JP7129965B2 - Pure water production method, pure water production system, ultrapure water production method, and ultrapure water production system - Google Patents

Description

The present invention provides an ultrapure water production method and an ultrapure water production system capable of sufficiently removing boron contained in raw water to obtain ultrapure water having a desired quality, and an ultrapure water production system having a good balance between water quality and water recovery rate. The present invention relates to a pure water production method and a pure water production system.

2. Description of the Related Art Conventionally, in water treatment, pure water and ultrapure water are produced using membrane treatment means, ion exchange means, decarbonation equipment, etc., in order to remove various ion components and hardness components.

In addition, in the field of manufacturing very precise equipment such as semiconductor manufacturing, high cleanliness is required for the parts to be manufactured, and ultrapure water is used for washing these parts. In recent years, a very low level of boron content in this ultrapure water is required, and various water treatment methods are being investigated.
In addition, from the viewpoint of safety, in recent years, there has been a demand for ultrapure water production by a method that does not use chemicals.

Since the electrodeionization apparatus can remove boron well without generating hardness scale, it is useful for obtaining high-purity water and is suitable for use in an ultrapure water production system. Moreover, unlike ordinary ion-exchange resin towers, regeneration with chemicals such as acids and alkalis is not required.

In the case of an electrodeionization apparatus, if the water to be treated contains both hardness components and carbonic acid, hardness scale is generated and the quality of the treated water is lowered. , a reverse osmosis membrane device for removing hardness components and a decarbonation device for removing carbonic acid are provided to constitute an ultrapure water production system (see Patent Documents 1 and 2, for example). It is also known that if the water to be treated by the electrodeionization apparatus contains carbonic acid, the ability of the electrodeionization apparatus to remove boron is reduced (see, for example, Patent Document 1).

In addition, in the production of ultrapure water, it is necessary to remove DO (dissolved oxygen) to a high degree, and a vacuum degassing device and a degassing membrane device are used, but the decarboxylation device often performs this function. .

Japanese Unexamined Patent Application Publication No. 2014-575 JP 2017-56384 A

As a decarbonation device, there are a degassing tower, a vacuum degassing tower, a degassing membrane, and the like. A membrane degassing device (MDG) using a degassing membrane is often used from the viewpoint that it is small, has a high ability to remove carbonic acid, and can also remove DO (dissolved oxygen). This membrane degassing device consists of a hollow fiber membrane in which a large number of hollow fibers are bundled, and the gap between the hollow fibers is as narrow as about 150 μm, for example. Therefore, the membrane degassing device has a structure that is vulnerable to foreign matter.

Therefore, if foreign matter is mixed in the ultrapure water production system for some reason and the water to be treated containing the foreign matter is supplied to the membrane degassing device, clogging occurs and the treatment cannot be continued. . On the other hand, ultrapure water production systems are strongly required to continuously supply ultrapure water, and as long as membrane degassing equipment is used, there is currently no way to eliminate this risk.

Accordingly, an object of the present invention is to provide an ultrapure water production method and an ultrapure water production system capable of stable operation without using a membrane degassing device for removing carbonic acid. Another object is to provide a pure water production method and a pure water production system that have a good balance between water quality and water recovery rate, which were discovered in the course of the study.

In the ultrapure water production method of the present invention, the water to be treated is treated with the first reverse osmosis membrane device, and then treated with the electrodeionization device and the boron removal device in that order, and the boron concentration is 1 ng. /L or less, wherein the electrodeionization device comprises a desalination chamber to which water to be treated of the electrodeionization device is supplied, and a desalination chamber. a mixture of an anion exchange resin and a cation exchange resin filled in the electrodeionization apparatus, the water to be treated of the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the electrodeionization The treated water of the apparatus is characterized in that the carbonic acid has been removed and contains 1 μg/L or less of boron.

The pure water production method of the present invention is a pure water production method in which the water to be treated is treated with a first reverse osmosis membrane device and then subsequently treated with an electrodeionization device, wherein the electrodeionization device is a deionization chamber to which the water to be treated of the electrodeionization apparatus is supplied; and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber, wherein The water to be treated by the ionization device contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization device has the carbonic acid removed and contains 1 μg/L or less of boron, and the electrodeionization device contains 1 μg/L or less of boron. The concentrated water of the device is mixed with the concentrated water of the first reverse osmosis membrane device to obtain mixed concentrated water, and the mixed concentrated water is passed through the second reverse osmosis membrane device. It is characterized by circulating to the front stage of the first reverse osmosis membrane device .

In the ultrapure water production system of the present invention, the water to be treated is sequentially treated with the first reverse osmosis membrane device, the electrodeionization device and the boron removal device to obtain an ultrapure water with a boron concentration of 1 ng / L or less. An ultrapure water production system for obtaining water, wherein the electrodeionization device comprises a desalination chamber to which the water to be treated of the electrodeionization device is supplied, and a shade filled in the desalination chamber. a mixture of an ion exchange resin and a cation exchange resin, the water to be treated by the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and , the second for treating the concentrated mixed water of the concentrated water from the first reverse osmosis membrane device and the concentrated water from the electrodeionization device, from which carbonic acid has been removed and contains 1 μg/L or less of boron; It is characterized by having a reverse osmosis membrane device and a circulation pipe for circulating the permeated water of the second reverse osmosis membrane device to the front stage of the first reverse osmosis membrane device.

The pure water production system of the present invention is a pure water production system in which water to be treated is treated in turn by a first reverse osmosis membrane device and an electrodeionization device , wherein the electrodeionization device a deionization chamber to which water to be treated in the deionization device is supplied; and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber, The water to be treated contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization device contains 1 μg/L or less of boron from which the carbonic acid has been removed, and the first reverse osmosis membrane device. a second reverse osmosis membrane device for treating a concentrated mixed water of the concentrated water of and the concentrated water of the electrodeionization device; and a circulation pipe for circulating to the front stage of the permeable membrane device.

According to the ultrapure water production method and the ultrapure water production system of the present invention, carbonic acid and boron can be removed without using a membrane degassing device for carbonic acid removal. Since clogging of the membrane degassing device does not occur, stable operation of the ultrapure water production system is possible.

