Separation of gases through gas enrichment membrane composites

Thin film composite membranes having as a permselective layer a film of a homopolymer of certain vinyl alkyl ethers are useful in the separation of various gases. Such homopolymers have a molecular weight of greater than 30,000 and the alkyl group of the vinyl alkyl monomer has from 4 to 20 carbon atoms with branching within the alkyl moiety at least at the carbon atom bonded to the ether oxygen or at the next adjacent carbon atom. These membranes show excellent hydrolytic stability, especially in the presence of acidic or basic gaseous components.

BACKGROUND OF THE INVENTION 
The use of semipermeable membranes for reverse osmosis or ultrafiltration 
processes is well known. For example, in a reverse osmosis process, high 
pressure saline water may be placed in contact with a semipermeable 
membrane which is permeable to water but relatively impermeable to salt. 
Concentrated brine and relatively pure water are separated thereby; the 
water may then be utilized for personal use such as drinking, cooking, 
etc. 
More recently certain membranes have been 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, the more permeable component of the mixture will 
pass through the membrane more rapidly than the less permeable 
component(s), affording a permeate stream (that passing through the 
membrane) enriched in the more permeable component and a residue stream 
enriched in the less permeable component(s) of the feed stream. 
This ability to separate gases from a mixture stream finds many 
applications in commercial uses. For example, gas separation systems may 
be used for oxygen enrichment of air, for improved combustion efficiencies 
and conservation of energy resources. Likewise, nitrogen enrichment of air 
may be applicable where inert atmospheres are required. Other applications 
for oxygen enriched gases may be improving selectivity and efficiency of 
chemical and metallurgical processes. Similarly, inert atmospheres such as 
may be provided for by this invention may also be utilized in chemical and 
metallurgical processes. Some other applications of gas separation include 
helium recovery from natural gas, hydrogen enrichment in industrial 
process applications, and scrubbing of acid gases. Specific uses for 
oxygen enrichment of air are breathing systems for submarines and other 
underwater stations, improved heart-lung machines, and other lung assist 
devices. Another specific application of a gas separation system is an 
aircraft to provide oxygen enrichment for life-support systems and 
nitrogen enrichment for providing an inert atmosphere for fuel systems. In 
addition, oxygen enriched air can be used in furnaces for more efficient 
combustion and in catalytic oxidation of organic compounds, e.g., 
mercaptans, hydrocarbons, alcohols, aldehydes, etc., to name but a few. 
Likewise, gas separation systems may be used for environmental benefits, 
e.g., methane can be separated from carbon dioxide in waste gases for 
sewage treatment processes and oxygen enriched air can be produced to 
enhance sewage digestion. 
The separation of gases by a selective separation process will provide a 
product which possesses a different proportion of the gases than was 
present in the original feed mixture. The membranes which may be utilized 
to effect such a selective separation must possess the ability to 
withstand the conditions to which they are subjected during the separation 
operation and must provide a sufficiently high flux so as to permit the 
use of these membranes in a commercially attractive process. Therefore, it 
is necessary to provide membrane composites which exhibit a highly 
selective separation with regard to various gases as well as providing an 
economically attractive flux. 
Membranes which are composites of a thin polymer film on a porous support 
have been reported. For example, U.S. Pat. No. 3,892,665 discloses a thin 
polymer film which is formed on the surface of a liquid, generally water, 
and is subsequently transferred to the surface of a porous supporting 
membrane. During the transfer of the thin polymer film, the porous support 
is maintained in a wetted stage with the liquid. Alternatively, the thin 
film can be formed on the surface of the porous membrane if the surface of 
the support is first wet with the transfer liquid. In either case the 
pores of the support member must be filled with liquid and, therefore, the 
liquid must be removed from the porous support at a period subsequent to 
the formation of the film in order to draw the film onto the support. In 
general, such a polymer film is a monomolecular layer which is formed on 
the surface of the water wherein the individual film-forming monomer 
and/or polymer chains are oriented and closely packed. Subsequently, the 
oriented monomolecular layer or film, which is limited to a thickness in 
the range of from about 5 to about 25 Angstroms, is transferred to the 
surface of the porous support membrane. This process may be repeated until 
multiple monolayers are deposited on the surface of the support, the total 
film thickness then being from about 10 to about 200 Angstroms. Other than 
van der Waals' forces, there is no bonding between the aggregate layers 
and the support, which means that the thin film of the finished membrane 
is weakly attached to the porous support and said membrane cannot 
withstand substantial back pressure when in operation. Obviously, this 
process is tedious and expensive and is not readily amenable to commercial 
use. 
