摘要
利用荷相反电荷聚电解质之间的静电吸附作用,通过自组装技术制备聚离子复合物膜业已被证明是一种行之有效的方法。但目前这方面的研究工作大多数局限于平板式和管式膜。由于中空纤维膜组件具有装填密度高、自支撑结构等优势,因此本研究试图采用动态负压LBL技术组装内皮层中空纤维聚离子复合物膜,并将其用于有机溶剂脱水的渗透汽化分离领域。本文以改性聚丙烯腈(PAN)中空纤维超滤膜为支撑体,在膜两侧形成负压的条件下,通过动态交替过滤聚丙烯酸(PAA)和聚乙烯亚胺(PEI)实现选择性分离层的超薄化制备。
本文深入考察了动态自组装条件对中空纤维聚离子复合物膜成膜及其渗透汽化性能的影响。发现当支撑体的截留分子量越小,或增加其复合派对数,可以提高复合物膜的渗透汽化性能;同时,在复合过程中,负压侧真空度越大,或聚离子溶液的循环流速越小,就越有利于致密分离层的形成。本文进一步研究了渗透汽化操作条件以及中空纤维聚离子复合物膜对不同醇/水分离体系的分离性能,结果表明,进料液温度降低,有利于提高其渗透汽化性能,此外,当分离体系中醇类物质分子量较大时,其渗透汽化性能越优异。当进料液温度为50℃,95wt%乙醇/水溶液时,派对数为2.5的中空纤维聚离子复合物膜渗透汽化性能如下:分离因子达到821.7,渗透通量为132.8g/ (m2·h)。
为进一步提高中空纤维聚离子复合物膜的渗透通量,改善其力学强度,本文还尝试通过液液置换法来实现PAN中空纤维基膜的表面水解。采用X-射线能谱和红外光谱检测,证实中空纤维膜经过表面水解,其内表面有羧基生成,即发生了水解反应,而其外表面、断面没有羧基生成。并且中空纤维膜表面水解后,其力学性能比整体水解的膜有所改善;中空纤维聚离子复合物膜的渗透汽化性能有所提高,在保证较高分离因子的同时,其渗透通量增加了一倍多。
Electrostatic layer-by-layer (LBL) adsorption of oppositely charged polyelectrolytes has proven to be a promising method for the preparation of polyion complex membranes. But now this method is mainly used to assemble flat sheet and tubular membranes. Since hollow fiber membrane has some advantages such as high-packing density, self-contained mechanical support, this study therefore seeked to assemble inner skin hollow fiber polyion complex membranes by using a dynamic LBL adsorption technique. Subsequently, polyion complex membranes were applied to the pervaporation dehydration of organic solvents. The assembly process was successfully accomplished by alternatively dynamically filtrating polyacrylic acid (PAA) and polyethyleneimine (PEI) on a hydrolyzed hollow fiber polyacrylonitrile (PAN) membrane under a negative pressure condition.
In this paper, the effects of dynamic assembly conditions on pervaporation performance of hollow fiber polyion complex membranes were investigated. It was found that the lower MWCO of PAN support membrane or the higher polyion bilayers numbers could improve pervaporation performances of polyion complex membranes. Meanwhile, the results showed that the higher negative pressure or the lower flow velocity could benefit for the formation of a defect-free selective layer. Then, the effects of operation conditions on the pervaporation separation behavior of various alcohol/water mixtures were subsequently investigated. It was found that the higher feed temperature and the larger molecular weight of alcohol could facilitate the pervaporation separation. In the case of pervaporation of 95wt% ethanol/water mixtures, under the temperature of 50℃, the separation factor and the permeate flux of hollow fiber polyion complex membranes with only 2.5 bilayers were about 821.7 and 132.8g/ (m2·h), respectively.
In order to improve the permeate flux and mechanical properties of polyion complex membrane, single-side surface hydrolysis of PAN hollow fiber membrane by liquid transpositional method were also studied. The experimental results of IR and EDX proved that the carboxyl group only formed on the inner surface of PAN hollow fiber membrane by surface hydrolysis, but not on the outer surface and cross-section. It was found that the mechanical properties of single-side surface hydrolyzed PAN membranes were improved compared with entirely hydrolyzed PAN membrane. The pervaporation flux highly increased while the selectivity was still kept at a relatively high level.
引文
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