Pure water production device and method

Abstract

To efficiently remove boron and an organic material.SOLUTION: A pure water production device 1 produces pure water from water to be treated containing boron and an organic material. The pure water production device 1 comprises: a first RO device 31 to which water to be treated is supplied; a pH adjusting-agent injector 37 that injects a pH adjusting agent into treated water treated in the first RO device 31; a second RO device 32 to which treated water comprising the pH adjusting agent which is injected thereinto, is supplied; an ultraviolet oxidation device 33 to which treated water treated in the second RO device 32 is supplied; and an ion exchange device 34 to which treated water treated in the ultraviolet oxidation device 33 is supplied, wherein the injector 37 is connected to a pH adjusting-agent feeder 36.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pure water production system and a pure water production method, and more particularly to a primary pure water production system for an ultrapure water production system. [Background technology]

[0002] In general, ultrapure water is produced using an ultrapure water production system consisting of a pretreatment system, a primary pure water system, and a secondary pure water system (subsystem). A large amount of ultrapure water is used in the cleaning process of manufacturing electronic components such as semiconductor devices. As semiconductors become finer, there is a demand for even higher purity ultrapure water used in the semiconductor manufacturing process, and in particular, there is a demand for reducing the boron concentration and total organic carbon (TOC). Patent Document 1 discloses a pure water production system in which a first reverse osmosis membrane separation device, an alkali addition device, a second reverse osmosis membrane separation device, an ultraviolet oxidation device, and an electrodeionization device are arranged in series. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-283710 A Summary of the Invention [Problem to be solved by the invention]

[0004] The pure water production system disclosed in Patent Document 1 has an electrodeionization device for removing boron, but it is difficult to efficiently remove boron using the electrodeionization device.

[0005] An object of the present invention is to provide a pure water producing apparatus and a pure water producing method capable of efficiently removing boron and organic matter. [Means for solving the problem]

[0006] The pure water production apparatus of the present invention for producing pure water from water to be treated that contains boron and organic matter includes a first reverse osmosis membrane separation device to which the water to be treated is supplied, a pH adjuster injection section that injects a pH adjuster into the water treated by the first reverse osmosis membrane separation device so that the pH of the water is in the range of 7 to 8.5, a second reverse osmosis membrane separation device to which the treated water into which the pH adjuster has been injected is supplied, an ultraviolet oxidation device to which the treated water treated by the second reverse osmosis membrane separation device is supplied, and a pure water production apparatus to which the treated water treated by the ultraviolet oxidation device is supplied, Strongly acidic cation exchange resin A regenerative ion exchange device filled with a strong basic anion exchange resin that reduces the boron concentration to 1ng / L or less; a cation exchange device filled only with a cation exchange resin, the cation exchange device being located downstream of the regenerative ion exchange device in the water flow direction of the regenerative ion exchange device; The injection part is connected to a pH adjuster supply part.

[0007] The method for producing pure water from water to be treated that contains boron and organic matter according to the present invention includes passing the water to be treated through a first reverse osmosis membrane separation device, a second reverse osmosis membrane separation device, an ultraviolet oxidation device, Strongly acidic cation exchange resin Regenerative ion exchange device filled with strong basic anion exchange resin A cation exchange device filled with only a cation exchange resin A pH adjuster is injected into the water to be treated between the first reverse osmosis membrane separation device and the second reverse osmosis membrane separation device to adjust the pH of the water to be treated within the range of 7 to 8.5, and the boron concentration of the treated water from the regenerative ion exchange device is reduced to 1 ng / L or less. Effect of the Invention

[0008] According to the present invention, it is possible to provide a pure water producing apparatus and a pure water producing method capable of efficiently removing boron and organic matter. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a pure water producing apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the pure water production apparatus and the pure water production method of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a pure water production apparatus 1 according to one embodiment of the present invention. The pure water production apparatus 1 is composed of a pretreatment system 2 on the upstream side and a primary pure water production system 3 on the downstream side, and the primary pure water production system 3 is connected to a secondary pure water production system (not shown) on the downstream side. The secondary pure water production system is also called a subsystem, and produces ultrapure water from the pure water produced in the primary pure water production system 3. The ultrapure water produced in the secondary pure water production system is supplied to a point of use (not shown). The raw water (hereinafter referred to as water to be treated) supplied to the pure water production apparatus 1 contains boron and organic matter.

