The Research Of The Alkylation Of Benzene And Ethylene On The Multi-scale Zeolites

The major research of the subject is the different reaction mechanism of theethylbenzene synthesis alkylation reaction and intrinsic kinetics. Because of therapidity of the alkylation in the zeolite catalyst, it is difficult to study by normalexperimental means. Recently years, the quantum chemical calcultations andmolecular modeling take advantage of the development of computer technology, makeit possible that we can use computer on the larger system of micro-level research. Thistopic mainly use quantum mechanics to discuss the reaction mechanism of thealkylation reaction of benzene and ethylene on the ZSM-5zeolite catalyst, andcombine with the adsorption data of the component in the system which obtain bymolecular mechanics.After some assumptions and approximation,we conclude the rateequation of the alkylation of benzene with ethylene on the ZSM-5zeolite catalyst bydifferent mechanism.First, we use the quantum mechanics method, adopt the B3LYP/6-31G level ofcalculation to investigate the acid zeolite catalyzed alkylation of benzene with ethaneand use a8T-cluster to represent the acid site of the zeolite. Using the densityfunctional theory to discuss the two acknowledged concerted mechanism and onestepwise mechanism from the aspect of formation energy and reaction activationenergery. The results showed that when reacted by concerted mechanism, the ethaneprotonation and C-C bond formation occur simultaneously. Otherwise when reactedby stepwise mechanism, start with the formation of a stable ethoxide intermediatewhich subsequently reacts with benzene to form the reaction product. The resultsshowed that the activation energy for the two different concerted mechanism is about41kcal/mol and37kcal/mol,respectively.And when reacted by stepwise mechanism thevalue is about58kcal/mol.By this result we conclude that the alkylation of benzene andethylene on the ZSM-5zeolite predominantly by concerted mechanism. But because ofthe low activation of the first step in the stepwise mechanism, we can not totally ignore the stepwise mechanism, so these two kinds of mechanism is competive in the reactionprocess.Second we use the classic transition state theory, calculate the rate coefficient ofdifferent mechanism combine with the data obatain from the mechanism study.Discuss the two kinds mechanism from the aspect of kinetics. We figure out thar therate coeffient of stepwise mechanism is much bigger than that of concertedmechanism.But because of the excess of the benzene in industrial practice,we can’tsimply ignore the concerted mechanism.Last we combine the adsorption data of the component in the system when theyadsorbed on the ZSM-5zeolite which obtain by molecular mechanism, after someassumptions and approximation and comnbine the quantum mechanics and molecularmechanism, we conclude the rate equation of the alkylation of benzene with ethyleneon the ZSM-5zeolite catalyst by different mechanism.