U.S. Pat. No. 3,526,588 discloses a macromolecular fractionation process 
and describes a porous ultrafiltration membrane which is selective on the 
basis of pore size. In contradistinction to this, it is essential that a 
thin film membrane for gas separation be nonporous, so that separation 
operates by a diffusion-solution mechanism of transport. U.S. Pat. No. 
3,767,737 which discloses a method for producing castings of "ultra-thin" 
polymer membranes is similar in nature to U.S. Pat. No. 3,892,665 in that 
the thin film of the membrane is formed on the surface of a liquid and 
transferred to the surface of a porous support membrane. The thin film 
polymer will thus inherently possess a disadvantage ascribed to the 
membrane of the former patent in that it cannot withstand substantial back 
pressure when in operation. In addition, U.S. Pat. No. 2,966,235 discloses 
a separation of gases by diffusion through silicone rubber which is not 
composited on a porous support material. 
U.S. Pat. No. 4,155,793 involves a continuous method for the preparation of 
membranes by applying a polymer to a microporous support. However, the 
method of production described in this patent involves the spreading of a 
polymer casting solution onto the surface of a liquid substrate. The 
polymer which is utilized is not soluble in the liquid substrate nor is 
the solvent which is used compatible with the microporous support. The 
polymer film which constitutes the membrane is formed on the surface of 
the liquid and is thereafter applied to the microporous support. U.S. Pat. 
No. 4,132,824 discloses an ultra-thin film of a polymer composite which 
comprises a blend of a methylpentene polymer and an 
organopolysiloxane-polycarbonate interpolymer for a thickness less than 
about 400 Angstroms in which the interpolymer is present in an amount of 
up to about 100 parts by weight per 100 parts by weight of the 
methylpentene polymer. Likewise, U.S. Pat. No. 4,192,824 describes a 
method for preparing the aforementioned interpolymer by depositing on the 
surface of a liquid casting substrate a casting solution which comprises a 
mixture of methylpentene polymer and from 0 to 100 parts by weight of an 
organopolysiloxane-polycarbonate copolymer. The casting solution spreads 
over the surface of the liquid casting substrate to form a thin film 
following which at least a portion of the thin film is removed from the 
surface of the substrate. Thereafter, the film may be used in contact with 
a porous support as a gas separation membrane. 
Other patents have also described various membranes for effecting a gas 
separation. In this respect, U.S. Pat. No. 4,230,463 describes a 
multicomponent membrane in which a material which exhibits selective 
permeation of at least one gas from a gaseous mixture is in occluding 
contact with a porous separation membrane. Various types of polymers are 
cited as being suitable for the porous separation membrane, the preferred 
polymer being a polysulfone. It is also stated in this patent that the 
porous separation membrane is preferably at least partially 
self-supporting and in some instances may be essentially self-supporting. 
European Patent Application No. 0031725 is drawn to an ultrathin solid 
membrane process which may be used for gas separation. This membrane is 
prepared by dissolving an additional polymer derived from at least one 
monomer selected from ethylenically unsaturated hydrocarbon monomers and 
conjugated unsaturated hydrocarbon monomers in an organic liquid medium 
which may, if so desired, contain another organic compound such as an 
alcohol, ketone, aldehyde, carboxylic acid, etc. The solvent solution is 
then spread on a liquid support such as water and the desired membrane is 
formed on the surface thereof. 
