Pure water production apparatus

Abstract

This pure water production apparatus comprises a first reverse osmosis membrane, an electrodeionization device 3, and a second reverse osmosis membrane. In the electrodeionization device 3, anion exchange membranes 11 and cation exchange membranes 12 are alternately arranged between an anode plate 15 and a cathode plate 16, and through compartmentalization by the anion exchange membranes 11 and the cation exchange membranes 12, a desalting chamber 13 and a concentration chamber 14 are formed, and an anode chamber and a cathode chamber are formed at respective ends. As water supply to the desalting chamber 13, permeated water W1 of a first reverse osmosis membrane device 1 is supplied to the desalting chamber 13 to obtain treated water W2. As water supply W4 to the concentration chamber 14, permeate of the first reverse osmosis membrane device 1 is supplied, and concentrated water W5 is discharged. In the electrodeionization device 3, the desalting chamber 13 is substantially filled with 100% by weight of an anion exchange resin. According to such a pure water production apparatus, the removal rate of weak acid ions (boron, silica, and the like) in a reverse osmosis membrane device can be improved without using chemicals.

Description

Pure water production device

[0001] The present invention relates to a pure water production device using an electric deionization device capable of improving the removal rate of weak acid ions (such as boron and silica) in a reverse osmosis membrane device used in pure water production devices such as primary pure water production devices and ultra-pure water production devices.

[0002] Conventionally, ultra-pure water used in the electronic industry field such as semiconductors is produced by treating raw water in an ultra-pure water production system composed of a pretreatment system, a primary pure water production device (pure water production system), and a subsystem (secondary pure water production device) for treating primary pure water.

[0003] In recent years, in primary pure water devices, the required boron concentration in the treated water has become lower, and simply applying an electric deionization device may not be able to satisfy the water quality. Therefore, as shown in FIG. 4, a system composed of a first reverse osmosis membrane 41, a second reverse osmosis membrane 42, and a pH adjustment mechanism 43 for adding an alkali such as NaOH provided upstream of the second reverse osmosis membrane 42 is used. In such a system, the treated water W is passed through the first reverse osmosis membrane 41, and an alkali is added to the permeated water (feed water) W1 to adjust it to a high pH of 9 or more to obtain adjusted water W2, which is then passed through the second reverse osmosis membrane 42, thereby increasing the boron removal rate of the pure water W3.

[0004] However, when the permeated water W1 is adjusted to a high pH and passed through the second reverse osmosis membrane 42 as described above, since chemicals such as NaOH are added, it becomes a load on the subsequent water treatment. In addition, since a large amount of chemicals such as NaOH are used, it is not preferable from the viewpoints of chemical usage amount and waste reduction.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a pure water production device capable of improving the removal rate of weak acid ions (such as boron and silica) in a reverse osmosis membrane device without using chemicals.

[0006] In view of the above objectives, the present invention provides a pure water production apparatus having a reverse osmosis membrane apparatus downstream of an electrodeionizer, wherein the electrodeionizer has a desalination chamber substantially filled with an anion exchanger (Invention 1). In the above invention (Invention 1), it is preferable that the anion exchanger is an anion exchange resin (Invention 2).

[0007] According to the inventions described above (Inventions 1 and 2), when feedwater is passed through the desalination chamber of an electrodeionizer in which an anion exchanger is substantially filled with an anion exchanger, only the anionic components in the feedwater are selectively removed, so the treated water becomes cation-rich, for example, Na ＋ When there is an excess of [unclear element], NaOH is produced, which increases the pH. In this way, the pH of the treated water in the subsequent reverse osmosis membrane device can be increased, thereby improving the removal rate of boron, silica, and other elements without the use of alkaline chemicals.

