Electrical deionized water production apparatus and pure water production method

Abstract

To suppress the back diffusion of cations and weak acids while suppressing the degradation of ion exchange performance.SOLUTION: An electrical deionized water production apparatus 1 has an anode 8, a cathode 7, a desalination chamber 2 provided between the anode 8 and the cathode 7, a first concentration chamber 3 provided on the cathode side of the desalination chamber 2 via a cation exchange membrane 5, and a second concentration chamber 4 provided on the anode side of the desalination chamber 2 via an anion exchange membrane 6. The EDI system 1 has at least one structure selected from: a structure in which the first concentration chamber 3 is filled with at least an anion exchange resin and a portion of the cation exchange membrane 5, which is an ion exchange membrane, is thicker than the other portions; and a structure in which the second concentration chamber 4 is filled with at least a cation exchange resin and a portion of the anion exchange membrane 6, which is an ion exchange membrane, is thicker than the other portions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrodeionization water production apparatus and a method for producing pure water. [Background technology]

[0002] There is known an electrodeionized water production apparatus (hereinafter sometimes referred to as an EDI apparatus) that removes ions from water to be treated. In the EDI apparatus, deionization compartments and concentration compartments are alternately arranged between an anode and a cathode. The deionization compartments and concentration compartments are partitioned by alternately arranged cation exchange membranes and anion exchange membranes. Patent Document 1 describes an EDI apparatus in which the deionization compartments and concentration compartments are filled with a mixed resin of an anion exchange resin and a cation exchange resin.

[0003] In the above EDI device, when the concentration compartment is filled with a cation exchange resin, a phenomenon in which ion components such as sodium move from the concentration compartment to the deionization compartment (hereinafter, sometimes referred to as back diffusion of cations) may occur. Also, when the concentration compartment is filled with anion exchange resin, a phenomenon in which weak acids such as carbonic acid move from the concentration compartment to the deionization compartment (hereinafter, sometimes referred to as back diffusion of weak acids) may occur.

[0004] As an example of an EDI device that suppresses the above-mentioned back diffusion, Patent Document 2 describes an EDI device that suppresses the back diffusion of a weak acid. In this EDI device, a cation exchange membrane provided between a deionization compartment and a concentration compartment adjacent to the cathode side of the deionization compartment is composed of a heterogeneous membrane and a homogeneous membrane. The heterogeneous membrane is disposed on the concentration compartment side, and the homogeneous membrane is disposed on the deionization compartment side. Patent Document 2 describes, as a first configuration example, a structure in which a two-layer structure of a heterogeneous membrane and a homogeneous membrane is provided over the entire contact area of ​​the cation exchange membrane that contacts the deionization compartment. Also, as a second configuration example, a structure in which a heterogeneous membrane is provided over the entire contact area, and a homogeneous membrane is provided on a part of the surface of the heterogeneous membrane on the deionization compartment side is described. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-195755 A [Patent Document 2] JP 2019-72694 A Summary of the Invention [Problem to be solved by the invention]

[0006] The EDI device described in Patent Document 1 has a problem in that the quality of treated water is deteriorated due to back diffusion of cations and weak acids.

[0007] In the EDI device described in Patent Document 2, the reverse diffusion of weak acids can be suppressed. However, in the above-mentioned first configuration example, there are cases where the ion exchange performance of moving cationic components from the deionization compartment to the concentration compartment cannot be fully exhibited. This is because the thickness of the cation exchange membrane in the entire contact area becomes thick. In addition, in the second configuration example, a part of the water to be treated flowing in the deionization compartment passes between the cationic homogeneous membrane and the cationic heterogeneous membrane, and is discharged as treated water without being able to remove the cationic components from the deionization compartment, which may result in a deterioration in the quality of the treated water.

[0008] An object of the present invention is to provide an electrodeionization water production apparatus and a method for producing pure water that can solve the above problems and suppress the back diffusion of cations and weak acids while suppressing the deterioration of ion exchange performance. [Means for solving the problem]

[0009] In order to achieve the above object, according to one aspect of the present invention, there is provided an electrodeionization water production apparatus having an anode, a cathode, a deionization compartment provided between the anode and the cathode, a first concentrating compartment provided on the cathode side of the deionization compartment via a cation exchange membrane, and a second concentrating compartment provided on the anode side of the deionization compartment via an anion exchange membrane, The present invention provides an electrodeionized water production apparatus having at least one of the following structures: a structure in which the first concentration chamber is filled with at least an anion exchange resin, and a portion of the ion exchange membrane, which is the cation exchange membrane, is made thicker than the other portions; and a structure in which the second concentration chamber is filled with at least a cation exchange resin, and a portion of the ion exchange membrane, which is the anion exchange membrane, is made thicker than the other portions.

