Synthetic method of high silica ZSM-5 zeolite

Abstract

The invention discloses a synthetic method of high-silica ZSM-5 zeolite, the method comprises the steps of adopting water glass as a silica source, adopting aluminum salts of aluminum sulfate, aluminum nitrate, aluminum chloride and the like, as well as organic aluminum compounds of sodium metaaluminate, isopropanol and the like as aluminum sources, using sulfuric acid or hydrochloric acid to regulate alkalinity, adding an organic template, simultaneously adding a guide adhesive, carrying out high-temperature crystallization at 120-200 DEG C, and then synthesizing the high-silica ZSM-5 zeolite with the SiO2/Al2O3 ratio which is greater than 100; and the molar ratio of raw materials is as follows: SiO2/Al2O3 is equal to 100-infinity, Na2O/SiO2 is equal to 0.05-0.20, and H2O/SiO2 is equal to 10-100. The organic template comprises tetrapropylammonium bromide, tetrapropylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium hydroxide, n-butylamine, ethylamine, hexamethylene diamine and any other organic matters which can synthesize the ZSM-5 zeolite or the mixture thereof, wherein the using amount of the organic template is that R/SiO2 is equal to 0.005-0.50; and the amount of silicon dioxide in the guide adhesive is 0-5% of the total weight of the silicon dioxide in a synthetic system. The synthetic method can synthesize the high-silica ZSM-5 zeolite with the SiO2/Al2O3 ratio which is greater than 100 and has the advantages of cheap raw materials, a small using amount of the organic template, and capability of realizing the control of product appearance and particle size by changing the relative using amount of the template and the guide adhesive.

Description

technical field [0001] The invention relates to the technical field of molecular sieve synthesis, in particular to a method for synthesizing high-silicon ZSM-5 zeolite. technical background [0002] ZSM-5 zeolite was first invented by the Mobil Petroleum Company of the United States (US3702886), and has been widely used in petrochemical fields such as shape-selective cracking, alkylation, isomerization, disproportionation dewaxing and etherification of hydrocarbons. [0003] The silicon-aluminum ratio, morphology and particle size of ZSM-5 zeolite have a great influence on its catalytic performance. ZSM-5 zeolite with low silicon-aluminum ratio can be synthesized without using organic template, but the synthesis of high-silica ZSM-5 zeolite requires a large amount of organic compounds as template. The synthesis method reported in US3702886 can only synthesize ZSM-5 zeolite with a silicon-aluminum ratio of less than 100, and needs to use a large amount of expensive tetraprop...

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Problems solved by technology

Banani Kalita et al. (Materials Research Bulletin 2009, 44, 254-258) synthesized nano-ZSM-5 zeolites with different silicon-to-aluminum ratios using different silicon sources. The silicon sources used were silica sol, fuming silica gel and tetraethylorthosilicate Esters, etc. are expensive, and the amount of template agent is relatively large

The guide gel is obtained by aging the silicon source in the oligomeric state and a higher amount of template agent at a lower temperature for a certain period of time. The guide gel contains a large number of molecular sieve pronuclei. Therefore, adding the guide gel as a seed crystal during the zeolite synthesis process can Shorten the induction time, increase the crystallization rate, suppress the heterocrystalline phase, and control the particle size of the zeolite. Gerardo Majano et al. (Ind.Eng.Chem.Res.2009, 48, 7084-7091) Esters are used as the silicon source, and nano-stacked ZSM-5 zeolite is synthesized by the method of guiding glue. This method can reduce the amount of template agent used to obtain ZSM-5 zeolite with high crystallinity, but completely use tetraethyl orthosilicate as the silicon source. It will lead to expensive production, and the author has not done research on zeolites with high silicon-aluminum ratio; Tang Yi et al. (Microporous and Mesoporous Materials 2010, 131, 103-114) synthesized ZSM with a silicon-aluminum ratio of about 40 by using a guiding glue method -5 zeolite, and its growth mechanism was discussed, it is considered that the seed crystal provides the surface for the growth of zeolite

It has not been reported that the crystallization of zeolite is promoted by adding a small amount of templating agent to provide the surface for zeolite growth by guiding colloidal seeds.

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