Note: Descriptions are shown in the official language in which they were submitted.
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PROCESSES FORMANUFACTLJRINGV.UATERFILTERMATERIALS
AND WATER FILTERS
FIELD OF TI-~ INVENTION
The present invention relates to the field of processes for manufacturing
water filter
materials and water filters, and, more particularly, to the field of processes
for manufacturing
water filters containing mesoporous activated carbon particles.
BACKGROUND OF THE INVENTION
Mater may contain many different kinds of contaminants including, for example,
particulates, harmful chemicals, and microbiological organisms, such as
bacteria, parasites,
protozoa and viruses. In a variety of circumstances, these contaminants must
be removed
before the water can be used. For example, in many medical applications and in
the
manufacture of certain electronic components, extremely pure water is
required. As a more
common example, any harmful contaminants must be removed from the water before
it is
potable, i.e., fit to consume. Despite modern water purification means, the
general
population is at risk, and in particular infants and persons with compromised
immune
systems are at considerable risk.
In the U.S. and other developed countries, municipally treated water typically
includes one or more of the following impurities: suspended solids, bacteria,
parasites,
viruses, organic matter, heavy metals, and chlorine. Breakdown and other
problems with
water treatment systems sometimes lead to incomplete removal of bacteria and
viruses. In
other countries, there are deadly consequences associated with exposure to
contaminated
water, as some of them have increasing population densities, increasingly
scarce water
resources, and no water treatment utilities. It is common for sources of
drinking water to be
in close proximity to human and animal waste, such that microbiological
contamination is a
major health concern. As a result of waterborne microbiological contamination,
an
estimated six million people die each year, half of which are children under 5
years of age.
In 1987, the U.S. Environmental Protection Agency (EPA) introduced the "Guide
Standard and P~acd for ~"estzng M~ogical LY~ater Purifiers". The protocol
establishes
minimum requirements regarding the performance of drinking water treatment
systems that
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are designed to reduce specific health related contaminants in public or
private water
supplies. The requirements are that the effluent from a water supply source
exhibits 99.99%
(or equivalently, 4 log) removal of viruses and 99.9999% (or equivalently, 6
log) removal of
bacteria against a challenge. Under the EPA protocol, in the case of viruses,
the influent
concentration should be 1x10 viruses per liter, and in the case of bacteria,
the influent
concentration should be 1x10$ bacteria per liter. Because of the prevalence of
Esd~erid~iet cdi
(E. culi, bacterium) in water supplies, and the risks associated with its
consumption, this
microorganism is used as the bacterium in the majority of studies. Similarly,
the MS-2
bacteriophage (or simply, MS-2 phage) is typically used as the representative
microorganism
for virus removal because its size and shape (i.e., about 26 nm and
icosahedral) are similar to
many viruses. Thus, a filter's ability to remove MS-2 bacteriophage
demonstrates its ability
to remove other viruses.
Due to these requirements and a general interest in improving the quality of
potable
water, there is a continuing desire to provide processes for manufacturing
filter materials and
filters, which are capable of removing bacteria and/or viruses from a fluid.
SUMNfARY OF THE INVENTION
A process for producing a water filter material is provided. The process
includes the
steps of providing a plurality of mesoporous activated carbon particles, and
treating said
plurality of mesoporous activated carbon particles to produce a plurality of
mesoporous
activated carbon particles having a bulk oxygen percentage byweight of less
than about 5%.
BRIEF DESCRIPTION OF THE DRAWINGS
~~Uhile the specification concludes with claims particularly pointing out and
distinctly
claiming the invention, it is believed that the present invention will be
better understood
from the following description taken in conjunction with the accompanying
drawings in
which:
FIG. 1a is a BET nitrogen adsorption isotherm of mesoporous and acidic
activated
carbon particles CA 10, and mesoporous, basic, and reduced-oxygen activated
carbon
particles TA4-CA 10.
FIG. 1b is a BET nitrogen adsorption isotherm of mesoporous and basic
activated
carbon particles RGC, and mesoporous, basic, and reduced-oxygen activated
carbon THe4-
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RGC.
FIG. 2a is a mesopore volume distribution of the particles of FIG. 1a.
FIG. 2b is a mesopore volume distribution of the particles of FIG. 1b.
FIG. 3a is a point-of-zero-charge graph of the particles of FIG. 1a.
FIG. 3b is a point-of-zero-charge graph of the particles of FIG. 1b.
FIG. 4 is a cross sectional side view of an axial flow filter made in
accordance with
the present invention.
FIG. 5a illustrates the E. c~ali bath concentration as a function of time for
the
activated carbon particles of FIG. 1a.
FIG. 5b illustrates the E. cdi bath concentration as a function of time for
activated
carbon particles of FIG. 1b.
FIG. 6a illustrates the MS-2 bath concentration as a function of time for the
activated carbon particles of FIG. 1a.
FIG. 6b illustrates the MS-2 bath concentration as a function of time for the
activated carbon particles of FIG. 1b.
FIG. 7a illustrates the E. cdi flow concentration as a function of the
cumulative
volume of water through 2 filters; one containing RGC mesoporous and basic
activated
carbon, and the other containing coconut microporous activated carbon
particles.
FIG. 7b illustrates the MS-2 flow concentration as a function of the
cumulative
volume of water through of 2 filters; one containing RGC mesoporous and basic
activated
carbon, and the other containing coconut microporous activated carbon
particles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
All documents cited are, in relevant part, incorporated herein by reference.
The citation
of any document is not to be construed as an admission that it is prior art
with respect to the
present invention.
I. Definitions
As used herein, the terms "filters" and "filtration" refer to structures and
mechanisms, respectively, associated with microorganism removal (and/or other
contaminant removal), via primarily adsorption andlor size exclusion to a
lesser extent.
As used herein, the phrase "filter material" is intended to refer to an
aggregate of
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filter particles. The aggregate of the filter particles forming a filter
material can be either
homogeneous or heterogeneous. The filter particles can be uniformly or non-
uniformly
distributed (e.g., layers of different filter particles) within the filter
maxerial. The filter
particles forming a filter material also need not be identical in shape or
size and may be
provided in either a loose or interconnected form. For example, a filter
material might
comprise mesoporous and basic activated carbon particles in combination with
activated
carbon fibers, and these filter particles may be either provided in loose
association or
partially or wholly bonded by a polymeric binder or other means to form an
integral
structure.
As used herein, the phrase "filter particle" is intended to refer to an
individual
member or piece, which is used to form at least part of a filter material. For
example, a fiber,
a granule, a bead, etc. are each considered filter particles herein. Further,
the filter particles
can vary in size, from impalpable filter particles (e.g., a very fine powder)
to palpable filter
particles.
As used herein, the phrase "filter material pore volume" refers to the total
volume of
the inter-particle pores in the filter material with sizes larger than 0.1
~.m.
As used herein, the phrase "filter material total volume" refers to the sum of
the inter-
particle pore volume and the volume occupied bythe filter particles.
As used herein, the terms "microorganism", "microbiological organism" and
"pathogen"
are used interchangeably. These terms refer to various types of microorganisms
that can be
characterized as bacteria, viruses, parasites, protozoa, and germs.
As used herein, the phrase "Bacteria Removal Index" (BRI) of filter particles
is
defined as:
BRI =100 x [1- (bath concentration of E. c~li bacteria at equilibrium /
control concentration of E. cr~i bacteria)],
wherein "bath concentration of E. ct~i bacteria at equilibrium" refers to the
concentration of
bacteria at equilibrium in a bath that contains a mass of filter particles
having a total external
surface area of 1400 cm2 and Sauter mean diameter less than 55 Vim, as
discussed more fully
hereafter. Equilibrium is reached when the E. ctalv concentration, as measured
at two time
points 2 hours apart, remains unchanged to within half order of magnitude. The
phrase
"control concentration of E. c~li bacteria" refers to the concentration of E.
cr~i bacteria in the
control bath, and is equal to about 3.7x109 CFU/L. The Sauter mean diameter is
the
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diameter of a particle whose surface-to-volume ratio is equal to that of the
entire particle
distribution. Note that the term "CFU/L" denotes "colony forming units per
liter", which is
a typical term used in E. cr~i counting. The BRI index is measured without
application of
chemical agents that provide bactericidal effects. An equivalent way to report
the removal
capability of filter particles is with the "Bacteria Log Removal Index"
(BLRI), which is
defined as:
BLRI =- log[1- (BRI/100)].
The BLRI has units of "log" (where "log" stands for logarithm). For example,
filter
particles that have a BRI equal to 99.99% have a BLRI equal to 4 log. A test
procedure for
determining BRI and BLRI values is provided hereafter.
