Influence of Electrodialyzer Channel Parameters on Chronopotentiometric Transition Time

For more than a century, the theoretical concepts proposed in the works of Sand have been used by scientists in the field of chronopotentiometry of electrode and membrane systems. The development of these representations makes it possible to more accurately determine the parameters of objects under study and to identify significant factors that seemed insignificant. In this article, using a nonstationary two-dimensional galvanostatic convective-diffusion model of salt ion transport, a theoretical analysis is made of the influence of the dimensions of the electrodialyzer flow-through desalting compartment on the transition time, τ, of chronopotentiograms. It is shown that the local density of electric current is distributed unevenly along the entire length of the desalting channel, and its value at the entrance is more than an order of magnitude higher than the average and is 1–13% (depending on the length of the channel) lower in the rest of the region. The Sand theory, in turn, assumes a uniform distribution of current density. It has been established that the τ values obtained using the two-dimensional model are greater than those calculated using the Sand equation, τ_s. As the desalting channel length L decreases, the difference between τ and τ_s increases from 3% (at L = 30 mm) to 14% (at L = 1 mm). The results obtained are in good agreement with the experimental data presented in the previous paper for the homogeneous Neosepta CMX membrane. The found dependence will reduce the error in measuring the properties of flow-through electrodialyzers using the chronopotentiometic transition time.