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  Electrochemical liquid treatment equipmentsUSPTO Application #: 20070056847Title: Electrochemical liquid treatment equipments Abstract: The present invention aims to provide electrode compartment structures in electrochemical liquid treatment equipments, which enable stable operation using pure water as an electrode compartment liquid requiring no concentration adjustment without adverse electrode reaction. The present invention relates an electrochemical liquid treatment equipment comprising ion exchange membranes between an anode and a cathode, which has an anode compartment defined by the anode and a cation exchange membrane and a cathode compartment defined by the cathode and an anion exchange membrane (12), each of the anode compartment and cathode compartment being packed with an ion exchanger (14) composed of a fibrous a material, each of the anode and cathode (11) being formed from a liquid- and gas-permeable and electrically conductive material, and the equipment also having an electrode compartment liquid flowing chamber (15) which is formed behind each of the anode and cathode. (end of abstract)
Agent: Wenderoth, Lind & Ponack, L.L.P. - Washington, DC, US Inventors: Masaji Akahori, Sota Nakagawa, Yohei Takahashi USPTO Applicaton #: 20070056847 - Class: 204252000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Cells, Diaphragm Type The Patent Description & Claims data below is from USPTO Patent Application 20070056847. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to electrode compartment structures in electrochemical liquid treatment equipments such as electrodialysis, electrolysis and electrodeionization. BACKGROUND ART [0002] In electrochemical liquid treatment equipments such as electrodialysis, electrolysis and electrodeionization, which are designed for various treatments by passing electricity from electrodes into a liquid to electrolyze or electrically dialyze substance in the liquid, the region containing each electrode plate is often separated by an ion exchange membrane to form an electrode compartment for wetting the electrode in which a liquid from a source other than the treating liquid is circulated. The liquid circulated in this electrode compartment is called electrode compartment liquid and generally consists of a solution containing an electrolyte substance to ensure conductivity. However, the use of the solution containing such an electrolyte substance had the problem that oxidizing or reducing products generated by electrode reactions become to be contained in the electrode compartment liquid to deteriorate the electrode or ion exchange membrane as the operation period progresses. The electrolyte in the electrode compartment liquid must be replenished because the operating voltage of the equipment increases with the resistance in the electrode compartment liquid when the concentration of the electrolyte in the electrode compartment liquid decreases. Moreover, electrode reaction products enter the effluent to degrade the product quality, or the pH of the electrode compartment liquid changes to precipitate substances in the electrode compartment liquid, thereby requiring interventions such as removal of electrode reaction products or replenishment of the electrolyte substance in the electrode compartment liquid. [0003] Thus, the design and operation related to the electrode compartment become complex and expensive materials having high corrosion resistance must be used as electrode materials and ion exchange membranes forming the electrode compartment. When drinking water is to be produced by deionizing brackish water through an electrodialysis (electric dialyzer), for example, an expensive fluorinated ion exchange membrane having high oxidation resistance must be used as an ion exchange membrane forming the anode compartment because chlorine gas is generated at the anode and reacts with water to produce highly oxidizing free chlorine and hypochlorous acid (HOCl). [0004] A method has been proposed by which a bipolar membrane is used in place of ion exchange membranes for diaphragms defining the anode and cathode compartments in an electrodialysis and the electrode compartment liquids for the anode and cathode compartments are separately circulated. If a diaphragm forming an electrode compartment consists of a bipolar membrane, substances in the electrode compartment liquid are scarcely affected because the bipolar membrane is permeable to little electrolyte substance so that only hydrogen ions (cathode compartment) or hydroxide ions (anode compartment) generated in the bipolar membrane flow into the electrode compartment and the hydrogen ions are converted into hydrogen gas at the surface of the cathode and the hydroxide ions are converted into oxygen gas at the surface of the anode. Thus, the method using a bipolar membrane enables continuous electric dialysis without replenishing the anode and cathode compartments with a chemical solution such as an acid or base as an electrolyte during operation. However, this method had the following problems: two electrode compartment liquid flowing systems are required; an expensive bipolar membrane is used; the equipment becomes bulky because the bipolar membrane is difficult to operate at high current densities; and it is difficult to form an anion exchanger region in the bipolar membrane from a fluorinated oxidation-resistant material. [0005] In processes for concentrating and recovering TMAH (tetramethylammonium hydroxide) from waste TMAH solution by electric dialysis, a method for preventing inclusion of impurities