Electrodialytic Desalination at High Currents - On the Interplay of Electroconvection, Water Dissociation and Channel Geometry

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Electroconvective vortices emerging in an electrodialysis cell increase the mass transfer significantly, since they convectively supply ion-rich solution to the membrane surface through the boundary layer where depletion takes place. Today, it is unclear if this beneficial effect also appears in spacer-filled channels subject to cross flow. Despite the importance of these vortices, the nature of their formation and their development is under extensive discussion. Additionally, water dissociation, which is the second crucial phenomenon for the potential current increase at high current densities, was omitted in most modeling approaches of electroconvection. At high driving forces water dissociates into H+ and OH- ions that also contribute to the current and interact with electroconvection. This process is not desired in most applications, because it lowers the flux of the ions of interest. Moreover, little is known about the influence of spacers on electroconvection. The question whether the spacers placed into a channel benefit vortices formation was not answered yet. The proposal aims to investigate the behavior of electroconvective vortices formed during electrodialysis at high current densities with a particular focus on the role of spacers placed in the channel.This unique research approach combines numerical and experimental methods with complementary competencies of the Russian and Germany research teams. The project will deliver deep insight into the interplay of electroconvection, convection induced by spacers and water dissociation at high current densities. The knowledge gained will potentially broaden the scope of electrodialytic desalination towards high current densities - a scope currently avoided due to incomplete comprehension of the phenomena involved.