Electrodeionized water production apparatus and its operating method

Abstract

To improve a removal performance of boron in an EDI apparatus (electric deionized water production apparatus).SOLUTION: In a desalination chamber 23 of an EDI apparatus 10 where treated water containing boron is supplied to the desalination chamber 23 to remove boron from the treated water, a particle size of 0.1 mm or more and 0.4 mm or less is defined as a small particle size and a particle size exceeding 0.4 mm is defined as a large particle size. Toward a flow direction of the treated water, a large particle size layer composed of a large-diameter ion exchange resin and a mixed particle size layer obtained by mixing the large-diameter ion exchange resin and a small-diameter ion exchange resin are arranged so that at least one large particle size layer exists on the upstream side of the mixed particle size layer. Furthermore, at least a part of the ion exchange resin filled in a concentration chamber 24 is a cation exchange resin.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electric deionized water production apparatus and an operation method thereof.

Background Art

[0002] In ultrapure water used for semiconductor device manufacturing and the like, further reduction of the boron content is required. However, boron in water is a weak acid component that is difficult to remove by a general ion exchange treatment of passing the water to be treated through an ion exchange resin. Therefore, in order to remove boron in the water to be treated, attempts have been made to use an electric deionized water production apparatus (EDI (Electrodeionization) apparatus). The EDI apparatus is an apparatus that generates deionized water from the water to be treated by combining electrophoresis and electrodialysis, and at least its desalting chamber is filled with an ion exchange resin. The EDI apparatus has an advantage of not requiring a treatment for regenerating the ion exchange resin with a chemical agent. However, even with an EDI apparatus, sufficient removal performance for weak acid components such as boron may not be obtained simply by filling the desalting chamber with a normal ion exchange resin.

[0003] Normal ion exchange resins are in the form of beads or granules, and their standard particle size exceeds 0.4 mm and is about 1 mm or less. In order to improve the removal performance of weak acid components in an EDI apparatus, it has been proposed to fill the desalting chamber with an ion exchange resin having a smaller particle size. For example, Patent Document 1 discloses filling a single bed in the desalting chamber of an EDI apparatus with an ion exchange resin having an average particle size of 150 to 250 μm. Patent Document 2 discloses filling a single bed in the desalting chamber with an ion exchange resin having an average diameter of 0.2 to 0.3 mm. Patent Documents 3 and 4 disclose filling an ion exchange resin having an average particle size of 0.1 to 0.4 mm in the intermediate region in the vertical direction in a desalting chamber through which the water to be treated flows in the vertical direction, and filling an ion exchange resin having an average particle size exceeding 0.4 mm in the upper and lower regions thereof.

[0004] Incidentally, in order to reduce the electrical resistance of the desalination chamber and improve the desalination efficiency during the operation of the EDI device, it is important to control the packing rate of the ion exchange resin in the desalination chamber. Patent Document 5 discloses that in order to reduce the electrical resistance of the desalination chamber, a group of ion exchange resin particles having multiple uniform particle sizes with different particle sizes is mixed and packed into the desalination chamber. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-150304 [Patent Document 2] Japanese Patent Publication No. 2017-176968 [Patent Document 3] Japanese Patent Publication No. 2019-177327 [Patent Document 4] Japanese Patent Publication No. 2020-78772 [Patent Document 5] Japanese Patent Application Publication No. 10-258289 [Overview of the project] [Problems that the invention aims to solve]

[0006] Even if the removal performance of boron components in the EDI device is improved by filling the desalination chamber with small-particle ion exchange resin, the boron removal performance may still be insufficient when removing boron to extremely low levels. For example, when trying to remove boron from water with a boron concentration of about 10 μg / L to obtain treated water with a boron concentration at the ng / L level, a single-stage EDI device may not be able to remove boron sufficiently, and it may be necessary to use two EDI devices connected in series.

[0007] The object of the present invention is to provide an EDI device with improved boron removal performance and a method for operating the same. [Means for solving the problem]

[0008] The present invention relates to an EDI apparatus (electrodeionized water production apparatus) comprising a desalination chamber partitioned by a pair of ion exchange membranes between an anode and a cathode and filled with ion exchange resin, and at least one concentration chamber arranged adjacent to the desalination chamber and filled with ion exchange resin, wherein particles with a diameter of 0.1 mm to 0.4 mm are defined as small particle size, and particles with a diameter greater than 0.4 mm are defined as large particle size, and in the desalination chamber, a large particle size layer made of large particle size ion exchange resin and a mixed particle size layer made of a mixture of large particle size ion exchange resin and small particle size ion exchange resin are arranged in the direction of the flow of the water to be treated in the desalination chamber, and at least a portion of the ion exchange resin filled in the concentration chamber is cation exchange resin, and water to be treated containing boron is supplied to the desalination chamber to remove boron from the water to be treated.

[0009] The operating method of the present invention is characterized in that, in the operating method of an EDI device based on the present invention, the concentration of hardness components in the water to be treated supplied to the desalination chamber is 0.1 mg / L or less. [Effects of the Invention]

[0010] According to the present invention, the boron removal performance in an EDI device can be improved, thereby making it possible to obtain deionized water with a boron concentration reduced to an extremely low level. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an EDI device according to the first embodiment of the present invention. [Figure 2] This is a diagram illustrating boron leakage. [Figure 3] This figure shows another example of the EDI device according to the first embodiment. [Figure 4] Figures (a) to (e) show examples of ion exchange resin packing in the desalination chamber. [Figure 5] This figure shows an EDI device according to a second embodiment of the present invention. [Figure 6] This figure shows another example of the EDI device according to the second embodiment. [Figure 7]It is a diagram showing another example of the EDI device of the second embodiment. [Figure 8] It is a flowchart showing the configuration of the pure water production system. [Figure 9] It is a diagram for explaining the EDI devices of Examples 1 and 2. [Figure 10] It is a diagram for explaining the EDI device of Comparative Example 1. [Figure 11] It is a diagram for explaining the EDI device of Comparative Example 2. [Figure 12] It is a diagram for explaining the EDI device of Comparative Example 3. [Figure 13] It is a diagram for explaining the EDI devices of Comparative Examples 4 and 5. [Figure 14] It is a diagram for explaining the EDI devices of Reference Examples 1 and 2.

