(587b) Design a Novel Miscible Polymer Blend of Polyimide and Sulfonated Polyimide to Develop High-Performance Dual-Layer Hollow Fiber Membranes for Pervaporation Dehydration of Biofuels

A novel miscible polymer blend of copoly(1,5- naphthalene/3,5-benzoic acid-2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropanedimide 6FDA-NDA/DABA and its sulfonated polyimide has been investigated as a water-selective layer to develop dual-layer hollow fiber membranes for biofuel dehydration via pervaporation. The high compatibility between polyimide and sulfonated polyimide, the increased hydrophilicity and enlarged d-space caused by sulfonate groups result in an excellent flux of > 3.0 kg/m²h for the fibers. Three different post-treatment approaches — thermal treatment, PDMS coating and POSS cross-linking modifications are employed to improve the membrane selectivity; their effects on density and thickness of the selective layer and separation performance are investigated with the help of various characterization techniques. Thermal treatment can densify the membrane structure; silicone coating seals the defects on the outer surface and restricts the direct contact between sulfonate groups with the feed; while POSS cross-linking creates the bridges among polymer chains to limit their extension during operation. These three post-treatment methods successfully restrict the membrane swelling and hence improve the selectivity of the fibers. Compared to other hollow fiber membranes, the newly developed hollow fibers have superior fluxes of approximately 2.0 kg/m²h and comparable separations factor of about 240 for ethanol dehydration. This study may provide useful insights for the exploration of new promising materials and post-treatment modifications for biofuel separations.