in particulate filters, and related
devices.
The filtering substrate is fashioned into particular shapes, designs, sizes,
and
configurations that are useful for filtering, in particular for filtering
particulate
matter. The filtering substrate is particularly useful for filtering
particulate
matter under extreme conditions (temperature, pressure, etc), such as
filtering
a flow of exhaust gas. The filtering substrate can be used in additional
applications in which the filtering of small particulate matter is required.
[0268] In one embodiment, the filtering substrate comprises, or alternatively
consists of or consists essentially of, a nSiRF-C composite as described above
for the catalytic substrate. The filtering substrate does not contain a
catalyst.
All variations, embodiments, and examples of materials suitable for use as the
substrate of a catalytic substrate are likewise suitable for the filtering
substrate
of the present invention.
[0269] The filtering substrate is shaped into configurations suitable for uses
described herein, in particular for use in particulate traps such as diesel
particulate traps and diesel particulate filters.
[0270] In one embodiment, a filtering substrate of the present invention is
alumina enhanced thermal barrier ("AETB") material or a like material known
to one of ordinary skill in the art. AETB is made from aluminaboriasilica
(also lcnown as alumina-boria-silica, aluminoborosilicate, and
aluminoboriasilicate) fibers, silica fibers, and alumina fibers. One commonly
68
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
known application for AETB is as an exterior tile on the Space Shuttle, ideal
for shuttle re-entry. The attributes that make AETB unique and desirable to
the space industry are also preferred in organic combustion technology.
AETB has a high melting point, low heat conductance and coefficient of
thermal expansion, ability to withstand thermal and vibrational shock, low
density, and very high porosity and permeability.
[0271] The filtering substrate of the present invention is optionally treated
with one or more chemical additives.
[0272] In another embodiment, the present invention is directed to a diesel
particulate trap comprising a filter as described herein without any catalyst
applied to it.
[0273] In another embodiment, the present invention is directed to a diesel
particulate trap comprising a filter as described herein in combination with a
CRT diesel particulate trap (NOX, HC adsorbers).
[0274] In another embodiment, the present invention is directed to a diesel
particulate trap comprising a filter as described herein in combination with
SCR.
[0275] In another embodiment, the filtering substrate comprises a plurality of
channels as described in more detail below. Furthermore, the filtering
substrate can be modified, altered, and/or enhanced in one or more aspects as
described herein and/or as known in the art.
Attributes of a Catalytic and Filtering Substrates
[0276] The present invention has one or more, preferably at least three, four,
five, six, seven, eight, nine, or ten, attributes which are advantageous over
conventional catalytic or filtering substrates.
Suitable for Use
[0277] The invention is directed in certain embodiments to a catalytic
substrate or filtering substrate comprising nSiRF-C and a catalyst, suitable
for
use in a catalytic converter. The substrate is suitable for use in any number
of
catalytic converters, filtering devices and applications thereof.
69
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0278] For example, the catalytic substrate and filtering substrate of the
present invention is suitable of use in any of the applications generally used
for prior art substrates. Suitable uses include, but are not limited to, the
use of
a substrate of the present invention in an exhaust system any 1) Mobile On-
Road Engines, Equipment, and Vehicles, including cars and light trucks;
highway and street motorcycles, three-wheeled motorcycle (e.g., motorized
tricycles, autorichshaws), motorized tricycles; heavy-duty highway engines,
such as trucks and buses; 2) Mobile Non-Road Engines, Equipment, and
Vehicles, including compression-ignition engines (farm, construction, mining,
etc.); small spark-ignition engines (lawn mowers, leaf blowers, chainsaws,
etc.); large spark-ignition engines (forklifts, generators, etc.); marine
diesel
engines (commercial ships, recreational diesel, etc.); marine sparlc-ignition
engines (boats, personal watercraft, etc.); recreational vehicles
(snowmobiles,
dirt bikes, all-terrain vehicles, etc.); locomotives; aviation (aircraft,
ground
support equipment, etc.); and 3) Stationary Sources, including hundreds of
sources, such as power plants, refineries, and manufacturing facilities.
[0279] In another embodiment, a catalytic substrate of the present invention
is
suitable for use in a particular vehicle if the substrate as described herein,
when a part of a catalytic converter, functions so that the vehicle meets the
emissions standards of any one of 1990, 2007, and 2010, as defined by the
EPA.
[0280] In another embodiment, the catalytic substrate catalyzes the reaction
of
pollutants to nonpollutants at a high level. For example, the conversion of
pollutants to nonpollutants is catalyzed at an efficiency of greater than 50%.
In another embodiment, the conversion of pollutants to nonpollutants is
catalyzed at an efficiency of greater than 60%. In still other embodiments,
the
conversion rate is selected from the group consisting of 70%, 80%, 90%, 91%,
92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, and 99.9%. In certain
embodiments, the conversion rate refers to the total conversion of non-
particulate pollutants. In other embodiments, the conversion rate refers to
the
conversion of specific non-particulate pollutants, e.g., NOx to N2, CO to CO2.
or HCs to CO2 and HZO. In other embodiments, the conversion rate refers to
the percentage of particulate matter removed from an exhaust gas.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0281] In another embodiment, a catalytic substrate of the present invention
is
suitable for use in a particular application if the catalytic substrate passes
certain OEM-prescribed and preferred tests, such as U.S. Federal Test
Protocol 75 (U.S. FTP75). Such tests are known in the art. (See for example
Document No. EPA420-R-92-009 , published by the U.S. EPA, available at
http://www.epa.gov/otaq/inventory/r92009.pdf, which is herein incorporated
by reference in its entirety). Additionally, as a back-cat or DPT in retrofit
applications, EPA and/or state/local agencies may have to approve of the
products for use, including the substrate contained therein.
Surface Area
[0282] The available surface area of a substrate is an important
characteristic
of filtering substrate or catalytic substrate. One characteristic of a
suitable
substrate for a catalytic converter is for it to have a high geometric surface
area (GSA). The high GSA allows for maximum reaction probability.
[0283] A large open frontal area (OFA) allows for greater amount of gas to
pass through without obstructing its flow and causing back-pressure. Open
frontal area (OFA) is defined as the part of the total substrate cross-section
area which is available for the flow of gas (i.e., the cross-section area of
the
filter inlet channels). It is typically expressed relative to the total
substrate
cross-section.
[0284] An attribute of the substrate of the present invention is its high
surface
area or high GSA. The surface area of the substrate is an important
characteristic for catalysis application. Surface area is the sum amount of
surface that exhaust emissions must pass across when traveling through an
exhaust filter. Increased surface area translates into an increased surface
for
chemical reactions to take place between pollutants and catalytic and thermal
processes, making a catalytic converter process quicker and more efficient.
Speed and efficiency can result in little to no clogging, which can cause
failure
of the exhaust system. Furthermore, the increased surface area of the
substrate
of certain embodiments also includes increased filtering efficiency and/or
capability.
71
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0285] Geometric surface area is the total surface area that precious metals
can be impregnated onto in one cubic inch. A substrate having a high gross
surface area is preferred. Certain embodiments of the present invention have a
much higher geometric surface area that can be impregnated with catalyst,
compared to conventional substrates, such as cordierite and SiC.
[0286] Gross wall volume is the total amount of wall volume that exists in a
one inch cube of configured substrate. Gross wall volume is calculated as
each wall surface area multiplied by each respective thickness and summed.
A substrate having a lower gross wall volume is preferred. In certain
embodiments, the gross wall volume of the substrate of the present invention
is lower than that of conventional substrate materials, such as cordierite and
SiC.
[0287] In certain embodiments, the gross wall volume of the catalytic
substrate is from about 0.5 to about 0.1, from about 0.4 to about 0.2, or
about
0.3 in3/in3 (cubic inches per cubic inch). In a preferred embodiment, the
gross
wall volume substrate is about 0.25 to about 0.28, more preferably about 0.27,
more preferably about 0.272 in3/in3.
[0288] Due to the lower gross wall volume of the present invention in certain
embodiments, a lower amount of catalyst, such as palladium, is needed to
perform the catalytic action with the present invention than a cordierite of a
similar size.,
Porosity and Perfneability
[0289] Pore attributes also affect mechanical and thermal attributes of the
substrate. A trade-off can exist between porosity and mechanical strength:
substrates of smaller pore size and lower porosity are stronger than those of
higher porosity for certain conventional substrates. Thermal attributes, both
specific heat capacity and thermal conductivity may decrease with increasing
porosity in certain materials (Yuuki 2003).
[0290] The first wall-flow monoliths, introduced in the late 1980's, had
channels as large as 35 m in diameter. In order to maximize filtration
efficiency, channels were made smaller, typically in the range of 10-15 m in
filters used in the 1990's. In the development of new materials, filter
72
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
manufacturers differentiate their target pore attributes, primarily in
consideration of the catalyst system to be applied (Ogyu, K., et al., 2003.
"Characterization of Thin Wall SiC-DPF", SAE 2003-01-0377; Yuuki, K., et
al., 2003, "The Effect of SiC Properties on the Performance of Catalyzed
Diesel Particulate Filter (DPF)," SAE 2003-01-0383). The applications can be
classified as follows:
[0291] Non-catalyzed filters, such as those used in fuel additive regenerated
systems: The main requirement is a high soot holding capacity. Certain
conventional filters have a porosity that is about 40-45% with pores between
10-20 m.
[0292] Catalyzed filters, such as those in passively regenerated systems
require more porosity and possibly larger pore size to enable coating with
increasingly more complex catalyst systems (as opposed to the simple
catalysts used in the 1990's, which often had very little or no washcoat
material). The substrates should have acceptably low pressure loss after being
coated with catalyst/washcoat systems at about 50 g/dm3 loading. Certain
prior art filters have a porosity of about 45-55% range. Additional heaters
may also be applied.
[0293] Filter/NOx adsorber devices, such as the DPNR system or CRT
(continuous regeneration trap) incorporate NOx storage/reduction systems and
require high washcoat loadings, possibly above 100 g/dm3. Certain prior art
substrates have a porosity of about 60% (a 65% porosity substrate has been
reported, with mechanical strength being the main limitation in increasing
porosity (Ichikawa, S., et al., 2003, "Material Development of High Porous
SiC for Catalyzed Diesel Particulate Filters," SAE 2003-01-0380).
[0294] Another attribute of certain embodiments of the catalytic or filtering
substrate of the present invention is its high porosity. In certain
embodiments,
the porosity of a substrate of the present invention is from about 60%, 70%,
80%, or 90%. In other embodiments, the substrate has a porosity of about
91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% (expressed as a percent
of pore space relative to the solid substrate).
[0295] In one embodiment, the porosity of an exemplary embodiment of the
present invention is approximately 97.26%. By comparison, cordierite is
about 18-42%. In this embodiment, the material of the present invention only
73
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
has about 2.74% material to obstruct the flow of exhaust gas. This fine web of
material actively catches the particulate and bums it off very effectively.
Due
to the trapping of particulates in depth filtration mode and not only along
channel walls, considerable PM buildup does not occur under situation where
regeneration time is longer than PM build-up time. High porosity translates
into better and more effective interaction between pollutants and the
catalyzed
or non-catalyzed substrate surface. At the same time, gas flow buildup can be
released laterally as well as along the intended gas flow direction.
[0296] Referring to FIGS. 22a and 22b, an exemplified substrate 2200, 2205
of the present invention is shown. Substrate 2200, 2205 is approximately
ninety-seven percent porous. As compared to the samples of cordierite in
FIGS. 2a and 2b and silicon carbide in FIG. 3, all being substantially the
same
scale, substrate 1200, 1205 is more porous and less dense. In FIG. 22b,
particular matter PM-10 2210 and PM-2.5 2225 is illustrated to scale. The
particulate matter PM-10 2210 and PM-2.5 2225 can easily permeate the
fibers of substrate 2205, as compared to the cordierite sample 205 exemplified
FIG. 2b. Also, compared to the silicon carbide 300 of FIG. 3, the density of
silicon carbide is about thirty to fifty times that of substrate 2200, 2205.
[0297] The higher porosity in certain embodiments of the present invention
provides a higher surface area and lowers the backpressure. As a result, the
present invention is more efficient at NOx reduction, hydrocarbon and CO
oxidation, and particulate matter trapping.
[0298] Pore characteristics, including volume percent porosity, size
distribution, structure, and interconnectivity determine the monolith ability
to
filter particulates. Additionally, if gas molecules can diffuse into a porous
substrate, the probability of a catalytic reaction increases dramatically.
Together with the cellular geometry, porosity characteristics also influence
the
monolith's hydraulic resistance to flow and the pressure drop. Some attributes
which are desired for high filtration efficiency (e.g., low porosity and small
pore size) are opposite to those required for low pressure drop. Others, such
as good pore interconnectivity and absence of closed, "dead end" pores, are
desired for both low pressure drop and high efficiency. The substrates of the
present invention in another embodiment provide both high filtration
efficiency and low pressure drop.
74
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Emissivity and Heat Conductauce
[0299] Another property of substrates used in catalytic converters and
particulate filters is emissivity. Emissivity is the tendency to emission
heat;
comparative facility of emission, or rate at which emission takes place, as of
heat from the surface of a heated body.
[0300] An ideal substrate takes into consideration the temperature that (1)
the
fastest ramp-up to high conversion efficiency; (2) is safest from thermal harm
(e.g., due to thermal shock or due to high-temperature melting/cracking of
substrate); (3) uses a minimal amount of auxiliary energy; and (4) is
inexpensive to produce. Increasing temperature requires additional energy and
expense. Further, certain amounts of the energy source are conducted, drawn,
or channeled away through thermal conductivity.
[0301] Emissivity is a ratio of reflectance with values between 0 and 1, with
one being perfect reflection. Different substrates used for catalytic
converters
and particulate filters have different emissivity values. High emissivity
allows
the catalyst substrate to minimize heat transfer out of the system, thereby
heating the air inside the catalytic converter or particulate filter faster.
The
emissivity is a measure of the heat reflectance property of the material and a
high value is desirable.
[0302] In certain embodiments, a substrate of the present invention preferably
has an emissivity of about 0.8 to 1Ø In another embodiment, the emissivity
of the substrate of the present invention is about 0.82, 0.84, 0.86, 0.88, and
0.9. Further suitable values for emissivity of a substrate of the present
invention include 0.81, 0.83, 0.85, 0.87, and 0.89. In other embodiments, the
emissivity is about 0.9, 0.92, 0.94, 0.96, or 0.98. Reflectivity of heat
allows
the gaseous material in the pores to heat up much faster since little heat is
retained by the substrate material itself. That results in quicker lightoff
and
little temperature rise of the outside surface of the substrate.
[0303] The thermal conductivity of a material is the quantity of heat that
passes in unit time through unit area of a plate, when its opposite faces are
subject to unit temperature gradient (e.g., one degree temperature difference
across a thickness of one unit). Thermal conductivity has the units of Watts
of
energy per meter thick and Kelvin changed (W/m-K). In preferred
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
embodiments, the substrate of the present invention have a low thermal
conductivity. For example, in one embodiment, the thermal conductivity of a
substrate of the invention is less than about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8,
or 0.9. In another embodiment, the thermal conductivity of a substrate of the
invention is less than about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08,
or
0.09. In another embodiment, the thermal conductivity of a substrate of the
invention is from about 0.1 to about 0.01, from about 0.2 to about 0.02, from
about 0.3 to about 0.03, from about 0.4 to about 0.04, from about 0.5 to about
0.05, from about 0.6 to about 0.06, from about 0.7 to about 0.07, from about
0.8 to about 0.08, or from about 0.9 to about 0.09. In another embodiment, the
thermal conductivity of the present invention is approximately 0.0604 W/m-K.
[0304] By comparison, a sample of cordierite is about 1.3 to 1.8 W/m-K.
These results indicate that, by way of example of a particular embodiment, if
1000 Watts of heat energy is lost from a given volume of cordierite material,
only 33 Watts would be lost from the same volume of the material from the
present invention. Thus, the material of the present invention has a thermal
conductivity thirty times greater than cordierite.
[0305] Additionally, in other embodiments, the process of preparing the
substrate further comprises preparing a catalytic substrate or filtering
substrate
further comprising an emissivity enhancing agent, said process comprising
applying an emissivity enhancing agent to said substrate, preferably to a
nSiRF-C, more preferably an AETB, OCTB, or FRCI material. Other
preferred substrates include any of the specific substrates disclosed herein.
In
further embodiments, the catalytic substrate further comprises an emissivity
enhancing agent and a catalyst selected from the group consisting of
palladium, platinum, rhodium, derivatives thereof, and mixtures thereof.
Other physical and chemical modifications as described herein can be applied
to such embodiments. Emissivity enhancing agents are known in the art.
Thertnal Attributes
[0306] A substrate having a low coefficient of thermal expansion allows for
the substrate to withstand rapid changes in temperature without significant
expansion or contraction. A suitable coefficient of thermal expansion also
76
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
allows for the substrate to expand with heat at the same rate as the
protective
matting around it and the canister.
[0307] It is also preferable for the substrate material to withstand a high
range
of temperatures so that it does not cause a catalytic converter or particulate
filter meltdown if the temperature rises to a high value, for example, during
occasional fuel burning. Additionally, if the substrate material can withstand
high temperatures, the catalytic converter or filter can be placed closer to
the
engine.
[0308] Related properties include low thermal mass and heat capacity. A
material that has a low thermal heat mass and heat capacity allows for less
heat energy to be wasted in raising the temperature of the catalyst substrate.
If
the catalyst substrate heats up quickly, more of the heat energy coming via
the
exhaust gas is used to trigger the light-off of the catalyst components.
[0309] Thermal conductivity is the capability of the material to conduct heat
as a consequence of molecular motion. More specifically, thermal
conductivity is also a measure of the quantity of heat that passes in unit
time
through unit area of a plate whose thickness is unity, when its opposite faces
differ in temperature by one degree. The more a material conducts heat, the
more energy is needed to overcome loss and reach the required temperature.
Preferably, a material reflects heat, rather than conducts. A lower thermal
conductivity value is preferred so more heat energy is utilized in the pore
spaces and not lost from the absorption by the substrate. The chemistry of
different substances determines the level of thermal conductivity.
Additionally, the thermal conductivity of the filter medium is a major
influence on the efficiency of an exhaust emission filter, since loss of
temperature negatively impacts reactivity. A low thermal conductivity is
preferred because more of the heat energy generated is reflected back at the
particulates, and will remain in the pore space. In other words, the lower the
thermal conductivity, the lower the loss of heat. Lower heat loss translates
into less energy needed to obtain the desired temperature range for catalytic
conversion and higher energy efficiency.
[0310] Specific heat is the heat in calories required to raise the temperature
of
one gram of a substance one degree Celsius. A substrate with a high specific
heat will reflect ambient heat, e.g., from an exhaust or an auxiliary source,
77
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
back into the pore space where combustion or catalytic reduction and
oxidation processes require the heat. For instance, under extreme conditions,
e.g., the Arctic, it will take longer to heat up a low specific heat filter
and cool
hot filters, increasing the chance for external heat damage. A lower specific
heat is preferable because is reaches operating temperature faster and with
less
energy.
[0311] In certain embodiments, a substrate of the present invention has a
number of preferred thermal attributes. Preferably, the material is such that
heating of the air in the pore space occurs preferentially compared to the
heating of the substrate. Preferably, the substrate of the present invention
has
a high melting point, and in certain embodiments, a higher melting point than
conventional substrates. A high melting point is preferred, in part, due to
the
extreme temperatures to which a catalytic substrate or filtering substrate is
exposed.
[0312] In a preferred embodiment, a substrate of the present invention
preferably has a high melting point. In one embodiment, the melting point is
greater than about 1500 F. In another embodiment, the melting point is
greater than about 2000 F. In another embodiment, the melting point is
greater than about 2500 F. In a further embodiment, the melting point of the
substrate is about 2000 to about 4000 F. In a further embodiment, the
melting point of the substrate is about 3000 to about 4000 F. Other suitable
melting point ranges include from about 3000 to about 3100, from bout 3100
to about 3200, from about 3200 to about 3300, from about 3300 to about 3400,
from about 3400 to about 3500, from about 3500 to about 3600, from about
3600 to about 3700, from about 3700 to about 3800, from about 3800 to about
3900, and from about 3900 to about 4000. In another preferred embodiment,
the substrate has a melting point of approximately 3632 degrees Fahrenheit.
[0313] In one embodiment of the present invention, the substrate has a melting
point of approximately 3,632 degrees Fahrenheit. For example, if a vehicle is
situated in below freezing temperatures, a blast of 1,500 degree Fahrenheit
exhaust fumes will not cause the substrate to crack or fracture. Similarly,
certain embodiments of the substrate will not overheat and crack. Certain
samples of cordierite have a melting point of about 1,400 degrees Celsius.
78
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0314] The specific heat of an exemplary embodiment of the present invention
is approximately 640 J/kg-K (Joules per kilogram-Kelvin). A sample of
cordierite is about 750 J/kg-K. Even though the cordierite has a greater
specific heat, cordierite filters have a greater mass to heat up. The result
is
more heat energy is needed to reach operating temperature making the
cordierite less efficient.
[0315] A multiple use temperature limit is the maximum temperature in which
a substance can be subjected a plurality of times without substantial
degradation. The higher the temperature a substrate can continue to operate
without micro-fractures or spallation, the less chance of the substrate
breaking
or cracking over time. This in turn means the substrate is more durable over a
wider temperature range. A higher multiple use temperature limit is preferred.
A suitable multiple use temperature limit for certain embodiments of the
catalytic or filtering substrates of the present invention is one selected
from the
group consisting of about 2000 C, 2100 C, 2200 C, 2300 C, 2400 C, 2500 C,
2600 C, 2700 C, 2800 C, 2900 C, 3000 C, and 3100 C.
[0316] The multiple use temperature limit of an exemplary embodiment of the
present invention is 2,980 degrees Celsius. A sample of cordierite is about
1,400 degrees Celsius. The embodiment of the present invention can
withstand more than twice the temperature than cordierite before breaking
down. This permits the material to function in a greater range of exhaust
environments.
[0317] The coefficient of thermal expansion is a ratio of the increase of the
length (linear coefficient), area (superficial), or volume of a body for a
given
rise in temperature (usually for zero to one degree Celsius) to the original
length, area, or volume, respectively. These three coefficients are
approximately in the ratio 1:2:3. When not specifically expressed, the cubical
coefficient is usually intended. The less a substrate will expand when heated,
the less chance of leaking, fracturing, or damage to filter assembly. A lower
thermal expansion is preferred to ensure that the substrate keeps its
dimensions even when heated or cooled.
[0318] The coefficient of thermal expansion for an exemplary embodiment of
the present invention is approximately 2.65 x 10-6 W/m-K (Watts per meter
Kelvin). A sample of cordierite is about 2.5 x 10"6 W/m-K to 3.0 x
79
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
10-6 W/mK. The thermal expansion of a material of the present invention is
less than ten times that of cordierite.
[0319] The coefficient of thermal expansion of the substrate is preferably
compatible with the coefficient of thermal expansion of any washcoat.
[0320] In one embodiment, a catalytic or filtering substrate of the present
invention, compared to certain prior art substrates such as cordierite, has an
increased resistance to damage by thermal or mechanical stress; has a lower
risk of clogging with soot and/or ash; is more tolerant to additive ash
accumulation when used with fuel additive regeneration; and has good
efficiency for particle number reduction.
Density
[0321] When considering substrates to be used in catalytic converters or
diesel
particulate filters, it is preferable to use a substrate that has a low
density. The
material having a low density reduces the weight of the substrate and hence
the overall weight of the vehicle. Furthermore, low density is complimentary
to high porosity and permeability
[0322] Higher density translates into a higher weight. Weight is a large
factor
pertaining to any engine in motion. The heavier the part, the more energy is
needed to move it. In order for these filters to accommodate the increased
volume of particulate generated by a engine, the filter sizes have to
increase,
which adds to vehicle weight and manufacturing and operating costs. Thus, a
lower density material is desired. Of course, the density is not so low that
structural integrity is insufficient.
[0323] Another attribute of the substrate of the present invention is its
density.
The density of the substrate is lower than that of certain conventional
filters
and substrates used for filtering and as catalytic substrate. Density is the
ratio
of mass of a portion of matter to its volume. Greater density requires more
energy to reach operating temperature. In other words, more energy is needed
to heat up a dense material than a less dense material. Greater density
directly
translates into greater weight for set volume. Weight is detrimental to a
vehicle's mileage and performance, as the engine must work harder to move
heavier equipment. Increased density also translates into more heat required
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
to achieve the proper temperature for catalytic activity or "light off ' to
occur.
The density of some materials currently used as substrates or filters are
higher
than optimal. For example, a sample of cordierite is about 2.0 to 2.1 g/cm3.
Thus, there is a need for a substrate and a filter having a lower density. The
density of the substrate of the present invention is lower than that of
cordierite.
[0324] In one embodiment, the catalytic substrate of the present invention
preferably has a low density. The density of the substrate of the present
invention may be in the range from about 2 to about 50 pounds per cubic foot
(lb/ft3). In a preferred embodiment, the density of the substrate is in the
range
of about 5 to about 30 pounds per cubic foot, more preferably, from about 8 to
16 pounds per cubic foot. Other preferred embodiments include catalytic
substrate that has a density of about 8, 9, 10, 11, 12, 13, 14, 15, or
161b/ft3. A
low density that still imparts structural integrity is preferred.
[0325] In one embodiment, the substrate of the invention has a density of
about 8 lbs/ft3 and 22 lbs/ft3, preferably from about 81bs/ft3 and 221bs/ft3.
In
another embodiment, the substrate comprises AETB-8 or AETB-16, having
densities of about 8 lbs/ft3 and about 16 lbs/ft3 respectively. Other suitable
densities include a density selected from about 9, 10, 11, 12, 13, 14, 15, and
16
lbs/ft3.
[0326] In another embodiment, the density of the substrate is approximately
0.10 to approximately 0.25 g/cm3 (grams per cubic centimeter).
Structural Irategrity
[0327] The structural integrity of the substrate material is a characteristic
that
is important to consider. Structural integrity refers to the material's
ability to
withstand vibrational and mechanical stresses, i.e., shake and bake. For
example, substrate strength is important for withstanding packaging loads and
subsequent use in the engine exhaust stream with the related exposure to
various stresses, including engine vibrations, road shock, and temperature
gradients. High-strength substrates are desirable for robust catalytic
converter
systems and particulate filters. The strength of the substrate material may be
controlled by the type of intra- and intercrystalline bonding, the porosity,
pore
size distribution, and flaw population. Additionally, substrates can be
81
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
strengthened by the application of chemical/material coatings on the inside of
outside. The strength of the cellular structure of the substrate may further
determined by its dimensions, cross-sectional symmetry, and its cellular
attributes, such as cell density, channel geometry, and wall thickness.
Substrate strength must exceed the stress to which the material is exposed
during both packaging and operation. If the stress exceeds the strength, the
substrate will crack.
[0328] Structural integrity of a material may be measured by the material's
tensile modulus. Tensile modulus is a material's resistance to rupture.
Specifically, the greater longitudinal stress a material can bear without
tearing
asunder. Tensile modulus is usually expressed with a reference to a unit area
of cross section, the number of pounds per square inch, or kilograms per
square centimeter necessary to produce rupture. Tensile modulus is relevant
in whether the substrate can withstand the force generated by violent, exhaust
gas flow pressure.
