Synthesis Of Nanosized ZSM-5 And Its Catalytic Performance For The Production Of Ethylbenzene From Benzene And Dilute Ethylene

In this dissertation,nanosized ZSM-5 was hydrothermally synthesized using tetrapropylammonium bromide as template,silica sol and aluminum chloride hexahydrate as silicon and aluminium sources.Taking this as parent zeolite,a series of nanosized ZSM-5 with different acidities were obtained by treatment with nitric acid for different times before removing organic template.The nanosized ZSM-5 was then treated with a combination of high-temperature steam and citric acid.And the nanosized ZSM-5 was synthesized in the laboratory with hydrothermal reactors of different capacities and synthesized in a 20L autoclave with different aluminum sources.All shaped catalysts were evaluated at different times on two fixed beds.Design the orthogonal test,optimize the synthesis conditions,compare the evaluation results,and finally 60 g of shaped catalyst was evaluate on a pilot plant.The structure and acidity of samples were characterized by XRD,SEM,NH₃-TPD,XRF,XPS,Ar physical adsorption,TGA and Py-FTIR.The acidity of nanosized ZSM-5 treated by different methods and its effect on the alkylation of benzene with dilute ethylene were systematically investigated.The conclusions were shown as follows:?1?The nanosized ZSM-5 was monodispersed,and its grain size was about 500 nm in length and 100 nm in thickness.Nitric acid treatment changed the acid density and acid amount of nanosized ZSM-5.Compared with parent material,the acid density of zeolite treated with nitric acid for 16 h was slightly reduced,while the outer surface had the least acid sites.Under the reaction conditions,EB and DEB selectivity was increased to over 96%,the coking rate reduced from 0.06 to 0.03 wt%/h and the content of xylene in product was reduced by 20%.?2?Three levels and four factors?silicon-aluminum ratio of ZSM-5,steam temperature,treatment time,and temperature of citric acid?orthogonal experiments were designed to optimize the post-treatment process of catalyst.The feeding ratio of molecular sieve was adjusted,and it was found that different silicon-aluminum ratios did not affect the morphology of ZSM-5.According to the analysis of experimental data,it can be obtained that the best post-treatment method is 600?steam treatment for 7 h,and 50?citric acid treatment for 12h.?3?Nanosized ZSM-5 was synthesized by hydrothermal kettles of different capacities?100mL,200 mL,2 L,20 L?step by step,and the synthesis was repeated with a 20 L autoclave to provide reference data for subsequent synthesis of larger specifications.The molecular sieves synthesized in different reactors were well-crystallized.The particles are uniform,and no hybrid crystals appear.The crystal size was basically 100 nm thick and 500 nm long.Finally,the evaluation results were similar,and the scale-up synthesis from 200 mL to 20 L was successfully achieved.?4?The nanosized ZSM-5 with aluminum chloride as the aluminum source was extruded,and the best post-treatment process was adopted to obtain final catalyst.The catalyst prepared in the laboratory were evaluated on a pilot plant for benzene alkylation with dilute ethylene.By comparing the reaction results,the catalytic performance of the catalyst prepared in the laboratory was comparable to that of the industrial catalyst.