On the kinetics of phenol oxidation in supercritical water

Phenol oxidation in supercritical water was carried out in a tubular laboratory-scale reactor operated at a temperature range of 380 degrees C to 450 degrees C and pressures between 230 and 265 bar The phenol feed concentrations were between 500 and 1,000 mg/L, while oxygen was fed into the reactor at 50 to 1,000% of the stoichiometric amount needed to oxidize phenol completely to carbon dioxide. Phenol conversions from 16 to 96% were attained as the reactor residence times varied from 15 to 203 s. The oxidation obeys a parallel-consecutive reaction scheme that involves multiring, intermediate products such as phenoxy-phenol, biphenol, dibenzo-dioxin, maleic acid, and succinic acid. Experimental results showed that the phenol disappearance rate is represented well by a power-law kinetic model in which the rate is proportional to the 0.4 power of the oxygen mole fraction and roughly linearly proportional to the phenol mole fraction. The pressure effect on the disappearance rate was appropriately accounted for by introducing the molar volume of the reaction mixture, which was readily calculated by an equation of state. Total organic carbon reduction can be estimated by a lumped kinetic equation. In the P-T region the activation energy of the phenol disappearance was 124.7 kJ/mol.