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

出现在电渗析池中的电对流涡流显著增加了传质，因为它们通过发生耗尽的边界层对流地将富含离子的溶液供应到膜表面。今天，尚不清楚这种有益的效果是否也出现在受到交叉流的间隔填充通道中。尽管这些漩涡的重要性，其形成和发展的性质是在广泛的讨论。此外，水解离，这是第二个关键现象的潜在电流增加在高电流密度，被忽略在大多数模拟方法的电对流。在高驱动力下，水解离成H+和OH-离子，这些离子也有助于电流并与电对流相互作用。该过程在大多数应用中是不期望的，因为它降低了感兴趣的离子的通量。此外，很少有人知道的电对流的影响的间隔。通道中放置间隔物是否有利于涡流的形成，这一问题尚未得到解答。该提案旨在研究在高电流密度下电渗析过程中形成的电对流涡流的行为，特别关注放置在通道中的间隔物的作用。这种独特的研究方法将数值和实验方法与俄罗斯和德国研究团队的互补能力相结合。该项目将深入了解电对流，由间隔物引起的对流和高电流密度下的水解离的相互作用。所获得的知识将有可能扩大电渗析脱盐的范围向高电流密度-目前避免的范围，由于所涉及的现象的不完全理解。

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.