Molecular sieve abstract
A process for the production of a molecular sieve adsorbent blend
product with improved performance characteristics produced by preparing
a zeolite powder, preparing a highly dispersed attapulgite fiber
binder, mixing the zeolite powder with the highly dispersed attapulgite
binder to form a mixture, forming molecular sieve adsorbent products
into a shaped material and calcining 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
What is claimed is:
1. A process for the production of a molecular sieve adsorbent
blend product with improved performance characteristics comprising
preparing a zeolite product; preparing an attapulgite binder comprising
highly dispersed attapulgite fibers; mixing the zeolite with the
attapulgite binder and water to produce a mixture; forming a molecular
sieve adsorbent product from the mixture; and calcining the adsorbent
product to form the molecular sieve adsorbent blend product, wherein
the tapped bulk density of the highly dispersed attapulgite fibers,
as measured according DIN/ISO 787 is more than about 550 g/l.
2. The process of claim 1 wherein the water adsorption capacity
of the highly dispersed attapulgite fibers is greater than about
35 percent.
3. The process of claim 1 wherein the attapulgite binder comprises
from about 5 to about 30 percent, by weight, of the molecular sieve
adsorbent blend product.
4. The process of claim 1 wherein the attapulgite binder comprises
from about 5 to about 20 percent by weight of the molecular sieve
adsorbent blend product.
5. The process of claim 1 further comprising blending a pore forming
agent with the highly dispersed attapulgite binder and zeolite powder.
6. 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 product.
7. A molecular sieve adsorbent blend product formed by the process
of claim 1.
8. A molecular sieve adsorbent blend product comprising a zeolite
blended with a highly dispersed attapulgite binder, wherein the
tapped bulk density of the highly dispersed attapulgite binder is
more than about 550 g/l.
9. The product of claim 8 wherein the water adsorption capacity
of the highly dispersed attapulgite fibers is more than about 35
percent.
10. The product of claim 8 wherein the highly dispersed attapulgite
binder comprises from about 5 to about 30 percent by weight of the
molecular sieve adsorbent blend product.
11. The product of claim 8 wherein the highly dispersed attapulgite
binder comprises from about 5 to about 20 percent by weight of the
molecular sieve adsorbent blend product.
12. The product of claim 8 further comprising a pore forming agent.
Molecular sieve description
CROSS REFERENCE TO RELATED APPLICATIONS
NONE
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to molecular sieve adsorbents and more particularly
to a molecular sieve adsorbent blend comprising a zeolite and a
highly dispersed attapulgite binder. This invention also relates
to a process for the preparation of a molecular sieve adsorbent
blend comprising blending a zeolite with a highly dispersed attapulgite
binder.
2. Background Art
Zeolites are hydrated metal alumino silicates having the general
formula
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. Adsorption of these molecules is limited by
the size of the zeolite channels. The rate of adsorption is limited
by the laws of diffusion.
One limitation on the utilization of these zeolite crystals is
their extremely fine particle size. Large naturally-formed agglomerates
of these crystals break apart easily. Because the pressure drop
through the bed is prohibitively high, these zeolite crystals cannot
be used in fixed beds for various 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.
Therefore, it is desirable to agglomerate these crystals with other
materials to provide an agglomerate mass of the crystals which exhibits
a reduced pressure drop.
To permit the utilization of these molecular sieve crystals, different
types of clays are used as binders 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.
U.S. Pat. No. 3219590 discloses another molecular sieve blend
comprising a kaolin-type clay and a lignosulfonate which functions
as the binding agent.
Adsorbent materials comprising a type 5A zeolite molecular sieve
and a kaolin clay binder, wherein the kaolin comprise from about
10 to about 40 percent of the composition, are disclosed in U.S.
Pat. No. 5001098.
Molded bodies containing dealuminated zeolite Y and a binder material
are disclosed in U.S. Pat. No. 5316993.
An adsorbent and/or catalyst blended with a binder system comprising
a colloidal metal oxide, an oxide adsorbent and an acid are disclosed
in U.S. Pat. No. 5948726.
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.
