Apparatus for producing electrodeionized water and method for producing pure water using same

Abstract

In a desalination chamber (23) of an electrodeionized water production device (10), among anion exchange resins and cation exchange resins, the cation exchange resin having a large particle diameter preferably having a particle diameter of more than 0.4 mm is set to L1, the anion exchange resin having a large particle diameter preferably having a particle diameter of more than 0.4 mm is set to L2, and the cation exchange resin having a small particle diameter preferably having a particle diameter of 0.1-0.4 mm (inclusive) is set to S1; the desalination chamber (23) is filled with at least three resins selected from the group consisting of combinations thereof, where S2 is an anion exchange resin having a small particle diameter, preferably having a particle diameter of 0.1-0.4 mm.

Description

Technical Field

[0001] The invention relates to an electrodeionized water manufacturing device and a method for manufacturing pure water using the electrodeionized water manufacturing device. Background Art

[0002] As one of the devices that produces deionized water from treated water, there is an electrodeionization water production device (also called an EDI (Electrodeionization) device. Hereinafter, the electrodeionization water production device will also be referred to as an EDI device.). The EDI device is a device that combines electrophoresis and electrodialysis, and has a structure in which a desalination chamber divided by a pair of ion exchange membranes is arranged between an anode and a cathode. In the EDI device, at least the desalination chamber is filled with ion exchange resin. In the EDI device, treated water is passed into the desalination chamber while a DC voltage is applied between the anode and the cathode, thereby desalting the treated water in the desalination chamber, and the treated water, from which the ion components have been removed, flows out of the desalination chamber.

[0003] Patent Document 1 addresses the technical challenges of increasing the removal efficiency of carbonic acid components, silica components, and the like contained in the treated water, suppressing voltage increases, and increasing current density. To address this technical challenge, Patent Document 1 divides the desalination chamber into multiple chambers by placing a partitioning member within the chamber. Anion exchange resin and cation exchange resin are mixed and filled throughout the chamber, with the anion exchange resin being equal to or greater than the cation exchange resin by volume. Furthermore, along the flow of water within the desalination chamber, the mixing ratio of the anion exchange resin on one side, upstream, and downstream, is set to 66-80% by volume, while the mixing ratio of the anion exchange resin on the other side is set to 50-65% by volume.

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2005-193205 Summary of the Invention

[0005] Technical problem to be solved by the invention In the EDI device described in Patent Document 1, the anion exchange resin is filled in the desalination chamber at a higher ratio than the cation exchange resin, so that a high anion removal rate can be obtained. On the other hand, paragraph

[0018] of Patent Document 1 states that "If the ratio of the anion exchange resin is increased, the OH - The amount of ions produced increases, but H + ions decrease, so Na + The removal of ions is reduced, making the resistivity of the treated water worse. From this description, it can be seen that due to the small proportion of cation exchange resin, sodium ions (Na +) and other cations, resulting in a decrease in the resistivity of the treated water when the EDI device is operated for a long time. This results in a decrease in the quality of the treated water. Furthermore, there is a demand for an electrodeionized water production device that can remove impurity ions from the treated water in an energy-efficient manner.

[0006] An object of the present invention is to provide an EDI device and a method for producing pure water using the same, wherein the EDI device can produce high-purity deionized water in an energy-saving manner even when the EDI device is operated for a long time.

[0007] Technical solutions to technical problems The EDI device (electrodeionized water production device) of the present invention is an electrodeionized water production device having the following structure: an anode; a cathode; a desalination chamber, which is arranged between the anode and the cathode, divided by an anion exchange membrane located on the anode side and a cation exchange membrane located on the cathode side, and filled with an anion exchanger and a cation exchanger; and a concentrating chamber, which is arranged on the cathode side of the cation exchange membrane and filled with an anion exchanger and a cation exchanger, wherein: The anion exchanger and the cation exchanger are anion exchange resin and cation exchange resin, respectively. When the large-particle cation exchange resin in the anion exchange resin and the large-particle anion exchange resin is L1, the large-particle anion exchange resin is L2, the small-particle cation exchange resin is S1, and the small-particle anion exchange resin is S2, the desalination chamber is filled with at least three resins selected from the combination thereof.

[0008] The method for producing pure water of the present invention is characterized by supplying treated water having a sodium ion concentration of 0.1 ppm (mg / L) or higher and 0.7 ppm or lower to a desalination chamber while applying a DC voltage between the anode and cathode using the electrodeionized water production apparatus of the present invention, thereby producing pure water as deionized water. Alternatively, the method for producing pure water of the present invention is characterized by supplying treated water having a total carbonic acid concentration of 0.5 ppm as CO₂ (mgCO₂ / L) or higher and 5.0 ppm as CO₂ or lower to a desalination chamber while applying a DC voltage between the anode and cathode using the electrodeionized water production apparatus of the present invention, thereby producing pure water as deionized water.

[0009] Effects of the Invention According to the present invention, it is possible to provide an EDI device capable of producing high-purity deionized water in a power-saving manner even when the EDI device is operated for a long time, and a method for producing pure water using the EDI device. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1This is a diagram showing an EDI device according to one embodiment of the present invention.

[0011] Figure 2 This is a schematic cross-sectional view showing the mechanical structure of the EDI device.

[0012] Figure 3 yes Figure 2 The assembled perspective view of the EDI device is shown.

[0013] Figure 4 This is a diagram showing an EDI device according to another embodiment.

[0014] Figure 5 This is a diagram showing an EDI device according to another embodiment.

[0015] Figure 6 This is a diagram illustrating the movement of carbonic acid from the concentrating compartment to the desalting compartment.

[0016] Figure 7 It shows that for Example 1, Comparative Examples 1 and 2, SV=450h is estimated. -1 A graph showing the relationship between the operating differential pressure during operation and the volume ratio of four ion exchange resins. DETAILED DESCRIPTION

[0017] The electrodeionized water production device (EDI device) of the present invention comprises: an anode; a cathode; a desalination chamber, between which an anion exchanger and a cation exchanger are filled, separated by an anion exchange membrane located on the anode side and a cation exchange membrane located on the cathode side; and a concentrating chamber, located on the cathode side of the cation exchange membrane and filled with an anion exchanger and a cation exchanger. It should be noted that in this specification, anion exchangers and cation exchangers are sometimes collectively referred to as ion exchangers.

