Crosslinked and crosslinkable hollow fiber membrane and method of making same utility
A composition of and a method of making high performance hollow fiber membranes is described. The membranes have a high resistance to plasticization by use of a predetermined amount of crosslinking. The preferred polymer material for the membrane is a polyimide polymer comprising covalently bonded ester crosslinks. The resultant hollow fiber membrane exhibits a high permeability of CO 2 in combination with a high CO 2 /CH 4 selectivity. Another embodiment provides a method of making the hollow fiber membrane from a monesterified polymer followed by final crosslinking after hollow fiber formation.
1. A composite polymer membrane, comprising:
a crosslinked polyimide polymer having covalent ester crosslinks; and having a CO 2 permeance of at least 20 GPU and a CO 2 /CH 4 selectivity of greater than 20, at 35 degrees C. and a pressure of 100 psia.
2. A composite 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.
3. A composite polymer membrane, comprising:
a polyimide polymer made from the monomers A+B+C;
where A is a dianhydride of the formula;
where X 1 and X 2 are the same or different halogenated alkyl group, phenyl or halogen;
where R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 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; and
wherein the ratio of B to C is between 1:4 and 8:1, and wherein said composite polymer membrane further comprises at least some covalent ester crosslinks.
4. The composite polymer membrane of claim 3 where X 1 and X 2 are CF 3 .
5. The composite polymer membrane of claim 3 where R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are H.
6. The composite polymer membrane of claim 3 wherein the dianhydnde is 6FDA.
7. he composite polymer membrane of claim 3 wherein C is DABA.
8. The composite polymer membrane of claim 3 wherein B is a diamino aromatic compound.
9. The composite polymer membrane of claim 3 wherein B is a methyl substituted diamino benzene.
10. The composite polymer membrane of claim 3 wherein the ratio of B to C is between 17:3 and 3:2.
11. The composite polymer membrane of claim 3 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.
12. The composite polymer membrane of claim 1 wherein the membrane is a flat sheet.
13. The composite polymer membrane of claim 12 wherein the membrane comprises a layer in a flat stack permeator.
14. The composite polymer membrane of claim 1 wherein the ester crosslinks are formed by the monoesterification of a polyimide polymer having carboxylic acid sites incorporated therein, with a diol.
15. The composite polymer membrane of claim 14 wherein the diol is selected from the group consisting of ethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,2 butanediol, benzenedimethanol, and 1,3 butanediol.
16. The composite polymer membrane of claim 3 wherein the ratio of B to C is between 4:1 and 3:2.
17. The composite polymer membrane of claim 3 wherein the polyimide polymer has an average molecular weight of between 20,000 and 200,000.
18. The composite polymer membrane of claim 3 wherein the membrane has an average molecular weight greater than the entanglement MW of the polymer.
19. The composite polymer membrane of claim 3 wherein the membrane has an average molecular weight of between 40,000 and 140,000.