Note: Descriptions are shown in the official language in which they were submitted.
CA 02607750 2012-11-14
METHOD OF AGGLOMERATION
[0001] BY INVENTORS: Christina Borgese, Marc Privitera, Kristine Tippet,
Charles
Fritter, and Amanda Walker
FIELD OF THE INVENTION
[0002 ]The present invention relates generally to an agglomeration process for
forming
porous agglomerated materials. More particularly, the present invention
relates to a pan
agglomeration process for forming porous absorbent materials suitable for use
as animal
litter.
BACKGROUND OF THE INVENTION
[0003 ]Clay has long been used as a liquid absorbent, and has found particular
usefulness as an animal litter.
[0004 ]Because of the growing number of domestic animals used as house pets,
there
is a need for litters so that animals may micturate, void or otherwise
eliminate liquid
or solid waste indoors in a controlled location. Many cat litters use clay as
an
absorbent. Typically, the clay is mined, dried, and crushed to the desired
particle size.
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CA 02607750 2012-11-14
[0005 ]Other absorbent materials that are used alone, in combination, or in
combination with clay include straw, sawdust, wood chips, wood shavings,
porous
polymeric beads, shredded paper, bark, cloth, ground corn husks, cellulose,
water-
insoluble inorganic salts, such as calcium sulfate, silica gel and sand.
[0006 ]Some clay litters have the ability to clump upon wetting. For example,
sodium
bentonite is a water-swellable clay which, upon contact with moist animal
waste, is
able to agglomerate with other moistened sodium bentonite clay particles. The
moist
animal waste is contained by the agglomeration of the moist clay particles
into an
isolatable clump, which can be removed from the container (e.g., litterbox)
housing
the litter. However, the clump strength of clay litters described above is
typically not
strong enough to hold the clump shape upon scooping, and inevitably, pieces of
the
litter break off of the clump and remain in the litter box, allowing waste
therein to
create malodors. Further, raw clay typically has a high clump aspect ratio
when
urinated in. The result is that the wetted portion of clay will often extend
to the
container containing it and stick to the side or bottom of the container.
[0007 ]Illustrative bentonite based litter compositions are disclosed in U.S.
Pat. Nos.
5,503,111; 5,386,803; 5,317,990; 5,129,365 and RE 33,983.
[0008 }Additives, such as starch or sugar based binders can be added to non-
bentonite
clays to create a litter material that behaves like a bentonite clay, i.e.,
upon contact
with liquid (or moist) dross, readily agglomerates with other moistened clay
particles.
US Patent 5,359,961 discloses a clumping non-swelling clay based litter.
[0009 ]What is needed is an absorbent material suitable for use as a cat
litter/liquid
absorbent that has better clumping characteristics, i.e., clump strength and
aspect
ratio, than absorbent materials heretofore known.
2
CA 02607750 2007-10-25
[00010 ]Another problem inherent in typical litters is the inability to
effectively
control malodors. Clay has very poor odor-controlling qualities, and
inevitably waste
build-up leads to severe malodor production. One attempted solution to the
malodor
problem has been the introduction of granular activated carbon (GAC) (20-8
mesh)
into the litter. However, the GAC is usually dry blended with the litter,
making the
litter undesirably dusty. Other methods mix GAC and clay and compress the
mixture
into particles. In either case, the GAC concentration must typically be 1% by
weight
or higher to be effective. GAC is very expensive, and the need for such high
concentrations greatly increases production costs. Further, because the clay
and GAC
particles are merely mixed, the litter will have GAC agglomerated in some
areas, and
particles with no GAC.
[00011 ]The human objection to odor is not the only reason that it is
desirable to
reduce odors. Studies have shown that cats prefer litter with little or no
smell. One
theory is that cats like to mark their territory by urinating. When cats
return to the
litterbox and don't sense their odor, they will try to mark their territory
again. The net
effect is that cats return to use the litter box more often if the odor of
their markings
are reduced.
[00012 ]Agglomeration processes have been around for decades. However, most
agglomeration processes result in compacted agglomeration products with bulk
densities equal to or higher than the raw feed material. Shipping costs of
these
agglomeration products often results in higher costs to the manufacturer due
to the
increase in weight.
[00013 ]Another problem with typical agglomeration processes is that the
compaction
used produces dense agglomerated materials that lack porosity, which results
in
, limited utility.
[00014 ]What is needed is an absorbent material with improved odor-controlling
properties, and that maintains such properties for longer periods of time.
[00015 ]What is further needed is an absorbent material with odor-controlling
properties comparable to heretofore known materials, yet requiring much lower
concentrations of odor controlling actives.
[00016 ]What is still further needed is an absorbent material with a lower
bulk density
while maintaining a high absorbency rate comparable to heretofore known
materials.
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SUMMARY OF THE INVENTION
[00017 ]The present invention provides composite absorbent particles and
methods
for making the same. An absorbent material is formed into a particle,
preferably, by
an agglomeration process. An optional performance-enhancing active is coupled
to
the absorbent material during the agglomeration process, homogeneously and/or
in
layers. Exemplary actives include antimicrobials, odor absorbers/inhibitors,
binders
(liquid/solid, silicate, ligninsulfonate, etc.), fragrances, health indicating
materials,
nonstick release agents, and mixtures thereof. Additionally, the composite
absorbent
particle may include a core material.
[00018 ]Methods disclosed for creating the absorbent particles include a pan
agglomeration process, a high shear agglomeration process, a low shear
agglomeration process, a high pressure agglomeration process, a low pressure
agglomeration process, a rotary drum agglomeration process, a mix muller
process, a
roll press compaction process, a pin mixer process, a batch tumble blending
mixer
process, and an extrusion process. Fluid bed process may also represent a
technique
for forming the inventive particles.
[00019 ]The processing technology disclosed herein allows the "engineering" of
the
individual composite particles so that the characteristics of the final
product can be
predetermined. The composite particles are particularly useful as an animal
litter.
Favorable characteristics for a litter product such as odor control, active
optimization,
low density, low tracking, low dust, strong clumping, etc. can be optimized to
give the
specific performance required. Another aspect of the invention is the use of
encapsulated actives, i.e., formed into the particle itself and accessible via
pores or
discontinuities in the particles. Encapsulation of actives provides a slow
release
mechanism such that the actives are in a useful form for a longer period of
time.
Thus, the present invention's engineered composite particle optimizing the
performance enhancing actives is novel in light of the prior art.
[00020 ]An aspect of the invention comprises a method for forming porous
agglomerated particles comprising: (a) providing feed particles between 50-325
Tyler
number equivalent without pre-wetting the feed particles: (b) feeding said
feed
particles into a pan agglomerator such that the feed particles enter
substantially at the
back of the pan; (c) providing a uniform distribution of uniformly-sized
liquid
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droplets onto the feed particles and growing agglomerate particles; (d)
rotating and
tilting the pan such that the liquid droplets are not applied directly to the
bed of the
pan; and (f) forming porous agglomerated particles that have a moisture
content
between 0 and 40 percent.
[0020A] Accordingly, in one aspect the present invention resides in a method
for
forming porous agglomerated particles comprising: (a) providing feed particles
less
than 5000 microns without pre-wetting the feed particles; (b) feeding said
feed
particles into a pan agglomerator such that the feed particles enter
substantially at the
back of the pan to significantly reduce dust formation; (c) forming a falling
curtain
comprising growing agglomerate particles, wherein the growing agglomerate
particles
fall over the entering feed particles; (d) providing a uniform distribution of
uniformly-
sized liquid droplets onto the curtain of feed particles and growing
agglomerate
particles; (e) rotating and tilting the pan such that the liquid droplets are
not applied
directly to the bed of the pan; and (0 forming porous agglomerated particles
that have
a moisture content between 0-75 percent.
[0020B] In another aspect, the present invention resides in a method for
forming
porous agglomerated absorbent particles suitable for use as an animal litter
comprising: (a) providing feed particles less than 5000 microns without pre-
wetting
the feed particles; (b) feeding said feed particles into a pan agglomerator
such that the
feed particles enter substantially at the back of the pan to significantly
reduce dust
formation, wherein said feed particles comprise an absorbent material suitable
for use
as an animal litter; (c) forming a falling curtain comprising growing
agglomerate
particles, wherein the growing agglomerate particles fall over the entering
feed
particles; (d) providing a uniform distribution of uniformly-sized liquid
droplets onto
the curtain of feed particles and growing agglomerate particles;
(e) rotating and tilting the pan such that the liquid droplets are not applied
directly to
the bed of the pan; and (0 forming porous agglomerated absorbent particles
suitable
for use as an animal litter that have a moisture content between 0-75 percent.
In a preferred method, some of the feed particles grow into agglomerated
particles as they move unidirectionally from the back of the pan to the
surface of the
pan.
More preferably, the back of the pan has a greater depth than the surface of
the
pan.
CA 02607750 2013-10-28
In yet another aspect, the pan is tiered, ramped or a combination thereof.
In another aspect, the feed particles enter the back of the pan through the
axis
of the pan.
In still another aspect, the feed particles comprise a bentonite clay and
activated carbon.
Preferably, the porous agglomerated particles have a bulk density reduction of
at least 5%, and most preferably, a bulk density reduction between 5-75%.
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BRIEF DESCRIPTION OF THE DRAWINGS
[00021 ]For a fuller understanding of the nature and advantages of the present
invention,
as well as the preferred mode of use, reference should be made to the
following detailed
description read in conjunction with the accompanying drawings.
[00022 ]Fig. 1 illustrates several configurations of absorbent composite
particles
according to various embodiments of the present invention.
[00023 ]Fig. 2 is a process diagram illustrating a pan agglomeration process
according
to a preferred embodiment.
[00024 ]Fig. 3 depicts the structure of an illustrative agglomerated composite
particle
formed by the process of Fig. 2.
[00025 ]Fig. 4 is a process diagram illustrating another exemplary pan
agglomeration
process with a recycle subsystem.
[00026 ]Fig. 5 is a process diagram illustrating an exemplary pin mixer
process for
forming composite absorbent particles.
[00027 ]Fig. 6 is a process diagram illustrating an exemplary mix muller
process for
forming composite absorbent particles.
[00028 ]Fig. 7 is a graph depicting malodor ratings.
[00029 ]Fig. 8 depicts the clumping action of composite absorbent particles
according
to a preferred embodiment.
[00030 ]Fig. 9 depicts disintegration of a composite absorbent particle
according to a
preferred embodiment.
[00031 ]Fig. 10 is a process diagram illustrating an exemplary pan
agglomeration
process capable of rapid water uptake and evaporation.
[00032 ]Fig. 11 is an illustration of an exemplary embodiment of a single step
pan
with an over/under feed.
[00033 ]Fig. 12 is an illustration of an exemplary over/under feed.
[00034 ]Figs. 13a and 131) are illustrations of the formation of particle-to-
particle
bonds.
[00035 ]Fig. 14 is an illustration of an exemplary stepped pan.
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BEST MODES FOR CARRYING OUT THE INVENTION
[00036] The following description includes the best embodiments presently
contemplated for carrying out the present invention. This description is made
for the
purpose of illustrating the principles of the present invention and is not
meant to limit
the inventive concepts claimed herein.
[00037] Before describing the present invention in detail, it is be to be
understood that
this invention is not limited to particularly exemplified systems or process
parameters
as such may, of course, vary. It is also to be understood that the terminology
used
herein is for the purpose of describing particular embodiments of the
invention only,
and is not intended to limit the scope of the invention in any manner. As is
generally
accepted by those of ordinary skill in the animal litter art, the following
terms have the
following meanings. The terms scoopable and clumping litter as used herein
refer to a
litter that agglomerates upon wetting such that the soiled portion can be
removed from
the litter box leaving the unsoiled portion available for reuse. The term non-
clumping
or poorly clumping as used herein refers to a litter material doesn't
agglomerate upon
wetting to the extent that the soiled portion could be easily removed from the
litter
box. As will be discussed in further detail below, additives may be added to a
non-
clumping or poorly clumping litter substrate to create clumping behavior.
[00039] It must be noted that, as used in this specification and the appended
claims,
the singular forms "a", "an" and "the" include plural referents unless the
content
clearly dictates otherwise. Thus, for example, reference to a "color masking
agent"
includes two or more such agents.
