Theoretical kinetics of hydrogen abstraction reactions from propanol isomers by hydroperoxyl radical: Implication for combustion modeling

Abstract

Propanol isomers are potential alternatives to conventional fossil fuels and have attracted considerable attentions from combustion community. Hydrogen atom abstraction reactions from alcohols by HO2 radical plays an important role in alcohol oxidation chemistry. In this work, the temperature-dependent rate constants and branching ratios of the hydrogen atom abstraction reactions from n-propanol and iso-propanol by HO2 were calculated using the multistructural variational transition state theory with small-curvature tunneling approach. Results show that the multistructural torsional anharmonicity effects significantly influence the calculation of site-specific rate constants and branching ratios, which need to be considered for reaction systems having multiple distinguishable structures. Significant discrepancy observed in the theoretically calculated rate constants from different sources highlight the necessity and importance of accurate calculation efforts, as it can provide the experimentally unavailable site-dependent rate constants and branching ratios. The effects of our newly calculated rate constants were examined by incorporating them into a recent chemical kinetic model developed by Saggese et al. The chemical kinetic model implemented with our newly calculated rate constants exhibits decreased fuel reactivity, especially at low temperatures and high pressures. Also, the chemical kinetic model using our theoretical calculations shows better prediction in the mole fractions of aldehydes, which are key oxidation intermediates in propanol oxidation.