Kinetics of pyrolysis of the pollutant perfluorooctanesulfonic 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, k 1 . The sultone then rapidly liberates SO 2 and forms perfluorooctanoyl fluoride with a rate constant, k 2 with k 2 ≫ k 1 such that the overall rate constant k′ ≈ k 1 . Products observed from both reactors in the above temperature range comprised HF, SO 2 , 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 k 1 = (1.3 ± 0.5) × 10 14 exp(−253 ± 5 kJ/mol/RT) s −1 .

Pyrolysis of perfluorooctanesulfonic acid (PFOS) (200−450 PPMV) was studied in an α-alumina flow reactor under plug flow conditions at temperatures from 450 to 1000 °C and helium flow velocities of 100, 200, and 300 mL min −1 . Major products at the lowest temperatures were HF, SO 2 , and perfluorooctanyl fluoride (C 8 F 16 O). A new low-temperature product, C 2 F 4 , was detected in significant quantities from the decomposition of PFOS. The pyrolysis mechanism was studied by quantum chemical calculation at the b3lyp/GTLarge//b3lyp/6-31G(d,p) and G4MP2 levels of theory to develop a thermochemical analysis and preliminary chemical kinetic model for the decomposition. Alongside the previously postulated initiation of pyrolysis via an α-sultone intermediate to C 8 F 16 O, we have discovered a competitive direct fission route for PFOS into C 8 F 17 radicals and HOSO 2 . C 8 F 17 rapidly fissions CF 2 radicals, which are the source of the observed C 2 F 4 . At the lowest temperatures, an acceleration in the rates of production of C 2 F 4 , HF, and SO 2 was observed in the α-alumina reactor when compared with predictions of the kinetic model. An alumina nanocluster was subjected to quantum chemical analysis to show that PFOS can be both chemisorbed and physisorbed on an alumina surface, a process that might explain the experimental observation of an acceleration of decomposition in an α-alumina reactor at low temperatures.

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Chlorpyrifos (CPF) is a widely used pesticide; however, limited experimental work has been completed on its thermal decomposition. CPF is known to decompose into 3,5,6-trichloro-2-pyridinol (TCpyol) together with ethylene and...