Study on Diesel Hydrotreating Kinetics and the Synergistic Effect of CoMo and NiMo Catalysts

Diesel ultradeep desulfurization technology is pivotal in producing clean diesel. This paper examines the kinetic characteristics of the CoMo ultradeep desulfurization catalyst in the diesel hydrotreating process. Integrating the inhibitory effects of hydrogen sulfide, nitrogen-containing compounds, and aromatic hydrocarbons, a three-lump kinetic model for hydrodesulfurization is established. Variations in flow composition along the reactor axial direction under isothermal and adiabatic conditions are simulated. Results indicate that, under adiabatic conditions, the initial removal rate of sulfur-containing compounds is slower compared to isothermal conditions when achieving the same desulfurization depth. Under the adiabatic conditions, beyond the 60% catalyst bed, the reactor enters a low-efficiency zone, and simultaneously, the efficiency of hydrogen utilization also decreases, where the maximum efficiency difference can reach up to 16%. Stacking with a NiMo catalyst, loading the CoMo catalyst in the upper part of the reactor exhibits better selectivity toward the saturation of polyaromatics, implying more effective utilization of hydrogen. It is considered in this study that loading 40% of the CoMo catalyst in the upper part of the reactor not only enhances the hydrogen utilization rate by 4% but also reduces hydrogen consumption by around 8%.