[0008] In the above invention (Invention 1), the desalination chamber and concentration chamber of the electrodeionizer are partitioned by a cation exchange membrane and an anion exchange membrane, and it is preferable that the cation exchange membrane is a homogeneous cation exchange membrane (Invention 3). In the above invention (Invention 3), it is preferable that the homogeneous cation exchange membrane has a film thickness of 500 μm or less (Invention 4). Furthermore, in the above invention (Invention 4), it is preferable that the maximum height (RY) of the homogeneous cation exchange membrane is 20 μm or more (Invention 5). The maximum height (RY) is obtained by taking a reference length from the roughness curve in the direction of its average line, measuring the distance between the peak line and the trough line of this taken portion in the direction of the vertical magnification of the roughness curve, and expressing this value in micrometers (μm).

[0009] According to the above inventions (inventions 3 to 5), by partitioning the area with a dense, thin, homogeneous cation exchange film, current flows even when only anion exchanger is filled into the desalination chamber, and OH is generated by water dissociation. － Because this method improves the regeneration efficiency of the anionic resin in the desalination chamber, the removal rate of anionic components is improved compared to conventional electrodeionizers, and the removal rate of weak acid ions such as boron can be improved without the use of chemicals.

[0010] In the above invention (Invention 3), it is preferable that the pH of the treated water from the electrodeionizer is 8.5 or higher and less than 11 (Invention 6).

[0011] According to the above invention (Invention 6), by setting the pH of the treated water of the electrodeionizer to 8.5 or higher and less than 11, the removal rate of weak acid ions such as boron can be further improved without using chemicals.

[0012] In the above inventions (inventions 1 to 6), it is preferable to have a reverse osmosis membrane, a nanofiltration membrane, or an ultrafiltration membrane in front of the electrodeionizer (invention 7).

[0013] According to the above invention (Invention 7), by reducing the fine particles and ionic impurities in the water to be treated in the electrodeionizer, the water quality of the treated water passed through the desalination chamber of the electrodeionizer, in which the desalination chamber is substantially filled with an anion exchanger, can be improved, thereby improving the water quality of the treated water in the subsequent reverse osmosis membrane device.

[0014] The pure water production apparatus of the present invention has a reverse osmosis membrane apparatus downstream of an electrodeionizer, and the electrodeionizer has a desalination chamber substantially filled with an anion exchanger. Therefore, when the water to be treated is passed through the desalination chamber of this electrodeionizer, the pH of the treated water in the downstream reverse osmosis membrane apparatus can be increased, and the removal rate of weak ions such as boron and silica can be increased without using alkaline chemicals.

[0015] This is a flow diagram showing the configuration of a two-stage reverse osmosis membrane treatment apparatus and an electrodeionizer in a pure water production apparatus according to one embodiment of the present invention. This is a schematic diagram showing the configuration of the electrodeionizer in the above embodiment. This is a schematic diagram showing the configuration of an electrodeionizer in a comparative example (conventional example). This is a flow diagram showing the configuration of a conventional two-stage reverse osmosis membrane treatment apparatus and electrodeionizer.

[0016] The pure water production apparatus of the present invention will be described below with reference to the attached drawings.

[0017] [Pure Water Production Apparatus] The pure water production apparatus of this embodiment only needs to have a reverse osmosis membrane apparatus downstream of the electrodeionizer, and can be suitably applied to the primary pure water production apparatus in an ultrapure water production apparatus.

[0018] Specifically, the pure water production apparatus includes a first reverse osmosis membrane 1, a second reverse osmosis membrane 2, and an electrodeionizer 3 installed upstream of the second reverse osmosis membrane 2, as shown in Figure 1.

