Electrodeionization apparatus

Abstract

Provided is an electrodeionization apparatus in which a concentration chamber 5 and a desalting chamber 6 are defined and formed by an anion exchange membrane 3 and a cation exchange membrane 4 between an anode 2 and a cathode 1, concentrated water is distributed to the concentration chamber 5, raw water is distributed to the desalting chamber 6 and taken out as product water. The electrodeionization apparatus is characterized in that: the desalting chamber 5 is substantially filled only with an anion exchanger (a strong anion exchange resin); and the cation exchange membrane 4 is a homogeneous membrane. It is preferable that the cation exchange membrane is a strong cation exchange membrane.

Description

Electrodeionizer

[0001] The present invention relates to an electrodeionizer, and more particularly to an electrodeionizer in which an anion exchange resin (hereinafter sometimes referred to as an anion resin) is filled into a desalination chamber.

[0002] Electrodeionizers generally form desalination and concentration chambers by alternately arranging cation exchange membranes and anion exchange membranes between the cathode and anode, and filling the desalination chamber with ion exchange resin. Ion exchange membranes, such as cation exchange membranes and anion exchange membranes, can be heterogeneous or homogeneous. Heterogeneous membranes are made by adding a binder such as polystyrene to powdered ion exchange resin. Homogeneous membranes include those made by polymerization of styrene-divinylbenzene, etc., and homogeneous membranes made by graft polymerization of monomers having various anion exchange or cation exchange functions.

[0003] In an electrodeionizer, raw water is passed through a desalination chamber and concentrated water is passed through a concentration chamber. When an electric current is passed between the cathode and anode, ions move from the desalination chamber to the concentration chamber through an anion exchange membrane and a cation exchange membrane, thereby obtaining deionized water (pure water) from the desalination chamber.

[0004] In an electrodeionizer, the ion exchange resin is continuously regenerated by passing an electric current between the electrodes.

[0005] In other words, by passing an electric current between the electrodes, the dissociation of water occurs inside the electrodeionizer, resulting in the formation of OH － , H ＋ This occurs. The generated H ＋ , OH － Since it acts as a regenerator for the ion exchange resin in the desalination chamber, in an electrodeionizer, the ion exchange resin is continuously regenerated during operation.

[0006] In conventional electrodeionizers, the desalination chamber is filled with anionic resin and cation exchange resin (hereinafter sometimes referred to as cation resin).

[0007] Patent Document 1 describes that by filling only an anion resin in a desalination chamber, the removal rate of weakly acidic components such as silica and carbonic acid can be improved.

[0008] Japanese Patent Application Laid-Open No. 2001-170646

[0009] Generally, the dissociation of water tends to proceed at the contact point between an anion exchange membrane (hereinafter sometimes referred to as an anion membrane) and a cation resin. That is, H ＋ and OH － are preferentially generated at the contact point between the cation resin filled in the desalination chamber of the electro-deionization device and the anion membrane (arranged on the anode side of the desalination chamber).

[0010] The OH － generated at the contact point between this anion membrane and the cation resin moves toward the anode. Therefore, most of the generated OH － permeates through the anion membrane and moves to the concentration chamber, and does not contribute much to the regeneration of the ion exchange resin in the desalination chamber.

[0011] When only an anion resin is filled in the desalination chamber as in Patent Document 1, OH － generated by the dissociation of water at the contact point between the cation membrane (arranged on the cathode side of the desalination chamber) and the anion resin moves across the desalination chamber toward the anode side, and it is expected that the regeneration of the anion resin will proceed.

[0012] However, according to the research of the present inventor, when using a cation membrane made of a heterogeneous membrane that has been mainly used in conventional electro-deionization devices as the cation membrane and filling only an anion resin in the desalination chamber, the conduction resistance is large, and even when a voltage is applied between the anode and the cathode, almost no current flows, and scale derived from anion components is likely to occur in the desalination chamber, and it was found that the ion removal performance of the electro-deionization device cannot be sufficiently exhibited.

[0013] An object of the present invention is to provide an electro-deionization device having excellent anion removal performance.

[0014] The present invention has the following gist.

[0015] [1] An electrodeionizer in which a concentration chamber and a desalination chamber are partitioned between an anode and a cathode by an anion exchange membrane and a cation exchange membrane, concentrated water is circulated into the concentration chamber, raw water is circulated into the desalination chamber and extracted as produced water, characterized in that substantially only an anion exchanger is filled into the desalination chamber, and the cation exchange membrane is a homogeneous membrane.

[0016] [2] The electrodeionizer according to [1], characterized in that the thickness of the cation exchange membrane is 500 μm or less.

[0017] [3] The electrodeionizer according to [1] or [2], characterized in that the surface roughness RY of the cation exchange membrane is 20 μm or more.

[0018] [4] The cation exchange membrane is a strong cation exchange membrane. An electrodeionizer according to any of [1] to [3].

[0019] [5] The anion exchanger is a strong anion exchange resin. An electrodeionizer according to any of [1] to [4].

