WO1993012869A1

WO1993012869A1 - Meta, para-bisphenol based polymer gas separation membranes

Info

Publication number: WO1993012869A1
Application number: PCT/US1992/011082
Authority: WO
Inventors: Edgar S. Sanders, Jr.; Raymond W. Mah
Original assignee: The Dow Chemical Company
Priority date: 1991-12-20
Filing date: 1992-12-17
Publication date: 1993-07-08
Also published as: JP3275077B2; JPH07502200A; US5152811A; EP0623050A1

Abstract

The invention relates to novel meta, para-bisphenol based condensation uncross-linked polymer membranes and a method of separating gases using such membranes.

Description

META. PARA-BISPHENOL BASED POLYMER GAS SEPARATION MEMBRANES

This invention relates to novel semi-permeable gas separation membranes based upon uncross-linked polymers containing meta, para-bisphenol moieties and a process for separating gases using said membranes.

The use of semi-permeable membranes to separate gases is well known in the art. Membranes have been used to recover or isolate a variety of gases including hydrogen, helium, oxygen, nitrogen, carbon monoxide, carbon dioxide, water vapor, hydrogen sulfide, ammonia, and/or light hydrocarbons. Applications which are of particular interest include the separation of hydrogen or helium from gas mixtures such as mixtures containing nitrogen, carbon monoxide, carbon dioxide, water vapor, and/or light hydrocarbons. For example, the separation and recovery of hydrogen for recycle is often necessary in various hydrocracker, hydrotreater, and catalytic cracking processes used in the oil refinery industry. Other applications of interest include the separation of carbon dioxide from light hydrocarbons or other crude oil components such as hydrogen sulfide as part of the tertiary oil recovery process. Additional applications include the recovery of an enriched oxygen stream from air for use in fermentation processes or to enhance combustion in furnaces. Alternatively, an enriched nitrogen stream may be obtained from air for use as an inert atmosphere over flammable fluids or to enhance the storage longevity of perishable foodstuffs. Membranes can be used to accomplish such separations.

Such membrane separations are based on the relative permeability of two or more gaseous components through the membrane. In order to separate a gas mixture into two portions, one of which is richer and one of which is leaner in at least one gaseous component, the feed mixture is brought into contact with one side of a semi-permeable membrane through which at least one of the gaseous components selectively permeates. A gaseous component which selectively permeates through the membrane passes through the membrane more rapidly than at least one other gaseous component of the mixture. The gas mixture is thus separated into a stream which is enriched in the selectively permeating gaseous component or components and a stream which is depleted in the selectively permeating gaseous component or components- A relatively non-permeating gaseous component passes more slowly through the membrane than at least one other gaseous component of the mixture. An appropriate membrane material is chosen so that some degree of separation of the gas mixture can be achieved-

Membranes for gas separation have been fabricated from a wide variety of natural and synthetic polymeric materials, including rubbers, polysiloxanes, cellulose esters and ethers, aromatic polyimϊdes, polyaramides, polysulfones, poiyethersulfones, polyesters, and polycarbonates- An ideal gas separation membrane is characterized by the ability to operate under high temperatures and/or pressures while possessing a high gas separation factor (permselectϊvity) and high gas permeability. While solvent resistance under operating conditions is also preferred, gas separation membranes are preferably fabricated from polymers which are easily processed- The problem is finding membrane materials which possess all the desired characteristics- Polymers which possess high separation factors generally have low gas permeabilities, while those polymers which possess high gas permeabilties generally have lo permselectivities- In the past, a choice between a high gas separation factor and a high gas permeability has been unavoidably necessary- Furthermore, some polymeric membrane materials which would otherwise be considered useful exhibit poor performance under high operating temperatures and pressures. Still other polymeric membrane materials capable of operating at high temperatures and pressures are typically difficult to fabricate into membranes. Solvent resistance is often obtainable only with polymeric materials which are diffkultto fabricate into membranes. What is needed is a membrane capable of separating gas mixtures and which possesses a high permselectivity, high gas permeability, flexibility to operate under extreme conditions of temperature and pressure, as well as improved solvent resistance under operating conditions and ease of fabrication-

The invention concerns a semi-permeable gas separation membrane characterized by a thin discriminating region of an uncross-linked condensation polymer possessing repeat units of the following structure, referred to hereinafter as Formula I:

wherein R represents individually in each occurrence a hydrogen radical, a monovalent C.-

C_B hydrocarbyl radical, a C^-C₈ monovalent halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen;

L represents a direct bond or a divalent C -C₁₅ hydrocarbyl radical, a divalent C.-C_l5 halohydrocarbyl radical, -S-, -SO-, -S0₂-, or-SS-;

R¹ represents individually in each occurrence -CO-, -CS-, -S0₂-,

wherein

Z represents individually in each occurrence a hydrogen radical, a monovalent C^-C.. hydrocarbyl radical, a C^C_g monovalent halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen;

R² represents:

wherein

R^r represents independently in each occurrence a hydrogen radical, a monovalent C^ hydrocarbyl radical, a monovalent C.-C₃ halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical, and a halogen or L' represents a direct bond or a divalent C_t-C_]S hydrocarbyl radical, a divalent C_t-C_l5 halo-hydrocarbyl radical, -0-, -S-, -SO- -S0₂-, or -SS-; x is a positive number between 0 and 1 inclusive; y is a positive number between 0 and 1 inclusive; and n is a positive integer representing a degree of polymerization which provides a number- average molecular weight of at least 3,000.

