(545ak) Modeling the Ionic Transport in an Electrodialysis Cell: Investigating the Impacts of Non-Ideal Solution Behavior in the Cell

Electrodialysis (ED) is an electro-membrane desalination technique in which ions are separated from a saline solution via selective transport through ion exchange membranes (IEMs) in the existence of an imposed electric field. Modeling the transport phenomena is a key to identify the optimum operating conditions to reduce energy consumption of the ED process. We use the fundamental applied equations for electrochemical systems including the Navier-Stokes, continuity, molar mass balance, and the Nernst-Planck to develop a 2-dimensional ion transport model for desalination of aqueous NaCl solution in an ED cell, considering the co-ion transport through IEMs. This study addresses the impact of the non-ideal behavior of electrolytes on ionic transport in both spacer-free and spacer-filled ED systems. The non-ideality of the electrolyte solution inside channels and IEMs is modeled by applying the polyelectrolyte NRTL activity coefficient model. The flow pattern in spacer-filled channels is determined considering the laminar flow assumption and submerged spacer configuration. The COMSOL Multiphysics software is used to numerically solve the set of developed equations employing the finite element method. The comparison of the ideal and the non-ideal solution models results demonstrates a slight deviation among them for concentrations up to 0.5 mol/kg NaCl for both spacer-free and spacer-filled ED systems. However, the eddy promotion in spacer-filled channels reduces the thickness of diffusion boundary layers, thus, the limiting current is reached at higher imposed potential compared to that of the spacer-free cell.