[0019] As schematically shown in Figure 2, this electrodeionizer 3 alternately arranges anion exchange membranes 11 and cation exchange membranes 12 between an anode plate 15 and a cathode plate 16. By forming compartments with these anion exchange membranes 11 and cation exchange membranes 12, a desalination chamber (D chamber) 13 and a concentration chamber (C chamber) 14 are formed, and an anode chamber and a cathode chamber (not shown) are formed at both ends. In this case, the number of desalination chambers is preferably 10 to 100, particularly 40 to 60. In this embodiment, permeate (feed water) W1 from the first reverse osmosis membrane device 1 is supplied as the feed water for the desalination chamber 13 to obtain treated water W2. Also, permeate from the first reverse osmosis membrane device 1 is supplied as the feed water (water to be concentrated) W4 for the concentration chamber 14 to discharge concentrated water W5.

[0020] The electrodeionizer 3 described above has a desalting chamber 13 filled with substantially 100% by weight (based on dryness) of an anion exchange resin, preferably a strong anion exchange resin, as an anion exchange agent. In this specification, substantially 100% by weight of anion exchange resin means not only the case of anion exchange resin alone, but also the case of an anion exchange resin of 75% by weight or more, particularly 90% by weight or more, and even 95% by weight or more, and a small amount of cation exchange resin may be mixed in. The concentration chamber 14 is filled with a mixed ion exchange resin in which, based on dryness, the anion exchange resin as an anion exchange agent and the cation exchange resin as a catio exchange agent are in a weight ratio of 30:70 to 70:30, particularly 40:60 to 60:40.

[0021] Furthermore, the cation exchange membrane 12 is preferably a strong cation exchange membrane, and more preferably a homogeneous cation exchange membrane. When a homogeneous membrane is used as the cation membrane, the resistance between the anode and cathode becomes smaller compared to when a heterogeneous membrane is used, and current flows more easily when a voltage is applied between the two electrodes. Then, H is generated at the contact point between the anion exchanger such as an anionic resin and the cation membrane made of a homogeneous membrane. ＋ and OH － Of these, OH － The material moves across the desalination chamber 13 toward the anode, and during this time, the anion exchange material such as the anion resin in the desalination chamber 13 is sufficiently regenerated. As a result, productive water (desalination water) with sufficiently removed anionic components is obtained, and scale formation in the desalination chamber is also suppressed.

[0022] The homogeneous cation exchange membrane 12 preferably has a film thickness of 500 μm or less, and more preferably 300 μm or less. The lower limit of the film thickness of the homogeneous cation exchange membrane 12 is about 100 μm. Furthermore, the maximum height (RY) of the homogeneous cation exchange membrane 12 is preferably 20 μm or more, and more preferably 25 μm or more. The upper limit of the maximum height (RY) is about 50 μm. By using such a homogeneous cation exchange membrane 12, water dissociation occurs well in the desalination chamber, and the removal rate of weak acid ions such as boron can be improved. As a cation membrane made of such a homogeneous membrane, commercially available products such as CMB manufactured by ASTOM Corporation (surface height (RY): 33 μm, film thickness: 215 μm) and TYPE10 manufactured by Fujifilm Corporation (surface height (RY): 27 μm, film thickness: 128 μm) can be used. It is preferable to use a homogeneous membrane as the anion exchange membrane 11.

[0023] In this type of electrodeionizer 3, 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.

[0024] (Reverse Osmosis Membrane) There are no particular restrictions on the first reverse osmosis membrane apparatus 1 and the second reverse osmosis membrane apparatus 2, but it is common to use an ultra-low pressure reverse osmosis membrane. An ultra-low pressure reverse osmosis membrane has a membrane surface effective pressure (water temperature 25°C, pure water (RO permeate)) of 0.4 to 0.9 MPa and a permeation flux of 0.4 to 0.9 m ３ / (m ２ This reverse osmosis membrane has a performance of removing over 90% of NaCl and over 30% of boron. Furthermore, ultra-low pressure reverse osmosis membranes and extremely low pressure reverse osmosis membranes, which can operate at even lower pressures, can also be used.

[0025] [Operation Method of the Pure Water Production System] The operation method of the pure water production system described above will be explained based on Figures 1 and 2.

