A kind of cha-rho type composite molecular sieve and its preparation method and application

Abstract

The invention discloses a CHA-RHO type composite molecular sieve and its preparation method and application. The phosphorus source, the aluminum source and the deionized water are mixed according to the molar ratio of 0.5-3:1:50-100, and then dried, roasted, After pulverization, the granular phosphorus aluminum dry glue is obtained; the granular phosphorus aluminum dry glue, template agent R, silicon source and deionized water are mixed uniformly according to the molar ratio of 1:0.5~3:0.05~0.25:25~50, and then crystallized and cooled , suction filtration, washing and drying to obtain molecular sieve raw powder; molecular sieve powder roasted to obtain CHA-RHO type SAPO compound molecular sieve. The composite molecular sieve of the present invention comprises 90-99% by weight of CHA-type molecular sieve and 1-10% of RHO-type molecular sieve; 2 :Al 2 o 3 The molar ratio is 0.05-0.35:1. The composite molecular sieve has small crystal grains, low silicon content, long service life and high catalytic activity. It is used as a catalyst in the reaction of methanol dehydration to low-carbon olefins. It has high olefin selectivity and can greatly reduce the homogeneity of low-carbon olefins. Polymerization to increase the yield of olefins; it can also be used as an adsorbent to adsorb and separate small molecular 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 ...

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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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