Mode for Carrying Out the Invention

[0012] Next, embodiments of the present invention will be described with reference to the drawings. Generally, in an electro-deionized water production device (EDI device), a desalination chamber partitioned by a pair of ion exchange membranes is provided between an anode and a cathode, and the desalination chamber is filled with ion exchange resin. Then, when the EDI device applies a DC voltage between the anode and the cathode and supplied the water to be treated to the desalination chamber, desalination (deionization) treatment is performed on the water to be treated. As a result, water from which ionic components have been removed is discharged from the desalination chamber as treated water. Among the ionic components removed from the water to be treated in the desalination chamber, the anionic component moves to a compartment adjacent to the desalination chamber through an ion exchange membrane provided on the anode side in the desalination chamber, and the cationic component moves to another compartment adjacent to the desalination chamber through an ion exchange membrane provided on the cathode side in the desalination chamber. The compartment into which ionic components move from the desalination chamber through the ion exchange membrane is the concentration chamber. In the present invention, regarding the particle size of the ion exchange resin, a particle size of 0.1 mm or more and 0.4 mm or less is defined as a small particle size, and a particle size exceeding 0.4 mm is defined as a large particle size.

[0013] In the EDI device according to the present invention, in order to improve the efficiency of removing boron from the water to be treated, a large particle size layer made of large-particle ion exchange resin and a mixed particle size layer made of a mixture of large-particle ion exchange resin and small-particle ion exchange resin are arranged in the desalination chamber in the direction of the flow of the water to be treated in the desalination chamber. The particle size of bead-shaped or granular ion exchange resin is usually 1 mm or less, so a large-particle ion exchange resin with a particle size of more than 0.4 mm and less than or equal to 1 mm may be used. The particle size of the ion exchange resin can be measured using a sieve, but the catalog value of the ion exchange resin manufacturer may be used as the particle size in the present invention. In the present invention, a mixed particle size layer of anion exchange resin may be made by mixing large-particle anion exchange resin (AER) and small-particle anion exchange resin, or a mixed particle size layer of cation exchange resin may be made by mixing large-particle cation exchange resin (CER) and small-particle cation exchange resin.

[0014] Here, we will explain the mixing ratio of large-particle ion exchange resins and small-particle ion exchange resins in the mixed particle size layer. Since ion exchange resins are bead-shaped or granular, regardless of particle size, their apparent volume, including the voids between particles, can be measured. Therefore, let L be the apparent volume of the large-particle ion exchange resin before mixing, and S be the apparent volume of the small-particle ion exchange resin. It is preferable that the mixing ratio L:S be between 1:3 and 10:1, and more preferably between 1:1 and 5:1. If the proportion of large-particle ion exchange resins is too high, sufficient removal performance for weak acid components such as boron cannot be obtained. Therefore, in order to achieve the effects of the present invention, it is considered necessary that L:S = 10:1 or less, with a lower proportion of large-particle ion exchange resins. On the other hand, if the proportion of small-particle ion exchange resins is too high, it may lead to an increase in the differential pressure of the water flow. It should be noted that even after mixing large-particle ion exchange resins and small-particle ion exchange resins to form a mixed particle size layer, the mixing ratio of large-particle ion exchange resins and small-particle ion exchange resins can be determined. For example, the mixed particle size layer can be removed from the desalination chamber, classified using a sieve to separate it into ion exchange resins with a particle size of 0.1 mm to 0.4 mm and ion exchange resins with a particle size of more than 0.4 mm, and the mixing ratio L:S can be determined by measuring the apparent volume of each.

[0015] Furthermore, in the EDI device according to the present invention, the concentration chamber is also filled with ion exchange resin, and at least a portion of the ion exchange resin filled in the concentration chamber is cation exchange resin. Although only cation exchange resin may be filled in the concentration chamber, the applied voltage in the EDI device tends to increase when hardness components such as calcium and magnesium are contained in the water to be treated or the water supplied to the concentration chamber at, for example, 0.05 to 0.1 mg / L. Therefore, it is preferable to fill the concentration chamber with a mixture of anion exchange resin and cation exchange resin. When anion exchange resin and cation exchange resin are mixed and filled into the entire concentration chamber, the apparent volume of the anion exchange resin is A, and the apparent volume of the cation exchange resin is C. The mixing ratio A:C of these ion exchange resins is preferably between 20:80 and 60:40, and more preferably between 20:80 and 50:50. Even after mixing the anion exchange resin and cation exchange resin and filling the concentration chamber, the mixing ratio A:C of the anion exchange resin and cation exchange resin can be determined in the same manner as described above. The concentration chamber may be filled only with large-particle ion exchange resin. To suppress the increase in applied voltage caused by the placement of cation exchange resin in the concentration chamber, it is preferable to ensure that the concentration of hardness components in the treated water supplied to the desalination chamber is 0.1 mg / L or less, for example, by placing a reverse osmosis membrane device upstream of the EDI device, as described later. The concentration of hardness components is calculated by converting the amounts of calcium and magnesium into the amount of calcium carbonate (CaCO3), and the calculation formula is as follows: Hardness [mg / L] = (Calcium content [mg / L] × 2.5) + (Magnesium content [mg / L × 4.1]) It is represented by [this].

