An Alternative Kinetic Model of the Iodide-Iodate Reaction for Its Use in Micromixing Investigations

The Villermaux-Dushman method, one of the most extensively used test reaction systems for micromixing characterization, has been widely criticized for years due to uncertainties regarding the incomplete dissociation of sulfuric acid and the proposed kinetic study by Guichardon et al. In this work, a renewed study of the kinetics of the iodide-iodate reaction is presented, using perchloric acid to avoid issues concerning incomplete acid dissociation. The experimental results are in good agreement with the fifth order rate law for the iodide-iodate reaction. The reaction rate coefficient strongly depends on the ionic strength and can be modeled with a Davies-like equation. When implemented in the incorporation model, the kinetic model presented in this study can be used to estimate micromixing times that are in line with the theoretical engulfment time. This is observed in two different reactors with low and high intensity of mixing: an unbaffled stirred vessel and a rotor-stator spinning disc reactor. The results from the latter are also compared with the second Bourne reaction, giving very similar micromixing times. The use of sulfuric acid in combination with the kinetic model from Guichardon et al. also provides micromixing times of the same order of magnitude; presumably their kinetic model indirectly accounts for the second proton dissociation rate in the overall reaction rate coefficient. The kinetic model presented in this study in combination with perchloric acid is suggested as an alternative to characterize micromixing behavior.