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Reaction Mechanism Of Benzene And Ethylene In The Micro-Level Molecular Sieve And Intrinsic Kinetics

Posted on:2014-03-11Degree:MasterType:Thesis
Country:ChinaCandidate:D ZhangFull Text:PDF
GTID:2251330425996902Subject:Chemical Engineering
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The primary research of the subject is ethylbenzene synthesis alkylation reaction mechanism and intrinsic kinetics. The alkylation reaction of benzene with ethylene in the zeolite catalyst very rapidly, it is difficult to study by experimental means. In recent years, the development of computer technology, making a larger development of quantum chemical calculations and molecular modeling, using a computer on the larger system of micro-level research become possible, this topic use quantum chemistry and molecular modeling methods to study the reaction mechanism and the intrinsic dynamics of benzene and ethylene in zeolite catalyst alkylation reaction.Firstly, studying the absorption behavior of benzene and ethylene on the three different types of zeolite with the way is quantum chemical calculations. Calculated through the ONIOM method, we establish three zeolite cluster model, and benzene and ethylene were separately calculated on the zeolite adsorption. Structure parameters and adsorption energies of benzene and ethylene are gained in zeolite adsorption, and obtaining the result of the calculation. The one result is the smaller zeolite channels, the more stability. And the other calculated results obtained on benzene adsorption, have been the impact the zeolite acidity of acid sites for ethylene adsorption. By molecular simulation methods and then we calculated the mesoscopic scale behavior of benzene and ethylene adsorption on ZSM-5zeolite. Studying to use GCMC method to simulate the behavior of benzene and ethylene molecules adsorbed on ZSM-5zeolite. We changed the type of adsorption to study the interaction between different adsorption characteristics, and both of the benzene and ethylene molecules under the different temperatue and pressure. The studies show that the ethylene molecules kinetic diameter less than the kinetic diameter of the benzene molecules, at higher pressures, the amount of adsorption of ethylene in zeolite is greater than the amount of adsorption of benzene; benzene and ethylene molecules are adsorbed in zeolite, existence of competitive adsorption behavior; under the higher temperature, lower pressure, the amount of ethylene in the zeolite is far less than the amount of benzene adsorption. Secondly, the acid zeolite catalyzed alkylation of benzene with ethene is investigated at the B3LYP/6-31G*level of calculation with a4T-cluster representing the Bransted acid site of the zeolite. According to the formation energy and reaction activation energy the reaction mechanism has been analyzed. Three different reaction mechanism of alkylation-two concerted mechanism and one stepwise mechanism has been analyzed by density functional theory. The results showed that ethene protonation and C-C bond formation occur simultaneously in the concerted mechanism. The stepwise mechanism starts with the formation of a stable ethoxide intermediate which subsequently reacts with benzene to form the reaction product. The activation energy for the concerted mechanism is about38kcal/mol, while it was45kcal/mol for the stepwise mechanism. The results showed that alkylation of benzene with ethylene occurred through both concerted mechanism and stepwise mechanism, and they are competitive to each other.Finally, the intrinsic kinetics alkylation reaction of benzene with ethylene were studied, we use the data obtained in the study of the classical equations and reaction mechanism of the transition state theory to the relationship between the reaction rate constant and temperature. This rate constant is obtained by using the micro-level calculations. Then the two different reaction mechanism intrinsic kinetics equations were obtained.
Keywords/Search Tags:ethylene, benzene, zeolite, adsorption, quantum chemical calculations, molecular modeling, reaction mechanism, intrinsic kinetics
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