Investigation On The Preparation Of Unsupported CoMo Catalysts With Hollow Tubule Structure For Thiophene Hydrodesulfurization

In recent years,with the serious environmental pollution caused by the usage of high-sulfur fuel,many countries have promulgated more stringent environmental regulations to limit the content of sulfur in commercial fuel.At present,hydrodesulfurization（HDS）technology is still the main hydrotreating technique in refineries,the key to HDS technology is the HDS catalyst.Traditional supported Co（Ni）Mo/Al₂O₃ catalysts cannot efficiently remove the large sulfur-containing compounds from petroleum under mild conditions due to their low loading capacity,small pore size,and strong metal-support interaction.Therefore,the development of novel catalysts to improve the performance of traditional catalysts has become the main innovation direction.In order to solve the problem of high mass transfer resistance of sulfur-containing macromolecules in traditional catalysts,in this study,the unsupported HDS catalysts with the hollow tubular structure were prepared,and the active phase structure was further tuned to increase the dispersity of Mo atoms.The fixed bed reactor was employed to evaluate the thiophene HDS performance of the prepared catalysts,and the SEM,TEM,XRD,etc.techniques were used to explore the structure-activity relationship of these catalysts.The specific research contents are as follows:The catalysts were prepared by impregnation method with absorbent cotton used as the template.The effect of calcination temperature,precursor concentration,and CoMo molar ratio on the structure and performance of these CoMo HDS catalysts were investigated.The pore structure and composition of active sites of the catalysts were characterized by various characterization methods,and the HDS performance of the catalysts was evaluated.The results showed that the macroporous tubular structure of the catalyst was beneficial to reduce the mass transfer resistance of the macromolecular reactants/products and increase the dispersion of the active metals and the accessibility of the active sites.The CoMo-3 catalyst exhibited the thiophene conversion of 95.82%at 360°C and 1 MPa of H₂ pressure.In order to increase the dispersion of the Mo atoms in the catalysts,the effect of the amount of P123 on the HDS performance of the catalysts was further investigated,and the structure-activity relationship of the catalyst was also analyzed with the combination of the characterization and evaluation results.The addition of P123 could significantly influence the morphology and performance of the catalysts.Compared to the parent CoMo P123,the dispersion of the Mo atoms in the CoMo P123-0.6 catalyst（the addition of P123:0.6 g）increased from 0.270 to 0.309,and the thiophene conversion increased from 95.82%to 97.20%at 360℃ and 1 MPa of H₂ pressure.The low-temperature N₂ adsorption-desorption showed that this catalyst had a low specific surface area,which further proved that the macroporous tubular structure in the catalyst was beneficial to the HDS reaction of thiophene.Combined with the actual industrial production,the investigation on the molding operation and the subsequent HDS performance tests of the prepared unsupported catalyst was carried on.The particle size of the catalyst was successfully increased from 80-120 mesh to 60-80 mesh,while the HDS performance was only reduced by about 1.6%-3.5%.Finally,the macroscopic reaction kinetics of the catalyst was further studied under the different reaction conditions.The results showed that the pseudo-second-order kinetic equation well fits the catalyst performance,and the activation energy was around 45.73 k J/mol.This study indicated that the macroporous tubular structure in the catalyst is conducive to the removal of sulfur-containing macromolecules,which can provide the experimental and theoretical foundation for the design and development of novel unsupported mesoporous tubular HDS catalysts.