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Comparison of the thermal destruction of C1 and C2 fluorine/chlorine homologues in a pilot-scale research furnace: modeling and experiments
Citation:
Denison, M., D. Swensen, M. Cremer, B. Van Otten, J. Wendt, J. Krug, G. Dildine, W. Roberson, E. Shields, Pertti Virtaranta, J. Mattila, P. Lemieux, W. Linak, R. Burnette, S. McDonald, AND G. Whitfield. Comparison of the thermal destruction of C1 and C2 fluorine/chlorine homologues in a pilot-scale research furnace: modeling and experiments. 40th International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors, Charlotte, NC, September 13 - 14, 2023.
Impact/Purpose:
PFAS and fluor-organic wastes are an emerging pollutant class with little in the way of published data to inform decisions regarding the efficacy of thermal treatment technologies to control emissions. There are concerns about whether conditions within the large variety of combustors and incinerators used to dispose PFAS laden wastes adequately mineralize PFAS (forming CO2 and HF) or if fluoro-organic structures survive to be emitted as products of incomplete combustion (PICs). While PFAS are new to the thermal destruction community, these industries have a long history successfully treating chloro-organic wastes. While comparable bond energies suggests that chlorocarbons may be easier to destroy in thermal systems, this is not universally true. This study compares kinetic model predictions for three C1 and C2 fluorinated compounds (CF4, CHF3, and C2F6) with their chlorinated homologues (CCl4, CHCl3, and C2Cl6) within a simulated incineration environment to quantify the relative temperatures and other conditions required to mineralize both sets of halogenated species.
Description:
PFAS are a class of thousands of anthropogenic compounds widely used by industry and present in many consumer products. PFAS are valued for their hydrophobic and lipophobic properties, as well as their chemical and thermal stability. While definitions vary, PFAS are typically characterized by the presence of one or more per- or poly-fluorinated methyl (-CF3) or methylene (-CF2-) groups. C-F bond energies are among the strongest organic bond. This leads to concerns about whether conditions within the large variety of combustors and incinerators used to dispose PFAS laden wastes adequately mineralize PFAS (forming CO2 and HF) or if fluoro-organic structures survive to be emitted as products of incomplete combustion (PICs). This study compares kinetic model predictions for three C1 and C2 fluorinated compounds (CF4, CHF3, and C2F6) with their chlorinated homologues (CCl4, CHCl3, and C2Cl6) within a simulated combustion environment. Fluoro- and chloro-organic kinetics were taken from the literature. An ideal plug flow treatment and a measured temperature/residence time profile of an EPA research furnace was used. Model calculations were set up to allow the fluoro- or chloro-organic compound to be introduced at multiple locations through the flame and at post-flame locations along the temperature/residence time profile corresponding to physical ports on the research furnace. Model results, including comparisons with the measured data, characterizing species destruction and PIC formation as a function of injection temperature will be presented. Identified rate controlling steps in the mechanisms will also be presented including common reactions between the mechanisms where F is replaced with Cl.