[0329] Additionally, a substrate should have a good coatability so that the
washcoat and/or a catalytic coat can be applied to the substrate. Likewise,
the
substrate should have washcoat compatibility, allowing for the catalysts to
mount well onto the substrate so that catalysts are not displaced from their
location during normal wear and tear of the system. Good coatability and
washcoat compatibility also enhances the long-term effectiveness of the
catalytic converter system. Good coatability and washcoat compatibility also
increases the lifetime of the catalyst.
[0330] Another attribute of the substrate of the invention is its structural
integrity. Structural integrity of a material may be measured by the
material's
tensile modulus. Tensile modulus is a material's resistance to rupture.
Specifically, the greater longitudinal stress a material can bear without
tearing
asunder. Tensile modulus is usually expressed with a reference to a unit area
of cross section, the number of pounds per square inch, or kilograms per
square centimeter necessary to produce rupture. Tensile modulus is relevant
in whether the substrate can withstand the force generated by violent, exhaust
gas flow pressure.
[0331] A catalytic substrate according to the present invention preferably has
a higher tensile modulus. For example, in one embodiment, the substrate of
82
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the present invention has an axial strength of about 2.21 MPa. Of course,
higher axial strengths are suitable as well. Other suitable values include 1,
2,
3, 4, 5, 6, 7, 8, 9 and 10 MPa.
[0332] Furthermore, structural integrity of the catalytic substrate of the
invention is such that it can withstand the conditions encountered during its
use in a catalytic converter in commercial vehicles.
[0333] In another embodiment, the substrate of the invention, e.g., nSiRF-C,
preferably has a high structural integrity and a low density.
Reduction of Pollutants
[0334] The substrate plays an important role in enhancing the catalytic
activity
of the catalyst materials coated on it. Additionally substrates are used to
trap
particulate material which is then burnt off as volatile gases.
[0335] Another advantage of the substrate of the present invention is its
increased ability to reduce the amount of pollutants in an exhaust gas. The
present invention has enhanced catalytic and filtering capabilities as
compared
to certain conventional technologies.
[0336] In certain embodiments, the substrate of the present invention is
capable of reducing CO emission from an exhaust gas by at least about 50%.
In one embodiment, the substrate of the present invention is capable of
reducing CO emission from an exhaust gas by at least about 60%, 70%, 80%,
or 90%. In another embodiment, the substrate is capable of reducing CO
emission by at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,
99.5%, 99.9%, or 100%.
[0337] In certain embodiments, the substrate of the present invention is
capable of reducing NOx emission from an exhaust gas by at least about 50%.
In one embodiment, the substrate of the present invention is capable of
reducing NOx emission from an exhaust gas by at least about 60%, 70%, 80%,
or 90%. In another embodiment, the substrate is capable of reducing NOx
emission by at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,
99.5%, 99.9%, or 100%.
[0338] In certain embodiments, the substrate of the present invention is
capable of reducing HC emission from an exhaust gas by at least about 50%.
83
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
In one embodiment, the substrate of the present invention is capable of
reducing HC emission from an exhaust gas by at least about 60%, 70%, 80%,
or 90%. In another embodiment, the substrate is capable of reducing HC
emission by at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,
99.5%, 99.9%, or 100%.
[0339] In other embodiments, the substrate of the present invention is capable
of reducing VOC emission from an exhaust gas by at least 50%. In one
embodiment, the substrate of the present invention is capable of reducing
VOC emission from an exhaust gas by at least about 60%, 70%, 80%, or 90%.
In another embodiment, the substrate is capable of reducing VOC emission by
at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, or
100%.
[0340] In other embodiments, the substrate of the present invention is capable
of reducing PM-10 emission from an exhaust gas by at least 50%. In one
embodiment, the substrate of the present invention is capable of reducing
PM-10 emission from an exhaust gas by at least about 60%, 70%, 80%, or
90%. In another embodiment, the substrate is capable of reducing PM-10
emission by at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,
99.5%, 99.9%, or 100%.
[0341] In other embodiments, the substrate of the present invention is capable
of reducing PM-2.5 emission from an exhaust gas by at least 50%. In one
embodiment, the substrate of the present invention is capable of reducing
PM-2.5 emission from an exhaust gas by at least about 60%, 70%, 80%, or
90%. In another embodiment, the substrate is capable of reducing PM-2.5
emission by at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,
99.5%, 99.9%, or 100%.
Reduced Weiglat
[0342] It is a goal of the vehicle manufacturers to reduce the overall weight
of
the vehicle to improve its fuel economy and engine efficiency. Heavy
substrates add un-necessary weight to the vehicle. Additionally, if substrates
are not efficient enough in reducing pollution, more than one substrates may
84
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
be required to play in line to reach target pollution levels. This greatly
enhances the overall weight of the vehicle.
[0343] Additionally, current catalytic converters require the use of
additional
devices which are often heavy and clunky. Some of these devices, such as
heat shields and particular matting, are used to deal with the temperature of
the
catalytic converter. Others, such as oxygen sensors, are required to meet
certain government regulations.
[0344] In certain embodiments of the present invention, the catalytic
substrate
or filtering substrate has reduced weight in comparison to a conventional
catalytic or filtering substrates. This is due, in part, to the lower density
of the
substrate of the present invention compared to certain conventional
substrates.
Alternatively, the lower weight may be due to the need for a smaller amount
of catalytic or filtering substrate because of the improved filtering and
catalytic function of some embodiments of the present invention compared to
conventional technologies. A lower weight of a catalytic or filtering
substrate
has a number of benefits. For example, a lower weight of a substrate may
translate into improved fuel efficiency for vehicles. Furthermore, a lower
weight would translate into easier to handle and possible safer handheld
engine devices.
[0345] In a preferred embodiment, the exterior surface of the substrate does
not heat up to the same extent as conventional catalytic converter substrates
during use. In some embodiments, the need for a heat shield and/or insulation
is reduced.
Acoustical Attributes
[0346] Acoustic attenuation may be defined as either the diminution of
thickness, thinness, emaciation; diminution of density; diminution of force or
intensity; or weakening of acoustic energy (sound). In one embodiment of the
present invention, the acoustic attenuation is the substrate's ability to
attenuate
or dampen acoustic energy in engine exhaust. A substrate of the present
invention can replace or compliment an engine's muffler assembly, as
disclosed herein, thus decreasing exhaust noise and exhaust system costs. A
higher acoustic attenuation is preferred.
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0347] In another embodiment the porosity, density and size of the substrate
may be varied to 'rune' the acoustical attenuation for desired applications.
[0348] In another embodiment, the acoustical attenuation of the substrate
maybe coupled with standard metal-muffler based techniques to dampen
and/or 'tune' the sound existing the exhaust system.
Type of Flow
Flow-tlarough
[0349] In one aspect, the substrate is structured for a flow-through use. The
flow-through configuration is known in the art. In one embodiment, the
channels (or pores) are essentially aligned parallel to each other across the
entire length of the substrate. Gas flow enters the substrate at one end and
runs down the through the channels through the entire length of the substrate
to exit on the other side.
[0350] Any number of flow-through configurations are useful and suitable for
the catalytic substrate of the present invention. Flow through configurations
that are known in the art can be applied to the catalytic substrate of the
present
invention.
[0351] In one embodiment, the flow through configuration coinprises a
plurality of substantially parallel channels that extend fully through the
length
of the substrate.
[0352] In another embodiment, the walls of the channels are not parallel to
the
lateral or surface of the substrate.
Wall-flow
[0353] Another embodiment of the invention is a catalytic substrate or
filtering substrate of the present invention configured in the wall flow
configuration. It has been surprisingly determined that a catalytic substrate
comprising an nSiRF-C of the present invention can be configured in the wall
flow configuration.
[0354] In another aspect of the invention, the substrate has a wall-flow
configuration. For example, the substrate is used in a wall-flow catalytic
86
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
converter or a wall-flow particulate filter. The wall-flow configuration can
take any one of a number of physical arrangements. A substrate having a wall
flow configuration can have one or more the attributes described herein.
Further, a substrate having a wall flow configuration may further comprise one
or more of the following: a catalyst, a washcoat, an oxygen-storing oxide, and
an emissivity enhancer Additionally, a substrate consisting of a wall flow
configuration may be further modified, enhanced, or altered as described
herein..
[0355] In one embodiment, the channel wall thickness is any value described
below. Preferred channel wall thickness from about 2 mils to about 6 mils. In
other embodiments, the channel wall thickness ranges from about 10 mils to
about 17 mils. Other suitable values include 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12,
13, 14, 15, 16, 17, 18, 19 and 20 mis.
[0356] In other embodiments of the wall-flow substrate, the cell density of
the
substrate is about 400 cpsi (cells per square inch) with a wall thickness of
about 6 mils, or the cell density is about 900 cpsi with a channel wall
thickness
of about 2 mils. Additional embodiments include those in which the cpsi is
about 50, 100, 150, 200, 250, 300, or 350.
[0357] Ceramic wall-flow monoliths, which are derived from the flow-
through cellular supports used for catalytic converters, became the most
common type of diesel filter substrate. They are distinguished, among other
diesel filter designs, by high surface area per unit volume and by high
filtration efficiencies. Monolithic diesel filters consist of many small
parallel
channels, typically of square cross-section, running axially through the part.
Diesel filter monoliths are obtained from the flow-through monoliths by
plugging channels. Adjacent channels are alternatively plugged at each end in
order to force the diesel aerosol through the porous substrate walls which act
as a mechanical filter. To reflect this flow pattern, the substrates are
referred to
as the wall-flow monoliths. Wall-flow monoliths are most commonly available
in cylindrical shapes, although oval cross-section parts are also possible for
space constrained applications.
[0358] Wall-flow filter walls have a distribution of fine pores which have to
be controlled in the manufacturing process. Filtration mechanism on monolith
wall-flow filters is a combination of cake and depth filtration. Depth
filtration
87
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
is the dominant mechanism on a clean filter as the particulates are deposited
in
the inside of pores. As the soot load increases, a particulate layer develops
at
the inlet channel walls and cake filtration becomes the prevailing mechanism.
Certain conventional monolith filters have filtration efficiencies of about
70%
of total particulate matter (TPM). Higher efficiencies can be observed for
solid PM fractions, such as elemental carbon and metal ash.
[0359] According to certain embodiments of the present invention, it is
preferred to have material which is porous so more gases can pass easily
through the pores, interacting with catalysts deposited in the core of the
fibrous composite. Additionally, having porous walls allows in certain
embodiments for higher degree of depth filtration which would also be a
desirable attribute.
[0360] Substrates of the present invention in a wall flow configuration comes
in much more direct contact with the exhaust gas. Material pore
characteristics (size, percent porosity, pore connectivity, open vs closed
pores,
etc.) influence the physical interaction between gas and filter material and
affect such attributes as filtration efficiency and pressure drop.
Furthermore,
substrate durability depends on the material resistance to chemical attack by
exhaust gas components. In particular, materials need to be resistant to
corrosion by metal ash which may be part of diesel particulates. Resistance to
sulfuric acid corrosion is also required, especially if filters are used with
fuels
of higher sulfur content. Additionally, due to the possibility of the release
of
high quantities of heat during filter regeneration, filter materials are
required
to demonstrate excellent thermal attributes in terms of resistance to both
high
temperatures and high temperature gradients. Insufficient temperature
tolerance may result in melting of the material, while insufficient thermal
shock resistance causes cracking. Other potential problems include
microcracking and spallation. In particular embodiments, the filtering
substrate and catalytic substrate of the present invention solves one or more
of
these problems.
[0361] Important considerations in designing the exact geometry of a wall-
flow monolith is includes the following parameters: cell density, repeat
distance (even distribution of pressure drop over the entire wall flow
filter),
88
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
wall thickness, open frontal area, specific filtration area, and mechanical
integrity factor.
[0362] In specific embodiments of the present invention, the wall flow
configuration has half of the channels blocked. In another configuration, the
substrate of the invention has a wall flow configuration wherein the blocking
wall of the channel is located at the beginning or end of a channel. In
another
configuration, the blocking wall is located at the middle of a channel, or
alternatively is located anywhere between the beginning and end of a channel.
[0363] Additionally, any percentage of the channels may be included in a wall
flow configuration, e.g., 10%, 25%, 50%, 75%, 90%, 95%, etc.
Channels and Channel Openings
[0364] In one embodiment, the catalytic or filtering substrate does not
contain
a plurality of channels extending through the length of the substrate. In
certain
embodiments, the catalytic or filtering substrate, given its porosity and
permeability, does not need to have the channels placed in the substrate for
the
substrate to function in its intended uses, e.g., in a catalytic converter.
Any
potential back pressure is relieved by the porosity and permeability alone by
placing the emissions in the path of a catalytic substrate. If a membrane
configuration without channels is used, a preferred use is in a low flow-rate
environment so as to reduce the chance of the substrate failing structurally.
The thin membrane configuration would preferably be used in a "low flow-
rate" environment such as in a fireplace or possibly a power plant. Here the
flow rate is low and in some instances constant (power plant). It is
understood, of course, that such a configuration is suitable for use in other
applications as well, including vehicles and stationary engines.
[0365] In another embodiment, a catalytic or filtering substrate of the
invention, in one embodiment, has a plurality of channels extending
longitudinally through at least a portion of the substrate. The plurality
channels allow a fluid medium, e.g., a gas or a liquid, to flow through the
substrate. The plurality of channels extend from the frontal surface towards
the rear surface. Other channels may extend from the rear surface to the
frontal surface.
89
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0366] The channels can extend through the entire length of the substrate. In
such an embodiment, a channel will have a first channel opening on the frontal
surface of the substrate and a second channel opening on the rear surface.
Alternatively, a channel extends through a portion of the substrate. In
certain
embodiments, the channel extends through about 99%, 97%, 95%, 90%, 85%,
80%, 70%, 60%, or 50% of the length of the substrate.
[0367] The channel holes, or channel openings, of a substrate can be formed
in any number of shapes. For example, the channel openings may be circular,
triangular, square, hexagonal, etc. In preferred embodiments, the channel
openings are triangular, square, or hexagonal..
[0368] In one embodiment, the channel openings are formed such that the
thickness of the substrate material between adjacent channels is substantially
uniform throughout the substrate. Variation in wall thickness may be from
about 1% to about 50% in certain embodiments.
[0369] - In another embodiment, the channels are arranged so that the walls of
adjacent channels are parallel to each other. For example, the triangular,
square, or hexagonal channels may be formed such that the walls of adjacent
channels are parallel to each other.
[0370] The diameter or cross-sectional distance of the channels in the
substrate of the present invention can vary. In certain embodiments, the
channels have a diameter or cross-sectional distance of about 5 cm to about
100 mn. In certain embodiments, a channel has a diameter of about 100
nanometers. Other suitable values include a distance or diameter selected
from about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
and 20
mils.
[0371] A channel may vary in size along its length. For example, the channel
may be about 0.04 inch across at its opening but then gradually decrease in
size approaching either the end wall or point of the channel or the opening at
the end of the channel. In one embodiment, the channel is a square shape
opening at the frontal surface of sides of about 10 mils. The channel extends
through the length of the substrate and has a second opening on the rear
surface. The channel opening of the rear surface has a square shape with sides
of about 4 mils. The channel becomes gradually smaller along its length from
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the frontal surface to the rear surface. Other similar configurations of
course
are contemplated.
[0372] The size of the channel opening may vary as well. For example, in
certain embodiments, the diameter or (cross sectional distance) is from about
1
mil to about 100 mils. Other suitable ranges for the sized of the channel
opening include, but are not necessarily limited to, about 1 to about 500
mils,
from about 1 to about 100 mils, from about 1 to about 10 mils. Other suitable
sizes include a distance or diameter selected from about 1, 2, 3, 4, 5, 6, 7,
8, 9,
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 mils. The substrate of the
invention may also have channels of varying sizes. That is, some channels of
an embodiment of a substrate has a first plurality of channels having a first
diameter or cross-sectional distance and a second plurality of channels having
a second diameter or cross-sectional distance. By way of example, a substrate
of the present invention comprises, in one embodiment, one or more channels
having a cross-sectional distance of about 5 mils and further comprises one or
more channels having a cross-sectional distance of about 7 mils. Other
variations of these embodiments are understood to be within the scope of the
present invention.
[0373] In other embodiments, the channel diameter or cross-sectional distance
can be about 5 cm, 4 cm, 3 cm, 2 cm, or 1 cm. Substrates having channels of
larger diameter or cross-sectional distance are preferred for larger exhaust
systems which may have exhaust pipes of one or more feet in diameter.
[0374] The thickness of the channel wall may vary as well. For example, the
channel wall may be less than 1 mil thick. Other suitable values for the
channel wall thickness include 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 mils.
[0375] The channels can be measured in terms of the number of channels per
square inch. In certain embodiments, a substrate of the present invention has
from about 50 to about 100,000 channels per square inch. Other suitable
values include 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000. Other
embodiments include a catalytic or filtering substrate having 2000 channels
per square inch.
[0376] In one embodiment, the substrate of the present invention comprises
600 cpsi and a wall thickness of 6 mils. The cell density of a sample
substrate
of the present invention is compared with two samples of cordierite. The first
91
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
and second cordierite samples are 100 cpsi with 17 mil wall thickness and 200
cpsi with 12 mil wall thickness, respectively. In comparison, the substrate of
the present invention in this embodiment has 600 cpsi with 6 mil walls.
[0377] In an exemplary embodiment, the substrate is drilled with 0.04 inch
diameter channels spaced every 0.06 inches across the entire filter. These
channels are smaller than conventional cordierite wall flow channels. The
result is vastly increased surface area as compared to cordierite, even
without
taking into consideration the surface area existing in the massive pore space
of
the substrate material. The channels are preferably "blind" channels. Exhaust
emission is forced to pass through the channel walls, rather than flowing in
and out of the channels without reacting with the catalyst.
[0378] A further embodiment is directed to a catalytic or filtering substrate
comprising a plurality of channels having a pyramidal shape. The pyramidal
shapes of the channels are such that they can be applied to any number of
substrate materials, including and in addition to the substrates of the
present
invention, such as nSiRF-C. The pyramidal channels can be configured such
that each channel has two channel openings, e.g., a flow through configuration
having one on the frontal surface of the substrate and one on the rear surface
of the substrate. Alternatively, the pyramidal channels can be configured such
that each channel has only one opening, e.g., a wall flow configuration. In
this
embodiment, the opening of certain channels is situated on the frontal
surface,
whereas the opening of other channels is situated on the rear suiface.
Preferably, the channels are positioned so that adjacent channels have the
opposite configuration with respect to the location of the channel opening.
Furthermore, in certain embodiments of the pyramidal wall flow
configuration, the channel terminates at an undrilled portion of the
substrate.
This undrilled portion of the substrate may be either flat or pointed. If the
undrilled portion is flat, the longitudinal cross-sectional area of the
channel
appears trapezoidal. If the undrilled portion is pointed, the longitudinal
cross
area of the channel appears triangular.
92
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Shapes and Forms
[0379] The catalytic and filtering substrates comprise a number of suitable,
and heretofore, unknown configurations. The substrates are three-dimensional
and generally have a front surface (or area or face) and a rear surface (or
area
or face) connected by the body of the substrate to one or more lateral
surfaces.
The front and rear surfaces can be any number of shapes as described herein.
The front surface refers to the surface through which the fluid enters the
substrate. The rear surface refers to the surface through which the fluid
exits
the substrate. Generally the surface is flat but may, in certain embodiments,
be non-flat.
[0380] In certain embodiments, the substrate has the shape of a cylinder. The
cylinder composed of the substrate is used, for example, to catalyze the
reduction of NO in a exhaust gas.
[0381] Any number of suitable lengths and widths or diameters are suitable
for the substrate of the present invention. Suitable lengths include 1, 2, 3,
4, 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 inches. Of course,
longer lengths may be preferred in diesel applications and for use in
stationary
engines, such as those used in pharmaceutical and chemical plants,
manufacturing plants, power plants, and the like. In another respect, the
shape
of the substrate can be described based on its frontal surface shape. The
substrate of the present invention can be prepared such that the frontal
surface
has one of several physical configurations. The frontal surface shape can be
any number of shapes, including but not limited to circular, triangular,
square,
oval, trapezoidal, rectangular, and the like. Three-dimensionally, the
substrates may be in the form of a cylinder or a substantially flat disc.
Commerically available substrates generally exist as one of these three
designs. Substrates can have squared corners or rounded corners. Rounded
corners are preferable on the frontal surface shape of the substrate. Thus, in
one embodiment, the substrate of the present invention has a square shape
with rounded corners. In another embodiment, the substrate has a rectangular
frontal shape with rounded corners. In another embodiment, the substrate has
a trapezoidal frontal shape with rounded corners.
93
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0382] Exemplary dimensions for a catalytic substrate according to the present
invention include but are not limited to, those having a circular cross-
sectional
shape and having a diameter of about 3.66, about 4.00, about 4.16, about 4.66,
about 5.20, about 5.60, or about 6.00 inches. In other embodiments, the
catalytic substrate has the shape of a oval cylinder with cross-sectional
dimensions (minor and major axis respectively) of about 3.15 by about 4.75
inches, about 3.54 by about 5.16 inches, or about 4.00 by about 6.00 inches.
[0383] In another embodiment, the catalytic substrate has a shape and size
that
is suitable for use in a head cat. Generally, a head cat will be smaller in
size
than conventional catalytic converters found on exhaust systems of engines.
The determination of a suitable size and shape of the head cat is within the
ability of one of ordinary skill in the art. The size and shape of the head
cat is
configured based on the particular head and engine with which the head cat
will be used. For example, a conventional cordierite round substrate that is
approximately 4 lh inches in diameter has a front surface area of about 28.27
square inches. On a Ford 4.6 V-8, for example, there are two pre-cats having
a substrate of approximately this dimension. These two conventional pre-cats
can be replaced by eight head-cats comprising a nSiRF-C substrate comprising
a diameter of about 1.13 inches.
[0384] Alternatively, the cylinder is used to catalyze the oxidation of carbon
monoxide and unburned hydrocarbons in an exhaust gas. The length of the
cylinder may be greater than, equal to, or less than the diameter of the
cylinder.
[0385] Different shapes and configurations of the filtering substrate and
catalytic substrate can be used based on the particular application, e.g.,
stationary engine, on-road vehicle, off-road vehicle, etc.
[0386] In another embodiment, the catalytic substrate is shaped to replace the
commercially used substrate of a commercially available catalytic converter.
In this embodiment, the substrate of the invention will have a shape and
dimensions that are substantially identical to substrates of available
cataltyic
converters that use a different substrate. For example, many catalytic
converters currently used contain a substrate that is made from cordierite.
The
shape and size of the cordierite of catalytic converters is known or can be
determined by analysis. The substrate of the present invention is then
94
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
prepared, either by machining or molding as described below, such that the
shape and size of the substrate of the present invention is substantially
identical to that of the known cordierite substrate.
Membrane Configuration
[0387] Alternatively, the substrate has a membrane configuration. In such a
configuration, the length of the substrate is substantially less than the
width or
diameter of the substrate. A longer travel length for exhaust through a
substrate corresponds to a build up of backpressure in certain conventional
catalytic converters and particulate filters. In the thinner substrate of
certain
embodiments of the present invention, backpressure will be minimized, and
the exhaust gas will move through the filter system with less effort and
increased filtering capabilities. This reduction in backpressure results in
the
engine running more efficiently meaning better gas mileage and more power.
[0388] In one embodiment of the present invention, the substrate is two inches
in diameter and 1/16th inches thick and has 400 times the surface area of a
conventional cordierite filter that has a four inch diameter and is six inches
long. Since the substrate itself has been reduced in size, a canister can also
be
reduced in size, resulting in just a small bulge in the exhaust line.
Alternatively, the substrate can be housed in the exhaust manifold.
[0389] In another embodiment, the substrate is in the form of a membrane. In
this instance, the membrane comprising the substrate material as described
herein having any number of shapes as described above, and wherein the
length of the substrate is substantially less than the width or diameter. The
dimension can be described as a ratio of, e.g., width to length, or diameter
to
length. Suitable diameter to width ratios include, but are not limited to,
about
20:1, 19:1, 18:1, 17:1, 16:1, 15:1, 14:1, 13:1, 12:1, 11:1, 10:1, 9:1, 8:1,
7:1,
6:1, and 5:1.
[0390] Furthermore, a substrate having a membrane configuration can be
stacked together with one or more separate substrate embodiments. With a
membrane configuration, a number of catalytic or filtering substrates having a
membrane configuration can be stacked together. For example, a plurality,
e.g., 5, of catalytic or filtering substrates having a cylinder (or disc)
shape with
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
a diameter of about 1 inch and a length of about 0.2 inch can be stacked
together to form a substrate pile having a certain length, e.g., about 1 inch.
[0391] In the case of a membrane configuration, in one embodiment, the
catalytic substrate does not contain a plurality of channels running through
the
substrate. Because of the shorter distance through which the gas must travel
and because, in part, of the high porosity of and low drop pressure caused by
the present invention, it is possible to form a substrate pile comprising a
plurality of catalytic substrates having a membrane configuration.
[0392] Furthermore a stacked membrane configuration also includes stacked
membrane configurations in which the individual substrates are not
perpendicular to the floor of the catalytic converter or particulate filter.
In this
embodiment, the substrate may be machined or molded so that the angle
between the side(s) (lateral surface) of the substrate and the face (front or
rear
surface) is about 90 or is less than or greater than 90 , e.g., 80 , 70 ,
etc.
Pre-Sintering Addition of Catalyst
[0393] In another embodiment, the catalytic substrate as described herein
further comprises a catalyst, wherein the catalyst is added to the substrate
material prior to the sintering process. In this case, the catalyst is
generally
added to the slurry before the green billet is produced. In other embodiments,
the catalyst is added to the fibers in the mixer. Alternatively, the catalyst,
if in
the form of a liquid, is added to the slurry in certain embodiments. The
substrate may be formed from a slurry that comprises one or more catalysts.
In one embodiment, the catalyst, upon sintering, adheres to the fibers of the
substrate. In another embodiment, the catalyst is located within the pores of
channel walls as opposed to be adhered mainly to the surface of the channel
walls.
Zonation of Substrate
[0394] In another embodiment, the catalytic substrate as described herein is
prepared such that different zones in the substrate have different attributes.
In
other words, one or more physical characteristics or attributes of the
catalytic
substrate are not uniform, or the same, throughout the entirety of the
substrate.
96
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
For example, in certain embodiments, different zones or regions of the
substrate have different densities, different catalysts, different catalyst
mixtures, different channel configurations, different porosities, different
permeabilites, and/or different thermal attributes. By way of example, in one
embodiment, a catalytic substrate of the present invention comprises a nSiRF-
C composite and a first and second catalyst, wherein said first catalyst is
applied to a first zone of said substrate and said second catalyst is applied
to a
second zone of said substrate. In a further embodiment, the substrate has a
different degrees of structural integrity through the body of the substrate.
For
example, as described herein, a densification coating may be added to the
surface of the substrate to increase hardness of its surface which would
lessen
possible damage.
Washcoat
[0395] Another aspect of the present invention is directed to a catalytic or
filtering substrate as described herein further comprising a washcoat. In
other
embodiments, the catalytic substrate further comprises a catalytic washcoat,
e.g., the washcoat comprises a catalyst in addition to a washcoat material.
Alternatively, in another embodiment, the washcoat material has catalytic
activity.
[0396] Suitable washcoats include silica, titania, unimpregnated zirconia,
zirconia impregnated with a rare earth metal oxide, ceria, co-formed rare
earth
metal oxide-zirconia, and combinations thereof. Other suitable washcoats are
disclosed in, e.g., U.S. Patent Nos. 6,682,706; 6,667,012; 4,529,718;
4,722,920; 5,795,456; and 5,856;263, all of which are herein incorporated by
reference in their entirety.
