Wet Air Oxidation of Organic Acids and Phenol for Odour Control Processes

Abstract

The treatment of odorous pollutants by catalytic wet air oxidation (CWAO) was investigated for model water solutions of different organic acids, such as acetic, succinic and p-hydroxybenzoic acids, and phenol. CWAO reactions of phenol and acetic acid runs were carried out in a continuous micropilot trickle-bed reactor for about 300 h. Experiments were performed with carbon-supported catalysts PZ-65 (0.6 % Ru+5 % CeO2/ Sibunit), PZ-68 (0.6 %Ru + 8 % CeO2/ Sibunit) and carbon material Sibunit-4 at 180 °C for phenol oxidation and at 200 °C for acetic acid oxidation at 50 bar air total pressure. The treated solution was periodically analyzed, collected and submitted to a recycling run. Total organic carbon content (TOC), inorganic carbon content (IC) and concentrations of separate organic substances Ci were analyzed by means of a TOC-meter and an HPLC. The CWAO of succinic and p-hydroxybenzoic acids have been investigated in a batch reactor at 140 °C and 50 bar air total pressure. All catalysts were rather active in oxidation of phenol and the activity was found very stable in all cases. No deactivation was observed. After several sets of recycling of treated solutions on catalyst PZ-68, the oxidation activity measured on a fresh phenol solution was found similar to the initial activity. CWAO experiments with acetic acid have shown that Sibunit catalyst did not exhibit catalytic activity up to temperature of 225 °C, whereas the promoted Ru-CeO2/Sibunit catalysts exhibited high activity at 200 °C; however, their activity decreased significantly as a function of time on stream after 100 h. Transmission electron microscopic (TEM) investigations of (Ru+CeO2)/Sibunit catalysts have shown that 1nm-large Ru-particles are associated with 5 nm-large CeO2 particles supported on the carbon surface. This association is probably very beneficial to the activity of the catalyst. The results of study have demonstrated that CWAO over Ru-carbon supported catalysts may a suitable technique for degradation of diluted aqueous solutions of organic acids and odour control processes. The mineralization is complete, and a leaching of the metal by the water-organic solutions is most insignificant.