Villermaux–Dushman Test of Micromixing Characterization Revisited: Kinetic Effects of Acid Choice and Ionic Strength

The well-known Villermaux–Dushman system is nowadays widely used for examining the micromixing efficiency either in batch or continuous intensified reactors. However, a bibliographic review shows that kinetic data are too scattered for a reliable determination of the micromixing times. The Dushman reaction kinetics is then reexamined with the use of sulfuric and perchloric acids. The results confirm the fifth-order rate law. More precisely, the I–, H+, and IO3 – dependence orders on the rate law are, respectively, 2, 2, and 1, under any condition. To be more consistent with the reactant concentrations used in the Villermaux–Dushman test, we extend their studied range, namely, 1.6 × 10–3 M ≤ [I–]0 ≤ 1.6 × 10–2 M, 1.2 × 10–4 M ≤ [H+]0 ≤ 1.57 × 10–2 M, and 4 × 10–5 M ≤ [IO3 –]0 ≤ 2.1 × 10–4 M. The ionic strength varies up to 2 M. The experimental results show that the rate constant is still ionic-strength-dependent. The results obtained with sulfuric and perchloric acids are found to be consistent and in relatively good agreement at small ionic strengths (μ ≤ 0.1 M) only. At a higher ionic strength, the use of sulfuric acid requires sustained attention to the constant of the second dissociation equilibrium. The nonideal solution behavior raising at a high ionic strength makes its estimation deeply sensitive.