In another aspect, the invention concerns a process of separating gases comprising:

A. contacting one side of a semi-permeable gas separation membrane with a feed gas mixture under pressure, wherein the membrane divides a separation chamber into a high pressure side into which the feed gas mixture is fed and a low pressure side;

B. maintaining a pressure differential across the membrane under conditions such that at least one gaseous component in the feed gas mixture selectively permeates through the membrane from the high pressure side to the low pressure side of the membrane;

C removing from the low pressure side of the membrane permeated gas which is enriched in at least one selectively permeating gaseous component;

D. removing from the high pressure side of the membrane non-permeated gas which is depleted in at least one selectively permeating gaseous component; wherein the membrane comprises a thin discriminating region of an uncross-linked condensation polymer possessing repeat units corresponding to Formula I.

The membranes of this invention possess good gas permselectivity and gas permeability, reasonable mechanical strength, and good temperature resistance. The membranes can be endowed with good solvent resistance and are readily fabricated.

The gas separation membranes of this invention are fabricated from uncross- linked polymers containing meta, para-bisphenol moieties and preferably comprise polycarbonates, polythiocarbonates, polyestercarbonates, polyesters, polyetheresters, polysulfones, and polyethers based upon 3,4'-dihydroxybisphenolic monomers, 3,4'- dihydroxybisphenolic monomers, and 4,4'-dihydroxybisphenolic monomers.

R is preferably a hydrogen radical, a monovalent C.-C₈ hydrocarbyl radical, a C^C_g halohydrocarbyl radical or a halogen. More preferably, R is a hydrogen radical, a monovalent C_t-C hydrocarbyl radical, a monovalent C.-C₄ halohydrocarbyl radical or a halogen. Preferred halogens are fluorine, chlorine, and bromine; most preferred halogens are chlorine and bromine.

L preferably is a direct bond, a divalent C -C hydro-carbyl radical, or a divalent ^{c C} _i5 halohydrocarbyl radical. More preferably, L is a divalent C^-C₈ hydrocarbyl radical or a divalent C^C_g halohydrocarbyl radical. Preferred halohydrocarbyl radicals include -C₆H₅CI- and

-ccι₂.

Preferably, R¹ is individually in each occurrence -CO-, -CS-, -COC.Z₄CO-, -COCZ C CO-, -COC_ιnZ_fiCO- or -COC Z ,C0-. Most preferably, R¹ is individually in each occurrence -CO-, -CS-, -COC₆Z.CO- or -COC₁₅Z_ι2CO-.

Z preferably is individually in each occurrence a hydrogen radical, a monovalent C^C_g hydrocarbyl radical, a C.-C₈ monovalent halohydrocarbyl radical or a halogen. Z most preferably is individually in each occurrence a hydrogen radical, a monovalent C₁-C₄ hydrocarbyl radical, a monovalent C_t-C. halohydrocarbyl radical or a halogen. R' preferably is independently in each occurrence a hydrogen radical, a monovalent C,-^ hydrocarbyl radical, a monovalent C₁-C₄ halohydrocarbyl radical or a halogen. Preferred halogens are fluorine, chlorine, and bromine; most preferred halogens are chlorine and bromine.

L' preferably is a direct bond, a divalent C^C_g hydro-carbyl radical, a divalent C_t-C₈ halohydrocarbyl radical, -O-, -S-, -SO-, or -S0₂-. L' most preferably is a direct bond, a divalent C₁-C₄ hydrocarbyl radical, a divalent C₁-C₄ halohydrocarbyl radical, -0-, -S-, -SO-, or -S0₂-. Preferred halohydrocarbyl radicals are -C₇H₅CI- and -CCI₂-. x is preferably a positive number between 0.33 and 1 inclusive, more preferably between 0.67 and 1 inclusive, and most preferably 1. y is preferably a positive number between 0 and 0.75 inclusive, more preferably between 0 and 0.50 inclusive, and most preferably between 0 and 0.25 inclusive. n is preferably a positive number between 10 and 2,000, more preferably between 40 and 1 ,000.

The condensation polymers useful in this invention may be prepared by the reaction of a bisphenol with phosgene, thiophosgene, sulf uric acid, or other aromatic acid such as terephthalic acid, isophthalic acid, or 3-tert-butyl isophthalic acid, or their derivatives such as terephthaloyl chloride, isophthaloyl chloride, or hydroxy benzoic acid, or a combination thereof. The starting materials may be individual monomeric species as well as oligomeric speoes of the previously described compositions The polymerization may be accomplished by the use of a homogeneous solution technique whereiπ the starting material and an optional monofunctional terminating species are dissolved in a suitable o^rganic solvent, such as methylene chloride in the presence of a base, such as pyridine, and condensed with a gaseous 5 liquid, orsolid condensing species. The reaction is preferably carried out in a dry inert atmosphere such a dry nitrogen or argon and at temperatures between 0°Cand the boiling point of the solvent. Upon completion of the polymerization, the reaction mixture isacidified with a dilute solution of an acid such as hydrochloric acid, washed with water remove residual pyridϊnium salts, passed through an ion exchange column to remove residual entrained water, 10 and precipitated in a non-solvent such as heptane The precipitated polymer is recovered by filtration, optionally air dried, and subsequently dried under vacuum at elevated temperature.

