TW201936516A - Electrical deionized water production apparatus - Google Patents

Abstract

The invention provides a novel structure of an electric deionized water manufacturing device capable of efficiently removing weak acid components from treated water diffused from a concentration chamber into a desalination chamber. The electro-deionized water manufacturing device is provided with at least one desalination processing section between a cathode and an anode facing each other. The desalination processing section has a desalination chamber filled with at least an anion exchanger, and one pair of the desalination chambers located on both sides of the desalination chamber. The concentration chamber and desalination chamber are adjacent to the cathode-side concentration chamber of the pair of concentration chambers by a cation exchange membrane, and are adjacent to the anode side of the pair of concentration chambers by the first anion exchange membrane. A concentration chamber in which a second anion exchange membrane that is not the same as the cation exchange membrane is disposed on a part of the surface of the cation exchange membrane on the side of the desalination chamber, and the anion exchanger and the second anion exchange membrane are desalted. At least a part of the chamber-side surface is in contact.

Description

Electric deionized water manufacturing device

The present invention relates to an apparatus for producing deionized water.

In recent years, an electric deionized water manufacturing apparatus (hereinafter, sometimes referred to as an “EDI apparatus”) that does not require regeneration by chemicals has been developed and put into practical use. The EDI device is a device that combines electrophoresis and electrodialysis. The basic structure of a general EDI device is as follows. That is, the EDI device has a desalination chamber, a pair of concentration chambers disposed on both sides of the desalination chamber, an anode (positive) chamber disposed on the outside of one of the condensation chambers, and a cathode (negative electrode) chamber disposed on the other side of the condensation chamber . The desalination chamber includes an anion exchange membrane and a cation exchange membrane arranged opposite to each other, and an ion exchanger (anion exchanger or / and cation exchanger) filled between these exchange membranes. The anion component and the cation component in the treated water pass through the anion exchange membrane and the cation exchange membrane, respectively, and move from the desalination chamber to the concentration chamber, and the treated water, that is, deionized water is obtained from the desalination chamber, and the concentration is obtained from the concentration chamber. water.

In the production of deionized water, the treated water is passed through the desalination chamber in a state where a DC voltage is applied between electrodes provided in the anode chamber and the cathode chamber, respectively. Desalting compartment to the capture anion exchanger using anion component _{^{(Cl -, CO 3 2-,}} HCO 3 -, SiO 2 , etc.), and captured by cation exchanger component cations ^{(Na +, Ca 2+, Mg} 2+ , etc.) . Meanwhile, for example, anion exchange desalting compartment of the body of water from the reaction solution of the interface thereof with the cation exchange occurs, generating hydrogen ions and hydroxide ions ^{_{(H 2 O → H + +}} OH -). The ion component captured by the ion exchanger is freed from the ion exchanger by exchanging with the aforementioned hydrogen ions and hydroxide ions. The released ionic components are electrophoresed along the ion exchanger to the ion exchange membrane (anion exchange membrane or cation exchange membrane), and then moved to the concentration chamber by electrodialysis on the ion exchange membrane. The ionic components moving to the concentration chamber are discharged by the water flowing through the concentration chamber.

In the EDI device, the weak acid component contained in the concentrated water diffuses into the treated water through a cation exchange membrane that separates the concentration chamber and the desalination chamber, and reduces the purity of the treated water. This phenomenon is caused by the form of non-ionized molecules (neutral molecules) due to weak acid components represented by carbonic acid, or silicon dioxide (silicic acid), boron (boric acid) in response to changes in pH, etc. Affected by the selective permeability of the cation exchange membrane. For example, in the case of carbonic acid, there is a balanced relationship represented by the formulas (1) to (3). In the case of carbonic acid, the non-ionized molecules (neutral molecules) are in the form of CO ₂ and H ₂ CO ₃ , and they can easily pass through the cation exchange membrane.

[Chemical 1]

Patent Document 1 discloses an EDI device capable of suppressing the mixing of weak acid components from the concentration chamber to the desalination chamber into the treated water. This device uses an ion exchange membrane to separate the desalination chamber into a first small desalination chamber and a second small desalination chamber. The first small desalination chamber is filled with an anion exchanger, and the second small desalination chamber is exchanged with the ion through which the treated water finally passes. The order in which the bodies become anion exchangers is filled with anion exchangers and cation exchangers.

In addition, Patent Document 1 discloses that in order to promote the hydrolysis and ionization reaction and to achieve an appropriate distribution of the current density, the anion exchanger on the cathode side of the anion exchanger filled in the second small desalination chamber faces the anion exchange membrane surface with the anion exchange membrane surface of the bipolar membrane. The bipolar membrane is arranged in a bulk manner.

Patent Documents 2 and 3 also disclose the use of a bipolar membrane in an EDI device. Patent documents 4, 5 and non-patent document 1 disclose bipolar membranes.
[Prior technical literature]
[Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2012-161758 Patent Document 2: International Publication No. 2013/018818 Patent Document 3: International Publication No. 2011/152226 Patent Document 4: Japanese Patent Application Laid-Open No. 7-10121 Patent Document 5: Japanese Patent Application Laid-Open No. 2010-132829
[Non-patent literature]

Non-Patent Literature 1: Tanaka Yoshiyuki, "Basics and Applications of Ion Exchange Membrane", 2016, Maruzen Publishing, p15-18.

[Problems to be Solved by the Invention]

In an EDI plant, it is very important to efficiently remove weak acid components from the treated water that diffuse from the concentration chamber to the treated water in the desalination chamber.

The object of the present invention is to provide a new structure EDI device capable of efficiently removing weak acid components from the treated water which diffuses from the concentration chamber to the treated water in the desalination chamber.
[Means for solving problems]

According to an aspect of the present invention, there is provided an electric deionized water manufacturing device,
At least one desalination unit is provided between the cathode and the anode facing each other,
The desalination processing unit has a desalination chamber filled with at least an anion exchanger and a concentration chamber provided on one side of the desalination chamber,
The desalination chamber is adjacent to the concentrating chamber on the cathode side of the pair of concentrating chambers by a cation exchange membrane, and is adjacent to the anode side of the concentrating chamber of the pair by a first anion exchange membrane. The concentration chamber is characterized by:
A second anion exchange membrane, which is not the same as the cation exchange membrane, is provided on a part of the surface of the cation exchange membrane on the side of the desalination chamber.
The anion exchanger is in contact with at least a part of the surface of the second anion exchange membrane on the side of the desalination chamber.
[Effect of the invention]

According to the present invention, it is possible to provide a new structure EDI device capable of efficiently removing weak acid components from the treated water that diffuses from the concentration chamber to the treated water in the desalination chamber.

An EDI device filled with an anion exchanger in the desalination chamber can use the anion exchanger to capture weak acid components that diffuse from the concentration chamber to the desalination chamber and remove them from the treated water. However, in the area near the outlet of the desalination chamber, a part of the weak acid component diffused from the concentration chamber is easily discharged from the desalination chamber and mixed into the treated water before being captured and removed by the anion exchanger in the desalination chamber. It is thought that this phenomenon occurs because the weak acid component diffused from the concentration chamber does not sufficiently contact the anion exchanger and leaks to the treated water side.

