Modeling of the Tertiary Current Distribution Inside the Chlor-Alkali Electrolysis Cell

During the past decade the study of industrial electrochemical systems, such as electrolysis cells, fuel cells and batteries using numerical simulations, became widespread. This progress is possible partially due to the development of user friendly simulation tools, such as COMSOL Multiphysics^®, based on the solution of differential equations using the finite element method (FEM). Moreover, capabilities specifically dedicated to electrochemical systems, such as the primary/secondary/tertiary current distribution modules, were recently introduced. They enable fast and efficient way of building models with complex geometries and different boundary and initial conditions.

Specifically, the modeling of industrial chlor-alkali membrane cells for chlorine and sodium hydroxide production from brine solution is important for the design of new cells, as well as for the understanding and the improvement of existing cells [1]. Following P. Byrne et al. [2], we studied the distribution of the potential, the current density and the concentrations of different species inside a `lantern` cell of the ICI FM-21 electrolyser.

The pseudo-tertiary current distribution was calculated without the rough approximation used in [2], which neglected the migration motion of the ions in the diffusion boundary layer. In addition, a time-dependent full tertiary current distribution was found, and the growing diffusion boundary layer near the electrodes was visualized. This time-dependent study may be useful in describing the turn-on process of the electrolysis cell, when convective currents may be neglected.

[1] S. Lakshmanan, T. Murugesan, Clean Techn. Environ. Policy 16, 225 (2014).

[2] P. Byrne, P. Bosander, O. Parhammar and E. Fontes, J. Appl. Electrochem. 30, 1361 (2000).