Effect of the ion-exchange-membrane/solution interfacial characteristics on the mass transfer at severe current regimes

Abstract

In the electrodialysis of dilute solutions, performed at intense current regimes, the membrane electrical conductance and diffusion permeability are no more crucial. Of more importance become the membrane properties that control increase in the overlimiting mass transfer of salt ions, as well as H+ and OH− ions in membrane systems. In this work different methods of the improving of mass-exchange characteristics of commercial ion-exchange membranes intended for operation at intense current regimes are discussed. They are based on modern concepts of mechanisms of the electroconvection (which proceeds as electroosmosis of 2nd kind), as well as mechanisms of H+ and OH− ions generation at the membrane/solution interface. Influence on the membrane electrochemical and mass-exchange characteristics is possible via (a) control of chemical nature of fixed groups at membrane surfaces, in order to weaken their catalytic activity with respect to water dissociation reaction, (b) increase in the surface hydrophobicity, and (c) design of electrical inhomogeneity of the membrane/solution interface; the purpose is the facilitating of intense development of electrical convection.