Note: Descriptions are shown in the official language in which they were submitted.
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REDUCED-EMISSIONS COMBUSTION UTILIZING MULTIPLE-
COMPONENT METALLIC COMBUSTION CATALYST AND
LIGHTLY CATALYZED DIESEL OXIDATION CATALYST
Description
Background of the Invention
[0001] The invention concerns a new process for to reduce emission of
pollutants of the
type generated by incomplete combustion, e.g., particulates, unburned
hydrocarbons and
carbon monoxide, while avoiding increasing the production of NOa.
[0002] Diesel engines have a number of important advantages over engines of
the Otto
type. Among them are fuel economy, ease of repair and long life. From the
standpoint of
emissions, however, they present problems more severe than their spark-
ignition
counterparts. Emission problems relate to particulate matter (PM), nitrogen
oxides (NOX),
unburned hydrocarbons (HC) and carbon monoxide (CO). NOx is a term used to
describe
various chemical species of nitrogen oxides, including nitrogen monoxide (NO)
and
nitrogen dioxide (NO2), among others. NO is of concern because it is believed
to undergo a
process known as photo-chemical smog formation, through a series of reactions
in the
presence of sunlight and hydrocarbons, and is significant contributor to acid
rain. NO2 on
the other hand has a high potential as an oxidant and is a strong lung
irritant. Particulates
(PM) are also connected to respiratory problems. As engine operation
modifications are
made to reduce particulates and unburned hydrocarbons on diesel engines, the
NOX
emissions tend to increase.
[0003] After treatment devices, such as diesel particulate filters (DPFs) and
diesel
oxidation catalysts (DOCs), have been proposed to reduce the emission of
particulates and
gaseous hydrocarbons and carbon monoxide from diesel engines. These devices
are greatly
stressed in older engines and are in need of efficiency improvements in newer
engines. In
all cases, they are expensive due in significant part to the cost of precious
metals used
required to be effective. It would be desirable to reduce the cost of DOC
devices and/or
improve their efficiency.
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[0004] NOZ, being a strong oxidant, has been recognized by the art for playing
a useful role
in burning diesel particulates. Cooper, et al., U. S. Patent No. 4,902,487,
implements this
reaction through the use of a heavily catalyzed DOC upstream of an uncatalyzed
DPF. The
heavily catalyzed DOC converts NO present in the exhaust to NO2, which
oxidizes carbon
particulates to help regenerate the filter. As a first element in Example 2 of
that patent, a
conventional ceramic monolith supported catalyst was employed containing
approximately
80 gm/ft3 Pt. Typical loadings of platinum are reportedly 30 to 90 gm/ft3 of
DOC volume.
More recently a manufacturer of such devices has introduced a system which
utilizes a
heavily catalyzed DPF to help with low temperature regeneration. Total
precious metal
loadings are now reportedly 90 to 120 gm/ft3. A result of this approach is
large quantities of
excess NOa escaping the system. NOa is a strong lung irritant and
concentrations have been
limited in exhaust gas by MSHA and are proposed to be capped at 20% of exhaust
nitrogen
oxides by CARB. However, in this type of system, the art finds it necessary to
utilize high
platinum loadings to achieve satisfactory regeneration despite the high cost
of the platinum
and the associated problems of NOa emission.
[0005] Another commercial effort has been made to improve regeneration of the
soot filter
of the Cooper type, and generate high NOZ emissions and aid DPF regeneration
through the
use of cerium or iron fuel additives. See United States Patent No. 6,767,526
to Blanchard,
et al., which employs a DOC with a DPF or a DPF alone with fixed platinum
loadings of
unspecified concentrations sufficient to oxidize NO to NO2. It does not
address the high
cost of platinum related to the Cooper system or the adverse effect of NO2
emissions.
[0006] Anotller commercially tested system uses a DOC upstream of a new wire
mesh
filter but needs the heavily catalyzed DOC which forms high NO2 in the exhaust
to
regenerate the uncatalyzed wire mesh filter. See, for example, EP 1 350 933.
