(374a) Development of Polymeric Ionic Liquid Thin Films for Ion-Selective Anion Exchange Membranes in Electrodialysis Separations

The onset of climate change and rising global population has caused greater water scarcity, a considerable problem which threatens our world. Ion exchange membranes have been used for water purification since 1950s in a process called Electrodialysis (ED). ED is an electrically-driven separation process aimed at water treatment through ion removal, which is achieved through the selective control and transport of ionic species. ED is a popular water treatment method; however, ED is limited by membrane scaling, lack of ion selectivity, and high energy consumption for high salinity feeds. Recent studies suggest that ion-selective ion exchange membranes can enhance selective ion separations in ED systems, resulting improved productivity for water treatment. This study is focused on the synthesis of unique ionic liquid-based anion exchange membranes in order to obtain ion-selectivity in ED systems through addition of a divalent ion repulsion layer. Thin films of polymerizable ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethane)sulfonimide and trioctyl-(4-vinylbenzyl)phosphonium bis(trifluoromethane)sulfonimide were coated and cured on the anion exchange membrane in order to enhance ion selectivity. The membrane characteristics were studied through FTIR, SEM, AFM, contact angle measurement, and ED performance. Results suggest that while imidazolium coatings were incompatible with ED systems due to rapid degradation, phosphonium coatings exhibited enhanced ion selectivity with negligible dissolution of selective layer and comparable separation efficiency to uncoated membranes. However, as current selective layers are thick (~150 μm), ED productivity decreased, indicating that thinner films would be more beneficial.