FIG. 7 (a) shows an example of a conventional EDI device, and conceptually shows the vicinity of the boundary between the desalination chamber 23 and the concentration chamber 24 on the cathode side of the desalination chamber 23. In this EDI device, the cation exchange membrane 33 is divided into a desalination chamber 23 and a concentration chamber 24 on the cathode side of the desalination chamber 23. The desalination chamber 23 is filled with a granular anion exchange resin 51 as an anion exchanger, and the anion exchange resin 51 is in contact with the surface of the cation exchange membrane 33 on the side of the desalination chamber. In such a device, the portion of the cation exchange membrane 33 that is in contact with the anion exchange resin 51 is a weak acid component diffused from the concentration chamber 24 through the cation exchange membrane 33, and can be ionized by the ion exchange reaction of the anion exchange resin 51. And capture. Carbonates such as (H ₂ CO ₃₎ is converted to the anion exchange resin 51 bicarbonate ion (HCO ₃ ^-) or carbonate ions (CO ₃ ^2-) and be captured. The captured anions can move along the anion exchange resin 51 to the concentration chamber on the opposite side (anode side). On the other hand, it is considered that weak acid components are released from the cation exchange membrane 33 into the liquid phase in the desalination chamber 23 in a portion where the cation exchange membrane 33 is not in contact with the anion exchange resin 51, and a portion of the weak acid component is directly mixed into the treated water.

The present inventors have found that, as shown in FIG. 7 (b), a structure in which the anion exchange membrane 40 is arranged on the surface of the cation exchange membrane 33 of the demineralizing chamber 23 and the concentration chamber 24 on the side of the desalination chamber is overlapped, and it may be effective to solve the aforementioned problem. . According to this structure, a weak acid component diffused to the desalination chamber side through the cation exchange membrane 33 passes through the anion exchange membrane 40. At this time, the weak acid component is converted from a neutral molecule to an anion by ion exchange inside the anion exchange membrane 40, and thus becomes an ion form that is easily captured by the anion exchange resin 51 inside the desalination chamber 23.

In order to realize the structure as shown in FIG. 7 (b), the inventors of the present invention discussed a case where a bipolar membrane was used instead of the cation exchange membrane 33 of FIG. 7 (a). A bipolar membrane-based cation exchange membrane and an anion exchange membrane are integrated into a membrane, and generally have a structure in which a cation exchange membrane and an anion exchange membrane are bonded together. In addition, the bipolar membrane is configured such that the bonding surface of the cation exchange membrane and the anion exchange membrane has a structure that optimizes the dissociation reaction to water and makes the dissociation reaction of water easy to proceed. For this purpose, generally, a substance having a catalytic effect for hydrolysis and separation is introduced on the bonding surface. As the catalyst component, for example, a catalyst component such as a metal (especially a heavy metal ion) or a tertiary amine such as that disclosed in Non-Patent Document 1 is used.

FIG. 9 shows a structure using a bipolar film as described above. The bipolar membrane 50 includes a cation exchange membrane portion 50c and an anion exchange membrane portion 50a. On the bonding surface of the cation exchange membrane portion 50c and the anion exchange membrane portion 50a, H ₂ O is converted into H ⁺ and OH ⁻ and consumed by the hydrolysis and ionization reaction, so it is necessary to efficiently supply water. This water system is supplied by the water which permeates the bonding surface in the thickness direction of each membrane part (50a, 50c). Therefore, in order to smoothly supply water, at least one of the cation exchange membrane portion 50c and the anion exchange membrane portion 50a of the bipolar membrane 50 needs to be thinned. However, from the viewpoint of strength and manufacturing problems, there may be cases where the thickness of the cation exchange membrane portion and the anion exchange membrane portion cannot be reduced.

On the other hand, in order to more reliably ionize the weak acid component diffused from the concentration chamber in the anion exchange membrane 40 with the structure shown in FIG. 7 (b), a thicker anion exchange membrane 40 is suitable. It can be seen that it is ideal to realize a structure as shown in FIG. 7 (b) without using a bipolar film. In addition, a bipolar membrane having a bonded structure of an anion exchange membrane and a cation exchange membrane is more costly than an anion exchange membrane or a cation exchange membrane composed of a single ion exchanger. Therefore, from the viewpoint of cost, it is also preferable not to use a bipolar film.

In this regard, the present inventors have discovered that by making the cation exchange membrane 33 and the anion exchange membrane 40 not the same body, and superposing the anion exchange membrane 40 on a part of the surface of the cation exchange membrane 33 on the side of the desalination chamber side instead of All of them can be supplied horizontally to the interface between the cation exchange membrane 33 and the anion exchange membrane 40. According to this structure, when determining the thickness of each ion exchange membrane, it is not necessary to consider the supply of water to the interface of these ion exchange membranes. Therefore, the degree of freedom in design is high, and it is easy to thicken the anion exchange membrane 40.

This structure is conceptually shown in FIG. 8. The illustration of the anion exchange resin 51 is omitted in FIG. 8. In FIG. 8, it can be seen that the cation exchange membrane 33 and the anion exchange membrane 40 seem to be separated, but these membranes can abut.

At the interface between the cation exchange membrane 33 and the anion exchange membrane 40, if the hydrolysis reaction proceeds and consumes H ₂ O, the water in the desalination chamber 23 will pass from the end of the anion exchange membrane 40 (the end along the paper surface in FIG. 8). ) And cation exchange membrane 33. Further, OH ⁻ ions are supplied to the desalination chamber 23 through the anion exchange membrane 40, and H ⁺ ions are supplied to the concentration chamber 24 through the cation exchange membrane 33.

In addition, the present inventors have also found that when a bipolar membrane is used instead of the anion exchange membrane 40 in the structure shown in FIG. 8 (see Comparative Example 3 described later), a phenomenon in which a current flows intensively through the bipolar membrane may occur. It is thought that this is due to the significant promotion of the bipolar membrane by the hydrolysis ionization reaction.

In contrast, in the structure shown in FIG. 8, the voltage at which the hydrolysis ionization reaction proceeds at the interface where the ion exchange membranes that are not homogeneous overlap each other will approach the contact point of an ordinary ion exchange resin and ion exchange membrane (for example, FIG. 7). (a) The voltage at which the cation exchange membrane 33 contacts the anion exchange resin 51 in the hydrolysis ionization reaction. Therefore, according to the structure shown in FIG. 8, compared with the case where a bipolar membrane having a catalyst function is used in a hydrolyzed reaction part, the former is more likely to suppress the phenomenon that a current flows intensively.

This invention is based on the said knowledge. According to the present invention, the weak acid component diffused from the concentration chamber can be efficiently treated, and high-purity treated water can be obtained. In addition, the current concentration that occurs when the bipolar membrane is used as described above can be alleviated, and as a result, a higher-purity treated water can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 shows a basic aspect of an EDI device according to the present invention. The EDI device is provided with at least one desalting unit between the cathode 12 and the anode 11 facing each other. The desalination processing unit includes a desalination chamber 23, and concentration chambers 22 and 24 provided on one side of the desalination chamber 23, and further includes an anion exchange membrane (AEM) 32 and a cation exchange membrane (CEM) which are first anion exchange membranes. 33.

The desalination chamber 23 is adjacent to the cathode-side concentration chamber 24 among the pair of concentration chambers 22 and 24 through the cation exchange membrane 33 and is adjacent to the pair of concentration chambers 22 and 24 through the anion exchange membrane 32. Concentration chamber 22 on the anode side. Therefore, the desalination chamber 23 is divided into an anion exchange membrane 32 on the side facing the anode 11 and a cation exchange membrane 33 on the side facing the cathode 12.

In the EDI device shown in FIG. 1, a concentration chamber 22, a desalination chamber 23, and a concentration chamber 24 are sequentially arranged from the anode chamber 21 side between the anode chamber 21 having the anode 11 and the cathode chamber 25 having the cathode 12. . The anode chamber 21 and the concentration chamber 22 are adjacent to each other through a cation exchange membrane 31, and the concentration chamber 24 and the cathode chamber 25 are adjacent to each other through an anion exchange membrane 34.