Therefore, according to the ultrapure water production method and the ultrapure water production system of the present invention, ultrapure water of predetermined water quality can be stably obtained for a long period of time.

In addition, according to the pure water production method and the pure water production system of the present invention, water can be treated without using a membrane deaerator for removing carbonic acid, and clogging of the membrane deaerator due to contamination by foreign matter is avoided. stable production of pure water. Moreover, the pure water production method of the present invention can obtain treated water having a good balance between water quality and water recovery rate.

1 is a diagram showing a schematic configuration of an ultrapure water production system used in an ultrapure water production method according to an embodiment of the present invention; FIG. FIG. 2 is a diagram showing a schematic configuration of an ultrapure water production system used in another ultrapure water production method according to an embodiment of the present invention; FIG. 2 is a diagram showing a schematic configuration of an ultrapure water production system used in still another ultrapure water production method according to an embodiment of the present invention; 1 is a diagram showing a schematic configuration of a pure water production system used in a pure water production method according to an embodiment of the present invention; FIG. FIG. 10 is a diagram for explaining the difference in water quality between the pure water production system of Example 3 and its comparative system;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the ultrapure water production method according to the first embodiment of the present invention will be described in detail with reference to FIG.

[Ultrapure water production method]
In the ultrapure water production method according to one embodiment of the present invention, water to be treated is treated with a first reverse osmosis membrane device, and then treated with an electrodeionization device and a boron removal device in that order. and an ultrapure water production method for obtaining ultrapure water having a boron concentration of 1 ng/L or less.

In this ultrapure water production method, the water to be treated in the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the treated water in the electrodeionization apparatus is free of carbonic acid and free of boron. It is characterized by containing 1 μg/L or less.

Before explaining this ultrapure water production method, first, an ultrapure water production system used in this ultrapure water production method will be explained with reference to the drawings. As shown in FIG. 1, the ultrapure water production system used here has a configuration in which the water to be treated is treated in the order of the first reverse osmosis membrane device 2, the electrodeionization device 3, and the boron removal device 4. It is an ultrapure water production system 1.

The first reverse osmosis membrane device 2 (RO1) used in the present embodiment can be a reverse osmosis membrane device known in the art without particular limitation, and removes organic impurities and salts contained in the water to be treated. Remove. As the reverse osmosis membrane used in the first reverse osmosis membrane device 2, for example, various organic polymer membranes or ceramic membranes made of cellulose acetate, an aliphatic polyamide system, an aromatic polyamide system, or a composite system thereof are used. can.

In addition, as the reverse osmosis membrane used in the first reverse osmosis membrane device 2, any of an ultra-low pressure type, a low pressure type, a medium pressure type, or a high pressure type can be applied. Alternatively, a high pressure type is preferable. For example, when the boron concentration in the raw water is high, it is possible to reduce the burden of boron removal in the latter stage by using a medium-pressure type or a high-pressure type. As the type of membrane module, a hollow fiber module, a tubular module, a spiral module, a flat membrane module, and the like can be applied, and a spiral module is preferable because a large membrane area per unit volume can be obtained.

This first reverse osmosis membrane device 2 may be a two-stage reverse osmosis membrane device (two-stage RO) in which two reverse osmosis membrane devices are connected in series. Since the water quality of the water supplied to the electrodeionization device 3 is improved, the load on the electrodeionization device 3 and subsequent ones is reduced, and the quality of the ultrapure water obtained is expected to be improved. In the present embodiment, since the water quality of the water supplied to the electrodeionization device 3 has a wide tolerance, the first reverse osmosis membrane device 2 is performed in one stage, thereby simplifying the water purifying device 1. , and it is also possible to obtain ultrapure water of high purity.

The electrodeionization device 3 (EDI) used in this embodiment can be any known electrodeionization device in this field without particular limitation, and mainly removes salts. The electrodeionization device 3 removes ion components from the permeated water obtained by the first reverse osmosis membrane device 2, and also removes carbonic acid and boron.

The electrodeionization device 3 has, for example, anion-exchange membranes and cation-exchange membranes alternately arranged between the anode and the cathode, and desalination partitioned by the anion-exchange membrane and the cation-exchange membrane. It has alternating chambers and concentration chambers into which concentrated water containing removed ion components flows. The electrodeionization apparatus 3 has a mixture of anion-exchange resin and cation-exchange resin filled in the deionization chamber, and electrodes for applying a DC voltage.

In the electrodeionization apparatus 3, for example, the water to be treated is supplied to the desalination compartment and the concentration compartment in parallel, and the mixture of the anion exchange resin and the cation exchange resin in the desalination compartment is the ion component in the water to be treated. to adsorb. The adsorbed ionic components are transferred to the concentration compartment by the action of direct current, and the concentrated water in the concentration compartment is discharged out of the system.

The electrodeionization apparatus 3 can continuously remove ionic components without using any chemicals such as acid or alkali for regenerating the ion exchange resin. Therefore, it is possible to improve the safety of ultrapure water production, reduce the production cost, and downsize the apparatus, leading to an improvement in production efficiency.

The boron removal device 4 used in the present embodiment is arranged after the electrodeionization device 3 and is a device capable of efficiently removing boron from the treated water treated by the electrodeionization device 3 . Examples of the boron removal device 4 include an electrodeionization device, a boron-selective ion-exchange resin device, or a mixed-bed ion-exchange resin device of a boron-selective ion-exchange resin and a cation-exchange resin and/or an anion-exchange resin. Any of the above may be mentioned. These devices are described below.

The description of the electrodeionization apparatus is omitted because it is the same as the description of the electrodeionization apparatus 3 described above. If an electrodeionization device is selected as the boron removal device 4, the configuration is a two-stage electrodeionization device (two-stage EDI) in which two electrodeionization devices are connected in series.

