Modelling of the synthetic dye Orange II degradation using Fenton’s reagent: From batch to continuous reactor operation

In this work, a simple kinetic model was used to study the azo dye Orange II (O-II) degradation using Fenton’s reagent, in the Fenton-like stage. The effects of pH, temperature, Cl− concentration and initial concentrations of O-II, hydrogen peroxide (H2O2) and ferrous ion catalyst (Fe2+) on the degradation rate have been investigated in a batch reactor. The apparent kinetic constants, kap, for O-II degradation were determined in the following ranges of experimental conditions: 2.0 ≤ pH ≤ 4.0, 283 K ≤ T ≤ 323 K, 0 M≤CCl−≤1×10−2 M0 M≤CCl−≤1×10−2 M, 3×10−5 M≤COIIo≤1×10−4 M3×10−5 M≤COIIo≤1×10−4 M, 1×10−4 M≤CH2O2 o≤1×10−3 M1×10−4 M≤CH2O2 o≤1×10−3 M and 2.5×10−6 M≤CFeo2+≤2×10−5 M2.5×10−6 M≤CFeo2+≤2×10−5 M. A pseudo first-order reaction rate with respect to O-II concentration was found to be adequate to fit the data in these experiments, in which kap depends on the initial conditions following a power-law dependency (at optimum pH of 3 and absence of chloride ions). This equation, without further fitting parameters, was successfully used to validate experiments performed in a continuous stirred tank reactor (CSTR). The ability of the model predictions was also checked by performing experiments in the CSTR out of the above-mentioned ranges (used for the kinetic study).