A kind of synthetic method of nanometer all-silicon beta molecular sieve

Abstract

The invention discloses a synthesis method of a nano all-silicon Beta molecular sieve. The synthesis method is characterized by comprising the steps that a Beta molecular sieve subjected to deep dealumination is taken as a crystal seed, an all-silicon MWW molecular sieve is taken as a precursor, and the precursor, a template agent, water and the crystal seed are mixed according to the mole ratio 1:(0.3-0.5):(1-8):(0.01-0.1) of SiO2 in the precursor to the template agent to the water to the crystal seed; hydrothermal static crystallization is conducted for 12-48 hours at the temperature of 130 DEG C to 180 DEG C; a crystallization product is filtered, washed, dried and then calcined for 5-8 hours at the temperature of 500 DEG C to 700 DEG C, and then the nano all-silicon Beta molecular sieve is obtained. Compared with the prior art, the synthesis method has the advantages that a single complete Beta crystal structure is achieved, the crystallization time is short, the crystal grain size is small, mass transfer is better promoted, the preparation process is simple, environmentally friendly, green and good in safety, the yield is high, and the economic benefit and the industrialized application and popularization prospect are good.

Description

technical field [0001] The invention relates to the technical field of Beta molecular sieves, in particular to a method for synthesizing nanometer all-silicon Beta molecular sieves using all-silicon MWW molecular sieves as a silicon source in an alkali-free metal and fluoride ion system. Background technique [0002] Beta molecular sieves are a type of molecular sieves with a three-dimensional twelve-membered ring (pore size 6.6 Å × 6.7 Å) channel structure. Aluminum-containing hydrogen-type Beta molecular sieves have excellent thermal stability, hydrothermal stability and acidity, making Beta molecular sieves It has shown excellent catalytic performance in hydroisomerization, hydrocracking, cumene from benzene and propylene, aromatics alkylation, and toluene disproportionation. In the catalytic cracking of crude oil, the combined use of Beta molecular sieve and USY will It increases the octane number of gasoline. [0003] Transition metal atoms with variable valence charac...

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Problems solved by technology

However, the templates used in these hydrothermal synthesis methods are relatively expensive or the synthesis process is cumbersome, and are not suitable for large-scale industrial production.

[0005] In 1996, A. Corma et al published a report on the synthesis of all-silicon Beta molecular sieves by using the seed crystal method in the Journal of Chemical Communications (Chem. Commun., 1996, 1339). , with tetraethyl orthosilicate as silicon source, and the initial gel mixture needs to be hydrothermally treated at 413 K for 14 days to obtain all-silicon Beta molecular sieve with good crystallinity. The problem of this method is that the synthesis period is long and the operation is repeated. Poor sex

In 2005, Olivier Larlus et al. (Chem. Mater., 2005, 17, 881) also reported the synthesis of all-silicon molecular sieves in an alkali metal ion system through the seed crystal method, but the molecular sieves obtained by this method had a larger grain size

However, these methods have problems and deficiencies such as large molecular sieve grain size, unfavorable mass transfer, long crystallization cycle, poor operation repeatability, and the need to use fluorine ions that are harmful to the environment.

[0008] Patent (CN104556086A) discloses a method for synthesizing all-silicon molecular sieves using organic quaternary ammonium salts; A method for synthesizing all-silicon molecular sieves; the patent (CN104556089A) discloses a method for synthesizing all-silicon molecular sieves. The common feature of these methods is to combine silicon sources, templating agents, optional inorganic ammonium salts, polyols, peroxides and water In the process of forming the mixture, the silicon source is added in two times, and an aging step is required between the two additions of the silicon source. Although these methods do not have the disadvantages of fluoride-assisted crystallization, they require additional hydrogen peroxide and polyols The addition of hydrogen peroxide, especially the addition of hydrogen peroxide, has certain dangers

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