Thermal degradation of perfluorooctanoic acid (PFOA)

Per - and polyfluoroalkyl substances (PFAS) are a group of environmental contaminants, that are dispersed throughout the world. A number of areas have been affected by their persistence and biomagnification. PFAS remediation of contaminated material requires extensive knowledge of the species involved. A method to simplify the study of the thermal degradation of PFAS is presented in this paper, providing a solution to experimental and analytical challenges. A three-zone furnace allowed manipulation of both reaction temperature and gas flowrate (and consequently residence time). The PFAS compound could be charged and vaporised in a separate zone. Adopting this experimental methodology, a kinetic model describing the decomposition of the PFAS can be devised. When reacting under an inert nitrogen atmosphere, perfluorooctanoic acid (PFOA) degraded at temperatures above 450 °C. The products observed were found to be hydrofluoric acid (HF) and carbon dioxide (CO2), along with a perfluoro-1-heptene species. Additional products of 1H-perfluorohexane or 1H-perfluoroheptane were also observed when residence times were increased. The effect of water vapour was also investigated, with similar behaviour to pyrolysis being observed, where a significantly higher concentration of HF was detected under otherwise similar reaction conditions. These preliminary results suggest water vapour accelerates the rate of PFAS decomposition.