TITLE: Multicomponent membranes
United States Patent 4737165

ABSTRACT:
A multicomponent membrane which may be used for separating various
components which are present in a fluid feed mixture comprises a
mixture of a plasticizer such as a glycol and an organic polymer cast
upon a porous organic polymer support. The membrane may be prepared by
casting an emulsion or a solution of the plasticizer and polymer on the
porous support, evaporating the solvent and recovering the membrane
after curing.

INVENTORS:
Kulprathipanja, Santi (Hoffman Estates, IL)
Kulkarni, Sudhir S. (Hoffman Estates, IL)
Funk, Edward W. (Highland Park, IL)

APPLICATION NUMBER: 06/727163
PUBLICATION DATE: 04/12/1988
FILING DATE: 04/25/1985

ASSIGNEE: UOP Inc. (Des Plaines, IL)
PRIMARY CLASS: 95/51
OTHER CLASSES: 96/12, 96/13, 210/490
INTERNATIONAL CLASSES: B01D59/14; B01D67/00; B01D69/12; B01D69/14; B01D71/70; (IPC1-7):
B01D59/14
FIELD OF SEARCH: 264/41, 210/490, 210/491, 210/500.2, 210/500.27, 210/650, 210/651,
210/654, 55/16, 55/158

US PATENT REFERENCES:
4519909 Microporous products May, 1985 Castro 210/500.27
4454085 Process for producing asymmetrical hollow filament membranes of
polyamide June, 1984 Schindler et al. 264/41
4230463 Multicomponent membranes for gas separations October, 1980 Henn
et al. 55/16
3532527 PERMEABLE SEPARATORY MEMBRANES October, 1970 Skiens 106/176
2673825 Process of manufacturing vapor permeable fluid repellent
fabrics March, 1964 Biefeld et al. 154/128

PRIMARY EXAMINER: Spear, Frank
Attorney, Agent or Firm:
Mcbride, Thomas K.
Spears Jr., John F.
Nelson, Raymond H.
Parent Case Data:
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of our copending application
Ser. No. 550,667 filed Nov. 10, 1983, now abandoned, all teachings of
which are incorporated herein by reference thereto.

