(110h) Evolved Gas Analysis and Modeling of the Thermal Degradation Products from Polytetrafluoroethylene Using TGA-MS and Process Design Simulation

Fluoropolymers such as polytetrafluoroethylene (PTFE) are classified as polymeric per- and polyfluoroalkyl substances (PFAS). The industrial manufacturing of fluoropolymers can lead the production and evolution of monomeric and oligomeric PFAS in the environment. [Lohman, Environ. Sci. Tech. 2020] There is ongoing emphasis to develop methods to detect and quantify PFAS contamination and evaluate potential disposal mechanisms, to include incineration. [EPA 2020] The persistence of any PFAS byproducts in the environment present a challenge due to the abundance of stable carbon-fluorine bonds. In our current study, we perform thermal degradation studies on PTFE using Thermogravimetric Analysis from 20 to 1000 °C, coupled with Mass Spectrometry (TGA-MS). Based on the observed TGA/MS experiments conducted on PTFE in open air combustion conditions, a proposed mechanism using a C16 molecule, CF₃(CF₂)₁₄CF₃, was developed. The kinetic and thermodynamic parameters were evaluated by Density Functional Theory (DFT) to compare and verify the proposed reaction mechanisms from the experimental TGA/MS data. In addition, process design models were developed using kinetic and thermodynamic reactors before and after the determined gel point for PTFE. CHEMCAD™ was used study the mass and energy balance for the combustion reaction process. Gibbs reactor-based calculations were developed under thermodynamic and chemical equilibrium during combustion to determine bulk reaction products, heat duty of the reactor, enthalpy, and Gibbs Free Energy. Furthermore, the TGA-MS data provides an understanding of the potential gaseous degradation products during the thermal breakdown of PTFE. The separation of individual byproducts and isolation of gaseous byproducts is still a challenge. Ongoing studies aim to investigate potential reaction pathways leading to the degradation of PTFE to correlate with the DFT mechanistic modeling for kinetic and thermodynamic parameters. Process design models are being developed to quantify the mass and energy balance of large-scale incineration of fluoropolymers.