Theoretical and Experimental Study of Joint Osmotic and Electroosmotic Water Transfer through a Cation-Exchange Membrane

Abstract

Using the previously developed cell model of a charged membrane and the principles of linear thermodynamics of irreversible processes (the Onsager approach), exact and approximate (in the case of an ideally selective membrane) analytical formulae for calculating the osmotic and electroosmotic permeability of the membrane in aqueous solutions of 1:1 electrolyte at constant electric current density and concentration gradient were suggested. The formulae have been successfully verified by our own experimental data for the extrusion cation-exchange membrane MF−4SC p.29 in NaCl solution up to concentrations of 3 M. The contribution of electroosmotic and osmotic water fluxes to the total water transport through the mentioned individual perfluorinated ion-exchange membrane under conditions close to the process of electrodialysis concentrating was experimentally estimated. The cases of co- and counter-directed osmotic and electroosmotic water fluxes are studied. A good correspondence between theoretical and experimental results was obtained, which made it possible to determine the physicochemical parameters of the electromembrane system (the diffusion coefficients of individual ions and the coefficient of equilibrium distribution of electrolyte molecules in the membrane matrix, the characteristic exchange capacity of the cell model). The achieved results make it possible to fully characterize existing and promising types of ion-exchange membranes based on the developed cell model of a charged membrane.

Electrochemical Measurement of Water Transport Numbers in Anion-Exchange Membranes

“…These include volumetric water measurements under an applied electrical bias and the use of the Scatchard equation to differentiate true and apparent water transport numbers. [51][52][53][54] The method of interest here to determine i Τ is the electrochemical technique developed by Fuller and Newman, in which an exchange membrane is placed between two separate abutting chambers. 3,38 Water-vapor activity on the membrane upstream side is varied while holding the downstream-side water activity constant, and the open-circuit voltage(OCV) is measured as a function of water activity.…”

Ion and Molecule Transport in Membrane Systems 3.0 and 4.0

“…Filippov and Shkirskaya theoretically and experimentally studied osmotic and electroosmotic water transports [16]. The theoretical study is based on the well-known cell model [17] of a charged membrane involving the principles of irreversible thermodynamics.…”

The Space Charge Model. A new analytical approximation solution of Poisson-Boltzmann equation: the extended homogeneous approximation

“…Nanofiltration membranes (NF) are particularly relevant for industrial applications because of their valuable features, such as pore diameters smaller than 2 nm [1][2][3]. NF has several advantages over other filtration processes, including lower energy consumption, lower operating pressures, and the ability to selectively remove specific components.…”