KINETICS OF CO2 FORMATION FROM THE OXIDATION OF PHENOLS IN SUPERCRITICAL WATER

Global power-law rate expressions were determined for the formation of CO2 from the oxidation of aqueous solutions of phenol and 2-chlorophenol. The oxidation experiments were accomplished in a plug-flow reactor at temperatures between 300 and 420-degrees-C and pressures from 185 to 278 atm. These conditions included oxidations in both near-critical and supercritical water. Reactor residence times ranged from 1.2 to 109 s. The initial reactant concentrations were between 8.0 X 10(-5) and 2.1 X 10(-3) M, and the initial oxygen concentrations ranged from 5.5 X 10(-3) to 4.8 X 10(-2) M. The phenolic compound was always the limiting reactant, and the excess oxygen was between 180% and 1360%. Nonlinear regression analysis of the kinetics data for the formation of CO2 from phenol oxidation revealed that the reaction was 0.82 +/- 0.20 order in total organic carbon and 0.71 +/- 0.26 order in oxygen. The activation energy was 6.2 +/- 2.6 kcal/mol. The rate law for CO2 formation from 2-chlorophenol was 0.51 +/- 0.08 order in total organic carbon and 0.80 +/- 0.13 order in oxygen. The activation energy for this rate law was 9.0 +/- 5.8 kcal/mol. The uncertainties given here represent 95% confidence intervals. There was no statistically significant dependence of the rate of CO2 formation on the water concentration for either compound. The low activation energies suggest that the major pathways leading to CO2 do not include carbon monoxide or acetic acid as refractory intermediates. For both phenolic compounds, the conversion of organic carbon to CO2 was always less than the conversion of the phenol, indicating that products of incomplete oxidation were present.