Sorption and Diffusion Phenomena in Pervaporative Dehydration of Acetic Acid through a PVA-PES Composite Membrane

Abstract

Dehydration of dilute acetic acid solution was carried out in a pervaporation pilot plant unit using commercial polyvinyl alcohol-polyethersulfone composite membrane. Membrane swelling coefficients obtained by dynamic swelling study were found to increase with increasing water concentration in the feed. For 10% (by volume) feed water concentration swelling coefficient of the membrane was 0.3053 which increased to 0.4919 at 90% feed water concentration. Pervaporation separation index (PSI) was found to decrease with increasing feed concentration whereas enrichment factor increased. For 10% feed water concentration acetic acid and water diffusion coefficients were estimated to be 1.8963 × 10⁻¹² and 11.843× 10⁻¹² m²/s respectively, which rose to 6.8732 × 10⁻¹² and 40.973 × 10⁻¹² m²/s respectively at 90% feed water concentration. The study indicates that in addition to the effect of differences in diffusivity for the permeating components, preferential sorption contributes to a major extent to selective transport in pervaporation.