[0397] Generally, a washcoat can be applied in certain embodiments, from an
aqueous slurry. The alumina powder and/or other washcoat oxides are milled
to the required particle size. The particle size distribution of the washcoat
powder affects the mechanical strength of the finished washcoat and its
adhesion to the substrate, as well as the rheological attributes of the slurry
during the washcoating process. Alumina, a very hard material, is, in certain
embodiments, milled using air-jet or ball mills.
97
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0398] In the next step, the materials are dispersed in acidified water in a
tank
with a high-shear mixer. The solid content in the slurry is typically 30-50%.
After prolonged mixing, the alumina suspension becomes a stable colloidal
system.
[0399] The amount of washcoat deposited on the substrates depends on, and
can be controlled by, the rheological attributes (viscosity) of the slurry.
The
aluminum oxide slurry, in certain instances, is a nonnewtonian fluid which
changes its viscosity with time and with the amount of mechanical energy
supplied to the system (shear rate). At any steady sheer rate, the viscosity
of
the slurry is a function of its pH. In certain embodiments, the viscosity can
be
controlled by pH adjustment. Precise viscosity control, however, is probably
the biggqst challenge in the washcoating process due to the nonnewtonian
character of alumina systems.
[0400] The washcoat slurry can be applied to the substrates using any known
methods and procedures, including dipping or pouring over the parts, and/or in
a specialized coating machine. Excess slurry is cleared from channels with
compressed air. The substrates can then be dried and calcined to bond the
washcoat to the monolith walls.
[0401] In certain embodiments, the washcoat can be applied in one, two, or
more layers. Each layer can be dried and calcined before the processing of
next layer. There are several reasons for the application of multi-layer
washcoats: (1) the catalyst design may require a different chemical
formulation for each layer, and (2) coating/process equipment constraints,
e.g.,
an inability to handle very viscous slurries which are needed to apply a thick
washcoat in one-pass operation.
[0402] Typical thickness of the washcoat layer is 20-40 m but values outside
of the range can also be used in the present invention. These numbers
correspond, for example, to a washcoat loading of about 100 g/L on a 200 cpsi
substrate, up to about 200 g/L on a 400 cpsi substrate. The specific surface
area of catalyst washcoat materials is in certain embodiments between 100 and
200 m2/g. Of course, other values are useful in the present invention.
[0403] Noble metals and other catalysts in a complex catalyst system may
react with each other, with washcoat components, or with the support material
and produce undesired, catalytically inactive compounds. If such reactions
98
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
occur in a given catalytic system, they are difficult to prevent in the
conventional washcoat technology. Since the catalytic metals are impregnated
onto the finished washcoat layer, the contact between reacting components
cannot be avoided.
[0404] Segregated washcoat technologies have been developed to physically
separate noble metals by fixing them on a particular base metal oxide of the
washcoat before the washcoat is applied to the substrate. Through the use of
washcoat layers with different oxides and/or noble metals, the components of
a catalytic system can be separated. Additional benefit of this technology
include a control of the noble metal/base metal ratio and an improved noble
metal dispersion. Such technology can be applied to the present invention.
Thus, in a preferred embodiment, the present invention is directed to a
catalytic substrate comprising a nSiRF-C, at least two catalytic metals, and a
washcoat, wherein said two catalytic metals are physically separated.
[0405] Segregated Washcoat Schematic: Segregated washcoats were first
applied for automotive 3-way catalysts. An example of such a catalyst is a tri-
metal system which includes platinum, palladium and rhodium. The first layer
of the catalyst is composed of Pd/Al203. The second (surface) layer is
composed of Rh/Pt/Ce-Zr. That design prevents the formation of palladium-
rhodium alloys which otherwise could cause catalyst deactivation.
[0406] Aluminum oxide or alumina is the basic material for emission control
catalyst washcoat. The high surface area gamma crystalline structure
(-y-A1203) is used for catalyst applications. It is characterized by high
purity.
Presence of certain elements in the A1203 can influence its thermal stability,
both negative and positive. Small amounts of Na20 present in A1203 act as a
flux, enhancing the sintering of alumina. In contrast, several metal oxides,
including La203, Si02, BaO, and CeO2 have a stabilizing effect on alumina
surface area and reduce its sintering rate. Stabilized aluminas are
commercially available.
[0407] In other embodiments, cerium dioxide, or ceria, is a component of the
catalyst washcoat, added, for example, in quantities of up to 25%. In other
embodiments, ceria is add in quantities of about 5%, 10%, 15%, 20%, and
25%. Ceria is an important promoter in the automotive emission control
catalyst. One function of ceria in the three-way catalyst is oxygen storage,
99
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
which is possible through a cycling between Ce4+ and Ce3+. Other effects
attributed to ceria include stabilization of alumina, promotion of the steam
reforming reaction, promotion of noble metal dispersion, and promotion of
noble metal reduction.
[0408] Certain diesel oxidation catalyst formulations include high loadings of
ceria. The function of ceria is catalytic oxidation/cracking of the soluble
organic fractions of diesel particulates.
[0409] High surface area cerium oxide can be produced, for example, by
calcination of cerium compounds. The BET surface area of ceria can be as
high as 270 m2/g. In other embodiments, for example in a three-way catalyst,
ceria of about 150 m2/g surface area is used. High temperature stabilized
varieties, which are capable of withstanding 900-1000 C, have surface areas
of about 6-60 m2/g and are suitable for use in the present invention.
[0410] A catalytic substrate or filtering substrate of the invention in other
embodiments further comprises zirconium oxide. In certain embodiments, the
zirconium oxide increases the thermal stability of the substrate.
[0411] Titanium dioxide is used with some diesel catalysts as an inert, non-
sulfating carrier. Two important crystal structures of titanium dioxide
include
anatase and rutile. The anatase form is important for catalyst applications.
It
has the highest surface area of 50-120 m2/g and is thermally stable up to
500 C. The rutile structure has a low surface area of below 10 m2/g. A
conversion of anatase into rutile, which takes place at about 550 C, leads to
catalyst deactivation. In another embodiment of the present invention, the
catalytic substrate comprises a nSiRF-C, preferably an AETB or OCTB, a
catalyst, and titanium oxide.
[0412] Zirconium oxide can be used as a thermal stabilizer and promoter of
ceria in the automotive three-way catalyst and also as a non-sulfating
component of diesel oxidation catalyst washcoats. Zirconium oxide has a
BET surface area of 100-150 m2/g. It rapidly looses its surface area at
500-700 C. Better thermal stability can be achieved by the use of a wide
range of dopants including La, Si, Ce, and Y.
[0413] Zeolites are synthetic or naturally occurring alumina-silicate
compounds with well defined crystalline structures and pore sizes. The
dimensions of zeolite pores are typically between 3 and 8 A, which falls into
100
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the range of molecular sizes. Any molecule of a larger cross-sectional area is
prevented from entering the channel of the zeolite cage. For this reason,
zeolites are often referred to as molecular sieves. Zeolites are characterized
by
high specific surface areas. For example, the ZSM-5 zeolite has surface area
of about 400 m2/g. Zeolite mordenite has a surface area of about 400-500
m2/g. Most zeolites are thermally stable up to 500 C.
[0414] Zeolites for some catalytic applications are ion exchanged with metal
cations. The acid form of zeolite (HZ) is first treated with an aqueous
solution
containing NH4+ (NH4.NO3) to form the ammonium exchanged zeolite
(NW+Z-). This is then treated with a salt solution containing a catalytic
cation
forming the metal exchanged zeolite (MZ).
[0415] Zeolites, due to their repeatable and well defined pore structure, are
excellent adsorption materials. They have been used as adsorbents in
numerous applications including drying, purification and separation. Synthetic
zeolites are also used as catalysts in petrochemical processing.
[0416] In recent years, zeolites have been increasingly used for diesel
emission control, both as catalysts (SCR, lean NOX catalyst) and adsorbers
(hydrocarbon traps in diesel oxidation catalysts).
[0417] It is understood that further embodiments of the invention include any
of the specific substrate embodiments described herein, further comprising any
of the specific washcoat embodiments.
Oxygen-Storing Oxide
[0418] In another embodiment, the catalytic substrate or filtering substrate
of
the present invention further comprises an oxygen-storing oxide. The oxygen-
storing oxide, for example CeO2, has an oxygen storing capacity (hereafter
abbreviated as "OSC"), that is, the capacity to occlude gaseous oxygen and to
release the occluded oxygen. More specifically, CeO2 is added for adjusting
the oxygen concentration of gaseous atmosphere, so that excess oxygen in the
gaseous atmosphere is occluded into the crystalline structure of CeO2 in an
oxygen-rich state (i.e., fuel-lean state which may be simply referred to as
"lean
state") for assisting the catalytic converter in reducing NOX to N2 while
releasing the occluded oxygen into the gaseous atmosphere in a CO- and/or
101
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
HC-rich state (i.e., fuel-rich state which may be simply referred to as "rich
state") for assisting the catalytic converter in oxidizing CO and HC to CO2
and
H2O. Thus, the catalytic activity of the catalytic substrate is enhanced by
the
addition of CeO2. Other oxygen-storing oxides include Pr6O11 and the like, as
disclosed in U.S. Patent No. 6,576,200. Further embodiments include any
specific substrate embodiment described herein, further comprising an
oxygen-storing oxide, e.g., CeO2.
SOx oxidation
[0419] In the presence of certain metal catalysts, especially platinum, sulfur
present in the fuel, for example in diesel fuel, is converted to SOx which can
then create environmentally harmful sulfuric compounds, such as sulfuric acid
fumes, in the exhaust. Most sulfates are typically formed over platinum
catalysts at relatively high exhaust temperatures of about 350-450 C. While
there is a dire need to remove sulfur from the gasoline and diesel fuel
formulations, in the interim, catalyst formulations have tried to reduce that
problem to their best possible extent.
[0420] An exemplary platinum catalyst developed by Engelhard is composed
of 5-150 g/ft3 Pt/Rh at 5:1 ratio and 30-1500 g/ft3 of MgO (U.S. Patent No.
5,100,632 (Engelhard Corporation)). The catalyst can be impregnated onto
substrates from water based solutions. A filter coated with the catalyst
preferably is used for exhaust temperatures of 375-400 C to regenerate. The
function of rhodium in the above formulation is to suppress the catalytic
oxidation of SO2 and, thus, the sulfate mask in the catalyst.
[0421] A catalytic substrate of the present invention may, in certain
embodiments, provide solutions to these problems by, for example, having an
improved thermal profile and thereby reducing thermal breakdown of the
catalyst.
[0422] Catalyst poisoning is a significant source of catalyst deactivation. It
can occur when substances which are present in exhaust gases chemically
deactivate the catalytic sites or cause fouling of the catalytic surface.
Poisons
in exhaust gases from internal combustion engines may be derived from lube
oil components or from the fuels.
102
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0423] Interactions between different catalyst species or between catalyst
species and carrier components are another temperature-induced mode of
catalyst deactivation. An example is the reaction between rhodium and CeO2
in an automotive three-way catalyst. This type of problem can be reduced by
using alternative carriers and special washcoat technologies which physically
separate the reacting components and are known in the art.
[0424] A further advantage of the present invention is that a nSiRF-C can be
pumped with different zones to separate physically incompatible components,
or alternatively can be utilized as a stacked membrane configuration with
incompatible components in separate membrane substrates.
[0425] Catalyst deactivation may also occur due to a physical washcoat loss
through erosion and attrition. That mechanism may also be important for
emission control catalyst because of the high gas velocities, temperature
changes, and differences in thermal expansion between the washcoat and
substrate materials.
Catalyst Cover
[0426] In certain applications, adsorber catalysts are used to convert NO,t
into
salts which can then be manually removed in a regenerative process.
However, the presence of sulfur in the fuel can lead to the formation of
insoluble SO4 salts, such as barium sulfate, which can form a protective
coating on top of the catalysts and reduce their efficiency. An advantage of
certain embodiments of the present invention is that the catalytic substrate
is
less susceptible to reduced efficiency due to the coating from sulfate salts.
[0427] In another embodiment, the catalytic substrate or filtering substrate
of
the present invention further comprises a protective coating suitable for
ceramics. For example, such a suitable protective coating is disclosed in U.S.
Patent No. 5,296,288, which is incorporated herein by reference in its
entirety.
This coating is also known as Protective Coating for Ceramic Materials
(PCC). Another suitable, and related coating, is available as EmisshieldTM
coating (Wessex Incorporated, Blacksburg, VA). The emissivity agents in
EmisshieldTM enhance the emissivity of materials, especially at high
temperatures. Additionally, a protective coating may lessen damage from
103
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
external impact and wear forces. Suitable coatings are disclosed in U.S. Pat.
Nos. 5,702,761 and 5,928,775, issued to DiChiara, Jr. et al. and U.S. Pat. No.
5,079,082, issued to Leiser, et al., the disclosures of which are incorporated
herein by reference. Said coating can be used with one or more of the specific
filtering and catalytic substrates described herein.
[0428] In certain embodiments, the catalytic substrate or filtering substrate
is
resistant to damage from thermal shock and thermal cycling. However,
certain substrates are relatively soft and can be damaged by external impact
and wear forces. To lessen such damage, in a preferred embodiment, the
catalytic or filtering substrate of the present invention further comprises
one or
more protective coatings to the surface, preferably the exterior surface, of
the
substrate. Examples of suitable protective coatings are disclosed in U.S. Pat.
Nos. 5,702,761 and 5,928,775, and 5,079,082, the disclosures of which are
incorporated herein by reference. Thus, in a preferred embodiment, the
,invention provides a substrate having, among other attributes, a higher
porosity, a higher permeability, and a sufficient hardness compared to
conventional substrates. Said coating can be used with one or more of the
specific filtering and catalytic substrates described herein.
Pressure Drop
[0429] The present invention also provides a substrate that provides for an
improved pressure drop for catalytic converters and particulate filters. Thus,
in certain embodiments, a substrate of the present invention permits one to
provide a means for removing and/or filtering an exhaust gas without a
substantial buildup of back pressure, or alternatively with a lower buildup of
back pressure compared to conventional catalytic and particulate filters.
[0430] The flow of exhaust gas through a conventional catalytic converter
creates a substantial amount of backpressure. The backpressure buildup in a
catalytic converter is an important attribute to catalytic converter success.
If
the catalytic converter is partially or wholly clogged, it will create a
restriction
in the exhaust system. The subsequent buildup of backpressure will cause a
drastic drop in engine performance (e.g., horsepower and torque) and fuel
economy, and may even cause the engine to stall after it starts if the
blockage
104
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
is severe. Conventional attempts to reduce pollutant emissions are very
expensive, due to both the cost of materials and retrofitting or manufacturing
an original engine with the appropriate filter.
[0431] A substrate of the present invention has, in certain embodiments, the
attribute of producing a lower or smaller pressure drop than conventional
substrates used in catalytic converters or particulate filters. The present
invention in some embodiments provides a lower buildup of soot in the
particulate filter and in some instances allows less frequent need for
replacement of the filter compared to conventional particulate filters.
Specific Embodiments
[0432] The present invention is also directed to specific embodiments of the
catalytic and filtering substrates described above. Specific embodiments
include a substrate comprising, or alternatively consisting of or consisting
essentially of, a nSiRF-C and a catalyst. An additional embodiment is a
filtering substrate comprising a nSiRF-C and a plurality of channels.
[0433] For example, certain embodiments of the substrate have a plurality of
the attributes described above. In other embodiments, the substrate of the
invention has 2, 3, 4, 5, 6, 7, 8, 9, or 10 of the attributes described above.
The
specific embodiments can comprise any combination of attributes. The
catalytic substrate is further illustrated by the following nonlimiting
specific
embodiments.
[0434] In one embodiment, the substrate of the invention comprises a
nSiRF-C composite having a porosity of about 96% to about 99%; a density of
about 10 to about 14 lb/ft3; a plurality of channels having a wall-flow
configuration; and optionally a catalyst.
[0435] In one embodiment, the substrate of the invention comprises a
nSiRF-C composite comprising aluminaboriasilica fibers, silica fibers, and
alumina fibers having a porosity of about 96% to about 99%; a density of
about 10 to about 16 lb/ft3, preferably about 10, 11, 12, 13, 14, 15, or
161b/ft3;
a plurality of channels having a wall-flow configuration; and optionally a
catalyst. In other embodiments, the substrate further comprises a washcoat,
preferably of aluminaoxide or a derivated thereof.
105
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0436] In another embodiment, the substrate of the invention comprises a
substrate having one or more of the following attributes: tensile strength of
from about 100 to about 150, preferably about 130 to about 140, more
preferably about 133 psi; thermal conductivity of about 0.5 to about 0.9,
preferably about 0.7 to about 0.8, more preferably about 0.770 BTU-ft* /hr ft2
F; a thermal coefficient of expansion of about 1 to about 5 x 10"6, from about
1 to about 3 x 10-6, more preferably about 1.95 x 10-6 (tested from 77 F -
1000 F); an average density of from about 15.5 to about 17, preferably about
16 to about 16.8, more preferably about 16.30 /lb/ft3; and optionally a
catalyst.
[0437] In another embodiment, the substrate of the invention comprises a
substrate having one or more of the following attributes: tensile strength of
about 50 to about 70, preferably about 60 to about 65, more preferably about
63 psi; thermal conductivity of about 0.5 to about 0.9, preferably about 0.7
to
about 0.8, more preferably about 0.770 BTU-ft* /hr ft2 F; a thermal
coefficient of expansion of about 1 to about 5 x 10-6, from about 1 to about 3
x
10-6, more preferably about 1.77 x 10-6 (tested from 77 F - 1000 F); an
average density of from about 7 to about 9, preferably about 8.2 to about 8.6,
more preferably about 8.40 /lb/ft3; and optionally a substrate.
[0438] In another embodiment, the substrate of the invention comprises a
substrate having one or more of the following attributes: tensile strength~ of
about 60 to about 80, preferably about 70 to about 79, more preferably about
74 psi; thermal conductivity of about 0.5 to about 0.9, preferably about 0.7
to
about 0.8, more preferably about 0.765 BTU-ft* /hr ft2 F; a thermal
coefficient of expansion of about 1 to about 5 x 10-6, from about 1 to about 3
x
10-6, more preferably about 1.84 x 10-6 (tested from 77 F - 1000 F); an
average density of from about 9 to about 11, preferably about 9.5 to about
10.5, more preferably about 10 lb/ft3; and optionally a catalyst.
[0439] Another suitable catalytic substrate of the present invention is a
nSiRF-C as described herein; and a catalyst comprising: a carrier pre-doped
with copper oxide (CuO); at least one precious metal as a main catalyst
selected from the group consisting of platinum (Pt), palladium (Pd), rhodium
(Rh) and rhenium (Re), wherein the at least one precious metal is doped on the
surface of the pre-doped carrier; and at least one metal oxide as a co-
catalyst
selected from the group consisting of antimony trioxide (Sb203), bismuth
106
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
trioxide (BiZO3), tin dioxide (Sn02), and mixtures thereof, wherein the at
least
one metal oxide is doped on the surface of the pre-doped carrier. Such a
catalyst is described in U.S. Patent No. 6,685,899, which is incorporated by
reference in its entirety.
[0440] In one embodiment, the substrate is suitable for being used in a
catalytic converter that is placed inside the engine head before the exhaust
manifold in relation to the flow of exhaust gas.
[0441] Additional embodiments of the catalytic substrate include a catalytic
substrate comprising an nSiRF-C composite having the approximate attributes
shown in the following table.
Embodiment 1 Embodiment 2 Embodiment 3
Thermal
Conductivity 4-100 x10"2 W /m-K 5-7 x10-2 W/m-K 6.04 F-02 W/m-K
Specific Heat 10-150 J/mol K 600-700 x10 J/kg-K 640 x10" J/kg-K
ensity .05-5 gm/cc 0.1-0.3 gm/cc 0.2465 gm/ec
Emissivity .68-.97 0.7-0.92 0.88
xial Strength 1.5 to 3.5 MPa 2-3 MPa 2.21 MPa
4oise Attenuation 40-100 db 70-80 db 74 db
at 3500 rpm
orosity 80-99% 97-98% 97.26%
ermeability At least 600 900 - oo cd 1093 - oo cd
Regeneration Time 0.5 to 1.5 sec 0.6-0.9 0.75 sec
Surface Area 70,000-95,000 in 2 88,622 in
elting Point 1700-5000 3000-4000 C 3,000 C
Thermal Expansion 0.001x10"6 to 9x10"6 0.1x10"7
to 0.4 x 10"7 0.25 x 10"7 1/C
(CTE)
[0442] Another specific embodiment is directed to a catalytic substrate
comprising an nSiRF-C as described in Table 1; and a catalyst selected from
the group consisting of palladium, platinum, rhodium, derivatives thereof, and
combinations thereof.
[0443] A preferred substrate comprising high-grade non-woven refractory
fibers is 90% to 98% porous and has an emissivity value between 0.8 and 1Ø
[0444] In one embodiment, the filtering substrate of the present invention
comprises or consists essentially of a nSiRF-C and further includes a frontal
inlet end and an outlet end, a matrix of thin, porous, intersecting vertically
107
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
extending walls and horizontally extending walls, which define a plurality of
channels extending in a substantially longitudinal and mutually parallel
fashion between the frontal inlet end and the outlet end; the frontal inlet
end
includes a first section of cells plugged along a portion of their lengths in
a
non-checkered pattern and a second section of cells plugged in checkered
pattern, the first section of non-checkered plugged cells being smaller.than
the
second section of checkered plugged cells. Such a configuration is further
described in U.S. Patent No. 6,673,414, which is herein incorporated by
reference in its entirety. Up to three-fourth of the cells of the first
section may
be unplugged. Alternatively, up to one-half of the cells of the first section
may
be unplugged. Alternatively, up to one-fourth of the cells of the first
section
may be unplugged.
[0445] It is further understood that the invention is directed to embodiments
consisting of or consisting essentially of the limitations of the various
embodimetns. Thus, for example, having described one embodiment as a
catalytic substrate comprising a nSiRF-C and a catalyst, it is understood that
the invention further encompasses a catalytic substrate consisting of or
consisting essentially of a nSiRF-C and a catalyst.
Methods of Catalyzing a Reaction and Filtering
[0446] Another aspect of the invention is directed to a method of catalyzing a
reaction comprising providing a catalytic substrate of the present invention;
and directing a flow of a fluid over and/or through the catalytic substrate at
a
temperature sufficient to catalyze said reaction. Preferably, the reaction
converts pollutants to non-pollutants. For example, the catalytic substrate in
one embodiment converts carbon monoxide to carbon dioxide.
[0447] The method of catalyzing is performed using a substrate comprising
alumina enhanced thermal barrier as described herein. A number of substrates
[0448] In a preferred embodiment, the substrate contains a suitable catalysis.
[0449] In one embodiment, the present invention is directed to a method of
filtering an exhaust gas comprising providing a filtering or catalytic
substrate
of the present invention as described above, and directing a flow of a fluid,
108
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
e.g., a gas or liquid, through the substrate, wherein said gas contains
particulate matter.
[0450] In another embodiment, the method further comprises burning off of
the filtered particulate matter. The burning off of the filtered particulate
matter converts the accumulated particulate matter mainly into nonpollutant
[0451] This aspect of the present invention is of particular use with diesel
engines. In another aspect, the invention is directed to a method of filtering
wherein the filtering utilizes a diesel particulate filter.
[0452] Diesel engines (where compression alone ignites the fuel) have
recently come under worldwide scrutiny for their exhaust emissions, which
contain a large number of harmful particulates in addition to toxic gases.
Manufacturers' response has been to apply known catalytic converter
technology to diesel engines. Unfortunately, regulations regarding emission
standards have exceeded the physical and economic limitations of
conventional catalytic converters. Diesel emissions differ from gasoline
emissions in that a greater amount of particulate matter is generated. For
this
reason, existing technology for exhaust emission capture, combustion, and
oxidation will not comply sufficiently with the most stringent emission
standards.
[0453] A majority of buses are manufactured with or are retrofitted with 85%
efficient diesel particulate traps ["DPTs"]. DPTs have a high cost, are highly
complex, lower fuel economy, and have low durability. Further regulations
require 100 percent compliance by 2010 and DPTs alone cannot satisfy these
regualtory requirements. The high temperature of an engine or exhaust gas
permits the particulate matter to combust with a shorter residence time.
Moving the filter closer to the combustion chamber of the engine or adding an
auxiliary heat source can provide increased heat. Therefore, what is needed is
a filter that (1) can be placed in extremely high temperatures, i.e., above
500
degrees Celsius, such as near the combustion chamber; (2) is more resistant to
vibration degradation; and (3) still maintains or improves particulate matter
burning effect. The ability to achieve particulate matter burning even without
a catalyst would also provide significant savings on catalyst and coating
costs.
[0454] Once a filter captures particulate matter (e.g., soot), the particulate
matter needs to be completely combusted by raising its temperature
109
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
sufficiently in the presence of oxygen. Combustion of the particulate matter
can be accomplished by utilizing the existing temperature of the exiting
exhaust and/or providing an auxiliary source of heat. The time it takes to bum
the particulate matter at this temperature is referred to as the required
"residence time," "regeneration time," or "bumoff' period. A shorter
residence time of particulates in the substrate pores translates into a
reduced
occurrence of pore-clogging build up, which buildup can cause increased gas
flow backpressure requiring excessive energy to operate efficiently. Lower
residence time is, therefore, preferred.
[0455] One conventional DPT is exemplified in U.S. Patent No. 5,611,832
(Isuzu Ceramics Research Institute Co., Ltd.), which discloses a DPT for
collecting particulates from exhaust gas discharged from a diesel engine. The
DPT filter is constituted of a woven inorganic fiber covered with a silicon
carbide ceramic, and metallic wire nets disposed there between.
[0456] Additional uses of a filtering substrate or catalytic substrate
includes
ability to clean or filter from a fluid flow such pollutants and impurities
as:
dust/soot, smoke, pollen, fluids, bacteria/viruses, odor, oil, volatile
organic
compounds, liquids, methane, ethylene, and a wide variety of other chemicals,
including those chemicals listed as the EPA's 188 "toxic air pollutants."
