Molecular sieve abstract
A process for the production of a molecular sieve adsorbent blend
with improved performance characteristics produced by preparing
a zeolite material, which may include zeolite 13X, zeolite LSX or
mixtures thereof, preparing a binder which includes highly dispersed
attapulgite fibers alone or blended with a non-highly dispersed
attapulgite clay, mixing the zeolite material with the binder to
form a mixture, forming molecular sieve adsorbent blends into a
shaped material and treating the shaped material, wherein the tapped
bulk density of the highly dispersed attapulgite fibers measured
according to DIN/ISO 787 is more than about 550 g/ml.
Molecular sieve claims
1. A process for the production of a molecular sieve adsorbent
blend with improved performance characteristics comprising preparing
a zeolite material comprising zeolite 13X and zeolite LSX; preparing
a binder comprising highly dispersed attapulgite fibers, wherein
the tapped bulk density of the highly dispersed attapulgite fibers,
as measured according to DIN/ISO 787 is more than about 550 g/l;
mixing the zeolite material with the binder in solution to produce
a mixture; treating the zeolite material binder mixture to form
the molecular sieve adsorbent blend.
2. A process for the production of a molecular sieve adsorbent
blend with improved performance characteristics comprising preparing
a zeolite material comprising zeolite 13X and zeolite LSX; preparing
a binder comprising a blend of highly dispersed attapulgite fibers
and non-highly dispersed attapulgite fibers, wherein the tapped
bulk density of the highly dispersed attapulgite fibers, as measured
according to DIN/ISO 787 is more than about 550 g/l; mixing the
zeolite material with the binder blend in solution to produce a
mixture; treating the zeolite material binder blend mixture to form
the molecular sieve adsorbent blend product.
3. The process of claim 1 wherein the binder comprises from about
5 to about 30 percent, by weight, of the molecular sieve adsorbent
blend.
4. The process of claim 2 wherein the binder comprises from about
5 to about 30 percent by weight of the molecular sieve adsorbent
blend.
5. The process of claim 1 further comprising blending a pore forming
agent with the zeolite material binder product.
6. The process of claim 2 further comprising blending a pore forming
agent with the zeolite material binder blend product.
7. The process of claim 5 wherein the pore forming agent comprises
from about 2 to about 15 percent, by weight, of the molecular sieve
adsorbent blend.
8. The process of claim 6 wherein the pore forming agent comprises
from about 2 to about 15 percent, by weight, of the molecular sieve
adsorbent blend.
9. The process of claim 2 wherein the attapulgite binder comprises
at least about 20 percent highly dispersed attapulgite fibers.
10. A molecular sieve adsorbent blend product comprising a zeolite
material blended with a binder, wherein the binder comprises highly
dispersed attapulgite fibers having a tapped bulk density more than
about 550 g/l and wherein the zeolite material comprises a mixture
of zeolite 13X and zeolite LSX.
11. The product of claim 10 wherein a non-highly dispersed attapulgite
binder is blended with the highly dispersed attapulgite fibers to
form a binder mixture prior to blending the binder mixture with
the zeolite material mixture.
12. The product of claim 10 wherein the highly dispersed attapulgite
fibers comprise from about 2 to about 30 percent by weight of the
molecular sieve adsorbent blend.
13. The product of claim 11 wherein the blend of the highly dispersed
attapulgite fibers and the non-highly dispersed attapulgite binder
comprises from about 2 to about 30 percent by weight of the molecular
sieve adsorbent blend.
14. The product of claim 10 further comprising a pore forming agent.
15. The product of claim 11 further comprising a pore forming agent.
16. The product of claim 10 wherein the ratio of the zeolite 13X
to the zeolite LSX is from about 75:25 to about 60:40.
17. The product of claim 10 wherein cations of the zeolite material
comprise at least about 50 to about 95 percent calcium.
18. The product of claim 16 wherein a portion of the cations of
the zeolite material are selected from the group consisting of Group
III B cations and lanthanide series cations.
19. A process for separation of components of a gaseous or a liquid
feed stream comprising passing the components of the gaseous or
liquid feed stream over the molecular sieve adsorbent blend of claim
10.
20. A process for drying a gaseous feed stream comprising passing
the feed stream over the molecular sieve adsorbent blend product
of claim 10.
21. A process for adsorption of carbon dioxide from an air stream
comprising passing the air stream over the molecular sieve adsorbent
blend product of claim 10.
22. A process for removal of water from a gaseous or liquid ethanol
stream comprising passing the gaseous or liquid ethanol stream over
the molecular sieve adsorbent blend of claim 10.
23. A process for separation of nitrogen and oxygen from an air
stream comprising passing the air stream over the molecular sieve
adsorbent blend of claim 10.
24. A process for removal of sulfur and oxygen containing compounds
from a hydrocarbon stream comprising passing the hydrocarbon stream
over the molecular sieve adsorbent blend of claim 10.
25. A process for removal of carbon monoxide, carbon dioxide and
nitrogen from a hydrogen gas stream comprising passing the hydrogen
gas stream over the molecular sieve adsorbent blend of claim 10.
26. A process for removal of water from a gaseous or liquid hydrocarbon
stream comprising passing the gaseous or liquid hydrocarbon stream
over the molecular sieve adsorbent blend of claim 10.
27. A process to separate n-paraffins from a mixture of iso-paraffins
and n-paraffins comprising passing the mixture over the molecular
sieve adsorbent blend of claim 10.
28. A process for removal of water from a gaseous or liquid stream
of refrigerants comprising passing the gaseous or liquid stream
over the molecular sieve adsorbent blend of claim 10.
29. A process for removal of water and carbon dioxide from air
comprising passing the air over the molecular sieve adsorbent blend
of claim 10.
Molecular sieve description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. No. 10/054041 filed on Jan. 22 2002 now U.S. Pat. No. 6743745
and application Ser. No. 10/765018 filed on Jan. 26 2004.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] This invention relates to molecular sieve adsorbents and
more particularly to molecular sieve adsorbent blends comprising
a mixture of different zeolitic materials blended with a binder
containing at least partially highly dispersed attapulgite fibers.
This invention also relates to a process for the preparation of
molecular sieve adsorbent blends comprising mixing two or more different
zeolite materials with a binder containing at least partially highly
dispersed attapulgite fibers.
