U.S. patent application number 10/236778 was filed with the patent office on 2003-06-19 for polymer-bound nitrogen adsorbent.
Invention is credited to Chang, Chin-Hsiung, Gaita, Romulus, Yates, Stephen Frederic, Zhou, Shaojun James.
Application Number | 20030110948 10/236778 |
Document ID | / |
Family ID | 24448992 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030110948 |
Kind Code |
A1 |
Gaita, Romulus ; et
al. |
June 19, 2003 |
Polymer-bound nitrogen adsorbent
Abstract
A method of making a gas adsorbent comprises dissolving a
polymer in one or more first solvents to form a polymer solution;
mixing an inorganic adsorbent with the polymer solution to form a
precursor; molding the precursor; and leaching the first solvents
from the precursor with a second solvent.
Inventors: |
Gaita, Romulus; (Morton
Grove, IL) ; Yates, Stephen Frederic; (Arlington
Heights, IL) ; Zhou, Shaojun James; (Palatine,
IL) ; Chang, Chin-Hsiung; (Palatine, IL) |
Correspondence
Address: |
Honeywell International, Inc.
Law Department-M/S 36-2-0300
2525 West 190th Street
Torrance
CA
90504-6099
US
|
Family ID: |
24448992 |
Appl. No.: |
10/236778 |
Filed: |
September 6, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10236778 |
Sep 6, 2002 |
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09611432 |
Jul 7, 2000 |
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6451723 |
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Current U.S.
Class: |
96/108 ; 502/62;
96/153 |
Current CPC
Class: |
B01D 53/02 20130101;
B01J 20/28042 20130101; B01J 20/30 20130101; B01J 20/2808 20130101;
B01D 2257/102 20130101; B01J 20/183 20130101 |
Class at
Publication: |
96/108 ; 96/153;
502/62 |
International
Class: |
B01D 053/02 |
Claims
We claim:
1. A method of making a gas adsorbent, comprising: forming a
polymer solution; mixing an inorganic adsorbent with said polymer
solution to form a precursor; shaping said precursor; and leaching
said precursor.
2. The method of claim 1, wherein the step of forming comprises
dissolving a polymer in at least one first solvent.
3. The method of claim 1, wherein said inorganic adsorbent is
selected from the group consisting of a zeolite, activated alumina,
silica gel, carbon adsorbents and mixtures thereof.
4. The method of claim 1, wherein said precursor is in the form of
a dough or paste.
5. The method of claim 1, wherein the step of shaping comprises
molding said precursor.
6. The method of claim 1, wherein the step of leaching comprises
dissolving at least one first solvent in said precursor with at
least one second solvent.
7. A method of making a gas adsorbent, comprising: dissolving a
polymer in at least one first solvent to form a polymer solution;
mixing an inorganic adsorbent with said polymer solution to form a
precursor; molding said precursor; and leaching said at least one
first solvent from said precursor.
8. The method of claim 7, further comprising heating said precursor
to a temperature sufficient to substantially remove a second
solvent used in said leaching step, said heating step occurring
after the step of leaching.
9. The method of claim 7, further comprising creating micropores in
said precursor.
10. The method of claim 7, further comprising drying said precursor
after the step of leaching.
11. The method of claim 7, wherein said polymer solution is
characterized by an absence of said polymer suspended in said first
solvent.
12. The method of claim 7, wherein said polymer is selected from
the group consisting of polysulfone, polyamide, polyimide, epoxy,
polyolefin, polyether, polysiloxane, polyvinyl and polyketone.
13. The method of claim 7, wherein said at least one first solvent
is selected from the group consisting of N,N-dimethylformamide
(DMF) dimethyl sulfoxide (DMSO), acetone, 1,4-dioxane, methyl
cellosolve, pyridine and mixtures thereof.
14. The method of claim 7, wherein said polymer and at least one
first solvent are present in said polymer solution in a ratio
between about 1:5 and 1:10 by weight.
15. The method of claim 7, wherein said polymer and inorganic
adsorbent are present in said precursor in a ratio between about
40:60 and 5:95 by weight.
16. The method of claim 7, wherein the step of molding produces a
shaped precursor selected from the group consisting of droplets,
extrudates, discs, spiral wound modules, and hollow fibers.
17. The method of claim 7, wherein the step of leaching comprises
dissolving said at least one first solvent with a second
solvent.
18. The method of claim 17, wherein said second solvent is selected
from the group consisting of ethanol, methanol, water, and mixtures
thereof.
