Pure water production equipment

Abstract

To provide a pure water production system that can improve the removal rate of weak acid ions (such as boron and silica) in a reverse osmosis membrane system without using chemicals. [Solution] The pure water production apparatus consists of a first reverse osmosis membrane, an electrodeionizer 3, and a second reverse osmosis membrane. The electrodeionizer 3 alternately arranges anion exchange membranes 11 and cation exchange membranes 12 between an anode plate 15 and a cathode plate 16, and by forming compartments with these anion exchange membranes 11 and cation exchange membranes 12, a desalination chamber 13 and a concentration chamber 14 are formed, and an anode chamber and a cathode chamber are formed at both ends. Permeate W1 from the first reverse osmosis membrane apparatus 1 is supplied to the desalination chamber 13 as feedwater to obtain treated water W2. Permeate from the first reverse osmosis membrane apparatus 1 is supplied as feedwater W4 to the concentration chamber 14 to discharge concentrated water W5. This electrodeionizer 3 has the desalination chamber 13 filled with substantially 100% by weight of anion exchange resin.

Description

Technical Field

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

Background Art

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

[0003] In recent years, in the primary pure water apparatus, the boron concentration required for the treated water has become lower, and simply applying an electric deionization apparatus may not be able to satisfy the water quality. Therefore, as shown in FIG. 4, a system including 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 in front 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, and the adjusted water W2 is passed through the second reverse osmosis membrane 42, thereby increasing the boron removal rate of the pure water W3.

Summary of the Invention

Problems to be Solved by the Invention

[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] This invention has been made in view of the above problems, and aims to provide a pure water production apparatus that can improve the removal rate of weak acid ions (such as boron and silica) in a reverse osmosis membrane apparatus without using chemicals. [Means for solving the problem]

[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 in the desalination chamber, 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 [the substance], NaOH is produced, which raises 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 substances without using 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 the upstream stage 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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0015] [Figure 1] This is a flow diagram showing the configuration of a two-stage reverse osmosis membrane treatment device and an electrodeionizer in a pure water production apparatus according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing the configuration of the electrodeionizer in the above embodiment. [Figure 3] This is a schematic diagram showing the configuration of an electrodeionizer in a comparative example (conventional example). [Figure 4] This is a flowchart showing the configuration of a conventional two-stage reverse osmosis membrane treatment system and electrodeionization system. [Modes for carrying out the invention]

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

[0017] [Pure water production equipment] 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 shown schematically in Fig. 2, this electro-deionization device 3 alternately arranges anion exchange membranes 11 and cation exchange membranes 12 between an anode plate 15 and a cathode plate 16, and forms compartments by these anion exchange membranes 11 and cation exchange membranes 12, thereby forming desalination chambers (D chambers) 13 and concentration chambers (C chambers) 14, and forming anode chambers and cathode chambers (not shown) at both ends. In this case, the number of desalination chambers is preferably 10 to 100, particularly preferably about 40 to 60. In the present embodiment, permeate water (feed water) W1 of the first reverse osmosis membrane device 1 is supplied as the feed water of the desalination chamber 13 to obtain treated water W2. Further, permeate of the first reverse osmosis membrane device 1 is supplied as the feed water (concentrate feed water) W4 of the concentration chamber 14, and concentrated water W5 is discharged.

[0020] The electro-deionization device 3 as described above is substantially filled with 100% by weight (based on dry basis) of an anion exchange resin, preferably a strong anion exchange resin, as an anion exchanger in the desalination chamber 13. In this specification, substantially 100% by weight of the anion exchange resin means not only the case of only the anion exchange resin, but also that the anion exchange resin is 75% by weight or more, particularly 90% by weight or more, and further 95% by weight or more, and a small amount of cation exchange resin or the like may be mixed. In the concentration chamber 14, a mixed ion exchange resin of an anion exchange resin as an anion exchanger and a cation exchange resin as a cation exchanger is filled at a weight ratio of 30:70 to 70:30 (dry basis), particularly 40:60 to 60:40 (weight ratio).

[0021] Further, the cation exchange membrane 12 is preferably a strong cation exchange membrane and preferably a homogeneous cation exchange membrane. When a homogeneous membrane is used as the cation membrane, the resistance between the anode and the cathode becomes smaller than when a heterogeneous membrane is used, and current easily flows when a voltage is applied between the two electrodes. And H + and OH - Among them, OH -It moves across the desalination chamber 13 toward the anode, and during this time, anion exchangers such as anion resins in the desalination chamber 13 are sufficiently regenerated. As a result, product water (desalted water) with sufficiently removed anion components is obtained, and scale formation in the desalination chamber is also suppressed.

[0022] This homogeneous cation exchange membrane 12 preferably has a membrane thickness of 500 μm or less, particularly 300 μm or less. The lower limit of the membrane 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, particularly 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 can occur well in the desalination chamber, and the removal rate of weak acid ions such as boron can be improved. As such a cation membrane made of a homogeneous membrane, commercially available CMB (surface height (RY): 33 μm, membrane thickness: 215 μm) manufactured by ASTOM Co., Ltd., TYPE10 (surface height (RY): 27 μm, membrane thickness: 128 μm) manufactured by Fuji Film Co., Ltd., etc. can be used. In addition, as the anion exchange membrane 11, it is preferable to use a homogeneous membrane.