[0004] 2. Background Art
[0005] Zeolites are hydrated metal alumina silicates having the
general formula
M.sub.2/nO:Al.sub.2O.sub.3:xSiO.sub.2:yH.sub.2O
[0006] where M usually represents a metal of the alkali or alkaline
earth group, n is the valence of the metal M, x varies from 2 to
infinity, depending on the zeolite structure type, and y designates
the hydrated status of the zeolite. Most zeolites are three-dimensional
crystals with a crystal size in the range of 0.1 to 30 .mu.m. Heating
these zeolites to high temperatures results in the loss of the water
of hydration, leaving a crystalline structure with channels of molecular
dimensions, offering a high surface area for the adsorption of inorganic
or organic molecules. The adsorption capability of these molecules
is limited by the size of the zeolite channels. The rate of adsorption
is limited by the laws of diffusion.
[0007] A number of different zeolite particles of the faujasite-type
have been prepared which resemble the natural mineral faujasite.
Such zeolites are characterized by a relatively open zeolite framework
with comparatively large micropores and high intracrystalline void
volumes. Faujasites can be generally divided into zeolite X and
zeolite Y. Synthetic zeolite X and Y differ by virtue of their silicon
content with zeolite Y having a higher silicon:aluminum ratio. Type
X zeolites can be further subdivided into low silicon type X zeolites
(LSX), which are usually defined as being type X zeolites having
a Si/Al atomic ratio of 1.0 to about 1.15. (SiO.sub.2/Al.sub.2O.sub.3
ratio of about 2.0 to about 2.3). Type X zeolites with an Si:Al
ratio of about 1.15 to about 1.5 usually are designated as 13 X
zeolites (SiO.sub.2/Al.sub.2O.sub.3 ratio of about 2.3 to about
3.0). Notwithstanding these designations of Si/Al content, the transition
between zeolite 13 X and zeolite LSX is not clearly defined.
[0008] The synthesis of zeolite 13 X was first described in U.S.
Pat. No. 2882244 while the synthesis of zeolite LSX was first
disclosed in GB Patent 1051621.
[0009] An early application of synthetic faujasites was for the
purification of air and other gaseous mixtures, especially prior
to cryogenic distillation. Removal of carbon dioxide and water vapor
in this process is of great importance as these two gases can condense
and freeze during the cooling process, thus clogging the tubing
and valves of the cryogenic distillation apparatus and preventing
the production of liquid nitrogen and liquid oxygen.
[0010] The use of synthetic faujasite zeolites with SiO.sub.2.backslash.Al.sub.2O.sub.3
ratio between 2.0 and 2.3 has proved especially useful for the absorption
of carbon dioxide, especially at low partial pressures. This usefulness
is disclosed in U.S. Pat. No. 5531808 which discloses a higher
adsorption capacity of carbon dioxide on an LSX type zeolite compared
to a 13 X type zeolite. Especially useful zeolites of this type
contain sodium cations, as disclosed in WO 00/01478. See also WO
99/46031.
[0011] In addition to the use of a single type of zeolitic material,
such as zeolite 13 X or zeolite LSX, it has also been discovered
that it may be useful to combine two different types of zeolitic
material to form an adsorbent. For example, U.S. Pat. No. 6616732
(WO 01/24923) discloses a zeolite blend comprised of zeolite 13
X and a zeolite LSX, wherein preferably 50 to 90% of the mixture
is comprised of zeolite 13X and 50 to 10% of the blend is comprised
of zeolite LSX. The exchangeable cationic sites on these zeolites
are occupied at least about 80% with sodium cations or at least
70% with strontium cations, with the remaining cations being chosen
from Group IA, IIA, and IIIA or trivalent ions from the rare earth
or lanthanide series of the Periodic Table. The binder for this
blend is selected from silica, alumina and clays. This adsorbent
is particular suited to the decarbonation of gas flows contaminated
with CO.sub.2.
[0012] A composite adsorbent bed comprised of a conventional zeolite
13 X adsorbent and a lithium form of a zeolite X, utilized for vacuum
pressure swing adsorption operations for air separation, is disclosed
in U.S. Pat. No. 5203887.
[0013] The removal of impurities from a gaseous stream can be accomplished
using different techniques. If the trace elements which need to
be adsorbed are carbon dioxide and water vapor, the regeneration
of the adsorption system is done through heating the system. This
procedure is designated as TSA (Thermal Swing Adsorption). In an
alternative procedure the adsorption and desorption may be achieved
through changes of applied pressure. This procedure is designated
as PSA (Pressure Swing Adsorption). The removal of impurities can
be done with a column that is filled with a single type of adsorbent.
Alternatively, the adsorbent column may be filled with layers of
different types of adsorbents to remove each impurity using a selective
procedure. Such techniques are disclosed in WO 96/14916 EP 1092465
and U.S. Pat. No. 6106593.
[0014] One limitation on the utilization of zeolite crystals for
these processes is their extremely fine particle size. Naturally-formed
agglomerates of these crystals break apart easily. Because the pressure
drop through a bed formed solely from those crystals is exceptionally
high, these zeolite crystals cannot be used alone in fixed beds
for dynamic applications, such as drying of natural gas, drying
of air, separation of impurities from a gas stream, separation of
liquid product streams and the like. To make zeolite particles useful
for those processes, the crystals are blended with other materials
to provide an agglomerate mass which exhibits a reduced pressure
drop.
[0015] Different types of clays may be used as binders for these
zeolite crystal blends, including attapulgite, palygorskite, kaolin,
sepiolite, bentonite, montmorillonite and mixtures thereof. For
example, U.S. Pat. No. 2973327 discloses the use of a number of
different types of clays, including attapulgite, as a binder for
molecular sieves. The clay content of the bonded molecular sieve
can vary from as low as 1 percent to as high as 40 percent by weight,
although the preferred range is from about 10 to about 25 percent
by weight.
[0016] An adsorbent for separating gases comprising a binder and
a crystalline, low silica faujasite-type zeolite with a silica to
alumina molar ratio of 1.9 to 2.1 is disclosed in EP 0 940 174 A2.