The polymerization may also he accompl ished by the use of a heterogeneous mterfacial technique wherein the starting material and an optional monofunctional terminating species are dissolved in a solution of base, such as sodium hydroxide, and an t r_y orαanic solvent, such as methylene chloride, which solvates the gaseous, liquid, or solid condensing species as well as the polymerized product, and is facilitated by the use of a phase transfer catalyst, such a tetrabutylammonium bromide, or by the use of an amine catalyst, such as dimethyla inopyridine. The reaction is also preferably carried out in a dry inert atmosphere, such as dry nitrogen orargon, and at a temperature between 0^cCand the boiling 0 o'nt of both the aqueous solvent and organic solvent. Upon completion of the polymerization, the reaction mixture is acidi ied with a dilute solution of an acid, such as hydrochloric acid, the separated polymer containing organic phase is washed with water to remove residual sodium salts, passed through a coalescer or dried using a drying agent, such as magnesium suffate,to remove residual entrained water, and precipitated in a non-solvent such 5 as heptane The precipitated polymeris recovered byfiltration, optionallyair dried,and subsequently dried under vacuum at elevated temperature-

The uncross-linked polymers so formed possess a number-average molecular weight (M ) such that the polymers are useful for forming fibers, films, molded articles, foams, coatings, and the like. The number-average molecular weight of such polymers as measured by 0 gel permeation chromatography based upon polystyrene standards is preferably at least 3,000, more preferably at least 10,000; the number-average molecular weight of such polymers is preferably less than 500,000, more preferably less than 250,000. The weight-average molecular weight of such polymers as measured by gel permeation chromatography based upon polystyrene standards is preferably at least 6,000, more preferably at least 20,000; theweight- 5 average molecular weight of such polymers is preferably less-than 3 ,000,000, more prefer bly less than 500,000. The tnnsc^'c viscosity of suc polymersis preferably between 0,1 and 2.0- deciliters per gram, more preferably be een 0.2 and 1.0 de«l«ters per gram, as measured in a chlorinated hydrσcarboh.sofver&such ₃₅ methylene chloride. T*ιe uncroSsS- ^'nked polymers of this invention are preferably soluble in common chlorinated hydrocarbon solvents such as methylene chloride, chloroform, and chlorobenzene, as well as common polar aprotic solvents such as N-methyl-2-pyrrolidinone, dimethyl-acetamide, dimethylformamide, dimethyisulfoxide, and sulfolane. The uncross-linked polymers useful in this invention preferably possess glass transition temperatures of at least 50°C, more preferably of at least 70°C, even more preferably of at least 90°C. The polymers preferably possess a tensile strength as measured by ASTM D- 1708 of at least 4,000 psi (27,580 kPa), more preferably of at least 6,000 psi (41 ,370 kPa); the polymers also preferably possess a tensile modulus as measured by ASTM D-1708 of at least 100 kpsi (689,475 kPa), more preferably of at least 150 kpsi (1 ,034,215 kPa). The polymers preferably possess an elongation at break as measured by ASTM D-1708 of at least 2 percent, more preferably of at least 4 percent.

Such uncross-linked polymers are used to fabricate the semi-permeable membranes of this invention. The membranes of this invention may be formed into any useful configuration known to one skilled in the art. In particular, the membranes may be shaped in the form of flat sheets or films, hollow fibers of various cross-sectional shapes, or hollow tubes. Films and hollow fibers of substantially circular cross-section are preferred membrane configurations.

In addition, the membranes of this invention may possess any morphological structure known to one skilled in the art. In particular, the membrane may be a homogeneous membrane, a composite membrane, or an asymmetric membrane. Asymmetric and composite membranes are preferred; asymmetric membranes are more preferred. In the embodiment wherein the membranes possess a hollow fiber configuration, asymmetric membranes may have the discriminating region either on the outside of the hollow fiber, at the inside (lumen) surface of the hollow fiber, or located somewhere internal to both outside and inside hollow fiber membrane surfaces. In the embodiment wherein the discriminating region of the hollow fiber membranes is internal to both hollow fiber membrane surfaces, the inside surface and the outside surface of the hollow fiber membranes are porous, yet the membranes demonstrate gas discriminating ability, that is, the ability to separate gases. Homogeneous membranes are prepared by forming a continuous thin discriminating layer which is dense and free of voids and pores. Such membranes possess a discriminating region which generally has substantially the same structure and composition throughout the membrane. In one preferred embodiment, the uncross-linked polymers useful in this invention are dissolved in a solvent, thus forming a polymer/solvent solution which is cast onto a uniform surface from which the membrane may thereafter be readily separated.

Preferred casting sol vents for the polymers useful in this invention include chlorinated solvents such as methylene chloride and chloroform, and dipolar aprotic solvents such as N-methyl-2- pyrrolidinone, N,N-dimethylacetamide, and dimethylformamide. The polymer/solvent solution should be substantially homogeneous and possess sufficient viscosity to allow casting of the solution onto a uniform surface. Preferably, the solution of polymer/solvent contains polymer in weight percents of between 5 and 50, more preferably of between 10 and 40, even more preferably of between 10 and 30- The solution is cast onto a uniform surface possessing a low surface energy such as silicone or coated glass, or a surface to which the membrane will not adhere such as mercury, or a liquid with which the polymer is substantially immiscible, such as water. Alternatively, the membrane may be cast onto a surface which may be dissolved away from the membrane following curing and drying. Casting is performed by pouring the solution onto the 1 o appropriate surface and using an appropriate tool to form a film of the appropriate thickness. Acontinuous casting process may be achieved by casting the solution onto endless belts or rotating drums. Thereafter, the castsolution is exposed to curing or drying conditions. Such conditions are used to substantially remove the solvent, thereby leaving a thin discriminating layer of polymer which is homogeneous- The solution may be cured or dried either by exposure ^■J to a vacuum, exposure to elevated temperatures, by allowing the solvent to evaporate over time, or any combination thereof- Generally, it is preferable to expose the cast solution to elevated temperatures which are below the glass transition temperature (Tg) of the polymer, preferably less than Tg-100°C, more preferably less than Tg-50°C, even more preferably less thanTg-20°C. 0 Composite membranes are prepared by forming a continuous thin discriminating layer of the polymer on a porous supporting layer. Such membranes possess a discriminating layer which generally has a different structure and composition than the porous supporting layer. To prepare a composite membrane, a homogeneous discriminating layer can be formed and thereafter adhered to a porous supporting layer. Alternatively, the porous supporting 5 layer can be the surface upon which the discriminating layer is cast. In such an embodiment, the composite membrane is prepared by casting a solution as a coating on the porous support. Penetration of the polymer from which the discriminating layer is formed into the pores of the porous supporting layer is acceptable so long as the desired thickness of the membrane is not exceeded. The porous supporting layer is characterized in that it preferably does not 0 significantly impede the transport of gas through the membrane. In one embodiment, the porous supporting layer can be a metal or polymeric plate with a plurality of holes drilled through it. However, such a drilled plate is not advantageous because it may significantly reduce the effective area of the membrane. In a preferred embodiment, the porous supporting layer is a porous polymeric membrane. Examples of such porous polymeric membranes suitable 5 as porous supporting layers in composite membranes include commercially available porous cellulose ester and polysulfone porous membranes. Other preferred porous supporting layers include porous membranes fabricated from polycarbonates, polyester-carbonates, pofyϊmides, and polyethersulfones. Where such porous supporting membranes are thin or highly deformable, a frame or screen may also be used to adequately support the membrane. In one especially preferred embodiment, the porous polymeric supporting layer is a hoi low fiber of a porous polymeric membrane such as a microporous polysulfone membrane. The hollow fiber itself provides adequate support for the discriminating layer coated on the inside or the outside surface of the hollow fiber. After the solution is cast onto the porous supporting layer to form the thin discriminating layer, the membrane is then exposed to curing or drying conditions to substantially remove solvent from the discriminating layer such as described hereinbefore for the formation of homogeneous membranes.