[0010] According to another aspect of the present invention, there is provided a method for producing pure water, which uses the above-mentioned electrical deionized water production apparatus, and supplies water to be treated having a sodium ion concentration of 0.1 ppm or more or a total carbonate concentration of 0.5 mg-CO2 / L or more to the desalting chamber while applying a DC voltage between the anode and the cathode, to obtain pure water, which is deionized water. Effect of the Invention

[0011] According to the present invention, it is possible to suppress the back diffusion of cations and weak acids while suppressing the deterioration of ion exchange performance. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing the configuration of an electrodeionized water production apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram for explaining back diffusion of a weak acid. [Diagram 3] FIG. 4 is a schematic diagram showing the configuration of an electrodeionized water production apparatus according to a second embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram for explaining back diffusion of cations in a structure in which a concentration compartment is packed with a cation exchange resin. [Diagram 5] FIG. 2 is a schematic diagram for explaining the back diffusion of cations in a structure in which a concentration compartment is packed with an anion exchange resin. [Figure 6] FIG. 11 is a schematic diagram showing the configuration of an electrodeionized water production apparatus according to a third embodiment of the present invention. [Figure 7] FIG. 2 is a schematic diagram showing the configuration of an EDI device of Comparative Example 1. [Figure 8]FIG. 1 is a schematic diagram showing a configuration of an EDI device according to a first embodiment of the present invention. [Figure 9] FIG. 11 is a schematic diagram showing the configuration of an EDI device according to a second embodiment of the present invention. [Figure 10] FIG. 13 is a schematic diagram showing the configuration of an EDI device of Comparative Example 2. [Figure 11] FIG. 11 is a schematic diagram showing the configuration of an EDI device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiment are merely examples and are not intended to limit the scope of the present invention.

[0014] (First embodiment) Fig. 1 is a schematic diagram showing the configuration of an electrodeionization water production apparatus according to a first embodiment of the present invention. Referring to Fig. 1, the EDI device 1 has a deionization compartment 2, a first concentration compartment 3, a second concentration compartment 4, a cation exchange membrane 5, an anion exchange membrane 6, a cathode 7, and an anode 8.

[0015] The deionization chamber 2 is provided between the cathode 7 and the anode 8. The deionization chamber 2 is filled with a cation exchange resin and an anion exchange resin. More specifically, the deionization chamber 2 has a first region 2a on the upstream side and a second region 2b on the downstream side with respect to the flow direction of the raw water (water to be treated) flowing through the deionization chamber 2. The first region 2a is filled with a cation exchange resin and an anion exchange resin so that the ratio of the cation exchange resin is high. Specifically, the first region 2a is filled with a mixed resin in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the cation exchange resin is high. The second region 2b is filled with a cation exchange resin and an anion exchange resin so that the ratio of the anion exchange resin is high. Specifically, the second region 2b is filled with a mixed resin in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the anion exchange resin is high. Note that the deionization chamber 2 is not limited to the structure shown here. The deionization compartment 2 may be filled with at least one of a cation exchange resin and an anion exchange resin, and may have a single-layer structure or a multi-layer structure made up of multiple layers.

[0016] The first concentrating compartment 3 is provided adjacent to the cathode side of the deionization compartment 2 via a cation exchange membrane 5. The first concentrating compartment 3 is filled with at least anion exchange resin. As an example, in this embodiment, the first concentrating compartment 3 is filled with a mixed resin of a cation exchange resin and an anion exchange resin. The second concentrating compartment 4 is provided adjacent to the anode side of the deionization compartment 2 via an anion exchange membrane 6. In this embodiment, the second concentrating compartment 4 has the same structure as the first concentrating compartment 3.

[0017] The cation exchange membrane 5 is an ion exchange membrane and separates the deionization compartment 2 from the first concentration compartment 3. The anion exchange membrane 6 is an ion exchange membrane and separates the deionization compartment 2 from the second concentration compartment 4. A part 5c of the cation exchange membrane 5 is thicker in the direction opposite to the deionization compartment 2 (toward the first concentration compartment 3) than the other parts. More specifically, the cation exchange membrane 5 has a first cation exchange membrane 5a and a second cation exchange membrane 5b. The first cation exchange membrane 5a and the second cation exchange membrane 5b are both homogeneous membranes, but are not limited thereto. The first cation exchange membrane 5a and the second cation exchange membrane 5b may be heterogeneous membranes. A homogeneous membrane has a structure in which the entire membrane is chemically bonded by a high degree of cross-linking, a large number of ion exchange groups are uniformly distributed, and has the characteristic of low electrical resistance. The heterogeneous membrane is formed by dispersing fine powder of ion exchange resin (here, cation exchange resin) in a suitable binder (polymer compound) and heating it to form a membrane. The first cation exchange membrane 5a and the second cation exchange membrane 5b can be called the first ion exchange membrane and the second ion exchange membrane, respectively.

