CHA-RHO type composite molecular sieve as well as preparation method and application thereof

Abstract

The invention discloses a CHA-RHO type composite molecular sieve as well as a preparation method and application thereof. The preparation method comprises the following steps: uniformly mixing a phosphorus source, an aluminum source and deionized water according to the mole ratio being (0.5 to 3):1:(50 to 100), drying, roasting and crushing to obtain granular phosphorous and aluminum dry glue; uniformly mixing the granular phosphorous and aluminum dry glue, a template agent R, a silicon source and the deionized water according to the mole ratio being 1:(0.5 to 3): (0.05 to 0.25):(25 to 50), crystallizing, cooling, carrying out suction filtering, washing and drying to obtain molecular sieve raw powder; roasting the molecular sieve raw powder to obtain CHA-RHO type SAPO (Silicoaluminophosphate) composite molecular sieve. The composite molecular sieve disclosed by the invention is prepared from 90 to 99 weight percent of CHA type molecular sieve and 1 to 10 weight percent of RHO type molecular sieve; in a composite molecular sieve framework, the mole ratio of SiO2 to Al2O3 is (0.05 to 0.35):1. The composite molecular sieve has the advantages of small crystalline grains, low silicon content, long service life and high catalytic activity; the composite molecular sieve is used for a catalyst for a reaction of preparing lower olefins by catalytic dehydration of methanol and high higher olefin selectivity; by means of the composite molecular sieve, the oligomerization of the lower olefins can be greatly reduced, so that the yield of the olefins is increased; the composite molecular sieve can be used as an adsorbent for adsorbing and separating small-molecule gases.

Description

technical field [0001] The invention relates to a CHA-RHO composite molecular sieve and its preparation method and application. The composite molecular sieve contains CHA and RHO structures, has the characteristics of small crystal grains and low silicon content, and is mainly used for catalytic methanol dehydration to produce low-carbon olefins The catalyst and the adsorbent for adsorption and separation of small molecular gases greatly improve the reaction performance of methanol to olefins, and belong to the field of chemical synthesis technology and its application. Background technique [0002] Composite molecular sieve is a composite molecular sieve with a special structure, which is a co-crystal formed by two or more molecular sieves, or a composite crystal with the structural characteristics of two or more molecular sieves. Due to the particularity of the composite molecular sieve structure, this molecular sieve has a more reasonable distribution of acidity and good ...

AI Technical Summary

Problems solved by technology

CHA type molecular sieve is used in MTO reaction, its smaller pore size and larger specific surface area speed up the MTO reaction rate and improve the selectivity of the reaction, but it has the disadvantages of high carbon deposition, easy deactivation and short life; while RHO type Molecular sieves are weak acid molecular sieves. Although the low acid density can reduce the selectivity of propane, and the selectivity of ethylene plus propylene will increase accordingly, but when the acid density is too low, the catalyst activity will be too low, and the selectivity of low-carbon olefins will also decrease.

[0004] Although theoretically the co-crystal of weak acid RHO molecular sieve and CHA molecular sieve with high catalytic activity can adjust the acidity of the composite molecular sieve, but because the composition ratio of the two molecular sieves is difficult to match, the preparation of the composite molecular sieve is extremely difficult, even if it is successfully prepared. Molecular sieves, the density of composite molecular sieves, especially the content of silicon are relatively high, and the catalytic activity of composite molecular sieves is not ideal, the selectivity of ethylene and / or propylene is relatively low, and the service life of composite molecular sieves is also relatively low

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