HK1122268B

HK1122268B - Ion concentration regulation method and ion concentration regulation apparatus

Info

Publication number: HK1122268B
Application number: HK09102733.9A
Authority: HK
Inventors: 棚桥正和; 棚桥正治
Original assignee: 棚氏处理有限公司
Priority date: 2005-09-27
Filing date: 2006-09-25
Publication date: 2012-03-23

Description

Ion concentration adjusting method and ion concentration adjusting device

Technical Field

The present invention relates to an ion concentration adjustment method and an ion concentration adjustment device.

Background

At present, as a method for removing ions in an aqueous solution, a method using an ion exchange resin, a method using a liquid flow type capacitor have been proposed.

When a Flow-Through Capacitor (Flow-Through Capacitor) is used, ions are removed by adsorbing the ions on the electrode. For example, devices using a liquid flow type capacitor are described in U.S. Pat. No. 5192432, U.S. Pat. No. 5196115, Japanese patent application laid-open No. 5-258992, U.S. Pat. No. 5415768, U.S. Pat. No. 5620597, U.S. Pat. No. 5748437, Japanese patent application laid-open No. 6-325983, and Japanese patent application laid-open No. 2000-91169.

In the above-described flow type capacitor, the liquid to be treated is continuously supplied from the inlet into the capacitor in which the electrodes are arranged, and the liquid after treatment is continuously discharged from the outlet. Therefore, the closer to the inlet, the higher the ion concentration of the liquid to be treated, and the closer to the outlet, the lower the ion concentration. Further, since the adsorption of ions to the electrode occurs from the introduction port, the ion adsorption capacity of the electrode gradually decreases from the introduction port side. Therefore, when ions are removed using a liquid flow capacitor, it may be difficult to sufficiently exhibit the capability of the electrode.

Disclosure of Invention

Under such circumstances, an object of the present invention is to provide an ion concentration adjusting method and an ion concentration adjusting apparatus capable of effectively adjusting the ion concentration of a solution (liquid).

In order to achieve the above object, the method of the present invention for adjusting ion concentration includes (i) an adsorption step: in a container, in a state where a first ion-adsorbing electrode containing a first conductive substance capable of adsorbing ions and a second ion-adsorbing electrode containing a second conductive substance capable of adsorbing ions are immersed in a solution containing at least one kind of ions (L) other than hydrogen ions and hydroxide ions, a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as an anode, whereby anions in the solution are adsorbed on the first ion-adsorbing electrode and cations in the solution are adsorbed on the second ion-adsorbing electrode. In the ion adsorption step (i), the solution is treated in a batch manner. The voltage is higher than the voltage at which the solvent of the solution is electrolyzed, assuming that there is no voltage drop of the solution.

The ion concentration adjusting apparatus of the present invention includes a power supply for applying a voltage, a container capable of introducing and discharging a liquid, and first and second ion-adsorbing electrodes disposed in the container. The first ion-adsorbing electrode contains a first conductive substance capable of adsorbing ions, and the second ion-adsorbing electrode contains a second conductive substance capable of adsorbing ions. In this apparatus, (i) the adsorption step is performed in the container: in a state where the first and second ion-adsorbing electrodes are immersed in a solution containing at least one kind of ions (L) other than hydrogen ions and hydroxide ions, a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as an anode, whereby anions in the solution are adsorbed on the first ion-adsorbing electrode and cations in the solution are adsorbed on the second ion-adsorbing electrode. In the step (i), the solution is treated in a batch manner. The voltage is higher than the voltage at which the solvent of the solution is electrolyzed, assuming that there is no voltage drop of the solution.

In the present invention, the pH of the solution and the liquid to be treated can be adjusted by using the counter electrode. In the present invention, the amount of ion adsorption on the electrode can be adjusted by using the counter electrode.

According to the present invention, the ion concentration and pH of the liquid can be effectively adjusted using a small-sized apparatus.

Drawings

Fig. 1A is a diagram schematically showing an example of a process of the ion concentration adjustment method according to the present invention; FIG. 1B is a view schematically showing an expected state of adsorption of ions;

FIG. 2 is a view schematically showing a conventional ion removal method using a liquid flow type capacitor;

FIG. 3 is a diagram schematically showing an example of a voltage drop in the ion concentration adjustment method according to the present invention;

FIG. 4 is a view schematically showing another example of the steps of the ion concentration adjustment method according to the present invention;

FIG. 5 is a view schematically showing an example of an ion concentration adjusting apparatus according to the present invention;

fig. 6A to 6C are views schematically showing the configuration of an electrode group used in the example;

FIG. 7 is a view schematically showing the constitution of an electrode used in the embodiment;

FIG. 8 is a graph showing changes in applied voltage in the ion adsorption step of the example;

fig. 9 is a graph showing the relationship between the energization time and the current in the ion adsorption step of the example.

Detailed Description

Embodiments of the present invention will be described below. In the following description, the present invention is described by way of example, but the present invention is not limited to the example described below. In the description using the drawings, the same reference numerals are given to the same portions, and overlapping description may be omitted. The drawings used in the following description are schematic drawings.

[ method for adjusting ion concentration (method for adjusting liquid quality) ]

Next, the method of the present invention for adjusting the ion concentration will be described. For this process, hydrogen ions (H) are contained⁺) And hydroxide ion (OH)^-) A solution of at least one other ion (L) is disposed in the container. Hereinafter, this solution may be referred to as "solution (a)". The solvent of the solution (A) is water and/or an organic solvent. That is, the solution (a) is an aqueous solution or a nonaqueous solution (ion-containing nonaqueous solution). The solvent of the aqueous solution is water or a mixed solvent of water and an organic solvent. The solvent of the non-aqueous solution is an organic solvent. Examples of the organic solvent include: alcohols such as ethanol, ketones such as acetone, propylene carbonate, ethylene carbonate, and dimethyl carbonate. Alcohols such as ethanol are used in various fields such as industry and medical treatment. Ketones such as acetone are used for cleaning research instruments and for polishing solutions.

A first ion-adsorbing electrode containing a first conductive material capable of adsorbing ions and a second ion-adsorbing electrode containing a second conductive material capable of adsorbing ions are immersed in a solution (A) placed in a container. In this state, a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as an anode (that is, so that the second ion-adsorbing electrode serves as a cathode). By applying this voltage, anions in the solution (a) can be adsorbed on the first ion-adsorbing electrode, and cations in the solution (a) can be adsorbed on the second ion-adsorbing electrode.

If it is assumed that there is no voltage drop of the solution (a), the applied voltage is higher than the voltage at which the solvent of the solution (a) is electrolyzed. Hereinafter, the voltage at which the solvent of the solution (a) is electrolyzed when it is assumed that the voltage of the solution (a) is not decreased is sometimes referred to as "decomposition voltage of the solvent". For example, in the case where the solution (a) is an aqueous solution, the applied voltage is a voltage higher than 2 volts. Even when a voltage higher than the "decomposition voltage of the solvent" is applied, the solvent is not decomposed as long as the voltage drop due to the resistance of the solution (a) is sufficiently large.

When the voltage of the aqueous solution is decreased, water is electrolyzed by applying a voltage of 2 volts. In the method of the present invention, by applying a voltage higher than 2 volts, anions in the aqueous solution can be adsorbed on the first conductive substance of the first ion-adsorbing electrode, and cations in the aqueous solution can be adsorbed on the second conductive substance of the second ion-adsorbing electrode. The voltage to be applied may be higher than 3 volts, higher than 5 volts, or higher than 10 volts, as long as the influence of the electrolysis of water is not a problem. The higher the applied voltage is, the faster the ion removal rate is, so long as the electrolysis of water does not occur. The applied voltage is, for example, 500 volts or less, typically 200 volts or less.

When the solution (a) is a nonaqueous solution, the voltage applied is higher than the voltage at which the organic solvent of the solution (a) is electrolyzed, assuming that there is no voltage drop of the solution (a). However, the voltage to be applied is preferably equal to or lower than a voltage at which the electrolytic decomposition of the solvent is substantially less, for example, equal to or lower than a voltage at which the solvent is not substantially decomposed. When the resistance of the solution (a) is large, a voltage drop due to the resistance of the solution (a) increases, and therefore, a voltage much higher than the decomposition voltage of the solvent when the solution (a) is assumed to have no resistance is applied.

The method of the present invention is preferable as a method for removing ions from a solution having a low ion concentration (for example, a solution having a conductivity of less than 10 mS/cm). In the method of the present invention, ions in the solution can be removed by widening the interval between the electrodes, adding more solution therebetween and applying a voltage higher than 2 volts.

In the ion adsorption step (i)), the solution (a) is treated in a batch manner. In the treatment in the step other than the step (i), the liquid may be treated in a batch manner, or may be treated continuously in a liquid-passing manner.

In the existing treatment method using the liquid flow type capacitor, the solution is continuously treated. In contrast, in the method of the present invention, the solution (a) is treated in a batch manner in the ion adsorption step (i)). The batch system is a system in which the liquid in the container is treated without substantially changing the liquid in the container. When the treatment of the solution (a) is completed, usually, the solution (a) in the container is discharged and another liquid is introduced into the container. In general, the addition and discharge of the solution in the container are not performed until the end of the treatment, and the batch-type treatment is suitable as long as the addition and discharge of the solution in the container are not performed until the end of the treatment. That is, even if a small amount of solution is added and discharged without affecting the treatment, the batch system is suitable. For example, it is considered that the batch system is suitable even if a solution of 20 vol% or less (for example, 10 vol% or less, 5 vol% or less, or 1 vol% or less) of the solution in the container is added and/or discharged during the treatment.