[0018] The anion exchanger and cation exchanger filled in the desalination chamber are anion exchange resin (AER) and cation exchange resin (CER), respectively. In this specification, anion exchange resin and cation exchange resin are sometimes collectively referred to as ion exchange resin.

[0019] Ion exchange resins are in the form of beads or granules, and their particle size is usually 1 mm or less. The particle size of the ion exchange resin can be measured using a sieve (screen), or the value in the catalog of the ion exchange resin manufacturer can be used as the particle size in the present invention.

[0020] In the present invention, anion exchange resins and cation exchange resins are defined as follows according to particle size.

[0021] The cation exchange resin L1 having a large particle size is preferably a cation exchange resin having a particle size exceeding 0.4 mm, preferably 1 mm or less, and more preferably 0.7 mm or less.

[0022] The anion exchange resin L2 having a large particle size is preferably an anion exchange resin having a particle size exceeding 0.4 mm, preferably 1 mm or less, and more preferably 0.7 mm or less.

[0023] The cation exchange resin having a particle size of preferably 0.1 mm or more and 0.4 mm or less is used as the small-particle-size cation exchange resin S1.

[0024] The anion exchange resin having a particle size of preferably 0.1 mm or more and 0.4 mm or less is used as the small-particle-size anion exchange resin S2.

[0025] In the present invention, when the ion exchange resin is defined as above, the desalination chamber is filled with at least three ion exchange resins selected from their combination, preferably filled with large particle size cation exchange resin L1, large particle size anion exchange resin L2 and small particle size anion exchange resin S2.

[0026] In the present invention, the desalination chamber is filled with at least three of the four aforementioned ion exchange resins. In other words, at least one of an anion exchange resin and a cation exchange resin is filled with two resins having different particle sizes. This filling with two resins of different particle sizes allows the production of high-purity deionized water with minimal energy consumption, even during long-term operation of the EDI system.

[0027] In particular, the present invention achieves at least the same quality of the treated water as compared to an EDI in which the desalination chamber is filled with an anion exchange resin of the same particle size as the anion exchanger and a cation exchange resin of the same particle size as the cation exchanger (including a case where the anion exchange resin and the cation exchange resin have different particle sizes), thereby enabling the production of high-purity deionized water with energy conservation.

[0028] The desalting chamber may have a mixed particle size layer formed of two types of ion exchange resins having different particle sizes. Examples of such a configuration include the following.

[0029] 1) The ion exchange resin layers in the desalination chamber are all mixed particle size layers.

[0030] 2) Part of the ion exchange resin layer in the desalting chamber is a mixed particle size layer, and the other layers are, for example, of the following configuration.

[0031] a) The other layer is a layer (single bed) formed of any one of the four ion exchange resins.

[0032] b) The other layer is a combination of ion exchange resins having the same particle size, that is, a layer (mixed bed) in which a large-particle-size cation exchange resin L1 and a large-particle-size anion exchange resin L2 are mixed.

[0033] c) The other layer is a layer formed by mixing a cation exchange resin S1 having a small particle size and an anion exchange resin S2 having a small particle size.

[0034] d) Other layers are layers formed by laminating a plurality of the layers of b) and c) above.

[0035] In the mixed particle size layer within the desalination chamber, the mixing ratio L2:S2 of the large-particle anion exchange resin L2 and the small-particle anion exchange resin S2 is preferably within a range of 1:1 to 5:1. If the ratio of the large-particle anion exchange resin is too high, sufficient removal performance for weakly acidic components cannot be achieved, while if the ratio of the small-particle anion exchange resin is too high, the water flow pressure difference may increase. The mixing ratio L2:S2 of the large-particle anion exchange resin L2 and the small-particle anion exchange resin S2 can be determined by mixing the large-particle anion exchange resin L2 and the small-particle anion exchange resin S2 to form the mixed particle size layer, removing the mixed particle size layer from the desalination chamber, classifying it using a sieve to separate it into large-particle and small-particle sizes, and measuring the apparent volume of each particle.

[0036] EDI is usually operated at a flow rate faster than that of conventional ion exchange resin devices, i.e., SV = 150 to 300 h -1 The allowable operating pressure difference is about 0.2 MPa. Figure 7 It is known that the volume ratio of the four ion exchange resins filled in the desalination chamber, i.e., large-particle cation exchange resin L1, large-particle anion exchange resin L2, small-particle cation exchange resin S1, and small-particle anion exchange resin S2, preferably satisfies the following relationship.

[0037] That is, it is preferred to satisfy the relationship (S1+S2) / (L1+L2)<0.6, and in particular, (S1+S2) / (L1+L2)≤0.5. The volume referred to in this embodiment refers to the volume of the ion exchange resin in a free state. In other words, it is the apparent volume of the ion exchange resin when not constrained by a space such as a desalting chamber or a concentrating chamber, and also includes the voids between the particles of the ion exchange resin. Therefore, the total volume of the anion exchange resin and the cation exchange resin filled in the mixed bed refers to the apparent volume of the mixture of the anion exchange resin and the cation exchange resin in a free state. The volume of the anion exchange resin or the cation exchange resin alone is the apparent volume of each ion exchange resin alone in a free state. This apparent volume can be determined by separating each ion exchange resin from the mixture of the anion exchange resin and the cation exchange resin and measuring the apparent volume of each ion exchange resin after separation.

[0038] When the desalination chamber is filled with anion exchangers and cation exchangers, the desalination chamber can be divided into multiple zones arranged in the direction of the treated water flow. That is, the desalination chamber is divided into multiple zones along the flow of the treated water. Furthermore, it is preferred that the proportion of cation exchangers is increased in the upstreammost zone, and the proportion of anion exchangers is increased in the downstreammost zone.

