Thermal Destruction Pathways and Kinetics for NTf2 and Longer-Chain Bis(perfluoroalkanesulfonyl)imides (Bis-FASIs)

A growing number of recent studies have reported the global environmental occurrence of bis(perfluoroalkanesulfonyl)imides (bis-FASIs). While shorter-chain bis-FASIs such as NTf2 (aka bis(trifluoromethanesulfonyl)imide or bistriflimide) are often tied to the battery and energy sectors, aqueous film-forming foams may be potential sources of longer-chain bis-FASIs. As remediation technologies for the destruction of these persistent per- and polyfluoroalkyl substances (PFAS) are urgently needed but have not yet been identified, we investigated the effectiveness of incineration using quantum chemical calculations. At temperatures of around 600 °C, the parent bis-FASIs readily decompose through carbon–sulfur bond cleavage and to a minor extent through nitrogen–sulfur bond cleavage. However, mineralization of the released perfluoroalkyl substituent to HF and CO2 only proceeds at >900 °C. Temperature requirements slightly increase with perfluoroalkyl chain length due to the time required to break additional C–C bonds. Under conditions and temperatures ≥1000 °C typical for secondary combustion units in hazardous waste incinerators, complete thermal destruction of bis-FASIs is viable given all other process variables are optimized. The same may not be true for thermal treatment technologies operating at lower gas-phase temperatures unless catalytic effects lower activation barriers.