As used herein, the phrase "Virus Removal Index" (VRI) for filter particles is
defined
as:
VRI = 100 x [1- (bath concentration of MS-2 phages at equilibrium /
control concentration of MS-2 phages)],
wherein "bath concentration of MS-2 phages at equilibrium" refers to the
concentration of
phages at equilibrium in a bath that contains a mass of filter particles
having a total external
surface area of 1400 cm2 and Sauter mean diameter less than 55 pm, as
discussed more fully
hereafter. Equilibrium is reached when the MS-2 concentration, as measured at
two time
points 2 hours apart, remains unchanged to within half order of magnitude. The
phrase
"control concentration of MS-2 phages" refers to the concentration of MS-2
phages in the
control bath, and is equal to about 6.7x10 PFU/L. Note that the term "PFU/L"
denotes
"plaque-forming units per liter", which is a typical term used in MS-2
counting. The VRI
index is measured without application of chemical agents that provide
virucidal effects. An
equivalent way to report the removal capability of filter particles is with
the "Viruses Log
Removal Index" (VLRI), which is defined as:
VLRI =- log[1- (VRI/100)].
The VLRI has units of "log" (where "log" is the logarithm). For example,
filter
particles that have a VRI equal to 99.9% have a VLRI equal to 3 log. A test
procedure for
deternlining VRI and VLRI values is provided hereafter.
As used herein, the phrase "Filter Bacteria Log Removal (F-BLR)" refers to the
bacteria removal capability of the filter after the flow of the first 2,000
filter material pore
volumes. The F-BLR is defined and calculated as:
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F-BLR =-log [(effluent concentration of E. cdz)/(influent concentration of E.
cr~z)],
where the "influent concentration of E. cta~z" is set to about 1x108 CFU/L
continuously
throughout the test and the "effluent concentration of E. cdz" is measured
after about 2,000
filter material pore volumes flow through the filter. F-BLR has units of "log"
(where "log" is
the logarithm). Note that if the effluent concentration is below the limit of
detection of the
technique used to assay, then the effluent concentration for the calculation
of the F-BLR is
considered to be the limit of detection. Also, note that the F-BLR is measured
without
application of chemical agents that provide bactericidal effects.
As used herein, the phrase "Filter Viruses Log Removal (F-VLR)" refers to the
virus
removal capability of the filter after the flow of the first 2,000 filter
material pore volumes.
The F-VLR is defined and calculated as:
F-VLR =-log [(effluent concentration of MS-2)/(influent concentration of MS-
2)],
where the "influent concentration of IVIS-2" is set to about 1x10 PFU/L
continuously
throughout the test and the "effluent concentration of MS-2" is measured after
about 2,000
filter material pore volumes flow through the filter. F-VLR has units of "log"
(where "log"
is the logarithm). Note that if the effluent concentration is below the limit
of detection of
the technique used to assay, then the effluent concentration for the
calculation of the F-VLR
is considered to be the limit of detection. Also, note that the F-VLR is
measured without
application of chemical agents that provide virucidal effects.
As used herein, the phrase "total external surface area" is intended to refer
to the total
geometric external surface area of one or more of the filter particles, as
discussed more fully
hereafter.
As used herein, the phrase "specific external surface area" is intended to
refer to the
total external surface area per unit mass of the filter particles, as
discussed more fully
hereafter.
As used herein, the term "micropore" is intended to refer to an intra-particle
pore
having a width or diameter less than 2 nm (or equivalently, 20 l~).
As used herein, the term "mesopore" is intended to refer to an intra-particle
pore
having a width or diameter between 2 nm and 50 nm (or equivalently, between 20
l~ and 500
l~).
As used herein, the term "macropore" is intended to refer to an intra-particle
pore
having a width or diameter greater than 50 nm (or equivalently, 500 l~).
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As used herein, the phrase "total pore volume" and its derivatives are
intended to
refer to the volume of all the intra-particle pores, i.e., micropores,
mesopores, and
macropores. The total pore volume is calculated as the volume of nitrogen
adsorbed at a
relative pressure of 0.9814 using the BET process (ASTM D 4820 - 99 standard),
a process
well known in the art.
As used herein, the phrase "micropore volume" and its derivatives are intended
to
refer to the volume of all micropores. The micropore volume is calculated from
the volume
of nitrogen adsorbed at a relative pressure of 0.15 using the BET process
(ASTM D 4820 -
99 standard), a process well known in the art.
AS used herein, the phrase "sum of the mesopore and macropore volumes" and its
derivatives are intended to refer to the volume of all mesopores and
macropores. The sum
of the mesopore and macropore volumes is equal to the difference between the
total pore
volume and micropore volume, or equivalently, is calculated from the
difference between the
volumes of nitrogen adsorbed at relative pressures of 0.9814 and 0.15 using
the BET process
(ASTM D 4820 - 99 standard), a process well known in the art.
As used herein, the phrase "pore size distribution in the mesopore range" is
intended
to refer to the distribution of the pore size as calculated by the Barren,
Joyner, and Halenda
(BJI~ process, a process well known in the art.
As used herein, the term "carbonization" and its derivatives are intended to
refer to a
process in which the non-carbon atoms in a carbonaceous substance are reduced.
As used herein, the term "activation" and its derivatives are intended to
refer to a
process in which a carbonized substance is rendered more porous.
As used herein, the term "activated carbon particles" or "activated carbon
filter
particles" and their derivatives are intended to refer to carbon particles
that have been
subjected to an activation process.
As used herein, the phrase "point of zero charge" is intended to refer to the
pH
above which the total surface of the carbon particles is negatively charged. A
well known
test procedure for determining the point of zero charge is set forth
hereafter.
As used herein, the term "basic" is intended to refer to filter particles with
a point of
zero charge greater than 7.
As used herein, the term "acidic" is intended to refer to filter particles
with a point of
zero charge less than 7.
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As used herein, the phrase "mesoporous activated carbon filter particle"
refers to an
activated carbon filter particle wherein the sum of the mesopore and macropore
volumes
maybe greater than 0.12 mL/g.
As used herein, the phrase "microporous activated carbon filter particle"
refers to an
activated carbon filter particle wherein the sum of the mesopore and macropore
volumes
may be less than 0.12 mL/g.
As used herein, the phrase "mesoporous and basic activated carbon filter
particle" is
intended to refer to an activated carbon filter particle wherein the sum of
the mesopore and
macropore volumes may be greater than 0.12 mL/g and has a point of zero charge
greater
than 7.
As used herein, the phrase "mesoporous, basic, and reduced-oxygen activated
carbon
filter particle" is intended to refer to an activated carbon filter particle
wherein the sum of
the mesopore and macropore volumes may be greater than 0.12 mL/g, has a point
of zero
charge greater than 7, and has a bulk oxygen percentage by weight of 1.5% or
less.
As used herein, the phrase "mesoporous and acidic activated carbon filter
particle" is
intended to refer to an activated carbon filter particle wherein the sum of
the mesopore and
macropore volumes may be greater than 0.12 mL/g and has a point of zero charge
less than
7.
As used herein, the phrase "starting material" refers to any precursor
containing
mesopores and macropores or capable of yielding mesopores and macropores
during
carbonization and/or activation.
As used herein, the phrase "axial flow" refers to flow through a planar
surface and
perpendicularly to that surf ace.
As used herein, the phrase "radial flow" typically refers to flow through
essentially
cylindrical or essentially conical surfaces and perpendicularlyto those
surfaces.
As used herein, the phrase "face area" refers to the area of the filter
material initially
exposed to the influent water. For example, in the case of axial flow filters,
the face area is
the cross sectional area of the filter material at the entrance of the fluid,
and in the case of
the radial flow filter, the face area is the outside area of the filter
material.
As used herein, the phrase "filter depth" refers to the linear distance that
the influent
water travels from the entrance to the exit of the filter material. For
example, in the case of
axial flow filters, the filter depth is the thickness of the filter material,
and in the case of the
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radial flow filter, the filter depth is half of the difference between the
outside and inside
diameters of the filter material.
As used herein, the phrases "average fluid residence time" and/or "average
fluid
contact time" refer to the average time that the fluid is in contact with the
filter particles
inside the filter as it travels through the filter material, and are
calculated as the ratio of the
filter material pore volume to the fluid flow rate.
As used herein, the phrases "filter porosity" and/or "filter bed porosit~'
refer to the
ratio of the filter material pore volume to the filter material total volume.
As used herein, the phrase "inlet" refers to the means in which a fluid is
able to enter
the filter or filter material. For example, the inlet can be a structure that
is part of the filter,
or the filter material face area.
As used herein, an "outlet" refers to the means in which a fluid is able to
exit the
filter or filter material. For example, the outlet can be a structure that is
part of the filter, or
the cross sectional area of the filter material at the exit of the fluid.
II. Mesoporous Activated Carbon Filter Particles
Unexpectedly it has been found that mesoporous activated carbon filter
particles
adsorb a larger number of microorganisms compared to microporous activated
carbon filter
particles. Also, unexpectedly it has been found that mesoporous and basic
activated carbon
filter particles adsorb a larger number of microorganisms compared to that
adsorbed by
mesoporous and acidic activated carbon filter particles. Furthermore, it has
been found
unexpectedly that mesoporous, basic, and reduced-oxygen activated carbon
filter particles
adsorb a larger number of microorganisms compared to that adsorbed by
mesoporous and
basic activated carbon filter particles without reduced bulk oxygen percentage
by weight.
