Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study

This work investigates the Fenton oxidation of phenol in a semicontinuous reactor where the overall amount of H2O2 is distributed as a continuous feed upon the reaction time. The experiments were carried out at 25 °C and atmospheric pressure, with 100 mg/L initial phenol concentration and iron dosages from 1 to 100 mg/L. H2O2 aqueous solution was continuously fed during 4 h reaction time up to an overall dose varying within the range of 500–5000 mg/L. The results in terms of evolution of phenol, H2O2 and intermediates, as well as TOC abatement were compared with those obtained in conventional batch operation. It was found that the oxidation rates for phenol and intermediates were lower when adding the H2O2 continuously. However, a higher abatement of TOC was reached at the end of the 4-h reaction time, in spite of a similar overall H2O2 consumption. This is the result of a more efficient OH generation throughout the semicontinuous process, favouring the reaction with the organic species and reducing the occurrence of competitive scavenging reactions involving Fe2+, H2O2 and OH. Two kinetic models were proposed, one for describing the evolution of phenol, aromatics and H2O2 and the other for TOC. The influence of the operating conditions on the kinetic constants was also studied, looking for the optimal conditions in terms of both, environmental and economic points of view.