Synthesis、Characterization Of Layered Crystal SAPO-34 Zeolite And Catalytic Performance On MTO Reaction

Ethylene and propylene, chemical products from the oil and gas, has become indispensable to modern industrial chemical intermediates, China’s oil, resource-poor, high prices, the prices of domestic products can not compete with international products, production is also far from being able to meet market demand. Therefore, We need to find new, low-cost, efficient source of olefins to meet domestic needs. In China, the methanol has large output, low cost, and thus, the methanol to olefins (MTO/MTP) has a good economic and market outlook.The core technology of the methanol to olefins (MTO) is a catalyst, the economic benefits, or even the success or failure of the MTO depend on the catalyst performance. A large number of studies show that the CHA structure, chabazite of SAPO-34, due to its unique pore structure and moderate acidity, showed excellent catalytic activity, especially for selectivity of ethylene and propylene in the reaction of methanol to olefins (MTO).SAPO-34 zeolite can be synthesized by a variety of templates, but the morphology, catalytic properties of the product are quite different, recognized as the best of the catalytic properties of SAPO-34 was synthesized by tetraethyl ammonium hydroxide as the templating agent. In practical applications, expensive tetraethyl ammonium hydroxide makes the excellent performance of the catalyst cost unreasonably high, Looking for alternative templating agent to reduce the amount of tetraethyl ammonium hydroxide, while maintaining the high catalytic performance to become one of the important research goal.Lifetime, selectivity of SAPO-34 in the catalytic performance, in essence, directly related to the material physical property. It has a relationship with the SAPO-34 pore size, acid density, acid strength, grain size, crystal morphology.the catalytic properties were studied by means of XRD, BET, SEM, N2-adsorption/desorption, NH3-TPD techniques.In the optimization of the template program, We get a kind of special layered morphology of SAPO-34, the study investigated the synthesis methods and performance of such a layered SAPO-34, and compared with other common morphology of the molecular sieve in properties; The study investigated the hydrothermal stability of the layered SAPO-34 and found that the samples can meet the MTO process demanding higher hydrothermal environments on the thermal stability of zeolite water requirements; By comparison the layered SAPO-34 and traditional cubic SAPO-34 zeolite’s hydrothermal stability, we find the optimum synthesis of a high hydrothermal stability of SAPO-34 program. At the same time, the article also investigated the catalytic properties of the different SiO2/Al2O3 of the layered SAPO-34 in the MTO reaction, it provided the experimental basis in order to find the best catalytic performance of MTO catalyst. This paper outlines these following work:Ⅰ. The effects of different template for the synthesis of SAPO-34 molecular sieve and its properties was studied, The effects of different crystallization time of SAPO-34 crystal growth was studied. The use of seed directing agent method and add auxiliary template synthesized with a layered structure of SAPO-34, and studied the physical characteristics of the layered of SAPO-34. The results show that, as long as the directing agent-assisted dosage is appropriate can be synthesized with the lamellar structure of SAPO-34, and greatly reduce the amount of expensive templating agent tetraethyl ammonium hydroxide, thereby reducing the synthesis cost.Ⅱ. The hydrothermal stability of SAPO-34 molecular sieve, the self-maded, two sets of different morphology (layered and cubic) was studied, it was found that layered and cubic SAPO-34 have good hydrothermal stability. cubic SAPO-34 compared with the layered structure is more stable. It is noteworthy that, in a short (less than 12h) hydrothermal treatment, the degree of crystallinity of the cubic SAPO-34 can be increased, the crystals can become more perfect, the catalytic performance has improved, However, after a long period of hydrothermal treatment, the two morphologies of SAPO-34 showed good hydrothermal stability.Ⅲ. This article also investigated the reaction of layered SAPO-34 with different SiO2/Al2O3 and the physical and chemical properties of the layered of SAPO-34 and applied it to the methanol to olefins (MTO) and found that layered structure of SAPO-34 with 0.3SiO2/Al2O3 has the best crystal perfection, high specific surface area, acidity and catalytic performance.