Theoretical Analysis of the Optimum Bed Thickness of an Electrochemical Reactor

Aws Abdulmahdi Sadeq
Prof. Dr. Qasim J. M. Slaiman
Dr. Sarmad Talib Najim

     In this study, a theoretical analysis of optimum bed thickness for realizing a high efficiency and reaction conversion of an electrochemical reactor has been made based on flow-through porous electrode (FTPE) configuration. Another configuration of porous electrode (flow-by) has been reviewed beside the considered one. The method that has been used is to find out a mathematical model to represent the optimum bed thickness by taking a look into previous works concerned and collecting all related information, data, and models. It has been found that the optimum bed thickness can be classified into two categories depending on reactor operating conditions.Accordingly, models have to be classified into two groups: firstly,electrochemical reactors (ECRs) operating under electron transfer (activation) control, and secondly, (ECRs) operating under mass transfer control.The models that have been studied and tested are based on FTPE operating under mass transfer control according to the importance of this region in a wide range of applications. Seven models have been selected from literature survey related theoretically to optimum bed thickness of an electrochemical reactor operating under mass transfer control when electrode conductivity is much higher than electrolyte.The parameters that affect the optimum bed thickness have been visualized and reviewed, and almost all of them have been examined by experimental data from different sources and based on the various models. It has been found that the increase in electrolyte flow rate, concentration, limiting current density, and specific surface area reduce the optimum bed thickness, and the increase in electrolyte conductivity, void fraction, and overpotential range increases optimum bed thickness.  The most important design parameter that has a great effect on optimum bed thickness is found to be the electrolyte flow rate for any certain operation. The effect of electrolyte entrance (or electrode placement) on optimum bed thickness has been reviewed and the results have shown no significant effects.It has been concluded that the most appropriate two models to represent the optimum bed thickness of FTPE electrochemical reactor operating under mass transfer control based on the results are those predicted theoretically and stated by Kreysa [28] in (1978) and Doherty et al. [8] in (1996).