19. The method of claim 7, wherein said gas comprises nitrogen.
20. A gas adsorbent system, comprising: a housing; a molded gas
adsorbent disposed within said housing such that said gas adsorbent
is prevented from shifting within said housing in the absence of a
component that adheres said gas adsorbent to said housing, said gas
adsorbent having been formed from a polymer solution.
21. The system of claim 20, wherein said gas adsorbent
substantially completely fills said housing.
22. The system of claim 21, wherein said gas adsorbent comprises an
inorganic adsorbent and a polymeric membrane on a surface of said
inorganic adsorbent.
23. The system of claim 22, wherein said inorganic adsorbent is
selected from the group consisting of a zeolite, activated alumina,
silica gel, carbon and mixtures thereof.
24. The system of claim 22, wherein said polymeric membrane
comprises a polymer selected from the group consisting of
polysulfone, polyamide, polyimide, epoxy, polyolefin, polyether,
polysiloxane, polyvinyl and polyketone.
25. A gas adsorbent system, comprising: a housing; a molded gas
adsorbent within and substantially completely filling said housing
such that said gas adsorbent is prevented from shifting within said
housing in the absence of a component that adheres said gas
adsorbent to said housing, said gas adsorbent having been formed
from a polymer solution and an inorganic adsorbent.
26. The system of claim 25, wherein said housing is in the form of
a cylinder.
27. The system of claim 25, wherein said inorganic adsorbent
comprises activated zeolite 13X.
28. The system of claim 27, wherein said polymer solution comprises
polysulfone.
29. The system of claim 28, wherein said polysulfone and activated
zeolite 13X are present in a ratio of about 10:90 by weight.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to gas adsorption
and, more particularly, to an apparatus and method of selectively
adsorbing nitrogen over oxygen from a gas mixture.
[0002] The separation of gases, including nitrogen from oxygen, can
be useful in a wide variety of environments. As an example,
separating nitrogen from air for use in a cockpit of an aircraft
continues to be problematic. Of course, an inefficient means of
oxygen supply can impact the performance of the pilot. It can also
translate to higher maintenance costs for the separation system.
Many attempts to design gas separation systems have been made.
[0003] For example, a process for separating mixtures of oxygen and
nitrogen by the use of an adsorbent is shown in U.S. Pat. No.
5,672,195. Therein, it is explained that zeolites have been used
selectively to separate nitrogen from oxygen based on the strong
interactions between the quadrupole moment of the nitrogen molecule
and the cations of the zeolite. It was further noted that varying
the temperature and pressure has also been used to optimize the
nitrogen adsorption and desorption efficiency. The invention
employed zeolites that were agglomerated preferably.with an
inorganic binder and formed into spheres. The porosity of the
adsorbent was optimized to accelerate the adsorption kinetics. Some
drawbacks to this design include loss of capacity due to dilution
by the binder and, particularly, the generation of dust particles
due to attrition of the binder and movement of adsorbent
particles.
[0004] In U.S. Pat. No. 4,687,573, a sorbing apparatus for removing
one or more components from a gas or liquid fluid is disclosed. The
sorbing apparatus includes a chamber having a bed of sorbent
particles bound together by a polymeric binding agent and/or bound
to the chamber to prevent movement of the particles relative to one
another. The chamber includes ports to allow an inflow and outflow
of a fluid having the components to be removed, as well as a fluid
used to purge the components. The process of making the bed of
sorbent particles includes preheating inorganic sorbent particles
and mixing the heated particles with a powdered polymeric binding
agent. The mixture of particles and binding agent is placed under
pressure at a solid-liquid transition temperature and then cooled.
Optionally, the mixing and application of pressure may be done in a
mold to provide a desired shape. Some disadvantages, however, to
the above include the fact that the process is difficult to
control.
[0005] Latex polymer bonded crystalline molecular sieves in an
aqueous medium are shown in U.S. Pat. No. 4,822,492. It is pointed
out therein that zeolites bonded to inorganic oxides deteriorate in
aqueous media. However, the use of organic polymer binders in lieu
of inorganic polymer binders has alleviated such problems. Yet, the
use of an organic solvent at a high level has decreased the
adsorptive capacity. Thus, the invention used latex in place of the
organic polymer binder. The latex was generally a suspension of
polymer particles in water. A crystalline inorganic compound, such
as a zeolite, is mixed into the latex. An optional inorganic oxide
binder was used. The resulting mixture was dried to remove water
and then ground. Disadvantages with this disclosure include dust
formation.