Although not wishing to be bound by any theory, applicants hypothesize that,
with
regard to porosity, a large number of mesopores and/or macropores provides
more
convenient adsorption sites (openings or entrances of the mesopores /
macropores) for the
pathogens, their fimbriae, and surface polymers (e.g. proteins,
lipopolysaccharides,
oligosaccharides and polysaccharides) that constitute the outer membranes,
capsids and
envelopes of the pathogens because the typical size of such is similar to that
of the entrances
of the mesopores and macropores. Also, mesoporosity and macroporosity may
correlate
with one or more surface properties of the carbon, such as surface roughness.
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Also, not wishing to be bound by theory, applicants hypothesize that basic
activated
carbon surfaces contain the types of functionality that are necessary to
attract a larger
number of microorganisms compared to those attracted by an acidic carbon
surface. This
enhanced adsorption onto the basic carbon surfaces might be attributed to the
fact that the
basic carbon'surfaces attract the typically negatively charged microorganisms
and functional
groups on their surface. Applicants further hypothesize that basic carbon is
capable of
producing disinfectants when placed in water by reducing molecular oxygen.
Although the
final product of the reduction is hydroxide, applicants believe that reactive
oxygen
intermediates, such as superoxide, hydroperoxide, and/or hydroxy radicals, are
formed and
maybe sufficientlylong-lived to diffuse from carbon into bulk solution.
Furthermore, applicants believe that carbon becomes more basic as the bulk
oxygen
percentage by weight is reduced. A low bulk oxygen percentage by weight may
lead to
improved bacteria/viruses adsorption because there will be: (1) less
carboxylic acids and
hence a less negative surface to repel bacteria/viruses; and (2) a less
hydrated surface so that
water is more easily displaced by bacteria/viruses as they attempt to adsorb
to the surface
(i.e., less of an energy penalty for the bacteria/virus to displace other
species already
occupying sites on the surface). This latter reason (i.e., a less hydrated
surface) also ties in
with the idea that the ideal surface, discussed hereafter, should be somewhat
hydrophobic
(that is, it should have just enough oxygen substitution on the edge carbon
atoms to allow it
to wet out, but not so much as to make it excessively hydrophilic).
The filter particles can be provided in a variety of shapes and sizes. For
example,
the filter particles can be provided in simple forms such as powder, granules,
fibers, and
beads. The filter particles can be provided in the shape of a sphere,
polyhedron, cylinder, as
well as other symmetrical, asymmetrical, and irregular shapes. Further, the
filter particles can
also be formed into complex forms such as webs, screens, meshes, non-wovens,
wovens, and
bonded blocks, which may or may not be formed from the simple forms described
above.
Like shape, the size of the filter particle can also vary, and the size need
not be
uniform among filter particles used in any single filter. In fact, it can be
desirable to provide
filter particles having different sizes in a single filter. Generally, the
size of the filter particles
may be between about 0.1 ~.m and about 10 mm, preferably between about 0.2 ~.m
and
about 5 mm, more preferably between about 0.4 ~.m and about 1 mm, and most
preferably
to
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between about 1 ~,m and about 500 Vim. For spherical and cylindrical particles
(e.g., fibers,
beads, etc.), the above-described dimensions refer to the diameter of the
filter particles. For
filter particles having substantially different shapes, the above-described
dimensions refer to
the largest dimension (e.g. length, width, or height).
The filter particles may be the product of any precursor that contains
mesopores
and macropores or generates mesopores and macropores during carbonization
and/or
activation. For example, and not by way of limitation, the filter particles
can be wood-based
activated carbon particles, coal based activated carbon particles, peat-based
activated carbon
particles, pitch-based activated carbon particles, tar-based activated carbon
particles, bean-
based activated carbon particles, other lignocellulosic-based activated carbon
particles, and
mixtures thereof.
Activated carbon can display acidic, neutral, or basic properties. The acidic
properties are associated with oxygen-containing functionalities or functional
groups, such
as, and not by way of limitation, phenols, carboxyls, lactones, hydroquinones,
anhydrides,
and ketones. The basic properties have heretofore been associated with
functionalities such
as pyrones, chromenes, ethers, carbonyls, as well as the basal plane ~
electrons. The acidity
or basicity of the activated carbon particles is determined with the "point of
zero charge"
technique (Newcombe, G., et al., Cdloids and Surfaces A: Phasicr~d~emieal end
Engin~ringAspeets,
78, 65-71 (1993)), the substance of which is incorporated herein by reference.
The technique
is further described in section VI hereafter. Filter particles of the present
invention may
have a point of zero charge between 1 and 14, preferably greater than about 4,
preferably
greater than about 6, preferably greater than about 7, preferably greater than
about 8, more
preferably greater than about 9, and most preferably between about 9 and about
12.
The point of zero charge of activated carbons inversely correlates with their
bulk oxygen
percentage by weight. Filter particles of the present invention may have a
bulk oxygen
percentage by weight less than about 5%, preferably less than about 2.5%,
preferably less
than about 2.3%, preferably less than about 2%, more preferably less than
about 1.2%, and
most preferably less than about 1%, and/or greater than about 0.1%, preferably
greater than
about 0.2%, more preferably greater than about 0.25%, and most preferably
greater than
about 0.3%. Also, the point of zero charge of activated carbon particles
correlates with the
ORP of the water containing the particles because the point of zero charge is
a measure of
the ability of the carbon to reduce oxygen (at least for basic carbons).
Filter particles of the
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present invention may have an ORP less than about 570 mV, preferably less than
about 465
mV, preferably less than about 400, preferably less than about 360 mV,
preferably less than
about 325 mV, and most preferably between about 290 mV and about 175 mV.
The electric resistance of the activated carbon filter particles or filter
material is one of
their important properties as it relates to their ability to form a filter
block. For example, a
resistive heating method can be used to form filter blocks, wherein a filter
material is heated
bypassing electricity between 2 ends of the filter material. The electric
resistance of the filter
material will control its ability to heat in a short time. The electric
resistance is measured by
forming filter blocks using conditions as those mentioned in Examples 3 and 4,
supra, and
measuring the electric resistance between the 2 faces of the block by
contacting them with 2
electrodes from a voltmeter. Exemplary electric resistances of the filters of
Examples 3 and 4
are about 350 S2 and about 40 SZ, respectively. Also, the respective electric
resistances of
filters made with CARBOCHEM CA 10 of Example 1, supra, and TA4-CA10 of Example
2,
supra, are about 1.3 MS2, and about 100 S2.
Filter particles may be achieved by way of treating a starting material as
described
herebelow. The treatment conditions may include atmosphere composition,
pressure,
temperature, and/or time. The atmospheres of the present invention may be
reducing or
inert. Heating the filter particles in the presence of reducing atmospheres,
steam, or inert
atmospheres yields filter material with reduced surface oxygen functionality.
Examples of
suitable reducing atmospheres may include hydrogen, nitrogen, dissociated
ammonia, carbon
monoxide, and/or mixtures. Examples of suitable inert atmospheres may include
argon,
helium, and/or mixtures thereof.
The treatment temperature, when the activated carbon particles do not contain
any
noble metal catalysts (e.g., platinum, gold, palladium) may be between about
600°C and
about 1,200°C, preferably between about 700°C and about
1,100°C, more preferably
between about 800°C and about 1,050°C, and most preferably
between about 900°C and
about 1,000°C. If the activated carbon particles contain noble metal
catalysts, the treatment
temperature may be between about 100°C and about 800°C,
preferably between about 200°
C and about 700°C, more preferably between about 300°C and about
600°C, and most
preferably between about 350°C and about 550°C.
The treatment time may be between about 2 minutes and about 10 hours,
preferably
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between about 5 minutes and about 8 hours, more preferably between about 10
minutes and
about 7 hours, and most preferably between about 20 minutes and about 6 hours.
The gas
flow rate may be between about 0.25 standard L/h.g (i.e., standard liters per
hour and gram
of carbon; 0.009 standard ft3/h.g) and about 60 standard L/h.g (2.1 standard
ft3/h.g),
preferably between about 0.5 standard L/h.g (0.018 standard ft3/h.g) and about
30 standard
L/h.g (1.06 standard ft3/h.g), more preferably between about 1.0 standard
L/h.g (0.035
standard ft3/h.g) and about 20 standard L/h.g (0.7 standard ft3/h.g), and most
preferably
between about 5 standard L/h.g (0.18 standard ft3/h.g) and about 10 standard
L/h.g (0.35
standard ft3/h.g). The pressure can be maintained greater than, equa~ to, or
less tnan
atmospheric during the treatment time. As will be appreciated, other processes
for producing
a mesoporous, basic, and reduced-oxygen activated carbon filter material can
be employed.
Also; such treatment of a starting material as described above may be repeated
multiple
times, depending on the starting material, in order to obtain a filter
material.
A starting material may be commercially obtained, or may be made by the
methods
which are well known in the art, as described in, for example, Jagtoyen, M.,
and F.
