Design And Preparation Of Support And Active Phase Of FCC Naphtha Selective Hydrodesulfurization Catalyst

Nowadays hydrodesulfurization(HDS)is still the predominant technique for removing sulfur from fluid catalytic cracking(FCC)naphtha in industrial practice.However,conventional HDS techniques cause serious saturation of olefins that have high octane numbers,giving rise to great loss in product octane number.Therefore,selective HDS that can remove sulfur compounds with the lowest level of olefin saturation is highly desired,and the key to achieve this goal is the innovation of novel HDS catalysts with superior HDS selectivity.With the aim of developing new-generation selective HDS catalysts,this thesis investigates the effects of support macroporous structures,acidity and morphology of active phases on catalyst HDS activity and selectivity,explores the possibility of using kaolin clay based acidic support to prepare highly selective HDS catalyst simultaneously with olefin isomerization function,and attempts to synthesize Mo S2 with tunable size and morphology via the chemical exfoliation of nano-sized Mo S₂ particles to understand the catalyst morphology-performance relation.The main results achieved are summarized below:1.In the conventional design and preparation of HDS catalysts,an optimal catalyst is usually obtained by various trial-and-error methods that are full of contingency and blindness.To realize the rational design and controllable preparation of HDS catalysts,the first part of this thesis develops a two-dimensional lattice Boltzmann method with multi-relaxation-time collision operator to simulate the intraparticle diffusivities in alumina supports.The simulation results show that,in a series of virtual alumina supports with the identical mesoporous structure but different macroporous structures,which were reconstructed via the random generation of macro-mesopores,the intraparticle diffusivity increases sharply with the increasing macropore volume and diameter,with the one having macropore volume 0.55 cm³/g and macropore diameter500 nm simultaneously guaranteeing both satisfactory intraparticle diffusion performance and suitable crushing strength.Based on the above simulation results,five?-Al₂O₃ supports Al-x(x=1-5)with the identical mesoporous structure but different macroporous structures were synthesized from the same pseudo-boehmite precursor by using sodium polyacrylate and different amounts of water during shaping,from which five Co Mo/?-Al₂O₃ catalysts Co Mo/Al-x(x=1-5)were prepared.The HDS assessment results obtained using a real FCC naphtha as the feedstock show that,compared with the reference catalyst prepared from an alumina without macropores,the catalysts prepared from the aluminas with different macroporous structures displayed higher HDS selectivity due to the enhanced diffusion in macropores.The systematic characterization results demonstrate that the enhanced HDS activities and selectivities of the macroporous alumina supported catalysts are mainly attributed to the enhanced diffusion in macropores.2.The above HDS assessment results also show that the higher steric hindrance the olefins in the FCC naphtha have,the less they are hydrogenated to their corresponding saturated alkanes.In view of this result,the second part of this thesis prepares one modified kaolin clay support(AMK),from which a bifunctional Co Mo/AMK catalyst with both skeletal isomerization and HDS activity was prepared.Compared with the reference catalysts Co Mo/?-Al₂O₃ and Co Mo/HZSM-5,Co Mo/AMK displayed outstanding catalytic performance with higher HDS selectivity,higher isomerization activity and lower cracking selectivity.This can be attributed to the following reasons:(1)the synergistic effects of the appropriate B acidity and macro-mesoporous structure of Co Mo/AMK benefit the isomerization reactions but depress the cracking reactions;and(2)the sulfides over Co Mo/AMK have higher HDS activity.3.The third part of this thesis presents the synthesis of a series of Mo S2 with controlled morphologies via the chemical exfoliation method and the morphology-performance relationship of unsupported Co/Mo S₂ catalysts was obtained in the HDS of a model FCC gasoline.By comparing the catalytic performances of the unsupported Co/Mo S₂catalysts and the supported Co Mo/Al-1,it is found that the Co/Mo S₂catalysts have much higher HDS selectivity than Co Mo/Al-1 for the model gasoline despite the formers'poorer HDS activity,possibly because Co Mo/Al-1 has a high surface area and a higher dispersion of Mo S₂ slabs with lower stacking degree and shorter slab lengths;With the increasing exfoliation degree,the stacking number and slab length of exfoliated Mo S₂slabs decrease and thereby the ratio of rim/edge increases,leading to the increased HDS and HYD activity but the decreased HDS selectivity.Moreover,by comparing the catalytic performances of Ni/WS₂-1 with high curvature angle and Ni/WS₂-2 with low curvature angle,it is found that Ni/WS₂-1displayed higher thiophene HDS activity because the former has extra new active sites(sulfur vacancies)created by the curved layers.