Studies Of Cd/mg(b) Modified HZSM-5 Zeolite In Catalysis Of Methanol Aromatization

Aromatic hydrocarbons,such as benzene?B?,toluene?T?,xylene?X?and trimethylbenzene?TB?,are the important petrochemical raw ingredients.It plays an important role in medicine,energy and agriculture.However,in terms of manufacture,it is heavily relying on petroleum.To alleviate the utilization of petroleum resources,it is very important to develop a non-petroleum route to produce aromatics.In many processes,methanol to aromatics is an effective production process.In this thesis,Cd/Mg?B?modified HZSM-5 zeolites in catalysis of methanol aromatization were studied.The specific contents were as follows.1.HZSM-5 zeolite was impregnated with cadmium.The relationship between different loadings and the reaction performance was compared.Cd-modified HZSM-5zeolites were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Fourier-transform infrared spectrometer?FT-IR?,NH₃-temperature programmed esorption?NH₃-TPD?,thermogravimetric analysis?TGA?and N₂ adsorption-desorption isotherms.The results showed that cadmium species have excellent catalytic activity in methanol aromatization.On the reaction conditions of temperature at 400°C,weight hourly space velocity?WHSV?of 1.90 h^-1 and at normal pressure,the selectivity of total aromatic hydrocarbons and trimethylbenzene on 1.4 wt%Cd/H-ZSM-5 zeolite are 71.0%and34.0%,respectively.2.HZSM-5 zeolite was treated with an appropriate alkali solution.The treated HZSM-5 zeolite was impregnated with different proportions of cadmium and magnesium to prepare Cd?Mg modified HZSM-5 zeolite.The catalysts were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,NH₃-temperature programmed desorption?NH₃-TPD?,thermogravimetric analysis?TGA?and N₂ adsorption-desorption isotherms techniques.It is found that Cd and Mg addition on HZSM-5 zeolites improves the catalytic performance in MTA reaction.Under the reaction conditions of temperature at 390°C,weight hourly space velocity?WHSV?of 1.6 h^-1,0.1 MPa and the mass fraction of catalyst is 1.2 wt%Mg-0.8 wt%Cd,the selectivity of BTX and xylene are 57.7%and 25.7%,respectively.3.HZSM-5 zeolite was treated with an appropriate alkali solution.The treated HZSM-5 zeolite was impregnated with different proportions of cadmium and boron to prepare Cd?B modified HZSM-5 zeolite.The catalysts were characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,NH₃-temperature programmed desorption?NH₃-TPD?,thermogravimetric analysis?TGA?and N₂adsorption-desorption isotherms techniques.Under the reaction conditions of temperature at 415°C,weight hourly space velocity?WHSV?of 1.56 h^-1,0.1 MPa,and the mass fraction of catalyst is 1.0 wt%B-1.0 wt%Cd,the selectivity of BTX and xylene are 52.7%and 20.6%,respectively,in which above 82%p-xylene.Compared with the catalyst modified by cadmium,boron shows the longer catalytic life.