[00040] Unless defined otherwise, all technical and scientific terms used
herein have
the same meaning as commonly understood by one of ordinary skill in the art to
which the invention pertains. Although a number of methods and materials
similar or
7
CA 02607750 2013-10-28
equivalent to those described herein can be used in the practice of the
present
invention, the preferred materials and methods are described herein.
[00041 )All numbers expressing quantities of ingredients, constituents,
reaction
conditions, and so forth used in the specification and claims are to be
understood as
being modified in all instances by the term "about". Notwithstanding that the
numerical ranges and parameters setting forth the broad scope of the subject
matter
presented herein are approximations, the numerical values set forth in the
specific
examples are reported as precisely as possible. All numerical values, however,
inherently contain certain errors necessarily resulting from the standard
deviation
found in their respective testing measurements.
[00042] The following description includes embodiments presently contemplated
for
carrying out the present invention. This description is made for the purpose
of
illustrating the principles of the present invention and is not meant to limit
the
inventive concepts claimed herein.
[00043 }As used herein particle size refers to sieve screen analysis by
standard ASTM
methodology (ASTM method D6913-04e1). As used herein the term "agglomerate"
means a larger particle resulting from the binding together of smaller
particles. The
process of agglomerating can be described as taking "raw material" or "feed
particles"
and growing these particles into increasingly larger particles, i.e., "growing
agglomerates".
[00044 )Agglomerates can be agglomerated materials formed from smaller
particles
of the same substance (e.g., 100% bentonite) or agglomerated particles formed
from
smaller particles of different substances (e.g., 95% bentonite and 5% carbon).
Agglomerated particles formed from smaller particles of different substances
may be
herein referred to as composite particles or composites and composite
particles that
are blended with either composites having a different composition (e.g.,
composites
comprising bentonite and carbon blended with composites comprising bentonite
and
expanded perlite) and/or agglomerated absorbent material (e.g., agglomerated
bentonite) and/or non-agglomerated absorbent materials (e.g., non-agglomerated
bentonite) may be herein referred to as composite blends.
[00045 ]Non-agglomerated particles may be referred to herein as "raw material"
or
"feed particle(s)".
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[00046 ]The agglomerated materials produced from the processes disclosed
herein
weigh less than the raw materials and are potentially more porous than the raw
materials. The term bulk density reduction (BDR) refers to a reduction in bulk
density between the agglomerated material and the raw feed material. As will
be
discussed in detail below, the particles can be "engineered" with specific BDR
and/or
porosity parameters in mind.
[00047 ]Disclosed herein are several pan agglomeration processes that in
combination
with the raw materials used allows the manufacturer to control some of the
physical
properties of the resulting agglomerated particles, such as porosity, bulk
density, dust,
strength, as well as PSD (particle size distribution) without changing the
fundamental
composition and properties of the raw materials.
[00048 ]The methods disclosed herein have been found to be effective at
producing
animal litters with desired properties, so much of the discussion will focus
on
materials and material properties associated with animal litter. It should be
noted,
however, that the pan agglomeration processes described herein could be
appropriate
for use with other applications as well.
[00049 ]The present invention relates generally to composite absorbent
particles with
improved physical and chemical properties comprising an absorbent material and
optional performance-enhancing actives. By using various processes described
herein, such particles can be "engineered" to preferentially exhibit specific
characteristics including but not limited to improved odor control, lower
density,
easier scooping, better particle/active consistency, higher clump strength,
etc. One of
the many benefits of this technology is that the performance-enhancing actives
may
be positioned to optimally react with target molecules such as but not limited
to odor
causing volatile substances, resulting in surprising odor control with very
low levels
of active ingredient.
[00050 lA preferred use for the absorbent particles is as a cat litter, and
therefore
much of the discussion herein will refer to cat litter applications. However,
it should
be kept in mind that the absorbent particles have a multitude of applications,
and
should not be limited to the context of a cat litter.
[00051 ]One preferred method of forming the absorbent particles is by
agglomerating
granules of an absorbent material in a pan agglomerator. A preferred pan
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CA 02607750 2012-11-14
agglomeration process is set forth in more detail below, but is described
generally
here to aid the reader. Generally, the granules of absorbent material are
added to an
angled, rotating pan. A fluid or binder is added to the granules in the pan to
cause
binding of the granules. As the pan rotates, the granules combine or
agglomerate to
form particles. Depending on pan angle and pan speed among other factors, the
particles tumble out of the agglomerator when they reach a certain size. The
particles
are then dried and collected.
[00052 }The pan agglomerator is one method of tumble or growth agglomeration.
A
more detailed description of tumble/growth agglomeration can be found in
"Agglomeration Processes Phenomena, Technologies, Equipment" Chapters 6and 7
by Wolfgang Pietsch (2002),
[00053 }One or more performance-enhancing actives are preferably added to the
particles in an amount effective to perform the desired functionality or
provide the
desired benefit. For example, these actives can be added during the
agglomeration
process so that the actives are incorporated into the particle itself, or can
be added
during a later processing step.
[00054 ]Fig. 1 shows several embodiments of the absorbent particles of the
present
invention. These particles have actives incorporated:
1. In a layer on the surface of a particle (102)
2. Evenly (homogeneously) throughout a composite litter particle (104)
3. In a concentric layer(s) throughout the particle and/or around a core
(106)
4. In pockets or pores in and/or around a particle (108)
5. In a particle with single or multiple cores (110)
6. Utilizing non-absorbent cores (112)
7. No actives (114)
8. No actives, but with single or multiple cores (116)
9. In any combination of the above
[00055 }As previously recited hereinabove, other particle-forming processes
may be
used to form the inventive particles of the present invention. For example,
without
limitation, extrusion and fluid bed processes appear appropriate. Extrusion
process
typically involves introducing a solid and a liquid to form a paste or doughy
mass,
CA 02607750 2013-10-28
then forcing through a die plate or other sizing means. Because the forcing of
a mass
through a die can adiabatically produce heat, a cooling jacket or other means
of
temperature regulation may be necessary. The chemical engineering literature
has
many examples of extrusion techniques, equipment and materials, such as Duffy,
"Putting Crossflow Filtration to the Test," Chemical Engineering, pp. 1-
5(2002), and
Brodbeck et al., U.S. Patent 5,269,962, especially col. 18, lines 30-61
thereof. Fluid
bed process is depicted in Coyne et al., U.S. Patent 5,093,021, especially
col. 8 line 65
to col. 9, line 40.
Materials
[00056] Many liquid-absorbing materials may be used without departing from the
scope of the present invention. Illustrative absorbent materials include but
are not
limited to minerals, fly ash, absorbing pelletized materials, perlit, silicas,
other
absorbent materials and mixtures thereof. Preferred minerals include:
bentonites,
zeolites, fullers earth, attapulgite, montmorillonite diatomaceous earth,
opaline silica,
Georgia White clay, sepiolite, calcite, dolomite, slate, pumice, tobermite,
marls,
attapulgite, kaolinite, halloysite, smectite, vermiculite, hectorite, Fuller's
earth,
fossilized plant materials, expanded perlites, gypsum and other similar
minerals and
mixtures thereof. The preferred absorbent material is sodium bentonite having
a mean
particle diameter of about 5000 microns or less, preferably about 3000 microns
or
less, and ideally in the range of about 25 to about 150 microns.
[00057] Because minerals, and particularly clay, are heavy, it may be
desirable to
reduce the weight of the composite absorbent particles to reduce shipping
costs,
reduce the amount of material needed to fill the same relative volume of the
litter box,
and to make the material easier for customers to carry. To lower the weight of
each
particle, a lightweight core material, or "core," may be incorporated into
each particle.
The core can be positioned towards the center of the particle with a layer or
layers of
absorbent and/or active surrounding the core in the form of a shell. This
configuration
increases the active concentration towards the outside of the particles,
11
CA 02607750 2007-10-25
making the active more effective. The shell can be of any desirable thickness.
In one
embodiment with a thin shell, the shell has an average thickness of less than
about V2
that of the average diameter of the particle, and preferably the shell has an
average
thickness of not less than about 1/16 that of the average diameter of the
particle.
More preferably, the shell has an average thickness of between about 7/16 and
1/8
that of the average diameter of the particle, even more preferably less than
about 1/2
that of the average diameter of the particle, and ideally between about 3/8
and 1/8 that
of the average diameter of the particle. Note that these ranges are preferred
but not
limiting.
[00058 ]According to another embodiment comprising a core and absorbent
material
surrounding the core in the form of a shell, an average thickness of the shell
is at least
about four times an average diameter of the core. In another embodiment, an
average
thickness of the shell is between about 1 and about 4 times an average
diameter of the
core. In yet another embodiment, an average thickness of the shell is less
than an
average diameter of the core. In a further embodiment, an average thickness of
the
shell is less than about one-half an average diameter of the core.
[00059 'Other ranges can be used, but the thickness of the shell of absorbent
material/active surrounding a non-clumping core should be balanced to ensure
that
good clumping properties are maintained.
[00060 ]In another embodiment, the absorbent material "surrounds" a core
(e.g.,
powder, granules, clumps, etc.) that is dispersed homogeneously throughout the
particle or in concentric layers. For example, a lightweight or heavyweight
core
material can be agglomerated homogeneously into the particle in the same way
as the
active. The core can be solid, hollow, absorbent, nonabsorbent, and
combinations of
these.
[00061 ]Exemplary lightweight core materials include but are not limited to
calcium
bentonite clay, Attapulgite clay, Perlite, Silica, non-absorbent silicious
materials,
sand, plant seeds, glass, polymeric materials, and mixtures thereof. A
preferred
material is a calcium bentonite-containing clay which can weigh about half as
much
as bentonite clay. Calcium bentonite clay is non-clumping so it doesn't stick
together
in the presence of water, but rather acts as a seed or core. Granules of
absorbent
12
CA 02607750 2007-10-25
material and active stick to these seed particles during the agglomeration
process,
forming a shell around the seed.
[00062 ]Using the above lightweight materials, a bulk density reduction of
>10%,
>20%, preferably >30%, more preferably >40%, and ideally >50% can be achieved
relative to generally solid particles of the absorbent material (e.g., as
mined) and/or
particles without the core material(s). For example, in a particle in which
sodium
bentonite is the absorbent material, using about 50% of lightweight core of
calcium
bentonite clay results in about a 42% bulk density reduction.
[00063 ]Heavyweight cores may be used when it is desirable to have heavier
particles.
Heavy particles may be useful, for example, when the particles are used in an
outdoor
application in which high winds could blow the particles away from the target
zone.
Heavier particles also produce an animal litter that is less likely to be
tracked out of a
litter box. Illustrative heavyweight core materials include but are not
limited to sand,
iron filings, etc.
[00064 'Note that the bulk density of the particles can also be adjusted
(without use of
core material) by manipulating the agglomeration process to increase or
decrease pore
size within the particle.
[00065 }Note that active may be added to the core material if desired.
Further, the
core can be selected to make the litter is flushable. One such core material
is wood
pulp.
[00066 ]Performance-enhancing actives as defined herein mean any component
that
enhances the absorbent materials performance as an animal litter. Performance
enhancing actives can be agglomerated along with the absorbent particles or
can be
blended with or affixed to the absorbent material agglomerates. Illustrative
materials
for the performance-enhancing active(s) include but are not limited to
antimicrobials,
odor absorbers/inhibitors, binders, fragrances, health indicating materials,
nonstick
release agents, superabsorbent materials, light-weighting materials, heavy
weight
materials, reinforcing fiber materials and mixtures and combinations thereof.
One
great advantage of the particles of the present invention is that
substantially every
agglomerated particle contains an active, or in the case of an agglomerate
blend (i.e.,
agglomerated material blended with non-agglomerated material), the actives are
substantially distributed throughout the final product.
13
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[00067 ]Preferred antimicrobial actives are boron containing compounds such as
borax pentahydrate, borax decahydrate, boric acid, polyborate, tetraboric
acid, sodium
metaborate, anhydrous, boron components of polymers, and mixtures thereof.
[00068 ]One type of odor absorbing/inhibiting active inhibits the formation of
odors.