U.S. Pat. No. 3,335,545 is drawn to a process for gas separation by 
differential permeation, said process being effected through liquid or 
quasi-liquid films which behave substantially as polymeric films. Another 
U.S. Pat. No. 3,951,621, is drawn to a process for separating one or more 
components of a gaseous mixture utilizing a membrane of cross-linked 
hydrophilic poly(vinyl alcohol) and a polyamide such as nylon. In 
addition, the film contains complex-forming metal components which are 
active in the presence of water. The films are used as a free-standing 
self-supporting membrane. U.S. Pat. No. 4,248,913 discloses a process for 
preparing a membrane which comprises a blend of a vinylidene fluoride 
polymer and a hydrolyzed vinyl acetate polymer which forms a 
self-supporting film used in ultrafiltration processes. U.S. Pat. No. 
4,302,334 also discloses a microporous polymeric membrane based upon the 
membranes set forth in U.S. Pat. No. 4,248,913. In addition, the membranes 
may also include copolymers of vinyl acetate with other components such as 
acrylates, maleates and ethylene. 
The membranes described in U.S. Pat. Nos. 3,556,305 and 4,439,217 are 
superficially, but only superficially, analogous to the membrane of our 
invention. The former relates to membranes used in ultrafiltration and 
reverse osmosis where the membrane is a composite of a porous substrate, 
an adhesive, and a diffusive polymer or gellike film. Among the diffusive 
polymers was mentioned a mixture of poly(vinyl methyl ether) with a 
copolymer of vinyl methyl ether and maleic anhydride. U.S. Pat. No. 
4,439,217 teaches a permselective layer for gas separation composed of an 
organic polymer having pivalate groups in the side chains. The pivalate 
group is taught as being the permselective element, and the patentee 
teaches that pendant pivalate groups can be incorporated via 
homopolymerization of vinyl pivalate or copolymerization of the latter 
with other monomers including vinyl ethers generally and vinyl isobutyl 
ether specifically. But the patentee stresses that such comonomers are 
used solely to impart useful physical properties wholly unrelated to 
permselectivity. Consequently it is fair and accurate to state that the 
prior art is devoid of any teaching that homopolymers of vinyl alkyl 
ethers, and especially those of our invention, are useful as permselective 
elements in membranes for gas separation. 
As previously mentioned, the separation of various gases from a mixture 
thereof may become increasingly important in view of the necessity to 
conserve energy. A particular application would relate to increasing the 
thermal efficiency of combustion processes when utilizing fossil fuels in 
commercial combustion applications. Also, by utilizing a gas separation 
membrane in coal gasification, it may be possible to provide an oxygen 
enrichment of air for the production of low and medium British Thermal 
Unit (BTU) product gases as well as an oxygen enrichment of air for the 
combustion of these gases. For example, by placing a gas membrane 
separation system in close proximity to both gas production and gas 
combustion facilities, it would allow a site-located oxygen enrichment 
plant to supply both processes without the additional expense of 
transporting the gas or duplicating enrichment facilities. 
The requirements for an efficient oxygen enrichment membrane, for example, 
include the characteristics of being thermally stable at moderately 
elevated temperature; the ability to withstand high pressures without 
physically destroying the membrane; hydrolytic stability to water and/or 
water vapor; and existence in a physical form which is adaptable for use 
as a thin film composite membrane in sheet form or as a coating to hollow 
fine fibers. As will be shown in greater detail, we have now discovered a 
gas enrichment membrane composite which will possess all of the desirable 
characteristics enumerated. In particular, we have found that a membrane 
of a porous backing support having a permselective layer of a homopolymer 
of certain vinyl alkyl ethers is a quite convenient composite for various 
gas separations. In particular, homopolymers of such ethers where the 
alkyl group is branched either at the carbon bonded to the ether oxygen or 
at the next adjacent carbon atom form an especially useful permselective 
layer. 
SUMMARY OF THE INVENTION 
This invention relates to a process for the separation of gases. More 
specifically, the invention is concerned with a process for the separation 
of gases by passage of a gas mixture over a membrane of a particular 
composition whereby a permeate stream enriched in at least one component 
is obtained. In addition, the invention is also concerned with novel gas 
enrichment membrane compositions. 
It is therefore an object of this invention to provide a process for the 
separation of gases whereby a preferred gas enrichment stream may be 
obtained. 
A further object of this invention is to effect a separation of gases 
whereby a stream of gas which is enriched in a preferred gas is obtained, 
said process utilizing novel gas enrichment membrane composites. 
