Oxidation of nitrobenzene by fluidized-bed fenton process in the presence of chloride ions

Abstract

The objective of this study was to experimentally probe the chloride ions specifically affecting nitrobenzene oxidation by Fenton's reagent. Fluidized-bed experiments were carried out to investigate the effects of pH, Fe[superscript 2+], H2O2 and chloride concentration on the oxidation reaction. Results show that the best efficiency for nitrobenzene oxidation by fluidized-bed Fenton process was used Al[subscript 2]O[subscript 3] as the carrier which has pH[subscript pzc] of 9.16 and size of 2.50 mm. Optimum pH for nitrobenzene was 2.8. The removal efficiency oxidation of nitrobenzene by fluidized-bed Fenton process was better than Fenton process. The inhibition caused by chloride ions can be overcome by extending the reaction time if the concentration of chloride ions was low. At a high concentration of chloride ions, however, the oxidation of nitrobenzene was inhibited, and actually ceased due to the complexation of Fe–Cl. In this study, the chloride ion concentration was kept at 0.2 ˚M in the experiments when studying the effect of ferrous ion concentration on the Fenton reaction. If the ratio of [Cl−]/[Fe[superscript 2+]] was ≤200, the inhibition effect was very significant. In other words, adding more ferrous ions rather than hydrogen peroxide can break the inhibition originating from the chloride ions at an initial stage of pH 2.8. The inhibition effect of chloride ions on the nitrobenzene reaction depended on the reaction pH; the extent of inhibition decreased with increasing the initial pH as long as the pH was less than 6.