Reaction kinetics and implications of the decomposition and formation of C2H4O isomers

Abstract

Acetaldehyde, ethylene oxide, and vinyl alcohol are three C2H4O isomers that are ubiquitous in combustion over a wide temperature range. A comprehensive reaction kinetics study has been performed for reactions that occur on the same C2H4O potential energy surface, mainly including the unimolecular reactions of three C2H4O isomers and the recombination reaction of CH3 with HCO. Temperature- and pressure-dependent rate coefficients were updated or newly predicted by performing quantum chemical calculations coupled with RRKM/master equation simulations. The dominance of CC bond fission is reconfirmed for acetaldehyde decomposition at higher temperatures. The negligible contribution of CH4 + CO channel from usual tight intramolecular H-shift transition state provides indirect evidence for previously reported roaming mechanism that was proposed to explain the observation of CH4 + CO in acetaldehyde pyrolysis. For ethylene oxide pyrolysis, current experiment and kinetic prediction have a good consistency in branching ratios between the formation of acetaldehyde and vinyl alcohol products. The radicals of CH3 + HCO can also be directly generated from ethylene oxide through a well-skipping reaction mechanism especially at higher temperatures. For CH3 + HCO recombination, we highlight the importance of CH3CO + H channel that was often overlooked previously. Kinetic simulations show that the incorporation of updated rate coefficients and newly identified channels results in a measurable influence on C2 chemistry, indicating the possibility and necessity of further improvement of core mechanism in combustion kinetic models.