An abrasion-resistant granular zeolite formed by blending a zeolite
and a binder system is disclosed in U.S. Pat. No. 4420419. See
also U.S. Pat. No. 5292360 which discloses an adsorbent for the
purification of gases comprising a 5A zeolite molecular sieve and
a kaolin clay binder.
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.
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.
Accordingly it is an object of the invention to disclose a process
for the preparation of molecular sieve adsorbents with enhanced
diffusion rates.
It is a still further object of the invention to disclose a process
for the production of a molecular sieve adsorbent blend which is
especially useful in thermal swing adsorption (TSA) systems and
in pressure swing adsorption (PSA) systems.
It is a still further object of the invention to disclose molecular
sieve adsorbent blends which maintain their physical properties
and diffusion capabilities even with reduced binder percentages.
It is a still further object of the invention to disclose a process
for the production of a molecular sieve adsorbent blend utilizing
highly dispersed attapulgite fibers.
It is a still further object of the invention to disclose a molecular
sieve adsorbent blend comprising a zeolite powder and a highly dispersed
attapulgite binder.
It is a still further object of the invention to disclose a process
for drying a feed stream comprising passing the feed stream over
a molecular sieve adsorbent blend comprising a zeolite and a highly
dispersed attapulgite binder.
It is a still further object of the invention to disclose a process
for the adsorption of carbon dioxide from an air stream comprising
passing that air stream over a molecular sieve adsorbent blend comprising
a zeolite powder and a highly dispersed attapulgite binder.
It is still further object of the invention to disclose a process
for separation of components of a gaseous or liquid feed stream
comprising passing that gaseous or liquid feed stream over a molecular
sieve adsorbent blend comprising a zeolite powder and a highly dispersed
attapulgite binder.
These 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
The present invention is a process for the production of a molecular
sieve adsorbent blend with improved performance characteristics
comprising preparing a zeolite, preparing an attapulgite binder
containing highly dispersed attapulgite fibers, mixing the zeolite
with the attapulgite binder in an aqueous mixture, forming molecular
sieve adsorbent products from the mixture, and calcining the adsorbent
product to form a molecular sieve adsorbent blend, wherein the tapped
bulk density of the highly dispersed attapulgite fibers, is above
550 g/l as measured according to DIN/ISO 787 and wherein the water
adsorption capacity of the highly dispersed binder is above 35 percent
(w/w).
The present invention is also a molecular sieve adsorbent blend
comprising a zeolite blended with a highly dispersed attapulgite
binder, wherein the tapped bulk density of the highly dispersed
attapulgite binder is above 550 g/l as measured according to DIN/ISO
787 and wherein water adsorption capacity of the highly dispersed
binder is above 35 percent (w/w).
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 zeolite blended with a highly dispersed attapulgite
binder as defined above.
The invention is also a process for the separation of components
of a gaseous or liquid feed stream comprising passing the liquid
feed stream over a molecular sieve adsorbent blend comprising a
zeolite blended with a highly dispersed attapulgite binder as defined
above.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a molecular sieve adsorbent blend formed
from a zeolite blended with a highly dispersed attapulgite binder
and a process for formation of that product. The invention is based
on the discovery that the adsorption rate of a molecular sieve product
is not only dependent upon the size of the formed zeolite particles,
but also the type and characteristics of the binder blended with
the zeolite. It has been surprisingly discovered that the same type
and quantity of zeolite when blended with different binders produces
zeolite blends which exhibit different adsorption characteristics
depending upon the binder that is used. The phrase "adsorption
rate" or "sorption rate" or "mass transfer rate"
means the rate at which an adsorbate loading in a feed stream changes
over a given period of time for a given adsorption separation process.
The prior art suggests that the adsorption rate of a molecular
sieve adsorbent is only a function of the porosity and particle
size of the molecular sieve adsorbent. It has now been surprisingly
discovered that the type of binder that is used to bind the zeolite
crystals also plays a role in the adsorption rate of the zeolite
material.
Adsorbent aggregates or blends are formed by mixing zeolite crystals
with binder materials. Various types of zeolites may be used to
form the adsorbent blend including zeolite A, zeolite X, 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. Zeolites may be present in their alkali or alkaline earth
metal substituted form. 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 adsorbent is carbon
dioxide in a gas stream, the preferred zeolites include zeolite
X or 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.