[0457] A method of catalyzing a reaction and/or filtering a fluid may be
useful
in any number of industries or applications, in particular one or more of the
following: Aerospace Industry; Asbestos; Asphalt Roofing and Processing;
Auto and Light Duty Truck (surface coating); Benzene Waste Operations;
Boat Manufacturing; Brick and Structural applications; Clay Products
Manufacturing; Cellulose Products Manufacturing; Caroxymethylcellulose
Production; Cellulose Ethers Production; Cellulose Food Casing
Manufacturing; Cellophane Production; Chromium Electroplating; Coke
Oven: Pushing, Quenching,& Battery Stacks; Coke Ovens; Combustion
Turbines; Degreasing Organic Cleaners; Dry Cleaning; Engine Test
Cells/Stands; Fabric Printing, Coating& Dyeing; Ferroalloys Production;
Flexible Polyurethane Foam; Fabrication Operation; Flexible Polyurethane
Foam Production; Friction Products Manufacturing; Gasoline Distribution
(Stage 1); General Provisions; Generic MACT; Hazardous Waste Combustion;
Hazardous Organic NESHAP; Hydrochloric Acid Production; Industrial,
110
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Commercial and Institutional Boilers; Industrial Cooling Towers Process
Heaters; Integrated Iron & Steel; Iron Foundries (surface coating); Leather
Finishing Ops.; Lime Manufacturing; Magnetic Tape; Manufacturing
Nutritional Yeast; Marine Vessel Loading Operations; Mercury Cell Chlor-
Alkali Plants; Metal Coil (surface coating); Metal Can (surface coating);
Metal
Furniture (Surface Coating); Mineral Wool Products; Misc. Coating
Manufacturing; Misc. Metal Parts and Products; Municipal Solid Waste
Landfills; Natural Gas Transmission and Storage; Off-Site Waste Recovery
Operations; Oil & Natural Gas Production; Organic Liquids Distribution (non-
gasoline); Paper & Other Web (Surface Coating); Pesticide Active Ingredient
Production; Petroleum Refineries; Pharmaceuticals Production; Phosphoric
Acid/ Phosphate Fertilizer; Plastic Parts (Surface Coating); Polymers and
Resins; Polyether Polyols Products; Polybutadiene Rubber; Polysulfide
Rubber; Phenolic Resins; Polyethylene Terephthalate; Polyvinyl Chloride and
Copolymers Production; Portland Cement Manufacturing; Primary Aluminum
Production; Primary Lead Smelting; Primary Copper; Primary Magnesium
Refining; Printing/Publishing; Publicly Owned Treatment Works (POTW);
Pulp & Paper (non-combust) MACT I; Pulp & Paper (non-chem) MACT III;
Pulp and Paper (combustion sources) MACT II; Pulp & Paper Mills;
Reciprocating Int. Combust. Engine; Refractory Products Manufacturing;
Reinforced Plastic Composites Production; Secondary Aluminium; Secondary
Lead Smelters; Semiconductor Manufacturing; Shipbuilding & Ship Repair;
Site Remediation; Solvent Extraction for Vegetable Oil Production; Steel
Pickling-HCL Process; Taconite Iron Ore Processing;
Tetrahydrobenzaldehyde Manufacturing; Tire Manufacturing; Wet Formed
Fiberglass; Mat Production; Wood Building Products; Wood Furniture; and
Wool Fiberglass Manufacturing. Such industries and applications often utilize
EPA-regulated stationary sources of emissions.
[0458] Other suitable uses include a filtering or catalytic process in one or
more of the following applications: Cars (dust/soot, odor, oil filtration,
VOC,
methane, other chemicals (gaseous, solid, or liquid)); Water Jets (dust/soot,
odor, oil filtration, VOC, methane, other chemicals (gaseous, solid, or
liquid));
Snowmobiles (dust/soot, odor, oil filtration, VOC, methane, other chemicals
(gaseous, solid, or liquid)); Small engine (dust/soot, odor, oil filtration,
VOC,
111
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
methane, other chemicals (gaseous, solid, or liquid)); Motorcycles (dust/soot,
odor, oil filtration, VOC, methane, other chemicals (gaseous, solid, or
liquid));
Mobile Diesel Engines (dust/soot, odor, VOC, methane, other chemicals
(gaseous, solid, or liquid)); Stationary Diesel Engines (dust/soot, odor, VOC,
methane, other chemicals (gaseous, solid, or liquid)); Power Stations
(dust/soot, odor, VOC, methane, other chemicals (gaseous, solid, or liquid));
Refineries (VOC, other chemicals (gaseous, solid, or liquid)); and Chemical
and Pharmaceutical Manufacturing (dust/soot, bacteria/virus, odor, oil
filtration, VOC, methane, other chemicals (gaseous, solid, or liquid).
[0459] Furthermore, additional catalytic and/or filtering applications include
the use of a substrate according to the present invention in one or more of
the
following areas: Agricultural & Forestry Incineration Emissions; Bakeries
(dust/soot, smoke, odor, VOC, other chemicals (gaseous, solid, or liquid));
Bio-Medical Fluid Filtration; Breweries and wineries (odor); Cabin air (car,
submarine, space industry, airplane) (dust/soot, smoke, pollen,
bacteria/viruses, odor, VOC, other chemicals (gaseous, solid, or liquid));
Clean room applications (dust/soot, smoke, pollen, bacteria/viruses, odor,
oil,
VOC, methane, other chemicals)); Commercial Incineration Emissions (odor,
VOC, other chemicals (gaseous, solid, or liquid)); Commercial Toxic Organic
Emissions; Dry cleaners (VOC, other chemicals (gaseous, solid, or liquid));
Evaporative Emissions (such as Fuel Evaporation Management); Fireplaces);
Flame grilling (fast food) (dust/soot, smoke, odor, VOC, other chemicals
(gaseous, solid, or liquid); Fitness Centers); Fluid Filtration in General
(Drinking water treatment)); Food processing and storage (odor, other
chemicals (gaseous, solid, or liquid); Foundries (odor); Fuel Cells (VOC,
methane, other chemicals (gaseous, solid, or liquid); Gas Masks (dust/soot,
smoke, pollen, bacteria/viruses, odor, VOC, other chemicals (gaseous, solid,
or liquid); General VOC applications for processing/manufacturing (wood
products, coating industry, textile industry, etc); Glass/ceramics;
Greenhouses;
Home appliances - cold (Rechargeable appliances ) (odor, oil, VOC, other
chemicals (gaseous, solid, or liquid)); Home appliances - hot (Water Heaters
& Domestic Heaters Appliances) (odor, oil, VOC, other chemicals (gaseous,
solid, or liquid)); HVAC Sanitation); Hydrogen Reformation (VOC, methane,
other chemicals (gaseous, solid, or liquid)); Medical Growth Medium; Office
112
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
buildings; Oil/petrol transport; Other Electro-Magnetic Insulation (Electro-
Magnetic Shield); Paint usage; Petrol stations (odor, VOC); Polymer
processing (odor, VOC, other chemicals (gaseous, solid, or liquid); Recovery
of precious metals/catalysts from hot gases and liquids; Restaurant Fumes;
Sewage and bio-waste (bacteria/viruses, odor, VOC, methane, other chemicals
(gaseous, solid, or liquid)); Slaughter houses; Smoke Houses (dust/soot,
smoke); Sound Insulation; Swimming pools; Tanning studios; Tunnels and car
parks (dust/soot, odor, VOC, methane, other chemicals (gaseous, solid, or
liquid)); and Waste Incineration (dust/soot, odor, VOC, other chemicals
(gaseous, solid, or liquid)).
Process of Preparing A Catalytic or Filtering Substrate
[0460] In another aspect, the present invention is directed to a process of
preparing any one of the substrates (catalytic or filtering) as described
herein.
The present invention is also directed to a process of preparing a catalytic
substrate of the present invention. In another aspect, the present invention
is
directed to process of preparing a diesel particulate filter. A number of
methods as described below can be used to prepare the substrate.
[0461] In one aspect of the present invention, a catalytic substrate as
described
herein can be prepared using a commercially available billet of nSiRF-C. The
commercially available billet of nSiRF-C is machined into a suitable shape,
form, and size. A substrate of the invention can be prepared by as large brick
of suitable substrate material by machining the brick into a shape suitable
for
use in the present invention. The crude block can be easily cut or sawed into
a
preformed shape, and then sanded, turned or machined into the final desired
shaped "slug." Although the composition of the substrate material is very
resilient to chemical, heat, thermal, and vibrational shock, the hardness is
the
substrate material is low. This, low hardness permits machining with little or
minimal amount of resistance or wear on tools. Despite the fact that the block
has a low hardness and is soft, it is very durable and easy to machine,
sculpt,
or shape. For example, in certain embodiments, a substrate material is, on a
Moh's hardness scale, usually between 0.5 and 1.0 (or 1-22 on the Knoop
hardness scale) with talc being the softest at 1 (1-22 Knoop hardness) and
113
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
diamond being the hardest at 10 (8,000-8,500 Knoop hardness). Other
suitable values Certain prior art substrate materials are harder. For example,
silicon carbide has a Moh's hardness of 9-10 (2,000-2950 Knoop hardness).
[0462] With reduced effort compared to certain conventional substrates such
as cordierite, the billet is shaped, sanded, turned, or machined, providing
unlimited shaping capabilities of slug formation. The machining can range
from turning a cylinder on a lathe, sawing to shape with a keyhole saw, band
saw or jig saw, sanding the shape or smoothing the surface, or any other
method of machining commonly used on other solid materials and known in
the art. The billet can be machined down to very exacting tolerances with the
same accuracy as machining metals, woods, or plastics. If the billet is cast
in
cylindrical molds with the desired diameter of the final shape, the machining
would simply require cutting and sanding the cylindrical billet to the desired
thickness. This process also reduces substrate loss due to excessive
machining, and speeds up the preforming process as well.
[0463] In certain embodiments, the frontal shape of the substrate is circular
510, oval 520, and racetrack 530, as shown in FIG. 5. As is readily
understood, the shapes do not have to be exact. Three-dimensionally, the
substrates may be in the form of a cylinder or a substantially flat disc.
Designs
with squared corners, in certain applications, are not as effective. Although
easy to machine, square or angular designs have proven to be a trap for rust
and corrosives, e.g., road salt. Therefore, rounded corners are preferable on
the frontal surface shape of the slug in certain embodiments.
[0464] The billet may be shaped by a band saw, jig saw, CNC, or other
method known to one of ordinary skill in the art. The billet may be further
shaped by a hand rub, lathe sanding, belt sanding, or orbital sanding.
Airborne
particles are preferably vacuumed to prevent them from clogging the pores of
the material. Further, these particles can enter the bearings of the drill
press
and destroy it, grinding away and scoring the bearings. The ceramic dust is
also very fine and can be easily inhaled by operator.
[0465] In another embodiment, the present invention is directed to a method
of preparing a catalytic or filtering substrate according to the present
invention
comprising preparing a billet of a nSiRF-C composite; and optionally
machining said billet to form a substrate of the present invention. If the
billet
114
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
is prepared in a shape suitable for use in one or more processes of the
present
invention, the billet does not necessarily need to be machined to a different
shape. In this instance, the billet is prepared with a mold, as described
below,
having a suitable shape. Alternatively, the billet or substrate may be
machined
to a suitable shape. Further, as described in more detail below, a plurality
of
channels are machined into the substrate.
[0466] The step of preparing the billet (or substrate) comprises known
methods of preparing these materials. Any known method of preparing a
suitable billet or substrate can be used. For example, suitable processes are
disclosed in U.S. Patent Nos. 4,148,962 and 6,613,255, each of which is
incorporated by reference herein in its entirety.
[0467] By way of a non-limiting example, in one embodiment, the steps of
preparing a suitable substrate comprise:
heating a plurality of refractory silica fibers, refractory alumina fibers,
and refractory aluminoborosilicate fibers;
mixing said fibers;
washing said fibers;
optionally chopping said fibers to one or more lengths;
blending or mixing the chopped fibers into a slurry;
adjusting the viscosity of said slurry, preferably by adding thickening
agent;
adding a dispersant;
adding the slurry to a mold;
removing water the slurry to form a green billet;
removing the green billet from the mold;
drying the green billet in oven, preferably drying at a temperature of
about 250 F to about 500 F; and
heating, preferably prewarming and incrementally heating, the green
billet in an oven at approximately 2000-2500 F.
[0468] As stated above, the billet is then optionally machined to form a
substrate of the present invention.
[0469] In another embodiment, the process further comprises machining a
plurality of channels in the substrate.
115
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0470] In another embodiment, the process further comprises adding a
washcoat to the substrate.
[0471] In another embodiment, the process further comprises adding a
catalytic coating to the substrate.
[0472] In another embodiment, the process further comprises
[0473] In a further embodiment, the mixing of the fibers is performed after
the
washing and heating of the fibers.
[0474] In further embodiment, boron nitride is used in the process of making a
substrate of the present invention. BN => B + N2
[0475] In yet an additional embodiment, a thickening agent is used.
Preferably, the thickening agent and dispersant used in the process are
substantially removed from the substrate during a heating step. For example,
the thickening agent and dispersant may be combusted during the sintering
process.
[0476] The substrate 2510 is derived from a billet created by forming a rigid
configuration of chopped and/or non-woven inorganic fiber and a binding
agent. The billet is machined or worked into the desired external dimensions
for the substrate 2510. The interior of the substrate 2510 is then machined or
worked to provide the desired surface area enhancement configuration, e.g.,
channels, washcoat, or catalyst. A durable inorganic hardened coating 2511
may be applied to the substrate 2510 by brushing, spraying, dipping, or any
other common application method. In addition, the substrate 2510 may
include an oxidation or reduction catalyst applied by brushing, spraying,
dipping, or any other common application method.
[0477] In one einbodiment, the catalytic or filtering substrate of the present
invention comprises a nSiRF-C; and a coating comprising, in admixture,
silicon dioxide power in an amount of from 23.0 to 44.0 wt %; collodial
silicon dioxide in an amount from 25.0 to 45.0 wt %, water in an amount from
19.0 to 39.0 wt %; and one or more emittance agents selected from the group
consisting of silicon tetraboride, silicon hexaboride, silicon carbide,
molybdenum disilicide, tungsten disilicide and zirconium diboride; wherein
said protective coating has a solids content of from 45 to 55 wt %. Such a
coating is disclosed in U.S. Patent No. 5,296,288.
116
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0478] The present invention utilizes a plurality of high-grade non-woven
sintered inorganic refractory fibers, such as those present in AETB. Other
suitable materials for use as a nSiRF-C in the present invention include:
AETB-12 (having a composition of about 20% A1203, about 12% (14% B203,
72% A1203, 14% Si02; NEXTELTM fiber), and about 68% SiO2); AETB-8
(having a composition of about 20% A1203, aboutl2% (14% B203, 72%
A1203, 14% SiO2 NEXTELTM fiber), 68% Si02); FRCI-12 (having a
composition of about 78% wt. silica (SiO2), and 22% wt. aluminoborosilicate
(62% A1203, 24% Si02, 14% B2O3); and FRCI-20 (having a composition of
about 78% wt. silica (SiO2) and about 22% wt. aluminoborosilicate (62%
A1203, 24% Si0a, 14% B203).
[0479] In a preferred embodiment, the components of the inorganic fibers
consists, or consists essentially of, fibrous silica, alumina fiber, and
aluminoborosilicate fiber. In this embodiment, the fibrous silica comprises
approximately 50-90 (%) percent of the inorganic fiber mix, the alumina fiber
comprises approximately 5-50 (%) percent of the inorganic fiber, and the
aluminoborosilicate fiber comprises approximately 10-25 (%) percent of the
inorganic fiber mix. The fibers used to prepare the substrate of the present
invention may have both crystalline and glassy phases in certain embodiments.
[0480] Other suitable fibers include aluminoborosilicate fibers preferably
comprising aluminum oxide in the range from about 55 to about 75 percent by
weight, silicon oxide in the range from less than about 45 to greater than
zero
(preferably, less than 44 to greater than zero) percent by weight, and boron
oxide in the range from less than 25 to greater than zero (preferably, about 1
to
about 5) percent by weight (calculated on a theoretical oxide basis as A1203,
Si02, and B203, respectively). The aluminoborosilicate fibers preferably are
at least 50 percent by weight crystalline, more preferably, at least 75
percent,
and most preferably, about 100% (i.e., crystalline fibers). Sized
aluminoborosilicate fibers are commercially available, for example, under the
trade designations "NEXTEL 312" and "NEXTEL 440" from the 3M
Company. Further, suitable aluminoborosilicate fibers can be made as
disclosed, for example, in U.S. Patent No. 3,795,524, which is incorporated
herein by reference in its entirety.
117
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0481] Additional suitable fibers include aluminosilicate fibers, which are
typically crystalline, comprising aluminum oxide in the range from about 67 to
about 77, e.g., 69, 71, 73 and 75, percent by weight and silicon oxide in the
range from about 33 to about 23, e.g., 31, 29, 27, and 25, percent by weight.
Sized aluminosilicate fibers are commercially available, for example, under
the trade designation "NEXTEL 550" from the 3M Company. Further,
suitable aluminosilicate fibers can be made as disclosed, for example, in U.S.
Patent No. 4,047,965 (Karst et al.), the disclosure of which is incorporated
herein by reference.
[0482] In other embodiments, the fibers used to prepare the substrate of the
present invention comprise a-A1203 with Y203 and Zr02 additions, and/or
a-A12O3 with Si02 added (forming a-A1203/mullite)
[0483] Various specific materials can be used to prepare the catalytic
substrate. In one embodiment, the material used to prepare a substrate of the
present invention comprises, or alternatively consists or consists essentially
of,
refractory silica fibers and refractory aluminumborosilicate fibers. In
another
embodiment, the material used to prepare the catalytic substrate comprises
refractory silica fibers, refractory grade alumina fibers, and a binding
agent,
preferably a boronoxide or a boron nitride powder.
[0484] In one embodiment, the catalytic substrate of the present invention
comprises, or alternatively consists or consists essentially of, an alumina
enhanced thermal barrier ("AETB") material or a like material known to one
of ordinary skill in the art. AETB material is known in the art and more fully
described in Leiser et al., "Options for Improving Rigidized Ceramic
Heatshields", Ceramic Engineering and Science Proceedings, 6, No. 7-8, pp.
757-768 (1985) and Leiser et al., "Effect of Fiber Size and Composition on
Mechanical and Thermal Properties of Low Density Ceramic Composite
Insulation Materials", NASA CP 2357, pp. 231-244 (1984), both of which are
hereby incorporated by reference.
[0485] In another embodiment, the catalytic substrate comprises Ceramic tiles,
such as alumina enhanced thermal barrier (AETB) with toughened unipiece
fibrous insulation (TUFI) and/or reaction cured glass (RCG) coatings. Such
materials are known in the art.
118
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0486] Another suitable material is Fibrous Refractory Ceramic Insulation
(FRCI). In one embodiment, AETB is made from aluminaboriasilica (also
known as alumina-boria-silica, aluminoborosilicate, and aluminoboriasilicate)
fibers, silica fibers, and aluniina fibers. One commonly known application for
AETB is as an exterior tile on the Space Shuttle, ideal for shuttle re-entry.
AETB has a high melting point, low heat conductance, and coefficient of
thermal expansion, ability to withstand thermal and vibrational shock, low
density, and very high porosity and permeability.
[0487] In one embodiment, a first component of AETB is alumina fibers. In
preferred instances of the present invention, the alumina (A12O3 or aluminum
oxide, e.g., SAFFIL), is typically about 95 to about 97 weight percent alumina
and about 3 to about 5 weight percent silica in commercial form. In other
embodiments, alumina having a lower purity are also useful, e.g., 90%, 92%,
and 94%. In other embodiments, alumina having a higher purity are also
useful. Alumina can be produced by extruding or spinning. First, a solution
of precursor species is prepared. A slow and gradual polymerization process
is initiated, for example, by manipulation of pH, whereby individual precursor
molecules combine to form larger molecules. As this process proceeds, the
average molecular weight/size increases, thereby causing the viscosity of the
solution to increase with time. At a viscosity of about ten centipoise, the
solution becomes slightly adhesive, allowing fiber to be drawn or spun. In
this
state, the fiber may also be extruded through a die. In certain embodiments,
the average fiber diameter ranges from about one to six microns, although
larger and smaller diameter fibers are also suitable for the present invention
[0488] In one embodiment, a second component of an AETB is silica fiber.
Silica (SiO2, e.g., Q-fiber or quartz fiber), in certain embodiments, contains
over 99.5 weight percent amorphous silica with very low impurity levels.
Silica of lower purities, e.g., 90%, 95%, and. 97%, are also useful for the
invention. In certain embodiments, an amorphous silica is used that has a
low density (e.g., 2.1 to 2.2 g/cm3), high refractoriness (1600 degrees
Celsius),
low thermal conductivity (about 0.1 W/m-K), and near zero thermal
expansion.
[0489] In one embodiment, a third component of an AETB is
aluminaboriasilica fibers. In certain instances, aluminaboriasilica fiber
119
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
(3A12O3=2SiO2=B2O3, e.g., NEXTEL 312) is typically 62.5 weight percent
alumina, 24.5 weight percent silica, and 13 weight percent boria. Of course,
the exact percentages of the constituents of the aluminaboriasilca may vary.
It
is largely an amorphous product but may contain crystalline mullite. Suitable
aluminaboriasilica fibers and methods of making the same are disclosed, for
example, in U.S. Patent No. 3,795,524, the teachings of which are herein
incorporated by reference in their entirety.
[0490] Other suitable materials for use as a nSiRF-C in the present invention
include: AETB-12 (having a composition of about 20% A1203, about 12%
(14% B203, 72% A1203, 14% Si02, NEXTELTM fiber), and about 68% Si02);
AETB-8 (having a composition of about 20% A1203, aboutl2% (14% B203,
72% A1203, 14% SiO2 NEXTELTM fiber), 68% Si02); FRCI-12 (having a
composition of about 78% wt. silica (Si02), and 22% wt. aluminoborosilicate
(62% A1203, 24% SiO2, 14% B203); and FRCI-20 (having a composition of
about 78% wt. silica (SiO2) and about 22% wt. aluminoborosilicate (62%
A1203, 24% Si02, 14% B2O3).
[0491] In a preferred embodiment, the components of the inorganic fibers
consists, or consists essentially of, fibrous silica, alumina fiber, and
aluminoborosilicate fiber. In this embodirnent, the fibrous silica comprises
approximately 50-90 (%) percent of the inorganic fiber mix, the alumina fiber
comprises approximately 5-50 (%) percent of the inorganic fiber, and the
aluminoborosilicate fiber comprises approximately 10-25 (%) percent of the
inorganic fiber mix.
[0492] Similar fibers to those fibers of AETB, as described herein, may be
utilized in addition to or in the place of the AETB fibers.
[0493] Fiber production via melting can be performed in two general methods.
The first method involves a combination of centrifugal spinning and gaseous
attenuation. A glass stream of the appropriate viscosity flows continuously
from a furnace onto a spinner plate rotating at thousands of revolutions per
minute. Centrifugal forces project the glass outward to the spinner walls
containing thousands of holes. Glass passes through the holes, again driven by
centrifugal force, and is attenuated by a blast of heated gas before being
collected.
120
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0494] In the second melting technique, molten gas is fed into a heated tank
whose bottom surface is perforated by hundreds or thousands of holes,
depending on the application. Glass flows and is drawn through these holes,
forming individual fibers. The fibers are merged into strands and collected on
a mandrel.
[0495] In one embodiment, the AETB fiber mix in the slurry preferably
comprises three ingredients including fibrous glass, alumina fiber, and
aluminaboriasilica fibers. The fibrous silica will comprise approximately
50-90 percent of the inorganic fiber mix; the alumina fiber will comprise
approximately 5-50 percent of the inorganic fiber mix; and the
aluminaboriasilica will comprise approximately 10-25 percent of the inorganic
fiber mix. In other embodiments, the slurry comprises any mixture of fibers
that can be used make a substrate according to the invention as described
above.
[0496] In a preferred embodiment, the fibrous component of the substrate is a
mixture of 64% amorphous silica, 21% alumina, and 15% aluminaboriasilica
fiber, with trace amounts, e.g., 0.3 to 1.0 mg/m2, of a surface active agent
employed to aid in the dispersion of bulk fiber in the slurry prior to and
during
casting.
[0497] In one embodiment, the fibers in the slurry are only primarily
inorganic fibers. Preferably, in one embodiment, the present invention does
not use any carbon in formation of the substrate.
[0498] Alumina-zirconia fibers may be added to the inorganic fiber mix as a
fourth component or replacement component for other fibers.
Mix Fibers
[0499] In one step of an embodiment of the present invention, the fibers are
mixed. Any number of known methods of mixing the fibers can be used to
mix the fibers. An example is high-shear mixing which can be employed.
Heat Fibers
[0500] In one step of the present invention, the fibers are heated according
to
known methods. The fibers are first heated to allow for the fibers to be more
121
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
evenly chopped. The heat-treated fibers are washed to remove all of the dust,
debris, and loose particles, leaving only the fibers to process.
[0501] In a preferred embodiment, the fibers are heat cleaned
Wash Fibers
[0502] In one step of the present invention, the fibers are washed. In a
preferred method, the fibers are washed so that the fibers are substantially
free
of dust and particles. In one embodiment, the silica fibers are washed in acid
to remove impurities, rinsed, dried, and subsequently heat treated to impart
structural integrity.
Chop Fibers
[0503] In another step of the present invention, the fibers are chopped. Fiber
for use in the present invention can typically be obtained as bulk or chopped
fiber. Methods of chopping fibers are known in the art. Most methods are
continuous processes capable of handling multiple fibers or strands
simultaneously. Typically, the product is fed between a set of rotating wheels
or drums, one of which supports regularly spaced cutting blades. As the fiber
is drawn through the cutter, it is chopped to length. Although specific
manufacturing details remain proprietary for forming a blank from the
chopped fiber, the art typically involves one of two production mechanisms:
melting and sol gel. Preferably, the fibers are heat treated before the final
chopping.
[0504] Preferably, the fibers are then chopped to size. Suitable lengths of
the
fibers include, but are not limited to, about 0.1, 0.2, 0.3, 0.4, 0.5, or 0.6
inches.
Other suitable lengths include 1/8", 1/4", and 1/2". It is preferred that the
fibers are relatively uniform in size. In another embodiment, the fibers that
compose the catalytic substrate or the filtering substrate are an average 1/4
inch (approximately 1 hundredth of a meter) in length and about one to 12
microns in diameter, alternatively, one to six, or 10 to 12 microns with a
median fiber diameter of three microns. In a preferred embodiment,
particulate material is not added as it may clog pore space. Suitable fibers
for
122
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
use in the present invention are available commercially, e.g., from 3M. Of
course, in other embodiments, longer fibers are used.
Slurrying
[0505] In another step of the process of the invention, a slurry comprising
the
fibers is prepared. Rather than extruding a ceramic or wrapping a yarn or
fabric around a perforated tube, the substrate may be made by a common sol-
gel process. This is accomplished by first pulling (via a vacuum or gravity-
drawn) a well mixed sol of inorganic fibers and colloidal solution into a
fiber
mold which creates the sol blank or green billet or billet.
[0506] Alternatively, a squeeze-cast pressurizing process may be used where
pressure is reduced to negative value or a vacuum process. The vacuum
process allows the inorganic fiber blank to be formed with super low densities
while maintaining its strength. The sol-gel process in conjunction with the
pressurized process or vacuum process helps to produce exceptionally low
densities, which is extremely beneficial to the filtration of particulates.
[0507] The fibers are blended together in a slurry. In certain embodiments, a
slurry may contain 1 to 2 weight percent solids and is nearly as fluid as
water.
Alternatively, the slurry may contain from about 0.5 to about 5 weight percent
solids. Other weight percentages are acceptable as well, as is known in the
art.
[0508] The chopped fibers are mixed together in a slurry using a high-shear
mixer. Preferably, deionized water is used in the slurry to avoid impurities
that may act to flux or destabilize the fiber in service. In one embodiment,
the
slurry can be pumped through a centrifugal cyclone to remove shot glass and
other contaminants, including high soda particles.
[0509] Alternatively, organic fibers or particulate may be added to the fiber
slurry in proportions up to thirty percent by weight. During the firing stage
of
production, the organic fiber is volatilized or burned out of the article.
Burning the fiber leaves a void that allows a path for gases to escape. By
varying the type and proportion of polymeric fiber, the permeability of the
tile
can be tailored. Blanks produced via this method are porous, and thus capable
of active cooling through the introduction of bleed air.
