Potentiodynamic and Galvanodynamic Regimes of Mass Transfer in Flow-Through Electrodialysis Membrane Systems: Numerical Simulation of Electroconvection and Current-Voltage Curve

Abstract

Electromembrane devices are usually operated in two electrical regimes: potentiodynamic (PD), when a potential drop in the system is set, and galvanodynamic (GD), when the current density is set. This article theoretically investigates the current-voltage curves (CVCs) of flow-through electrodialysis membrane systems calculated in the PD and GD regimes and compares the parameters of the electroconvective vortex layer for these regimes. The study is based on numerical modelling using a basic model of overlimiting transfer enhanced by electroconvection with a modification of the boundary conditions. The Dankwerts’ boundary condition is used for the ion concentration at the inlet boundary of the membrane channel. The Dankwerts’ condition allows one to increase the accuracy of the numerical implementation of the boundary condition at the channel inlet. On the CVCs calculated for PD and DG regimes, four main current modes can be distinguished: underlimiting, limiting, overlimiting, and chaotic overlimiting. The effect of the electric field regime is manifested in overlimiting current modes, when a significant electroconvection vortex layer develops in the channel.

Electrodialysis with asymmetrically profiled membranes: Influence of profiles geometry on desalination performance and limiting current phenomena

“…Overlimiting currents can be explained only partially by the formation of charge carriers via water dissociation (H + and OH -) [37,38]. Electroconvection, instead, can be the main overlimiting mechanism involving the transport of salt ions [28,39,40]. Non-equilibrium electroconvection occurs through the development of an extended space charge region near the membrane and inhomogeneous electric fields causing dynamic vortices [41][42][43][44].…”

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

“…The current that is carried by H + and OH − generated through water dissociation can partially explain the appearance of overlimiting currents [84,[95][96][97][98][99]. Instead, other overlimiting mechanisms involve counter-ions by current-induced convection [67,88,91,[100][101][102][103][104][105][106][107][108]. Electroconvection is the primary process that alters the depleted region for dilute solutions.…”

Mathematical Modeling of the Effect of Pulsed Electric Field on the Specific Permselectivity of Ion-Exchange Membranes

“…The effect leads to a decrease in the electrolyte concentration in a thin layer near the membrane surface. The growth of the system resistance results in the current density decrease with time in the potentiostatic mode or an increase in the potential drop with time in the galvanostatic mode [ 5 , 6 ]. Depending on the mode, the system tends to a certain stationary value of the current density or potential drop.…”