Date of Award

August 2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Bethany Klemetsrud

Second Advisor

Alena Kubatova

Abstract

A comprehensive understanding of the breakdown of thermally desorbed environmental pollutants such as per- and poly-fluoroalkyl substances (PFAS) and plastics is not fully understood. In this dissertation, we developed comprehensive methods combining evolved gas analysis (EGA) with thermal desorption-pyrolysis (TD-Py) focused on thermal desorption and pyrolysis of PFAS and plastics with a detailed understanding of breakdown behavior during pyrolysis, as well as the identification of breakdown products. Additionally, we explored the applicability of EGA for kinetic analysis of pyrolyzed single and mixed plastic waste. First, we determined the applicability of evolved gas analysis (EGA) for a comprehensive understanding of breakdown behavior and identification of breakdown products of pyrolyzed environmental pollutants; in this case, the samples evaluated were PFAS. Evolved gas analysis – mass spectrometry (EGA-MS) was combined with thermal desorption – pyrolysis – gas chromatography – mass spectrometry (TD-Py-GC-MS) to study breakdown behavior and identify breakdown products. EGA-MS was used for quick screening of real-time behavior of PFAS and to determine significant temperatures for TD-Py-GC-MS, which provided detailed information about breakdown products. This method was tested on common PFAS, such as perfluorooctanoic acid (PFOA) and less studied PFAS (salts, alcohols, ethers). Thermal desorption and pyrolysis temperatures for tested samples were identified and breakdown products seen in the literature were confirmed, as well as novel breakdown products were observed. Therefore, the applicability of the newly developed method was confirmed. In the following work, we further explored the applicability of EGA for kinetic analysis of pyrolyzed samples aiming to combine experimental analysis with computational work. In the literature, kinetic analysis is commonly performed non-isothermally and experimental data is collected with thermogravimetric analysis (TGA). However, TGA instrumentation operates with large sample loading under longer non-isothermal conditions. Additionally, the instrument provides information only on sample mass-loss, but no knowledge of breakdown products can be obtained causing drawbacks to obtaining a complete set of information. Further, we studied the behavior of single and mixed plastic waste in early stages of isothermal pyrolysis. EGA was coupled with MS (EGA-MS) providing detailed information about real-time behavior of plastics during pyrolysis, as well as their breakdown products. By coupling EGA with a methanizer and flame ionization detector (EGA-mFID), the EGA signal was converted into mass-loss curves comparable to TGA mass-loss curves showing this method could further be used for kinetic analysis. The kinetic analysis was done using model-fitting approaches to standard and waste polystyrene and polypropylene single samples (PS-st, WPS, PP-st, WPP, respectively), as well as mixtures of WPS:WPP in mass ratios 1:1, 2:1, 8:1, 1:2, and 1:8. Kinetic models were fitted to experimental results and the best fit was determined by Akaike Information Criterion (AIC) and kinetic parameters, such as preexponential factor (A) and activation energy Ea, were determined. Additionally, Friedman isoconversional analysis was performed confirming observations about kinetic models and kinetic behavior determined by model-fitting approaches. While polystyrene showed single-step reaction, polypropylene and mixtures suggested a multi-step reaction mechanism. Therefore, in future work the development of Distributed Activation Energy Models/multi-step kinetic models are required to interpret the behavior of mixed plastics.

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Available for download on Wednesday, September 08, 2027

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