Binder materials are utilized to bind the individual zeolite crystals
together, to form shaped products and to reduce the pressure drop
during adsorption. However, in the past the binder material has
not enhanced the adsorption capability of the zeolite. In fact,
conventional binder materials have generally reduced the adsorption
capacity of the zeolites. Binder materials which have been utilized
with zeolites 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
binders have been used singly or in mixtures of two or more different
types of clay binders.
The inventors have discovered that a particularly useful blend
of zeolites and a clay binder is produced when the clay material
is an attapulgite clay which has been "highly dispersed."
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 particles. When blended with
zeolite crystals they tend to occupy space between the zeolite crystals
and may assist in the adsorption by the zeolite material without
increasing the overall adsorption of the zeolite blend.
In particular, attapulgite clay particles, even after mining and
work-up, are naturally formed in the shape of dense bundles of clumped
bristles. The existence of these bundles has been confirmed using
scanning electron microscopy (SEM). These bristles must be separated
or ground to permit their use as binders for zeolite particles.
Without grinding these attapulgite clay particles to a smaller size,
a non-porous layer of attapulgite clay particles is created in the
zeolite blend, preventing or substantially limiting, diffusion of
adsorbates through the blend. The conventional attapulgite clays
that have been utilized in the past are produced by dry grinding
the attapulgite clay. In the conventional process these dry ground
attapulgite clay bundles of bristles are then blended with the zeolite
crystals. However, even after this conventional grinding of the
attapulgite clay bundles, large bundles of attapulgite clay bristles
are still present. When these conventional attapulgite clay bundles
are blended with zeolite and formed into adsorbents, the capability
of the zeolite materials to adsorb the desired adsorbate is not
substantially enhanced.
The applicants' invention utilizes "highly dispersed"
attapulgite clay as the binder material that is blended with the
zeolite powder. The difference between conventional, dense attapulgite
clay bundles and the "highly dispersed" attapulgite clay
particles of the invention can be differentiated readily through
the use of a scanning electron microscopy. Another method to distinguish
between conventional dense attapulgite clay and the "highly
dispersed" attapulgite clay products of the invention is by
the use of tapped bulk density measurement as determined according
to DIN/ISO 787. Dense attapulgite clay binders 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 binders 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.
Another method to distinguish between conventional dense attapulgite
clay and highly dispersed attapulgite clay products of the invention
is by determining the water adsorption capacity of the attapulgite
clay products. To determine whether the clay binder is "highly
dispersed" the clay binder is fully saturated at 50 percent
relative humidity at 25.degree. C. to the point where 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 of
the weight between the fully hydrated clay and the dried clay is
the water adsorption capacity. For dense attapulgite clays, the
water adsorption capacity is below 30 percent whereas for the "highly
dispersed" attapulgite clay, the water adsorption capacity
is above 35 percent.
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.
This patent fails to disclose or suggest the use of this highly
dispersed attapulgite clay with zeolite. The process of U.S. Pat.
No. 6130179 utilizes a dispersant which disperses the individual
attapulgite particles in water such that they remain in suspension
even after other materials, including other clay and mineral species,
are removed from that solution. Once the "highly dispersed"
attapulgite clay is prepared, it is ready for use in the production
of the molecular sieve adsorbent product of the invention.
Generally the process to produce the molecular sieve adsorbent
blend product with improved performance characteristics according
to the invention is as follows: prepare the zeolite material, prepare
an attapulgite binder comprising highly dispersed attapulgite fibers,
mix the zeolite with the attapulgite binder in an aqueous mixture,
form an uncalcined material from the mixture, and calcine the material
to form the molecular sieve adsorbent blend product of the invention.
Once the appropriate zeolite material is chosen for a given application,
it is mixed with the highly dispersed attapulgite binder in the
presence of water. The zeolite powder and the highly dispersed attapulgite
binder are blended together with water. The amount of highly dispersed
attapulgite 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 blend. Conventional
mixtures of zeolite and non-highly dispersed attapulgite clay binders
utilize about 20 percent or more attapulgite clay. Sufficient water
is retained in or added to the mixture to make a formable mixture,
i.e., one that can be easily extruded.
