Development And Research Of High Performance Catalyst For Alkylation Of Benzene With Dilute Ethylene To Ethylbenzene

In this paper,a series of high silicate HZSM-5 zeolites with different Si/Al ratio were synthesized by seed-oriented method under hydrothermal condition.The effect of acid density was investigated on the alkylation of benzene with dilute ethylene,and optimizing the appropriate Si/Al ratio.The effects of acid strength were studied by synthesizing a series of[Fe]-[Al]-ZSM-5 zeolites with different Fe/Al ratio.For investigating the effect of diffusion properties on the alkylation of benzene with dilute ethylene,HZSM-5 catalysts with different b-axis thickness and alkaline treatment were prepared and evaluated.All samples were characterized by XRD,SEM,TEM,XRF,XPS,UV-Vis,FT-IR,UV-Raman,Ar physical adsorption,NH₃-TPD,Py-IR and TG-DTA.The conclusions were shown as follows:?1?The crystal of high silicate HZSM-5 zeolites with different Si/Al ratio were monodispersed,and each crystal sizes were 500 nm in length and 100 nm in thickness.With the increasing of the Si/Al ratio,the acid denstity of the samples decreased significantly.The conversion of benzene decreased slightly,and the ethyl-selectivity maintained above 99%,but the selectivity of toluene and xylene obviously decreased.These evidence displayed that the selectivity of xylene can be greatly reduced and the side reaction can be inhibited with the improving of the Si/Al ratio.?2?The[Fe]-[Al]-ZSM-5 zeolites with the same acid density but different Fe/Al ratio were synthesized.All of the samples showed the sheet-like morphology.With the decreasing of Fe/Al,the thickness of the samples became thicker and the acid strength increased obviously.The hierachical[Fe]-ZSM-5 zeolite can be obtained by alkaline treatment.The reaction performance showed that the conversion and stability of the catalysts enhanced greatly with the improving of acid strength.While the side reactions occurred dramatically,the ethyl selectivity decreased significantly,and the carbon species were more difficult to decompose.?3?The b-axis thickness of high silicate HZSM-5 zeolite can be effectively reduced from 8?m to 60 nm by adjusting the amount of seed addition,which shortens the diffusion distance of reactants and products,enhancing the diffusion property of catalysts,and also reducing the rate of carbon deposition.However,the acid density of the zeolite surface increased with the decreasing of b-axis thickness.The acidic sites distributed on the catalyst surface were beneficial to the occurrence of side reactions such as isomerization.?4?The hierarchical HZSM-5 zeolites with different pore structure were obtained by different alkaline treatment.The hierarchical HZSM-5 treated by NaOH had lots of macropores.The hierarchical HZSM-5 with many mesoporous was obtained by the co-treatment of TPAOH and NaOH.While the micropore structure remained in TPAOH treatment.Although the alkaline treatment significantly improved the catalysts diffusion,the selectivity of C₉ and C⁺₁₀enhanced remarkably,the carbon deposition rate of catalysts were not evidently reduced.This may be the good diffusion properties of high silicate HZSM-5 with a thickness of 100 nm on the b-axis,which was not the main reason for the deactivation of the catalyst.