CLAIMS:
What is claimed is:
1. A multicomponent membrane useable for the separation of components
of a fluid feed mixture comprising a mixture of a glycol plasticizer
having a molecular weight of from about 200 to about 600 and an organic
polymer comprised of silicone rubber cast on a porous polymeric
support, said porous polymeric support having a ratio of total surface
area to total pore cross-sectional area of from 5:1 to 900:1 and said
membrane comprising from 5 to 50 wt. % of said glycol plasticizer.
2. The multicomponent membrane as set forth in claim 1 in which said
glycol plasticizer possesses a high boiling point and a low partial
pressure, said glycol plasticizer being uniformly dispersed as an
emulsion in said organic polymer or in homogeneous phase as a solution
with said organic polymer.
3. The multicomponent membrane as set forth in claim 1 in which said
porous support comprises polysulfone.
4. The multicomponent membrane as set forth in claim 1 in which said
porous support comprises cellulose acetate.
5. The method as set forth in claim 4 in which said casting is effected
by pouring or spreading said emulsion or solution on said porous
support.
6. The multicomponent membrane as set forth in claim 1 wherein said
glycol plasticizer is present in an amount of from 20 to 50 wt. %.
7. A method for the maanufacture of a multicomponent membrane
comprising a glycol plasticizer having a molecular weight of from about
200 to about 600 and an organic polymer comprised of silicone rubber on
a porous polymeric support which comprises: (a) forming an emulsion or
a solution of said glycol plasticizer with said organic polymer in a
suitable solvent; (b) casting said emulsion or solution on said porous
support to form a multicomponent membrane, said support having a ratio
of total surface area to total pore cross-sectional area of from 5:1 to
900:1; and (c) curing said membrane at an elevated temperature for a
time sufficient to evaporate substantially all of said solvent, said
glycol plasticizer being present in said emulsion or solution in an
amount sufficient to yield a membrane comprised of from 5 to 50 wt. %
of said glycol plasticizer upon curing of said membrane.
8. The method as set forth in claim 7 in which said porous support
comprises polysulfone.
9. The method as set forth in claim 7 in which said porous support
comprises cellulose acetate.
10. The method as set forth in claim 7 in which said suitable solvent
comprises trifluorotrichloroethane which is liquid at standard
temperatures and pressures.
11. The method as set forth in claim 7 in which said emulsion or
solution is degassed prior to casting by exposure of said emulsion or
solution to at least a partial vacuum.
12. The method as set forth in claim 7 wherein said glycol plasticizer
is present in an amount of from 20 to 50 wt. %.
13. A process for separating a first fluid component from a fluid feed
mixture comprising a first component and a second component by
contacting said fluid feed mixture with the upstream face of a
multicomponent membrane comprising a mixture of a glycol plasticizer
having a molecular weight of from about 200 to about 600 and an organic
polymer comprised of silicone rubber on a porous polymeric support,
said support having a ratio of total surface area to total pore
cross-sectional area of from about 5:1 to about 900:1 at separation
conditions and said membrane comprising from about 5 to about 50 wt. %
of said glycol plasticizer, said first component in said feed mixture
having a greater steady state permeability than said second component
and recovering the permeate which emanates from the downstream face of
said membrane said permeate comprising a fluid product mixture in which
the proportion of said first component to second component is greater
than the proportion of first component to second component in said
fluid feed mixture.
14. The process as set forth in claim 13 in which said glycol
plasticizer has a high boiling point and a low partial pressure, said
glycol plasticizer being uniformly dispersed as an emulsion in said
organic polymer or as a solution with said organic polymer.
15. The process as set forth in claim 13 in which said porous support
comprises polysulfone.
16. The process as set forth in claim 13 in which said porous support
comprises cellulose acetate.
17. The process as set forth in claim 13 in which said separation
conditions include ambient temperature and a pressure in the range of
from about 10 to about 500 pounds per square inch gauge.
18. The process as set forth in claim 13 wherein said glycol
plasticizer is present in an amount of from 20 to 50 wt. %.

