Method for preparing molecular sieve with hierarchical structure using mesoporous material as indirect template

Abstract

The invention discloses a method for preparing a multi-level-structured molecular sieve by taking a mesoporous material as an indirect template agent. The method comprises the following steps: mixing aluminum oxide spheres or silicon oxide microspheres, an external silicon source or an aluminum source, phosphoric acid, a template agent and water to form a crystallization raw solution; transferring the uniformly mixed crystallization raw solution into a hydrothermal kettle taking tetrafluoroethylene as a lining, and ageing; after ageing, putting the hydrothermal kettle into a homogeneous reactor for crystallization; cooling a crystallized solution, taking out the crystallized solution and carrying out washing and centrifuging treatment; filtering an obtained solid-liquid mixture, washing and drying; and roasting to remove the template agent to obtain the multi-level-structured molecular sieve. The molecular sieve comprises mesopores and micropores; generation and diffusion of isobutylene in pore channels can be inhibited very well; isomeric hydrocarbon and aromatic hydrocarbon, which have relatively great molecules, can be subjected to more serious diffusion limitation; and meanwhile, the diffusion resistance of a target product, low-carbon olefin, particularly propylene, is reduced due to the presence of the mesopores, so that the prepared multi-level-structured molecular sieve is used as a catalyst, is not easy to inactivate and has good stability.

Description

technical field [0001] The invention belongs to the technical field of catalyst preparation for methanol-to-olefins, and in particular relates to a method for preparing a molecular sieve with a multi-level structure by using a mesoporous material as an indirect template. Background technique [0002] The catalyst for the methanol-to-olefins process is mainly ZMS-5, which is a two-dimensional intersecting channel of the MFI type, and the pore sizes are and Due to its good shape-selective effect and controllable acidity of its channels, it is widely used in methanol-to-aromatics, aromatics conversion, and other molecular sieve catalytic processes. Its good practical value and simple synthesis method make ZSM-5 the most in-depth research at present. of a zeolite. Due to the strong acidity, people modified it and applied it to the MTO process and did not get very good selectivity of low-carbon olefins, and a large amount of C in the product 5 ~C 10 Hydrocarbons (4.4-16.2%)...

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Problems solved by technology

[0004] Patents CN03121112.7 and CN200710043956.X disclose that the Na-modified ZSM-5 catalyst is used in the methanol conversion reaction to obtain a methanol conversion rate of 99%, and the propylene selectivity is 38-49%, but no catalyst deactivation is mentioned The problem

[0005] Patent CN201310462721.X proposes to use metal Ca, Mg, La, Ru and Na to modify molecular sieves ZSM-5, SAPO, USY and Beta to reduce the carbon deposition on the strong acidic sites, which is different from that before modification. The stability of the catalyst is significantly improved, and the Ru-modified molecular sieve with the best stability can still reach 40% of the propylene selectivity after 12 hours of reaction. However, the cost of the noble metal-modified catalyst is high, and it is not suitable for large-scale production.

[0006] Patent CN201110293745.8 uses two metal oxides to modify molecular sieves, one oxide is selected from Fe, Co, Mo, etc., and the other is selected from Ti, V, Cr, etc. The best effect is 0.2% Zn0 .5%V0.2%Mo-HZSM-5 has a selectivity of 40% under the condition of complete conversion of methanol, but the catalyst preparation process is relatively cumbersome, and the problem of carbon deposition on the catalyst has not yet been solved

[0007] In the patent documents reported above, although various methods have been used to modify molecular sieves, due to the characteristics of the pore structure of SAPO molecular sieves, the method of loading other metals cannot fundamentally solve the problem of diffusion resistance. The structure has great resistance to the diffusion of low-carbon olefins, which leads to the further reaction of low-carbon olefins to form carbon deposits. Therefore, the utilization rate of raw material methanol in the entire reaction process is poor, the catalyst is easily deactivated, and the selectivity of the target product propylene is low. Green Chemistry Requirements

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