Thin-film composite membranes with modified polyvinylidene fluoride substrate for ethanol dehydration via pervaporation

• TFC membranes are fabricated with PVDF hollow fiber substrates.
• A proper alkaline treatment of PVDF substrate enhances the surface hydrophilicity.
• PVDF dual-layer hollow fiber is the most suitable substrate morphology.
• Silicone rubber coating was applied to enhance the membrane selectivity.

For the first time, polyvinylidene fluoride (PVDF), because of its high stabilities and easy processability, was employed as the substrate material to fabricate the thin-film composite (TFC) hollow fiber membrane for ethanol dehydration. A surface modification of the PVDF substrate through an alkaline treatment was carried out before interfacial polymerization to conquer its hydrophobic nature. Various characterizations showed that a proper alkaline treatment can effectively enhance the surface hydrophilicity by introducing oxygen-containing functional groups. Different configurations of PVDF substrates were investigated and the most suitable morphology was found to be the dual-layer hollow fiber with more porous inner layer and relative denser outer surface. Silicone rubber coating was also applied to enhance the membrane selectivity. The highest separation performance showed a separation factor of 40 and a flux of 1288 g/m2 h with high long term stabilities. This study may provide important insights in exploring new substrate materials for TFC membranes.