18-冠-6/KOH络合体系催化制备高通量聚酰胺反渗透膜

Preparation of polyamide reverse osmosis membrane by using 18-crown-6/KOH complex catalyst

反渗透膜技术是一种重要的纯水供应技术,制备高通量反渗透膜成为研究热点。采用冠醚(18-crown-6)与KOH的络合性缚酸剂催化界面聚合反应制备聚酰胺反渗透膜,利用18-crown-6能与缚酸剂无机碱(KOH)形成络合物,加速KOH从水相到有机相的扩散,可以促进聚合反应的进行。通过此方法制备得到了厚度更薄、表面适度水解的分离膜,明显提高了膜的水通量。通过扫描电子显微镜和X射线光电子能谱技术显示,冠醚的添加可以有效抑制KOH导致的聚合单体的水解,保证膜具有合理的离子选择性,解决了使用纯KOH做缚酸剂时会明显降低膜分离性能的问题,对NaCl的截留率保持在90%以上,使用Cs^+作为截留离子发现,该膜对Cs^+同样具有良好的截留能力,说明缚酸剂对反渗透膜分离性能的改变基本不受电解质类型的影响。

The reverse osmosis membrane technology plays an important role in the supply of pure water. The high water production is always desirable. In this study, a new acid acceptor consisting of the crown ether （18- crown- 6）/KOH is used to catalyze the inteffacial polymerization reaction for the polyamide reverse osmosis membrane fabrication to increase the membrane flux. The 18- crown-6 and the KOH will form a complex compound, to help the diffusion of the KOH from the aqueous phase to the organic phase, so that the KOH can work more efficiently to catalyze the polymerization. Meanwhile, the 18-crown-6 can effectively inhibit the excess hydrolysis of the TMC from the KOH, preventing a significant deterioration in the ion rejection of the membrane. To verify the above reasoning, the SEM and XPS characterizations are used to show that the membrane has a thin and properly hydrolyzed surface morphology. The membrane performance test shows that the application of the （18-crown-6）/KOH as the acid acceptor can promote the membrane flux better （up to 72% increase） as compared with using only the KOH （38% increase）. Moreover, the use of the （18- crown-6）/KOH can help the membrane to maintain a reasonable NaCl rejection of above 90%. That solves the problem of rejection deterioration when only the KOH is used as the acid acceptor with a rejection of below 60%. Although Cs^＋ has a smaller hydraulic radius than that of Na^＋, this kind of membrane also enjoys a similarly excellent separation behavior with respect to CsNO3. That means that the （18-crown-6）/KOH catalyst composition is effective and applicable in future.