The present study investigates the oxidation of formic acid by the Fenton and Fenton-like reaction. An experimental study was performed at industrially relevant conditions, which means that the concentrations of reagents were generally higher than concentrations previously reported. The most interesting result is the fast oxidation rate of formic acid in the first two minutes of the Fe(II)/H2O2 reaction. In an industrial setting this fast initial oxidation can be used to remove a significant part of the formic acid without the need for large reactors with long residence times and large excesses of H2O2 and Fe(II). In contrast, the Fe(III)/H2O2 reaction shows a slower, constant decrease of formic acid over time strongly depending on temperature and H2O2 concentration. The initial decrease in formic acid concentration in the Fe(II)/H2O2 reaction could not be explained by previously proposed kinetic models for formic acid oxidation by the Fenton's reagent. The specific conditions used require a more elaborate kinetic model to describe the results obtained. In the Fe(II)/H2O2 reaction, the formic acid reacts with the [rad]OH radical and forms an [rad]OOH radical that regenerates the Fe(II). The reaction of Fe(III) and the [rad]OOH radical to regenerate Fe(II) and thereby restart the Fe(II)/H2O2 reaction can most likely explain the fast initial decrease observed. Furthermore, the addition of reactions describing the formation and decomposition of inorganic and ferric-formate complexes to the kinetic model improved the fit to all experimental data, in particular for the initial part of the reaction of Fe(II)/H2O2 with formic acid.
- Formic acid
- Kinetic modelling