Rate constants for H-atom abstraction reactions from mono-aromatic hydrocarbons by H, CH3, OH and 3O2: A systematic theoretical investigation

Abstract

Mono-aromatic hydrocarbons (MAHs) are key components in surrogate fuels formulation (e.g. toluene), as well as the initial building blocks of PAHs growth (e.g. benzene). Moreover, the viability and sustainability of biomass fast pyrolysis processes increased the interest in oxygenated aromatic hydrocarbons (e.g. anisole, phenol) as anti-knocking additives for gasoline fuels and reference components for bio-oils surrogates. Differently from other classes of compounds (e.g. n-alkanes, iso-alkanes) a systematic approach to build kinetic mechanisms based on reaction classes and rate rules is still lacking for MAHs. Taking advantage of automated tools to perform state-of-the-art theoretical calculations, this work provides a consistent set of 52 accurate rate constants for H-atom abstraction reactions from benzene, toluene, phenol, and anisole by H, CH3, OH, and 3O2 for direct implementation in existing kinetic models. New insights about the accuracy of the theoretical methodology are presented, assessing the impact of the level of theory used for electronic structure calculations, of the treatment of hindered rotors, and of the implementation of variational transition state theory in both Cartesian and internal coordinates. This investigation provides guidelines to develop appropriate theoretical protocols for the treatment of MAHs reactivity and for the quantification of the associated uncertainty, with the final aim of building fundamentally-based sets of reaction classes of relevance for the pyrolysis and oxidation of MAHs.