Catalysts And Process Study On Selective Hydrodesulfurization Of Fluid Catalytic Cracked Gasoline

The deep hydrodesulfurizaion of FCC gasoline is a puzzle for producing ultra clean gasoline, because octane-boosting olefins in FCC gasoline are often saturated during the hydrodesulfurization (HDS) reaction. It means that it needed to improve the HDS selectivity of catalyst. In this paper, the influence of surface properties to active phase and hyrodesulfurization slectivity of CoMoS/Al2O3 catalysts was investigated.CoMoS/Al2O3 catalysts were prepared by pore saturation impregnation method using alumina as supports with different surface properties. The catalysts were characterized by BET, Py-IR, XRD and HRTEM techniques. And the selective hydrodesulfuriation performance for FCC gasoline was measured in a high pressure flow micro-reactor. The results implied that the surface acidity of carriers were not determinant of selective HDS catalyst. Nevertheless, the surface acidity could affect the structure of CoMoS active phase that is the determinant of HDS selectivity.The pretreatment conditions either H2 or H2 with straight-run distillation have been investigated in the start-up process for CoMoS/γ-Al₂O₃. The results showed that CoMoS phase separated when the tempreture pretreatment above 300°C at H2 flowing. In addition, Co9S8 crystal can be found on the surface when the temperature increased to 350°C, which implid the CoMoS phase was destructed that leaded to the decrease of HDS activity.The selective HDS reaction conditions, such as reaction temperature, space velocity, H2 pressure and H2/oil ratio, were investigated. The results suggested that both desulfurization and hydrogenation activities increased with temperature increasing to 260°C. However, hydrodesulfurization activity decreased with space velocity increasing. High pressure was helpful to increase desulfurization activity and inhibit hydrogenation activity. In addition, it was unfavourable for improving selectivity when H2/oil ratio was too high or too low. CoMoS/γ-Al₂O₃ prepared with ATTM as precursor indicated high selectivity and HDS activity, the HDS ratio was about 83% with about 6% of HDO ratio under the condition of 260°C, 2.0MPa, H2/oil ratio 300:1 and LHSV 4h-1. It was also suggested that this CoMoS/γ-Al2O3 catalyst was an ideal catalyst for the selective hydrodesulfurization of FCC gasoline.