Kinetics of Perfluorooctanoic Acid and Glycerol-Derived 1-3-Diethoxypropan-2-Ol Oxidation on Solid Catalysts

Catalytic oxidation reactions can provide economical solutions to widespread environmental concerns, such as decomposition of environmental contaminants and replacement of crude-oil-derived chemicals with renewable substitutes. This report presents kinetic studies of the ozonolysis of perfluorooctanoic acid (PFOA) over solid iron(III) oxide (Fe₂O₃) microparticles, and the selective oxidation of 1,3-diethoxypropan-2-ol (DEP) over platinum-bismuth nanoparticles supported on SBA-15 (PtBi/SBA-15). PFOA is a prototypical perfluoroalkyl substance (PFAS), a class of harmful contaminants plaguing the United States’ and other nations’ water systems. DEP and its selective oxidation product, diethoxypropan-2-one (DEK), are derivatives of glycerol that may lead to greener alternatives to existing CO₂ absorbents produced from petroleum. Both reactions were studied using an iterative reactor design process to maximize reactor reusability and minimize volatile component (e.g., solvent, reactant, product) losses. Ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS) was used to analyze PFOA oxidation products, while gas chromatography with a flame ionization detector (GC FID) was used to analyze DEP oxidation products. Analysis of products of PFOA ozonolysis suggests a rate dependence on temperature consistent with the conversion—and not adsorption—of PFOA on Fe₂O₃. UPLC-MS indicated that new, presently unknown molecules were formed during reaction. DEP oxidation selectively formed DEK in water, but little to no DEK formed in neat solution or in other solvents. This reaction was further analyzed by measuring the reaction rate as a function of the inlet air flowrate, temperature, reaction time, and DEP concentration. The trends from these studies suggest that 0^th order behavior is easily achieved at relatively low inlet air flowrates, that the apparent activation energy is ~86 kJ mol^-1, and that the rate passes through a maximum with increasing initial DEP concentration up to ~0.2 M before decreasing at higher DEP concentrations. These results are consistent with previously reported studies of alcohol oxidation over supported Pt nanoparticles. Efforts to scale up the synthesis of DEK (from 3 mL to 300 mL) in order to perform physical property measurements of DEK have thus far been unsuccessful. DEK formation rates and DEP conversions are miniscule, suggesting either catalyst deactivation or poisoning by DEP, DEK, or a side product. These issues are discussed, along with opportunities for either oxidative dehydrogenation with alternate catalysts or oxidants, or direct dehydrogenation to produce DEK and hydrogen.