Adsorption Of Benzene Alkylation System In Zeolites Under Supercritical Condition By Molecular Simulation

This thesis contains three parts.The first part is the molecular simulation of adsorption behaviors of benzene alkylation system in supercritical condition.The second part investigates the adsorption of benzene alkylation with propylene in several zeolites,including ZSM一12,Mordenite,ZSM一5,p,MCM一22 and ITQ-14. Then,the adsorption behaviors of benzene and propylene in new type zeolite,ITQ一22, iS discussed. According to the benzene alkylation with olefins,the polymerization of olefins and further alkylation of benzene contribute to the deactivation of zeolites.In order to resolve this problem,there are two ways recommended by this thesis.One is to undergo the reaction in supercritical condition,because chemical reactions in supercritical conditions can be accelerated,the product selectivity can be improved and more importantly,catalyst coking can be reduced.The other way is using new type zeolites,because different zeolites have different selectivity of molecules and different stability of catalyst to the benzene alkylNion reaction.This thesis investigated the feasibility of the two ways mentioned above using molecular simulation method. Benzene alkylation reaction in supercritical condition is first way mentioned above,and the discussion of adsorption behavior of the benzene— propylene and benzene-ethylene alkylation system in ZSM一5 under supercritical condition is the first part of this thesis.The adsorption behaviors of benzene—propylene system in variety of conditions,including subcritical and supercritical conditions show that benzene alkylation reaction in supercritical condition increases the yield of products and improves the stability of zeolite.The result of this part consists of four points,(1)In vapor phase,the equilibrium ratio of benzene/propylene in simulation decreases and is close to 1:1 with the decrease of temperature,which is interestingly similar to the experimental results,where the selectivity of cumene is close to 100%with the decrease of temperature.It suggests that a high yield for benzene alkylation with propylene to produce cumene,the equilibrium ratio Of benzene/prOpylene,close to 1:1 in the pores of ZSM一5.This is in agreement with the reaction mechanism of benzene alkylation with propylene.(2)The adsorption behaviors in five different phases, including supercritical,near supercritical,gas,vapor,and liquid phases,are discussed。 The simulation results show that the equilibrium ratio of benzene/propylene is closer to 1:1 in supercritical and near supercritical phases than that in other phases.This is corresponding to the experimental results,where the selectivity of cumene is highest in supercritical condition.(3)The effect of the feed ratio of benzene/propylene(or ethylene)in supercritical condition is investigated.On the one hand,according tO benzene-propylene system,the equilibrium ratio of benzene/propylene is nearest to 1:1 when the feed ratio of benzene/propylene is 5:1.On the other hand,according to benzene— ethylene system,the equilibrium ratio of benzene/ethylene is nearest to 1:1 when the feed ratio of benzene/ethylene is 3:1.It suggests that the proper feed ratio is 5:1 to benzene--propylene system and 3:1 to benzene-ethylene system for the high values of the selectivity of cumene.(4)The adsorption isotherm of benzene and the localization of benzene molecules in ZSM一5 suggest that benzene molecules is 'commensurate freezing'in the interconnection of sinusoidal and straight channels. Using a new zeolite as the catalysit of benzene alkylation is another way mentioned above,and the discussion of adsorption behavior of the benzene— propylene system in several zeolites,including ZSM一5,ZSM一12,Mordenite,ZSM一5,p, MCM一22 and ITQ一14 under supercritical condition is the second part of this thesis. The simulation results,comparing with the experimental data,show that the new zeolite,ITQ一14,has the highest adsorption selectivity of benzene,and sugg...