Impact of feed impurities on catalysts for chlorine recycling

• Impact of CO and sulfur compounds on HCl oxidation catalysts is investigated.
• The occurrence of CO oxidation over RuO2 and IrO2 leads to hotspot formation.
• Chlorinated CeO2, U3O8, and CuCrO2 surfaces are inactive for CO oxidation.
• COS and SO2 severely poison all Deacon catalysts.
• HCl treatment enables regeneration of the sulfur-poisoned catalysts.

This study assesses the impact of feed impurities on the design of a robust catalytic process for chlorine recycling via HCl oxidation (Deacon reaction). The influence of CO, SO2, and COS was investigated over stable catalysts, including RuO2/SnO2-Al2O3, CeO2/ZrO2, U3O8/ZrO2, IrO2/TiO2, and CuCrO2. Carbon monoxide is detrimental for RuO2- and IrO2-based catalysts, since the highly exothermic oxidation to CO2 under Deacon conditions causes pronounced temperature rises leading to material and reactor instabilities. Advantageously, the other catalysts are practically unaffected by this impurity due to their inactivity for CO oxidation in the chlorinated state. Carbonyl sulfide and particularly sulfur dioxide severely poison all the catalysts investigated due to the strong adsorption of the sulfur compounds and active site blockage. However, the initial activity can be restored by treating the deactivated catalysts in HCl (without oxygen) at the reaction temperature. We discuss process strategies for feed purification and catalyst regeneration depending on the chosen catalytic system, which are of utmost important for the ultimate sustainability of the process.

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