A kind of method for preparing compound molecular sieve

Abstract

The invention provides a method for preparing a composite molecular sieve. The method comprises steps as follows: an aqueous solution of alkali and a molecular sieve are impregnated and mixed uniformly in a mass ratio of the molecular sieve (dry basis), alkali and H2O being (0.1-1):(0.01-1):(0.5-5), a solid mixture obtained by the impregnation is subjected to or not subjected to drying pretreatment and then is crystallized for 0.1-120 h at the temperature of 50-250 DEG C, and a composite molecular sieve product is obtained. According to the method, the Y molecular sieve is subjected to alkalitreatment, partial skeleton structure of the molecular sieve is dissolved properly, and content of secondary pores of the Y molecular sieve is increased. Meanwhile, silicon aluminum species dissolvedfrom the molecular sieve skeleton and residual alkali liquor further interact and are subjected to nucleation and crystallization again under a certain hydrothermal condition, and the nano ZSM-5 molecular sieve is generated. The USY / ZSM-5 composite molecular sieve has higher heavy oil conversion capacity, higher light oil yield and higher low-carbon olefin selectivity when applied to the heavy oilcracking reaction.

Description

technical field [0001] The invention relates to a structural design method for molecular sieves, in particular to a method for reconstructing molecular sieve crystals by using an alkaline solution to partially dissolve the molecular sieves and further in-situ crystallization. Background technique [0002] Petroleum, as the world's largest energy source, not only provides gasoline, diesel, aviation kerosene and other fuel oils for human daily life, but also provides basic organic chemical raw materials such as olefins and aromatics. In recent years, in order to meet the growing demand for fuel consumption, my country's oil refining capacity has expanded rapidly, and the current capacity is already overcapacitated. But now, it has become an inevitable trend to improve energy efficiency and develop new technologies of clean and low-carbon energy. In the future, new energy production capacity will continue to increase. Therefore, in order to further expand the development spac...

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Problems solved by technology

However, due to the limitations of the synthesis system, the degree of in-situ growth of the second phase molecular sieve cannot be guaranteed, and the silicon-aluminum ratio (Si / Al) of the obtained Y molecular sieve framework will not exceed 3, and the formed Y and ZSM-5 are generally large grains and non-mesoporous micron molecular sieves

Moreover, even if a composite molecular sieve with a better degree of in situ crystallization and a smaller molecular sieve grain size is obtained, subsequent steps such as ion exchange, hydrothermal treatment, and introduction of mesopores are still indispensable.

In addition, in addition to the unsolvable defects in the preparation of molecular sieves, the above schemes cannot well solve the problem of synergistic catalysis of Y and ZSM-5 molecular sieves.

This is mainly because the close contact and uniform dispersion of the two molecular sieves at the nanoscale cannot be achieved by the above synthesis method.

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