Preparation method of nanoscale pure silicon hierarchically porous Beta zeolite

Abstract

The invention provides a preparation method of nanoscale pure silicon hierarchically porous Beta zeolite. Compared with the existing synthesis method, the method breaks through limits of traditional hydrothermal synthesis of pure silicon Beta zeolite on the basis of fluoride, and the pure silicon Beta zeolite is obtained with a steam assisting method under the condition of fluorine absence for thefirst time. According to the method, a little crystallization liquid is needed, and emission of a large amount of crystallization waste liquid is avoided effectively; fluoride is not needed for synthesis, use quantity of a template agent is small, an inorganic silicon source is taken as a silicon source, and synthesis cost is low; utilization rates of a device and raw materials are high, and almost 100% of product yield can be realized; only 36 h is needed for synthesis, steps are simple, and energy consumption can be reduced effectively. A synthesized pure silicon Beta zeolite sample has theadvantages of being high in crystallinity degree and specific surface area, rich in hierarchically porous structure, nanoscale, good in hydrothermal stability and the like.

Description

technical field [0001] The present invention relates to a preparation method of a nano-scale pure silicon stepped pore Beta molecular sieve with a *BEA structure, specifically a method for synthesizing a molecular sieve with high crystallinity, high specific surface area, rich stepped pore structure, and water The invention discloses a preparation method of nano-scale pure silicon Beta molecular sieve with good thermal stability. Background technique [0002] Beta molecular sieve is the only molecular sieve with twelve-membered ring intersecting channel system, which has unique channel structure, acidity and good hydrothermal stability. As the most important catalytic core or catalyst carrier in the petrochemical industry, Beta molecular sieves have shown excellent performance in reactions such as hydroisomerization, hydrocracking, cumene from benzene and propylene, alkylation of aromatics, and disproportionation of toluene. catalytic performance. [0003] In order to make...

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Problems solved by technology

The synthesis cycle of this method is too long, the repeatability of the operation is poor, it is not easy to synthesize in a short time, and it does not use large-scale industrial production

In 2005, Olivier Larlus et al. (Chem.Mater., 2005, 881) also reported that pure silicon molecular sieves were synthesized by the seed crystal method in an alkali metal ion system, but the molecular sieves obtained by this method had a large grain size

The above methods of synthesizing pure silicon Beta molecular sieves are all assisted by introducing highly corrosive and highly toxic hydrofluoric acid into the synthesis system. Pollution and safety issues must limit their large-scale industrial application.

[0008] In 2018, Wang Baorong et al. (Micopor.Mesopor.Mat., 2018, 43) replaced the fluorine source that must be used in the hydrothermal synthesis of pure silicon Beta molecular sieves, such as hydrofluoric acid, with fluorine-containing salts (NaF, KF). Pure silicon Beta molecular sieves were synthesized in an alkaline environment, but the synthesized Beta molecular sieves had a larger particle size of about 0.7 μm, and the crystallization time was longer, which required 3 days

This method of synthesizing pure silicon Beta molecular sieves gets rid of the limitation of fluorine source, but the addition of additional hydrogen peroxide and polyols, especially the addition of hydrogen peroxide, has certain dangers

[0010] All there is following defect in the above-mentioned method about synthetic pure silicon Beta molecular sieve: (1) high waste, high pollution

At present, most of the methods for synthesizing pure silicon Beta molecular sieves are inseparable from the auxiliary crystallization of fluorine ions, and the direct discharge of the crystallization residual liquid containing excess silicon, fluorine, templates, etc. after hydrothermal crystallization will inevitably cause environmental pollution and Raw material waste; (2) The crystallization cycle is long, the repeatability of the operation is poor, and it is accompanied by miscellaneous crystals; (3) The crystal grains are large

The above-mentioned methods for synthesizing pure silicon Beta molecular sieves all introduce fluoride ions, and the particle diameter is mostly in the order of microns (about 10 microns); (4) the pore structure is single, mostly microporous structures (about 0.56~0.77 nanometers), which is not conducive to reaction mass transfer (5) product yield is low

The excess silicon in the waste liquid after crystallization cannot be fully utilized; (6) the amount of organic template required is large, and the silicon source is an organic silicon source, and the cost is high; (7) the crystallization requires a large amount of water, and finally the waste liquid discharge

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