Polyimide Asymmetric Membrane vs. Dense Film for Purification of MTBE Oxygenate by Pervaporation

Membrane properties are determined by their morphology, which may be symmetric (dense) or asymmetric (dense/porous). Two membrane types based on the poly[(4,4'-oxydiphenylene)pyromelliteimide] (symmetric dense and asymmetric dense/porous) were prepared for a comparative study of morphology, physical properties, and transport characteristics in the pervaporation of methanol/MTBEmixture over a wide range of concentrations including the azeotropic composition. The asymmetric membrane is a good example of improving the transport properties of the polyimide by creating structure composed of a thin dense top layer on the surface of sponge-like microporous substrate. It was found that the use of the asymmetric membrane allows increasing the total flux in separation of azeotropic mixture by 15 times as compared with the dense membrane.