Study On Formation Of Mercaptan And Preparation Of Highly Efficient Catalyst In Selective Hydrodesulfurization Process

The main gasoline blending components in China include catalytic cracking?FCC?gasoline,and approximately 80%of sulfur is derived from FCC gasoline.Therefore,the removal of sulfur compounds in FCC gasoline is crucial for the cleanliness of gasoline oil.However,in the hydrodesulfurization process,the H₂S formed by the removal of sulfides recombines with the olefin molecules to form a thiol?secondary thiol?,which increases the sulfur content of the product and excessive thiol sulfur content.To improve the desulfurization depth and realize the clean production of gasoline for vehicles,it is necessary to control the formation of secondary mercaptans in the hydrodesulfurization process.In this study,a CoMo/Ce Al₂O₃ catalyst was selected.The morphology of the catalyst was altered by changing the vulcanization conditions,and the effect of Mo S₂morphology on the surface of the catalyst on the formation of secondary thiols was determined.The results show that under different sulfurization conditions,the Mo S₂platelets on the surface of CoMo/Ce Al₂O₃ catalysts are different.When the length of Mo S₂ platelets is short and the number of stacking layers is high?320°C vulcanization for 6 h?,the mercaptan content in the reaction product low,and the desulfurization activity and selectivity are high.Based on these observations,the surface morphology of Mo S₂ on the surface of the catalyst was modified by changing the impregnation method for CoMo active metal and Ce auxiliary,which further reduced the formation of secondary mercaptan in the reaction process and improved the desulfurization depth.Finally,the catalyst prepared by different Ce impregnation methods was applied to FCC gasoline,and its reaction in actual oil was investigated.The results show that the Mo S₂ platelets on the surface of the CoMo Ce/Al₂O₃ catalyst prepared by impregnating Ce,followed by impregnattion with CoMo active metal?CoMo co-impregnation?have short platelets,high number of layers,low secondary mercaptan production during the reaction,and good desulfurization activity and selectivity.In the actual oil activity evaluation process,the CoMo Ce/Al₂O₃catalyst can reduce the sulfur content of the heavy fraction of Guangxi Petrochemical from 132 ug.g^-1 to 8.6 ug.g^-1,and the RON loss is 1.3 units.