[0007] In United States Patent No. 6,023,928, Peter-Hoblyn and Valentine
describe a
platinum FBC with a DOC or DPF and or Pt/Ce with a catalyzed or uncatalyzed
DPF but
does not describe minimizing platinum loadings or reduction in NO2.
Conventional DOC's
with high platinum loadings can convert sulfur into sulfate species increasing
particulates
and also increasing NO2. Catalyzed DOCs have not been considered effective,
only able to
provide PM reductions of 20 to 25%.
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[0008] What is needed is a system that provides good PM reduction while
minimizing the
generation and escape of NOZ.
BRIEF DESCRIPTION OF THE INVENTION
[009] It is an object of the invention to provide a system that provides good
PM reduction
through a catalytic exhaust treatment while minimizing the escape of NOa.
[0010] It is another object of the invention to provide a system that can
reduce system costs
by lowering the requirements for platinum catalyst while maintaining the
apparent benefit
of NO2 as an aid to soot oxidation in a DOC.
[0011] These and other objects are accomplished by the invention, which
provides an
improved diesel exhaust treatment system. In a principal aspect, the invention
provides a
method for reducing particulate emissions from a diesel engine while also
controlling
emissions of NO2 as a percent of exhaust total nitrogen oxides, comprising:
adding a fuel
borne catalyst comprising platinum and cerium and/or iron at a total metal
concentration of
from 2 to 15 ppm in the fuel to a diesel fuel; and passing exhaust produced by
the
combustion through a diesel oxidation catalyst having substrate with a
precious metal
catalyst thereon, the catalyst be present on the substrate in an amount of
less than 15 grams
per cubic foot of substrate.
Detailed Description of the Invention
[0012] As noted, the invention provides improved systems for diesel operation
and
preferably employs an FBC and an emissions after treatment device comprising a
lightly
catalyzed diesel oxidation catalyst, DOC, e.g., of conventional or alternative
construction.
The term FBC refers to fuel borne catalyst, which is typically a fuel soluble
or suspended
composition having a metal component that is released to the combustion
chamber in active
form during the combustion of the fuel in the diesel engine. The terms DOC and
FBC will
all be explained in greater detail below and are also known to the art as
evidenced by the
above citations.
[0013] The invention employs an emissions after treatment device treatment
comprising a
catalyst substrate that can be a DOC alone or with a DPF, the catalyst
substrate being
lightly catalyzed with precious metal, e.g., a platinum group metal. The
catalyst loading
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will be less that the art has seen the need for to convert NO to NO2 for use
as a soot
oxidant, preferably having a metal loading of less than 15 gm/ft3, e.g., 1 to
15 gm/ft3,
platinum group metal loading, desirably less than 10 gm/ft3, and most
preferably 3 to 5
gm/ft3. These low catalyst loadings aid in burning soot, without creating so
much NO2 that
excessive emission of the NOa becomes an environmental problem. Among the
suitable
precious metals for catalyzing the DOC are those identified in the Cooper, et
al., patent
identified above, and particularly comprises platinum group metal.
[0014] In one embodiment of the invention, a lightly catalyzed DOC contains
less than 15
grams per cubic foot (gm/ft3), e.g., 1 to 15 gm/ft3, platinum group metal
loading, desirably
less than 10 gm/ft3, and preferably 3 to 5 gm/ft3, used with a platinum and
cerium FBC at
0.015-0.5 ppm Pt and 0.5-8 ppm Ce and/or iron. Higher and lower levels of
additives may
be employed for portions of a treatment or operation cycle. A further
discussion of FBC
compositions is provided below.
[0015] The improved systems of the invention significantly reduce PM, e.g., by
30 to 50 %
in preferred embodiments, e.g., when used with ultra low sulfur diesel fuel
and does not
increase NO2 above baseline and has demonstrated the ability to maintain low
NO2
emissions, e.g., to below 20% of total nitrogen oxide species while also
minimizing the use
of platinum group metals.
