WET OXIDATION OF PHENOL BY HYDROGEN-PEROXIDE - THE KEY ROLE OF PH ON THE CATALYTIC BEHAVIOR OF FE-ZSM-5

This paper presents an original approach to the treatment of phenolic aqueous wastes using H2O2 with Fe-ZSM-5 as a heterogeneous catalyst, T he Fe-ZSM-5 zeolite with MFI structure allows a total elimination of p henol and a significant total organic carbon (TOC) removal at 90 degre es C and atmospheric pressure in a batch reactor. The studies with thi s Fe-ZSM-5 catalyst deal mainly with the influence of external diffusi on and pH on the oxidation process. It appears that the phenol degrada tion and the toxicity reduction, on the one hand, and the leaching-off of Fe(III) ions in the solution, on the other hand, depend strongly o n the pH. In these conditions, an optimum value exists at pH = 5, At h igher pH values, the system becomes less effective. At lower values, a significant leaching-off will induce homogeneous catalysis and the de gradation of the catalyst. Generally speaking, when this heterogeneous catalyst is used in the presence of H2O2, the reaction rates depend o n the degree of hydroxylation of the aromatic compound in contact with the catalyst. So, a chain radical mechanism could be envisaged. (C) 1 997 IAWQ. Published by Elsevier Science Ltd.