Study on thermal decomposition properties and its decomposition mechanism of pentafluoroethane (HFC-125) fire extinguishing agent

• A combination of two-approach study for thermal decomposition of pentafluoroethane.
• A possible decomposition mechanism is proposed.
• The mechanism relies on stabilization changes of reaction energies and barriers.
• Strictly confirm gas products with different pyrolysis temperature.

This paper investigates the thermal decomposition properties of pentafluoroethane (HFC-125) fire extinguishing agent, which is regard as the ideal replacement of HCFC and PFC, due to its good environmental performance and low-toxicity, on the pyrolysis properties within 600–850 °C, although the physical-chemical properties and extinguishing characteristics of HFC-125 have been widely reported, its decomposition mechanism is still unclear. With the help of analysis methods of gas chromatography (GC), ion chromatography (IC), gas chromatography–mass spectrometry (GC–MS) together with theoretical calculation, thermal decomposition details of HFC-125 is investigated, as well as possible thermal decomposition mechanism. The results show that the pyrolysis of HFC-125 occurs above 700 °C, the exhaust of HFC-125 pyrolysis products mainly contains CF2 = CFCF3, CHF3, CF2 = CF2, CF3CHCF2, HF, CF2 = C(CF3)2 and the component concentrations vary with pyrolysis temperature and residence time. What’s more, a possible decomposition mechanism is also proposed, according to the activation energy of being calculated by using the first order reaction kinetics model and the detail dissociation pathways and gaseous products are deduced using the density functional theory. By combining the experimental results and theoretical calculation, characteristics involved in the decomposition of HFC-125 are given for the first time. It is expected that these investigation results would be of great help to the further study of the fire suppression of HFC-125.

By combining the experimental results and theoretical calculation, it is expected to reveal the possible thermal decomposition process as well as its decomposition mechanism of HFC-125, accompanying with the release of HF gas.Figure optionsDownload as PowerPoint slide