[0016] Among the diesel fuels suitable for use in the invention are those
which typically
comprise a fossil fuel, such as any of the typical petroleum-derived fuels
including distillate
fuels. The diesel fuel can be of any of those formulations disclosed in the
above priority
patent applications, which are incorporated by reference herein in their
entireties. A fuel
can be one or a blend of fuels selected from the group consisting of
distillate fuels,
including diesel fuel, e.g., No. 2 Diesel fuel, No. 1 Diesel fuel, jet fuel,
e.g., Jet A, or the
like which is similar in boiling point and viscosity to No. 1 Diesel fuel,
ultra low sulfur
diesel fuel (ULSD) and biologically-derived fuels, such as those comprising a
"mono-alkyl
ester-based oxygenated fuel", i.e., fatty acid esters, preferably methyl
esters of fatty acids
derived from triglycerides, e.g., soybean oil, Canola oil and/or tallow.
[0017] Jet A and Diesel No. 1 are deemed equivalent for applications of the
invention, but
are covered by different American Society For Testing and Materials (ASTM)
specifications. The diesel fuels are covered by ASTM D 975, "Standard
Specification for
Diesel Fuel Oils". Jet A has the designation of ASTM D 1655, "Standard
Specification for
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Aviation Turbine Fuels". The term ultra low sulfur diesel fuel (ULSD) means
No. 1 or No.
2 diesel fuels with a sulfur level no higher than 0.0015 percent by weight (15
ppm) and
some jurisdictions require a low aromatic hydrocarbon content e.g., less than
ten percent by
volume.
[0018] The process of the invention employs a fuel-soluble, multi-metal
catalyst, i.e., an
FBC, preferably comprising fuel-soluble platinum and either cerium or iron or
both cerium
and iron. The cerium and/or iron are typically employed at concentrations of
from 0.5 to 20
ppm and the platinum from 0.0005 to 2 ppm, with preferred levels of cerium
and/or iron
being from 5 to 10 ppm, e.g., 7.5 ppm, and the platinum being employed at a
level of from
0.0005 to 0.5 ppm, e.g., less than 0.15 ppm. In some embodiments, the
treatment regimen
can call for the utilizing higher catalyst concentrations initially or at
defined intervals or as
needed--but not for the whole treatment as has been necessary in the past. The
cerium
and/or iron are preferred at levels of cerium and/or iron being from 2 to 10
ppm, e.g., 3-8
ppm, and the platinum being employed at a level of from 0.05 to 0.5 ppm, e.g.,
from0.1 to
0.5ppm, e.g., 0.15 ppm, for typical operations. The tests below run at these
levels show
surprising results in terms emissions utilizing a lightly catalyzed DOC.
[0019] The cerium and/or iron FBC is preferred at concentrations of 1 to 15
ppm cerium
and/or iron w/v of fuel, e.g., 4 to 15 ppm. A preferred ratio of cerium and/or
iron to
platinum for the FBC is from 100:1 to 3:1, e.g., more typically will be from
75:1 to 10:1. A
formulation using 0.15 ppm platinum with 7.5 ppm cerium and/or iron is
exemplary.
[0020] An advantage of low levels of catalyst (about 3 to 15 ppm total),
preferably below
12 ppm and more preferably below 8 ppm, is the reduction in ultra fine
particles resulting
from metal oxide emissions. Data published under the European VERT program
show that
at high FBC dose rates of 20 ppm, or 100 ppm, cerium the number of ultra fine
particles
increases dramatically above baseline. However, for a bimetallic used at
0.5/7.5 or 0.25/4
ppm there is no significant increase in the ultra fine particle number. It has
been found that
at low levels of FBC there is not a separate ultrafine oxide particle peak and
metal oxides
are contained in the soot over the entire particle size distribution. A
further advantage of
the low dose rates prescribed by the current invention is a reduction in the
contribution of
metal ash to overall engine emissions. For an engine meeting 1998 US emission
standards,
particulate emissions are limited to 100,000 g/hp-hr (0.1 gram/hp-hr). A
cerium FBC used
at 30 ppm in fuel represents a metal catalyst input loading to the engine of
6000 gg/hp-hr of
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metal or roughly 6% of untreated engine emissions. Therefore, low levels of
catalyst used
in the present invention of less than 8 ppm and preferably 4 ppm as a
bimetallic or
trimetallic FBC will, for example, contribute only 800 - 1600 gg/hp-hr of
catalyst loading
to the engine or 0.8 -1.6 10 of baseline soot emissions. This has the
advantage of reduced
metal ash emissions and reduces the contribution of the FBC to overall
particulate mass
emissions or loading of metal ash to downstream emission control devices.
