Kinetics of imidazolium-based ionic liquids degradation in aqueous solution by Fenton oxidation.

In the last few years, several works dealing with Fenton oxidation of ionic liquids (ILs) have proved the capability of this technology for their degradation, achieving complete ILs removal and non-toxic effluents. Nevertheless, very little is known about the kinetics of this process, crucial for its potential application. In this work, the effect of several operating conditions, including reaction temperature (50-90 °C), catalyst load (10-50 mg L-1 Fe3+), initial IL concentration (100-2000 mg L-1), and hydrogen peroxide dose (10-200% of the stoichiometric amount for the complete IL mineralization) on 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) oxidation has been investigated. Under the optimum operating conditions (T = 90 °C; [Fe3+]0 = 50 mg L-1; [H2O2]0 = 100% of the stoichiometric amount), the complete removal of [C4mim]Cl (1000 mg L-1) was achieved at 1.5-min reaction time. From the experimental results, a potential kinetic model capable to describe the removal of imidazolium-based ILs by Fenton oxidation has been developed. By fitting the proposed model to the experimental data, the orders of the reaction with respect to IL initial concentration, Fe3+ amount and H2O2 dose were found to be close to 1, with an apparent activation energy of 43.3 kJ mol-1. The model resulted in a reasonable fit within the wide range of operating conditions tested in this work.