KR102436864B1 - Electric deionized water production device - Google Patents

Abstract

Provided is an electric deionized water production apparatus having a novel configuration capable of efficiently removing weak acid components that have diffused from the concentration chamber into the water to be treated in the demineralization chamber from the water to be treated.
At least one desalting unit is provided between the opposing negative electrode and the positive electrode, and the desalting unit includes a desalting chamber filled with at least an anion exchanger, and a pair of enrichment chambers provided adjacent to both sides of the desalting chamber, the desalting chamber comprising: An electric deionized water production apparatus adjacent to the concentrating chamber on the cathode side of a pair of enrichment chambers via a cation exchange membrane and adjacent to the enrichment chamber on the anode side of the pair of enrichment chambers via a first anion exchange membrane, A second anion exchange membrane separate from the cation exchange membrane is superimposed on a part of the surface of the cation exchange membrane on the desalting chamber side, and the anion exchanger is in contact with at least a part of the surface of the second anion exchange membrane on the desalting chamber side.

Description

Electric deionized water production device

The present invention relates to an electric deionized water production apparatus.

In recent years, an electric deionized water manufacturing apparatus that does not require regeneration by a chemical (hereinafter, may be referred to as an "EDI apparatus") has been developed and put into practical use. EDI apparatus is a combination of electrophoresis and electrodialysis. The basic configuration of a typical EDI device is as follows. That is, the EDI device has a desalination chamber, a pair of enrichment chambers arranged on both sides of the desalination chamber, an anode (positive pole) chamber arranged outside one enrichment chamber, and a cathode (minus pole) arranged outside the other enrichment chamber. ) to provide a room. The desalting chamber has an anion exchange membrane and a cation exchange membrane disposed oppositely, and an ion exchanger (anion exchanger and/or cation exchanger) filled between these exchange membranes. The anion component and the cation component present in the water to be treated pass through the anion exchange membrane and the cation exchange membrane, respectively, and move from the desalting chamber to the concentration chamber, and from the desalting chamber, treated water, that is, deionized water, is obtained, and concentrated water is obtained from the concentration chamber. lose

In order to produce deionized water, water to be treated is passed through the demineralization chamber while a DC voltage is applied between the electrodes installed in the anode chamber and the cathode chamber, respectively. In the desalting chamber, anion components (Cl ^- , CO ₃ ^2- , HCO ₃ ^- , SiO ₂ , etc.) are converted by an anion exchanger to a cation component (Na ⁺ , Ca ²⁺ , Mg ²⁺ , etc.) by a cation exchanger. this is captured At the same time, for example, at the interface between the anion exchanger and the cation exchanger in the desalting chamber, a dissociation reaction of water occurs to generate hydrogen ions and hydroxide ions (H ₂ O → H ⁺ + OH ⁻ ). The ion component captured by the ion exchanger is released from the ion exchanger by exchanging with these hydrogen ions and hydroxide ions. The liberated ion component is electrophoresed to an ion exchange membrane (anion exchange membrane or cation exchange membrane) through an ion exchanger, is electrodialyzed with an ion exchange membrane, and is transferred to a concentration chamber. The ion component moved to the enrichment chamber is discharged by water flowing through the enrichment chamber.

In the EDI apparatus, a weak acid component contained in concentrated water passes through a cation exchange membrane separating the concentration chamber and the desalination chamber and diffuses into the treated water, resulting in a phenomenon in which the purity of the treated water is reduced. This is because weak acid components such as carbonic acid, silica (silicic acid), and boron (boric acid) take the form of partially non-ionized molecules (neutral molecules) depending on changes in pH, etc., so the effect of selective permeability by the cation exchange membrane It is due to what is difficult to receive. For example, with respect to carbonic acid, there is an equilibrium relationship expressed by formulas (1) to (3). In the case of carbonic acid, the forms of the non-ionized molecules (neutrophils) are CO ₂ and H ₂ CO ₃ , which can easily pass through a cation exchange membrane:

CO ₂ + H ₂ O ↔ H ₂ CO ₃ (1)

H ₂ CO ₃ ↔ H ⁺ + HCO ₃ ^- (2)

HCO ₃ ^- ↔ H ⁺ + CO ₃ ^2- (3)

Patent Document 1 discloses an EDI device capable of suppressing mixing of a weak acid component diffused from a concentration chamber to a desalination chamber into treated water. In this apparatus, the desalting chamber is divided into a first small deionization chamber and a second demineralization chamber by an ion exchange membrane, the first demineralization chamber is filled with an anion exchanger, and the target water is in the second demineralization chamber. Anion exchangers and cation exchangers are charged in the order that the ion exchanger passed last becomes the anion exchanger.

In Patent Document 1, a bipolar membrane is provided on the cathode side of the anion exchanger filled in the second demineralization chamber to promote the water dissociation reaction and at the same time realize an appropriate distribution of current density. Disclosed is that the face is disposed facing the anion exchanger.

Patent Documents 2 and 3 also disclose the use of a bipolar film in an EDI device. Patent Documents 4 and 5 and Non-Patent Document 1 disclose a bipolar film.

JP 2012-161758 A WO 2013018818 A WO 2011152226 A JPH7-11021A JP 2010-132829 A

Yoshinobu Tanaka, "Ion Exchange Membranes Fundamentals and Applications", Maruzen Publishing, 2016, p. 15-18

In the EDI system, it is very important to efficiently remove the weak acid component that has diffused from the concentration chamber into the water to be treated in the desalination chamber from the treatment water.

An object of the present invention is to provide an EDI device having a novel configuration capable of efficiently removing from the treatment water a weak acid component that has diffused from the concentration chamber into the water to be treated in the desalination chamber.

According to one aspect of the present invention,

At least one desalination treatment unit is installed between the opposite cathode and anode,

The desalting unit includes at least a desalting chamber filled with an anion exchanger, and a pair of concentration chambers provided adjacent to both sides of the desalting chamber,

The desalting chamber is adjacent to the concentration chamber on the cathode side of the pair of enrichment chambers via a cation exchange membrane, and is adjacent to the enrichment chamber on the anode side of the pair of enrichment chambers through a first anion exchange membrane, As an electric deionized water manufacturing device,

A second anion exchange membrane, which is separate from the cation exchange membrane, is superimposed and installed in a part of the surface of the cation exchange membrane on the desalting chamber side;

An electric deionized water production apparatus is provided, wherein the anion exchanger is in contact with at least a part of the surface of the second anion exchange membrane on the demineralization chamber side.

According to the present invention, there is provided an EDI device of a novel configuration capable of efficiently removing from the treatment water a weak acid component that has diffused from the concentration chamber into the water to be treated in the desalination chamber.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows the schematic structure of one embodiment of the EDI apparatus of this invention.
Fig. 2 is a schematic cross-sectional view showing a schematic configuration of an example in the case where the number of repetitions N is 2 in the apparatus shown in Fig. 1 .
3 is a schematic cross-sectional view showing the schematic configuration of another form of the EDI device of the present invention.
4 is a schematic cross-sectional view showing a schematic configuration of another form of EDI device of the present invention.
Fig. 5 is a schematic cross-sectional view showing the schematic configuration of another form of the EDI device of the present invention.
6 is a schematic cross-sectional view showing the schematic configuration of another form of EDI device of the present invention.
7 is a conceptual diagram for explaining the mechanism of the present invention.
8 is another conceptual diagram for explaining a water dissociation mechanism at an interface where a cation exchange membrane and an anion exchange membrane are superimposed (ie, overlapped).
9 is a conceptual diagram for explaining a water dissociation mechanism in a bipolar film.
10 is a conceptual diagram for explaining a situation in which anions and cations are discharged from an interface where two membranes are superimposed.

