Method for producing polyimide membranes

Abstract

The invention concerns polyimide membranes, preferably composed of P84 type 70 or P84 HT, having improved chemical and physical properties, a method of producing same and also their use.

1 . A membrane comprising a polyimide, wherein the polyimide comprises at least one dianhydride selected from the group consisting of 3,4,3′,4′-benzophenonetetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,4,3′,4′-biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, sulphonyldiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-propylidenediphthalic dianhydride, and at least one diisocyanate selected from the group consisting of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-methylenediphenyl diisocyanate, 2,4,6-trimethyl-1,3-phenylene diisocyanate, 2,3,4,5-tetramethyl-1,4-phenylene diisocyanate, wherein the amount of extraneous and crosslinking substances in the membrane is in the range from 0% to 5% by weight, the membrane has a solubility in DMF of 5 to 95%, the membrane has a layer thickness of the actual separating layer of not more than 1.5 μm, and the membrane is an integrally asymmetric membrane. 
     
     
         2 . The membrane according to  claim 1 , wherein the polyimide imide comprises: 
       
         
           
           
               
               
           
         
         where 0≤x≤0.5 and 1≤y≤0.5 and R represents one or more, identical or different moieties selected from the group consisting of the moieties Li, L2, L3 and L4, preferably in that the polyimide is a polymer where X=0, Y=1 and R consists of 64 mol % L2, 16 mol % L3 and 20 mol % L4, or is a polymer having the composition x=0.4, y=0.6 and R consists of 80 mol % L2 and 20 mol % L3. 
       
     
     
         3 . The membrane of  claim 1 , wherein the membranes is a flat sheet membrane on a backing fleece, or a hollow fibre membrane. 
     
     
         4 . The membrane of  claim 3 , wherein the backing fleece comprises polyphenylene sulphide, polyethylene terephthalate or polypropylene. 
     
     
         5 . A method for separating a gas mixture, comprising contacting the gas mixture with the membrane of  claim 1 , and separating at least one gas from the gas mixture, wherein the at least one gas is selected from the group consisting of methane, carbon dioxide, oxygen, nitrogen, hydrogen from process gases, water vapour and helium. 
     
     
         6 . The membrane of  claim 1 , wherein the amount of extraneous and crosslinking substances in the membrane is in the range from 0% to 1% by weight. 
     
     
         7 . The membrane of  claim 1 , wherein the membrane has a solubility in DMF of 10 to 80%. 
     
     
         8 . The membrane of  claim 1 , wherein the membrane has a solubility in DMF of 20 to 70%. 
     
     
         9 . The membrane of  claim 1 , wherein the membrane has a layer thickness of the actual separating layer of not more than 750 nm. 
     
     
         10 . The membrane of  claim 1 , wherein the membrane has a layer thickness of the actual separating layer of not more than 500 nm. 
     
     
         11 . The membrane of  claim 1 , wherein the membrane has a layer thickness of the actual separating layer of not more than 250 nm. 
     
     
         12 . The membrane of  claim 1 , wherein the membrane has a layer thickness of the actual separating layer of not more than 100 nm. 
     
     
         13 . The membrane of  claim 1 , wherein the polyimide is a polymer where X=0, Y=1 and R consists of 64 mol % L2, 16 mol % L3 and 20 mol % L4, or is a polymer having the composition x=0.4, y=0.6 and R consists of 80 mol % L2 and 20 mol % L3. 
     
     
         14 . The method of  claim 5 , wherein the at least one gas comprises a gas pair, wherein the gas pair is selected from the group consisting of:
 (a) methane and carbon dioxide;   (b) oxygen and nitrogen;   (c) hydrogen and process gases;   (d) water vapour and gases or gas mixtures; and   (e) helium and gases or gas mixtures.