[0026] First, a water supply pump (not shown) is driven to supply the water to be treated W to the first reverse osmosis membrane apparatus 1. The pH of the permeate (supply water to the electrodeionizer 3) W1 from this first reverse osmosis membrane apparatus 1 is 6.0 to 7.5, particularly around 6.5 to 7.5.

[0027] Next, the permeate (feedwater) W1 from the first reverse osmosis membrane apparatus 1 is passed through the electrodeionizer 3. As shown in Figure 2, the electrodeionizer 3 has a desalination chamber 13 that is substantially filled with 100% by weight of anion exchange resin. Therefore, when the permeate (feedwater) W1 passes through the desalination chamber 13, only the anionic components in the permeate (feedwater) W1 are selectively removed. As a result, the treated water W2 becomes cation-rich, and if there is an excess of Na, for example, NaOH is formed, and above all, the pH of the treated water W2 becomes 7 or higher.

[0028] At this time, it is preferable to control the operating current of the electrodeionizer 3 so that the pH of the treated water W2 is between 8.5 and less than 11. If the pH of the treated water W2 is less than 8.5, the removal rate of weak acid ions such as boron in the subsequent second reverse osmosis membrane 2 cannot be sufficiently improved, while it is difficult to raise the pH of the treated water W2 to 11 or higher simply by passing it through the desalination chamber 13 of the electrodeionizer 3.

[0029] Next, the treated water W2, whose pH has been adjusted to 8.5 to less than 11, is treated in a second reverse osmosis membrane apparatus 2. For example, the dissociation constant pKa of boron is 0.24, and at high pH levels of 9 or above, boron becomes ionized. As a result, the removal rate of weak acid ions such as boron, carbonic acid, and silica improves, and pure water W3 with an improved removal rate of weak acid ions such as boron can be obtained.

[0030] Then, the pure water W3, which is treated water in the second reverse osmosis membrane apparatus 3, can be treated with a general-purpose electrodeionizer as needed to remove trace amounts of ionic impurities contained in the pure water W3, thereby producing highly pure water.

[0031] The pure water production apparatus of the present invention has been described above with reference to the attached drawings, but the present invention only requires that a reverse osmosis membrane apparatus 2 be placed downstream of the electrodeionizer 3, in which the desalination chamber is substantially filled with an anion exchanger, and various modifications can be made. For example, a nanofiltration membrane or an ultrafiltration membrane may be provided instead of the first reverse osmosis membrane 1, or the first reverse osmosis membrane 1 may be omitted.

[0032] The present invention will be described in more detail below based on specific examples, but the present invention is not limited to the following examples.

[0033] [Test Electrodeionizer] <Example 1> An electrodeionizer with the configuration shown in Figure 2 was constructed with the following specifications: Size of anion exchange membrane, cation exchange membrane and electrode: 46 mm (length) x 48.5 mm (width) Cation exchange membrane: CMB manufactured by ASTOM Corporation (homogeneous membrane, surface height (RY): 33 μm, film thickness: 215 μm) Anion exchange membrane: AHA manufactured by ASTOM Corporation (homogeneous membrane, surface height (RY): 44 μm, film thickness: 219 μm) Resin in concentration chamber: Mixture and filling of 60% by weight of anion exchange resin and 40% by weight of cation exchange resin Cation exchange resin: KR-UC1 manufactured by Kurita Water Industries Ltd. Anion exchange resin: KR-UA1 manufactured by Kurita Water Industries Ltd.

[0034] <Example 2> The configuration was the same as in Example 1, except that Fujifilm Corporation's TYPE10 (surface height (RY): 27 μm, film thickness: 128 μm) was used as the cation exchange membrane.