The boron-selective ion-exchange resin apparatus includes known ones capable of selectively adsorbing boron, and can be used without particular limitation. Specific examples of the boron-selective ion-exchange resin include, for example, Amberlite (registered trademark: manufactured by Rohm and Haas) IRA-743T, Diaion CRB02 (Mitsubishi Kasei Co., Ltd.) and the like.

In addition, the mixed bed type ion exchange resin apparatus of the boron selective ion exchange resin and the cation exchange resin and/or the anion exchange resin includes the above boron selective ion exchange resin and other ion exchange resin in the ion exchange resin tower. It is a mixed-bed configuration that mixes In this case, as the ion exchange resin to be mixed with the boron-selective ion exchange resin, for example, a mixture of a strongly acidic cation exchange resin and/or a strongly basic anion exchange resin can be exemplified. More specifically, boron-selective ion-exchange/cation-exchange mixed bed resins, boron-selective ion-exchange/anion-exchange mixed-bed resins, and boron-selective ion-exchange/cation-exchange/anion-exchange mixed bed resins are mentioned. be done.

Here, as the strongly acidic cation exchange resin, a styrene-based resin having a sulfonic acid group as a functional group is preferable because the ion exchange resin is less hydrolyzed and the organic cation component is less eluted into ultrapure water. As the strongly acidic cation exchange resin, the H-type is preferable because it can remove cation components with low ion selectivity.

Commercial products of the strongly acidic cation exchange resin used here include Duolite CGP (manufactured by Rohm and Haas), Diaion SKT20L (manufactured by Mitsubishi Chemical Corporation), and the like.

In addition, as a strongly basic anion exchange resin, since the ion exchange resin is less hydrolyzed and the organic anion component is less eluted into ultrapure water, a styrene resin having a quaternary ammonium group as a functional group, etc. is preferably used. The strongly basic anion exchange resin is preferably OH type because it can remove anion components with low ion selectivity.

Commercial products of the strongly basic anion exchange resin used here include Duolite AGP (manufactured by Rohm and Haas) and Diaion SAT20L (manufactured by Mitsubishi Chemical Corporation).

When such an ultrapure water production system is used, the water to be treated is treated with the first reverse osmosis membrane device 2, subsequently treated with the electrodeionization device 3, and further treated with the boron removal device 4. . At this time, the first reverse osmosis membrane device 2 and the boron removal device 4 may be processed by a conventionally known method. On the other hand, the electrodeionization apparatus 3 contains carbonic acid and boron in the water to be treated, and is operated and treated so as to remove them in a well-balanced manner.

As for the water to be treated (supply water) of the first reverse osmosis membrane device 2, it is preferable that the value of the ratio of the hardness component to the silica component [hardness/silica] is 1 or more from the viewpoint of suppressing the generation of silica scale. . The value of this ratio is more preferably 2 or more, more preferably 5 or more.
The above ratio [hardness/silica] can be calculated, for example, by the following formula.
[Hardness/Silica] = hardness concentration (calcium carbonate conversion value of Ca + Mg) ÷ silica concentration (as SiO ₂ )

Moreover, the water to be treated (supply water) to the first reverse osmosis membrane device 2 may be adjusted in pH by adding acid or alkali, if necessary. In addition, a silica scale inhibitor, a hardness scale inhibitor, or a bacteriostatic agent may be added as necessary.

The first reverse osmosis membrane device 2 may be operated in the same manner as a conventionally known ultrapure water production method, and the water recovery rate is set to the Langerer index or silica saturation to avoid the generation of hardness scale or silica scale. It is set in consideration of solubility, etc. Depending on the water quality, for example, the first reverse osmosis membrane device 2 can be operated with a water recovery rate of about 70 to 90%.

That is, while the water to be treated supplied to the electrodeionization apparatus 3 contains carbonic acid concentration of more than 1 mg/L, preferably more than 1 mg/L and 50 mg/L or less, carbonic acid is sufficiently removed as the treated water after treatment. (for example, 10 μg/L (ppb) or less), and the boron concentration is 1 μg/L or less. This is because the water to be treated by the electrodeionization device 3 is not sufficiently carbonic acid removed in the preceding stage (no decarbonation device is provided), and the treated water after the treatment has a carbonic acid concentration of is reduced, and the boron concentration is also reduced to a predetermined concentration or less.

As the treated water of the electrodeionization apparatus 3, treated water having a boron concentration of 500 ng/L (ppt) or less is more preferable, and treated water having a boron concentration of 100 ng/L (ppt) or less is even more preferable.

By setting the carbonic acid concentration of the treated water of the electrodeionization apparatus 3 within the above range, it is possible to minimize the influence of carbonic acid on the apparatus installed in the subsequent stage.

In this embodiment, the technical meaning is that, in order to efficiently produce ultrapure water, the electrodeionization apparatus 3 simultaneously removes carbonic acid and boron, and performs these removals in a well-balanced manner. at the point.

In order to treat the water quality as described above, in the present embodiment, the treatment is performed with the recovery rate of the electrodeionization apparatus 3 set to 80% or more and less than 90%. Thus, by operating the electrodeionization apparatus with a recovery rate lower than the normal recovery rate of the conventionally known device configuration, it is possible to sufficiently remove carbonic acid as well as boron. Here, the boron concentration can be reduced to such an extent that preparations can be made for producing ultrapure water having a desired boron concentration by the subsequent boron removal device 4 .

The reason why the boron removal rate decreases due to the presence of carbonic acid is that when carbonic acid is removed in the electrodeionization apparatus, the carbonic acid concentration on the concentrated water side of the electrodeionization apparatus gradually increases. It is considered that this carbonic acid then flows back to the desalting chamber side. If the water recovery rate is set at 80% or more and less than 90%, the carbonic acid concentration on the concentrated water side can be lowered, so that this effect can be reduced.
Even if the recovery rate of the electrodeionization apparatus 3 is set to less than 80%, the boron removal rate is hardly improved, so it is not preferable to set the recovery rate of the electrodeionization apparatus 3 to less than 80%.

The electrodeionization device 3 preferably has a current value per treated water flow rate of 0.4 A/(m ³ /h) to 4.0 A/(m ³ /h) from the viewpoint of suitably removing carbonic acid and boron. , 0.8 A/(m ³ /h) to 2.5 A/(m ³ /h).