The mixture is blended using a conventional blending device, such
as a conventional mixer, until a mass of suitable viscosity for
forming 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.
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
the 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.
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.
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.
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.
Finally, the diffusion rate can be determined directly for certain
gases or liquids. The higher the diffusion rate, the faster the
adsorption rate.
It has been surprisingly discovered that by replacing a conventional
attapulgite binder with the same quantity of "highly dispersed"
attapulgite binder of the invention, 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
as high as 200 percent compared to products containing conventional
attapulgite clay binders. This improvement is especially important
because of the increased cost of the highly dispersed attapulgite
binder over conventional attapulgite binders.
A further surprising improvement is in the ability of the zeolite
adsorbent blend product to maintain its crush strength even when
the amount of the attapulgite binder that are added to the mixture
is reduced. Generally speaking, the more binder that is present
in the forming process, the better the crush strength for the finished
product. For conventional dense attapulgite binders, this improvement
in the crush strength is dramatic when the percentage of attapulgite
binder within the end product increases from zero 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 produces an end product with adequate crush strength
even when the quantity of the highly dispersed attapulgite binder
in the end product is as low as 10 percent or less. Further, at
any particular percentage of binder material, the crush strength
of a product produced using the highly dispersed attapulgite fiber
of the invention is higher than for a product made with a conventional
dense attapulgite binder.
It has also been surprisingly discovered that even when lower percentages
of a highly dispersed attapulgite fiber are utilized in an adsorbent
product, 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.
The highly dispersed attapulgite binder can be blended with zeolite
and used for a number of different processes. For example, the blend
of highly dispersed attapulgite clay and zeolite 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 material
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 highly dispersed attapulgite clay and zeolite can
be utilized which would be well known to a person skilled in the
art and which are covered by this invention.
These improvements are shown by the following examples:
EXAMPLES
Example 1
Samples of an attapulgite clay material that is conventionally
used as a binder for zeolites and a highly dispersed attapulgite
clay material were tested for tapped bulk density, residual water
and water adsorption capacity. Tapped bulk density was determined
according to DIN/ISO 787. (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.)
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.
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.
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
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 was significantly higher
than that of the conventional dense attapulgite clay.
Example 2
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.
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 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.
TABLE 2 Crush Strength in Relation to the Amount of Binder Used
Conven- 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 1/16" 1/16" 1/16" 1/16" 1/16" 1/16"
Extrud- ates Crush Strength 19.9 8.8 7.5 28.5 19.6 16.1 [N]
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
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.
TABLE 3 Influence of Binder Type and Binder Amount to Water Adsorption
Kinetics Conven- 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 1/l6" 1/l6" 1/l6" 1/l6" 1/l6"
1/l6" Extru- dates H.sub.2 O Adsorp- 121 130 122 136 133 96
tion Ki- netics at 1 mbar [min]
Example 4
Beaded Molecular Sieve 3A
A premixed zeolite 3A powder/attapulgite clay composition was added
continuously to a granulation pan. The zeolite 3A powder was acquired
from CU Chemie Uetikon 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.
TABLE 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 50%
r.h. [%] 20.1 21.3 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
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.
TABLE 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
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.
TABLE 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%
Conventional According to Invention Dense Attapulgite (10% Highly
Dispersed 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
The same preparation procedure was used as in Example 6 except
that zeolite 4A powder acquired from CU Chemie Uetikon 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%.
TABLE 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%
Conventional According to Invention Dense Attapulgite (15% Highly
Dispersed Binder) Attapulgite Clay) Bead Size [mm] 2-3 2-3 Crush
Strength [N] 57 41 Attrition [%] 0.03 0.01 Bulk Density [g/l] 729
710 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
A premixed zeolite 13X powder/organic additive/clay composition
was added continuously to a granulation pan. The 13X zeolite powder
was acquired from CU Chemie Uetikon 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.
TABLE 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]
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.
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. |