[0006] Currently Honeywell Normalair-Garrett Limited of England
markets a generic Onboard Oxygen Generation System (OBOGS) based on
the selective adsorption of nitrogen from air. This system consists
of a pressure swing adsorption unit in which air is fed into the
first of three cartridges at an elevated pressure. The first
cartridge contains an inorganic adsorbent that is selective for
nitrogen over oxygen. The adsorbent can be clay bound activated
zeolite 13X (HP-13X). The nitrogen is thereby removed from the air,
providing oxygen-enriched air for use in an aircraft. Periodically,
the cartridge in use as a nitrogen adsorbent is changed, the
pressure on the first cartridge is reduced, thereby allowing the
adsorbed nitrogen to be desorbed. However, the capacity of the
adsorbent mass within the cartridge is highly variable and the
performance of each cartridge also varies.
[0007] As can be seen, there is a need for an improved apparatus
for and method of separating nitrogen from air. Also needed is an
apparatus and method that has a high capacity and reliability for
nitrogen adsorption. A further need is for a method of making a
nitrogen adsorbent that is simple and low in cost. A nitrogen
adsorbent apparatus is also needed and that can be utilized in the
form of a cartridge that allows easy use and replacement, while
minimizing shifting of the adsorbent material within the cartridge
due to vibration or other shocks. The cartridge should also provide
good mass transfer kinetics and withstand heating up to about
200.degree. C.
SUMMARY OF THE INVENTION
[0008] In one aspect of the present invention, a method of making a
gas adsorbent comprises dissolving a polymer in at least one first
solvent to form a polymer solution; mixing an inorganic adsorbent
with the polymer solution to form a precursor; molding the
precursor; and leaching the at least one first solvent from the
precursor.
[0009] In another aspect of the present invention, a gas adsorbent
system comprises a housing; and a molded gas adsorbent within and
substantially completely filling the housing such that the gas
adsorbent is prevented from shifting within the housing in the
absence of a component that adheres the gas adsorbent to the
housing, with the gas adsorbent having been formed from a polymer
solution and an inorganic adsorbent.
[0010] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following drawings, description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a flow chart depicting one embodiment of a method
of making a gas adsorbent according to the present invention;
[0012] FIG. 2 is a perspective view of an embodiment of a gas
adsorbent system according to the present invention;
[0013] FIG. 3 is a graph of nitrogen gas loading versus nitrogen
gas partial pressure for gas adsorbents made according to an
embodiment of the present invention;
[0014] FIG. 4 is a graph of nitrogen gas loading versus nitrogen
gas partial pressure for gas adsorbents made according to an
embodiment of the present invention with varying heat treatment
periods;
[0015] FIG. 5 is a graph of nitrogen capacity versus treatment time
for a gas adsorbent according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Although the present invention can be particularly useful in
the context of an onboard oxygen generation system of an aircraft,
the present invention is not so limited. The apparatus and method
of the present invention may be generally practiced in the chemical
or gas processing contexts.
[0017] In describing a method of making a gas adsorbent in
accordance with one embodiment of the present invention, FIG. 1
depicts the acts or steps of such method. A polymer solution is
formed by a dissolving step 11 in which a polymer is dissolved in
one or more first solvents. The polymer is selected based on its
good mechanical strength at operating temperatures between
25.degree. C. and 200.degree. C., combined with a softening
temperature higher than the latter temperature but below the
decomposition temperature of the inorganic adsorbent described
below. The reference to "softening temperature" is intended to
refer to the temperature at which the polymer will yield or flow in
response to an applied force, while "decomposition temperature is
intended to refer to the temperature at which irreversible chemical
changes occur in the polymer. The polymer must also wet the
inorganic adsorbent and show good adhesion to the adsorbent. Thus,
the specific polymer used can vary. Examples of useful polymers
include polysulfone, polyamide, polyimide, epoxy, polyolefin,
polyether, polysiloxane, polyvinyl and polyketone. Preferably,
polysulfone is the polymer as a result of its good mechanical
strength over the required temperature range. Optionally, the
polymer is combined with a crosslinking or hardening agent that is
activated on heating, while in other cases, no such crosslinking
agent is necessary. Where used, the crosslinking agent must be
chosen with the choice of polymer in mind, since it is well known
to those skilled in the art that certain crosslinkers are used with
certain polymers. Thus, for example, various polyfunctional organic
amines are frequently used to crosslink epoxy polymers, and diols
or polyols are used to crosslink polymeric siloxanes.
