Study On Preparation And Properties Of Selective Hydrodesulfurization Catalysts For FCC Gasoline

With the increasing of environmental protection and energy saving requirements,motor gasoline is mainly manifested on the lead-free,low sulfur and sulfur free,low aromatics,low olefin and high octane number etc.Developing new hydrotreating catalysts with good selective hydrodesulfurization performance is practically essential.In this paper,the CoMo/?-Al₂O₃ catalysts modified with the metal additives.The influence of additive types and additive content on physicochemical properties of the catalysts and selectivity of the desulfurization is studied.The physicochemical properties of catalysts have been characterized by XRD,BET and H₂-TPR techniques.Experiments of hydrodesulfurization for FCC gasoline were carried out to optimize catalysts of CoMo-M₁/?-Al₂O₃?M₁ is Ce or La?,CoMo-M₂/?-Al₂O₃?M₂ is Fe or Cu?and CoMo-M₁-M₂/?-Al₂O₃ with the conditions of 240?,1.5 MPa,LHSV 2.0h^-1 and H₂/oil ratio300.The results of experiments illustrate that the added Ce oxide impacts the reducibility of reactive metal,which promotes the reduction of Mo6+ to Mo⁴⁺ on the surface of carriers and then form the reactive precursor of Co-Mo.This process improves the reducibility of catalysts,so as to improves the activity and selectivity of catalysts.Fe oxides can improve the specific surface area and the pore diameter of catalysts,and can change the reducibility of catalyst metal,which brings on improvement in the activity and selectivity of catalyst.While Cu oxide covers the surface of the catalyst,occupying the original activity of catalysts,which have a certain degree of inhibition for desulfurization and olefin saturation rate of Al₂O₃ catalyst.Results show that the CoMo/?-Al₂O₃ catalysts modified by Ce or Fe have better activity and selectivity for the hydrodesulfurization.The optimized preparation content is that the content of CoO and MoO₃ is 3wt% and 8wt%,the loading of CeO₂ is 1.5wt%,and Fe2O₃ is0.75wt%.Orthogonal experiments were carried out to optimize catalysts reaction conditions on CoMo-Ce-Fe/?-Al₂O₃.Results showed that the condition of 240?,1.0 MPa,LHSV 2.0h^-1 and H₂/oil ratio 250 were the best.The HDS ratio was 86.38% with 14.46% of HDYO ratio.The long-term test for the superior catalyst was carried out in the thesis.The results showed thatmodified CoMo-Ce-Fe/?-Al₂O₃ catalyst was an ideal catalyst which keeps stable reaction activity during the test time over 168 hours,which suggests modified CoMo-Ce-Fe/?-Al₂O₃ catalyst has excellent performance in selectivity of hydrodesulfurization for FCC gasoline.