Multicomponent ion transport in a mono- and bilayer cation-exchange membrane at high current density

Abstract

This work describes a model for bilayer cationexchange membranes used in the chlor-alkali process. The ion transport inside the membrane is modeled with the Nernst-Planck equation. A logistic function is used at the boundary between the two layers of the bilayer membrane to describe the change in the properties of each membrane layer. The local convective velocity is calculated inside the membrane using the Schlögl equation and the equation of continuity. The model calculates the ion concentration profiles inside the membrane layers. Modeling results of mono-and bilayer membranes are compared. The changes in membrane voltage drop and sodium selectivity are predicted. The concentration profile of sodium ions in the bilayer membrane is significantly different from the monolayer membrane. Without the applied current, a linear change in the sodium concentration is observed in the monolayer membrane and in each layer of the bilayer membrane. With an increase in current density, the stronger electromotive force in the carboxylate layer causes a decrease in the sodium concentration in the sulfonate layer, down to the fixed ionic group concentration. This significant decrease of sodium ion concentration in the sulfonate layer results in low concentrations of counter ions and as a consequence a higher permselectivity of the bilayer membrane is obtained when compared to the single-layer membrane. As a drawback, the resistance in the bilayer membrane increases.

Revisiting Chlor-Alkali Electrolyzers: from Materials to Devices

“…The use of a blend of PFSA and PFCA as an intermediate layer between the sulfonic acid and Fig. 7 Multicomponent ion transport in a bilayer cationexchange membrane (reprinted from [91] with permission from Springer Nature) carboxyl layers was proposed to minimize the difference in water transport between the two layers.…”

Математическая Модель Переноса Ионов В Процессе Электродиализа

“…Это аналогично и для катодной поверхности. Предполагается, что массоперенос на поверхности мембраны очень высок из-за очень значительного перемешивания электролита [17].…”

Blending the boundaries : enhancing ION transport with electrokinetics

“…In ED, the transport of ions can take place due to advection, migration and diffusion [100]. The total ionic flux can be expressed by the Nernst-Planck equation as given below [71,96]…”