Asymmetric membranes may be prepared by forming a thin discriminating layer on a porous supporting layer. Such membranes possess a discriminating layer which generally has the same composition but a different structure than the porous supporting layer. To prepare an asymmetric membrane, a solution of uncross-linked polymer, solvent, and optional non-solvent is formed and cast as hereinbefore described for homogeneous membranes. Preferred non-solvents for use in this invention include alcohols such as methanol, hydro- carbons such as heptane, and C₂-C₆ glycols. The cast solution is partially cured to remove a portion of the solvent and optional non-solvent. Thereafter, one or both surfaces of the partially cured membrane is contacted with a non-solvent for the polymer such as water so as to form a thin discriminating layer on one or both sides of the membrane while substantially removing the solvent and optional non-solvent from the membrane. The porous supporting layerformed provides support forthe thin discriminating layer without significantly impeding the transport of gas through the membrane. The drying step is performed in a manner similar to that described hereinbefore with respect to the formation of homogeneous membranes. Alternatively, an asymmetric membrane with two porous surfaces and an internal discriminating region may be formed. Flat sheet, tubular, and hollow fiber membranes which are homogeneous, composite, or asymmetric may be formed by extrusion from an appropriate solution of the uncross-linked polymer in a solvent and optional non-solvent. Such extrusion processes are well known to those skilled in the art and the formation of such membranes requires the adaptation of the hereinbefore described techniques. Extrusion is a preferred process for the fabrication of flat sheet, tubular, or hollow fiber membranes. In the case of extrusion, the components of the extrusion mixture may be combined prior to extrusion by mixing in any convenient manner with conventional mixing equipment, as for example, in a Hobart mixer. Alternatively, the extrusion mixture may be homogenized by extruding the mixture through a twin screw extruder, cooling the extrudate, and grinding or pelletizing the extrudate to a particle size readily fed to a single or twin screw extruder. The components of the extrusion mixture may also be combined directly in a melt- pot or twin screw extruder and extruded into membranes in a single step. The uncross-linked polymer, solvent, and optional non-solvent mixture is heated to a temperature at which the mixture becomes a substantially homogeneous fluid- The substantially homogeneous fluid is then extruded through a sheet, hollow tube, or hollow fiber die (spinnerette). Hollow fiber spinnerettes are typically multi-holed and thus produce a tow of multiple hollow fibers. The hollow fiber spinnerettes include a means for supplying fluid to the core of the extrudate. The core fluid is used to prevent collapse of the hollow fibers as theexitthe spinnerette. The core fluid may be a gas such as nitrogen, air, carbon dioxide, or other inert gas, or a liquid which is a non-solvent for the polymer such as water. Following extrusion, the membrane is treated as hereinbefore described for homogeneous, composite, or asymmetric membranes.

In one preferred embodiment, the membranes are annealed before use. The membrane is preferably exposed to temperatures above 50^CC and below 300°C for a period of time to partially densify the polymer. This procedure may optionally be performed under vacuum. Preferably, the homogeneous membranes useful in this invention have a thickness of between 5 microns and 500 microns, more preferably between 10 microns and 150 microns. Hollow fiber homogeneous membranes preferably have an outer diameter of between 50 microns and 800 microns, more preferably between 100 microns and 300 microns. _ Preferably, the effective discriminating layer in composite or asymmetric membranes has a thickness of between 0.02 microns and 10 microns, more preferably between 0.02 microns and 2 microns. Preferably, the supporting layer in composite or asymmetric membranes possesses a thickness of between 5 microns and 500 microns, more preferably between 10 microns and 150 microns. Hollow fiber composite or asymmetric membranes preferably have an outer diameter in the range of from 50 microns to 800 microns, more preferably in the range of from 100 microns to 300 microns.

The membranes are fabricated into flat sheet, spiral wound, tubular, or hollow fiberdevices by methods known in the art. See U.S. Patents 3,228,876; 3,422,008; 3,455,460; 3,475,331; 3,526.001; 3,528,553; 3,690,465; 3,702,658; 3,755,034; 3,801,401; 4,271,900; 3,872,014; 3,966,616; 4,045,851; 4,061,574; 4,080,296; 4,083,780; 4,220,535; 4,235,723; 4,265,763; 4,315,819; 4,430,219; 4,351,092; 4,367,139; 4,666,469; 4,707,167; 4,752,305; 4,758,341; 4,871,379; 4,929,259; 4,961,760; 5,013,331; and 5,013,437.