Derbyshire, Carb~an, 36(7-8), 1085-1097 (1998), and Evans, et al., Carben, 37,
269-274 (1999),
and Ryoo et al., J. Ph~s. C,hem B, 103(37), 7743-7746 (1999), the substances
of which are
herein incorporated by reference. Typical chemicals used for
activation/carbonization
include phosphoric acid, zinc chloride, ammonium phosphate, etc., which may be
used in
combination with the methods described in the two immediately cited journals.
The Brunauer, Emmett and Teller (BE'I~ specific surface area and the Barrett,
Joyner, and Halenda (BJH) pore size distribution can be used to characterize
the pore
structure of particles. Preferably, the BET specific surface area of the
filter particles may be
between about 500 m2/g and about 3,000 m2/g, preferably between about 600 m2/g
to
about 2,800 m2/g, more preferably between about 800 m2/g and about 2,500 m2/g,
and
most preferably between about 1,000 mz/g and about 2,000 m2/g. Referring to
FIG. 1a,
typical nitrogen adsorption isotherms, using the BET process, of a mesoporous,
basic, and
reduced-oxygen wood-based activated carbon (TA4-CA 10), and a mesoporous and
acidic
wood-based activated carbon (CA 10) are illustrated. Referring to FIG. 1b,
typical nitrogen
adsorption isotherms, using the BET process, of a mesoporous and basic wood-
based
activated carbon (RGG~, and a mesoporous, basic, and reduced-oxygen wood-based
activated carbon (THe4-RGG~ are illustrated.
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WO 2004/076360 PCT/US2003/005409
The total pore volume of the mesoporous and basic activated carbon particles
is
measured during the BET nitrogen adsorption and is calculated as the volume of
nitrogen
adsorbed at a relative pressure, P/Po, of 0.9814. More specifically and as is
well known in
the art, the total pore volume is calculated by multiplying the "volume of
nitrogen adsorbed
in mL(STP)/g" at a relative pressure of 0.9814 with the conversion factor
0.00156, that
converts the volume of nitrogen at STP (standard temperature and pressure) to
liquid. The
total pore volume of the filter particles may be greater than about 0.4 mL/g,
or greater than
about 0.7 mL/g, or greater than about 1.3 mL/g, or greater than about 2 mL/g,
and/or less
than about 3 mL/g, or less than about 2.6 mL/g, or less than about 2 mL/g, or
less than
about 1.5 mL/g.
The sum of the mesopore and macropore volumes is measured during the BET
nitrogen adsorption and calculated as the difference between the total pore
volume and the
volume of nitrogen adsorbed at P/Po of 0.15. The sum of the mesopore and
macropore
volumes of the filter particles may be greater than about 0.12 mL/g, or
greater than about
0.2 mL/g, or greater than about 0.4 mL/g, or greater than about 0.6 mL/g, or
greater than
about 0.75 mL/g, and/or less than about 2.2 mL/g, or less than about 2 mL/g,
or less than
about 1.5 mL/g, or less than about 1.2 mL/g, or less than about 1 mL/g.
The BJH pore size distribution can be measured using the Barren, Joyner, and
Halenda (BJI~ process, which is described in J. A~r,~r: Chem Soc:, 73, 373-80
(1951) and
Gregg and Sing, ADSORPTION, SURFACE AREA, AND POROSITY, 2nd edition,
Academic Press, New York (1982), the substances of which are incorporated
herein by
reference. In one embodiment, the pore volume may be at least about 0.01 mL/g
for any
pore diameter between about 4 nm and about 6 nm. In an alternate embodiment,
the pore
volume may be between about 0.01 mL/g and about 0.04 mL/g for any pore
diameter
between about 4 nm and about 6 nm. In yet another embodiment, the pore volume
may be
at least about 0.03 xnL/g for pore diameters between about 4 nm and about 6 nm
or is
between about 0.03 mL/g and about 0.06 mL/g. In a preferred embodiment, the
pore
volume may be between about 0.015 mL/g and about 0.06 mL/g for pore diameters
between about 4 nm and about 6 nm. FIG. 2a illustrates typical mesopore volume
distributions, as calculated by the BJH process, of a mesoporous, basic, and
reduced-oxygen
activated carbon (TA4-CA 10), and a mesoporous and acidic wood-based activated
carbon
(CA 10). FIG. 2b illustrates typical mesopore volume distributions, as
calculated bythe BJH
14
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
process, of a mesoporous and basic wood-based activated carbon (RGG~, and a
mesoporous,
basic, and reduced-oxygen wood-based activated carbon (THe4-RGG~.
The ratio of the sum of the mesopore and macropore volumes to the total pore
volume may be greater than about 0.3, preferably greater than about 0.4,
preferably greater
than about 0.6, and most preferably between about 0.7 and about 1.
The total external surface area is calculated by multiplying the specific
external
surface area by the mass of the filter particles, and is based on the
dimensions of the filter
particles. For example, the specific external surface area of mono-dispersed
(i.e., with
uniform diameter) fibers is calculated as the ratio of the area of the fibers
(neglecting the 2
cross sectional areas at the ends of the fibers) to the weight of the fibers.
Thus, the specific
external surface area of the fibers is equal to: 4~Dp , where D is the fiber
diameter and p is
the fiber density For monodispersed spherical particles, similar calculations
yield the
specific external surface area as equal to: 6~Dp , where D is the particle
diameter and p is
the particle density. For poly dispersed fibers, spherical or irregular
particles, the specific
external surface area is calculated using the same respective formulae as
above after
substituting D3,2 for D , where D3,z is the Sauter mean diameter, which is the
diameter of a
particle whose surface-to-volume ratio is equal to that of the entire particle
distribution. A
process, well known in the art, to measure the Sauter mean diameter is by
laser diffraction,
for example using the Malvern equipment (Malvern Instruments Ltd., Malvern,
U.K.). The
specific external surface area of the filter particles maybe between about 10
cm2/g and about
100,000 cm2/g, preferably between about 50 cm2/g and about 50,000 cm2/g, more
preferably between about 100 cmz/g and about 10,000 cm2/g, and most preferably
between
about 500 cm2/g and about 7,000 cmz/g.
The BRI of the mesoporous, or mesoporous and basic, or mesoporous, basic and
reduced-oxygen activated carbon particles, when measured according to the test
procedure
set forth herein, may be greater than about 99%, preferably greater than about
99.9%, more
preferably greater than about 99.99%, and most preferably greater than about
99.999%.
Equivalently, the BLRI of the mesoporous, or mesoporous and basic, or
mesoporous, basic
and reduced-oxygen activated carbon particles may be greater than about 2 log,
preferably
greater than about 3 log, more preferably greater than about 4 log, and most
preferably
greater than about 5 log. The VRI of the mesoporous, or mesoporous and basic,
or
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
mesoporous, basic and reduced-oxygen activated carbon particles, when measured
according
to the test procedure set forth herein, may be greater than about 90%,
preferably greater than
about 95%, more preferably greater than about 99%, and most preferably greater
than about
99.9%. Equivalently, the VLRI of the mesoporous, or mesoporous and basic, or
mesoporous, basic and reduced-oxygen activated carbon particles may be greater
than about
1 log, preferably greater than about 1.3 log, more preferably greater than
about 2 log, and
most preferably greater than about 3 log.
The steady state, one-dimensional, "clean" bed filtration theory (assuming
negligible
dispersive transport and desorption of microorganisms) for an axial flow
filter (Yao et al.,
Ertzirrnz Sci. Tedmd. 5, 1102-1112 (1971)), the substance of which is
incorporated herein by
reference, describes that:
C'~C° =exp(-~1,L), (1)
where C is the effluent concentration, Cn is the influent concentration, ~, is
the filter
coefficient with units of reciprocal length, and L is the depth of the filter.
Note that based
on the definitions above, the number of collisions that a non-attaching
microorganism will
experience as it travels over a distance L through the filter will be ~~,/a~L
, where a is the
"clean" bed sticking coefficient (also called, collision efficiency), defined
as the ratio of the
number of microorganisms that stick to the collector surface to the number of
microorganisms that strike the collector surface. Equation 1 is also valid for
radial flow
filters if L is substituted by Ro - Rl , where Ro is the outside radius and Ri
is the inside
radius, and the filter coefficient is averaged over the thickness of the
filter. The filter
coefficient for a particle-containing bed (not fibers) is as follows:
~ _ ~3~1- ~~l a~~2d~ , (2)
where s is the filter bed porosity, r~ is the single-collector efficiency,
defined as the ratio of
the number of microorganisms that strike the collector surface to the number
of
microorganisms that flow towards the collector surface, and d~ is the
collector particle
diameter. The factor (3/2) in the formula above is valid for spherical or
spherical-like
particles. For cylindrical particles (e.g. fibers) the term becomes (4/~c),
and d~ is then the
diameter of the cylinder. Also, note that the term "clean" bed means that the
collector
surfaces have not yet accumulated enough microorganisms to cause a reduction
in the
16
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
deposition efficiency of the new microorganisms (i.e., blocking).
