Polyimide membrane for separation of solvents from lube oil

Claim 1

The process of preparing a polyimide polymer membrane, said process comprising the steps of: (a) preparing a polyimide dope solution consisting essentially of: (1) a fully imidized polyimide polymer based on 5(6)-amino-1-(4'-aminophenyl)-1,3-trimethylindane and benzophenone tetracarboxylic dianhydride present in amounts of 20 to 28% by weight of said dope solution; (2) a solvent system for said polyimide which is water miscible and is selected from the group consisting essentially of N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, dioxane, γ-butyrolactone, water, ketones, alcohols, formamide, or a mixture thereof; (3) optionally, a viscosity enhancer present in amounts of less than 3% by weight of said dope solution consisting essentially of polyvinyl pyrrolidones, polyethylene glycols or urethanes; (4) optionally, a void suppressor present in amounts of less than 5% by weight of said dope solution consisting essentially of maleic acid; (b) casting a film of said polyimide dope solution onto a supporting substrate; (c) after an evaporation period, immersing said film cast on said substrate into a coagulating medium consisting essentially of water, alcohol, ketones or mixtures thereof; (d) treating the asymmetric membrane with a wash bath or baths containing a conditioning agent.