[0011] The pure water production system 1 includes a filter 21, an activated carbon tower 22, a first reverse osmosis membrane separation device (hereinafter referred to as the first RO device 31), a second reverse osmosis membrane separation device (hereinafter referred to as the second RO device 32), an ultraviolet oxidation device 33, a regenerative ion exchange device 34, and a cation exchange device 35, which are arranged in series in this order along a mother pipe L1 from upstream to downstream with respect to the flow direction D of the water to be treated. The filter 21 and the activated carbon tower 22 constitute a pretreatment system 2, and the devices from the first RO device 31 to the cation exchange device 35 constitute a primary pure water production system 3. In the pure water production process, the water to be treated is passed through the filter 21, the activated carbon tower 22, the first RO device 31, the second RO device 32, the ultraviolet oxidation device 33, the regenerative ion exchange device 34, and the cation exchange device 35 in this order and treated. Although not shown in the figures, pumps and other devices may be arranged between these devices.

[0012] The primary pure water production system 3 has a pH adjuster supply unit 36 ​​that supplies a pH adjuster. A pH adjuster injection unit 37 is provided in the mother pipe L1 between the first RO device 31 and the second RO device 32, and the injection unit 37 is connected to the pH adjuster supply unit 36. Therefore, a pH adjuster is injected into the water to be treated between the first RO device 31 and the second RO device 32. The pH adjuster may be one that increases or decreases the pH.

[0013] The water to be treated is pressurized by a raw water pump (not shown), and then passed through a filter 21 to remove relatively large particles such as dust, and then through an activated carbon tower 22 to remove impurities such as polymeric organic matter.

[0014] Next, the water to be treated is supplied to the first RO device 31. The first RO device 31 removes most of the ionic components from the water to be treated. A conventionally known device can be used as the first RO device 31. As the membrane, for example, a cellulose acetate or polyamide asymmetric membrane, or a composite membrane having a polyamide active layer can be used. As the membrane form, a flat membrane, a hollow fiber membrane, a spiral membrane, etc. can be used.

[0015] The treated water from the first RO device 31, from which ionic components have been removed by the treatment, is adjusted in pH with a pH adjuster. In this embodiment, the pH adjuster supply unit 36 ​​is provided to increase the pH of the water to be treated (to make it alkaline). For this purpose, the pH adjuster supply unit 36 ​​injects an alkaline agent such as NaOH into the mother pipe L1. The pH of the water to be treated is adjusted to about 7 to 8.5, preferably 7.5 to 8.0. The reason for limiting the pH to this range will be described later. The treated water, to which the pH adjuster has been injected and whose pH has been adjusted, is supplied to the second RO device 32, where it is further treated with ionic components, particularly hydrogen carbonate ions (HCO 3 - ) is removed. The second RO device 32 has the same configuration as the first RO device 31.

[0016] Next, the treated water from the second RO device 32 is supplied to the ultraviolet oxidation device 33. The ultraviolet oxidation device 33 irradiates the water to be treated with ultraviolet rays. The ultraviolet oxidation device 33 includes a stainless steel reaction tank and a tubular ultraviolet lamp installed in the reaction tank. As the ultraviolet lamp, for example, an ultraviolet lamp that generates ultraviolet rays including at least one of the wavelengths of 254 nm and 185 nm, or a low-pressure ultraviolet lamp that generates ultraviolet rays having wavelengths of 254 nm, 194 nm, and 185 nm is used. When the water to be treated is irradiated with ultraviolet rays having a wavelength of 185 nm or 254 nm, radicals are generated, and the decomposition of organic matter is promoted by these radicals. This provides a TOC reduction effect.