An illustrative material is a water soluble metal salt such as silver, copper,
zinc, iron,
and aluminum salts and mixtures thereof. Preferred metallic salts are zinc
chloride,
zinc gluconate, zinc lactate, zinc maleate, zinc salicylate, zinc sulfate,
zinc ricinoleate,
copper chloride, copper gluconate, and mixtures thereof. Other odor control
actives
include metal oxide nanoparticles. Additional types of odor
absorbing/inhibiting
actives include cyclodextrin, zeolites, activated carbon, acidic, salt-forming
materials,
and mixtures thereof.
[00069 ]The preferred odor absorbing/inhibiting active is Powdered Activated
Charcoal (PAC), though Granular Activated Carbon (GAC) can also be used. PAC
gives much greater surface area than GAC (something larger than powder (e.g.,
> 80
mesh U.S. Standard Sieve (U.S.S.S.))), and thus has more sites with which to
trap
odor-causing materials and is therefore more effective. PAC has only rarely
been
used in absorbent particles, and particularly animal litter, as it tends to
segregate out
of the litter during shipping, thereby creating excessive dust (also known as
"sifting").
By agglomerating PAC into particles, the present invention overcomes the
problems
with carbon settling out during shipping. Additionally, carbon is black in
color.
Agglomerating the PAC (and/or GAC) into the composite (or adding it to the
composites by a later processing step) aids in diluting the black color of the
carbon, a
factor known to be disliked by cat litter consumers. The above-mentioned
benefits of
incorporating carbon into the composites are true for composite blends, as
well.
Generally, the preferred mean particle diameter of the carbon particles used
is less
than about 500 microns, but can be larger. The preferred particle size of the
PAC is
about 150 microns (-100 mesh U.S.S.S.) or less, and ideally in the range of
about 25
to 150 microns, with a mean diameter of about 50 microns (-325 mesh U.S.S.S.)
or
less.
[00070 "The active may be calcium bentonite added to reduce sticking to a
litter box.
[00071 ]The active may also include a binder such as water, lignin sulfonate
(solid),
polymeric binders, fibrillated Teflon (polytetrafluoroethylene or PTFE), and
14
CA 02607750 2007-10-25
combinations thereof. Useful organic polymerizable binders include, but are
not
limited to, carboxymethylcellulose (CMC) and its derivatives and its metal
salts, guar
gum cellulose, xanthan gum, starch, lignin, polyvinyl alcohol, polyacrylic
acid,
styrene butadiene resins (SBR), and polystyrene acrylic acid resins. Water
stable
particles can also be made with crosslinked polyester network, including but
not
limited to those resulting from the reactions of polyacrylic acid or citric
acid with
different polyols such as glycerin, polyvinyl alcohol, lignin, and
hydroxyethylcellulose.
[00072 ]Dedusting agents can also be added to the particles in order to reduce
the dust
ratio. Many of the binders listed above are effective dedusting agents when
applied to
the outer surface of the composite absorbent particles. Other dedusting agents
include
but are not limited to gums, resins, water, and other liquid or liquefiable
materials.
[00073 ]A dye or pigment such as a dye, bleach, lightener, etc. may be added
to vary
the color of absorbent particles, such as to lighten the color of litter so it
is more
appealing to an animal, etc.
[00074 ]Suitable superabsorbent materials include superabsorbent polymers such
as
AN905SH, FA920SH, and F04490SH, all from Floerger. Preferably, the
superabsorbent material can absorb at least 5 times its weight of water, and
ideally
more than 10 times its weight of water.
[00075 ]Reinforcing fiber material(s) (hereinafter "fiber(s)") may be added to
increase
clump strength and/or reduce the overall bulk density of the litter material.
Fibers are
any solid material having a mean cylindrical shape and a length to diameter
aspect
ratio greater than one that helps to maintain the structural integrity of
litter clumps
once formed. The fibers may range in particle size from about mm to about 5mm.
The fibers are typically in the size range of about lnin to about 5mm prior to
agglomeration, but could be up to 6 inches depending on whether the process
used
first breaks down the material into a smaller size prior to forming composite
particles.
The fibers may comprise between 0.1 and 50% of the composite particle, but
typically
are present in an amount less than 20% (i.e., 19% or less).
[00076 ]Preferred fibers include any solid material that demonstrates a mean
cylindrical shape with a large length to diameter aspect ratio (e.g, 2 to 1 or
greater)
and the following two properties. First, a built tensile strength that is due
to
CA 02607750 2007-10-25
molecular orientation induced by the formation of the fiber whether natural or
synthetically produced. Second, a surface morphology that creates bonding
sites that
allow the fiber to reinforce the overall structure of the particle. The
bonding sites may
be created either by allowing association with other chemical elements and
structures
(e.g., hydrogen bonding as present in polyester) or by a physical interlocking
of
surface morphologies (e.g., puzzle pieces).
[00077 ]Fibers may be made of materials such as, but not limited to natural
materials,
e.g., wool, cotton, hemp, rayon, lyocell, paper, paper fluff, cellulose,
regenerated
cellulose, bird feathers, carbon, activated carbon, as well as synthetic
materials, e.g.,
polyester, nylon, plastics, polymers (including super absorbent polymers
(SAPs) and
copolymers). Combinations of these materials are also possible, as in the
multi-
component fibers discussed below. Illustrative reinforcing fibers include
paper fluff,
DuPont's Kevlar (poly-paraphenylene terephthalamide) yarn, PET (polyethylene
terephthalate), Tencel cellulose fiber, rayon, cotton, poultry feather parts,
cellulose,
and combinations thereof. Reclaim, i.e., a recycled mixture incorporating some
or all
of the synthetic materials listed above, could also be used.
[00078 ]In addition, fibers recovered as a byproduct or waste product from
another
process can also be incorporated in the absorbent particles. For example, the
fibrous
waste from a paper or tissue manufacturing process can be used. The size of
the fibers
is not critical, and can range from small particles captured by a dust
collection process
to relatively larger particles.
[00079 10ther performance-enhancing actives may be embedded within the fibers
or
attached to the surface of the fibers to augment a specific consumer-
benefiting
feature, such as odor control or enhanced absorptivity or both. Cotton fibers
embedded with activated carbon could be combined with an absorbent clay to
form
composite particles suitable for use as an animal litter having increased odor
control.
Non-woven fibers charged with SAPs (e.g., BASF luquafleece IS) can be combined
with an absorbent clay to form composite particles having increased
absorptivity. The
resulting litter compositions have the advantage of controlling odors and
moisture as
strong clumps are formed.
[00080 ]Benefits imparted by the fibers (either alone or in combination with
other
performance-enhancing actives) may include without limitation, increased
structural
16
CA 02607750 2007-10-25
integrity (e.g., less breakage and dust), increased clump strength, increased
liquid
absorption, abrasion resistance, animal attractant/repellant, visual
aesthetics, tactile
aesthetics, lower overall bulk weight, and increased odor control (e.g.,
activated
carbon fibers). Clump strength is a measure of the mechanisms that aid in the
formation of agglomerates (moist litter particles that stick together) in the
litter box.
Crimped fibers (helical and saw-tooth) may provide higher clumping strength or
reduced attrition in processing and handling.
[00081 ]Bicomponent and/or multi-component fibers may provide additional
benefits.
For example, one component of the fiber may melt and act as an adhesive during
the
agglomeration drying process to further enhance the strength of the composite
particles, while the other component may retain its length/integrity in order
to provide
a reinforcing benefit and increase clump strength. When the fiber is subjected
to the
melt temp of the lower meting component, the lower melting component acts as
the
adhesive, while the higher melting component retains the shape and a portion
of the
integrity of the fiber. Some examples include fibers made of both polyethylene
and
polyester, or polyethylene and polypropylene in a side by side or a sheath
/core
configuration.
[00082 ]Additional attributes may be present if the fibers are porous. Fiber
porosity
could lead to a three-fold benefit: (1) light-weighting (i.e., a decrease in
the bulk
density of the litter composition), (2) increased odor and/or moisture
absorption (i.e.,
within the pores due to an increase in surface area), and (3)
encapsulation/carrier
vehicle for performance-enhancing actives, such as odor absorbers, moisture
absorbers, antimicrobials, fragrances, clumping agents, etc. These benefits
combined
with the aforementioned additional clump strength and clump integrity are
unexpected. Generally lower density, higher porosity litter materials with
litter
additives work to decrease clump strength. This common drawback is overcome by
the composite particles disclosed herein.
[00083 ]When only 2% paper fluff fibers are added to a primarily sodium
bentonite
composition via a pilot plant scale pin mixer equipped with a rotary drier, a
13%
reduction in bulk density is observed.
[00084 ]The clump aspect ratio, which is defined as Square root ((longest
clump
length)2 + (shortest clump length) 2)/clump height may be affected by the
addition of
17
CA 02607750 2012-11-14
=
fibers to the composite particles. In general, it is desirable to have a round
clump,
which translates to an aspect ratio of about 0.5. Higher aspect ratios are
indicative of
less round, more "pancake-shaped" clumps, which may be acceptable, if other
benefits are gained (e.g., an increase in liquid absorption or a decrease in
clumps
sticking to the box).
[00085 ]The fibers can range in particle size from about mm to about 6 inches
(typically ranging between mm and 5mm) and generally are present in 0.1-50% by
weight of the composite particles. The size and shape of the fibers chosen may
aid in
controlling the particle size and shape of the resulting composite particles.
For
example, it is expected that longer fibers will yield larger agglomerate
particles and a
blend of fiber lengths will yield composite particles of varying particle
sizes.
[00086 ]U.S. Patent No. 5,705,030 assigned to the United States Department of
Agriculture,
describes a process for converting chicken feathers into fibers. According to
U.S. Patent No.
5,705,030, feathers from all avian sources have the characteristics which are
necessary for the production of useful fibers, therefore feathers from any
avian
species may be utilized. Feathers are made up of many slender, closely
arranged
parallel barbs forming a vane on either side of a tapering hollow shaft. The
barbs have
bare barbules which in turn bare barbicels commonly ending in hooked hamuli
and
interlocking with the barbules of an adjacent barb to link the barbs into a
continuous
vane.
[00087 ]Structurally, chicken feather fibers have naturally-occurring nodes
approximately 50 microns apart. These nodes are potential cleavage sites for
producing fibers of uniform 40-50 um lengths. In addition, feathers from
different
species vary in length: poultry feather fibers are approximately 2 cm in
length while
those derived from exotic birds such as peacocks or ostriches are 4 to 5 cm or
longer.
Feather fibers are also thinner than other natural fibers resulting in
products having a
smooth, fine surface.
[00088 ]The composition of wood pulp fiber is generally about 50% cellulose
with
the remainder being lignin and hemicelluloses. Hardwood trees have broad
leaves
and softwood trees have needle-like or scale-like leaves. Hardwood trees have
shorter
fibers compared to softwood trees. All freshly cut wood contains moisture.
Wood
18
CA 02607750 2007-10-25
pulp has a tendency to be at "equilibrium density", i.e., the density at which
the
addition of more water does not swell or flatten the wood. If the wood pulp
sheet is
low density and water is added, it flattens out to equilibrium density. If the
wood pulp
sheet is high density, it swells to the equilibrium density.
[00089 ]Equilibrium density plays a significant role when agglomerated with an
absorbent material suitable for use as a cat litter. While in an air stream,
if the density
of the wood pulp fiber is close to the density of the composite particles
formed, a
homogenous blend of fibers within the composite particles may be obtained. If
there
is a significant difference between the density of the wood pulp and the
density of the
composite particles formed, there is the possibility of fiber aggregation.
[00090 ]Wood pulp strength is directly proportional to fiber length and
dictates its
final use. A long fiber pulp is good to blend with short fiber pulp to
optimize on fiber
cost, strength and formation of paper. In general, pulp made from softwood
trees or
wood grown in colder climates have longer fibers compared to pulp made from
hardwood trees or wood grown in warmer climates.
