A Kinetic Study of the Inhibition Mechanism of Hexafluoropropylene (HFP) on Hydrogen Combustion.

Hexafluoropropylene (HFP) is used as an advanced fire extinguishing agent with high thermal stability, excellent fire suppression performance, and environmentally friendly characteristics. In this study, the inhibition mechanism of HFP during H2 combustion was analyzed, focusing on its reaction behavior with H and OH radicals to verify its interruption of the combustion chain reaction by scavenging key reactive radicals. The unimolecular pyrolysis process of HFP was investigated to characterize the heat absorption effect when it dissociates into small molecular fragments. The gas-phase kinetic properties of the proposed reaction pathway were analyzed by combining high-level quantum chemical calculations with the RRKM/master equation. The results show that the unimolecular dissociation reaction of HFP has a significant rate difference at low temperatures, but this difference gradually decreases with increasing temperature. In the substitution reaction pathway, the reaction rates of HFP with H and OH were much higher than those of H-abstraction, suggesting that it has an important influence in inhibiting H2 combustion. In addition, the addition reaction of HFP with H and OH also plays a key role in inhibiting combustion at low temperatures due to the presence of CC double bonds in the molecule. It is particularly noteworthy that the rate of the addition reaction of HFP with H increases significantly with increasing temperature, while the rate of the addition reaction with OH is lower than that of the former at high temperatures. The present study lays a data foundation for the establishment of a more accurate kinetic mechanism of combustion inhibition, which is of great significance for the design of new flame retardants.