Sorption,diffusion and pervaporation of water/ethanol mixtures in polyetherimide membranes

Homogeneous and composite aromatic polyetherimide membranes were prepared by casting from N-methylpyrrolidinone (NMP) solutions and by electrodeposition of polymer at the cathode, respectively. The membranes were evaluated for their sorption, diffusion and pervaporation separation of water from ethanol with emphasis on the breaking of azeotropic composition. The membrane performance was shown to be dependent on the feed concentration, but still selective towards water over the whole composition range of the feed mixture. By looking at the surface energy parameters, the determination of degree of swelling and the calculation of deviation coefficients (ε), an interesting insight was gained into the coupling effect in this solvent/membrane system. From the sorption, diffusion and temperature-dependent permeation behaviour, it could be concluded that in this system the diffusivity of permeant plays a major role in determining the pervaporation performance, rather than the solubility. © 1999 Society of Chemical Industry