Shock-tube study of the pyrolysis of the halon replacement molecule CF3CHFCF3

The kinetics of pyrolysis of CF3CKFCF3 have been studied in dilute mixtures (0.5 and 3 mol %) in argon in a single-pulse shock tube over the temperatu re range of 1200-1500 K, residence times behind the reflected shock of betw een 650 and 850 mu s, and pressures between 16 and 18 atm. Fluorinated prod ucts were quantified with gas chromatography and Fourier transform infrared spectroscopy; identification of unknown fluorocarbons and hydrofluorocarbo ns was performed with gas chromatography-mass spectrometry. The most signif icant products detected were C2F6, CF2=CHF, C2F4, C3F6, cyclo-C3F6 and CF3C HFCF2H. Traces of CF3H, CF4, C2F5H, C3F8, C4F6, and isomers of C4F8 were al so identified. A detailed kinetic reaction scheme is presented to model the experimental reactant and product yield profiles as a function of temperat ure. 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 s lower. From experiments and modeling, the following initiation rate constan ts were obtained: CF3CHFCF3 --> CF3 + CF3CHF (k(37) = 10(15.9) exp(-355.6 k J mol(-1)/RT) s(-1)), CF3CHFCF3 --> C3F6 + HF (k(38) = 10(12.9) exp(-291.2 kJ mol(-1)/RT) s(-1)), and CF3CHFCF3 + F --> CF3CFCF3 + HF (k(39) = 10(13.6 ) exp(-10.1 kJ mol(-1)/RT) cm(3) mol(-1) s(-1)).