A Model of the Anode from the Chlorate Cell

Abstract

This article presents a mathematical model that describes the physio-chemical properties of a chlorate cell. The chlorate cell involves the electrochemical evolution of a gas that impinges a large velocity on the electrolyte flowing between two participating electrodes that are only 3 mm apart. The model is written to take into account the diffusion, migration and convection transport mechanisms, of the electrolyte species, and assumes that the hydrodynamic flow is the laminar development of fluid between two parallel plates. The transport, of each of the species, and kinetic data, for all the chemical and electrochemical reactions and bireactions, are also involved in the model. Properties of the species are worked out with consideration to the high concentration and temperature of an electrolyte. The most important result from the model is the development of a diffusion layer of species along the height of the anode. This diffusion layer creates a substantial concentration overpotential, for chloride oxidation, especially at the top of the anode surface. This gives a non-uniform current density distribution on the anode that worsens as flow velocity decreases. Moreover, the model shows that the major bireaction is the production of oxygen from the electrochemical decay of hypochlorite and not from water splitting.