DESCRIPTION:
BACKGROUND OF THE INVENTION
In recent years reverse osmosis has attracted a great deal of interest
for utilization in fields involving purification of liquids. This is of
especial importance when utilizing this sytem in the purification of
water and especially saline water. Likewise, the process is also used
to remove impurities from liquids such as water or, in the field of
dialysis, blood. When utilizing reverse osmosis in the purification of
a saline water, a pressure in excess of the osmotic pressure of the
saline water feed solution is applied to the solution which is prepared
from purified water by the semipermeable membrane. Pure water thereby
diffuses through the membrane while the sodium chloride molecules or
other impurities which may be present in the water are retained by the
membrane. Discussions and descriptions of such treatment in general and
the state of art in the middle 1960's is set forth in the treatise
Desalinization by Reverse Osmosis, the M.I.T. Press, 1966, which was
edited by Ulrich Merten.
Various semipermeable membranes are now being used in commercial
processes for performing separations by the reverse osmosis treatment
of aqueous solutions either for the portion of relatively pure water or
for concentration of a liquid solution being treated or both. Such
semipermeable membranes which are being used commercially include the
early Loeb-type membranes made of cellulose diacetate by processes such
as described in U.S. Pat. Nos. 3,133,132 to Loeb et al. and 3,133,137
to Loeb et al. The Loeb-type membranes comprise the asymmetric type
which are characterized by a very thin, dense surface layer or skin
that is supported upon an integrally attached, much thicker supporting
layer. Other types of semipermeable membranes which are also in use
include membranes having been fabricated from polyamides, polyimides,
polyphenyl esters, polysulfonamides, polybenzimidazole, polyarylene
oxides, polyvinylmethyl ether and other polymeric organic materials.
It is taught in U.S. Pat. No. 4,243,701 to Riley et al. that certain
membranes may also be utilized for the separation of various gases. The
separation of a gas mixture utilizing a membrane is effected by passing
a feed stream of the gas across the surface of the membrane. Inasmuch
as the feed stream is at an elevated pressure relative to the effluent
stream, a more permeable component of the mixture will pass through the
membrane at a more rapid rate than will a less permeable component.
Therefore, the permeate stream which passes through the membrane is
enriched in the more permeable component while, conversely, the residue
stream is enriched in the less permeable component of the feed.
The use of adsorbents or molecular sieves in separating components from
fluid mixtures is also long known. In the adsorption type separation
process the adsorbent exhibits selectivity of one mixture component
over another or, with a molecular sieve, one component is more retained
than another. The adsorbent may be employed in the form of a dense
compact fixed bed which is alternatively contacted with the feed
mixture and desorbent materials. In the simplest case, the adsorbent is
employed in the form of a single static bed in which case the process
is only semicontinuous. In another embodiment, a set of two or more
static beds may be employed in fixed bed contacting with appropriate
valving so that the feed mixture is passed through one or more
adsorbent beds, while the desorbent materials can be passed through one
or more of the other beds in the set. The flow of feed mixture and
desorbent materials may be either up or down through the adsorbent.
The most commercially successful embodiment of the adsorptive type
separation process is the countercurrent moving-bed or simulated
moving-bed countercurrent flow system. In that system the adsorption
and desorption operations are continuously taking place which allows
both continuous production of an extract and raffinate stream and the
continual use of feed and desorbent streams. The operating principles
and sequence of such a flow system are described in U.S. Pat. No.
2,985,589 to Broughton et al.
There are numerous references which disclose the incorporation of
various materials with separation membranes. U.S. Pat. Nos. 3,457,170
to Havens; 3,878,104 to Guerrero; 3,993,566 to Goldberg et al.;
4,032,454 to Hoover et al.; and 4,341,605 to Solenberger et al. teach
the use of structural supports or reinforcement fibers or fabrics to
aid the membrane in resisting the high pressures used in the reverse
osmosis process. U.S. Pat. No. 3,556,305 to Shorr shows a "sandwich"
type reverse osmosis membrane comprising a porous substrate covered by
a barrier layer, in turn covered by a polymer of film bonded to the
barrier layer by an adhesive polymeric layer. U.S. Pat. No. 3,862,030
to Goldberg shows a polymeric matrix having an inorganic filler such as
silica dispersed throughout which imparts a network of microvoids or
pores of about 0.01 to about 100 microns, capable of filtering
microscopic or ultrafine particles of submicron size. U.S. Pat. No.
4,302,334 to Jakabhazy et al. discloses a membrane "alloy" comprising a
hydrophobic fluorocarbon polymer blended with polyvinyl alcohol polymer
which imparts hydrophilic properties to the membrane. U.S. Pat. No.
4,230,463 to Henis et al. discloses multicomponent membranes useful for
separating gases comprising a polymer coating on a porous separation
membrane which also may be a polymer such as a polysulfone. This patent
indicates that a ratio of total surface area to total pore
cross-sectional area must be at least 1000:1 as specifically set forth
in claims 5 and 19. This means that the porous polysulfone which is
commonly used as an ultrafiltration or reverse osmosis support cannot
be utilized inasmuch as the commonly used porous polysulfone has a
total area/pore cross-sectional area ratio in the range of from about
5:1 to about 900:1. In this respect, it is to be noted that the higher
the ratio, the smaller is the pore diameter, i.e., a tighter membrane.
As will hereinafter be shown in greater detail in the examples at the
end of the specification, the relatively greater porous supports, that
is, those which possess a low ratio are desirable for coating the
polysulfone with a combination of silicone rubber and a glycol
plasticizer. This is in contrast to prior references in which a highly
porous polysulfone is coated with only silicone rubber, thus leading to
a low selectivity. An additional difference which exists between the
membrane of U.S. Pat. No. 4,230,463 and the membrane of the present
invention is the unexpected stability of the latter with regard to
selectivity. The selectivity which is enjoyed at the outset of the
separation process utilizing the membrane of Henis et al. will be
effective for only a relatively short period of time, inasmuch as the
pressure difference will rapidly cause a deterioration of the membrane
with an attendant loss of selectivity and stability.
U.S. Pat. Nos. 2,673,825, 3,532,527 and 4,454,085 disclose membranes
which may be utilized in separation processes and involve the use of a
glycol in the preparation of the membrane. However, in these three
patents, the glycol is coagulated with water in the casting solution
and therefore most, if not all, of the glycol is leached out before
separation. Therefore, the glycol does not become an integral part of
the membrane as is present in the membrane of this invention.
Mixed matrix membranes such as molecular sieves incorporated with
polymeric membranes are also broadly disclosed in the art. In the
article "The Diffusion Time Lag in Polymer Membranes Containing
Adsorptive Fillers" by D. R. Paul and D. R. Kemp, J. Polymer Sci.;
Symposium No. 41, 79-93 (1973), the specific mixed membrane used was a
Type 5A (Linde) zeolite incorporated with a silicone rubber matrix. The
Paul et al. article illustrates that the zeolite "filler" causes a time
lag in reaching steady state permeation of the membrane by various
gases due to the adsorption of the gases by the zeolite. It is taught
in this article that once the zeolite becomes saturated by the
permeating gas, a steady state rate of permeation through the membrane
is reached so that the membrane selectivity is essentially the same as
if the zeolite was not present. The Paul et al. article teaches making
the mixed membrane by dispersing the molecular sieves into the fluid
silicone prepolymer prior to casting.
We have discovered novel multicomponent membranes, their method of
manufacture and uses for which they are uniquely suitable not disclosed
by any of the known art either alone or in combination.