[0020] In the electrodeionizer of the present invention, a homogeneous film is used as the cation film in an electrodeionizer in which an anionic resin is packed in the desalination chamber. As a result of the inventor's research, the following has become clear. That is, when a homogeneous film is used as the cation film, the resistance between the anode and cathode becomes smaller compared to when a heterogeneous film is used, and when a voltage is applied between the two electrodes, a current flows. And H is generated at the contact point between the anion exchanger such as anionic resin and the cation film made of a homogeneous film. ＋ and OH － Of these, OH － The material moves across the desalination chamber toward the anode, and during this time, the anion exchange material, such as the anionic resin, inside the desalination chamber is sufficiently regenerated. As a result, productive water (desalination water) with sufficiently removed anionic components is obtained, and scale formation inside the desalination chamber is also suppressed.

[0021] This is a schematic cross-sectional view of an electrodeionizer illustrating an embodiment of the present invention.

[0022] The embodiments will be described below with reference to Figure 1.

[0023] The electrodeionizer shown in Figure 1 has an anion membrane 3 and a cation membrane 4 arranged between electrodes (cathode 2, anode 1) to form two concentration chambers 5 and a desalination chamber 6 between them. The desalination chamber 6 is filled with an anion resin as an anion exchanger. A strong anion resin is preferred as the anion resin.

[0024] Furthermore, the concentration chamber 5, anode chamber 7, and cathode chamber 8 are also filled with an electrically conductive material such as an ion exchanger, activated carbon, or metal. Alternatively, the anion membrane 3 and cation membrane 4 may be arranged alternately to form the concentration chamber 5 and desalination chamber 6 alternately. In this case, the number of desalination chambers is preferably 10 to 100, particularly 40 to 60.

[0025] In this embodiment, a homogeneous film is used as the cation film 4. The cation film made of a homogeneous film preferably has a surface roughness RY (maximum height) of 20 μm or more, and particularly preferably 25 μm or more. However, a surface roughness RY of 100 μm or less is desirable. Surface roughness (maximum height) RY is defined as the distance between the peak and trough lines of a sample taken from the roughness curve in the direction of its mean line, measured in the direction of the vertical magnification of the roughness curve, and expressed in micrometers (μm). Furthermore, the cation film 4 preferably has a film thickness of 500 μm or less, and particularly preferably 300 μm or less.

[0026] A preferred method for measuring water permeability is to apply pressure to a certain membrane area from one side, pass water through it, measure the amount of water that permeates from the opposite side over a certain period of time, and then calculate the permeability by converting it to an average pressure per inlet, a certain membrane area, and a certain period of time.

[0027] As a cation film consisting of a homogeneous film, commercially available products such as ASTOM's CMB (surface roughness RY 33 μm, film thickness 215 μm) and Fujifilm's TYPE 10 (surface roughness RY 27 μm, film thickness 128 μm) can be used.

[0028] In this electrodeionizer, raw water is introduced from the inlet side of the desalination chamber 6, and the produced water (desalination water) is taken out from the outlet side of the desalination chamber 6. Part of the produced water or raw water flows through the concentration chamber 5, and the effluent from the concentration chamber 5 is discharged outside the system. Raw water and the like flow through the anode chamber 7 and the cathode chamber 8.

[0029] In this electrodeionizer, the cation membrane 4 is a homogeneous membrane, and only anionic resin is filled in the desalination chamber 6, so OH is generated at the contact point between the anionic resin and the cation membrane 4. － The material moves across the desalination chamber 6 toward the anode 1, and the anionic components adsorbed on the anionic resin in the desalination chamber 6 are selectively and sufficiently removed, making it less likely for scale to form and allowing for a relaxation of the water supply conditions.

[0030] In this electrodeionizer, OH is generated by water dissociation. － Because this improves the regeneration efficiency of the anionic resin in the desalination chamber, the removal rate of anionic components is improved compared to conventional electrodeionizers.

[0031] Furthermore, the anionic resin to be filled into the desalination chamber 6 only needs to be substantially anionic resin, and a small amount of cationic resin may be mixed in. Of the total amount of resin in the desalination chamber 6, 75% by weight or more, especially 90% by weight or more, and moreover 95% by weight or more (dry weight), should be anionic resin.

[0032] Examples and comparative examples are described below.

[0033] [Device Configuration] <Example 1> An electrodeionizer with the configuration shown in Figure 1 was configured with the following specifications.

