(10f) Modeling Incineration of Perfluorooctanoic Acid (PFOA) to Produce Shortened-Chain Perfluoro Carboxylic Acids (PFCAs) Using Reaction Mechanism Generator (RMG)

Poly- and perfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) are environmental contaminants. PFOA was used in aqueous film forming foam (AFFF) agents, waterproofing/oil-proofing, and as an industrial solvent/lubricant before being phased out due to health concerns. During the incineration of PFOA in EPA’s Rainbow Furnace, the formation of shortened-chain perfluorocarboxylic acids (PFCAs) was observed.

There are two possible reaction pathways for PFOA conversion to shortened-chain PFCAs; a low temperature pathway (<1000°C) and high temperature pathway (>1000°C). The low temperature pathway is initiated by HF elimination of PFOA to form an alpha-lactone which undergoes CO elimination to form an aldehyde. The aldehyde reacts with water to form a PFCA and HF. In the high temperature pathway, PFOA undergoes C-C bond dissociation followed by disproportionation between the alkyl radical and carboxylic acid radical resulting in an alkene and a PFCA. Previously, a model of EPA’s Rainbow Furnace was compared against experimental results and showed that a combination of the low temperature and high temperature pathways accounted for the overall trend of PFOA conversion to shortened-chain PFCAs but did not account for full destruction of PFOA.

Reaction Mechanism Generator (RMG) was used to construct a comprehensive mechanism for PFOA incineration that accounts for the conversion to shortened-chain PFCAs along with other relevant reactions. Elementary PFAS reactions were implemented in RMG as training data in order to create new reaction families and update existing reaction families. New reaction families include HF elimination of PFCAs, CO/COâ‚‚ elimination of alpha-lactones, and water substitution. The RMG-generated mechanism will be compared against experimental results to assess if a complete mechanism for PFOA incineration is achieved and to determine if RMG can be confidently used as a tool for PFAS simulations after the implementation of PFAS training reactions.