Shock-Tube Study of the Pyrolysis of the Halon Replacement Molecule CF_3CHFCF_3

摘要

The kinetics of pyrolysis of CF_3CHFCF_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 #mu#m, 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_2F_6, CF_2=CHF, C_2F_4, C_2F_6, cyclo-C_2F_6, and CF_3CHFCF_2H. Traces of CF_3H, CF_4, C_2F_5H, C_3F_8, C_4F_6, and isomers of C_4F_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 12-HF elimination was slower. From experiments and modeling, the following initiation rate constants were obtained: CF_3CHFCF_3 -> CF_3 + CF_3CHF(k_(37) = 10~(15.9) exp(-355.6 kJ mol~(-1)/RT) s~(-1)), CF_3CHFCF_3 -> C_2F_6_HF(k_(38) = 10~(12.9) exp(-291.2 kJ mol~(-1)/RT) s~(-1))), and CF_3CHFCF_3 + F -> CF_3CFCF_3 + HF (k_(39) = 10~(13.6) exp (-10.1 kJ mol~(-1)/RT)) cm~3 mol~(-1) s~(-1).