Total degradation of p-hydroxybenzoic acid by Ru-catalysed wet air oxidation: a model for wastewater treatment

Abstract

Catalytic wet air oxidation using heterogeneous catalysts is a promising technology for treatment of wastewaters. Wastewaters from olive oil mills are difficult to clean because effluents contain high levels of phenolic compounds that cannot be removed by biological treatment or incineration. Therefore, we tested the catalytic wet air oxidation of p-hydroxybenzoic acid, as model molecule of olive oil mills wastewaters, over Ru-supported CeO2–TiO2 mixed oxides. We focussed on the Ce/Ti molar ratio because this ratio modifies the properties of the Ru catalysts. Supports were prepared by using the sol–gel method. The Ru catalysts were prepared by impregnation. Those products were characterized by N2 adsorption–desorption, X-ray diffraction, H2 chemisorption, transmission electron microscopy and inductively coupled plasma. Catalytic wet air oxidation of p-hydroxybenzoic acid was performed in a batch reactor at 140 °C and 50 bar of air. Our results show that the most efficient catalyst was Ru with a Ce/Ti ratio of 1/5, which converted totally p-hydroxybenzoic after 7 h of reaction without Ru leaching. We explain this finding by an enhanced dispersion of Ru due to better structural properties of the CeO2–TiO2 support.© 2015, Springer International Publishing Switzerland.Postprint (author's final draft

Study of the catalytic wet air oxidation of p-hydroxybenzoic acid on a fresh ruthenium catalyst supported by different oxides

“…5 ], which reveals the presence of Ru particles in the range of 15–62 nm. A similar observation was noted by other researchers in the case of Ru/TiO 2 –CeO 2 catalysts [ 14 , 17 ]. Table 1 displays the average TiO 2 crystallite size of all the investigated samples, determined by Debye-Scherrer relation (Eq.…”

“…The complete oxidation of p-HBA produces only CO 2 and H 2 O. However, if mineralization is not fully complete, some intermediates may be formed, as reported in our previous studies using similar catalysts [ 14 , 28 ]. The main by-products detected are phenol, hydroquinone and maleic acid.…”

“…CWAO of p-HBA acid was carried out in a 300 ml autoclave equipped with a magnetically driven stirrer to avoid any mass transfer limitation. A given mass of catalyst (500 mg) and 150 ml of p-HBA solution (10 mM) was used for each experiment [ 8 , 14 ]. After the reactor had been purged at least three times with N 2 to remove any trace of oxygen, it was heated to the desired reaction temperature (140 °C), and then synthetic air (20 vol% O 2 in N 2 ) or pure oxygen was introduced into the reactor to reach a total pressure of 50 bar.…”

“…In our earlier studies, p-HBA CWAO was investigated in a batch reactor using ruthenium catalysts supported by mixed oxides, namely CeO 2 –TiO 2 [ 8 , 14 ] and CeO 2 –Al 2 O 3 [ 15 ]. The sol-gel method with the use of supercritical autoclave drying was employed to synthesize these mixed oxides.…”

Polyaniline films for efficient removal of aromatic acids from water

“…Furthermore, the removal of these compounds from water is a challenge to drinking water industry. In this context, several technologies have been widely used to clean the organic compounds form water including coagulation, adsorption, oxidation and membrane filtration (Lee et al 2015;Duan et al 2002;Borah and Mahiuddin 2008;Ayekoe et al 2015;Yates et al 2014;Hammedi et al 2015;Matilainen et al 2011). Among these techniques, the adsorption is the most promising.…”