(44n) Process Design and Mechanistic Modeling of the per- and Poly-Fluoroalkyl Substances (PFAS) Produced from the Thermal Degradation of Fluoropolymers

Patrick B. Dawson, Augustine H. Kim, Joseph D. Taptich¹, Juan D. Lucero, Tessy S. Ritchie¹, Victor A. Jaffett¹, Bryan A. Lagasse¹, Matthew L. Gettings¹, Simuck F. Yuk¹, Pamela L Sheehan², Enoch A. Nagelli¹

¹Department of Chemistry & Life Science, United States Military Academy, West Point, New York 10996

²U.S. Army Combat Capabilities Development Command, Explosive Ordnance Disposal, Demilitarization & Experimental Directorate, Army Futures Command, CCDC-AC, Picatinny Arsenal, New Jersey 07806

ABSTRACT

Per- and polyfluoroalkyl substances (PFAS) are primarily composed of fluoropolymers that have a high resistance to breakdown which allows for high versatility in everyday use but causes these substances to be problematic when disposing them. [1] The Environmental Protection Agency (EPA) is pursuing research that is related to PFAS waste streams when disposed through incineration. [2] This technique disposes of chemicals by combustion at high temperatures, upwards of 1000 to 1400 °C. Recently, the EPA expanded its Contaminant Candidate List to include several PFAS subtypes with thousands of distinct chemicals towards identifying additional PFAS that could potentially require future regulation under the Safe Drinking Water Act. [3] In our study, we are looking at the thermal degradation of polytetrafluoroethylene (PTFE) and neat polymers hexafluoropropylene (HFP) and polyvinylidene fluoride (PVDF) through process modeling in Aspen Plus. The thermal degradation process modeled in a Gibbs Reactor in atmospheric combustion conditions with varying oxygen flowrates and temperatures, ranging in temperatures of 250 to 1000 °C. The process feed stream to study the breakdown of PTFE is modeled as its constituent monomers which include HFP, perfluorobutyl ethylene (PFBE), chlorotrifluoroethylene (CTFE), and perfluoropropyl vinyl ethers (PPVEs) reacting with varying air flow rates of stoichiometric oxygen (­O₂) and nitrogen (N₂). Thermogravimetric analysis shows the degradation of PTFE initiates around 260 °C while the significant degradation occurs between 550 °C to 600 °C. [4] In addition, Density Functional Theory (DFT) calculations were also used to gain additional mechanistic understandings on the thermal degradation of relevant fluoropolymer structures. Overall, we aim to determine the type and concentration of PFAS products formed during combustion.

KEYWORDS: Per- and polyfluoroalkyl substances (PFAS), Fluoropolymers, Thermal Degradation Analysis, Combustion, Process Design, Aspen Plus, CHEMCAD.

CONTACT: Dr. Enoch A. Nagelli, Dept of Chemistry and Life Science, United States Military Academy, West Point, New York 10996. Email: enoch.nagelli@westpoint.edu TEL: 845-938-3904.

REFERENCES:

1. Kotthoff, M., Müller, J., Jürling, H., Schlummer, M., & Fiedler, D. (2015). Perfluoroalkyl and polyfluoroalkyl substances in consumer products. Environmental science and pollution research international, 22(19), 14546–14559. https://doi.org/10.1007/s11356-015-4202-7

2. S. Environmental Protection Agency. (2020, February). Per- and Polyfluoroalkyl Substances (PFAS): Incineration to Manage PFAS Waste Streams. https://www.epa.gov/sites/default/files/2019 09/documents/technical_brief_pfas_incineration_ioaa_approved_final_july_2019.pdf

3. S. Environmental Protection Agency. (2022, October). EPA Issues Final List of Contaminants for Potential Regulatory Consideration in Drinking Water, Significantly Increases PFAS Chemicals for Reviewhttps://www.epa.gov/ccl/contaminant-candidate-list-5-ccl-5

4. Ochi, Keiji. Kawano, Masahide. Matsuda, Muneaki. & Morita, Masatosi. (2008). Thermal Degradation Products of Polytetrafluoroethylene (PTFE) Under Atmospheric Condition. Department of Environmental Conservation, Ehime University, Tarumi 3-5-7, Matsuyama, Ehime 790-8566, Japan. https://docslib.org/doc/10173165/thermal-degradation-products-of-polytet...