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.