NaY-type molecular sieves and preparation method thereof

Abstract

The invention discloses microcrystal NaY-type molecular sieves and a preparation method thereof. In the microcrystal NaY-type molecular sieves, the molar ratio of SiO2 to Al2O3 is 4.0 to 6.0, and the average particle size is 100 to 700 nanometers. The microcrystal NaY-type molecular sieves are prepared by a method combining low-temperature synthesis directing agent, low-temperature synthesis gel and two-stage variable-temperature dynamic crystallization. The NaY-type molecular sieves have a relative crystallinity of over 80 percent after being roasted in the air at 600 DEG C for 3 hours or after undergoing hydrothermal treatment with vapor at 650 DEG C for 1 hour, as well as high thermostability and hydrothermal stability.

Description

technical field [0001] The invention relates to a Y-type molecular sieve and a preparation method thereof, in particular to a preparation method of a small-grain NaY-type molecular sieve. 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, the cra...

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Problems solved by technology

Also adopt the method for improving system basicity in USP4,66,099 and EP0435625A2, the crystal grain size of its synthesis product is below 100nm, although high basicity synthesis can obtain fine crystal grain, can not obtain the product that silicon-aluminum ratio is greater than 5, generally Only X-type molecular sieves and Y-type molecular sieves with a silicon-aluminum ratio of less than 5 can be obtained, and the thermal stability and hydrothermal stability of the synthesized molecular sieves are not ideal

[0009] The method for preparing fine-grained Y-type molecular sieves proposed in CN1081425A is to pre-crystallize 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 cool the NaY synthesis solution 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

The HY molecular sieve has a crystal retention of 28% after hydrothermal treatment at 750°C for 2 hours (see the data in Table 3 of Example 1 for details), and its hydrothermal stability is not good.

Since the second stage of crystallization adopts the method of static crystallization, without stirring, the intermediate product will be deposited at the bottom of the kettle and form a solid-like interface layer with the synthetic mother liquor, so the silicon atoms in the supernatant and aluminum atoms are more difficult to enter the framework of the molecular sieve, resulting in poor thermal stability and hydrothermal stability of the product, while increasing the preparation cost

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