[0017] One problem with conventionally formed zeolite blends is
decreased diffusion. The larger the diameter of the formed zeolites,
the slower the rate of diffusion of the molecules to be adsorbed.
Particularly in the field of pressure swing adsorption, this effect
is highly adverse to short cycle time and thus to productivity.
Enhanced kinetic values or faster mass transfer rates can result
in shorter cycle time and lower power consumption and thus higher
adsorbent productivity.
[0018] It has been recognized that a reduction in the particle
size of formed zeolites leads to shorter mass transfer zones and
shorter cycle times. This is based on the assumption that the time
needed for adsorbates to travel through the macropores of the adsorbents
limits the cycle time, i.e. macropore diffusion is the rate limiting
step in these processes. This problem can be improved by adding
pore forming compounds to the zeolite clay blend before the forming
step.
[0019] It is an object of the invention to disclose an improved
molecular sieve adsorbent blend comprising a blend of different
zeolite materials with a highly dispersed attapulgite binder which
can be utilized for a number of different adsorption processes.
[0020] This and other objects are obtained by the process for production,
the process for use and product of the invention disclosed herein.
SUMMARY OF THE INVENTION
[0021] The present invention is a process for the production of
a molecular sieve adsorbent blend with improved performance characteristics
comprising
[0022] preparing a mixture of different zeolite materials,
[0023] preparing a binder, at least partially comprising highly
dispersed attapulgite fibers, wherein the tapped bulk density of
the highly dispersed attapulgite fibers, is above 550 g/l as measured
according to DIN/ISO 787
[0024] combining the mixture of different zeolite materials with
the binder to form a blended zeolite binder product, and
[0025] treating the combined product to form the molecular sieve
adsorbent blend.
[0026] The present invention is also a molecular sieve adsorbent
blend comprising
[0027] a mixture of different zeolite materials blended with a
binder, wherein the binder at least partially comprises highly dispersed
attapulgite fibers, wherein the tapped bulk density of the highly
dispersed attapulgite fibers is above 550 g/l as measured according
to DIN/ISO 787.
[0028] The present invention is also a process for drying a feed
stream comprising passing the feed stream over a molecular sieve
adsorbent blend comprising a mixture of two or more different zeolite
materials blended with a binder, wherein the binder at least partially
comprises the highly dispersed attapulgite fibers, as defined above.
[0029] The invention is also a process for the separation of components
of a gaseous or liquid feed stream comprising passing the feed stream
over a molecular sieve adsorbent blend comprising a mixture of different
zeolite materials blended with a binder, at least partially comprising
the highly dispersed attapulgite fibers, as defined above.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention is a molecular sieve adsorbent blend
formed from a mixture of different zeolite materials blended with
a binder, wherein the binder comprises at least partially highly
dispersed attapulgite fibers, a process for formation of that blend,
and processes of use of that blend. The invention is based on the
discovery that the adsorption rate of a molecular sieve adsorbent
product is dependent not only upon the nature and composition of
the zeolite materials, but also the type and characteristics of
the binder blended with the zeolite materials. It has been surprisingly
discovered that the same type and quantity of mixtures of different
zeolite materials when blended with different binders produces molecular
sieve adsorbent blends exhibiting varying adsorption characteristics
depending upon the binder that is used. (The phrases "adsorption
rate", "sorption rate" or "mass transfer rate"
mean the rate at which an adsorbate loading in a feed stream changes
over a given period of time for a given adsorption/separation process.)
[0031] The prior art suggests that the adsorption rate of a particular
molecular sieve adsorbent is only a function of the porosity and
particle size of the particular zeolite material utilized. It has
now been surprisingly discovered that the type of binder that is
used to bind the zeolite crystals together also plays an important
role in the adsorption rate of the material.
[0032] Adsorbent molecular sieve aggregates or blends are formed
by mixing zeolite materials with binder materials. Various types
of zeolites may be used to form the adsorbent blends including zeolite
A, zeolite X, including zeolite 13 X and LSX, zeolite Y, zeolite
ZSM-5 zeolite Beta, synthetic mordenite and blends thereof. These
zeolites may be used singly or in mixtures of two or more zeolites.
The particular type of zeolite present in the blend depends upon
the adsorbate that is to be adsorbed from the feed stream. For example,
when the desired adsorbate is carbon dioxide in a gas stream, the
preferred zeolites are zeolite X, including zeolite 13 X and zeolite
LSX. When the adsorption process is for the purification of gases,
notably by pressure swing adsorption (PSA) and temperature swing
adsorption (TSA) methods, the preferred zeolites include zeolite
A or zeolite X, including zeolite 13 X.
[0033] One of the important uses for these zeolitic materials is
for the removal of carbon dioxide, water and other trace inorganic
gases, as well as various hydrocarbons, from a gas stream, especially
air. These trace gases can be selectively adsorbed by the zeolitic
adsorbent. To improve the adsorption of trace gases, such as carbon
dioxide, the zeolite or zeolite mixture should be optimized. For
example, it has been shown that zeolites with a low SiO.sub.2/Al.sub.2O.sub.3
ratio exhibit a higher adsorption capacity for carbon dioxide than
zeolites with a higher SiO.sub.2/Al.sub.2O.sub.3 ratio. In particular,
when zeolite 13 X is replaced by zeolite LSX, the breakthrough time
for the adsorption of carbon dioxide from an air stream can be extended,
as zeolite LSX has a higher adsorption capacity than zeolite 13
X. Notwithstanding, because of the increased cost of zeolite LSX,
the use of zeolite 13 X is often preferred.
[0034] Binder materials are utilized to bind individual zeolite
crystals together, to form shaped products and to reduce the pressure
drop during the adsorption process. In the past the binder material
has not enhanced the adsorption capability of the zeolite materials.
In fact, conventional binders have generally reduced the adsorption
capacity of the zeolites materials. Binders which have been utilized
with zeolite materials in the past include clay minerals, such as
kaolin, palygorskite-type minerals, such as attapulgite, and smectite-type
clay minerals, such as montmorillonite or bentonite. These clay
binder materials have been used singly or in mixtures of two or
more different types of clay binders.
[0035] The inventors have surprisingly discovered that a particularly
useful blend of zeolite materials and a binder material is produced
when at least a portion of the binder materials is an attapulgite
clay which contains "highly dispersed attapulgite fibers."