[0018] The first solvent(s) is chosen on its ability to dissolve
the selected polymer at near room temperature to the desired final
concentration. It must also be fully miscible with a second solvent
described below, and be easy to handle. It will be understood by
those skilled in the art that different polymers are soluble in
different solvents, so that the choice of solvent is necessarily
dependent on the choice of polymer. For the above polymers, the
first solvent(s) can include N,N-dimethylformamide (DMF); dimethyl
sulfoxide (DMSO); acetone; 1,4-dioxane; methyl cellosolve; pyridine
and mixtures thereof, as examples. N,N-dimethylformamide is
preferred because of the high solubility of polysulfone in this
solvent, and its lack of undesirable health, safety or
environmental characteristics. While the ratio of polymer to first
solvent(s) can likewise vary, a preferred ratio is between about
1:5 and 1:10 by weight and, more preferably about 1:5.5 by weight.
Above about 1:5, the polymer may not be entirely dissolved, or may
have a very high viscosity, while below about 1:10, the viscosity
of the precursor paste described below and generated after addition
of the inorganic adsorbent will be too low, causing handling
problems.
[0019] Thereafter, a mixing step 12 includes mixing an inorganic
adsorbent into the polymer solution to form a precursor. The
inorganic adsorbent is chosen based on its ability to adsorb a
selected element, such as nitrogen, from a gas mixture. In the case
of adsorbing nitrogen, the inorganic adsorbent can include zeolite,
activated alumina, silica gel, carbon molecular sieves and mixtures
thereof. While various zeolites can be useful, activated zeolite
13X is preferred due to its capability for selectively adsorbing
nitrogen from air. The term "activated zeolite 13X" generally
refers to an activated form of 13X (HP-13X, 13-HP) and which is
described in UOP Material Safety Data Sheet dated February 1997,
published by UOP Inc. and which is incorporated herein by
reference. As an example, activated zeolite 13X is manufactured by
UOP Inc. under the tradename OXYSIV.TM. 5 (Oxy-5).
[0020] The polymer is mixed with the inorganic adsorbent in a ratio
that is high enough (after the first solvent is removed as
described below) to provide good mechanical strength but no more
than enough for such strength since the inorganic adsorbent is the
active ingredient. Thus, the ratio of polymer to inorganic
adsorbent is preferably between about 40:60 and 5:95 by weight.
Above about 40:60, the final concentration of polymer in the
product will be too high, resulting in a reduction in gravimetric
capacity, and poorer mass transfer kinetics, while below about 5:95
the final product will be too weak mechanically. More preferably,
the ratio is about 10 to 90 by weight.
[0021] From the mixing step 12, a precursor is formed having the
consistency of a paste or dough. Such consistency is the result of
good mixing and the wetting of the inorganic adsorbent by the
polymer and the first solvent. The viscosity of this dough can be
adjusted by varying the amount of the first solvent used in the
dissolution step 11 described above. The optimal viscosity will
depend on the choice of shaping method below.
[0022] With the precursor in the consistency of a paste or dough,
the precursor can then undergo a shaping step 13. The shaping step
13 can include molding the precursor into various shapes in order
to compactly fit the produced gas adsorbent into a housing
cartridge described below. The molded precursor can be of various
shapes, such as droplets, extrudates, discs, spiral wound modules,
and hollow fibers.
[0023] The droplets can be formed by dripping the precursor into a
stirred vessel containing one or more second solvents described
below. As each droplet hits the surface of the second solvent(s),
it forms a surface skin sufficient to prevent it coalescing with
neighboring droplets. The suspension of droplets is kept at room
temperature with occasional stirring until the droplets are
hard.
[0024] To form the extrudates, the precursor is extruded through a
circular die and into a vessel containing one or more second
solvents described below. This generates long strings of
polymer/adsorbent, which after hardening can be chopped into a
convenient size.
[0025] For the disc shapes, the precursor is spread thinly on a
mesh support. The mesh support may be of any suitable material that
can tolerate temperatures up to about 200.degree. C. The resulting
sheets are then immersed in one or more second solvents described
below to harden the sheets. After hardening, the sheets are cut
into disks that may also contain holes to regulate the flow rate
through the disks. The holes can be formed by imperfect coating of
the precursor on the mesh support or by piercing the coating after
it has dried.