The desalination chamber 23 is filled with at least an anion exchanger. In the example shown in FIG. 1, the anion exchanger and the cation exchange system become a mixed bed (MB) and are filled in the desalination chamber 23. However, it is not limited to this, and only the anion exchanger may be filled in the desalination chamber 23. Alternatively, one or more anion exchanger beds (beds composed of anion exchangers) and one or more cation exchanger beds (beds composed of cation exchangers) may be provided in the desalination chamber 23. At this time, it is desirable to fill the anion exchanger bed and the cation exchanger bed in the desalination chamber in the order that the ion exchanger through which the treated water finally passes becomes an anion exchanger.

In this EDI device, a cation exchange system is filled in the anode chamber 21, and an anion exchange system is filled in the concentration chambers 22 and 24 and the cathode chamber 25. However, the anode chamber 21, the concentration chambers 22, 24, and the cathode chamber 25 do not necessarily need to be filled with an ion exchanger (anion exchanger or cation exchanger).

However, when the anion exchanger is filled in the concentration chambers 22 and 24, the effect of the present invention is significant. The reason is that when anion exchangers are filled in the concentration chambers 22 and 24, the diffusion of weak acid components from the concentration chamber to the desalination chamber tends to have a significant tendency.

For the anion exchanger, for example, an anion exchange resin (AER) is used, and for the cation exchanger, for example, a cation exchange resin (CER) is used. Ion exchange resin refers to a synthetic resin in which a functional group (ion exchange group) is introduced into a polymer matrix having a three-dimensional network structure. Spherical particles having a particle diameter of about 0.4 to 0.8 mm are generally used. Examples of the polymer matrix of the ion exchange resin include a styrene-divinylbenzene copolymer (styrene-based), and an acrylic-divinylbenzene copolymer (acrylic).

Ion exchange resins are roughly divided into cation exchange resins whose functional groups are acidic and anion exchange resins which are basic. In addition, depending on the type of ion exchange group introduced, there are strong acid cation exchange resins and weak acid cation exchange resins. , Strongly basic anion exchange resin, weakly basic anion exchange resin, etc. The strongly basic anion exchange resin includes, for example, a quaternary ammonium group as a functional group (ion exchange group), and the weakly basic anion exchange resin includes, for example, a primary to tertiary amine group as a functional group. For example, a strongly acidic cation exchange resin includes a sulfonic acid group as a functional group, and a weakly acidic cation exchange resin includes a carboxyl group as a functional group.

Next, the production of deionized water (treated water) using the EDI device shown in FIG. 1 will be described. The supplied water is passed through the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25, and a DC voltage is applied between the anode 11 and the cathode 12, and the treated water is passed through the desalination chamber 23. Then, the ionic components in the water to be treated are adsorbed on the ion exchangers in the desalination chamber 23, and are subjected to deionization (desalination) treatment, and the ionized water flows out of the desalination chamber 23 as treated water. At this time, in the desalination chamber 23, due to the application of a voltage, a dissociation reaction of water occurs mainly at the interfaces between different kinds of ion exchangers (or ion exchange membranes), and hydrogen ions and hydroxide ions are generated. Then, the ion components of the ion exchanger previously adsorbed in the desalination chamber 23 undergo ion exchange by the hydrogen ions and hydroxide ions, and are released from the ion exchanger. Among the released ionic components, anions move through the anion exchange membrane 32 to the concentration chamber 22 on the anode side, and are discharged from the concentration chamber 22 as concentrated water, and cations move to the cathode via the cation exchange membrane 33 The concentration chamber 24 on the side is discharged from the concentration chamber 24 in the form of concentrated water. As a result, the ion components supplied to the treated water in the desalination chamber 23 migrate to the concentration chambers 22 and 24 and are discharged, and at the same time, the ion exchanger in the desalination chamber 23 is regenerated. In addition, electrode water is discharged from the anode chamber 21 and the cathode chamber 25.

In the EDI device of the present invention, the surface of the cation exchange membrane 33 of the desalination chamber 23 and the concentration chamber 24 on the side of the desalination chamber 23 (hereinafter sometimes referred to as the "surface on the side of the desalination chamber") is partially overlapped with the system 2 Anion exchange membrane 40, not the entire area of the anion exchange membrane. The anion exchange membrane 40 and the cation exchange membrane 33 are not the same body, that is, the anion exchange membrane 40 is not integrated with the cation exchange membrane 33.

Since the cation exchange membrane 33 is provided so as to distinguish the concentration chamber 24 and the desalination chamber 23, the boundary between the desalination chamber 23 and the concentration chamber 24 is provided in substantially the entire area. On the other hand, as described above, the anion exchange membrane 40 is superposed on a part of the surface of the cation exchange membrane 33 on the side of the desalination chamber. Therefore, the area of the anion exchange membrane 40 is smaller than the area of the cation exchange membrane 33. With such a structure, the interface energy between the cation exchange membrane 33 and the anion exchange membrane 40 is in contact with the water in the desalination chamber 23. Therefore, as described with reference to FIG. 8, the water in the desalination chamber 23 can be supplied to the cation exchange membrane from between the end portion of the anion exchange membrane 40 (the end portion in the up-down direction in FIG. 1) and the cation exchange membrane 33. 33 and the anion exchange membrane 40 interface.

Hereinafter, a part of the region (that is, a region where the anion exchange membrane 40 is superimposed on the surface of the cation exchange membrane 33 on the side of the desalination chamber) may be referred to as an “overlap region”. With regard to one cation exchange membrane 33, there may be one overlapping region (see FIGS. 1 to 3 and 5 to 6), or there may be a plurality of overlapping regions spaced apart from each other (see FIG. 4). When there is an overlapping area on the side of the cation exchange membrane 33 on the side of the desalination chamber, an anion exchange membrane 40 may be overlapped in this area. When there is a plurality of overlapping areas on the surface of the cation exchange membrane 33 on the side of the desalination chamber, one piece of the anion exchange membrane 40 may be overlapped one by one in each area. When there are a plurality of overlapping regions, these regions may be spaced apart from each other along the water flow direction of the treated water in the desalination chamber 23.

Considering the viewpoint of preventing weak acid components from being mixed into the treated water, the overlapping region should include the surface of the cation exchange membrane 33 on the side of the desalination chamber to reach the end edge of the cation exchange membrane 33 on the side of the outlet of the desalination chamber (end edge of the treated water outlet side) Area. That is, if it is an overlapping area, the overlapping area should preferably reach the end edge of the cation exchange membrane 33 on the outlet side of the desalination chamber. When there are multiple overlapping regions, one of the multiple overlapping regions should preferably reach the end edge of the cation exchange membrane 33 on the outlet side of the desalination chamber. In particular, if there are multiple overlapping areas along the water passing direction of the treated water in the desalination chamber 23, there are multiple overlapping areas. Edge.

For example, the anion exchange membrane 40 has the same width as the cation exchange membrane 33 (dimension from the paper surface in the depth direction in FIG. 1), and has a length shorter than the cation exchange membrane 33 (dimension in the paper surface direction in FIG. 1). .