[0039] In a specific preferred embodiment, among the multiple zones, the zone located most upstream of the flow of the treated water is designated as the first zone, and the zone located most downstream is designated as the second zone. Furthermore, the first zone is filled with a mixture of anion and cation exchangers such that the volume ratio of the cation exchanger to the total volume of the anion and cation exchangers in the first zone is preferably greater than 50% and less than 90%, more preferably greater than 60% and less than 85%, and even more preferably greater than 70% and less than 80%. Furthermore, the second zone is filled with a mixture of anion and cation exchangers such that the volume ratio of the anion exchanger to the total volume of the anion and cation exchangers in the second zone is preferably greater than 50% and less than 90%, more preferably greater than 60% and less than 85%, and even more preferably greater than 70% and less than 80%. As a result, in the desalination chamber, cations such as sodium ions are preferentially removed at the most upstream location, while anions containing weak acidic components such as carbonic acid, silicon dioxide (silicic acid), and boron (boric acid) are preferentially removed at the most downstream location. Therefore, the EDI device can operate stably in a wide range of water quality related to the treated water. In addition, it can achieve high anion removal efficiency including weak acid components while preventing the reduction of the resistivity of the treated water due to leakage of cations.

[0040] When the desalination chamber is divided into multiple zones, the number of zones generated by the division can be two or more. There is no need to provide components such as spacers to physically separate the divided zones. When filling the desalination chamber with ion exchangers, the ion exchangers can be filled in a manner that varies the mixing ratio for each zone. When divided into two zones, the upstreammost zone refers to the zone located upstream of the two zones, and the downstreammost zone refers to the zone located downstream of the two zones. When the desalination chamber is divided into three or more zones, in zones other than the upstreammost zone and the downstreammost zone, either anion exchange resin or cation exchange resin can be filled in a single bed, or anion exchange resin and cation exchange resin can be mixed and filled in any mixing ratio.

[0041] With respect to the desalination chamber and the concentrating chamber, the length between the anode and the cathode along the direction of the electric field is referred to as the thickness. The thickness of the layer of the ion exchanger filled in the desalination chamber and the concentrating chamber is also defined in the same way. The thickness direction is a direction perpendicular to the flow direction of the treated water in the desalination chamber and the concentrating chamber. If the thickness of the layer of the ion exchanger in each of the multiple regions along the direction perpendicular to the flow direction of the treated water in the desalination chamber is less than 9 mm, it is confirmed that the water quality of the deionized water discharged from the desalination chamber is reduced. Therefore, the thickness of the layer of the ion exchanger in each of the multiple regions along the direction perpendicular to the flow direction of the treated water in the desalination chamber is preferably greater than 10 mm and less than 25 mm, and more preferably greater than 15 mm and less than 20 mm.

[0042] When the treated water or the water supplied to the concentrating chamber contains hardness components such as calcium or magnesium, for example, at 0.05 to 0.1 ppm as CaCO₃, the applied voltage in the EDI device tends to increase. In the EDI device according to the present invention, the concentrating chamber is also filled with an anion exchanger and a cation exchanger. Similar to the desalination chamber, an anion exchange resin and a cation exchange resin are used as the anion exchanger and cation exchanger, respectively, filled in the concentrating chamber. Preferably, the anion exchange resin and the cation exchange resin are mixed and filled in the concentrating chamber.

[0043] When anion exchange resin and cation exchange resin are mixed and filled throughout the concentrating compartment, the apparent volume of the anion exchange resin is represented by A, and the apparent volume of the cation exchange resin is represented by 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 the anion exchange resin and cation exchange resin are mixed and filled into the concentrating compartment, the mixing ratio A:C of the anion exchange resin and cation exchange resin can be determined in the same manner as described above. It is also possible to fill the concentrating compartment with only ion exchange resins with large particle sizes. To suppress the increase in applied voltage caused by the placement of cation exchange resin in the concentrating compartment, for example, a reverse osmosis membrane device is placed upstream of the EDI device. Furthermore, the concentration of hardness components in the treated water supplied to the desalination compartment is preferably 0.1 ppm as CaCO₃ or less. The hardness component concentration refers to the amount of calcium and magnesium converted to calcium carbonate (CaCO₃) and is expressed by the following formula.

[0044] Hardness [ppm as CaCO3] = (Calcium [ppm] × 2.5) + (Magnesium [ppm] × 4.1) Hereinafter, preferred embodiments will be described in detail with reference to the drawings.

[0045] Figure 1 The EDI device 10 according to one embodiment of the present invention is shown. In this EDI device 10, a concentrating chamber 22, a desalting chamber 23, and a concentrating chamber 24 are provided in order from the anode chamber 21 side between an anode chamber 21 including an anode 11 and a cathode chamber 25 including a cathode 12. The anode chamber 21 and the concentrating chamber 22 are adjacent to each other via a cation exchange membrane (CEM) 31. The concentrating chamber 22 and the desalting chamber 23 are adjacent to each other via an anion exchange membrane (AEM) 32. The desalting chamber 23 and the concentrating chamber 24 are adjacent to each other via a cation exchange membrane 33. The concentrating chamber 24 and the cathode chamber 25 are adjacent to each other via an anion exchange membrane 34. Therefore, the desalting chamber 23 is arranged between the anode 11 and the cathode 12, and is divided by the anion exchange membrane 32 arranged on the anode 11 side and the cation exchange membrane 33 arranged on the cathode 12 side. The treated water is supplied to the desalination chamber 23 and flows out of the desalination chamber 23 as deionized water (treated water) obtained by desalting the treated water. The concentration chambers 22 and 24 are supplied with the concentration chamber supply water and discharge the concentrated water. The anode chamber 21 and the cathode chamber 25 are both supplied with the electrode chamber supply water and discharge the electrode water. It should be noted that the electrode chamber (anode chamber 21 and cathode chamber 25) can also be configured to have a structure that also includes the concentration chambers 22 and 24 adjacent to the electrode chamber. In addition, Figure 1The flow of water in each chamber of the anode chamber 21, the concentration chamber 22, the desalination chamber 23, the concentration chamber 24 and the cathode chamber 25 is an example, and the flow direction of water in each chamber is arbitrary. For example, the flow of water in each chamber can also be independently controlled for each chamber. Figure 1 Direction opposite to that shown.