[0018] The first cation exchange membrane 5a is provided so as to contact the entire region including the first region 2a and the second region 2b of the deionization compartment 2. The second cation exchange membrane 5b is provided on the surface of the first cation exchange membrane 5a on the first concentration compartment 3 side (opposite the deionization compartment 2). The area of ​​the second cation exchange membrane 5b is smaller than the area of ​​the first cation exchange membrane 5a. The second cation exchange membrane 5b faces the second region 2b via the first cation exchange membrane 5a. The facing surfaces of the second cation exchange membrane 5b and the second region 2b have approximately the same area, but are not limited to this. As will be described in detail later, the area of ​​the second cation exchange membrane 5b may be different from the area of ​​the second region 2b as long as the ratio of the area of ​​the second cation exchange membrane 5b to the area of ​​the opening of the frame of the deionization compartment 2 is 60% or less.

[0019] The portion 5c of the cation exchange membrane 5 is a portion thickened by overlapping the second cation exchange membrane 5b on the first cation exchange membrane 5a. In the cation exchange membrane 5, the portion 5c is located downstream with respect to the flow direction of the water to be treated flowing through the deionization chamber 2. In this embodiment, the downstream end of the portion 5c is located at the most downstream part of the deionization chamber 2, but is not limited thereto. The portion 5c can be provided at any position downstream with respect to the flow direction of the water to be treated. In addition, two or more portions 5c may be provided, or a structure in which a plurality of second cation exchange membranes 5b are overlapped to make the portion thicker may be used. As shown in FIG. 1, in this embodiment, the concentrated water flows opposite to the water to be treated, and the portion 5c is located upstream with respect to the flow of the concentrated water in the first concentration chamber 3 in which the portion 5c is arranged.

[0020] 1 shows only one each of the deionization compartment 2 and the first and second concentrating compartments 3 and 4, but this is not limiting. In general, cation exchange membranes 5 and anion exchange membranes 6 are alternately arranged between the cathode 7 and the anode 8, and the deionization compartments 2 and concentrating compartments are alternately arranged in the multiple spaces partitioned by these cation exchange membranes 5 and anion exchange membranes 6. In this case, with the deionization compartment 2 as the reference, the concentrating compartment adjacent to the cathode 7 side of the deionization compartment 2 is defined as the first concentrating compartment 3, and the concentrating compartment adjacent to the anode 8 side of the deionization compartment 2 is defined as the second concentrating compartment 4.

[0021] Next, the production of deionized water (treated water) by the EDI device 1 of this embodiment will be briefly described. With a DC voltage applied between the cathode 7 and the anode 8, the water to be treated is passed through the first concentrating chamber 3, the second concentrating chamber 4, and the deionization chamber 2. The water to be treated may be, for example, the permeate of a reverse osmosis membrane device used in a pure water production system or the like.

[0022] Among the ionic components in the treated water, Na + Cations (positive ions) such as Cl move to the cathode 7 due to the electric field. -Anions (negative ions) such as cations and anions move toward the anode 8 due to the electric field. Cations pass through cation exchange membrane 5 and move to the first concentrating chamber 3, and anions pass through anion exchange membrane 6 and move to the second concentrating chamber 4. In this way, deionization (demineralization) processing is carried out in the deionization chamber 2, and deionized water flows out as treated water (pure water). Meanwhile, concentrated water containing cations is discharged from the first concentrating chamber 3, and concentrated water containing anions is discharged from the second concentrating chamber 4. The direction in which the water to be treated flows in the deionization chamber 2 is opposite to the direction in which the water to be treated flows in the first and second concentrating chambers 3, 4.

[0023] According to the EDI device 1 of the present embodiment, it is possible to suppress the back diffusion of a weak acid in the production of the above-mentioned deionized water (treated water). The effect of suppressing the back diffusion of a weak acid will be specifically described below.

[0024] 2 is a schematic diagram for explaining the reverse diffusion of a weak acid. In this example, the deionization compartment 2 located on the left side of the drawing is used as the reference. A first concentration compartment 3 is disposed on the cathode side of this deionization compartment 2 via a cation exchange membrane 5, and another deionization compartment 2 is disposed on the cathode side of this first concentration compartment 3 via an anion exchange membrane 6.