At least a part of the surface of the anion exchange membrane 40 on the side of the desalination chamber 23 is in contact with the anion exchanger. In this aspect, the mixed bed (MB) and the surface of the anion exchange membrane 40 on the side of the desalination chamber are in contact. Therefore, the anion exchanger (especially the anion exchange resin) contained in the mixed bed comes into contact with the surface of the anion exchange membrane 40 on the side of the desalination chamber. Thereby, the weak acid component diffused from the concentration chamber and converted from a neutral molecule to an anion through the anion exchange membrane 40 is easily passed along the anion exchanger filled in the desalination chamber 23, and then passed through the anion exchange membrane 32, so that Efficiently discharge to the concentration chamber 22. In view of this point, in order to form a path for anions to move from the anion exchange membrane 40 to the anion exchange membrane 32 using an anion exchanger, it is desirable to provide an anion exchanger bed or a mixed bed in the desalination chamber so that the anion exchange membranes 40 and 32 are connected.

As for the cation exchange membrane 33 and the anion exchange membrane 40, it is well-known in the field | area which can respectively use an EDI apparatus and an electrodialysis apparatus (ED).

The film thicknesses of the cation exchange membrane 33 and the anion exchange membrane 40 are generally about 100 μm to 700 μm, and particularly about 200 to 600 μm.

Considering the viewpoint of preventing current concentration, it is desirable that neither the cation exchange membrane 33 nor the anion exchange membrane 40 contains a catalyst component for promoting a hydrolytic reaction as contained in a bipolar membrane.

Ion exchange membranes can be broadly divided into heterogeneous membranes and homogeneous membranes. Heterogeneous membranes are obtained by dispersing fine powder of ion exchange resin in a suitable binder (polymer compound) and heating to form a film. The membrane surface of the heterogeneous membrane has a portion composed of an inactive polymer compound without ion exchange groups. Heterogeneous membranes are easier to produce than homogeneous membranes. On the other hand, a homogeneous membrane is synthesized as a membrane-shaped ion exchanger. A homogeneous membrane is an excellent ion-exchange membrane in view of the fact that the entire membrane is chemically bonded using a high degree of cross-linking, has a structure in which a large number of ion exchange groups are uniformly distributed, and has a lower electrical resistance than a heterogeneous membrane. In order to improve the mechanical strength, the heterogeneous film and the homogeneous film are generally integrated with a mesh or a non-woven fabric as a reinforcing body. In addition, the ion exchange membrane is classified into an anion exchange membrane and a cation exchange membrane in the same manner as the ion exchange resin depending on the type of the functional group to be introduced.

In the present invention, any one of a heterogeneous film and a homogeneous film can be used. However, for the cation exchange membrane 33 and the anion exchange membrane 40, any one of a homogeneous membrane / homogeneous membrane, a heterogeneous membrane / homogeneous membrane, a homogeneous membrane / heterogeneous membrane should be used (the type of the cation exchange membrane 33 is indicated before the slash "/" "," Indicates the type of anion exchange membrane 40). That is, at least one of the cation exchange membrane 33 and the anion exchange membrane 40 is preferably a homogeneous membrane. The reason is that the heterogeneous membrane has some inactive regions without ion-exchange groups. Therefore, if a heterogeneous membrane / heterogeneous membrane combination is used at the position where the hydrolytic ionization reaction occurs, there may be fewer hydrolytic ionization reaction points and a higher voltage. Case.

The cation exchange membrane 33 and the anion exchange membrane 40 can be brought into contact with each other in a wet state by being superposed together. When the two are brought into contact with each other in a wet state, when water is consumed by hydrolysis and reaction, water is sucked from the overlapping ends, and water supply between the two becomes easy. The contact position between the two functions as a reaction unit for hydrolysis.

When incorporating the cation exchange membrane 33 and the anion exchange membrane 40 into the EDI device, a method in which the respective membranes are superimposed and incorporated in a dry state, and then passed through water to become a wet state may be adopted. Or when the two are incorporated into the EDI device, they are superimposed and incorporated in a wet state. For example, when the cation-exchange membrane 33 and the anion-exchange membrane 40 are overlapped, the respective membranes can be brought into a wet state, and the surface can be washed with clean pure water or the like, and then the surfaces can be stained and then overlapped. The two can be fixed to each other using an appropriate method.

In addition, the superimposed end portion of the cation exchange membrane 33 and the anion exchange membrane 40 may be a part of which is capable of supplying (suctioning) water from the desalination chamber 23 to the hydrolysis and reaction unit (not sealed, (That is, open). For example, one part of the overlapping ends may be unsealed and the other parts may be sealed. The ends can also be open in all areas. Examples of sealing methods include adhesion using an adhesive, fusion welding in which a film constituent material is melted and integrated by heating, ultrasonic vibration, or the like, and a method of holding and fixing using a frame.

As for the anode 11 and the cathode 12, those known in the field of EDI devices can be used. For example, stainless steel is used for the cathode, and noble metal such as platinum, or a noble metal plated electrode is used for the anode.

The cation exchange membrane 31 and the anion exchange membranes 32 and 34 may be those known in the field of EDI devices. Although not shown, the anode 11 and the cathode 12, the anode chamber 21, the concentration chambers 22 and 24, the desalination chamber 23, the cathode chamber 25, the cation exchange membranes 31 and 33, and the anion exchange membranes 32, 34, and 40 can be used. Housed in a suitable frame (not shown).

Regarding the supply water and the treated water, those known in the field of EDI devices can also be used. Generally speaking, the permeated water of reverse osmosis membrane (RO) is used, and it is better to use RO membrane after two or more treatments. In addition, decarbonation towers and decarbonation membranes are sometimes used to remove carbonic acid. In addition, in recent years, the water treated with EDI has been used for supply water and treated water.

In the device shown in FIG. 1, the supply water is introduced into the anode chamber 21, the concentration chambers 22 and 24, and the cathode chamber 25 from below, and the water (electrode water or concentrated water) is discharged from above. In the desalination chamber 23, the water to be treated is supplied from above, and the water to be treated is discharged to the bottom. However, the present invention is not limited to this, and the traveling direction of water can be appropriately determined. In addition, instead of supplying water to the anode chamber 21 from the outside, the outlet water (electrode water) of the cathode chamber 25 may be supplied to the anode chamber 21, and vice versa.

The diffusion of the weak acid component from the concentration chamber 24 to the desalination chamber 23 is also affected by the concentration of the weak acid component in the concentration chamber 24. The higher the concentration, the larger the amount of diffusion. In the concentration chamber 24, as it goes from its inlet to its outlet, the concentration ratio increases and the concentration of the weak acid component also increases. By arranging the inlet side of the concentration chamber 24 adjacent to the outlet side of the desalination chamber 23, it is possible to suppress a larger amount of diffusion from the concentration chamber 24 from occurring near the treated water outlet of the desalination chamber 23. Therefore, the traveling direction of water in the concentration chamber 24 and the adjacent desalination chamber (the form shown in FIG. 1 refers to the desalination chamber 23 and the form shown in FIG. 6 refers to the second small desalination chamber 27). The direction of travel should be countercurrent.

In addition, a structure in which the concentration chamber has both an electrode chamber is also included in the present invention. For example, the cathode may be provided in the concentration chamber 24 shown in FIG. 1 and the cathode chamber 25 may be omitted. Even in this case, the desalination processing unit composed of the desalination chamber and the pair of concentration chambers is disposed between the cathode and the anode.

The EDI device may have a plurality of desalination processing sections. Therefore, a plurality of basic structures (ie, tanks) composed of [concentration chamber | first anion exchange membrane (AEM) | desalination chamber | cation exchange membrane (CEM) (with second anion exchange membrane superimposed] | concentration chamber]) A cell set is arranged side by side between the anode and the cathode. At this time, adjacent concentrating chambers can be shared between adjacent tank chamber sets. Therefore, the anion exchange membrane 32, the desalination chamber 23, the cation exchange membrane 33 (the anion exchange membrane 40 is superimposed), and the concentration chamber 24 can be formed into a single tank chamber set, and a plurality of the tank chamber sets can be arranged away from the anode Between the concentration chamber 22 closest to the chamber 21 and the cathode chamber 25. In FIG. 1, “N” means the number of the chamber chamber sets, and N is an integer of 1 or more.

