Electrodialysis To Concentrate Waste Ionic Liquids: Optimization of Operating Parameters

As a novel solvent, ionic liquids have been used in a series of industrial fields, in which large amounts of waste ionic liquids are generated and need to be concentrated and recycled rather than discharged. The disposal of aqueous ionic liquid solutions may cause environmental issues due to slow degradation and toxicity. Electrodialysis (ED) was proposed here to concentrate dilute aqueous solutions of ionic liquids. The effects of the membrane types, applied voltage drops across the ED membrane stack and operating modes, including partial cyclic operation mode, and changes in the volume ratio of concentrated solution to dilute solution (V c/V d) were investigated systematically. Results indicate that the membrane type and operating voltage drop across the membrane stack were optimized as CJMC/MA membranes and 10 V, respectively. Also, it shows that the concentration efficiency of the volume ratio of 1:8 is superior to that of partial cyclic operation mode because high concentration ratio (4.5), low energy consumption (9.46 kWh/m3), and low water transport (10.3%) can be achieved. In addition, membrane fouling was monitored, which showed that anion-exchange membranes were stable in the concentrating process. Nevertheless, the absorption of foulants on the membrane surface has some effect on the concentrating process, which should be overcome in industrial application. Overall, the ED process is a feasible technology to concentrate and recycle waste ionic liquids.