Beta zeolite synthesis and its attention, catalytic properties

The research on multi-stage pore zeolites has attracted a lot of attention because of their potential and practical applications. Among them, macroporous high-silica zeolites with three-dimensional twelve-membered pore structure, named Beta zeolites, have special pore structure and powerful acid catalytic properties and structural selectivity, which are widely used in petroleum refining and petrochemical processes such as hydrocracking, isomerization, alkylation and dewaxing. 

In practice, the addition of a small amount of Beta zeolite or modified Beta zeolite to FCC catalysts can significantly improve the hydrothermal stability, carbon resistance and wear resistance of cracking catalysts, and Beta zeolite has rapidly developed into a very important new catalytic material in recent years. catalytic material.

Generally speaking, the main raw materials for the synthesis of Beta zeolites include aluminum source, silicon source and template agent. In some preparation processes, a certain amount of crystalline species or crystallization promoters are added to promote the modification and crystallization of Beta zeolites, or to change and adjust their physicochemical properties. The specific synthesis processes include.

First, the synthesis of Beta zeolites by hydrothermal gelation crystallization. This method is the most common method in the field of molecular sieve synthesis, which mainly involves mixing the aluminum source, silicon source and template agent required for the synthesis of Beta zeolite in a certain condition and order before the synthesis process is carried out, and then making the mixed materials form a slurry, and then crystallizing them into molecular sieves under a certain temperature and pressure. 

This method has the advantages of homogeneous synthesis and stable product, but usually the amount of template agent is large, so it increases the preparation cost, which also determines the high cost of raw materials of Beta zeolite.

Secondly, Beta zeolite is synthesized by the guide agent method. This method is generally divided into two steps, the first is the synthesis of the guide agent: sodium aluminate, tetraethylammonium hydroxide, silica and other raw materials are mixed uniformly and aged at a certain temperature to obtain the guide agent; then the raw materials for the synthesis of Beta zeolite are mixed uniformly in a certain ratio, and 1%-5% of the guide agent is added and crystallized at a certain temperature to obtain Beta zeolite. 

This technique can reduce the amount of template agent used, and can also quickly improve the crystallization rate of Beta, but it also has obvious disadvantages: the silica-alumina content of Beta zeolite prepared in this technique is low, and the value is between 5-50, and it will increase the cost of synthesis, and the process is relatively complex.

Third, surface wetting and crystallization method for the synthesis of Beta zeolites. This method is based on the hydrothermal gelation crystallization method and continues to reduce the amount of templating agent in the system to reduce costs, which can effectively reduce the cost of zeolite synthesis and shorten the overall crystallization time.

The reaction properties of Beta zeolites prepared by different methods have deviated from each other, and the data tables are shown below. The difference lies in the size of the grains and the degree of activity during the crystallization process. Generally speaking, the smaller grain size of Beta zeolite facilitates the diffusion of reactants and products, which improves the activity of the catalyst, which needs to be noted in practical applications.