Journal of Membrane Science, Vol.496, 250-258, 2015
Efficient and stable anion exchange membrane: Tuned membrane permeability and charge density for molecular/ionic separation
Herein, we are reporting improved process for chloromethylation of polysullone (PS) by in situ Friedel-Craft reaction without the use of chloromethyl methyl ether (CME). Further, in situ amination (Menshutkin reaction) was carried out to prepare quaternized ammonium polysullone (QAPS). QAPS of varied degree of chloromethylation (DCM) (44.01-65.67%) was used for preparing anion-exchange membranes (AEMs) and it was observed that their pore morphology was highly dependent on membrane drying conditions (temperature and RH). As representative case, QAPS membrane (DCM: 44.01% and named as AEM-1(NF)(x): x indicates drying temperature) dried at low temperature (30 degrees C (RH: 75%); 45 degrees C (RH: 54%) and 60 degrees C (RH: 12%)) showed nano-porous nature with 5.28-1.89 Lm(-2) h(-1) bar(-1) permeability corresponding to 59.31-80.23% salt rejection. Further, permeability of AEM-1(NF), followed the trend: AEM-1(NF)(30) > AEM-1(NF)(45)> AEM-1(NF)(60). Formation of porous structure of these membranes was attributed to the phase inversion of the QAPS polymer due to presence of atmospheric water at low temperature (high RH). In addition, QAPS membranes (different DCM values) dried at 80 degrees C (RH: < 5%), exhibited completely dense nature with negligible permeability and named as AEM-1, AEM-2 and AEM-3 (DCM; 44.01; 53.87 and 65.67, respectively). Especially, AEM-3 (DCM: 65.67%) was designed to possess all the required properties such as high water uptake (22.20%), ion-exchange capacity (1.597 mequiv g(-1)), and counterion transport number (0.96), along with reasonable conductivity (8.45 mS cm(-1)) due to quaternary ammonium group functionality. Chronopotentiometric and i-v studies of AEMs revealed excellent electro-transport property for AEM-3, while its electrodialysis (ED) performance confirmed the suitability for electro-membrane applications. Reported method is novel for preparing stable alkaline membrane with tuneable permeability and charged nature for separations of molecules/ions by pressure and/or electro-driven technologies. (C) 2015 Elsevier B.V. All rights reserved.