First-principles kinetic study on benzene alkylation with ethanol vs. ethylene in H-ZSM-5
2019
Wang, Dong | Wang, Chuan-Ming | Yang, Guang | Du, Yu-Jue | Yang, Wei-Min
Kinetic insights into reaction activity and selectivity are important not only for understanding the nature of catalytic reactions but also for designing better catalysts. Here, by utilizing DFT calculations and microkinetic modeling, we systematically studied and compared the reaction mechanism (including both the stepwise and the concerted pathways) and kinetic performance of benzene ethylation by ethanol or ethylene in H-ZSM-5. We demonstrate that, under operating conditions, the activity of ethanol-involved reaction is dominantly governed by the stepwise mechanism, while that of ethylene-involved reaction is hundreds of times higher than the former and is mainly contributed from the concerted pathway. Ethylbenzene selectivity from the ethylene process is generally higher than the ethanol process, and the selectivity of both processes show positive correlations to the reaction temperature and benzene concentration. For the formation of diethylbenzene byproducts, we observed inevitable occupation of more intersection space to accommodate the extra ethyl chain but comparable barriers with ethylbenzene production, offering possibilities to further improve the selectivity by moderately tailoring zeolite pore structures. Based on the kinetic trends, we theoretically predict that the benzene-ethanol alkylation process would prefer a relatively higher operating temperature but lower pressure than the traditional ethylene process.
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