[00091 ]Processing conditions also contribute to fiber length. When made from
the
same wood, chemical pulps tend to have longer fibers compared to semi-chemical
pulp and mechanical pulp. Examples of long fiber pulp (>10mm) are cotton,
hemp,
flax and Jute. Examples of medium fiber pulp (2-10mm) are Northern softwoods
and
hardwoods. Examples of short fiber pulp (<2mm) are tropical hardwoods, straws
and
grasses.
[00092 ]The core mentioned above can also be considered an active, for example
including a lightweight material dispersed throughout the particle to reduce
the weight
of the particle, a core made of pH-altering material, etc. A preferred
embodiment is to
bind actives directly to the surface of composite absorbent particles. The use
of
extremely low levels of actives bound only to the surface of absorbent
particles leads
to the following benefits:
1. the use of extremely small particle size of the active material results
in a very high surface area of active while using a very small amount
of active,
2. with actives present only on the surface of the substrate, the waste of
expensive actives that would be found with 'homogeneous'
19
CA 02607750 2007-10-25
composite particles [where actives are found throughout the
substrate particles] is eliminated,
3. segregation of actives from substrates is eliminated; thus, the actives
remain dispersed and do not end up on the bottom of the litter
container,
4. by using very low levels of expensive actives, the cost of the product
is greatly reduced,
5. binding of small particle size actives directly to the substrate surface
results in lower dust levels than in bulk added product.
[00094 ]Surprisingly, low levels of PAC [0.2-0.3%] have been found to provide
excellent odor control in cat litter when they are bound to the surface of a
material
such as sodium bentonite clay. For example, binding of small amounts of PAC
particles to sodium bentonite substrate particles using xanthan gum or
fibrillatable
PTFE as binder results in litter materials with superior odor adsorbing
performance.
In this example, the PAC is highly effective at capturing malodorous volatile
organic
compounds as they escape from solid and liquid wastes due to the high surface
area of
the PAC, and its preferred location on the surface of the sodium bentonite
particles.
[00095 ]Another aspect of the invention is the use of Encapsulated Actives,
where the
actives are positioned inside the particle, homogeneously and/or in layers.
Because of
the porous structure of the particles, even actives positioned towards the
center of the
particle are available to provide their particular functionality.
Encapsulation of
actives provides a slow release mechanism such that the actives are in a
useful form
for a longer period of time. This is particularly so where the active is used
to reduce
malodors.
[00096 ]In addition to liquid-absorbing clay materials, filler materials such
as
limestone, sand, calcite, dolomite, recycled waste materials, zeolites, silica
gel and
gypsum can also be incorporated with the clay materials to reduce the cost of
the litter
without significantly decreasing the material's performance as a litter.
[00097 ]Because clays are heavy, it may be desirable to reduce the weight of
the
composites to reduce shipping costs, reduce the amount of material needed to
fill the
same relative volume of the litter box, and to make the material easier for
customers
to carry. Exemplary light-weighting materials include but are not limited to
perlite,
CA 02607750 2007-10-25
expanded perlite, volcanic glassy materials having high porosities and low
densities,
vermiculite, expanded vermiculite, pumice, silica gels, opaline silica, tuff,
and
lightweight agricultural byproducts. When selecting a light-weighting
material, the
effect the light-weighting material will have on the litter's performance is
an
important consideration. Factors to evaluate include how the light-weighting
material
will effect cost, ease of manufacture, clumping, tracking, absorbency, odor
control,
sticking to the box, dust, etc. In some cases, the light-weighting materials
may also
be performance-enhancing.
[00098 ]One embodiment disclosed herein utilizes expanded perlite having a
bulk
density of 5 lb/ft3. Expanded perlites having bulk densities greater than 5
lb/ft3 may
also be used. Perlite is a generic term for a naturally occurring siliceous
rock. The
distinguishing feature which sets perlite apart from other volcanic glasses is
that when
heated to a suitable point in its softening range, it expands from four to
twenty times
its original volume. This expansion is due to the presence of two to six
percent
combined water in the crude perlite rock. Firing, i.e., quickly heating to
above 1600 F
(871 C), causes the crude rock to pop in a manner similar to popcorn yielding
a very
open, highly porous structure referred to as expanded perlite. Once the
perlite is
expanded, it can then be gently crushed to form materials having varying
structural
properties. The perlite can be obtained either expanded or unexpanded and the
firing
step can be performed on site prior to agglomeration. Significant cost savings
in
shipping can result from expanding the perlite on site.
[00099 ]A particular source of perlite is Kansas Minerals. Perlite obtained
from
Kansas Minerals is believed to be somewhat physically unique after being
popped. It
is expected that hollow spheres are formed during the firing process, however,
when
the Kansas Minerals material is examined under a microscope, it appears as
though
only a portion of the material comprises hollow spheres. The other portion
comprises
broken spheres. Without being bound by any particular theory, it is possible
that the
wall thickness of the expanded perlite spheres initially formed through the
firing
process are very thin and thus, tend to break apart. Whatever the cause of
this
physical property, it is believed to result in a material that is particularly
well suited
for use in the agglomeration processes of the present invention. The
combination of
21
CA 02607750 2007-10-25
approximately 50/50 hollow spheres to broken spheres has been observed to
perform
particularly well.
[000100 ]A source of expanded volcanic ash is Harborlite World Minerals.
Expanded
volcanic ash from Harborlite has a bulk density of about 3 lb/ft3 and has also
been
successfully incorporated into agglomerated absorbent materials.
[000101 ]Another suitable, expandable mineral similar to perlite is
vermiculite. In all
examples containing expanded perlite, expanded vermiculite could be
substituted for
the perlite with similar results expected. Although geological differences may
exist
between expanded perlite and expanded volcanic ash (and perlite and volcanic
ash),
the two terms are synonymously used herein.
[000102 ]Various embodiments of the present invention utilize light-weighting
materials having the following mean particle diameters: about 1500 microns or
less;
about 500 microns or less; ranging from about 1 to about 100 microns.
[000103 ]Using the above lightweight materials, a bulk density reduction of 10-
50%
can be achieved relative to generally solid particles of the absorbent clay
material
(e.g., as mined). For example, composites in which sodium bentonite (Black
Hills
Bentonite, Mills, Wyoming) is the absorbent clay material (bulk density 67
lb/ft3),
using about 17% of expanded perlite, e.g., Kamco 5, (Kansas Minerals, Mancato,
Kansas) having a bulk density of 5 lb/ft3 results in up to a 53% bulk density
reduction. Using roughly13% of the 51b/ft3 expanded perlite results in about a
43%
reduction in bulk density. Using roughly 5% of the 51b/ft3 expanded perlite
results in
about a 37% reduction in bulk density.
[000104 ]The bulk density of the composites formed can be adjusted by
manipulating
the agglomeration process to increase or decrease pore size within the
particle.
[000105 ]Heavyweight materials may be added to the absorbent material when it
is
desirable to have heavier particles. Heavy particles may be useful, for
example, when
the particles are used in an outdoor application in which high winds could
blow the
particles away from the target zone. Heavier particles also produce an animal
litter
that is less likely to be tracked out of a litter box. Illustrative
heavyweight materials
include but are not limited to sand, iron filings, etc.
22
CA 02607750 2007-10-25
Pan Agglomeration and Other Particle Creation Processes
[000106 ]The agglomeration process in combination with the unique materials
used
allows the manufacturer to control the physical properties of particles, such
as bulk
density, dust, strength, as well as PSD (particle size distribution) without
changing the
fundamental composition and properties of absorbent particles.
[000107 ]One benefit of the pan agglomeration process of the present invention
is
targeted active delivery, i.e., the position of the active can be "targeted"
to specific
areas in, on, and/or throughout the particles. Another benefit is that because
the way
the absorbent particles are formed is controllable, additional benefits can be
"engineered" into the absorbent particles, as set forth in more detail below.
[000108 ]As absorbent clay(s) is a preferred absorbent material, much of the
discussion will involve the use of absorbent clay(s). However, it should be
kept in
mind that other absorbent materials suitable for use as animal litter may be
used in
place of the absorbent clay(s) discussed herein.
[000109 ]Fig. 2 is a process diagram illustrating a pan agglomeration process
200
according to a preferred embodiment. In this example, the absorbent granules
are
bentonite clay and the active is PAC. Cores of a suitable material, here
calcium
bentonite clay, are also added. The absorbent particles (e.g., bentonite
powder) is
mixed with the active (e.g., PAC) to form a dry mixture, which is stored in a
hopper
202 from which the mixture is fed into the agglomerator 206. Alternatively,
the
absorbent granules and active(s) may be fed to the agglomerator individually.
For
example, liquid actives can be added by a sprayer. The cores are preferably
stored in
another hopper 204, from which they are fed into the agglomerator. A feed
curtain
can be used to feed the various materials to the agglomerator.
[000110 ]Jn this example, the agglomerator is a pan agglomerator. The pan
agglomerator rotates at a set or variable speed about an axis that is angled
from the
vertical. Water and/or binder is sprayed onto the granules in the agglomerator
via
sprayers 208 to raise/maintain the moisture content of the particles at a
desired level
so that they stick together. Bentonite acts as its own binder when wetted,
causing it to
clump, and so additional binder is not be necessary. The pan agglomeration
process
gently forms composite particles through a snowballing effect broadly
classified by
experts as natural or tumble growth agglomeration. Fig. 3 depicts the
structure of an
23
CA 02607750 2007-10-25
illustrative agglomerated composite particle 300 formed during the process of
Fig. 2.
As shown, the particle includes granules of absorbent material 302 and active
304
with moisture 306 or binder positioned interstitially between the granules.
[000111 ]Depending on the pan angle and pan speed, the particles tumble off
upon
reaching a certain size. Thus, the pan angle and speed controls how big the
particles
get. The particles are captured as they tumble from the agglomerator. The
particles
are then dried to a desired moisture level by any suitable mechanism, such as
a rotary
or fluid bed. In this example, a forced air rotary dryer 210 is used to lower
the high
moisture content of the particles to less than about 15% by weight and ideally
about
8-13% by weight. At the outlet of the rotary dryer, the particles are screened
with
sieves 212 or other suitable mechanism to separate out the particles of the
desired size
range. Tests have shown that about 80% or more of the particles produced by
pan
agglomeration will be in the desired particle size range. Preferably, the
yield of
particles in the desired size range is 85% or above, and ideally 90% or
higher. The
selected particle size range can be in the range of about 10 mm to about 100
microns,
and preferably about 2.5 mm or less. An illustrative desired particle size
range is
12x40 mesh (1650-400 microns).
[000112 ]The exhaust from the dryer is sent to a baghouse for dust collection.
Additional actives such as borax and fragrance can be added to the particles
at any
point in the process before, during and/or after agglomeration. Also,
additional/different actives can be dry blended with the particles.
[000113 ]Illustrative composite absorbent particles after drying have a
specific weight
of from about 0.15 to about 1.2 kilograms per liter and a liquid absorbing
capability of
from about 0.6 to about 2.5 liters of water per kilogram of particles.
Preferably, the
particles absorb about 50% or more of their weight in moisture, more
preferably about
75% or more of their weight in moisture, even more preferably greater than
approximately 80% and ideally about 90% or more of their weight in moisture.
[000114 ]Specific examples of compositions that can be fed to the agglomerator
using
the process of Fig. 2 include (in addition to effective amounts of active):
= 100% Bentonite Powder
= 67% Calcium Bentonite Clay (core) & 33% Bentonite Powder
= 50% Calcium Bentonite Clay (core) & 50% Bentonite Powder
24
CA 02607750 2007-10-25
= Perlite (core) & Bentonite Powder
= Sand (core) & Bentonite Powder
[000116 ]Table 1 lists illustrative properties for various compositions of
particles
created by a 20" pan agglomerator at pan angles of 40-60 degrees and pan
speeds of
20-50RPM. The total solids flow rates into the pan were 0.2-1.0 kg/min.