The solution (A) contains hydrogen ions (H)⁺) And hydroxide ion (OH)^-) At least one other ion (L). When the solution (a) is an aqueous solution, the solution (a) contains at least one kind of ion (L) in addition to hydrogen ions and hydroxide ions. The solution (A) contains, for example, at least one kind of cation (L) other than hydrogen ions⁺) And at least one anion (L) other than hydroxide ion^-) Both of them are aqueous solutions. The anion other than the hydrogen ion is not limited, and may be, for example: alkali metal ions such as sodium ion or potassium ion, calcium ion and magnesiumAlkaline earth metal ions such as ions, transition metal ions such as iron ions, and ammonium ions. The ions other than the hydroxide ions are not limited, and may be organic ions such as oxalic acid ions, chloride ions, sulfate ions, or nitrate ions.

The concentration of the ion (L) in the solution (a) can be reduced by the step (i). However, in the initial stage of ion removal, a voltage lower than the "decomposition voltage of the solvent" described above may be applied. For example, when the solution (a) is an aqueous solution, a voltage of 2 volts or less may be applied in the initial stage.

Hereinafter, the first ion-adsorbing electrode may be referred to as a "first electrode", and the second ion-adsorbing electrode may be referred to as a "second electrode". When a voltage is applied between the first electrode and the second electrode such that the first electrode serves as an anode (i.e., such that the second electrode serves as a cathode), positive charges are accumulated on the surface of the first conductive material of the first electrode, and negative charges are accumulated on the surface of the second conductive material of the second electrode. As a result, the anion (L)^-) Adsorbed on the first conductive material of the first electrode, cation (L)⁺) Adsorbed on the second conductive material of the second electrode.

Preferably, the voltage applied between the first electrode and the second electrode is changed according to the concentration of the ions (L) in the solution (a). By applying a voltage in a range in which the solvent (water and/or organic solvent) of the solution (a) is not electrolyzed, ions can be efficiently removed. Since the voltage drop of the solution (a) is large as the concentration of the ions (L) in the solution (a) is small, the solvent is not electrolyzed even when a high voltage is applied. Therefore, the voltage applied between the first electrode and the second electrode can also be increased as ions are removed. When a voltage is applied between the first electrode and the second electrode such that the value of the current flowing between the first electrode and the second electrode is constant, the voltage applied between the first electrode and the second electrode increases as the concentration of the ions (L) in the solution (a) decreases. In this case, it is preferable to set the current value in a range in which the solvent is not electrolyzed on the first and second electrodes. However, the voltage application may be performed before the electrolysis occurs in the first electrode and/or the second electrode, and the gas generation may be set as a reference for stopping or terminating the voltage application.

The shape of the first and second electrodes is not limited, and a flat plate-like electrode may be used. Ions of the solution (a) disposed in a region other than the region between the first electrode and the second electrode are difficult to be processed. Therefore, it is preferable that the solution (a) is disposed substantially between the first electrode and the second electrode. For example, it is preferable that 70% by volume or more of the solution (a) is disposed between the surface including the sheet-like first electrode and the surface including the sheet-like second electrode, and more preferably 90% by volume or more of the solution (a) is disposed between the surfaces.

In the batch process, the amount of the solution (a) disposed between the first electrode and the second electrode is preferably determined based on the relationship between the amount of the ions (L) contained in the solution (a) and the ion adsorption energy of the electrode. Specifically, it is preferable to adjust the amount of the solution (a) disposed between the electrodes so that the total of the ion adsorption energy of the first electrode and the ion adsorption energy of the second electrode is 0.3 times the amount of the ions (L) contained in the solution (a). When the total amount of the ions (L) is 0.3 times or more, the ion (L) concentration of the solution (A) can be reduced to one fifth or less by 5 times of the treatment. In addition, when the total amount is 1 time or more of the ions (L), theoretically, most of the ions can be removed by one treatment. Both the solutions (a) disposed between the electrodes can be changed by changing the distance between the electrodes.

The first and second conductive substances are substances capable of reversibly adsorbing ions. A substance having a large specific surface area can be used for the first and second conductive substances. For example, porous materials are used as the first and second conductive materials. More specifically, the first and second conductive materials used for the electrodes of the flow capacitor may be used. A typical example of the first and second conductive materials is a porous carbon material. Among carbon materials, activated carbon is preferably used because of its large specific surface area. For example, the first and second conductive materials may be conductive sheets formed by aggregating granular activated carbon. The first and second conductive materials may be conductive sheets formed by agglomerating granular activated carbon and conductive carbon. The first and second conductive materials may be activated carbon blocks formed by aggregating activated carbon particles. The first and second conductive materials may be activated carbon fiber cloths, that is, cloths (cloths) formed using activated carbon fibers. As the activated carbon fiber cloth, for example, ACC5092-10, ACC5092-15, ACC5092-20 and ACC5092-25 manufactured by Karanol (カイノ - ル) Co., Ltd., Japan, can also be used.

The first and second electrodes (ion-adsorbing electrodes) preferably have a structure through which ions easily pass. By using such an electrode, the bias of the ion concentration in the solution can be suppressed. For example, when granular activated carbon is used as the conductive material, it is preferable to form an electrode by coating the granular activated carbon on a porous current collector and a current collector having through holes such as punched metal. In addition, activated carbon fiber cloth is particularly preferably used for the electrode.

When the solution (a) is an aqueous solution, the method may further comprise, after the step (i): and (a) adjusting the pH of the solution (A) by applying a voltage between a counter electrode immersed in the solution (A) and one electrode selected from the first and second electrodes. After the treatment for removing ions, the pH of the solution (a) may change, and the pH can be adjusted in the step (a).

The Counter Electrode (Counter Electrode) is disposed between the first Electrode and the second Electrode, for example. In the method of the present invention, the distance between the first electrode and the second electrode can be made larger than that of the flow-type capacitor, and therefore, a counter electrode can be disposed between the two. The counter electrode is preferably shaped so as not to inhibit the passage of ions between the first electrode and the second electrode as much as possible. The electrode having a porous load may be a mesh-like electrode or a flat plate-like electrode having a plurality of through holes formed therein. These electrodes are preferred because ions can pass through them. The counter electrode is preferably an insoluble electrode. An example of the counter electrode is an electrode whose surface is covered with a metal (for example, Pt) that is likely to cause water decomposition, and for example, an electrode composed of a Pt electrode and Ti coated with Pt.

The actual surface area (surface area measured by BET method or the like) of the counter electrode is 10 times or less (for example, 5 times or less) the surface area on the outer surface (surface area of the outer shape). Examples of such a counter electrode include a general metal electrode.

The step (a) is performed by immersing the counter electrode in the solution (a) and applying a voltage between the first electrode or the second electrode and the counter electrode. When the pH of the solution becomes low, a voltage is applied between the first electrode and the counter electrode such that the first electrode serves as a cathode and the counter electrode serves as an anode. Thereby, with respect to the first electrode, anions adsorbed on the first electrode are discharged, and cations are adsorbed on the first electrode. On the other hand, the counter electrode generates hydrogen ions and oxygen gas by the electrolysis of water. As a result, the pH of the solution decreases.

When the pH of the aqueous solution increases, a voltage is applied between the second electrode and the counter electrode so that the second electrode serves as an anode and the counter electrode serves as a cathode. Thereby, with respect to the second electrode, cations adsorbed on the second electrode are discharged, and anions are adsorbed on the second electrode. On the other hand, the counter electrode generates hydrogen ions and oxygen gas by the electrolysis of water. As a result, the pH of the solution rises.

In the method of the present invention, the following ion release step (ii) may be performed after the step (i). In the step (ii), first, the solution (a) in the container is converted into another liquid (hereinafter, sometimes referred to as liquid (B)). Next, a voltage is applied between the first electrode and the second electrode with the first electrode being a cathode (i.e., with the second electrode being an anode). The voltage application causes the anions adsorbed on the first electrode and the cations adsorbed on the second electrode to be released into the liquid (B), and the voltage for decomposition in the step (ii) is not limited, and may be, for example, a voltage that does not substantially cause the solvent of the liquid (B) to be electrolyzed.

The Liquid (B) may be an Aqueous Liquid (Aqueous Liquid), or may be a non-Aqueous Liquid for the day. The aqueous liquid is water or an aqueous solution. The nonaqueous solution is an organic solvent or a nonaqueous solution containing ions. In the case where the solution (a) is an aqueous solution, an aqueous liquid is usually used as the liquid (B). When the solution (a) is a nonaqueous solution, a nonaqueous liquid is usually used as the liquid (B).

The liquid (B) is different from the solution (a), but may contain a part of the solution (a). In general, the solution (a) having passed through the step (i) is discharged from the container, and then another liquid is introduced into the container, whereby the solution in the container is replaced. According to the step (ii), the concentration of the ions (L) in the liquid (B) can be increased.

