Synthesis Of Three-dimensionally Ordered Mesoporous-imprinted ZSM-5 Zeolite And Catalytic Performance Evaluation In Methanol To Propylene Reaction

Propylene is one of the most important raw chemical materials and has been widely used for the production of polypropylene,propylene oxide,acetone and other products.The demand for propylene has rapidly increased in recent years.As a main non-oil route for the production of propylene,methanol-to-propylene?MTP?process can crucially alleviate the shortage of petroleum resources in China,and further promote the clean and high-efficiency utilization of coal,representing great prospect of application and practical significance.The key point for MTP technology is the development of high-performance catalysts.Three-dimensionally ordered mesoporous-imprinted ZSM-5 zeolite?3DOm-i ZSM-5?possesses highly interconnected micropores and mesopores,which can be considered as an ideal catalyst candidate for the MTP reaction.However,the synthesis of 3DOm-i ZSM-5 based on the confined space synthesis?CSS?approach was time-consuming and restricted to the carbon template?3DOm Carbon?.Besides,the intermediates?Si O₂ colloidal crystal and 3DOm Carbon?in the synthesis process had to been removed by corrosion and calcination,which made the synthesis of 3DOm-i ZSM-5 be high-cost and with limited yield.In view of this,the thesis devoted to the synthesis design and process optimization of 3DOm-i ZSM-5 to achieve template-free synthesis and sufficient utilization of the synthesis precursor of Si O₂ colloidal crystal.Moreover,the obtained 3DOm-i ZSM-5 by the modified synthesis approach was used as catalyst for the MTP reaction in comparison to the conventional ZSM-5 and 3DOm-i ZSM-5 by CSS approach.In addition,phosphorus modification was proceeded to further enhance the catalytic capacity of 3DOm-i ZSM-5 catalysts in the MTP reaction.1)Synthesis design:The confined space synthesis of 3DOm-i zeolite based on the typical hard-template strategy,and the nucleation and growth of zeolite crystals happened within the vacant carbon template?3DOm Carbon?.And the 3DOm Carbon was reversed from Si O₂ colloidal crystals,which were removed by strong alkali and caused a waste of Si O₂ raw materials in this process.To solve this problem,the occupied 3DOm Carbon by Si O₂ colloidal crystals were used as both precursor and template and the Si O₂ colloidal crystals was used as silicon source for the synthesis of 3DOm-i zeolite by solid conversion.Furthermore,in order to get rid of the limitation of 3DOm Carbon,one-step crystallization of Si O₂ colloidal crystal to 3DOm-i zeolite by solid conversion was first proposed for the fabrication of 3DOm-i zeolite without the structure inversion of 3DOm Carbon.It was proven that the obtained 3DOm-i ZSM-5 by the two proposed synthesis strategies possessed approximately consistent three-dimensional ordered structure and acid activity with the products by the traditional confined space synthesis method.It was worth mention that the new synthesis methods showed obvious advantages in terms of product yield and cost as well as time saving.The costs of raw materials for solid conversion with 3DOm Si O₂-C and solid conversion with Si O₂colloidal crystal were only 4.3%and 3.1%of the traditional confined space synthesis method,but the synthesis time was shortened by 50%and 77.8%.2)MTP evaluation:The catalytic capacity of 3DOm-i ZSM-5 was evaluated by the MTP reaction in comparison to the commercial ZSM-5?CZ5?.The results showed that 3DOm-i ZSM-5presented a much longer catalytic lifetime and a higher selectivity of propylene as well as propylene/ethylene ratio than CZ5 due to their highly interconnected hierarchical porosity and suitable acidity.In addition,3DOm-i ZSM-5 zeolites were appropriately passivated by phosphorus modification,and the modified 3DOm-i ZSM-5 exhibited improved catalytic performances?the selectivity of propylene increased by 3.5%?5.4%?in the MTP reaction.Although the 3DOm-i ZSM-5 catalysts prepared by the new methods showed similar catalytic performances in the MTP reaction with the product prepared by the confined space synthesis method,the proposed new synthesis methods revealed obvious economical efficiency by taken into account of the cost in material synthesis and catalytic performance.It can be expected that the work in this thesis provided not only a scalable synthesis strategy fot 3DOm-i zeolite,but also a material basis for the development of high-performanced MTP catalysts.