Autocatalytic oxidation of nitrobenzene using hydrogen peroxide and Fe(III)

The kinetics of nitrobenzene (NBE) oxidation using excess of hydrogen peroxide (HP) and catalytic amounts of ferric salts (represented as Fe(III)) was investigated over a wide range of experimental conditions. The temporal profiles of NBE concentration display an autocatalytic kinetic behavior. The main products identified were 4-nitrophenol, 3-nitrophenol, 2-nitrophenol, 1,3-dinitrobenzene, 4-nitrocatechol, 1,4-benzoquinone and NO2−. The initial reaction rates rise with [Fe(III)] and [HP], although they decrease with organic matter loading. On the other hand, the rates of the catalytic phase increase linearly with [Fe(III)]0 but display a more complex dependence on organic matter and HP concentrations. The effects of temperature and dissolved oxygen concentration were also studied. Depending on the temperature range analyzed, different activation energies and oxygen demands are observed, indicating a complex overall process that involves several stages. The results of this study can be useful for the rational design of efficient wastewater purification methodologies. A simple kinetic model capable of quantitatively predicting the experimental results associated with the initial phase is proposed. Since the overall efficiency of the autocatalytic system is limited by the slowness of the initial phase, the equations derived provide valuable insights for reactor design purposes.