Low-silicon composite molecular sieve, and synthetic method and application thereof

Abstract

A low-silicon composite molecular sieve comprises, by mass, 2-25% of an SAPO-5 molecular sieve and 75-98% of an SAPO-34 molecular sieve, and a molar ratio of SiO2 / Al2O3 is 0.07-0.15. The low-silicon composite molecular sieve has the advantages of low silicon, low cost, simple synthesis technology, high average diolefin selectivity in a methanol-to-olefin reaction, and long life.

Description

technical field [0001] The invention belongs to a molecular sieve and its preparation method, in particular to a low-silicon composite molecular sieve, its synthesis method and its application. Background technique [0002] The methanol-to-olefins (MTO) process is a new process for preparing low-carbon olefins such as ethylene and propylene from coal or natural gas through methanol. In U.S. Patent No. 4,440,871, U.S. Carbide Corporation (UCC) developed a new series of silicoaluminophosphate molecular sieves (SAPO-n). Among them, SAPO-34 molecular sieve is made of SiO 2 , AlO 2 - 、PO 2 + Three kinds of tetrahedrons are connected with each other and have a chabazite-like (CHA) structure. It is an ellipsoidal cage composed of eight-membered rings and a three-dimensional pore structure. The diameter of the window is 0.38 nanometers, and the spatial symmetry group is R3m. SAPO-34 is currently recognized as the best molecular sieve for MTO reaction. The study found that the...

AI Technical Summary

Problems solved by technology

[0003] Patent CN102372290A discloses a synthesis method of SAPO-5 and SAPO-34 symbiotic molecular sieves, which solves the problem of single pore size and low activity of porous materials in technical synthesis, but the preparation of SiO in the gel mixture 2 :Al 2 o 3 =(0.1-2.0):1.0, the Si content in the prepared product is higher

[0004] Patent CN102336413A discloses a method for synthesizing low-silicon pure-phase SAPO-34 molecular sieves, using a two-step method, first preparing high-silicon SAPO-34 initial gel, crystallizing at a suitable temperature for a certain period of time, and then adding aluminum phosphate and organic amines The formed gel continues to crystallize, and the synthesis process is more complicated

[0005] Patent CN103011195A discloses a method for preparing hydrogen-type SAPO-5 and SAPO-34 symbiotic hierarchical porous molecular sieves in one step, which uses an organosilicon surfactant while using tetraethylammonium hydroxide as a template agent, and the template agent contains The higher the proportion, the higher the synthesis cost

Images