Synthesis method of fine grain ZSM-5 zeolite molecular sieve with high silicon aluminium ratio

Abstract

The invention relates to a synthesis method of fine grain ZSM-5 zeolite molecular sieve with high silicon aluminium ratio, which comprises using a surface active agent, charging it into acidified aluminium salt solution, then slowly dropping alkaline solution formed from sodium silicate, template agent and seed crystal into aluminium saline solution, the overall composition of the obtained reaction mixture being Na2O:Al2O3:SiO2:H2O=1.5-4.0:1:20-280:500-2000 by mol ratio, then subjecting the reaction mixture to thermal crystallization through the conventional method.

Description

technical field [0001] The invention belongs to the technical field of molecular sieve synthesis. In particular, it relates to a method for synthesizing small-grain ZSM-5 molecular sieves with a high silicon-aluminum ratio. Background technique [0002] The ZSM-5 molecular sieve (USP3702886, 1972) invented by Mobil Petroleum Company of the United States has been widely used in petrochemical processes such as selective cracking, alkylation, isomerization, disproportionation, dewaxing, and etherification of hydrocarbons. application. The synthesis method of the ZSM-5 molecular sieve reported in USP3702886 is to use a silicon source. Aluminum source. Alkali, water and tetrapropyl ammonium hydroxide organic template are mixed to form a reaction mixture, and then the reaction mixture is crystallized at 100-175° C. for 6 hours to 60 days (organic method). There are also a large number of reports (such as EP0098641A2, CN85100463A, etc.) on the synthetic method (inorganic method...

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Problems solved by technology

Although the density of the colloid is relatively high in this method, so the single-pot yield is relatively high, but because the precipitated silica gel is used as the silicon source, the preparation process is complicated, and the crystallization process requires vigorous stirring, and the synthesis cost is relatively high.

[0006] In 2001, CN1303816 patent reported a method for rapidly synthesizing small-grain ZSM-5 molecular sieves by using the directing agent method. The method is to first synthesize the directing agent, and then use the directing agent instead of the organic amine template in the synthesis. This method does not need to add salt class, the synthesis cost is lower, but the directing agent must be synthesized first, so the synthesis cycle is longer

If the silicon-aluminum ratio is low, the thermal stability and hydrothermal stability of the catalyst will be poor. To improve the heat resistance of the catalyst, some high-temperature-resistant substances must be added to the ZSM-5 molecular sieve, such as inert silicon and metal oxides. etc. This operation is cumbersome and increases the synthesis cost

[0009] How to increase the silicon-aluminum ratio of the small-grain ZSM-5 molecular sieve is an important issue. Generally speaking, the higher the silicon-aluminum ratio of the feedstock, the more viscous the colloid obtained when synthesizing the molecular sieve, and the greater the amount of water required. Therefore, the single-pot production rate reduction

In the prior art, when using water glass as a silicon source to synthesize ZSM-5, the general product molecular sieve accounts for less than 8% of the weight of water in the synthesis system, the water-aluminum ratio of the feed is generally greater than 1500, and the water-silicon ratio is greater than 30, otherwise the resulting The colloid is too viscous, and miscellaneous crystals such as mordenite and quartz are prone to appear, so ZSM-5 products with high crystallinity cannot be obtained