Tailoring ion exchange membranes to enable low osmotic water transport and energy efficient electrodialysis

Abstract

Ion exchange membranes have been applied for water desalination since the 1950s in a process called electrodialysis, ED. Parallel to the transport of ions across ion exchange membranes, water molecules are transported from diluate to concentrate compartments reducing ED efficiency. In this study tailor made meshed membranes were prepared by embedding polymeric meshes with significantly reduced open area into an ion conductive polymer. These membranes were characterized to assess their transport properties. It is shown that by changing mesh open area, material and surface properties, it is possible to significantly reduce osmotic water transport. Polyamide mesh embedded in a cation exchange polymer showed an eightfold decrease of the water mass transport coefficient. Unexpectedly, osmotic water transport was not affected when the same mesh material was embedded in an anion exchange polymer. A decrease of the osmotic water transport for meshed anion exchange membranes was achieved by using a polyethylene terephthalate mesh. Despite the associated electrical resistance increase, application of meshed membranes increased diluate yield and allowed for more energy efficient operation in case ED is confined to a low current density regime.