The decomposition of nitrous oxide at 1.5 ⩽ P ⩽ 10.5 atm and 1103 ⩽ T ⩽ 1173 K

Abstract

AbstractReaction experiments on mixtures of N2O/H2O/N2 were performed in a variable pressure flow reactor over temperature, pressure, and residence time ranges of 1103–1173 K, 1.5–10.5 atm, and 0.2–0.8 s, respectively. Mixtures of approximately 1% N2O in N2 were studied with the addition of varying amounts of water vapor, from background to 3580 ppm. Experimentally measured profiles of N2O, O2, NO, NO2, H2O, and temperature were compared with predictions from detailed kinetic modeling calculations to assess the validity of a reaction mechanism developed from currently available literature thermochemical and rate constant parameters. Sensitivity and reaction flux analyses were performed to determine key elementary reaction path processes and rates.Reaction rate constants for the uni‐molecular reaction, N2O → N2 + O, were determined at various pressures in order to match overall experimental and numerical decomposition rates of N2O. The numerical model included a newly determined rate constant for N2O + OH → HO2 + N2 with an upper limit of 5.66 × 108 cm3 mol−1 sec−1 at 1123 K. This is considerably smaller than presently reported in the literature. The experimentally observed rate of N2O decomposition was found to be slightly dependent on added water concentration. The rate constant determined for the elementary decomposition is strongly dependent on the choice of rate constants for the N2O + O ⇔ N2 + O2 and N2O + O ⇔ NO + NO reactions. In the absence of accurate data at the temperatures of this work, and based on these and other experiments in this laboratory, we presently recommend rate constants from the review of Baulch et al. The basis for this recommendation is discussed, including the impact on the rate constants derived for elementary nitrous oxide decomposition. The uncertainties in the rate constants as reported here are ±30%.The present mechanism was applied to previously reported high‐pressure shock tube data and yields a high‐pressure limit rate constant a factor of three larger than previously reported at these temperatures. The following expressions for the elementary decomposition reaction are recommended: k = 9.13 × 1014 exp (−57, 690/RT) cm3 mol−1 s−1 and k∞ = 7.91 × 1010 exp(−56020/RT) s−1. Simple Lindemann fits utilizing these parameters reproduce the pressure dependent rate constants measured here within ±25%. © 1995 John Wiley & Sons, Inc.