Shock-Tube Study of the Pyrolysis of the Halon Replacement Molecule CF 3 CHFCF 3

The kinetics of pyrolysis of CF 3 CHFCF 3 have been studied in dilute mixtures (0.5 and 3 mol %) in argon in a single-pulse shock tube over the temperature range of 1200−1500 K, residence times behind the reflected shock of between 650 and 850 μs, and pressures between 16 and 18 atm. Fluorinated products were quantified with gas chromatography and Fourier transform infrared spectroscopy; identification of unknown fluorocarbons and hydrofluorocarbons was performed with gas chromatography−mass spectrometry. The most significant products detected were C 2 F 6, CF 2 CHF, C 2 F 4, C 3 F 6, cyclo-C 3 F 6, and CF 3 CHFCF 2 H. Traces of CF 3 H, CF 4, C 2 F 5 H, C 3 F 8, C 4 F 6, and isomers of C 4 F 8 were also identified. A detailed kinetic reaction scheme is presented to model the experimental reactant and product yield profiles as a function of temperature. The results of modeling showed that the major initiation reaction was the C−C bond fission reaction. The abstraction of the secondary H atom by F atoms was also predicted to be important, whereas 1,2-HF elimination was slower. From experiments and modeling, the following initiation rate constants were obtained: CF 3 CHFCF 3 → CF 3 + CF 3 CHF ( k 37 = 10 15.9 exp(−355.6 kJ mol -1 / RT ) s -1 ), CF 3 CHFCF 3 → C 3 F 6 + HF ( k 38 = 10 12.9 exp(−291.2 kJ mol -1 / RT ) s -1 ), and CF 3 CHFCF 3 + F → CF 3 CFCF 3 + HF ( k 39 = 10 13.6 exp(−10.1 kJ mol -1 / RT ) cm 3 mol -1 s -1 ).