The adsorbed ions may be released into the liquid (B) by a method other than the step (ii). For example, by short-circuiting the first electrode and the second electrode without applying a voltage, anions and cations adsorbed on the electrodes can be released. In the case where the liquid (B) is an aqueous liquid, a counter electrode may be added to the liquid (B), and a voltage may be applied between the first electrode and the counter electrode so that the first electrode serves as a cathode, whereby anions adsorbed on the first electrode may be released into the liquid (B). Alternatively, a counter electrode may be added to the liquid (B), and a voltage may be applied between the second electrode and the counter electrode so that the second electrode serves as an anode, whereby cations adsorbed on the second electrode may be released into the liquid (B).

When the liquid (B) is an aqueous liquid, the step (a') may be included after the step (ii). In the step (a'), the pH of the liquid (B) is adjusted by applying a voltage between the counter electrode immersed in the liquid (B) and one electrode selected from the first and second electrodes. This step (a') is the same as the step (a) described above.

When the liquid (B) is an aqueous liquid, the step (B) may be included after the step (ii). In the step (B), a voltage is applied between the counter electrode immersed in the liquid (B) and at least one electrode selected from the first and second electrodes, thereby controlling a ratio of a charge amount of the anion adsorbed on the first electrode to a charge amount of the cation adsorbed on the second electrode. When a voltage is applied between the first and second electrodes and the counter electrode, the voltage may be applied in a state where the first electrode and the second electrode are short-circuited.

In the method of the present invention, the relationship between the voltage between the first electrode and the second electrode and the first relationship between the first and/or second electrode and the reference electrode may be determined in advance by measurement in an initial state. When the above-mentioned relationship deviates from the relationship obtained in advance after the repetition of the treatment, it can be judged that the balance between the charge amount of the anion adsorbed on the first electrode and the charge amount of the cation adsorbed on the second electrode is lost.

At this time, the ratio of the charge amount of the anions adsorbed on the first electrode to the charge amount of the cations adsorbed on the second electrode is calculated based on the voltage between the first and second electrodes and the potential difference between at least one electrode selected from the first and second electrodes and the reference electrode. Then, the balance of the charge amount is controlled based on the calculation result. The reference electrode may be a general electrode such as a hydrogen electrode.

In the method of the present invention, the liquid (B) which has undergone the ion release step (ii)) may be replaced with another solution, and the adsorption step (i)) may be further performed. As described above, in the method of the present invention, the step (i) and the step (ii) may be repeated a plurality of times. By repeating the ion adsorption step and the ion release step while replacing the solution in the container, a solution having a high ion (L) concentration and a solution having a low ion (L) concentration can be obtained. That is, the method of the present invention can be used as a method for increasing the ion concentration of a liquid and/or a method for decreasing the ion concentration of a liquid.

After the ion adsorption step and the ion release step are performed, particularly after the ion adsorption step and the ion release step are alternately repeated, the balance between the charge amount of the anion adsorbed on the first electrode and the charge amount of the cation adsorbed on the second electrode may be lost. In this case, by applying a voltage between one of the first and second electrodes and the counter electrode, ions adsorbed on the one electrode are released, and the balance of the charge amount can be controlled.

When the solution (a) is an aqueous solution, the method of the present invention may include a step of applying a voltage between the first electrode and the second electrode until oxygen is generated from the first electrode and hydrogen is generated from the second electrode in the step (i) of at least one of the plurality of times. According to this configuration, it is possible to correct the breakdown of the balance of the charge amount due to the repetition of the processing.

The method of the present invention may further comprise, after the step (ii) of at least one of the plurality of times, a step of applying a voltage between the first electrode and the second electrode in a state where the first electrode and the second electrode are short-circuited, so as to release the anions adsorbed on the first electrode and the cations adsorbed on the second electrode. According to this configuration, it is possible to correct the disruption of the balance of the amount of adsorbed ions caused by the repetition of the treatment.

In the method of the present invention, in an initial state, that is, in a stage where the first treatment is performed, it is preferable that: the charge amount of the anions adsorbed on the first electrode until oxygen is generated at the first electrode and the charge amount of the cations adsorbed on the second electrode until hydrogen is generated at the second electrode are substantially equal. Specifically, it is preferable that: the charge amount of the anions adsorbed on the first electrode until the oxygen gas is generated is in the range of 0.9 to 1.1 times the charge amount of the cations adsorbed on the second electrode until the hydrogen gas is generated.

In the method of the present invention, the charge amount of the anion that can be adsorbed on the first conductive substance may be set to a range of 1.1 to 2 times the charge amount of the cation that can be adsorbed on the second conductive substance. With this configuration, the first conductive material and the second conductive material can be adsorbed with high ion balance. For example, when the first conductive material and the second conductive material have the same specific surface area (the ion adsorption capacities of the two are the same), the weight of the first conductive material contained in the first electrode may be set to be in the range of 1.1 to 2 times (preferably in the range of 1.2 to 1.5 times) the weight of the second conductive material contained in the second electrode. Further, as shown in example 7, when ions are adsorbed in a potential region within a decomposition voltage of water in a high concentration ion solution until the solution becomes a saturated state, the amount of the adsorbed ions is measured, whereby the charge amount of the ions that can be adsorbed on the conductive substance can be determined. Specifically, in the cyclic voltammetry, a method of measuring the amount of adsorbed ions by slowing down the rate of voltage rise so as to sufficiently cause adsorption of ions in a high-resistance portion in an electrode may be employed.

The specific surface areas of the first and second conductive materials are 900m²The ratio of the carbon atoms to the carbon atoms may be greater than or equal to g. The upper limit of the comparative surface area is not particularly limited, and is 2500m, for example²The ratio of the carbon atoms to the carbon atoms may be less than or equal to g. A conductive material having a smaller specific surface area, for example, 300m may be used²A conductive material having a specific weight of at least one of the foregoing units. In the present specification, the "specific surface area" is a value measured by a BET method using nitrogen gas.

As described above, the first and second conductive materials may contain activated carbon. The first electrode may include a first wiring connected to the first conductive material, and the second electrode may include a second wiring connected to the second conductive material.

When the first and second conductive materials contain activated carbon, the resistance of the conductive materials is relatively high, and thus the voltage applied to the solution may be non-uniform due to the resistance of the conductive materials. In this case, it is preferable to use a wiring to suppress the influence of the voltage drop by the conductive material. The wiring is preferably formed so that the voltage drop by the conductive material is lower than the voltage drop by the solution.

When the first and second conductive materials contain activated carbon and the first and second electrodes contain wiring, it is preferable that a metal having a smaller oxygen overvoltage than the activated carbon be present on the surface of the first wiring, and that a metal having a smaller oxygen overvoltage than the activated carbon be present on the surface of the second wiring. In the method of the present invention, although the initialization of the electrode and the like may be performed by decomposing water, in this case, the generation of gas on the surface of the wiring by using the wiring formation can be suppressed. In addition, the wiring is preferably a wiring that is difficult to dissolve when the liquid is handled. As a metal whose hydrogen overvoltage and oxygen overvoltage are smaller than that of the activated carbon, that is, a metal which is likely to generate gas than the activated carbon, platinum (Pt) can be mentioned, for example.

In the method of the present invention, platinum may be present on the surfaces of the first and second wirings. An example of the wiring is a wiring coated with platinum, and for example, a wiring obtained by coating titanium and a valve metal (valve metal: for example, aluminum, tantalum, niobium, or the like) used for an electrolytic capacitor with platinum can be used. A particularly preferred example is a titanium wiring coated with platinum.

In the method of the present invention, in the step (i), the voltage applied between the first electrode and the second electrode may be controlled based on the resistance value between the first electrode and the second electrode. The resistance of the solution (or the voltage drop of the solution) varies according to the ion concentration in the solution. Therefore, the treatment can be efficiently performed by changing the applied voltage or stopping the application of the voltage based on the resistance of the solution (or the voltage drop of the solution).

In the method of the present invention, in the step (i), the voltage applied between the first electrode and the second electrode may be controlled based on the value of the current flowing between the first electrode and the second electrode. The amount of electric charge of the ions adsorbed on the ion-adsorbing electrode can be estimated based on the value of the electric current flowing between the electrodes. Therefore, the amount of electric charge of the ions adsorbed on the electrodes is estimated from the amount of current flowing between the electrodes, and the applied voltage is changed or the application of the voltage is stopped based on the estimated value, thereby efficiently performing the treatment.

In the method of the present invention, a plurality of first electrodes and a plurality of second electrodes may be used in the step (i). The ion concentration adjustment capability can be improved by using a plurality of electrodes. One of the first electrode and the second electrode may be singular, and the other may be plural. In the step using a counter electrode, a plurality of counter electrodes may be used.

In the method of the present invention, in the step (i), the voltage may be applied so as to gradually decrease the value of the current flowing between the first electrode and the second electrode. Here, "gradually decrease" includes a case of continuously decreasing and a case of stepwise decreasing.

From another point of view, the present invention relates to a method for sterilizing an aqueous solution using the above method. That is, in the step (i), the potential of the aqueous solution is set to a potential equal to or higher than the oxygen evolution potential. Active oxygen radicals generated at the electrodes have an ability to sufficiently oxidize bacteria, and thus, the aqueous solution can be sterilized.

