Preparation method of small-grain NaY-type molecular sieve

Abstract

The invention discloses a preparation method of a small-grain NaY-type molecular sieve. According to the invention, an amorphous silica-alumina precursor, a directing agent synthesized under a low temperature, part of a silicon source, and the like are mixed under a low temperature, such that silica-alumina gel is prepared; and crystallization is carried out, such that the small-grain NaY-type molecular sieve is obtained. According to the amorphous silica-alumina precursor, a part of a silicon-containing material is added in an aluminum-containing material before and/or during a gelling process; and the rest of the silicon-containing material is added after gelling and before aging, such that silica-alumina forms a stable structure, and can cooperate with subsequent steps. With the method, a phenomenon of silicon agglomeration or loss caused by the addition of a large amount of the silicon source in prior arts is avoided. The addition amount of silicon is reduced; silicon effective utilization rate is improved; the silica-to-alumina ratio is improved; and the obtained small-grain molecular sieve has good stability. The small-grain NaY-type molecular sieve provided by the invention can be used in a hydrocracking reaction, and has good cracking activity and product selectivity.

Description

technical field [0001] The invention relates to a method for preparing a Y-type molecular sieve, in particular to a method for preparing a small-grain NaY-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

[0011] At present, during the preparation process of small-grain NaY molecular sieves in the existing method, silicon and aluminum are easily lost, the utilization rate of silicon is low, and the distribution of silicon and aluminum is not uniform, and agglomeration is easy to occur. Therefore, the existing method is still unable to prepare silicon-aluminum ratio. , and small crystal NaY molecular sieve with good thermal stability and hydrothermal stability

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