Early stage deactivation of heavy crude oil hydroprocessing catalysts

Four different CoMo catalysts supported by alumina, alumina–titania, alumina–silica and carbon were used to study the early stage of deactivation. Hydrodemetallization (HDM) and hydrodesulfurization (HDS) activities of these catalysts have been tested in high pressure, high temperature micro-plant by using heavy crude oil as feed. Thiophene activity of the spent catalysts was compared with the fresh and regenerated catalysts. The results show that the alumina and alumina–titania supported CoMo catalysts exhibit high and stable performance for both HDM and HDS activities. Though the initial activities of alumina–silica supported CoMo catalyst are high, the activities decrease rapidly with time-on-stream. Having higher acidic sites may cause this rapid deactivation. Thermogravimetric analysis results also support that the nature of deposited carbon on this catalyst is different from the coke deposited on the other three catalysts. SEM-EDX results show that vanadium sulfides are more preferably deposited at the outer surface of carbon catalyst. Thiophene HDS activity of fresh, spent and regenerated results suggest that the deactivation of alumina catalyst is cause of coke deposition whereas both metal sulfides and coke depositions are responsible for CoMo/Al2O3–TiO2 and CoMo/Al2O3–SiO2 catalysts deactivation, particularly at the early stage of hydroprocessing of the heavy oil.