[ ion concentration adjustment device (liquid quality adjustment device) ]

The ion concentration adjusting apparatus of the present invention is an apparatus for carrying out the ion concentration adjusting method of the present invention. Therefore, the matters described in the description of the ion concentration adjustment method may not be repeated.

The ion concentration adjusting device of the present invention includes: a power source for applying a voltage, a container capable of introducing and discharging a liquid, and first and second electrodes (ion-adsorbing electrodes) arranged in the container. The first electrode contains a first conductive substance capable of adsorbing ions, and the second ion-adsorbing electrode contains a second conductive substance capable of adsorbing ions. In this apparatus, the above-described ion adsorption step (i)) is performed. In step (i), the solution (a) is treated in a batch manner. If no voltage drop is caused by the solution (a), the voltage applied in the step (i) is higher than the voltage at which the solvent of the solution (a) is electrolyzed.

The ion concentration adjusting apparatus of the present invention executes the ion concentration adjusting method of the present invention. Specifically, in this apparatus, the above-described step (i) is performed. In this apparatus, for example, other steps than the step (i) may be performed.

The device of the present invention may also include a counter electrode that may be disposed within the container. The counter electrode is an electrode for generating oxygen and/or hydrogen, and is preferably an insoluble electrode. In the device including the counter electrode, the step of applying a voltage between the first and/or second electrode and the counter electrode as described above may be performed. For example, the step (ii), the step (a), and the step (a') may be performed.

The power source is a power source for applying a voltage between the first electrode and the second electrode and between at least one electrode selected from the first and second electrodes and the counter electrode. The power source is usually a dc power source, but may be a pulse power source or an ac power source, as long as the effects of the present invention can be obtained. The power supply may be used in combination with a time switch, a coulometer, and a pH meter to adjust the ion concentration. For example, a constant current power supply and a timer may be used in combination, or a constant current power supply or a constant voltage power supply and a coulometer and/or a pH meter may be used in combination.

According to the ion concentration adjusting apparatus of the present invention, the ion concentration adjusting method of the present invention can be easily performed. Since the ion-adsorbing electrode, the conductive material, the counter electrode, and the like are described above, redundant description is omitted.

The container is not particularly limited as long as it can hold the liquid to be treated. For example, when the liquid to be treated is an aqueous solution, it may be a container capable of holding an aqueous salt solution, an acidic aqueous solution, and an alkaline aqueous solution. The container preferably includes a mechanism for facilitating replacement of the liquid in the container. For example, the container preferably includes an inlet port for allowing a liquid to flow into the container and a discharge port for discharging the liquid in the container. By using a container having an inlet and an outlet, continuous treatment of the liquid can be performed. In addition, by providing valves for the inlet and the outlet, respectively, batch processing of the liquid can be easily performed.

The apparatus of the present invention may further include a pump for introducing and discharging the liquid.

Further, the apparatus of the present invention preferably includes a control device for performing each step, as in the case of the known pH adjusting apparatus and ion concentration adjusting apparatus. Such a control device may be substantially the same as a known control device including an arithmetic processing unit and a storage unit. Programs for performing the respective steps, target values of ion concentrations (or conductivities of liquids), and the like are recorded in the storage unit. The control device may control the voltage applied to the electrode based on a target value of the ion concentration (and input values from the respective sensors as necessary) or the like.

In the method and apparatus of the present invention, the amount of the liquid to be batch-processed is not particularly limited. The amount may be 1cm by way of example²The surface area (surface area determined by the size of the outline) of the outer surface of the first or second conductive material is in the range of 0.1 ml to 10 ml.

[ embodiment mode 1 ]

Next, an example of the ion concentration adjustment method and apparatus according to the present invention will be described with reference to the drawings. Hereinafter. Although an example in which the solution (A) is an aqueous solution and the liquid (B) is water is described, the same method and apparatus can be used when the solution (A) and/or the liquid (B) is a non-aqueous liquid.

Fig. 1A schematically shows a main part of an ion concentration adjustment apparatus 100 used in the ion concentration adjustment method according to embodiment 1. The ion concentration adjustment device 100 includes: a container 10, a first electrode (first ion-adsorbing electrode) 11 and a second electrode (second ion-adsorbing electrode) 12 disposed in the container 10. An inlet 10a for introducing a liquid and an outlet 10b for discharging the liquid are connected to the container 10. Valves 10c are provided in the inlet 10a and the outlet 10b, respectively.

In the ion concentration adjustment method of the present invention, as shown in fig. 1A, a first electrode 11 and a second electrode 12 are immersed in an aqueous solution 13 in a container 10, and a voltage is applied between the electrodes. At this time, a voltage is applied between the first electrode 11 and the second electrode 12 so as to be an anode and a cathode. The applied voltage is a voltage higher than 2 volts.

Next, a case where the aqueous solution 13 is a sodium chloride aqueous solution and the ion-adsorbing conductive substance is activated carbon fiber cloth will be described. However, when an aqueous solution in which other salts are dissolved is used, or when other ion-adsorbing substances are used, the treatment can be performed in the same manner.

The voltage applied between the first electrode 11 and the second electrode 12 may be constant or may be changed according to the progress of the treatment. For example, a voltage may be applied so that a current flowing between the first electrode 11 and the second electrode 12 is constant. At this time, since the rise in voltage has a correlation with the change in IR attenuation between the electrodes, the amount of charge of the ions adsorbed on the electrodes can be estimated from the rise in voltage. By measuring the voltage by changing the current to be applied and subtracting the voltage of the IR drop from the potential difference between the electrodes, the rise in voltage can be determined more accurately.

Due to the application of the voltage, chloride ions are adsorbed on the activated carbon fiber cloth (not shown) of the first electrode 11, and sodium ions are adsorbed on the activated carbon fiber cloth (not shown) of the second electrode. As a result, the sodium chloride concentration of the aqueous solution 13 decreases.

The aqueous solution 13 in the vessel 10 is treated in a batch mode. That is, the aqueous solution 13 does not move from the container 10 until the end of the treatment. According to this method, ions can be removed more efficiently than in the conventional treatment using a liquid flow type capacitor. The following explains the mechanism.

Fig. 2 shows a conventional case of using a fluid flow type capacitor. In the flow capacitor 20, first and second electrodes 21 and 22 for adsorbing ions are arranged. The solution 24 is continuously introduced into the capacitor 20 from the inlet 23 and is treated. The treated aqueous solution 24 is continuously discharged from the discharge port 25. Since ions in the aqueous solution 24 pass through the capacitor 20 subjected to the ion removal treatment and are removed, the ion concentration near the inlet 23 is higher than the ion concentration near the outlet 25.

When a voltage is applied between the first electrode 21 and the second electrode 22, a voltage drop occurs due to the resistance of the aqueous solution 24. The voltage drop is larger as the ion concentration of the aqueous solution 24 is lower, and therefore, the voltage drop by the aqueous solution 24 is larger as the distance from the discharge port 25 is closer. Therefore, even if a voltage (for example, 2V or less) is applied to the water in the aqueous solution 24 so as not to cause electrolysis, only a part of the water is used for ion removal in the vicinity of the discharge port, and the ability to remove ions in the vicinity is lowered. On the other hand, since the ions of the aqueous solution 24 near the discharge port are removed and the conductivity is lowered, it is necessary to apply a voltage in consideration of the voltage drop by the aqueous solution 24 in order to apply a sufficient voltage to the portion. When such a voltage is applied, a high voltage is applied to the aqueous solution 24 near the introduction port 23. As a result, water decomposition occurs near the introduction port 23. Therefore, in the conventional method using a liquid flow type capacitor, the voltage applied between the electrodes is a voltage at which substantially no electrolysis of water occurs (2V or less: considering overvoltage). As a result, the conventional method cannot achieve ion removal using the entire electrode uniformly and effectively.

In contrast, in the method of the present invention, the voltage drop caused by the aqueous solution 13 in the container 10 is substantially constant at any part of the electrodes. Therefore, by applying a voltage in consideration of the voltage drop caused by the aqueous solution 13, a voltage suitable for removing ions can be applied to the entire aqueous solution 13. As a result, the conductive material of the electrode can be effectively usedAll ions were efficiently removed. In the apparatus 100 of fig. 1A, fig. 3 schematically shows a state where a voltage is applied to the aqueous solution 13. Even if the voltage V applied between the first electrode 11 and the second electrode 12 exceeds 2 volts, it is only necessary to subtract the voltage drop IR from the voltage V to obtain [ Delta E ]⁺+ΔE^-And (c) is equal to or lower than the decomposition voltage of water, the electrolysis of the aqueous solution 13 can be suppressed.

After the treatment for reducing the concentration of sodium chloride in the aqueous solution 13 is completed, the aqueous solution 13 is discharged from the container 10, and water is injected into the container 10 instead. It is not clear in detail, however, as shown in fig. 1B, the anions adsorbed on the activated carbon fiber cloth 11a of the first electrode 11 are attracted by the positive charges existing on the surface of the activated carbon fiber cloth 11a by coulomb force. Similarly, it is presumed that the cations adsorbed on the activated carbon fiber cloth 11a of the second electrode 12 are attracted by the negative charges existing on the surface of the activated carbon fiber cloth by coulomb force. Therefore, it is considered that the adsorbed ions are relatively stably adsorbed to the activated carbon fiber cloth as long as the surface charge of the cloth is present.