CA 02607750 2013-10-28
Table 1
Bentonite Bulk
to Core Final Density Clump
Core Water Ratio Moisture (kg/I) Strength
0.70-
None 15-23% 100:0 1.0-1.4% 0.78 95-97
Calcium 0.60-
bentonite 15-23 50:50 3.4 0.66 95-97
Calcium 0.57-
bentonite 15-18 33:67 4.3-4.4 0.60 93-95
0.81-
Sand 10-12 50:50 2.0 0.85 97-98
Sand 6-8 33:67 1.6-2.4 0.92 97
0.36-
Perlite 15-19% 84:16 0.39 97%
0.27-
Perlite 16-23% 76:24 0.28 95-97%
[000117 ]Clump strength is measured by first generating a clump by pouring 10
ml of
pooled cat urine (from several cats so it is not cat specific) onto a 2 inch
thick layer of
litter. The urine causes the litter to clump. The clump is then placed on a
1/2" screen
after a predetermined amount of time (e.g., 6 hours) has passed since the
particles
26
CA 02607750 2007-10-25
were wetted. The screen is agitated for 5 seconds with the arm up using a Ro-
Tap
Mechanical Sieve Shaker made by W.S. Tyler, Inc. The percentage of particles
retained in the clump is calculated by dividing the weigh of the clump after
agitation
by the weight of the clump before agitation. Referring again to the Table 1
above,
note that the clump strength indicates the percentage of particles retained in
the clump
after 6 hours. As shown, >90%, and more ideally, >95% of the particles are
retained
in a clump after 6 hours upon addition of an aqueous solution, such as
deionized water
or animal urine. Note that? about 80% particle retention in the clump is
preferred.
Also, note the reduction in bulk density when a core of calcium bentonite clay
or
perlite is used.
[000118 ]Fig. 4 is a process diagram illustrating another exemplary pan
agglomeration process 400 with a recycle subsystem 402. Save for the recycle
subsystem, the system of Fig. 4 functions substantially the same as described
above
with respect to Fig. 2. As shown in Fig. 4, particles under the desired size
are sent
back to the agglomerator. Particles over the desired size are crushed in a
crusher 404
and returned to the agglomerator.
[000119 ]The diverse types of clays and mediums that can be utilized to create
absorbent particles should not be limited to those cited above. Further, unit
operations used to develop these particles include but should not be limited
to: high
shear agglomeration processes, low shear agglomeration processes, high
pressure
agglomeration processes, low pressure agglomeration processes, mix mullers,
roll
press compacters, pin mixers, batch tumble blending mixers (with or without
liquid
addition), and rotary drum agglomerators. For simplicity, however, the larger
portion
of this description shall refer to the pan agglomeration process, it being
understood
that other processes could potentially be utilized with similar results.
[000120 ]Fig. 5 is a process diagram illustrating an exemplary pin mixer
process 500
for forming composite absorbent particles. As shown, absorbent particles and
active
are fed to a pin mixer 502. Water is also sprayed into the mixer. The
agglomerated
particles are then dried in a dryer 504 and sorted by size in a sieve screen
system 506.
Table 2 lists illustrative properties for various Compositions of particle
created by pin
mixing.
27
CA 02607750 2007-10-25
Table 2
Bentonite to Water Bulk Clump Strength
Lightweight Clay Ratio Addition Density -6 hours
Zeolite (39 lb/ft3) 50:50 20 59 91
Bentonite (64
lb/ft3) 100:0 20 67 95
=
[000121 ]Fig. 6 is a process diagram illustrating an exemplary mix muller
process 600
for forming composite absorbent particles. As shown, the various components
and
water and/or binder are added to a pellegrini mixer 602. The damp mixture is
sent to
a muller agglomerator 604 where the mixture is agglomerated. The agglomerated
particles are dried in a dryer 606, processed in a flake breaker 608, and then
sorted by
size in a sieve screen system 610.
[000122 ]Table 3 lists illustrative properties for various compositions of
particles
created by a muller process. Note that the moisture content of samples after
drying is
2-6 weight percent.
28
CA 02607750 2007-10-25
Table 3
Clump
Calculated Actual Strength - 6
Bentonite: Water Bulk Bulk hours
Clay Addition Density Density (% Dust
Clay (wt%) (wt%) (lbIft3) (Ibifts) Retained)
(mg)
GWC
(32 lb/ft3) 50:50 33 43 45 83 39
GWC
(32 lb/ft3) 50:50 47 43 42 56 34
Taft DE
(22 lb/ft3) 50:50 29 33 46 86 38
Taft DE
(22 lb/ft3) 50:50 41 33 43 76 35
[000123 ]The composite absorbent particle can be formed into any desired
shape. For
example, the particles are substantially spherical in shape when they leave
the
agglomeration pan. At this point, i.e., prior to drying, the particles have a
high
enough moisture content that they are malleable. By molding, compaction, or
other
processes known in the art, the composite absorbent particle can be made into
non-
spherical shapes such as, for example, ovals, flattened spheres, hexagons,
triangles,
squares, etc. and combinations thereof.
Example 1
[000124 ]Referring again to Fig. 1, a method for making particles 102 is
generally
performed using a pan agglomeration process in which clay particles of <200
mesh
(<74 microns), preferably <325 mesh (<43 microns) particle size premixed with
particles of active, are agglomerated in the presence of an aqueous solution
to form
particles in the size range of about 12x40 mesh (about 1650-250 microns).
Alternatively, the particles are first formed with clay alone, then
reintroduced into the
pan or tumbler, and the active is added to the pan or tumbler, and a batch run
is
performed in the presence of water or a binder to adhere the active to the
surface of
the particles. Alternatively, the active can be sprayed onto the particles.
Example 2
CA 02607750 2007-10-25
[000125 ]A method for making particles 104 is generally performed using the
process
described with relation to Fig. 2, except no core material is added.
Example 3
[000126 ]A method for making particles 106 is generally performed using the
process
described with relation to Fig. 2, except that introduction of the absorbent
granules
and the active into the agglomerator are alternated to form layers of each.
Example 4
[000127 IA method for making particles 108 is generally performed using the
process
described with relation to Fig. 2, except that the active has been pre-clumped
using a
binder, and the clumps of active are added. Alternatively, particles of
absorbent
material can be created by agglomeration and spotted with a binder such that
upon
tumbling with an active, the active sticks to the spots of binder thereby
forming
concentrated areas. Yet another alternative includes the process of pressing
clumps of
active into the absorptive material.
Example 5
[000128 ]A method for making particles 110 is generally performed using the
process
described with relation to Fig. 2.
Example 6
[000129 ]A method for making particles 112 is generally performed using the
process
described with relation to Fig. 2.
Example 7 & 8
[000130 JA method for making particles 114 and 116 are generally performed
using
the process described with relation to Fig. 2, except no active is added.
[000131 ]In addition, the performance-enhancing active can be physically
dispersed
along pores of the particle by suspending an insoluble active in a slurry and
spraying
CA 02607750 2007-10-25
the slurry onto the particles. The suspension travels into the pores and
discontinuities,
depositing the active therein.
Control Over Particle Properties
[000132 ]Strategically controlling process and formulation variables along
with
agglomerate particle size distribution allows for the development of various
composite particles engineered specifically to "dial in" attribute
improvements as
needed. Pan agglomeration process variables include but are not limited to raw
material and ingredient delivery methods, solid to process water mass ratio,
pan
speed, pan angle, scraper type and configuration, pan dimensions, throughput,
and
equipment selection. Formulation variables include but are not limited to raw
material specifications, raw material or ingredient selection (actives,
binders, clays
and other solids media, and liquids), formulation of liquid solution used by
the
agglomeration process, and levels of these ingredients.
[000133 ]The pan agglomeration process intrinsically produces agglomerates
with a
narrow particle size distribution (PSD). The PSD of the agglomerates can be
broadened by utilizing a pan agglomerator that continuously changes angle
(pivots
back and forth) during the agglomeration process. For instance, during the
process,
the pan could continuously switch from one angle, to a shallower angle, and
back to
the initial angle or from one angle, to a steeper angle, and back to the
initial angle.
This variable angle process would then repeat in a continuous fashion. The
angles
and rate at which the pan continuously varies can be specified to meet the
operator's
desired PSD and other desired attributes of the agglomerates.
[000134 ]By knowledge of interactions between pan, dryer, and formulation
parameters one could further optimize process control or
formulation/processing cost.
For example, it was noted that by addition of a minor content of a less
absorptive clay,
we enabled easier process control of particle size. For example, by addition
of
calcium bentonite clay the process became much less sensitive to process
upsets and
maintains consistent yields in particle size throughout normal moisture
variation.
Addition of calcium bentonite clay also helped reduce particle size even when
higher
moisture levels were used to improve granule strength. This is of clear
benefit as one
31
CA 02607750 2007-10-25
looks at enhancing yields and having greater control over particle size
minimizing
need for costly control equipment or monitoring tools.
[000135 ]For those practicing the invention, pan agglomeration manipulation
and
scale-up can be achieved through an empirical relationship describing the
particle's
path in the pan. Process factors that impact the path the particle travels in
the pan
include but are not limited to pan dimensions, pan speed, pan angle, input
feed rate,
solids to process liquid mass ratio, spray pattern of process liquid spray,
position of
scrapers, properties of solids being processed, and equipment selection.
Additional
factors that may be considered when using pan agglomerators include particle
to
particle interactions in the pan, gravity effects, and the following
properties of the
particles in the pan: distance traveled, shape of the path traveled, momentum,
rotational spin about axis, shape, surface properties, and heat and mass
transfer
properties.
[000136 ]The composite particles provide meaningful benefits, particularly
when
used as a cat litter, that include but are not limited to improvements in
final product
attributes such as odor control, litter box maintenance benefits, reduced
dusting or
sifting, and consumer convenience. As such, the following paragraphs shall
discuss
the composite absorbent particles in the context of animal litter, it being
understood
that the concepts described therein apply to all embodiments of the absorbent
particles.
[000137 ]Significant odor control improvements over current commercial litter
formulas have been identified for, but are not limited to, the following
areas:
= Fecal odor control (malodor source: feline feces)
= Ammonia odor control (malodor source: feline urine)
= Non-ammonia odor control (malodor source: feline urine)
[000138]Odor control actives that can be utilized to achieve these benefits
include but
are not limited to powdered activated carbon, silica powder (Type C), borax
pentahydrate, and bentonite powder. The odor control actives are preferably
distributed within and throughout the agglomerates by preblending the actives
in a
batch mixer with clay bases and other media prior to the agglomeration step.
The pan
agglomeration process, in conjunction with other unit operations described
here,
allows for the targeted delivery of actives within and throughout the
agglomerate, in
32
CA 02607750 2007-10-25
the outer volume of the agglomerate with a rigid core, on the exterior of the
agglomerate, etc. These or any targeted active delivery options could also be
performed in the pan agglomeration process exclusively through novel
approaches
that include, but should not be limited to, strategic feed and water spray
locations,
time delayed feeders and spray systems, raw material selection and their
corresponding levels in the product's formula (actives, binders, clays, and
other
medium), and critical pan agglomeration process variables described herein.
[000139]Additionally, the pan agglomeration process allows for the
incorporation of
actives inside each agglomerate or granule by methods including but not
limited to
dissolving, dispersing, or suspending the active in the liquid solution used
in the
agglomeration process. As the pan agglomeration process builds the granules
from
the inside out, the actives in the process's liquid solution become
encapsulated inside
each and every granule. This approach delivers benefits that include but
should not
be limited to reduced or eliminated segregation of actives from base during
shipping
or handling (versus current processes that simply dry tumble blend solid
actives with
solid clays and medium), reduced variability in product performance due to
less
segregation of actives, more uniform active dispersion across final product,
improved
active performance, and more efficient use of actives. This more effective use
of
actives reduces the concentration of active required for the active to be
effective,
which in turn allows addition of costly ingredients that would have been
impractical
under prior methods. For example, dye or pigment can be added to vary the
color of
the litter, lighten the color of the litter, etc. Disinfectant can also be
added to kill
germs. For example, this novel approach can be utilized by dissolving borax
pentahydrate in water. This allows the urease inhibitor (boron) to be located
within
each granule to provide ammonia odor control and other benefits described
here. One
can strategically select the proper actives and their concentrations in the
liquid
solution used in the process to control the final amount of active available
in each
granule of the product or in the product on a bulk basis to deliver the
benefits desired.