BRIEF SUMMARY OF THE INVENTION
This invention relates to a multicomponent membrane which is useful for
separating components of a fluid mixture. More specifically, the
invention is concerned with a multicomponent membrane, a process for
preparing this membrane and a process involving the use thereof for the
separation of components which are present in a fluid feed mixture,
said membrane comprising a mixture of a plasticizer and an organic
polymer cast on a porous organic polymer support.
It is therefore an object of this invention to provide a multicomponent
membrane useful for separation of various components present in a fluid
feed mixture.
Another object of this invention is found in a process for preparing a
multicomponent membrane useful for the separation of components in a
fluid feed membrane.
In one aspect an embodiment of this invention is found in a
multicomponent membrane useable for the separation of components of a
fluid feed mixture comprising a mixture of a glycol plasticizer having
a molecular weight of from about 200 to about 600 and an organic
polymer cast on a porous support, said porous support having a ratio of
total surface area to total pore cross-sectional area of from about 5:1
to about 900:1.
Another embodiment of this invention resides in a method for the
manufacture of a multicomponent membrane comprising a glycol
plasticizer having a molecular weight of from about 200 to about 600
and an organic polymer on a porous support which comprises: (a) forming
an emulsion or a solution of said glycol plasticizer with said organic
polymer in a suitable solvent; (b) casting said emulsion or solution on
said porous support to form a multicomponent membrane; and (c) curing
said membrane at an elevated temperature for a time sufficient to
evaporate substantially all of said solvent.
Yet another embodiment of this invention is found in a process for
separating a first fluid component from a fluid feed mixture comprising
a first component and a second component by contacting said fluid feed
mixture with the upstream face of a multicomponent membrane comprising
a mixture of a glycol plasticizer having a molecular weight of from
about 200 to about 600 and an organic polymer on a porous support, said
support having a ratio of total surface area to total pore
cross-sectional area of from about 5:1 to about 900:1 at separation
conditions, said first component in said feed mixture having a greater
steady state permeability than said second component and recovering the
permeate which emanates from the downstream face of said membrane said
permeate comprising a fluid product mixture in which the proportion of
said first component to second component is greater than the proportion
of first component to second component in said fluid feed mixture.
A specific embodiment of this invention is found in a multicomponent
membrane which comprises a mixture of a glycol plasticizer having a
molecular weight of from about 200 to about 600 and silicone rubber
cast upon a polysulfone support, said support having a ratio of total
surface area to total pore cross-sectional area of from about 5:1 to
about 900:1.
Another specific embodiment of this invention is found in a method for
the manufacture of a multicomponent membrane which comprises forming an
emulsion or solution of polyethylene glycol and silicone rubber in a
solvent comprising trifluorotricholorethane, casting said emulsion or
solution on a polysulfone support to form a multicomponent membrane and
curing said membrane at an elevated temperature for a time sufficient
to evaporate substantially all of said solvent.
Other objects and embodiment will be found in the following detailed
description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As hereinbefore described, the present invention is concerned with
multicomponent membranes which are useful in separating various
components which are present in fluid feed mixtures. In addition, the
invention is also concerned with a process for preparing these
particular membranes as well as to processes involving the use thereof.
The present invention, in a manner not known to the art, incorporates a
plasticizer with an organic polymer and a porous polymeric support to
create the desired multicomponent membrane and thereafter utilizing
that creation in a process for separating fluid components from each
other which would otherwise be difficult or impossible to separate.
It has now been unexpectedly discovered that the multicomponent
membrane which forms the basis for the present invention will exhibit a
stability when utilized in a process for separating these components
which is not present in other membranes such as those prepared by
coating a porous support with only a polymer such as silicone rubber or
those which are formed by treating a porous support with a plasticizer.
The multicomponent membrane of the present invention is formed by a
process in which a plasticizer such as a glycol of the type hereinafter
set forth in greater detail is immobilized in an organic polymer such
as silicone rubber in either an emulsion or solution phase which is
thereafter coated on the porous support.
Those skilled in the art of membrane separation technology know that
different components of a fluid system may pass through a properly
selected membrane at different rates due to different diffusivity and
solubility characteristics (hereinafter collectively referred to as
"permeability") of each component in the membrane. This phenomenon may
be expressed in terms of a separation factor as defined in the formula:
##EQU1## where αA/B=separation factor;
(C[A] /C[B])P=concentration of component A÷concentration of component B
in the permeate phase (emanating from the downstream face of the
membrane);
(C[A] /C[B])R=concentration of component A÷concentration of component B
in the raffinate phase (at the upstream face of the membrane).
The higher the separation factor, the better the separation that will
be achieved.
We have made the discovery that when a properly selected plastizizer is
incorporated with a particular membrane in a certain manner to obtain a
multicomponent membrane, a surprising and unexpected increase will
occur with regard to the separation factor of that membrane for a given
fluid mixture. We have thus obtained by our discovery a viable process
in which fluid components may be separated from a mixture because of
the marked differences in their respective permeabilities through the
multicomponent membrane, which marked differences do not occur in a
plasticizer-free membrane.
The multicomponent membrane of our invention incorporates a plasticizer
with a membrane material comprising a first organic polymer with a
porous second organic polymer support such as polysulfone or cellulose
acetate. The plasticizer may be any material which is included in the
commonly understood meaning of that term, i.e., a chemical which
imparts flexibility, workability or stretchability to the first and
second polymers. The plasticizer would most likely comprise a liquid
having a high boiling point and low partial pressure dispersed
uniformly as an emulsion in the first polymer, or in homogeneous phase
as a solution with the first polymer. The selection of specific
ingredients for the multicomponent membrane will depend on the feed
mixture from which the components are to be separated. For example, the
feed mixture may be a liquid or a gas, but in the latter case we have
found a multicomponent membrane comprising glycol having a molecular
weight from about 200 to about 600 (preferably from about 5 wt. % to
about 50 wt. %) incorporated with silicone rubber as the first polymer
and a porous polysulfone membrane support as the second polymer to have
significant utility, particularly in separating carbon dioxide from
methane. In that separation, carbon dioxide is the more permeable gas.
The membrane of the present invention includes a porous organic polymer
support upon which the mixture of plasticizer and first organic polymer
is cast. In the preferred embodiment of the present invention, the
preferred support material will comprise polysulfone although cellulose
acetate may also be utilized. It is believed that the plasticizer not
only has the capability of altering the permeability of the first
organic polymer with which it is mixed, but it also acts on the second
polymeric support material by softening it and causing its pores to
shrink while at the same time facilitating the plugging of the pores
with the first polymer in admixture with the plasticizer.
Separation may be effected by the present invention over a wide range
of separation conditions. Ambient temperature and a moderate pressure
of from about 10 psig to about 500 psig on the upstream face of the
mixed matrix membrane would be entirely adequate. This is in marked
distinction to the reverse osmosis processes which require that osmotic
pressures be exceeded, which in some instances would reach several
thousand psig. To a first-order approximation, the flux or permeation
through the membrane is directly proportional to the pressure
differential across the membrane.
Another aspect of our invention is the method that we have discovered
to make multicomponent membranes. In its broadest embodiment the method
involves forming an emulsion or solution of a plasticizer with a first
organic polymer dissolved in a suitable solvent, and casting the
emulsion or solution onto the porous second polymer support to obtain
the multicomponent membrane. A suitable solvent, particularly when the
first polymer in admixture with the plasticizer is silicone rubber,
comprises a Freon which is liquid at standard temperature and pressure,
such as trifluorotrichloroethane. The concentration of first polymer in
solvent should be from about 0.5 wt. % to about 50 wt. % for obtaining
a membrane of maximum flux capability. The emulsion or solution is
preferably degassed prior to casting by exposure to at least a partial
vacuum so as to minimize the formation of pinholes or voids within the
membrane.
Casting in accordance with the method of the present invention is
effected by pouring or spreading the plasticizer/first polymer emulsion
or solution onto the porous second polymer support and curing the
membrane by exposing it to an elevated temperature for a sufficient
time to evaporate substantially all of the solvent.
In a less preferred, but still viable embodiment of the method of the
present invention, the membrane incorporating the porous second organic
polymer support may be constructed in two steps. In a first step, the
plasticizer is poured or coated onto the support. In a second step, the
first polymer solution is cast onto the support. Curing is then
effected as discussed above.
The following examples are presented for illustrative purposes only and
are not intended to limit the scope of our invention.

