Preparation method for small-grain Y type molecular sieve

Abstract

The invention discloses a preparation method for a small-grain Y type molecular sieve. According to the method, a NaY type molecular sieve raw material with a high silica-alumina ratio, a high degree of crystallization and good stability is employed and successively undergoes alkali washing, ammonium exchange, aluminum removal and silicon supplement, hydro-thermal treatment and treatment with a mixed solution of acid and an ammonium salt; and the obtained small-grain Y type molecular sieve has a high SiO2 / Al2O3 mol ratio and a high proportion of secondary pores, remains the stability of a Y type molecular sieve and has a high specific surface area and a high degree of crystallization. The small-grain Y type molecular sieve prepared in the invention is applicable as a cracking component for a hydrocracking catalyst used for high and medium oil and enables the hydrocracking catalyst to have good activity, medium oil selectivity and product properties.

Description

technical field [0001] The invention relates to a preparation method of a Y-type molecular sieve, in particular to a preparation method of a small-grain Y-type molecular sieve. Background technique [0002] Y-type molecular sieve is currently the most common cracking active component in the field of heavy oil cracking. The crystal grain is generally about 1000nm. After the reaction, the product is also difficult to diffuse out, so its cracking activity and selectivity of the target product are restricted. Compared with conventional Y-type molecular sieves, small-grain Y-type molecular sieves have a larger outer surface area and more active centers on the outer surface, which is conducive to improving the cracking capacity of macromolecular hydrocarbons, and thus has superior catalytic performance. At the same time, reducing the grain size of the Y-type molecular sieve can also improve the utilization rate of active sites on the inner surface. In general, the diffusion of r...

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Problems solved by technology

[0004] The method for preparing fine-grained Y-type molecular sieves proposed in CN1081425A is to precrystallize the NaY synthesis solution at 80°C to 180°C for 1 to 10 hours, then add the directing agent after cooling to room temperature, and then add the directing agent at 80°C to 100°C. Continue to crystallize for 5 to 25 hours, the process steps are more complicated and difficult to control, and the hydrothermal stability of the fine-grained Y-type molecular sieve obtained is poor

CN1382632A discloses a super-stabilizing method of small-grain Y-type zeolite, which is obtained by contacting the dry gas of silicon tetrachloride with small-grain NaY zeolite and washing it. The stability is poor, and the inventive method adopts gas-phase dealumination to supplement silicon to process molecular sieves, which makes the thermal and hydrothermal stability of the product worse, and the activity is low

[0014] At present, due to the poor hydrothermal stability and unstable structure of small-grain NaY molecular sieves, small-grain Y-type molecular sieves with complete structure, high crystallinity and many secondary pores cannot be obtained after subsequent modification.

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