Catalytic wet oxidation of phenol: Kinetics of the mineralization rate

Phenol mineralization in the aqueous phase was studied employing oxygen as the oxidant. The reaction was carried out at intermediate oxygen pressures (3.2-16 bar) and temperatures (127-180 degreesC) employing a commercial catalyst supplied by Engelhard (Cu-203T). Two experimental setups were used: a basket stirred-tank reactor (BSTR) with the liquid phase in batch and an integral fixed-bed reactor (FBR) with concurrent upflow of the gas and liquid phases. These two apparatuses allowed the catalyst concentration to be changed over a wide range (4-1150 g/L) so that the influence of this variable could be more accurately determined. It was found that the reaction takes place to a significant extent both in the liquid phase and on the catalyst surface. A kinetic model for phenol mineralization was discriminated on the basis of a two-stage power-law kinetic expression. The first stage corresponds to the induction period, and the second to the steady state. This model was able to predict accurately the experimental results over the entire range of the variables studied. The catalyst concentration was included in this model with a power-law order of about 0.5 found for both the induction and steady-sate regions.