Dynamic Adsorption/Desorption Process Model for Capacitive Deionization
Dynamic Adsorption/Desorption Process Model for Capacitive Deionization
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DOI：
10.1021/jp809644s
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发表时间：
2009-04-09
影响因子：
3.7
通讯作者：
van der Wal, A.
中科院分区：
文献类型：
--
作者：
Biesheuvel, P. M.;van Limpt, B.;van der Wal, A.
在电容去离子 (CDI) 中，在相对放置的电极上施加电势差，导致从水溶液和部分离子耗尽的产物流中吸附离子。 CDI 是一个以顺序模式运行的动态过程；即，达到一定的离子吸附能力后，降低施加的电压，离子被释放回溶液中，从而形成离子浓缩的溶液。 CDI的能量输入非常小，而且不涉及需要定期更换的离子交换材料。在这里，我们提出了 CDI 的动态过程模型，其中包括电极极化层中离子的存储和释放。极化层的电荷和离子吸附能力使用平衡 Gouy-Chapman-Stem (GCS) 模型进行描述，而从本体溶液到极化层的电荷转移速率则根据欧姆定律进行建模，即仅取决于传质层上的电场项。模型中的一个重要元素是微分电荷效率：相对于电子电流的有效除盐率，基于GCS模型推导了其解析表达式。我们基于假设 CDI 晶胞中理想混合的过程模型，给出了流出物盐浓度和电子电流的结果，两者都是时间的函数。理论结果与示例数据集非常吻合。
In capacitive deionization (CDI), an electrical potential difference is applied across oppositely placed electrodes, resulting in the adsorption of ions from aqueous solution and a partially ion-depleted product stream. CDI is a dynamic process which operates in a sequential mode; i.e., after a certain ion adsorption capacity has been reached, the applied voltage is reduced, and ions are released back into solution, resulting in a solution concentrated in ions. The energetic input of CDI is very small, while there are no ion-exchange materials involved that need to be replaced regularly. Here we present a dynamic process model for CDI which includes the storage and release of ions in/from the polarization layers of the electrodes. The charge and ion adsorption capacity of the polarization layers is described using the equilibrium Gouy-Chapman-Stem (GCS) model, while the charge transfer rate from bulk solution into the polarization layer is modeled according to Ohm's law, i.e., depends solely on an electric field term across a mass-transfer layer. An important element in the model is the differential charge efficiency: the effective salt removal rate relative to the electronic current, for which an analytical expression is derived based on the GCS model. We present results for the effluent salt concentration and electron current, both as function of time, based on a process model that assumes ideal mixing in the CDI unit cell. The theoretical results are in very good agreement with an example data set.