Kinetics and Products from o-Cresol Oxidation in Supercritical Water

Dilute aqueous solutions of o-cresol (2-methylphenol) were oxidized in a tubular flow reactor at near-critical and supercritical conditions. The power-law rate expression that best correlates the kinetics of o-cresol disappearance is rate = 10^5.7 exp(−29700/RT)[o-cresol]^0.57[O2]^0.22[H₂O]^1.44. The power-law rate expression that best correlates the experimental results for the conversion of organic carbon to CO₂ is rate = 10^6.8 exp(−34000/RT)[TOC]°^.34[O₂]^0.73[H₂O]^1.18. All concentrations are in moles per liter, the activation energy is in calories per mole, and the rate is in moles per liter per second. The most abundant products from o-cresol oxidation were typically phenol, 2-hydroxybenzaldehyde, 1,3-benzodioxole, indanone, CO, and C0₂. 2-Hydroxybenzaldehyde was the major primary product. A reanalysis of published kinetics data for the oxidation of two other ring-containing compounds (pyridine and 4-chlorophenol) in supercritical water revealed that the rate laws previously reported for these two compounds do not provide the best correlation of the experimental data. We report the new rate laws, which are similar to those for o-cresol, 2-chlorophenol, and phenol in that the global reaction orders are between 0.55 and 0.9 for the organic compounds and between 0.2 and 0.5 for oxygen.