Generally speaking, clay particles, especially attapulgite clay
particles, exist as dense materials with very limited adsorption
capabilities. These conventional clay binder particles are different
in size and shape from the zeolite materials. When blended with
zeolite materials, they tend to occupy space between the zeolite
materials without increasing the overall adsorption of the blend.
[0036] In particular, attapulgite clay particles, even after mining
and work-up, are naturally formed in dense bundles of clumped bristles
or fibers. The existence of these bundles has been confirmed using
scanning electron microscopy (SEM). These fibers must be separated
or ground to permit their use as binders for zeolite materials.
Without grinding these attapulgite clay bundles to a smaller size,
a non-porous layer of attapulgite clay fibers is created in the
zeolite blend, preventing or substantially limiting, diffusion of
adsorbates through the blend. The conventional attapulgite clays
that have been utilized are produced by dry grinding the attapulgite
clay. In this conventional process these dry ground attapulgite
clay bundles of fibers are then blended with the zeolite materials.
However, even after conventional grinding of the attapulgite clay
fibers, large bundles of attapulgite clay fibers are still present.
When these conventional attapulgite clay bundles are blended with
zeolite materials and formed into adsorbent blends, the capability
of the zeolite materials to adsorb the desired adsorbate is not
enhanced.
[0037] The applicants' invention utilizes "highly dispersed"
attapulgite clay fibers as at least a portion of the binder material
that is blended with the zeolite materials.
[0038] Dense attapulgite clay bundles of fibers can be differentiated
from "highly dispersed" attapulgite clay fibers of the
invention readily through the use of scanning electron microscopy.
Another method to distinguish between conventional dense attapulgite
clay fibers and the "highly dispersed" attapulgite clay
fibers of the invention is by the use of tapped bulk density measurement
as determined according to DIN/ISO 787. Dense attapulgite clay binder
fibers contain a residual water content of about 20-25 percent and
have a tapped bulk density of about 400 g/l to about 530 g/l. "Highly
dispersed" attapulgite binder fibers also contain residual
water of about 20-25 percent but have a tapped bulk density of about
550 g/l to about 700 g/l.
[0039] Another method to distinguish between conventional dense
attapulgite clay fibers and highly dispersed attapulgite clay fibers
of the invention is by determining the water adsorption capacity
of the respective attapulgite clay fibers. To determine whether
the clay fibers are "highly dispersed", the clay fibers
are fully saturated at 50 percent relative humidity at 25.degree.
C. until an equilibrium adsorption capacity is achieved. This process
may take up to 72 hours. After full hydration of the clay is achieved,
the clay is dried at 550.degree. C. for at least two hours. The
difference in the weight between the fully hydrated clay and the
dried clay is the water adsorption capacity. For dense attapulgite
clay fibers, the water adsorption capacity is below 30 percent,
whereas for the "highly dispersed" attapulgite clay fibers,
the water adsorption capacity is above 35 percent.
[0040] While any process which produces attapulgite fibers which
are "highly dispersed", as defined above, is within the
scope of the invention, one preferred process is disclosed in U.S.
Pat. No. 6130179 the contents of which are incorporated by reference
into this application. The process of U.S. Pat. No. 6130179 utilizes
a dispersant which disperses the individual attapulgite clay fibers
in water such that they remain in suspension even after other materials,
including other clays and mineral species, are removed from that
solution. Once the "highly dispersed" attapulgite clay
fibers are prepared, they are ready for use in the production of
the molecular sieve adsorbent blends of the invention. Notwithstanding,
this patent fails to disclose or suggest the use of these highly
dispersed attapulgite clay fibers with zeolite.
[0041] Generally the process to produce the molecular sieve adsorbent
blend with improved performance characteristics according to the
invention is as follows:
[0042] prepare the zeolite materials, which may comprise a mixture
of different zeolite materials,
[0043] prepare an attapulgite binder, at least partially comprising
highly dispersed attapulgite fibers,
[0044] mix the zeolite material or different zeolite materials
with the attapulgite fibers, preferably in an aqueous mixture,
[0045] form an uncalcined blended product from the mixture, and
[0046] calcine the blended product to form the molecular sieve
adsorbent blend product of the invention.
[0047] Once the appropriate zeolite materials are chosen for a
given application, they are mixed with the binder, which must be
comprised at least partially of the highly dispersed attapulgite
fibers, in the presence of a liquid, preferably water. The zeolite
material and the binder, which must be comprised at least partially
of the highly dispersed attapulgite fibers, are blended together
preferably with the water. The amount of binder that is utilized
can range from 5 to about 30 percent by weight, preferably from
about 5 to about 20 percent and most preferably in the range of
about 10 percent of the product. In contrast, conventional mixtures
of zeolite materials and non-highly dispersed attapulgite clay binders
are required to utilize about 20 percent or more attapulgite clay.
[0048] The highly dispersed attapulgite binder fibers comprise
at least 10 percent, by weight, preferably at least 20 percent by
weight and most preferably at least 50 percent by weight of the
total binder material utilized to produce the adsorbent blend product.
The remaining binder material may be conventional attapulgite binder.
Sufficient water is retained in or added to the mixture to make
a formable mixture, i.e., one that can be easily extruded.
[0049] The components of the mixture are blended using a conventional
blending device, such as a conventional mixer, until a mass of suitable
viscosity for forming the end product is obtained. The blended mixture
is then formed into the appropriate shaped product, for example,
by extrusion. The products can be formed in any conventional shape
such as beads, pellets, tablets or other such conventional shaped
products. Once the formed products are produced into the appropriate
shape, they are calcined, preferably at about 600.degree. C., for
about 30 minutes to 2 hours.
[0050] In an optional preferred embodiment, a pore forming agent
may be added to the zeolite/attapulgite clay mixture during the
mixing step to enhance the total pore volume of the end product.
Among acceptable pore forming agents are fibers, including rayon,
nylon, sisal, flax and the like and organic polymers, including
corn starch, starch derivatives, lignosulfonates, polyacrylamide,
polyacrylic acid, cellulose, cellulose derivatives and the like.
The amount of the pore forming agent that may be added is from about
2 to about 15 percent, by weight.
