Modification of polyamide reverse osmosis membranes for the separation of urea
Modification of polyamide reverse osmosis membranes for the separation of urea
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DOI：
10.1016/j.memsci.2022.120584
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发表时间：
2022-05-01
影响因子：
9.5
通讯作者：
Weinman, Steven T.
中科院分区：
文献类型：
--
作者：
Habib, Shahriar;Weinman, Steven T.
反渗透(RO)膜是海水淡化的黄金标准，已经使用了30多年。尽管反渗透膜对一价和二价盐离子表现出优异的阻隔性能，但它们不会将尿素等小分子、中性和不带电荷的分子排除到生产饮用水的水平，特别是在近中性的pH条件下。由于界面聚合反应的快速、不可控的性质，聚酰胺层包含网络和聚集自由体积孔(孔)。由于尿素截留主要以尺寸排斥机制为主，因此需要通过减小自由体积来减少尿素通过膜的速率。在这方面，对反渗透膜进行改性以增加交联度和/或减小自由体积孔尺寸是一种理想的方法。我们假设，如果聚酰胺层可以用二胺修饰，那么尿素的截留率将会增加。在这项工作中，我们用碳化二亚胺化学反应对商业膜(杜邦XLE和BW30XFR)的聚酰胺反渗透膜分离层进行了改性，然后在后改性阶段应用了间苯二胺(MPD)和热处理。用ATR-FTIR、XPS、SEM、接触角测角仪和电动分析仪对改性膜进行了表征。使用死端搅拌槽测试了膜的透水性能、氯化钠截留率和尿素截留率。与对照膜相比，改性XLE膜和改性BW30XFR膜对尿素的截留率分别从16.8%和48.4%提高到54.9%和64.6%，而水的透过率分别降低了4.7和2.7倍。结果表明，MPD与热处理相结合可显著提高膜对尿素的截留率。
Reverse osmosis (RO) membranes are the gold standard for water desalination and have been in use for over three decades. Even though RO membranes exhibit excellent performance rejecting monovalent and divalent salt ions, they do not reject small, neutral, and uncharged molecules, such as urea, to a level to produce potable water, especially at near-neutral pH. Due to the fast, uncontrolled nature of the interfacial polymerization reaction, the polyamide layer contains both network and aggregate free volume holes (pores). Because urea rejection is dominated by the size exclusion mechanism, reducing the free volume to reduce the passage of the urea through the membrane is needed. In this regard, the modification of RO membranes to increase the degree of cross-linking and/or decrease the free volume hole size is an ideal approach. We hypothesize that if the polyamide layer can be modified with a diamine, then the urea rejection will be increased. In this work, we modified polyamide RO membrane separation layers of commercial membranes (Dupont XLE and BW30XFR) using the carbodiimide chemistry followed by the application of m-phenylenediamine (MPD) and heat treatment in the post-modification stage. The modified membranes were characterized using ATR-FTIR, XPS, SEM, contact angle goniometry, and electrokinetic analyzer. Membranes were performance tested for water permeance, NaCl rejection, and urea rejection using a dead-end stirred cell. Compared to the control membranes, the modified XLE membranes and modified BW30XFR membranes improved the urea rejection from 16.8% to 54.9% and from 48.4% to 64.6%, but a reduction in water permeance by a factor of up to 4.7 and 2.7 respectively. The results show that combining the application of MPD and heat treatment can enhance the urea rejection of the membranes significantly.