In the EDI apparatus in which the desalting chamber is filled with an anion exchanger, the weak acid component that has diffused from the concentration chamber to the desalting chamber can be captured by the anion exchanger and removed from the treated water. However, a part of the weak acid component that has diffused from the concentration chamber into a region close to the outlet of the desalting chamber is discharged from the desalting chamber before being trapped by the anion exchanger in the desalting chamber and removed, and is likely to be mixed into the treated water. This phenomenon is considered to occur because the weak acid component that has diffused from the concentration chamber leaks to the treated water side without sufficiently contacting the anion exchanger.

Fig. 7(a) conceptually shows the vicinity of the boundary between the demineralization chamber 23 and the enrichment chamber 24 on the cathode side of an example of a conventional EDI apparatus. In this EDI apparatus, the cation exchange membrane 33 divides the desalination chamber 23 and the concentration chamber 24 on the cathode side thereof. The desalting chamber 23 is filled with an anion exchange resin 51 in particle form as an anion exchanger, and the anion exchange resin 51 is in contact with the surface of the cation exchange membrane 33 on the desalting chamber side. In such an apparatus, the weak acid component that has diffused from the concentration chamber 24 through the cation exchange membrane 33 is removed from the anion exchange resin 51 at the portion where the cation exchange membrane 33 and the anion exchange resin 51 are in contact. ) can be ionized and captured by an ion exchange reaction. For example, carbonic acid (H ₂ CO ₃ ) is converted into hydrogen carbonate ions (HCO ₃ ⁻ ) or carbonate ions (CO ₃ ²⁻ ) by the anion exchange resin 51 and captured. The captured anions can pass through the anion exchange resin 51 and move to the concentrating chamber on the opposite side (anode side). On the other hand, in the portion where the cation exchange membrane 33 is not in contact with the anion exchange resin 51, the weak acid component is released from the cation exchange membrane 33 in the liquid phase in the desalting chamber 23, and a part thereof is mixed into the treated water as it is. is believed to be

As shown in Fig. 7(b), the present inventors have a configuration in which the anion exchange membrane 40 is superimposed on the surface of the desalting chamber side of the cation exchange membrane 33 dividing the desalting chamber 23 and the enrichment chamber 24. , found that there is an effective possibility to solve the above-mentioned problems. According to this configuration, the weak acid component that has diffused toward the desalination chamber side through the cation exchange membrane 33 permeates 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 in the anion exchange membrane 40 , and thus is in the form of an ion that is easily captured by the anion exchange resin 51 inside the desalting chamber 23 .

The present inventors studied using a bipolar membrane instead of the cation exchange membrane 33 of FIG. 7(a) in order to realize the configuration as shown in FIG. The bipolar membrane is a membrane in which a cation exchange membrane and an anion exchange membrane are integrated, and usually has a structure in which a cation exchange membrane and an anion exchange membrane are attached to each other. In addition, the bipolar membrane has a structure in which the attachment surfaces of the cation exchange membrane and the anion exchange membrane are optimized for the dissociation reaction of water, and is configured so that the dissociation reaction of water proceeds easily. For this purpose, as a rule, a substance having a catalytic action for dissociation of water is introduced at the adhesion surface. As the catalyst component, for example, a catalyst component such as a metal (especially a heavy metal ion) or a tertiary amine as disclosed in Non-Patent Document 1 is used.

9 shows a configuration using the bipolar film as described above. The bipolar membrane 50 includes a cation exchange membrane part 50c and an anion exchange membrane part 50a. On the attachment surface of the cation exchange membrane part 50c and the anion exchange membrane part 50a, H ₂ O is converted into H ⁺ and OH ⁻ by the water dissociation reaction and consumed, so it is necessary to supply water efficiently. This water is supplied by moisture penetrating each of the membrane parts 50a and 50c to the attachment surface in the thickness direction. Therefore, at least one of the cation exchange membrane part 50c and the anion exchange membrane part 50a of the bipolar membrane 50 needs to be thinned so that water supply can be performed smoothly. However, there are cases in which the thickness of the cation exchange membrane part and the anion exchange membrane part cannot be made thin due to strength or manufacturing problems.

On the other hand, in the configuration shown in Fig. 7(b), in order to more reliably ionize the weak acid component that has diffused from the concentration chamber in the anion exchange membrane 40, it is considered that the thicker the anion exchange membrane 40 is suitable. Therefore, it turned out to be preferable to realize the configuration as shown in Fig. 7(b) without using the bipolar film. In addition, a bipolar membrane having an anion exchange membrane and a cation exchange membrane attached structure is high in cost compared to an anion exchange membrane or a cation exchange membrane composed of a single ion exchanger. Therefore, it is preferable not to use a bipolar film|membrane also from a viewpoint of cost.

In this regard, the present inventors separate the cation exchange membrane 33 and the anion exchange membrane 40 to provide an anion exchange membrane 40 in a part, not all, of the surface of the cation exchange membrane 33 on the desalting chamber side. It has been found that water can be smoothly supplied to the interface between the cation exchange membrane 33 and the anion exchange membrane 40 by stacking them. According to this configuration, in 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 configuration is conceptually shown in FIG. 8 . In addition, in FIG. 8, illustration of the anion exchange resin 51 is abbreviate|omitted. In addition, although the cation exchange membrane 33 and the anion exchange membrane 40 seem to be separated in FIG. 8, these membranes may be in contact.

When the water dissociation reaction proceeds at the interface between the cation exchange membrane 33 and the anion exchange membrane 40 and H ₂ O is consumed, the water in the desalting chamber 23 is discharged from the end of the anion exchange membrane 40 (the ground in FIG. 8 ). end) and the cation exchange membrane 33 . Then, OH ⁻ ions are supplied to the desalting 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, when a bipolar membrane is used instead of the anion exchange membrane 40 in the configuration shown in FIG. 8 (refer to Comparative Example 3 to be described later), a phenomenon in which current flows concentrating on the bipolar membrane may occur. It was confirmed by examination. This is considered to be because the water dissociation reaction is remarkably promoted by the bipolar film.

In contrast, in the configuration shown in Fig. 8, the voltage at which the water dissociation reaction proceeds at the interface where separate ion exchange membranes are superimposed on each other is the contact point between the normal ion exchange resin and the ion exchange membrane (e.g., Fig. 7(a)). The voltage of the water dissociation reaction proceeding at the contact point between the cation exchange membrane 33 and the anion exchange resin 51 in FIG. Therefore, according to the configuration shown in Fig. 8, it is easier to suppress the phenomenon in which current flows intensively compared to the case where a bipolar membrane having a catalytic function is used for the reaction portion of water dissociation.

The present invention has been made based on the knowledge described above. According to the present invention, the weak acid component diffusing from the concentration chamber can be efficiently treated, and it becomes possible to obtain treated water of high purity. In addition, as described above, the current concentration that occurs when the bipolar film is used can also be alleviated, and as a result, it becomes possible to obtain treated water of higher purity.

EMBODIMENT OF THE INVENTION Hereinafter, although the form of this invention is described in detail, referring drawings, this invention is not limited by this.

1 shows a basic aspect of an EDI device according to the present invention. In the EDI apparatus, at least one desalting unit is provided between the negative electrode 12 and the positive electrode 11 which are opposed to each other. This desalting unit includes a desalting chamber 23 and a pair of concentration chambers 22 and 24 provided adjacent to both sides of the desalting chamber 23, and an anion exchange membrane (AEM) as a first anion exchange membrane ( 32) and a cation exchange membrane (CEM) 33 .