[0023] In such an electro-deionization device 3, due to the high regeneration efficiency of the anion resin in the desalination chamber by OH generated by water dissociation, the removal rate of anion components is improved compared to conventional electro-deionization devices. -

[0024] (Reverse osmosis membrane) There are no particular restrictions on the first reverse osmosis membrane device 1 and the second reverse osmosis membrane device 2, but it is common to use an ultra-low pressure type reverse osmosis membrane. The ultra-low pressure type reverse osmosis membrane has a permeation flux (flux) of 0.4 - 0.9 m 3 / (m 2 ·day) at a membrane surface effective pressure (water temperature 25 °C, pure water (RO permeate)) of 0.4 - 0.9 MPa, a NaCl removal rate of 90% or more, and a boron removal rate of 30% or more. Also, an extremely ultra-low pressure type reverse osmosis membrane or an extremely extremely ultra-low pressure type reverse osmosis membrane that can be operated at a lower pressure than this can also be applied.

[0025] ​[Operating method for a pure water production system] The operation method of the pure water production system described above will be explained with reference to 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 device 1. The pH of the permeate (supply water to the electrodeionizer 3) W1 from this first reverse osmosis membrane device 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 second reverse osmosis membrane 2 in the subsequent stage 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. This improves the removal rate of weak acid ions such as boron, carbonic acid, and silica, thus allowing us to obtain pure water W3 with an improved removal rate of weak acid ions such as boron.

[0030] Then, the pure water W3, which is treated 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. [Examples]

[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] [Electrodeionization device for testing] <Example 1> The electrodeionizer with the configuration shown in Figure 2 was constructed with the following specifications. Anion exchange membrane, cation exchange membrane, and electrode dimensions: 46mm (height) x 48.5mm (width) Cation exchange membrane: CMB manufactured by ASTOM Corporation (homogeneous film, surface height (RY): 33 μm, film thickness: 215 μm) Anion exchange membrane: AHA manufactured by ASTOM Corporation (homogeneous film, surface height (RY): 44 μm, film thickness: 219 μm) Concentration chamber resin: Mixture and filling of 60% by weight anion exchange resin and 40% by weight 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 electrodeionizers for Comparative Examples 1 and 2, the apparatus shown in Figure 3 was prepared. In Figure 3, the electrodeionizer 21 alternately arranges anion exchange membranes 22 and cation exchange membranes 23 between an anode plate 26 and a cathode plate 27, and by forming compartments with these anion exchange membranes 22 and cation exchange membranes 23, a desalination chamber (D chamber) 24 and a concentration chamber (C chamber) 25 are formed, and an anode chamber and a cathode chamber (not shown) are formed at both ends. Permeate water (feed water) W1 from the first reverse osmosis membrane apparatus 1 is supplied to the desalination chamber 13 as the feedwater for the desalination chamber 24 to obtain treated water W2. Permeate water from the first reverse osmosis membrane apparatus 1 is supplied as the feedwater (water to be concentrated) W4 for the concentration chamber 25 to discharge concentrated water W5. The desalination chamber 24 and concentration chamber 25 of this electrodeionizer 21 were filled with anion exchange resin and cationic resin in a weight ratio of 60:40. The same anion exchange resin and cationic resin as in Example 1 were used. In addition, Evoqua's AS0069 (heterogeneous film, surface height (RY): 16.5 μm, film thickness: 715 μm) was used as the cation exchange membrane 23.

[0036] The electrodeionizers shown in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were configured as shown in Table 1. In Table 1, the mixture consists of anion exchange resin and cation exchange resin mixed and filled in a weight ratio of 60:40 (based on dryness).

[0037] [Table 1]

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

[0039] [Table 2]

[0040] Then, water with the properties shown in Table 3 below was supplied to the desalination and concentration chambers of each electrodeionizer.

[0041] [Table 3]

[0042] The pH of the treated water W2 and concentrated water W5 in these electrodeionizers was measured. The results, along with the feedwater pH, are shown in Table 4.

[0043] [Table 4]

[0044] As is clear from Table 4, in Comparative Examples 1 and 2, the pH of the treated water decreased slightly, while in Examples 1 and 2, the pH of the treated water was 9.0 and 9.3, respectively. The dissociation constant pKa of boron is 0.24, and boron ionizes at high pH levels of 9 or above. Therefore, by installing a reverse osmosis membrane downstream of this electrodeionizer, the removal rate of weak acid ions such as boron, carbonic acid, and silica can be improved. [Explanation of symbols]

[0045] 1. First reverse osmosis membrane 2. Second reverse osmosis membrane 3. Electrodeionizer 11 Anion exchange membrane 12 Cation exchange membrane 13 Desalination room (D room) 14 Concentration room (C room) 15 Anode plate 16 Cathode Plate W: Water to be treated W1 Permeated water (water supply) W2 treated water (adjusted water) W3 Pure water W4 Concentrate water W5 Concentrated water

Claims

1. A pure water production apparatus having a reverse osmosis membrane apparatus downstream of an electrodeionizer, The aforementioned electrodeionizer is a pure water production apparatus in which an anion exchanger is substantially filled 100% in the desalination chamber.

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 electrodeionizer has a reverse osmosis membrane, a nanofiltration membrane, or an ultrafiltration membrane in front of it.

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