[0046] Inside the desalination chamber 23, at least three of the four ion exchange resins, including the large-particle cation exchange resin L1, the large-particle anion exchange resin L2, the small-particle cation exchange resin S1, and the small-particle anion exchange resin S2, are mixed in the desalination chamber. Preferably, the large-particle cation exchange resin L1, the large-particle anion exchange resin L2, and the small-particle anion exchange resin S2 are mixed. In other words, the ion exchange resin layer is configured in a mixed bed (MB) configuration. Note that, in Figures 1 to 6 In the figures, the large-particle cation exchange resin L1 and the small-particle cation exchange resin S1 are not distinguished by particle size and are described as CER. The large-particle anion exchange resin L2 and the small-particle anion exchange resin S2 are not distinguished by particle size and are described as AER. That is, in each figure, CER and AER include cases where the particle size is the same and cases where two particle sizes are included.

[0047] Along the flow of the treated water in the desalination chamber 23, the interior of the desalination chamber 23 is divided into two areas: area A and area B. Area A is the area on the upstream side of the flow of the treated water, that is, the area on the inlet side of the treated water. Area B is the area on the downstream side of the flow of the treated water, that is, the area on the outlet side of the deionized water. In both areas A and B, anion exchange resin and cation exchange resin are filled in a mixed bed, but the mixing ratio of anion exchange resin to cation exchange resin varies between areas. In area A, which is the inlet side of the treated water, the volume ratio of cation exchange resin to the total volume of anion exchange resin and cation exchange resin filled therein in a mixed bed manner is greater than 50% and less than 90%. Therefore, in area A, if considered in terms of volume ratio, the content of cation exchange resin is greater than the content of anion exchange resin. In contrast, in region B, which serves as the outlet for deionized water, the volume ratio of the anion exchanger to the total volume of the anion exchange resin and cation exchange resin packed therein in a mixed bed configuration is greater than 50% and less than 90%. In region B, the anion exchange resin content is greater than the cation exchange resin content, based on volume ratio. No partitions or other elements are provided between regions A and B. Treated water flowing between the ion exchange resin particles in region A flows directly into the spaces between the ion exchange resin particles in region B. When a partition is provided between regions A and B, a simple mesh or net-like partition can be used to prevent mixing of the ion exchange resins between the two regions.

[0048] In the EDI device 10, the anode chamber 21 is filled with a cation exchange resin, the concentrating chamber 22 is filled with an anion exchange resin and a cation exchange resin in a mixed bed, and the cathode chamber 25 is filled with an anion exchange resin. Alternatively, the concentrating chamber 22 may be filled with a single bed of anion exchange resin. On the cathode 12 side of the desalting chamber 23, the concentrating chamber 24, which is adjacent to the desalting chamber 23 via a cation exchange membrane 33, is filled with anion exchange resin and cation exchange resin. It should be noted that the anode chamber 21, the concentrating chamber 22, and the cathode chamber 25 do not necessarily need to be filled with ion exchange resin. Preferably, the anode chamber 21, the concentrating chamber 22, and the cathode chamber 25 are also filled with ion exchange resin to reduce the DC voltage applied between the anode 11 and the cathode 12 during transport of the EDI device 10. The filling rate of the ion exchanger, such as the ion exchange resin, in at least one of the desalting chamber 23 and the concentrating chamber 24 is preferably 100% or more and 110% or less, and more preferably 105% or more and 110% or less. Here, the filling factor refers to the value obtained by applying a DC voltage between the anode 11 and cathode 12 while passing water through the space filled with the ion exchanger (desalting chamber 23 or concentrating chamber 24), regenerating the ion exchanger. The apparent volume of the ion exchanger in its free state, removed from the space, is then divided by the volume of the space. Setting the filling factor to a value exceeding 100% eliminates internal voids. This prevents the ion exchange resin from flowing during water flow, allowing compartmentalization without the need for separators.

[0049] Next, the ion exchange resins used in the desalting chamber 23, the concentrating chamber 24 located on the cathode side of the desalting chamber 23, and even the anode chamber 21, concentrating chamber 22, and cathode chamber 25 in the EDI device 10 of this embodiment will be described. Common polymer bases for ion exchange resins include styrene-divinylbenzene copolymers, known as "styrene-based" resins, and acrylic acid-divinylbenzene copolymers, known as "acrylic-based" resins. Ion exchange resins are formed by modifying these polymer bases with ion exchange groups and are broadly classified into cation exchange resins (where the ion exchange groups exhibit acidic properties) and anion exchange resins (where the ion exchange groups exhibit basic properties). Furthermore, ion exchange resins can be classified into strongly acidic cation exchange resins, weakly acidic cation exchange resins, strongly basic anion exchange resins, and weakly basic anion exchange resins, depending on the type of ion exchange groups introduced. Examples of strongly basic anion exchange resins include those containing quaternary ammonium groups as ion exchange groups. Examples of weakly basic anion exchange resins include those containing primary, secondary, or tertiary amines as ion exchange groups. Examples of strongly acidic cation exchange resins include those having sulfonic acid groups as ion exchange groups. Examples of weakly acidic cation exchange resins include those having carboxyl groups as ion exchange groups. Any of these ion exchange resins can be used as the ion exchange resin filled in the device of the present invention.

[0050] Next, the operating method of the EDI device 10 of this embodiment will be described. In the EDI device 10 of this embodiment, as in a conventional EDI device, while applying a DC voltage between the anode 11 and the cathode 12, the treated water is supplied to the desalination chamber 23, and the feed water is supplied to the anode chamber 21, the concentrating chambers 22 and 24, and the cathode chamber 25. In the desalination chamber 23, the ion components in the treated water are desalted by the ion exchange resin, and the H generated by the dissociation of water caused by the applied DC voltage is converted into H. + ions and OH - ions to regenerate the ion exchange resin. + ) concentration is, for example, 0.1 ppm to 0.7 ppm. By supplying this treated water to the desalination chamber 23, pure water with a resistivity exceeding 10 MΩ·cm can be obtained from the desalination chamber 23 over a long period of time. The total carbonic acid concentration in the treated water is, for example, 0.5 ppm CO2 to 5.0 ppm as CO2.

