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Austin C, Purohit AL, Thomsen C, Pinkard BR, Strathmann TJ, Novosselov IV. Hydrothermal Destruction and Defluorination of Trifluoroacetic Acid (TFA). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:8076-8085. [PMID: 38661729 DOI: 10.1021/acs.est.3c09404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Per- and polyfluoroalkyl substances (PFAS) have received increased attention due to their environmental prevalence and threat to public health. Trifluoroacetic acid (TFA) is an ultrashort-chain PFAS and the simplest perfluorocarboxylic acid (PFCA). While the US EPA does not currently regulate TFA, its chemical similarity to other PFCAs and its simple molecular structure make it a suitable model compound for studying the transformation of PFAS. We show that hydrothermal processing in compressed liquid water transforms TFA at relatively mild conditions (T = 150-250 °C, P < 30 MPa), initially yielding gaseous products, such as CHF3 and CO2, that naturally aspirate from the solution. Alkali amendment (e.g., NaOH) promotes the mineralization of CHF3, yielding dissolved fluoride, formate, and carbonate species as final products. Fluorine and carbon balances are closed using Raman spectroscopy and fluoride ion selective electrode measurements for experiments performed at alkaline conditions, where gas yields are negligible. Qualitative FTIR gas analysis allows for establishing the transformation pathways; however, the F-balance could not be quantitatively closed for experiments without NaOH amendment. The kinetics of TFA transformation under hydrothermal conditions are measured, showing little to no dependency on NaOH concentration, indicating that the thermal decarboxylation is a rate-limiting step. A proposed TFA transformation mechanism motivates additional work to generalize the hydrothermal reaction pathways to other PFCAs.
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Affiliation(s)
- Conrad Austin
- Mechanical Engineering Department, University of Washington, Seattle, Washington 98195, United States
- Aquagga, Inc., Tacoma, Washington 98402, United States
| | - Anmol L Purohit
- Mechanical Engineering Department, University of Washington, Seattle, Washington 98195, United States
| | - Cody Thomsen
- Mechanical Engineering Department, University of Washington, Seattle, Washington 98195, United States
- Aquagga, Inc., Tacoma, Washington 98402, United States
| | - Brian R Pinkard
- Mechanical Engineering Department, University of Washington, Seattle, Washington 98195, United States
- Aquagga, Inc., Tacoma, Washington 98402, United States
| | - Timothy J Strathmann
- Civil and Environmental Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Igor V Novosselov
- Mechanical Engineering Department, University of Washington, Seattle, Washington 98195, United States
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Savage N. How to take 'forever' out of forever chemicals. Nature 2023:10.1038/d41586-023-03876-9. [PMID: 38097794 DOI: 10.1038/d41586-023-03876-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
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