Maxwell–Stefan model of multicomponent ion transport inside a monolayer Nafion membrane for intensified chlor-alkali electrolysis

Abstract

A mathematical model based on a generalized Maxwell-Stefan equation has been developed to describe multicomponent ion and water transport inside a cation-exchange membrane. This model has been validated using experimental data and has been used to predict concentration profiles, membrane potential drop, and transport numbers of ions and water for the chlor-alkali process at increased current densities. Several improvements have been made to previously developed Maxwell-Stefan models. In our model, the generalized Maxwell-Stefan equation is written in terms of concentration instead of mole fraction and the fixed group (membrane) concentration is assumed to be constant. We have adapted the Augmented matrix method using the built-in partial differential equation parabolic elliptic (pdepe) solver in Matlab®, and both the concentration and the electrical potential gradients have been solved simultaneously. The boundary conditions are determined with the Donnan equilibrium at the membrane-solution interface. We have also employed semi-empirical correlations to define the Maxwell-Stefan diffusivities inside the membrane. For the bulk diffusivities, we applied the correlations for the concentrated solution instead of the values at infinite dilution. With the diffusivities presented in this work, the model shows a better fit to the experimental data than with previously reported fitted diffusivities. Prediction of the sodium transport number and water transport number is generally good, whereas the deviations with regard to membrane potential might also be related to issues with the experimental data. The model predicts an increase in both sodium and water transport numbers at increased current density operation of chlor-alkali production.

Coupling a Chlor-Alkali Membrane Electrolyzer Cell to a Wind Energy Source: Dynamic Modeling and Simulations

“…The outlet concentration of NaCl W out an,NaCl in wt% can be calculated from C out an, NaCl with the help of Equation (26), where ρ out an, (NaCl+H 2 O) is the outlet density of brine, which can be obtained from the empirical expressions given in Equations ( 27)- (30) [34,[51][52][53].…”

“…The exit concentration of water in the anolyte C out an,H 2 O is calculated based on the outlet density of brine and concentration of NaCl W out an,NaCl as given in Equation (31) [34,51].…”

Impact of Initial Cyclic Loading on Mechanical Properties and Performance of Nafion

“…The interest in Nafion is derived from its unique structure [ 1 , 2 ] and properties (i.e., good chemical and thermal stability, high hydrophilicity of ionic-water domains, and ion-conductivity to cations, as well as permeability to water, etc. ); there it is used in various models [ 3 ] and applications ranging from various sensors [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ], fuel cells [ 16 ], and water electrolyzers [ 17 ] to chlor-alkali cells [ 18 ]. In addition, Nafion is the key constituent in the ionic polymer–metal composites (IPMCs) working as sensors and actuators [ 19 , 20 ].…”

Estimation of activity coefficients for aqueous organic redox flow batteries: Theoretical basis and equations

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