[0051] However, a typical EDI device can have multiple basic structures consisting of "concentration chamber | ion exchange membrane | desalination chamber | ion exchange membrane | concentration chamber" arranged in parallel between the anode and cathode via an ion exchange membrane. In this case, two adjacent concentration chambers sandwiching an ion exchange membrane can be formed into a single concentration chamber by removing the sandwiched ion exchange membrane. Figure 1 In the illustrated EDI device 10, an anion exchange membrane 32, a desalination chamber 23, a cation exchange membrane 33, and a concentrating chamber 24 form a single basic structure. N (N is an integer greater than or equal to 1) of these basic structures can be arranged between the concentrating chamber 22 closest to the anode chamber 21 and the anion exchange membrane 34 adjacent to the cathode chamber 25. The ability to arrange multiple basic structures in parallel is indicated by the notation "×N" in the figure. When multiple basic structures are arranged in parallel, the concentrating chambers sandwiched between two adjacent desalination chambers 23 are all concentrating chambers 24 filled with both anion exchange resin and cation exchange resin.

[0052] In the EDI device 10 in which a plurality of basic structures are arranged in parallel, the desalination chamber 23 and the concentration chamber 24 are repeatedly arranged. For example, as shown in Japanese Patent Gazette No. 2015-199038, a plurality of frames each having an opening can be stacked in one direction so that an ion exchange membrane (anion exchange membrane and a cation exchange membrane) is sandwiched between them, and each chamber such as the desalination chamber 23 and the concentration chamber 24 can be composed of an ion exchange membrane respectively arranged in a frame and a pair of openings of the frame. The frame is manufactured, for example, by injection molding of plastic. In order to increase the thickness of the desalination chamber 23, in the stack of frames, the two or more continuous frames can be arranged in such a way that the ion exchange membrane is not arranged between the two or more continuous frames so that the two or more continuous frames can constitute the desalination chamber 23 as a whole. Figure 1 In the illustrated EDI device 10, the thickness of the desalting chamber 23 is, for example, approximately 20 mm, while the thickness of the concentrating chambers 22 and 24 is approximately 10 mm. Therefore, one desalting chamber can be formed of two frames, and each concentrating chamber 22 and 24 can be formed of one frame.

[0053] Figure 2 Indicates that when Figure 1 The EDI device 10 shown is an example of a mechanical structure in which a plurality of basic structures are arranged in parallel. Figure 3 yes Figure 2 An exploded perspective view of the EDI device 10 is shown. Figure 2 The ion exchange resins respectively filled in the anode chamber 21 , the concentrating chambers 22 and 24 , the desalting chamber 23 , and the cathode chamber 25 are not shown. Figure 2The EDI device 10 shown has a structure composed of multiple stacked frames 41 to 45, each of which has an opening. The anode 11 and cathode 12 are located at opposite ends of the stacking direction of the frames 41 to 45, facing each other through the openings of the frames 41 to 45. The anode chamber 21, the concentrating chamber 22, the desalting chamber 23, the concentrating chamber 24, and the cathode chamber 25 are respectively formed by the frames 41, 42, 43, 44, and 45. The anode 11 is fixed to the frame 41 via a pressure plate 46, and the cathode 12 is fixed to the frame 45 via a pressure plate 47. With respect to the desalting chamber 23, two frames 43 overlap to form a single desalting chamber. That is, the two frames 43 are adjacent to each other so that their openings together form the desalting chamber 23. If the thickness of the desalting chamber 23 needs to be further increased, the desalting chamber 23 can be formed by three or more frames 43.

[0054] Frame 41 constituting anode chamber 21 and frame 42 constituting concentrating chamber 22 are adjacent to each other, but the openings of these frames 41 and 42 are separated by cation exchange membrane 31, thereby partitioning anode chamber 21 and concentrating chamber 22 from each other. Similarly, anion exchange membrane 32 is disposed between adjacent frames 42 and 43, cation exchange membrane 33 is disposed between adjacent frames 43 and 44, and anion exchange membrane 34 is disposed between adjacent frames 44 and 45.

[0055] By sequentially stacking frames to form concentrating chambers 22 and 24 and desalting chamber 23 while sandwiching ion exchange membranes in this manner, it is possible to easily manufacture an EDI device 10 having the above basic structure, with multiple frames arranged in parallel. When stacking the frames, the frames are stacked with their openings facing upward. When filling each chamber (anode chamber 21, concentrating chamber 22, desalting chamber 23, concentrating chamber 24, and cathode chamber 25) with ion exchange resin, the frames constituting each chamber are stacked, the ion exchange resin is then filled into the openings of the frames, and then the ion exchange membranes are sandwiched, with the next frame placed on top.

[0056] Figure 4 FIG. 1 shows another embodiment of an EDI device 10. In the EDI device according to the present invention, when the desalination chamber 23 is divided into regions along the flow direction of the treated water, the desalination chamber 23 can be divided into three or more regions. Figure 4 In the example shown, Figure 1 In the desalination chamber 23 of the EDI device 10 shown, region C is provided between region A and region B. Region C is also filled with anion exchange resin and cation exchange resin in a mixed bed, but the mixing ratio of anion exchange resin to cation exchange resin in this region is arbitrary, and either anion exchange resin or cation exchange resin may be filled in a single bed. Figure 4 In the illustrated EDI device 10 , the anion exchange resin is filled in a single bed up to the concentrating chamber 22 adjacent to the anode chamber 21 .