The basic structure of the EDI device according to the present invention has been described above, but the present invention can be widely applied to EDI devices having various structures. Hereinafter, a configuration example of an EDI device to which the present invention is applicable will be described.

An EDI apparatus having an embodiment having two desalination processing units will be described with reference to FIG. 2. This EDI device is a device shown in FIG. 1, and two tank chamber sets are arranged between the concentration chamber 22 and the cathode chamber 25 closest to the anode chamber 21. In FIG. 2, the symbols showing the constituent elements constituting the tank chamber set near the cathode chamber 25 are denoted by "'(apostrophe)".

The anode chamber 21 is filled with a cation exchange resin (CER), and the concentration chamber 22 and the cathode chamber 25 are filled with an anion exchange resin (AER). The concentration chambers 24 and 24 'are each filled with an anion exchange resin (AER). Each of the desalination chambers 23 and 23 'is filled with an anion exchange resin and a cation exchange resin in the form of a mixed bed (MB).

The anode chamber 21 and the concentration chamber 22 are divided by a cation exchange membrane 31. The concentration chamber 22 and the desalination chamber 23 are divided by an anion exchange membrane 32. The desalination chamber 23 and the concentration chamber 24 are divided by a cation exchange membrane 33. The concentration chamber 24 and the desalination chamber 23 'are divided by an anion exchange membrane 32'. The desalination chamber 23 'and the concentration chamber 24' are divided by a cation exchange membrane 33 '. The concentration chamber 24 'and the cathode chamber 25 are divided by an anion exchange membrane 34.

An anion exchange membrane 40 is superposed on the cation exchange membrane 33. An anion exchange membrane 40 'is superposed on the cation exchange membrane 33'.

The configurations of the anion exchange membranes 32 'and 40', the desalination chamber 23 ', the cation exchange membrane 33', and the concentration chamber 24 'may be the same as those of the anion exchange membranes 32 and 40, the desalination chamber 23, the cation exchange membrane 33, and the concentration chamber 24, respectively. Different.

Also in this embodiment, the same effects as the embodiment shown in FIG. 1 can be obtained.

Further, CO ₃ ^2-, HCO ₃ ^- and the like from the anion of a weak acid will be moved to the concentrate chambers 23 24 'through the anion exchange membrane 32' from the desalting compartment. Therefore, in the concentrating chamber 24, the supplied water contains the weak acid component originally contained, and also contains the weak acid component moved through the anion exchange membrane 32 '. Therefore, the concentration of the weak acid component in the concentration chamber 24 becomes high, and the diffusion phenomenon of the weak acid component from the concentration chamber 24 to the desalination chamber 23 is liable to become significant. Accordingly, the present invention is particularly effective in an EDI device having a plurality of desalination processing units.

FIG. 3 shows another form of the EDI device according to the present invention. This EDI device is the same as that shown in FIG. 1, except that the cation exchange resin (CER) is disposed in the region on the inlet side of the desalination chamber 23 and the anion exchange resin (AER) is disposed in the region on the outlet side. That is, in the desalination chamber 23, a bed made of a cation exchange resin (a cation exchange resin bed, that is, a cation exchanger bed) and a bed made of an anion exchange resin (anion exchange resin) are stacked one by one in the water passing direction of the treated water. Resin bed, ie anion exchanger bed). That is, the anion exchanger bed and the cation exchanger bed are filled in the desalination chamber in the order that the ion exchanger through which the treated water passes last becomes an anion exchanger. Then, on the cathode side of the anion exchanger bed in the desalination chamber 23, that is, between the anion exchanger bed and the cation exchange membrane 33, an anion exchange membrane 40 is disposed. The anion exchange membrane 40 is not provided on the cathode side of the cation exchanger bed in the desalination chamber 23.

As shown in FIG. 3, the lengths of the beds in the desalination chamber 23 along the water passing direction (lengths along the paper surface in FIG. 3) can be the same as each other, but they can also be different.

Of course, in this form, the anion exchange membrane 32, the desalination chamber 23, the cation exchange membrane 33 (the anion exchange membrane 40 is superimposed), and the concentration chamber 24 can be combined into one tank chamber set, and N (N is an integer of 1 or more) Each of these tank chamber sets is disposed between the concentration chamber 22 and the cathode chamber 25 that are closest to the anode chamber 21.

The EDI device shown in FIG. 4 is the same as that shown in FIG. 3, except that the desalination chamber 23 is divided into four regions along the flow direction of the treated water, and the first cation exchanger bed, the first anion exchanger bed, and the first The arrangement of the two cation exchanger beds and the second anion exchanger bed is obtained by arranging ion exchange resins in the respective areas in order from the inlet side of the water to be treated. An anion exchange membrane 40 (overlapping the cation exchange membrane 33) is disposed on the cathode side of the first anion exchanger bed and on the cathode side of the second anion exchanger bed, respectively. The anion exchange membrane 40 is not disposed on either the cathode side of the first cation exchanger bed or the cathode side of the second cation exchanger bed. In this device, there are two overlapping regions (the region where the anion exchange membrane 40 is overlapped on the side of the cation exchange membrane 33 on the side of the desalination chamber), and they are separated from each other along the water passing direction of the treated water in the desalination chamber 23 And exist. Furthermore, one of the two overlapping regions, which is located most downstream in the water passing direction, reaches the end edge of the cation exchange membrane 33 on the outlet side of the desalination chamber.

As shown in FIG. 4, the lengths of the beds in the desalination chamber 23 along the water flow direction may be the same as each other, but may be different. In addition, the number of each bed is four as shown in Fig. 4, but it may be five or six or more in the range that is feasible in manufacturing.

The EDI device shown in FIG. 5 is the same as that shown in FIG. 1, but in the desalination chamber 23, an anion exchanger bed is provided on the anion exchange membrane 40 side of the desalination chamber to replace the mixed bed (MB). In the region of the desalination chamber 23 where the anion exchange membrane 40 does not exist in the water flow direction of the treated water, a mixed bed is provided in the same manner as that shown in FIG. 1.

That is, in this form, a mixed bed (MB) of an anion exchange resin and a cation exchange resin is arranged near the entrance side area of the desalination chamber 23, and an anion exchanger bed (AER bed) is arranged near the exit side area. That is, the mixed bed and the anion exchanger bed are stacked in the desalination chamber 23 one by one along the water passing direction.

In the EDI device according to the present invention, an intermediate ion exchange membrane (IIEM) may be provided between the anion exchange membrane on the anode side and the cation exchange membrane on the cathode side of each desalination chamber, and the desalination chamber is made of the intermediate ion exchange membrane. It is divided into the first small desalination chamber and the second small desalination chamber. In addition, the treated water can be supplied to one of the first small desalination chamber and the second small desalination chamber, and the water flowing out from the small desalination chamber can flow into the other small desalination chamber. 2 small desalination chambers are connected. As the intermediate ion exchange membrane, both anion exchange membrane and cation exchange membrane can be used. At this time, let the small desalination chamber near the anode side be the first small desalination chamber, and let the small desalination chamber near the cathode side be the second small desalination chamber. For example, the first small desalination chamber is filled with at least an anion exchanger, and the second small desalination chamber is filled with at least a cation exchanger.