[0051] When the adsorbent blend is to be utilized to adsorb trace
gases, particularly from air using a pressure swing absorption or
thermal swing absorption, improved adsorption occurs when the zeolitic
material is zeolite LSX. Zeolite LSX has a longer break through
time for carbon dioxide adsorption than does zeolite 13 X. When
the conventional attapulgite clay binder is replaced by the highly
dispersed attapulgite clay fiber disclosed in the invention, the
break through time for a blend containing only zeolite 13 X, is
almost the same as when the conventional attapulgite clay binder
is used. However, it has been surprisingly discovered that when
the zeolite 13 X is replaced by zeolite LSX, the break through time
for the blend of the zeolite LSX with the highly dispersed attapulgite
fibers is substantially greater than when the zeolite LSX is combined
with a conventional attapulgite binder. For example, when pure zeolite
LSX is used with highly dispersed attapulgite fiber comprising about
12 percent of the blend, the increase in the break through time
is at least 50 percent and preferably about 67 percent. In contrast,
when the zeolite LSX is used with a conventional attapulgite binder
of the same concentration, the break through time only increased
about 35 percent. Notwithstanding, significant improvements occur
in the break through time when the amount of zeolite 13 X that is
replaced with LSX is as little as 20 percent, preferably at least
25 percent and in a most preferred embodiment at least 40 percent.
In one preferred embodiment the ratio of the zeolite 13X to the
zeolite LSX is from about 75:25 to about 60:40.
[0052] The zeolitic materials when formed using conventional procedures
contain a high percentage of sodium cations, generally at least
about 90 percent. The remaining cations are generally potassium
cations usually in the range from about 1 to about 10 percent. It
has been surprisingly discovered that the adsorption capability
of the composition can be improved by reducing the sodium ions to
5 percent or less, maintaining the potassium ions at 25 percent
or less and ion exchanging the remaining cations of the zeolitic
material with alkaline earth metal cations, especially calcium cations,
preferably from about 50 to about 95 percent, and most preferably
from about 75 to about 85 percent. Any remaining cations can be
comprised of alkali metals, such as sodium or potassium, preferably
potassium, other alkaline earth metal cations, Group IIIB cations,
or cations from the lanthanide series.
[0053] Products produced by the process of the invention show improved
adsorption rates. The adsorption rate can be determined using several
different methods. For example, in one preferred process, the adsorbent
product produced according to the invention can be tested to determine
the time necessary to achieve 95 percent of the maximum adsorption
capacity of the material. The shorter the time to achieve this value,
the faster the adsorption rate.
[0054] In another process to determine the adsorption rate of the
molecular sieve adsorbent blend of the invention, the amount of
the adsorbed product that has been adsorbed over a given period
of time can be determined.
[0055] In a further process of comparison of adsorption, the mass
transfer zone of the blend of the invention can be compared to that
of a conventional blend under given conditions. The shorter the
mass transfer zone, the higher the adsorption rate.
[0056] Finally, the diffusion rate can be determined directly for
certain gases or liquids. The higher the diffusion rate, the faster
the adsorption rate.
[0057] It has been surprisingly discovered that by replacing some
or all of a conventional attapulgite binder with "highly dispersed"
attapulgite fibers, there is an improved adsorption rate, regardless
of which method is used to measure that rate. The improvement in
adsorption rate is at least about 10 percent and may be as high
as 200 percent compared to products wherein only conventional attapulgite
clay binders are used. This improvement is important because of
the higher cost of the highly dispersed attapulgite fibers over
conventional attapulgite binders.
[0058] A further surprising improvement is the ability of the molecular
sieve adsorbent blend to maintain its crush strength even when the
amount of the highly dispersed attapulgite fibers that are added
is less than is used with conventional attapulgite clay binders.
Generally speaking, the more binder that is present, the better
the crush strength of the finished product. For conventional dense
attapulgite binders, this improvement in crush strength is dramatic
when the percentage of attapulgite binder within the end product
increases from 10 to about 20 percent of the composition. Products
made with conventional dense attapulgite binder of 10 percent or
less are not practical as their crush strength drops below acceptable
levels. It has been surprisingly discovered that a product produced
using the highly dispersed attapulgite fibers of the invention produce
an end product with adequate crush strength even when the quantity
of the highly dispersed attapulgite fibers in the end product is
as low as 10 percent or even less. Further, at any particular percentage
of binder material, the crush strength of a product produced using
the highly dispersed attapulgite fibers of the invention is higher
than for a product made solely with a conventional dense attapulgite
binder.
[0059] It has also been surprisingly discovered that even when
lower percentages of highly dispersed attapulgite fibers are utilized
in an adsorbent product than conventionally are used when a conventional
dense attapulgite clay is used, the rate of water adsorption increases.
This is evidenced by a reduction in the amount of time that is necessary
to achieve a particular predetermined amount to be adsorbed. This
improvement is at least 10 percent and in many cases as much as
30 percent or more.
[0060] While it is known that improved adsorption occurs, particularly
of trace gases using a TSA or PSA procedure for the purification
of air, when the zeolitic material that is used is a zeolite LSX
in contrast to a zeolite 13 X, it has been surprisingly discovered
that this improvement is greater than expected when some or all
of the conventional attapulgite binder, that is normally utilized
in the production of the adsorbent material, is replaced with the
"highly dispersed" attapulgite fibers of the invention.
[0061] The highly dispersed attapulgite fibers or blend of conventional
attapulgite binder and highly dispersed attapulgite fibers can be
combined with various mixtures of zeolites and used for a number
of different processes. For example, the blend can be used for drying
a feed stream, such as for the removal of water from a gaseous or
liquid ethanol stream. The blend can also be used for the separation
of nitrogen from an air stream. Further, the blend can be used for
the removal of sulfur and oxygen containing compounds from a hydrocarbon
stream. Another use for this blend is for the removal of carbon
monoxide, carbon dioxide and nitrogen from a hydrogen gas stream.
