Study On Morphology Effect Of Ni-Mo/Al₂O₃ Catalyst In Ebullated Bed Residue Hydrotreating

With the increase in the degree of heavy crude oil supply and stringent environmental protection regulations,ebullated bed residue hydrogenation technology has triggered extensive attention due to its stronger feedstock adaptability,flexible device operation and long operating cycle.Catalyst is the core of ebullated bed residue hydrogenation technology,which directly determines the performance and economic benefits of hydrogenated products.Compared with the cylindrical catalyst designed for foreign ebullated bed,Sinopec Dalian Research Institute of Petroleum and Petrochemicals independently developed a new type of STRONG ebullated bed residue hydrogenation micro-spherical catalyst,which has a significantly different particle morphology and microstructure.This research is aimed to conduct a comprehensive study of morphology effect of Ni-Mo/Al₂O₃ catalyst in ebullated bed residue hydrogenation from the perspectives of microscopic by combining experiments and theoretical calculations,revealing the mechanism of morphology effect on the ebullated bed residue hydrogenation performance.First,the cylindrical and spherical Ni-Mo/Al₂O₃ catalysts were prepared by extrusion molding method and special shaping method based on STRONG ebullated bed technology respectively,and then were evaluated in ebullated bed residue hydrotreating.Compared with the cylindrical catalyst,the spherical catalyst exhibits more excellent hydrogenation activity and stability.This is due to the higher bed expansion rate of spherical catalyst during the sulfidation process,which enhances the transfer ability of sulfurizing agent in the presulfidation stage.This,together with the weaker metal-support interaction on spherical catalyst,promotes the formation of a highly active TypeⅡactive phase.In addition,the spherical catalyst with a larger pore size and pore volume facilitates the diffusion of large molecular impurities into the pores,so that the carbon deposits in the spherical catalyst is less and lighter,the metal deposits is evenly distributed,and the deactivation is delayed.Secondly,in order to further study the effect of particle morphology on the formation process of active phase Mo S₂,the grain model was used to simulate the macro-kinetics of catalyst presulfidation reaction,focusing on the investigation of the variation law of sulfidation reaction rate and conversion of Mo O₃.The kinetic model results show that the initial reaction rate and conversion of Mo O₃ decrease with the increase of particle size,but increase with the increase of the porosity.This is because the larger particle size increases the internal diffusion resistance,while the larger porosity enhances mass transfer ability.Therefore,the Mo O₃ on the spherical catalyst has a higher initial reaction rate and overall conversion than the cylindrical catalyst,mainly due to its larger porosity,smaller structure size and weaker metal-support interaction.Finally,molecular simulation was used to further understand the diffusion properties of the sulfur-containing model compounds of vacuum residue in the alumina pores,revealing the diffusion regulation of reactants in the pores with different sizes.The results show that the diffusion coefficient of guest molecules increases with the increase of pore size,because the increase of pore size weakens the interaction between the pore wall and the guest molecules,thereby reducing the diffusion resistance.For different molecules,addition of benzene ring and methyl side chain will increase the interaction between molecules and channel and the steric hindrance,and increase the diffusion resistance.This further confirms that the spherical catalyst with larger pore size in the experiment is beneficial to improve the performance of the residue hydrogenation reaction.