Determination of limiting current density and current efficiency in electrodialysis units
Determination of limiting current density and current efficiency in electrodialysis units
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DOI：
10.1016/j.desal.2018.07.028
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发表时间：
2018-11-01
期刊：
影响因子：
9.9
通讯作者：
Micale, Giorgio
中科院分区：
文献类型：
--
作者：
La Cerva, Mariagiorgia;Gurreri, Luigi;Micale, Giorgio
电渗析（艾德）单元的设计和操作的关键参数是极限电流密度（LCD）。这通常与扩散限制电流密度相一致，其对应于与膜相邻的层中的完全溶质耗尽。从电极与溶液接触（即无膜）的测量中获得的电流-电压曲线与该解释一致，并显示出识别LCD的水平平台。然而，真实的艾德系统显示出更复杂的行为，具有减小斜率的道而不是平台和电流增加更显著（过限电流）的第三区域。在极限区所涉及的现象还没有完全特征化，并且在艾德单位中LCD的确定仍然是模糊的。在目前的工作中，我们探讨了相关的问题，识别的LCD，通过测量艾德单位，评估的影响，操作条件和验证一个简化的过程模拟器。提出了一种基于电流效率的LCD测量方法，并与文献中提出的其他方法进行了比较。还确定了第二个限制量，即临界电流密度，低于该值，扩散现象占主导地位的迁移，并提出了一种评估方法。
A crucial parameter for the design and operation of electrodialysis (ED) units is the limiting current density (LCD). This is often identified with the diffusion-limited current density, which corresponds to the complete solute depletion in the layer adjacent to the membrane. Current-voltage curves obtained from measurements with electrodes in contact with the solution (i.e. without membranes) are consistent with this interpretation and exhibit a horizontal plateau identifying LCD. However, real ED systems show more complex behaviours, with a reduced-slope tract instead of a plateau and a third region in which the current increases more markedly (overlimiting current). The phenomena involved in the limiting region are not yet totally characterized and the determination of LCD in ED units is still ambiguous. In the present work, we explore the issues related to the identification of LCD, by measurements on ED units, assessing the influence of operating conditions and validating a simplified process simulator. A new method to determine LCD, based on the current efficiency, is proposed and compared with other methods presented in the literature. A second limiting quantity is also identified, i.e. the critical current density, below which diffusion phenomena prevail on migration and a method for its assessment is proposed.