CHARACTERISTICS OF ION-EXCHANGE MEMBRANES FOR ELECTRODIALYSIS ON THE BASIS OF IRREVERSIBLE THERMODYNAMICS

Three transport quantities (electrical conductivity, apparent transport number, permeability coefficient) and the membrane thickness describe the performance of ion-exchange membranes in electrodialysis. The relationship between these parameters and the efficiency of energy conversion in that process is given. Two systems are discussed - with one membrane and with a pair of cation- and anion-exchange membranes. It is found that both systems are analogous and can be discussed in terms of the same equations. The experimental data for a polystyrenesulfonate membrane and perfluorosulfonate Nation membranes in aqueous solutions of NaC1 are presented. The maximum conversion of energy for these membranes is in the range of 0.6 to 0.9 (for c-approximately less-than-or-equal-to 0.5 mol/dm3) and depends to a great extent on the concentration. At the high coupling, which these membranes show (q > 0.97), the further increase of conversion of energy can be achieved only by improving their electrical conductivity.