Method for in-situ crystallized synthesis of small-grain ZSM-5 molecular sieve by using direct method

Abstract

The invention provides a method of crystallized preparation of a ZSM-5 molecular sieve in-situ by using a direct method without a template. The method comprises pre-treating high-temperature-roasted kaolin microspheres containing a characteristic structural unit of a five-membered ring by using sodium silicate, adding acid to prepare a reaction mixture, and performing hydrothermal crystallization to obtain in-situ products containing the ZSM-5 molecular sieve and ex-situ ZSM-5 molecular sieve. The kaolin microsphere in-situ crystallized ZSM-5 molecular sieve has a relative crystallinity being capable of being adjusted within 65 % according to requirements, has a crystal size being 0.1-3 [mu]m, is good in wear resistance performance and can be used as a catalytic addictive for increasing propylene yield in a FCC technology. The co-produced ex-situ ZSM-5 molecular sieve has a crystallinity being more than 90 %, and a crystal size of 0.1-3 [mu]m, and can be used for preparing a semi-synthetic catalyst.

Description

technical field [0001] The invention relates to a method for synthesizing small-grain ZSM-5 molecular sieves through direct method and in-situ crystallization of kaolin microspheres as raw materials. Background technique [0002] Due to its unique three-dimensional pore structure, good hydrothermal stability and excellent shape-selective catalytic performance, ZSM-5 molecular sieve is introduced into FCC catalysts to increase the octane number of gasoline and increase the production of low-carbon olefins. [0003] There are generally two ways to introduce active components in FCC catalysts. One is to mix active components with matrix and binder to make slurry, and prepare microsphere catalysts through spray drying, roasting and other procedures, which are called semi-synthetic catalysts. The second is to prepare microspheres by spraying kaolin first, and after roasting, the molecular sieve active component is grown on the kaolin microspheres by hydrothermal crystallization u...

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Problems solved by technology

[0012] In the above-mentioned patents or documents, the relative crystallinity of ZSM-5 molecular sieve synthesized by template method in situ crystallization is relatively high, but the template itself is expensive, and it will pollute the environment during the post-treatment process of removing the template. In addition, in industrial production The template agent is often removed by high-temperature calcination, which requires energy consumption. Therefore, the use of the template agent will greatly increase the cost of in-situ crystallization catalyst generation, which should be avoided as much as possible; the other type in the above-mentioned patents or documents does not use The method of in-situ crystallization of ZSM-5 molecular sieve of the template agent, but all need to use one or another seed crystal, there are complicated process flow, low raw material utilization rate, harsh pretreatment conditions, expensive silicon source, must use Such or that kind of seed crystals, long crystallization time and other shortcomings

Moreover, the key indicators such as relative crystallinity and specific surface area of ​​kaolin microspheres in situ crystallized ZSM-5 molecular sieves obtained by these methods are generally not high, and there is a problem of low synthesis efficiency, and the non-situ crystallization reaction produced in situ The performance and application of ZSM-5 molecular sieve products are not considered

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