Per- and polyfluoroalkyl substances (PFAS) are of concern because of their wide distribution in the environment and potential health risks to humans and animals. Thermal treatment is a commonly used current technology that is thought to be promising in destroying PFAS completely. Thermal treatment of PFAS is used in the reactivation of granular activated carbon (GAC), processing of biosolids, and soil remediation, with pyrolysis (in the absence of oxygen) being mostly used. PFAS can be well removed (&gt;99%) during pyrolysis, and parts of fluorine can be mineralized into inorganic fluoride. However, the fluorine mass balance is rarely achieved during PFAS pyrolysis, indicating gaseous and condensed PFAS formations, which may cause secondary contamination. To understand the overlooked gaseous product formations, we used simultaneous thermal analyzer (STA) coupled with mass spectrometry (MS) and FTIR spectroscopy to help identify the key reactions and their conditions. LC-MS was used to analyze condensed products. During pyrolysis of (perfluorooctanesulfonic acid) PFOS and (perfluorobutane sulfonic acid) PFBS, at least 5 key reactions, 5 fluorinated organics, and some inorganic products at temperatures below 1,100 degrees Celsius were observed. Quantum chemical calculations were used to elucidate PFAS pyrolysis mechanisms. Identified products and computational studies were combined to explain the thermal decomposition pathways and kinetics. This study has implications that PFAS pyrolysis needs further attention for the control of gaseous and condensed PFAS.

Thermal decomposition of two perfluoroalkyl sulfonic acids: Gaseous and condensed product formations and mechanisms

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