Sorption, diffusion, and pervaporation of benzene/cyclohexane mixtures on silver-Nafion membranes

Abstract

Pervaporation (PV) of benzene (Bz) and cyclohexane (Cx) was performed using Nafion-117 membranes containing silver and sodium ions. The effects of membrane conditioning methods and operating conditions on the permeability and selectivity of PV processing were studied. Membranes treated with NaOH, ion-exchanged with AgNO 3, and swollen in glycerol yielded higher Bz fluxes and better separations. Increasing operating temperatures enhanced the Bz and Cx fluxes, and the activation energy was 50.1 kJ/mol for Bz and 55.1 kJ/mol for Cx. The solution-diffusion model was used to elucidate the mass-transfer mechanism. The sorption isotherms of the liquid mixtures in the membranes were determined. The diffusivity coefficients were calculated and compared using PV results and sorption kinetics data. Results indicate that PV selectivity is governed by the sorption and/or the diffusion phenomena depending diffusivity on the membrane—permeant characteristics. Although the pure Bz uptake by the Ag + membranes was only 1.5 times that of the pure Cx uptake, the sorption selectivity in the binary solutions was increased to 15–19. This indicates that the extent of solvent sorption is greatly influenced by competition between Bz and Cx.