Incineration of Perfluorooctanoic Acid Leads to Regeneration of Smaller Perfluorocarboxylic Acids

Perfluorooctanoic acid (PFOA) and other per and polyfluorinated alkyl substances (PFAS) are emerging environmental contaminants of concern. Incineration is a common method of PFAS destruction and disposal, but due to the strength and stability of C-F chemical bonds, the process is poorly understood. In the present work, we demonstrate that destruction of PFOA in a pilot-scale incinerator leads to a mixture of smaller perfluorocarboxylic acids (PFCAs). We use chemical ionization mass spectrometry to measure the concentration of PFCAs ranging from C2 to C9. The actual yield of PFCAs depends upon the location of PFOA injection and thus upon the peak temperature experienced within the furnace. A chemical kinetic mechanism is developed to explain the results. Two different pathways are considered: a low-temperature pathway that proceeds through a short-lived α-lactone intermediate and a high-temperature pathway that proceeds through cleaving a C-C bond in the alkyl backbone. Theoretical modeling of PFOA incineration at peak temperatures of ∼1130 and ∼1020 K predicts the formation of trifluoroacetic acid and other small PFCAs.