Degradation of olive oil mill effluents by catalytic wet air oxidation: 2-Oxidation of p-hydroxyphenylacetic and p-hydroxybenzoic acids over Pt and Ru supported catalysts

Catalytic wet air oxidation of p-hydroxyphenylacetic acid and p-hydroxybenzoic acid, two important pollutants present in the olive oil mill wastewaters, was studied in a batch reactor using platinum and ruthenium catalysts supported on titanium and zirconium oxides at 140 °C and 50 bar of total air pressure. Reaction pathways for the oxidation of these two substrates were proposed, with formation of different aromatic compounds and short-chain organic acids through hydroxylation and decarboxylation reactions.It was observed that the conversion and the mineralization of these two substrates were markedly affected by the nature of the ruthenium precursor (RuCl3 or Ru(NO)(NO3)3), with the non-chlorine containing salt giving the best performances. Calcination of the catalyst precursor before reduction was detrimental. The nature of the metallic precursor (H2PtCl6 or Pt(NH3)4(NO3)2) had little influence on the catalytic properties of platinum catalysts, whereas the textural properties of the support were an important factor.