The blend can also be used for the removal of water from a gaseous
or liquid hydrocarbon stream or for the removal of water from a
gaseous or liquid stream of refrigerants. Another use is for the
removal of water and carbon dioxide from air. The adsorbent blend
of the invention may also be used for the separation of organic
compound, such as for the separation of n-paraffins from a mixture
of iso-paraffins and n-paraffins or for the conversion of certain
organic compounds. There are a number of other processes for which
this blend of a binder, comprising at least partially highly dispersed
attapulgite fibers, and mixture of different zeolites can be utilized
which would be well known to a person skilled in the art and which
are covered by this invention.
[0062] These improvements are shown by the following examples:
EXAMPLES
Example 1
[0063] Samples of an attapulgite clay material that is conventionally
used as a binder for zeolites and highly dispersed attapulgite clay
fibers were tested for tapped bulk density, residual water and water
adsorption capacity. Tapped bulk density was determined according
to DIN/ISO 787.
[0064] (Actigel 208 obtained from ITC Floridin was used as the
highly dispersed attapulgite clay in all examples. The conventional
attapulgite clays were of different brands and obtained from ITC
Floridin.)
[0065] A clay sample of about 10 grams was weighed in a porcelain
crucible (weighing precision 1 mg) and heated to 550.degree. C.
for 2 hours. The sample was cooled to room temperature in a desiccator
and weighed (weighing precision 1 mg). The weight difference led
to the residual water amount.
[0066] Another clay sample of about 10 grams was weighed in a porcelain
crucible (weighing precision 1 mg) and was water saturated at 50
percent relative humidity and 20.degree. C. The equilibrium was
reached within 72 hours. The sample was weighed (weighing precision
1 mg) and heated to 550.degree. C. for 2 hours. The sample was cooled
to room temperature in a desiccator and weighed (weighing precision
1 mg). The weight difference of the fully hydrated sample and fully
dried sample led to the water adsorption capacity given in Table
1 below. The fully dried mass was taken as 100 percent clay.
1 TABLE 1 Attapulgite Clay Sample Highly Conventional Conventional
Conventional Dispersed Dense Dense Dense Clay Clay 1 Clay 2 Clay
3 Tapped Bulk 617 398 .+-. 31 529 .+-. 20 428 Density (g/ml) 595
(average of (average of 459 660 17 samples) 21 samples) Residual
Water 22.3 25.5 21.4 25.5 as Received (%) 21.7 22.6 23.7 Water 36.8
28.8 25.0 29.7 Adsorption 36.0 28.8 Capacity (%) 36.0
[0067] As is clear from the Table, the bulk density of the highly
dispersed clay was significantly higher than the bulk density of
the conventional dense attapulgite clay. In addition, the water
adsorption capacity of the highly dispersed attapulgite clay fibers
was significantly higher than that of the conventional dense attapulgite
clay.
Example 2
[0068] The crush strength of samples of a molecular sieve adsorbent
blend product prepared using a conventional dense attapulgite clay
was compared with a molecular sieve adsorbent blend product prepared
using a highly dispersed attapulgite clay.
[0069] To determine the crush strength of the various samples,
molecular sieve blends were prepared. Sodium A molecular sieve was
blended with various amounts of both a conventional dense attapulgite
clay and the highly dispersed attapulgite clay. To 100 grams of
the molecular sieve/clay binder mixture about 30 to 40 grams of
water were added and then blended for up to 180 minutes using a
conventional blender. The product was then extruded in the form
of {fraction (1/16)}" extrudates. These extrudates were then
dried at approximately 120.degree. C. for 8 to 12 hours and then
calcined at 600.degree. C. for about 2 hours.
2TABLE 2 Crush Strength in Relation to the Amount of Binder Used
Con- ven- Conven- Conven- Highly Highly Highly tional tional tional
Dis- Dis- Dis- Dense Dense Dense persed persed persed Binder Binder
Binder Binder Binder Binder (20%) (15%) (10%) (20%) (15%) (10%)
Size of {fraction (1/16)}" {fraction (1/16)}" {fraction
(1/16)}" {fraction (1/16)}" {fraction (1/16)}" {fraction
(1/16)}" Extrudates Crush 19.9 8.8 7.5 28.5 19.6 16.1 Strength
[N]
[0070] Surprisingly the crush strength of a product made with 20
percent highly dispersed attapulgite fibers was significantly greater
than a product made with the same percentage of a conventional dense
attapulgite binder. Further, the crush strength remained at a reasonably
high level even when the amount of the highly dispersed attapulgite
fiber was reduced to 10 percent, whereas the crush strength of the
material using the conventional attapulgite binder dropped rather
significantly.
Example 3
Water Adsorption Kinetics
[0071] The materials prepared in Example 2 were tested for water
adsorption kinetics. It was surprisingly discovered that the amount
of binder did not have an impact on the water adsorption kinetics
of the material made with the conventional binder. In contrast,
it was surprisingly discovered that when the amount of the highly
dispersed attapulgite fiber was reduced to 10 percent, the rate
of adsorption of water to reach 95 percent of adsorption capacity
increased dramatically. Details are shown in the attached Table
3.
3TABLE 3 Influence of Binder Type and Binder Amount to Water Adsorption
Kinetics Con- Con- ven- ven- Conven- Highly Highly Highly tional
tional tional Dis- Dis- Dis- Dense Dense Dense persed persed persed
Binder Binder Binder Binder Binder Binder (20%) (15%) (10%) (20%)
(15%) (10%) Size of {fraction (1/16)}" {fraction (1/16)}"
{fraction (1/16)}" {fraction (1/16)}" {fraction (1/16)}"
{fraction (1/16)}" Extrudates H.sub.2O 121 130 122 136 133
96 Adsorption Kinetics at 1 mbar [min]
Example 4
Beaded Molecular Sieve 3A
[0072] A premixed zeolite 3A powder/attapulgite clay composition
was added continuously to a granulation pan. The zeolite 3A powder
was acquired from Zeochem AG. During the beading process, water
was sprayed on the powder mixture to maintain a constant humidity.
The powder mixture was added at a speed of 300 kg/hr. After having
finished the addition of the powder mixture, the beads were rolled
for another 10 minutes. The green beads were dried at 100.degree.
C. and then calcined at 600.degree. C. The calcined beads were stored
in well closed containers and analyzed. Table 4 gives the comparative
results for the two different beaded materials. While physical properties,
such as crush strength and bulk density were generally the same
for both samples, mass transfer zone was reduced significantly and
water adsorption rate was surprisingly faster for the product made
with the highly dispersed attapulgite clay.