EXAMPLE I
Multicomponent membranes were prepared both by a conventional
technique, i.e., without addition of a plasticizer, and in accordance
with the method of the present invention. For the conventional method,
a commercial silicone rubber was dissolved in trifluorotrichloroethane,
the solution degassed by means of exposure to vacuum and the solution
cast both on a glass plate and a highly porous polysulfone membrane.
The cast membranes were cured at temperatures between 40° C. to 82° C.
for one hour.
For the method of the present invention, about 20 to 50 percent by
weight of one of the following compounds (additive): tetraethylene
glycol (TEG), 600 molecular weight polyethylene glycol (PEG), propylene
carbonate (PC) or propylene glycol (PG), was added to the above casting
solution. The additives were emulsified in silicone rubber phase by
vigorous shaking. After degassing the casting solution, the
multicomponent membranes were then cured at 82° C. for one hour.
The following Table I sets forth separation factors for a CO[2] /CH[4]
separation obtained from various combinations or individual components
of the above materials. The feedstream used was a 30/70, CO[2] /CH[4]
mixture and conditions included 50 psi across the membrane and 25° C.
 TABLE I
______________________________________
POROUS POLY- % SULFONE MEMBRANE ADDITIVE BACKING α CO[2] /CH[4]
______________________________________
Sil Rub No No 4.8
Sil Rub No No 5.0
Sil Rub No Yes 4.6
Sil Rub No Yes 4.1
Sil Rub/TEG
50 No 7.5
Sil Rub/TEG
43 No 6.4
Sil Rub/PG
47 No 6.4
Sil Rub/PEG
47 No 7.0
Sil Rub/TEG
46 Yes 18.5
Sil Rub/TEG
46 Yes 13.7
Sil Rub/TEG
47 Yes 12.5
Sil Rub/TEG
50 Yes 11.8
Sil Rub/TEG
46 Yes 11.0
Sil Rub/TEG
47 Yes 11.9
Sil Rub/TEG
50 Yes 12.2
Sil Rub/PC
50 Yes 9.62
Sil Rub/PEG
20 Yes 11.5
Sil Rub/PEG
47 Yes 10.0
Porous Polysulfone 1
TEG Coated Porous Polysulfone
6.4
TEG Coated Porous Polysulfone
8.8
______________________________________
It is clear from the data of Table I that the silicone rubberglycol
combination yields a higher α than the silicone rubber alone but still
far too low to be of commercial interest. When the membrane includes
the porous organic polymer (polysulfone) support, as required by the
present invention, the separation factors are markedly better than the
supported and unsupported silicone rubber or supported glycol without
polymer in admixture therewith.
Further mention is made at this point to the aforementioned U.S. Pat.
No. 4,230,463 (Henis et al.) to compare the data presented therein with
that shown hereinabove. In Henis et al. the separation factors for
CO[2]/CH[4] with silicone rubber cast over polysulfone may be
calculated to be about 16. This would seem to compare quite favorably
with the results of the membrane of the present invention cast on
polysulfone until one considers the polysulfone used by Henis et al. as
compared to that of the present invention. The former, as described in
Henis et al. in column 21, is not unduly porous and has a large ratio
of total surface area to total pore cross-sectional area. In
particular, Henis et al. discloses the use of membranes having ratios
of total surface area to total pore cross-sectional area of about
1000:1 (e.g., see claims 5 and 19) as opposed to the porous second
organic polymer support of the present invention where such ratio may
vary from about 5:1 to about 900:1. The type of membrane of Henis et
al. may be conducive to high separation factors, but the rate of
passage of fluid through the membrane (flux) is greatly restricted.
The polysulfone support used to obtain the data in Table I above (and
in the following examples) was very porous, having a ratio of total
surface area to total pore cross-sectional area of about 30:1 and with
relatively large diameter pores (100-300 Angstroms). To obtain a high
separation factor through use of such a support as does the present
invention is indeed an achievement. The above hypothesis as to the
effect of the plasticizer on the large pores, i.e., shrinking them and
facilitating their plugging with polymer, is clearly borne out by the
observed data.

