Small-grain high-Si Y-type molecular sieve and preparation method thereof

Abstract

The invention discloses a small-grain high-Si Y-type molecular sieve and a preparation method thereof. The small-grain high-Si Y-type molecular sieve is a product prepared by using a small-grain NaY molecular sieve as a raw material and selecting proper modification processes, namely ammonia exchange, ammonium hexfluorosilicate for dealuminzation and silicon supplement, hydro-thermal treatment and aluminum salt aqueous solution treatment. The small-grain NaY molecular sieve used by the method can guarantee the skeleton continuity of the molecular sieve product, reduce the collapse possibilityof skeleton structure and maximally retain the integrity of Si-Al-O structure of the product during the subsequent medication treatments due to the high thermal and hydrothermal stabilities, high Si-Al ratio, high stability and uniform skeleton Si-Al structure; therefore, the product still has a crystalline retention degree as high as above 95 percent while having the greatly improved Si-Al ratio. The Y-type molecular sieve can be used as the active component for the hydrocracking catalysts to improve the activities of the catalysts, selectivity of the target product and the quality of the product.

Description

technical field [0001] The invention relates to a Y-type molecular sieve and a preparation method thereof, in particular to a small-grain Y-type molecular sieve and a preparation method thereof. Background technique [0002] At present, molecular sieves that can be used as cracking active components in the field of heavy oil cracking include Y-type, β-type and ZSM, among which Y-type molecular sieves are most commonly used. At present, the methods for industrially producing Y-type molecular sieves basically adopt the directing agent method proposed by GRACE Company of the United States in USP 3639099 and USP 4166099. The crystal grains of the obtained common Y-type molecular sieves are generally about 1000nm, and the crystal grains are relatively large. The pores are relatively long, and the diffusion resistance is high. It is difficult for macromolecules to enter the pores for reaction, and it is also difficult for the products after the reaction to diffuse out. Therefore, ...

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Problems solved by technology

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. Stability is just relatively poor, and this inventive method adopts the mode of vapor phase dealumination of silicon to process molecular sieve simultaneously, and this makes the thermal and hydrothermal stability of product worse, and activity is low; Small, high energy consumption and other disadvantages

Especially when the small-grain NaY zeolite (such as adopting the NaY zeolite synthesized by CN1081425A in the embodiment) with poor thermal stability and hydrothermal stability is modified, its crystallization retention is below 95%, due to the poor performance of raw materials , the stability of the silicon-aluminum framework structure in the molecular sieve is poor, and it is easy to cause the removal of the framework aluminum during the modification process, and at the same time, a part of the framework silicon is also removed, which is easy to cause part of the framework to collapse, making the product The crystallization retention is low, and the activity of molecular sieves is not high

The modification method of comparative example 3 is to exchange ammonium with ammonium sulfate first, and then add ammonium fluorosilicate, and the obtained small grain BM-3 has a lower degree of crystallization retention, which is only 70%. In comparative example 3, the raw material It is prepared by the method of non-directing agent, so the skeleton silicon-alumina of its raw material is relatively low. In the process of post-processing, it is easy to cause large-scale collapse of the skeleton silicon-alumina, resulting in poor activity of the product and lower crystallization retention.

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