Catalytic wet air oxidation of phenol: Review of the reaction mechanism, kinetics, and CFD modeling

Advanced oxidation processes, specifically catalytic wet air oxidation (CWAO), are considered as useful and robust methods for the treatment of refractory organic compounds such as phenol in wastewater. This paper reviews reaction mechanisms, kinetics and computational fluid dynamics (CFD) modeling...

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Bibliographic Details
Published in:Critical reviews in environmental science and technology 2021-09, Vol.51 (17), p.1891-1923
Main Authors: Makatsa, Tladi J., Baloyi, Jeffrey, Ntho, Thabang, Masuku, Cornelius M.
Format: Article
Language:English
Subjects:
Acetic acid
Aerodynamics
Carbon dioxide
Catalysts
Channeling
Computational fluid dynamics
Computer applications
Deactivation
Fluid dynamics
Hydrodynamics
Intermediates
Kinetics
kinetics modeling
Mathematical models
Nuclear engineering
Nuclear safety
Organic compounds
Oxidation
phenol oxidation
Phenols
reaction mechanism
Reaction mechanisms
Reactors
Velocity
Wastewater
wastewater treatment
Wet oxidation
Wet oxidation process
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Summary:Advanced oxidation processes, specifically catalytic wet air oxidation (CWAO), are considered as useful and robust methods for the treatment of refractory organic compounds such as phenol in wastewater. This paper reviews reaction mechanisms, kinetics and computational fluid dynamics (CFD) modeling of CWAO of phenol. Different reaction mechanisms have been proposed by various researchers to account for possible intermediates during phenol oxidation. These mechanisms can be either direct or indirect; with the indirect path resulting in the formation of intermediates, while with the direct mechanism, no intermediates are formed, the reaction proceeds straight to carbon dioxide and water. Acetic acid is considered as the most stable intermediate of phenol oxidation. Power law and Langmuir-Hinshelwood models were used to account for the adsorption/desorption of the reactants on the surface of the catalyst. The reviewed studies show that phenol conversion increases with increased temperature, pressure, gas velocity and decreases with increasing liquid space velocity. The formation of hot spots next to the walls of the reactor leads to safety issues and may cause catalyst deactivation and reactor thermal run away. This prompted a review of liquid mal-distribution and the formation of hot spots inside the reactor using the CFD modeling technique. In most cases, liquid channeling was observed, resulting in the formation of hot spots and catalyst deactivation.
ISSN:1064-3389
1547-6537
DOI:10.1080/10643389.2020.1771886