Catalytic Wet Air Oxidation of Aqueous Organic Mixtures

Abstract

Catalytic Wet Air Oxidation (CWAO) has been investigated for the treatment of water contaminated by 4-hydroxybenzoic acid (4HBA) and equimolar mixture of phenol-4HBA. Both batch measurements for kinetics determination and continuous fixed 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 pollutant concentration, the variation of 4HBA during the batch may be even higher on the solid than in the aqueous phase.

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

“…This deterioration of the carbon textural properties e already reported during the oxidation of phenols e is usually attributed to the deposition of condensation products, irreversibly adsorbed and minimally oxidised, which block the access to micropores (Cordero et al, 2008). As observed for successive adsorption and oxidation runs performed in an autoclave reactor (Creanga Manole et al, 2007), this ageing occurs mainly after the first oxidation followed by quasi stable behaviour both for adsorption and oxidation (Fig. 5b).…”

“…As was shown with commercial ACs that catalytic activity is significantly reduced when reusing the same AC sample in successive oxidations (Creanga Manole et al, 2007), deactivation has also been tested on the best SBCMs, these being SA_DRAW and hardened SA_DRAW.…”

“…This second step can be performed in mild conditions (typically 150 C and 20 bar of air) as activated carbons have been found to promote the liquid phase oxidation of several organic compounds, in particular phenols (Fortuny et al, 1998;Suarez-Ojeda et al, 2005;Santos et al, 2005;Creanga Manole et al, 2007).…”

AD–OX: A sequential oxidative process for water treatment—Adsorption and batch CWAO regeneration of activated carbon

“…In order to avoid an unknown period of AC stabilization, this work was indeed achieved with aged AC, yet extensively used in the same fixed bed (similar temperature and pressure conditions, same model pollutants) for many continuous oxidation runs, thus undergoing continuous simultaneous adsorption -oxidation for more than 300hrs. It has been verified that this used AC has reached a quasi steady state by repeating experiments in reference conditions [28]. It has also been estimated that AC consumption by direct oxidation is very limited as discussed below.…”

“…Most often wastewaters are mixtures of several pollutants. To investigate the feasibility of the AD-OX process with complex mixtures, a model mixture of phenol and 4HBA has been treated in this work, following previous studies on batch and continuous CWAO of phenol [9] and 4-hydroxybenzoic acid [27,28] on activated carbon.…”