4TABLE 4 Comparative Results of a Conventional 3A Molecular Sieve
and a Molecular Sieve Produced with 10% Highly Dispersed Attapulgite
Clay as a Beneficiated Attapulgite Binder Reference Material According
to Invention (20% Dense (10% Highly Dispersed Attapulgite Binder)
Attapulgite Clay) Bead Size [mesh] 4 .times. 8 4 .times. 8 Crush
Strength [N] 51 46 Bulk Density [g/l] 721 687 Water Adsorption 20.1
21.3 50% r.h. [%] Water Mass Transfer 253 167 Zone [mm] Water Adsorption
184 105 Kinetic (time to reach 95% ads. capacity; 4 mbar) [min]
Example 5
Beaded Molecular Sieve 3A for Natural Gas Drying
[0073] A premixed zeolite 3A powder/organic additive/clay composition
was added continuously to a granulation pan. During the beading
process, water was sprayed onto the powder mixture to keep a constant
humidity. The powder mixture was added at a speed of 300 kg/hr.
After having finished the addition of the powder mixture, the beads
were rolled for another 10 minutes. The green beads were dried at
100.degree. C. and then calcined at 630.degree. C. The calcined
beads were stored in closed containers and analyzed. The amount
of organic additive was kept constant for both experiments. Table
5 gives the comparative results of the two different beaded materials.
While physical properties, attrition, and bulk density are generally
the same for both samples, water adsorption rate increased surprisingly
for the product produced using the highly dispersed attapulgite
clay. The beads are much smaller than in Example 4 but the increase
in the adsorption rate was still very high, indicating that the
effect is intrinsic.
5TABLE 5 Comparative Results of a Conventional 3A Molecular Sieve
Used for Natural Gas Drying and a Molecular Sieve Produced with
10% Highly Dispersed Attapulgite Clay as a Beneficiated Attapulgite
Reference Material (20% Conventional According to Invention Dense
Attapulgite (10% Highly Dispersed Binder) Attapulgite Clay) Bead
Size [mesh] 8 .times. 12 8 .times. 12 Attrition [%] 0.04 0.02 Bulk
Density [g/l] 730 722 Water Adsorption 22.2 22.7 50% r.h. [%] Water
Adsorption 14.1 18.5 Kinetic at p/p.sub.0 = 0.03 after 120 min.
[%]
Example 6
Beaded Molecular Sieve 5A
[0074] A premixed zeolite 5A powder/clay composition was added
continuously to a granulation pan. The zeolite 5A powder was acquired
from Zeochem Ltd. During the beading process, water was sprayed
onto the powder mixture to keep a constant humidity. The powder
mixture was added at a speed of 300 kg/hr. After having finished
the addition of the powder mixture, the beads were rolled for another
10 minutes. The green beads were dried at 100.degree. C. and then
calcined at 630.degree. C. The calcined beads were stored in closed
containers and analyzed. Table 6 gives the comparative results of
the two different beaded materials. While butane adsorption capacity
increased within expectations, nitrogen adsorption kinetic increased
surprisingly, certainly more than was anticipated.
6TABLE 6 Comparative Results of a Conventional 5A Molecular Sieve
and a Molecular Sieve Produced with 10% Highly Dispersed Attapulgite
Clay as a Beneficiated Attapulgite Binder Reference Material (20%
According to Invention Conventional Dense (10% Highly Dispersed
Attapulgite Binder) Attapulgite Clay) Bead Size [mesh] 8 .times.
12 8 .times. 12 N-Butane Adsorption 8.0 9.3 Capacity; 1 bar/25.degree.
C. [%] Nitrogen Kinetic 0.17 0.39 Value [1/s]
Example 7
Beaded Molecular Sieve 4A
[0075] The same preparation procedure was used as in Example 6
except that zeolite 4A powder acquired from Zeochem AG was used
for the beading process. The amount of the binder for the new formulation
was increased to 15%. The drying and the calcination process followed
the same temperature profiles as was used in Example 6. The results
are given in Table 7. The Example using 15% of the highly dispersed
attapulgite binder showed a surprising improvement in the adsorption
rate. The mass transfer zone dropped from 137 mm to 106 mm and the
water adsorption capacity after 120 minutes increased from 15.0%
to 17.2%.
7TABLE 7 Comparative Results of a Conventional 5A Molecular Sieve
and a Molecular Sieve Produced with 15% Highly Dispersed Attapulgite
Clay as a Beneficiated Attapulgite Binder Reference Material (20%
According to Invention Conventional Dense (15% Highly Dispersed
Attapulgite Binder) Attapulgite Clay) Bead Size [mm] 2-3 2-3 Crush
Strength [N] 57 41 Attrition [%] 0.03 0.01 Bulk Density 729 710
[g/l] Water Mass Transfer 137 106 Zone [mm] Water Adsorption 15.0
17.2 Kinetic at p/p.sub.0 (after 120 min.) [%]
Example 8
Beaded Molecular Sieve 13X Used for Air Purification and/or for
Air Separation
[0076] A premixed zeolite 13X powder/organic additive/clay composition
was added continuously to a granulation pan. The 13X zeolite powder
was acquired from Zeochem AG. During the beading process, water
was sprayed onto the powder mixture to keep a constant humidity.
The powder mixture was added at a rate of 500 kg/hr. After having
finished the addition of the powder mixture, the beads were rolled
for another 10 minutes. The green beads were dried at 100.degree.
C. and then calcined at 620.degree. C. The calcined and cooled beads
were stored in air tight containers and analyzed. The analytical
results of the finished product are given in Table 8. Again, the
physical properties remained within expectations, but the adsorption
rate increased for the composition of the invention much more than
expected, especially for the adsorption of nitrogen.
8TABLE 8 Comparative Results of a Conventional 13X Molecular Sieve
Used for Air Prepurification and for Air Separation, and a Molecular
Sieve Produced with 10% Highly Dispersed Attapulgite Clay as a Beneficiated
Attapulgite Binder Reference Material (16% Dense According to Invention
Conventional (10% Highly Dispersed Attapulgite Binder) Attapulgite
Clay) Bead Size [mm] 1.0-2.0 1.0-2.0 Attrition [%] 0.05 0.07 Bulk
Density [g/l] 640 638 Water Adsorption 28.1 30.7 Capacity 50% r.h.
