Crosslinked and crosslinkable hollow fiber membrane and method of making same

Abstract

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 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.

What is claimed is:  
     
         1 . A hollow fiber polymer membrane, comprising: 
 a crosslinked polyimide polymer having ester crosslinks; and having a CO 2  permeability of at least 20 Barrers and a CO 2 /CH 4  selectivity of greater than 30, at 35 degrees C. and a pressure of 100 psia.    
     
     
         2 . A hollow fiber polymer membrane, comprising: 
 a crosslinked polyimide polymer having at least some ester crosslinks and having a ratio of crosslinkable sites to imide groups of between 3:8 and 1:16.    
     
     
         3 . A hollow fiber polymer membrane material, 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.    
     
     
         4 . A method of making a crosslinked hollow fiber membrane, comprising: 
 preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites;    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 monoesterified membrane material;    forming a monoesterified hollow fiber from the monoesterified membrane material; and    subjecting the monoesterified hollow fiber to transesterification conditions to form a crosslinked hollow fiber membrane.    
     
     
         5 . The hollow fiber polymer membrane material of  claim 3  where X 1  and X 2  are CF 3 .  
     
     
         6 . The hollow fiber polymer membrane material of  claim 3  where R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are H.  
     
     
         7 . The hollow fiber polymer membrane material of  claim 3  wherein the dianhydride is 6FDA.  
     
     
         8 . The hollow fiber polymer membrane material of  claim 3  wherein C is DABA.  
     
     
         9 . The hollow fiber polymer membrane material of  claim 3  wherein B is a diamino aromatic compound.  
     
     
         10 . The hollow fiber polymer membrane material of  claim 3  wherein B is a methyl substituted diamino benzene.  
     
     
         11 . The hollow fiber polymer membrane of  claim 3  material wherein the ratio of B to C is between 17:3 and 3:2.  
     
     
         12 . The hollow fiber polymer membrane material of  claim 3  wherein the ratio of B to C is between 17:3 and 3:1.  
     
     
         13 . The hollow fiber polymer membrane material of  claim 3  wherein said membrane material is subjected to esterification conditions in the presence of 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 to form a hollow fiber polymer membrane monoester.  
     
     
         14 . The hollow fiber polymer membrane monoester of  claim 13  wherein at least 60% of the carboxylic acid functionality is converted to a monoester.  
     
     
         15 . The hollow fiber polymer membrane material of  claim 13  wherein the hollow fiber membrane monoester is subjected to transesterification conditions to form a crosslinked hollow fiber polymer membrane.  
     
     
         16 . The hollow fiber polymer membrane of  claim 1  wherein the polyimide is 6FDA.  
     
     
         17 . The hollow fiber 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.  
     
     
         18 . The hollow fiber polymer membrane of  claim 17  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.  
     
     
         19 . The hollow fiber polymer membrane of  claim 17  wherein the diol is selected from the group consisting of ethylene glycol 1,2 propane diol, and 1,3 propane diol.  
     
     
         20 . The hollow fiber polymer membrane material of  claim 3  wherein the ratio of B to C is between 4:1 and 3:2.  
     
     
         21 . The hollow fiber polymer membrane material of  claim 3  wherein the membrane material has an average molecular weight of between 40,000 and 200,000.  
     
     
         22 . The hollow fiber polymer membrane material of  claim 3  wherein the membrane material has an average molecular weight greater than the entanglement MW of the polymer.  
     
     
         23 . The hollow fiber polymer membrane material of  claim 3  wherein the membrane material has an average molecular weight of between 70,000 and 140,000.  
     
     
         24 . A method of making a crosslinked hollow fiber membrane, comprising: 
 preparing a polyimide polymer comprising a predetermined quantity of crosslinkable sites;    forming a hollow fiber from said polyimide polymer;    treating the hollow fiber 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 monoesterified hollow fiber; and    subjecting the monoesterified hollow fiber to transeesterification conditions to form a crosslinked hollow fiber membrane.    
     
     
         25 . The method of making a crosslinked hollow fiber membrane of  claim 4  wherein the polyimide polymer is treated with a diol in the presence of a esterification catalyst.