[0021] The fuel can contain detergent (e.g., 50-300 ppm), lubricity additive
(e.g., 25 to
about 500 ppm), other additives, and suitable fuel-soluble catalyst metal
compositions, e.g.,
0.1-2 ppm fuel soluble platinum group metal composition, e.g., platinum COD or
platinum
acetylacetonate and/or 2-20 ppm fuel soluble cerium and/or iron composition,
e.g., cerium
as a soluble compound or suspension, cerium octoate, ferrocene, iron oleate,
iron octoate
and the like. The fuel as defined, is combusted without the specific need for
other treatment
devices although they can be used especially for higher levels of control on
diesels.
[0022] Among the specific cerium coinpounds are: cerium III acetylacetonate,
cerium III
napthenate, and cerium octoate, cerium oleate and other soaps such as
stearate,
neodecanoate, and other C6 to C24 alkanoic acids, and the like. Many of the
cerium
compounds are trivalent compounds meeting the formula: Ce (OOCR)3 wherein
R=hydrocarbon, preferably C2 to C22, and including aliphatic, alicyclic, aryl
and alkylaryl.
Preferably, the cerium is supplied as cerium hydroxy oleate propionate complex
(40%
cerium by weight) or a cerium octoate (12% cerium by weight). Preferred levels
are toward
the lower end of this range.
[0023] Among the specific iron compounds are: ferrocene, ferric and ferrous
acetyl-
acetonates, iron soaps like octoate and stearate (commercially available as
Fe(III)
compounds, usually), iron napthenate, iron tallate and other C6 to C24
alcanoic acids, iron
penta carbonyl Fe(CO)5 and the like.
[0024] Any of the platinum group metal compositions, e.g., 1,5-cyclooctadiene
platinum
diphenyl (platinum COD), described in U.S. Pat. No. 4,891,050 to Bowers, et
al., U.S. Pat.
No. 5,034,020 to Epperly, et al., and U.S. Pat. No. 5,266,083 to Peter-Hoblyn,
et al., can be
employed as the platinum source. Other suitable platinum group metal catalyst
compositions include commercially-available or easily-synthesized platinum
group metal
acetylacetonates, including substituted (e.g., alkyl, aryl, alkyaryl
substituted) and
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unsubstituted acetylacetonates, platinum group metal dibenzylidene acetonates,
and fatty
acid soaps of tetramine platinum metal complexes, e.g., tetramine platinum
oleate.
[0025] The invention can employ a DOC alone or it can be used with other
devices
including DPFs, particulate reactors, partial filters or NOX adsorbers can
also be used and
benefit from reduced engine out emissions of the current invention. See the
examples
below, for the engine out results and the benefits of the FBC with catalyzed
DOC devices
to reduce NOZ and particulate emissions. While not wishing to be bound by any
theory, the
unexpectedly good results with after treatment devices as well as for engine
out emissions,
this may be because the platinum is not present in amounts sufficient to
produce excessive
amounts of NO2 and yet produces some NO2 which is sufficient to foster
oxidation of the
carbon in the particulates in the presence of low levels of cerium and/or
iron. NO2 is a
strong lung irritant and can be generated in large quantities by traditional
use of heavily
catalyzed aftertreatment devices such as DOCs, DPFs or combinations. The net
result of the
limited NO2 production due to low platinum concentrations and the cerium
and/or iron
being present in low but sufficient amounts is to produce greater than
expected reductions
in particulates (as well as other species resulting from incomplete oxidation)
and at the
same time control the amount of NO2 generated and released. Unlike the prior
art, then, the
invention has found that high NO2 production rates are not necessary and,
indeed, has
found a way to provide emissions less irritating to humans.
[0026] The following examples are presented to further explain and illustrate
the invention
and are not to be taken as limiting in any regard. Unless otherwise indicated,
all parts and
percentages are by weight.