The demineralization chamber 23 is adjacent to the concentration chamber 24 on the cathode side of the pair of enrichment chambers 22 and 24 via a cation exchange membrane 33, and is one of the pair of enrichment chambers 22 and 24. It is adjacent to the concentration chamber 22 on the anode side via an anion exchange membrane 32 interposed therebetween. Accordingly, the desalting chamber 23 is partitioned by an anion exchange membrane 32 positioned on the side facing the anode 11 and a cation exchange membrane 33 positioned on the side facing the cathode 12 .

In the EDI device shown in FIG. 1 , between the anode chamber 21 provided with the anode 11 and the cathode chamber 25 provided with the cathode 12 , in order from the anode chamber 21 side, the enrichment chamber ( 22), a desalination chamber 23 and a concentration chamber 24 are provided. The anode chamber 21 and the enrichment chamber 22 are adjacent to each other with a cation exchange membrane 31 interposed therebetween, and the enrichment chamber 24 and the cathode chamber 25 are adjacent to each other with an anion exchange membrane 34 interposed therebetween.

The desalting chamber 23 is filled with at least an anion exchanger. In the example shown in FIG. 1, in the desalting chamber 23, an anion exchanger and a cation exchanger become a mixed bed (MB) and are filled. However, the present invention is not limited thereto, and only the anion exchanger may be filled in the desalting chamber 23 . Alternatively, one or more anion exchanger beds (beds of anion exchangers) and one or more cation exchanger beds (beds of cation exchangers) are installed in the desalination chamber 23 . it may be In this case, it is preferable that the anion exchanger phase and the cation exchanger phase are filled in the desalting chamber in the order that the ion exchanger through which the to-be-treated water last passes becomes the anion exchanger.

Further, in this EDI device, a cation exchanger is filled in the anode chamber 21 , and an anion exchanger is filled in the concentrating chambers 22 , 24 and the cathode chamber 25 . However, the anode chamber 21, the concentration chambers 22, 24 and the cathode chamber 25 are not necessarily filled with an ion exchanger (anion exchanger or cation exchanger).

However, when the concentrating chambers 22 and 24 are filled with an anion exchanger, the effect of the present invention is remarkable. This is because, when the anion exchanger is filled in the concentrating chambers 22 and 24, the diffusion phenomenon of the weak acid component from the concentrating chamber to the desalting chamber tends to be remarkable.

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

Ion exchange resins are broadly classified into cation exchange resins in which functional groups are acidic and anion exchange resins in which basicity is present, and depending on the type of ion exchange group to be introduced, strongly acidic cation exchange resins, weakly acidic cation exchange resins, strongly basic anion exchanges resins, and weakly basic anion exchange resins. Strongly basic anion exchange resins, for example, have a quaternary ammonium group as a functional group (ion exchange group), and weakly basic anion exchange resins include, for example, primary to tertiary amines as functional groups. . Strongly acidic cation exchange resins, for example, have a sulfonic acid group as a functional group, and weakly acidic cation exchange resins have, for example, a carboxyl group as a functional group.

Next, the production of deionized water (treated water) by the EDI apparatus shown in Fig. 1 will be described. A demineralization chamber (23) in a state in which supply water is passed through the anode chamber (21), the enrichment chambers (22, 24) and the cathode chamber (25), and a DC voltage is applied between the anode (11) and the cathode (12). The water to be treated is passed through the Then, the ion component in the to-be-treated water is adsorbed to the ion exchanger in the desalting chamber 23 , and deionization (desalting) treatment is performed, and the deionized water flows out from the desalting chamber 23 as treated water. At this time, in the desalting chamber 23, a dissociation reaction of water occurs mainly at the interface between different types of ion exchangers (which may be ion exchange membranes) by the applied voltage, and hydrogen ions and hydroxide ions are generated. Then, the ion components adsorbed to the ion exchanger in the desalting chamber 23 are first ion exchanged by the hydrogen ions and the hydroxide ions and released from the ion exchanger. Anions among the liberated ion components move to the concentration chamber 22 on the anode side via the anion exchange membrane 32 , and are discharged as concentrated water from the concentration chamber 22 , and the cations pass through the cation exchange membrane 33 . Thus, it moves to the concentration chamber 24 on the cathode side, and is discharged as concentrated water from the concentration chamber 24 . As a result, the ion component in the water to be treated supplied to the desalination chamber 23 is transferred to the concentration chambers 22 and 24 and discharged, and at the same time, the ion exchanger in the desalination chamber 23 is regenerated. Further, electrode water is discharged from the anode chamber 21 and the cathode chamber 25 .

In the EDI apparatus according to the present invention, the surface of the cation exchange membrane 33 that divides the desalting chamber 23 and the enrichment chamber 24 on the desalting chamber 23 side (hereinafter referred to as “desalting chamber side surface” may be referred to in some cases). ), an anion exchange membrane 40, which is a second anion exchange membrane, is disposed overlappingly in some, but not all, regions. The anion exchange membrane 40 is separate from the cation exchange membrane 33 , that is, it is not integrated with the cation exchange membrane 33 .

The cation exchange membrane 33 is provided so as to partition the concentrating chamber 24 and the demineralizing chamber 23 , and thus is provided in substantially the entire area of the boundary between the demineralizing chamber 23 and the concentrating chamber 24 . On the other hand, as described above, the anion exchange membrane 40 is superposed on a portion of the demineralization chamber side surface of the cation exchange membrane 33 . Accordingly, the area of the anion exchange membrane 40 is smaller than the area of the cation exchange membrane 33 . With this configuration, the interface between the cation exchange membrane 33 and the anion exchange membrane 40 can be in contact with the water in the desalting chamber 23 . Accordingly, as described with reference to FIG. 8 , from between the end of the anion exchange membrane 40 (the end in the vertical direction in the paper in FIG. 1 ) and the cation exchange membrane 33 , the cation exchange membrane 33 and the anion exchange membrane 40 . It is possible to supply water in the desalination chamber 23 to the interface of .

Hereinafter, the partial region (that is, the region where the anion exchange membrane 40 overlaps among the demineralization chamber side surfaces of the cation exchange membrane 33) is sometimes referred to as an “overlapping region”. Regarding one cation exchange membrane 33, there may be one overlapping region (refer to Figs. 1 to 3 and Figs. 5 to 6), or a plurality of overlapping regions may exist apart from each other (refer to Fig. 4). When there is one overlapping region on the demineralization chamber side of the cation exchange membrane 33, one anion exchange membrane 40 may be overlapped in the region. When a plurality of overlapping regions are present on the demineralization chamber side of the cation exchange membrane 33, one anion exchange membrane 40 may be overlapped in each region. In addition, when a plurality of overlapping regions exist, these regions may exist apart from each other along the flow direction of the to-be-treated water in the demineralization chamber 23 .

From the viewpoint of preventing the weak acid component from mixing into the treated water, the overlapping region reaches the end of the desalting chamber outlet of the cation exchange membrane 33 (the end of the treated water outlet) among the face of the demineralization chamber side of the cation exchange membrane 33 . It is preferable to include an area where That is, if there is one overlapping region, it is preferable that the overlapping region reaches the end of the cation exchange membrane 33 on the demineralization chamber outlet side. When there are a plurality of overlapping regions, it is preferable that one of the plurality of overlapping regions reaches the end of the cation exchange membrane 33 on the outlet side of the desalting chamber. In particular, when there are a plurality of overlapping regions in the desalting chamber 23 along the water flow direction of the to-be-treated water, the overlapping regions located at the most downstream in the water passage direction are on the outlet side of the desalting chamber of the cation exchange membrane 33 . It is desirable to reach the end.

