Polarization in Ion-Exchange Membrane Electrodialysis

Abstract

m = number of components N = Avogadro's number n = number of chain linkages P = total pressure g = number of principal moments of inertia R = radius of gyration of molecule T = absolute temperature u = molar volume u partial molar volume y = vapor-phase mole fraction z = compressibility factor -Greek Letters 9 = fugacity coefficient c = intermolecular potential energy u = diameter of molecule as defined by eq 9 Subscripts i, J , 1 , 2 = components mix = mixture Literature CitedA theoretical model for polarization in ion-exchange membrane electrodialysis is developed. The model incorporates "repulsion zones" in the solutions adjacent to the membrane surface where co-ion-fixed charge repulsion dominates. In these zones the recombination rate of H+ and OH-ions is therefore strongly affected by the local electric field. Experimental data are used to compute thicknesses of these zones. The results show that for cation-exchange membranes, very high concentrations of H+ ion are built up at the membrane surface during polarization, creating additional counterions (Hf) for current-carrying. The decrease in the recombination rate of H+ and OH-ions near the membrane is responsible for this.

Water Dissociation

“…Patel et al (1977) developed the theoretical model incorporated with "repulsion zones" in the solutions adjacent to the membrane surface. Patel et al (1977) developed the theoretical model incorporated with "repulsion zones" in the solutions adjacent to the membrane surface.…”

“…The interface potential difference relates to the Donnan potential (Donnan, 1924), repulsion zone (Patel et al, 1977), and space charge (Rubinstein and Shtilman, 1979;Rubinstein, 1981). With an elevated electric current, however, electrolyte concentration of the solution contacting a desalting surface of the membrane is decreased.…”

Mass transport in a boundary layer and in an ion exchange membrane: Mechanism of concentration polarization and water dissociation

“…This phenomenon induces the dissolution of counter ions combined with the ion exchange groups into the solution phase to form ionized exchange groups and the change of electric potential in the membrane to form potential difference at the membrane/solution interface. The interface potential difference relates to the Donnan potential [48], repul sion zone [28] and space charge [9,10]. The electric potential in the membrane reflects the electrochemi cal free energy barrier, i.e.…”

“…It generates H + ions and OH -ions, which carry an electric current instead of electrolyte counter ions decreased due to concentra tion polarization. The mechanism of the water disso ciation reaction is investigated extensively from the view points of the diffusional model [27], repulsion zone [28], Wien effect [29,30], protonation and deprotonation reaction [31,32], etc. The water disso ciation is an equilibrium reaction to dissociate H 2 O molecules into H + and OH -ions and its intensity is governed by the forward reaction rate constant k a and the reverse reaction rate constant k b .…”

Dielectric Relaxation on the Intermediate Layer in a Bipolar Membrane under the Water Splitting Phenomenon

“…The water splitting phenomenon on charged membranes has been one of the serious problems of the electrodialysis process (1,2). When an external electric field is applied to a charged membrane, the electric current attributes to the counterions due to the permselectivity.…”