EXAMPLE II
For this example additional tests were run on selected membranes to
determine not only separation factors but also the flux in ml/min of
permeate obtained from a 30/70, CO[2] /CH[4] feed through 24 cm^2 of
membrane of about 50 to 300 microns thickness with a differential
pressure of 50 psi.
The first two tests were on a pure silicone rubber membrane and a
silicone rubber membrane which included a mixture of about 20 to 50 wt.
% glycols (80/20, PEG/TEG). The results were as follows:
______________________________________
Membrane Flux (ml/min) α CO[2] /CH[4]
______________________________________
Silicone rubber 3.75 4.90
Silicone rubber/
0.2-0.5 7.2 ± 0.4
PEG (600 MW) + TEG
(average of several runs)
______________________________________
This data showed a decrease in flux when plasticizer was added to the
silicone rubber, but also an increase in the separation factors.
Next, polysulfone support (same as that of Example I) was incorporated
into the membrane in accordance with the present invention with the
following results:
______________________________________
Membrane (inc. polysulfone) Flux (ml/min) α CO[2] /CH[4]
______________________________________
Silicone rubber/TEG
0.2-1.1 13.3 ± 2.6
Silicone rubber/
0.5-1.9 15.4 ± 4.5
PEG (600 MW + TEG
Silicone rubber/
0.8-2.9 22.95 ± 2
PEG (400)
Porous polysulfone alone
very fast .about.1
(with only 2 psi across
the membrane)
______________________________________
This data showed not only a significant increase in flux when
polysulfone support was added to the membrane, but also an amazing
increase in separation factors. As one would expect, porous polysulfone
alone is incapable of enabling a separation.