The membranes are sealingly mounted in a pressure vessel in such a manner that the membrane separates the vessel into two fluid regions wherein fluid flow between the two regions is accomplished byfluid permeating through the membrane. Under certain conditions, it may be highly desirable to provide support for the membrane when the membrane is employed in a separation apparatus or process. In one embodiment, the peripheral area of the membrane is affixed to a framing structure which supports the outer edge of the membrane. The membrane can be affixed to the framing structure by a clamping mechanism, adhesive, chemical bonding, or other techniques known in the art. The membrane affixed to the frame can then be sealingly engaged in the conventional manner in a vessel so that the membrane surface inside the framing support separates two otherwise non-communicating regions in the vessel. One skilled in the art will recognize that the structure which supports the membrane can be an internal part of the vessel or even the outer edge of the membrane.

The membrane divides the separation chamber into two regions, a high pressure side into which the feed gas mixture is introduced and a low pressure side. One side of the membrane is contacted with a feed gas mixture under pressure, while a pressure differential is maintained across the membrane. In the embodiment wherein the membrane is in hollow fiber form, the feed gas mixture may be introduced on the outside or the inside of the hollow fiber. At least one gaseous component in the gas mixture selectively permeates through the membrane more rapidly than the other gaseous component or components in the gas mixture. Gas which is enriched in the selectively permeating gaseous component or components is thus obtained on the low pressure side of the membrane which is removed from the low pressure side of the membrane as permeate. Gas depleted in the selectively permeating gaseous component or components is obtained on the high pressure side of the membrane which is removed from the high pressure side of the membrane as non-permeate. Gas permeability is defined as (amount of permeant)(membrane thickness)

P = (area)(time)(driving force across the membrane)

A standard permeability measurement unit is the Barrer (Ba), which is equal to (centimeter)³ (STP) (centimeter)

10 ,-10 .

(centimeter)² (second) (centimeter Hg) cm³ (STP) cm abbreviated hereinafter as 10^'10 . cm²s cmHg

The reduced gas flux isdefined as (permeability) ÷ (membrane thickness). A standard reduced flux unit is

(centimeter)³ (STP)

(centimeter)² (second) (centimeter Hg) abbreviated hereinafter as cm³ (STP) 10-⁶- cm²scmHg Alpha, the gas separation factor or gas selectivity, is defined as the ratio of the permeability or flux of the faster permeating gas to the permeabi lity or f I ux of the slower permeating gas.

The membranes of this invention are particularly useful for separating gas mixtures containing at least one gas selected from the group consisting of hydrogen, helium, oxygen, nitrogen, carbon monoxide, carbon dioxide, argon, water vapor, hydrogen sulfide, ammonia, nitrogen oxides, sulfur oxides, and light hydrocarbons. As used herein, the term light hydrocarbons refers to gaseous saturated and unsaturated C hydrocarbons such as methane, ethane, ethylene, propane, propylene, butane, and butyiene. Preferably, the membranes useful in this invention exhibita permselectivity of an oxygen/nitrogen gas mixture at30°C of 2.5, more preferably 3.5, and even more preferably 4.0. Preferably, the membranes have a permeabilityfor oxygen at 30°C of 0.01 Barrer, more preferably 0.05 Barrer, and even more preferably 0.1 Barrer. Preferably, the membranes have a reduced gas flux for oxygen at 30°C of

cm³ (STP)

1.0 X 10^"3 , more preferably cm²scmHg cm³ (STP) 5.0 X 10^"9 , and most preferably

Preferably, the membranes useful in this invention exhibit a permselectivity of a helium/methane gas mixture at 30°Cof 20, more preferably 35, most preferably 50. Preferably, the membranes have a permeability for helium at30°C of 2.0 Barrers, more preferably 3.5 Barrers, most preferably 5.0 Barrers. Preferably, the membranes have a reduced gas flux for helium at 30°C of

cm³ (STP) 1.0 X 10^"8 , more preferably cm²scmHg cm³ (STP)

5.0 X 10^a ,.and most preferably cm²scmHg

cm³ (STP)

1.0 X I 0^"7- cπrs cmHg The separation process is carried out at pressure and temperatures which do not deleteriously affect the membrane. Preferably, the pressure on the high pressure side of the membrane is between 10 psig (69 kPa) and 1,000 psig (6,895 kPa), more preferably between 50 psig (345 kPa) and 500 psig (3,447 kPa). The temperature of the feed gas mixture is preferably between -50°C and 100°C, more preferably between -20°C and 100°C. The temperature of the membrane is independent of the temperature of the feed and is preferably between -50°C and 100°C, more preferably between -20°C and 80°C.

The membrane devices used in the process of this invention may be arranged in parallel, series, recycle, or cascade configurations. The membrane separation process of this invention may be combined with non-membrane separation processes such as cryogenic distillation and pressure or temperature swing adsorption.

The following Examples are included to illustrate the invention.

Monomer Synthesis Example 1 - Preparation of 2,2-Bis(3-bromo-4-hvdroxy-phenyl-4'-bromo-3'- hydroxyphenvQpropane.

10.95 grams (g) (48 mmoles) of 2,2-bis-(4-hydroxyphenyl-3'- hydroxyphenyl)propane were dissolved in a 500 milliliter (mL) Erlenmeyer flask containing a magnetic stir bar and 100 mL of methylene chloride and 5 mL of methanol. Aliquots of bromine solution (5 mL of Br₂ diluted to 100 mL with methylene chloride) were added to the solution over a period of about 20 minutes (min.). The extent of reaction was monitored using an HP 5890 Gas Chromatograph equiped with a 5 foot (1.5 meter) HP-1 methyl silicone gum column. Two product peaks were obtained. Additionally, a small aliquot of product was removed from the reaction mixture, extracted with aqueous sodium sulfite, dried with magnesium sulfate, and derivatized with a small amount of acetyl chloride in the presence of pyridine. The derivatized product was analyzed using an HP 1090 Liquid Chromatograph equipped with a Spheri-10 RP-18 column. Once again, two product peaks were obtained (6.48 min. (major, derivatized dibromo species) and 7.38 min. (minor)). The sample mixture was isolated as a gummy, tacky solid.

