Incineration of the ultrashort-chain PFAS trifluoroacetic acid: Reactor surface impacts on the evolution of transient decomposition and recombination intermediates

TFA and DFA decompose via HF loss starting from 200 °C. • Alumina surfaces enhance the thermal mineralization of TFA. • Alumina surfaces promote CF 2 recombination to C 2 F 4 and perfluorocyclopropane as PIDs. • Hydrogenation of TFA reduces persistent intermediates formation. • Perfluorocyclopropane may serve as an indicator of surface-mediated PIDs. While thermal destruction remains one of the most effective treatments for ultrashort-chain per- and polyfluoroalkyl substances (PFAS) such as trifluoroacetic acid (TFA) at full scale, their evolution during incineration processes remains poorly understood, particularly those promoted by material surfaces in contact with the PFAS stream. Here we resolve the intrinsic and surface-mediated mechanisms of the pyrolysis of TFA and its non-PFAS analogue difluoroacetic acid (DFA) using synchrotron vacuum-ultraviolet photoionization mass spectrometry. Both compounds decompose primarily via HF elimination followed by decarboxylation or decarbonylation. Surprisingly, alumina surfaces facilitate the elimination of HF from TFA, but promote the formation of tetrafluoroethylene and perfluorocyclopropane as products of incomplete destruction (PIDs) from a bottom-up growth of CF 2 . These findings suggest that perfluorocyclopropane may serve as a promising indicator of surface-catalyzed recombination reactions during full-scale incineration. In contrast, DFA generates hydrogen-containing intermediates that undergo rapid secondary reactions, suppressing the formation of PIDs and enhancing overall incinerability. Our findings provide benchmark mechanistic insight into ultrashort-chain PFAS decomposition and call for systematic evaluation of surface effects that promote PID formation. Download: Download high-res image (116KB) Download: Download full-size image