Computational Investigation of the Reaction Mechanism for the Thermal Treatment of Hexafluoropropylene Oxide Dimer Acid (GenX)

Hexafluoropropylene oxide dimer acid (HFPO-DA, C₃F₇OCF(CF₃)C(O)OH), more commonly referred to as GenX, belongs to a category of environmental contaminants known as poly- and perfluoroalkyl substances. A detailed chemical kinetic mechanism was developed for the thermal destruction of GenX. The rate constants for the majority of the elementary reactions were computed using microcanonical rate theory and the master equation. Additional rate constants were obtained using an automatic reaction mechanism generator, RMG. The mechanism was used to predict the various destruction products in two different reactor configurations: an isothermal batch reactor and a nonisothermal plug flow reactor. For the isothermal batch reactor, the impact of temperature and humidity was evaluated. The detailed simulations predict that GenX decomposes unimolecularly to C₃ and C₂ perfluoroaldehydes (C₂F₅CFO and CF₃CFO). Water was critical to the decomposition of C₂F₅CFO and CF₃CFO in the low-temperature furnace model (650 °C), where unimolecular pathways were slow. The ultimate decomposition byproducts were hydrogen fluoride (HF) and carbonyl fluoride (CF₂O). GenX mineralization can be achieved in the presence of water through the water-catalyzed hydrolysis of CF₂O, resulting in the formation of CO₂ and HF.