Dynamically Formed Inner Skin Hollow Fiber Composite Membrane For Alcohol Permselective Pervaporation

In recent years, the exploitation and utilization of new energy have increasingly attached attentions due to global energy crisis issue. Fuel ethanol has widely been recognized as a sort of clean and sustainable energy. In recent decades, pervaporation has gained increasing attention for the recovery of ethanol from broth due to its operational simplicity, nontoxicity to microorganism, and economical superiority. Currently, the plate-and-frame is the dominating module configuration employed in pervaporation. In comparison with the plate-and-frame module, the hollow fiber has the advantages such as high-packing density, a self-contained mechanical support, a self-contained vacuum channel and economical superiority. Thus, it is a promising PV membrane module for potential application.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℃), 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.With 3-aminoprogyltrlethoxylilane as a coupling and surface modification agent for Silicalite nanoparticles, polydimethylsiloxane (PDMS)-Silicalite/PS hollow fiber composite membrane were successfully prepared through dynamically coating PDMS-Silicalite solution on the inner surface of PS hollow fiber support. The PV performance of three kinds of membrane including PDMS/PS composite membrane,PDMS-Silicalite/PS composite membrane with 0.25wt.% unmodified Silicalite and PDMS-Silicalite/PS composite membrane with 0.25wt.% modified Silicalite were firstly compared. The effects of Silicalite concentration, ultrasonic time and feed temperature on the pervaporation performance of 8 wt.% ethanol/water solutions were also investigated. The appropriate conditions were:ultrasonic time 10h, Silicalite concentration 0.15wt.%. Under the given conditions, in the case of pervaporation separation of 8 wt.% ethanol-water mixture (50℃), the membrane had a separation factor of 10.0 and a permeate flux of 10676 g/(m2.h), respectively. SEM, AFM and contact angle analyses confirmed the formation of a more hydrophobic hybrid selective layer on the inner surface of hollow fibers.