Shock Tube Study of the Oxidation of C3F6by N2O

Abstract

The kinetics of the high-temperature oxidation of C3F6 by O(3P) have been studied by experiment, using a single-pulse shock tube, and by kinetic modeling. The O atoms were generated by the thermal decomposition of N2O. Three mixtures, each diluted in argon, were studied: 0.6 mol % of C3F6 with 1.5 mol % N2O; 6.2 mol % of C3F6 with 0.6 mol % of N2O; and 6.3 mol % of N2O and 0.7 mol % of C3F6. The temperatures were in the range 1300−1600 K, the residence times behind the reflected shock were in the range 550−850 μs, and the pressures were between 16 and 20 atm. Fluorinated products have been quantified with gas chromatography, oxidized products with Fourier transform infrared spectroscopy; identification of unknown fluorocarbons has been performed with gas chromatography−mass spectrometry. The most significant products detected were C2F6, C2F4, CF2O, CO, CO2, and CF4. A detailed kinetic scheme is presented to model the experimental reactant and product yields as a function of temperature. Modeling showed that O-addition to either carbon of the double bond of C3F6 occurs. The rate constant for O-addition to the terminal carbon of the double bond, C3F6 + O(3P) → 3CF3CF + CF2O, was deduced to be k71 = 1012.7T0.05 exp(−0.4 kJ mol-1/RT) cm3 mol-1 s-1, and for addition to the central carbon, C3F6 + O(3P) → CF3 + CF2CFO, k72 = 1012.5 cm3 mol-1 s-1. Under oxidizer-rich conditions, ignition of the C3F6 occurred. Rate of production analyses showed that ignition was propagated by an F atom chain involving the CF2 + O and unimolecular CFO decomposition reactions. Under C3F6-rich conditions, single- and double-bond pyrolysis were the important destruction routes.