Quantitative Calculation And Molecular Simulation Of Alkylation Of Benzene With Propylene

Cumene is an intermediate product widely used in industry.Demand has increased rapidly in recent years.However,the mechanism of its internal alkylation is unclear.Therefore,this paper mainly studied the mechanism calculation and electron transfer analysis of the alkylation of benzene with propylene by BEA molecular sieves and ZSM-5 molecular sieves,and simulated the adsorption properties of the reaction.First,the reaction mechanism of alkylation of benzene with propylene by BEA zeolites was studied.Based on DFT theory and Gaussian 09 software,the mechanism of alkylation of benzene and propylene catalyzed by BEA zeolites represented by 5T model was studied in this paper.In this paper,two reaction mechanisms are proposed,namely,the associative and consecutive reaction mechanisms.It was calculated that the associative reaction mechanism takes four steps,including the co-adsorption of benzene and propylene,alkylation,and the formation of the products and desorption,which requires four steps.The consecutive reaction mechanism requires seven steps.First,propylene is adsorbed and protonated,then propylene and benzene are alkylated to fonn products and desorption.It was calculated that the energy barrier of the associative reaction mechanism is 106kJ/mol;the energy barrier for first step of the consecutive reaction mechanism is 66 kJ/mol,and the energy barrier for first step of the consecutive reaction mechanism is 294 kJ/mol.It is concluded that benzene and propylene are mainly the associative reaction mechanism on BEA zeolite and the consecutive reaction mechanism is difficult to carry out by comparing the activation energy of the two mechanisms.The electron transfer analysis on BEA zeolite has been further studied.It is found that the electrochemical properties of zeolite skeleton play an important role in the alkylation of benzene and propylene.Next,the mechanism of alkylation of benzene with propylene by ZSM-5 zeolites was studied.The 8T model was used instead of ZSM-5 molecular sieve to study the mechanism.The adsorption state,transition state,product structure and energy change of the reaction were calculated.Two mechanisms of reaction were obtained,namely the associative reaction mechanism and the consecutive reaction mechanism.The reaction process,like the BEA molecular sieve,passes through the protonation step and the alkylation step.The difference is that the energy barrier of the two molecular sieves is different.Comparing the alkylation of associative reaction between BEA zeolite and ZSM-5 zeolite,the reaction activation energy on ZSM-5 zeolite(99 kJ/mol)is slightly lower than that of BEA zeolite(106 kJ/mol).Therefore,alkylation of benzene and propylene is easier to perform on ZSM-5 molecular sieves.For the second step of the consecutive reaction,the energy barrier of alkylation step by ZSM-5 zeolite catalytic is 229 kJ/mol,which is also lower than that alkylation step for BEA zeolite catalyst(294 kJ/mol).Based on the mechanism calculation,the adsorption properties of the above two kinds of zeolites were studied in this paper.According to the fitting of the experimental results and the simulation results,the parameters of the corrected force field are obtained.The distribution of adsorbed particles and adsorption isotherms of benzene and propylene on BEA and ZSM-5 molecular sieves were obtained through the simulation of the force field parameters in the MS software.It is found that the BEA molecular sieve channel has high selectivity for benzene in the adsorption of mixtures,and the adsorption amount of benzene is obviously greater than that of propylene.The adsorption of propylene and benzene on ZSM-5 molecular sieve is close,and the competitive adsorption of propylene to benzene is obviously enhanced.