When the above-described treatment is performed by the electrodeionization device 3, the subsequent treatment by the boron removal device 4 efficiently produces ultrapure water having a desired quality of 1 ng/L (1 ppt) or less of boron concentration, and It can be obtained without using a membrane deaerator. That is, since carbonic acid is removed by the electrodeionization device 3, the effect of carbonic acid on the boron removal device 4 can be eliminated. The burden of boron removal to 4 is reduced, and efficient removal becomes possible. In addition, since the membrane degassing device is not installed, the ultrapure water production system can be stably operated without the trouble of clogging of the membrane degassing device with foreign matter, and the desired ultrapure water can be obtained continuously. be able to.
The boron removal device 4 may be appropriately selected depending on the quality of the water (boron concentration) obtained by the electrodeionization device 3 .

Carbonic acid in the present embodiment includes carbon dioxide, hydrogen carbonate ions and carbonate ions, and the carbonic acid concentration means the total carbonic acid (CO ₂ +HCO ₃ ⁻ +CO ₃ ²⁻ ) concentration is the _CO2 equivalent concentration.).

(Modification)
In the above description, the treatment is performed under the operating conditions of the electrodeionization apparatus 3, but treated water of desired quality can also be obtained by using a specific apparatus as follows.

That is, the ultrapure water production system used in this modification has the same configuration as that shown in FIG. A device with a width of 2 mm or more and 6 mm or less is used. In this modified example, the recovery rate is not particularly limited, and can be operated at 90% or more.

Thus, even by using an electrodeionization apparatus with a relatively narrow cell width of 2 mm or more and 6 mm or less in the deionization chamber, it is possible to contain 10 μg/L or less of carbonic acid and 1 μg/L or less of boron as described above. can obtain treated water. The cell width of the desalting chamber is more preferably 2 mm or more and 4 mm or less.

Compared to, for example, the migration speed of strong ions such as chloride ion and sodium ion, the migration speed of ions to the adjacent concentrating compartment side is lower than that of weak ions such as boron and carbonic acid. It is assumed that the width has a large effect. That is, by reducing the cell width of the desalting chamber, the boron removal rate is greatly improved, the influence of carbonic acid is reduced, and treated water having the water quality required in this embodiment can be obtained.

(Second embodiment)
Next, an ultrapure water production method and an ultrapure water production system according to a second embodiment of the present invention will be described with reference to FIG.

[Ultrapure water production system]
As shown in FIG. 2, the ultrapure water production system in this embodiment is configured to treat the water to be treated in the order of the first reverse osmosis membrane device 2, the electrodeionization device 3, and the boron removal device 4. In addition, the ultrapure water production system 10 has a second reverse osmosis membrane device 11 and a circulation pipe 12 for circulating the treated water of the second reverse osmosis membrane device 11 .

Here, devices having the same configurations as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. That is, since the first reverse osmosis membrane device 2, the electrodeionization device 3, and the boron removal device 4 are the same as those of the first embodiment, only different configurations will be described below.

As with the first reverse osmosis membrane device 2, the second reverse osmosis membrane device 11 in the present embodiment can be a reverse osmosis membrane device known in the art without particular limitation. Similar to the permeable membrane device 2, organic impurities and salts such as carbonic acid and boron contained in the water to be treated are removed. The second reverse osmosis membrane device 11 mixes the concentrated water from the electrodeionization device 3 with the concentrated water from the first reverse osmosis membrane device 2 to form mixed concentrated water, and the mixed concentrated water is treated water. and Then, the mixed concentrated water is treated by the second reverse osmosis membrane device 11 to remove impurities such as salts contained in the mixed concentrated water.

The circulation pipe 12 in the present embodiment is a pipe for returning the treated water (permeated water) obtained in the second reverse osmosis membrane device 11 to the front stage of the first reverse osmosis membrane device 2 for circulation. be. Through this circulation pipe 12, the concentrated water in the first reverse osmosis membrane device 2 and the electrodeionization device 3 can be used again as the water to be treated for ultrapure water production after removing impurities.

[Ultrapure water production method]
In the ultrapure water production method of this embodiment, the water to be treated is treated with the first reverse osmosis membrane device 2 , subsequently treated with the electrodeionization device 3 , and further treated with the boron removal device 4 . Here, the first reverse osmosis membrane device 2, the electrodeionization device 3, and the boron removal device 4 may be processed as described in the first embodiment.

In the present embodiment, furthermore, the concentrated water obtained when treated with the first reverse osmosis membrane device 2 and the concentrated water obtained when treated with the electrodeionization device 3 are mixed to obtain mixed concentrated water. This mixed concentrated water is treated with the second reverse osmosis membrane device 11 . The treatment by the second reverse osmosis membrane device 11 may be performed by a conventionally known method. In addition, let the concentrated water obtained here be waste water.

On the other hand, the permeated water obtained by the treatment of the second reverse osmosis membrane device 11 is returned and circulated to the front stage of the first reverse osmosis membrane device 2 using the circulation pipe 12 . That is, this permeated water is again passed through the first reverse osmosis membrane device 2 and treated.

By circulating in this manner, the concentrated water of the electrodeionization device 3 contains carbonic acid. contains its carbonic acid. Since the permeated water containing carbonic acid is circulated in this way, the water to be treated in the first reverse osmosis membrane device has a higher carbonic acid concentration than the water to be treated that was originally supplied. does not extremely increase the load on the electrodeionization apparatus 3, and can maintain the water quality of the treated water (permeate water) of the electrodeionization apparatus 3 within a desired range.

On the other hand, due to this improvement in carbonic acid concentration, the carbonic acid concentration in the treated water obtained as the permeated water of the first reverse osmosis membrane device 2 is improved compared to the case where the circulation is not performed, so that the pH thereof is slightly inclined to the acidic side. contributes to improving the recovery rate in the second reverse osmosis membrane device 11 . Therefore, the present embodiment has the advantage of being able to improve the recovery rate while maintaining the quality of the treated water without increasing the load on the electrodeionization apparatus 3 so much. Thereby, ultrapure water can be produced more efficiently.