Example 2 - Preparation of 2,2-Bis(3,5 dibromo-4--hvdroxyphenyl-4'6'-dibromo-3'- hvdroxyphenyl) propane.

10.95 g (48 mmoles) of 2,2-bis-(4-hydroxy-phenyl-3'-hydroxyphenyl) propane were dissolved in a 500 mL Erlenmeyer flask containing a magnetic stir bar and 100 mL of methylene chloride and 5 mL of methanol. Aliquots of bromine solution (10 mL of Br₂ diluted to 100 mL with methylene chloride) were added to the solution over a period of several hours. The extent of reaction was monitored using an HP 5890 Gas Chromatograph equiped with a 5 foot (1.5 meter) HP-1 methyl silicone gum column. Three product peaks were obtained. Additionally, a small aliquot of product was removed from the reaction mixture, extracted with aqueous sodium sulfite, dried with magnesium sulfate, and derivatized with a small amount of acetyl chloride in the presence of pyridine. The derivatized product was analyzed using an HP 1090 Liquid Chromatograph equipped with a Spheri-10 RP-18 column. Once again, three product peaks were obtained (7.38 min. (minor), 7.82 min. (minor), and 8.15 min. (major)). The sample was isolated as a white, free flowing, powdery solid after recrystallϊzation from methanol/water.

Polymer Synthesis Example 3 - Preparation of Polv(2,2-bis(4-hydroxyphenyl--3'-hvdroxy- phenyl)propane)carbonate.

10 g (43.8 mmoles) of white, powdery 2,2,bis(4-hydroxyphenyl-3'-hydroxyphenyl) propane were weighed and transferred to a three-neck, 500 mL round bottom flask equipped with a stirrer, sparge tube for dry nitrogen, and a pH electrode. 7.4 g (92.5 mmoles) of 50 percent NaOH solution was diluted to a volume of 50 mLwϊth water and transferred to the flask. Stirring was initiated and the solid was dissolved within a few minutes. Fifty milliliters of methylene chloride was added to the flask and stirring was continued. An addition funnel was fitted to the flask and 41 mL of phosgene/methylene chloride (96.4 mmoles of 2.32 M sol ution) was transferred to the funnel. Phosgene solution was added dropwisetothe stirred solution overa period of about 20 min. while maintaining the pH of the aqueous phase at 10.5 with occasional additions of 1 N NaOH. When the phosgene addition was complete, the aqueous phase was tested forthe presence of phenates (negative) and the organic phase was tested for chloroformates (positive). Eighty milligrams (mg) (0.7 mmoles) of N,N-dimethylamino-pyridine was weighed and added at once to the heterogeneous mixture. Slowly, the acidity began to increase; the pH was maintained at 9 with the addition of 1 N NaOH. The reaction was judged complete when no chloroformates could be detected in the organic phase. The reaction mixture was acidified with 1 N HCI, washed with water and phase separated- The organic phase was dried using magnesium sulfate and the clear water-white solution was precipitated in 4 volumes of heptane- The fluffy white solid was air dried, then oven dried under vacuum at 80°C overnight.

Asmall sample of dried polymer (about 125 mg) was dissolved in a 25 mL volumetricflask with methylene chloride. Size exclusion analysis was performed using a Hewlett Packard 1090 Liquid Chromatograph equipped with a pair of duPontZorbax PSM Trϊmodal columns and a diode array detector. The eluting solvent was HPLC grade tetrahydrofuran (THF). The calibration curve was established using narrow standard polystyrene samples monitored at 254 nm. The sample was found to have a weight-average molecuIarweϊght(Mw) of about 75,000. Example 4 - Preparation of Polv(2,2-bis(3-bromo-4-hvdroxyphenyl-4'-bromo-3'- hvdroxyphenvQpropane carbonate.

5 g (13 mmoles) of the 2,2-bis(3--bromo-4-hydroxyphenyl-4'-bromo-3'- hydroxyphenyl)-propane were weighed into a 100 mL screw-cap bottle and dissolved in methylene chloride (25 mL) and 25 mL of 1 N aqueous sodium hydroxide (25 mmoles). Phosgene in methylene chloride (2.32 M, 10 mL) was added to the mixture. The mixture was then shaken for ten min. Additional aqueous sodium hydroxide was added to maintain the alkalinity (pH approximately 10). When the aqueous phase was found to be free of phenates, a small amount of N,N-dimethylaminopyridine (16 mL, 0.13 mmoles) was added to the mixture and vigorous shaking was continued. After 10 min., additional aqueous sodium hydroxide solution was added to the mixture to maintain the alkalinity (pH approximately 10). During this period, a small volume of phosgene solution (2.32 M, 2 mL) was also added to the mixture. Vigorous shaking was once more initiated and continued until the milky emulsion thickened o into a massive gum-like liquid. The contents were transferred to a Waring blender, further diluted with methylene chloride and water, and stirred for several minutes. The mixture was acidified with dilute acid (1 N HCI). The stirring was then stopped and the mixture was allowed to separate into two liquid phases. The aqueous phase was discarded and the organic phase was washed with water. The hazy organic solution was then dried over anhydrous magnesium 5 sulfate and filtered through a Celite bed on a fritted glass filter. The clear solution was reduced in volume and precipitated in four volumes of heptane. The white, fiberous solid was air dried and oven dried under vacuum at 80°C for sixteen hours (hr.).