123
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Adjusting Viscosity
[0510] In another embodiment, viscosity is adjusted to a suitable range. A
higher viscosity prevents fibers from "laying down," i.e., laying flat or
becoming oriented only in a substantially horizontal direction. Boron nitride
may be added as a thickening agent to coat the fibers in preparation for high-
strength sintering. In one embodiment of the present invention, boron nitride
is added and aluminaboriasilica fiber is not utilized in the slurry.
Adding Dispersant
[0511] In one embodiment, the process comprises adding one or more
dispersants to the mixture or slurry.
[0512] In one embodiment of the present invention, one or more surface active
agents are added to the slurry during the process of the invention. The
surface
active agent is used in quantities of about 5 to about 10 weight percent. The
surface active agent is employed to aid in the dispersion of bulk fiber in the
slurry prior to and during casting to prevent the fibers from bundling
together.
[0513] In one embodiment of the present invention, one or more catalysts as
described above are added to the slurry. By adding a catalyst at this stage of
the process, a substrate having the catalyst impregnated within the porous
material is made. In one embodiment, this configuration eliminates the need
for further washcoating or catalyzing.
Molding
[0514] In one embodiment, the slurry is poured into a mold to form a billet.
The shape of the mold may take any shape desired. In certain embodiments,
the shape of the mold will produce a substrate having a shape suitable to be
used in a catalytic converter or particulate filter. For example, the mold may
be in the shape of a cylinder. Alternatively, the mold is in the shape of a
pentagon. Preferably, the slurry is not allowed to settle in the mold because
the fibers may lay down. In one embodiment, a vacuum suction method is
employed to keep the fibers from settling down and to maintain uniform
porosity and density of the material throughout the billet. The vacuum suction
124
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
technique may be employed from any number of directions to control the fiber
arrangement and density with the green billet.
[0515] By way of example, a billet of the material of the catalytic or
filtering
substrate is produced in a mold of 24 inches by 24 inches (576 in2) x 4 inches
having rounded corners. Of course, billets may be produced of larger or
smaller sizes.
[0516] The material of the mold can be any material that is stable with water,
including but not limited to, metal or plastic. Other suitable materials
include
aluminum, PLEXIGLAS, and other synthetic materials. Aluminum is very
durable over the long term whereas PLEXIGLAS material is cheap and easy to
machine. Suitable permeable surfaces are available in the form of a fine
metallic mesh screen. Semi-permeable surfaces larger than about 50 in2 may
under certain circumstances preferably use a backing or support structure to
prevent sagging.
[0517] There are embodiments in which an anaerobic, i.e., oxygen free,
environment may be desirable during casting. The oxygen-free atmosphere
creates an environment which minimizes metal oxidation and uniquely
strengthens the fiber bonds. The soaked billet is placed into a chamber, e.g.,
a
large plastic bag, filled with ammonia gas. Ammonia is most commonly used
because of its low cost and availability. Nitrogen and/or hydrogen gas may
also be introduced. Nitrogen is preferred to hydrogen, since hydrogen is
volatile. In fact, any gas may be introduced as long as a reducing and oxygen
free environment is maintained. Preferably, the gas is provided at a constant
flow until the soaked sol billet has formed into a gel billet. At that point,
the
gas is turned off and the gel billet is exposed to the open air, allowing the
gases to escape.
[0518] Carbon or organic-based shape-formers may be used as hole-forming
rods which are introduced into the green billet during the molding stage.
Upon high temperature sintering, these rods may disintegrate and leave behind
the desired plurality of channels.
125
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Dewatering the Slurry
[0519] In one embodiment of producing the billet, the slurry is placed in the
enclosed mold where at least one dimension is adjustable and at least one wall
is semi-permeable. Compressive force is applied via the adjustable wall and
water is expelled from the slurry via the semi-permeable wall where fiber
collects and felts. Compression is continued until the desired preform, i.e.,
billet, dimensions are achieved. This method is generally limited to simple
geometrics like blocks or cylinders.
[0520] Gravity is typically not a sufficient driving force, therefore
requiring
the use of a vacuum pump. The vacuum pump uses very little to no pressure.
In some instances, a vacuum is employed to dewater, but the suction using is
very slight. The vacuum is used as a means to speed up the drying process
with great sensitivity to avoid increasing the density. Preferably, only mild
vacuum assistance is used.
[0521] More complicated-shaped billets can be prepared by an alternative
method, for example, in which a head of slurry is placed and maintained over
a semi-permeable mold form. Low pressure is established outside the
permeable form via the vacuum pump. The differential pressure drives water
through the permeable form where fiber collects and felts. The differential
pressure is sustained until the desired thickness is achieved. This process is
suited to applications where the desired substrate is highly curved, as
billets
can be produced near-net-shape or close to their final form.
[0522] Injecting or mixing multiple (two or more) slurry recipes and varying
the vacuum rate of pull (a plurality of times) provides a billet with some
areas
denser than others and/or areas with different physical properties. The
billets
can have graduated or different layers or cores with different chemical
compositions and densities. The billets can have one or a plurality of zones,
each with a unique shape, location, and physical properties as needed. Each
zone can change as needed for changing the strength, heat or electrical
conductivity, catalyst adhesion capability, thermal expansion, vibrational or
thermal shock, weight, porosity and permeability, sound dampening, or any
other preferable property.
126
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0523] By using different slurry recipes and molding techniques, the billets
can also be layered. In addition, the billet is not restricted only to
parallel
planar layers, such as layers on a cake, but the billets can be formed with
horizontal, angled, spherical, pyramidal, and free-form layers, or any other
configuration known in the art. It should also be noted that the density of
the
billet could be chemically and physically altered, if desired, during this
process.
[0524] The billets can also be formed by placing a plurality of billets, of
different chemistry and in any configuration, whether cured or uncured, inside
or within another billet. The core billets can be manually placed into the
billet
or injected into the core. The result is a core or a plurality of cores of
less or
more density. The shape or form of these cores and billets is unlimited as is
the combination of layering the cores. Cores may even be created inside
cores. The process can be repeated an unlimited number of times as needed
yielding a unique number of combinations of billets in unlimited shapes.
Drying the Green Billet
[0525] In one step of an embodiment, the slurry in the mold is oven-dried long
enough to dewater, i.e., drive off any water it may contain. Water can be
drained out by gravitational forces. Slight vacuum assistance may be utilized.
Other methods known in the art can of course be used.
Remove Green Billet from Mold and Drying Green Billet
[0526] In one step of an embodiment of the invention, the green billet is
removed from the mold. Generally, the billet can be removed when it is dry
enough to handle. Alternatively, the billet is removed when it is dry enough
to
be manipulated by a machine.
[0527] For example, when the billet is dry enough to be handled, it is removed
from the mold. The billet is then dried in an oven. A low enough temperature
is used so as to complete dewatering process and permit fibers to remain
substantially in their intended configuration. Most preferably, the
temperature
is sufficient to dry the billet as required but insufficient to cause any or
substantially any sintering of the billet. In another preferred embodiment, a
127
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
temperature of about 250 to 500 degrees Fahrenheit is used in this step. In a
further embodiment, the billet is dried at a temperature of about 180 C for
about 2 to about 6, preferably about 4 hours. Other times and temperatures as
are known in the art may be used.
[0528] A dried billet is then optionally soaked in a sol-gel binder,
preferably
an alumina sol gel binder, for a period of time, e.g., a few days, at various
temperatures, as is known in the art, as the billet "wicks" (i.e., soaks up)
the
binder solution into the billet. A suitable binder is known in the art and may
be required to impart preform structural integrity as well as to promote
sintering. The billet may utilize a single or multiple binder process to vary
the
strength and conductivity of the billet. Applying a binder several times will
increase the strength of the billet but may also reduce or plug up the pore
spaces. Any suitable binder may be used. The binder may be an oxide binder
such as Si02 or A12O3. The oxide binder may also be a glass configuration, a
crystalline configuration, or other inorganic binder. A binder may be applied
using known techniques and methods, such as those disclosed in U.S. Patent
No. 3,549,473, the teachings of which are incorporated herein by reference in
their entirety.
Drying the Green Billet (Sintering)
[0529] In another step of an embodiment of the present invention, the green
billet is heat cured. The temperature for heat-curing, or sintering, is
generally
a higher temperature than that used for drying the green billet. In one
embodiment, the temperature is incrementally increased over one or more
hours, preferably several hours, until the desired temperature is reached. In
one embodiment, the oven is pre-warmed and incrementally heated to
approximately 2000-2500 F. Other temperatures known in the art are
suitable.
[0530] In a preferred embodiment, after gelling the binder, the billet is
cured
by heating the billet to about 200 degrees Fahrenheit for about four hours,
and
then slowly increasing the temperature to about 600 degrees Fahrenheit over
about a five hour period. After achieving and maintaining the maximum
temperature, the billet is quickly quenched. The end result is a rigid
inorganic
128
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
fiber billet. Once again, the process of heat curing the blanks can vary in
the
temperatures used, length of time to cure, the temperature and time of
quenching, the temperature incremental increases, and the incremental
temperature increase timing.
[0531] Billets are fired to supply the necessary energy to sinter fiber-to-
fiber
contacts, thereby forming bonds that impart strength to the substrate. For
example, strength can be increased by increasing the number of fiber-to-fiber
contacts. Increasing the number of contacts increases density and tortuosity.
The more tortuous a pore network becomes, the lower the permeability.
Sintering does not cause the fibers to melt together, but instead binds them
chemically. The billet is progressively heated in a high temperature furnace.
The billet is pre-warmed and then incrementally heated to approximately 2000
to 2500 degrees Fahrenheit until a desired density and fusion are obtained.
Secondary chemicals such as the thickening agent are combusted away in
preferred embodiments. A substrate comprising, or alternatively consisting of
or consisting essentially of, the sintered fibers remains.
[0532] In a preferred embodiment, the viscosity (thickening agent) chemicals
and dispersant are combusted away.
[0533] In other embodiments, multiple curing steps are performed. This can
be done to increase hardness of the substrate.
[0534] The variables in the drying and curing processes can be adjusted
according to the desired density, strength, porosity, or permeability, or
resistance to high temperatures, of the fiber blank. In certain embodiments,
the curing process can use a plurality of curing applications and can vary the
heating and cooling intervals and approaches. The billet can also be rapidly
cooled to quench or temper the billet. The slurry may undergo additional heat
or other treatments, such as densification coatings or multiple curing and
sintering.
Physical Modification
[0535] In certain embodiments of the process, the billet is coated with a
catalyst. In one method of applying catalysts to a substrate, the substrate
may
be formed from a slurry that contains catalysts. Other suitable methods of
129
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
applying a catalyst may be used. Another advantage of the present invention
is that it has been surprisingly discovered that a catalyst can be applied to
the
nSiRF-C material using methods that can apply catalyst to other materials.
[0536] In another embodiment in the present invention, catalyst is added to
the
slurry prior to molding. In this instance, a catalytic substrate is formed
having
the catalyst reside directly onto the individual fibers that constitute the
substrate. This method of adding catalyst to the substrate, in certain
embodiments, provides an efficient method of dispersing catalyst into the core
of the catalyst substrate and not have the catalyst reside only along the
channel
walls. In this embodiment, a washcoat is not necessary.
Machining
[0537] A billet in the form of a crude block can be cut or sawed into a
specified shape, and then sanded, turned or machined into the final desired
shaped "slug." Although the composition of the material is very resilient to
chemical, heat, thermal and vibrational shock, in preferred embodiments, the
hardness is very low. This low hardness permits machining with little or a
minimal amount of resistance or wear on tools. Despite the fact that the
billet
in certain embodiments has a low hardness and is soft, it is very durable and
easy to machine, sculpt, or shape. On a Moh's hardness scale, the material is
usually between 0.5 and 1.0 (or 1-22 on the Knoop hardness scale) - with talc
being the softest at 1 (1-22 Knoop hardness) and diamond being the hardest at
(8,000-8,500 Knoop hardness). For example, silicon carbide has a Moh's
hardness of 9-10 (2,000-2950 Knoop hardness). In relation to other known
substances, the billet is very soft and effortless to machine or sculpt as
Styrofoam or Balsa wood.
[0538] The billet can be shaped, sanded, turned, or machined, providing
unlimited shaping capabilities of, slug formation. The machining can range
from turning a cylinder on a lathe, sawing to shape with a keyhole saw, band
saw or jig saw, sanding the shape or smoothing the surface, or any other
method of machining commonly used on other solid materials and known in
the art. The billet can be machined down to very exacting tolerances with the
same accuracy as machining metals, woods, or plastics. If the billet is cast
in
130
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
cylindrical molds with the desired diameter of the final shape, the machining
would simply require cutting and sanding the cylindrical billet to the desired
thickness. This process also reduces substrate loss due to excessive
machining, and speeds up the preforming process as well.
[0539] There many possible frontal and rear surface shapes including circular
510, oval 520, and racetrack 530, as shown in FIG. 5. Three-dimensionally,
the substrates may be in the form of a cylinder or a substantially flat disc.
Conventional substrates exist as one of these three designs. Designs with
squared corners are not as effective. Although easy to machine, square or
angular designs have proven to be a trap for rust and corrosives, e.g., road
salt.
Therefore, rounded corners are preferable on the frontal surface shape of the
slug.
[0540] The billet or substrate or slug may be shaped by a band saw, jig saw,
CNC, or other method known to one of ordinary skill in the art. The slug may
be further shaped by a hand rub, lathe sanding, belt sanding, or orbital
sanding. Airborne particles must be vacuumed to prevent them from clogging
the pores of the material. Further, these particles can enter the bearings of
the
drill press and destroy it, grinding away and scoring the bearings. The
ceramic dust is also very fine and can be easily inhaled by operator.
[0541] The shaped slug is utilized as a substrate in the present invention.
The
surface area of the substrate is an important characteristic for catalysis
application. Surface area is the sum amount of surface that exhaust emissions
must pass across when traveling through an exhaust filter. Increased surface
area translates into more room for chemical reactions to take place between
pollutants and catalytic and thermal processes, making a catalytic converter
process quicker and more efficient. Speed and efficiency can result in little
to
no clogging, which can cause failure of the exhaust system.
[0542] In one embodiment, the substrate of the present invention has a gross
surface area of 83.58 square inches per cubic inch. This translates into a
much
higher area that can be impregnated with precious metals, as compared to the
cordierite samples having comparable macrodimensions (e.g., diameter, length
and width). Note, however, that this gross surface area calculation does not
even include the density, porosity, and permeability of the different
materials.
131
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0543] In one exemplary embodiment of the present invention, the substrate is
used in an exhaust filter system for a diesel engine. The substrate is created
using AETB formulation and formed in approximately 13"x13"x5" billets
with a density between 8 and 25 pounds per cubic foot. From the billet, a five
inch tall cylinder slug which is six inches in diameter or an oval right-
cylinder
slug is cut from the billet using a diamond tipped or tungsten-carbide band
saw. This slug is further machined to exact tolerances on a spinning lathe
(for
right circular cylinders) or on a belt sander forming the substrate.
Preparing Holes and Channels in Substrate
[0544] In an embodiment of the present invention, a plurality of channels are
formed in the filtering or catalytic substrate substantially longitudinal to
the
intended gas flow. The channels extend through the length of the substrate,
either partially or fully. Figures 5-14 show schematic diagrams exemplifying
certain embodiments of the present invention having a plurality of channels.
In certain embodiments, the channels extend at an angle to the flow of fluid.
[0545] The inside surfaces of these channels can be chemically coated so as to
capture and treat more pollutants in a small volume of substrate. When
channels are formed in the substrate, smaller diameter channels, e.g., small
channels having 200, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300,
1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, or 2500
cpsi, are preferred to retain a high surface area.
[0546] In another embodiment, the channels extend through the entire length
of the substrate. Such a substrate has a flow through configuration.
[0547] Alternatively, the channels do not extend through the entire length of
the substrate but extend from about 50% to about 99% through the length of
the substrate. Such a substrate is considered a wall-flow configuration. The
undrilled portion remaining in the channels of the wall-flow substrate may
have a varied thickness. FIG. 8 shows a wall-flow pattern substrate 820
according to an embodiment of the present invention with an undrilled portion
840, 845 of varied wall thickness. In this embodiment, alternating entering
channels have a wider wall thickness than other entering channels as well as
the exit channels. However, the varied undrilled portion thickness may be
132
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
configured in any combination such that the entering or exit channels have a
thinner or thicker undrilled portion, and wherein the all of the undrilled
portions may or may not be substantially similar in thickness. The wall
thickness is so thin and porous that the exhaust gas 830 passes from emission
entering channels through the walls into exit channels, trapping emission
particulate. The length between the inner edges 850 and 855 of the undrilled
portions is known as a crossover region. Where the undrilled portion 840 is
thicker in some or all entering channels, emission flow 830 is likely to go
through the channel walls of the substrate in the crossover region and exit
the
substrate 820. The emission flow 830 may still pass through thinner undrilled
portion 845. In another embodiment of the present invention, the undrilled
portion of the channel has a selective impregnation of catalysts, such that
the
amount of catalysts differs from that on the channel walls.
[0548] The thiclcness of this undrilled portion is limited. Gas flow increases
by increasing the surface area of the walls with equivalent thicknesses. If
the
undrilled portion is too thin, it could rupture from excessive backpressure.
Mechanical Drilling
[0549] Once an embodiment of a substrate is cut from the billet and machined,
it can be inserted into a drilling holder for drilling. A plurality of
channels can
be drilled into the substrate in the direction substantially parallel to the
major
axis of the cylinder and the flow of exhaust emission. The smaller the channel
diameter, the more channels can fit into the substrate.
[0550] In an alternative embodiment, channels are drilled into a substrate.
The substrate is placed in a metal holder for drilling. The holder can be for
example a pair of large metal arms that firmly holds the substrate slug in
place
and keeps it from moving while not crushing the substrate. The holder
engages the substrate and holds it steady for drilling. After drilling one
side of
the substrate, the holder rotates precisely 180 degrees to allow for drilling
in
the opposite side of the substrate. If the rotation is not precisely 180
degrees,
the drilled channels will not be properly aligned or parallel. Further, the
pressure at the ingress needs to be substantially identical or similar to the
pressure at the egress. Preferably, in order to ensure parallel walls, the
holder
133
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
must not move the substrate in an more than 0.0001 inches in any unwanted
direction.
[0551] The channels of the substrate of the invention can be prepared using a
mechanical drilling process. In one embodiment, computer number control
("CNC") drilling is used, which is common among machine shops and is the
preferred method. CNC drilling is much slower and is not as economically
feasible in mass manufacturing environments requiring production of
thousands of filters per day. CNC drilling performs with high precision and
accuracy. CNC drilling is done by making multiple passes with the drill bit.
The CNC drills a little further into the substrate on each pass, removing
fibrous material as the bit comes out.
[0552] The drill bit can be tungsten carbide due to its tough and brittle
nature,
or can be a similar material known to one of ordinary skill in the art.
[0553] The drill bit penetrates at a feed rate of about ten feet per minute.
The
slow feed rate is necessary in order to prevent the drill bit from melting.
When the drill bit penetrates at a'feed rate of twenty-five feet per minute,
the
drill bit melts. Also, due to the tremendous pore space, the drill bit has a
tendency to "walk" or move around. A slower penetration rate cures this
problem.
[0554] Rotating the drill bit at a slow rate is preferable. The drill bit
should
rotate at approximately 200 revolutions per minute. Rotating the drill bit at
higher rate, such as about 10,000 revolutions per minute, may cause the drill
bit to melt. The drill bit is kept cool throughout the drilling with
lubrication
such as water, alcohol, or glycerin.
[0555] Once the substrate is cut and sanded to final dimensions, channels are
cut or drilled into the substrate. In this exemplary embodiment, the channels
are cut using a DPSSL. Since the substrate is so porous and permeable, the
substrate does not need to as thick as conventional filters. In addition,
thinner
or smaller substrates are less costly to produce because cutting one billet
can
produce multiple substrates and requires a reduced amount of any coatings or
catalysts to be applied.
134
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Water drilling
[0556] In another embodiment, water cutting (or water drilling) is used for
forming channels. Water cutting uses a fine spray of water with very high
pressure and cuts holes in the substrate. However, the water jet cannot be
stopped during the cutting process to leave a blind hole (i.e., a channel that
does not go through the substrate completely). The physical characteristics of
the water jet limit the size of the channel opening to a diameter no smaller
than the diameter of the jet. In certain embodiments, a rectangular hole could
be created with the jet.
Gas-drilling
[0557] In another aspect of the invention, a gas drilling method is used to
prepare the substrate. Gas-drilling is known in the art and can be applied to
substrates of the present invention to prepare channels in the substrate.
Combing
[0558] In another embodiment, the channels are formed or shaped using a
comb process. The comb is a preferably a metal device with a plurality of
tines that can be forced into (e.g., broaching) the substrate. The combs used
for broaching comprise a plurality of tines. Tine length, width, thickness,
and
shape may be varied according to the desired properties, configurations, and
dimensions of the channels.
[0559] In certain embodiments, the comb is forced into the substrate
substantially perpendicular to the surface of the substrate. In other
embodiments, the comb is forced into the substrate at an angle to the surface
of the substrate. Using a comb is a preferred method, in particular for
forming
blind channels. It is understood that a suitable comb can also be made so that
the comb is made of a rows and columns of tines e.g., 4 x 4, or 16 by 16.
[0560] In general, the comb process comprises repeatedly forcing the comb
into the substrate material a plurality of times until most or all of the
channel
is shaped. This process is referred to herein as pecking. Optionally the comb
may be removed from the channel after each forcing into so that excess
135
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
substrate material can be cleared from the channel by, for example, air. It is
preferable to prevent fiber build-up during the pecking/broaching steps. Fiber
build up may cause walls to rupture or the entire. To manage this property, a
vacuum and/or compressed air can be employed to clear the channels and drill
bit surfaces.
[0561] In one embodiment, the comb is forced into the substrate with a force
sufficient to displace or dislodge an amount of substrate material from the
channel wall. In a preferred embodiment, a sufficient amount of force is
applied to the comb so that the tines extend about 0.1 inches into the
channel.
Other suitable values include 0.05 0.15, and 0.2. Preferably, the amount of
force applied to form or shape the channels is an amount sufficient to form or
shape the channel without substantially damaging the channel wall. The
process comprises forcing the tines into the substrate repeatedly until the
channels is produced of desired length and shape.
[0562] The shape of the tines dictates the shape of the channels. For example,
a rectangular-shaped tine on the comb is used to create rectangular shaped
channels with a rectangular shaped channel opening.
[0563] A wedge-shaped tine on the comb is used to create wedge-shaped
channels. Utilizing a wedge-shaped tine produces channels wherein the walls
are parallel with a square-shaped opening. As shown in FIG. 17, a substrate
1700 incorporates parallel wedge-shaped "blind" channels 1702, i.e., channels
with no exit hole. 'The blind channels 1702 force gases 1704 to pass through
the pore space channels walls prior to exit.
[0564] A four-sided pyramid-shaped tine on the comb is used to create a
pyramidal-shaped channel. The walls are parallel and opening is substantially
square-shaped. However, the wall thickness at the channel opening is minimal
as the channels meet at a point, rather than being adjoined by a wall with a
flat
front. This results in a decrease in frontal surface area, and thus a decrease
in
backpressure. With four-sided pyramid-shaped shaped tines, shims are not
needed to separate the combs. In this embodiment, with reference to Figure
16, a suitable comb has tines which come to a point rather than have a flat
end.
Of course, various other shapes of tines are encompassed by the present
invention.
136
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0565] A tent-shaped tine on the comb is used to create a polygonal-shaped
channel. Frontal surface area is minimized with polygonal-shaped channels.
[0566] Referring to FIG. 16, the dimensions of an exemplary comb 1600 are
shown according to an embodiment of the present invention. The comb 1600
is approximately 6.000 inches long and 0.0308 inches wide. The comb 1600
comprises a base 1610 from which a plurality of tines 1620 extend. The base
1610 is 0.4375 inches high. The plurality of tines 1620 are 1.250 inches long
and 0.0308 inches wide, and spaced by 0.010 inches.
[0567] In one embodiment of the comb process, the channels are first formed
by a drill bit and are circular. In order to produce shaped channels with
parallel walls, according to one embodiment of the present invention, tines of
combs broach (i.e., press or stamp) the circular channels to create the shaped
channel. An embodiment of a comb 1500 is shown in FIG. 15. Preferably,
broaching is done on a CNC press. The impression left behind is shaped
channels and channel openings. The cell wall thickness may be varied as
described above. In certain embodiments, the combing process produces a
catalytic or filtering substrate having a channel wall thickness of about 4
mils
to about 20 mils, preferably about 6 mils to about 10 mils.
[0568] In the comb process, metal combs may be placed in a box called a jig
and mounted in the CNC press for broaching. Within the jig, the combs are
separated by shims. The spacing between the combs is a low tolerance,
requiring the combs to be held tightly in the jig to restrict movement during
broaching. Referring to FIG. 16, a shim 1630 is utilized as a spacer for comb
1600. Shim 1630 has dimensions of 0.010 inches wide, 6.000 inches in
length, and 0.4375 inches high.
[0569] Preferably, at least one screen is provided over the combs to keep the
tines aligned. Preferably, the screens are floating to distribute alignment as
needed. Additionally, the screens are helpful for tines of varying lengths,
for
example from about 0.5 inches to about 6.0 inches long. The at least one
screen may be located anywhere along the tines, such as floating, spring-
loaded, or fixed. The at least one screen may be floating along the tines. The
tines are not affixed to the at least one screen, rather the screens are
placed on
the tines such that the screens are adjustable. The at least one screen may be
spring-loaded on the tines. By spring-loading the screen, the pressure of the
137
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
substrate against the screen maintains the distance between the tines at
approximately the edge of the substrate. The at least one screen may also be
fixed to the tines, at any position along the length of the tines.
[0570] Another embodiment of the present invention is directed to a process
of preparing a catalytic or filtering substrate having a plurality of
channels,
comprising using a comb to peck at the substrate to form the plurality of
channels. This process, in preferred embodiments, is a stepwise process. That
is, the entire channel is not formed with one insertion of the tine of the
comb.
Rather, the tines of the comb are repeatedly inserted and removed in small
increments until the desired length of the channel is obtained. Preferably,
the
channels are cleared of dislodged substrate material between each peck or
every other peck
[0571] In another embodiment, the comb process is an automated process
utilizing machines and/or robots to form the channels.
Method of Making Combs
[0572] There are a number of methods of making combs for use in the present
invention. The combs may be made of a material including, but not limited to,
stainless steel, tungsten, or key stock. Methods of shaping the comb include
laser cutting, water cutting, and electronic discharge machining, or utilizing
other shaping methods available to one of ordinary skill in the art.
[0573] DPSSL may be used to manufacture combs. Water cutting may also
be employed to manufacture the combs. For example, thirty to forty combs
are made with one cutting using a water cutting process in one embodiment.
[0574] Electronic discharge machining ("EDM") is an alternative method to
manufacturing combs. EDM is a thermal erosion process whereby conductive
material is removed by a series of recurring electrical discharges between an
electrode and a conductive workpiece, in the presence of a dielectric fluid.
EDM may similarly be used on the substrate if the substrate is made
electroconductive. There are at least two types of EDM: (1) ram and (2) wire.
