Wet Air Oxidation of Phenol on Oxides of Fe(III), Mn(IV), Ti(IV) and Goethite

Background: Phenol and its derivatives exist in water bodies due to the discharge of polluted wastewater from industrial, agricultural, and domestic activities into water bodies. Various industries like pharmaceutical, petrochemical and coal processing industries discharge phenolic compounds into water bodies. Phenol and substituted phenols are quite toxic to humans. Objective: Oxidative destruction of phenol in water was carried out at ambient temperature by using laboratory-synthesized goethite and commercial Fe2O3, TiO2, and MnO2 as catalysts in the presence and the absence ofH2O2. Methods: The reactions were carried out in a batch reactor in 100 mL conical flasks. After mixing the reactants (Phenol and H2O2) and the catalyst in appropriate amounts, the flasks were capped, and the contents were agitated in a water bath shaker (NSW, India) at a constant temperature of 300 K for a predetermined time interval. Results: The results have been characterized in terms of percentage destruction of the Phenol. The catalyst Goethite was able to bring about 15.8 to 23.5% destruction as the reactant-H2O2 mole ratio was increased from 1:1 to 1:20 with a fixed catalyst load of 0.2 gL^-1. The total conversion of phenol increases smoothly with an increase in the reaction time from 60 to 300 min in all cases except Fe2O3, in which case the reaction does not advance after 60 min. Interestingly, the catalyst MnO2, brings about 94.4 % oxidative conversion of phenol with the same loading in the absence of H2O2, i.e., in wet air oxidation. It is also found that a 1:1 mixture of MnO2 + TiO2 gives 100 % conversion for a catalyst load of ≥ 6 gL^-1 in the absence of H2O2. Conclusion: It is found that phenol could be completely oxidized to harmless end products at room temperature. For this purpose, MnO2 has been found to be the most active catalyst among the ones tested, whether H2O2 is present or not in the reaction mixture. The three oxides Fe2O3, goethite and TiO2 can perform better only in the presence of H2O2.