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

In addition, the anion exchanger is in contact with at least a part of the surface of the anion exchange membrane 40 on the demineralization chamber 23 side. In this embodiment, the mixed phase MB is in contact with the surface of the anion exchange membrane 40 on the demineralization chamber side. Therefore, the anion exchanger (especially anion exchange resin) contained in the mixed phase is in contact with the surface of the anion exchange membrane 40 on the desalting chamber side. Thereby, the weak acid component diffused from the concentration chamber and converted from neutral molecules to anions by the anion exchange membrane 40 passes through the anion exchanger filled in the desalting chamber 23 and also through the anion exchange membrane 32 Therefore, it is easy to efficiently discharge to the enrichment chamber 22 . From this point of view, an anion exchanger phase or a mixed phase is formed in the desalting chamber so as to be in contact with the anion exchange membranes 40 and 32 so as to form a path for the movement of anions by the anion exchanger from the anion exchange membrane 40 to the anion exchange membrane 32 . It is preferable to have it installed.

As the cation exchange membrane 33 and the anion exchange membrane 40, those known in the field of EDI devices and electrodialysis devices (ED) can be used, respectively.

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

Both the cation exchange membrane 33 and the anion exchange membrane 40 preferably do not contain a catalyst component for promoting the water dissociation reaction as contained in the bipolar membrane from the viewpoint of preventing current concentration.

Ion exchange membranes can be roughly divided into heterogeneous membranes and homogeneous membranes. The heterogeneous membrane is formed by dispersing a fine powder of an ion exchange resin in a suitable binder (polymer compound) and heating it to form a membrane. On the membrane surface of the heterogeneous membrane, there is a portion made of an inert high molecular compound in which an ion-exchange group does not exist. The heterogeneous membrane is easier to manufacture than the homogeneous membrane. On the other hand, the homogeneous membrane is an ion exchanger synthesized in the form of a membrane. A homogeneous membrane is an excellent ion exchange membrane in that the entire membrane is chemically bonded by a high degree of crosslinking, has a structure in which a large number of ion exchangers are uniformly distributed, and has low electrical resistance compared to a heterogeneous membrane. In both the heterogeneous membrane and the homogeneous membrane, it is common that a mesh or nonwoven fabric is integrated as a reinforcing body for the purpose of improving mechanical strength. Also, like the ion exchange resin, the ion exchange membrane is classified into an anion exchange membrane and a cation exchange membrane according to the type of functional group to be introduced.

In the present invention, it is possible to employ either a heterogeneous film or a homogeneous film. However, for the cation exchange membrane 33 and the anion exchange membrane 40, it is preferable to use any one of a homogeneous membrane/homogeneous membrane, a heterogeneous membrane/homogeneous membrane, and a homogeneous membrane/heterogeneous membrane (a cation exchange membrane before a slash "/") (33) indicates the type of the anion exchange membrane 40 after "/"). That is, at least one of the cation exchange membrane 33 and the anion exchange membrane 40 is preferably a homogeneous membrane. This is because, since the heterogeneous membrane has an inactive region without some ion exchangers, the reaction point for water dissociation may decrease and the voltage may increase if a combination of a heterogeneous membrane/heterogeneous membrane is used at a location where the water dissociation reaction occurs.

The cation exchange membrane 33 and the anion exchange membrane 40 can be brought into contact in a wet state by overlapping them together. By bringing the protons into contact with each other in a wet state, when water is consumed in the water dissociation reaction, water is sucked from the overlapping end, thereby facilitating the water supply between the two. In addition, the contact point of both functions as a reaction part for water dissociation.

When the cation exchange membrane 33 and the anion exchange membrane 40 are installed in the EDI apparatus, a method may be employed in which the respective membranes are superimposed in a dry state, and then made wet by passing water through. Alternatively, when both are installed in the EDI device, they may be installed overlapping each other in a wet state. For example, when superimposing the cation exchange membrane 33 and the anion exchange membrane 40, each membrane can be in a wet state, and the contamination on the surface can be superimposed while flowing with clean pure water or the like. In addition, by using suitable means, both can be fixed to each other.

In addition, as for the overlapping end of the cation exchange membrane 33 and the anion exchange membrane 40, a part of it should just be capable of supplying (sucking) water from the desalting chamber 23 to the water dissociation reaction part (without sealing). , that is, it is open). For example, a part of the overlapping edge part may not be sealed, but the other part may be sealed. The end portion may be open over the entire region. As the sealing means, there are adhesion using an adhesive, welding in which a film-forming material is melted and integrated by heating or ultrasonic vibration, and a method of clamping and fixing by means of a frame body.

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

As the cation exchange membranes 31 and the anion exchange membranes 32 and 34, those known in the field of EDI devices can be used. In addition, 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 anion exchange membranes 32, 34 and 40 can be accommodated in a suitable frame body (not shown).

As feed water or to-be-treated water, what is well-known in the field of an EDI apparatus can be used. Generally, the permeate of a reverse osmosis membrane (RO) is used, and it is more preferable that two or more stages of treatment with the RO membrane are used. In addition to this, it is also possible to remove carbonic acid using a decarboxylation tower or a decarboxylation film. In recent years, water treated by EDI may be used as feed water or untreated water.

In the apparatus shown in Fig. 1, supply water is introduced into the anode chamber 21, the enrichment chambers 22 and 24, and the cathode chamber 25 from the bottom, and water (electrode water or concentrated water) is discharged from the top, while , the desalination chamber 23 is supplied with untreated water from above and discharged from below. However, it is not limited to this, The flow direction of water can be determined suitably. Note that, instead of supplying water to the anode chamber 21 from the outside, the outlet water (number of electrodes) from the cathode chamber 25 may be supplied to the anode chamber 21 or vice versa.

The diffusion of the weak acid component from the concentration chamber 24 to the demineralization chamber 23 is also affected by the concentration of the weak acid component in the concentration chamber 24, and the higher the concentration, the greater the diffusion amount. In the concentration chamber 24, from the inlet to the outlet, the concentration magnification increases and the concentration of the weak acid component also increases. By arranging the inlet side of the enrichment chamber 24 adjacent to the outlet side of the demineralization chamber 23, more diffusion from the enrichment chamber 24 occurs at a position close to the outlet of the treated water of the demineralization chamber 23 can be suppressed Therefore, the flow direction of water in the enrichment chamber 24 is the direction of the flow in the adjacent demineralization chamber (the demineralization chamber 23 in the form shown in Fig. 1 and the second demineralization and demineralization chamber 27 in the form shown in Fig. 6). It is desirable to make it countercurrent to the flow direction of the water.

Moreover, the structure in which the enrichment chamber also serves as an electrode chamber is also included in this invention. For example, the cathode may be provided in the enrichment chamber 24 shown in FIG. 1 and the cathode chamber 25 may be omitted. Even in this case, the desalting processing unit composed of the desalting chamber and the pair of concentrating chambers is disposed between the negative electrode and the positive electrode.

