Analysis of a novel chlorine recycling process based on anhydrous HCl oxidation

• Gas phase HCl electrolysis combined with oxygen reduction reaction (oxygen depolarized cathode) for chlorine production.
• Determination of potential losses in half-cell measurements under technically relevant conditions.
• Optimization of gas diffusion electrodes with respect to Nafion and catalyst loadings.
• The optimal Nafion content in the catalyst layer for HCl oxidation is much higher than for other gas phase reactions, such as the oxygen reduction in the cathode.
• Nafion improves catalyst dispersion, but catalyst utilization depends on the diffusion and absorption properties of the educts in the ionomer phase.

A novel process for the recycling of chlorine based on the gaseous HCl oxidation on gas diffusion electrodes has been investigated. The cathodic and anodic reactions have been analyzed separately as half-cell reactions in a cyclone flow cell and optimized regarding catalyst as well as ionomer loadings. For the anodic hydrogen chloride oxidation, an optimal value of ca. 60 wt% Nafion has been found, whereas for the cathodic oxygen reduction a value below 37 wt% has been obtained. This discrepancy was mainly attributed to the different absorption and transport properties of HCl in Nafion compared to oxygen. The main potential losses in the reactor were identified at the cathode.

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