[0575] Using the EDM ram, i.e., die sinking, an electrode/tool is attached to
a
ram which is connected to one pole, usually the positive pole, of a pulsed
power supply. The workpiece is connected to the negative pole. The
138
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
workpiece is then positioned so that there is a gap between the workpiece and
the electrode. The gap is then flooded with the dielectric fluid. Once the
power supply is turned on, thousands of direct current, or DC, impulses per
second cross the gap, beginning the erosion process. The spark temperatures
generated can range from 14,000 degrees to 21,000 degrees Fahrenheit. As the
erosion continues, the electrode advances into the work while maintaining a
constant gap dimension.
[0576] Preferably, the wire EDM method is preferred for comb manufacture.
The wire method uses a consumable, electrically charged wire as an electrode
to make intricate cuts as it moves in preset patterns around the workpiece.
[0577] When walls are too thin, any rough edges on the tines may tear the
walls entering or exiting during broaching. Accordingly, the combs are be
polished to remove any burrs or sharp edges that could catch on the fibers.
Cutting and polishing the combs can generate heat, which may warp the comb.
A tolerance is preferably maintained of approximately 0.0001 inches in order
to insure the hole generated is parallel and not ruptured.
[0578] The combs used for broaching comprise a plurality of tines. Tine
length, width, thickness, and shape may be varied according to the desired
attributes of the channels. Referring to FIG. 16, the dimensions of a comb
1600 are shown according to an embodiment of the present invention. The
comb 1600 is approximately 6.000 inches long and 0.0308 inches wide. The
comb 1600 comprises a base 1610 from which a plurality of tines 1620 extend.
The base 1610 is 0.4375 inches high. The plurality of tines 1620 are 1.250
inches long and 0.0308 inches wide, and spaced by 0.010 inches.
Laser Machining
[0579] Other methods include diode-pumped solid-state laser ("DPSSL")
drilling; chemical lasers, e.g., COi, electron beam ("EB") drilling; or
electrode
drilling machines ("EDM"), or utilizing other methods known to one of
ordinary skill in the art. Any laser suitable for cutting the material of the
combs may be used.
[0580] The substrate may be cut using laser drilling, such as DPSSL drilling.
This method drills with a laser programmed using a CAD program. The CAD
139
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
program is loaded into a CAM program. The laser cuts with oxygen or,
preferably, nitrogen in fine pulses. The DPSSL allows channels to be cut at a
rate of about 2,000 channels per minute. In one embodiment, the channels
have an approximate diameter of 100 nanometers. Laser drilling may be
employed using known techniques and methods as disclosed in U.S. Patent
No. 4,686,128, the teachings of which are incorporated herein by reference in
their entirety. In one embodiment, the process uses laser drilling to prepare
channels having a depth (or length) of about 0.5 inch or less.
[0581] In one embodiment, the channels produced are large enough for the
particulates to enter but small enough that the majority of the particulates
are
removed from the exhaust gas flow.
[0582] In addition, in one embodiment, the substrate material is about ninety-
seven porous, which means that there is a tremendous amount of room for
gases to pass through the substrate. This large porosity also provides an
additional surface area for the particulate to deposit onto.
[0583] Pulsed Lasers
Gator Series G355-3 G532-5 G532-10
Wavelength 355 532 1064 nm
Average Output Power3 5 10 W
Pulse Repetition Rate z' 0-15,000 0-15,000 0-15,000 Hz
Pulse Energy 0.3 0.5 1 mJ
Pulse Duration (FWHM) "
15 3 15 3 15 -
3 ns
Beam Diameter (1/e2) " 1.0* 1.0 0.7 mm
Spatial Mode TEMOO TEMoo TEMoo
M2,)
<1.2 <1.2 <1.2
[0584] 1) Measured at 10 kHz reptition rate;
140
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0585] 2) Externally triggered from 0-15,000 Hz (attenuated power).
Internally triggered from 7500 Hz to 15,000 Hz. Real Random Firing Mode
for external triggering between 0 and 15,000 Hz in full power mode is
optional; 3) Gator lasers utilize a closed loop water system for temperature
control..
[0586] Preferably, the substrate material is substantially free of impurities,
such as carbon, when being machined by a laser.
Molding Holes
[0587] In an alternative embodiment, the substrate of the present invention is
prepared with channels preformed in the billet. In this embodiment, the use of
channel formers produces channels in the billet. The channel formers are rods
having a suitable size and shape to form a desired channel when the green
billet is formed.
[0588] Various types of material can be used for said channel formers. For
example, the channel formers may be a strong durable material, such as metal
or polymer that is able to withstand the temperatures of the drying process.
Once the green billet or the final billet is formed, the rods are removed to
leave the channels. The channels may be further machined as described
above.
[0589] Alternatively, in other embodiments, the rods are made of a material
that can evaporate or disintegrate upon exposure to a suitable source of
radiation or heat, such as laser or heat. In another embodiment, the channel
formers are made of carbon, carbon derivatives, or the like.
Specific Embodiments
[0590] In certain embodiments, the channels are drilled using a CNC drill,
which is computer controlled to maintain uniformity, as described below. The
drilling process is performed under a constant water shower to prevent dust
from becoming airborne, which is an OSHA hazard, and may get into the
bearings of the drill and destroy it.
[0591] The drilled substrate is optionally oven dried to drive or bake off any
water or other liquid that may reside in the pore space before any catalytic
141
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
applications. Baking time is not critical. A sufficient time is used to remove
the majority or substantially all water. Evaporation of the water can be
determined by simply weighing the substrate. Baking time primarily speeds
up the dewatering process. After heating the filter element for several
different intervals, the weight will level off and the substrate is ready for
any
catalyst or coating application.
[0592] In a preferred embodiment, the channels of the substrate are first
prepared by drilling and then shaped using the comb method. Due to the low
heat conductance nature of preferred substrates, when the substrate is
drilled,
most heat generated during drilling and cutting process is reflected back at
the
drill bit and away from the substrate. For this reason, the drill bits may
absorb
some of the heat and expand, overheat, and/or melt. Preferably, cooling the
drill bit is performed, preferably with water. In another embodiment, the
drill
operated at a reduced drill speed, e.g., 200 RPM, to minimize the generation
of
heat. Of course, other drill speeds, both faster and slower are suitable. In
another preferred embodiment, the drilling uses two or four or six faceted
drills with modified twists and head (drill tip) configurations
[0593] Additionally, in a preferred embodiment, the channel is drilled over a
plurality of drilling attempts. For example, a channel that is about one inch
in
length may be prepared by drilling into the substrate at depths of about 0.1
inch at a time until the final length is attained. The channel can be cleared
of
drilled substrate material between drilling attempts.
[0594] Center-punching and pilot holes
[0595] Pecking methodology is utilized because vacuuming of cut fibers must
be removed
[0596] In a preferred embodiment, the blind channels were drilled a fraction
deeper than our intended depth to allow the fibers to be packed into that
extra
area during the combing process. The combs were programmed to go the
depth of the wall flow configuration indicated and that extra void
accommodates any loose substrate material remaining in the channels.
142
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Product by Process
[0597] In another embodiment, the present invention is directed to a product
prepared according to the process described herein. Specifically, the
invention
is directed to a catalytic substrate prepared according to any one of the
specific
embodiments described herein. In another aspect, the present invention is
directed to a filtering substrate prepared according to any one of the
specific
embodiments described herein.
Applications
[0598] Various embodiments and applications of the invention are discussed
below. These example applications are discussed for illustrative purposes
only and are not limiting of the scope of the invention. Any of the
embodiments of the catalytic substrate and filtering substrate described above
can be used in the various applications.
Catalytic Converter
[0599] In another embodiment, the present invention is directed to a catalytic
converter comprising a catalytic substrate of the present invention. The
catalytic converter of the present invention can be used in an engine exhaust
system in a similar manner in which known catalytic converters are used. Of
course, the catalytic converter of the present invention has advantages over
prior art catalytic converters. Because of these advantages, the catalytic
converter can be used in ways in which known catalytic converters cannot be
used.
[0600] Any of the specific embodiments of the substrate of the invention, as
described above, may used in one or more of the specific applications, e.g.,
catalytic converters. In a specific embodiment, the catalytic converter
comprises a catalytic substrate of the present invention; a matting
surrounding
said catalytic substrate; and a canister, preferably a metal canister; and
optionally further comprises a washcoat, and optionally further comprises
[0601] Another aspect of the present invention is directed to a catalytic
converter that is position in or adjacent to the exhaust manifold of an
exhaust
143
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
system of the engine, said converter comprising a catalytic substrate of the
present invention. Such a catalytic converter is referred to as a manifold
catalytic converter (other terms include mani-cat, manifold converter, and the
like). A mani-cat of the present invention includes mani-cats known in the
art,
wherein the catalytic substrate of the present invention is used in place of
the
prior art substrate. Such mani-cats are disclosed in, e.g., U.S. Patent Nos.
6,605,259; and 5,692,373.
[0602] In another embodiment, the invention is directed to an improved
catalytic converter, the improvement comprising the novel substrate as
described herein. Any one of the specific embodiments of the substrate can be
used in the improved catalytic converter.
[0603] In another embodiment, the invention is directed to an improved
catalytic converter for treating internal combustion engine exhaust comprising
a substrate, a metal oxide washcoat, and at least one catalyst adhered to the
metal oxide particles, the improvement comprising the substrate comprising a
nSiRF-C composite and a catalytic metal.
[0604] In another embodiment, the invention is directed to an improved
catalytic converter for treating internal combustion engine exhaust comprising
a substrate, a metal oxide washcoat, and at least one catalyst adhered to the
metal oxide particles, the improvement comprising the substrate comprising a
nSiRF-C composite and a catalytic metal.
[0605] In another embodiment, the invention is directed to an improved
catalytic converter for treating internal combustion engine exhaust comprising
a substrate, a metal oxide washcoat, and at least one catalyst adhered to the
metal oxide particles, the improvement comprising the substrate comprising an
AETB composite
[0606] In another embodiment, the present invention is directed to a main-cat
having a catalytic substrate comprising a nSiRF-C composite and a catalyst.
The main-cat (sometimes referred to as an underfloor catalytic converter) is
located partially or totally within the head of an engine. In one embodiment,
the main-cat comprises a catalytic substrate of the present invention, wherein
said substrate has a density of about 12 lb/ft3, has a porosity of about 97%,
has
a low thermal expansion, has a high structural integrity, and has low heat
conductance. In a preferred embodiment, the main-cat comprises about 600
144
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
cpsi and having a wall thickness of about 6 mils. The main-cat in this
embodiment has a wall-flow configuration. In a preferred embodiment, the
main-cat has a channel shape of substantially box (varying lengths through the
substrate) with substantially square openings (or holes). In a preferred
embodiment, the catalytic substrate of the main-cat is made using the comb
method. Additionally, in this embodiment, the catalytic substrate comprises
an alumina washcoat. In this embodiment, the main-cat is capable of
catalyzing both oxidation and reduction of pollutants, e.g., it has a catalyst
capable of oxidizing pollutants and it has a catalyst capable of reducing
pollutants. The canister of the main-cat is prepared by a swagging method. In
a preferred embodiment, the main-cat comprises two substrate units. The
main-cat, in certain embodiments is used alone, or alternatively is used in
combination with a pre-cat. In a preferred embodiment, the main-cat
comprises an intumescent matting. The main-cat can be used in all internal
combustion engines. The main-cat can be used with fuel-borne catalysts.
Moreover, the substrate of the main cat may be protection enhanced
[0607] The main catalytic converter of the present invention, as described
above, is also used, in certain embodiments with one or more aftertreatment
systems. Such aftertreatment systems include an NOx adsorber, a HC
adsorber, a SCR systems, and the like
[0608] Furthermore an embodiment having the same or similar configurations
and attributes as the main catalytic converter described above can be used for
a membrane catalyst. The membrane catalyst comprises a catalytic substrate
having a membrane configuration as described above.
[0609] In another embodiment, the present invention is directed to a head-cat
having a catalytic substrate comprising a nSiRF-C composite and a catalyst.
The head-cat is located partially or totally within the head of an engine. In
one
embodiment, the head-cat comprises a catalytic substrate of the present
invention, wherein said substrate has a density of about 12 lb/ft3, has a
porosity of about 97%, has a low thermal expansion, has high structural
integrity, and has low heat conductance. In a preferred embodiment, the head-
cat comprises about 600 cpsi and having a wall thickness of about 6 mils. The
head-cat in this embodiment has wall-flow configuration. In a preferred
embodiment, the head-cat has a channel shape of substantially pyramidal with
145
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
substantially square openings (or holes). In a preferred embodiment, the
catalytic substrate of the head-cat is made using the comb method. In this
embodiment, the head-cat is capable of catalyzing both oxidation and
reduction of pollutants, e.g., it has a catalyst capable of oxidizing
pollutants
and it has a catalyst capable of reducing pollutants. The head-cat, in certain
embodiments is used alone, or alternatively is used in combination with a pre-
cat. In a preferred embodiment, the head-cat comprises a hybrid matting. The
head-cat can be used in all internal combustion engines. The head-cat can be
used with fuel-borne catalysts.
[0610] One or more head cats can be used with the same engine. The use of a
head cat in accordance with the present invention would also have one or more
of the following advantages: reduce weight of the under-floor exhaust system;
increased filtration of exhaust particulate matter that an intercooler would
otherwise pick up, thereby improving the life of inter-cooler; no matting is
required; rattling sounds in heat shields reduced; reduced muffler size;
enhanced burn-off of particulate matter; in case of a failure of one head cat,
in
certain embodiments, the exhaust gas would still be effectively treated with
the other functioning head cats, e.g., the other three on a 4-cyclinder
engine.
Head-cats are advantageous for boats, watercraft, motorcycles, small handheld
engines, leaf-blowers, and related engines, and in other applications in which
a
nonexposed catalytic converter is preferred.
[0611] In another embodiment, a catalytic converter of the present invention
could be placed between the head and the exhaust manifold as shown in
Figure 41. In this embodiment, the catalytic converter section is placed
between the engine head and the exhaust manifold. An advantage over
conventional systems is that the converter is very close to the combustion
chamber, thus increasing efficiency. For instance, this embodiment could put
these on the Ford 4.6 liter and it would fit all of their engines. This in
turn
means that it would fit on the Ford Explorer, Mustang, Crown Victoria,
Econoline, 150/250/350 pickup, Expedition, and every other product that Ford
puts the engine on, such as Lincoln products. It would also fit in certain
embodiments on the various model years that used it those many years. That
one 4.6 casting would be useful for millions of vehicles in the U.S. alone. It
is
also friendly for the oxygen sensors to go into as well.
146
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0612] In another embodiment, the present invention is directed to a back-cat
having a catalytic substrate comprising a nSiRF-C composite and a catalyst. In
another embodiment, the catalytic converter of the present invention is a back-
cat. The back-cat is located after the main catalytic converter. In one
embodiment, the back-cat comprises a catalytic substrate of the present
invention, wherein said substrate has a density of about 12 lb/ft3, has a
porosity of about 97%, has a low thermal expansion, has high structural
integrity, and has low heat conductance. In a preferred embodiment, the back-
cat comprises about 600 cpsi and having a wall thickness of about 6 mils. The
back-cat in this embodiment has wall-flow configuration. In a preferred
embodiment, the catalytic substrate of the back-cat is made using the comb
method. In a preferred embodiment, the back-cat has channel holes of varying
shapes, including triangular, square, and hexagonal. Likewise the channel
shape can vary. In this embodiment, the back-cat is capable of catalyzing both
oxidation and reduction of pollutants, e.g., it has a catalyst capable of
oxidizing pollutants and it has a catalyst capable of reducing pollutants. The
back-cat, in certain embodiments is used alone, or alternatively is used in
combination with a pre-cat. In a preferred embodiment, the back-cat
comprises a non-intumescent matting. The back-cat can be used in all internal
combustion engines. In another embodiment, the back-cat is used in
conjunction without fuel-borne catalysts. Generally, the back-cat of the
embodiment is place near the standard muffler location, although other
locations are possible. In an alternative embodiment, the back-cat is
integrated into a muffler. Such an embodiment may comprise: a) the substrate
itself acting as and replacing a muffler, or b) the substrate is placed inside
the
typical metal muffler assembly so it is integrated into the muffler.
[0613] In another embodiment, the invention is directed to a diesel oxidation
catalyst (DOC), wherein the substrate of the DOC is a catalytic substrate as
described herein. In a preferred embodiment, the substrate of the DOC of the
invention is an AEBT or an OCBT, preferably AEBT-10, AEBT-12, AEBT-
16, or OCBT-10. The embodiment of the DOC has a catalyst selected from
the group consisting of palladium, platinum, rhodium, mixtures thereof, and
derivatives thereof.
147
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0614] Other suitable embodiments include a catalyzed DPF comprising a
catalytic substrate of the present invention, preferably the substrate
comprising
an AETB material such as AEBT-12, and further comprising a catalyst.
Particulate Filter (DPF, DPT)
[0615] In another embodiment, the present invention is directed to a
particulate filter comprising a catalytic substrate of the present invention.
The
particulate filter of the present invention can be used in an engine exhaust
system in a similar manner in which known catalytic converters are used. Of
course, the particulate filter of the present invention has advantages over
prior
art catalytic converters. Because of these advantages, the catalytic converter
can be used in ways in which known catalytic converters cannot be used.
[0616] In another embodiment, the invention is directed to an improved
particulate filter, the improvement comprising the novel substrate as
described
herein. Any one of the specific embodiments of the substrate can be used in
the improved particulate filter.
[0617] In another embodiment, the invention is directed to an improved
particulate filter for treating internal combustion engine exhaust comprising
a
filtering substrate, the improvement comprising the substrate comprising a
nSiRF-C composite having a plurality of channels extending into and
optionally through the substrate. The configuration of the channels can vary
as provided for above.
[0618] In another embodiment, the invention is directed to an improved
particulate filter for treating internal combustion engine exhaust comprising
a
filtering substrate, the improvement comprising the substrate comprising a
nSiRF-C composite having about 100 to about 1000, preferably about 600
channels extending partially through the substrate, and wherein said substrate
has a wall-flow configuration.
[0619] In another embodiment, the invention is directed to an improved
particulate filter for treating internal combustion engine exhaust comprising
a
substrate, and a metal oxide washcoat, the improvement comprising the
substrate comprising AETB.
148
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0620] In another embodiment, the present invention is directed to a diesel
particulate filter (DPF) having a filtering substrate comprising a nSiRF-C
composite as described above. The filtering substrate is configured to be
suitable for use in the DPF. The DPF is located partially or totally within
the
head of an engine. In one embodiment, the DPF comprises a filtering
substrate of the present invention, wherein said substrate has a density of
about 12 lb/ft3, has a porosity of about 97%, has a low thermal expansion, has
a high structural integrity, has low heat conductance. In a preferred
embodiment, the main-cat comprises about 600 cpsi and having a wall
thickness of about 6 mils. The main-cat in this embodiment has wall-flow
configuration. In a preferred embodiment, the main-cat has a channel shape of
substantially box (varying lengths through the substrate) with substantially
square openings (or holes). In a preferred embodiment, the catalytic substrate
of the main-cat is made using the comb method. Additionally, in this
embodiment, the catalytic substrate comprises an alumina washcoat. In this
embodiment, the main-cat is capable of catalyzing both oxidation and
reduction of pollutants, e.g., it has a catalyst capable of oxidizing
pollutants
and it has a catalyst capable of reducing pollutants. The canister of the main-
cat is prepared by a swagging method. In a preferred embodiment, the main-
cat comprises two substrate units. The main-cat, in certain embodiments is
used alone, or alternatively is used in combination with a pre-cat. In a
preferred embodiment, the main-cat comprises an intumescent matting. The
main-cat can be used in all internal combustion engines. The main-cat can be
used with fuel-borne catalysts. Moreover, the substrate of the main cat may be
protection enhanced. The protection coating may be applied to the inside or to
the external surface of the substrate.
Canning Types
[0621] The catalytic converter of the present invention has a canister. The
canister can be prepared according to known methods in the art. Furthermore,
the canister of the catalytic converter or particulate filter of the present
invention may use materials known in the art, e.g., steel, to make the
canister.
149
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0622] In a preferred embodiment, the catalytic converter of the present
invention has an exit pipe that can be attached to a tailpipe of commercially
available vehicles. Preferably, the catalyst converter fits tailpipes having a
diameter of about 21/2 or 3 inches.
[0623] For example, suitable canisters include those made according to any
one of the following methods: clamshell, tourniquet, shoebox, stuffing, and
swaging. The above canning methods utilize two different gap control
mechanisms: (1) fixed gap and (2) fixed canning force. From the welding
process perspective, the methods produce converters with one or two seams.
These classifications are illustrated in Table 4 (Rajadurai 1999).
Fixed Gap Fixed Force
Single Seam Stuffing, Swaging Tourniquet
Dual Seam Clam Shell Shoebox
[0624] Closing the can using a fixed force offers a more accurate gap density
control by eliminating the dimensional tolerance influence of the substrate,
can, and the mat itself. Closing the can to a fixed gap has the advantage of
producing a converter of fixed final dimensions, which simplifies the
converter design, primarily in respect to welding of cones to the finished
can.
[0625] The single seam design is usually preferred for round or oval
converters of low aspect ratios, where it can provide uniform gap density
distribution. Single seam shells also provide more manufacturing flexibility
and require less expensive tooling. The dual seam design is usually required
for oval converters with high aspect ratios. In this case, reinforcing ribs
are
stamped in the shell to prevent its deformation and the resulting gap
nonuniformity. The dual seam shells are produced in stamping processes
which require very expensive tooling and have to be justified by high
production volumes.
Clamshell
[0626] In one embodiment, the catalytic converter of the present invention
comprises a canister made with the clamshell technique. In another
150
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
embodiment, the particulate filter comprises a canister made with a clamshell
technique. In North America, clamshell has been traditionally the most
common design of the underfloor converter in passenger cars and light trucks.
Construction of a clamshell catalytic converter is illustrated in Figure 6.
The
ceramic catalyst substrate(s) is wrapped in the mat and placed in the bottom
part of the shell. Then, another symmetrical part of the shell is placed on
the
top, pressed together and welded.
[0627] Tongue and groove design is used for the mounting mat to avoid
bypassing of the substrate by exhaust gases. The converter illustrated above
also includes end seals. The seals are used here to protect the mat against
gas
impingement and erosion, rather than to prevent leaks. Most converters which
utilize mats do not have end seals. Whenever wire mesh mount is used instead
of the mat the end seals are required, at least at the inlet face of the
substrate.
[0628] Clamshell converters are often equipped with external heat shields.
Internally insulated designs were also developed, with the inside of clamshell
stampings lined with an extra layer of thermal insulation.
[0629] Older designs of catalytic converters included support rings or deep
pockets in the clamshell stampings to prevent axial movement of the substrate
within the can. In a properly designed converter, which utilizes intumescent
mats of high holding pressures, such measures are not required. There are
many automotive converters without axial support of the substrate, which still
show an impressive durability record. However, the axial support may be
required for larger and heavier substrates or when non-intumescent mats of
lower holding pressure are used. Another consideration is the erosion of mat.
The converter shell profiles or end cones should be designed in such a way as
to shelter the mat from direct impingement of hot exhaust gases. Some
converter manufacturers impregnate mat edges, which are exposed to the gas,
with chemicals to improve their erosion resistance. High holding pressures in
modern converters also improve the mat resistance to erosion.
[0630] Dual monolith converters are used in many automotive applications.
Two or more monoliths may be used due to monolith length manufacturing
constraints or to combine catalysts of different specifications in one
converter.
In most dual monolith converters the substrates are separated by space, which
is maintained by forming separate pockets in the clamshell stamping. In some
151
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
designs, the space between substrates is maintained by a metal or ceramic
ring.
A butted monolith position, with no space in between, is also possible. The
butted design, which offers less pressure drop than the spaced design, has
been
used in some commercial converters for gasoline engines (Kuisell, R.C., 1996,
"Butting Monoliths in Catalytic Converters," SAE 960555).
[0631] The converter shell geometry has to provide the required mat
compression. The clamshell profiles include stamped reinforcing ribs in order
to provide the necessary stiffness and uniform pressure distribution. This is
especially important for flat oval catalyst substrates. Care should be taken
while designing the ribs that no excessive pressure areas exist which could
cause damage to the substrate or the mat. The clamshell method puts high
requirements on the dimensional tolerances of the monoliths, as well as the
clamshell stampings. The mat compression during clamshell canning proceeds
until the half-shells close, producing a certain gap thickness. The gap
thickness is determined by the dimensions of the monolith and of the shell.
Therefore, any variations in the size of monoliths result in variations in the
mat density and, consequently, in the canning pressure that may cause
converter durability problems.
[0632] Tourniquet is the most common method which allows direct control of
the mounting pressure during canning process. Since tourniquet is insensitive
to dimensional differences which may occur among the substrate monoliths, it
is capable of producing the most robust catalytic converters. In practice, the
tourniquet method is limited to round or close-to-round catalyst substrate
cross-sections. Its suitability to oval or flat-oval automotive converters
that are
used in the underfloor position is very limited. Tourniquet was once more
popular among car makers in Europe, but it became more common in North
America as automotive converters migrated from the underfloor location to the
engine close-coupled position. Tourniquet is also suitable for large diameter
catalytic converters for heavy-duty diesel engines. A tourniquet catalytic
converter is shown in
[0633] In the tourniquet technique the substrate is first wrapped in a tongue-
and-groove shaped mat. Then, the wrapped monolith is placed inside a
longitudinally split can. The can is fabricated by rolling a rectangular piece
of
sheet metal. The part of the rectangle which goes underneath the overlap is
152
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
usually tapered. In some designs the overlapping part of the can is formed,
through an additional stamping operation, into a protruding lip to provide
space for the can edge underneath the overlap. Such design prevents the inside
edge of the can from cutting into the mat or creating a local pressure buildup
which may damage the canned part, especially when thin mats are used. Next,
the can with the wrapped monolith is placed in the tourniquet machine which
applies a controlled force to the assembly. The can is tack welded when still
under pressure, removed from the machine and seam welded. A push-out test
is sometimes carried out as a quality assurance measure. Axial monolith
displacement caused by applying a controlled force is measured in a special
test apparatus. Finally, the converter headers or end cones, as well as
flanges
and/or ports, are welded to the converter body in a separate operation. The
final assembly may be tested for weld quality by pressurizing with air while
submerged in water.
[0634] The tourniquet machine includes a loop of a steel band that applies the
force to canned parts. One end of the loop is attached rigidly to the machine
while the other is pulled by a pneumatic or hydraulic actuator. In some
machines vibration is applied during canning to minimize the closing force
and to assure more uniform distribution of pressure.
[0635] The actual required canning force to achieve a target mount density for
a given mat can be determined through a series of tests. Several converters
should be closed using different closing forces. The canning force that
produced the desired mat density should be selected. Due to mat pressure
relaxation, it is important that the tourniquet machine produces repeatable
closing speed and time patterns. After the target closing force is reached,
the
machine should maintain the can at constant position, to allow for tack
welding, rather than at constant force. Applying constant force to the can as
the mat pressure relaxes would cause over-compression of the mat.
[0636] The shoebox technique utilizes a split, two part shell similar to the
clamshell method. The shell, however, is closed under fixed force with the
edges of one of the half-shells overlapping those of the other. Therefore, the
shoebox offers the robust packaging benefits of tourniquet in respect to its
insensitivity to dimensional tolerances of the substrate.
153
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0637] Reinforcing ribs can be stamped on the shoebox shells. Thus, this
technique allows for canning of flat-oval substrates in cases where tourniquet
would be inadequate.
