Core-shell structured ZSM-5 composite molecular sieve and preparation method thereof

Abstract

The invention discloses a core-shell structured ZSM-5 composite molecular sieve and a preparation method thereof. The molecular sieve has the properties that: total mole ratio of silicon oxide / aluminum oxide is 50-65, the total specific surface area is 350-400m<2> / g, the total pore volume is 0.18-0.23ml / g; the mole ratio of silicon oxide / aluminum oxide of the core phase is 80-120, the mole ratio of silicon oxide / aluminum oxide of the shell phase is 30-41, both the core and the shell have the pore channel topological structure of a ZSM-5 molecular sieve, and the shell content is 25wt%-50wt% (in terms of the total weight of the composite molecular sieve). The preparation method involved in the invention includes: in the first step, crystallizing a mixture of a silicon source A, a ZSM-5 molecular sieve, sodium hydroxide and water; and in the second step, adding a silicon source B and an aluminum source into the mixture obtained in the first step, conducting further crystallization, and washing, drying and roasting the crystallization product, thus obtaining the ZSM-5 composite molecular sieve. The core-shell structured ZSM-5 composite molecular sieve provided by the invention is not added with any template, thus saving cost, and being green and environment-friendly. And a good carrier is provided for isomerization, alkylation and other shape selective catalytic processes.

Description

technical field [0001] The invention belongs to the field of composite molecular sieve synthesis, and in particular relates to a core-shell structure ZSM-5 composite molecular sieve and a preparation method thereof. Background technique [0002] At present, composite molecular sieves have attracted more and more researchers' attention. Various composite molecular sieves are constantly being synthesized. In 2006, Younes Bouizi (Chem Mater 2006, 18, 4959-4966) reported a composite molecular sieve Silicalite-1 / MFI with a core-shell structure. In the method, ZSM-5 molecular sieve is wrapped with Silicalite-1 molecular sieve to form a core-shell composite molecular sieve with ZSM-5 as the core and Silicalite-1 as the shell, and the coverage rate is 70% through one synthesis process. The specific synthesis process is as follows: first, nano-scale Silicalite-1 seeds are deposited on the surface of ZSM-5 molecular sieves through tetrapropylammonium hydroxide, tetraethyl orthosilic...

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Problems solved by technology

[0004] Silicalite-1 / ZSM-5 composite molecular sieve is a kind of isomorphic composite molecular sieve with core-shell structure and belongs to MFI topological structure, but its disadvantage is that because ZSM-5 molecular sieve is replaced by Silicalite-1 The molecular sieve is completely wrapped, and the surface does not have any acidity. Although the shape selection effect of the Silicalite-1 / ZSM-5 composite molecular sieve is better than that of the ZSM-5 molecular sieve, the conversion rate is low

[0005] In CN101723401A, a ZSM-5 molecular sieve composite molecular sieve with a core-shell structure with different silicon-aluminum ratios is synthesized, and a ZSM-5 zeolite molecular sieve with a relatively low silicon-aluminum ratio is used as a seed crystal, and is added to a high-silicon-aluminum ratio shell rubber forming material In , the ZSM-5 molecular sieve composite molecular sieve with core-shell structure was synthesized by hydrothermal method, but ethylenediamine was added as a template during the synthesis process, the synthesis cost was high, and it polluted the environment

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