Next, a voltage is applied between the first electrode 11 and the second electrode 12 so that the first electrode 11 is a negative electrode and the second electrode 12 is a positive electrode. By this voltage application, anions adsorbed on the conductive material of the first electrode 11 and cations adsorbed on the conductive material of the second electrode 12 are released into water. As a result, as shown in fig. 4, the water in the container 10 becomes an aqueous sodium chloride solution 41.

After the ion release step is completed, the sodium chloride aqueous solution in the container 10 is discharged, and then a new aqueous solution 13 without removing ions is introduced into the container 10. Then, the treatment described with reference to fig. 1A is performed to remove sodium chloride from the aqueous solution 13. Subsequently, the sodium chloride aqueous solution 41 is introduced into the container 10 again, and sodium ions and chloride ions adsorbed on the electrode are released. By repeating such treatment, a large amount of an aqueous solution from which sodium chloride is removed and an aqueous sodium chloride solution having a high sodium chloride concentration can be obtained. In addition, when an aqueous solution having a high ion concentration or an aqueous solution having a low ion concentration is not required, the aqueous solution may be discarded after each treatment. Further, the ion removal treatment may be repeated for the aqueous solution subjected to the ion removal treatment.

When the same treatment is repeated for the same aqueous solution (a) or the same aqueous liquid (B), the apparatus of the present invention may be provided with one or more other containers for temporarily removing these liquids from the container 10. In this case, the apparatus of the present invention may be provided with a pump for transferring the liquid from one container to another container.

According to the method of the present invention, the ion concentration can be effectively adjusted in comparison with the case of using the liquid flow type capacitor. Japanese laid-open patent publication No. 2000-91169 discloses a method using a specific surface area of 2200m²A flow type capacitor containing 400g of activated carbon per gram was treated with an aqueous NaCl solution having a concentration of 0.01 mol/liter at a flow rate of 0.1 liter/min for 5 minutes (about 0.5 liter) to reduce the NaCl concentration to 0.002 mol/liter or less. In contrast, for the process of the invention, a specific surface area of 2200m is used²0.34g of activated carbon per g, and 30ml of an aqueous NaCl solution having a concentration of 0.01 mol/l were treated for 15 minutes, whereby the concentration could be reduced to 0.0018 mol/l (see examples). This is because the amount of ion removal per unit weight of the activated carbon can be 70 times or more (400/(0.34X 0.5/0.03) ≥ 70) according to the method of the present invention, as compared with the conventional method using a liquid flow type capacitor.

In addition, the amount of the activated carbon fiber cloth is set to 3 times so that the time required for the treatment of the aqueous solution is approximately the same as that of the apparatus disclosed in Japanese patent laid-open No. 2000-91169. At this time, the amount of activated carbon used was 17g (0.34 × (0.5/0.03) × 15/5), which corresponds to twenty-one-third of the amount in the apparatus of Japanese patent laid-open No. 2000-91169.

The method of the present invention can be carried out with a simple apparatus, and can easily and inexpensively carry out treatments such as softening of hard water, production of pure water, removal of chlorine gas (removal by ionizing chlorine gas dissolved in a liquid), and the like. Accordingly, the apparatus for carrying out the present invention is suitable as an apparatus for home use. According to the method and apparatus of the present invention, alkaline water and acidic water can be prepared while reducing the ion concentration. Further, since the potential of the cathode is close to the potential at which water is electrolyzed, chlorine gas can be decomposed into chlorine ions.

The principle of adsorption of ions in an aqueous solution is the same as that of an electric double layer capacitor. Here, the first electrode and the second electrode are the same, that is, the first conductive material and the second conductive material are assumed to be the same material and the same amount. In this case, the charge amount of the anions adsorbed on the first electrode until hydrogen gas is generated on the first electrode as an anode is smaller than the charge amount of the cations adsorbed on the second electrode until oxygen gas is generated on the second electrode as a cathode (see example 7). Therefore, when the first conductive material of the first electrode and the second conductive material of the second electrode are the same material and the same amount, the potential of the first electrode (anode) reaches the decomposition potential of water first. In order to suppress only gas generation in the other electrode, it is preferable that the amount of charge accumulated on the first electrode until oxygen gas is generated on the first electrode side is the same as the amount of charge accumulated on the second electrode until hydrogen gas is generated on the second electrode side.

From the experimental results of the inventors, it was confirmed that when the measurement is performed on an electrode having only activated carbon, it is preferable that (the amount of activated carbon in the first electrode): [ the amount of activated carbon in the second electrode ] be in the range of 1.1: 1 to 2: 1.

When removing ions in the aqueous solution, a voltage is applied so that a current flowing between the first electrode and the second electrode becomes constant, whereby the processing speed can be increased. When a voltage is applied by using such a constant current method, if the set current density is too high, the voltage applied between the electrodes may be too high, and water may be decomposed to generate gas. When gas is generated, the voltage application may be stopped for a certain time and then turned on. The ions adsorbed on the activated carbon move due to the stop of the voltage application, so that the weight bias of the ions is eliminated, and when the voltage application is restarted, the voltage applied between the electrodes is reduced.

When a voltage higher than 2V and not higher than 5V is applied between the first electrode and the second electrode, the speed of removing ions in the aqueous solution is not so high, but gas generation can be suppressed to improve the current utilization efficiency.

When ions adsorbed on the conductive material are released, the first electrode and the second electrode may be short-circuited, or a voltage may be applied between the first electrode and the second electrode so that the first electrode serves as a cathode and the second electrode serves as an anode. When the liquid (B) is an aqueous liquid, ions may be released by applying a voltage between the first or second electrode and the counter electrode in the liquid (B).

When the ion adsorption step and the ion release step are performed, there may be a difference between the charge amount of the anion adsorbed to the first electrode and the charge amount of the cation adsorbed to the second electrode due to electrolysis of impurities or pH adjustment of an aqueous solution. In this case, it is preferable to eliminate the difference using a counter electrode.

For example, when dissolved oxygen in the aqueous solution consumes electrons in the cathode (second electrode) to become hydroxide ions, anions having the charge amount of the consumed electrons are additionally adsorbed on the anode (first electrode). As a result, the charge amount of the anion adsorbed on the first electrolysis is larger than the charge amount of the cation adsorbed on the second electrolysis.

When the ion emission step is performed in this state, all the cations of the second electrode are emitted, but the anions are adsorbed on the first electrode. After the voltage application for the ion release step is continued to release the anions adsorbed on the first electrode, positive charges are accumulated on the surface of the second electrode to adsorb the anions. Therefore, anions are adsorbed on both the first electrode and the second electrode. When the ion adsorption step is performed in this state, the anions are released from the second electrode until all the anions in the second electrode are released, and the state where the anions are adsorbed by the first electrode is maintained, and the ion concentration is not changed. Thus, the balance between the charge amount of the anions adsorbed on the first electrode and the charge amount of the cations adsorbed on the second electrode is lost, and the efficiency is lowered.

Therefore, when such an ion imbalance occurs, it is preferable to perform an operation of releasing all the ions adsorbed on the electrode (hereinafter, sometimes referred to as "initialization of the electrode").

For example, when the anions adsorbed on the first electrode are excessive, a voltage is applied so that the first electrode and the second electrode are short-circuited, and the two electrodes serve as a cathode and a counter electrode serves as an anode. By applying this voltage, excess anions adsorbed to the first electrode can be released, and a state in which no ions are adsorbed to any of the electrodes can be achieved. When the cations adsorbed on the second electrode are excessive, a voltage may be applied so that the first electrode and the second electrode are short-circuited, and the two electrodes serve as an anode and a counter electrode serve as a cathode. By initializing the electrodes in this way, a decrease in efficiency can be suppressed.

Fig. 5 shows an example of an ion concentration adjusting apparatus provided with a counter electrode. The ion concentration adjusting apparatus 200 shown in fig. 5 includes a container 10, a first electrode 51, a second electrode 52, a counter electrode 53, and a power source 54. An inlet 50a for introducing a liquid and an outlet 50b for discharging the liquid are connected to the container 50. The first electrode 51 and the second electrode 52 are ion-adsorbing electrodes. As shown in fig. 5, these electrodes are typically immersed in the liquid 55 being treated. However, the electrode that does not require processing may be removed from the container 50.

Fig. 5 shows a case where the power source 54 is connected to the first electrode 51 and the second electrode 52. The device 200 is configured to allow a power source to be connected to either electrode. Therefore, the electrode device 200 includes the switches 56 and 57. The power supply and the switch are controlled by a control device (not shown). The device of the present invention may further include a wiring and a switch for short-circuiting the first electrode and the second electrode.

Examples

The present invention will be described in further detail with reference to examples. In addition, unless otherwise specified, the activated carbon fiber cloth used in the following examples is an activated carbon fiber cloth manufactured by Karanol (カイノ - ル) (product number: ACC5092-25, 100-130 g/m/g/m in unit area amount)²About 0.5mm in thickness and 1850 to 2100mg/g in iodine adsorption amount). The specific surface area of the activated carbon fiber cloth is about 2000m²More than g.

[ example 1 ]

In example 1, an example of removing tap water based on the present invention will be described.

