Synthesis And Modification Of ZnZSM-5 And Application On Toluene Alkylation With CH₃Br

p-Xylene is a basic organic chemical material with great market demand and important industrial value.In recent years,the route of preparing p-xylene from toluene alkylation has attracted the attention of many researchers because of its remarkable cost advantage.A new synthesis route is proposed by our group to prepare p-xylene by toluene methylation with CH₃Br,and some research results has been obtained.In this dissertation,the catalysts of ZnZSM-5 and hierarchical ZnZSM-5were designed to improve the catalyst activity and stability towards the alkylation of toluene with CH₃Br.A variety of characterization methods has been used to characterize and analyze the structure,morphology and surface acid properties of the as-synthesized zeolites.The relationship between the physicochemical properties of catalysts and catalytic performances was also discussed.The main innovative results and conclusions were summarized as follows:?1?ZnZSM-5 was synthesized in one-step by isomorphous substitution method.The effects of addition amounts of Zn on the catalytic performance were investigated.The results showed that adding appropriate amount of zinc citrate can increase the acid sites on the surface of catalyst,which is beneficial to promote the toluene conversion by the full reaction of reactants.At the same time,Zn can be di rectly introduced into the framework of the catalyst by isomorphous substitution method.The increased mesoporous volume inside the crystal of the catalyst can reduce the diffusion limitation of products,which is conducive to improve the conversion of toluene and the stability of the catalyst.?2?In order to further improve the catalytic performance of the catalyst,hierarchical ZnZSM-5 was prepared by dissolution-recrystallization of the ZnZSM-5with the best catalytic performance in TPAOH aqueous solution.Compared with ZnZ5,hierarchical TPA-ZnZ5 has higher stability.It was found that the dissolution-recrystallization of the zeolite via TPAOH treatment could introduce a large number of mesopores into the surface of the zeolite,which would facilitate t he rapid diffusion of the products,thus improve the stability of the catalyst.At the same time,the presence of TPA⁺could protect the original microporous structure of the zeolite from damage.?3?Amplification of the p-xylene process for the alkylation of toluene with CH₃Br was designed.The process mainly comprises three sections:alkylation section,pre-separation section and para-xylene purification section,including process design,material and energy balance,reactor selection and shop layout.The process has the advantages of simple process,high utilization of materials,energy saving and environmental protection.