PREPARATION OF ASYMMETRIC POLYIMIDE MEMBRANE FOR WATER-ETHANOL SEPARATION IN PERVAPORATIN BY THE PHASE INVERSION PROCESS

The preparation of polyimide pervaporation membranes for the separatio n of aqueous ethanol solutions was investigated. Asymmetric membranes were prepared by the phase inversion process from casting solutions co mposed of aromatic polyimide (PI-2080), N,N'-dimethylformamide (DMF) a nd 1,4-dioxane. The membranes were annealed at 300-degrees-C in a vacu um oven and were measured at 25-degrees-C for an aqueous 95 vol% ethan ol solution in pervaporation. Membranes made from a casting solution c omposed of 25 wt% polyiminde, 37.5 wt% DMF and 37.5 wt% dioxane, showe d a molecular weight cut-off of 600. The membranes which were annealed at 300-degrees-C for 3 h exhibited a separation factor alpha(H2O/EtOH ) = 900 with a flux of 1.0 kg/m2 h for an aqueous 95 vol% ethanol solu tion at 60-degrees-C.