Place Holder 2.

Electrodialysis (ED) is a promising technology for brine concentration. However, the implementation of ED for this challenging application requires ion-exchange membranes (IEMs) that are highly permeable and highly selective when contacted by brines. Although commercial IEMs for treating concentrated salt solutions exist, further improvements in IEM throughput and selectivity are needed for ED to become competitive in this space. To guide the development of IEMs for brine concentration, a better understanding of the interconnection between membrane structure and transport properties is required. Commercial IEMs used for brine concentration have low degrees of swelling, but there is a poor understanding of ion transport in such materials, making it difficult to rationally design IEMs with desired transport properties. To fill this gap, we synthesized a series of cross-linked IEMs with varying degrees of swelling and extremely high fixed charge concentrations. We measured the ion transport properties of the IEMs at salt concentrations representative of brines and extracted the IEM counter-ion/co-ion selectivity using ion concentrations and diffusion coefficients in the membrane. Overall, we observed little change in selectivity as IEM swelling decreased, but counter-ion throughput decreased about one order of magnitude over the IEM swelling range explored. The IEM selectivity was significantly affected by the external salt concentration, with a decrease of approximately one order of magnitude in IEM selectivity when the external salt concentration increased from 1 to 5 molal NaCl. To contextualize the performance of the membranes, we compared their transport properties to those of 28 state-of-the-art commercial IEMs. Some of the novel IEMs had combinations of throughput and selectivity that surpassed the upper bound defined by the commercial membranes. Finally, we evaluated the performance of the synthesized membranes for brine concentration in bench-scale ED experiments, demonstrating their potential for this application.