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.