[0034] Size of anion membrane, cation membrane and electrode: 46 mm (vertical) × 48.5 mm (horizontal) Desalination chamber thickness: 10 mm Concentration chamber thickness: 5 mm Anode chamber and cathode chamber thickness: 0.3 mm each Cation membrane: ASTOM CMB (homogeneous membrane, surface roughness RY 33 μm, membrane thickness 215 μm) Anion membrane: ASTOM AHA (homogeneous membrane, surface roughness RY 44 μm, membrane thickness 219 μm) Cation resin: KR-UC1 manufactured by Kurita Water Industries Ltd. Anion resin: KR-UA1 manufactured by Kurita Water Industries Ltd. Resin in desalination chamber: 100% anion resin Resin in concentration chamber: Mixed filling of 60% anion resin and 40% cation resin Filling material in electrode chamber: The same as that in the concentration chamber

[0035] <Example 2>The same configuration as in Example 1 was used, except that TYPE 10 (homogeneous membrane, surface roughness RY 27 μm, membrane thickness 128 μm) manufactured by Fuji Film was used as the cation membrane.

[0036] <Comparative Example 1>The same configuration as in Example 1 was used, except that AS0069 (heterogeneous membrane, surface roughness RY 16.5 μm, membrane thickness 715 μm) manufactured by Evoqua was used as the cation membrane.

[0037] <Comparative Example 2>The same configuration as in Comparative Example 1 was used, except that the desalination chamber was filled with anion resin and cation resin in a weight ratio of 60:40.

[0038] <Water flow and power-on operation>The following raw water with the following water quality prepared using ultrapure water and reagent grade was passed downward at a rate of 600 mL / min through the desalination chambers of the electro-deionization devices of Example 1, 2 and Comparative Example 1, 2.

[0039] Na: 427 μg / L Ca: 6 μg / L Mg: 5 μg / L Cl: 100 μg / L NO ３ : 100 μg / L CO ２ : 500 μg / L B: 10 μg / L SiO ２ : 150 μg / L

[0040] Ultra-pure water was passed upward through each concentration chamber at a rate of 50 mL / min. The above raw water was passed upward through the anode chamber and the cathode chamber at a rate of 50 mL / min, respectively.

[0041] Target current density 90A / m ２ Table 1 shows the applied voltage and current values ​​when power is supplied.

[0042]

[0043] <Results and Discussion> In Examples 1 and 2, where the cation film was a homogeneous film and only anionic resin was filled into the desalination chamber, it was confirmed that operation was possible as current was supplied at an applied voltage of 8.3V or 8.2V (0.2A). Furthermore, comparing Examples 1 and 2 with Comparative Example 2, it was found that since Examples 1 and 2 had a lower applied voltage than Comparative Example 2, it was possible to lower the operating voltage.

[0044] In Comparative Example 1, where the cation film was a heterogeneous film and only anionic resin was filled into the desalination chamber, no current flowed even when a voltage of 20V was applied (0.0A). Therefore, it was found that the combination of a heterogeneous cation film and anionic resin resulted in high resistance, no current flow, and therefore desalination treatment was not possible.

[0045] In Comparative Example 2, where the cation film was a heterogeneous film and the desalination chamber was filled with a mixture of cation resin and anionic resin, current flowed (0.2 A), but the applied voltage was high (8.5 V).

[0046] [Water Quality Measurement of Produced Water (Desalinated Water) During Operation of Electrodeionizer] <Water Flow Example 1> In Example 1 and Comparative Example 1 above, the water quality of the produced water after 50 hours of water flow was measured, and the remaining percentage of each ion was calculated. The results are shown in Table 2.

[0047] <Water Flow Example 2> The procedure was the same as in Water Flow Example 1, except that the raw water described above was diluted 10 times with ultrapure water and then used as the water to be treated. The results are shown in Table 3.

[0048] <Water Flow Example 3> The procedure was the same as in Water Flow Example 1, except that the raw water described above was diluted 100 times with ultrapure water and then used as the water to be treated. The results are shown in Table 4.

[0049]

[0050]

[0051]

[0052] As shown in Tables 2-4, Example 1 demonstrated a higher anion removal rate, particularly for monovalent anions, compared to Comparative Example 1.

[0053] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of achieving the effects of the invention. This application is based on Japanese Patent Application No. 2024-206521, filed on 27 November 2024, which is incorporated herein by reference in its entirety.

[0054] 1. Anode 2. Cathode 3. Anion exchange membrane (anion membrane) 4. Cation exchange membrane (cation membrane) 5. Concentration chamber 6. Desalination chamber

Claims

1. An electrodeionizer in which a concentration chamber and a desalination chamber are partitioned between an anode and a cathode by an anion exchange membrane and a cation exchange membrane, concentrated water flows through the concentration chamber, raw water flows through the desalination chamber, and is extracted as produced water, characterized in that substantially only an anion exchanger is filled into the desalination chamber, and the cation exchange membrane is a homogeneous membrane.

2. The electrodeionizer according to claim 1, characterized in that the thickness of the cation exchange membrane is 500 μm or less.

3. The electrodeionizer according to claim 1, characterized in that the surface roughness RY of the cation exchange membrane is 20 μm or more.

4. The electrodeionizer according to claim 1, wherein the cation exchange membrane is a strong cation exchange membrane.

5. The electrodeionizer according to any one of claims 1 to 4, wherein the anion exchange material is a strong anion exchange resin.

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