Preparation And Properties Of SBA-15Zeolite-based Gasoline Deep Hydrodesulfurization Catalysts

Nearly80%of commercial gasoline in China is by-product of the fluid catalytic crackingprocess （FCC） in a petroleum refinery. The FCC process enhances gasoline production andeven the increasing demand, but it was limited by its drawback in relative high sulfur level ofgasoline which collides with the increasing awareness of the impact of environmentalpollution all around the world. Although many attempts have been proceeded to improve theFCC process, such as the application of new types of catalysts and additives, the sulfur levelof gasoline production is still not low enough to accord with the stringent fuel specifications.Such high degree of sulfur removal needs deep hydrodesulfurization （HDS）, but the IndustrialHDS process will inevitably decrease the olefins content leading to a serious loss of octanenumber （RON）, and further reduce the economical and practical efficiency of gasolineproductions.Micro-mesoporous molecular sieves attract significant interest of the intensive study andare find to have numerous applications due to their unique structures and properties, such asuniform tunable mesopore channels, intersections of dual-pore system, surface acidity andhydrothermal stability. Moreover, benefitted by the hierarchical pore structure and appropriateacidity, Micro-mesoporous molecular sieves are expected to be used as deephydrodesulfurization catalysts, further realize high dispersion of active components andefficient reduction of the sulfur level of gasoline productions. However, the information ofcatalytic mechanisms by Micro-mesoporous molecular sieves based HDS catalyst is stillinsufficient, such as the desulfurization reaction of sulfides and hydrogenation reaction ofolefin, moreover, the parameters of the HDS reaction also need to be optimized. Due to that,systematic research in the preparation, modification and evaluation of Micro-mesoporousmolecular sieves based HDS catalyst are needed.In this work, micro-mesoporous molecular sieve SBA-15is employed as deephydrodesulfurization catalyst, and with the aim of deep investigation of the relationshipbetween the activity and selectivity of HDS catalysts, a systematic study of the effects ofactive components, activity group distribution and reaction conditions on HDS catalytic performance was proceeded. Moreover, the HDS reaction mechanisms, such as the reactionpath of rearrangement between olefin and H2S were studied. The specific research contentsand results are summarized mainly as following.A series of CoMo/Support（SBA-15,MCM-41andγ-Al₂O₃） were prepared, the impacts ofCo/Mo ratio and reaction conditions on the catalytic activity were investigated in a autoclavereactor. The structure, surface property and regeneration of the catalysts were characterizedand analyzed comprehensively. The results revealed that the CoMo catalyst based on SBA-15was founded to have better activity than those based on MCM-41andγ-Al₂O₃, which suggeststhat the acidity of SBA-15is suitable to the HDS reaction than the other two catalysts. The0.4CoMo/SBA-15catalyst with MoO₃loaded by15wt.%and Co/Mo of0.4has the best HDSactivity. The optimum reaction conditions: temperature is280℃, the initial reaction ofhydrogen pressure is1.2MPa and the stirring rate is500rpm. The amount of catalyst is0.2gand reaction solution volume is50mL.The metal oxides MO （V2O₅,CeO₂and Cr₂O₃） were used to modify the SBA-15, and0.4CoMo/MO（x）-SBA-15catalysts were prepared in this work. The effects of the types of themodified metal oxides and the content of metal oxides on HDS performance and selectivitywere investigated in a autoclave reactor. The results based on a comprehensivecharacterization and analysis for the catalyst structure, surface property and regeneration ofthe catalysts showed that among the four types of metal oxide modifiedCoMo/MO（x）-SBA-15catalysts, the catalysts modified by V2O5, CeO2and Cr2O₃showedbetter activity of HDS and selectivity than the catalyst of0.4CoMo/SBA-15, and also had asuperior performance to the current commercial catalysts under the same condition. With themodification content of15wt.%, the catalyst showed the best hydrodesulfurization activity.However, the catalyst modified by strong alkaline metal oxide K₂O has lower desulfurizationrate and selectivity.Performances of0.4CoMo/SBA-15and0.4CoMo/V₂O₅（15）-SBA-15catalysts on thereaction of1-hexene and H₂S were detected in this work. The reaction path between1-hexeneand H2S on both catalysts was obtained. The results revealed that the formation of mercaptans and thioethers can be promoted by H₂S, and the transformation reaction of1-hexene towardshexane,2-hexene and3-hexene can be inhibited by H₂S. Although the increase in H2S caninhibit the hydrogenation saturation and isomerization reactions for1-hexene, but it does notmeet the original intention of the gasoline deep desulfurization, which is to reduce thehydrodesulfurization depth in system. Therefore, in order to meet the requirement of the deepdesulfurization of gasoline during the hydrodesulfurization reaction, do try to remove the H2Sgenerated in the reaction system to ensure that the catalyst has higher hydrodesulfurizationactivity. Consolidating the unmodified and modified catalysts on the reaction regular ofolefins with H₂S and the GC-MS analysis of the product, the reaction path between H2S andolefin under the HDS catalyst based on SBA-15was obtained.