Catalytic Wet Oxidation of Phenol:  Kinetics of the Mineralization Rate

Abstract

Phenol mineralization in the aqueous phase was studied employing oxygen as the oxidant. The reaction was carried out at intermediate oxygen pressures (3.2-16 bar) and temperatures (127-180 °C) employing a commercial catalyst supplied by Engelhard (Cu-203T). Two experimental setups were used: a basket stirred-tank reactor (BSTR) with the liquid phase in batch and an integral fixed-bed reactor (FBR) with concurrent upflow of the gas and liquid phases. These two apparatuses allowed the catalyst concentration to be changed over a wide range (4-1150 g/L) so that the influence of this variable could be more accurately determined. It was found that the reaction takes place to a significant extent both in the liquid phase and on the catalyst surface. A kinetic model for phenol mineralization was discriminated on the basis of a twostage power-law kinetic expression. The first stage corresponds to the induction period, and the second to the steady state. This model was able to predict accurately the experimental results over the entire range of the variables studied. The catalyst concentration was included in this model with a power-law order of about 0.5 found for both the induction and steady-sate regions.

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

“…The mode preferred in industry is the TBR [196] allowing for a variety of flow regimes depending on the gas and liquid flow rates employed. The same situation holds for CWAO, however only a few of the available studies attempted to experimentally assess the impact of gasliquid hydrodynamics and mass transfer on reactor performance under CWAO conditions [28,29,56,191,197]. Non-idealities in TBR operation during CWAO were detected by various researchers.…”

“…A higher reaction temperature shifted the reaction system to the gas-limited region and fully wetted catalyst particles lead to additional resistance for gas-liquid oxygen mass transfer. Santos et al [56,191] conducted phenol oxidation runs in a fixed bed reactor at different catalyst concentrations mixing inert and catalytic particle of same size. The authors reported a critical catalyst concentration below which the apparent reaction rate was not longer proportional to the catalyst concentration because of a significant homogeneous contribution to the reaction.…”

“…The lumping strategy can give good fits of the experimental data, but the empirically calculated kinetic parameters should not be used for extrapolation purposes. Homogeneous polymer formation [64,191] and catalyst deactivation [215] were successfully described by combined homogeneous and heterogeneous rate equations. The few models that involve mechanistic aspects proposed the use of free radical mechanism based rate equations or Langmuir-Hinshelwood and Eley-Redeal type rate equations.…”

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: A review

“…They give off unpleasant odor and taste even at very low concentrations [21]. Moreover, phenol is considered to be an intermediate in the oxidation pathway of higher molecular weight aromatic compounds and thus is mainly taken as a model compound for advanced wastewater treatments [22,23].…”

Fe salts as catalyst for the wet oxidation of o-chlorophenol

“…Among all the wet oxidation technologies, WAO, which can mineralise pollutants at elevated temperature and pressure, has the ability to convert most organic and inorganic compounds into end products such as minerals, carbon dioxide and water (Shende and Mahajani, 1997;Santos et al, 2001). WAO has been demonstrated as a viable process for o-chlorophenol wastewater treatment Lei and Wang, 2000).…”