The Comparative and Combined Effects of Nitric Oxide and Higher Alkanes in Sensitizing Methane Oxidation

Abstract

The comparative and combined effects of nitric oxide (NO) and higher alkanes on methane oxidation were examined by experimentation and kinetic modeling. Experiments were conducted using fuel-lean, lower-alkanes mixtures with NO (0–400 ppm v/v) in an atmospheric flow reactor at residence time of 2 s over the temperature range of 820–950 K. NO was found to greatly promote methane conversion, and its sensitizing effect strengthened with the increasing concentration that was added to the system. The promoting effect of higher alkanes on methane conversion was also evident, particularly at zero or low NO concentrations. A strong dependency of the sensitizing effect on the concentration of higher alkanes present was also observed. The kinetic mechanism from Le Cong et al., performed reasonably well in reproducing the experimental trends. However, the sensitizing propensity of higher alkanes in the presence of NO could not be unambiguously ranked under all conditions. Modification to the kinetic mechanism of Le Cong et al., was attempted. Specifically, the submechanism of C3 peroxy radicals was added, but the modeling results indicated a lower impact on methane conversion than was initially expected. The most sensitive reactions were revealed, and the generalized reaction pathways for methane oxidation sensitized by higher alkanes, with or without the presence of NO, were also proposed, following detailed sensitivity analysis.