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Determining Thermal Stability and Degradation of Neat and Adsorbed Perfluoroalkyl Substances using Hyphenated TGA-FTIR-GC-MS
Citation:
Mezgebe, B., A. Tegenaw, AND E. Sahle-Demessie. Determining Thermal Stability and Degradation of Neat and Adsorbed Perfluoroalkyl Substances using Hyphenated TGA-FTIR-GC-MS. Presented at American Chemical Society (ACS) Fall 2023 - Meeting, San Francisco, CA, August 13 - 17, 2023.
Impact/Purpose:
This study aims to improve our understanding of the thermal stability of selected per- and poly-fluoroalkyl substances (PFAS) and afford insight into their decomposition mechanism on carbon and polymer-based spent adsorbents during regeneration. Thermal treatment is routinely used to reactivate the spent granular activated carbon (GAC) from water purification facilities. Hence, the study also investigates the decomposition mechanisms of spent GAC during thermal reactivation.
Description:
This project aims to improve our understanding of the thermal stability of selected per- and poly-fluoroalkyl substances (PFAS) and afford insight into their decomposition mechanism on carbon and polymer-based spent adsorbents during regeneration. The study also includes thermogravimetric analysis of PFAS-contaminated bio-solids. A hyphenated system of TGA-FTIR-GC-MS was used to study the evaporation and degradation properties of PFAS. We studied three perfluoroalkyl carboxylic acids (PFCAs), three perfluoroalkyl sulfonic acids (PFSAs), and hexafluoropropylene oxide (HFPO) dimer acid (GenX) in oxidative anoxic atmospheres. The study includes thermal desorption and degradation kinetics. We studied the role of carbon chain length (NCF2) and polar heads of PFAS on their desorption and thermal decomposition. PFAS with high affinity for adsorption, such as perfluorooctanesulfonic acid (PFOS), required higher temperatures to desorb. Online FTIR is used to detect volatile organ0ifluorine species. The gas composition from the emitted flue gas of TGA suggests that PFAS evaporates at lower temperatures than from the adsorbent. We demonstrated that the hyphenated method is robust in obtaining thermal decomposition pathways in fluorinated organic compounds.