As shown in fig. 6A, a current collector 62 was attached to an activated carbon fiber cloth 61 of about 3cm × 5cm to prepare an electrode (ion-adsorbing electrode) 60. The current collector 62 is made by coating platinum on titanium. Further, a gasket 63 made of acrylic resin having the shape shown in fig. 6B was prepared.

Next, two electrodes 60 were disposed on both sides in a container having an internal volume of 60 ml. At this time, as shown in fig. 6C, a spacer is disposed between the two electrodes 60. The distance between the two electrodes is about 17 mm. Then, 40ml of tap water having a conductivity of 150. mu.S/cm was added to the vessel.

Then, a current of 60mA was passed between the two electrodes 60 for 1 minute, 3 minutes, and 5 minutes, and then changes in conductivity and pH were measured. When the current was applied for 1 to 5 minutes, ions in the tap water were adsorbed on the electrode, and the conductivity of the tap water was reduced to 140. mu.S/cm (1 minute), 120. mu.S/cm (3 minutes), and 105. mu.S/cm (5 minutes). on the other hand, the pH was almost unchanged after the current was applied for 1 to 5 minutes.

Subsequently, two electrodes 60 and one spacer were placed in a container having an internal volume of 45ml in the same manner as described above. Then, 28ml of tap water having a conductivity of 150. mu.S/cm was charged into the vessel, a current of 10mA was allowed to flow between the electrodes, and then, the change in conductivity of the tap water was measured. At this time, the distance between the two electrodes was about 13 mm. The decrease in conductivity is a decrease in the concentration of ions in tap water. In addition, the pH of the treated tap water was also measured. The measurement results are shown in Table 1.

[ Table 1 ]

Current value [ mA ]	Time of energisation [ minute ]	Electric quantity (c)	Initial conductivity change (. mu.S/cm) → Final	pH
					10	10	6	150→136	7.3
10	15	9	150→123	6.6
					10	20	12	150→121	4.1
10	30	18	150→87	5.7
					10	60	36	150→19	7.1

As shown in table 1, when a current was applied, the pH was not changed in the initial stage, and ions were removed. However, as the amount of ions removed increases, the pH drops greatly and the water becomes acidic. Then, when the current flow was continued, the conductivity was greatly reduced and Ph was restored to about 7.

In this embodiment, the ion adsorption capacity (ion adsorption possible energy) of the anode is the same as that of the cathode. Therefore, when the current is continued to flow, the potential of the anode reaches the potential generated by oxygen. As a result, oxygen gas is generated at the anode, the ion concentration in the water increases, and the pH of the water decreases. It is believed that the increase in pH as the current continues to flow is due to the production of hydrogen at the cathode in addition to the production of oxygen at the anode.

[ example 2 ]

Three ion-adsorbing electrodes similar to those of example 1 were prepared, and the three electrodes were disposed in parallel on both sides and in the center of a container having an internal volume of 45 ml. Further, the same spacers as in example 1 were disposed between the electrodes. The distance between the two electrodes is about 6 mm. Then, 29ml of tap water was added to the vessel. Next, the following experiment was performed.

In experiment 1, ions in tap water were removed by applying a voltage for 5 minutes so that two electrodes on both sides were anodes and one electrode in the center was a cathode. The voltage was applied in such a manner that the current flowing between the anode and the cathode was 20 mA.

Next, in experiment 2, the ions adsorbed in experiment 1 were released from the electrode. At this time, a voltage was applied for 5 minutes so that the two electrodes on both sides were cathodes and anodes and the center electrode was an anode. The voltage was applied in such a manner that the current flowing between the anode and the cathode was 20 mA.

In experiment 3, the same experiment as in example 1 was performed except that the time for flowing the current was changed. In experiments 4 to 6, the same experiment as in example 1 was performed, except that the current flowing between the electrodes and the energization time were changed.

Table 2 shows the change in conductivity of the treated tap water and the pH of the treated tap water in experiments 1 to 6.

[ Table 2 ]

Experiment of	Current value [ mA ]	Time of energisation [ minute ]	Electric quantity (c)	Initial stage of voltage change [ V ] → Final stage	Initial conductivity change (. mu.S/cm) → Final	pH
							1	20	5	6	4.6→12.5	145→59	7.0
2	20	5	6		59→150	7.1
							3	20	10	12		145→30	6.9
4	100	2	12	25→60	172→67	7.2
							5	200	1	12		172→75	6.9
6	200	2	24		172→50	6.5

In example 2, unlike example 1, the ion adsorption amount of the anode was set to 2 times the ion adsorption amount of the cathode. As a result, the pH fluctuation caused by the treatment was hardly observed.

In experiment 1, the conductivity of tap water decreased due to the removal of ions, and in experiment 2, the conductivity of tap water became the same value as the initial value due to the release of ions.

In experiments 4 to 6 in which the current value was high, the efficiency of ion removal, that is, the removal of ions with respect to the electric quantity was reduced. This is because the influence of the resistance of the activated carbon fiber cloth is large, and the ion adsorption amount becomes uneven in the electrode. In order to suppress such a decrease in efficiency, it is effective to gradually decrease the current flowing between the electrodes or to stop the application of voltage for a certain time.

[ example 3 ]

In example 3, as shown in FIG. 7, a wire 71 was arranged so as to be continuous with the surface of an activated carbon fiber cloth 61 (size: 3 cm. times.5 cm) to form an electrode 70. The wiring was formed by coating the surface of a titanium wire with platinum. In addition, a separator composed of polyethylene was prepared.

The same apparatus as in example 2 was constructed, except that the electrode 60 of fig. 6 was replaced with the electrode 70 of fig. 7, and the spacer was replaced with a separator. Then, 30ml of tap water or 30ml of an aqueous NaCl solution (conductivity: 588. mu.S/cm) was added to the vessel (internal volume: 45ml) of the apparatus, and then an experiment for removing ions was carried out.

Experiments 7 to 11 were carried out while changing the anode-cathode current value and the energization time. In addition, experiments 12 were performed in which electrode groups called anode/separator/cathode/separator/anode were disposed in two containers to remove ions. Table 3 shows the conductivity change and the final pH of the liquid resulting from the ion removal.

Watch (3)

Experiment of	Liquid, method for producing the same and use thereof	Current value [ mA ]	Time of energisation [ minute ]	Electric quantity (c)	Initial conductivity change (. mu.S/cm) → Final	pH
							7	Tap water	5	20	6	181→46	7.1
8	Aqueous NaCl solution	5	30	9	588→397	10.0
							9	Aqueous NaCl solution	10	30	18	588→250	10.1
10	Aqueous NaCl solution	50	10	30	588→180	7.1
							11	Aqueous NaCl solution	25	20	30	588→155	6.9
12	Aqueous NaCl solution	25	20	30	588→150	7.2

Since the wiring is formed on the counter electrode, the efficiency of ion removal is improved. In example 3, since the ion adsorption capacity on the album was 2 times that of the cathode, hydrogen gas was generated at the cathode before oxygen gas at the anode when the current was continued to flow. Since hydroxide ions are released into the liquid as hydrogen gas is generated at the cathode, the pH of the liquid rises as the treatment proceeds. However, when the current is continued to flow, the pH decreases and the liquid becomes approximately neutral. It is considered that the reason why the PH becomes neutral is that oxygen gas formed at the anode in addition to hydrogen gas at the cathode is generated.

The change in pH resulting from the treatment of example 3 was formed in the opposite direction to the change in pH resulting from the treatment of example 1. Thus, it is considered that the most appropriate ratio of the ion adsorption capacity on the anode and the ion adsorption capacity on the cathode exists between the ratio of example 1 and the ratio of example 3. In addition, the results of example 1 and example 3 show that the potential of the electrode can be controlled by the decomposition reaction of water. Therefore, when the ratio of the ion adsorption capacity on the anode and the ion adsorption capacity on the cathode is set to a value close to the optimum value, even if the balance of the adsorption amounts of cations and anions is lost, the balance can be eliminated by decomposing water at the anode and/or the cathode.

In experiment 12 in which the amount of the activated carbon fiber cloth was set to 2 times, no decomposition of water was caused and the pH was not changed even when the same amount of electricity was supplied.

In addition, when oxygen is generated on the anode using the electrode of example 3 provided with the wiring, first, when oxygen is generated from the surface of the wiring to further increase the potential of the anode, oxygen is also generated from the surface of the activated carbon fiber cloth. This is considered to be because the oxygen overvoltage of platinum is smaller than that of activated carbon. Similarly, platinum has a lower hydrogen overvoltage than activated carbon.

[ comparative example ]

First, 6 electrodes provided with the wiring described in example 3 were prepared. In addition, 3 pieces of the spacer described in example 1 and the spacer described in example 3 were prepared. These electrodes, gaskets and separators were disposed in a container (inner volume: 45ml) in such a configuration of anode/separator/gasket/cathode/gasket/separator/anode/separator/gasket/cathode. The distance between the anode and the cathode of the tie-in is about 4 mm.

Next, about 30ml of an aqueous NaCl solution having a concentration of about 0.0084 mol/L was added to the vessel to conduct an ion removal test. The voltage applied between the electrodes was fixed at 1V.

In use, the voltage application was stopped every 1-order decrease in the value of the current flowing between the electrodes, and then the anode-cathode voltage (steady potential), and the conductivity and pH of the aqueous solution were measured. After the final 130-minute treatment, the stable potential, conductivity and pH were measured. The measurement results are shown in Table 4.