[0016] [First Embodiment] Figure 1 shows an EDI device 10 according to a first embodiment of the present invention. In this EDI device 10, a concentration chamber 22, a desalination chamber 23, and a concentration chamber 24 are provided between an anode chamber 21 equipped with an anode 11 and a cathode chamber 25 equipped with a cathode 12, in order from the anode chamber 21 side. The anode chamber 21 and the concentration chamber 22 are adjacent separated by a cation exchange membrane (CEM) 31, the concentration chamber 22 and the desalination chamber 23 are adjacent separated by an anion exchange membrane (AEM) 32, the desalination chamber 23 and the concentration chamber 24 are adjacent separated by a cation exchange membrane 33, and the concentration chamber 24 and the cathode chamber 25 are adjacent separated by an anion exchange membrane 34. Therefore, the desalination chamber 23 is partitioned between the anode 11 and the cathode 12 by a pair of ion exchange membranes (here, an anion exchange membrane 32 and a cation exchange membrane 33). The desalination chamber 23 is filled with ion exchange resin and supplied with water to be treated. The treated water (deionized water) obtained as a result of desalination treatment of the water flows out of the desalination chamber 23. In the example shown here, the desalination chamber 23 is filled with anion exchange resin. The interior of the desalination chamber 23 is divided into two regions in the direction of the flow of water to be treated. The region on the water inlet side is filled with large-particle anion exchange resin to form a large-particle layer, and the region on the water outlet side is filled with a mixture of large-particle and small-particle anion exchange resin to form a mixed-particle layer. In the diagram, the large-particle layer made of anion exchange resin is labeled "large-particle AER," and the mixed-particle layer made of anion exchange resin is labeled "large- and small-particle mixed AER." In the illustrated example, the boundary between the large-particle layer and the mixed-particle layer is approximately in the center of the desalination chamber 23 in the direction of the flow of water to be treated.

[0017] Furthermore, in the EDI device 10, cation exchange resin is filled into the anode chamber 21, and anion exchange resin is filled into the cathode chamber 25. In the concentration chambers 22 and 24, anion exchange resin and cation exchange resin are mixed and filled, as indicated by "AER+CER" in the figure. Although it is not always necessary to fill the anode chamber 21 and cathode chamber 25 with ion exchange resin, it is preferable to fill the anode chamber 21 and cathode chamber 25 with ion exchange resin in order to lower the DC voltage that should be applied between the anode 11 and cathode 12 when the EDI device 10 is in operation. Concentration chambers 22 and 24 are supplied with concentration chamber water and discharged. Electrode chamber water is supplied to the cathode chamber 25, and the electrode chamber water supplied to the cathode chamber 25 passes through the cathode chamber 25 before being supplied to the anode chamber 21 and discharged from the anode chamber 21 as electrode water. Furthermore, the concentration chamber and electrode chamber (anode chamber 21 and cathode chamber 25) can be combined into a single configuration.

[0018] Generally, an EDI device can have multiple basic configurations consisting of [concentration chamber | ion exchange membrane | desalination chamber | ion exchange membrane | concentration chamber] arranged side by side with an ion exchange membrane between the anode and cathode. In this case, two adjacent concentration chambers separated by an ion exchange membrane can be combined into a single concentration chamber by removing the membrane in between. In the EDI device 10 shown in Figure 1, the anion exchange membrane 32, desalination chamber 23, cation exchange membrane 33, and concentration chamber 24 form one basic configuration, and N (N is an integer greater than or equal to 1) of these basic configurations can be arranged between the concentration chamber 22 closest to the anode chamber 21 and the anion exchange membrane 34 adjacent to the cathode chamber 25. The fact that multiple basic configurations can be arranged side by side is indicated by the notation "×N" in the figure.

[0019] Next, the production of deionized water (treated water) using the EDI device 10 shown in Figure 1 will be explained. Similar to a typical EDI device, the water supplied to the concentration chambers 22 and 24 is passed through the concentration chambers 22 and 24, the water supplied to the electrode chamber is supplied to the cathode chamber 25, and the water supplied to the electrode chamber discharged from the cathode chamber 25 is also passed through the anode chamber 21. With a DC voltage applied between the anode 11 and the cathode 12, the water to be treated is passed through the desalination chamber 23. As a result, ionic components in the water to be treated are adsorbed by the ion exchange resin in the desalination chamber 23, move within the desalination chamber due to the action of the electric current, and are discharged to the adjacent concentration chamber, thereby proceeding with deionization (desalination), and deionized water flows out of the desalination chamber 23 as treated water. In the desalination chamber 23, the water to be treated first passes through a large particle layer, where strong acid components and weak acid components that are relatively easily adsorbed by the anion exchange resin are removed from the water to be treated. Subsequently, components that are relatively difficult to remove, such as boron, contained in the treated water are adsorbed by the anion exchange resin and removed from the treated water as it passes through the mixed particle size layer containing small-particle anion exchange resin. As a result, treated water from which weak acid components such as boron have been sufficiently removed is discharged from the desalination chamber 23. Although the water flow resistance is greater in the mixed particle size layer than in the large particle size layer, as will become clear from the examples described later, the increase in water flow differential pressure can be kept within an acceptable range by controlling the packing rate in the desalination chamber 23.

[0020] In the desalination chamber 23 of the EDI device 10 of this embodiment, there may be one large particle layer and one mixed particle layer, or at least one of the large particle layer and the mixed particle layer may be provided in two or more layers. However, in order to improve the removal efficiency, it is preferable to have a configuration in which relatively easy-to-remove components in the treated water are removed first, followed by components that are relatively difficult to remove. Therefore, in the EDI device 10 of this embodiment, no matter which mixed particle layer is considered, at least one large particle layer is present upstream of that mixed particle layer. That is, the large particle layer and the mixed particle layer are arranged in the desalination chamber 23 so that the treated water passes through the large particle layer first before passing through the mixed particle layer. It is preferable to place the mixed particle layer in the desalination chamber 23 near the outlet of the treated water. In this case, the mixed particle layer may be placed in contact with the outlet of the treated water, or at least a part of the mixed particle layer may be included within a range of 25% of the length of the desalination chamber 23 along the flow of the treated water from the outlet of the treated water. The desalination chamber 23 contains both a mixed particle size layer and a large particle size layer. Preferably, the proportion of the mixed particle size layer is such that, for example, the total packing height of the ion exchange resin along the flow of the water to be treated in the mixed particle size layer is 20% to 80% of the length of the desalination chamber 23 along the flow of the water to be treated. If the proportion of the mixed particle size layer is too small, the removal performance of weak acid components containing boron will decrease. Since small particle size ion exchange resins are generally more expensive than large particle size resins, if the proportion of the mixed particle size layer is too large, the impact on cost cannot be ignored. In this specification, the packing height of the ion exchange resin along the flow of the water to be treated in the large particle size layer and the mixed particle size layer may be referred to as the packing height of that layer. The length of the desalination chamber 23 refers to the length of the desalination chamber 23 along the flow of the water to be treated, specifically the length of the portion of the desalination chamber 23 in which the ion exchange resin is provided.

