Coke Decomposition Kinetic Model of Spent Hydrodesulfurization Catalysts

Recycling residue hydrodesulfurization (HDS) catalysts is essential due to frequent deactivation. Petroleum coke's high ignition temperature and complex combustion behavior stem from its graphite-like structure and low volatile matter. This study investigates petroleum coke combustion and oxidation kinetics with metal catalysts. Data from HDS catalysts (5% Co-10% Mo/active kaolin and 5% Co-10% Mo/active bentonite) are crucial for industrial regenerator simulations. Iraqi mineral clays, treated and loaded with cobalt and molybdenum, were used in HDS reactions of Iraqi gas oil with 10200 ppm sulfur at 360°C, 12 bar, and WHSV of 2 h⁻¹. Spent catalysts, coated with coke, were analyzed, and coke was removed using thermogravimetric analysis (TGA) at heating rates of 2.5, 5, and 10°C/min. MATLAB software assessed coke accumulation's impact on combustion activation energy via model-free and model-based methods. Activation energies for coke combustion were 46.48, 87.71, and 102.68 kJ/mol for hydrocarbons, soft coke, and hard coke, respectively, on 5% Co-10% Mo/active kaolin, and 41.98, 68.11, and 100.38 kJ/mol for 5% Co-10% Mo/active bentonite. TGA revealed 7.553% and 7.977% total weight loss in kaolin and bentonite catalysts. The model-based method was most effective for regenerating aged HDS catalysts at 850°C, especially for hard coke removal. DTG analysis showed two concavities, indicating soft coke below 350°C and hard coke between 350 and 850°C. For 5%Co-10%Mo/kaolin catalysts, peak temperatures (Tpeak) were 517, 526, and 610°C at heating rates of 2.5, 5, and 10°C/min. Bentonite catalysts showed lower Tpeak values.