Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2001-09-07
2002-10-08
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S530000
Reexamination Certificate
active
06462935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to capacitive deionization (CDI) of liquids containing charged species, such as industrial waste streams, city sewage and seawater, etc. More particularly, this invention relates to replaceable flow-through capacitors (FTCs) for removing charge-carrying materials from inorganic and organic aqueous solutions.
Background of the Invention
Water is one of the most precious resources to human. It is appropriate to describe the importance of water as “water gives us life”. About three-quarter of the earth surface is covered by water, 98% of which is salt water and the remaining 2% is fresh water. Most of the fresh water is trapped in polar ice caps leaving less than 1% be suitable for direct use. As population grows with increasing urbanization and industrialization. which augment water consumption and waste generation, many countries in the world are thus suffering from water scarcity and environmental pollution. According to a UN prediction, there will be 48 countries, accounting for 32% of the world population, lack of fresh water by the year 2025. Water is vital to both the quality of life and prosperity of economy. Contaminated water can impart illness to people and cost governments millions of dollars to clean the polluted sites. Without fresh water, the daily life and activities of human will be hampered. Providing sufficient sources of fresh water to their people may be the responsibility of governments, yet it is the obligation of people on this globe to conserve water use, to recover useful resources and to reduce pollution.
Desalination of seawater is likely the most economical way to produce fresh water. Seawater is free, unlimited and available all year long unaffected by weathers. Seawater also has the highest content of total dissolved solids (TDS) among all brackish waters. Furthermore, liquid wastes, whether organic or inorganic in nature, frequently contain charged species resulted from hydrolysis, decomposition, flocculation, biological or chemical reactions of solutes. The total amount of charged species in seawater and liquids are expressed as TDS in terms of ppm (parts per million). Whether in desalination or waste treatments, reduction of TDS or deionization is one of the major goals of a purification protocol which may include sedimentation, adsorption, filtration, ozonation, etc. The aforementioned processes are arranged at either upstream or downstream of deionization for pre-treating or post-treating feed liquids. TDS of feed liquids has to be reduced to a certain level of ppm for domestic consumption or industrial applications. Deionization may be achieved using some popular techniques such as ion-exchange, distillation, reverse osmosis (RO), and electrodialysis. In comparison, CDI is relatively new and less known to the general public. In choosing a deionization method, one has to consider the cost of materials and operation, permeate flux (or yield , as well as salt rejection rate.
Most ion-exchange resins for deionization are expensive synthesized materials, which will release relatively benign ions in exchange for toxic ions. With use, the resins will become saturated and require regeneration. Regeneration of ion-exchange resins demands the use of strong acids or strong bases, as well as a lot of rinsing water. Hence, ion-exchange is water-wasteful, and it generates secondary pollution from chemicals used for regeneration. In order to attain fresh water, heat must be invested to seawater or raw waters in a distillation pot. Ions are then left behind as sludge in the pot. Distillation is an energy intensive process requiring a large operation space, for example, an evaporation column of more than 100 m (>300 ft) tall is employed as taught in U.S. Pat. No. 4,636,283 issued to Nasser. Nevertheless, distillation is the most widely used method in the desalination of seawater in the world. Commercially, RO is the second most popular desalination technique. It uses membranes to extract fresh water from brackish waters, while ions are still present in the feed waters. RO depends on high pressure, e.g., 800-1200 psig, to force the permeate (pure water) to pass through the nano-pores of the membranes. High operation pressure and low permeate flux are two disadvantageous characters of RO. While a high operation pressure of RO means a high operation cost, a low permeate flux imparts low throughputs. Lastly, electrodialysis utilizes both a DC electric field and ion-permeable membranes for deionization. There are at least three compartments, i.e., anode, middle and cathode, in each electrodialysis unit. Brackish waters flow in the middle compartment, and ions are drawn to the anode or the cathode compartment by electrostatic attraction in conjunction with selective permeation of membranes. Both the electrodes and the membranes of electrodialysis are extremely costly for treating large quantity of liquids. In terms of pollution reduction, ions are not entrapped or collected in the membrane techniques such as RO and electrodialysis. Therefore, these techniques are merely for liquid purification methods rather than for pollution reduction. On the contrary, CDI is a technique that can perform purification and pollution reduction with high recycle rates of feed liquids.
While solid particles are easily removed by a filtering media, charged species can be effectively detained by an electric field. It is a natural phenomenon that ions respond swiftly and reversibly to an electrostatic attraction. Within liquids containing charged species, such electrostatic attraction is most conveniently created between two parallel conductive plates under an application of an electric current. As charged species flow through the charged plates, they are quickly adsorbed by the plates, resulting in the reduction of TDS. Such a method of desalination is named as capacitive deionization (CDI), and the setup for carrying CDI is known as flow-through capacitor (FTC). The application of FTC was published three decades ago by J. Newman et. al., in J. Electrochem Soc.: Electrochemical Technology, March 1971, Pages 510-517, entitled “Desalting by Means of Porous Carbon Electrodes”. It is incorporated by reference herein. Three representative prior arts of CDI are cited here to examine their commercial perspective, they are U.S. Pat. No. 5,779,891 issued to Andelman, U.S. Pat. No. 5,858,199 to Hanak and U.S. Pat. No. 5,954,937 to Farmer. All three patents are also incorporated by reference herein. The '891 patent uses graphite foil as conductive backing and activated carbon as ion-adsorbing material to form electrodes by physical compression. No chemical bonding, which is more reliable in electric connection than physical compression, exists between the active material and the substrate. A gold compression contact is also used to bind the electrode leads and the wire leads, which are connected to a DC power supply. The inclusion of precious metal will economically prevent the FTC from becoming a consumer product. Furthermore, platinum or other catalytic metal is doped with the carbon electrodes in '891 patent for electrochemically destroying chlorinated hydrocarbons (CHCs). For a higher efficiency of detoxification, CHCs are better treated with ozone than electrolysis. In order to attain the shortest and the straightest flow path, holes arc cut on the electrodes of FTC in '891 patent for aligning with the perforation of the liquid-feeding pipe. Not only the adsorbing area is compromised, the specific orientation of the electrodes also complicates the manufacturing process, which again will increase the cost of the devices and impair the commercial merit of the product.
For the separation of ionic substances from liquids, the patent '199 utilizes a combination of an electric field and a compound centrifugal force or Coriolis force. Incorporating a mechanical rotator in the apparatus results in a high operation cost and is difficult to use. In addition to carbons, the '199 patent also
Hsieh Fei-Chen
Hsieh Yu-His
Lee Chin-Hui
Lo Wan-Ting
Shiue Chia-Chann
Dinkins Anthony
Lih-Ren Shiue
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