TY - JOUR
T1 - Modeling and validation of concentration dependence of ion exchange membrane permselectivity
T2 - Significance of convection and Manning's counter-ion condensation theory
AU - Kingsbury, R. S.
AU - Coronell, O.
N1 - Funding Information:
This work was funded by the University of North Carolina Research Opportunities Initiative (ROI) program and the Gillings Innovation Labs Program of the University of North Carolina at Chapel Hill . R. Kingsbury was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1144081 . Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors also thank Riley Vickers for assistance reviewing mathematical equations and model consistency.
Funding Information:
This work was funded by the University of North Carolina Research Opportunities Initiative (ROI) program and the Gillings Innovation Labs Program of the University of North Carolina at Chapel Hill. R. Kingsbury was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1144081. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors also thank Riley Vickers for assistance reviewing mathematical equations and model consistency.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/2/15
Y1 - 2021/2/15
N2 - Electrodialysis, reverse electrodialysis, and related electrochemical processes are increasingly important technologies for water purification and renewable energy generation and storage. The electrical efficiency of these processes is directly related to the permselectivity of the ion exchange membranes (IEMs) – defined as the extent to which the membrane permits the passage of counter-ions (ions of opposite charge to the membrane, e.g., cations for a cation exchange membrane) while blocking passage of co-ions. Permselectivity is not a material constant, but rather depends on the concentration and composition of the electrolyte solutions in contact with the IEM. Thus, even though permselectivity is routinely measured at standardized conditions (usually 0.5 M/0.1 M NaCl or KCl), the practical utility of such data is limited because we lack an accurate, quantitative way of using it to predict permselectivity under relevant process conditions. Moreover, the concentration dependence of IEM permselectivity has historically been studied primarily by evaluating the performance of (reverse) electrodialysis stacks rather than individual membranes, which has made it difficult to relate the concentration dependence of permselectivity to specific membrane characteristics. In this study, we measured the permselectivity of four commercial IEMs in six different concentration gradients employing 4 M and 0.5 M NaCl as the high salt concentration. We then constructed a predictive model of membrane permselectivity based on the extended Nernst-Planck equation and investigated how accounting for convection and electrostatic effects (via Manning's counter-ion condensation theory) affected model accuracy. We demonstrate that accurate, quantitative predictions of IEM permselectivity as a function of external salt concentrations are possible and require knowledge of only four easily measured membrane properties: water uptake, water permeability, charge, and thickness.
AB - Electrodialysis, reverse electrodialysis, and related electrochemical processes are increasingly important technologies for water purification and renewable energy generation and storage. The electrical efficiency of these processes is directly related to the permselectivity of the ion exchange membranes (IEMs) – defined as the extent to which the membrane permits the passage of counter-ions (ions of opposite charge to the membrane, e.g., cations for a cation exchange membrane) while blocking passage of co-ions. Permselectivity is not a material constant, but rather depends on the concentration and composition of the electrolyte solutions in contact with the IEM. Thus, even though permselectivity is routinely measured at standardized conditions (usually 0.5 M/0.1 M NaCl or KCl), the practical utility of such data is limited because we lack an accurate, quantitative way of using it to predict permselectivity under relevant process conditions. Moreover, the concentration dependence of IEM permselectivity has historically been studied primarily by evaluating the performance of (reverse) electrodialysis stacks rather than individual membranes, which has made it difficult to relate the concentration dependence of permselectivity to specific membrane characteristics. In this study, we measured the permselectivity of four commercial IEMs in six different concentration gradients employing 4 M and 0.5 M NaCl as the high salt concentration. We then constructed a predictive model of membrane permselectivity based on the extended Nernst-Planck equation and investigated how accounting for convection and electrostatic effects (via Manning's counter-ion condensation theory) affected model accuracy. We demonstrate that accurate, quantitative predictions of IEM permselectivity as a function of external salt concentrations are possible and require knowledge of only four easily measured membrane properties: water uptake, water permeability, charge, and thickness.
KW - Donnan equilibrium
KW - Ion exchange membrane
KW - Manning theory
KW - Membrane potential
KW - Permselectivity
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U2 - 10.1016/j.memsci.2020.118411
DO - 10.1016/j.memsci.2020.118411
M3 - Article
AN - SCOPUS:85092722635
SN - 0376-7388
VL - 620
JO - Journal of Membrane Science
JF - Journal of Membrane Science
M1 - 118411
ER -