(378u) Modeling the Ion Transport and Adsorption Behavior in a Membrane Capacitive Deionization (mCDI) Cell

In the arid west, the freshwater supply of many communities is limited leading to increased interest in tapping brackish water resources. Although reverse osmosis is the most common technology to upgrade saline waters, there is also interest in developing and improving alternative technologies. Here we focus on Capacitive Deionization (CDI) and specifically compare and contrast behavior between conventional CDI and membrane CDI (mCDI). The primary purpose of mCDI is to enhance the separation between salts and water. In this study, a comprehensive two-dimensional model describing ion transport and adsorption behavior was developed and solved numerically, taking advantage of Darcy’s Law, Nernst-Planck equation, Donnan equilibrium and Nernst equation considering non-ideal membrane. The model behavior was supported by the experimentally observed variations in transient effluent concentration under different operating conditions. The advantages of mCDI over conventional CDI in adsorption amount and ion separation rates were shown in the simulation results. The simulated concentration, potential and ion flux distributions in the mCDI and CDI cells were used to better understand the device’s behavior and optimal operating conditions. The model was used to examine the potential influences of cell geometry, membrane properties and operating conditions on the mCDI performance.