[0025] The cation exchange membrane 5 is an ion exchange membrane that selectively allows cations to pass through. The principle is that the membrane itself is negatively charged to prevent the passage of negatively charged anions. In the area near the cation exchange membrane 5 of the first concentration compartment 3, a low pH state (H + The carbon dioxide flowing into the EDI device 1 is HCO3 - However, when it moves from the deionization compartment 2 (right side of Fig. 2) through the anion exchange membrane 6 to the first concentration compartment 3, it changes to the form of H2CO3 in the area near the cation exchange membrane 5. It then moves to the deionization compartment 2 (left side of Fig. 2) through the cation exchange membrane 5 as uncharged carbon dioxide (CO2). This type of reverse diffusion of weak acids is noticeable when the first concentration compartment 3 is filled with an anion exchange resin.

[0026] According to the EDI device 1 of the present embodiment, the portion 5c of the cation exchange membrane 5 is made thicker, and it is possible to suppress the permeation of carbon dioxide (CO2) through this portion 5c.

[0027] In addition, permeation of cations is also suppressed in the portion 5c (thick portion). For this reason, if the entire cation exchange membrane 5 is made thick, the movement of cations from the deionization compartment 2 to the first concentrating compartment 3 is suppressed, and as a result, the water quality of the treated water may deteriorate. In the EDI device 1 of this embodiment, only the portion 5c of the cation exchange membrane 5 is made thick, so that the movement of cations from the deionization compartment 2 to the first concentrating compartment 3 via the cation exchange membrane 5 can be sufficiently maintained.

[0028] Regarding the back diffusion of weak acids generated upstream of the flow of the water to be treated in the deionization chamber 2, carbon dioxide gas (CO2) that has moved to the deionization chamber 2 may undergo an ionization process and be captured by the ion exchange resin in the deionization chamber 2, and may be removed to the concentration chamber by an electric field. On the other hand, regarding the back diffusion of weak acids generated downstream of the flow of the water to be treated in the deionization chamber 2, carbon dioxide gas (CO2) that has moved to the deionization chamber 2 is discharged as treated water as it is. According to the EDI device 1 of this embodiment, a portion 5c (thick portion) of the cation exchange membrane 5 is located downstream of the flow of the water to be treated. Therefore, the back diffusion of weak acids can be effectively suppressed.

[0029] Furthermore, a part 5c of the cation exchange membrane 5 is thickened by overlapping the second cation exchange membrane 5b on the first cation exchange membrane 5a. For example, when the second cation exchange membrane 5b is formed on the surface of the first cation exchange membrane 5a on the desalting compartment 2 side, the water to be treated flowing through the desalting compartment 2 passes between the second cation exchange membrane 5b and the first cation exchange membrane 5a (interface) and is discharged as treated water with insufficient transfer of cationic components. In the EDI device 1 of this embodiment, the second cation exchange membrane 5b is formed on the surface of the first cation exchange membrane 5a on the first concentration compartment 3 side (opposite side to the desalting compartment 2). This makes it possible to prevent the water to be treated from passing between the second cation exchange membrane 5b and the first cation exchange membrane 5a (interface) and being discharged as treated water with insufficient transfer of cationic components.

[0030] Furthermore, the deionization compartment 2, the first concentration compartment 3, and the second concentration compartment 4 may each have a frame with an opening. In this case, the cation exchange membrane 5 is sandwiched between the frame of the deionization compartment 2 and the frame of the first concentration compartment 3, and the anion exchange membrane 6 is sandwiched between the frame of the deionization compartment 2 and the frame of the second concentration compartment 4. The cation exchange membrane 5 is in contact with the entire opening of the frame of the deionization compartment 2. The ratio of the area of ​​the second cation exchange membrane 5b to the area of ​​this opening is, for example, 10% or more and 60% or less, more preferably 50% or less. Within this range, it is possible to suppress the back diffusion of weak acids while maintaining the exchange of cations between the deionization compartment 2 and the first concentration compartment 3, and to meet the water quality required for the treated water (pure water).

[0031] Furthermore, by suppressing the back diffusion of weak acids, it is possible to provide highly pure water. For example, with a DC voltage applied, water to be treated having a total carbon dioxide concentration of 0.5 mg-CO2 / L or more and 5.0 mg-CO2 / L or less is supplied to the desalting chamber 2. In this case, highly pure water can also be obtained. Water to be treated having a total carbon dioxide concentration of 0.5 mg-CO2 / L or more may be supplied to the first concentrating chamber 3. In this case, highly pure water can be obtained due to the effect of suppressing the back diffusion of weak acids.

[0032] Second embodiment 3 is a schematic diagram showing the configuration of an electrodeionized water production apparatus according to a second embodiment of the present invention. The EDI device 1A of this embodiment has basically the same configuration as the EDI device 1 of the first embodiment, but differs in that a part of the anion exchange membrane 6, not the cation exchange membrane 5, is made thicker. To avoid duplication of explanation, detailed explanation of the same configuration as the EDI device 1 of the first embodiment will be omitted.