In one aspect an embodiment of this invention resides in a process for the 
separation of a preferred gas from a gaseous feed mixture containing at 
least two dissimilar gases which comprises passing a stream of said 
mixture over the surface of a membrane which is a composite comprising a 
porous support backing material having a thin film of one or more 
homopolymers of certain vinyl alkyl ethers composited on the surface of 
said support at separation conditions, and recovering a permeate in which 
the proportion of said preferred gas to other gases is greater than the 
proportion of said preferred gas to other gases in said gaseous feed 
mixture. 
Another embodiment of this invention is a gas enrichment membrane which 
comprises a porous support backing material having composited on the 
surface thereof a thin film of one or more homopolymers of specific vinyl 
alkyl ethers. 
A specific embodiment of this invention is a process for the separation of 
oxygen from a gaseous feed mixture containing oxygen and nitrogen which 
comprises passing said mixture over the surface of a membrane of a 
polysulfone having a thin film of poly(vinyl isobutyl ether) on the 
surface of said polysulfone at a temperature in the range of from about 
ambient to about 70.degree. C. and a pressure in the range of from about 
20 to about 100 pounds per square inch and recovering a permeate stream 
enriched in oxygen. 
Another specific embodiment of this invention is a gas enrichment membrane 
which comprises polysulfone having composited on the surface thereof a 
thin film of poly(vinyl isobutyl ether). 
Other objects and embodiments will be cited in the following detailed 
description of the invention. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention is concerned with a process for the separation of 
gases utilizing as separation means a gas enrichment membrane composite. 
The gas membrane composite which is utilized to effect the desired 
separation comprises as the active or permselective layer a thin film of a 
homopolymer of particular vinyl alkyl ethers composited on the surface of 
a porous support backing material. More specifically, the alkyl moieties 
of the vinyl alkyl ether monomer contain four to twenty carbon atoms and 
are branched at least at the carbon bonded to the ether oxygen or at the 
next adjacent carbon. The membranes of our invention are quite desirable 
in part because the homopolymers which are the active, permselective layer 
are readily available or can be easily prepared. The homopolymers are 
readily soluble in organic solvents at ambient temperature leading to ease 
and simplicity of composite fabrication. The composites also show good 
selectivity in some gas separations and exhibit a reasonable flux for 
their selectivity. In addition, our polymers show much better chemical 
stability than poly(vinyl esters) and poly(vinyl ketals), especially in 
their resistance to hydrolysis, and more particularly in their hydrolytic 
stability in the presence of an acid or base. 
The separation of the gases is accomplished by a selective permeation 
process where different gases present in a gaseous feed stream mixture 
will pass through a properly selected membrane at different rates due to 
the different permeability factors exhibited by the individual gases 
present in the mixture. That part of the membrane which effects this gas 
separation process is called the permselective layer and in this invention 
are homopolymers of certain vinyl alkyl ethers, the polymers forming a 
thin film which is composited on the surface of a porous support backing 
material. 
The porous support backing material has pores providing relatively little 
resistance to gas flow. It is contemplated within the scope of this 
invention that the porous support backing material may be either synthetic 
or naturally occurring. Examples of porous support backing materials which 
may be employed include polymers such as polysulfone, sulfonated 
polysulfone, blends of polysulfone and sulfonated poly(ether sulfone), 
polycarbonate, microporous polypropylene, polyamides, polyphenylene oxide, 
polyesters, natural fabrics such as canvas, cotton, linen, etc., synthetic 
fabrics such as polyesters, either woven or nonwoven, Dacron, Nylon, 
Orlon, etc. Among these polysulfone and sulfonated polysulfone polymers 
are preferred porous supports. Blends of polysulfone and from 0.1 to 5 
weight percent sulfonated poly(ether sulfone) also are quite useful, 
especially blends containing 0.5-2 weight percent of the latter. 
Inasmuch as the composite membrane of the present invention will comprise a 
thin film composited on a backing support, the latter being used to add 
mechanical strength to the finished membrane composition, it is possible 
to utilize the thin film wherein the thickness of the film can vary from 
about 100 to about 10,000 Angstroms, and more commonly from about 1,000 to 
about 5,000 Angstroms. By utiliizing the film which possesses the 
aforesaid thickness, it is possible to obtain a relatively high flux of 
the gas which permeates through the membrane. 
