Generalized study of the temporal behaviour in recirculating electrochemical reactor systems

This paper outlines and compares mathematical models to predict the temporal variation of concentration and current in an electrochemical reactor coupled with a reservoir operating with continuous recirculation of the electrolyte. The reservoir is considered as a well mixed tank while the dispersion model is used for the reactor. The performances according to the idealized models to represent a reactor, stirred tank and plug flow, are also deduced as limiting cases. Applied studies carried out in rotating cylinder electrodes using the removal of copper from dilute solutions as test reaction are reported. The experimental data are correlated with the theoretical model, numerically solved, using a dimensionless number β, proportional to the kinetic constant, as fitting parameter. The results in accordance with this rigorous model are compared with those of the conventional equations based on the stirred tank model and the error in the evaluation of the kinetic constant can be as high as 26%. From an engineering point of view, a generalized plot to estimate the error is reported, which requires as inputs the experimental slope of the temporal variation of concentration in the reservoir, the Peclet number and the ratio between the reservoir and reactor space times.

► In recirculating systems all the models predict a linear temporal variation of the logarithm of the concentration.
► The hydrodynamics has a strong influence in the evaluation of the kinetic constant.
► The dispersion model is appropriate for rotating cylinder electrodes.