[0021] Weak acid components such as boron in the treated water are adsorbed by ion exchange onto the anion exchange resin constituting the mixed particle size layer, and then move as anions through the anion exchange membrane 32 to the concentration chamber 22 on the anode 11 side. In the concentration chamber 22, it is preferable that the anion concentration is low in the water flowing at a position opposite the mixed particle size layer of the desalination chamber 23, with the anion exchange membrane 32 in between. Also, as mentioned above, it is preferable that the mixed particle size layer in the desalination chamber 23 be located close to the outlet. For these reasons, it is preferable that the flow of the outlet water in the desalination chamber 23 and the flow of the concentration chamber supply water supplied to the concentration chamber 22 are in the opposite direction.

[0022] Next, we will explain how the boron removal rate can be increased in the EDI device 10 of this embodiment by describing the phenomenon of boron component leakage from the desalination chamber 23. Figure 2 is a diagram illustrating the leakage of boron component from the desalination chamber 23. Here, the desalination chamber 23 and the concentration chamber 24 are alternately arranged between the anode 11 and the cathode 12, the desalination chamber 23 is filled with a mixture of large-particle ion exchange resin and small-particle ion exchange resin, and the concentration chamber 24 is filled with anion exchange resin in a single bed. The boron component in the water to be treated is captured as a boron-containing anion by the anion exchange resin in the desalination chamber 23 on the right side of the figure, and moves to the concentration chamber 24 on the anode 11 side via the anion exchange membrane 32. If the boron component is boric acid (H3BO3), then in water, boric acid undergoes the reaction H3BO3 + H2O → H + +B(OH)4 - Since it dissociates, the boron-containing anion is B(OH)4 - Therefore, when boron-containing anions move to the concentration chamber 24, they are captured by the anion exchange resin in the concentration chamber 24. Then, due to the electric field caused by the applied DC voltage, these boron-containing anions move to the vicinity of the cation exchange membrane 33 in the concentration chamber 24, but since they are anions, they cannot move through the cation exchange membrane 33. Consequently, in the concentration chamber 24, boron-containing anions are concentrated near the cation exchange membrane 33 located on the anode 11 side. In addition, due to the applied DC voltage, hydrogen ions (H) are transferred from the desalination chamber 23 on the anode 11 side to the concentration chamber 24 via the cation exchange membrane 33.+ ) moves in. As a result, the pH of the region near the cation exchange membrane 33 in the concentration chamber 24 decreases. This region is a region where boron-containing anions are concentrated, but due to the hydrogen ions, water and, for example, boric acid are produced from the boron-containing anions, and a layer of water containing a high concentration of boric acid is formed near the cation exchange membrane 33 in the concentration chamber 24. Since boric acid is a neutral molecule, it can move across the cation exchange membrane 33, and thus moves from the concentration chamber 24 to the desalination chamber 23 via the cation exchange membrane 33. In the end, the boron component removed from the treated water in one desalination chamber 23 dissolves back into the treated water in another desalination chamber 23 located on the anode 11 side of that desalination chamber 23, and the boron component leaks into the treated water discharged from the desalination chamber 23.

[0023] To prevent such leakage of boron components, it is advisable to ensure that a region with a reduced pH does not form near the cation exchange membrane 33 in the concentration chamber 24. To achieve this, it is effective to quickly move the hydrogen ions that have moved to the concentration chamber 24 via the cation exchange membrane 33 to the cathode 12 side within the concentration chamber 24. Therefore, in the EDI device 10 based on the present invention, a cation exchange resin is present in the concentration chamber 24.

[0024] If it is acceptable for the electrode water discharged from the anode chamber 21 to contain boron, then it is not necessary to fill the concentration chamber 22 adjacent to the anode chamber 21 with cation exchange resin (i.e., the concentration chamber without a desalination chamber 23 between it and the anode chamber 21). Furthermore, since the boron component migrates mainly from the mixed particle size layer in the desalination chamber 23 to the concentration chamber 24 via the anion exchange membrane 32, it is considered that in the concentration chamber 24, cation exchange resin only needs to be present in the region opposite to the region in the desalination chamber 23 that is the mixed particle size layer, separated by the anion exchange membrane 32.

[0025] Figure 3 shows another example of the EDI apparatus 10 of the first embodiment. The EDI apparatus 10 shown in Figure 2 is an EDI apparatus 10 shown in Figure 1 which has two sets of the basic configuration (i.e., N=2). In this configuration, the concentration chamber 22 adjacent to the anode chamber 21 is filled only with anion exchange resin, while the other concentration chamber 24 (i.e., the concentration chamber 24 adjacent to the desalination chamber 23 on the cathode 12 side of the desalination chamber 23 via the cation exchange membrane 33) is divided into a region filled only with anion exchange resin and a region filled with a mixture of cation exchange resin and anion exchange resin. The region in the concentration chamber 24 where the cation exchange resin and anion exchange resin are mixed and filled is the region adjacent to the region in the desalination chamber 23 where the mixed particle size layer is formed, separated by the cation exchange membrane 33, that is, the region where boron-containing anions move from the desalination chamber 23 which is closer to the cathode 12 via the anion exchange membrane 32. Furthermore, the region in the concentration chamber 24 that is filled only with anion exchange resin faces the region in the desalination chamber 23 where a large particle size layer is formed, separated by the cation exchange membrane 33. In the EDI apparatus 10 shown in Figure 3, the cation exchange resin is present in the region of the concentration chamber 24 from which boron-containing anions move from the desalination chamber 23 located on the cathode 12 side. Therefore, with respect to the concentration chamber 24, leakage of boron components into the desalination chamber 23 located on the anode 11 side can be prevented.