A small sample of dried polymer (125 mL) was dissolved in a 25 mL volumetric flask with methylene chloride. The poly(2,2-bis(3-bromo-4-hydroxyphenyl-4'-bromo-3'- 0 hydroxyphenyl)-propane) carbonate sample was analyzed and found to have a number- average molecular weight (Mn) of about 85,975 and a weight-average molecular weight (Mw) of about 439, 539.

Example 5 - Preparation of Polv(2.2-bis(3,5 dibromo-4-hydroxyphenyl-4'6'-dibromo-3'- hydroxyphenyl)propane)-carbonate. The process of Example 4 was repeated with the exception that 7.07 g (13 mmoles) of 2,2-bis-(3,5-dibromo-4-hydroxy-4'6'-dibromo-3'-hydroxyphenyl)-propane was used in place of 2,2-bis(3-bromo-4-hydroxyphenyl-4'-bromo-3'-hydroxyphenyl)propane. Example 6 - Preparation of Polv(2.2-bis(4-hvdroxyphenyl-3'-hvdroxy- phenyl)propane)terephthaloyl-co-isophthaloyl ester carbonate (E/C = 2/1. T/l = 8/2). A three neck, 250 mL round bottom flask, equipped with a stirrer, nitrogen sparge tube, and an addition funnel, was charged with 5.00 g (21.9 mmoles) of 2,2-bis(4- hydroxyphenyl-3'-hydroxyphenyl)propane, 50 mL of methylene chloride, and 5 mL (62 mmoles) of pyridine. The resultant clear, colorless solution was stirred under nitrogen for 10 min. A mixture of terephthaloyl chloride (1.776 g; 8.75 mmoles), and isophthaloyl chloride (0.440 g; 2.17 mmoles), was dissolved in 20 mL of methylene chloride and transferred to an addition funnel. An aliquot of phosgene/methylene chloride solution (5.0 mL; 12.2 mmoles), was also transferred to the addition funnel. The flask was immersed in a water bath and moderate stirring of the solution was continued while the acid chloride/phosgene solution was added dropwise over a period of 15 min. When the addition was complete, an additional 0.2 g (1 mmole) of 2,2-bis(4-hydroxyphenyl-3'-hydroxyphenyl)propane was added to the stirring solution, followed by the slow addition of 2 mL of phosgene/methylene chloride solution. Stirring was continued foranother 30 min.

The viscous solution was diluted with 50 mL of methylene chloride, washed with 30 mLof 1 N HCI, and transferred to a separatory funnel. The organic phase was washed twice with water. The colorless, water-wet organic phase was dried with magnesium sulfate and filtered through Celite to yield a clear, colorless solution. The polymerwas found to have a weight-average molecular weight (Mw) of 102,000 and a number-average molecular weight (Mn) of 27,700, based on polystyrene standards and a polydispersity of 3.7. Example 7 - Preparation of Poly (2,2-bis(4-hvdroxy-phenyl)propane)carbonate - Comparative Example.

The process of Example 3 was repeated with the exception that 10 g (43.8 mmoles) of 2,2-bis-(4-hydroxyphenyl)propane was used.

Example 8 - Preparation of Polv(2,2-bis(3,5-dibromo-4--hvdroxyphenyl)propane)carbonate - Comparative Example-

The process of Example 3 was repeated with the exception that 23.8 g (43.8 mmoles) of 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane was used. Membrane Preparation

The polymers of Examples 3, 4, 5, and 6 were used to prepare membranes therefrom. Films were obtained by casting 20 weight percent polymer solution onto glass plates, allowing the solutions to slowly devolatilize, removing the films from the glass plates, and placing the films in a heated vacuum oven to remove residual solvent. The gas permeabilities of nitrogen, oxygen, helium, methane, and carbon dioxide were measured on a dense film having a diameter of about 3.8 centimeters using a constant- volume, variable-pressure apparatus. The permeability coefficients were measured at25°C using a feed pressure of 50 psig (340 kPa). Performance data forthe membranes are reported in Table I

TABLE I

Claims

1. A semi-permeable gas separation membrane characterized by a thin discriminating region of an uncrosslinked condensation polymer possessing repeat units of the structure:

wherein

R represents individually in each occurrence a hydrogen radical, a monovalent C.-

C₈ hydrocarbyl radical, a C_t-C₈ monovalent halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen;

L represents a direct bond or a divalent C -C_ts hydrocarbyl radical, a divalent C.-C₁₅ halohydro-carbyl radical, -S-,-SO-,-S0₂-, or-SS-;

R^l represents individually in each occurrence -CO-, -CS-, -S0₂-,

0 0 II II

0

wherein

Z represents individually in each occurrence hydrogen radical, a monovalent C^C_g hydrocarbyl radical, a C^ monovalent halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen;

R² represents:

wherein

R' represents independently in each occurrence hydrogen radical, a monovalent C_τ-C₈ hydrocarbyl radical, a monovalent C^C_g halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen, and L' represents a direct bond or a divalent C..-C hydrocarbyl radical, a divalent C_t-C₁₅ halo-hydrocarbyl radical, -0-, -S-, -SO-, -S0₂- or -SS-; x is a positive number between 0 and 1 inclusive; y is a positive number between 0 and 1 inclusive; and n is a positive number representing a degree of polymerization which provides a number- average molecular weight of at least 3,000. 5

2. The membrane of Claim 1 wherein Rrepresents individually in each occurrence a hydrogen radical, a monovalent C.-C₈ hydrocarbyl radical, a ^-C_& monovalent halohydrocarbyl radical ora halogen.

3. The membrane of Claim 2 wherein R represents individually in each occurrence a hydrogen radical, a monovalent C₁-C₄ hydrocarbyl radical, a C₁-C₄ monovalent .

