Preparation Of Hierarchical Materials For Hydrocracking Catalysts And The Study Of Its Property

Hydrocracking is an important production process for heavy oil lightening.In order to obtain high quality kerosene?low freezing point?and diesel oil?low freezing point?,the catalyst needs to have suitable cracking activity and good isomerization activity in the reaction process.It is required that the catalyst has appropriate acidity and smooth pores,which can promote the diffusion of reactants and products,avoid excessive cracking,and achieve the purpose of improving the output and quality of kerosene and diesel products.Based on these requirements,by preparing small particle ? molecular sieves and preparing?/MCM-41 composite molecular sieves with cascade channels,the pore structure and acid properties of ? molecular sieves are modulated to meet the requirements of the acidic components of the hydrocracking catalyst.Firstly,the ? molecular sieve with high crystallinity is prepared by hydrothermal synthesis method,and the particle size of?zeolite is adjusted while maintaining high crystallinity by adding seed crystal,adding organic dispersant and adjusting the crystallization time.The results show that with the decrease of particle size,the acidity of?zeolite increases,the amount of acid increases,and the external specific surface area and mesoporous pore volume increase.Meanwhile,the?zeolite molecular sieve with smaller particle size has better medium oil selectivity.When the conversion rate is about 76%,the selectivity of the medium oil can reach 36%.Secondly,MCM-41 mesoporous molecular sieves are separately synthesized before the preparation of composite molecular sieves,and Al-MCM-41 molecular sieves are obtained by aluminum modification.The hydrocracking catalysts with Al-MCM-41 as the acidic component have better medium oil selectivity,but the conversion rate is low.Finally,the?/MCM-41 micro-mesificate composite molecular sieve with core-shell structure is synthesized by two-step hydrothermal method.After optimization of the synthesis conditions,Al is modified into the mesoporous shell to prepare?/Al-MCM-41?x?series of composite molecular sieves.Compared with the original ? molecular sieve,the specific surface area and total pore volume of the composite molecular sieve increase significantly,and the mesoporous contribution rate increases significantly.At the same time,as the Si/Al ratio of the outer shell increases,the proportion of weak acid and medium strong acid increases,and the center of L acid increases.The composite molecular sieve is used as the acidic component of the hydrocracking catalyst carrier,and the catalysts are reacted at 8.0 MPa,320°C and space velocity 2 h^-1.The reaction results show that the reaction conversion rate remain within the range of 67-72%,and the medium oil selectivity is about 9%higher than that of the single ? molecular sieve catalysts.