The Research On Preparation And Catalytic Properties Of Shape-selective Catalysts For Alkylation Of Toluene With Methanol

P-xylene is an important basic organic raw material,which is closely related to human life.Toluene methanol alkylation synthesis of p-xylene is considered to be the most economical and promising p-xylene production technology.The catalyst is the core of toluene methanol alkylation reaction.The results show that the shape selectivity of the catalyst can be significantly improved by adjusting the acidity and pore size of HZSM-5 zeolite.Therefore,the alkylation of toluene with methanol has been systematically studied in this paper with shape-selective catalyst acidity and pore size control as the main breakthrough points.In this paper,the B/HZSM-5 catalyst and HZSM-5@silicalite-1 catalyst were prepared by boron impregnation and hydrothermal method,respectively,using HZSM-5 zeolite as the precursor.The catalytic performance of toluene methanol alkylation reaction and p-xylene isomerization reaction on the catalyst was investigated.In addition,XRD,SEM,TEM,N₂ physical adsorption and desorption,NH₃-TPD,Py-IR,IR and other characterization methods were used to study the physical and chemical properties of the shape-selective catalyst,and the relationship between the physical and chemical properties and the catal ytic performance was analyzed.The main research contents of this paper are as follows:（1）B/HZSM-5 catalyst was prepared by impregnation method.The catalyst with high selectivity can be prepared by adjusting the loading amount of boron.The results showed that the modification of boron eliminated the influence of strong acid sites on the reaction,and with the increase of boron loading,the amount of weak Bronsted acid sites increased,while the amount of weak Bronsted acid sites increased,which was beneficial to inhibit the isomerization reaction of p-xylene and the further methylation reaction of xylene,and improved the selectivity of p-xylene.（2）HZSM-5@silicalite-1 catalyst was synthesized by hydrothermal method.Under the optimal reaction conditions,the conversion of toluene over the0.6HZSM-5@silicalite-1 catalyst was 34.15%,and the selectivity of p-xylene reached96.77%.The results show that the synthesis of core-shell catalyst and the acidity of the catalyst can be controlled by changing the amount of seed crystal added.（3）The p-xylene isomerization performance of B/HZSM-5 and HZSM-5@silicalite-1 catalysts was investigated.The experiments show that the pore size of zeolite mainly affects the selectivity of p-xylene,while the acidity mainly affects the conversion rate of toluene,and the strong acid site on the external surface of the catalyst is the main reason for the decrease of the se lectivity of p-xylene.（4）The kinetics of alkylation of toluene with methanol over0.6HZSM-5@silicalite-1 catalyst was studied.The experimental results show that the activation energy of p-xylene isomerization reaction is lower than that of toluene methanol alkylation and xylene further alkylation.In the catalytic reaction process,p-xylene isomerization reaction is very easy to occur,so it is also easy to lead to the reduction of p-xylene selectivity.