Experimental and Modeling High-Pressure Study of Ammonia-Methane Oxidation in a Flow Reactor

The present work deals with an experimental and modeling analysis of the oxidation of ammonia-methane mixtures at high pressure (up to 40 bar) in the 550-1250 K temperature range using a quartz tubular reactor and argon as a diluent. The impact of temperature, pressure, oxygen stoichiometry, and CH₄/NH₃ ratio has been analyzed on the concentrations of NH₃, NO₂, N₂O, NO, N₂, HCN, CH₄, CO, and CO₂ obtained as main products of the ammonia-methane mixture oxidation. The main results obtained indicate that increasing either the pressure, CH₄/NH₃ ratio, or stoichiometry results in a shift of NH₃ and CH₄ conversion to lower temperatures. The effect of pressure is particularly significant in the low range of pressures studied. The main products of ammonia oxidation are N₂, NO, and N₂O while NO₂ concentrations are below the detection limit for all of the conditions considered. The N₂O formation is favored by increasing the CH₄/NH₃ ratio and stoichiometry. The experimental results are simulated and interpreted in terms of an updated detailed chemical kinetic mechanism, which, in general, is able to describe well the conversion of both NH₃ and CH₄ under almost all of the studied conditions. Nevertheless, some discrepancies are found between the experimental results and model calculations.