[0026] The spiral wound modules are made by the precursor being
spread thinly on a mesh support to form sheets as above. However,
instead of cutting the sheets into disks, the sheets are rolled
around a porous metal hollow rod to form a cylinder. A spacer made
of any porous material that tolerates the temperatures in the
process (e.g., metals or plastics) may optionally be rolled up with
the sheet to improve mass transfer. The ends of the cylinder are
sealed with a suitable material such as epoxy to ensure that at one
end of the cylinder, the flow can only pass through the central
rod, while at the other end, the flow can only come from the sides
of the rolled cylinder. Optionally, as above, the modules can be
formed with holes. With the hollow fibers, the precursor is
extruded through a die to generate hollow fibers or tubes. The
fibers should be extruded into one or more second solvents
described below to harden the fibers from the outside, as well as
flow the second solvent(s) into the center of the fibers to harden
them from the inside. Once hardened, the fibers are cut to a
desired length and bundled. The ends of the fibers are sealed so
that at one end the flow is to the interiors of the fibers, while
at the other ends, the flow is from the space between the
fibers.
[0027] After the shaping step 13, the shaped precursor undergoes a
leaching step 14. In such step 14, the first solvent(s) is
dissolved or leached from the shaped precursor by one or more
second solvents. The act of leaching generates porosity in the
shaped precursor preferably on the order of about 0.01 to 20
microns and, more preferably, about 10 microns. The resulting
porosity in the shaped precursor enhances the mass transfer of air
to the gas adsorbent sites. Although the second solvent(s) readily
dissolves the first solvent(s), the second solvent(s) is a
non-solvent to the polymer. It is also desirable that the second
solvent(s) be somewhat volatile, non-toxic, and non-viscous.
Accordingly, the second solvent(s) can include ethanol, methanol,
water, and mixtures thereof, as examples.
[0028] Following the leaching of the first solvent(s), an initial
drying step 15 includes drying the shaped precursor in air at room
temperature. The extent of drying is such that the shaped precursor
is non-tacky and easy to handle. Next, the dried, shaped precursor
undergoes a further drying step 16 wherein the precursor is heated
at a temperature (and optionally under vacuum) in order to
substantially remove the second solvent by evaporation. What is
meant by "substantially remove" is that the remaining content of
volatile material is less than about 25% by weight
[0029] Next, the dried and shaped precursor (or gas adsorbent) can
be placed into a housing or cartridge in a filling step 17. By such
filling step 17, the gas adsorbent substantially completely fills
the housing whereby the gas adsorbent is prevented from shifting
within the housing in the absence of a component that adheres the
gas adsorbent to the housing. The term substantially completely
fills" means and refers to essentially filling the entirety of the
housing such that the total void space between the gas adsorbents
themselves as well as between the gas adsorbents and the housing is
about 10 to 30%. Optionally, the gas adsorbent may be loaded into
the housing under pressure to ensure maximum loading of the
adsorbent in the housing. Where the adsorbent has been shaped into
droplets or chopped extrudates, it is important that the packed
density of the adsorbent be between 0.50 and 0.65 g/mL in order to
ensure that, after step 18, there is effective adhesion between the
droplets or extrudates.
[0030] After the filling step 17, the housing filled with the
shaped precursor undergoes a heating step 18 near or above the
softening temperature of the polymer in an inert gas to ensure
immobilization of the gas adsorbent in the cartridge such that the
gas adsorbent substantially completely fills the housing. The
adsorbent is accordingly prevented from shifting within the housing
in the absence of a component that adheres the gas adsorbent to the
housing. The heating step 18 also creates a maximum degree of
porosity, namely, about 30 to 40%. The porosity is needed to enable
a flow of gas to pass through the gas adsorbent.
[0031] For the heating step 18 in inert gas, it is preferred to use
hot inert gas. External heating of the loaded cartridge or module
is not as effective. A temperature gradient from the module wall to
the middle of the module tends to cause uneven treatment of all
adsorbent or extrudate material. It is important to create porosity
with the passing of the hot gas when the precursor is softened and
the extrudates are immobilized. On the other hand, the softening of
the precursor may plug the entrance to the micropores of the
inorganic adsorbent. Therefore, during the heat treatment 18,
diffusion of gaseous molecules in and out of the micropores is
important to establishing and maintaining microporosity of the
final shaped adsorbent.