(Third embodiment)
An ultrapure water production method and an ultrapure water production system according to a third embodiment of the present invention will be described with reference to FIG.

[Ultrapure water production system]
As shown in FIG. 3, the ultrapure water production system in this embodiment includes the first reverse osmosis membrane device 2, the electrodeionization device 3, and the electrodeionization device 21 as the boron removal device, in this order. In addition to the structure for treating water, it has a second reverse osmosis membrane device 11 and a circulation pipe 12 for circulating the treated water of the second reverse osmosis membrane device 11. 2 is an ultrapure water production system 20 having an ultraviolet oxidation device 22 (TOC-UV) and a mixed-bed ion exchange device 23 (MB).

Here, devices having the same configurations as those in the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted. That is, the first reverse osmosis membrane device 2, the electrodeionization device 3, the second reverse osmosis membrane device 11, and the circulation pipe 12 are the same as those described in the first embodiment or the second embodiment. Therefore, only the different configurations are described below.

The electrodeionization device 21 in this embodiment is the electrodeionization device specified as the boron removal device 4, as described in the first embodiment. That is, it clearly indicates that the configuration is referred to as a two-stage EDI.

Next, as the ultraviolet oxidation device 22 (TOC-UV) in this embodiment, a conventionally known ultraviolet oxidation device can be used. The ultraviolet oxidation device 22 has, for example, an ultraviolet lamp capable of irradiating ultraviolet rays having a wavelength of about 185 nm. It oxidatively decomposes organic matter that increases carbon) concentration. The ultraviolet lamp used in the ultraviolet oxidation device 22 does not have to be a lamp that emits only ultraviolet rays with a wavelength of about 185 nm. A low pressure mercury lamp can be used.

The ultraviolet oxidation device 22 decomposes water with ultraviolet rays having a wavelength of about 185 nm to generate OH radicals, and the OH radicals oxidize and decompose organic substances in the water to be treated into organic acids. It should be noted that the amount of ultraviolet irradiation in the ultraviolet oxidation device 22 can be appropriately changed according to the water quality of the water to be treated. For example, the ultraviolet irradiation amount can be 0.1 to 0.7 kW·h/m ³ . The amount of UV irradiation is preferably adjusted within the above range according to the desired water quality required for the treated water. For example, from the viewpoint of suppressing the amount of ultraviolet irradiation, it is preferable to set it to about 0.1 to 0.4 kW · h / m ³ , and if it is desired to obtain higher purity water quality, the amount of ultraviolet irradiation can be reduced as necessary. That's it.

As the mixed-bed ion exchange device 23, a device filled with a mixture of cation exchange resin and anion exchange resin can be used, and it may be either a regenerative type or a non-regenerative type. The mixed-bed ion exchange device 23 adsorbs and removes low-molecular-weight ion components generated by the oxidative decomposition of organic matter in the preceding ultraviolet oxidation device 22 . By combining the ultraviolet oxidation device 22 and the mixed-bed ion exchange device 23 of the present embodiment, it is possible to remove organic matter remaining in the water to be treated and obtain ultrapure water with a reduced TOC concentration. Instead of the mixed-bed ion exchange device 23, a single-bed column using either a cation exchange resin, an anion exchange resin, or a boron-selective ion-exchange resin alone, or a mixed bed using two or more of them It is also possible to use a double-bed tower using either tower.

[Ultrapure water production method]
In the ultrapure water production method of this embodiment, the water to be treated is treated with the first reverse osmosis membrane device 2, then treated with the electrodeionization device 3, and further treated with the electrodeionization device as the boron removal device. It is processed by the device 21 . Here, the first reverse osmosis membrane device 2, the electrodeionization device 3, and the electrodeionization device 21 may be processed as described in the first embodiment.

Further, in the present embodiment, further, the concentrated water obtained when treated with the first reverse osmosis membrane device 2 and the concentrated water obtained when treated with the electrodeionization device 3 are mixed and mixed and concentrated. Water is obtained and this mixed concentrated water is treated with the second reverse osmosis membrane device 11 . The permeated water obtained in the second reverse osmosis membrane device 11 is returned and circulated to the front stage of the first reverse osmosis membrane device 2 through the circulation pipe 12 . The processing by these configurations may be performed as described in the second embodiment.

In addition to this circulation, in this embodiment, the concentrated water from the electrodeionization device 21 can also be returned to the upstream stage of the first reverse osmosis membrane device 2, circulated, and subjected to ultrapure water production again. . In FIG. 3, this circulation is shown to be returned by joining with the circulation pipe 12 through the circulation pipe 24, but this may be performed independently.

The treated water obtained by the electrodeionization device 21 is further treated by the ultraviolet oxidation device 22 and the mixed-bed ion exchange device 23, and the treatments in these devices may be performed by known methods.

Here, the treatment by the ultraviolet oxidation device 22 and the mixed-bed ion exchange device 23 is exemplified. A water production system can be configured and an ultrapure water production method can be implemented thereby.

In the ultrapure water production method of the above-described embodiment, raw water is treated stepwise through pretreatment, primary pure water treatment, and secondary pure water treatment according to a known treatment method. It is preferable that the device configurations specifically shown in the first to third embodiments are included as the device configuration for the primary pure water treatment.

As the pretreatment device, a conventionally known pretreatment device may be provided. It is preferable to install the equipment according to the requirements and operate so as not to cause problems such as scale in the reverse osmosis membrane equipment.

Also, a membrane degassing device may be installed at an arbitrary position after the boron removal device 4 (electrodeionization device 21). The membrane degassing device installed here is provided mainly to remove dissolved oxygen (DO). When installed at such a position, impurities such as hardness components and carbonic acid are removed to a high degree in the previous stage, so the possibility of problems such as clogging of the film, which is mentioned as a problem, occurs is extremely small. Moreover, by installing such a membrane degassing device, it is possible to produce ultrapure water with DO<1 μg/L. This membrane degassing device can also be installed in the secondary pure water treatment as described above. If a membrane degassing device is installed in each of the primary pure water treatment and the secondary pure water treatment, it is possible to obtain ultrapure water with a further reduced DO, for example, ultrapure water with DO < 0.5 µg/L or less. can.