[0057] Figure 5 An EDI device 10 according to another embodiment is shown. Figure 5 The EDI device 10 shown is Figure 1 In the illustrated EDI device 10, the concentrating chamber 24, located on the cathode 12 side of the deionizing chamber 23, is divided into two regions: region P and region Q, along the direction of water flow. Region P opposes region A of the deionizing chamber 23 via the cation exchange membrane 33. Similarly, region Q opposes region B of the deionizing chamber 23 via the cation exchange membrane 33. "Opposing" here means that, when viewed perpendicular to the surface of the ion exchange membrane (here, the cation exchange membrane 33), the region on one side of the ion exchange membrane at least partially overlaps with the region on the other side of the ion exchange membrane. Region P of the concentrating chamber 24 is filled with anion exchange resin and cation exchange resin in a mixed bed. Region Q can be filled with the cation exchange resin in a single bed or a mixed bed of anion exchange resin and cation exchange resin. When filling in a mixed bed, the volume of the cation exchange resin must be at least 50% of the total volume of the ion exchange resin in region Q. By increasing the ratio of the cation exchange resin in the region Q in this manner, it is possible to suppress leakage of weak acid components represented by carbonic acid, silicon dioxide (silicic acid), and boron (boric acid) into the deionized water discharged from the desalination chamber 23. Figure 5 In the illustrated EDI device 10 , the anion exchange resin is also filled in a single bed up to the concentrating chamber 22 adjacent to the anode chamber 21 .

[0058] Figure 6 This diagram illustrates the leakage of carbonic acid from the desalination chamber. Here, the desalination chamber 23 and the concentrating chamber 24 are alternately arranged between the anode 11 and the cathode 12. The desalination chamber 23 is filled with an anion exchange resin (AER) and a cation exchange resin (CER) in a mixed bed, while the concentrating chamber 24 is filled with an anion exchange resin in a single bed. Carbonic acid in the treated water (free carbonic acid (CO2), bicarbonate ions (HCO3) - ) and carbonate ions (CO3 2- )), is captured by the anion exchange resin as bicarbonate ions or carbonate ions in the desalination chamber 23 on the right side of the figure, and moves to the concentration chamber 24 on the anode 11 side through the anion exchange membrane (AEM) 32. As a result, the ion type of the anion exchange resin in the concentration chamber 24 becomes HCO3 -Then, the electric field generated by the applied DC voltage causes the bicarbonate ions (and carbonate ions) to move to the vicinity of the cation exchange membrane 33 in the concentrating chamber 24. However, since they are anions, they cannot pass through the cation exchange membrane 33. Therefore, in the concentrating chamber 24, the bicarbonate ions (and carbonate ions) are concentrated near the cation exchange membrane 33 located on the anode 11 side. In addition, the hydrogen ions (H + ) passes from the desalination chamber 23 on the anode 11 side through the cation exchange membrane 33 to the concentrating chamber 24. As a result, the pH in the area near the cation exchange membrane 33 in the concentrating chamber 24 decreases. This area is where bicarbonate ions (and carbonate ions) are concentrated. However, due to the hydrogen ions, water and carbon dioxide (CO2) are generated from the bicarbonate ions (and carbonate ions), and a water layer containing a high concentration of carbon dioxide forms near the cation exchange membrane 33 in the concentrating chamber 24. Furthermore, since carbon dioxide, a neutral molecule, can pass through the cation exchange membrane 33, it moves from the concentrating chamber 24 to the desalination chamber 23 via the cation exchange membrane 33. As a result, the carbonic acid component removed from the treated water in a desalination chamber 23 is redissolved in the treated water in a desalination chamber 23 located closer to the anode 11 than the desalination chamber 23, and the treated water discharged from the desalination chamber 23 contains carbonic acid components.

[0059] Regarding the leakage of carbonic acid components from the desalination chamber, the present inventors have obtained the following insights. Specifically, (1) if the total carbonic acid concentration of the treated water supplied to the desalination chamber exceeds 0.5 ppm as CO2, the effect of leakage caused by the above-mentioned mechanism tends to begin to appear. (2) Generally, the total carbonic acid concentration in the water supplied to the EDI device is reduced by the pretreatment performed in the upstream stage of the EDI device, and is therefore usually below 55 ppm as CO2. The total carbonic acid mentioned here refers to free carbonic acid (CO2), bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ), and the total carbonic acid concentration (ppm as CO2) is expressed by converting the concentration of total carbonic acid to CO2.

[0060] In order to prevent such leakage of carbonic acid components, it is conceivable to prevent the formation of a region with a low pH near the cation exchange membrane 33 in the concentrating chamber 24. Therefore, it is effective to quickly move the hydrogen ions that have moved to the concentrating chamber 24 via the cation exchange membrane 33 to the cathode 12 side within the concentrating chamber 24. Figure 5In the illustrated EDI device 10, the volume ratio of the cation exchange resin in region Q of the concentrating chamber 24, corresponding to region B in the desalination chamber 23 where carbon dioxide is to be removed from the treated water, is set to 50% or greater. This configuration prevents the formation of a water layer containing a high concentration of carbon dioxide in the region near the cation exchange membrane 33 in the concentrating chamber 24. Consequently, the movement of carbon dioxide from the concentrating chamber 24 to the desalination chamber 23 via the cation exchange membrane 33 is suppressed.

[0061] One method for suppressing the movement of carbon dioxide from the concentrating chamber 24 to the desalting chamber 23 is to set the volume ratio of the cation exchange resin in region Q to 50% or greater. Another method involves setting the volume ratio of the cation exchange resin in region P of the concentrating chamber 24, which faces region A, to be lower than the volume ratio of the cation exchange resin in region A, the most upstream region of the desalting chamber 23. Simultaneously, setting the volume ratio of the anion exchange resin in region Q of the concentrating chamber 24, which faces region B, to be lower than the volume ratio of the anion exchange resin in region B, the most downstream region of the desalting chamber 23. Since the amount of cation exchange resin in region A is high, anions are less likely to move from the desalting chamber. However, in this method, increasing the amount of anion exchange resin in region P, which faces region A, can promote the movement of carbonic acid components from the desalting chamber to the concentrating chamber.

[0062] Example Hereinafter, the present invention will be described in further detail with reference to Examples and Comparative Examples.

