Ethanol is partially oxidized in a continuous supercritical water reactor at temperatures from 500 to 530 °C, constant pressure of 25 MPa, initial ethanol concentration of 5 wt %, residence times of 3−8 s, and oxidant-to-fuel stoichiometric equivalence ratios of 5, 7.5, and 10%. The experimental conditions are selected to study the regime where ethanol oxidation happens rapidly but below the temperature necessary to initiate hydrolysis reactions. The reactions and interactions of intermediate species can be analyzed, leveraging previous experimental results and the existing body of literature on ethanol hydrolysis, pyrolysis, and oxidation. Higher oxidant concentration increases ethanol destruction and gasification efficiency, although significant coke/char buildup is qualitatively observed within the reactor. Product yields from the experiments are used to infer significant reaction mechanisms, and a pathway is postulated for the counterintuitive formation of char under the studied conditions.
<p>A small-scale supercritical water oxidation reactor is designed
and fabricated to study the destruction of hazardous wastes. The downward bulk
flow is heated with the introduction of pilot fuel (ethanol/water mixture), and
oxidant (H<sub>2</sub>O<sub>2</sub>/water mixture). Both streams are introduced
coaxially. The fuel dilution is varied from 2 to 7 mol% ethanol/water, and the
oxidant-to-fuel stoichiometric equivalence ratio (Φ<sub>AF</sub>), is varied from 1.1 to 1.5. Higher ethanol
concentrations in the pilot fuel stream and operation near-stoichiometric results in a more stratified temperature
profile, i.e., highest local fluid temperatures near the top and the lowest
temperatures at the bottom of the reactor. Steady operation at 603.5 °C is achieved with a nominal
residence time of 25.3 s at 7 mol% fuel dilution and Φ<sub>AF</sub> of 1.1. At the lowest pilot fuel dilution (2 mol%),
the temperature profile is nearly uniform, approaching a distributed reaction
regime.</p>
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