The secondary pure water treatment is composed of at least an ultraviolet irradiation device, a non-regenerative ion exchange device (polisher), and an ultrafiltration membrane device in that order. A membrane degassing device may be installed at any location. Also, an oxidizing agent removing resin device may be installed after the ultraviolet irradiation device.
As the oxidizing agent removing resin used here, a palladium-supported resin device that decomposes and removes hydrogen peroxide with a palladium (Pd)-supported resin, or a reducing resin filled with a reducing resin having a sulfite group and/or a hydrogen sulfite group on the surface. equipment and the like.

(Fourth embodiment)
Next, a pure water production method and a pure water production system according to a fourth embodiment of the present invention will be described with reference to FIG.

[Pure water production system]
As shown in FIG. 4, the pure water production system in this embodiment has a configuration in which the water to be treated is treated in the order of the first reverse osmosis membrane device 2 and the electrodeionization device 3, and the second reverse osmosis device A pure water production system 30 having a membrane device 11 and a circulation pipe 12 for circulating the treated water of the second reverse osmosis membrane device 11 .

This pure water production system 30 has a configuration in which the boron removal device 4 is omitted from the ultrapure water production system 10 described in the second embodiment. It is used for Here, devices having the same configurations as those in the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted. That is, the first reverse osmosis membrane device 2, the electrodeionization device 3, the second reverse osmosis membrane device 11, and the circulation pipe 12 have already been described in the first and second embodiments. , and the configuration of each device is as described above.

The difference from the first embodiment and the second embodiment is that the boron removal device 4 is omitted. becomes possible.

[Pure water production method]
In the pure water production method of this embodiment, the water to be treated is treated with the first reverse osmosis membrane device 2 and then treated with the electrodeionization device 3 . Further, the concentrated water obtained when treated with the first reverse osmosis membrane device 2 and the concentrated water obtained when treated with the electrodeionization device 3 are mixed to obtain mixed concentrated water, which is mixed The concentrated water is treated with the second reverse osmosis membrane device 11 . Here, the first reverse osmosis membrane device 2, the electrodeionization device 3, the second reverse osmosis membrane device 11, and the circulation pipe 12 may be processed as described in the second embodiment.

As already described in the second embodiment, the permeated water obtained by the treatment of the second reverse osmosis membrane device 11 is returned to the front stage of the first reverse osmosis membrane device 2 using the circulation pipe 12, Since the concentrated water of the electrodeionization device 3 contains carbonic acid, the mixed concentrated water and the treated water, which are the water to be treated of the second reverse osmosis membrane device 11, are circulated and circulated in this manner. Some permeate contains its carbonic acid. Since the permeated water containing carbonic acid is circulated in this way, the water to be treated in the first reverse osmosis membrane device has a higher carbonic acid concentration than the water to be treated that was originally supplied. does not extremely increase the load on the electrodeionization apparatus 3, and can maintain the water quality of the treated water (permeate water) of the electrodeionization apparatus 3 within a desired range.

On the other hand, due to this improvement in carbonic acid concentration, the carbonic acid concentration in the treated water obtained as the permeated water of the first reverse osmosis membrane device 2 is improved compared to the case where the circulation is not performed, so that the pH thereof is slightly inclined to the acidic side. contributes to improving the recovery rate in the second reverse osmosis membrane device 11 . Therefore, the present embodiment has the advantage of being able to improve the recovery rate while maintaining the quality of the treated water without increasing the load on the electrodeionization apparatus 3 so much. Thus, pure water can be produced efficiently.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
(Example 1)
Ultrapure water production system (RO1 -EDI1-EDI2) was constructed, and Atsugi city water was used as raw water to prepare water to be treated with a boron concentration of 10 μg / L (ppb), a carbonic acid concentration of 3.6 mg / L (ppm), and a pH of 7.4.

First, the water to be treated is supplied to the first reverse osmosis membrane device 2 having 12 reverse osmosis membrane modules (manufactured by Toray Industries, Inc., trade name: TM820K; crosslinked wholly aromatic polyamide composite membrane), and the operating pressure is 2 MPa. , water flow treatment at a recovery rate of 90%.

Subsequently, the water recovery rate was 83% (current: 10 A, treatment flow rate: 10 (m ³ /h)), and further treated with an electrodeionization device (manufactured by Evoqua Water Technologies, trade name: VNX-55EX) as the boron removal device 4 with a water recovery rate of 90% (current: 10A, treatment flow rate : 10 (m ³ /h)) to obtain ultrapure water.

Table 1 summarizes the boron concentration, carbonic acid concentration and resistivity of the water to be treated and the treated water obtained at this time. Carbonic acid was sufficiently removed by the electrodeionization device 3 (EDI1). Further, in Table 1, the boron removal rate of the electrodeionization apparatus and the boron removal apparatus (two-stage EDI) for the water to be treated by the electrodeionization apparatus was 99.96%, which was very good.

(Example 2)
An ultrapure water production system having the same device configuration as in Example 1 was prepared, except that the cell width of the deionization chamber of the device used as the electrodeionization device 3 (EDI 1) in Example 1 was customized to 3 mm. did.

Water to be treated under the same conditions as in Example 1, except that the recovery rate of the electrodeionization apparatus 3 (EDI 1) was set to 90% (current: 10 A, treatment flow rate: 10 (m ³ /h)). to obtain ultrapure water.

Table 1 summarizes the boron concentration, carbonic acid concentration and resistivity of the water to be treated and the treated water obtained at this time. Carbonic acid was sufficiently removed by the electrodeionization device 3 (EDI1). Further, in Table 1, the boron removal rate of the electrodeionization apparatus and the boron removal apparatus (two-stage EDI) for the water to be treated by the electrodeionization apparatus was 99.96%, which was very good.