The EDI apparatus may be provided with a plurality of desalting units. Therefore, the basic configuration (i.e., cell set) consisting of [Concentration chamber|First anion exchange membrane (AEM)|Demineralization chamber|Cation exchange membrane (CEM) (second anion exchange membrane overlapping)|Concentration chamber] Multiple can be juxtaposed between them. In this case, neighboring enrichment chambers may be shared between neighboring cell sets. Therefore, assuming that one cell set is composed of the anion exchange membrane 32, the desalting chamber 23, the cation exchange membrane 33 (the anion exchange membrane 40 is superimposed) and the enrichment chamber 24, this cell set is A plurality of portions may be disposed between the enrichment chamber 22 and the cathode chamber 25 closest to the anode chamber 21 . In FIG. 1, "N" means the number of this cell set, and N is an integer of 1 or more.

As mentioned above, although the basic structure of the EDI apparatus based on this invention was demonstrated, this invention is widely applicable to EDI apparatus of various structures. Hereinafter, a configuration example of an EDI device to which the present invention can be applied will be described.

The EDI apparatus of the form provided with two desalination processing parts is demonstrated using FIG. In this EDI apparatus, in the apparatus shown in FIG. 1 , two sets of cells are arranged between the enrichment chamber 22 and the cathode chamber 25 closest to the anode chamber 21 . In Fig. 2, reference numerals indicating the constituent elements constituting the cell set on the side closer to the cathode chamber 25 are denoted by "' (dash)".

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). Both the enrichment chambers 24 and 24' are filled with an anion exchange resin (AER). Both the desalting chambers 23 and 23' are filled with an anion exchange resin and a cation exchange resin in a mixed bed (MB).

The anode chamber 21 and the enrichment chamber 22 are partitioned by a cation exchange membrane 31 . The concentration chamber 22 and the desalination chamber 23 are partitioned by an anion exchange membrane 32 . The desalination chamber 23 and the concentration chamber 24 are partitioned by a cation exchange membrane 33 . The concentration chamber 24 and the desalination chamber 23' are partitioned by an anion exchange membrane 32'. The desalination chamber 23' and the enrichment chamber 24' are partitioned by a cation exchange membrane 33'. The concentration chamber 24' and the cathode chamber 25 are partitioned 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 anion exchange membranes 32' and 40', the desalting chamber 23', the cation exchange membrane 33', and the concentration chamber 24' have the configuration of the anion exchange membranes 32 and 40, the desalting chamber 23, and the cation, respectively. The exchange membrane 33 and the concentration chamber 24 may be the same as or different from each other.

Also in this aspect, the effect similar to the aspect shown in FIG. 1 can be acquired.

By the way, anions derived from a weak acid such as CO ₃ ² - or HCO ₃ ^- move from the demineralization chamber 23 ′ to the concentration chamber 24 through the anion exchange membrane 32 ′. Therefore, in the enrichment chamber 24, in addition to the weak acid component originally contained in the feed water, the weak acid component that has migrated through the anion exchange membrane 32' is also contained. Therefore, the concentration of the weak acid component in the concentration chamber 24 is relatively high, and the diffusion phenomenon of the weak acid component from the concentration chamber 24 to the demineralization chamber 23 tends to become remarkable. Therefore, this invention is especially effective in EDI apparatus provided with a plurality of desalting units.

3 shows another form of an EDI device according to the present invention. This EDI device is the same as that shown in Fig. 1, except that, in the desalting chamber 23, a cation exchange resin (CER) is disposed in the inlet area, and an anion exchange resin (AER) is disposed in the outlet area. . That is, in the desalination chamber 23, a phase made of a cation exchange resin (a cation exchange resin phase, thus a cation exchanger phase) and a phase made of an anion exchange resin (an anion exchange resin phase, thus an anion exchanger phase) are provided, are stacked one by one in each direction. That is, the anion exchanger phase and the cation exchanger phase are filled in the desalting chamber in the order that the ion exchanger through which the to-be-treated water last passes becomes the anion exchanger. Then, the anion exchange membrane 40 is disposed on the negative electrode side on the anion exchanger in the desalting chamber 23 , that is, between the anion exchanger phase and the cation exchange membrane 33 . On the cathode side on the cation exchanger in the desalting chamber 23, the anion exchange membrane 40 is not disposed.

As shown in FIG. 3, the length in the water flow direction of each phase in the demineralization chamber 23 (the length in the vertical direction of the paper in FIG. 3) can be made equal to each other, but may be different.

Naturally, in this form as well, assuming that one cell set is composed of the anion exchange membrane 32, the desalting chamber 23, the cation exchange membrane 33 (the anion exchange membrane 40 overlaps) and the concentration chamber 24, this N (N is an integer greater than or equal to 1) can be arranged between the enrichment chamber 22 and the cathode chamber 25 closest to the anode chamber 21 .

The EDI apparatus 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 water flow direction of the to-be-treated water, and the first cations are sequentially from the inlet side of the to-be-treated water. The ion exchange resin is disposed in each region such that the exchanger phase, the first anion exchanger phase, the second cation exchanger phase, and the second anion exchanger phase are aligned. Then, an anion exchange membrane 40 (overlapping the cation exchange membrane 33) is disposed on the cathode side on the first anion exchanger and on the cathode side on the second anion exchanger, respectively. The anion exchange membrane 40 is not disposed on both the negative electrode side on the first cation exchanger and the negative electrode side on the second cation exchanger. In this device, there are two overlapping regions (the region where the anion exchange membrane 40 overlaps in the demineralization chamber side surface of the cation exchange membrane 33), and they exist apart from each other along the direction in which the water to be treated in the desalination chamber 23 flows. do. And, among the two overlapping regions, one overlapping region located at the most downstream in the water flow direction reaches the end of the cation exchange membrane 33 on the outlet side of the desalination chamber.

As shown in FIG. 4, although the length in the water flow direction of each phase in the desalination chamber 23 can be made mutually equal, it may be different. In addition, although the number of each phase is also 4 in FIG. 4, 5 pieces, 6 pieces, or more may be sufficient within a manufacturing-possible range.

The EDI apparatus shown in FIG. 5 is the same as that shown in FIG. 1, except that in the desalting chamber 23, on the desalting chamber side of the anion exchange membrane 40, instead of the mixed bed MB, an anion exchanger bed is provided. In the demineralization chamber 23, in the region where the anion exchange membrane 40 does not exist in the water-to-be-treated water passing direction, a mixed phase is provided, similarly to the embodiment shown in FIG. 1 .

That is, in this form, the mixed bed MB of anion exchange resin and cation exchange resin is arranged in the inlet region of the desalting chamber 23, and the anion exchanger bed (AER phase) is arranged in the outlet region. That is, in the desalting chamber 23, a mixed phase and an anion exchanger phase are laminated one by one in the water flow direction.

In the EDI apparatus according to the present invention, in each desalting chamber, an intermediate ion exchange membrane (IIEM) is provided between the anode side anion exchange membrane and the cathode side cation exchange membrane, and the desalting chamber is separated by the intermediate ion exchange membrane from the first demineralization chamber. and a second demineralization chamber. Then, the first and second demineralization and demineralization are supplied to one demineralization chamber of the first demineralization chamber and the second demineralization chamber so that the water flowing out from the demineralization chamber flows into the other demineralization chamber. Threads can be arranged in communication. As the intermediate ion exchange membrane, both an anion exchange membrane and a cation exchange membrane can be used. At this time, let the demineralization demineralization chamber on the anode side be a 1st demineralization chamber, and let the demineralization demineralization chamber at the cathode side be a 2nd demineralization demineralization chamber. For example, at least an anion exchanger is filled in the first demineralization chamber, and at least a cation exchanger is filled in the second demineralization chamber.

