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.