Study on the deactivation mechanism of waste lubricating oil hydrogenation catalyst

Objective  The aim is to study the deactivation mechanism of waste lubricating oil hydrogenation catalyst.

Methods  Taking NiMo/γ-Al₂O₃ catalyst as the research object, the catalyst and oil before and after hydrogenation were characterized and analyzed, so as to find out the cause of catalyst deactivation.

Results  The catalyst showed superior initial hydrogenation activity, and the removal rates of sulfur(S), nitrogen(N) and chlorine (Cl) could reach 83.6%, 81.7%, and 99.7%, respectively. However, with the progress of the reaction, the activity of the catalyst decreased seriously from the 4th week. The characterization of the catalyst before and after the reaction showed that the specific surface area and pore volume of the catalyst decreased significantly after the reaction, and the silicon content in the catalyst composition increased significantly after the reaction.

Conclusions  The reason for the decrease of catalyst activity was neither the loss of active metal nanoparticles, nor the damage of catalysts microstructure, but with the hydrogenation reaction, the silicon in the oil was gradually deposited on the catalyst surface after hydrogenation, resulting in the active site being covered and unable to contact with the reactants. On the other hand, the accumulation of silicon in the fixed bed pipeline limited the mass transfer and heat transfer efficiency, and reduced the reactivity.