Example 1
[0027] This example reports testing on a 1990 International DT 466 7.61iter
diesel engine
operated over replicate hot transient test cycles on an engine dynamometer.
Emissions
results are the average of triplicate tests and are measured in units of
grams/hp-hr. Testing
on untreated No. 2 diesel fuel with > 300 ppm sulfur produced baseline
particulate
emissions of 0.253 gr/hr-hr and NOa of 1.1 g/hp-hr or 18% of total nitrogen
oxides in the
exhaust. Use of a bimetallic FBC in the No. 2D fuel at a dose rate of 0.15 ppm
Pt and 7.5
ppm Ce reduced PM by 15% to 0.215 gr/hp-hr with NO2 reduced to 12% of total
nitrogen
oxide emissions.
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[0028] Installation of a lightly catalyzed ceramic DOC with 3 grams/cu ft of
precious metal
loading operated on untreated No. 2D fuel produced PM emissions of 0.196 gr/hp-
hr or a
23% reduction from baseline. No measurement of NO2 was made due to
unavailability of
test equipment. Use of FBC treated No. 2D with the lightly catalyzed DOC
reduced PM
emissions to 0.178 gr/hp-hr for a 30% reduction while fiutlier reducing NO2
emission to
8% of total nitrogen oxide emissions.
[0029] Use of the same DOC with the engine operated on FBC treated ULSD (<15
ppm S)
reduced PM by 34% to 0.168 gr/hp-hr with NOa emissions at 8% of total NOx.
These
results demonstrate the ability of the FBC to enhance the overall PM reduction
efficiency of
a lightly catalyzed DOC even on No. 2D fuel where the use of traditional
heavily catalyzed
devices can cause conversion of sulfur species to sulfate particulate
emissions and increase
NO2 emissions.
[0030] Another unexpected benefit of the FBC used with a lightly catalyzed DOC
is the
reduction in NO2 emissions versus baseline. NO2 emissions are generally
increased with
traditional heavily catalyzed devices, but are decreased by over 50% with the
FBC/DOC
combination described in the invention.
[0031] Emissions Results for 1990 International DT 466 7.6 Liter Engine
(g/hp-hr)
Fuel/Device HC CO NOx NO NO2 PM
Baseline No. 2D 0.3 1.4 6.f 5.0 1.1 0.253
Baseline No. 2D + FBC (0.15/7.5) 0.3 1.3 6.0 5.3 0.7 0.215
Baseline No.2D + DOC (no FBC) 0.2 0.7 6.0 ND ND 0.196
Baseline No. 2D + DOC + FBC 0.2 0.7 6.0 5.5 0.5 0.178
(0.15/7.5)
ULSD + FBC + DOC (0.15/7.5) 0.2 0.5 5.3* 4.9 0.4** 0.168
* Duplicate Measurements
** Single Measurement
Example 2
[0032] This example presents the results of testing over a single cold and
triple hot FTP
transient test cycles for the FBC/DOC coinbination on a 1990 Cummins 8.3 liter
6 CTA,
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275 hp medium heavy-duty engine certified to meet 1991 emission standards for
NOx and
PM. The engine was initially run on untreated No. 2D fuel (> 300 ppm Sulfur)
with no
exhaust aftertreatment DOC installed. Particulate emissions were determined
from the
average composite at 0.190 gr/hp-hr.
[0033] Fuel was switched to FBC treated commercial ULSD (< 15 ppm) and a
degreened
DOC-1 was installed in the engine exhaust. The engine was run for 16 hours and
tested for
emissions. Average particulate emissions were reduced by over 53% to 0.089
gr/hp-hr.
Total NO2 was also reduced by more than 50% from 0.9 gr/hp-hr to 0.4 gr/hp-hr.
[0034] The DOC was a 9.5" dia. x 6" L 400 cpsi ceramic substrate made by
Corning, Inc.
and catalyzed with 3 gr/cu ft. of precious metal by Clean Air Systems, Inc. of
New Mexico.
It was installed in a stainless steel can with conventional inlet and outlet
cones. The FBC
was a platinum/cerium bimetallic used at a dose rate of 0.5 ppm/7.5 ppm.
