Detection of volatile hydroperfluoroalkanes during hydrothermal liquefaction of perfluoroalkyl carboxylic acids at circumneutral pH

TY - JOUR

T1 - Detection of volatile hydroperfluoroalkanes during hydrothermal liquefaction of perfluoroalkyl carboxylic acids at circumneutral pH

AU - Wen, Junying

AU - Neha, Shukla

AU - Biller, Patrick

AU - Kristensen, Kasper

AU - Vergeynst, Leendert

N1 - Publisher Copyright: © 2024 The Authors

PY - 2024/9

Y1 - 2024/9

N2 - Hydrothermal liquefaction (HTL) is a promising technology for converting wet organic waste such as sewage sludge into biocrude oil while simultaneously destroying per- and polyfluoroalkyl substances (PFAS). This study tracked the fate and degradation of six representative PFAS in water to address the effect of perfluoroalkyl chain length on degradation rates and the formation of volatile transformation products at 300–350 °C. While perfluorosulfonic acids were recalcitrant, perfluoroalkyl carboxylic acids (PFCAs) were rapidly and completely decarboxylated to hydroperfluoroalkanes (1 H-perfluoroheptane in the case of perfluorooctanoic acid). The volatile hydroperfluoroalkane was subsequently defluorinated without detectable fluorocarbon intermediates yielding 30–60 % defluorination for ammonium perfluoro(2-methyl-3-oxahexanoate), perfluorobutanoic acid and perfluorooctanoic acid after 2 h at 350 °C. Increasing temperature (especially at 350 °C) and longer perfluoroalkyl chains substantially enhanced the defluorination. This is the first study to report volatile hydroperfluoroalkanes from PFCAs in HTL, raising concern about the potential emission of long-lived greenhouse gasses into the atmosphere, but also opening new avenues for PFAS destruction through HTL.

AB - Hydrothermal liquefaction (HTL) is a promising technology for converting wet organic waste such as sewage sludge into biocrude oil while simultaneously destroying per- and polyfluoroalkyl substances (PFAS). This study tracked the fate and degradation of six representative PFAS in water to address the effect of perfluoroalkyl chain length on degradation rates and the formation of volatile transformation products at 300–350 °C. While perfluorosulfonic acids were recalcitrant, perfluoroalkyl carboxylic acids (PFCAs) were rapidly and completely decarboxylated to hydroperfluoroalkanes (1 H-perfluoroheptane in the case of perfluorooctanoic acid). The volatile hydroperfluoroalkane was subsequently defluorinated without detectable fluorocarbon intermediates yielding 30–60 % defluorination for ammonium perfluoro(2-methyl-3-oxahexanoate), perfluorobutanoic acid and perfluorooctanoic acid after 2 h at 350 °C. Increasing temperature (especially at 350 °C) and longer perfluoroalkyl chains substantially enhanced the defluorination. This is the first study to report volatile hydroperfluoroalkanes from PFCAs in HTL, raising concern about the potential emission of long-lived greenhouse gasses into the atmosphere, but also opening new avenues for PFAS destruction through HTL.

KW - 1 H-perfluoroheptane

KW - Defluorination

KW - Fluorine balance

KW - PFAS

KW - Poly- and perfluorinated alkyl substances

UR - http://www.scopus.com/inward/record.url?scp=85196261498&partnerID=8YFLogxK

U2 - 10.1016/j.jhazmat.2024.134955

DO - 10.1016/j.jhazmat.2024.134955

M3 - Journal article

C2 - 38901253

AN - SCOPUS:85196261498

SN - 0304-3894

VL - 476

JO - Journal of Hazardous Materials

JF - Journal of Hazardous Materials

M1 - 134955

ER -