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Per- and Polyfluoroalkyl Substances
Published in Caitlin H. Bell, Margaret Gentile, Erica Kalve, Ian Ross, John Horst, Suthan Suthersan, Emerging Contaminants Handbook, 2019
Ian Ross, Erica Kalve, Jeff McDonough, Jake Hurst, Jonathan A L Miles, Tessa Pancras
Oligomerization has been reported to be one of the three manufacturing processes typically employed for the manufacture of PFASs (OECD 2018b). Oligomerziation is reported to produce highly branched oligomers through oligomerization of tetrafluoroethylene and can be controlled to yield short-chain compounds (Jarnberg et al. 2006). The process results in branched products—tetramer C8F16; pentamer C10F20; and hexamer C12F24—and these intermediates can be converted to other PFASs (Deem 1973; Jarnberg et al. 2006). Oligomerization using direct fluorination is also used in industrial processes to generate PFECAs and PFESAs through a polymerization reaction (Lagow and Inoue 1978; Costello and Moore 1988). Oligomerization is also used to process hexafluoropropylene oxide (HFPO) into a perfluoropolyether carbonyl fluoride that can be further converted into an acid, acid salt, ester, amide or alcohol such as the ammonium salt of HFPO-DA (Flynn et al. 2003).
Survey on the current leachate treatments of public municipal solid waste landfills and the potential impact of per- and polyfluorinatedalkyl substances in the Eastern and Northwestern United States
Published in Journal of the Air & Waste Management Association, 2023
Mert Gokgoz, Wuhuan Zhang, Nimna Manage, Mery Mbengue, Stephanie Bolyard, Jiannan Chen
Although there was an interim guidance document published by the United States Environmental Protection Agency (EPA) in 2021 for non-consumer products, as of the survey date, there were no regulations for PFASs concentrations in landfill leachate before discharge to the disposal facilities, nor are there regulations to manage the disposal and destruction of these molecules (EPA 2022). Some of the short-chain PFASs are considered to be potential source of contamination due to higher uptake than longer chains. Recently, EPA announced the proposed National Primary Drinking Water Regulation (NPDWR) for 6 PFAS, including PFOA (MCL = 4 ppt), perfluorooctane sulfonic acid (PFOS, MCL = 4 ppt), perfluorononanoic acid (PFNA, hazardous index = 1), hexafluoropropylene oxide dimer acid (HFPO-DA, hazardous index = 1), perfluorohexane sulfonic acid (PFHxS, hazardous index = 1), and perfluorobutane sulfonic acid (PFBS, hazardous index = 1) (EPA 2023). These lower limits could eventually impact the leachate discharge levels upstream of WWTPs, and such change could begin that affect leachate treatment decisions by landfills and impact the costs of landfill operations.
Experimental Study of Pool Boiling on Heaters with Nanomodified Surfaces under Saturation
Published in Heat Transfer Engineering, 2022
Sergey Khmel, Evgeniy Baranov, Victor Vladimirov, Alexey Safonov, Evgeny Chinnov
The HWCVD method and experimental setup are described in detail elsewhere [41]. The method consists of depositing fluoropolymer coatings from a precursor gas activated by a heated wire catalyst. The deposition of coatings was carried out as follows. Copper substrates were placed on a thermostatically controlled water-cooled substrate holder located in a vacuum chamber. The vacuum chamber was evacuated to a pressure of 0.13 Pa. Next, hexafluoropropylene oxide used as a precursor gas was supplied to the chamber. The precursor gas pressure was set at 67 Pa. Then, the Nichrome wire activator was heated with an electric current to a temperature of 680 °C. After that, the sliding gate was opened to start deposition. The deposition time was 10 min. The thickness of the coating was about 100 nm.
Fabrication of Hydrophobic Coated Tubes for Boiling Heat Transfer Enhancement
Published in Heat Transfer Engineering, 2021
Alexey I. Safonov, Denis V. Kuznetsov, Anton S. Surtaev
Fluoropolymer coatings were deposited onto the surface of the tubes by the HWCVD method [52–54]. The experimental setup for depositing coatings, described in detail in [55] was upgraded. The cooled substrate holder was replaced by a mechanism allowing for uniformly deposited coatings on rotating cylindrical surfaces. The conditions of the deposition process under which persistent hydrophobic fluoropolymer coatings are formed were determined. The parameters of the deposition process: the temperature of the nickel-chrome activator filament was 640 °C, the pressure of the hexafluoropropylene oxide (HFPO) precursor gas was 0.5 Torr, the distance from the activating filament to the tube surface was 70 mm, the deposition time was 600 minutes, and the tube rotation speed during deposition was 1 rpm.