into the concentrate has been proposed by supplying a TMAH solution to the anode and cathode compartments to reduce inclusion of impurities into the TMAH solution recovered and also supplying a TMAH solution into an extra liquid chamber formed in the anode compartment in order that heavy amine odor-emitting impurities generated by oxidative decomposition of TMAH in the anode compartment may not penetrate the ion exchange membrane into the concentrate. However, this method had the following disadvantages: the procedure for preparing the TMAH solution supplied to the extra liquid chamber is complex; adverse electrode reactions generating impurities cannot be avoided so that the TMAH solutions circulating in the electrode compartments and extra liquid chamber include impurities and cannot be recovered and recycled. [0006] In electrodeionization apparatus, a method has been proposed by which the anolyte (anode compartment liquid) containing oxidizing substances such as free chlorine discharged from the anode compartment is treated through an activated carbon adsorption column to recycle/reuse the anolyte. However, this method had the following problems: the equipment becomes expensive because of the necessity of the activated carbon adsorption column and its postfilter; and the ion exchange membrane forming the anode compartment cannot be sufficiently prevented from deterioration because oxidizing substances are generated in the anode compartment. [0007] In processes for treating water containing hydrofluoric acid through an electrodeionization (electric deionizer), a method has been proposed by which an electrode compartment liquid channel in each electrode compartment is packed with an ion-conducting spacer in the form of a diagonal net so that the effluent from the electrodeionization poorly containing electrolyte substances can be used as the electrode compartment liquid and adverse electrode reactions are prevented by using the electrode compartment as a deionization compartment to prevent inclusion of electrolyte substances from adjacent compartments. The configuration of an electrode compartment proposed by such a method is shown in FIG. 1. In the conventional electrode compartment structure 1 shown in FIG. 1, an electrode compartment 4 is defined by an electrode 2 and an ion exchange membrane 3, and an ion-conducting spacer 5 having ionic conductivity is packed within the electrode compartment 4 and an electrode compartment liquid inlet 6 and an electrode compartment liquid outlet 7 are connected to the electrode compartment 4. The treated water equivalent to pure water is supplied as an electrode compartment liquid via inlet 6 and discharged via outlet 7 upon ionic conduction by the action of the ion-conducting spacer 5. Such a method of packing the electrode compartment with an ion-conducting spacer is advantageous for avoiding adverse electrode reactions because the treated water equivalent to pure water is supplied to the electrode compartment, but it was insufficient for reducing the operating voltage because a diagonal net having a certain level of mesh size must be used as a spacer to be packed in the electrode compartment in view of the necessity of ensuring a liquid flow in the electrode compartment, which means a small contact area between the electrode surface and ion-conducting spacer and between the ion-conducting spacer and ion exchange membrane and therefore a small area in which ionic conduction occurs. Another problem was that gaseous components generated by electrode reactions were captured by meshes of the spacer and grown to bubbles, which adhered to the electrode surface to increase the voltage drop in the electrode compartment. Thus, a large effluent was needed to remove bubbles from the electrode compartment and a large channel had to be ensured by packing a plurality of expensive ion-conducting spacers to reduce pressure loss, resulting in an increase in cost. Because of these problems, the above method of packing the electrode compartment with an ion-conducting diagonal net spacer involved a high operating voltage and a limited range of usable current density, e.g. this method could be applied to electrodeionization for producing pure water at low operating current densities such as 0.02-0.2 A/dm.sup.2 but hardly applied to electrodialysis at high operating current densities such as 1-20 A/dm.sup.2. [0008] As described above, problems remain unsolved in connection with the electrode compartment liquid in the electrode compartments in electrochemical liquid treatment equipments such as electrolysis (electrolyzers), electrodialysis and electrodeionization. In the electrode compartments of common electrodialysis, a water channel is ensured by packing a plastic spacer, but no current flows if pure water is supplied to the electrode compartments because pure water is an insulator. Thus, an electrolyte solution had to be supplied to the electrode compartments in conventional equipments. [0009] If a fluorine ion-containing solution is used, for example, as an electrode compartment liquid, however, the electrode is corroded by hydrofluoric acid with the result that the durability and economy of the electrode are jeopardized and metal ions dissolved from the electrode are diffused into a treated fluid and included as impurities. If a chlorine ion-containing solution is to be used as an electrode compartment liquid, free chlorine is generated at the anode to deteriorate the ion exchange membrane by oxidation and therefore, an expensive fluorinated membrane resistant to oxidative deterioration must be used as an ion exchange membrane forming