Kinetic investigation of the Dushman reaction at concentrations relevant to mixing studies in stirred tank reactors

Experimental studies have been performed concerning the kinetics of the Dushman reaction at conditions relevant to mixing studies in stirred laboratory vessels. The reactive system has been tested by varying the amount of the reactive and non-reactive components. By this approach, information on the absolute value of the reaction rate is not accessible. However, relative influences of the reactants and a potential influence of the ionic strength can be observed. It was found that the ionic strength has no observable influence on the rate of the Dushman reaction as opposed to a rate law, generally accepted for mixing studies. Feeding sulfate separately to the bulk solution and the acid feed reveals that local concentrations relevant to mixing studies are high acid concentrations (close to the feed concentrations) and correspondingly low concentrations of I− and IO3−. Based on the experimental findings, we suggest the following reaction orders: H+, 0.6; IO3−, 0.6; I−, 1.4. Using perchloric acid instead of sulfuric acid yields higher optical densities of the resulting solutions. This effect was found to be more severe than assumed previously.

► Kinetic examinations closest possible to the corresponding mixing experiments. ► In contrast to previous findings we suggest new reaction orders. ► No influence of the ionic strength is found. ► For the derivation of micromixing times the role of sulfate as a base needs to be considered.