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Capacitive deionization

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Capacitive deionization (CDI), sometimes called electrosorption desalination, is a technology for desalination and water treatment in which salts and minerals are removed from water by applying an electric field between two porous (often, carbon) electrodes, similar to Electric double-layer capacitor. Counterions are stored in the electrical double layers which form at the solution/matrix interface inside the porous electrodes, with the ions of positive charge (cations) stored in the negatively charged electrode, and vice-versa for the anions, which are stored in the positively biased electrode (anode).

Principle of work

Although CDI (also known as "Flow Through Capacitor") is a complex process of nonlinear dynamics, it is still possible to describe in simple words. Deionization, or removal of ions from an aqueous solution of CDI occurs during charging of two or more pairs of electrodes with high surface water. The electrodes are typically made of charcoal, but other materials are also possible, such as carbon nanotubes (CNT). Anions and cations in solution are electrically absorbed by polarization electric fields on the anode than the cathode electrode by a direct current (DC) power source (Welgemoed and Schutte 2005). The removal of ions in the process depends not only on the potential applied between the anode and cathode, but also depend on the concentration of dissolved solids influential. Electrical double layer (EDL), the theory has proven to be useful for predicting how the ions can be removed depending on the concentration of salt and the cell voltage applied (Zhao et al., 2010).

Technological development

Membrane capacitive deionization

Membrane capacitive deionization (MCDI) is a modification of the CDI, without membranes. The difference is that the membranes of cation exchange, anion exchange membranes, or both, are placed in front of the anode and cathode (Andelman, 2002, Lee et al., 2006, Li et al., 2008). The advantage is that the membrane insertion coions within the material of the electrodes are prevented from returning to the solution bulk and mass transfer has increased 40 times since diffusion mechanism. This has the potential to increase the efficiency for the removal of ions compared to CDI without membranes.

Reversed CDI

Instead of putting energy into the CDI stack charge the cell and thus produce potable water from brackish water energy can be extracted from a cell CDI-flowing water under high salinity and low tide salinity sequentially. During this process of reverse-CDI, a low voltage is applied during continuous flow of water with high salinity, i.e. 0.5 V. When flowing fresh water, salt ions scattered by carbon electrodes against the electrostatic force. Therefore, the electrostatic energy of the system increases. If a resistance or an electrical appliance is connected to the phone, the electricity can be extracted (Brogioli, 2009).

Working Group on CDI in the world

Voltea, a breakthrough in water desalination. Leiden, Netherlands.
Aqua EWP US Patent Application 11,864,879

Wetsus that combines scientific excellence RELEVANT TO Commercial Fini. Leeuwarden, the Netherlands.
Korea Electric Power Research Insitutue. SOUTH KOREA.

Bybliography

1. Arnold, B. B. and G. W. Murphy (1961). "Studies on the Electrochemistry of carbon and carbon chemically modified surfaces. Journal of Physical Chemistry 65 (1): 135 - &.
2. Biesheuvel, P. M. (2009). "The analysis of the thermodynamic cycle for the capacitive deionization." Journal of Colloid and Interface Science 332 (1): 258-264.
3. Biesheuvel, P. M. B. van Limpt, et al. (2009). Dynamic adsorption / desorption process model for capacitive deionization. " Journal of Physical Chemistry C 113 (14): 5636-5640.
4. Brogioli, D. (2009). "Extraction of renewable energy from a difference Salinity using a capacitor." Physical Review Letter 103, 05,801.
5. H. Li, Y. Gao, L. Pan, Y. Zhang, Y. Chen, and Z. Sun, "Desalination Electrosorptive nanotubes and carbon nanofibers electrodes and ion-exchange membranes," Water Research 42 4923 (2008).
6. J.-B. Lee, K.-K. Park, H.-M. Eum and CW Lee, "Desalination of a thermal power station wastewa-ter membrane capacitive deionization," Desalination 196 125 (2006).
7. MD Andelman, "the flow through the barrier charge-capacitor," Can. CA Patent 2444390 (2002).
8. Oren, Y. (2008). "Delonization capacitive (CDI) for the desalination and water treatment - past, present and future (a review)." Desalination 228 (1-3): 10-29.
9. Postel, S. (1992). Last Oasis: Facing Water Scarcity. New York, W.W. Norton & Company.
Welgemoed, T. J. and C. F. Schutte (2005). "Delonization Capacitive Technology (TM): An alternative desalination." Desalination 183: 327-340.
10. R. Zhao, PMBiesheuvel, M. Miedema, H. Bruning, A. van der Wal. "The efficiency of charge: a functional tool to probe the internal structure of double layer porous electrodes, and the application in the modeling of capacitive deionization" J. Phys. Chem. Lett, accepted (2010)
11. RD Atlas "REQUEST TO U.S. Letters Patent" Hybrid capacitive deionization and electro-deionization (CDI - EDI) Electrochemical Cell for the purification of fluids, "patent application 11/864, 879

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