Based on the above "clean" bed filtration model, the F-BLR and F-VLR can be
calculated as follows:
F - BLR or F - VLR = -log(C/Ca ) _ (~1.L/2.3) . (3)
The single-collector efficiency, r~ , is calculated using the Rajagopalan and
Tien
model (RT model; AIChE J., 22(3), 523-533 (1976), and AIChE J., 28, 871-872
(1982)) as
follows:
~ = 4As~sPe-z~3 + ASLoI~sR'sia + 0.00338ASG6~sR-ars ~ (4)
where AS = 2 _ 3 2+ 3 55- 2 6 ' ~ _ ~l - ~~1/3 , Pe is the dimensionless
Peclet number
v y y
3,u~Ud d Lo is the dimensionless London - van der Waals number
Pe = ' "'
kT '
Lo = 4H , R is the dimensionless interception number R = ~'" ,
9 ,ud U G is the
g P»t
dimensionless sedimentation number G = ~ pf ~"' , ,u is the dynamic fluid
viscosity
1 B,uU
(equal to 1 mPa~s for water), U is the superficial fluid velocity (calculated
as: U = 4Q~~D2 ,
for axial flow filters, where Q is the fluid flowrate, and D is the diameter
of the face area of
the filter; and U(R) = Q~2~RX for radial flow filters, where X is the length
of the filter,
and R is the radial position between R~ and Ro ), d", is the microorganism
diameter (or
diameter of an equivalent sphere, if the microorganism is non spherical), k is
the
Boltzmann's constant (equal to 1.38x10-23 kg~mzlsz~K), T is the fluid
temperature, H is the
Hamaker constant (it is typically equal to 10-2° J), g is the
gravitational constant (equal to
9.81 m/s2), p", is the density of the microorganisms, and p f is the fluid
density (equal to 1
g/mL for water). For the purposes and the materials of the present invention,
H is equal to
10-2° J, T is equal to 298 K, p", is equal to 1.05 g/mL, ,u is equal to
1 mPa~s. Also, for the
purposes of the present invention, d~ is the volume median diameter DV,o.s ,
which is the
particle diameter such that 50% of the total particle volume is in particles
of smaller
diameter. Also, the average fluid residence time is calculated as:
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CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
z = ~ ~~ , for axial flow filters, and
z - s~(Ro -RZ ~ , for radial flow filters. (5)
The sticking coefficient, a, is typically calculated experimentally, for
example using
the "microbe and radiolabel kinesis" (MARK) technique described in Gross et
al. (LY~aterRes.,
29(4), 1151-1158 (1995)). The single-collector efficiency, r~, of the filters
of the present
invention may be greater than about 0.002, preferably greater than about 0.02,
preferably
greater than about 0.2, preferably greater than about 0.4, more preferably
greater than about
0.6, and most preferably between about 0.8 and about 1. The filter
coefficient, ~, , of the
filters of the present invention may be greater than about 10 m 1, preferably
greater than
about 20 m 1, more preferably greater than about 30 m 1, most preferably
greater than about
40 m 1, and/or less than about 20,000 m 1, preferably less than about 10,000 m-
1, more
preferably less than about 5,000 m 1, and most preferably less than about
1,000 m 1.
The F-BLR of filters of the present invention containing mesoporous, or
mesoporous and basic, or mesoporous, basic, and reduced-oxygen activated
carbon particles,
when measured according to the test procedure set forth herein, may be greater
than about 2
logs, preferably greater than about 3 logs, more preferably greater than about
4 logs, and
most preferably greater than about 6 logs. The F-VLR of filters of the present
invention
containing mesoporous, or mesoporous and basic, or mesoporous, basic, and
reduced-
oxygen activated carbon particles , when measured according to the test
procedure set forth
herein, may be greater than about 1 log, preferably greater than about 2 logs,
more preferably
greater than about 3 logs, and most preferably greater than about 4 logs.
In one preferred embodiment of the present invention, the filter particles
comprise
mesoporous activated carbon particles that are wood-based activated carbon
particles. These
particles have a BET specific surface area between about 1,000 m2/g and about
2,000 m2/g,
total pore volume betvcreen about 0.8 mL/g and about 2 mL/g, and sum of the
mesopore
and macropore volumes between about 0.4 mL/g and about 1.5 mL/g.
In another preferred embodiment of the present invention, the filter particles
comprise mesoporous and basic activated carbon particles that are wood-based
activated
carbon particles. These particles have a BET specific surface area between
about 1,000 mz/g
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WO 2004/076360 PCT/US2003/005409
and about 2,000 m2/g, total pore volume between about 0.8 mL/g and about 2
mL/g, and
sum of the mesopore and macropore volumes between about 0.4 mL/g and about 1.5
mL/g.
In yet another preferred embodiment of the present invention, the filter
particles
comprise mesoporous, basic, and reduced-oxygen activated carbon particles that
were
initially acidic and rendered basic and reduced-oxygen with treatment in a
dissociated
ammonia atmosphere. These particles are wood-based activated carbon particles.
The
treatment temperature is between about 925°C and about 1,000°C,
the ammonia flowrate is
between about 1 standard L/h.g and about 20 standard L/h.g, and the treatment
time is
between about 10 minutes and about 7 hours. These particles have a BET
specific surface
area between about 800 mz/g and about 2,500 m2/g, total pore volume between
about 0.7
mL/g and about 2.5 mL/g, and sum of the mesopore and macropore volumes between
about 0.21 mL/g and about 1.7 mL/g. A non-limiting example of an acidic
activated carbon
that is converted to a basic and reduced-oxygen activated carbon is set forth
below.
In even yet another preferred embodiment of the present invention, the filter
particles comprise mesoporous, basic, and reduced-oxygen activated carbon
particles, that
were initially mesoporous and basic, with treatment in an inert (i.e., helium
atmosphere.
These particles are wood-based activated carbon particles. The treatment
temperature is
between about 800°C and about 1,000°C, the helium flowrate is
between about 1 standard
L/h.g and about 20 standard L/h.g, and the treatment time is between about 10
minutes and
about 7 hours. These particles have a BET specific surface area between about
800 mz/g
and about 2,500 m2/g, total pore volume between about 0.7 mL/g and about 2.5
mL/g, and
sum of the mesopore and macropore volumes between about 0.21 mL/g and about
1.7
mL/g. A non-limiting example of a basic activated carbon that is converted to
a basic and
reduced-oxygen activated carbon is set forth below.
III. Treatment Examples
EXAMi'LE 1
Treatment of a Mesoporous and Acidic Activated Carbon To Produce a Mesoporous,
Basic,
and Reduced-C~gen Activated Carbon
About 2 kg of the CARBOC,~3EM~ CA 10 mesoporous and acidic wood-based
activated carbon particles from Carbochem, Inc., of Ardmore, PA, are placed on
the belt of a
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CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
furnace Model BAGM manufactured by C. I. Haves, Inc., of Cranston, RI. The
furnace
temperature is set to about 950°C, the treatment time is about 4 hours,
and the atmosphere
is dissociated ammonia flowing with a volumetric flowrate of about 12,800
standard L/h
(i.e., about 450 standard ft3/h, or equivalently, about 6.4 standard L/h.g).
The treated
activated carbon particles are called TA4-CA 10, and their BET isotherm,
mesopore volume
distribution, and point of zero charge analyses are illustrated in FIGS. 1a,
2a, and 3a,
respectively Numerical values for BET, the sum of mesopore and macropore
volumes,
point of zero charge, BRI/BLRI, VRI/VLRI, bulk oxygen percentage by weight,
and ORP
are shown in Section VI.
EXAMPLE 2
Treatment of a Mesoporous and Basic Activated Carbon To Produce a Mesoporous,
Basic,
and Reduced-Oxygen Activated Carbon
About 2 kg of the Mead~Uestvaco Nuchar~ RGC mesoporous and basic wood-
based activated carbon particles from Mead~Uestvaco Corp., of Covington, VAy
are placed
on the belt of a furnace Model BALM manufactured by C. I. Haves, Inc., of
Cranston, RI.
The furnace temperature is set to about 800°C, the treatment time is 4
hours, and the
atmosphere is helium flowing with a volumetric flowrate of about 12,800
standard L/h (i.e.,
about 450 standard ft3/h, or equivalently, about 6.4 standard L/h.g). The
treated activated
carbon particles are called THe4-RGC, and their BET isotherm, mesopore volume
distribution, and point of zero charge analyses are illustrated in FIGS. 1b,
2b, and 3b,
respectively. Numerical values for BET, the sum of mesopore and macropore
volumes,
point of zero charge, BRI/BLRI, VRI/VLRI, bulk oxygen percentage by weight,
and ORP
are shown in Section VI.