The thin film which is composited on the porous support backing material is 
a homopolymer of a vinyl alkyl ether. It is desirable to avoid crystalline 
polymers, or polymers with significant crystalline regions, because such 
polymers are brittle, therefore mechanically undesirable, and often 
exhibit lower flux than films from noncrystalline polymers. We have found 
that chain branching in the alkyl moiety reduces crystallinity, and the 
vinyl alkyl ethers of our invention preferably have chain branching in the 
alkyl moiety at least at the carbon adjacent to the ether oxygen (the 
alpha-carbon) or at the next adjacent carbon (the beta-carbon). The alkyl 
moiety can have from four up to about 20 carbon atoms, although the lower 
alkyl moieties containing four through about eight carbons are preferred, 
and the isobutyl moiety is especially preferred. 
According to the foregoing the vinyl alkyl ethers used as monomers in this 
invention have the formula, 
##STR1## 
where R.sub.1, R.sub.2, and R.sub.3 are independently selected from the 
group consisting of hydrogen or alkyl moieties subject to the constraints 
that the sum of carbon atoms in R.sub.1, R.sub.2, and R.sub.3 is from 3 to 
about 19, and at least one of R.sub.1 and R.sub.2 is not hydrogen; or 
##STR2## 
where R.sub.4, R.sub.5 and R.sub.6 are independently selected from the 
group consisting of hydrogen or alkyl moieties subject to the constraints 
that the sum of carbon atoms in R.sub.4, R.sub.5, and R.sub.6 is from 2 to 
about 18, and at least one of R.sub.4 and R.sub.6 is not hydrogen. 
Examples illustrative of monomers from which the homopolymers result 
include vinyl isobutyl ether, vinyl secbutyl ether, vinyl tert-butyl 
ether, vinyl 1,1 -dimethylpropyl ether, vinyl 1-methylbutyl ether, vinyl 
1, 2-dimethylpropyl ether, vinyl 2, 2-dimethylpropyl ether, vinyl 
2-methylbutyl ether, and the branched chain analogues of vinyl hexyl 
ethers, vinyl heptyl ethers, vinyl octyl ethers, vinyl nonyl ethers, vinyl 
decyl ethers, and so forth. It is to be understood that the aforementioned 
list of ethers are only representative of the class of monomers which may 
be employed to form the thin film of the composites, and that the present 
invention is not necessarily limited thereto. 
For good film forming properties the homopolymer should have a minimum 
molecular weight of about 30,000. However, a molecular weight from about 
200,000 up to about 1,000,000 is preferred in the practice of our 
invention. 
The thin film membrane composites may be prepared in either a continuous or 
hand-casting operation. For example, when a hand-casting operation is 
employed, a casting solution is prepared by dissolving the solid polymer 
in an appropriate solvent which may include: a halogenated solvent such as 
trichlorotrifluoroethane; a paraffinic hydrocarbon solvent such as 
pentane, hexane, and heptane; or a cycloparaffinic solvent such as 
cyclopentane, cyclohexane, cycloheptane. In all cases temperatures may 
range from ambient (20.degree.-25.degree. C.) up to the reflux temperature 
of the particular solvent which is employed. Upon reaching a complete 
solution, if elevated temperatures are used, the solution is cooled to 
room temperature and filtered to render the solution free of any residual 
solid material which may be present. The amount of polymer which may be 
present in the solvent solution will vary in accordance with the desired 
thickness of the film which is to be obtained. In the preferred embodiment 
of the invention, the polymer will be present in the solution in an amount 
in the range of from about 0.1 to about 5% by weight of the solution. The 
solution is then cast upon the surface of the desired porous support 
backing material and excess solution is removed. The resultant coated 
support is then cured by being subjected to an elevated temperature which 
may range from about 25.degree. to about 150.degree. C. for a period of 
time which may range from about 1 minute to about 24 hours. 