[0035] An identical field aged DOC-2 which had been operated in commercial
field service
for 1000 hours on FBC treated ULSD was also tested using FBC treated ULSD.
Average
particulate emissions were reduced by 48% to 0.098 gr/hp-hr and NO2 emissions
were held
to 13% of overall nitrogen oxide representing a level of 0.6 gr/hp-hr.
[0036] In another test, an identical DOC-3 that had been operated in
commercial service for
1100 hours on FBC treated No. 2D at a 0.15/7.5 ppm dose rate was tested on FBC
treated
No. 2D at 0.15/7.5 ppm. Overall PM reduction was to a level of 0.113 gr/hp-hr
while total
NO2 was reduced from 0.9 gr/hp-hr to 0.5 gr/hp-hr representing 10% of total
nitrogen oxide
emissions versus 19% for the baseline NO2 emissions on No. 2D fuel.
[0037] These data support the unexpected high level of particulate reduction
achieved by
low levels of FBC with a lightly catalyzed DOC and confirm that PM
performance,can be
maintained at high levels even after commercial service with the use of FBC
treated fuel.
There is also an unexpected reduction in NOa from the combination of FBC and
DOC,
which is an advantage over heavily catalyzed devices which tend to increase
NO2
emissions.
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[0038] Emissions from a 1990 (1991 Certified) Cummins 8.3 Liter Engine
(Average Composite Emissions gr/hp-hr)
Fuel/Device HC CO NOx NO2 % NO2 PM
Baseline No. 2D 0.39 0.78 4.8 0.9 19% 0.190
DOC-1 (degreened) + FBC + 0.16 0.28 4.5 0.4 9% 0.089
ULSD
DOC-2 (aged) + FBC + ULSD 0.24 0.36 4.7 0.6 13% 0.098
DOC-3 (aged) + FBC + No. 2D 0.29 0.66 4.8 0.5 10% 0.113
Example 3
[0039] This example reports testing that further confirms the benefits of low
levels of FBC
in ULSD combined with a lightly catalyzed DOC. In this Example testing was
conducted
on a 1995 Navistar DT466, 7.6 liter engine over a single cold and three hot
test cycles. The
average of three composite emissions results was calculated and reported in
grams/bhp-hr.
Baseline emission results on untreated No. 2D fuel (> 300 ppm S) show average
PM
emissions of 0.106 gr/hp-hr with NOa emissions at 1.1 gr/hp-hr representing
23% of total
NOx emissions.
[0040] Use of ULSD (< 15 ppm S) treated with a bimetallic FBC at 0.15/7.5 ppm
reduced
PM by 31 % to 0.073 gr/hp-hr with NO2 reduced to 0.8 gr/hp-hr or 19% of total
NOx
emissions. Reductions in HC, CO and NOx were also observed for the FBC/ULSD
combination.
[0041] In a further test, a degreened lightly catalyzed DOC-1 from Example 2
was installed
in the exhaust and the engine was run on FBC treated ULSD. Overall PM
emissions were
reduced by 45% to 0.058 gr/hp-hr while NO2 was reduced to 0.6 gr/hp-hr
representing 14%
of overall NOx emissions. Further reductions in HC, CO and NOx were also
noted.
[0042] Emissions from a 1995 Navistar DT 466 7.6 liter Engine
(g/hp-hr)
Fuel/Device HC CO NOx NO2 % NOZ PM
Baseline No. 2D 0.3 1.3 4.8 1.1 23% 0.106
ULSD + FBC 0.2 1.0 4.3 0.8 19% 0.073
ULSD + FBC + DOC 0.1 0.5 4.2 0.6 14% 0.058
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[0043] The above description is intended to enable the person skilled in the
art to practice
the invention. It is not intended to detail all of the possible modifications
and variations
which will become apparent to the skilled worker upon reading the description.
It is
intended, however, that all such modifications and variations be included
within the scope
of the invention which is seen in the above description and otherwise defined
by the
following claims. The claims are meant to cover the indicated elements and
steps in any
arrangement or sequence which is effective to meet the objectives intended for
the
invention, unless the context specifically indicates the contrary.
