JP7383141B2 - TOC removal device and TOC removal method - Google Patents

Description

The present invention relates to an apparatus for removing TOC from water to be treated and a method for removing TOC.

BACKGROUND ART Conventionally, pure water such as ultrapure water from which impurities such as organic substances, ionic components, particulates, and bacteria have been highly removed has been used as cleaning water in the manufacturing process of semiconductor devices and the manufacturing process of liquid crystal devices. In particular, when manufacturing electronic components including semiconductor devices, a large amount of pure water is used in the cleaning process, and demands on the quality of the water are increasing year by year.
For example, it is required to reduce total organic carbon (TOC) as a trace impurity. In other words, an ultraviolet oxidation device (UV oxidation device) is installed before the ion exchange resin device of the primary system (primary pure water system), and after decomposing and removing TOC components, it is sent to the subsystem (secondary pure water system). A water supply configuration is adopted. In order to obtain water with reduced TOC, it is important to reduce TOC efficiently in the primary system, which also makes it possible to reduce the burden on the UV oxidizer in the subsystem.

By the way, due to the demand for non-chemical products, there is a demand for replacing the primary ion exchange resin device with an electrical regenerative deionization device (EDI).
Patent Document 1 discloses that a primary system is equipped with an ultraviolet oxidation device and an ion exchange device in this order, organic matter in the water to be treated is decomposed by the ultraviolet oxidation device, and the water to be treated in which the organic matter has been decomposed is treated by the ion exchange device. It is described that the ion exchange device is a regenerative ion exchange device in which one or more stages of electrical regenerative deionization devices are connected in series.

Japanese Patent Application Publication No. 2017-127875

The present inventors found that the energy efficiency of the UV oxidizer is poor when trying to obtain treated water with a reduced TOC concentration in the flow of UV oxidizer → EDI → EDI as in the method described in Patent Document 1. I discovered that. That is, the TOC contained in the water to be treated includes ionizable ionic TOC that can be removed by EDI and non-ionic TOC that cannot be removed by EDI. It has also been found that in the above-described flow, ionizable TOC that can be removed by EDI is also UV-oxidized, and therefore the energy efficiency of the UV oxidation device is degraded accordingly.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a TOC removal device and a TOC removal method that have good energy efficiency in a UV oxidation device and can reduce TOC in water to be treated.

The present inventors have discovered that by appropriately combining a plurality of electrical regenerative deionization devices and a UV oxidation device, the TOC concentration can be efficiently reduced while improving the energy efficiency of the UV oxidation device.

That is, the present invention provides a first electrical regenerative deionization device to which water to be treated is supplied, an ultraviolet oxidation device to which treated water treated by the first electrical regeneration deionization device is supplied, and a UV oxidation device to which the treated water is supplied. The present invention relates to a TOC removal device as a primary pure water system , which includes a second electrical regeneration type deionization device to which treated water treated with an ultraviolet oxidation device is supplied.

Moreover, the present invention removes TOC using a TOC removal device as a primary pure water system having a first electrical regenerative deionization device, an ultraviolet oxidation device, and a second electrical regeneration deionization device. A TOC removal method, comprising: (a) supplying the water to be treated to the first electro-regenerative deionization device for treatment; and (b) treated water from the first electro-regeneration deionization device. (c) supplying treated water from the ultraviolet oxidation device to the second electrical regenerative deionization device for treatment. Regarding.

According to the present invention, it is possible to provide a TOC removal device and a TOC removal method that have high energy efficiency in a UV oxidation device and can reduce TOC in water to be treated.

1 is a conceptual diagram showing the configuration of a TOC removal device according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing the configuration of an apparatus used in a comparative example. FIG. 3 is a diagram showing changes in TOC value due to application of current when ultrapure water (UPW) is passed through EDI.

The present invention will be described below with reference to the drawings, but the present invention is not limited to the configuration shown in the drawings.