Fig. 6 shows an example of an EDI device in which the desalting chamber is divided into two demineralization chambers by an intermediate ion exchange membrane in this way. In this EDI apparatus, each desalting chamber 23 in the EDI apparatus shown in FIG. 1 is connected to an anode 11 by an intermediate ion exchange membrane 36 located between an anion exchange membrane 32 and a cation exchange membrane 33. It has the structure partitioned into the 1st demineralization chamber 26 on the side and the 2nd demineralization demineralization chamber 27 on the side of the cathode 12 side. The first demineralization chamber 26 is located between the anion exchange membrane 32 and the intermediate ion exchange membrane 36 , and the second demineralization chamber 27 is located between the cation exchange membrane 33 and the intermediate ion exchange membrane 36 . . The first demineralization chamber 26 and the second demineralization chamber 26 and the second demineralization chamber 26 so that the water to be treated is supplied to the first demineralization and demineralization chamber 26 and the water flowing out from the demineralization and demineralization chamber 26 flows into the second demineralization and demineralization chamber 27 . A demineralization chamber 27 communicates.

The first demineralization chamber 26 is filled with an anion exchange resin. A cation exchange resin is disposed in an inlet region of the second demineralization chamber 27, and an anion exchange resin is disposed in an outlet region. That is, in the second demineralization and demineralization chamber 27 , a cation exchanger phase and an anion exchanger phase are provided in this order along the flow direction of the to-be-treated water. The to-be-treated water is supplied to the first demineralization and demineralization chamber 26 , and the outlet water of the first demineralization and demineralization chamber 26 is sent to the second demineralization chamber 27 , and the deionized water from the second demineralization and demineralization chamber 27 is supplied. It is obtained as treated water. Accordingly, the desalting chamber 23 is filled with an anion exchanger phase and a cation exchanger phase in the order that the ion exchanger through which the to-be-treated water passes last becomes an anion exchanger.

On the cathode side on the anion exchanger in the second demineralization chamber 27, an anion exchange membrane 40 (overlapping the cation exchange membrane 33) is disposed. The anion exchange membrane 40 is not disposed on the cathode side on the cation exchanger in the second demineralization chamber 27 . There is one overlapping region described above (the region where the anion exchange membrane 40 overlaps among the demineralization chamber side surfaces of the cation exchange membrane 33 ). This overlapping region reaches the end of the cation exchange membrane 33 on the outlet side of the desalting chamber. Here, the outlet of the desalination chamber is the outlet of the treated water, and in this apparatus, the outlet of the second demineralization and demineralization chamber 27 .

As shown in FIG. 6, although the length of the water flow direction of each phase in the 2nd demineralization chamber 27 can mutually be made equal, they may differ.

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

In the apparatus shown in FIG. 6 , the flow of water in the first demineralization and demineralization chamber 26 and the flow of water in the second demineralization and demineralization chamber 27 are countercurrent. However, it is not limited to this, These flows may be co-current.

The water to be treated is supplied to the first demineralization and demineralization chamber 26 . The anion component in the supplied to-be-treated water is captured while the to-be-treated water passes through the first demineralization chamber 26 . The anion component captured in the first demineralization and demineralization chamber 26 moves to the concentrating chamber 22 adjacent to the first demineralization and demineralization chamber 26 via an anion exchange membrane 32 , It is discharged out of the system together with the concentrated water flowing through it.

Then, the water to be treated that has passed through the first demineralization and demineralization chamber 26 is supplied to the second demineralization and demineralization chamber 27 . The to-be-treated water supplied to the 2nd demineralization and desalination chamber 27 first passes through the cation exchanger bed, and then passes through the anion exchanger bed. In that case, the cation component in the to-be-treated water is captured in the process of the to-be-processed water passing through a cation exchanger bed. Specifically, the cation component captured by the cation exchanger in the second demineralization and demineralization chamber 27 moves to the concentration chamber 24 adjacent to the second demineralization and demineralization chamber 27 via the cation exchange membrane 33 . Thus, it is discharged from the enrichment chamber 24 together with the concentrated water to the outside of the system.

Further, in the second demineralization and demineralization chamber 27, the water to be treated, which has passed through the cation exchanger bed, passes through the anion exchanger bed in the next step. At this time, the anion component in the to-be-processed water is capture|acquired again. Specifically, the anion component captured by the anion exchanger in the second demineralization and demineralization chamber 27 is disposed in the first demineralization chamber (27) adjacent to the second demineralization chamber (27) via the intermediate ion exchange membrane (36). 26). The anion component that has moved to the first demineralization and demineralization chamber 26 moves through the anion exchange membrane 32 to the concentration chamber 22 adjacent to the first demineralization chamber 26 and flows through the concentration chamber 22 . It is discharged out of the system together with concentrated water.

Here, the weak acid component (carbonic acid, silica, or boron) contained in the concentrated water in the concentration chamber 24 passes through the cation exchange membrane 33 in the form of a neutral molecule, and the diffusion moves to the second demineralization and desalination chamber 27 . Consider the case in which the phenomenon occurred.

The weak acid component moved from the concentration chamber 24 to the second demineralization chamber 27 is uniformly diffused on the anode side surface of the cation exchange membrane 33 . That is, the weak acid component is not only the surface area of the cation exchange membrane 33 in contact with the anion exchange membrane 40, but also the surface area of the cation exchange membrane 33 in contact with the cation exchanger phase in the second demineralization and desalination chamber 27. it spreads And, since the weak acid component is not captured depending on the cation exchanger, the weak acid component diffused into the region in contact with the cation exchanger phase of the anode side surface of the cation exchange membrane 33 passes through the cation exchanger phase together with the water to be treated. do. However, in the second demineralization and demineralization chamber 27, a cation exchanger phase and an anion exchanger phase are laminated along the water flow direction of the to-be-treated water. Accordingly, the weak acid component that has passed through the cation exchanger is ionized and captured again on the anion exchanger in the next step, and moves to the first demineralization and desalination chamber 26 . The weak acid component that has moved to the first demineralization and desalination chamber 26 passes through the anion exchange membrane 32 , moves to the concentration chamber 22 , and is discharged out of the system together with the concentrated water flowing through the concentration chamber 22 .

As described above, in this form, even if the weak acid component has passed through the cation exchange membrane 33, since there is an anion exchanger phase in the next step, it is easy to discharge the weak acid component from the concentration chamber 22, and as a result, the treated water It is easy to suppress a decrease in purity. Of course, even in this form, the weak acid component diffused to the surface region of the cation exchange membrane 33 in contact with the anion exchange membrane 40 can be efficiently removed from the water to be treated by the anion exchange membrane 40 .

From the above description, it is understood that the final end of the stack of ion exchangers provided in the desalting chamber, particularly in the second demineralization and demineralization chamber 27, is preferably an anion exchanger. The kind, the order of lamination, and the number of laminations of the ion exchanger phase in the previous stage rather than the anion exchanger phase in the final stage are not particularly limited.

Moreover, in the EDI apparatus according to this aspect, the anion exchanger is filled in the first demineralization chamber 26 to which the to-be-treated water is first supplied, and the cation exchange is in the second demineralization and desalination chamber 27 to which the to-be-treated water is supplied next. The sieve phase and the anion exchanger phase are stacked in this order. Accordingly, the water to be treated first passes through the anion exchanger bed. Thereby, the anion component is removed from the to-be-processed water, and the pH of the to-be-processed water rises.