[0035] <Comparative Examples 1 and 2> As general-purpose electrodialysis devices of Comparative Examples 1 and 2, those shown in FIG. 3 were prepared. In FIG. 3, the electrodialysis device 21 alternately arranges anion exchange membranes 22 and cation exchange membranes 23 between an anode (anode) plate 26 and a cathode (cathode) plate 27, and forms partitions with these anion exchange membranes 22 and cation exchange membranes 23 to form a desalination chamber (D chamber) 24 and a concentration chamber (C chamber) 25, and forms an anode chamber and a cathode chamber (not shown) at both ends. As the feed water to the desalination chamber 24, the permeated water (feed water) W1 of the first reverse osmosis membrane device 1 is supplied to the desalination chamber 13 to obtain treated water W2. Further, as the feed water (concentrated water to be concentrated) W4 of the concentration chamber 25, the permeation of the first reverse osmosis membrane device 1 is supplied and concentrated water W5 is discharged. In the desalination chamber 24 and the concentration chamber 25 of this electrodialysis device 21, an anion exchange resin and a cation resin were filled so that the weight ratio was 60:40. The anion exchange resin and the cation resin used were the same as those in Example 1. Further, as the cation exchange membrane 23, AS0069 (heterogeneous membrane, surface height (RY): 16.5 μm, membrane thickness: 715 μm) manufactured by Evoqua was used. [[ID=,3]]

[0036] The electrodialysis devices shown in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were each configured as shown in Table 1. In Table 1, the mixing was performed by mixing and filling an anion exchange resin and a cation exchange resin at a weight ratio of 60:40 (based on the dry basis).

[0037]

[0038] The electrodialysis devices of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were operated under the conditions shown in Table 2 below.

[0039]

[0040] And water having the properties shown in Table 3 below was supplied to the desalination chamber and the concentration chamber of each electrodialysis device.

[0041]

[0042] The pH of the treated water W2 and the concentrated water W5 in these electrodialysis devices was measured. The results are shown in Table 4 together with the feed water pH.

[0043]

[0044] As is clear from Table 4, in Comparative Example 1 and Comparative Example 2, the pH of the treated water decreased slightly, while in Example 1 and Example 2, the pH of the treated water was 9.0 and 9.3, respectively. The dissociation constant pKa of boron is 0.24, and at a high pH of 9 or higher, boron ionizes. Therefore, by installing a reverse osmosis membrane at the latter stage of this electro-deionization device, it can be said that the removal rate of weak acid ions such as boron, carbonic acid, and silica is improved.

[0045] 1 First reverse osmosis membrane 2 Second reverse osmosis membrane 3 Electro-deionization device 11 Anion exchange membrane 12 Cation exchange membrane 13 Desalination chamber (D chamber) 14 Concentration chamber (C chamber) 15 Anode plate 16 Cathode plate W Treated water W1 Permeate water (feed water) W2 Treated water (adjusted water) W3 Pure water W4 Concentrated water to be treated W5 Concentrated water

Claims

1. A pure water production apparatus having a reverse osmosis membrane apparatus downstream of an electrodeionizer, wherein the electrodeionizer has a desalination chamber substantially filled with an anion exchanger.

2. The pure water production apparatus according to claim 1, wherein the anion exchange body is an anion exchange resin.

3. The pure water production apparatus according to claim 1, wherein the desalination chamber and concentration chamber of the electrodeionizer are partitioned by a cation exchange membrane and an anion exchange membrane, and the cation exchange membrane is a homogeneous cation exchange membrane.

4. The pure water production apparatus according to claim 3, wherein the homogeneous cation exchange membrane has a film thickness of 500 μm or less.

5. The pure water production apparatus according to claim 4, wherein the maximum height (RY) of the homogeneous cation exchange membrane is 20 μm or more.

6. The pure water production apparatus according to claim 3, wherein the pH of the treated water from the electrodeionizer is 8.5 or higher and less than 11.

7. A pure water production apparatus according to any one of claims 1 to 6, wherein the apparatus has a reverse osmosis membrane, a nanofiltration membrane, or an ultrafiltration membrane upstream of the electrodeionizer.

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