Separation of 1-butanol by pervaporation using a novel tri-layer PDMS composite membrane

A novel tri-layer composite membrane consisting of the active layer polydimethylsiloxane (PDMS, Sylgard® 184) and dual support layers of high porosity polyethylene (PE) and high mechanical stiffness perforated metal was investigated for the separation of 1-butanol from aqueous solution by means of pervaporation. The experimental data show that total flux and separation factor are both increased by placing a layer of hydrophobic PE between the PDMS and the metal support. The enhancement is especially obvious at low temperatures. With the feed solution of 2% 1-butanol at 37 °C, the PDMS/PE/Brass support composite membrane confers a total flux of 132 g/h/m2 and a separation factor of 32. With the increase of the PDMS thickness, the separation factor increases as the total flux declines. It is suggested that while the water flux remains stable, the 1-butanol flux has linear relationship with respect to the feed concentration of 1-butanol. The overall mass transfer coefficient for butanol was determined to be 6.9E−7 m/s using the resistance-in-series model. Using a semi-empirical Sherwood number correlation, the mass transfer coefficient of 1-butanol through the liquid side boundary layer was estimated to be 25.5E−7 m/s. This is more than 3 times higher than the overall mass transfer coefficient, indicating that the membrane dominates the mass transfer of the pervaporation process.