The mutually sensitied oxidation of ethylene and NO: An experimental and kinetic modeling study

Abstract

Experimental measurements in conjunction with kinetic modeling have been used to study the NO-accelerated oxidation of ethylene. The reaction between ethylene, O2, and NO was investigated experimentally over a wide range of reactant gas compositions for the temperature range 650–1000 K. The product distribution at low temperatures was found to be quite different from that observed for unpromoted ethylene oxidation, specifically the presence of formaldehyde in similar yields to CO. At higher temperatures, CO and CO2 become the dominant products. The kinetic model developed here allows semiquantitative prediction of the products and extent of reaction. Through kinetic modeling, considerable insight has been gained into the mechanism of NO-promoted ethylene oxidation. Under conditions of low oxygen concentration or at temperatures above 850 K, the mechanism was found to have much in common with unpromoted ethylene oxidation. However, below 850 K or at high oxygen concentrations, the major reaction pathway is through OH addition to ethylene and the subsequent reactions of hydroxyethyl radical. Without consideration of OH addition to ethylene, the observed concentrations of formaldehyde are grossly underestimated. Flux and sensitivity analysis has shown that the NO-promoted oxidation of ethylene involves a complex set of reactions in partial equilibria. The effect of reactant gas composition on the equilibrium concentrations of important intermediate species allows many of the complexities of NO/O2/C2H4 reaction kinetics to be understood.