[0032] The different shapes of precursors mentioned above lend
themselves to different methods of filling the gas adsorbent in the
housing or cartridge. For example, in the case of precursor
droplets, and after the leaching step 14, the droplets can be
placed in the housing and then formed into a single mass. This can
be accomplished by (1) adding a binder, such as epoxy, to the
droplets, (2) heating the mass under pressure to a temperature near
or above the softening temperature of the polymer, or (3) adding
again the first solvent to make the droplets sticky and then
evaporating the first solvent. With the hollow fibers, the hardened
fibers can be bundled and packed in the cartridge. Once bundled and
packed, the fibers can be sealed as described above.
[0033] FIG. 2 schematically depicts a gas adsorbent system
comprising one or more housings 19 filled with a gas adsorbent 20
that is characterized by a polymeric membrane on a surface of an
inorganic adsorbent. In this embodiment, the gas adsorbent is in
the shape of extrudates. The system may also include valves 21 on
either sides of the housings 19 to enable a flow of gas into and
out of the housings 19.
EXAMPLE 1
[0034] 493.75 grams of UOP, Inc. 13X zeolite powder were mixed with
400.8 gram of a N,N-dimethylformamide (DMF) solution containing
15.4 wt. % of polysulfone. To this mixture, 230 grams of DMF were
added to make a precursor dough in an automatic mixer. The dough
was extruded through an air-driven extruder into a 5-gallon bucket
of de-ionized water.
[0035] The extruded material was kept in water for 3 hours and
removed for air drying at 25.degree. C. After 31/2 hours, 1108.1
grams of material were obtained. The extruded material was then
heated at 120.degree. C. in a vacuum oven (70 torr) for 16 hours. A
final weight of 566.75 grams was obtained.
EXAMPLES 2-4
[0036] Following the general procedure of Example 1, various
amounts of mixtures were used to prepare extruded materials with
UOP 13X, polysulfone, and DMF. Table 1 summarizes results of
Examples 1-4.
1 TABLE 1 Ex- Ex- Ex- Ex- ample ample ample ample 1 2 3 4 13X
zeolite, grams 493.75 519.01 530.34 493.82 15.4% polysulfone in
DMF, grams 400.8 400.2 400.8 401.1 DMF, grams 230.0 215.1 220.0
232.0 13X in the final extrudate, wt. % 88.9 89.4 89.6 88.9
Expected N.sub.2 capacity at 800 torr, 0.391 0.393 0.394 0.391
mmole/g Extrudate after air dry, grams 1036.7 940.1 1006.6 1032.05
Extrudate after vacuum drying, 566.75 598.05 598.25 623.00 grams
Weight loss during static capacity 18.92 19.85 19.40 22.05
measurement, % Static N.sub.2 capacity at 800 torr, 0.37 0.34 0.38
0.37 mmole/g
[0037] The static performance of the polymer bound extrudates
prepared as illustrated in Examples 1-4 was evaluated by measuring
the adsorption capacity of the adsorbent material for nitrogen with
a Micromeritics ASAP2000 instrument (Micromeritics Instrument
Corporation, Norcross, Ga.). An extrudate sample of 0.4 grams was
heated at 210C under vacuum (4 micrometer Hg) for about 40 hours.
During the heat treatment, chemical species adsorbed by the
adsorbent were desorbed from the adsorbent material. The sample was
then exposed to a controlled addition of nitrogen at 25.degree. C.
Nitrogen gas pressure was monitored until a constant pressure was
measured. The difference between the amount of nitrogen introduced
and the gas remaining in the gas phase determined the capacity of
the adsorbent at the gas pressure. A series of loading capacities
for different gas pressures at a constant temperature of 25.degree.
C. thus represented the static nitrogen isotherm on the
polymer-bound adsorbent. The same isotherm was also obtained for
the 13X zeolite used for the adsorbent preparation.
[0038] Results of the static isotherm measurement are illustrated
in FIG. 3. The N.sub.2 capacity value at 800 mmHg is listed in
Table 1 along with the percent weight loss measured during the
vacuum heat-treatment. With a N.sub.2 capacity of 0.44 mmole/g for
13X zeolite powder and by knowing the composition of the extrudate,
one can calculate the expected N.sub.2 capacity for the extrudate
by multiplying 0.44 mmole/g by the weight percent of 13X in the
bound adsorbent. Except for the adsorbent material in Example 2,
measured capacities are in good agreement with those
calculated.
EXAMPLE 5
[0039] Following the general procedure of Example 1, 127.95 grams
of UOP 13X zeolite were mixed with 106.5 grams of a DMF solution
containing 15.4% of polysulfone. 39.15 grams of DMF were added to
the mixture to make a precursor dough. The dough was extruded into
a second solvent of methanol (500 grams). After 25 minutes, the
first methanol was discarded and another 500 grams of methanol were
added. After additional 60 minutes, the methanol was decanted.