[0026] In the EDI apparatus 10 shown in Figures 1 and 3, a large particle size layer made of anion exchange resin is placed on the inlet side of the desalination chamber 23, and a mixed particle size layer made of anion exchange resin is placed on the outlet side of the desalination chamber 23. As is clear from the above explanation, the arrangement of ion exchange resins in the desalination chamber 23 is not limited to that shown in Figures 1 and 3. Figures 4(a) to 4(e) show another example of the arrangement of ion exchange resins in the desalination chamber 23 by depicting only the desalination chamber 23 and the ion exchange membranes on both sides of it. Figure 4(a) shows the desalination chamber 23 in the EDI apparatus 10 shown in Figure 1, with the large particle size layer placed at a small packing height adjacent to the outlet of the desalination chamber 23, and the mixed particle size layer placed between the large particle size layer on the inlet side and the large particle size layer on the outlet side of the desalination chamber 23. In the example shown in Figure 4(a), the packing height of the mixed particle size layer is approximately 36% of the length of the desalination chamber 23, and the packing height of the large particle size layer on the outlet side is approximately 14% of the length of the desalination chamber 23.

[0027] To remove ionic impurities, which are cations, the desalination chamber 23 may be filled not only with anion exchange resin but also with cation exchange resin (CER). Figure 4(b) shows a desalination chamber 23 in which a large particle size layer made of cation exchange resin, a large particle size layer made of anion exchange resin, a large particle size layer made of cation exchange resin, and a mixed particle size layer made of anion exchange resin are arranged in this order from the inlet side. The packing height of each layer is approximately the same. In Figure 4(b), an anion exchange membrane 37 is placed at the interface where the cation exchange membrane 33 and the anion exchange resin in the desalination chamber 23 come into contact, in order to promote the dissociation reaction of water on the cathode 12 side of the anion exchange resin. The desalination chamber 23 shown in Figure 4(c) is the same as the desalination chamber 23 shown in Figure 4(b), but the large particle size layer on the outlet side of the two large particle size layers of cation exchange resin is replaced with a mixed particle size layer made of cation resin. The anion exchange membrane 37 provided in contact with the cation exchange membrane 33 is not necessarily required. The configurations shown in Figures 4(d) and 4(e) are obtained by removing the anion exchange membrane 37 from the configurations in Figures 4(b) and 4(c), respectively, with the anion exchange resin in contact with the cation exchange membrane 33 on the cathode 12 side. In the present invention, either the anion exchange resin or the cation exchange resin may be used as the mixed particle size layer, but when the purpose is to remove boron, it is preferable to provide at least one of the large particle size layer made of the anion exchange resin and the mixed particle size layer made of the anion exchange resin in the desalination chamber 23, and it is particularly preferable to provide the mixed particle size layer made of the anion exchange resin.

[0028] [Second Embodiment] In the EDI apparatus according to the present invention, the desalination chamber itself is divided into two small desalination chambers by an ion exchange membrane, and the water to be treated is supplied to one of the small desalination chambers, and the water flowing out of one small desalination chamber is supplied to the other small desalination chamber. Deionized water is obtained as treated water from the other small desalination chamber. The EDI apparatus 10 of the second embodiment of the present invention shown in Figure 5 divides the desalination chamber 23 of the EDI apparatus 10 shown in Figure 1 into two small desalination chambers 26 and 27 by an intermediate ion exchange membrane, which is an anion exchange membrane 36, and the arrangement of ion exchange resins within the desalination chambers is different. The small desalination chamber located on the side closer to the anode 11 with the anion exchange membrane 36 in between is the first small desalination chamber 26, and the small desalination chamber located on the side closer to the cathode 12 is the second small desalination chamber 27. The water to be treated is supplied to the first small desalination chamber 26, and the outlet water from the first small desalination chamber 26 is supplied to the second small desalination chamber 27. The water discharged from the second small desalination chamber 27 is treated water (deionized water) from the EDI device 10. When the desalination chamber is divided into a first small desalination chamber 26 on the inlet side and a second small desalination chamber 27 on the outlet side, the length of the desalination chamber means the sum of the length of the portion in the first small desalination chamber 26 where ion exchange resin is provided and the length of the portion in the second small desalination chamber 27 where ion exchange resin is provided, along the flow of the water to be treated.

[0029] In the EDI apparatus 10 shown in Figure 5, the flow direction in the first small desalination chamber 26 and the flow direction in the second small desalination chamber 27 are opposite to each other, i.e., countercurrent. Also, the flow direction in the concentration chamber 22 on the anode 11 side is the same as the flow direction in the adjacent first small desalination chamber 26, and the two are in a parallel flow relationship. The flow direction in the second small desalination chamber 27, which is the outlet side of the desalination chamber, and the flow direction in the adjacent concentration chamber 24 are in a countercurrent relationship. The first small desalination chamber 26 is filled with anion exchange resin as a large particle size layer. In the second small desalination chamber 27, the inlet side is filled with cation exchange resin, and the outlet side is filled with anion exchange resin as a mixed particle size layer. The cation exchange resin is usually provided as a large particle size layer, but it may also be a mixed particle size layer. In the second small desalination chamber 27, the boundary between the mixed particle size layer of anion exchange resin and the cation exchange resin is located at approximately half the length of the second small desalination chamber 27, or in other words, at approximately 25% of the length of the desalination chamber when measured from the outlet side of the desalination chamber. The anion exchange membrane 37 is provided at the interface where the cation exchange membrane 33 and the anion exchange resin in the second small desalination chamber 27 come into contact. Alternatively, the anion exchange membrane 37 may be omitted, allowing the anion exchange resin in the second small desalination chamber 27 to be in direct contact with the cation exchange membrane 33. In the EDI apparatus 10 shown in Figure 5, the water to be treated passes through the mixed particle size layer of anion exchange resin, making it possible to efficiently remove weak acid components such as boron.

