Asymmetric polyimide membranes

Claim 2

An asymmetric polyimide membrane comprising a unitary membrane having a thin dense skin supported on a porous substructure, characterized in that (a) said skin and substructure are composed of a fully imidized polymer based on 5(6)-amino-1-(4'-aminophenyl)-1,3-trimethylindane; (b) it has a pre diameter of less than 20 Å; (c) it has a CO 2 /CH 4 selectivity of at least 20; and (d) it has CO 2 permeability of at least 1 SCFH/ft 2 at 100 psi.

Claim 3

The asymmetric polyimide polymer membrane according to claim 1 wherein said CO 2 /CH 4 selectivity is at least 30 and said CO 2 permeability is at least 2.0 SCFH/ft 2 at 100 p.s.i..

Claim 4

The asymmetrical polyimide polymer membrane according to claims 1 or 2 characterized in that it is formed into a flat sheet.

Claim 5

The as polyimide polymer membrane according to claims 1 or 2 characterized in that it is formed into a hollow fiber configuration.

Claim 6

The membrane of claim 1 having mechanical strength sufficient to withstand a pressure of at least 500 psi.

Claim 7

The process of preparing a polyimide polymer membrane having a pore diameter of less than 20 Å units, a CO 2 /CH 4 selectivity of at least about 20, and a CO 2 permeability of at least 1.0 SCFH/ft 2 at 100 p.s.i., said process comprising the steps of: (a) preparing a polyimide dope solution consisting essentially of: (1) a fully imidized polyimide polymer based on 5(6)-amino-1-(4'-aminophenyl)-1,3-trimethylindane present in amounts of 20 to 28% by weight of said dope solution; (2) a solvent system for said polyimide which is water miscible and is selected from the group consisting essentially of N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, dioxane, γ-butyrolactone or a mixture thereof; (3) a low molecular weight non-solvent system present in amounts of less than 10% by weight of said dope solution consisting essentially of water, ketones, alcohols, or formamide; (4) a viscosity enhancer present in amounts of less than 3% by weight of said dope solution consisting essentially of polyvinyl pyrrolidones, polyethylene glycols or urethanes; (5) a void supressor present in amounts of less than 5% by weight of said dope solution consisting essentially of maleic acid; casting a film of said polyimide dope solution onto a supporting substrate; (c) evaporating said solvent system under conditions of time, temperature and air flow rate sufficient to produce a polyimide membrane final product characterized by a CO 2 /CH 4 selectivity of at least about 20 and a CO 2 permeability of at least about 1.0 SCFH/ft 2 at 100 p.s.i.; (d) immersing said film cast on said substrate into a coagulating medium consisting essentially of water, alcohol, ketones or mixtures thereof; and (e) washing and drying the thusly prepared asymmetric polyimide membrane.

Claim 8

The process of preparing a polyimide polymer membrane having a pore diameter of less than 20 Å units, a CO 2 /CH 4 selectivity of at least about 20, and a CO 2 permeability of at least 1.0 SCFH/ft 2 at 100 p.s.i., said process comprising the steps of: (a) preparing a polyimide dope solution consisting essentially of: (1) a fully imidized polyimide polymer based on 5(6)-amino-1-(4'-aminophenyl)-1,3-trimethylindane present in amounts of 20 to 28% by weight of said dope solution; (2) a solvent system for said polyimide which is water miscible and is selected from the group consisting essentially of N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, dioxane, γ-butyrolactone or a mixture thereof; (3) a low molecular weight non-solvent system present in amounts of less than 10% by weight of said dope solution consisting essentially of water, ketones, alcohols, or formamide; (4) a viscosity enhancer present in amounts of less than 3% by weight of said dope solution consisting essentially of polyvinyl pyrrolidones, polyethylene glycols or urethanes; (5) a void supressor present in amounts of less than 5% by weight of said dope solution consisting essentially of maleic acid; casting a film of said polyimide dope solution onto a supporting substrate; (c) evaporating said solvent system under conditions of time, temperature and air flow rate sufficient to produce a polyimide membrane final product characterized by a CO 2 /CH 4 selectivity of at least about 20 and a CO 2 permeability of at least about 1.0 SCFH/ft 2 at 100 p.s.i.; (d) immersing said film cast on said substrate into a coagulating medium consisting essentially of water, alcohol, ketones or mixtures thereof; and (e) washing and drying the thusly prepared asymmetric polyimide membrane.

Claim 9

The process of preparing a polyimide polymer membrane according to claim 6 under conditions of time, temperature, and air flow rate sufficient to produce a polyimide membrane final product characterized by a CO 2 /CH 4 selectivity of at least 30 and a CO 2 permeability of at least 2.0 SCFH/ft 2 at 100 p.s.i.

Claim 10

The process of claim 6 characterized in that said solvent system consists of a mixture of two solvents, one solvent having a boiling point of less than 102° C. selected from the group consisting essentially of tetrahydrofuran and dioxane and the other solvent having a boiling point of greater than 150° C. selected from the group of N-methyl-2-pyrrolidone, N,N-dimethylformamide and γ-butyrolactone wherein the proportions of said high boiling point solvent to said low boiling point solvent present are from 25:75 to 75:25.

Claim 11

The asymmetric polyimide polymer membrane prepared according to the process of claim 6 or 7 characterized in that it is formed into a flat sheet configuration.

Claim 12

The asymmetric polyimide polymer membrane prepared according to the process of claim 6 or 7 characterized in that it is formed into a hollow fiber configuration.