[0063] [Example 1] Assembled by stacking frames Figure 1 The EDI device 10 of the structure shown. In the concentration chambers 22 and 24, anion exchange resin and cation exchange resin are mixed and filled in a volume ratio of 1:1. The thickness of the desalination chamber 23 is set to 8.7 mm, and the size of the opening formed in the frame for the desalination chamber 23 is set to 300 mm × 150 mm. In the desalination chamber 23, in the area A on the upstream side of the flow of the treated water, anion exchange resin (A) and cation exchange resin (K) are mixed and filled in a volume ratio (A:K) of 2:8. In the area B on the downstream side of the flow of the treated water, anion exchange resin and cation exchange resin are mixed and filled in a volume ratio (A:K) of 7:3. While applying a DC voltage between the anode 11 and the cathode 12, by setting SV = 300h -1The EDI device was operated by passing treated water through each desalination chamber 23 at a flow rate of 4 L / min. 1200 hours after the start of operation, the resistivity of the treated water, which was deionized water, obtained from the desalination chamber 23 was measured and used as the water quality value of the treated water. The treated water used had a sodium ion concentration of 0.3 ppm and a total carbonic acid concentration of 1.0 ppm as CO2. When the operating current was set to 3.5 A, the operating voltage was 23.6 V, the operating differential pressure was 0.057 MPa, and the power consumption was 82.6 W.

[0064] The average particle size of the ion exchange resins used is 0.55 to 0.65 mm (large particle size CER) for the cation exchange resins used in the desalting compartment 23 (areas A and B) and the concentrating compartments 22 and 24, and 0.50 to 0.65 mm (large particle size AER) for the anion exchange resins used in the concentrating compartments 22 and 24.

[0065] The average particle sizes of the anion exchange resins used in desalination chamber 23 (areas A and B) were 0.50 to 0.65 mm (large particle size AER) and 0.28 to 0.34 mm (small particle size AER). The volume ratio of the large particle size AER to the small particle size AER was 5:1. The results are shown in Table 1.

[0066] [Comparative Example 1] EDI device 10 was assembled and operated in the same manner as in Example 1, except that the volume ratio (A:K) of the anion exchange resin (A) to the cation exchange resin (K) in region A was changed to 3:7, the volume ratio (A:K) in region B was changed to 8:2, and the anion exchange resin used in the desalination chamber was changed to only large-particle AER (average particle size 0.50 to 0.65 mm). Water quality values ​​were determined 1200 hours after the start of operation. The results are shown in Table 1.

[0067] [Comparative Example 2] EDI device 10 was assembled and operated in the same manner as in Example 1, except that the anion exchange resin used in the desalination chamber was changed to only small-particle AER (average particle size 0.28 to 0.34 μm). Water quality values ​​were determined 1200 hours after the start of operation. The results are shown in Table 1.

[0068] [Table 1]

[0069] According to the comparison between Example 1 and Comparative Example 1, the EDI of Example 1 filled with two types of ion exchange resins with different particle sizes as the anion exchange resin in the desalination chamber can achieve excellent treated water quality compared with the EDI of Comparative Example 1 filled with only a large particle size ion exchange resin as the anion exchange resin in the desalination chamber.

[0070] In addition, according to the comparison between Example 1 and Comparative Example 2, the EDI of Example 1 can suppress the operating voltage and pressure difference to a low level, and can suppress the power consumption to a low level, when the water quality of the treated water is the same, compared with the EDI of Comparative Example 2 which is only filled with a small-particle ion exchange resin.

[0071] The volume ratio (S1+S2) / (L1+L2) of the large particle size resin (L1, L2) to the small particle size resin (S1, S2) of the ion exchange resin is plotted on the horizontal axis, and SV=300h, which is estimated as the condition of Example 1 based on the measured data, is plotted on the horizontal axis. -1 SV = 450h, 1.5 times the flow rate -1 The values ​​obtained by the operating pressure difference during operation [MPa] were used as the vertical axis, and the values ​​of three points of Example 1, Comparative Examples 1 and 2 were made into a graph, and the least squares method was used to fit it. The results are as follows: Figure 7 shown.

[0072] Here, the EDI may be operated at a flow rate 1.5 times the normal flow rate. Considering that the allowable pressure difference at the 1.5 times flow rate is about 0.2 MPa, it can be seen that (S1+S2) / (L1+L2)<0.6 is preferable.

[0073] [Example 2] The anion exchange resin used in the desalination chamber 23 was changed to a large-particle AER (average particle size 0.50-0.65 mm), and the cation exchange resin was changed to a mixture of large-particle CER (average particle size 0.55-0.65 mm) and small-particle CER (0.28-0.32 mm) at a volume ratio of 1:1. Furthermore, the desalination chamber 23 was not divided into zones; instead, the anion exchange resin and cation exchange resin were mixed and filled throughout the desalination chamber 23 at a volume ratio (A:K) of 6:4. Otherwise, the EDI device 10 was assembled in the same manner as in Example 1. Furthermore, the EDI device 10 was operated in the same manner as in Example 1, except that water with a sodium ion concentration of 0.6 ppm and a total carbonic acid concentration of 3.0 ppm as CO₂ was used as the treated water. Water quality values ​​were determined. When the operating current is set to 2.5A, the operating voltage is 11.1V, the operating voltage difference is 0.078MPa, and the power consumption is 27.75W.

[0074] The results are shown in Table 2.

[0075] [Comparative Example 3] The EDI device 10 was assembled and operated in the same manner as in Example 2, except that the cation exchange resin used in the desalination chamber 23 was changed to only small-particle CER (average particle size: 0.28 to 0.32 mm). The water quality values ​​were determined. The results are shown in Table 2.

[0076] [Table 2]

[0077] According to the comparison between Example 2 and Comparative Example 3, compared with the EDI of Comparative Example 3 in which only a small-particle-sized ion exchange resin is filled as the cation exchange resin in the desalination chamber, the EDI of Example 2 in which two ion exchange resins with different particle sizes are filled as the cation exchange resin in the desalination chamber obtains excellent treated water quality.

[0078] This shows that the effects of the present invention can be obtained even when the two ion exchange resins having different particle sizes are changed from the anion exchange resin in Example 1 to a cation exchange resin.

