The Charged Nanofiltration Membrane

　　Zhang Haoqin, Wan Yazhen, Liu Jindun*, Liu Haixia

　　(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450002)

　　Abstract The development on charged nanofiltration(NF) membrane, which includes the preparing methods, the haracterization techniques, the transport mechanism models and their applications, was introdued in this paper. The potential measure for solving the subsistent problems encountered in the development of the charged NF membrane was suggested. The negatively charged membranes have been successfully applied, but the positively charged membranes need to be developed in further. Although many advanced apparatuses have been used for characterization of membranes, it is very difficult to measure some important parameters of the membranes. Thus it will be very important to establish the standard method for testing and characterizing these membranes. Many transport mechanism models have been proposed such as the space-charge model, the electrostatic and steric-hindrance model, Donnan steric pore model and dielectric exclusion etc. However these models need to be further developed for the separation of mixtures.

　　The fouling and cleaning of NF membranes should be thoroughly investigated in the commercial applications. Compared with the developed country, China has to enhance its applied research as well as the basic research so as to promote the industrial application of the charged NF membranes.

　　Key words Charged Nanofiltration membrane, Preparation, Characterization, Application,Separation mechanism

　　早期的膜分离过程，是基于一种物理筛分的原理，即膜允许比其孔径小的组分透过而截留比其孔径大或相近的组分。在应用过程中，若待分离组分介质粒径很小，所用膜的孔径也须相应减小，这势必会造成通量下降、操作费用升高等问题。为了避免上述缺陷，近几年来荷电膜得到了迅速的发展，尤其是荷电纳滤膜，由于其独特的分离特性而受到重视。荷电纳滤膜是含有固定电荷的膜, 其分离原理，除了中性膜的基于孔径大小的物理筛分之外，还有着独特的静电吸附和排斥作用。荷电纳滤膜中引入了荷电基团，膜的亲水性得到加强，透水量增加，适于低压操作，抗污染以及选择透过性方面都具有优势，可以用大孔径膜吸附分离直径较小的物质；分离相对分子质量相近而荷电性能不同的组分[1，2]。根据膜中固定电荷电性的不同,可将荷电纳滤膜分为荷正电纳滤膜和荷负电纳滤膜。根据荷电位置不同，可分为表层荷电膜和整体荷电膜。目前已工业化的多为表层荷负电膜。本文介绍了国内外近年来荷电纳滤膜的研究进展,包括荷电纳滤膜制备方法、表征技术、传递机理及其在各方面的应用等;分析了存在的问题，讨论了可能的解决方法，对以后的研究提出了一些建议。

　　1 荷电纳滤膜的制备

　　复合膜是当前发展最快、研究最多的膜,一般指在多孔的支撑膜(基膜)上复合一层很薄的、致密的、有特种功能的另一种材料。与一体化膜比较,复合膜的表面致密层厚度很薄, 从而使膜同时具有高的溶质分离率和透过速度。

　　1.1 荷负电纳滤膜

　　目前常用的纳滤膜有: 聚芳香酰胺类、聚呱嗪酰胺类、磺化聚砜类、聚乙烯醇类等。芳香聚酰胺类、聚呱嗪酰胺类是采用界面聚合方法制备荷电表层；磺化聚砜类、聚乙烯醇类则是采用涂敷法制备荷电表层。

　　1.1.1 界面聚合法 界面聚合是利用两种反应活性很高的单体(或预聚物)在两个不互溶的溶剂界面处发生聚合反应，从而在多孔支撑体上形成一薄层。例如，首先将支撑膜浸在含有呱嗪的水溶液中，然后再将膜浸入含有均苯三甲酰氯的有机溶液中，通过界面聚合反应可制备聚呱嗪酰胺复合纳滤膜。由于呱嗪与均苯三甲酰氯的反应中有氯化氢生成，为了使反应能够顺利进行，常需加入酸接受剂中和氯化氢；为了使两种界面聚合单体能有效的接触，常需加入表面活性剂。界面聚合方法制备了大量的工业用纳滤膜，属于聚呱嗪酰胺类的有：Film Tec 公司的NF40和NF40HF；日本东丽公司的UTC-20HF 和UTC-60；美国ATM 公司的ATF-30 和ATF-50 等。属于聚芳香酰胺类的主要为NF 系列：NF200 和NF270 的特点为有中等的透盐度，钙的透过率为50%～65%，有机物的脱除率(TOC

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