Effects of polydimethylsiloxane (PDMS) molecular weight on performance of PDMS/ceramic composite membranes

The objective of this work was to investigate the effect of polydimethylsiloxane (PDMS) molecular weights on the pervaporation performance and the confinement behavior of PDMS/ceramic composite membranes for the separation of ethanol from aqueous solutions by pervaporation. PDMS with three different molecular weights was used to prepare PDMS/ceramic composite membranes. Due to the fact that high molecular weight PDMS tends to suppress the formation of defects, and as a result improves the constrained degree of the membrane, the PDMS/ceramic composite membrane fabricated with the highest molecular weight PDMS exhibited a better performance than the other two counterparts prepared with lower molecular weight PDMS. The total flux and the separation factor of a PDMS/ceramic composite membrane with a thin defect-free PDMS layer of 5 μm were 1.6 kg/m2 h and 8.9, respectively, at 40 °C when 5 wt.% of ethanol was used in the feed solution. Furthermore, the ceramic support showed a unique advantage in constraining the swelling of the separation layer, when compared with the conventional polymer support, which significantly improved the membrane stability, especially for PDMS with high molecular weights.