Preparation and characterization of vinyltriethoxysilane (VTES) modified silicalite-1/PDMS hybrid pervaporation membrane and its application in ethanol separation from dilute aqueous solution

To improve the affinity between silicalite-1 and polydimethylsiloxane (PDMS), the silicalite-1 particles were modified by a silane coupling agent vinyltriethoxysilane (VTES) and incorporated into polydimethylsiloxane (PDMS) matrix for the preparation of silicalite-1/PDMS hybrid membranes. The modified silicalite-1 particles were examined by XRD, FT-IR and TGA, and the results showed that the silane coupling agent was bonded to the surface of silicalite-1 particles through chemical bonds and the modification did not influence the framework of silicalite-1 crystals. VTES could enhance the interaction of silicalite-1 particles with PDMS through chemical bonds and hence suppressed the formation of microvoids at polymer–silicalite-1 interface, as a result, the thermal stability of the hybrid membrane could be improved. The effect of silicalite-1 loading on the pervaporation performances of the hybrid membranes with dilute ethanol solutions was investigated. As compared with the unmodified hybrid membranes, the VTES modified silicalite-1/PDMS hybrid membranes effectively improved the pervaporation selectivity at different silicalite-1 loadings. With increasing silicalite-1 loading, membrane selectivity increased for both unmodified and VTES modified silicalite-1/PDMS hybrid membranes, and a selectivity of 32 was obtained when VETS modified silicalite-1 loadings was 67%. It was also found that with increasing silicalite-1 loading, the total flux of both unmodified and VTES modified silicalite-1/PDMS hybrid membranes decreased while the ethanol flux of both hybrid membranes increased. With increasing the feed ethanol concentration at a given temperature, the total flux, ethanol flux, and ethanol concentration in permeate increased almost proportionally, while water flux decreased and the separation factor decreased slightly. An increase in temperature increased the permeation fluxes of both ethanol and water, while the separation factor was more or less constant at a given ethanol concentration.