Shock-tube studies on the reactions of 2H-heptafluoropropane with H and 0(³P) atoms and the subsequent reactions

Abstract

High-temperature kinetics of several important reactions for flame suppression by 2H-heptafluoropropane (CF₃CHFCF₃, HFC-227ea) have been studied using a shock tube-atomic resonance absorption spectroscopy technique. The rate coefficients for the initial reactions CF₃CHFCF₃+H→CF₃CFCF₃+H₂ (la) and CF₃CHFCF₃+0(³P)→CF₃CFCF₃+OH (2a) were determined from the decays of H and 0(³P) atoms to be K_1a=10^{−9.15±0.66}exp[−(63±14) kJ·mol⁻¹ /RT] cm³molecule⁻¹s⁻¹ (1000–1180 K) and k_2a= 10^{−10.27±0.67}exp[−(56±13) kJ.mol⁻¹/RT] cm³molecule⁻¹s⁻¹ (880–1180 K), respectively. The TST calculation showed that these experimental results were theoretically reasonable.

Subsequently, the reactions of CF₃CFCF₃ radicals, which are the product of reactions (la) and (2a), were studied. The rate coefficients for the reactions CF₃CFCF₃+H→CF₃CFCF₂+HF (3a) and CF₃CFCF₃+0(³P)→CF₃CFO+CF₃ (4a) had no temperature dependence and were obtained as k₃= 10^{−9.98±0.83} cm³ molecule⁻¹s⁻¹ (1010–1050 K) and k_4a= 10^{−10.84±0.84} cm³ molecule⁻¹ s⁻¹ (930–1050 K). These results mean that H atoms have higher reactivity with CF₃CFCF₃ than 0(³P) atoms, similarly to the kinetic results for the reactions of other fluoroalkyl radicals such as CF₃. At temperatures higher than 1050 K, the thermal decomposition of CF₃CFCF₃ radicals was found to be dominant over reactions (3a) and (4a). So the rate coefficient for the reaction CF₃CFCF₃→CF₃CF+CF₃ (5a) was also measured to be k_5a=10^10.85±0.91exp[−(163±20) kJ.mol⁻¹ /RT] s⁻¹ (1050–1300 K).