Synthesis And Post-treatment Of MWW Molecular Sieve

Because MCM-49 molecular sieve has a unique pore structure and acid distribution,it exhibits excellent catalytic reaction performance in reactions such as alkylation,disproportionation and isomerization.However,the pores of MCM-49 molecular sieve belong to micropores and are confined to two-dimensional space.The diffusion of larger molecular reactants and products in the pores is easily restricted.Therefore,it is a hot research topic to try to improve its mass transfer performance.Based on previous studies,this paper studies partial substitution of HMI or uses other organic amines as template to synthesize MCM-49 molecular sieve,and explores its optimized synthesis and post-treatment methods,and adopts XRD,XRF,TPD,BET and TEM.Characterization technology to study its physicochemical properties and catalytic properties,providing a basis for the application of MCM-49 molecular sievesThe synthesis of MCM-49 molecular sieve mainly involves the selection of synthetic raw materials?template,silicon source,aluminum source,and seed crystal?and synthesis conditions?raw material ratio and crystallization conditions?.It is confirmed that the synthesis temperature of MCM-49 molecular sieve is Between 144 and 147 ^oC is preferred.The choice of solid silica gel for silica source is better than that of silica sol.The pure phase MCM-49can be synthesized between Na₂O/Al₂O₃ ratio of 2.7-3.1.The templating agent plays a crucial role in the synthesis process.The most commonly used templating agent for MCM-49 molecular sieves is hexamethyleneimine?HMI?.HMI has a strong template effect.Most of the negative charge in the MCM-49 molecular sieve framework is balanced by protonated HMI,and the HMI in the pores acts to stabilize the molecular sieve skeleton.However,because HMI is expensive and highly toxic,attempts have been made to reduce the amount of HMI or to find alternatives to HMI during the synthesis of MCM-49 molecular sieves.Studies have shown that both HMI-containing mixtures and cyclohexylamine can be used in the synthesis of MCM-49 molecular sieves.In this paper,under the premise that the total amount of templating agent ratio is 5?with the ratio of Al₂O₃?,try to replace HMI with CHA.The maximum amount of CHA can be 1.5mol or3.5HMI+1.5CHA to synthesize pure phase MCM-49.Multistage pore MCM-49 molecular sieves with uniform intracrystalline mesopores were prepared by treating MCM-49 molecular sieves in a mixed solution of NaOH and CTAB.By systematically investigating the influence of solution composition and treatment conditions on the pores of MCM-49,the suitable conditions for preparing multi-stage pore MCM-49molecular sieve were determined:CTAB concentration was 0.1-0.2 mol/L,NaOH concentration was 0.3-0.6 mol/L,and treatment was carried out.The temperature is 70-110 ^oC and the treatment time is 2-22 h.Through the follow-up analysis of the preparation process of multi-stage pore MCM-49 molecular sieve,the possible formation process of intra-crystal mesopores was inferred.