[0033] At least a cation exchange resin is filled in the second concentration chamber 4. As an example, in this embodiment, a mixed resin of a cation exchange resin and an anion exchange resin is filled in the second concentration chamber 4. The first concentration chamber 3 has the same structure as the second concentration chamber 4.

[0034] A portion 6c of the anion exchange membrane 6 is thicker in the direction opposite to the deionization compartment 2 (toward the second concentration compartment 4) than the other portions. More specifically, the anion exchange membrane 6 has a first anion exchange membrane 6a and a second anion exchange membrane 6b. The first anion exchange membrane 6a and the second anion exchange membrane 6b are both homogeneous membranes, but are not limited thereto. The first anion exchange membrane 6a and the second anion exchange membrane 6b may be heterogeneous membranes. The first anion exchange membrane 6a and the second anion exchange membrane 6b can be called the first ion exchange membrane and the second ion exchange membrane, respectively.

[0035] The first anion exchange membrane 6a is provided so as to contact the entire region including the first region 2a and the second region 2b of the deionization compartment 2. The second anion exchange membrane 6b is provided on the surface of the first anion exchange membrane 6a on the second concentration compartment 4 side (opposite the deionization compartment 2). The area of ​​the second anion exchange membrane 6b is smaller than the area of ​​the first anion exchange membrane 6a. The second anion exchange membrane 6b faces the second region 2b via the first anion exchange membrane 6a. The facing surfaces of the second anion exchange membrane 6b and the second region 2b have approximately the same area, but are not limited to this. As will be described in detail later, the area of ​​the second anion exchange membrane 6b may be different from the area of ​​the second region 2b as long as the ratio of the area of ​​the second anion exchange membrane 6b to the area of ​​the opening of the frame of the deionization compartment 2 is 60% or less.

[0036] The portion 6c of the anion exchange membrane 6 is a portion that is thickened by overlapping the second anion exchange membrane 6b on the first anion exchange membrane 6a. In the anion exchange membrane 6, the portion 6c is located downstream with respect to the flow direction of the water to be treated flowing through the desalting chamber 2. In this embodiment, the downstream end of the portion 6c is located at the most downstream part of the desalting chamber 2, but is not limited to this. The portion 6c can be provided at any position downstream with respect to the flow direction of the water to be treated. Furthermore, two or more portions 6c may be provided, or a structure in which a plurality of second anion exchange membranes 6b are overlapped to make the portion thicker may be used.

[0037] In the EDI device 1A of this embodiment, similarly to the EDI device 1 of the first embodiment, a deionization (demineralization) process is performed in the deionization chamber 2, and deionized water flows out as treated water (pure water). In the first concentration chamber 3, concentrated water containing cations is discharged, and in the second concentration chamber 4, concentrated water containing anions is discharged.

[0038] According to the EDI device 1A of the present embodiment, it is possible to suppress the back diffusion of cations in the production of the above-mentioned deionized water (treated water). The effect of suppressing the back diffusion of cations will be specifically described below.

[0039] Generally, the anion exchange membrane 6 is considered to be impermeable to cations, but as the current is increased, it becomes permeable to a small extent to cations. Fig. 4 is a schematic diagram for explaining the back diffusion of cations in a structure in which the concentration compartment is filled with a cation exchange resin. Fig. 4 shows the movement of NaOH.

[0040] As shown in FIG. 4, the second concentrating chamber 4 is adjacent to the anode side of the deionization chamber 2 via the anion exchange membrane 6, and the second concentrating chamber 4 is filled with a cation exchange resin. In this structure, ultrapure water (UPW) is passed through the deionization chamber 2, and NaOH with a conductivity of 80 μS / cm is passed through the second concentrating chamber 4. At this time, a part of the NaOH passes through the anion exchange membrane 6 and moves to the deionization chamber 2 due to the current being applied. As a result, the NaOH in the treated water flowing out of the deionization chamber 2 increases, and the conductivity of the treated water increases to about 4.2±0.38 μS / cm when the current value is 1.0 A. As an example, the change in treated water quality (μS / cm) with respect to the change in current value (A) is shown in Table 1 below. [Table 1]

[0041] Fig. 5 is a schematic diagram for explaining the back diffusion of cations in a structure in which the concentration compartment is packed with an anion exchange resin. Fig. 5 shows the movement of NaOH.

