Exploring the low-temperature oxidation chemistry of cyclohexane in a jet-stirred reactor: An experimental and kinetic modeling study

Abstract

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500−742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window (∼80 K) was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 (2013)], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O 2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O 2 and the decomposition of cyclohexylperoxy radical, both producing cyclohexene and HO 2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-1-al and OH radical.

Chemical kinetics of cyclic ethers in combustion

“…Two recent JSR studies at Shanghai [522,528] with SVUV-PIMS analysis present mole fraction profiles as a function of temperature of a lumped C6H10O species assumed to include the three molecules of Fig. 33a (1,2-epoxycyclohexane, 1,4-epoxycyclohexane, hex-5-enal) together with cyclohexanone.…”

“…Several studies [418,515,528,530,531] have shown that the ring-opening step is fast, which would explain why 5-hexenal is detected in high quantities. As shown in [528], the calculated or estimated rate expressions of five studies [418,515,528,530,531] deviate by several orders of magnitude, which in part might be caused by different methodologies used and partly by the existences of several conformers. Given this severe uncertainty in the rate expressions, the overprediction of the 5-hexenal yield by only a factor of two seen in Fig.…”