(382f) A Chemical Kinetic Mechanism for Ethanol Oxidation in Supercritical Water

Supercritical water is a promising medium for oxidation and decomposition processes which can be used in future waste-to-energy and recycling systems. The development of detailed chemical kinetic mechanisms for organic compounds in these processes is critical to the advancement of this technology, yet nearly all existing comprehensive mechanisms include only C1 compounds. The primary objective of this work was to construct and evaluate a new detailed chemical kinetic mechanism for the oxidation of ethanol in supercritical water, a known reaction product of waste biomass and plastic. This objective was accomplished by augmenting an existing mechanism for methanol oxidation in supercritical water with C2 chemistry from an existing mechanism for air-dilute hydrocarbon combustion. Mechanism predictions for product yield were then compared to experimental observations from two previous studies of ethanol oxidation and decomposition in supercritical flow reactors for highly dilute ethanol mixtures with 0.5-2 equivalence ratio operating near 400-500°C, 245 bar.

Mechanism predictions for ethanol and various reaction products during oxidation were generally in excellent agreement with experimental observations, within known reaction rate uncertainties. Minor errors exist, which can possibly be improved by refinement of the interrelated kinetics of acetaldehyde, methanol, and formaldehyde. The successful adoption of existing air-dilute oxidation chemistry without modification beyond established uncertainty bounds suggests that major chemical kinetic pathways and rate models may not be significantly different for supercritical water. On the other hand, mechanism predictions for decomposition processes were very poor, highlighting significant departures from air-dilute pyrolysis kinetics possibly driven by the presence of OH radicals. The new ethanol mechanism developed here provides an excellent foundation for future refinement and inclusion of higher organic species. Given its unique evaluation against multiple experimental benchmarks and the incorporation of a well validated C1 mechanism, the present mechanism represents a significant improvement over those in the literature.