[0042] As shown in FIG. 5, the second concentrating chamber 4 is adjacent to the anode side of the deionization chamber 2 via the anion exchange membrane 6, and the second concentrating chamber 4 is filled with anion exchange resin. In this structure, ultrapure water (UPW) is passed through the deionization chamber 2, and NaOH with a conductivity of 80 μS / cm is passed through the second concentrating chamber 4. At this time, when electricity is applied, some of the NaOH passes through the anion exchange membrane 6 and moves to the deionization chamber 2, but the amount of movement is small. For example, when the current value is 1.0 A, the conductivity of the treated water only increases to about 0.18 μS / cm. As an example, the change in treated water quality (μS / cm) with respect to the change in current value (A) is shown in Table 2 below. [Table 2]

[0043] As can be seen from the results of Tables 1 and 2 above, when the concentration compartment is filled with cation exchange resin, back diffusion of cations occurs, and there is a high possibility that the quality of the treated water will decrease. According to the EDI device 1A of the present embodiment, the portion 6c of the anion exchange membrane 6 is made thicker, and it is possible to suppress the permeation of cations through this portion 6c.

[0044] In addition, the permeation of anions is also suppressed in the portion 6c (thick portion). For this reason, if the entire anion exchange membrane 6 is made thick, the movement of anions from the deionization compartment 2 to the second concentrating compartment 4 is suppressed, resulting in a deterioration in the quality of the treated water. In the EDI device 1A of this embodiment, only the portion 6c of the anion exchange membrane 6 is made thick, so that the movement of anions from the deionization compartment 2 to the second concentrating compartment 4 via the anion exchange membrane 6 can be sufficiently maintained.

[0045] Regarding the back diffusion of cations generated upstream of the deionization compartment 2, there is a possibility that the cations that have migrated to the deionization compartment 2 may be captured by the ion exchange resin in the deionization compartment 2 and may be removed to the concentration compartment by the electric field. On the other hand, regarding the back diffusion of cations generated downstream of the deionization compartment 2, the cations that have migrated to the deionization compartment 2 are simply discharged as treated water. According to the EDI device 1A of this embodiment, a portion 6c (thick portion) of the anion exchange membrane 6 is located on the downstream side. Therefore, the back diffusion of cations can be effectively suppressed.

[0046] Furthermore, a part 6c of the anion exchange membrane 6 is thickened by overlapping the second anion exchange membrane 6b on the first anion exchange membrane 6a. For example, when the second anion exchange membrane 6b is formed on the surface of the first anion exchange membrane 6a on the desalting compartment 2 side, the water to be treated flowing through the desalting compartment 2 passes between the second anion exchange membrane 6b and the first anion exchange membrane 6a (interface), and is discharged as treated water with insufficient exchange of anion components. In the EDI device 1A of this embodiment, the second anion exchange membrane 6b is formed on the surface of the first anion exchange membrane 6a on the second concentration compartment 4 side (opposite side to the desalting compartment 2). This makes it possible to prevent the water to be treated from passing between the second anion exchange membrane 6b and the first anion exchange membrane 6a (interface) and being discharged as treated water with insufficient exchange of anion components.

[0047] In the EDI device 1A of this embodiment, similarly to the first embodiment, the deionization compartment 2, the first concentrating compartment 3, and the second concentrating compartment 4 may each be configured with a frame having an opening. In this case, the anion exchange membrane 6 is in contact with the entire opening of the frame of the deionization compartment 2. The ratio of the area of ​​the second anion exchange membrane 6b to the area of ​​this opening is, for example, 10% or more and 60% or less, more preferably 50% or less. Within this range, it is possible to suppress the back diffusion of cations while maintaining the exchange of anions between the deionization compartment 2 and the second concentrating compartment 4, and it is possible to satisfy the water quality required for the treated water (pure water).

[0048] Furthermore, by suppressing the back diffusion of cations, it is possible to provide highly pure water. For example, with a DC voltage applied, water to be treated having a sodium ion concentration of 0.1 ppm or more and 0.7 ppm or less is supplied to the desalting chamber 2. In this case, highly pure water can also be obtained. Alternatively, water to be treated having a sodium ion concentration of 0.1 ppm or more and 0.7 ppm or less may be supplied to the second concentrating chamber 4. In this case, highly pure water can be obtained due to the effect of suppressing the back diffusion of cations.

[0049] (Third embodiment) 6 is a schematic diagram showing the configuration of an electrodeionized water production apparatus according to a third embodiment of the present invention. The EDI device 1B of this embodiment has basically the same configuration as the EDI device 1 of the first embodiment, except that a part of the anion exchange membrane 6 is thickened. To avoid duplication of explanation, detailed explanation of the same configuration as the EDI device 1 of the first embodiment will be omitted. The first concentration compartment 3 and the second concentration compartment 4 are filled with a mixed resin of a cation exchange resin and an anion exchange resin.