[0017] Next, the treated water from the ultraviolet oxidation device 33 is supplied to the regenerative ion exchange device 34, where ion components are removed. At this time, boron that could not be completely removed by the previous equipment (such as the first and second RO devices 31 and 32) is almost completely removed by the regenerative ion exchange device 34. The regenerative ion exchange device 34 means an ion exchange device filled with a regenerative ion exchange resin. Instead of the ion exchange resin, a monolithic or fibrous ion exchanger can be used. The regenerative ion exchange device 34 has a cation-filled section 34A filled with a strongly acidic cation exchange resin and an anion-filled section 34B filled with a strongly basic anion exchange resin. The cation-filled section 34A and the anion-filled section 34B can be configured as towers filled with each resin alone (two-bed, two-tower type), or can be configured by partitioning one tower into the cation-filled section 34A and the anion-filled section 34B (multiple-bed packed type or two-bed, one-tower type). In either case, the anion-loaded section 34B is preferably provided downstream of the cation-loaded section 34A in the direction of flow of the treated water treated in the second RO device 32. By using a strongly acidic cation exchange resin and a strongly basic anion exchange resin, various ions other than boron can be removed. A non-regenerative ion exchange device may be used instead of the regenerative ion exchange device 34.

[0018] Boron is removed by a strong basic anion exchange resin. It is also known to use a boron selective resin to remove boron, but the boron selective resin is prone to elution of organic matter from the resin, which may be disadvantageous in reducing TOC. In this embodiment, since a general strong acid cation exchange resin and a strong basic anion exchange resin are used, the elution of organic matter from the resin can be suppressed. Therefore, it is possible to reduce TOC while ensuring boron removal performance. In addition, the strong acid cation exchange resin has the effect of lowering the pH of the treated water, which can reduce the hydroxide ion concentration of the treated water. The hydroxide ions compete with the boron ions, reducing the efficiency of the strong basic anion exchange resin in removing boron ions. By arranging the strong acid cation exchange resin upstream of the strong basic anion exchange resin, the concentration of hydroxide ions can be reduced and boron ions can be removed more efficiently.

[0019] The regenerative ion exchange device 34 has a higher boron removal efficiency than other ion removal devices, such as an electrodeionized water production device (EDI). When using EDI to remove boron, the boron concentration in the concentration compartment increases, causing boron to diffuse back from the concentration compartment to the deionization compartment, resulting in boron leaking into the EDI-treated water. For this reason, it is difficult to reduce the boron concentration to 1 ng / L (ppt) or less using EDI. In contrast, the regenerative ion exchange device 34 adsorbs boron ions, making it possible to reduce the boron concentration to 1 ng / L or less.

[0020] Next, the treated water from the regenerative ion exchange device 34 is supplied to the cation exchange device 35. The cation exchange device 35 is located downstream of the regenerative ion exchange device 34 in the water flow direction. The cation exchange device 35 is filled with a cation exchange resin, preferably a strong acid cation exchange resin. In the regenerative ion exchange device 34, the quality of the treated water may deteriorate after regeneration with a regenerant, and it may take time to restore the water quality to a predetermined level. This is because the regenerant (impurity ions resulting from the regenerant) attached to the resin flows out into the treated water. In particular, NaOH, a typical regenerant for anion exchange resins, has poor washability in the washing process after regeneration, and Na ions are likely to remain. By passing the treated water through the cation exchange device 35, Na ions can be removed, and the start-up time of the regenerative ion exchange device 34 after resin regeneration can be shortened. For the same reason, the water to be treated may be passed through an anion resin to remove anions from the water to be treated. However, since the regenerant for the cation exchange resin (e.g., HCl) can be washed relatively easily compared to the regenerant for the anion exchange resin, there is little need to pass the water to be treated through the anion resin. Depending on the quality of the water to be treated, the cation exchange device 35 may be omitted. As the cation exchange device 35, it is preferable to use a cation polisher tower filled with a regenerated resin. This is because, as described above, the regenerant for the cation exchange resin can be washed relatively easily, so there is little need to use a non-regenerated resin. However, it is also possible to use a non-regenerated resin as the cation exchange device 35.

