Theoretical studies of unimolecular thermal decomposition reactions of n-hexane and n-hexene isomers

Abstract

Alkenes are not only important components of commercial transportation fuels, but also important intermediates during combustion processes for all hydrocarbon and many alternative fuels. The research of combustion reaction mechanisms and combustion characteristics of alkenes requires accurate rate constants of key reactions during the oxidation processes of alkenes. In the present work, dominant reaction channels of unimolecular thermal decomposition of n-hexane and three isomers of n-hexene: 1-hexene, 2-hexene, and 3-hexene are investigated by using theoretical calculations. Potential energy surfaces and minimum energy paths (MEPs) of bond dissociation reactions are carried out at the CBS-QB3 level of theory. The difference between the thermal decomposition behavior of n-hexane and n-hexene are discussed. Subsequently, the high pressure limit rate constants for all decomposition reaction channels are calculated via variational transition state theory (VTST), while the temperature- and pressure-dependent rate constants are computed by using Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) simulations. The impact of the CC bond location and rate constants obtained in this work are systematically discussed and compared with those available from literatures. Further, sensitivity analysis are performed to investigate the uncertainty of the predicted rate constants. This work provides sound quality rate coefficients for initial thermal decomposition reactions of n-hexane and the three isomers of hexene over a wide range of temperature (800–2200K) and pressure (0.01–100atm), which will be valuable for the development of detailed combustion reaction mechanisms for hydrocarbon fuels.