[0050] The anion exchange membrane 6 is the same as that described in the second embodiment. That is, the EDI device 1B of this embodiment has the cation exchange membrane 5 described in the first embodiment and the anion exchange membrane 6 described in the second embodiment.

[0051] In the EDI device 1B of this embodiment, similarly to the EDI device 1 of the first embodiment, a deionization (demineralization) process is performed in the deionization chamber 2, and deionized water flows out as treated water (pure water). In the first concentration chamber 3, concentrated water containing cations is discharged, and in the second concentration chamber 4, concentrated water containing anions is discharged.

[0052] According to the EDI device 1B of this embodiment, in the production of the above-mentioned deionized water (treated water), it is possible to suppress both the back diffusion of the weak acid and the back diffusion of the cations. The effect of suppressing the back diffusion of the weak acid and the cations is as described in the first and second embodiments. Furthermore, the EDI device 1B of this embodiment provides the same effects as those described in the first and second embodiments.

[0053] In the above-mentioned first to third embodiments, the deionization compartment 2 may have a multi-layer structure in which the first regions 2a and the second regions 2b are alternately arranged in the flow direction of the water to be treated. For example, the deionization compartment 2 may have a four-layer (four-tiered multiple bed) structure. When the deionization compartment 2 has a multi-layer structure, from the viewpoint of maintaining the transfer of ions, it is preferable to make the cation exchange membrane beside the first region 2a, in which the proportion of cation exchange resin is high, thin, and to make the anion exchange membrane beside the second region 2b, in which the proportion of anion exchange resin is high, thin. On the other hand, from the viewpoint of suppressing back diffusion, it is preferable to partially thicken the cation exchange membrane 5 and the anion exchange membrane 6 in the downstream portion closer to the treated water side.

[0054] Next, the effects of the EDI device of the present invention will be specifically described with reference to Comparative Examples 1-2 and Examples 1-3.

[0055] Comparative Example 1 FIG. 7 is a schematic diagram showing the configuration of the EDI device of Comparative Example 1. The EDI device 100A of Comparative Example 1 has the same configuration as the EDI device 1 shown in FIG. 1, but the cation exchange membrane is different. In the EDI device 100A, the cation exchange membrane 5A has a constant thickness. The first concentration chamber 3 and the second concentration chamber 4 are filled with a mixed resin in which a cation exchange resin and an anion exchange resin are mixed in a ratio of 5:5. In the desalting chamber 2, the first region 2a is filled with a mixed resin (MB1) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the cation exchange resin is high. The second region 2b is filled with a mixed resin (MB2) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the anion exchange resin is high.

[0056] The specific resistance of treated water was measured in the EDI device 100A of Comparative Example 1. The measured value was 14.9 MΩ·cm.

[0057] Example 1 FIG. 8 is a schematic diagram showing the configuration of an EDI device according to a first embodiment of the present invention. The EDI device according to the first embodiment is the EDI device 1 shown in FIG. 1. The first concentration compartment 3 and the second concentration compartment 4 are filled with a mixed resin in which a cation exchange resin and an anion exchange resin are mixed in a ratio of 5:5. In the deionization compartment 2, the first region 2a is filled with a mixed resin (MB1) in which a cation exchange resin and an anion exchange resin are mixed so that the proportion of the cation exchange resin is higher. The second region 2b is filled with a mixed resin (MB2) in which a cation exchange resin and an anion exchange resin are mixed so that the proportion of the anion exchange resin is higher.

[0058] The treated water resistivity was measured for the EDI device 1 of Example 1. The measured value was 15.5 MΩ·cm. It was found that the treated water resistivity was improved compared to the EDI device 100A of Comparative Example 1.

[0059] Example 2 FIG. 9 is a schematic diagram showing the configuration of an EDI device according to a second embodiment of the present invention. The EDI device according to the second embodiment is the EDI device 1A shown in FIG. 3. The first concentration chamber 3 and the second concentration chamber 4 are filled with a mixed resin in which a cation exchange resin and an anion exchange resin are mixed in a ratio of 5:5. In the deionization chamber 2, the first region 2a is filled with a mixed resin (MB1) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the cation exchange resin is higher. The second region 2b is filled with a mixed resin (MB2) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the anion exchange resin is higher.

[0060] The resistivity of treated water was measured for the EDI device 1A of Example 2. The measured value was 16.1 MΩ·cm. It was found that the resistivity of treated water was improved compared to the EDI device 100A of Comparative Example 1.

[0061] Comparative Example 2 Fig. 10 is a schematic diagram showing the configuration of an EDI device of Comparative Example 2. The EDI device 100B of Comparative Example 2 has a similar configuration to that of Comparative Example 1 shown in Fig. 7, but differs in the ratio of the mixed resin filled in the first concentration chamber 3 and the second concentration chamber 4. In the EDI device 100B, the first concentration chamber 3 and the second concentration chamber 4 are filled with a mixed resin (MB2) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the anion exchange resin is higher.