Extrudates recovered from the methanol solution were heated at
100.degree. C. under vacuum for 15 hours.
[0040] 35.16 grams of the dry extrudate were pressed into a
stainless steel tube with a 2.8-cm diameter and a length of 10.2
cm. The packed tube was inserted into a hot-gas treatment
apparatus. A stream of dry nitrogen was pre-heated by a gas heater
to 230.degree. C. and introduced to the packed tube at a flow rate
of 3.0 liters/min. The packed tube was also heated at 210.degree.
C. by a heating tape. The exit gas temperature, the inlet gas
temperature, and the heating tape temperature were continuously
monitored. After about one hour, heating was stopped and the
immobilized adsorbent was cooled down in the flow of nitrogen. The
final weight was measured to be 30.49 gram.
[0041] The immobilized adsorbent with the stainless steel tube was
removed from the hot-gas treatment apparatus and inserted into a
dynamic test unit (described below for Example 6) for
evaluation.
EXAMPLES 6-9
[0042] Extrudate materials prepared with the general procedure of
Example 1 were packed and hot-gas treated as described in Example
5. This immobilized module was inserted into a dynamic test unit
for evaluation. This test unit has a cross section area of 6.16
cm.sup.2 and a total volume of 62.56 cm.sup.3. The unit was first
tested with a similar module packed with glass beads of 3 mm
diameter (86.08 grams). A washout test was conducted to measure the
total system void space at a nitrogen flow rate of 2450
cm.sup.3/min. Subsequently, a module packed with the clay-bound
beads of 13X (Oxy-5) was tested for comparison with modules
prepared with the present method.
[0043] The washout test was conducted by first heating the test
tube with a heating tape to 210.degree. C. in a constant flow of
dry nitrogen for a period of 8 hours. After cooling, the weight of
the total test module and the net weight of the adsorbent material
were determined. A constant flow of pure oxygen at 25.degree. C.
was introduced into the test cell while the effluent gas was
continuously monitored by an oxygen sensor. At a constant effluent
concentration of 100% oxygen, the inlet gas was switched
electronically to pure nitrogen. Effluent gas concentrations were
recorded by a desktop computer. The total amount of nitrogen
integrated until the complete breakthrough of nitrogen in the
effluent represented the amount of nitrogen required to fill the
total void of the test unit and the amount that was adsorbed in the
adsorbent under the dynamic condition. By subtracting the void
volume obtained by the glass bead measurement, the dynamic capacity
of the adsorbent material can be calculated.
[0044] Results of testing on several materials prepared in Examples
5-9 are summarized in Table 2. These results show that by applying
the present invention, substantial improvement in the dynamic
capacity for N.sub.2 on the per weight basis can be achieved.
Similar volumetric efficiencies can be obtained at a lower pressure
drop. The 13X zeolite is bound and immobilized with an organic
binder that resists dissolution in water. Therefore, the bound
adsorbent is stable to the attrition and water attack.
[0045] While the examples used here are for the development of an
oxygen generating adsorbent, the process can be for any adsorbents
that require low pressure drop and high resistance to attrition and
water damage.
2 TABLE 2 Oxy-5 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 13X, grams 127.9
127.9 63.97 127.95 3086 15.4% polysulfone in DMF, grams 106.5 106.5
53.25 106.50 2571 DMF, grams 39.2 39.2 19.57 42.30 1056 Second
solvent MeOH MeOH H.sub.2O H.sub.2O H.sub.2O 13X in the final
extrudate, wt. % 88.6 88.6 88.6 88.6 88.6 Extrudate, mm 1.2 1.2 1.2
1.2 1.2 Hot gas temperature, .degree. C. 210 200 200 200 210 Hot
gas flow rate, liter/min 3.0 3.5 3.5 3.5 3.7 Hot gas pressure, psi
4.6 Hot gas treatment time, min. 57 57 42 50 50 Weight loss during
hot-gas treatment, % 13.3 10.4 26.0 Final packing density,
g/cm.sup.3 0.628 0.487 0.507 0.477 0.458 0.509 N.sub.2 capacity,
mmole/g 0.237 0.250 0.231 0.257 0.303 0.306 N.sub.2 capacity,
mmole/cm.sup.3 0.149 0.122 0.117 0.123 0.139 0.156 Pressure drop,
psi 0.34 0.82 0.26 0.20 0.14 0.36
EXAMPLE 10
[0046] Extrudate materials were prepared following the general
procedure of Example 1. The polymer-bound material was heated and
tested for its equilibrium nitrogen capacity in the ASAP2000
instrument following the general procedure of Example 5. After
16.0, 41.0 and 45.8 hours, nitrogen isotherms were taken as shown
in FIG. 4 and Table 3.
