Comparative studies on performance of interpolymer and heterogeneous ion-exchange membranes for water desalination by electrodialysis

As the preparation of interpolyme- type anion-exchange membranes involves several steps and the use of hazardouschemicals such as chloromethyl ether and trimethyl amine, it was envisaged to prepare heterogeneous anion-exchange membranes through a simple technique involving casting of a solution containing a binder and a polyelectrolyte. Electrochemical characterization of interpolymer and heterogeneous membranes was carried out by measurement of electrical resistance, counter-ion transport number, ion-exchange capacity and volume fraction of water. Interpolymer ion-exchange membranes exhibited better electrochemical and electrodialytic properties in comparison to a heterogeneous membrane. In order to develop alternate anion-exchange membranes, a heterogeneous type of anion-exchange membrane was prepared, and its electrodialytic performance in combination with an interpolymer cation-exchange membrane was studied. Electrodialysis experiments in recirculation mode of operation were performed under varied feed concentrations and applied potential gradients in two configurations: (1) interpolymer cation- and anion-exchange membranes and (2) interpolymer cation- and heterogeneous anion-exchange membranes, packed together, in order to assess their comparative efficiencies for water desalination by electrodialysis. Under both configurations energy consumption and current efficiency were similar under comparable experimental conditions, but the rate of desalination from configuration (1) was much faster.