Polyimide membranes made of polymerization solutions

Abstract

The invention relates to polyimide membranes and to a phase inversion method for the production thereof. The polyimide membranes can be used to separate different gas mixtures.

1 . A process for producing a polyimide membrane, the process comprising:
 (a) forming a casting solution comprising a polyimide; and   (b) forming a polyimide membrane from the casting solution,   by a phase inversion process,   wherein the polyimide has not been isolated as a solid material and then redissolved prior to forming said casting solution.   
     
     
         2 . The process of  claim 1 , further comprising forming the polyimide from an aromatic dianhydride,
 an aromatic diisocyanate,   an aprotic dipolar solvent, or mixtures thereof.   
     
     
         3 . The process of  claim 1 , wherein
 the polyimide is a polyimide of formula (I):   
       
         
           
           
               
               
           
         
         R is selected from the group consisting of 
       
       
         
           
           
               
               
           
         
         0<x<0.5; and 
         1>y>0.5. 
       
     
     
         4 . The process of  claim 1 , wherein the casting solution further comprises a water-soluble additive. 
     
     
         5 . The process of  claim 1 , wherein the forming (b) of the polyimide membrane comprises coating a backing fleece with the casting solution. 
     
     
         6 . The process of  claim 1 , wherein the polyimide membrane is crosslinked with at least one aliphatic diamine or polyethyleneimine. 
     
     
         7 . The process of  claim 1 , wherein the forming (b) of the polyimide membrane comprises forming an integrally asymmetrically hollow fiber membrane by spinning a hollow fiber with a two-material die from the casting solution and a bore solution in a continuous process. 
     
     
         8 . The process of  claim 7 , wherein the forming (b) satisfies at least one condition selected from the group consisting of:
 the bore solution comprises a mixture of water and an alcohol with at least one selected from the group consisting of dimethylformamide, dimethylacetamide, N-methylpyrrolidinone, N-ethylpyrrolidinone, sulfolane, and dimethyl sulfoxide;   the two-material die is at a distance of 1 to 60 cm from a spin bath of water into which the hollow fiber is spun and an integrally asymmetrical hollow fiber membrane is formed by precipitating the polymide;   during the spinning a hollow thread is subjected to a flow of a dry thermostated stream of nitrogen or air before entry into a spin bath in order to adjust separation properties of the polyimide membrane;   the polyimide is crosslinked with at least one aliphatic diamine or polyethyleneimine;   a crosslinking of the polyimide occurs by dipping the polyimide into a solution of diamine in water or at least one alcohol;   a crosslinking of the polyimide occurs at temperatures between 0 and 90° C.;   a crosslinking time for a crosslinking of the polyimide is between 10 seconds and 16 hours; and   a concentration of diamine in a crosslinking of the polyimide is between 0.01% by weight and 50% by weight.   
     
     
         9 . A polyimide membrane obtained by the process of  claim 1 . 
     
     
         10 . The polyimide membrane of  claim 9 , comprising a polyimide having an Mp>100 000 g·mol −1  and a PDI in the range from 1.7 to 2.3. 
     
     
         11 . The polyimide membrane of  claim 9 , wherein:
 the polyimide is a polyimide of formula (II):   
       
         
           
           
               
               
           
         
         R is selected from the group consisting of 
       
       
         
           
           
               
               
           
         
         0<x<0.5; and 
         1>y>0.5. 
       
     
     
         12 . The polyimide membrane of  claim 9 , in the form of:
 a micro-, ultra- or nanofiltration membrane suitable for separating homogeneous dissolved or particulate products from organic solvents or from water; or   a no-pore membrane suitable for separation of gases.   
     
     
         13 . The polyimide membrane of  claim 9 , in the form of:
 an integrally asymmetrical flat sheet membrane on a backing fleece; or   an integrally asymmetrical hollow fiber membrane.   
     
     
         14 . The polyimide membrane of  claim 13 , wherein the polyimide membrane is an integrally asymmetrical hollow fiber membrane suitable for separating a wide variety of gas mixtures. 
     
     
         15 . A casting solution comprising a polyimide, wherein the polyimide is not isolated as a solid material and then redissolved. 
     
     
         16 . The process of  claim 4 , wherein the water-soluble additive is at least one selected from the group consisting of a water-miscible solvent, a non-solvent, and a pore-former. 
     
     
         17 . The process of  claim 5 , further comprising vaporizing some solvent of the casting solution with a dry thermostated stream of nitrogen or air, after the coating of the backing fleece with the casting solution, to adjust separation limits of the polyimide membrane. 
     
     
         18 . The process of  claim 6 , satisfying at least one condition selected from the group consisting of:
 the polyimide membrane is crosslinked with at least one aliphatic diamine selected from the group consisting of diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, diaminooctane, diaminodecane, diaminododecane, bis-4,4′-(aminomethyl)benzene, a oligoethyleneimine, and a polyethyleneimine;   the polyimide membrane is crosslinked by dipping into a solution of diamine in water or at least one alcohol;   the polyimide membrane is crosslinked at temperatures between 0 and 90° C.;   a crosslinking time is between 10 seconds and 16 hours; and   a concentration of diamine is between 0.01% by weight and 50% by weight.   
     
     
         19 . The polyimide membrane of  claim 13 , wherein the polyimide membrane is an integrally asymmetrical flat sheet membrane on a backing fleece of polyphenylene sulfide, polyethylene terephthalate or polypropylene. 
     
     
         20 . The polyimide membrane of  claim 14 , wherein the integrally asymmetrical hollow fiber membrane is suitable for separating at least one selected from the group consisting of:
 methane and carbon dioxide;   oxygen and nitrogen;   hydrogen and process gases; and   water vapor and a gas or a mixture of gases.