[%] CO.sub.2 Adsorption 12.6 13.6 Capacity 45 mbar/25.degree. C.
[%] Water Adsorption 17.0 19.2 Kinetic at p/p.sub.0 = 0.03 (after
120 min.) [%] Nitrogen Kinetic 0.20 0.33 Value [1/s]
[0077] As is shown from these examples, there are surprising improvements
in the performance of molecular sieve adsorbent blends using attapulgite
binder produced from highly dispersed attapulgite fibers. This improvement
in crush strength, adsorption kinetics and other characteristics
as shown in the Examples was surprising and dramatic.
Example 9
Beaded Molecular Sieve 13 X Used for Air Purification Using Conventional
Attapulgite Binder (Comparative Example)
[0078] A zeolite 13 X powder, organic additive, and conventional
attapulgite clay binder mixture was added continuously to a granulation
wheel. The 13 X zeolite powder was obtained from Zeochem AG, Uetikon,
Switzerland, and the attapulgite binder was obtained from ITC Floridin,
Hunt Valley, Md. and is of the type disclosed in Example 1. During
the granulation process sufficient water was sprayed on the zeolite
and binder in order to maintain sufficient humidity to obtain a
beaded material. The powder mixture was added at a rate of 500 kg/hr.
After the entire mixture was added to the wheel, the finished beads
were rolled for an additional ten minutes. The final mixture contained
16 percent binder by weight. The green beads were screened to a
grain size of 1.6-2.6 mm, dried at a 100.degree. C. and calcined
at a temperature of 620.degree. C. The calcined and cooled material
was packed in air tight drums and analyzed. The break through time
for carbon dioxide was 158 minutes.
Example 10
Beaded Zeolite 13 X/LSX for Air Purification Using a Blend of a
Highly Dispersed Attapulgite Binder and a Conventional Attapulgite
Binder
[0079] A mixture of sodium LSX zeolite and 13 X zeolite (mixed
at a ratio of 33:67 LSX:13X), organic additives and a mixture of
highly dispersed attapulgite fibers and a conventional attapulgite
binder (mixed in a ratio of 33:67 highly dispersed to conventional
attapulgite) were added continuously to a granulation wheel. The
zeolite materials were obtained from Zeochem AG with both the highly
dispersed attapulgite clay fibers and the conventional attapulgite
clay binder obtained from IT Floridin. (See Example 1) These zeolitic
and binder materials were used for all remaining Examples. During
the granulation process, water was sprayed on the zeolite and binder
mixture in order to maintain a constant humidity sufficient to obtain
beaded material. The powdered mixture was added at a rate of 500
kg/hr. After having finished the addition of the powder material,
the beads were rolled for an additional ten minutes. The green beads
were dried at a temperature of 100.degree. C. and then calcined
at 620.degree. C. The calcined and cooled beads were stored in air
tight containers and analyzed. The final mixture contained 12 percent
binder by weight. The break through time for carbon dioxide was
at 206 minutes.
Examples 11 through 16
[0080] Production of beaded zeolite 13 X/LSX for air purification
containing a blend of highly dispersed attapulgite fibers and conventional
attapulgite binder. A number of zeolite blends were produced using
various ratios of 13 X to LSX zeolite powders. To these mixtures
organic additives were added. These mixtures were added to one or
two attapulgite clay binders and moistened with water. 2 kg of the
final blend were put in an Eirich laboratory mixer RO2. The material
was mixed to a point were beads were formed. The green beads were
strained to a size of 1.6-2.6 mm, dried at a 100.degree. C. and
calcined at 620.degree. C. The calcined material was cooled under
dry conditions, packed in air tight containers and analyzed.
[0081] Determination of Break Through Time.
[0082] The calcined and cooled zeolite materials were filled in
an adsorption column with a diameter of 30 mm at a pressure of 6.times.10.sup.5
Pa, a temperature of 25.degree. C. and a gas flow rate of 2.4 m.sup.3/hr,
wherein the gas is purified nitrogen containing 450 ppm of carbon
dioxide. The gas was passed through the column. The concentration
of carbon dioxide is determined at the outlet of the adsorption
column with an IR detector. The break through is achieved as carbon
dioxide emerges at the outlet of the column.
Example 11
[0083] Zeolite 13 X was used as the zeolitic material. The binder
system comprised 50 percent highly dispersed attapulgite clay fibers
and 50 percent conventional attapulgite clay binder from ITS Floridin.
The amount of the binder in the finished product was 12 percent.
The break through time was 161 minutes.
Example 12
[0084] Zeolite 13 X and zeolite LSX were mixed at a ratio of 67:33.
The clay binder system was a 50/50 mixture of the highly dispersed
attapulgite fibers and a conventional attapulgite clay binder at
a 12 percent mixture. The break through time was 192 minutes.
Example 13
[0085] Zeolite 13 X and zeolite LSX were mixed together at a ratio
of 50:50 with a binder system comprising highly dispersed attapulgite
fibers and conventional attapulgite clay mixed at a ratio of 50:50.
The binder comprised 12 percent of the mixture by weight. The break
through time was 216 minutes.
Example 14
[0086] A 100 percent zeolite LSX was used. The binder system comprised
12 percent of the mixture by weight and was comprised of 50 percent
highly dispersed attapulgite fibers and 50 percent conventional
attapulgite clay. The break through time was 269 minutes.
Example 15. (Comparative Example)
[0087] 100 percent zeolite LSX was used with a conventional attapulgite
clay binder comprising 16 percent of the material by weight. The
break through time was 213 minutes.
Example 16. (Comparative Example)
[0088] Zeolite 13 X and zeolite LSX were combined at a ratio of
50:50 with a conventional attapulgite clay comprising 16 percent
by weight. The break through time was 195 minutes.
[0089] As is clear from these Examples, improved performance is
achieved when the binder used contains at least a portion of highly
dispersed attapulgite clay fibers.
[0090] Although the invention has been described in detail, it
is clearly understood that the same is by no way to be taken as
a limitation. The scope of the present invention can only be limited
by the appended claims. |