Preparation and pervaporation performance of vinyl-functionalized silica membranes

Abstract

Pervaporation using hydrophobic membranes to separate azeotropic and thermally degradable mixtures, and organics from aqueous solutions with low concentrations has attracted attention. On the other hand, distillation, which is the conventional and commercialized separation method, is unsuitable for the separation of these mixtures. In this study, an α-alumina substrate coated with a γ-alumina layer in both hollow fiber and tubular geometries was used for preparation of vinyl-functionalized silica (VFS) membranes by the sol-gel method using vinyltrimethoxysilane as the silica precursor. Silica functionalized with vinyl groups shows excellent affinity for ethyl acetate (EA) based on Hansen solubility parameters [1]. The VFS membrane prepared on a tubular alumina substrate at 453K showed the EA flux of 0.85kgm–2h–1 and separation factor of 77.3 for pervaporation of a 5% (mass fraction) EA aqueous solution at 295K. An α-alumina hollow fiber was further used instead of the conventional tubular substrate to improve the EA flux. The hollow fiber-supported VFS membrane has a flux of 2.53kgm–2h–1, which is three times higher than that prepared on the tubular-substrate, and a separation factor of 81.5 for the pervaporation of a 5% (mass fraction) EA from aqueous solution at 295K. The fluxes of methyl acetate and methyl ethyl ketone for the hollow fiber-supported VFS membrane are also about three times higher than those obtained for tube-supported VFS membranes.