When the desired membrane is prepared in a continuous manner, the casting 
solution which has been prepared in a manner similar to that described 
above is placed in a trough which is provided with a roller. The porous 
support backing material is continuously passed under the roller in such a 
manner that the surface of the support is contacted with the polymer 
casting solution. The rate of passage of the porous support material 
through the casting solution is sufficient to impart a coating on the 
surface of the support which will possess a predetermined thickness after 
evaporation of the solvent. Again, in the preferred embodiment of the 
invention, the rate of passage of the porous support backing material 
through the casting solution will be at a rate of about 0.1 to about 20 
ft/min. After passage through the casting solution, the porous support 
material which contains the thin film membrane composited on the surface 
thereof will be treated so as to remove any excess solution and after the 
solvent has been evaporated, the membrane is cured in a manner similar to 
that hereinbefore set forth. 
The film of homopolymer in the composite generally will be as thin as 
possible to maximize flux, and usually is in the range from 100 to 10,000 
Angstroms, even more commonly between about 1,000 and 5,000 Angstroms. 
Film thickness may be varied by varying the concentration of the polymer 
in the casting solution, by varying the speed at which the casting 
solution is applied, or by varying the gap between the support surface and 
the application knife edge. 
The process for separating gases from mixtures thereof utilizing the gas 
enrichment membrane compound of the present invention may be effected in 
any suitable manner which is known in the art. By utilizing these 
membranes, it is possible to obtain a separation of gases involving 
selectivities which may be greater than 2.7 at a flux which may be in the 
range of from about 0.1 to about 10 cc/min-psi. The process is effected by 
contacting one surface of a membrane of the type set forth in the present 
specification with a gaseous mixture, said membrane exhibiting a selective 
permeation of one gas in the mixture over that of the remaining gas or 
gases present in the gaseous feed mixture. 
The apparatus which may be employed to effect the desired separation may be 
any separation device which is known in the art. For example, the 
separation device may be used in either single stage or multistage 
membrane plants. One type of configuration in which the gas membrane may 
be used may comprise a spiral wound element. In this type of element, two 
sheets of the membrane of the present invention are separated by the 
porous support backing material, the latter both affording a support for 
the thin film composite membrane against the operating pressure as well as 
providing a flow path for the gaseous output. The thin film composite 
membranes are sealed around three edges or sides in order to prevent 
contamination of the product gas while the fourth edge or side is sealed 
to a product tube. The product tube is provided with perforations inside 
of the edge seal area in order that the product gases can be removed from 
the porous support material. The resulting configuration is in the form of 
an envelope which is rolled up about the center tube in the form of a 
spiral along with a mesh spacer which separates the facing surface 
membrane. More than one such envelope may be sealed to the product tube if 
desired. By utilizing such a type of element, it is possible to take 
advantage of a number of factors which include, among others, a large 
membrane surface area per unit volume, a convenient and simple pressure 
design and configuration, which, in turn, will lead to a compact module 
plant arrangement, flexibility and ease in installation and in replacement 
of the elements inasmuch as the modules may comprise two or more 
disposable units connected in series. 
It is contemplated within the scope of this invention that the membranes 
may be used for the separation of various gases from each other, although 
not necessarily with equivalent results. For example, the separation of 
carbon dioxide from methane and natural gas to remove non-combustible 
material is a potentially important application, as are the separation of 
hydrogen sulfide from industrial gas streams and sulfur dioxide from flue 
gas. Because of their hydrolytic stability in the presence of an acidic or 
basic gaseous component, our membranes may be especially advantageous in 
the foregoing separations, as well as in the separation of ammonia from 
hydrogen or nitrogen. Our membranes also are useful in the separation of 
oxygen and nitrogen, and other examples of mixtures of gases which may be 
subjected to the separation process of the present invention include 
CH.sub.4 /H.sub.2, CO.sub.2 /H.sub.2, H.sub.2 O/NH.sub.3, CO.sub.2 /CO, 
NO.sub.2 /NO, CS.sub.2 /N.sub.2 O, H.sub.2 S/CO, SO.sub.2 /CO, SO.sub.2 
/N.sub.2, etc. The reaction conditions which may be employed for effecting 
the separation of the gases will include temperatures in the range of from 
about 20.degree. to about 70.degree. C. and a pressure which may range 
from about 20 to about 100 pounds per square inch (psi). 