[000140]Targeted active delivery methods should not be limited to the targeted
active
delivery options described here or to odor control actives exclusively. For
example,
another class of active that could utilize this technology is animal health
indicating
actives such as a pH indicator that changes color when urinated upon, thereby
33
CA 02607750 2007-10-25
indicating a health issue with the animal. This technology should not be
limited to cat
litter applications. Other potential industrial applications of this
technology include
but should not be limited to laundry, home care, water filtration, fertilizer,
iron ore
pelletizing, pharmaceutical, agriculture, waste and landfill remediation, and
insecticide applications. Such applications can utilize the aforementioned
unit
operations like pan agglomeration and the novel process technologies described
here
to deliver smart time-releasing actives or other types of actives and
ingredients in a
strategic manner. The targeted active delivery approach delivers benefits that
include
but should not be limited to the cost efficient use of actives, improvements
in active
performance, timely activation of actives where needed, and improvements in
the
consumer perceivable color of the active in the final product. One can
strategically
choose combinations of ingredients and targeted active delivery methods to
maximize
the performance of actives in final products such as those described here.
[000141]Litter box maintenance improvements can be attributed to proper
control of
the product's physical characteristics such as bulk density, clump strength,
attrition or
durability (granule strength), clump height (reduction in clump height has
been found
to correlate to reduced sticking of litter to the bottom of litter box),
airborne and
visual dust, lightweight, absorption (higher absorption correlates to less
sticking to
litter box ¨ bottom, sides, and corners), adsorption, ease of scooping, ease
of carrying
and handling product, and similar attributes. Strategically controlling
process and
formulation variables along with agglomerate particle size distribution allows
for the
development of various cat litter particles engineered specifically to "dial
in" attribute
improvements as needed. Pan agglomeration process variables include but are
not
limited to raw material and ingredient delivery methods, solid to process
water mass
ratio, pan speed, pan angle, scraper type and configuration, pan dimensions,
throughput, and equipment selection. Formulation variables include but are not
limited to raw material specifications, raw material or ingredient selection
(actives,
binders, clays and other solids medium, and liquids), formulation of liquid
solution
used by the agglomeration process, and levels of these ingredients. For
example,
calcium bentonite can be added to reduce sticking to the box.
[0001421Improvements in consumer convenience attributes include but are not
limited to those described here and have been linked to physical
characteristics of the
34
CA 02607750 2007-10-25
product such as bulk density or light weight. Because the absorbent particles
are
made from small granules, the pan agglomeration process creates agglomerated
particles having a porous structure that causes the bulk density of the
agglomerates to
be lower than its initial particulate form. Further, by adjusting the rotation
speed of
the pan, porosity can be adjusted. In particular, a faster pan rotation speed
reduces the
porosity by compressing the particles. Since consumers use products like cat
litter on
a volume basis, the pan agglomeration process allows the manufacturer to
deliver
bentonite based cat litters at lower package weights but with equivalent
volumes to
current commercial litters that use heavier clays that are simply mined,
dried, and
sized. The agglomerates' reduced bulk density also contributes to business
improvements previously described such as cost savings, improved logistics,
raw
material conservation, and other efficiencies. Lightweight benefits can also
be
enhanced by incorporating cores that are lightweight. A preferred bulk density
of a
lightweight litter according to the present invention is less than about 1.5
grams per
cubic centimeter and more preferably less than about 0.85 g/cc. Even more
preferably, the bulk density of a lightweight litter according to the present
invention is
between about 0.25 and 0.85 g/cc, and ideally for an animal litter 0.35 and
0.50 g/cc.
[000143]The porous structure of the particles also provides other benefits.
The voids
and pores in the particle allow access to active positioned towards the center
of the
particle. This increased availability of active significantly reduces the
amount of
active required to be effective. For example, in particles in which carbon is
incorporated in layers or heterogeneously throughout the particle, the porous
structure
of the absorbent particles makes the carbon in the center of the particle
available to
control odors. Many odors are typically in the gas phase, so odorous molecules
will
travel into the pores, where they are adsorbed onto the carbon. By mixing
carbon
throughout the particles, the odor-absorbing life of the particles is also
increased.
This is due to the fact that the agglomeration process allows the manufacturer
to
control the porosity of particle, making active towards the center of the
particle
available.
[000144]Because of the unique processing of the absorbent particles of the
present
invention, substantially every absorbent particle contains carbon. As
discussed above,
other methods merely mix GAC with clay, and compress the mixture into
particles,
CA 02607750 2007-10-25
resulting in aggregation and some particles without any carbon. Thus, more
carbon
must be added. Again, because of the way the particles are formed and the
materials
used (small clay granules and PAC), lower levels of carbon are required to
effectively
control odors. In general, the carbon is present in the amount of 5% or less
based on
the weight of the particle. In illustrative embodiments, the carbon is present
in the
amount of 1.0% or less, 0.5% or less, and 0.3% or less, based on the weight of
the
particle. This lower amount of carbon significantly lowers the cost for the
particles,
as carbon is very expensive compared to clay. The amount of carbon required to
be
effective is further reduced because the agglomeration process incorporates
the carbon
into each particle, using it more effectively. As shown in the graph 700 of
Fig. 7, the
composite absorbent particles according to a preferred embodiment have a
malodor
rating below about 15, whereas the non-agglomerated control has a rating of
about 40,
as determined by a Malodor Sensory Method.
Description of Malodor Sensory Method:
I. Cat boxes are filled with 2,500 cc of test litter.
2. Boxes are dosed each morning for four days with 30g of pooled feces.
3. On the fourth day the center of each box is dosed with 20 ml pooled urine.
4. The boxes into sensory evaluation booths.
5. The boxes are allowed to equilibrate in the closed booths for 30 --45
minutes before panelist evaluation.
6. The samples are then rated on a 60 point line scale by trained panelists.
[000145]Preferably, the agglomerated particles exhibit noticeably less odor
after four
days from contamination with animal waste as compared to a generally solid
particle
of the absorbent material alone under substantially similar conditions.
[000146]The composite absorbent particles of the present invention exhibit
surprising
additional features heretofore unknown. The agglomerated composite particles
allow
specific engineering of the particle size distribution and density, and
thereby the
clump aspect ratio. Thus, hydraulic conductivity (K) values of < 0.25 cm/s as
measured by the following method can be predicted using the technology
disclosed
36
CA 02607750 2007-10-25
herein, resulting in a litter that prevents seepage of urine to the bottom of
the box
when sufficient litter is present in the box.
[000147]Method for measuring Hydraulic Conductivity
Materials:
1. Water-tight gas drying tube with 7.5 centimeter diameter
2. Manometer
3. Stop watch
4. 250m1 graduated cylinder
Procedure:
1. Mix and weigh sample
2. Pour the sample into the Drying tube until the total height of the
sample is 14.6 centimeters.
3. Close the cell.
4. Use vacuum to pull air through and dry the sample for at least 3
minutes.
5. When the sample is dry, saturate the sample slowly with water by
opening the inlet valve.
6. Allow the water exiting the drying tube to fill the graduated cylinder.
7. Deair the system using vacuum, allowing the system to stabilize for 10
minutes.
8. After 10 minutes, record the differential pressure as displayed by the
manometer.
9. Record at least 4 differential pressure measurements, waiting 3 minutes
between each measurement.
10. Record the flow rate of the water entering the graduated cylinder.
11. Calculate the Hydraulic Conductivity, K, using Darcy's Law
Q= -KA (ha-hb)/L
Q= Flow Rate
K= Hydraulic Conductivity
37
CA 02607750 2007-10-25
A= Cross Sectional Area
L= Bed Length
Ha-Hb= Differential Pressure
[000148]One of the distinguishing characteristics of the optimum K value is a
litter
clump with a very low height to length ratio (flat). By controlling the
particle size of
the litter, clump strength and clump profile can be controlled. This is
important
because the smaller the clumps are, the less likely they are to stick to
something like
the animal or litterbox. For instance, with prior art compacted litter, if a
cat urinates 1
inch from the side of the box, the urine will penetrate to the side of box and
the clay
will stick to the box. However, the present invention allows the litter
particles to be
engineered so urine only penetrates about I/2 inch into a mass of the
particles.
[000149]Agglomerated composite particles according to the present invention
also
exhibit interesting clumping action not previously seen in the literature.
Particularly,
the particles exhibit extraordinary clump strength with less sticking to the
box,
especially in composite particles containing bentonite and PAC. PAC is
believed to
act as a release agent to reduce sticking to the box. However, intuitively
this should
also lead to reduced clump strength, not increased clump strength. The
combination
of stronger clumps yet exhibiting less sticking to the box is both surprising
and
counter-intuitive. The result is a litter with multiple consumer benefits
including
strong clumps, low urine seepage, and little sticking to the box.
[000150]While not wishing to be bound by any particular theory, the increased
clump
strength is believed to be due to at least some of the PAC-containing granules
"falling
apart" and releasing their bentonite particles to reorder themselves, and this
'reordering' produces a stronger clump. As shown in Figs. 8 and 9, this can
best be
described as a disintegration of more-water-soluble pieces of the agglomerated
composite particles 800 when in contact with moisture 802, allowing the pieces
804
of the particles to attach to surrounding particles. This "reordering"
produces a
stronger clump. In testing, the visual appearance of the cores is a signal
that at least
some of the granules decompose to snialler particles, and these particles are
"suspending" in the urine and are free to occupy interstitial spaces between
particles,
forming a stronger clump. This creates a network of softened agglomerated
particles
38
CA 02607750 2007-10-25
where broken particle pieces are attaching to others and creating a web of
clumped
material. Note however that the particles described herein should not be
limited to
clumping or scoopable particles.
[00015 l]As mentioned above, the composite absorbent particles have particular
application for use as an animal litter. The litter would then be added to a
receptacle
(e.g., litterbox) with a closed bottom, a plurality of interconnected
generally upright
side walls forming an open top and defining an inside surface. However, the
particles
should not be limited to pet litters, but rather could be applied to a number
of other
applications such as:
= Litter Additives ¨ Formulated product can be pre-blended with standard
clumping or non-clumping clays to create a less expensive product with some
of the benefits described herein. A post-additive product could also be
sprinkled over or as an amendment to the litter box.
= Filters ¨ Air or water filters could be improved by either optimizing the
position of actives into areas of likely contact, such as the outer perimeter
of a
filter particle. Composite particles with each subcomponent adding a benefit
could also be used to create multi-functional composites that work to
eliminate
a wider range of contaminants.
= Bioremediation / Hazardous / Spill Cleanup ¨ Absorbents with actives
specifically chosen to attack a particular waste material could be engineered
using the technology described herein. Exemplary waste materials include
toxic waste, organic waste, hazardous waste, and non-toxic waste.
= Pharma / Ag ¨ Medications, skin patches, fertilizers, herbicides,
insecticides,
all typically use carriers blended with actives. Utilization of the technology
described herein reduce the amount of active used (and the cost) while
increasing efficacy.
= Soaps, Detergents, and other Dry Products ¨ Most dry household products
could be engineered to be lighter, stronger, longer lasting, or cheaper using
the
technology as discussed above.
= Mixtures of Different Particles ¨ The composite particles can be dry
mixed
with other types of particles, including but not limited to other types of
composite particles, extruded particles, particles formed by crushing a source
39
CA 02607750 2012-11-14
material, etc. Mixing composite particles with other types of particles
provides the benefits provided by the composite particles while allowing use
of lower cost materials, such as crushed or extruded bentonite. Illustrative
ratios of composite particles to other particles can be 75/25, 50/50, 25/75,
or
any other ratio desired. For example, in an animal litter created by mixing
composite particles with extruded bentonite, a ratio of 50/50 will provide
enhanced odor control, clumping and reduced sticking, while reducing the
weight of the litter and lowering the overall cost of manufacturing the
litter.
= Mixtures of Composite Particles with Actives¨ The composite particles can
be
dry mixed with actives, including but not limited to particles of activated
carbon.
