Kinetics of Decomposition of PFOS Relevant to Thermal Desorption Remediation of Soils

Kinetics of pyrolysis of the pollutant perfluorooctane-sulfonic acid (PFOS) in inert bath gases have been studied in two flow reactors constructed of α-alumina and of stainless steel (SS) at temperatures between 400 and 615 °C. Results from the SS reactor give support to previous and our own quantum chemical calculations based on smaller perfluorinated sulfonates, according to which initiation of decomposition of PFOS first takes place by elimination of HF to form an unstable α-sultone with a rate constant, k1. The sultone then rapidly liberates SO 2 and forms perfluorooctanoyl fluoride with a rate constant, k2 with k2 ≫ k1 such that the overall rate constant k′ ≈ k1. Products observed from both reactors in the above temperature range comprised HF, SO2 , and perfluorooctanoyl fluoride. The value of the rate constant for the formation of HF and SO 2 measured in the SS reactor was found to be k1 = (1.3 ± 0.5) × 10 14 exp(−253 ± 5 kJ/mol/RT) s−1.