(Comparative example 1)
Using the same ultrapure water production system used in Example 1, the operating conditions of the electrodeionization device 3 (EDI 1) were 95% (current: 10 A, treatment flow rate: 10 (m ³ /h)). Water treatment was performed under the same conditions as in Example 1, except that

Table 1 summarizes the boron concentration and resistivity of the water to be treated and the treated water obtained at this time.

In addition, each component obtained in the above examples and comparative examples was measured as follows to obtain the numerical value.
[pH] CP-200 (manufactured by Horiba, trade name) was used to measure pH.
[Boron] Samples were taken and analyzed by an inductively coupled plasma mass spectrometer (ICP-MS) to calculate the boron concentration.
[Carbonic acid] The total carbonic acid concentration was measured using TOC-900 On-Line (manufactured by GE).

(Example 3)
In this example, the function and effect of circulating concentrated water in the pure water production system shown in FIG. 4 were confirmed. The individual devices are the same as those used in the above examples.

First, as shown in FIG. 5, in a water treatment system in which the first reverse osmosis membrane device (RO1) and the electrodeionization device (EDI) are arranged in this order, (a) when there is no circulation, ( b) When the concentrated water of the electrodeionization device is circulated, (c) the concentrated water of the first reverse osmosis device and the concentrated water of the electrodeionization device are treated by the second reverse osmosis device (RO2). In the case of circulating the permeated water, the pH of the waste water and the carbonic acid concentration of the permeated water treated with the first reverse osmosis membrane device were measured for the three configurations. Atsugi city water (carbonic acid concentration: 3.6 mg/L (ppm), pH: 6.4) was used as the water to be treated.

In FIG. 5, A indicates the carbonic acid concentration measurement point, and B indicates the pH measurement point.
In FIG. 5(a), in the first reverse osmosis membrane apparatus, since carbonic acid is difficult to remove, it is included in the permeated water side, and its waste water (concentrated water) swings to the alkaline side compared to the water to be treated, and the pH is 7.5. 74. In addition, the permeated water contains a large amount of carbonic acid, and the concentration of carbonic acid is 3.6 mg/L (ppm), which is about the same as that of the water to be treated. The water recovery rate of the first reverse osmosis membrane device is 70%.

In FIG. 5(b), unlike FIG. 5(a), the concentrated water of the electrodeionization device is circulated upstream of the first reverse osmosis membrane device. Since carbonic acid is effectively removed in the electrodeionization device, the concentration of carbonic acid in the concentrated water increases, and since this is circulated to the front stage of the first reverse osmosis membrane device, the carbonic acid concentration at measurement point A is 12 ppm, which is much higher than the water to be treated. This increase in carbonic acid concentration causes deterioration of the water quality of the water permeated through the electrodeionization apparatus thereafter, and this configuration is not preferable in the production of ultrapure water. On the other hand, since the pH of the concentrated water of the electrodeionization apparatus is low, the pH of the feed water of the first reverse osmosis membrane apparatus is lowered, so the first reverse osmosis membrane apparatus is operated at a water recovery rate of 84%. ing. The pH at the measurement point B is more acidic than in FIG. 5(a).

In FIG. 5(c), in contrast to FIG. 5(a), the concentrated water from the first reverse osmosis membrane device and the concentrated water from the electrodeionization device are mixed to form mixed concentrated water, and this mixed concentrated water is After passing water through the second reverse osmosis membrane device, the permeated water is circulated to the front stage of the first reverse osmosis membrane device. Unlike FIG. 5(b), the concentrated water from the electrodeionization device is not circulated as it is, but is once processed by the second reverse osmosis membrane device and then circulated, so the carbonic acid concentration at measurement point A is 5. 0.5 ppm, but there is no problem in ultrapure water production because the carbonic acid can be sufficiently removed by subsequent treatment with an electrodeionization apparatus. On the other hand, since the feed water of the second reverse osmosis membrane device is mixed with the concentrated water of the electrodeionization device and the pH is lowered, the feed water of the first reverse osmosis membrane device is mixed with the second reverse osmosis water. Since the treated water of the membrane device is mixed and the pH is lowered, both the first reverse osmosis membrane device and the second reverse osmosis membrane device have a higher water recovery rate than in FIG. 5(a). Therefore, the total water recovery rate of the first reverse osmosis membrane device and the second reverse osmosis membrane device is the same as in FIG. 5(b). The pH at the measurement point B is on the acid side as in FIG. 5(b).

As described above, in the water treatment of FIGS. In b), the carbonic acid content increased, which was not preferable. Here, "good" means the case where ultrapure water can be produced by subsequent treatment with a boron removal apparatus as shown in FIG. Also, the water recovery rate in this water treatment was as low as about 50% in FIG. 5(a), and as good as about 71% in FIGS. 5(b) and 5(c). Therefore, it was found that FIG. 5(c) has a good balance between the water quality and the water recovery rate, and is preferable as an apparatus configuration to be applied to ultrapure water production.

Moreover, when the method of FIG. 5(c) is used, since the concentrated water of the electrodeionization apparatus is removed by the second reverse osmosis membrane apparatus and then circulated, the boron concentration of the concentrated water of the electrodeionization apparatus Since the boron concentration at the measurement point B does not increase, there is also an effect that the boron concentration in the treated water of the electrodeionization apparatus does not increase. In addition, when the EDI is operated with a reduced water recovery rate, the water recovery rate of the entire water purifier can be improved. This configuration is very suitable for producing ultrapure water.

In the method of FIG. 5(c), the concentrated water of the electrodeionization device supplied to the second reverse osmosis membrane device may contain the electrode water of the electrodeionization device. In this case, since the electrode water of the electrodeionization apparatus may contain a small amount of residual chlorine, the residual chlorine may be removed with activated carbon or the like before being sent to the second reverse osmosis membrane apparatus. Further, since the electrode water of the electrodeionization apparatus contains hydrogen, the hydrogen concentration may be reduced by treating the water with a scrubber or temporarily storing it in a tank. Also, the electrode water of the electrodeionization apparatus may be drained separately. In this case, treatment of residual chlorine and hydrogen contained in the electrode water becomes unnecessary.

