Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1995-01-27
1996-07-23
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204518, 204551, 204554, 204600, 204627, 204665, 204673, B01D 1706, B03C 502, C10G 3302
Patent
active
055386113
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The method is known by which ionic substances are removed from water containing them by the utilization of electrostatic forces using an electric double-layer capacitor.
For example, the specification of U.S. Pat. No. 5,192,432 describes a flow-through capacitor for controlled charge chromatography comprising a spirally wound plurality of adjacent layers including a first electrically conductive backing layer, a first high surface area conductive layer, a first non-conductive porous spacer layer, a second conductive backing layer, a second high surface area conductive layer and a second non-conductive porous spacer layer. It is also shown in the same specification that this capacitor finds application in, for example, the purification of water containing ionic substances, such as sodium chloride.
SUMMARY OF THE INVENTION
The invention relates to a flow-through, electric, double-layer capacitor of planar configuration utilizing active carbon layers. The invention further relates to a method of treating a fluid containing ionic substances with this flow-through, electric, double-layer capacitor of planar configuration.
The flow-through capacitor disclosed is U.S. Pat. No. 5,192,432 is of interest. However, since this flow-through capacitor comprises a plurality of adjacent layers in a spirally wound form, channeling tends to occur on passage of a fluid, and it was found that when this flow-through capacitor is applied to the purification of a liquid containing ionic solutes, the rate of removal of the ionic substances is not constant but fluctuates and, moreover, the mean rate of removal is fairly lowered. It was thus discovered that this flow-through capacitor can hardly be employed in the purification of liquids on an industrial scale.
Under the circumstances, this invention has for its object to provide a flow-through, electric, double-layer capacitor providing for high and steady rates of removal of ionic substances and for industrial-scale application and a method of treating fluids with said flow-through, electric, double-layer capacitor.
The planar, flow-through, electric, double-layer capacitor of the invention comprises a separator (1) consisting in an electrically-insulating, porous, flow-through sheet, active carbon layers (2), (2) each comprising a high specific area activated carbon as disposed on either side of said separator (1), collector electrodes (3), (3) disposed externally of said active carbon layers (2), (2) and retaining plates (4), (4) disposed externally of said collector electrodes (3), (3).
The method of treating a fluid according to the invention is characterized in that while a fluid containing ionic substances is passed through said planar, flow-through, electric, double-layer capacitor, application of a direct current constant voltage to the collectors (3), (3) and short circuiting or reversed connection between the two collectors (3), (3) are alternately repeated.
The invention is now described in detail.
The separator (1) is an electrically-insulating, organic or inorganic sheet across which fluids are ready to flow, such as filter paper, a porous polymer film, a woven cloth or a nonwoven cloth, for instance. The thickness of the separator is about 0.01 mm to 0.5 mm and preferably about 0.02 mm to 0.3 mm.
The active carbon layers (2), (2) are layers each comprising a high specific area activated carbon as a main component. The high specific area activated carbon mentioned above means an activated carbon with a BET specific surface area of not less than 1000 m.sup.2 /g, preferably not less than 1500 m.sup.2 /g and, for still better results, 2000 m.sup.2 /g to 2500 m.sup.2 /g. When the BET specific surface area of carbon is too small, the rate of removal of ionic substances from a fluid is low. If the BET specific surface area is too large, the rate of removal of ionic solutes rather tends to decrease, suggesting that it is not mandatory to provide for more than necessary expansion of BET surface area.
The form of activated carbon is optional. T
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Johnson et al, "The Electrosorb Process for Desalting Water" Mar. 1970, The Office of Saline Water Research and Development Progress Report No. 516, U.S. Dept. of the Interior PB 200 056.
Johnson et al, "Desalting by Means of Porous Carbon Electrodes", Mar. 1971, pp. 510-517, J. Electrochem. Soc. Electrochemical Technology (vol. 118, No. 3).
Ganzi et al, "Water Purification and Recycling Using the CD1 Process", Feb. 1992, pp. 49-53, Environmental Progress (vol. 11, No. 1).
Crowley Richard P.
Marc D. Andelman
Niebling John
Wong Edna
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