Performance of a nanofiltration membrane for removal of ethanol from aqueous solutions by pervaporation

Abstract

In this study, the performance of a hydrophobic nanofiltration membrane (SolSep 3360) for treating alcoholic solutions by pervaporation is investigated and compared to a conventional pervaporation membrane (PV 1070, Sulzer Chemtech and Pervatech PDMS). Both binary ethanol/water mixtures and common multicomponent mixtures (alcoholic beverages) are examined. The experiments were performed at feed ethanol concentrations up to 50 vol% and at temperatures up to 45 °C. The effects of feed ethanol content and temperature were studied in terms of: (1) fluxes and permeances of individual components, and (2) separation factor, enrichment factor and selectivity of ethanol to water. Using permeance and selectivity instead of flux and separation/enrichment factor allows the effects on performance evaluation of operating conditions, such as temperature and swelling, to be decoupled. In this way the contribution by nature of the membrane to separation performance can be clarified and quantified. In addition, previous analyses indicate that the aqueous activity coefficient and the saturated vapour pressure play an important role when evaluating the membrane performance in terms of permeance and selectivity. This is confirmed by this study. Furthermore, it was found that multicomponent alcoholic beverages behave in exact the same manner as binary ethanol/water mixtures. Using a nanofiltration membrane for pervaporation purposes is a suitable possibility, because of the higher fluxes and permeances, while remaining a good separation factor and selectivity. The difference between nanofiltration and pervaporation membranes is explained by the influence of swelling, making the membrane more dense, and the different interactions between permeating molecules and the membrane.