Performance of heterogeneous catalytic wet oxidation for the removal of phenolic compounds: Catalyst characterization and effect of pH, temperature, metal leaching and non-oxidative hydrothermal reaction

The present study investigated the efficiency of catalytic wet oxidation (CWO) for the destruction of three phenolic compounds (phenol, o-cresol and 2,5-dimethylphenol) individually as well as in mixture (phenolics concentration = 10 g/L, NaOH concentration = 10 g/L, chemical oxygen demand (COD) = 24000 mg/L, total organic carbon (TOC) =7800 mg/L and pH=13). The oxidative hydrothermal reaction was carried out in a laboratory scale high pressure batch reactor (capacity = 0.7 L) at moderate temperature (120–160 C) and pressure (oxygen partial pressure = 0.8 MPa) conditions in the presence of a heterogeneous catalyst (i.e., 5% Cu/activated carbon). After 4 h CWO reaction on the mixture of phenolics at a reaction temperature of 160 C and initial reaction pH of 9.0, TOC and COD were reduced by 90% and 82%, respectively. The phenolics removal was mainly due to the oxidation reaction and the contribution of other reactions such as adsorption and/or hydrolysis was lower. The copper leaching in the solution was found to be 15–26 ppm. The characterization of recovered catalyst showed increase in carbon content thus confirming the deposition of carbonaceous deposit