Electrolyzer Technologies in Toluene Direct Electro-hydrogenation for Methylcyclohexane Synthesis

Abstract

This review presents an overview of the development of an electrolyzer for the direct electrohydrogenation of toluene, a one-step electrochemical process for directly synthesizing methylcyclohexane from toluene and water utilizing solid polymer electrolyte (SPE) membranes. Reducing the cell voltage and enhancing the current efficiency are important to improve the performance of a toluene direct electrohydrogenation electrolyzer. To improve these characteristics, the electrolyzer components consisting of the flow field, the diffusion layer, the anode mesh size, and the collector and cathode catalyst layer were modified and optimized. Investigation of the flow field structure found that the porous carbon flow field exhibited the highest performance, with remarkable improvement in current efficiency. Decrease in current efficiency indicates hydrogen gas generation at the cathode. However, loading of the Pt catalyst in the porous carbon flow field on the cathode side resulted in chemical reaction of the hydrogen gas generated in the catalyst layer with toluene utilizing the Pt catalyst, which significantly improved the overall current efficiency. Smaller mesh size of the anode and heat-pressing treatment of the anode current collector reduced the cell voltage with increased cathode catalyst utilization ratio by improvement of surface pressure uniformity and membrane flatness. The toluene permeation properties of various SPE membranes were determined and the relationship between the catalyst layer thickness and electrolysis performance was clarified. The developed technologies improved the cell voltage at 0.4 A cm⁻² current density from 2.10 to 1.72 V and achieved more than 90 % toluene conversion in continuous single-flow operation.