IV. Filters of the Present Invention
Referring to FIG. 4, an exemplary filter made in accordance with the present
invention will now be described. The filter 20 comprises a housing 22 in the
form of a
cylinder having an inlet 24 and an outlet 26. The housing 22 can be provided
in a variety of
forms, shapes, sizes, and arrangements depending upon the intended use and
desired
performance of the filter 20, as known in the art. For example, the-filter 20
can be an axial
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
flow filter, wherein the inlet 24 and outlet 26 are disposed so that the
liquid flows along the
axis of the housing 22. Alternatively, the filter 20 can be a radial flow
filter wherein the inlet
a
24 and outlet 26 are arranged so that the fluid (e.g., either a liquid, gas,
or mixture thereof)
flows along a radial of the housing 22. Either in axial or radial flow
configuration, filter 20
may be preferably configured to accommodate a face area of at least about 0.5
in.2 (3.2 cm2),
more preferably at least about 3 in? (19.4 cm2), and most preferably at least
about 5 in? (32.2
cm2), and preferably a filter depth of at least about 0.125 in. (0.32 cm) of
at least about 0.25
in. (0.64 cm), more preferably at least about 0.5 in. (1.27 cm), and most
preferably at least
about 1.5 in. (3.81 cm). For radial flow filters, the filter length may be at
least 0.25 in. (0.64
cm), more preferably at least about 0.5 in. (1.27 cm), and most preferably at
least about 1.5
in. (3.81 cm). Still further, the filter 20 can include both axial and radial
flow sections.
The housing may also be formed as part of another structure without departing
from
the scope of the present invention. While the filters of the present invention
are particularly
suited for use with water, it will be appreciated that other fluids (e.g.,
air, gas, and mixtures of
air and liquids) can be used. Thus, the filter 20 is intended to represent a
generic liquid filter
or gas filter. The size, shape, spacing, alignment, and positioning of the
inlet 24 and outlet
26 can be selected, as known in the art, to accommodate the flow rate and
intended use of
the filter 20. Preferably, the filter 20 is configured for use in residential
or commercial
potable water applications, including, but not limited to, whole house
filters, refrigerator
filters, portable water units (e.g., camping gear, such as water bottles),
faucet-mount filters,
under-sink filters, medical device filters, industrial filters, air filters,
etc. Examples of filter
configurations, potable water devices, consumer appliances, and other water
filtration
devices suitable for use with the present invention are disclosed in US patent
nos. 5,527,451,
5,536,394, 5,709,794, 5,882,507, 6,103,114, 4,969,996, 5,431,813, 6,214,224,
5,957,034,
6,145,670, 6,120,685, and 6,241,899, the substances of which are incorporated
herein by
reference. For potable water applications, the filter 20 may be preferably
configured to
accommodate a flow rate of less than about 8 L/min, or less than about 6
L/min, or
between about 2 L/min and about 4 L/min, and the filter may contain less than
about 2 kg
of filter material, or less than about 1 kg of filter material, or less than
about 0.5 kg of filter
material. Further, for potable water applications, the filter 20 may be
preferably configured
to accommodate an average fluid residence time of at least about 3 s,
preferably at least
about 5 s, preferably at least about 7 s, more preferably at least about 10 s,
and most
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WO 2004/076360 PCT/US2003/005409
preferably at least about 15 s. Still further, for potable water applications,
the filter 20 may
be preferably configured to accommodate a filter material pore volume of at
least about 0.4
cm3, preferably at least about 4 cm3, more preferably at least about 14 cm3,
and most
preferably at least about 25 cm3.
The filter 20 also comprises a filter material 28 which may be used in
combination
with other filter systems including reverse osmosis systems, ultra-violet
light systems, ionic
exchange systems, electrolyzed water systems, and other water treatment
systems known to
those with skill in the art.
The filter 20 also comprises a filter material 28, wherein the filter material
28 includes
one or more filter particles (e.g., fibers, granules, etc.). One or more of
the filter particles can
be mesoporous, more preferably mesoporous and basic, and most preferably
mesoporous,
basic and reduced oxygen and possess the characteristics previously discussed.
The
mesoporous; or mesoporous and basic; or mesoporous, basic and reduced oxygen
activated
carbon filter material 28 can be combined with particles formed from other
materials or
combination of materials, such as activated carbon powders, activated carbon
granules,
activated carbon fibers, zeolites, inorganics (including activated alumina,
magnesia,
diatomaceous earth, silica, mixed oxides, such as hydrotalcites, glass, etc.),
cationic materials
(including polymers such as polyaminoamides, polyethyieneimine,
polyvinylamine,
polydiallyldimethylammonium chloride, polydimethylamine-epichlorohydrin,
polyhexamethylenebiguanide, poly [2-(2-ethoxy)-ethoxyethlyl-guanidinium
chloride which
may be bound to fibers (including polyethylene, polypropylene, ethylene
ma.leic anhydride
copolymers, carbon, glass, etc.) and/or to irregularly shaped materials
(including carbon,
diatomaceous earth, sand, glass, clay, etc.), and mixtures thereof. Examples
of filter materials
and combinations of filter materials that mesoporous and basic activated
carbon may be
combined with are disclosed in US patent nos. 6,274,041, 5,679,248, which are
herein
incorporated by reference, and US patent application 09/628,632, which is
herein
incorporated by reference. As previously discussed, the filter material can be
provided in
either a loose or interconnected form (e.g., partially or wholly bonded by a
polymeric binder
or other means to form an integral structure).
The filter material may be used for different applications (e.g., use as a pre-
filter or
post-filter) by varying the size, shape, complex formations, charge, porosity,
surface
structure, functional groups, etc. of the filter particles as discussed above.
The filter material
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CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
may also be mixed with other materials, as just described, to suit it for a
particular use.
Regardless of whether the filter material is mixed with other materials, it
may be used as a
loose bed, a block (including a co-extruded block as described in US patent
no. 5,679,248,
which is herein incorporated by reference), and mixtures thereof. Preferred
methods that
might be used with the filter material include forming a block filter made by
ceramic-carbon
mix (wherein the binding comes from the firing of the ceramic), using powder
between non-
wovens as described in LJS patent no. 6,077,588, which is herein incorporated
by reference,
using the green strength method as described in US patent no. 5,928,588, which
is herein
incorporated by reference, activating the resin binder that forms the block,
which is herein
incorporated by reference, or by using a resistive heating method as described
in PCT
Application Serial No. WO 98/43796.
V. Filter Examples
EXAMPLE 3
Filter Containing Mesoporous and Basic Activated Carbon Particles
About 18.3 g of Nuchar~ RGC mesoporous and basic activated carbon powder
(with DV,o.S equal to about 45 ~,m) from MeadWestvaco Corp. of Covington, VA,
is mixed
with about 7 g of Microthene~ loindensity polyethylene (LDPE) FN510-00 binder
of
Equistar Chemicals, Inc. of Cincinnati, OH, and about 2 g of Alusil~ 70
aluminosilicate
powder from Selecto, Inc., of Norcross, GA. The mixed powders are then poured
into a
circular aluminum mold with about 3 in. (about 7.62 cm) internal diameter and
about 0.5 in.
(about 1.27 cm) depth. The mold is closed and placed in a heated press with
platens kept at
about 204°C for 1 h. Then, the mold is allowed to cool to room
temperature, opened, and
the axial flow filter is removed. The characteristics of the filter are: face
area: about 45.6
cm2; filter depth: about 1.27 cm; filter total volume: about 58 mL; filter
porosity (for pores
greater than about 0.1 P,m): about 0.43; and filter material pore volume (for
pores greater
than about 0.1 P,m): about 25 mL (as measured by mercury porosimetry). The
filter is placed
in the Teflon~ housing described in the test procedures below. When the flow
rate is about
200 mL/min, the pressure drop of this filter is about 17 psi (about l.2bar,
0.12 MPa) for
about the first 2,000 filter pore volumes. Numerical values for F-BLR, F-VLR,
r~, and a are
23
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
shown in Section VI.
EXAMPLE 4
Filter Containing Microporous and Basic Activated Carbon Particles
About 26.2 g of coconut microporous and basic activated carbon powder (with
DV,o.s equal to about 92 ~,m) is mixed with 7 g of Microthene~ low density
polyethylene
(LDPE) FN510-00 binder of Equistar Chemicals, Inc. of Cincinnati, OI Z, and
about 2 g of
Alusil~ 70 aluminosilicate powder from Selecto, Inc., of Norcross, GA. The
mixed powders
are then poured into a circular aluminum mold with about 3 in. (about 7.62 cm)
internal
diameter and about 0.5 in. (about 1.27 cm) depth. The mold is closed and
placed in a heated
press with platens kept at about 204°C for 1 h. Then, the mold is
allowed to cool to room
temperature, is opened, and the axial flow filter is removed. The
characteristics of the filter
are: face area: about 45.6 cm2; filter depth: about 1.27 cm; filter total
volume: about 58 mL;
filter porosity (for pores greater than about 0.1 ~,m): about 0.44; and filter
material pore
volume (for pores greater than about 0.1 ~,m): about 25.5 mL (as measured by
mercury
porosimetry). The filter is placed in the Teflon~ housing described in the
test procedures
below. When the flow rate is about 200 mL/min, the pressure drop of this
filter is about 17
psi (about l.2bar, about 0.12 MPa) for about the first 2,000 filter pore
volumes. Numerical
values for F-BLR, F-VLR, r~, and a are shown in Section VI.
