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Pervaporation Characteristics of Silica-Zirconia Membranes for Separation of Aqueous Organic Solutions

Abstract: Application of pervaporation membranes to practical separation and purification processes would be much more attractive if the separation performance (dux and selectivity) can be further improved. In addition to higher flux and selectivity, membrane stability at higher temperatures is quite important for efficient and economic separation in practical processes, considering that pervaporation at higher temperature preferably gives higher fluxes, resulting in smaller required membrane areas. In this respect, inorganic porous membranes could find a wider application in practical separation and purification processes. In this work, porous silica-zirconia membranes of pore size less than 1 nm were fabricated by improved sol-gel techniques to study the pervaporation characteristics of various aqueous organic solutions (isopropanol, I-propanol, acetone, tetrahydrofuran, and ethanol) at temperatures from 50 C to their normal boiling points. The water fluxes for these aqueous mixtures, with the exception of aqueous ethanol solution at the normal boiling point, exceeded 7kg·m−2 h−1 with separation factors larger than several hundreds at 10wt% water in the feed. The water-flux dependency on the feed concentration can be determined roughly by the vapor-liquid equilibrium; however, it is not always proportional to the partial vapor pressure of the feed at the separation temperature. The detailed separation characteristics are discussed based on a simple model of porous membranes proposed previously.