[0030] In the second embodiment, in which the desalination chamber is divided into two smaller desalination chambers by an intermediate ion exchange membrane, the preferred mixing ratio of large-particle ion exchange resin and small-particle ion exchange resin in the mixed particle size layer, and the preferred ratio of the total packing height of the mixed particle size layer to the length of the desalination chamber, are the same as those described in the first embodiment. In the second embodiment, it is also preferable to provide the mixed particle size layer at a position close to the outlet of the treated water in the desalination chamber as a whole, and at least a portion of the mixed particle size layer may be included within 25% of the length of the desalination chamber from the outlet of the treated water.

[0031] Figure 6 shows another configuration example of the EDI device of the second embodiment. The EDI device 10 shown in Figure 6 is the same as the EDI device 10 shown in Figure 5, but the anion exchange resin filling the first small desalination chamber 26 is a mixed particle size layer, and instead the anion exchange resin filling the second small desalination chamber 27 is a large particle size layer.

[0032] Figure 7 shows yet another configuration example of the EDI device of the second embodiment. The EDI device 10 shown in Figure 7 is the same as the EDI device 10 shown in Figure 5, but the anion exchange resin filling the first small desalination chamber 26 is a mixed particle size layer. In this EDI device 10, the anion exchange resin filling the second small desalination chamber 27 is a large particle size layer.

[0033] The EDI device based on the present invention has been described above. The EDI device can be used, for example, to produce pure water or ultrapure water from raw water. Figure 8 is a flow diagram showing the configuration of a pure water production system using the EDI device 10 described above. Electrodes and ion exchange membranes are not shown in this figure. Although this figure is depicted as using the EDI device 10 of the first embodiment, it is also possible to use the EDI device 10 of the second embodiment. A reverse osmosis (RO) membrane device is provided to which raw water is supplied, and a reverse osmosis membrane 41 is provided inside the reverse osmosis membrane device 40. The water that does not permeate the reverse osmosis membrane 41 in the reverse osmosis membrane device 40 (RO concentrated water) contains many impurities, and the RO concentrated water is blown out. The water that permeates the reverse osmosis membrane 41 in the reverse osmosis membrane device 40 (RO permeate water) is water that contains relatively few impurities and is supplied to the desalination chamber 23 of the EDI device 10 as water to be treated. A portion of the RO permeate water is supplied to the concentration chambers 22, 24 and the cathode chamber 25 as water to be supplied to the concentration chamber and the electrode chamber. Alternatively, in order to prevent the diffusion of boron from the concentration chambers 22 and 24 from having an effect, a portion of the deionized water discharged from the desalination chamber 23 may be supplied to the concentration chambers 22 and 24 and the cathode chamber 25 as the supply water for the concentration chambers and the supply water for the electrode chambers, or pure water or ultrapure water supplied from outside the system may be supplied to the concentration chambers 22 and 24 and the cathode chamber 25. The electrode water discharged from the anode chamber 21 is blown out to the outside, and the concentrated water discharged from the concentration chambers 22 and 24 is also blown out to the outside.

[0034] A DC voltage is applied between the anode (not shown in Figure 8) located in the anode chamber 21 and the cathode (not shown in Figure 8) located in the cathode chamber 25. RO permeate is supplied to the desalination chamber 23 as the water to be treated, and desalination is performed in the desalination chamber 23, from which pure water (deionized water) is extracted. Weak acidic components contained in the raw water, especially boron, are easily absorbed through the reverse osmosis membrane 41 and contained in the RO permeate. When an EDI device is installed downstream of the reverse osmosis membrane device to remove boron, conventional EDI devices do not have sufficient boron removal performance, so two EDI devices are sometimes connected in stages. However, by using the EDI device 10 of each embodiment described above, boron in the water to be treated can be sufficiently removed by installing only one EDI device 10 downstream of the reverse osmosis membrane device 40. Furthermore, as will become clear from the examples and comparative examples described later, the EDI apparatus based on the present invention can reduce the differential water pressure in the desalination chamber, so a reverse osmosis membrane apparatus with a low operating pressure, i.e., an ultra-low pressure reverse osmosis membrane apparatus and an extremely low pressure reverse osmosis membrane apparatus, can be used as the reverse osmosis membrane apparatus 40.

[0035] As described above, according to the EDI apparatus based on the present invention, by placing a mixed particle size layer, which is a mixture of large-particle ion exchange resin and small-particle ion exchange resin, in the desalination chamber, and by making at least a portion of the ion exchange resin filling the concentration chamber a cation exchange resin, the removal rate of boron components can be improved, making it possible to obtain pure water and ultrapure water of higher quality. Improving the removal rate of boron components in the EDI apparatus leads to miniaturization of components such as reverse osmosis membrane devices installed upstream of the EDI apparatus, and miniaturization of components such as ion exchange devices installed downstream of the EDI apparatus. [Examples]

[0036] Next, the present invention will be described in more detail with reference to examples, reference examples, and comparative examples. In the following description, the mixing ratio when a mixed particle size layer is formed by mixing a large-particle-size ion exchange resin and a small-particle-size ion exchange resin is expressed as L:S. L is the apparent volume of the large-particle-size ion exchange resin before mixing, and S is the apparent volume of the small-particle-size ion exchange resin before mixing. In the following examples and comparative examples, a gel-type strongly basic anion exchange resin with a particle size range of 0.50 to 0.65 mm and a styrene-based matrix was used as the large-particle-size anion exchange resin (AER), and a gel-type strongly basic anion exchange resin with a particle size range of 0.28 to 0.34 mm and a styrene-based matrix was used as the small-particle-size anion exchange resin. As the cation exchange resin (CER), a gel-type strongly acidic cation exchange resin with a particle size range of 0.60 to 0.70 mm and a styrene-based matrix was used. This cation exchange resin is a large-particle-size cation exchange resin.