Moreover, the to-be-processed water which has passed through the 1st demineralization chamber 26 is supplied to the 2nd demineralization chamber 27 in which the cation exchanger phase and the anion exchanger phase are laminated|stacked in this order. That is, the to-be-treated water that has passed through the anion exchanger bed in the first demineralization and demineralization chamber 26 then passes through the cation exchanger bed and then again passes through the anion exchanger bed. That is, according to the structure of this aspect, the to-be-processed water passes through an anion exchanger phase and a cation exchanger phase alternately.

Here, the capture ability of the anion component of the anion exchanger becomes high when the pH of the to-be-treated water is low, and the capture ability of the cation component of the cation exchanger becomes high when the pH of the to-be-treated water is high. Therefore, according to the configuration of this embodiment in which the to-be-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 component is removed by passing through the anion exchanger, and the pH rises. The treated water continues to pass over the cation exchanger. Therefore, the cation removal reaction by the cation exchanger is accelerated more than usual.

Further, the cation component is removed by passing through the cation exchanger bed, and the water to be treated whose pH has been lowered continues to pass through the anion exchanger bed. Therefore, the anion removal reaction by an anion exchanger is accelerated|stimulated more than usual. Accordingly, not only the ability to remove the anion component containing carbonic acid, silica, or boron is further improved, but also the ability to remove the cationic component is improved, and thus the purity of the treated water is further improved.

As described above, it is preferable to alternately use the cation exchanger phase and the anion exchanger phase in the order that the ion exchanger through which the to-be-treated water last passes becomes the anion exchanger. This applies not only to the form shown in FIG. 6 but also to the form shown in FIGS. 3 and 4 .

Example

[Example 1]

Using an EDI apparatus having the configuration shown in Fig. 6, the treated water was treated to obtain treated water (deionized water). The specifications and test conditions of the EDI device are shown below.

Moreover, the specifications and conditions of the enrichment chambers 22 and 24 are mutually common, and the specifications and conditions of the concentrated water obtained from these are mutually common. In addition, the cation exchange resin (CER) filled in a part (entrance side area|region) of the anode chamber 21 and the 2nd demineralization chamber 27 is mutually common. The anion exchange resin (AER) filled in the remainder (exit side region) of the cathode chamber 25, the concentration chambers 22 and 24, the first demineralization chamber 26 and the second demineralization chamber 27 is common to each other. to be. The cation exchange membranes 31 and 33 are common to each other, and the anion exchange membranes 32 and 34 and the intermediate ion exchange membrane 36 are common to each other.

In addition, in the following, "vertical" means the vertical direction (direction along the flow direction of water) in the drawing, and "horizontal" means the paper depth direction.

・Number of cell sets (N): 1

·Anode chamber 21: Dimensions length 100 × width 100 × thickness 10 mm, CER filling

Cathode chamber 25: Dimensions length 100 × width 100 × thickness 10 mm, AER filling

Concentration chambers (22, 24): Dimensions length 100 × width 100 × thickness 10 mm, AER filling

· First demineralization chamber 26: Dimensions length 100 × width 100 × thickness 10 mm, AER filling

· Second demineralization chamber 27: Dimensions length 100 × width 100 × thickness 10 mm, CER (inlet 1/2 area) and AER (outlet side 1/2 area) filling

CER: Strongly acidic cation exchange resin

·AER: Strong basic anion exchange resin

·Cation exchange membranes (31, 33): homogeneous membrane, effective membrane dimension of current conducting part length 100mm width 100mm, thickness 290㎛

· Anion exchange membranes 32 and 34 and intermediate ion exchange membrane 36: homogeneous membrane, effective membrane dimensions of the current conducting part: 100 mm in length x 100 mm in width, 220 μm in thickness

·Anion exchange membrane (40): homogeneous membrane, effective membrane dimensions of current conducting part length 50 × width 100 mm, thickness 220㎛

Supply water and water to be treated: 2-stage RO (reverse osmosis membrane) permeated water, electrical conductivity 2.0 to 2.5 μS/cm

・Processed water (deionized water) flow rate: 25 ℓ/h

Concentrated water flow rate: 6 ℓ/h

・Electrode water flow rate: 5 ℓ/h (common to both positive and negative electrodes)

·Applied current value: 0.5A.

A second anion exchange membrane (40) was disposed on the negative electrode side of the anion exchange resin formed in the half of the outlet side of the second demineralization chamber (27). At this time, the position of the demineralization chamber outlet end of the cation exchange membrane 33 (the upper end in the vertical direction of the paper) was aligned with the position of the demineralization chamber outlet end of the anion exchange membrane 40 . In addition, the position of the cation exchange membrane 33 in the transverse direction (depth of the sheet) was aligned with the position of the anion exchange membrane 40 in the transverse direction.

[Comparative Example 1]

The anion exchange membrane 40 was not used. That is, only the cation exchange membrane 33 was used between the second demineralization chamber 27 and the concentration chamber 24 . Other than that, it carried out similarly to Example 1, the to-be-processed water was treated, and the treated water was obtained.

[Comparative Example 2]

Instead of the second anion exchange membrane 40, a cation exchange membrane was used. This cation exchange membrane was made of the same material and thickness as the cation exchange membranes 31 and 33 used in Example 1, and the longitudinal and lateral dimensions and arrangement positions were the same as the second anion exchange membrane 40 used in Example 1. Other than that, it carried out similarly to Example 1, the to-be-processed water was treated, and the treated water was obtained.

[Evaluation 1]

For Example 1 and Comparative Examples 1 and 2, after continuous operation for about 500 hours, respectively, the total concentration of carbonic acid in the treated water (CO ₂ , H ₂ CO ₃ , HCO ₃ ⁻ and CO ₃ ^2- ) value) was measured, and also the specific resistance of the treated water was measured. The results are shown in Table 1. The concentration of total carbonic acid is an index indicating the concentration of carbonic acid leaked into the treated water without being completely removed after diffusion from the concentration chamber to the desalination chamber. The value of the specific resistance is not limited to carbonic acid, and other ions are included as an indicator of the purity of the treated water.

In Example 1, compared with Comparative Examples 1 and 2, there was little leakage of carbonic acid, and the purity of treated water was high.

Example 1 Comparative Example 1 Comparative Example 2 Total carbonic acid [㎍CO ₂ /ℓ] < 0.5 56.8 35.2

cm]resistivity [㏁

cm] 17.7 8.0 8.3

[Example 2]

Except having changed the conditions as follows, it carried out similarly to Example 1, the to-be-processed water was treated, and treated water was obtained.

Supply water and water to be treated: 2-stage RO (reverse osmosis membrane) permeated water, electrical conductivity 4.0 to 4.5 μS/cm

·Applied current value: 1.0A.

[Example 3]

As the second anion exchange membrane 40, a heterogeneous anion exchange membrane was used. The vertical and horizontal dimensions and arrangement positions of this anion exchange membrane (heterogeneous) were the same as those of the second anion exchange membrane 40 used in Example 2. In addition, the thickness of this anion exchange membrane (heterogeneity) was 580 mu m. Other than that, it carried out similarly to Example 2, the to-be-processed water was processed, and treated water was obtained.

[Comparative Example 3]

Instead of the second anion exchange membrane 40, a bipolar membrane was used. The longitudinal and lateral dimensions and the arrangement position of this bipolar membrane were the same as those of the second anion exchange membrane 40 used in Example 2. In addition, the bipolar membrane was arranged so that the anion exchange membrane part faces the second demineralization chamber 27 side. For the bipolar membrane, a thickness of 220 µm including the anion exchange membrane part and the cation exchange membrane part was used. Other than that, it carried out similarly to Example 2, the to-be-processed water was processed, and treated water was obtained.

