Study of current chronograms, structure of dissociation, recombination and equilibrium regions in problems of non-stationary 1:1 electrolyte transfer in membrane systems using a mathematical model

The joint research of the dissociation-recombination reaction and space charge along with their effect on the transfer of 1:1 electrolyte ions appears to be a relevant issue. The article is a theoretical study of the dissociation, recombination and equilibrium areas and the features of salt ion transfer in each of these areas using the method of mathematical modeling. In the article, for the first time, on the basis of a mathematical model of non-stationary transfer of 1:1 electrolyte, the main regularities of the influence of the dissociation and recombination non-catalytic reaction on the transfer of 1:1 salt ions and electroconvection are theoretically established. In particular, the chronograms of the current density with and without taking into account the dissociation/recombination reaction of water, the structure of the dissociation regions, recombination and equilibrium were examined, the dependences on the input parameters were determined: the initial concentration, the potential sweep rate. It has been shown that in the boundary layers of ion-exchange membranes, the dissociation reaction prevails over the recombination reaction due to the fact that in these regions the electric field strength takes such high values that the electric field breaks the water molecules and separates the Н+ and ОН- ions, preventing them from recombining. It has been demonstrated for the first time that in the middle part of the desalination channel, a region is formed where the recombination of H+ and OH- ions predominates. This reaction is local in nature, so all H+ and OH- ions cannot recombine at the same time. As a result, in the region of recombination, an excess of H+ ions emerges on the one side and OH- on the other side, in other words, an electric double layer is developed in the middle part of the desalination channel, and the recombination region is rather narrow. The obtained theoretical results and conclusions can be applied to analyze the operation of electrodialysis machine desalination channels.

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