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Thermal treatment of hexafluoropropylene oxide dimer acid (HFPO-DA) using a pilot-scale research combustor
Citation:
Weber, N., G. West, W. Roberson, J. Mackie, J. Mattila, P. Burnette, M. Allen, W. Preston, Bill Linak, AND J. Krug. Thermal treatment of hexafluoropropylene oxide dimer acid (HFPO-DA) using a pilot-scale research combustor. JOURNAL OF HAZARDOUS MATERIALS. Elsevier Science Ltd, New York, NY, 495:0, (2025). https://doi.org/10.1016/j.jhazmat.2025.138905
Impact/Purpose:
Hexafluoropropylene oxide dimer acid (HFPO-DA) is a commonly found environmental contaminant. HFPO-DA is likely to encounter high temperature combustion conditions during remedial action involving hazardous waste incineration (HWI) and municipal waste combustors. However, little is known about HFPO-DA’s behavior in combustion environments. Using two aqueous HFPO-DA solutions injected in the pilot-scale ‘Rainbow furnace’, insights into the destruction and formation of products of incomplete combustion (PICs) have been found. Near combustion blank concentrations of HFPO-DA were measured along with DEs >99.99% for all experimental conditions examined. However, significant quantities of both polar and non-polar volatile fluorocarbon PICs were observed. This suggests that DE alone might be insufficient in determining the effectiveness of thermal treatment HFPO-DA and the measurement of PICs is needed. The total PIC concentration was found to decrease with higher temperatures signifying that temperature is key to high DEs and limited PIC formation.
Description:
The thermal decomposition of single-component aqueous solutions of hexafluoropropylene oxide dimer acid (HFPO-DA), a “GenX” process chemical, was investigated in a pilot-scale research combustor. Two solutions containing target HFPO-DA concentrations of ~500 and 4000 mg/L were atomized at three post-flame temperatures of ~920, 860, and 750 °C, during which the stack gases were characterized for combustion products including fluorocarbon products of incomplete combustion (PICs). Analytical techniques included Other Test Method 50 (OTM-50) and real-time analysis using Fourier transform infrared spectroscopy (FTIR) and chemical ionization mass spectrometry (CIMS). Quantum chemical calculations were performed to identify pathways for the thermal decomposition of HFPO-DA. Identified PICs included 1H-perfluoroalkanes, fluoroether E-1 (heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether), and two ultra short-chain perfluorocarboxylic acids (PFCAs): trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA). Most PIC concentrations increased with decreasing peak temperatures with ~40-60% of the fluorine in the HFPO-DA converted into PICs at the lowest peak temperature examined (~750 °C). At higher peak temperatures, lower PIC concentrations were observed, suggesting that temperature is a critical parameter for mineralization. Modeling results proposed that the thermal decomposition of HFPO-DA can pass through 1,1,1,2,2,3,3-heptafluoro-3-[(1,2,2-trifluoroethenyl)oxy]propane (perfluoropropylvinyl ether, or PPVE) or fluoroether E-1 intermediate species with the PPVE route offering lower energy barriers.
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DOI: Thermal treatment of hexafluoropropylene oxide dimer acid (HFPO-DA) using a pilot-scale research combustor