[0079] [Example 3] For each treated water having a total carbonic acid concentration (ppm as CO₂) of 4.0, 3.0, and 0.9, an EDI device 10 identical to that of Example 1 was assembled and operated in the same manner as in Example 1 to determine water quality values ​​(resistivity) relative to the carbonic acid concentration. The sodium ion concentration of the treated water was 0.6 ppm when the total carbonic acid concentration was 4.0 and 3.0 ppm as CO₂, and 0.3 ppm when the total carbonic acid concentration was 0.9 ppm as CO₂. The results are shown in Table 3.

[0080] [Comparative Example 4] The EDI device 10 was operated in the same manner as in Example 3, except that the EDI device having the same structure as that in Comparative Example 2 was used, and the water quality value (resistivity) relative to the carbonic acid concentration was determined. The results are shown in Table 3.

[0081] [Table 3]

[0082] [Example 4] For each type of treated water with sodium concentrations (ppm) of 0.7, 0.3, and 0.1, an EDI device 10 identical to that used in Example 1 was assembled and operated in the same manner as in Example 1 to determine water quality values ​​(resistivity) relative to sodium concentration. The treated water had a total carbonic acid concentration of 3 ppm as CO₂ when the sodium concentration was 0.7 and 0.3 ppm, and a total carbonic acid concentration of 1.0 ppm as CO₂ when the sodium concentration was 0.1 ppm. The results are shown in Table 4.

[0083] [Comparative Example 5] The EDI device 10 was operated in the same manner as in Example 4, except that the same configuration as in Comparative Example 2 was used, and the water quality value (resistivity) relative to the sodium concentration was determined 300 hours after the start of operation. The results are shown in Table 4.

[0084] [Table 4]

[0085] As can be seen from the comparison between Example 3 and Comparative Example 4, and between Example 4 and Comparative Example 5, when two ion exchange resins with different particle sizes are used as the ion exchange resins filled in the desalination chamber, excellent effects can be obtained for water quality with respect to carbonic acid concentration and water quality with respect to sodium concentration.

[0086] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0087] This application claims priority based on Japanese patent application No. 2023-35577 filed on March 8, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0088] Description of Reference Numerals 10 Electrodeionized water production device (EDI device) 11 Anode 12 cathode 21 Anode chamber 22, 24 Concentration Room 23 Desalination Chamber 25 cathode chamber 31, 33 Cation exchange membrane (CEM) 32, 34 Anion Exchange Membrane (AEM) 41~45 frame 46, 47 pressure plates.

Claims

1. An electrodeionized water production device, characterized in that: have: anode; cathode; a desalination chamber, which is arranged between the anode and the cathode, is divided by an anion exchange membrane located on the anode side and a cation exchange membrane located on the cathode side, and is filled with an anion exchanger and a cation exchanger; as well as The concentrating chamber is provided on the cathode side of the cation exchange membrane and is filled with an anion exchanger and a cation exchanger, wherein: The anion exchanger and the cation exchanger are anion exchange resin and cation exchange resin, respectively. When the large-particle cation exchange resin in the anion exchange resin and the large-particle anion exchange resin is L1, the large-particle anion exchange resin is L2, the small-particle cation exchange resin is S1, and the small-particle anion exchange resin is S2, the desalination chamber is filled with at least three resins selected from the combination thereof.

2. The electrodeionized water production device according to claim 1, wherein: The particle sizes of the large-particle cation exchange resin L1 and the large-particle anion exchange resin L2 exceed 0.4 mm, and the particle sizes of the small-particle cation exchange resin S1 and the small-particle anion exchange resin S2 are 0.1 mm to 0.4 mm.

3. The electrodeionized water production device according to claim 2, wherein: The desalination chamber has a mixed particle size layer containing a mixture of a large-particle cation exchange resin L1 exceeding 0.4 mm, a large-particle anion exchange resin L2 exceeding 0.4 mm, and a small-particle anion exchange resin S2 exceeding 0.1 mm and exceeding 0.4 mm.

4. The electrodeionized water production device according to claim 2, wherein: The mixed particle size layer in the desalination chamber is mixed in a ratio of L2:S2 ranging from 1:1 to 5:

1.

5. The electrodeionized water production device according to claim 1, wherein: The volume ratio of the resin filled in the desalting chamber satisfies the relationship of (S1+S2) / (L1+L2)<0.

6.

6. The electrodeionized water production device according to claim 1, wherein: The desalination chamber is divided into the plurality of regions in such a manner that the plurality of regions are arranged in a direction of flow of the treated water in the desalination chamber. The area located on the upstream side of the flow of the treated water among the multiple areas is designated as the first area, and the area located on the downstream side is designated as the second area. The first area is filled with a mixture of anion exchangers and cation exchangers in such a manner that the volume ratio of the cation exchangers in the first area to the total volume of the anion exchangers and cation exchangers is greater than 50% and less than 90%. The second area is filled with a mixture of anion exchangers and cation exchangers in such a manner that the volume ratio of the anion exchangers in the second area to the total volume of the anion exchangers and cation exchangers is greater than 50% and less than 90%.

7. The electrodeionized water production device according to claim 1, wherein: The thickness of the ion exchanger layer in each of the plurality of regions along a direction perpendicular to the flow direction of the water to be treated in the desalination chamber is 10 mm or more and 25 mm or less.

8. The electrodeionized water production device according to claim 1, wherein: At a position facing the second region across the cation exchange membrane, the volume ratio of the cation exchanger filled in the ion exchanger of the concentrating chamber is 50% or more.

9. A method for producing pure water, characterized in that: Using the electrodeionized water production apparatus according to claim 1 , the treated water having a sodium ion concentration of 0.1 ppm to 0.7 ppm is supplied to the desalination chamber while applying a DC voltage between the anode and the cathode to obtain pure water as deionized water.

10. A method for producing pure water, characterized in that: Using the electrodeionized water production apparatus according to claim 1, while applying a DC voltage between the anode and the cathode, the treated water having a total carbonic acid concentration of 0.5 ppm as CO2 or more and 5.0 ppm as CO2 or less is supplied to the desalination chamber to obtain pure water as deionized water.

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