Gas-phase oxidation chemistry of the three cresol isomers

Despite their importance in the chemistry of aromatic compounds and as platform molecules from lignin decomposition, cresol isomers (ortho, meta, and para) are currently only considered as a single lumped species in detailed kinetic models. Furthermore, there are no experimental results available on the combustion of cresol isomers due to their extremely low volatility. This paper presents a recently developed detailed kinetic mechanism for the combustion of cresol isomers, driven by theoretically calculated rate constants for H-abstractions from the three isomers and for the decomposition of the addition products of the resulting radicals with O₂. It also presents the first-ever quantification of species during the oxidation of the cresol isomers in a jet-stirred reactor, as well as the first measurements of the laminar burning velocity of cresol isomers using a flat flame burner, with a different behavior for p-cresol compared to the other two. The new detailed kinetic model produces accurate predictions of mole fractions of fuel, CO, CO₂, ethylene, and more deviations for heavier products. Experimental data showed similar reactivity but significant differences in the nature and distribution of products depending on the position of hydroxy and methyl groups. Satisfactory burning velocity predictions were obtained for o-cresol and fair ones for m-cresol in lean mixtures. However, the large deviations observed for p-cresol suggest the need for further model improvement. Flow rate analyses revealed significant differences in the primary fuel consumption steps between the three isomers, explaining the observed differences in the products.