Assessment of carbon monoxide formation in Fenton oxidation process: The critical role of pollutant nature and operating conditions

This work assesses the carbon monoxide formation upon Fenton process, the most popular method for Advanced Oxidation Processes (AOPs). CO concentrations in the order of 11,000 mg/Nm(3) were measured in the Fenton oxidation of phenol after 180 min reaction at 90 degrees C and 3 bar. The Fenton oxidation performed on phenol and its oxidized intermediates such as hydroquinone, catechol and short-chain acids allows concluding that CO is produced through the oxidative cleavage of aromatic rings; the hydroquinone route being more selective to CO than catechol. In all cases, the carbon mass balance was satisfactorily closed to 100%. The study of the influence of the operational conditions shows that CO production is clearly favoured at H2O2 dosage above the stoichiometric value and low temperatures (T < 90). The H2O2 dosage was the most influence variable. The results of this work evidence for the first time the production of noxious amounts of CO along with CO2 in Fenton processes. This finding highlights the importance of evaluating not only liquid phase intermediates due to their recalcitrant and/or toxic behavior, but also gas phase because of CO emissions.