Thermal Mineralization of Perfluorooctanesulfonic Acid (PFOS) to HF, CO₂, and SO₂

Abstract

Utilizing air (O2) as the bath gas at reaction temperatures between 500 and 1000 °C, the thermal decomposition of perfluorooctanesulfonic acid (PFOS) in an α-alumina reactor was studied. It was found that in an air bath gas (and in the absence of water vapor), COF2 and trace amounts of C2F4 were detected. Quantum chemical calculations at the G4MP2 level of theory confirmed that CF2 radicals can react with O2 to form COF2 and an O (3P) atom. The inclusion of 2000 or 20 000 ppmv of water vapor (H2O(g)) to the air bath gas proved to be the key step to mineralizing all PFOS into hydrogen fluoride (HF), CO2, and SO2. At temperatures above 850 °C (0.95–0.84 s residence time), a feed of 20 000 ppmv of H2O(g) in air was observed to produce a product stream in which no gaseous fluorocarbon products were detected, with only HF, SO2, and CO2 being produced. A sulfur balance confirmed that 100 ± 5% of all the S in PFOS had converted into SO2 with a chemical kinetic model predicting in excess of 99.99999% destruction removal efficiency of PFOS at temperatures above 700 °C. Furthermore, from an elementary balance of F and C atoms, it was determined that at 1000 °C, approximately 99 ± 5% of F atoms present in PFOS have been converted into HF, and approximately 100 ± 5% of C atoms had been converted into CO2. A chemical kinetic model was developed to understand the importance of both O2 and water vapor in the overall thermal decomposition of PFOS, leading to complete mineralization. In the presence of both O2 and H2O(g), it was found that relatively high concentrations of OH radicals were produced, with significant contribution to OH formation attributed to the well-known chain branching reaction O(3P) + H2O → OH + OH.

Pilot-Scale Thermal Destruction of Per- and Polyfluoroalkyl Substances in a Legacy Aqueous Film Forming Foam

“…Note that similar results have been both experimentally and computationally derived under pyrolytic and oxidative conditions. Thermolysis often yields 1 H -perfluorocarbons and 1-perfluoroalkenes with PFCAs, − ,,, with PFSAs forming the same compounds as well as perfluorocarbons. , Computational studies predict similar products − , using various computational methods. All the referenced models have a lactone or sulfone intermediate with HF elimination as the first step to the loss of the functional group.…”

High temperature behaviour of Ag-exchanged Y zeolites used for PFAS sequestration from water

“…Thermal decomposition of perfluorooctanesulfonic acid in air or under excess oxygen could produce COF 2 , SO 2 , CO 2 , CO and HF above 600 °C. 51 As reported by Wang et al , 52 the PFAS fate can be adequately assessed by using analytical techniques able to close the F mass balance and measure the total fluorine ( i.e. CIC, PIGE, NMR, INAA).…”

Characterizing Volatile Emissions and Combustion Byproducts from Aqueous Film-Forming Foams Using Online Chemical Ionization Mass Spectrometry

“…Thus, we speculate SiH 2 F 2 O 2 We detected sulfur oxides (SO x ) in the AFFF combustion emissions (Figure 1d), likely arising from the thermal oxidation of sulfur-containing functional groups of legacy and contemporary AFFFs. 51 For instance, the legacy 3M formulation primarily consists of PFOS and other PFSA surfactants. Contemporary AFFF formulations commonly utilize sulfurcontaining fluorotelomer surfactants, including FTABs and FTSASs.…”

“…For instance, thermal decomposition of PFOS is initiated by loss of the sulfonate headgroup (following an initial elimination of HF) to yield sulfur dioxide (SO 2 ) or sulfur trioxide (SO 3 ). 51,56 Liberated SO 2 may also oxidize to SO 3 under postflame conditions. 61 Emissions of SO x into the atmosphere contributes to acid deposition and sulfate aerosol production and may detrimentally harm climate and human health.…”

“…Generally, these emissions increased substantially with decreasing peak injection temperature (∼820 to ∼760 °C), likely corresponding to less efficient thermal transformation of fluorinated precursors within the AFFF solutions . This trend was mirrored by relatively lower yields of HF in lower temperature injection ports with diminished mineralization of PFAS within the furnace (Figure c). ,, We focus only on gaseous emissions here but acknowledge the possibility of particulate matter formation during these combustion processes. Exploration of particulate products from AFFF incineration therefore warrants a future study.…”