[000152]It has been observed that one drawback to using the pan agglomeration
processes of Figs. 2 and 4 with clay feed materials is that they tend to be
very dusty at
the initial stages, which creates less than optimal operating conditions. This
pre-
wetting step is necessitated by limiting physical constraints. For example,
the water
uptake rate of the fine powder feed particle and growing agglomerate surfaces
is
generally insufficient without a pre-wetting step. The result is extreme
dusting at the
pan because the solid to available water ratios are exceeded in the uptake and
growth
zones in the pan. The materials have generally been pre-wetted to form a
compact
particle seed by adding enough moisture to the initial powder to roughly have
15 ¨
25% water with a target of 20% by weight in a pre-formed particle. The pre-
wetting
is usually accomplished by mixing in a compaction shear device, such as pin
mixers
or pug mills. The pre-wetted particle is fed into the pan where additional
liquid is
added to bring the final moisture up to the 30-40% wt range and the particles
to the
various sizes determined by pan residence time and final moisture. Final
moisture
values for clay particles tend to be between 30-35%, whereas final moisture
values for
agglomerated blends of clay and a light-weighting agent tend to be between 35-
40%.
Techniques for combining a pin-mixing step with a pan agglomeration process
are
described in US Patent Publication No. US2006/0243212 filed April 29, 2005,
published November 2, 2006,
CA 02607750 2007-10-25
[000153]Pre-wetting has been found to increase the density of the thus-formed
agglomerates making sufficient BDR hard to accomplish. However, it has been
demonstrated that using these common feed systems without the pre-wetting step
. _
leads to a very dusty environment which results in decreased yield and
inconsistent
product from the pan.
[000154]The pan agglomeration designs of the present invention eliminate the
need
for a pre-wetting step, thus eliminating the need to use additional equipment
such as a
pin-mixer, which can result in huge cost-saving in the manufacturing process.
Porosity and available surface area can be variables that are manipulated by
the
described process. Functional attributes such as density, permeability,
binding
strength and dissolution rate are then made controllably available for
applications to
consumer functional products, e.g. animal litter.
Single Step Pan Agglomeration
[000155]Figure 10 shows a pan agglomerator feed system that uses a single step
pan,
(i.e., the pan is all one depth and not tiered). The pan is a 39 inch and has
been run at
pan angles from 50-60 degrees and pan speeds around 21-22 rpm. Aside from
controlling the pan settings as detailed above, alterations and additions, as
detailed
below, to the pan configuration have resulted in improved results and have
eliminated
the need for a pre-wetting step.
[000156]Pan agglomeration feed systems are dependent upon the material
characteristics and the desired particle formed in the pan. When referring to
the pan
1606, as shown in Figs. ha and 11b, the top of the pan 1606a refers to highest
vertical position of the pan as the pan rotates; the bottom of the pan 1606b
refers to
the lowest vertical position of the pan as the pan rotates; the back of the
pan 1606c
refers to the depth location at the bed of the pan; the surface of the pan
1606d refers to
depth location furthest away from the bed of the pan. Assuming the pan is
rotating in
a clockwise direction, typically a powder-sized (about 325 through 50 Tyler
Series
mesh) feed particle is fed in the 12 o'clock to 3 o'clock position 1608 of the
pan.
Feed particle size may be smaller for clay (e.g., between 200-325 mesh for
sodium
bentonite clay) and larger for light-weighting agents (e.g., between 10-200
mesh for
expanded perlite). A liquid spray, typically water or a water solution that
may contain
other chemicals, is fed approximately in the 3 o'clock to 6 o'clock 610 or the
9
41
CA 02607750 2007-10-25
o'clock to 12 o'clock 612 quadrants of the pan for dust control and particle
growth.
The actual back of the pan is metal and is typically coated with a thin layer
of material
which will be referred to herein as the pan bed or bed of the pan. To avoid
confusion
the bulk of material circulating at any given time, which sits atop the pan
bed will be
referred to herein as the bed of material or material bed.
[000157]The agglomerate particles are formed by allowing the feed particles to
enter
the "growth zone" 1614 of the pan which is defined as the eye. The hoof of the
pan
contains the portion of material located in 1616. The eye of the pan is the
dynamic
embodiment of the mass in the hoof. The smaller particles start at the back of
the eye
bed and grow larger as they pick up the distributed water. As they grow
larger, the
interstitial space between the growing particles becomes greater thus the
smaller
particles fall back down into the lower part of the eye. This is commonly
known in
the art as sifting segregation.
[000158]In normal pan operations the small particles are fed on the surface
1606d of
the material bed and some have to sift down to the back of the pan 1606c first
in order
to then be grown into agglomerates. This action densifies the particle. In
addition, in
normal operations, the bed depth contributes to the compaction and
densification due
to the downward force of gravity and the weight of material on the lower layer
particles.
[000159]The present invention overcomes the problems of excessive dust
formation
and particle densification. The inventors have found that creating a curtain-
like
device 1618 that flows over the newly added dry feed substantially reduces
dust
formation and eliminates particle densification. Device 1618 is referred to as
an
"angel feed" and is more clearly illustrated in Fig. 12. A material curtain
("an over
curtain") depicted by arrows 1730 and 1732 is formed which allows the dry
powder
1731 to be contained just prior to addition into the rotating nucleated
particles and
thus reduces the free dust by 50¨ 99% when measured by mass. Arrows 1730
represent material that falls from scraper 1618a and arrows 1732 represent
material
that falls from scrapers 1624 along the surface 1738 of the feeder. A diverter
1734
may be used to help control the direction of material flow. 'Feeder lip 1740
further
assists with helping to control the direction of material flow. Feeder 1628
feeds feed
particles under the material curtain through feed material exit 1736. Thus,
the
42
CA 02607750 2013-10-28
agglomeration process is no longer limited to the addition of relatively small
amounts
of powder to pre-wetted seed particles.
[000160]Additionally, a substantially unidirectional flow of material from the
back of
the pan upward to the surface is enabled, i.e., some of the small feed
particles start at
the back of the pan and grow into agglomerates as they rise to the surface,
thereby
eliminating the step of sifting segregation.
[000161]For animal litter applications the desired feed material is an
absorbent clay,
however, other compounds such as antimicrobial agents, odor absorbing
compounds,
light-weighting agents, fragrances, fixing agents, binding agents, litter
filler materials,
supplemental absorbent materials, supplemental deodorants, dust controlling
agents,
release agents, health indicating agents, and mixtures and combinations
thereof can be
added to the primary components of the litter material. These additional
compounds
can added at any time. For example, they may be added to the primary feed
material
or agglomerates thereof, further agglomerated with the initial agglomerates as
a
secondary coating, sprayed on during a spray-coating step, or dry blended with
the
agglomerated particles.
[000162]Fig. 10 illustrates an improved pan agglomeration process suitable for
making animal litter. This process creates a 5-50% BDR compared to the raw
material feed. The BDR can be significantly increased (to about 75%) with the
addition of a light-weighting agent such as expanded perlite or cellulose
fibers. The
general steps for making pan agglomerated animal litter 1016 using the process
of
Fig. 10 are as follows (operating conditions and dimensions are those of a
pilot plant
39 inch pan agglomerator). (1) Raw materials held in a feeder(s) 1002 (more
than one
feeder could be used, e.g, it may be desirable to meter-in activated carbon)
are dry
blended, (e.g., in a screw auger 1004) and fed into a rotating pan 1006 via an
"Angel"
or "Over/Under" feed (not shown). (2) Moisture 1010 is delivered to the pan
through
eight 4001 spray nozzles (not shown). As those skilled in the art can
appreciate,
sprayer size and number would increase as the process is scaled-up. The pan
utilizes
both gravitational and centripetal forces to slowly build particles using a
rolling
action. The particle size of the exiting granules is dependent on the
orientation of the
spray nozzles, the size of the water droplets, the rotational speed of the pan
and the
angle of the pan. The pan is a self-classifying system with particles exiting
once they
43
CA 02607750 2013-10-28
grow to a certain size. (3) Material exits pan 1006 and is conveyed to a dryer
1012.
Both rotary and vibratory fluid bed (VFB) dryers have been used effectively by
the
inventors. Those skilled in the art will appreciate that other drying means
could also
be used. The material exits the dryer having a moisture level between 0-10%.
(4)
The dried agglomerate feed is then screened. For example, the material can be
split
and fed into 2 Sweco screeners 1008a and '1008b screening ¨6/+40 mesh,
although
more or less screeners with differing mesh sizes could also be used. (5) The
agglomerated particles are then dedusted. For example, the particles can be
conveyed
through a dedusting device 1014 for air classification (i.e., dedusting) and
collected in
drums for testing in real time.
[000163]Particles have been formed using a bentonite clay, carbon and water
formula
matrix. Expanded perlite and Expanded Volcanic ash have also been introduced
into
various formulas. Cellulosic fibers could also be incorporated. Typical
formulations
are as shown in Table 4:
Table 4
Component Formula Range
Carbon 0 ¨ 1 %
Expanded Volcanic Ash 0-20 %
Expanded Perlite 0-20 `)/0
Clay Balance
Recycle Stream 0-20 %
Angel (Over/Under) Feed Agglomerator
[0001641The pan parameters of the system outlined above will affect the rate
at which
water is transferred from the sprayers to the clay particles, i.e., "water
uptake rate".
Such parameters include: Pan Angle (p), Pan Speed (n), Nozzle Placement, Water
Droplet Size, Water Droplet Velocity, Raw Material Variability,
Segregation/Insufficient Mixing of Inbound Dry Material, Feed System and
Location,
Scraper/Curtain Placement, Throughput, Dryer Inlet Chute, Bed Vibration,
Supply
(Heating) Zone Air, Center Weir, and Cooling Zone Air.
[0001651The desired solid PSD (particle size distribution) is dependent on the
water
uptake rate chosen. The water uptake rate is dictated by the distribution and
flow
characteristics of the liquid as well as the porosity and bulk density
characteristics of
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CA 02607750 2007-10-25
the inbound material. The liquid droplet size of the binding water in
conjunction with
the liquid distribution over the solid feed creates clay to clay bonds having
sufficient
strength to withstand the high temperatures needed for incorporating a high
evaporation rate into the process. Strong clay to clay particle bonds are
formed which
leads to an increase in overall particle strength of the agglomerated
particles as a
whole. Thus, the inventive process couples the rate at which water is
incorporated
into growing rotating particles in a tumbling agglomerator, e.g., a pan
agglomerator,
with the rate at which the water is driven off of the particles through
evaporation to
build substantial particle strength.
[000166]The pan angle, pan speed and pan dimensions (diameter and depth) are
all
interdependent parameters. The operating parameters and conditions detailed
below
are for a 39 inch diameter pilot plant scale pan agglomerator having a depth
of 8
inches.
Pan Angle (13)
[000167]The pan or tilt angle is measured from the horizontal line at the base
of the
pan to the line created by the pan bed. Various tilt angles were tested. r3
equal to
about 55 was found to be appropriate. It was observed that a relatively high
pan or
tilt angle allows less material to fit inside the pan thereby decreasing the
throughput
capabilities of the pan. Relatively high tilt angles shorten the residence
time of the
material providing less time to grow agglomerates which either result in the
formation
of smaller particles or in the ejection of unagglomerated material from the
pan
prematurely. Furthermore, relatively high tilt angles affect material flow
patterns
tending to disrupt the shape of the falling curtain of material and causing
the pan bed
to be exposed. The pan bed refers to a relatively thin layer of material that
covers the
actual metal pan bed. An exposed pan bed could lead to water directly hitting
it
which creates clay buildup. As buildup occurs, chunks of material break off of
the
pan and fall into the growing agglomerates. The chunks continue to grow and
compete with the agglomerates for water, hindering the water uptake rate of
the
agglomerates.
Pan Speed (n)
[000168]Pan speed is measured in rpm. Pan speed may be scaleable among pans of
different diameters on an equal ft/min basis. According to literature, desired
pan
CA 02607750 2007-10-25
speed settings for ideal material flow distribution are % of critical speed or
nc where
nc=42.3(sin(3/D))0.5 and D=pan diameter in meters. According to the literature
a
calculation of 28 rpm would be appropriate, however, that speed was too fast
for the
pilot plant set up used. A pan speed of 21 rpm or 214 ft/min. was tested and
found to
be effective when used with a 39 inch pan and a tilt angle of 55 . A pan speed
that is
too high, compacts the agglomerates forming round, smooth surface, hard balls.
