A novel method to fabricate high permeance, high selectivity thin-film composite membranes

We report a thin-film composite (TFC) membrane fabrication method based on transfer of a pre-formed, cured active layer onto a microporous support. The active layer is cast on a polyvinyl alcohol (PVA) water-soluble film and cured, then the active side of the bilayer is placed against the skin side of the microporous support and the water soluble layer is dissolved. This method can be used with supports of relatively high pore size and porosity, thus reducing mass transfer resistance from the support. Ethanol-selective pervaporation from aqueous solution was chosen for the evaluation of the TFC membranes. In comparing results with a 10 μm polydimethylsiloxane (PDMS) active layer on two supports, a TFC made with a high porosity support showed 47% higher total permeance than that of a TFC made with a low porosity support. While the TFC with the low porosity support showed a selectivity (ratio of ethanol permeance to water permeance, mole basis) of 0.66, the selectivity of the TFC with the high porosity support was 0.76, approaching the selectivity of a thick, unsupported PDMS membrane. ZSM-5/PDMS mixed matrix active layer TFCs were also prepared, and showed significantly enhanced performance compared to unfilled PDMS TFCs. A method for commercial fabrication is proposed.