Xiaoling Duan,Cunwen Wang,Tielin Wang,Xiaolin Xie,Xingping Zhou,Yunsheng Ye
A series of quaternary ammonium polysulfone (QAPSU) anion exchange membranes used the chlorotrimethylsilane instead of toxic chloromethyl methyl ether and quaternized-functionalized by trimethylamine ethanol solution were prepared. The effect of chloromethylation reaction time on membrane morphologies and physiochemical properties such as ion exchange capacity, water swelling, and membrane area resistance, mechanical and thermal stabilities was investigated. When being applied in electro-electrodialysis (EED) for purifying phosphoric acid solution, the QAPSU membranes exhibit high purification efficiency, especially all the metal ions (Fe, Mg, Ca) removal rates reach over 60%, which suggests that the QAPSU membranes have a high potential for EED application.
Nanofiltration (NF) is considered a competitive purification method for acidic stream treatments. However, conventional thin-film composite NF membranes degrade under acid exposures, limiting their applications in industrial acid treatment. For example, wet-process phosphoric acid contains impurities of multivalent metal ions, but NF membrane technologies for impurity removal under harsh conditions are still immature. In this work, we develop a novel strategy of acid-resistant nanofiltration membranes based on interfacial polymerization (IP) of polyethyleneimine (PEI) and cyanuric chloride (CC) with the s-triazine ring. The IP process was optimized by orthogonal experiments to obtain positively charged PEI-CC membranes with a molecular weight cut-off (MWCO) of 337 Da. We further applied it to the approximate industrial phosphoric acid purification condition. In the tests using a mixed solution containing 20 wt% P2O5, 2 g/L Fe3+, 2 g/L Al3+, and 2 g/L Mg2+at 0.7 MPa and 25 °C, the NF membrane achieved 56% rejection of Fe, Al, and Mg and over 97% permeation of phosphorus. In addition, the PEI-CC membrane exhibited excellent acid resistance in the 48 h dynamic acid permeation experiment. The simple fabrication procedure of PEI-CC membrane has excellent acid resistance and great potential for industrial applications.
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