(265e) Combustion Products from Thermal Treatment of Polymers Containing per- and Poly-Fluoroalkyl Substances

Combustion Products from Thermal Treatment of Polymers Containing Per- and Poly-fluoroalkyl Substances

Nathaniel J. Olsavsky¹, Victoria M. Kearns¹, Connor Beckman¹, Harry L. Moore Jr.¹, Preston C. Haney², Pamela L Sheehan², F. John Burpo¹, H. Daniel Bahaghighat^1*, Enoch A. Nagelli^1*

¹Department of Chemistry & Life Science, Chemical Engineering Program, 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

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals used in various commercial industries to include food packaging, non-stick repellent, and waterproof products [1]. The Environmental Protection Agency (EPA) is currently looking for ways to safely dispose of PFAS waste, to include incineration [1]. Incineration is a technique that disposes of chemicals by breaking down the chemicals at high temperatures, upwards of over 1000 °C to 1400 °C [1]. Incineration has been used on other related compounds, but PFAS present a challenge when attempting to breakdown due to the high electronegativity of fluorine [1]. Research on the efficacy of this method is currently limited, as it is unknown yet what happens when smaller PFAS are formed or when undesirable products form due to partial combustion [1]. At this time, research is being performed on a small scale, so another challenge will be to scale this process once a successful technique can be identified to safely dispose of PFAS waste. In our study, we analyze the combustion products for polymer gaskets made from polytetrafluorethylene (PTFE) known as TEFLON, vinylidene difluoride/hexafluoropropylene copolymer (Viton A, and Viton B) and polychlorotrifluoroethylene (Kel-F 800). Moreover, analytical tools are used to model the molecular thermal degradation products resulting from the combustion of highly fluorinated compounds. Our models will help understand the initial oxidation and combustion of the polymers themselves up to 200 °C together with the high temperature degradation (beyond 1000 °C) of the post-combustion products. Modeling the dynamic behavior using batch, semi-batch, and continuous reactors for the chemical decomposition of gas products, and heat- and mass-transfer involved in the processes in both oxidative and inert environments will help inform the reactor design needed for the incineration of the fluoropolymers within desired temperature ranges for combustion. Moreover, together with our modeling efforts, chemical characterization with Fourier-Transform Infrared Spectroscopy (FTIR) is used to identify differences in chemical functional groups within the polymers before and after combustion at the identified temperature ranges. Thermoanalytical methods such as Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) are used for characterizing thermal degradation of the fluoropolymers. Solid residues from DTA, DSC and TGA are examined via Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX) to identify surface morphology and elemental changes after thermal degradation.

KEYWORDS: Per- and polyfluoroalkyl substances (PFAS), Fluoropolymers, Thermal Degradation Analysis, Combustion, Reactor Design

CONTACT: Enoch A. Nagelli, Email: enoch.nagelli@westpoint.edu

References

[1] B. Gullett and A. Gillespie. “Per- and Polyfluoroalkyl Substances (PFAS): Incineration to Manage PFAS Waste Streams” EPA Technical Brief Innovative Research for a Sustainable Future, U.S. Environmental Protection. February 2020.