Decoupling the influence of sorption and diffusion on membrane permselectivity in pervaporation for ethanol dehydration

Abstract

Pervaporation is a membrane-based separation process capable of breaking azeotropes, where permselectivity arises from both sorption and diffusion contributions. However, conventional pervaporation measurements rarely distinguish between these two factors. In this study, we decouple the contributions of sorption and diffusion selectivity in ethanol–water separation using crosslinked polyvinyl alcohol membranes. By conducting separate sorption and pervaporation experiments across a range of feed compositions, we reveal that sorption selectivity exhibits a monotonic trend governed by the dynamic interplay between membrane swelling and feed water content. At intermediate ethanol concentrations, enhanced water uptake leads to peak sorption selectivity. In contrast, at high ethanol content—most relevant to ethanol dehydration applications—membrane swelling is suppressed, and diffusion selectivity becomes the dominant factor driving overall transport selectivity. These findings provide mechanistic insights into the composition-dependent separation behavior in pervaporation and offer a rational framework for optimizing membrane performance in industrial dehydration processes.