[ Table 4 ]

Applying a voltage [ V ]	Cumulative application time	Initial stage of current value (mA → final stage	Stabilized potential [ V ]	Initial conductivity change (. mu.S/cm) → Final	pH
						1	16	95→9.5	0.800	947→538	9.6
1	39	45→4.5	0.890	→380	9.7
						1	72	29→2.9	0.915	→327	9.8
1	108	26→2.6	0.924	→305	9.6
						1	238	22→1.2	0.953	→215	7.5

As shown in Table 4, the pH of the aqueous solution was increased simultaneously with the start of the treatment. In addition, the conductivity decreased with the treatment, and the ions were removed even if the applied voltage was 1 volt. However, the steady potential increases as ions are adsorbed on the electrode. That is, even if the voltage applied between the electrodes is 1 volt, the voltage (electric field) in the aqueous solution applied between the electrodes is a value obtained by subtracting the steady potential from 1 volt. For example, the stable potential when the treatment was carried out for 16 minutes was 0.8 volts, and the voltage applied to the aqueous solution was 0.2 volts. Therefore, the ability of the electrode to adsorb ions is reduced, and the efficiency of removing ions is reduced. Thus, even if a voltage equal to or lower than the decomposition voltage of water is applied between the electrodes, efficient treatment cannot be performed.

[ example 4 ]

An experiment for ion removal was performed by applying a voltage between the electrodes by a constant current method using the same apparatus as in the comparative example. Specifically, a voltage was applied so that the current flowing between the anode and the cathode was 200 mA. In example 4, an aqueous NaCl solution having a conductivity of 800. mu.S/cm was treated.

In experiment 13, the voltage application was continued until the conductivity of the aqueous solution became about 100. mu.S/cm. In experiment 14, the voltage increase rate was monitored, and the voltage application was stopped at a point when the voltage increase rate decreased. In experiment 15, after the voltage application of experiment 14 was stopped, the voltage was applied again until the conductivity of the aqueous solution became 100. mu.S/cm. In experiments 13 to 15, the change in voltage, the change in conductivity of the aqueous solution, and the pH of the aqueous solution were measured. The measurement results are shown in Table 5.

[ Table 5 ]

Experiment of	Current value [ mA ]	Time of energisation [ minute ]	Electric quantity (c)	Initial stage → final stage of voltage application (V)	Initial conductivity change (. mu.S/cm) → Final	pH
							13	200	9.5	114	2.5→60	800→106	6.0
14	200	3.5	42	2.5→70	800→280	6.8
							15	200	1.7	20	4.4→83	280→105	6.4

Fig. 8 shows the transition of the applied voltage in experiment 13. The voltage rises from 2.5V (initial) to 67V and then reaches 60V (final). The horizontal axis 1 scale of fig. 8 is 32 seconds. The voltage rise started to slow down approximately after 200 seconds from the start of voltage application. This is considered to be due to the occurrence of a decomposition reaction of water.

Therefore, in experiment 14, the voltage application was stopped after 210 seconds (3.5 minutes) from the start of the voltage application. When estimated from the conductivity, at this time, about 65% of the sodium and chloride ions had been removed.

In about 10 minutes required for the measurement after the voltage application was stopped, the ions adsorbed on the activated carbon fiber cloth moved, and the ion distribution was uniformed. As a result, the potential of the electrode was lowered, and a current of 200mA was also applied thereto at a low voltage. When the voltage of experiment 15 was applied after the end of the measurement of experiment 14, the applied voltage was decreased to 4.4V. In experiment 15, after the applied voltage increased to 83V after about 1.7 minutes from the start of voltage application, the voltage increase rate started to decrease. The conductivity was reduced to about 100. mu.S/cm by applying a voltage for 1.7 minutes. The total voltage application time of experiments 14 and 15 was 5.2 minutes, which was shorter than the voltage application time (9.5 minutes) of experiment 13, but the removal of ions was comparable. By performing the treatment under the condition that the electrolysis of water is not caused, the particles can be efficiently removed at a high current.

[ example 5 ]

In the experiment of example 5, the electrode 70 and the separator described in example 3 were used. One electrode contained about 0.17g of activated carbon.

Two electrodes were disposed on both sides of a container having an internal volume of 45ml, and a separator was disposed between the two electrodes. To this vessel, 30ml of an aqueous NaCl solution (conductivity: 1117. mu.S/cm, pH: 6.32) was added at a concentration of 0.01 mol/L to conduct an ion removal experiment.

In experiment 16, a voltage was applied so that the current value became 200 mA. After the voltage application for 5 minutes, the measurement was performed, and the aqueous solution after the measurement was further processed in experiment 17. In experiment 17, a voltage was applied so that the current value was 100 mA.

In experiment 18, a voltage was applied so that the current value was 65 mA. After the voltage application for 15 minutes, the measurement was performed, and the aqueous solution after the measurement was further processed in experiment 19. In experiment 19, a voltage was applied so that the current value was 35 mA. The measurement results are shown in Table 6.

[ Table 6 ]

Experiment of	Current value [ mA ]	Time of energisation [ minute ]	Electric quantity (c)	Initial stage → final stage of voltage application (V)	Initial conductivity change (. mu.S/cm) → Final	Initial stage of concentration change (mol/l) → Final stage	pH
								16	200	5	60	20→55	1117→435	0.01→0.0037	3.7
17	100	10	60	20→60	→211	→0.0018	6.1
								18	65	15	59	10→30	1117→318	0.01→0.0027	4.1
19	35	30	63	10→35	→162	→0.0014	6.2

In example 5, an aqueous solution having a high ion concentration and a conductivity 5 times or more that of tap water was treated. In experiment 16, the treatment was performed at a current value 3 times or more the current value of experiment 18, but since the treatment was performed in a state where the ion adsorption capacity was excessive, the change in conductivity of experiment 16 was much inferior to the change in conductivity of experiment 18. In addition, by conducting experiment 17 at a current value which was continuously decreased in experiment 16, the removal of ions was able to reach the level of tap water, as in experiment 19. As shown in experiments 16 to 19, ions can be removed in a short time with the same amount of electricity by increasing the initial current value and decreasing the current value as the ions are removed.

[ example 6 ].

First, two apparatuses similar to those of the comparative example were prepared. About 30ml of tap water having a conductivity of 170. mu.S/cm was charged into the vessel (internal volume: 45ml) of the apparatus to conduct an ion removal experiment. First, the treatment was performed by changing the current and voltage in three steps to reduce the conductivity to about 15. mu.S/cm. Table 7 shows the change in applied voltage during the treatment, the change in conductivity due to the treatment, and the pH after the treatment.

[ Table 7 ]

Current value [ mA ]	Time of energisation [ minute ]	Initial stage → final stage of voltage application (V)	Initial conductivity change (. mu.S/cm) → Final	pH
					200	3	10→120	170→61.0	6.6
50	5	10→50	→29.6	6.6
					30	15	10→40	→14.5	6.5

Next, the treated water is transferred to a new apparatus, and ion removal treatment is performed again. Table 8 shows the change in conductivity of the treatment and the pH after the treatment.

[ Table 8 ]

Current value [ mA ]	Time of energisation [ minute ]	Initial conductivity change (. mu.S/cm) → Final	pH
				20	20	15→2.1	6.4

In example 6, the conductivity of tap water can be lowered to that of pure water.

[ example 7 ]

In example 7, as the activated carbon fiber cloth, an activated carbon fiber cloth ACC5092-25 (described above) and an ACC5092-10 (unit area amount 200 g/m) manufactured by Karanol, Japan K.K. (カイノ - ル) were used²About 0.6mm in thickness and 2000m in specific surface area²/g) two kinds of electrodes. Platinum wires (wires) are disposed on the surface of the activated carbon fiber cloth as a current collector.

Periodic voltammetric measurements are performed using the two electrodes, and from the results, the potential for the anode and cathode to reach the potential for the electrolysis of the generated water from the steady potential (RP) is determinedThe amount of electricity. The amount of ions adsorbed on the electrode was estimated from the electric quantity, and the evaluation results are shown in table 9. In addition, the electric quantity and the quantity of adsorbed ions in Table 9 are each 1cm of the activated carbon fiber cloth²The numerical value of (c). The potential window (potential window: region where water is not electrolyzed) of the aqueous solution was 1.49 volts in the case of the Pt electrode-Pt electrode and 1.95 volts in the case of the activated carbon electrode-activated carbon electrode.

[ Table 9 ]

As shown in table 9, the amount of electricity from the state where the ions are not adsorbed to the electrolysis that generates water differs on the anode and the cathode. When the activated carbon fiber cloth is ACC5092-25, the electric quantity is 1: 1.35. When the activated carbon fiber cloth is ACC5092-10, the electric quantity is 1: 1.30.

From the results in table 9, it is found that when activated carbon fiber cloth is used as the ion-adsorbing material and Pt is present on the surface of the current collector, it is preferable to set the amount of activated carbon in the anode to about 1.35 times the amount of activated carbon in the cathode. With this configuration, when the same amount of ions are adsorbed to the anode and the cathode, both electrodes reach a gas generation potential.

The ratio of the amount of ion adsorption on the anode to the amount of ion adsorption on the cathode varies depending on the materials of the ion-adsorbing material and the current collector, but it is generally preferable to increase the capacity of the anode.

