Non-thermal Plasma for Coke Elimination in an Aged Hydrotreating Catalyst: Comparison with a Coked Zeolite

The removal of coke from an aged industrial hydrodesulfurization catalyst, using DBD non-thermal plasma with a pin to plate geometry, was investigated. One of the most important processes in a refinery for removing sulfur-containing compounds is the hydrodesulfurization (HDS) process. The aged catalyst was introduced into the plasma reactor as a thin wafer. After 130 minutes of plasma treatment, with P=30W, 70% of coke was removed while more than 40% of sulfur was still present. Characterization of catalyst at different location of the wafer show that coke was more easily removed at the center, closed to the pin electrode where the electric field is more intense. The formation of an unexpected phase, under the plasma discharge, was highlighted, it corresponds to the family of Keggin HPA PMo12O403-, which could be an interesting precursor of catalyst for HDS process. Comparing with a coked zeolite, the rate of regeneration is lower for the HDS catalyst under plasma discharge, while a lower temperature is required under conventional thermal oxidation. It is explained by the presence of metal particles, which could be responsible for the limitation in O-atoms formation under plasma.