FIG. 6 shows an example of an EDI device in which a desalination chamber is divided into two small desalination chambers by using an intermediate ion exchange membrane as described above. The EDI device has a structure in which each of the desalination chambers 23 in the EDI device shown in FIG. 1 is divided into the first side near the anode 11 by using an intermediate ion exchange membrane 36 located between the anion exchange membrane 32 and the cation exchange membrane 33. One small desalination chamber 26 and a second small desalination chamber 27 on the cathode 12 side. The first small desalination chamber 26 is located between the anion exchange membrane 32 and the intermediate ion exchange membrane 36, and the second small desalination chamber 27 is located between the cation exchange membrane 33 and the intermediate ion exchange membrane 36. The first small desalination chamber 26 and the second small desalination chamber 27 communicate with each other such that after the treated water is supplied to the first small desalination chamber 26, the water flowing out of the first small desalination chamber 26 flows into the second small desalination chamber 27.

The first small desalination chamber 26 is filled with an anion exchange resin. A cation exchange resin is arranged in the entrance side area of the second small desalination chamber 27, and an anion exchange resin is arranged in the exit side area. That is, the cation exchanger bed and the anion exchanger bed are installed in the second small desalination chamber 27 in this order along the water flow direction of the water to be treated. The treated water is supplied to the first small desalination chamber 26, and the outlet water of the first small desalination chamber 26 is sent to the second small desalination chamber 27, and deionized water is obtained from the second small desalination chamber 27 as treated water. . Therefore, the anion exchanger bed and the cation exchanger bed are filled in the desalination chamber 23 in the order that the ion exchanger through which the treated water passes last becomes an anion exchanger.

On the cathode side of the anion exchanger bed in the second small desalination chamber 27, an anion exchange membrane 40 (overlapping the cation exchange membrane 33) is arranged. The anion exchange membrane 40 is not disposed on the cathode side of the cation exchanger bed in the second small desalination chamber 27. One of the aforementioned overlapping regions (the region where the anion exchange membrane 40 is overlapped on the surface of the cation exchange membrane 33 on the side of the desalination chamber) exists. This overlapping region reaches the end edge of the desalting chamber outlet side of the cation exchange membrane 33. Here, the outlet of the desalination chamber is the treated water outlet, and in this device, it is the outlet of the second small desalination chamber 27.

As shown in FIG. 6, the lengths of the beds in the second small desalination chamber 27 along the water flow direction may be the same as each other, but may be different.

As the intermediate ion exchange membrane 36, for example, an anion exchange membrane is used.

In the device shown in FIG. 6, the water flow in the first small desalination chamber 26 and the water flow in the second small desalination chamber 27 are countercurrent. However, it is not limited thereto, and these water flows may be cocurrent.

The water to be treated is supplied to the first small desalination chamber 26. Anion components in the supplied treated water are captured while the treated water passes through the first small desalination chamber 26. In the first small desalination chamber 26, the captured anion component moves along the first small desalination chamber 26 through the anion exchange membrane 32 to the adjacent concentration chamber 22, and is discharged to the concentrated water passing through the concentration chamber 22 to the concentration chamber 22. Outside the system.

The to-be-treated water passing through the first small desalination chamber 26 is then supplied to the second small desalination chamber 27. The treated water supplied to the second small desalination chamber 27 first passes through the cation exchanger bed, and then passes through the anion exchanger bed. At this time, the cation component in the treated water is captured during the process of the treated water passing through the cation exchanger bed. Specifically, the cation component captured by the cation exchanger in the second small desalination chamber 27 moves through the cation exchange membrane 33 to the concentration chamber 24 adjacent to the second small desalination chamber 27, and moves from the concentration chamber 24 and the concentrated water. Drained out of the system together.

Then, in the second small desalination chamber 27, the treated water that has passed through the cation exchanger bed passes through the anion exchanger bed in the next stage. At this time, the anion components in the treated water will be captured again. Specifically, the anion component captured by the anion exchanger in the second small desalination chamber 27 moves to the first small desalination chamber 26 adjacent to the second small desalination chamber 27 through the intermediate ion exchange membrane 36. The anion component moving to the first small desalination chamber 26 moves through the anion exchange membrane 32 to the concentration chamber 22 adjacent to the first small desalination chamber 26 and is discharged to the outside of the system together with the concentrated water passing through the concentration chamber 22.

Here, the diffusion of the weak acid component (carbonic acid, silicon dioxide, or boron) contained in the concentrated water in the concentration chamber 24 passing through the cation exchange membrane 33 and moving to the second small desalination chamber 27 in the form of neutral molecules is considered. Situation.

The weak acid component moving from the concentration chamber 24 to the second small desalination chamber 27 is uniformly diffused on the anode-side surface of the cation exchange membrane 33. That is, the weak acid component will not only diffuse into the surface area where the cation exchange membrane 33 is in contact with the anion exchange membrane 40, but also in the area where the cation exchange membrane 33 is in contact with the cation exchanger bed in the second small desalination chamber 27. Surface area. Moreover, the weak acid component is not captured by the cation exchanger, so the weak acid component diffused into the area of the anode side surface of the cation exchange membrane 33 that contacts the cation exchanger bed will pass through the cation exchanger bed with the treated water. However, in the second small desalination chamber 27, a cation exchanger bed and an anion exchanger bed are stacked in the water passing direction of the water to be treated. Therefore, the weak acid component passing through the cation exchanger bed is ionized and captured again in the anion exchanger bed in the next stage, and moves to the first small desalination chamber 26. The weak acid component moved to the first small desalination chamber 26 moves through the anion exchange membrane 32 to the concentration chamber 22 and is discharged to the outside of the system together with the concentrated water passing through the concentration chamber 22.

In this way, even if the weak acid component passes through the cation exchange membrane 33 in this form, there is still an anion exchanger bed in the next stage, so the weak acid component can be easily discharged from the concentration chamber 22, and as a result, the purity of the treated water can be easily suppressed from decreasing. Of course, in this embodiment, the weak acid component diffused to the surface area where the anion exchange membrane 40 is in contact with the anion exchange membrane 33 can be efficiently removed from the water to be treated by the anion exchange membrane 40.

From the above description, it can be understood that the final stage of the laminated body of the ion exchanger bed provided in the desalination chamber, particularly in the second small desalination chamber 27, is preferably an anion exchanger bed. There is no particular limitation on the type, stacking order, and number of stacks of the ion exchanger bed in the previous stage compared to the anion exchanger bed in the final stage.

In the EDI device of this embodiment, the first small desalination chamber 26 first supplied with water to be treated is filled with an anion exchanger, and the second small desalination chamber 27 supplied with water to be treated is sequentially stacked with cations. Exchanger bed and anion exchanger bed. Therefore, the treated water will first pass through the anion exchanger bed. As a result, anion components are removed from the water to be treated, and the pH of the water to be treated is increased.

The treated water passing through the first small desalination chamber 26 is supplied to a second small desalination chamber 27 in which a cation exchanger bed and an anion exchanger bed are sequentially stacked. That is, the treated water passing through the anion exchanger bed in the first small desalination chamber 26 will then pass through the cation exchanger bed and then pass through the anion exchanger bed again. In short, according to the structure of this form, the treated water will alternately pass through the anion exchanger bed and the cation exchanger bed.

Here, the ability of the anion exchanger to capture anion components is high when the pH of the treated water is low, and the ability of the cation exchanger to capture cation components is high when the pH of the treated water is high. Therefore, according to the structure in which the treated water first passes through the anion exchanger bed, and then alternately passes through the cation exchanger bed and the anion exchanger bed, the anion components are removed by passing through the anion exchanger and the pH is increased. Water then passes through the cation exchanger bed. Therefore, the cation removal reaction for which the cation exchanger is made is promoted more than usual.