Stuffing
[0638] In the stuffing technique, the mat wrapped monolith is pushed into a
cylindrical can. The can is usually made of a section of tube but it can also
be
rolled of sheet metal and welded. Non-cylindrical shapes (e.g., trapezoidal)
are also possible. This method is applicable to both small sized passenger car
converters and large converters for heavy duty engines. A stuffing cone is
used to facilitate smooth insertion of the monolith (Li, F.Z., 2000, "The
Assembly Deformation and Pressure of Stuffed Catalytic Converter
Accounting for the Hysteresis Behavior of Pressure vs. Density Curve of the
Intumescent Mat", SAE 2000-01-0223), as shown in the figure. After
completing the operation, the end cones are welded to each end of the cylinder
to complete the can assembly.
[0639] Although stuffed converters have similar appearance to the tourniquet
assemblies, the actual mechanism of substrate holding is the same as in the
clamshell design. In particular, the mat mounting pressure is determined by
geometrical dimensions of the shell and of the monolith. As a consequence,
high repeatability of substrate diameters is required when stuffing technique
is
used.
[0640] A modification of the stuffing technique-termed SoftMount
Technology-has been proposed by Corning (Eisenstock, G., et al., 2002,
"Evaluation of SoftMount Technology for Use in Packaging Ultra Thinwall
Ceramic Substrates", SAE 2002-01-1097). The objective was to minimize the
peak mat pressure during stuffing to allow for canning of ultra-thin wall
substrates characterized by lower strength. The key idea is to employ a
tapered
cylindrical tool called an arbor, positioned ahead of the substrate, to take
the
peak pressure response of the mat during insertion.
[0641] In the SoftMount method, the mat is first inserted into the can where
it
is held on a flange during the process. Then, the mat-lined can is pushed down
over the arbor and the substrate (i.e., the arbor is positioned on the
substrate).
154
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
The arbor is chamfered inward at the end to slip easily into the can-mat
assembly. The arbor compresses the mat against the can as it moves through.
As the substrate moves into position replacing the arbor in the can, it is not
exposed to the instantaneous peak loads required to compress the mat.
Swaging
[0642] In swaged converters, the converter shell is machined down to the
desired diameter after the mat-wrapped substrate has been inserted. Swaging is
a newer packaging technique, performed in fully automated, CNC-controlled
equipment suitable for high volume production for passenger car applications.
Swaged converters can be manufactured from one section of tube together
with their end cones, which are obtained in a spin forming process in the same
production machine.
[0643] The gap control mechanism can be classified as constant gap thickness,
as it is the case with stuffing, but CNC-controlled production lines can
automatically account for differences in the substrate diameter. Swaged
converters must be initially formed to diameters slightly less than the target
diameter of finished product, to allow the shell to "spring back" after
machining. This is a disadvantage of this method, which may lead to excessive
peak pressures and substrate damage during canning.
[0644] Catalytic converter headers provide the transition between the inlet
and
outlet pipes and the substrate cross-section. Most converter headers are
shaped as cones or funnels with axial gas flow. Other designs, such as
truncated headers (Wendland, D.W., et al., 1992, "Effect of Header Truncation
on Monolith Converter Emission Control Performance", SAE 922340) or
headers with tangential gas inlet are possible but uncommon. The function of
the inlet header is to diffuse the inlet flow, i.e., to decrease the gas
velocity
and increase its static pressure with as little loss in total pressure as
possible.
In practice, combined header losses can constitute from 10% to 50% of the
overall converter pressure drop, depending on geometry and flow conditions.
These pressure losses can be minimized by designing converter inlet headers
which would provide more uniform flow distribution. There is also a notion
that uniform flow distribution in a catalytic converter improves its emission
155
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
performance and/or durability. In one embodiment of the present invention,
the catalytic converter or particulate filter has a header having an angle of
about 30%.
Matting
[0645] A catalytic converter or particulate filter of the present invention
also
optionally comprises a matting. Any of the embodiments recited above or
below may comprise a matting. In certain embodiments, the present invention
further comprises a mat (or matting or batting). For example, a catalytic
converter of the present invention, in an embodiment, comprises a catalytic
substrate as described above, a mat, and a canister. Mats useful for use in
the
present invention are known in the art.
[0646] A mat in certain embodiments can be selected based on a number of
attributes as described herein and known in the art. The catalytic converter
canister is preferably designed in such a way as to provide the required
mounting pressure for a given catalytic substrate and a given mat. The
mounting pressure of the mat increases exponentially during the compression
from its initial bulk density to the final target density. The mounting
pressure
exhibits viscoelastic relaxation, i.e., the peak initial pressure that occurs
at the
canning decreases significantly during the first seconds or minutes thereafter
due to the realignment of mat fibers (Myers 2000). The mounting pressure loss
of intumescent mats due to the relaxation varies between 30 and 60% of the
initial peak mounting pressure.
[0647] Due to the mat relaxation, as well as later in-service pressure losses,
the mounting pressure is not a convenient parameter for the canning process
specification. Instead, the mounting density-often called the gap bulk
density (GBD)-is commonly used for that purpose. Typical mat mounting
densities along with their bulk (uncompressed) densities, are listed in Table
2.
The exact density for a given application should be consulted with the mat
manufacturer. The exact density for a given application should be consulted
with the mat manufacturer. called basis weight. The weight/area is expressed
in g/mZ or kg/m2 (since these are units of mass rather than weight, the
customary term "weight/area" should be, strictly speaking, replaced by
156
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
"mass/area"). Available mats have their weight/area in the range from 1050 to
6200 g/m2 and uncompressed thickness between 1.5 and 10 mm. Intumescent
mats of 3000 - 4000 g/m2 are typically used for automotive converters. Higher
mat weights, such as 6200 g/m' (6.2 kg/m''), are recommended for more
demanding applications or for large converters.
[0648] Another important property of catalytic converter mounting mats is
their weight/area ratio, sometimes also called basis weight. The weight/area
is
expressed in g/m2 or kg/m2 (since these are units of mass rather than weight,
the customary term "weight/area" should be, strictly speaking, replaced by
"mass/area"). Available mats have their weight/area in the range from 1050 to
6200 g/m2 and uncompressed thickness between 1.5 and 10 mm. Intumescent
mats of 3000 - 4000 g/m2 are typically used for automotive converters. Higher
mat weights, such as 6200 g/mZ (6.2 kg/m2), are recommended for more
demanding applications or for large converters.
[0649] Packaging mats can undergo erosion caused by the impingement of hot
exhaust gases. Resistance to erosion is an important characteristic of the
mat.
The resistance to erosion depends strongly on gap bulk density. (Rajadurai,
S.,
et al., 1999. "Single Seam Stuffed Converter Design for Thinwall Substrates",
SAE 1999-01-3628).
[0650] Many other attributes of the mounting mats are specified and/or tested
and are available from mat manufacturers. The list of these attributes
includes
thermal conductivity, gas sealing attributes, friction coefficients, and more.
[0651] During the design of a mounting system, the following considerations,
in certain embodiments, are accounted for:
[0652] Mounting Pressure: Assuming that the mounting mat is the sole means
of connecting the substrate to the shell (i.e., the converter has no end seals
or
support rings), the mechanical connection is provided by the radial pressure
in
combination with friction at the mat surface. Mounting pressure is the
minimum pressure required to hold the substrate in place.
[0653] Peak Mounting Pressure. As mentioned earlier, mats behave like
viscoelastic solids, producing high peak mounting pressures during initial
compression, followed by a gradual relaxation to reach the residual mounting
pressure. In thin wall substrates, the peak pressures may cause damage to the
catalyst core during packaging. The transient behavior of mats has to be also
157
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
considered when designing canning methods that rely on constant force, as
opposed to constant gap size, such as tourniquet.
[0654] Temperature Behavior. For intumescent mats, the mat pressure
depends upon achieving sufficient temperature to activate the vermiculite. An
inlet temperature of at least 500 C is required for vermiculite activation;
higher inlet temperatures may be needed, depending on heat transfer
conditions in the particular system. In gasoline applications, the mat is
activated on the vehicle during the initial hours of engine operation. Oven-
treatment of catalytic converters may be required in diesel applications,
where
the exhaust gas temperature may never reach sufficient levels during regular
vehicle operation. Vermiculite expansion is in part reversible, causing the
mat
to expand as temperatures increase and contract when the converter is cooled
down. This property of vermiculite more than compensates for the expansion
of converter shell, producing very high mounting pressures at higher
temperatures. In contrast, non-intumescent mats show approximately constant
mounting pressure across the temperature range. The slight decrease of the
pressure with increasing temperature visible in Figure 4 can be attributed to
gap expansion due to the thermal expansion of the converter shell. At
temperatures above 500 C, intumescent mats provide higher holding pressures
than non-intumescent mats. However, at temperatures below 500 C, the
mounting pressure from intumescent mats is actually much less than that from
non-intumescent mat. Therefore, non-intumescent mats are the preferred
mounting material in many diesel applications where the converter inlet
temperature remains below 500 C. Intumescent mats of reduced vermiculite
content produce mounting pressures between the conventional intumescent
mats and non-intumescent mats. Hybrid mats show pressure levels similar to
non-intumescent mats, but they maintain a certain pressure boost at high
temperature, which counteracts the gap expansion.
[0655] Gap Expansion. When the converter is exposed to high temperature,
the gap thiclcness increases due to the differences in thermal expansion
coefficients between the substrate and the shell. The thermal expansion of the
gap can be a significant source of mounting pressure loss. The gap expansion
is especially critical in applications where non-intumescent mats are used, as
it
cannot be compensated by vermiculite expansion. As a design guideline, the
158
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
gap expansion should be kept below 10% (Olson, J.R., 2004, "Diesel Emission
Control Devices - Design Factors Affecting Mounting Mat Selection," SAE
2004-01-1420).
[0656] Gap expansion depends on the following design factors:
[0657] Substrate diameter: larger substrates result in higher percentage gap
expansion. Therefore, gap expansion can be still a problem in heavy-duty
diesel applications, despite the relatively low converter temperature.
[0658] Gap thickness: thicker gaps result in less gap expansion.
[0659] Shell temperature: higher temperatures produce more gap expansion.
[0660] Shell material CTE: steels of higher thermal expansion coefficients
produce higher gap expansion. Therefore, the gap expansion is easier to
control using ferritic (as opposed to austenitic) steel grades.
[0661] Mat Aging. Once the converter is put in service, the intumescent mat
expands, causing an increase of mounting pressure. A number of other aging
factors are responsible for gradual irreversible loss of mounting pressure, as
follows: thermal cycling; vibration acceleration and other mechanical factors;
soaking of the mat by water (condensate, vehicle washing); and organic binder
burn-out when the mat is first heated.
Advantages and Disadvantages of Current Mats
[0662] Conventional applications utilize intumescent and non-intumescent
fibrous mats for mounting a honeycomb substrate in canisters, as exemplified
in European Patent Application No. EP0884459 to Locker and European
Patent Specification No. EP0912820 to Hwang. In accordance with one
conventional system, the fibrous mat only allows for mounting a larger
catalyst member in a canister.
Intumescent Mats
[0663] Intumescent mats were originally developed for gasoline converters.
By the early 1990's, they became the most common type of ceramic mat used
in catalytic converters for all internal combustion engine applications,
including diesel. Intumescent mats have the property of partly irreversible
expansion once exposed to high temperatures. Thermal expansion curves for
159
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the mats are available from several manufacturers including 3M and Unifrax.
Once expanded, they increase the holding pressure on the substrate providing
a very secure mounting system. Because of their temperature expansion
characteristics, intumescent mats can actually increase their mounting
pressures at high temperatures, compensating for the mounting pressure loss
due to the thermal expansion of the steel housing.
[0664] Intumescent mats are made of alumina-silica ceramic fibers and
contain vermiculite, which provides their thermal expansion. Typical
compositions have 30-50% of alumina-silica fibers, 40-60% of vermiculite,
and 4-9% of an organic binder (typically acrylic latex). After the converter
is
assembled, the mat has to be exposed to temperatures on the order of about
500 C to achieve the initial expansion, which is usually achieved on the
vehicle during the initial hours of engine operation. The organic mat binder,
which decomposes at high temperatures, is responsible for the characteristic
odor emitted when the mat is first heated.
[0665] The vermiculite component imposes relatively low maximum
operating temperature limits for intumescent mats. The mats lose their
holding pressure dramatically at temperatures of about 750 C. That
temperature is usually defined as the average mat temperature. Therefore,
mats can be used at higher exhaust temperatures provided there is a
temperature gradient across the mat due to heat losses from the outside
converter shell. The use of intumescent mats is limited in hot isothermal
applications where no heat loss occurs through the converter wall. Such
situations include catalysts mounted inside mufflers, e.g., for motorcycle
applications.
[0666] High content of the vermiculite component is also responsible for high
mounting pressures, especially at higher exhaust temperatures. The pressure
from intumescent mats was found to be excessive for ultra-thin wall
substrates, resulting in possible damage to the parts. For these applications,
mat manufacturers introduced reduced vermiculite intumescent mats
(sometimes referred to as "advanced" or "2nd generation" intumescent mats),
which provide less mounting pressure than the conventional design.
160
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Non-Intumescent Mats
[0667] Non-intumescent mats do not contain vermiculite. Therefore, they can
provide much higher temperature limits of about 1250 C. The main
component of non-intumescent mats is alumina fiber, with addition of organic
binders. In certain embodiments of the present invention, the catalytic
converter or particulate filter comprises a substrate as described herein and
a
non-intumescent mats may be better with fibrous materials.
[0668] The substrate support relies on built-in compression or fiber "spring,"
which supplies constant holding pressure across the application temperature
range. Since the converter shell expands with temperature, a decrease of the
effective converter mounting pressure is observed at higher temperatures.
Therefore, the non-intumescent mats, quite opposite to vermiculite mats, hold
the catalyst substrate most securely at low temperatures. As the temperature
increases, the substrate inside the converter is held with decreasing force.
[0669] Non-intumescent mats can be used not only in high temperature
applications which cannot withstand high mounting pressures (thin wall
substrates), but also in low temperature converters, such as those for diesel
engines. Since they are not dependant on the vermiculite expansion, they do
not require oven treatment in low temperature diesel converters.
Hybrid Mats
[0670] An improved catalytic converter or particulate filter of the present
invention may further comprise a hybrid mat. Such mats are known in the art.
A hybrid mat, in one embodiment, incorporate a two-layered design: a layer of
intumescent mat on top of a layer of non-intumescent mat. Their attributes
and performance are also in-between, with better low temperature mounting
pressure than intumescent mats, but higher high temperature pressure than
non-intumescent mats. In a preferred embodiment, the improved diesel
particulate filter of the present invention comprises a hybrid mat, for use in
both light- and heavy-duty applications.
161
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Wire Mesh
[0671] Knitted stainless steel wire mesh may be used instead of mats to
package ceramic catalyst substrates. Wire mesh is often considered to exhibit
less favorable mounting pressure characteristics than mats, but is still used
in
some catalytic converters (traditionally, wire mesh had been used by Ford).
End seals are always required with wire mesh to prevent bypassing of the
substrate by gas.
Auxiliary Heating Source
[0672] As another configuration or exemplary embodiment to those
previously disclosed, the filter element could include the addition of a
series of
electric heating rods added to the substrate after the catalyst is applied.
Preferably, the heating elements are applied after the catalyst to prevent the
curing process from harming any electrical contacts. In one embodiment, the
heating elements or rods are placed approximately 1/4 inch apart from each
edge or any distance that is desired. In certain embodiments, one could also
use a wire mesh configuration, or other heating element described herein, that
is placed perpendicular to the gas flow direction and installed during the
formation of the fiber blank. The electrical contacts could be protected with
Nextel fabric or a similar material. The heating elements could be activated
before an engine starts as a prewarmer and will remain in operation, either
partially or in full operation, until the exhaust temperature exceed the
temperatures achieved by auxiliary heating elements.
[0673] The use of auxiliary heating source applied to the filter foundation
may
be useful to increase the temperature inside of the filter foundation and/or
to
evenly distribute additional heat throughout the filter foundation making it
more efficient. The auxiliary heat source may be comprised of resistant
electric heating elements. The heating elements may have a rod configuration
which can be inserted after filter foundation formation or during the sol-gel
process. The filter foundation can have one or more electric heating elements
applied and the heating elements can be heated simultaneously, independently,
and in a cycled, patterned, or random series. The heating elements could be in
the form of a wire mesh configuration which can be inserted during or after
162
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the filter foundation formation. The filter can employ the use of a single
wire
mesh or a plurality of wire mesh heating elements and those heating elements
can be heated simultaneously or individually. Additionally, the mesh heating
elements can be heated in a cycled, patterned or random series. The heating
elements may also utilize rods, spirals or helical configurations inserted
during
or after formation. The filter foundation may incorporate one or more spiral
or
helical heating elements which may be heated simultaneously or
independently including the use of a cycled, patterned or random series.
Finally, the filter foundation may incorporate a combination of any of the
heating elements previously described.
[0674] In addition to the resistant electrical heating elements described
above
the auxiliary heat source may also use infra-red or microwave heat heating
elements. The various heat sources may be implemented inside of the filter
foundation itself or may be employed to heat the filter foundation as an
exterior heating element. Once again, various heat sources may be applied
independently or in combination with any of the other heating elements or
sources.
[0675] The filter foundation will be encased in a casing with sufficient
durability to protect the filter foundation from normal impacts encountered
with vehicle transportation. Such a casing may include a common metal
casing such as stainless steel, steel or another metal alloy. The material may
also be non-metallic including ceramic-based casings. The filter foundation
may be encapsulated in insulation or batting prior to being enclosed in the
casing. The present invention may also incorporate a heat shield.
[0676] The entry and exit tubes of the filter foundation may be coated with an
oxidation catalyst. The catalyst may make the radiation process quicker which
results in the system as a whole treating the exhaust in a much faster time.
The catalysts may be a noble metal catalysts including those which are
platinum, palladium, or are rhodium based, as well as others. The catalyst
may be applied directly to the filter foundation surface. Application of the
catalyst may be sprayed on, applied by dipping the filter foundation into a
solution or injected into the filter foundation itself. The use of an
oxidation
catalyst will promote the ignition of the particulate matter at a lower
163
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
temperature. In addition, a catalyst can also be used as a supplemental heater
within the filter foundation itself.
[0677] The exhaust filter system can be integrated with the engine exhaust
path including integration inside the exhaust manifold of the engine itself.
Because the filter foundation is so durable to heat and vibration it can be
placed immediately next to an engine exhaust as it exits the engine block. The
unique ability of the filter foundation to withstand high heat and increased
vibrational stress allows the placement of the present invention much closer
to
the engine. The close placement provides advantage over conventional
exhaust filters or catalytic converters which cannot withstand such high heat
or vibrational stress.
[0678] While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to those skilled in the art
that
various changes and modifications can be made therein without departing
from the spirit and scope thereof. Thus, it is intended that the present
invention cover the modifications and variations of this invention provided
they come within the scope of the appended claims and their equivalents.
Specific Embodiments of A Catalytic Converter
[0679] The catalytic converter and particulate filter of the present invention
are further illustrated by the following nonlimiting specific embodiments. A
number of specific embodiments recited herein exemplify but do not
necessarily limit the scope of the invention. A catalytic converter of the
present invention can be used on any number of engines and veliicles. Thus,
in one embodiment, a catalytic converter of the present invention is suitable
for use on a vehicle or engine produce by any one of the following
companies: Daimler-Chrysler; Chrysler; Dodge; Eagle; Jeep; Plymouth;
General Motors; AM General (e.g., HUMMERs); Buick; Cadillac; Chevrolet;
Geo; GMC; Hummer; LaSalle; Oldsmobile; Pontiac; Saturn; Ford;
Continental; Lincoln; Mercury; Ace Motor Corp; American Motors; Avanti
BMW; Daimler-Chrysler; Fiat; Ford; GAZ; General Motors; Honda;
Mitsubishi; Renault; Peugeot; Toyota; and Volkswagen Group. Others include
164
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Holden; Lightburn; Hartnett; Alpha Sports; Finch; Amuza; Australian Kitcar;
FPV; Bavariacars; Birchfield; G-Force; Bomac; Bullet; Homebush;
Carbontech; HSV; Classic Glass; Kraftwerkz; Classic Revival; Cobra Craft;
Piper; Daktari; PRB; Daytona; Python; Deuce Customs; RCM; Devaux; RMC;
DRB; Roaring Forties; Elfin; Robnell; Evans; Austro-Daimler; OAF; Puch;
Steyr; Steyr-Daimler-Puch; FN; Germain; Miesse; Minerva; Nagant; Vivinus;
Gurgel; Puma; A-E; AC; Allard; Alvis; Ariel; Armstrong Siddeley; Ashley;
Aston Martin; Austin; Austin-Healey; Bentley; Berkeley; Bond; Bristol; BSA;
Caterham; Clan; Daimler; Dellow; De Lorean; Elva; F-L; Fairthorpe; Ford;
Frazer Nash; Gilbern; Ginetta; Gordon-Keeble; Hillman; Humber; Jaguar;
James and Browne; Jensen; Jowett; Lagonda; Lanchester; Land Rover; Lea-
Francis; Lister; Locost; Lotus; M-R; Marcos; McLaren; MG; Morgan; Morris;
Mini; Ogle; Panther; Peerless/Warwick; Piper; Range Rover; Reliant; Riley;
Rochdale; Rolls-Royce; Rover; S-W; Singer; Standard; Sterling; Sunbeam;
Swallow; Talbot; Tornado; Trident; Triumph; Turner; TVR; Vanden Plas;
Vauxhall; Wolseley; Bricklin; McLaughlin; Aero; Jawa; Laurin & Klement;
Praga; Skoda; Tatra; Walter; Kewet; Elcat; Valmet; RaceAbout; Amilcar;
Alpine, aka. Alpine-Renault; Bonnet; Bugatti; CD; CG; Citroen; DB; De
Dion-Bouton; Delage; Delahaye; Delaunay-Belleville; Facel Vega; Gordini;
Hispano-Suiza; Hotchkiss; Peugeot; Renault; Rosengart; Simca; Sizaire-
Naudin; Talbot; Tracta; Venturi; Voisin; A-G; Amphicar; Audi; Auto-Union;
BMW; Fendt; Glas; Goggomobil; H-P; Heinkel (Heinkel Trojan); Horch;
Kasbohrer-Setra; Kleinschnittger; MAN; Magirus; Maybach; Mercedes-Benz;
Merkur; Messerschmitt; Neoplan; NSU; Opel; Porsche; S-W; Smart; Stoewer;
Titan; Trabant; Volkswagen (VW); Wartburg; Wanderer; Thomond; Bajaj
Tempo; Hindustan; Mahindra; Maruti; Premier; Reva; San Storm; Sipani;
Tata; Abarth; Alfa Romeo; Autobianchi; Bugatti Automobili SpA; De
Tomaso; Dino; Ferrari; Fiat; Iso; Innocenti; Isotta Fraschini; Itala;
Lamborghini; Lancia; Maserati; OM; Piaggio; Qvale; Vespa; Zust; Daihatsu;
Honda (also Acura); Isuzu; Mazda; Mitsubishi; Mitsuoka; Nissan aka. Datsun
(also Infiniti); Subaru; Suzuki; Toyota (also Lexus); Proton; ACE; AMI;
AMM ; Bufori; Inokom; Naza; Perodua; Swedish Assembly; Tan Chong; TD
2000; Donkervoort; Spyker; DAF; Pyonghwa; Tokchon; Kewet; Think aka.
Pivco; Troll; Syrena; UMM; Aro; Dacia; Marta; Oltcit; Volga; Moskvitch;
165
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
GM Daewoo Motors; Hyundai Motor Company; Kia Motors; Renault
Samsung Motors; SsangYong Motor Company; Nilsson; Nordic Uhr; S.A.M.;
Saab; Scania; Thulin; Tidaholm; Tjorven (sold as Kalmar on the export
market); Volvo; and Yugo.
Catalytic or Filtering Muffler
[0680] In another embodiment, the present invention is also directed to a
catalytic muffler comprising a catalytic or filtering substrate of the present
invention. As described herein, the catalytic substrate or filtering substrate
is
housed together with a muffler in a single cannister.
[0681] In one embodiment, the catalytic muffler of the present comprises a
catalytic muffler of known design in which the prior art catalytic substrate
is
replaced with the catalytic substrate of the present invention. Suitable known
catalytic mufflers include those disclosed in 6,622,482; 6,604,6004;
6,341,662; and 4,457,895.
Exhaust Systems
[0682] In another embodiment, the present invention is directed to an exhaust
system comprising a catalytic substrate of the present invention. An exhaust
system generally comprises a number of components. The exhaust system
comprises an engine and a suitable means for directing exhaust gas away from
the engine.
[0683] The exhaust system comprises an internal combustion engine and a
conduit for directing the exhaust gas away from the exhaust ports of the
combustion chamber. Other optional components of an exhaust system
include an exhaust manifold, a muffler, and an exhaust pipe.
[0684] In another embodiment, the present invention is directed to an exhaust
system comprising a filtering substrate of the present invention.
[0685] In another aspect, the present invention is directed to an improved
exhaust system utilizing a catalytic substrate of the present invention. In
another aspect, the present invention is directed to an improved exhaust
system utilizing a filtering substrate of the present invention.
166
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0686] The exhaust system of the present invention is suitable for use with
any
one of the following: 1) Mobile On-Road Engines, Equipment, and Vehicles,
including cars and light trucks; highway and street motorcycles; heavy-duty
highway engines, such as trucks and buses; 2) Mobile Non-Road Engines,
Equipment, and Vehicles, including compression-ignition engines (farm,
construction, mining, etc.); small spark-ignition engines (lawn mowers, leaf
blowers, chainsaws, etc.); large spark-ignition engines (forklifts,
generators,
etc.); marine diesel engines (commercial ships, recreational diesel, etc.);
marine spark-ignition engines (boats, personal watercraft, etc.); recreational
vehicles (snowmobiles, dirt bikes, all-terrain vehicles, etc.); locomotives;
aviation (aircraft, ground support equipment, etc.); and 3) Stationary
Sources,
including hundreds of sources, such as power plants, refineries, and
manufacturing facilities. In another embodiment, the invention is directed to
an exhaust system comprising a substrate, catalytic converter, particulate
filter,
or catalytic muffler of the present invention.
[0687] Other suitable exhaust systems of the present invention include those
used in certain marine vehicles. The catalyst is typically positioned in an
exhaust pipe leading from the engine. This exhaust pipe that leads through a
chamber in the hull of the craft to an outlet near the stem. This arrangement
causes the exhaust pipe to be susceptible to vibration, especially with prior
art
substrates. In addition, in personal watercraft the amount of space in which
the engine may be positioned is limited so as to maintain the craft small in
dimension and with a low center of gravity. Moreover, certain prior art
substrates such as cordierite should not be placed too close to the engine
(overheating and melting is possible). A marine vehicle exhaust system
comprising a catalytic converter or particulate filter of the present
invention
may overcome one or more of these problems. The catalytic converter or
particulate filter may be positioned in the marine exhaust system at the same
place the traditional converter or filter is positioned, or it may be placed
in
another position. For example, in certain embodiments, the catalytic converter
is smaller than a prior art catalytic converter but has substantially the same
efficiency in removing and/or filtering pollutants. See for example U.S.
Patent
No. 5,983,631 (Yamaha Hatsudoki Kabushiki Kaisha).
167
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0688] In other embodiments, the exhaust system of the present invention
comprises one or more additional aftertreatment devices or methods that are
used to reduce or limit the pollutants that are emitted from an exhaust
system.