As described above, the ultrapure water production method and the ultrapure water production system of the present embodiment provide ultrapure water having a predetermined water quality in which the boron concentration is significantly reduced, with a simple device configuration and a membrane deaeration device. It has been found that a stable result can be obtained without causing problems due to clogging.
Moreover, it was found that the pure water production method and the pure water production system of the present embodiment can treat water with a good balance between the treated water quality and the water recovery rate.

Therefore, the ultrapure water production method and ultrapure water production system of the present embodiment are excellent methods and systems capable of stably obtaining ultrapure water of predetermined water quality for a long period of time. Moreover, the pure water production method and the pure water production system of the present embodiment are methods and systems that achieve a good balance between predetermined water quality and water recovery rate.

1, 10, 20... Ultrapure water production system, 2... First reverse osmosis membrane device (RO1), 3, 21... Electrodeionization device, 4... Boron removal device, 11... Second reverse osmosis membrane device , 12, 24 Circulation pipe 22 Ultraviolet oxidizer (TOC-UV) 23 Mixed-bed ion exchanger (MB) 30 Pure water production system

Claims (15)

After the water to be treated is treated with the first reverse osmosis membrane device, it is subsequently treated with the electrodeionization device and the boron removal device in that order to obtain ultrapure water with a boron concentration of 1 ng/L or less. A method for producing ultrapure water,
The electrodeionization apparatus includes a deionization chamber to which water to be treated of the electrodeionization apparatus is supplied, and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber. have
The water to be treated by the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization apparatus contains 1 μg/L or less of boron from which the carbonic acid has been removed. A method for producing ultrapure water, characterized by: 2. The method for producing ultrapure water according to claim 1, wherein the electrodeionization apparatus is operated at a recovery rate of 80% or more and less than 90%. 2. The method for producing ultrapure water according to claim 1, wherein the cell width of the deionization chamber of the electrodeionization device is 2 mm or more and 6 mm or less. The concentrated water from the electrodeionization device is mixed with the concentrated water from the first reverse osmosis membrane device to obtain mixed concentrated water, and the mixed concentrated water is passed through the second reverse osmosis membrane device. The method for producing ultrapure water according to any one of claims 1 to 3, wherein the permeated water is circulated to the upstream stage of the first reverse osmosis membrane device. The boron removal device is an electrodeionization device, a boron-selective ion-exchange resin device, or a mixed-bed ion-exchange resin device of a boron-selective ion-exchange resin and a cation-exchange resin and/or an anion-exchange resin. 5. The method for producing ultrapure water according to any one of 1 to 4. 6. The method for producing ultrapure water according to claim 5, wherein the boron removal device is an electrodeionization device, and the concentrated water from the electrodeionization device is circulated upstream of the first reverse osmosis membrane device. The method for producing ultrapure water according to any one of claims 1 to 6, wherein no membrane degassing treatment is performed in the preceding stage of the boron removal device. In a pure water production method in which water to be treated is treated with a first reverse osmosis membrane device and then treated with an electrodeionization device,
The electrodeionization apparatus includes a deionization chamber to which water to be treated of the electrodeionization apparatus is supplied, and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber. have
The water to be treated by the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization apparatus has the carbonic acid removed and contains 1 μg/L or less of boron,
The concentrated water from the electrodeionization device is mixed with the concentrated water from the first reverse osmosis membrane device to obtain mixed concentrated water, and the mixed concentrated water is passed through the second reverse osmosis membrane device. and circulating the permeated water to the front stage of the first reverse osmosis membrane device. An ultrapure water production system for obtaining ultrapure water having a boron concentration of 1 ng/L or less by sequentially treating water to be treated with a first reverse osmosis membrane device, an electrodeionization device and a boron removal device. and
The electrodeionization apparatus includes a deionization chamber to which water to be treated of the electrodeionization apparatus is supplied, and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber. have
The water to be treated by the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization apparatus has the carbonic acid removed and contains 1 μg/L or less of boron,
a second reverse osmosis membrane device for treating concentrated mixed water of the concentrated water of the first reverse osmosis membrane device and the concentrated water of the electrodeionization device;
a circulation pipe for circulating the permeated water of the second reverse osmosis membrane device to the front stage of the first reverse osmosis membrane device;
An ultrapure water production system characterized by comprising: 10. The ultrapure water production system according to claim 9, wherein the electrodeionization device has a cell width of 2 mm or more and 6 mm or less. The boron removal device is an electrodeionization device, a boron-selective ion-exchange resin device, or a mixed-bed ion-exchange resin device of a boron-selective ion-exchange resin and a cation-exchange resin and/or an anion-exchange resin. 11. The ultrapure water production system according to 9 or 10. 12. The ultrapure water according to claim 11, wherein the boron removal device is an electrodeionization device, and has a circulation pipe for circulating concentrated water from the electrodeionization device to a stage preceding the first reverse osmosis membrane device. manufacturing system. The ultrapure water production system according to any one of claims 9 to 12, wherein the first reverse osmosis membrane device is a reverse osmosis membrane unit in which two reverse osmosis membrane devices are connected in series. 14. The ultrapure water production system according to any one of claims 9 to 13, which does not have a membrane degassing device in the preceding stage of said boron removing device. A pure water production system for sequentially treating water to be treated with a first reverse osmosis membrane device and an electrodeionization device,
The electrodeionization apparatus includes a deionization chamber to which water to be treated of the electrodeionization apparatus is supplied, and a mixture of anion exchange resin and cation exchange resin filled in the deionization chamber. have
The water to be treated by the electrodeionization apparatus contains more than 1 mg/L of carbonic acid, and the water treated by the electrodeionization apparatus has the carbonic acid removed and contains 1 μg/L or less of boron,
a second reverse osmosis membrane device for treating concentrated mixed water of the concentrated water of the first reverse osmosis membrane device and the concentrated water of the electrodeionization device;
a circulation pipe for circulating the permeated water of the second reverse osmosis membrane device to the front stage of the first reverse osmosis membrane device;
A pure water production system comprising:

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