Properties and structure of heterogeneous ion-exchange membranes after exposure to chemical agents

Effects of Alkaline Cleaning on the Conversion and Transformation of Functional Groups on Ion-Exchange Membranes in Polymer-Flooding Wastewater Treatment: Desalination Performance, Fouling Behavior, and Mechanism

“…The increased electrical resistance of the AEMs conflicted with the aforementioned enhancement of the water content, likely because the degraded polymer matrix of the AEMs had a more heterogeneous distribution of the functional groups. As presented in Figure e, the IEC of the AEM decreased after aging in the NaOH solution, which was also closely related to the increases in electrical resistance . Herein, the rapid increase in the membrane resistance corresponded to the progressive reduction of the IEC levels when aging within 1 day.…”

“…The IEMs, which were identical to those used in curve 1 in Figure a, were applied in an ED process with 0.05 M NaCl solution (i.e., the feed solution without the addition of a foulant) for 6 h. Then, the desalination rates were measured (see curve 2 in Figure a) and were significantly enhanced in comparison with those of the immediately measured case (see curve 1 in Figure a). A reasonable explanation was that a weak acidic condition was generated due to the inevitable dissociation of water molecules during the ED process , and promoted the ionization of the tertiary amine on the aged AEMs . To further understand this proposal, a group of aged AEM samples, which were identical to those used in curve 1 in Figure a, was immersed in 0.1 M HCl solution for 6 h, and then the desalination rates were measured (see curve 3 in Figure a).…”

“…As presented in Figure 2e, the IEC of the AEM decreased after aging in the NaOH solution, which was also closely related to the increases in electrical resistance. 54 Herein, the rapid increase in the membrane resistance corresponded to the progressive reduction of the IEC levels when aging within 1 day.…”

“…Numerous studies have discussed the degradation of AEMs in terms of the stability of the polymer backbone and/or cationic groups at high pH values. − It has been indicated that typical quaternary ammonium groups degrade through three mechanisms, including nucleophilic substitution, ,, elimination processes, − and ylide-formation routes, − resulting in various degradation products. The polymer backbones of AEMs can also degrade under alkaline conditions through dehydrochlorination, chain scission, or dehydrofluorination reactions. ,,− Despite the numerous articles related to these degradation mechanisms, how these mechanisms affect the ED performance and membrane-fouling behavior remains unclear. The degradation mechanisms of a commercial AEM should be identified and applied in evaluating the changes in the desalination performance and fouling behaviors of aged AEMs, which will be helpful in ED and cleaning-process optimization and membrane modification.…”

Donnan Membrane Process for the Selective Recovery and Removal of Target Metal Ions—A Mini Review

“…IEMs are designed and produced to have desirable characteristics such as high permselectivity, high conductivity, good mechanical strength, structural stability and high chemical and thermal stability [ 57 , 58 , 59 ]. The characteristics are also dependent on factors such as size of the ion exchange resin, resin loading, resin distribution, polymer used, solvent and method.…”