Thermal Decomposition of Perfluorooctanesulfonic Acid (PFOS) in the Presence of Water Vapor

The thermal decomposition of perfluorooctanesulfonic acid (PFOS) was studied in an α-alumina reactor between 500 and 1000 °C using helium as a carrier gas. In addition to He carrier gas and between 150 and 300 ppm of PFOS, the effect of water vapor (H2O(g)) at two different concentrations (1700 and 10,000 ppm) on the reaction was examined. The main products, at both 1700 and 10,000 ppm of H2O(g), were HF, C2F4, CO, and SO2. Moreover, as the reaction temperature increased, an increase in the concentration of HF and CO was observed, concomitant with a decrease in the fluorocarbon concentration. Additionally, the α-alumina reactor was observed to have reduced surface activity in the presence of water vapor. Quantum chemical calculations, performed at the G4MP2 level of theory combined with a chemical kinetic model, were used to understand the influence that water vapor and OH radicals have on the CF2 and CF3 radicals that are present. It was found that at temperatures above 850 °C in 10,000 ppm of water vapor, there is a substantial decrease in the fluorocarbon concentration.