3 TABLE 3 Extrudate Example 10 Heat treatment temp. (.degree. C.)
210 210 210 Total treatment time (hr) 16.0 41.0 45.8 Weight loss
(%) 17.96 18.92 19.40 N.sub.2 capacity @ 800 mmHg 0.345 0.375 0.380
(mmole/g)
[0047] These data show that at 210.degree. C. the polymer-bound
extrudate requires a minimum of about 40 hours to be fully
activated for the adsorption of nitrogen. Extrudates prepared in
this example were packed in a full size module for the enrichment
of oxygen in air. The module had a cross section area of 88.25 cm
2, a length of 11.5 cm and a volume of 1015 cm.sup.3. 710 grams of
the extrudate were packed into the adsorbent module under pressure
in five portions. Two metal filters were placed on both ends of the
module.
[0048] FIG. 4 shows the effect of heat-treatment at 210C on N.sub.2
isotherms for polymer-bound extrudate prepared according to Example
1. The packed module was installed into a hot-gas treatment
apparatus similar to that used in Example 5. A stream of dry
nitrogen was pre-heated by a gas heater to 235.degree. C. and
introduced to the packed module at a flow of 56.6 liters/min. The
packed module was also heated externally by two heating tapes. The
inlet gas temperature, exit gas temperature, heating tape
temperatures, gas flow rate and pressure were continuously
monitored. After a hot gas treatment duration, the module was
cooled down to room temperature. The weight of the extrudate was
measured. A dynamic washout test was conducted following the
general procedure of Examples 6-9. A washout time was also measured
from the introduction of nitrogen to the time that the effluent
nitrogen reached 63%.
[0049] Results of the hot-gas treatment are summarized in Table 4
and FIG. 5. As shown in FIG. 5, data are somewhat scattered.
However, the trends are that the activation of the immobilized
module also requires more than 40 hours.
4TABLE 4 Sample Immobilized module (Example 10) Exit gas temp.
(.degree. C.) 175 172 176 182 177 Treatment duration (hr) 4 16.5
9.5 8 7 Total treatment time (hr) 4 20.5 30 38 45 Adsorbent weight
(g) 578.12 575.08 575.08 575.30 574.50 Weight loss (%) 18.57 19.00
19.00 18.97 19.08 Dynamic N.sub.2 capacity 10769.5 11460.7 11500.6
12300.6 12006.6 (cm.sup.3) Washout time (sec.) 21.6 23.0 23.1 24.8
24.2
EXAMPLE 11
[0050] Following the general procedure of Example 10, a full-size
module was prepared using 581.3 grams of polysulfone-bound 13X
extrudates synthesized with the general procedure described in
Example 1. Results of hot gas activation are summarized in Table
5.
5TABLE 5 Sample Immobilized module (Example 11) Exit gas temp.
(.degree. C.) 166 190 171 Treatment duration (hr) 5.5 14.25 10.00
Total treatment time (hr) 5.5 19.75 29.75 Adsorbent weight (g)
476.93 475.89 475.47 Weight loss (%) 17.95 18.13 18.20 Dynamic
N.sub.2 capacity (cm.sup.3) 10399.0 10635.8 10802.2 Washout time
(sec.) 21.3 22.0 22.3
[0051] As can be appreciated by those skilled in the art, the
present invention provides an improved apparatus for and method of
separating nitrogen from air. Also provided is an apparatus and
method that has a high capacity and reliability for nitrogen
adsorption. The present invention for a method of making a nitrogen
adsorbent is simple and low in cost. The nitrogen adsorbent
apparatus can be utilized in the form of a cartridge that allows
easy use and replacement, while minimizing shifting of the
adsorbent material within the cartridge due to vibration or other
shocks. The cartridge also provides good mass transfer kinetics and
withstands heating up to about 200.degree. C.
[0052] It should be understood, of course, that the foregoing
relates to preferred embodiments of the invention and that
modifications may be made without departing from the spirit and
scope of the invention as set forth in the following claims.
* * * * *