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

Abstract

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.

Performance of Supported Copper Catalysts for Oxidative Degradation of Phenolics in Aqueous Medium: Optimization of Reaction Conditions, Kinetics, Catalyst Stability, Characterization, and Reusability

“…It should be noted that the removal of organics due to adsorption has not been considered in the kinetic analysis. Based on our earlier studies, it can be stated that the adsorption of phenolic compounds on the AC-supported catalyst is likely to be very low under elevated temperature conditions. Hence, this may not have a significant impact on the kinetic constants.…”

“…Details about the reactor and its operation are provided in our earlier publication. 18 For a typical run, 250 mL of wastewater was poured into the reactor followed by a predetermined amount of the catalyst. After reaching the set temperature, oxygen was purged into the reactor and the reactor contents were subjected to vigorous stirring at 1000 rpm.…”

“…The WO and CWO runs with synthetic wastewater were carried out in a high-pressure batch reactor (0.7 L capacity) made of stainless steel 316. Details about the reactor and its operation are provided in our earlier publication . For a typical run, 250 mL of wastewater was poured into the reactor followed by a predetermined amount of the catalyst.…”

“…Several research studies on WO and CWO of the synthetic wastewaters containing model compounds like phenols, − ferulic acid (a lignin model compound), − and carboxylic acids have been reported in the literature. Moreover, simulated and real industrial effluents have also been treated by noncatalytic and catalytic hydrothermal oxidative processes. − …”

Eggshell-supported Catalysts for the Advanced Oxidation Treatment of Humic Acid Polluted Wastewaters

“…In this context, the use of catalyst in WO process (CWO) is an interesting alternative for the destruction of refractory organic compounds. In fact, CWO has been successfully employed in the treatment of diverse industrial wastewaters (textile, paper, food, chemical, pharmaceutical, and alumina industries) [11]. Additionally, CWO can reduce the severity of the WO conditions.…”