Efficient removal of oil from spent hydrodesulphurization catalysts using microwave pyrolysis method

Abstract

Spent hydrodesulphurization (HDS) catalysts generally contain about 20% oil, the presence of which hinders the metallurgical processes for recovering valuable metals. In this study, a new approach was developed to remove oil from spent HDS catalysts by microwave pyrolysis. Firstly, the effects of the pyrolysis temperature and time on removing oil were investigated using microwave and conventional pyrolysis. The results show that removing oil using microwave pyrolysis was superior to using conventional pyrolysis in terms of energy savings, speed, and removal ratio. Under the optimum pyrolysis conditions (700 °C, 30 min, and an inert atmosphere), about 64% and 25% removal of carbon and sulfur, respectively, and 25% weight loss were achieved with the proposed method, while using conventional pyrolysis, only 40% and 18% removal of carbon and sulfur, respectively, and 20% weight loss were achieved. The properties of the raw spent HDS catalysts and pyrolysis products, including their morphologies and elemental states, were investigated using SEM-EDS, XPS, and FTIR. The results of these analyses indicate that the proposed method not only removes oil efficiently, but can also remove elemental carbon from spent catalysts. Finally, the main components of recovered oil and gas were investigated using FTIR, GC–MS, and GC–TCD analyses.