[0021] In this manner, in this embodiment, two RO units 31, 32 are provided upstream of the ultraviolet oxidation unit 33 and the regenerative ion exchange unit 34, and the pH of the water to be treated is adjusted between the two RO units 31, 32. The reasons for this are as follows. First, in the primary pure water production system 3 of this embodiment, the regenerative ion exchange unit 34 and the ultraviolet oxidation unit 33 are provided in order to reduce the boron concentration and TOC of the water to be treated. However, the carbon dioxide (H 2 CO 3) reduces the efficiency of boron removal by the strong basic anion exchange resin. Carbonic acid also consumes the radicals generated in the ultraviolet oxidation device 33 (a radical scavenger), and therefore reduces the efficiency of TOC reduction. As a countermeasure, it is possible to provide a degassing device (a carbon dioxide degassing tower, a membrane degassing device, a vacuum degassing tower, a nitrogen degassing device, a catalytic resin deoxidizing device, etc.), but this leads to an increase in the amount of equipment. Also, the membrane of the degassing device is prone to clogging, which can be disadvantageous in terms of maintenance.

[0022] Therefore, in this embodiment, the RO devices 31 and 32 are provided upstream of the ultraviolet oxidation device 33 and the regenerative ion exchange device 34 to remove carbon dioxide in advance. Since the RO devices are also provided in the existing pure water production system 1, this does not lead to an increase in the number of facilities. However, since it is difficult to directly remove carbon dioxide using the RO device, the carbon dioxide is ionized to produce bicarbonate ions (HCO 3 - ) is generally eliminated from the mixture of carbonic acid and hydrogen carbonate ion. 2 CO 3 ←→H + +HCO 3 - At low pH, there is a chemical equilibrium between HCO 3 - The proportion of HCO 3 - The proportion of HCO increases by adjusting the pH to 7-8.5. 3 - The lower limit of pH is 7.0 because the proportion of HCO 3 - This is to increase the ratio of 0.1 to 0.5 in order to efficiently remove carbonate. This reduces the anion load, improving the efficiency of boron removal by the strong basic anion exchange resin and extending the life of the strong basic anion exchange resin. There is no particular restriction on the upper limit of pH from the viewpoint of removing carbonate, but the higher the pH, the lower the TOC decomposition efficiency in the ultraviolet oxidation device 33. For this reason, the upper limit of pH is set to 8.5.

[0023] The reason for adjusting the pH in the first RO device 31 and the second RO device 32 is as follows. If the pH adjustment is performed in the upstream stage of the first RO device 31, the pH of the water to be treated at the inlet of the first RO device 31 will increase. 3 - ←→H + +CO 3 2- There is also a chemical equilibrium between CO and the pH. 3 2- As a result, CO 3 2- combines with Ca ions in the treated water to form CaCO 3 If scale occurs, the membranes of the first and second RO devices 31 and 32 are likely to be clogged. Therefore, in this embodiment, hardness components (Ca ions) are first removed in the first RO device 31. As a result, hardness components, which are the cause of scale, are removed from the water to be treated that is supplied to the second RO device 32, making it possible to adjust the pH without considering the scale. In other words, the first RO device 31 and the second RO device 32 are provided for completely different purposes. That is, the second RO device 32 works in cooperation with the pH adjuster supply unit 36 ​​to remove carbonic acid, which deteriorates the boron removal efficiency of the regenerative ion exchange device 34 and the TOC reduction efficiency of the ultraviolet oxidation device 33. In order to prevent scale that is likely to occur due to pH adjustment, the first RO device 31 removes hardness components in advance, thereby suppressing scale generation in the second RO device 32. In addition, since the water to be treated before pH adjustment is supplied to the first RO device 31, the possibility of scale generation in the first RO device 31 is low.

