High-temperature oxidation of CO and CH4

The oxidation of moist carbon monoxide and the post-induction-phase oxidation of methane were studied in a turbulent flow reactor. Reactants, stable intermediates, and products were determined spatially by chemical sampling and gas-chromatographic analysis. The carbon monoxide-oxygen reaction in the presence of water was studied at atmosphericpressure, and over the following ranges: temperature, 1030°–1230°K; equivalence ratio, 0.04–0.5; and water concentration, 0.1%–3.0%. The over-all rate expression found was −d[CO]/dt=1014.6±0.25 exp[(−40,000±1200)/RT][CO]1.0[H2O]0.5[O2]0.25 mole cm−3 sec−1. The data support the fact that hydroxyl radical concentration in the reaction exceeds that at thermal equilibrium by as much as 2 orders of magnitude. The post-induction-phase reaction of methane and oxygen was studied at atmospheric pressure, over the temperature range of 1100°–1400°K and equivalence ratio range of 0.05–0.5. The over-all methane disappearance-rate expression was found to be −d[CH4]/dt=1013.2±0.20 exp[(−48,400±1200)/RT][CH4]0.7[O2]0.8, mole cm−3 sec−1. The rate was shown to be independent of water concentrations added initially or produced in the reaction. The over-all appearance rate of carbon dioxide in the methane-oxygen reaction is described byd[CO2]/dt=1014.75±0.40 exp[(−43,000±2200)/RT][CO]1.0[H2O]0.5[O2]0.25 mole cm−3 sec−1. This correlation represents rates of carbon dioxide formation 3.5 times slower than those found in the independent study of the moist carbon monoxide reaction. From these and other experiments it was possible to deduce thatCH4+OH→CH3+H2O (3) is not the only mechanism contributing to the observed rate of disappearance of methane. It was concluded that the reaction CH4+O→CH3+OH (4) is of major importance in both oxygen-and fuel-rich systems at high temperatures. Furthermore, the experimental data support that these two reactions, as well as CH3+H2→CH4+H (−5) contribute to the methane results reported here.