The following examples are given for purposes of illustrating the various 
aspects of the present invention including the synthesis of the thin film 
composite membrane, the casting of the thin film composite membrane on a 
porous support backing material and a process for utilizing the membrane 
composite in the separation of gases. However, it is to be understood that 
these examples are given merely for the purpose of illustration and that 
the present process is not necessarily limited thereto.

EXAMPLE I 
To prepare the membrane composition of the present invention, casting 
solutions were prepared by stirring various weight percentages of the 
poly(vinyl isobutyl ether) with either hexane or cyclohexane which acted 
as the solvent for the homopolymer at room temperature or at temperatures 
up to the reflux temperature of the solvent until a complete solution of 
the polymer in the solvent was obtained. The polymer was present in the 
solutions in weight percentages ranging from 1.0 to 5.0. After complete 
solutions of the polymer were obtained, the solutions were allowed to cool 
to room temperature and were filtered free of any residual solid material 
in order to obtain a pure polymer solution. 
The membrane was then prepared by placing the polymer casting solution in a 
6 inch long by 11/2 inch wide by 1 inch deep cating trough which was 
provided with a roller fitted along the length thereof. The amount of 
casting solution which was employed in the trough was sufficient enough so 
that the surface of the solution wetted the surface of the roller. 
A strip of microporous polysulfone support having a width of about 5 inches 
was passed under the roller in the trough in such a manner so that one 
surface of the polysulfone support contacted the polymer casting solution. 
In a continuous casting process the polysulfone support was passed through 
the solution at casting speeds which ranged from 2.0 to 4.0 ft/min 
allowing a contact time which ranged from 2.0 to about 15.0 seconds. The 
resulting membrane composition comprising a thin film homopolymer 
composited on the surface of the porous support backing material was then 
placed in a vertical position and maintained thereat until all the solvent 
had evaporated. Following this, the membrane was then cured at a 
temperature of about 50.degree. C. for a period of about 30 minutes. 
EXAMPLE II 
To evaluate the membranes as gas separation or gas enrichment membrane 
composites, circular 31/2 inch diameter samples of the membranes were cut 
out with a die. The membranes were loaded into stainless steel test cells 
and a gaseous feed mixture having a composition of aapproximately 21% 
oxygen and 79% nitrogen (pure air) was charged to the cell. The cells were 
provided with a gas inlet for the feed gas and an outlet port for the gas 
permeate. The flow was set at a pressure of 20 psi while maintaining a 
temperature of 25.degree. C. The results of these tests are set forth in 
the table below. 
TABLE 
______________________________________ 
Selectivity and Flux Data for Poly(vinyl isobutyl ether) 
Membranes on Polysulfone Supports. 
Casting Average Average 
Casting Solution 
speed O.sub.2 /N.sub.2 
Qo.sub.2 
Wt. % Polymer Solvent 
ft/min. Selectivity 
(cc/min-psi) 
______________________________________ 
2.0 Cyclohexane 
2.0 3.18 0.195 
2.0 Cyclohexane 
3.0 3.38 0.180 
2.0 Cyclohexane 
4.0 3.20 0.158 
3.0 Cyclohexane 
2.0. 3.78 0.123 
3.0 Cyclohexane 
3.0 3.69 0.115 
3.0 Cyclohexane 
4.0 3.66 0.110 
4.0 Cyclohexane 
2.0 2.26 0.0174 
4.0 Cyclohexane 
3.0 3.84 0.0529 
______________________________________ 
EXAMPLE III 
In this example the desired membranes were obtained utilizing a hand 
casting procedure in place of the continuous type of casting which was 
employed in the previous examples. The membranes were prepared by casting 
a solution of poly(vinyl isobutyl ether) dissolved in cyclohexane onto the 
surface of a polysulfone support, removing excess solution and allowing 
the solvent to evaporate. The dry membranes were then cured at a 
temperature of about 50.degree. C. for a period of 30 minutes. As in the 
previous examples, samples of the membranes were cut and utilized in a 
test cell while employing air as the feed mixture. The results of these 
tests are set forth in the table below. The contrasting results obtained 
for the two 3 weight percent samples demonstrate that the polysulfone must 
be of high quality and free of surface defects in order to achieve the 
highest membrane performance. 
