Abstract
A crucial chain-branching step in autoignition is the decomposition of ketohydroperoxides (KHP) to form an oxy radical and OH. Other pathways compete with chain-branching, such as “Korcek” dissociation of γ-KHP to a carbonyl and an acid. Here we characterize the formation of a γ-KHP and its decomposition to formic acid + acetone products from observations of n ‑butane oxidation in two complementary experiments. In jet-stirred reactor measurements, KHP is observed above 590 K. The KHP concentration decreases with increasing temperature, whereas formic acid and acetone products increase. Observation of characteristic isotopologs acetone‑ d 3 and formic acid- d 0 in the oxidation of CH 3 CD 2 CD 2 CH 3 is consistent with a Korcek mechanism. In laser-initiated oxidation experiments of n -butane, formic acid and acetone are produced on the timescale of KHP removal. Modelling the time-resolved production of formic acid provides an estimated upper limit of 2 s ‑1 for the rate coefficient of KHP decomposition to formic acid + acetone.
This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences. The Lawrence Berkeley National Laboratory researchers were supported under contract no. DE-AC02-05CH11231, the gas phase chemical physics program through the Chemical Sciences Division of Lawrence Berkeley National Laboratory.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the USDOE’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the USDOE or the United States Government. L.S. was supported as part of the Argonne-Sandia Consortium in High-Pressure Combustion Chemistry. The KAUST researchers were supported by competitive research funding from the King Abdullah University of Science and Technology. Argonne National Laboratory is supported by the USDOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences under contract no. DE-AC02-06CH11357.D.M.P.-V. acknowledges financial support provided by the UCF through the Seed Funding Programand the technical support by James Breen, Erik Granlund, and William Thur during the designing and fabrication of the JSR system. P. D. has received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement No. 291049-2G-CSafe.