Mechanistic and kinetic studies of the degradation of diethyl phthalate (DEP) by homogeneous and heterogeneous Fenton oxidation

Abstract

In this work, the degradation of diethyl Phthalate (DEP) by homogeneous and heterogeneous Fenton oxidation was investigated. The influence of several parameters was determined such as the initial pH, the catalyst concentration, the hydrogen peroxide concentration and the initial concentration of DEP on the oxidative degradation kinetics and mineralization efficiency. Different iron sources were tested (Ferrous sulfate, Ferric oxide, Pyrite and FeF2) leading to homogeneous and heterogeneous Fenton system. Ferrous sulfate is used for deeper investigation given its fast catalytic decomposition of hydrogen peroxide directly to generate hydroxyl radicals OH known as the Fenton reaction. The experimental results showed that DEP was completely removed by the hydroxyl radicals (•OH) action generated from Fenton’s reaction under the optimal conditions 100 ppm DEP, [H2O2] = 1000 ppm, [Fe2+] = 50 ppm, and pH = 3.2. Furthermore, under these conditions, more than 95% of the initial TOC was removed, meaning almost complete mineralization of the organic compounds after 300 min of treatment. The absolute rate constant for the DEP oxidation reaction by the hydroxyl radical was determined using the competition kinetics method and found to be 4.4x109 M−1 s−1. HPLC analysis of treated solutions revealed that phtalic acid, 1,2-dihydroxybenzene, 1,2,4-trihydroxybenzene, maleic acid, formic acid and oxalic acid were the intermediates found. Oxalic acid was the major and most persistent oxidized product found at the end of the treatment. Based on the identified reaction intermediates by HPLC and TOC results, a mechanism was proposed for the mineralization of DEP during Fenton process. Finally, it can be said that the Fenton process is a suitable and efficient method for DEP removing and its intermediates from water.