[Evaluation 2]

For Examples 2, 3 and Comparative Example 3, after continuous operation for about 500 hours, respectively, the total carbonic acid concentration, resistivity, and sodium concentration in the treated water were measured, and the voltage (anode 11 and cathode 12) voltage) and the current share ratio were measured. The results are shown in Table 2. In the table, "upper current share ratio" and "under current share factor" are respectively defined as follows.

(on current share) = (value of current flowing through the region where the second anion exchange membrane 40 or bipolar membrane is installed)/(total current value),

(under current sharing ratio) = (value of current flowing through the region where the second anion exchange membrane 40 or the bipolar membrane of the cation exchange membrane 33 does not overlap)/(total current value).

As for the current share, the negative electrode plate used as the negative electrode 12 is divided into two up and down to correspond to the above region, and the current values flowing through the upper and lower negative electrode plates are measured with an ammeter, and the ratio of each current value to the total applied current value is calculated. saved it.

In Example 2, as compared with Comparative Example 3, the vertical difference in the current sharing ratio was small, the sodium concentration in the treated water was low, and the specific resistance of the treated water was high. That is, in Example 2, compared with Comparative Example 3, a large amount of current was distributed to the cation resin layer inside the desalting chamber, the removal of cations became favorable, and the purity of the treated water was high. In Example 3, the tendency was further increased, the sodium concentration in the treated water was low, and the specific resistance of the treated water was the highest. As described above, since the heterogeneous membrane has an inactive region in which some ion exchangers do not exist, it is considered that the water dissociation reaction becomes difficult to proceed and the current can be more suppressed from flowing upward.

Example 2 Example 3 Comparative Example 3 Total carbonic acid [㎍CO ₂ /ℓ] < 0.5 < 0.5 < 0.5

cm]resistivity [㏁

cm] 15.0 15.7 13.6 Na [μg/L] 3.1 2.4 5.3 voltage [V] 8.6 10.5 8.5 current share factor 60% 52% 70% current share ratio 40% 48% 30%

Further, in the configuration according to the present invention, when the water to be treated in the desalting chamber enters the interface between the cation exchange membrane 33 and the anion exchange membrane 40, the weak acid component contained in the water to be treated is an anion exchange membrane 40 It is easily removed from the interface through On the other hand, as in Comparative Example 3, in a configuration using a bipolar membrane instead of the anion exchange membrane 40, when the water to be treated in the desalting chamber enters the interface between the cation exchange membrane 33 and the bipolar membrane, the treated water contains It is difficult to remove the anionic component from the interface. This is because the movement of the anion component is blocked by both the cation exchange membrane 33 and the cation exchange membrane portion of the bipolar membrane. As a result, negative ions leak into the treated water, resulting in deterioration of water quality.

For example, as shown in Fig. 10(b), when anions and cations (indicated as "C ⁺ A ^- ") enter the interface between the cation exchange membrane 33 and the anion exchange membrane 40, Anions (indicated by "A ^- " in the drawing) move to the desalting chamber 23 through the anion exchange membrane 40 and are easily captured by the anion exchange resin inside the desalting chamber 23 . The cations (indicated by "C ⁺ " in the drawing) are removed from the interface through the cation exchange membrane 33 . On the other hand, in the configuration using the bipolar membrane 50 instead of the anion exchange membrane 40 as shown in FIG. 10( a ), the cation (C ⁺ ) Silver is removed through the cation exchange membrane 33 , but the anions (A ⁻ ) cannot pass through neither the bipolar membrane 50 nor the cation exchange membrane 33 . As a result, for example, negative ions are discharged from the end of the interface (the upper end in the vertical direction of the paper in FIG. 10 ) and leaked into the treated water as it is.

11: positive 12: negative
21: anode chamber 22, 24: enrichment chamber
23: desalination chamber 25: cathode chamber
26: first de-salting chamber 27: second de-salting chamber
31, 33: cation exchange membrane (CEM) 32: first anion exchange membrane (AEM)
34: anion exchange membrane (AEM) 36: intermediate ion exchange membrane (IIEM)
40: second anion exchange membrane (AEM) 50: bipolar membrane
51: anion exchange resin

Claims (7)

At least one desalination treatment unit is installed between the opposite cathode and anode,
The desalting unit includes at least a desalting chamber filled with an anion exchanger, and a pair of concentration chambers installed adjacent to both sides of the desalting chamber,
The desalting chamber is adjacent to the concentration chamber on the cathode side of the pair of enrichment chambers via a cation exchange membrane, and is adjacent to the enrichment chamber on the anode side of the pair of enrichment chambers through a first anion exchange membrane, As an electric deionized water manufacturing device,
The desalination chamber has an inlet side to which the target water is supplied and an outlet side through which the target water is discharged opposite to the inlet side so as to pass the target water through;
A second anion exchange membrane, which is separate from the cation exchange membrane, is superimposed and installed in a part of the surface of the cation exchange membrane on the desalting chamber side;
The electric deionized water production apparatus, characterized in that the anion exchanger is in contact with at least a part of a surface of the second anion exchange membrane on the demineralization chamber side. According to claim 1, wherein the area on the desalting chamber side of the cation exchange membrane, where the second anion exchange membrane overlaps, is an area on the desalting chamber side of the cation exchange membrane that reaches the end of the desalting chamber outlet side of the cation exchange membrane. Including, electric deionized water manufacturing apparatus. The anion exchanger bed according to claim 1 or 2, wherein the desalting chamber comprises an anion exchanger bed, which is a bed of anion exchangers, in the order that the ion exchanger through which the water to be treated last passes becomes the anion exchanger. An electric deionized water production apparatus comprising at least one and at least one cation exchanger bed, which is a bed of cation exchangers. The first cation exchanger phase, the first anion exchanger phase, the second cation exchanger phase, and the second anion exchanger phase are provided in the desalting chamber in this order along the flow direction of the to-be-treated water, ,
The second anion exchange membrane is disposed on the negative electrode side on the first anion exchanger and on the negative electrode side on the second anion exchanger, respectively;
The second anion exchange membrane is not disposed on both the cathode side on the first cation exchanger and the cathode side on the second cation exchanger. 4. The method of claim 3, wherein the desalting chamber is provided with an intermediate ion exchange membrane that is an ion exchange membrane positioned between the first anion exchange membrane and the cation exchange membrane, and is formed into a first demineralization chamber and a second demineralization chamber by the intermediate ion exchange membrane. compartmentalized,
The first demineralization chamber is located between the first anion exchange membrane and the intermediate ion exchange membrane,
The second demineralization chamber is located between the cation exchange membrane and the intermediate ion exchange membrane,
The first demineralization and demineralization chamber communicates with the second demineralization and demineralization chamber so that the water to be treated is supplied to the first demineralization chamber and the water flowing out from the first demineralization and demineralization chamber flows into the second demineralization and demineralization chamber, ,
An anion exchanger bed is installed in the first demineralization chamber,
A cation exchanger phase and an anion exchanger phase are installed in this order in the second demineralization chamber, along the water flow direction of the to-be-treated water;
The second anion exchange membrane is disposed on the cathode side of the anion exchanger installed in the second demineralization chamber,
The second anion exchange membrane is not disposed on the cathode side of the cation exchanger provided in the second deionization chamber. The electric deionized water production apparatus according to claim 1 or 2, wherein the pair of concentrating chambers are filled with at least an anion exchanger. The apparatus according to claim 1 or 2, wherein the second anion exchange membrane is a heterogeneous membrane, and the cation exchange membrane is a homogeneous membrane.

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