Preparation Of Catalyst With Large Penetrable Pores And Its Catalytic Performance In Hydrodesulfurization Reaction(HDS)

Hydrodesulfurization of diesel oil belongs to the internal diffusion control process.Improving the pore structure of the catalyst,such as increase the poral size and decrease the pore tortuosity of catalyst can effectively increase the diffusion rate of the reactant molecules,thereby promoting the hydrodesulfurization reaction.In this paper,carbon black and fibers were used as composite templates to prepare penetrable porous alumina and the pore diffusion factor is proposed to characterize the effect of pore structure of catalyst on the reactant molecules diffusion rate.Furthermore,Ni-Mo active component was loaded on penetrable porous alumina to prepare hydrodesulfurization catalyst,and 4,6-DMDBT?4,6-dimethyldibenzothiophene?was used as a model reactant to investigate the effect of pore structure of support on hydrodesulfurization activity of catalyst.The specific research contents are as follows:Firstly,the effect of the amount of carbon black on the pore structure of alumina was investigated.It was found that as the amount of carbon black increased,the average pore size and pore volume of the alumina increased,but the crushing strength decreased significantly.When 30 wt%carbon black was used as the template,the carrier had the best pore structure.The pore volume of the support increased from 0.59m L/g to 0.73 m L/g,the average pore size increased from 7.23 nm to 10.00 nm,and crushing strength decreased by only 2.51 N/mm.With 30 wt%carbon black as template,the effect of fiber content on the properties of penetrable porous alumina was investigated.It was found that the fiber resulted in the formation cross-sectional penetrable pore in the support.As the amount of fiber increased,the pore volume and average pore diameter of the penetrable porous alumina increased slightly,and crushing strength decreased.When 30 wt%carbon black and 3 wt%fiber were used the template,the properties of the penetrable porous alumina was optimal.Then,the pore diffusion factor,which is defined as the ratio of the pore restriction factor to the pore tortuosity,is proposed to characterize the influence of the pore structure of catalyst on the internal diffusion rate.A method for determination of the pore diffusion factor of catalyst is established,that is,measuring the effective diffusion coefficients of the catalysts and a model catalyst which has a well-defined pore structure respectively and then calculating the pore diffusion factor based on the relative ratio of the effective diffusion coefficients and the pore parameters of the catalysts and the model catalyst.The Si O₂ opal surfacely-modified by Al₂O₃ was used as the model catalyst,and the effective diffusion coefficients are measured using n-octane?50 wt%?,1,3,5-tritoluene?50 wt%?and 2,6-dimethylpyridine?1000 ppm?as adsorption solvents,and 4,6-DMDBT as adsorption solute.The effects of the amount of carbon black template and fiber template on pore diffusion factor of catalyst were investigated.It was found that the effective diffusion coefficients of 4,6-DMDBT in the alumina increased with the amount of carbon black and fiber.It was also found that when the amount of carbon black increased from 10 wt%to 40 wt%,the pore diffusion factor of catalyst increased significantly from 0.441 to 0.564.When 30 wt%carbon black template was used,compared to alumina without fiber template,the addition of fiber template increased the pore diffusion factor of prepared alumina.The pore diffusion factor of prepared porous alumina increased from 0.511 to 0.558 with the increase of fiber template from 1wt%to 4 wt%.However,when the fiber template changed from 1 wt%to 4 wt%,the pore diffusion factor of the prepared alumina increased slightly.Finally,the hydrodesulfurization catalyst was prepared by loading Ni-Mo active component on the penetrable porous alumina.The effects of the amount of carbon black and fiber template on the physicochemical properties and performance of the catalysts were investigated.It was found that the carbon black and fiber template had almost no effect on the acidity and surface coordination morphology of the catalysts.With the increase of the amount of carbon black,the average pore size,pore volume and the number of layers of Mo S₂ platelets of catalyst increased,and the conversion of4,6-DMDBT increased,which was in accordance with the increase of the pore diffusion factor of the Al₂O₃ support.However,when the amount of carbon black increased from 30 wt%to 40 wt%,the increasing trend of conversion of 4,6-DMDBT became more gentle.At this time,the diffusion rate of the reactant molecules was equal to or higher than the reaction rate,and the reaction was not controlled by diffusion process.When the amount of carbon black template was 30 wt%,the pore volume,pore diameter and the number of Mo S₂ platelets of the catalyst increased slightly with the amount of fiber increasing from 1 wt%to 4 wt%.The conversion rate of 4,6-DMDBT increased but the incrasing amplitude was very small,which was consistent with the increase trend of the its alumins support's pore diffusion factor.It shows that a small amount of fiber is enough to penetrate the pore.Considering the properties and performance of the penetrable porous catalysts,it is determined that 30wt%of carbon black and 3 wt%of fiber is the optimum amount.