The Preparation Of PVA Vapor Permeation Membrane Separating Ethanol-water Closed Azeotrope

The shortage of the fossil fuel resources induces the need of searching for alternative energy sources. As a renewable resource, ethanol gasoline project has been listed in the development project of "the tenth five-year-plan" in China.Water content of fuel ethanol must be under 0.8%. Fuel ethanol is obtained from anhydrous ethanol. However, owing to the limit of the maximum concentration of ethanol azeotropic composition by conventional distillation, 95.57 wt%, it has to adopt some special technologies to produce anhydrous ethanol, which include azeotropic distillation molecular sieve or membrane separations, etc.. However, compared with membrane separations, the formers have the disadvantage of high energy consumption and high costs. Meanwhile, as an economical alternative technology, vapor permeation wins an advantage over other technics with less sensitivity to concentration polarization on the feed side of the membrane, no phase change across the membrane surface and the longer life-span than RO, UF, MF due to the low degree of membrane swelling.In this study, firstly, the polyvinyl alcohol (PVA) membrane was prepared by crosslink-esterifing with oxalic acid and results proved that all crosslinked membranes had similar IR characteristics, though they were crosslink-esterified by different crosslinking agent and catalyst. We found that oxalic acid crosslinked membrane with sodium hydroxide had better IR characteristics, if lower heat treatment temperature is adopted. Compared with the traditional technics of producing crosslink-esterified PVA membrane, producing processes are decreased and energy consumption is economized.In this study, we prepared ultrafiltration membrane of polyvinylidene fluoride (PVDF) as porous support membrane, and prepared the PVA/PVDF composite membranes on the support membrane by spread method. The analysis of SEM showed that the thickness of the active layer was uniform and less than 10 μm and it combined well with the porous layer. Then we adopted vapor permeation to research on the separation performance of PVA/PVDF. The results showed that with the increasing of the crosslinkage, the separation factor increased while the permeation flux decreased. And for the composite membranes with different crosslinking agents, different catalysts, different support membranes, we found PVA-OA with the sodium hydroxide hadbetter separation performance, under similar experimental conditions. Finally, we investigated the effects of the feed concentration on the separation performances of the membranes. The results showed that the separation coefficient of the composite membranes increased with the feed concentration. The results showed that using this kind of membrane can be applied to separating closed azeotropic point ethanol-water mixtures by vapor permeation.