Compaction aids in improving particle attrition, but it also increases the
bulk density
of the individual particles, thereby negatively affecting BDR (bulk density
reduction).
High pan speeds cause the material to be lifted and carried along the edge of
the pan
due to centripetal forces. Low pan speeds prevent the material from tumbling
along
the bed of the pan. This lack of rolling action prevents even water
distribution among
agglomerates and prevents the particle-to-particle interaction required to
build strong,
round agglomerates. Effects of both high and low pan speeds prevent the pan
from
having a falling curtain of material, causing the pan bed to be exposed, which
for the
reasons previously discussed, is undesirable.
Nozzle Placement
[000169]A uniform distribution of liquid droplets is key to particle growth.
The
distribution of liquid droplets is effected by nozzle placement. To cover an
even
amount of material, nozzles are placed in the direction of flow of material.
Fig. 11
shows one configuration of nozzle placement and water flow distribution. In
this
embodiment, eight 4001 flat spray nozzles were used. Nozzles 1620 in the upper
portion of the pan were used to grow agglomerates. Nozzles 1622 in the lower
portion of the pan were used to control dust and send dryer material under the
eye
(which is located in quadrant 1614 and the lower portion of quadrant 1612) of
the pan.
The spray coverage of nozzles 1620 are shown as ovals 1621 and the spray
coverage
of nozzles 1622 are shown as ovals 1623. Shifting the growth nozzles towards
the
eye results in larger agglomerates, whereas shifting the nozzles away from the
eye
results in smaller agglomerates.
Nozzles that spray directly on any surface of the pan bed will contribute to
buildup.
Over spraying due to incorrect nozzle placement will also result in excessive
build up
on the pan bed and/or on the scraper(s) which results in scraper shavings or
chunks.
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CA 02607750 2013-10-28
Aside from poor agglomerate formation, build up creates pressure on the
scrapers and
can strain the motor of the pan.
Water Droplet Size and Velocity
[000170]Droplet size is based on nozzle type, number of nozzles, moisture
delivery,
and pump pressure. Eight 4001 flat spray hydro nozzles from Spraying Systems
Co.
were tested. Less water is required to form agglomerates with small water
droplets
delivered from air-atomized nozzles. More water is required to form
agglomerates
from hydro nozzles. This is due to the nature of the water distribution.
Smaller
droplets create an even distribution of wetting. Larger droplets are unable to
wet the
bed of material as efficiently as smaller droplets when water delivery is held
constant.
Small droplets form small narrow bridges 1804 among the raw material particles
1802
during agglomerate growth as shown in Fig. 13a. Large droplets form large,
wider
bridges 1804 as shown in Fig. 13b. When the particles form water droplet
bridges,
the dry material begins to dissolve into the water, creating a bridge of
material that
remains in place once the water has evaporated. Stronger particle-to-particle
bonds
are formed from the larger bridge. This is due to the presence of more
material
between the particles. However, if the water droplets are too big, the water
across the
bridge will start to encompass the particles and hinder quenching, which will
be
discussed in more detail later.
[000171 'The velocity of the water droplet leaving the nozzle head is
dependant upon
nozzle type, moisture delivery, and pump pressure. Water droplets with high
velocities can cut through thin areas of the falling film of material and
reach the bed
of the pan where they can cause buildup, chunking, and imbalance to the water
uptake
rate.
Raw Material Variability
Inbound raw materials can have varying attributes. Moisture, density, and
particle
size variability are all aspects that can affect the finished product
characteristics. For
example, sodium bentonite clay varies in the moisture that it holds
internally.
Variation in moisture causes variations in the water uptake rate of the
material, and
the moisture addition must be changed in response to these variations.
Significant
47
CA 02607750 2013-10-28
variations in raw material density or particle size can affect both the
attrition and final
bulk density of the dried agglomerates.
[000172]It has been found that varied moistures of inbound raw materials can
compact differently in the screw auger, resulting in an inconsistent delivery
of raw
materials to the pan. Additionally, the flow characteristics of the inbound
material
will likely be affected.
Segregation or Insufficient Mixing of Inbound Dry Material
[0001731Dry material, especially mixtures of dry materials with substantially
different characteristics (e.g., bulk density, particle size distribution,
moisture) can
segregate in conveyance or have trouble mixing. Particle segregation or
insufficient
mixing delivers an inbound feed of constantly changing material to the pan.
Certain
materials uptake water faster than other materials causing constant change to
the pan
moisture addition (e.g., expanded perlite absorbs water differently than
clay).
Over/Under (Angel) Feed System
[000l74]Referring again to Fig. 11, the over/under feed system serves a dual
purpose
of center scraper 1618a as well as dry material feeder 1618. The dry material
feeds in
through a tube 1628 and then fans out into the angel feed device 1618. The
material
is delivered near the bottom right quadrant 1610 of the pan, right of the eye.
Referring to Fig. 12, the over portion cascades down the face 1738 of the pan
creating
an over curtain over the "under" dry material.
[000175]The unders (i.e., material not agglomerated to a sufficient size to be
ejected
from the pan) are delivered directly onto the pan bed. As discussed, a dry
layer of
material (i.e., pan bed) is created on the direct surface of the pan,
preventing wet
material from sticking to the actual metal surface of the pan. The over
curtain
contains the under feed of dry material, preventing the feed from exiting the
pan as
dust. The over curtain also ensures that the dry particles will not exit the
pan before
they have a chance to turn into agglomerates, allowing for the PSD (particle
size
distribution) to stay within a tight range. The angel feed system improves the
overall
yield by reducing dust, buildup, and unders.
Scraper Placement
[000176]Scrapers scrape wet material off the pan bed and walls. The scrapers
are
placed slightly off the edge of the pan surfaces and cover the entire surface
of the pan.
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CA 02607750 2013-10-28
Scraper placement directs material flow. Referring to Fig. 11, three scrapers
1618a
and 1624 are positioned where they will redirect flow to the curtain. The
scraper
orientation can be used to direct the flow of material in the pan. In the case
of the
embodiment depicted in Fig. 11, scrapers 1624 direct the circulating material
onto the
angel feed system, creating the "over" curtain that prevents the dry inbound
"under"
material from exiting the pan. If the scrapers do not properly cover the
entire surface
of the pan, rings of buildup will form in the pan bed. As the material
continues to
build on the surface of the pan, the material closest to the pan begins to dry
out.
When the material dries out, it loses suction with the pan wall and falls off
in chunks
into the circulating bed of material. These chunks compete with the
agglomerates for
moisture, affecting the water uptake rate.
Throughput
[000177]Throughput is defined as the amount of material that enters the pan on
a dry
lb/hr basis. Low throughputs (i.e., about 0-500 lb/hr for the 39 inch pan)
increase the
residence time of material because less inbound material is present to push
the
agglomerates out. Increased residence time can lead to building large smooth
agglomerates that are significantly compacted. However, low throughputs can
attribute to a starved pan. High throughputs (i.e., about 1250-2000 lb/hr for
the 39
inch pan) decrease the residence time of the agglomerates, sometimes pushing
out the
raw material before it is fully agglomerated. Additionally, high throughputs
can
attribute to a flooded pan. For example, an 800 lb/hr throughput has been
tested and
found to be effective for a 39 inch pan.
Back Axial Feed Tiered (Stepped) Pan Agglomerator
{000178)Referring to Fig. 14, a stepped or tiered pan agglomerator is another
embodiment of a pan agglomeration system that uses the rate at which water is
incorporated into growing rotating particles through the use of a tumbling
agglomeration method coupled with the rate at which the water is driven off of
the
particles through evaporation to build substantial particle strength.
[000179]In this embodiment, the bed depth is minimized by using a stepped pan
946 ,and this in combination with the unique back axial feed 924, insures that
the
particles grow from the upward direction and the compaction due to the
downward
sifting segregation as the small particles fall through the growth zone is
removed.
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CA 02607750 2013-10-28
Figure 14 shows a 39 inch 3 step pan. Step 1 909 is 27 inches in diameter and
about
3 inches deep. Step 2 911 is about 3 inches wide and recessed an additional 3
inches
in depth. Step 3 913 is about 3 inches wide and recessed an additional 11/2
inches.
However, those skilled in the art will appreciate that the diameter, depth and
number
of steps could be varied and customized. Nozzles 920 grow agglomerates,
whereas
nozzles 922 wet the dry material and knock down dust. Arrows 925 show the
direction of spray from nozzles 920 and 922,. Nozzles could be placed over
either
Step 2 or Step 3 if one or more coatings are desired.
[000180]In another embodiment a ramp as opposed to steps could also be used to
vary the depth of the pan from the center outward.
[000181]Aggomerated particles can be formed on the back fed axial step pan
agglomerator using a bentonite clay, carbon and water formula matrix. Expanded
perlite and Expanded volcanic ash can also been introduced into various
formulas.
Typical formulations are as shown in Table 5:
Table 5
Component Formula Range
Carbon 0 ¨ 1 %
Expanded Volcanic Ash 0-20 %
Expanded Perlite 0 ¨ 20 A
Clay Balance
Recycle Stream 0-20 %
[000182]The general steps for making pan agglomerated cat litter are similar
to those
outlined above. The raw materials are dry blended in a screw auger and fed
into the
rotating pan. Referring to Fig. 14, in this embodiment, the feed particles
enter
through a back axial feed 924 in the center of the pan 906 under the curtain
of
rotating particles formed in the eye of the pan, i.e., the growth zone.
Moisture is
delivered to the pan through eight 4001 spray nozzles 920 and 922. The pan
utilizes both gravitational and centripetal forces to slowly build particles
using a
rolling action. The steps (or tiers) in the pan allow the continued growth of
the
particle without having to subject the particle to the full depth of the
growth zone (the
pan eye). This prevents the weight of the larger particles from compacting and
_ _
CA 02607750 2007-10-25
=
densifying the smaller particles. The back axial feed allows the feed
particles which
are generally a fine powder to flow along the surface of the pan thereby
taking
advantage of the full length of the shortened growth zone depth.
[000183]The particle size of the exiting granules is dependent on the
orientation of
the spray nozzles, the size of the water droplets, the rotational speed of the
pan and
the angle of the pan. Like the single step pan, the back axial feed pan is a
self-
classifying (or self-sieving) system with particles exiting once they grow to
a certain
size. Material exits the pan as discussed with reference to the single step
pan
agglomerator and is conveyed to a dryer.
[000184]Both a vibratory fluid bed (VFB) and a rotary driers have been used.
VFB
driers tend to result in less dense and less polished (less rounded) finished
particles,
whereas rotary driers tend to result in more dense and more polished fmished
particles. Less dense and more rounded particles are desired.
[000185]Typically, agglomerated clay-based particles are brought back down to
a
moisture level between 5-15% because it was thought that overdrying would lead
to
an increase in attrition (the tendency of particles to fall apart). Typical
drying
temperatures used are in the 525 F range. The inventors have surprisingly
found that
by rapidly drying the agglomerated particles at elevated temperatures as
opposed to
using routine parameters, improved particle strength is achieved (e.g,
bringing
moisture levels down to about 0-2% actually resulted in hard particles with
improved
attrition). Rapid drying has been accomplished by feeding agglomerates into
temperatures around 650-700 F to achieve 0-2% moisture levels. However, the
long
term attrition and low moisture of these particles increase in humid
environments.
[000186]To avoid rehydration of the particles, drying conditions that allow
rapid
drying of the particle bridges as shown in 1804 as opposed to the entire
particles 1802
themselves may be necessary. The bridges would form into hard bonds, while the
particles themselves would retain about 6-10% moisture. Rapid drying of the
particle
bridges can be accomplished by feeding agglomerates into temperatures around
1100 F with short residence times to achieve 6-10% particle moisture levels.
Because
moisture is bound within the particle, the moisture would tend to expand
outward
from the center of the particle towards the particle surface during the rapid
drying
process which would keep the particle surfaces relatively cool and avoid
overdrying.
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CA 02607750 2007-10-25
[000187]While various embodiments have been described above, it should be
understood that they have been presented by way of example only, and not
limitation.
Thus, the breadth and scope of a preferred embodiment should not be limited by
any
of the above-described exemplary embodiments, but should be defined only in
accordance with the following claims and their equivalents.
52
