Catalytic Oxidation of 4-Hydroxybenzoic Acid on Activated Carbon in Batch Autoclave and Fixed-Bed Reactors

Catalytic Wet Air Oxidation (CWAO) has been investigated for the treatment of water contaminated by 4-hydroxybenzoic acid (4HBA). Both batch measurements for kinetics determination and continuous trickle bed operation have been performed on the same Activated Carbon (AC). After a fast initial deactivation AC was proved stable and efficient at moderate temperature and oxygen pressure, like for phenol degradation. The kinetic study in the case of highly adsorbing material as AC may require complex approach to account for the variation of adsorbed reactants during batch oxidation. Adsorption isotherms at reaction temperature and with aged AC have been obtained according to Langmuir equation and used in 4HBA mass balance to derive more significant kinetic parameters. At high catalyst loading and relatively low 4HBA concentration, the variation of 4HBA during the batch oxidation may be even higher on the solid than in the aqueous phase. Some data in continuous trickle bed reactor or upflow flooded bed reactor indicate a similar oxidation behavior as in batch mode despite very different liquid-solid ratios