Structural Characteristics And Reaction Process Of Bifunctional Catalysts For Alkylation Of Toluene Side Chains To Styrene

Styrene is a basic chemical raw material and plays an important role in organic chemical production.Benzene and ethylene are mainly used in industry to first undergo alkylation to generate ethylbenzene,and ethylbenzene is then catalytically dehydrogenated to prepare styrene by two-step method.The process flow is relatively complicated,and it is necessary to develop a new process for producing styrene.The study found that the toluene side chain alkylation process can obtain styrene through a one-step process,and it is simple and low in energy intensity,and has a good foreground.The side chain alkylation of toluene requires catalysts with certain steric structure and acid-base sites.Layered double oxides（LDO）have layered structures and different acid-base sites and are used in a variety of acid-base catalysis reactions.In this paper,MgAl-LDO was introduced into the toluene side chain alkylation reaction to prepare two-dimensional layered catalysts Cs/MgAl-LDO@X and H₃BO₃/Cs/MgAl-LDO@X.The structure and properties of the catalyst were analyzed by XRD,SEM,TPD,and the reaction performance was evaluated.MgAl-LDH@Zeolite was prepared by co-precipitation method using different zeolites as supports,magnesium nitrate as magnesium source,and aluminum nitrate as aluminum source.Cs/MgAl-LDO@Zeolite was obtained after impregnation with Cs,drying and calcination.The test found that X zeolites had the best performance.The precursor Mg-Al@X was characterized,and it was found that the characteristic peaks of Mg-Al hydrotalcite could be seen in the XRD pattern,and MgAl-LDO was evenly distributed on the surface of the zeolite in the form of flakes in the SEM picture,indicating that the MgAl-LDO successfully grown on X zeolites.After impregnation with Cs and calcination,the skeleton structure of the catalyst was less damaged,and the acid-base characterization showed that the acid content was greatly reduced,and medium-strong base site strength increases.A series of Cs/MgAl-LDO@X were prepared by changing MgAl-LDO growth amount,Mg-Al ratio,Cs impregnation amount,titration p H,preparation time,post-treatment solvent,etc.The optimal preparation conditions were determined by performance test.The reaction conditions were studied,and it was found that the Cs/MgAl-LDO@X had the best performance when the raw material ratio was 5,the temperature was 425℃,and the space velocity was 2 h^-1.The conversion of toluene was4.33%,the selectivity of styrene reached 60.07%.The acid-base properties of the catalyst were adjusted by impregnating different acidic substances and boron-containing substances on Cs/MgAl-LDO@X,and it was found that the reaction performance of impregnating H₃BO₃ was the best.The H₃BO₃/Cs/MgAl-LDO@X was characterized,and it was found that the intensity of XRD characteristic peaks increased after immersion in H₃BO₃,and the H₃BO₃ was evenly distributed on the catalyst surface.The SEM image showed that H₃BO₃/Cs/MgAl-LDO@X still held a two-dimensional layered structure,acid-base characterization found that impregnated H₃BO₃ covered weak acid sites and brought strong acid sites,the total acid content increased,and the alkali strength weakened.A series of catalysts were prepared by changing the way of adding and amount of H₃BO₃.The catalyst with the addition of 5 wt%H₃BO₃ by double dip method had the best performance.The reaction process of H₃BO₃/Cs/MgAl-LDO@X was studied,and it was found that when the raw material ratio was 5,the temperature was 450℃,and the space velocity was 2 h^-1,the property was the best.The conversion of toluene was 8.05%,the selectivity of styrene reached 66.30%.