10 halohydrocarbyl radical ora halogen.

4. The membrane of Claim 2 wherein the halogens are chlorine or bromine.

5. The membrane of Claim 1 wherein L represents a direct bond or a divalent C,- C₁₅ hydrocarbyl radical or a divalent C^C^ halohydrocarbyl radical.

6. The membrane of Claim 5 wherein L represents a divalent C.-C₈ hydrocarbyl 15 radical ora divalent C.-C₆ halohydrocarbyl radical.

7. The membrane of Claim 1 wherein R¹ represents individually in each occurrence -CO-, -CS-,-COC₆Z₄CO- or -COC_]SZ₁₂CO-, wherein Z represents individually in each occurrence a hydrogen radical, a monovalent C,-C₄ hydrocarbyl radical, a C.--C, monovalent halohydrocarbyl radical ora halogen. 0

8. The membrane of Claim 1 wherein R² represents:

wherein 0 R' represents independently in each occurrence a hydrogen radical, a monovalent C_τ-C₄ hydrocarbyl radical, a monovalent C,-C₄ halohydrocarbyl radical ora halogen.

9. The membrane of Claim 8 wherein the halogens are bromine or chlorine.

10. The membrane of Claim 1 wherein L' represents a direct bond or a divalent C.- ^ C₈ hydrocarbyl radical, a divalent C.-C₈ halohydrocarbyl radical, -0-, -S-, -SO- or -S0₂-.

11. The membrane of Claim 10 wherein L' is a direct bond or a divalent C 1-C 4 hydrocarbyl radical, a divalent C^-C^ halohydrocarbyl radical, -0-, -S-, -SO- or -S0₂-.

12. The membrane of Claim 1 wherein x is a positive number between 0.33 and 1 inclusive.

13. The membrane of Claim 12 wherein x is a positive number between 0.67 and 1 inclusive.

14. The membrane of Claim 1 wherein y is a positive number between 0 and 0.75 inclusive.

15. The membrane of Claim 14wherein y is a positive number between O and 0.50 inclusive.

16. The membrane of Claim 15 wherein y is a positive number between O and 0.25 inclusive.

17. The membrane of Claim 1 wherein n is a positive number between 10 and

2,000.

18. The membrane of Claim 1 wherein the membrane is composite or asymmetric.

19. The membrane of Claim 1 wherein the membrane is a hollow fiber.

20. The membrane of Claim 1 wherein the permselectivity for oxygen nitrogen at

30°C is at least 4.0.

21. The membrane of Claim 20 wherein the permeability for oxygen at 30°C is at least 0.1 Barrer.

22. The membrane of Claim 20 wherein the reduced gas flux for oxygen at 30°C is at least cm³ (STP) 1.0 X 1 O^"8 . cm²s cmHg

23. The membrane of Claim 1 wherein the permselectivity for helium/methane at 30°C is at least 50.

24. The membrane of Claim 23 wherein the permeability for helium at 30°C is at least 5.0 Barrers.

25. The membrane of Claim 23 wherein the reduced gas flux for helium at 30°C is at least cm³ (STP) 1.0 X 10-⁷ . cm²s cmHg

26. A process of separating gases comprising:

A. contacting one side of a semi-permeable gas separation membrane with a feed gas mixture under pressure, wherein the membrane divides a separation chamber into a high pressure side into which the feed gas mixture is fed and a low pressure side; B. maintaining a pressure differential across the membrane under conditions such that at least one gaseous component in the feed gas mixture selectively permeates through the membrane from the high pressure side to the low pressure side of the membrane;

C. removing from the low pressure side of the membrane permeated gas which is enriched in at least one selectively permeating gaseous component; and

D. removing from the high pressure side of the membrane non-permeated gas which is depleted inatleastone selectively permeating gaseous component; wherein the membrane is characterized byathin discriminating region of an uncross-linked condensation polymer possessing repeat units of the structure:

wherein

C_g hydrocarbyl radical, a C.-C₃ monovalent halohydrocarbyl radical, a -N0₂ radical, a-S0₃H radical ora halogen;

L represents a direct bond or a divalent C -C hydrocarbyl radical, a divalent C -C halohydro-carbyl radical, -S-, -SO-, -S0₂-, or -SS-;

R' represents individually in each occurrence -CO-, -CS-, -S0₂-,

0 II

wherein

Z represents individually in each occurrence a hydrogen radical, a monovalent C,-~₈ hydrocarbyl radical, a C^C_g monovalent halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical ora halogen;

R² represents:

wherein

R' represents independently in each occurrence a hydrogen radical, a monovalent

C_t-C₈ hydrocarbyl radical, a monovalent ~.-~_% halohydrocarbyl radical, a -N0₂ radical, a -S0₃H radical or a halogen, and

L' represents a direct bond ora divalent C^C^ hydrocarbyl radical, a divalent C^

C₁₅ halo-hydrocarbyl radical, -0-, -S-, -SO-, -S0₂- or -SS-; x is a positive number between 0 and 1 inclusive; y is a positive number between 0 and 1 inclusive; and n is a positive integer representing a degree of polymerization which provides a number- average molecular weight of at least 3,000.

27- The process of Claim 26 wherein the feed gas mixture contains at least one of the gases hydrogen, helium, oxygen, nitrogen, argon, carbon monoxide, carbon dioxide, water vapor, hydrogen sulfide, nitrogen oxides, sulfur oxides, ammonia or light hydrocarbons.

28. The process of Claim 26 wherein the pressure of the feed gas mixture is between 10 psig (69 kPa) and 1 ,000 psig (6895 kPa).

29. The process of Claim 26 wherein the temperature of the feed gas mixture is between -50°C and 100°C.

30. The process of Claim 26 wherein the temperature of the membrane is between -50^σC and 100°C.