TABLE 
______________________________________ 
CASTING 
SOLUTION 
CONCENTRA- AVERAGE AVERAGE 
TIONS O.sub.2 /N.sub.2 
Qo.sub.2 
(wt. %) SOLVENT SELECTIVITY (cc/min-psi) 
______________________________________ 
1.0 Cyclohexane 
0.98 13.6 
2.0 " 2.82 0.25 
3.0 " 4.10 0.10 
3.0 " 1.28 0.78 
______________________________________ 
EXAMPLE IV 
A similar set of membranes were prepared in a manner identical to that set 
forth in Example 1 above. In this preparation the support which was 
utilized comprised a standard polysulfone, a water damp support of 
polymers containing a sulfonated poly(ether sulfone) and a dry support of 
polysulfone containing 1.0 wt. % of the sulfonated poly(ether sulfone). 
The membranes which were recovered were then tested in a manner similar to 
that set forth in Example II above. The results which were obtained when 
utilizing the various types of supports are set forth in the following 
table: 
TABLE 
__________________________________________________________________________ 
Selectivity and Flux Data for Poly(vinyl isobutyl ether) Membranes 
on various Supports 
CASTING 
CASTING 
# OF AVERAGE 
AVERAGE 
CONC. SPEED SAMPLES 
Qo.sub.2 
O.sub.2 /N.sub.2 
SUPPORT 
(wt. %).sup.a 
(FT/MIN) 
TESTED 
(cc/min-psi) 
SELECTIVITY 
__________________________________________________________________________ 
1 3.0 3.0 8 0.119 3.55 
1 2.5 3.0 8 0.242 2.55 
2 2.5 3.0 8 0.246 3.60 
3 2.5 3.0 11 0.124 4.95 
__________________________________________________________________________ 
1. Standard polysulfone support. 
2. Waterdamp support of polysulfone containing 1 wt. % sulfonated 
poly(ether sulfone). 
3. Dry support of polysulfone containing 1% sulfonated poly(ether sulfone 
.sup.a All membranes cast from cyclohexane solutions. 
EXAMPLE V 
In this example, membranes were prepared in a manner identical to that set 
forth in Example IV above. In this preparation, the casting solution 
consisted of 2.5 weight percent of poly(vinyl isobutyl ether) dissolved in 
cyclohexane. The casting solution was applied continuously to the surface 
of a dry support of polysulfone containing 1.0 weight percent of the 
sulfonated poly(ether sulfone) at a casting speed of 3.0 ft./min. 
The membranes which were recovered were fabricated into three, single-leaf, 
2".times.10" spiral-wound test elements. The three elements were tested 
using air as the feed mixture. The flow through the element was set to 
maintain a pressure of 20 psi while maintaining a temperature of 
25.degree. C. Analysis of the permeate gas through the elements gave the 
following performance results. 
TABLE 
______________________________________ 
Selectivity and Flux Data for Test Elements 
of Poly(vinyl isobutyl ether) Membranes. 
Qo.sub.2 .alpha. 
Element # (cc/min psi) 
(O.sub.2 /N.sub.2) 
______________________________________ 
1 0.12 4.51 
2 0.13 6.05 
3 0.13 6.05 
______________________________________ 
EXAMPLE VI 
Other membranes also may be prepared utilizing a process similar to that 
set forth in the previous examples in which a solution containing from 
about 1 to about 5% by weight of poly(vinyl sec-butyl ether), poly(vinyl 
tert-butyl ether), poly(vinyl 2, 2-dimethyl-propyl ether) or poly(vinyl 
2-ethylhexyl ether), cast in either a continuous manner or by hand on 
porous support backing material which may comprise a polysulfone or a 
blend of polysulfone and sulfonated poly(ether sulfone). After allowing 
the solvent to evaporate, the thin film composite of the poly(vinyl ether) 
on the surface of the support may be cured and utilized as a gas 
separation membrane to obtain a gaseous product mixture which contains a 
greater proportion of a preferred gas such as oxygen than was present in 
the original gaseous feed mixture.