In addition, the cation component is removed by passing through the cation exchanger bed, and the treated water after the pH is lowered will then pass through the anion exchanger bed. Therefore, the anion removal reaction for which the anion exchanger is made is promoted more than usual. Therefore, not only the removal ability of anion components including carbonic acid, silicon dioxide, or boron is improved, but also the removal ability of cationic components is improved, so the purity of the treated water will be further improved.

As described above, it is preferable to alternately use the cation exchanger bed and the anion exchanger bed in the order that the ion exchanger through which the treated water passes last becomes an anion exchanger. This is not only for the form shown in FIG. 6, but also for the form shown in FIGS. 3 and 4.
[Example]

[Example 1]
An EDI device having a structure shown in FIG. 6 was used to treat treated water and obtain treated water (deionized water). The specifications and test conditions of the EDI device are shown below.

In addition, the specifications and conditions of the concentration chambers 22 and 24 are the same, and the specifications and conditions of the concentrated water obtained by them are also the same. The cation exchange resin (CER) filled in one part (the inlet-side region) of the anode chamber 21 and the second small desalination chamber 27 is the same. The anion exchange resin (AER) filled in the remaining portions (outlet-side regions) of the cathode chamber 25, the concentration chambers 22, 24, the first small desalination chamber 26, and the second small desalination chamber 27 is the same. The cation exchange membranes 31 and 33 are the same, the anion exchange membranes 32 and 34 and the intermediate ion exchange membrane 36 are the same.

In the following, "longitudinal" means the direction along the paper surface in the figure (direction along the direction of travel of water), and "horizontal" means the direction from the paper surface to the depth.
・ Number of tank chamber sets (N): 1 ・ Anode chamber 21: size 100 × width 100 × thickness 10 mm, filled with CER
・ Cathode chamber 25: size 100 × width 100 × thickness 10 mm, filled with AER
・ Concentration chambers 22 and 24: size 100 × width 100 × thickness 10 mm, filled with AER
・ First small desalination chamber 26: size 100 × width 100 × thickness 10 mm, filled with AER
・ Second small desalination chamber 27: size 100 × width 100 × thickness 10 mm, filled with CER (1/2 area on the inlet side) and AER (1/2 area on the outlet side)
・ CER: Strongly acidic cation exchange resin ・ AER: Strongly basic anion exchange resin ・ Cation exchange membranes 31 and 33: Homogeneous membranes, effective membrane size of the current-carrying part 100 × 100 mm in length, 290 μm in thickness
・ Anion exchange membranes 32 and 34 and intermediate ion exchange membranes 36: Homogeneous membranes, effective membrane size of the current-carrying part 100 × 100 mm in length, 220 μm in thickness
・ Anion exchange membrane 40: Homogeneous membrane, the effective membrane size of the current-carrying part is 50 × 100mm in width and 220μm in thickness
・ Supply and treated water: 2-stage RO (reverse osmosis membrane) permeate water, conductivity 2.0 ~ 2.5μS / cm
・ Flow of treated water (deionized water): 25L / h
・ Concentrated water flow: 6L / h
・ Water flow rate of electrode: 5L / h (same for anode and cathode)
・ Applied current value: 0.5A.

A second anion exchange membrane 40 is disposed on the cathode side of the anion exchange resin bed formed in a region on the outlet side 1/2 of the second small desalination chamber 27. At this time, the position of the cation exchange membrane 33 near the outlet side of the desalination chamber (upper end in the vertical direction on the paper surface) and the position of the anion exchange membrane 40 near the outlet side of the desalination chamber are aligned. The position of the cation exchange membrane 33 in the lateral direction (from the paper surface deeper) is aligned with the position of the anion exchange membrane 40 in the lateral direction.

[Comparative Example 1]
The anion exchange membrane 40 is not used. That is, only the cation exchange membrane 33 is used between the second small desalination chamber 27 and the concentration chamber 24. Except for this, treated water was treated in the same manner as in Example 1, and treated water was obtained.

[Comparative Example 2]
The second anion exchange membrane 40 was replaced with a cation exchange membrane. This cation exchange membrane system is a membrane of the same material and thickness as the cation exchange membranes 31 and 33 used in Example 1, and its vertical and horizontal dimensions and arrangement positions are the same as those of the second anion exchange membrane 40 used in Example 1. Except for this, treated water was treated in the same manner as in Example 1, and treated water was obtained.

[Evaluation 1]
For Example 1 and Comparative Examples 1 and 2, after continuously operating for about 500 hours, the total carbon dioxide concentration (total concentration of CO ₂ , H ₂ CO ₃ , HCO _3- ^, and CO ₃ ^{2-) in} the treated water was measured. ), And the specific resistance of the treated water was measured. The results are shown in Table 1. The total carbonic acid concentration is an index indicating the concentration of carbonic acid that has leaked into the treated water without being completely removed after diffusing from the concentration chamber to the desalination chamber. The specific resistance value is not limited to carbonic acid, but also includes other ions, and is an indicator of the purity of treated water.

Compared with Comparative Examples 1 and 2, the leakage of carbonic acid in Example 1 was less, and the treated water had higher purity.

[Table 1]

[Example 2]
The conditions were changed as follows, except that treated water was treated in the same manner as in Example 1 to obtain treated water.
・ Supply and treated water: 2-stage RO (reverse osmosis membrane) permeate water, conductivity 4.0 ~ 4.5μS / cm
・ Applied current value: 1.0A.

[Example 3]
As the second anion exchange membrane 40, a heteroanion exchange membrane was used. This anion exchange membrane (heterogeneous) has the same vertical and horizontal dimensions and positions as those of the second anion exchange membrane 40 used in Example 2. The thickness of the anion exchange membrane (heterogeneous) was 580 μm. Except for this, treated water was treated in the same manner as in Example 2 and treated water was obtained.

[Comparative Example 3]
The second anion exchange membrane 40 is replaced with a bipolar membrane. This bipolar membrane has the same vertical and horizontal dimensions and positions as those of the second anion exchange membrane 40 used in Example 2. Moreover, the bipolar membrane system is arrange | positioned so that the anion exchange membrane part may face the 2nd small desalination chamber 27 side. As the bipolar membrane, a total thickness of 220 μm including an anion exchange membrane portion and a cation exchange membrane portion is used. Except for this, treated water was treated in the same manner as in Example 2 and treated water was obtained.

[Evaluation 2]
For Examples 2, 3 and Comparative Example 3, after continuous operation for about 500 hours, the total carbonic acid concentration, specific resistance, and sodium concentration in the treated water were measured, and the voltage (voltage between the anode 11 and the cathode 12) was measured. , Current distribution rate. The results are shown in Table 2. In the table, the "current distribution ratio above" and "current distribution ratio below" are respectively defined as follows.
(On current distribution ratio) = (Current value flowing through the area where the second anion exchange membrane 40 or bipolar membrane is provided) / (Total current value),
(At current distribution ratio) = (current value flowing through the cation exchange membrane 33 in a region where the second anion exchange membrane 40 or the bipolar membrane is not overlapped) / (total current value).

The current distribution rate is divided into two upper and lower cathode plates that are used as the cathode 12 in a manner corresponding to the above area. The current value flowing through the upper and lower cathode plates is measured by an ammeter respectively, and the current values are calculated to obtain the total applied voltage. The ratio of the current value.