[ example 8 ]

First, the same apparatus as in comparative example was prepared. Tap water having a conductivity of 167. mu.S/cm was added to the vessel of the apparatus, and ions in the tap water were adsorbed on the electrodes by applying a voltage for 5 minutes. A voltage was applied between the electrodes so that a current of 20mA flowed. After 5 minutes of voltage application, the same operation was again performed by replacing the water in the container with tap water, so that ions in the tap water were adsorbed on the electrodes. This ion adsorption step was performed 5 times on the same electrode, and ions were accumulated on the electrode.

Next, 31ml of fresh tap water was added to the vessel. Then, the two electrodes are short-circuited, and thereby ions adsorbed on the electrodes are released into the tap water. The ion concentration in the tap water is increased by this ion release step.

Table 10 shows the change in applied voltage in each step and the conductivity and pH of the aqueous solution after the treatment.

[ Table 10]

	Amount of tap Water [ ml]	Initial stage → final stage of voltage application (V)	Change in conductivity [ mu S/cm ]	pH
					First ion adsorption step	31	0.8→4.5	112	6.9
Second ion adsorption step	33	0.9→6.0	94	7.5
					Third ion adsorption step	33	1.0→7.5	83	7.5
Fourth ion adsorption step	32	1.0→6.3	89	7.4
					Fifth ion adsorption step	33	1.0→6.1	92	7.4
Ion discharge step	31	-0.5→0	496	7.4

As shown in table 10, the salt concentration in the aqueous solution can be increased by the ion release step.

[ example 9 ]

In example 9, an example of removing ions in the nonaqueous electrolytic solution will be described.

First, 18.5ml of a nonaqueous electrolytic solution was charged into a container (internal volume: 27.6ml) made of a chlorinated polyethylene resin. The solvent of the non-aqueous electrolyte adopts propylene carbonate. The solute is methyl triethyl ammonium tetrafluoroborate (TEMA BF)₄). The initial concentration of the solution was 0.0294 moles/liter.

Next, one anode electrode and one cathode electrode were immersed in the nonaqueous electrolytic solution. Both electrodes are homopolar and the electrode shown in figure 7 is used. The spacing between the two electrodes was set to 4 mm.

Subsequently, the conductivity of the nonaqueous electrolytic solution was measured while applying a constant voltage of 2.4 volts between the two electrodes for 280 minutes. As a result, the conductivity of the nonaqueous electrolytic solution was changed from 750. mu.S/cm (initial) to 164. mu.S/cm (final). This change is considered to be caused by anions (TEMA) and anions (BF) in the nonaqueous electrolytic solution₄ ^-) Has been removed.

Fig. 9 shows a relationship between a current value flowing between the electrodes and an energization time. As shown in fig. 9, as the energization time elapses, ions are removed and the liquid resistance increases, so that the current value decreases.

[ example 10]

In example 10, another example of removing ions in the nonaqueous electrolytic solution will be described. Example 10 the same experiment as in example 9 was carried out, except that the initial concentration of the nonaqueous electrolytic solution and the energization method were changed.

In example 10, the concentration of the nonaqueous electrolytic solution was set to 0.0036 mol/liter. Further, a constant current of 20mA was allowed to flow for 7 minutes. As a result, the conductivity of the solution was changed from 137.5. mu.S/cm (initial) to 42.9. mu.S/cm (final).

[ example 11 ]

In example 11, a further example of removing ions in the nonaqueous electrolytic solution will be described. Example 11 the same experiment as in example 9 was carried out, except that the initial concentration of the nonaqueous electrolytic solution and the energization method were changed.

In example 11, the initial concentration of the nonaqueous electrolytic solution was set to 0.0044 mol/liter. Further, a constant current of 10mA was allowed to flow for 7 minutes. As a result, the conductivity of the solution was changed from 140.3. mu.S/cm (initial) to 8.0. mu.S/cm (final).

In examples 9 to 11, the conductivity may be saturated during the energization time. Therefore, the time required until the final conductivity is reached is shorter than the energization time of the embodiment.

Industrial application

The present invention can be applied to a method and an apparatus for adjusting an ion concentration of a liquid. The present invention can be applied to a method and an apparatus for adjusting the ion concentration and pH of a liquid.

Claims

1. An ion concentration adjustment method for adjusting an ion concentration, comprising:

the following (i) step: in a container, in a state in which a first ion-adsorbing electrode containing a first conductive material capable of adsorbing ions and a second ion-adsorbing electrode containing a second conductive material capable of adsorbing ions are immersed in a solution containing at least one kind of ions (L) other than hydrogen ions and hydroxide ions, a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as an anode, thereby adsorbing anions in the solution onto the first ion-adsorbing electrode and cations in the solution onto the second ion-adsorbing electrode;

(ii) in the step (i), the solution is treated in a batch manner,

under the assumption that there is no voltage drop due to the solution, the voltage is a voltage higher than a voltage at which the solvent of the solution is electrolyzed,

the first ion-adsorbing electrode adsorbs the negative ions by the positive charges accumulated on the surface of the first conductive material,

the second ion-adsorbing electrode adsorbs the positive ions by using negative charges accumulated on the surface of the second conductive material.

2. The ion concentration adjustment method according to claim 1, wherein after the step (i),

comprises the following (ii) step: and a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as a cathode, whereby the anions adsorbed on the first ion-adsorbing electrode and the cations adsorbed on the second ion-adsorbing electrode are released into the liquid.

3. The ion concentration adjustment method according to claim 1,

the solution is an aqueous solution, and the solution is,

the voltage is higher than 2 volts.

4. The method for adjusting ion concentration according to claim 1, wherein the solution is a non-aqueous solution.

5. The method of adjusting an ion concentration according to claim 2, wherein the step (i) and the step (ii) are repeated a plurality of times.

6. The method of adjusting ion concentration according to claim 1, wherein the first conductive material and the second conductive material have a specific surface area of 900m²More than g.

7. The method of adjusting ion concentration according to claim 1, wherein the first conductive material and the second conductive material contain activated carbon.

8. The ion concentration adjustment method according to claim 1, wherein the first ion-adsorbing electrode includes a first wiring connected to the first conductive substance, and the second ion-adsorbing electrode includes a second wiring connected to the second conductive substance.

9. The ion concentration adjustment method according to claim 8,

a metal having an oxygen overvoltage smaller than that of activated carbon is present on the surface of the first wiring,

a metal having a hydrogen overvoltage smaller than that of activated carbon is present on the surface of the second wiring.

10. The method of adjusting an ion concentration according to claim 1, wherein in the step (i), a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode within a range in which a solvent of the solution is not electrolyzed.

11. An ion concentration adjustment apparatus, comprising: a power supply for applying a voltage, a container capable of introducing and discharging a liquid, and a first ion-adsorbing electrode and a second ion-adsorbing electrode arranged in the container,

the first ion-adsorbing electrode contains a first conductive material capable of adsorbing ions,

the second ion-adsorbing electrode contains a second conductive material capable of adsorbing ions,

performing the following step (i) in the container: applying a voltage between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as an anode in a state where the first ion-adsorbing electrode and the second ion-adsorbing electrode are immersed in a solution containing at least one kind of ions (L) other than hydrogen ions and hydroxide ions, thereby adsorbing anions in the solution to the first ion-adsorbing electrode and adsorbing cations in the solution to the second ion-adsorbing electrode;

(ii) in the step (i), the solution is treated in a batch manner,

under the assumption that no voltage drop is caused by the solution, the voltage is a voltage higher than a voltage at which the solvent of the solution is electrolyzed,

12. The ion concentration adjusting apparatus according to claim 11, further comprising a counter electrode disposed in the container.

13. The ion concentration adjusting apparatus according to claim 11, wherein after the step (i),

the following step (ii) is carried out: and a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode so that the first ion-adsorbing electrode serves as a cathode, whereby the anions adsorbed on the first ion-adsorbing electrode and the cations adsorbed on the second ion-adsorbing electrode are released into the liquid.

14. The ion concentration adjustment apparatus according to claim 11,

the solution is an aqueous solution, and the solution is,

the voltage is higher than 2 volts.

15. The ion concentration adjusting apparatus according to claim 11, wherein the solution is a non-aqueous solution.

16. The ion concentration adjusting apparatus according to claim 11, wherein the first conductive material and the second conductive material have a specific surface area of 900m²More than g.

17. The ion concentration adjusting apparatus according to claim 11, wherein the first conductive material and the second conductive material contain activated carbon.

18. The ion concentration adjustment apparatus according to claim 11, wherein the first ion-adsorbing electrode includes a first wiring connected to the first conductive substance, and the second ion-adsorbing electrode includes a second wiring connected to the second conductive substance.

19. The ion concentration adjusting apparatus according to claim 18, wherein a metal having an oxygen overvoltage smaller than that of activated carbon is present on the surface of the first wiring,

20. The ion concentration adjusting apparatus according to claim 18, wherein platinum is present on the surfaces of the first and second wires.

21. The ion concentration adjustment apparatus according to claim 11, wherein in the step (i), a voltage is applied between the first ion-adsorbing electrode and the second ion-adsorbing electrode within a range in which a solvent of the solution is not electrolyzed.