Dynamically formed inner skin hollow fiber polydimethylsiloxane/polysulfone composite membrane for alcohol permselective pervaporation

This work is concerned with the preparation of alcohol permselective inner skin hollow fiber composite membrane using a dynamic cross-flow coating method. The membranes were successfully prepared by dynamically coating polydimethylsiloxane (PDMS) on the inner surface of the polysulfone (PS) hollow fibers under a pressure-driven process. The strategy of alternating PDMS casting solution direction was firstly explored to ensure the formation of a uniform and defect-free selective layer. Subsequently, the effects of coating time, polymer concentration, and crosslink agent concentration on alcohol permselective performance were investigated. The appropriate conditions were: coating time, 60 min; PDMS concentration, 22.8 wt.%; and TEOS concentration, 1.5 wt.%. Under the given conditions, in the case of pervaporation separation of 8 wt.% ethanol–water mixture (50 °C), the membrane had a separation factor of 6.4 and a permeate flux of 265 g/(m2 h), respectively. The pervaporation separation behavior of various alcohol/water mixtures with the alcohols being t-butanol, 2-propanol was also investigated. SEM, AFM and contact angle analyses confirmed the formation of selective layer on the inner surface of hollow fibers. Therefore, it indicates that the dynamic cross-flow coating technique is a unique approach to the construction of selective layer on porous hollow fiber substrates, which could emerge as a powerful technique for the preparation of a range of separation membranes.