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A composition of and a method of making high performance crosslinked membranes are described. The membranes have a high resistance to plasticization by use of crosslinking. The preferred polymer material for the membrane is a polyimide polymer comprising covalently bonded ester crosslinks. The resul

A composition of and a method of making high performance crosslinked membranes are described. The membranes have a high resistance to plasticization by use of crosslinking. The preferred polymer material for the membrane is a polyimide polymer comprising covalently bonded ester crosslinks. The resultant membrane exhibits a high permeability of CO2 in combination with a high CO2/CH4selectivity. Another embodiment provides a method of making the membrane from a monesterified polymer followed by final crosslinking after the membrane is formed.

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1. A hollow fiber polymer membrane comprising: a polyimide polymer membrane material made from a crosslinkable polymide polymer having an average molecular weight of at least 20,000 and including the monomers A+B+C;where A is a dianhydride of the formula; where X1 and X2 are the same or different ha

1. A hollow fiber polymer membrane comprising: a polyimide polymer membrane material made from a crosslinkable polymide polymer having an average molecular weight of at least 20,000 and including the monomers A+B+C;where A is a dianhydride of the formula; where X1 and X2 are the same or different halogenated alkyl group, phenyl or halogen;where R1, R2, R3, R4, R5, and R6 are H, alkyl, or halogen;where B is a diamino cyclic compound without a carboxylic acid functionality;where C is a diamino cyclic compound with a carboxylic acid functionality; andwherein the ratio of B to C is between 1:4 and 8:1; andwherein the hollow fiber polymer membrane material further comprises at least some covalent ester crosslinks. 2. The hollow fiber polymer membrane of claim 1 wherein the ratio of B to C is between 1:4 and 4:1. 3. The hollow fiber polymer membrane of claim 1 where R1 R2, R3, R4, R5, and R6 are H. 4. The hollow fiber polymer membrane of claim 1 wherein the dianhydride is 6FDA. 5. The hollow fiber polymer membrane of claim 1 wherein C is DABA. 6. The hollow fiber polymer membrane of claim 1 wherein B is a diamino aromatic compound. 7. The hollow fiber polymer membrane of claim 1 wherein B is a methyl substituted diamino benzene. 8. The hollow fiber polymer membrane of claim 1 wherein the ratio of B to C is 3:2. 9. The hollow fiber polymer membrane of claim 1 wherein said ester crosslinks are made using a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, benzenedimethanol, and 1,3 butanediol. 10. The hollow fiber polymer membrane material of claim 9 wherein the hollow fiber membrane material is subjected to transesterification, conditions to form a crosslinked hollow fiber polymer membrane. 11. The hollow fiber polymer membrane material of claim 1 wherein the ratio of B tai C is between 4:1 and 3.2. 12. The hollow fiber polymer membrane of claim 1 wherein the polyimide polymer has an average molecular weight of between 20,000 and 200,000. 13. The hollow fiber polymer membrane of claim 1 wherein the membrane material has an average molecular weight greater than the entanglement MW of the polymer. 14. The hollow fiber polymer membrane of claim 1 wherein the polyimide polymer has an average molecular weight of between 40,000 and 140,000. 15. A method of making a crosslinked hollow fiber membrane, comprising: preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites and having an average molecular weight of at least 20,000;treating the polyimide polymer with a diol selected from the group consisting of ethylene glycol, propyleneglycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, and 1,3 butanediol, at esterification conditions, to form a monoesterified polymer;forming a monoesterified hollow fiber from the monoesterified polymer; and subjecting the monoesterified hollow fiber to transesterification conditions to form a covalently crosslinked hollow fiber membrane; wherein the polyimide polymer is made from the monomers A+B+C; where A is a dianhydride of the formula; where X1 and X2 are the same or different halogenated alkyl group, phenyl or halogen;where R1, R2, R3, R4, R5, and R6 are H, alkyl, or halogen;where B is a diamino cyclic compound without a carboxylic acid functionality;where C is a diamino cyclic compound with a carboxylic acid functionality; andwherein the ratio of B to C is between 1:4 and 8:1. 16. The method of making crosslinked hollow fiber membrane of claim 15 wherein the polyimide polymer is treated with a diol in the presence of an esterification catalyst. 17. A hollow fiber polymer membrane comprising: a crosslinked polyimide polymer having covalent ester crosslinks formed from a crosslinkable polymer having an average molecular weight of at least 20000; and having a CO2 permeance of at least 20 GPU and a CO2/CH4 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia. 18. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer has an average molecular weight of between 20,000 and 200,000. 19. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer has an averan molecular weight of between 30,00(1 and 160,000. 20. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer has an average molecular weight of between 40,000 and 140,000. 21. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer has an average molecular weight of between 60,000 and 120,000. 22. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer has an average molecular weight greater than the entanglement molecular weight of the polymer. 23. The hollow fiber polymer membrane of claim 17 wherein: the ester crosslinks are made using a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, benzenedimethanol, and 1,3 butanediol. 24. The hollow fiber polymer membrane of claim 17 wherein: the crosslinkable polymer is formed by the monoesterification of a polyimide polymer having carboxylic acid sites incorporated therein, with a diol, followed by transesterification, to form a crosslinked polyimide polymer. 25. A polymer comprising: a polymer which has been monoesterified with a diol to form, a crosslinkable polymer having an average molecular weight of at least 20,000 andwhich can be formed into a membrane and transesterified to provide a crosslinked membrane having a CO2 permeance of at least 20 GPU and a CO210-14 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia. 26. The polymer of claim 25 wherein: the crosslinkable polymer has an average molecular weight of between 20,000 and 200,000. 27. The polymer of claim 25 wherein: the crosslinkable polymer has an average molecular weight of between 40,000 and 140,000. 28. The polymer of claim 25 wherein: the crosslinkable polymer has an average molecular weight of between 60,000 and 120,000. 29. A process for producing hydrocarbon products comprising: separating two gases having different molecular sizes in a feedstream including these two gas components, the process including: (a) providing a hollow fiber crosslinked polymer membrane made from polyimide polymer having an average molecular weight of at least 20,000 and having covalent ester crosslinks and having a CO2 permeance of at least 20 CPU and a C02/CH4 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia, the membrane having feed and permeate sides and which is selectively permeable to a first gas component over a second gas component, and (b) directing a feedstream including the first and second gas components to the feed side of the membrane and withdrawing a retentate stream depleted in the first gas component and withdrawing a permeate stream enriched in the first gas component from the permeate side of the membrane. 30. A hollow fiber polymer membrane comprising: a crosslinked polyimide polymer having at least some covalent ester crosslinks and having a ratio of crosslinkable sites to imide groups of between 3:8 and 1:16, the crosslinked polyimide polymer being made from polyimide polymer having an average molecular weight of at least 20,000. 31. The hollow fiber polymer membrane of claim 1 wherein the ratio of B to C is between 17:3 and 3:2. 32. The hollow fiber polymer membrane of claim 1 wherein the ratio of B to C is between 17:3 and 3:1. 33. The hollow fiber polymer membrane of claim 1 wherein: the ratio of B to C is between 4:1 and 3.2. 34. A method of making a crosslinked hollow fiber membrane, comprising: preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites the polyimide polymer having a molecular weight of at least 20,000;treating the polyimide polymer with a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, and 1,3 butanediol, at esterification conditions, to form a mono esterified polymer; forming a mono esterified hollow fiber from the mono esterified polymer; and subjecting the mono esterified hollow fiber to trans esterification conditions to form a covalently crosslinked hollow fiber membrane.