VI. Test and Calculation Procedures
The following test procedures are used to calculate the BET, point of zero
charge,
BRI/BLRI, VRI/VLRI, bulk oxygen percentage by weight, ORP, F-BLR, and F-VLR
values
discussed herein. Also discussed herein are calculation procedures for single-
collector
efficiency, filter coefficient, average fluid residence time, and F-BLR
~~Uhile measurement of the BRI/BLRI and VRI/VLRI values is with respect to an
aqueous medium, this is not intended to limit the ultimate use of filter
materials of the
present invention, but rather the filter materials can ultimately be used with
other fluids as
previously discussed even though the BRI/BLRI and VRI/VLRI values are
calculated with
respect to an aqueous medium. Further, the filter materials chosen below to
illustrate use of
24
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
the test procedures are not intended to limit the scope of the manufacture
and/or
composition of the filter materials of the present invention or to limit which
filter materials
of the present invention can be evaluated using the test procedures.
BET Test Procedure
The BET specific surface area and pore volume distribution are measured using
a
nitrogen adsorption technique, such as that described in ASTM D 4820-99, the
substance of
which is herein incorporated by reference, by multipoint nitrogen adsorption,
at about 77K
with a Coulter SA3100 Series Surface Area and Pore Size Analyzer manufactured
by Coulter
Corp., of Miami, FL. This process can also provide the micropore, mesopore,
and
macropore volumes. For the TA4-CA 10 filter particles of Example 1, the BET
area is
about 1,038 m2/g, micropore volume is about 0.43 mL/g, and the sum of the
mesopore and
macropore volumes is about 0.48 mL/g. For the THe4-RGC filter particles of
Example 2,
the BET area is about 2,031 mz/g, micropore volume is about 0.81 mL/g, and the
sum of
the mesopore and macropore volumes is about 0.68 mL/g. Note that the
respective values
of the starting materials CA 10 and RGC are: about 1,309 m2/g; about 0.54
mL/g; about
0.67 mL/g; and about 1,745 m2/g; about 0.70 mL/g; about 0.61 mL/g,
respectively. Typical
BET nitrogen isotherm and the mesopore volume distribution for the filter
material of
Examples 1 and 2 are illustrated in FIGS. 1a and 1b, respectively: As will be
appreciated,
other instrumentation can be substituted for the BET measurements as is known
in the art.
Point Of Zero Charge Test Procedure
About 0.010 M aqueous KCl solution is prepared from reagent grade KCl and
water
that is freshly distilled under argon gas. The water used for the distillation
is deionized by a
sequential reverse osmosis and ion exchange treatment. About 25.0 mL volume of
the
aqueous KCl solution is transferred into six, about 125 mL flasks, each fitted
with a 24/40
ground glass stopper. Microliter quantities of standardized aqueous HCl or
NaOH solutions
are added to each flask so that the initial pH ranges between about 2 and
about 12. The pH
of each flask is then recorded using an Orion model 420A pH meter with an
Orion model
9107BN Triode Combination pH/ATC electrode, manufactured by Thermo Orion Inc.,
of
Beverly, MA, and is called "initial pI~'. About 0.0750 ~ 0.0010 g of activated
carbon
particles are added to each of the six flasks, and the aqueous suspensions are
stirred (at about
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
150 rpm) while stoppered for about 24 hours at room temperature before
recording the
"final pI~'. FIG. 3a shows the initial and final pH values for the experiments
run with CA
10, and TA4-CA 10 activated carbon materials, and FIG. 3b shows the initial
and final pH
values for the experiments run with RGC and The4-RGC activated carbon
materials. The
point of zero charge for the CA 10, TA4-CA 10, RGC, and THe4-RGC is about 5.0,
about
9.7, about 8.8, and about 8.6, respectively. As will be appreciated, other
instrumentation can
be substituted for this test procedure as is known in the art.
BRI/BLRI Test Procedure
A PB-900TM Programmable JarTester manufactured by Phipps & Bird, Inc., of
Richmomd, VA, with 2 or more Pyrex~ glass beakers (depending on the numbers of
materials tested) is used. The diameter of the beakers is about 11.4 cm (about
4.5") and the
height is about 15.3 cm (about 6"). Each beaker contains about 500 mL of
dechlorinated;
municipally supplied tap vcrater contaminated with the E. crali microorganisms
and a stirrer
that is rotated at about 60 rpm. The stirrers are stainless steel paddles
about 7.6 cm (about
3") in length, about 2.54 cm (about 1") in height, and about 0.24 cm (about
3/32") in
thickness. The stirrers are placed about 0.5 cm (about 3/16") from the bottom
of the
beakers. The first beaker contains no filter material and is used as a
control, and the other
beakers contain sufficient quantity of the filter materials, having a Sauter
mean diameter less
than about 55 ~,m, so that the total external geometric surface area of the
materials in the
beakers is about 1400 cm2. This Sauter mean diameter is achieved by a) sieving
samples with
broad size distribution and higher Sauter mean diameter or b) reducing the
size of the filter
particles (e.g., if the filter particles are larger than about 55 ~.m or if
the filter material is in an
integrated or bonded form) by any size-reducing techniques that are well known
to those
skilled in the art. For example, and by no way of limitation, size-reducing
techniques are
crushing, grinding, and milling. Typical equipment that is used for size
reduction includes
jaw crushers, gyratory crushers, roll crushers, shredders, heavy duty impact
mills, media mills,
and fluid-energy mills, such as centrifugal jets, opposed jets or jets with
anvils. The size
reduction can be used on loose or bonded filter particles. Any biocidal
coating on the filter
particles or the filter material should be removed before conducting this
test. Alternatively,
uncoated filter particles can be substituted for this test.
26
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
Duplicate samples of water, each about 5 mL in volume, are collected from each
beaker for assay at various times after insertion of the filter particles in
the beakers until
equilibrium is achieved in the beakers that contain the filter particles.
Typical sample times
are: about 0, about 2, about 4 and about 6 hours. Other equipment can be
substituted as
known in the art.
The E. cr~i bacteria used are the ATCC # 25922 (American Type Culture
Collection,
Rockville, MD). The target E. cdi concentration in the control beaker is set
to be about
3.7x109 CFU/L. The E. ct~i assay can be conducted using the membrane filter
technique
according to process # 9222 of the 20~ edition of the "Standard Processes for
the Exdr~n~ttion
Water and W~astez.~tte~'' published by the American Public Health Association
(APHA),
~lashington, DC, the substance of which is herein incorporated by reference.
The limit of
detection (LOD) is about 1x103 CFU/L.
Exemplary BRI/BLRI results for the filter materials of Examples 1 and 2 are
shown
in FIG. 5a and FIG. 5b. The amount of the CA 10 mesoporous and acidic
activated carbon
maxerial is about 0.75 g, and that of the TA40-CA 10 mesoporous, basic, and
reduced-
oxygen activated carbon material is about 0.89 g. The amount of the RGC
mesoporous and
basic activated carbon material is about 0.28 g, and that of the THe4-RGC
mesoporous,
basic, and reduced-oxygen activated carbon material is about 0.33 g. All four
amounts
correspond to about 1,400 cm2 external surface area. The E. cdi concentration
in the control
beaker'in FIG. 5a is about 3.7x109 CFU/L, and that in FIG. 5b is about 3.2x109
CFU/L.
The E. cr~i concentrations in the beakers containing the CA 10, TA4-CA 10,
RGC, and
THe4-RGCsamples reach equilibrium in about 6 hours, and their values are:
about 2.1x106
CFU/L, about 1.5x104 CFU/L, about 3.4x106 G'FU/L, and about 1.2x106 CFU/L,
respectively. Then, the respective BRIs are calculated as about 99.94%, about
99.9996%,
about 99.91%, and about 99.97%, and the respective BLRIs are calculated as
about 3.2 log,
about 5.4 log, about 3.0 log, and about 3.5 log.
VRI/VLRI Test Procedure
The testing equipment and the procedure are the same as in BRI/BLRI procedure.
The first beaker contains no filter material and is used as control, and the
other beakers
contain a sufficient quantity of the filter materials, having a Sauter mean
diameter less than
about 55 ~,m, so that there is a total external geometric surface area of
about 1400 cm2 in the
27
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
beakers. Any biocidal coating on the filter particles or the filter material
should be removed
before conducting this test. Alternatively, uncoated filter particles or
filter material can be
substituted for this test.
The MS-2 bacteriophages used are the ATCC # 15597B from the American Type
Culture Collection of Rockville, MD. The target MS-2 concentration in the
control beaker is
set to be about 2.07x109 PFU/L. The MS-2 can be assayed according to the
procedure by C.
J. Hurst, Apps EYerzro~z M~., 60(9), 3462(1994), the substance of which is
herein
incorporated by reference. Other assays known in the art can be substituted.
The limit of
detection (LOD) is about 1x103 PFU/L.
