Modeling and validation of concentration dependence of ion exchange membrane permselectivity: Significance of convection and Manning's counter-ion condensation theory

Electrodialysis, reverse electrodialysis, and related electrochemical processes are increasingly important technologies for water purification renewable energy generation storage. The electrical efficiency of these is directly to the permselectivity ion exchange membranes (IEMs) – defined as extent which membrane permits passage counter-ions (ions opposite charge membrane, e.g., cations a cation membrane) while blocking co-ions. Permselectivity not material constant, but rather depends on concentration composition electrolyte solutions in contact with IEM. Thus, even though routinely measured at standardized conditions (usually 0.5 M/0.1 M NaCl or KCl), practical utility such data limited because we lack an accurate, quantitative way using it predict under relevant process conditions. Moreover, dependence IEM has historically been studied primarily by evaluating performance (reverse) electrodialysis stacks than individual membranes, made difficult relate specific characteristics. In this study, four commercial IEMs six different gradients employing 4 high salt concentration. We then constructed predictive model based extended Nernst-Planck equation investigated how accounting convection electrostatic effects (via Manning's counter-ion condensation theory) affected accuracy. demonstrate that predictions function external concentrations possible require knowledge only easily properties: uptake, permeability, charge, thickness.