Study On Preparation And Catalytic Performance Of Molecular Sieve Hydrocracking Catalyst

Under the increasingly stringent environmental protection policies and the market's downward trend in the diesel-gas ratio forecast,it is becoming more and more important to achieve efficient conversion and utilization of FCC diesel.Among them,the catalyst plays a key role as the core of hydrocracking technology.In this paper,starting from the preparation process of hydrocracking catalysts,a series of catalysts were prepared by equal volume impregnation method.Moreover,the pore structure and the surface acid properties were characterized and analyzed.The catalytic performance of the hydrocracking reaction of tetralin was investigated on a fixed bed hydrogenation reactor.Ni-Mo-P type hydrocracking catalyst with three different types of molecular sieves and four different Beta molecular sieves of silica-alumina ratio was prepared by equal volume impregnation method.The results showed that catalyst CAT-B had larger mesoporous surface area and pore volume,and the contents of weak acid and mid-strong acid were significantly higher than those of the other two catalysts.At the same conversion of tetralin,the catalyst CAT-B has the highest selectivity for hydrocracked products with BTX and the lowest selectivity for condensation products.In four types of Ni-Mo-P catalysts with Beta molecular sieves of different silica-alumina ratio,With the increase of silica-alumina ratio,the amount of weak acid and medium strong acid on the surface of catalyst decreased gradually,and the B/L ratio showed a tendency to increase first and then decrease.the conversion of tetralin decreases gradually,the selectivity of BTX product increases first and then decreases.According to the comprehensive characterization and evaluation results,it is concluded that Beta zeolite with silica-alumina ratio of 40 is most suitable as an acidic carrier component for tetralin hydrocracking.The effects of metal type and metal content on the physico-chemical properties and catalytic properties of the catalyst were investigated.The results show that the crystal structure of catalyst CAT-a is intact,the strength and acid amount of medium strong acid is the largest,and the interaction force between metal component and carrier is the weakest,which is beneficial to the dispersion of the surface active metal of the carrier.In the tetralin hydrocracking reaction process,it shows higher catalytic activity.Among the Ni-MoP/Beta catalysts with five different metal components,the pore size distribution of catalyst CAT-18 was the most in the range of 4~10nm.The more weak acids and medium strong acids favored the cracking of reactants.The highest conversion of tetralin in the bed reactor and the highest selectivity for BTX products.Therefore,the Ni-Mo binary metal active component with a loading of 18wt% is the most suitable hydrogenation component for tetralin hydrocracking.The two kinds of zeolite carrier compounding process was studied,and the Ni-MoP/Beta-ZSM-5 catalyst was prepared by the equal volume impregnation method.It was found that the pore structure of the catalyst after the compounding is highly concentrated,the metal components are evenly dispersed on the carrier,the LZT-BZ-3 catalyst has the largest B/L value and the B acid increase rate more than the other catalysts,its surface active metal is easy to reduce.The evaluation results show that catalysts for the compound of Beta molecular sieves and ZSM-5 molecular sieves combine the advantages of both in pore structure and acid properties and has good tetralin hydrocracking activity.Among them,the catalyst LZT-BZ-3 has the highest tetralin conversion and hydrocracking product selectivity.