the anode compartment. If an organic alkali-containing solution is to be used as an electrode compartment liquid, hazardous oxidative decomposition products are generated by electrode reactions as described above. [0010] For these reasons, an inorganic alkaline aqueous solution such as sodium hydroxide, an acid aqueous solution such as sulfuric acid or a salt aqueous solution such as sodium sulfate is commonly used as an electrolyte substance in the electrode compartment liquid, but the concentration of the electrode compartment liquid varies because the electrode compartment functions as a deionization compartment or concentration compartment during operation. Thus, some interventions are needed such as continuous replenishment of the circulating electrode compartment liquid with the electrolyte substance or partial extraction and dilution of the electrode compartment liquid., as well as complex procedures such as the adjustment and control of the concentration of the electrolyte substance in the electrode compartment liquid during operation. Another problem was that if an electrolyte different from the composition to be recovered by the electrochemical liquid treatment equipment is used as an electrode compartment liquid, it was included as impurity in a recycled fluid. [0011] The present invention aims to solve the problems of the prior art as described above and to provide electrode compartment structures in electrochemical liquid treatment equipments, which enable stable operation using pure water as an electrode compartment liquid requiring no concentration adjustment without adverse electrode reaction. DISCLOSURE OF THE INVENTION [0012] To solve the problems described above, the present invention provides an electrochemical liquid treatment equipment comprising ion exchange membranes between an anode and a cathode, which has an anode compartment defined by the anode and a cation exchange membrane and a cathode compartment defined by the cathode and an anion exchange membrane, each of the anode compartment and cathode compartment being packed with an ion exchanger composed of a fibrous material, each of the anode and cathode being formed from a liquid- and gas-permeable and electrically conductive material, and the equipment also having an electrode compartment liquid flowing chamber which is formed behind each of the anode and cathode. BRIEF EXPLANATION OF THE DRAWINGS [0013] FIG. 1 is a schematic view showing an example of an electrode compartment structure in a conventional electrochemical liquid treatment equipment. [0014] FIG. 2 is a schematic view showing the structure of an embodiment of an electrochemical liquid treatment equipment according to the present invention. [0015] FIG. 3 is a schematic view of a water treatment system used in the examples of the present invention and comparative examples. EMBODIMENTS OF THE INVENTION [0016] Specific embodiments of electrochemical liquid treatment equipments according to the present invention are explained below with reference to the attached drawings. [0017] FIG. 2 is a schematic view showing an electrode compartment structure in an electrochemical liquid treatment equipment according to an embodiment of the present invention. The electrode compartment structure 10 in the electrochemical liquid treatment equipment A comprises an electrode compartment 14 defined by an electrode 11 and an ion exchange membrane 12; and an electrode compartment liquid flowing chamber 15 behind the electrode 11. The electrochemical liquid treatment equipment A comprises another electrode compartment structure opposed to the electrode compartment structure 10 shown in FIG. 2 (i.e. a reversed counterpart on the right side of the electrode compartment structure 10 in FIG. 2 with the ion exchange membrane 12 being on the left side), and ion exchange membranes are appropriately placed between both electrode compartment structures. In the case where the electrochemical liquid treatment equipment is an electrodeionization, for example, cation exchange membranes and anion exchange membranes are at least partially alternately arranged between the opposed electrode compartment structures to form a deionization compartment and a concentration compartment. In an alternative case where the electrochemical liquid treatment equipment is an electrodialysis for recovering acids and alkalis, cation exchange membranes and anion exchange membranes are at least partially alternately arranged between the opposed electrode compartment structures to form an acid compartment, an ionization compartment, an alkali compartment and a water splitting compartment. [0018] As used herein, the expression "behind the electrode" means "behind" viewed from the electrode on the opposite side and may be translated into "outside" the electrochemical liquid treatment equipment composed of two opposed electrodes. [0019] An electrode compartment liquid inlet 16 and an electrode compartment liquid outlet 17 are connected to the electrode compartment liquid flowing chamber 15. If desired, a vent 18 connected to the electrode compartment liquid outlet 17 may be formed. The electrode compartment 14 is packed with an ion exchanger 13 consisting of a fibrous material. The ion exchanger can be composed of a fibrous material in the form of a woven or nonwoven fabric or the like. Continue reading... Full patent description for Electrochemical liquid treatment equipments Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrochemical liquid treatment equipments patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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