Pervaporation dehydration of C₂-C₄ alcohols by 6FDA-ODA-NDA/Ultem^® dual-layer hollow fiber membranes with enhanced separation performance and swelling resistance

A novel copoly(4,4′-diphenyleneoxide/1,5-napthalene-2,2′-bis (3,4-dicarboxyl phenyl) hexa fluoro propane diimide) 6FDA-ODA-NDA/Ultem^® 1010 dual-layer hollow fiber membrane for pervaporation dehydration has been fabricated via co-extrusion process. Not only can it achieve impressive alcohol dehydration performance without any post-treatment but also it particularly minimizes the membrane's swelling behavior towards aqueous alcohol solution. For isopropanol, n-butanol and t-butanol dehydrations of 85/15 (alcohol/water) wt.% feed solutions, the 6FDA-ODA-NDA/Ultem^® 1010 dual-layer hollow fiber membrane can successfully attain permeate containing more than 99.7 wt.% water with considerably high flux which implies to a distinctive separation factor of the respective alcohol system. The outstanding dehydration performance of 6FDA-ODA-NDA/Ultem^® 1010 dual-layer hollow fiber membranes on various aqueous alcohol feeds can be attributed to: (1) a precise formulation of the outer- and inner-layer dope compositions; (2) the size of d-space created in the outer-layer is a good match for size exclusion mechanism in the alcohol dehydration systems; (3) a relatively low water uptake and less swelling characteristics of the Ultem^® 1010 polyimide as a supporting layer. By adjusting spinning parameters, i.e. outer-layer dope flow rate and air gap distance, the separation performance of 6FDA-ODA-NDA/Ultem^® 1010 dual-layer hollow fiber membranes can be further improved.