EXAMPLE III
To study the reproducibility of the performance data for various
membranes, sixteen separately made membranes were tested. The first
five comprised silicone rubber and a blend of PEG (600 MW) and TEG in
the ratio of 80/20 (PEG/TEG) on polysulfone. The next eleven were
blends of silicone rubber and PEG (400 MW) on polysulfone. The results
obtained with the same feedstock and test conditions as above were as
follows:
______________________________________
Membrane Flux (ml/min) α CO[2] /CH[4]
______________________________________
Silicone rubber +
1.1 17.03
PEG (600) + TEG
Silicone rubber +
1.3 17.02
PEG (600) + TEG
Silicone rubber +
1.1 18.50
PEG (600) + TEG
Silicone rubber +
1.6 6.40
PEG (600) + TEG
Silicone rubber +
0.5 16.30
PEG (600) + TEG
Silicone rubber +
.85 24.82
PEG (400)
Silicone rubber +
.85 21.03
PEG (400)
Silicone rubber +
1.42 25.59
PEG (400)
Silicone rubber +
1.7 23.91
PEG (400)
Silicone rubber +
1.2 24.08
PEG (400)
Silicone rubber +
2.9 19.55
PEG (400)
Silicone rubber +
1.9 19.55
PEG (400)
Silicone rubber +
1.8 7.23
PEG (400)
Silicone rubber +
1.2 19.19
PEG (400)
Silicone rubber +
1.0 25.65
PEG (400)
Silicone rubber +
2.2 21.04
PEG (400)
______________________________________
The above data illustrates a generally high order of reproducibility of
results when using samples from different batches of membranes of the
present invention having the same composition. The test runs showing
low flux values are attributed to use of a relatively thick membrane
and the test runs showing low α' s are probably due to a gross defect
in the support. Membranes showing a flux of about 3.0 ml/min and an α
of about 20.0 are considered to have a high degree of commercial
viability.

