A kinetic study of the inhibition mechanism of HFC-227ea on hydrogen combustion

Abstract

HFC-227ea (2H-Heptafluoropropane, CF3CHFCF3) shows promise as an alternative to halon for fire suppression. This study delves into the inhibition mechanism of HFC-227ea on hydrogen combustion. The reactions of HFC-227ea with H and OH were investigated to demonstrate the ability of this inhibitor to chemically scavenge these two key radicals. The unimolecular decomposition chemistry of HFC-227ea was explored to characterize the endothermic effect resulting from its dissociation into smaller fragments. High-level quantum chemical calculations and RRKM/master-equation analysis were combined to predict gas-phase kinetics of the proposed reaction pathways. For H and OH radical scavenging, the reaction process primarily proceeds via H abstraction from the central carbon of HFC-227ea, whereas F abstraction is rather difficult due to the inert and unreactive nature of C-F bond. For initial pyrolysis of HFC-227ea, ten decomposition channels were proposed, and kinetic parameters were obtained within a wide range of temperature and pressure. The findings indicate that at atmospheric pressure the CC bond fission is the dominant pathway above 1050 K, and 1,2-HF elimination becomes more important below 1050 K. By incorporating the new rate constants of the proposed reaction pathways into C1-C3 fluorinated hydrocarbon combustion mechanism, a chemical kinetic model was developed to illustrate the inhibition effect of HFC-227ea on hydrogen combustion. Simulation results suggest that HFC-227ea initially inhibits hydrogen combustion by consuming H and OH radicals, with the CC bond fission playing a minor role. Subsequent processes will be governed by the interplay of chemical and physical inhibiting effects of the generated products. The present study offers valuable insights for the design and evaluation of fire extinguishing agents.