Exemplary VRI/VLRI results for the filter materials of Examples 1 and 2 are
shown in FIG. 6a and FIG. 6b.The amount of the CA 10 mesoporous and acidic
activated
carbon material is about 0.75 g, and that of the TA40-CA 10 mesoporous, basic,
and
reduced-oxygen activated carbon material is about 0.89 g. The amount of the
RGC
mesoporous and basic activated carbon material is about 0.28 g, and that of
the THe4-RGC
mesoporous, basic, and reduced-oxygen activated carbon material is about 0.33
g. All four
amounts correspond to about 1,400 cm2 external surface area. The MS-2
concentration in
the control beaker in FIG. 6a is about 6.7x10 PFU/L, and that in FIG. 6b is
about 8.Ox10~
PFU/L. The MS-2 concentrations in the beakers containing the CA-10, TA4-CA 10,
RGC,
and THe4-RGC samples reach equilibrium in 6 hours, and their values are about
4.1x104
PFU/L, about 1x103 PFU/L, about 3x103 PFU/L, and less than about 1.0x103 PFU/L
(limit
of detection), respectively. Then, the respective VRIs are calculated as about
99.94%, about
99.999%, about 99.996%, and > about 99.999%, and the respective VLRIs are
calculated as
about 3.2 log, about 5 log, about 4.4 log, and > about 5 log.
Bulk Oxygen Percentage by Weight Test Procedure
The bulk oxygen percentage by weight is measured using the PerkinElmer Model
240
Elemental Analyzer (Oxygen Modification; PerkinElmer, Inc.; VUellesley, MA).
The
technique is based on pyrolysis of the sample in a stream of helium at about
1000°C over
platinized carbon. The carbon samples are dried overnight in a vacuum oven at
about
100°C. As Will be appreciated, other instrumentation can be substituted
for this test
procedure as is known in the art. Exemplary bulk oxygen percentage by weight
values for
the filter materials CA 10, TA4-CA 10, RGC and THe4-RGC are about 8.3%, about
1.1%,
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CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
about 2.3%, and about 0.8%, respectively.
ORP Test Procedure
The ORP is measured using the platinum redox electrode Model 96-78-00 from
Orion
Research, Inc. (Beverly, MA), and following the ASTM standard D 1498-93. The
procedure
involves the suspension of about 0.2 g of carbon in about 80 mL of tap water,
and reading
the electrode reading, in mV, after about 5 min of gentle stirring. As will be
appreciated,
other instrumentation can be substituted for this test procedure as is known
in the art.
Exemplary ORP values for the filter materials CA 10, TA4-CA 10, RGC and THe4-
RGC are
about 427 mV, about 285 mV, about 317 mV, and about 310 mV, respectively.
F-BLR Test Procedure
The housings for the axial flow filters with mesoporous carbon are made from
Teflon~
and consist of 2 parts, i.e., a lid and a base. Both parts have an outside
diameter of about
12.71 cm (about 5") and inside diameter of about 7.623 cm (about 3"). The lid
counter sets
in the base with an o-ring (about 3" ID and about 1/8" thickness) compression
seal. The
inlet and outlet hose barb connectors are threaded into the lid and base with
about 1/16"
NPT pipe threads. About 1/a" thick by about 2 3/4" OD stainless steel diverter
(with about
3/ 16" hole on the upstream side and about 6 mesh screen on the downstream
side) is
counter set into the lid of the housing. The function of the diverter is to
distribute the inlet
flow over the entire face of the filter. The lid and base of the housing
engage such that a
compression seal exists sealing the filter within the housing. The lid and the
base held
together using four about 1/" fasteners.
The filter is mounted inside the housing and water contaminated with about
1x10$
CFU/L E. chi flows through at a flowrate of about 200 xnL/min. The total
amount of water
flowing in can be about 2,000 filter material pore volumes or more. The E. cdi
bacteria used
are the ATCC # 25922 (American Type Culture Collection, Rockville, MD). The E.
chi
assay can be conducted using the membrane filter technique according to
process # 9222 of
the 20~ edition of the "Stdndan~ Processes for the Exarninatzon of Water and
Wastez~zter'' published
by the American Public Health .Association (APHA), Washington, DC, the
substance of
which is herein incorporated by reference. Other assays known in the art can
be substituted
(e.g. COLILERT~). The limit of detection (LOD) is about 1x102 CFU/L when
measured
29
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
by the membrane filter technique, and about 10 CFU/L when measured by the
COLILERT~ technique. Effluent water is collected after the flow of about the
first 2,000
filter material pore volumes, assayed to count the E. chi bacteria present,
and the F-BLR is
calculated using the definition.
Exemplary results used to calculate F-BLR are shown in FIG. 7a for the axial
flow
filters of Example 3 and Example 4. The flowrate used in FIG. 7a is about 200
mL/min and
the influent concentration of E. cr~i varied between about 1x10$ and about
1x109 CFU/L.
The filters are challenged with about 20 L once a~week (every Tuesday) and the
effluent
water is assayed as described above. The average fluid residence time for the
RGC filter is
about 7.5 s, and that of the coconut filter is about 7.65 s. The F-BLR of the
RGC filter of
Example 3 is calculated as about 6.8 log. For the coconut filter of the
Example 4 the
collection of the effluent water is stopped at about 40 L (which is~
equivalent to about 1,570
filter material pore volumes) as the filter shows almost complete breakthrough
at that
volume of water. The F-BLR is calculated as about 1.9 log at about 1,570
filter material pore
volumes.
F-VLR Test Procedure
The housings for the axial flow filters with mesoporous carbon are the same as
those
described in the F-BLR procedure above. ~Xlater contaminated with about 1x10
PFU/L
MS-2 flows through a housing/filter system at a flowrate of about 200 mL/min.
The total
amount of water flowing in can be about 2,000 filter material pore volumes or
more. The
MS-2 bacteriophages used are the ATCC # 15597B (American Type Culture
Collection,
Rockville, MD). The MS-2 assay can be conducted according to the procedure by
C. J.
Hurst, Apps Er~ci7rnz Micr~bid., 60(9), 3462 (1994), the substance of avhich
is herein
incorporated by reference. Other assays known in the art can be substituted.
The limit of
detection (LOD) is 1x103 PFU/L. Effluent water is collected after the flow of
about the first
2,000 filter material pore volumes, assayed to count the MS-2 bacteriophages
present, and
the F-VLR is calculated using the definition.
Exemplary results used to calculate F-VLR are shown in FIG. 7b for the axial
flow
filters of Example 3 and Example 4. The flowrate used in FIG. 7b is about 200
mL/min
and the influent concentration of MS-2 varied around about 1x10 PFU/L. The
filters are
challenged with about 20 L once a week (every Tuesday) and the effluent water
is assayed as
CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
described above. The F-VLR of the RGC filter of Example 3 is calculated as >
about 4.2
log. For the coconut filter of the Example 4 the collection of the effluent
water is stopped at
about 40 L (which is equivalent to about 1,570 filter material pore volumes)
as the filter
shows alinost complete breakthrough at that volume of water. The F-BLR is
calculated as
about 0.3 log at about 1,570 filter material pore volumes.
Calculation Procedures for Single-collector Efficiency Filter
CoefficientLAverage Fluid
Residence Time~and F-BLR
The single-collector efficiency calculation for the filters uses Equation 4
and the
dimensionless numbers described after that equation. Exemplary calculations
for the axial
flow RGC filter of Example 3 using the following parameters: s = 0.43 , d", =1
~,m,
d~ = 45 ~.m, H =10-zo J, p", =1.058 g/mL, p f =1.0 g/mL, ,u =1 mPa~s, T = 298
K,
water flowrate Q = 200 . mL/min, filter diameter D = 7.623 cm, and U = 0.0007
m/s, give
r~ = 0.01864 . For the same parameters and for a =1, the filter coefficient is
calculated
according to Equation 2 as: ~, = 354.2 m 1. Furthermore, the F-BLR of the same
filter is
calculated according to Equation 3 as about 1.95 log. Similar exemplary
calculations for the
coconut filter of Example 4, using the same parameters as above, give r~ =
0.00717 and
~, = 65.5 m 1. Finally, the F-BLR of the same filter is calculated according
to Equation 3 as
about 0.36 log.
The present invention may additionally include information that will
communicate to
the consumer, by words and/or by pictures, that use of carbon filter particles
and/or filter
material of the present invention will provide benefits which include removal
of
microorganisms, and this information may include the claim of superiority over
other filter
products. In a highly desirable variation, the information may include that
use of the
invention provides for reduced levels of nano-sized microorganisms.
Accordingly, the use of
packages in association with information that will communicate to the
consumer, by words
and or by pictures, that use of the invention will provide benefits such as
potable, or more
potable water as discussed herein, is important. The information can include,
e.g.,
advertising in all of the usual media, as well as statements and icons on the
package, or the
filter itself, to inform the consumer.
The embodiments described herein were chosen and described to provide the best
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CA 02516595 2005-08-19
WO 2004/076360 PCT/US2003/005409
illustration of the principles of the invention and its practical application
to thereby enable
one of ordinary skill in the art to utilize the invention in various
embodiments and with
various modifications as are suited to the particular use contemplated. All
such
modifications and variations are within the scope of the invention as
determined by the
appended claims when interpreted in accordance with the breadth to which they
are fairly,
legally and equitably entitled.
32
