Normal butane oxidation: Measurements of autoxidation products in a jet-stirred reactor

Abstract

The autoxidation of n-butane was studied experimentally in a jet-stirred reactor at 1 atm (560–720 K) and 10 atm (530–1030 K) for an equivalence ratio of 1. Samples of reacting mixtures were analysed in the gas phase by gas chromatography (GC) using several detectors (Flame ionization detector, thermal conductivity detector, quadrupole mass spectrometer), hydrogen peroxide analyser, and Fourier transform infrared spectroscopy. In addition to the fuel and oxygen, 37 products were quantified. Liquid phase samples were obtained by trapping the reacting mixtures in cooled acetonitrile (273 K). The liquid samples were analysed by high resolution mass spectrometry (HRMS Orbitrap Q-Exactive), either after flow injection or separation by high pressure liquid chromatography (HPLC). Besides stable species, several other low-temperature oxidation products, such as hydroperoxides and ketohydroperoxides, were detected. Products of third O2 addition on fuel’s radicals were also detected by high resolution mass spectrometry. To assess the presence of hydroxyl or hydroperoxyl groups in the products of oxidation we performed H/D exchange with D2O. Qualitative and quantitative results showed the same trends in terms of variation of mole fractions and signal intensities versus reacting temperature. Kinetic modelling was performed using a literature detailed kinetic reaction mechanism already used to simulate previous n-butane oxidation experiments in the cool-flame regime, showing that improvements are needed to better describe the oxidation of n-butane under the present conditions.