[0037] [Example 1] The EDI apparatus 10 shown in Figure 5 was assembled. Figure 9 shows the configuration of the main parts of the EDI apparatus 10 used in Example 1. Cells (frames) with an opening of 150 mm × 300 mm and a thickness of 10 mm were used for the concentration chambers 22, 24 and the small desalination chambers 26, 27. The EDI apparatus 10 was assembled by filling the cells in each chamber with ion exchange resin and stacking these cells in the thickness direction with an ion exchange membrane in between. The mixed particle size layer provided in the second desalination chamber 27 was filled with a mixture of large particle size anion exchange resin and small particle size anion exchange resin in an L:S ratio of 5:1. The concentration chambers 22 and 24 were filled with a mixture of large particle size anion exchange resin and large particle size cation exchange resin. The water to be treated, with a boron concentration of 10 μg / L, is sequentially passed through the small desalination chambers 26 and 27 at a rate of 100 L / h, while the supply water is passed through the concentration chambers 22 and 24 at a rate of 10 L / h each, with a current density of 1.1 A / dm². 2 The EDI device 10 was operated by applying a DC voltage between the anode 11 and cathode 12 in such a manner. Then, 2500 hours after the start of operation, the boron concentration in the treated water was measured and the boron removal rate was calculated. The results are shown in Table 1.

[0038] [Example 2] An EDI apparatus 10 was assembled in the same manner as in Example 1, except that the mixing ratio L:S of large-particle anion exchange resin and small-particle anion exchange resin in the mixed particle size layer was 1:1. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0039] [Comparative Example 1] In the EDI apparatus 10 of Example 1, instead of filling the concentration chambers 22 and 24 with a mixture of cation exchange resin and anion exchange resin, only large-particle cation exchange resin was filled, and the second small desalination chamber 27 was fitted with a large-particle layer consisting only of large-particle anion exchange resin instead of the mixed particle size layer. Figure 10 shows the configuration of the main parts of the EDI apparatus 10 used in Comparative Example 1. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0040] [Comparative Example 2] In Comparative Example 1, instead of filling the concentration chambers 22 and 24 with cation exchange resin alone, a mixture of large-particle anion exchange resin and large-particle cation exchange resin was packed into the EDI apparatus 10. Figure 11 shows the main components of the EDI apparatus 10 used in Comparative Example 2. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0041] [Comparative Example 3] In Comparative Example 1, the EDI apparatus 10 was assembled in which, instead of filling the concentration chambers 22 and 24 with cation exchange resin alone, large-particle anion exchange resin alone was filled. Figure 12 shows the configuration of the main parts of the EDI apparatus 10 used in Comparative Example 3. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0042] [Comparative Example 4] In the EDI apparatus 10 of Example 1, instead of filling the concentration chambers 22 and 24 with a mixture of anion exchange resin and cation exchange resin, an EDI apparatus 10 was assembled in which only large-particle anion exchange resin was filled. The mixing ratio L:S of large-particle anion exchange resin to small-particle anion exchange resin in the mixed particle size layer of this EDI apparatus is 5:1. Figure 13 shows the configuration of the main parts of the EDI apparatus 10 used in Comparative Example 4. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0043] [Comparative Example 5] An EDI apparatus 10 was assembled in the same manner as in Comparative Example 1, except that the mixing ratio L:S of large-particle anion exchange resin and small-particle anion exchange resin in the mixed particle size layer was 1:1. The EDI apparatus 10 was operated in the same manner as in Example 1, and the boron removal rate was determined after 2500 hours from the start of operation. The results are shown in Table 1.

[0044] [Table 1]

[0045] In the EDI devices of Examples 1 and 2, which are based on the present invention, the boron removal rate after 2500 hours of operation was 99.96%, demonstrating a high boron removal rate. From this, it was found that by installing just one stage of the EDI device based on the present invention, the boron concentration in the treated water can be reduced to, for example, less than 10 ng / L.

[0046] In contrast, in Comparative Examples 1-3, where large-particle anion exchange resin and small-particle anion exchange resin were not mixed and filled in the desalination chamber, the boron removal rate was lower compared to Examples 1 and 2. Comparing Comparative Examples 1-3, Comparative Example 1, in which only cation exchange resin was filled in the concentration chamber, showed the highest boron removal rate, but there is a risk of increased applied voltage if the treated water or the water supplied to the concentration chamber contains any hardness components. Although not shown in Table 1, in Comparative Examples 1 and 2, the phenomenon of increased differential pressure of the water flowing through the chamber was observed as the operating time increased compared to Examples 1 and 2. On the other hand, in Comparative Example 3, in which only anion exchange resin was filled in the concentration chamber, the boron removal rate was lower compared to Comparative Examples 1 and 2. Even when large-particle anion exchange resin and small-particle anion exchange resin were mixed and filled in the desalination chamber, as shown in Comparative Examples 4 and 5, when only anion exchange resin was filled in the concentration chamber, the boron removal rate did not improve. From these findings, it was determined that in order to improve the boron removal rate, at least a portion of the desalination chamber should be filled with a mixture of large-particle anion exchange resin and small-particle anion exchange resin, and at least a portion of the ion exchange resin filled in the concentration chamber should be cation exchange resin. In this case, it was also found that it is preferable to fill the concentration chamber with a mixture of anion exchange resin and cation exchange resin.