EXAMPLE IV
One test run was made of the embodiment of the present invention where
the membrane was made by first coating a porous polysulfone with the
plasticizer (PEG+TEG) and then adding the polymer (silicone rubber)
solution. The feedstock and test conditions were the same as in the
previous examples. The data obtained (averaged over several runs) was a
flux of 0.2-1.2 ml/min and an α of 12.3±3.3. Thus, even the less
preferred method of making the membrane of the present invention will
produce a potentially useful membrane.

EXAMPLE V
A final study was made concerning the use of porous cellulose acetate
as a membrane support. The membrane, in addition to that support,
included silicone rubber and PEG (400 MW) plasticizer. The feedstock
used was CO[2] and CH[4] in a ratio of 30 to 70, respectively, and the
pressure differential across the membrane was 95 psi. The following
data was obtained using membranes of the above composition from four
different batches.
______________________________________
Batch No. Flux (ml/min) α CO[2] /CH[4]
______________________________________
1 0.6 27.3
2 0.35 26.6
3 0.35 21.1
4 0.40 22.9
______________________________________
The above data shows cellulose acetate to be an acceptable support for
the membrane of the present invention, although the flux rates are
somewhat small, particularly considering that the pressure drop used
was almost twice that of the previous tests involving the use of
polysulfone support.
It should be noted that a membrane made of cellulose acetate alone
showed a flux of 2.3 ml/min but a separation factor of only 12.89.

EXAMPLE VI
To illustrate the stability of the multicomponent membrane of the
present invention, a membrane which was prepared according to the
method set forth in Example I above was exposed to either carbon
dioxide or methane gas at pressures ranging from 25 to 50 psi and
temperatures ranging from ambient to 70° C. or both with and without
the presence of water in the feed gas. The membranes were subjected to
this gas for a period well in excess of six months. At the end of this
six-month period, the membranes still maintained the ability to effect
the separation of gases while maintaining a steady rate flux.