Compared with Comparative Example 3, the current distribution rate in Example 2 is smaller, the sodium concentration in the treated water is lower, and the specific resistance of the treated water is higher. That is, compared with Comparative Example 3, the current in the cationic resin layer in the desalination chamber of Example 2 was more distributed, the removal of cations was better, and the purity of the treated water was higher. In Example 3, this tendency was greater, the sodium concentration in the treated water was low, and the specific resistance of the treated water was the highest. As mentioned above, it is considered that the heterogeneous membrane has an inactive region where part of the ion-exchange group does not exist, so that the hydrolysis reaction is not easy to proceed, and the concentration of electric current on the upper side is suppressed.

[Table 2]

In addition, according to the structure of the present invention, when the treated water in the desalination chamber enters the interface between the cation exchange membrane 33 and the anion exchange membrane 40, the weak acid component contained in the treated water passes through the anion exchange membrane 40 from the interface. Remove easily. On the other hand, as in Comparative Example 3, a bipolar membrane is used instead of the anion exchange membrane 40. When the treated water in the desalination chamber enters the interface between the cation exchange membrane 33 and the bipolar membrane, the treated water contains It is difficult to remove anionic components from this interface. The reason is that the movement of the anion component is prevented by both the cation exchange membrane 33 and the cation exchange membrane portion of the bipolar membrane. As a result, anions may leak into the treated water and cause a decrease in water quality.

For example in FIG. 10 (b), when the anion and cation (FIG labeled "C ⁺ A ^-") when entering the cation exchange membrane 33 and the interface between the anion exchange membrane 40, an anion (FIG labeled "A ^- ") Will move to the desalination chamber 23 through the anion exchange membrane 40 and be easily captured by the anion exchange resin inside the desalination chamber 23. Cations (labeled "C ⁺ " in the figure) are removed from this interface through the cation exchange membrane 33. On the other hand, as shown in FIG. 10 (a), the structure of the anion exchange membrane 40 is replaced with the bipolar membrane 50. Although the interface between the cation exchange membrane 33 and the bipolar membrane 50, cations (C ⁺ ) pass through the cations. The exchange membrane 33 is removed, but the anion (A ⁻ ) does not pass through the bipolar membrane 50 or the cation exchange membrane 33. As a result, anions are discharged from, for example, the end of the interface (the upper end in the up-down direction in the paper surface in FIG. 10), and leak directly into the treated water.

11‧‧‧Anode

12‧‧‧ cathode

21‧‧‧Anode Room

22‧‧‧Concentration Room

23‧‧‧Desalination Room

23’‧‧‧Desalination Room

24‧‧‧Concentration Room

24’‧‧‧Concentration Room

25‧‧‧ cathode chamber

26‧‧‧The first small desalination room

27‧‧‧The second small desalination room

31‧‧‧ cation exchange membrane (CEM)

32‧‧‧The first anion exchange membrane (AEM)

32’‧‧‧The first anion exchange membrane (AEM)

33‧‧‧ cation exchange membrane (CEM)

33’‧‧‧ cation exchange membrane (CEM)

34‧‧‧ Anion exchange membrane (AEM)

36‧‧‧ Intermediate ion exchange membrane (IIEM)

40‧‧‧Second anion exchange membrane (AEM)

40’‧‧‧Second anion exchange membrane (AEM)

50‧‧‧bipolar membrane

50a‧‧‧Anion exchange membrane section

50c‧‧‧Cation exchange membrane department

51‧‧‧ anion exchange resin

[Fig. 1] A schematic cross-sectional view showing a schematic structure of one form of an EDI device of the present invention.

[Fig. 2] A schematic cross-sectional view showing a schematic configuration of an example when the number of repetitions N is 2 in the device shown in Fig. 1. [Fig.

[Fig. 3] A schematic sectional view showing a schematic structure of another form of the EDI device of the present invention.

[Fig. 4] A schematic cross-sectional view showing a schematic structure of another embodiment of the EDI device of the present invention.

[Fig. 5] A schematic cross-sectional view showing a schematic structure of still another form of the EDI device of the present invention.

[FIG. 6] A schematic cross-sectional view showing a schematic structure of still another form of the EDI device of the present invention.

[Fig. 7] (a) and (b) are conceptual diagrams for explaining the mechanism of the present invention.

[Fig. 8] Another conceptual diagram for explaining the mechanism of hydrolysis and dissociation at the interface where the cation exchange membrane and the anion exchange membrane overlap.

[Fig. 9] A conceptual diagram for explaining the mechanism of hydrolysis and ionization in a bipolar membrane.

[Fig. 10] (a) and (b) are conceptual diagrams for explaining a state in which anions and cations are discharged from an interface where two films are overlapped.

Claims (7)

An electric deionized water manufacturing device is provided with at least one desalination processing section between a cathode and an anode facing each other, The desalination processing unit has at least a desalination chamber filled with an anion exchanger and a concentration chamber provided on one side of the desalination chamber, The desalination chamber is adjacent to the concentration chamber on the cathode side of the pair of concentration chambers by a cation exchange membrane, and is adjacent to the anode side of the pair of concentration chambers by the first anion exchange membrane. The concentration chamber is characterized by: A second anion exchange membrane, which is not the same as the cation exchange membrane, is provided on a part of the surface of the cation exchange membrane on the side of the desalination chamber. The anion exchanger is in contact with at least a part of the surface of the second anion exchange membrane on the side of the desalination chamber. For example, the electric deionized water production device of the scope of application for a patent, wherein the region includes a region on the side of the cation exchange membrane on the side of the desalination chamber to the outlet side end of the cation exchange membrane. For example, the electric deionized water manufacturing device for patent application No. 1 or 2, wherein the desalination chamber contains one or more beds made of anion exchangers in the order that the ion exchangers through which the treated water passes last become anion exchangers. That is, anion exchanger bed, and one or more beds composed of cation exchanger, that is, cation exchanger bed. For example, in the electric deionized water manufacturing device of the third scope of the application for a patent, in the desalination chamber, a first cation exchanger bed, a first anion exchanger bed, a first 2 a cation exchanger bed and a second anion exchanger bed, and The second anion exchange membrane is respectively provided on the cathode side of the first anion exchanger bed and on the cathode side of the second anion exchanger bed. The second anion exchange membrane is not provided on either the cathode side of the first cation exchanger bed or the cathode side of the second cation exchanger bed. For example, the apparatus for producing deionized water according to item 3 of the patent application, wherein the desalination chamber includes an intermediate ion exchange membrane which is an ion exchange membrane located between the first anion exchange membrane and the cation exchange membrane, and uses the intermediate The ion exchange membrane zone is divided into a first small desalination chamber and a second small desalination chamber, and The first small desalination chamber is located between the first anion exchange membrane and the intermediate ion exchange membrane, The second small desalination chamber is located between the cation exchange membrane and the intermediate ion exchange membrane. Communicating the first small desalination chamber and the second small desalination chamber so that the water to be treated is supplied to the first small desalination chamber and the water flowing out of the first small desalination chamber flows into the second small desalination chamber, An anion exchanger bed is provided in the first small desalination chamber, The second small desalination chamber is provided with a cation exchanger bed and an anion exchanger bed in this order along the water passing direction of the treated water. The second anion exchange membrane is arranged on the cathode side of the anion exchanger bed provided in the second small desalination chamber, The second anion exchange membrane is not disposed on the cathode side of the cation exchanger bed provided in the second small desalination chamber. For example, the electric deionized water production device of the first or second scope of the patent application, wherein the pair of concentration chambers are filled with at least an anion exchanger. For example, the electric deionized water manufacturing device according to item 1 or 2 of the patent application scope, wherein the second anion exchange membrane is a heterogeneous membrane and the cation exchange membrane is a homogeneous membrane.