[0024] Example 1 Two ion exchange resin containers (columns) with an inner diameter of 26 mm and a height of 1 m connected in series were filled with a strongly basic anion exchange resin (anion resin) and a strongly acidic cation exchange resin (cation resin), respectively, and simulated raw water was passed through them. The amount of liquid passed (the ratio of the total liquid volume of the water to be treated to the volume of the resin filled) until the boron concentration in the treated water reached 5 ng / L (ppt) was calculated. AMBERJET ESG4002(OH) (Organo Corporation) was used as the anion resin, and AMBERJET ESG1024(H) (Organo Corporation) was used as the cation resin, and 314 ml of anion resin or cation resin was filled into each column. Reagents were added to ultrapure water, and the concentrations were adjusted to Na concentration 36 μg / L, boron concentration 12 μg / L, Si concentration 1 μg / L, Cl concentration 1 μg / L, and HCO 3 Concentration 150μg / L, CO 2 A simulated raw water with a concentration of 245 μg / L and pH adjusted to 7 was prepared and passed through the column at a flow rate of 28.8 L / h (linear velocity LV = 55 m / h, spatial velocity SV = 91.7 / h).

[0025] In Example 1, the upstream column was filled with a cationic resin, and the downstream column was filled with an anionic resin. In Comparative Example 1, the upstream column was filled with an anionic resin, and the downstream column was filled with a cationic resin. In Comparative Example 2, the pH of the simulated raw water was adjusted to 9.6, the upstream column was filled with a cationic resin, the downstream column was filled with an anionic resin, and a column filled with a cationic resin was added downstream of the downstream column, and the simulated raw water was passed through the cationic resin, anionic resin, and cationic resin in that order. The flow rate at which the boron concentration reached 5 ng / L (ppt) was 8930 in Example 1, 7350 in Comparative Example 1, and 7700 in Comparative Example 2. From this, it was confirmed that passing water through the cationic resin and anionic resin in that order suppresses boron leakage and improves boron removal efficiency, rather than passing water through the anionic resin and cationic resin in that order. It is also believed that passing water through the cation resin first and then the anion resin extends the life of the resin and reduces the frequency of resin regeneration.

[0026] It is considered that the boron removal performance of the anion resin was reduced because the pH of the simulated raw water was high in Comparative Example 2. As described later, a pH that is too close to the alkaline side is not preferable in terms of reducing TOC, but is also not preferable in terms of boron removal efficiency and frequency of resin regeneration.

[0027] Example 2 A simulated raw water was passed through a test device equivalent to the primary pure water production system 3 shown in FIG. 1 (i.e., the first RO device 31 to the cation exchange device 35 were provided in this order, and a pH adjuster injection section 37 was provided between the first RO device 31 and the second RO device 32), and the water quality of the treated water from the cation exchange device 35 was measured. The reverse osmosis membranes of the first and second RO devices 31 and 32 were made of ultra-low pressure membrane ES20 manufactured by Nitto Denko Corporation, the strongly basic anion exchange resin was made of AMBERJET ESG4002(OH) (manufactured by Organo Corporation), and the strongly acidic cation exchange resin was made of AMBERJET ESG1024(H) (manufactured by Organo Corporation). Reagents were added to the ultra-pure water to prepare simulated raw water adjusted to pH 6.3, TOC 186 μg / L, Na concentration 6.5 μg / L, and boron concentration 33.8 μg / L. In Comparative Example 3, no pH adjustment was performed at the inlet of the second RO device 32. Therefore, the pH of the simulated raw water in the second RO device 32 was 5.2. In Comparative Example 4, the pH of the inlet water of the second RO device 32 was adjusted to 10.5. The results are shown in Table 1. The carbon dioxide concentration and boron concentration were reduced to the same extent in Example 2 and Comparative Examples 3 and 4, but the TOC was the lowest in Example 2. In Comparative Example 3, the pH was low, and the carbon dioxide removal efficiency in the second RO device 32 was reduced. For this reason, the carbon dioxide concentration of the water to be treated supplied to the ultraviolet oxidation device 33 remained high, and it is considered that the TOC reduction effect in the ultraviolet oxidation device 33 was reduced. In Comparative Example 4, the pH was high, and it is considered that the TOC reduction effect in the ultraviolet oxidation device 33 was reduced. It was confirmed that by passing the treated water through the first RO device 31, the second RO device 32, the ultraviolet oxidation device 33, and the regenerative ion exchange device 34 in that order, and adjusting the pH between the first RO device 31 and the second RO device 32, the TOC and boron concentrations of the treated water can be efficiently reduced.

