The Effects of Mixing and Oxidant Choice on Laboratory-Scale Measurements of Supercritical Water Oxidation Kinetics

The use of laboratory-scale equipment to measure intrinsic oxidation kinetics in supercritical water environments was evaluated in this study. The objectives were two-fold: (1) to compare the use of hydrogen peroxide with dissolved oxygen as an oxidant and (2) to characterize the dynamics and intensity of mixing organic reactant and oxidant streams. Methanol was used as the model organic as the oxidation rate exhibits a first-order dependence according to extensive earlier studies. No statistically significant difference was observed in the reaction rates or product distributions for the use of either dissolved oxygen gas or hydrogen peroxide that was preheated and fully decomposed before mixing with methanol at supercritical water conditions (500 °C, 246 bar). The intensity of mixing was shown to be an important factor in determining effective mixing times for the reactant and oxidant. Although hydrodynamic effects are certainly dependent on the design and geometry of the mixing tee in the reactor system, fully turbulent ( Re > 10 000) cross-flow between entering oxidant and organic streams was found to reduce mixing times to 1 s or less.