[0062] The specific resistance of treated water was measured in the EDI device 100B of Comparative Example 2. The measured value was 12.7 MΩ·cm.

[0063] Example 3 Fig. 11 is a schematic diagram showing the configuration of an EDI device according to a third embodiment of the present invention. The EDI device 1 of the third embodiment has the same configuration as that of the first embodiment shown in Fig. 8, but the ratio of the mixed resin filled in the first concentration chamber 3 and the second concentration chamber 4 is different. In the EDI device 1 of the third embodiment, the first concentration chamber 3 and the second concentration chamber 4 are filled with a mixed resin (MB2) in which a cation exchange resin and an anion exchange resin are mixed so that the ratio of the anion exchange resin is higher.

[0064] The treated water resistivity was measured for the EDI device 1 of Example 3. The measured value was 15.4 MΩ·cm. It was found that the treated water resistivity was improved compared to the EDI device 100B of Comparative Example 2. [Explanation of symbols]

[0065] 1. Electrodeionized water production equipment 2 Desalination room 3. First Concentration Chamber 4. Second Concentration Chamber 5. Cation exchange membrane 6 Anion exchange membrane 7 Cathode 8 Anode

Claims

1. An electrodeionization water production apparatus having an anode, a cathode, a deionization compartment provided between the anode and the cathode, a first concentrating compartment provided on the cathode side of the deionization compartment via a cation exchange membrane, and a second concentrating compartment provided on the anode side of the deionization compartment via an anion exchange membrane, an anion exchange resin filled in the first concentration chamber and a portion of the ion exchange membrane, which is the anion exchange membrane, that is, the cation exchange membrane, that is, the cation exchange resin is filled in the second concentration chamber and a portion of the ion exchange membrane, which is the anion ...cation exchange resin is filled in the second concentration chamber and a portion of the cation exchange resin is filled in the second concentration chamber and a portion of the cation exchange resin is filled in the second concentration chamber and a portion of the cation exchange resin is filled in the second concentration chamber and a portion of the cation exchange resin is filled in the second concentration chamber and a portion of the cation exchange resin is filled in the second concentration chamber.

2. 2. The electrodeionization water production apparatus according to claim 1, wherein the portion of the ion exchange membrane is located downstream in a flow direction of the water to be treated flowing through the deionization compartment.

3. 2. The electrodeionization water production apparatus according to claim 1, wherein the ion exchange membrane comprises a first ion exchange membrane and at least one second ion exchange membrane having an area smaller than that of the first ion exchange membrane, the first ion exchange membrane being disposed on the side of the desalting compartment, and the at least one second ion exchange membrane being overlapped on a surface of the first ion exchange membrane opposite the desalting compartment to form the part.

4. 4. The electrodeionization water production apparatus according to claim 3, wherein the deionization compartment comprises a frame body having an opening, the first ion exchange membrane is in contact with the entire opening of the frame body, and the ratio of the area of ​​the second ion exchange membrane to the area of ​​the opening is 60% or less.

5. 4. The electrodeionization apparatus of claim 3, wherein the first ion exchange membrane and the second ion exchange membrane are each a homogeneous membrane.

6. 4. The electrical deionization water production apparatus of claim 3, wherein the deionization compartment has a first region on the upstream side and a second region on the downstream side with respect to the flow direction of the water to be treated flowing through the deionization compartment, and the second ion exchange membrane is located in the second region.

7. The first region is filled with a cation exchange resin and an anion exchange resin such that the ratio of the cation exchange resin is high, 7. The electrodeionization water production apparatus according to claim 6, wherein the second region is filled with the cation exchange resin and the anion exchange resin such that the ratio of the anion exchange resin is higher in the second region.

8. 2. The electrodeionization water production apparatus according to claim 1, wherein the first and second concentration compartments are filled with a mixed resin of the anion exchange resin and the cation exchange resin, respectively.

9. The electrodeionized water production apparatus according to claim 1 is used to produce deionized water having a sodium ion concentration of 0.1 ppm or more or a total carbonate concentration of 0.5 mg-CO2 or more in a state where a DC voltage is applied between the anode and the cathode. ２ / L or more of water to be treated is supplied to the deionization chamber to obtain deionized pure water.

10. The water to be treated having a sodium ion concentration of 0.1 ppm or more is supplied to the second concentration chamber, or the total carbon dioxide concentration is 0.5 mg-CO ２ 10. The method for producing pure water according to claim 9, wherein the water to be treated is supplied to the first concentrating chamber in an amount of at least 1000 ml / L.

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