[0047] [Reference example 1] The increase in water pressure differential due to the mixing and filling of large-particle and small-particle anion exchange resins in the desalination chamber was investigated. In the EDI apparatus 10 shown in Figure 1, the concentration chambers 22 and 24 were filled only with large-particle anion exchange resins, and a mixed particle size layer of large-particle and small-particle anion exchange resins was provided throughout the entire desalination chamber 23. Furthermore, as the ion exchange membrane that partitions the desalination chamber 23 on the cathode 12 side, an anion exchange membrane 37 and a cation exchange membrane 33 were superimposed so that the desalination chamber 23 side was the anion exchange membrane 37. Figure 14 shows the configuration of the main parts of the EDI apparatus 10 used in Reference Example 1. Cells (frames) with openings of 100 mm × 100 mm and a thickness of 10 mm were used for both the concentration chambers 22 and 24 and the desalination chamber 23. The EDI device 10 was assembled by filling each chamber's cell with ion exchange resin and stacking these cells in the thickness direction with an ion exchange membrane in between. The mixed particle size layer in the desalination chamber 23 was filled with a mixture of large particle size anion exchange resin with a particle size of 0.6-0.7 mm and small particle size anion exchange resin with a particle size of 0.3 mm, with an L:S ratio of 1:1. The concentration chambers 22 and 24 were filled with large particle size anion exchange resin with a particle size of 0.6-0.7 mm. At this time, the packing ratio of the anion exchange resin in the desalination chamber 23 was set to 1.1. The packing ratio is the value obtained by applying a DC voltage between the anode 11 and the cathode 12 while passing water through the desalination chamber 23 filled with ion exchange resin to regenerate the ion exchange resin, and then dividing the apparent volume of the ion exchange resin in its free state after it is removed from the desalination chamber 23 by the volume of the desalination chamber 23. A "free state" refers to a state in which the ion exchange resin is not confined to a space such as a desalination chamber or concentration chamber.

[0048] The water to be treated, with a boron concentration of 100 μg / L, is passed through the desalination chamber 23 at a rate of 25 L / h, while the supply water is passed through the concentration chambers 22 and 24 at a rate of 5.5 L / h each, with a current density of 1.1 A / dm². 2The EDI device 10 was operated by applying a DC voltage between the anode 11 and cathode 12 in such a manner. Then, as in Example 1, the boron removal rate and the water flow differential pressure were determined after 2500 hours from the start of operation. The results are shown in Table 2.

[0049] [Reference example 2] The EDI device 10 was assembled in the same manner as in Reference Example 1, except that the packing ratio of the anion exchange resin in the desalination chamber 23 was set to 1.2. The EDI device 10 was operated in the same manner as in Reference Example 1, and the boron removal rate and water flow differential pressure were determined after 2500 hours from the start of operation. The results are shown in Table 2.

[0050] [Table 2]

[0051] From the results of Reference Examples 1 and 2, even when the mixing ratio L:S of large-particle anion exchange resin to small-particle anion exchange resin was 1:1, meaning the proportion of small-particle anion exchange resin was quite large, the differential pressure of the water flow was small. No significant difference in the differential pressure of the water flow was observed when the filling rate of the anion exchange resin was in the range of 1.1 to 1.2. From these findings, it was found that the differential pressure of the water flow can be sufficiently low with the EDI device based on the present invention. Even when the mixing ratio L:S was 1:3 in Reference Examples 1 and 2, no increase in the differential pressure of the water flow was observed. [Explanation of Symbols]

[0052] 10 EDI equipment 11 Anode 12 Cathode 21 Anode chamber 22,24 Concentration chamber 23 Desalination room 25 Cathode Chamber 26, 27 Small desalination chamber 31,33 Cation exchange membrane (CEM) 32, 34, 36, 37 Anion exchange membrane (AEM) 40 Reverse osmosis membrane equipment 41 Reverse osmosis membrane

Claims

1. An electro-deionized water production apparatus comprising a desalination chamber, which is divided between an anode and a cathode by a pair of ion exchange membranes consisting of a first ion exchange membrane located on the anode side and a second ion exchange membrane located on the cathode side, and is filled with ion exchange resin and supplied with water to be treated; and a concentration chamber, which is located adjacent to the desalination chamber via the second ion exchange membrane and is filled with ion exchange resin, Particles with a diameter of 0.1 mm or more and 0.4 mm or less are considered small particle size, and particles with a diameter greater than 0.4 mm are considered large particle size. In the desalination chamber, a large particle size layer made of large particle size ion exchange resin and a mixed particle size layer made of a mixture of large particle size anion exchange resin and small particle size anion exchange resin are arranged in the direction of the flow of the water to be treated in the desalination chamber. Let L be the apparent volume of the large-particle anion exchange resin and S be the apparent volume of the small-particle anion exchange resin. In the mixed particle size layer, the large-particle anion exchange resin and the small-particle ion exchange resin are mixed in a mixing ratio such that L:S is in the range of 1:3 to 10:

1. At least a portion of the ion exchange resin packed into the concentration chamber is a cation exchange resin, An electro-deionized water production apparatus characterized in that the water to be treated, which contains boron, is supplied to the desalination chamber to remove boron from the water to be treated.

2. The electro-deionized water production apparatus according to claim 1, wherein the ion exchange resin filled in the concentration chamber is a large-particle ion exchange resin.

3. The electrolytic deionized water production apparatus according to claim 1 or 2, wherein the concentration chamber is filled with an anion exchange resin and a cation exchange resin in a mixed state.

4. The electrolytic deionized water production apparatus according to claim 3, wherein the apparent volume of the anion exchange resin is A and the apparent volume of the cation exchange resin is C, and the mixing ratio A:C of the anion exchange resin and the cation exchange resin in the concentration chamber is in the range of 20:80 to 60:

40.

5. The electro-deionized water production apparatus according to claim 1 or 2, wherein the mixed particle size layer and the large particle size layer are arranged such that at least one large particle size layer is located upstream of the mixed particle size layer in the desalination chamber.

6. The electro-deionized water production apparatus according to claim 1 or 2, wherein the desalination chamber is provided with an intermediate ion exchange membrane located between the pair of ion exchange membranes, and is divided into a first small desalination chamber and a second small desalination chamber by the intermediate ion exchange membrane, and the first small desalination chamber and the second small desalination chamber are in communication such that the water to be treated is supplied to one of the small desalination chambers and the water flowing out of that small desalination chamber flows into the other small desalination chamber.

7. The electro-deionized water production apparatus according to claim 6, wherein an anion exchange resin is filled in the first and second small desalination chambers, the small desalination chamber closer to the anode, and a large particle size cation exchange resin is filled in the small desalination chamber closer to the cathode, and the mixed particle size layer made of anion exchange resin is arranged therein.

8. An operating method for an electric deionized water production apparatus according to claim 1 or 2, characterized in that the concentration of hardness components in the water to be treated supplied to the desalination chamber is 0.1 mg / L or less.

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