Dehydration of ethanol/water mixtures by pervaporation using soluble polyimide membranes

A series of soluble polyimides derived from 3,3',4,4'-benzhydrol tetracarboxylic dianhydride (BHTDA) with various diamines such as 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (BATB), 1,4-bis(4-aminophenoxy)2,5-di-tert-butylbenzene (BADTB), and 2,2'-dimethyl-4,4'- bis(4-aminophenoxy)biphenyl (DBAPB) were investigated for pervaporation separation of ethanol/water mixtures. Diamine structure effect on the pervaporation of 90 wt% aqueous ethanol solution through the BHTDA-based polyimide membranes was studied. The separation factor ranked in the following order: BHTDA-DBAPB>BHTDA-BATB>BHTDA-BADTB. The increase in molecular volume for the substituted group in the polymer backbone increased the permeation rate. As the feed ethanol concentration increased, the permeation rate increased, while the water concentration in the permeate decreased for all polyimide membranes. The optimum pervaporation performance was obtained by the BHTDA-DBAPB membrane with a 90 wt% aqueous ethanol solution, giving a separation factor of 141, permeation rate of 255 g m(-2) h(-1) and 36000 pervaporation separation index (PSI) value. (C) 2006 Society of Chemical Industry.