Poly(vinyl acetal) membrane for pervaporation of benzene–isooctane solution

Separation of aromatic–aliphatic mixture is one of the challenging tasks in chemical industries. In this work, an attempt has been made to recover benzene from binary mixture of benzene and isooctane through pervaporation (PV) using a laboratory-made dense, non-porous (homogeneous) membrane from poly(vinyl acetal). The membrane was characterized by FTIR, X-ray diffraction (XRD) and sorption test. The solution–diffusion model was used to elucidate the mass transfer mechanism that occurs within the membrane during pervaporation process. It was observed that the separation behavior is not due to molecular sieving; instead, it appears to be due to preferential sorption (sorption on external surface, pore entering and sorption in pores) of one species, which prevents the other organic from sorbing and transporting through the membrane. The diffusivity coefficients were estimated using sorption kinetics data and PV results. The preferential permeability of membrane to benzene over isooctane was inferred due to preferential sorption and diffusion of benzene. Further, PV selectivity was also observed to be governed by sorption and/or by diffusion phenomena. Sorption selectivity was observed to be higher than pervaporation selectivity in binary solutions. Further, extent of solvent sorption is greatly influenced with the composition of benzene–isooctane solution.