[0028] [Table 1] [Explanation of symbols]

[0029] 1 Pure water production equipment 2 Pretreatment System 31st Pure Water Production System 21 Filter 22 Activated carbon tower 31 First reverse osmosis membrane separation device (first RO device) 32 Second reverse osmosis membrane separation device (second RO device) 33 Ultraviolet oxidation device 34 Regenerative Ion Exchanger 35 Cation exchanger 36 pH adjuster supply section 37 Injection part D Flow direction of treated water L1 main tube

Claims

1. A pure water producing apparatus for producing pure water from treated water containing boron and organic matter, a first reverse osmosis membrane separation device to which the water to be treated is supplied; a pH adjuster injection section that injects a pH adjuster into the treated water treated by the first reverse osmosis membrane separation device so that the pH of the treated water is in the range of 7 to 8.5; a second reverse osmosis membrane separation device to which the treated water into which the pH adjuster has been injected is supplied; an ultraviolet oxidation device to which the treated water treated in the second reverse osmosis membrane separation device is supplied; a regenerative ion exchange device to which the treated water from the ultraviolet oxidation device is supplied, which is filled with a strong acid cation exchange resin and a strong basic anion exchange resin, and which reduces the boron concentration to 1 ng / L or less; a cation exchange device that is located downstream of the regenerative ion exchange device in the water flow direction of the regenerative ion exchange device and is filled with only a cation exchange resin; The injection section is connected to a pH adjuster supply section of the pure water production apparatus.

2. 2. The pure water producing apparatus according to claim 1, wherein the regenerative ion exchange device has a cation-filled section filled with a strongly acidic cation exchange resin and an anion-filled section filled with the strongly basic anion exchange resin, and the anion-filled section is located downstream of the cation-filled section in the water flow direction in the ion exchange device.

3. A method for producing pure water from treated water containing boron and organic matter, comprising the steps of: The method comprises passing the water to be treated through a first reverse osmosis membrane separation device, a second reverse osmosis membrane separation device, an ultraviolet oxidation device, a regenerative ion exchange device filled with a strongly acidic cation exchange resin and a strongly basic anion exchange resin, and a cation exchange device filled with only a cation exchange resin, in that order; A pH adjuster is injected into the water to be treated between the first reverse osmosis membrane separation device and the second reverse osmosis membrane separation device to adjust the pH of the water to a range of 7 to 8.5; The method for producing pure water, wherein the boron concentration of the treated water from the regenerative ion exchange device is reduced to 1 ng / L or less.

4. 4. The method for producing pure water according to claim 3, wherein the regenerative ion exchange device has a cation-filled section filled with a strongly acidic cation exchange resin and an anion-filled section filled with the strongly basic anion exchange resin, and the anion-filled section is located downstream of the cation-filled section in the water flow direction in the regenerative ion exchange device.

Images