Suitable devices and methods include CRT, EGR, SCR, ACERT, and the like.
For example, in one embodiment, the exhaust system comprises a catalytic
converter of the present invention and a CRT. The exhaust system may
further comprise an SCR system. Additional combinations and variations are
possible and are understood to be within the scope of the invention.
[0689] In another embodiment, the present invention is directed to an exhaust
system comprising a NOx adsorber having a catalytic substrate comprising a
nSiRF-C composite and a catalyst. The main-cat is located partially or totally
within the head of an engine. In one embodiment, the main-cat comprises a
catalytic substrate of the present invention, wherein said substrate has a
density of about 12 lb/ft3, has a porosity of about 97%, has a low thermal
expansion, has a high structural integrity, has low heat conductance. In a
preferred embodiment, the main-cat comprises about 600 cpsi and having a
wall thickness of about 6 miles. The main-cat in this embodiment has wall-
flow configuration. In a preferred embodiment, the main-cat has a channel. In
a preferred embodiment, the channels of the catalytic substrate of the main-
cat
are made using the comb method. Additionally, in this embodiment, the
catalytic substrate comprises an optional washcoat. In this embodiment, the
main-cat is capable of catalyzing both oxidation and reduction of pollutants,
e.g., it has a catalyst capable of oxidizing pollutants and it has a catalyst
capable of reducing pollutants. In a preferred embodiment, the NOx
combination exhaust system comprises an intumescent matting. The main-cat
can be used in all internal combustion engines. The NOx combination system
is preferably used without fuel-borne catalysts. Generally, the NOx
combination exhaust system has the substrate located near the muffler,
although other locations are possible.
Vehicles
[0690] In another embodiment, the present invention is directed to an
improved vehicle, said improvement comprising a catalytic converter or a
168
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
particulate filter according to the present invention. The improved vehicle
includes in various embodiments, any of the specific embodiments of catalytic
converters and particulate filters described herein.
[0691] Suitable exemplary improved vehicles include vehicles made by one or
more of the following companies: Daimler-Chrysler; Chrysler; Dodge; Eagle;
Jeep; Plymouth; General Motors; AM General (e.g., HTT1VI1VIERs); Buick;
Cadillac; Chevrolet; Geo; GMC; Hummer; LaSalle; Oldsmobile; Pontiac;
Saturn; Ford; Continental; Lincoln; Mercury; Ace Motor Corp; American
Motors; Avanti BMW; Daimler-Chrysler; Fiat; Ford; GAZ; General Motors;
Honda; Mitsubishi; Renault; Peugeot; Toyota; Volkswagen Group; and Yugo.
EXAMPLES
Example 1
[0692] Residence time, or burn off time, is the amount of time for
hydrocarbons form the exhaust emissions to abide within the emission filter to
complete combustion or oxidation. The residence time of the present
invention is significantly better than conventional systems. FIG. 19 provides
a
graph of the residence times 1902, 1904, 1906, 1908 required to combust or
burn soot at temperatures 600 Kelvin, 900 Kelvin, 1000 Kelvin, and 1200
Kelvin, respectively. The more kinetic energy possessed by particles, the
higher likelihood of a successful reaction. As shown in FIG. 19, the residence
time 1902 to combust or burn soot having 0.9 soot mass at 600 degrees Kelvin
is much longer than the residence time 1908 at 1200 degrees Kelvin. The
longer the residence time, the smaller the allowable through-put volumes and
the greater the risk of more particulate accumulating on and clogging the
filter
pores. Clogging can also be a result of the ceramic material overheating to
the
point of melting, thereby blocking or clogging the pores. Residence time
values 1902, 1904, 1906 are indicative of cordierite samples. Residence times
1902, 1904, 1906 range from about two minutes to twenty hours to complete
combustion. Residence time 1908 represents an embodiment of the present
invention and requires only about 0.75 seconds to complete combustion.
169
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Example 2
Substrates
[0693] Substrates 1-7 were prepared as described herein. AETB-12 was
purchased from COI Ceramics and used as the nSiRF-C material of choice
with a density of 121bs/ft3. The substrate/filter was machined from AETB-12
billets measuring 8 x 8 x 4 using standard carbide drill bits tipped machining
methods described in this patent. The substrate was machined in a cylindrical
shape with the following dimensions: radius of 2 inches, longitudinal length
of
1 inch.
[0694] Flow-through, wall-flow and mixed flow-through/wall-flow channels
were drilled into the substrate using standard CNC drilling methods described
in this patent and known in the art. A 0.042" diameter stainless steel drill
bit
was used at 10,000 RPM to drill the channels. During the drilling process, it
was observed that due to the high thermal emissivity and conductivity of the
material, the drill bit was exposed to high temperature environments that led
to
damage and eventual melting of the drill-bits. Wall thickness was not
measured.
[0695] Substrates 1 and 2 had a flow through configuration. Substrates 3-6
had a wall flow configuration. Substrate 3 had about 25% of the channels as
flow through and about 75% as wall flow. Substrate 4 had about 50% of the
channels as flow through and about 50% as wall flow. Substrate 5 and 6 had
about 75% of the channels as flow through and about 25% as wall flow.
[0696] Some of the substrates were coated with an alumina washcoat,
followed by a 5:1 Pt:Rh ratio catalyst coating. Specifically, Substrates 1, 2,
and 7 were not coated with any chemical. Substrates 3, 4, 5, and 6 were given
a uniform washcoating utilizing standard techniques known in the prior art.
The mass of washcoat applied to each substrate is given in the column titled
Mass of Washcoat. Following the washcoating, a catalyst mixture comprising
5:1 Pt/Rh was applied to the substrates 3, 4, 5, and 6 using standard methods.
The mass of catalyst mixture applied to each substrate/filter is given in the
column titled Mass of Catalyst (g/ft3). The substrates with washcoat and
170
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
precious metal catalyst loadings were canned using techniques known in the
prior art.
Substrate Weigh of WET washcoat Estimated FIRED Mass of H20 ABS. WET (GMS)
Mass of
Number Dry amount of (gram Washcoat Catalyst
Substrate GMS NET washcoat s) (G/IN3) WET WT. H20 ABS (grams)
(grams) g/in3 (GMS) (GMS/IN
3)
1 29.0 178. 149.4 2.91 63.0 2.71 --- ---
2 28.9 182. 153.1 2.99 65.3 2.90
0
3 30.0 158. 128.0 2.50 61.0 2.50 167.4 8.47 164.9 24.3 Pt
0 4.8 Rh
4 30.4 163. 132.9 2.59 61.9 2:51 168.4 8.50 155.1 21.3 Pt ~
3 4.4 Rh
5 30.3 165. 135.4 2.64 62.0 2.52 169.8 8.58 170.4 25.3 Pt
7 ':5:1 Rh
30.9 184. 153.7 3.00 67.3 2.90 202.5 31.6 Pt
6 6.3 R'
Ave=8.52 Ave=30.9
S/D=0.23 S/D=5.0
N=3 N = 4 -=
7 24.3 105. 80.8 2.47 44.6 2.54 99.7 20.2 Pt
1 4.0 Rh
Example 3
Preparation of Catalytic and Filtering Substrates
[0697] Substrates/Filters were prepared exactly as described in Example 2
unless mentioned explicitly.
[0698] In a marked difference from the substrate/filters in Exainple 1, the
final
depth of 3/4 inches into the 1 inch slug the comb assembly was removed from
the CNC and the opposite (mirror image) comb assembly was mounted onto
the CNC punch and the same process for pecking method of broaching was
employed. The end result this machining methodology is a 600 cpsi with 6
mil walls and 1/2 inch wall flow overlap. As shown in Figure 28, the
dimensions of the substrate/filter in wall-flow configuration were 1" diameter
by 1" thickness and the pattern inside that slug was 0.8" by 0.8" square. This
substrate was used to conduct an early-stage successful Delta P-test to
observe
171
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
the drop in pressure observed in a N2 gas flow due to the obstruction in flow
caused by wall-flow configuration. Figure 29 demonstrates the drop in
pressure measured in a reactor-tube flow-measurement system as a function of
gas flow rate for temperatures of 27 C, 29 C and 400 C. Figure 30
demonstrates the drop in pressure measured in the same reactor as a function
of temperature at a constant flow rate of 125 SLPM. These initial results were
positive and indicative that the nSiRF-C substrates/filters do not generate
high
back-pressure in the wall-flow configuration.
Example 4
Preparation of Catalytic and Filtering Substrates
[0699] Substrates/Filters were prepared exactly as described in Example
12unless mentioned explicitly.
[0700] In a marked difference from the substrates in Example 1, three
different substrates were generated using AETB-11, AETB-12, and AETB-16
billets purchased from COI Ceramics with densities of 11, 12, and 16 lbs/ft3
respectively.
[0701] For the substrate/filter created from AETB-11, the final depth of 3/4
inches into the 1 inch slug the comb assembly was removed from the CNC and
the opposite (mirror image) comb assembly was mounted onto the CNC punch
and the same process for pecking method of broacliing was employed. The
end result this machining methodology is a 600 epsi with 6 mil walls and 1/2
inch wall flow overlap. For the substrates/filters created from AETB-12 and
AETB-16, the final depth of 7/8 inches into the 1 inch slug the comb assembly
was removed from the CNC and the opposite (mirror image) comb assembly
was mounted onto the CNC punch and the same process for pecking method
of broaching was employed. The end result this machining methodology is a
600 cpsi with 6 mil walls and 3/4 inch wall flow overlap.
[0702] The dimensions of the all substrates/filters tested in this stage were
1"
diameter by 1" thickness. The substrates were exposed to another early-stage
Delta P-test to observe the drop in pressure observed for substrates material
density and wall-flow configuration as a function of space hourly velocity.
This particular test was conducted at 932 Fahrenheit temperature. The results
172
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
of our tests are summarized in Figure 31. In addition to the data observed for
our AETB-11, AETB-12 and AETB-16 substrates/filters, the results reported
by Coming for their 400/6.6 flow-through cordierite substrates/filters and
200/12 cordierite DPT (wall-flow configuration). Corning data was obtained
through Coming Technical Reports. Our results indicate that while Coming
DPT in wall flow configuration causes excessive backpressure compared to
cordierite flowthrough filter, our nSiRF-C filters generate back-pressure
equivalent to the cordierite flow-through substrate even when they are used in
a wall-flow configuration. It can be inferred that since backpressure had been
a big problem in wall-flow DPTs, as observed in Figure 31, using wall-flow
DPTs made of nSiRF-C materials, as invented in this patent, leads to an
excellent alternative. Additionally it is also observed that a comparison of
back-pressures observed with AETB- 11 substrate/filter versus the AETB- 12
and AETB-16 substrates/filters allows us to infer that increasing the
'overlap'
channel length leads to better back-pressure performance.
[0703] Figure 32 is the same test performed at an operating temperature of
1100 Farenheit and the trends in results are almost identical.
Example 5
Preparation of Catalytic and Filtering Substrates
[0704] Substrates/filters were prepared as described in Example 2 unless
mentioned explicitly.
[0705] AETB-12 was purchased from COI Ceramics and used as the nSiRF-C
material of choice with a density of 12 lbs/ft3. A laser-based channel
drilling
technique was tested to generate holes at 3000 cpsi and 30000 cpsi. The holes
were drilled using a DPSS laser system as describe din this patent and in
related prior art elsewhere. The holes generated using a pulsed, high-energy
laser system were square in shape and due to the particular configuration,
presented a high frontal surface area. The presence of a high frontal surface
area (caused by a large value for wall thickness of channels) was obvious in
the Delta-P tests carried out using the same test-flow reactor as described in
Example 3. It was observed that for the early-stage prototype created using
laser-based drilling techniques to be a success, the Delta back-pressure had
to
be brought to a value less than 10 inches of water. Further modifications can
173
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
be done to decrease (or increase) the cell density and to alter the wall
thickness
as prescribed by the need of the application.
[0706] Figure 33 shows the change in pressure as a function of N2 gas flow-
rate for the AETB-12 substrate/filter with 30000 cpsi cell density at 27 C and
400 C. Figure 34 shows the change in pressure as a function of operating
temperature for various N2 gas flow-rates for AETB-12 substrate/filter with
30000 cpsi cell density.
[0707] Figure 35 shows the change in pressure as a function of N2 gas flow-
rate for the AETB-12 substrate/filter with 3000 cpsi cell density at 29 C and
400 C.
Example 6
Diesel Particulate Filter
[0708] The substrate is created using the AETB formulation and formed into a
billet having the dimensions of about 13 inches x about 13 inches x about 5
inches with a density of about between 8 pounds per cubic foot. From the
billet, a five inch tall cylinder slug which is about six inches in diameter
is cut
from the billet using a diamond tipped saw. This substrate is further machined
to exact tolerances (within .001 inches) on a spinning lathe.
[0709] Then a plurality of channels are formed in the substrate to form a
substrate containing 600 channels per square inch and having a wall flow
configuration. The channels are formed using the combined drilling and
comb techniques described herein. The channels are square shape having a
dimension of about 6 mils by 6 mils. The adjacent walls of adjacent channels
are substantially parallel to each other. The channels do not extend through
the entire length of the substrate but are approximately 4.9 inches in length.
174
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Example 7
Measurement of Gross Surface Area
[0710] The first and second cordierite samples have a gross surface area of
33.2 and 46.97 square inches per cubic inch, respectively. Thus, in a one inch
cube of the first cordierite sample, there is 33.20 square inches of surface
to
put the precious metal loadings. A sample of a substrate of the present
invention has a gross surface area of 83.58 square inches per cubic inch.
[0711] The gross wall volumes for both the first and second cordierite samples
are 0.311 in3/in3 (cubic inches per cubic inch). The gross wall volume of the
substrate of the present invention is 0.272 cubic inches per cubic inch. While
this value is less than the first and second cordierite samples, the present
invention has a much higher porosity and permeability, making the smaller
gross wall volume more efficient.
Example 8
Activity Test
[0712] An activity test measures the amount of pollutants entering and exiting
the filter. In an activity test, a sample filter is placed in a reactor and
gases of
a known flow rate and temperature are pumped through the material. The
activity test then measures the amount of pollutants exiting the filter.
Referring to FIG. 24, an activity test of an exemplary substrate 2410 of the
present invention and a sample of cordierite 2420 is shown. The test measured
the activity of toluene at a concentration of 500 ppm and space velocity of
40,000 per hour. The cell density of the two samples were both 400 cpsi.
[0713] The test illustrates that the substrate 2410 of the present invention
has a
faster light off time and at a significantly lower temperature than the
cordierite
sample 2420. Substrate 2410 achieved 85% destruction at a temperature about
335 degrees Fahrenheit in about three to four seconds. Cordierite 2420
achieved 85% destruction at about 380 degrees Fahrenheit. Substrate 2410
then achieved 90% destruction at about 360 degrees Fahrenheit in about four
to five seconds. Cordierite 2420 achieved 90% destruction at about 450
175
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
degrees Fahrenheit in about eight seconds. Substrate 2410 achieved
substantially 100% destruction at about 425 degrees Fahrenheit in about five
seconds. Cordierite 2420 is projected to achieve substantially 100%
destruction at about 800 degrees Fahrenheit in about 28 seconds.
Example 9
Permeability of a Catalytic Substrate
[0714] The permeability of an exemplary embodiment of Example 2of the
present invention is approximately 1093 cd (centidarcies). Other testing
values were over the maximum number measured by the testing equipment.
In comparison to conventional systems, a sample of cordierite has a
permeability of about 268 cd.
Example 10
Testing a Catalytic Converter of Example 2
[0715] Similar to an activity test, the EPA utilizes a test known as Federal
Test Procedure ("FTP") 75 that actually mounts the filter on the tailpipe of a
car and drives the car under specified conditions. The EPA uses this test for
emission certification of vehicles. FTP 75 tests the conditions of the vehicle
in
three phases. The first phase includes crank and non-idle hold and driving for
505 seconds. This phase reflects conditions experienced at the beginning of a
trip when the engine and the emission control system begin operation at
ambient temperature and are not performing at optimum levels (i.e., the
catalyst is cold and has not reached the "light off" temperature needed to
efficiently control emissions coming from the engine) until part way through
the trip. The second phase includes 864 seconds of driving with a non-idle
hold, shutdown, and five extra sampling seconds. This phase reflects the
condition of the engine when the vehicle has been in continuous operation
long enough for all systems to have attained stable operating temperatures.
The vehicle then has a soak time between 540 seconds and 660 seconds. This
soak time reflects the condition of an engine that has been turned off and has
176
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
not cooled to ambient conditions. The third phase is a crank and non-idle hold
and driving for 505 seconds. Under these circumstances, the engine and
catalyst are warm and, although not at peak operating efficiency when started,
still have significantly improved emissions performance relative to the cold
start mode.
Example 11
Thermal Testing of a Catalytic Substrate
[0716] The thermal conductivity of an exemplary embodiment of the present
invention is approximately 0.0604 W/m-K (Watts of energy per meter thick
and Kelvin changed). By comparison, a sample of cordierite is about 1.3 to
1.8 W/m-K. These results indicate that, if 1000 Watts of heat energy is lost
from a given volume of cordierite material, only 33 Watts would be lost from
the same volume of the material from the present invention. Thus, the
material of the present invention has a thermal conductivity thirty times
greater than cordierite.
[0717] The specific heat of an exemplary embodiment of the present invention
is approximately 640J/kg-K (Joules per kilogram-Kelvin). A sample of
cordierite is about 750 J/kg-K. Even though the cordierite has a greater
specific heat, cordierite filters have a greater mass to heat up. The result
is
more heat energy is needed to reach operating temperature making the
cordierite less efficient.
[0718] A multiple use temperature limit is the maximum temperature in which
a substance can be subjected a plurality of times without any degradation. The
higher the temperature a substrate can continue to operate without micro-
fractures or spallation, the less chance of the substrate breaking or cracking
over time. This in turn means the substrate is more durable over a wider
temperature range. A higher temperature limit is preferred.
[0719] The multiple use temperature limit of an exemplary embodiment of the
present invention is 2,980 degrees Celsius. A sample of cordierite is about
1,400 degrees Celsius. Thus, the material of the present invention can
withstand more than twice the temperature than cordierite before breaking
177
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
down. This permits the material to function in a greater range of exhaust
environments.
[0720] The coefficient of thermal expansion is a ratio of the increase of the
length (linear coefficient), area (superficial), or volume of a body for a
given
rise in temperature (usually for zero to one degree Celsius) to the original
length, area, or volume, respectively. These three coefficients are
approximately in the ratio 1:2:3. When not specifically expressed, the cubical
coefficient is usually intended. The less a substrate will expand when heated,
the less chance of leaking, fracturing, or damage to filter assembly. A lower
thermal expansion is preferred to ensure that the substrate keeps its
dimensions even when heated or cooled.
[0721] The coefficient of thermal expansion for an exemplary embodiment of
the present invention is approximately 2.65 x 10-6 W/m-K (Watts per meter
degree Kelvin). A sample of cordierite is about 2.5 x 10-6 W/m-K to 3.0 x 10-
6 W/m-K. The thermal expansion of the material of the present invention is
less than ten times that of cordierite.
[0722] The coefficient of thermal expansion of the substrate is preferably, in
one embodiment, compatible with the coefficient of thermal expansion of the
washcoat. If the coefficient of thermal expansion is not similar, the washcoat
will spallate, delaminate, "flake" or peel off the substrate, resulting in the
precious metals being blown away or plugging the pore spaces. This would
eventually lead to increased backpressure, overheating and system failure.
Example 13
Structural Integrity
[0723] The tensile modulus of AETB-12 is approximately 2.21 MPa (mega-
Pascal of pressure which equals approximately 100,000 times the pressure of
one atmosphere of pressure). A sample of cordierite is about 25.0 MPa.
Although the cordierite is about ten times stronger, the material of the
present
invention can withstand 200,000 atmospheres of pressure before rupture. This
value is sufficient for uses described herein.
178
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
Example 13
Acoustical Testing
[0724] Acoustic attenuation may be defined as either the diminution of
thickness, thinness, emaciation; diminution of density; diminution of force or
intensity; or weakening. In one embodiment of the present invention, the
acoustic attenuation is the substrate's ability to attenuate or dampen
acoustic
energy in engine exhaust. A substrate of the present invention can replace or
compliment an engine's muffler assembly, as disclosed herein, thus decreasing
exhaust noise and exhaust system costs. A higher acoustic attenuation is
preferred.
[0725] Currently, there are no accredited laboratory tests that can be applied
to
the present invention in any configuration. All American Society for Testing
and Materials ("ASTM") acoustical tests are applied to a large space such as a
sound-proofed room and not a material. However, in simple test using a
sound meter, the noise from automobiles was found to be at least 25 decibels
less than conventionally muffled vehicles when a substrate of the present
invention is in the exhaust system. For reference, 110 decibels is the level
that
will cause permanent damage to human ears, and 60 decibels is the amount of
noise in a luxury automobile at idle with the windows rolled up.
Example 14
Comparison to Prior Art Substrates
[0726] A sample of a suitable nSiRF-C (AETB-12) was compared to
cordierite and SiC, measuring a number of attributes.
AETB-12 Cordierite Silicon Carbide
(SiC)
Thermal 6.04 x 10_2 W/m-K 1.3-1.8 W/m-K 20 W/mK
Conductivity
Specific Heat 640 J/kg-K 750 J/kg-K 950 J/kg-K
Density 0.2465 gm/cc 2-2.1 gm/cc 3.2 gm/cc
Emissivity 0.88 .13 .90
xial Strength 2.21 Mpa 2.5 Mpa 18.6 Mpa
179
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
4oise Attenuation 74 db 100db 100 db
at 3500 rpm
orosity 97.26% 18-42% 30-40%
ermeability 1093 - oo cd 268 cd 6.65 cd
Regeneration Time 0.75 sec 2 min-20 hrs 50 sec-20 hrs
Surface Area 88,622 in 847 in 847 in
elting Point 3,000 C 1,400 C 2400
Thermal Expansion 0.25 x 10-71/C 0.7 x 10-61/C 4-5 x 10-61/C
(CTE)
[0727]
EXAMPLE 15
[0728] In one embodiment, the substrate of the present invention has 600 cpsi
with 6 mil walls. The cell density of a sample substrate of the present
invention is compared with two samples of cordierite. In comparison, the
first and second cordierite samples are 100 cpsi with 17 mil wall thickness
and
200 cpsi with 12 mil wall thickness, respectively. In comparison, the
substrate
of the present invention in this embodiment has 600 cpsi with 6 mil walls.
[0729] In this exemplary embodiment, the substrate is drilled with 0.04 inch
diameter channels spaced every 0.06 inches across the entire filter. These
channels are smaller than conventional cordierite channels. The result is
vastly increased surface area as compared to cordierite, even without talcing
into consideration the surface area existing in the massive pore space of the
substrate material. The channels are preferably "blind" channels. Exhaust
emission is forced to pass through the channel walls, rather than flowing in
and out of the channels without reacting with the catalyst.
[0730] The channels are drilled using a CNC drill, which is computer
controlled to maintain uniformity. The drilling process is performed under a
constant water shower to prevent dust from becoming airborne, which is an
OSHA hazard, and may get into the bearings of the drill and destroy it.
[0731] The drilled substrate is oven dried to drive or bake off any water or
other liquid that may reside in the pore space before any catalytic
applications.
Baking time is not variable and evaporation of the water can be determined by
simply weighing the substrate. Baking time primarily speeds up the
180
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
dewatering process. After heating the filter element for several different
intervals, the weight will level off and the substrate is ready for any
catalyst or
coating application.
[0732]
Glossary
[0733] The term "substrate" as used herein refers to a solid surface on which
pollutants can be converted to nonpollutants. A substrate is understood to
include a filter element, catalytic substrate, or filtering substrate.
[0734] The term "high grade refractory fiber" as used herein refers to.
[0735] The term "sintered" as used herein refers to material that has been
heated without melting.
[0736] The term "non-woven" as used herein means that there is no interlacing
or interweaving pattern of fibers present.
[0737] The term "billet" as used herein refers to an unshaped or unmachined
block of substrate material.
[0738] The term "green billet" as used herein refers to a billet that has not
been cured.
[0739] The term "frontal surface" as used herein refers to surface through
which the fluid enters the substrate. In certain embodiments, the channels
have openings in the frontal surface and the channels are perpendicular to the
frontal surface.
[0740] The term "rear surface" as used herein refers to the surface through
which the fluid exits the substrate. In certain embodiments, the channels have
openings in the rear surface and the channels are perpendicular to the rear
surface.
[0741] The term "mil" as used herein refers to a unit of measurement and is
equivalent to a thousandth of an inch.
[0742] The term "light off temperature" as used herein refers to the
temperature at which conversion of the reaction in catalytic converter is 50%.
That is, the light off temperature is the temperature at which 50% of one or
more pollutants, or alternatively total pollutants, are converted into
nonpollutants.
181
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
[0743] The term "burn off" as used herein refers to a process of combusting
particulate matter and other material that is filtered by a substrate. For
example, burn off may occur in a diesel particulate filter (DPF).
[0744] The term "channel" as used herein refers to a three-dimensional
opening in the substrate that extends through at least a portion of the
substrate
and has a definitive shape and length.
[0745] The term "channels per square inch" as used herein refers to the
number of channels present in a cross-sectional square inch of the substrate.
The term cells per square inch is synonymous.
[0746] The term "channel shape" as used herein refers to the three-
dimensional shape of the channel.
[0747] The term "PM" as used herein refers to particulate matter. Common
measurements of PM include PM-10 and PM-2.5.
[0748] The term "gross surface area" as used herein is the total surface area
and represents the total surface area that precious metals can be impregnated
onto in one cubic inch.
[0749] The term "2-way catalytic converter" as used herein refers to a
catalytic converter that only oxidizes the gas-phase pollution of HC and CO to
COZ and H20.
[0750] The term "3-way catalytic converter" as used herein refers to a
catalytic converter that oxidizes CO and HC to COZ and H2O and also reduces
NOx to N2.
[0751] The term "4-way catalytic converter" as used herein refers to a
catalytic converter that performs the oxidation and reduction as described for
a
3-way catalytic converter but also traps particulates to burn them off
(regeneration can occur in active or passive mode).
[0752] The term "thermal conductivity" as use herein refers to
[0753] The term "suitable for use" as used herein refers meeting the
requirements of particular regulatory guidelines.
[0754] The term "cross-sectional distance" as used herein refers to
[0755] The term " aftertreatment system" as used herein refers to
[0756] The term "thermal conductivity" as used herein refers to the quantity
of
heat that passes in unit time through unit area of a plate of a given
material,
182
CA 02563802 2006-10-20
WO 2005/113126 PCT/US2004/012963
when its opposite faces are subject to unit temperature gradient (e.g., one
degree temperature difference across a thickness of one unit).
[0757] The term "matting" as used herein generally refers to any material that
is used to provide insulation and/or protection to a substrate. Matting is
sometimes also referred to as batting.
[0758] The term "boron binder" as used herein refers to an agent present in a
nSiRF-C after the sintering process and that is derived from a boron biding
agent.
[0759] The term "pecking" as used herein refers to a process of forming or
reshaping a channel in a substrate by way of repeatedly forcing a tine into
and
out of a substrate material until the desired length of the channel is
obtained.
[0760] Having now fully described this invention, it will be understood by
those of ordinary skill in the art that the same can be performed within a
wide
and equivalent range of conditions, formulations and other parameters without
affecting the scope of the invention or any embodiment thereof. All patents
and publications cited herein are fully incorporated by reference herein in
their
entirety.
183
