Abstract:

Chitosan (CS) is a competitive material for pervaporation membranes due to its richness in natural resources and excellent hydrophilicity. However, the high crystallinity and intense hydrogen bond interactions endow CS with compact structure and low permeability, which has limited its application. To address this issue, CS was blended with polyether-polyamide block copolymer Pebax 1657 and coated on NaOH-hydrolyzed polyacrylonitrile (PAN) ultrafiltration substrates to fabricate composite membranes. The membranes were applied in pervaporative separation of water from ethanol, and were further applied in intensifying esterification of lactic acid and ethanol by pervaporation. NaOH-hydrolyzed PAN substrates showed an increased hydrophilicity, which was beneficial to the interfacial stability enhancement of the composite membranes. When blended with CS, the rigid polyamide segments could destruct the crystalline regions within CS, thus enable the increase in permeation flux; the hydrophilic and the flexible polyether segments could help to enhance the membrane selectivity. The optimal pervaporation performance in improving the yield of ethyl lactate were achieved when the mass ratio of CS to Pebax was 2:1, with a permeation flux of 703 g·m^-2·h^-1, and a separation factor of 308 (increased by 61% and 65% compared with CS control membrane, respectively), while the yield of ethyl lactate (after 8 h of reaction) increased from 58% to 73%.

Key words: polymers, blend, membranes, pervaporation, esterification

摘要：

壳聚糖(chitosan, CS)作为渗透蒸发膜材料来源广泛、亲水性好,但结构致密、渗透性较低。为改善CS膜的分离性能,将CS与聚醚-聚酰胺嵌段共聚物Pebax 1657共混,涂覆在NaOH水解处理的聚丙烯腈(polyacrylonitrile,PAN)超滤膜表面制备复合膜,用于渗透蒸发醇水分离过程,并进一步用渗透蒸发方法对乳酸-乙醇酯化反应进行强化。Pebax的聚酰胺与聚醚链段分别发挥调节膜结构与促进水跨膜传递的作用,有效地提高了膜分离性能。CS与Pebax质量比为2:1时,渗透蒸发醇水分离性能及对酯化反应强化的性能达到最优:渗透通量703 g·m^-2·h^-1、分离因子308,较未改性CS膜分别提高61%、65%;反应8 h后的乳酸乙酯产率由58%提高至73%。

关键词: 聚合物, 共混, 膜, 渗透蒸发, 酯化