In FIG. 1, a TOC removal device 100 according to the present invention includes a first electrical regeneration deionization device (EDI-1) 30 to which water to be treated 10 is supplied via a pump 45, and a first electrical regeneration deionization device (EDI-1) An ultraviolet oxidation device (UV oxidation device) 40 to which water treated by the deionization device 30 is supplied, and a second electric regenerative deionization device to which water treated by the ultraviolet oxidation device (UV oxidation device) 40 is supplied. A device (EDI-2) 50 is provided.
Then, when the water to be treated 10 is supplied to the first electro-regenerative deionization device 30, the first electro-regeneration deionization device 30 removes ionizable TOC from the water to be treated. The treated water (that is, the treated water from which ionizable TOC has been removed by the first electroregenerative deionization device 30) is then supplied to the ultraviolet oxidation device 40 to decompose nonionic TOC components. Ru. Thereafter, the treated water (that is, the treated water supplied to the ultraviolet oxidation device 40 and in which nonionic TOC components have been decomposed) is sent to the second electroregenerative deionization device (EDI-2) 50, TOC decomposed in the ultraviolet oxidation device 40 is removed by a second electrical regenerative deionization device (EDI-2) 50, and treated water 20 is obtained.

The ultraviolet oxidation device 40 used in the present invention is installed for the purpose of decomposing organic matter. Therefore, it is preferable to use an ultraviolet oxidation device that performs ultraviolet oxidation treatment by irradiating ultraviolet light having a wavelength of 200 nm or less. Note that the subsystem may also be equipped with an ultraviolet oxidation device, but for example, in equipment where the TOC concentration of ultrapure water is required to be 1 μg/L or less, primary pure water with a relatively high dissolved oxygen (DO) concentration is used. By installing an ultraviolet oxidizer in a water system, it is possible to reduce overall energy costs. Due to the presence of dissolved oxygen, hydroxyl radicals and hydrogen peroxide are generated from the dissolved oxygen by ultraviolet irradiation, and it is expected that the TOC decomposition efficiency will be improved.
Furthermore, the amount of energy of the ultraviolet rays irradiated in the present invention is not particularly limited and depends on the amount of nonionic TOC components contained in the water to be treated, but for example, 0.1 to 0.5 kW/h/ Examples include ^m3 .

Next, EDI used in the present invention will be explained. EDI consists of a desalination chamber divided by an ion exchange membrane and filled with an ion exchanger, a concentration chamber that concentrates the ions desalted in the desalination chamber, and an anode and a cathode for passing current. This is a device with The device is operated by applying current to simultaneously perform deionization (desalination) of the water to be treated using the ion exchanger and regeneration treatment of the ion exchanger. The water to be treated that has passed through the EDI is desalinated by an ion exchanger filled in a desalination chamber, and is discharged to the outside of the EDI as EDI treated water. Similarly, concentrated water in which ions are concentrated is discharged to the outside as EDI concentrated water.

Here, in EDI, a water dissociation reaction (H ₂ O → H ⁺ +OH ^- ) progresses by applying an electric current, and the ions captured by the ion exchanger pass through the ion exchanger to the ion exchange membrane and concentration. Move to the room.
The amount of moving ions depends on the current value, so if an excessive current value is applied to water with a low ion load, in addition to the movement of ions captured by the ion exchanger, the water dissociation reaction will be excessive. will occur. As a result, the ion exchanger itself deteriorates, the ion exchange groups break down, and the operating voltage increases. At this time, there is a possibility that a part of the broken ion exchanger may increase the TOC concentration of the treated water.
In other words, in the present invention, it is desirable to operate with the power consumption of the second EDI lower than the power consumption of the first EDI. This is because the ion load of the feed water of the second EDI is small as the ionizable TOC in the water to be treated is removed by the first EDI. The same EDI may be used as the first EDI and the second EDI, or different EDIs may be used.

Note that the recovery rate of EDI is calculated based on the amount of treated water supplied to EDI and the amount of treated water obtained. That is, EDI recovery rate=(EDI treated water amount)/(EDI treated water amount)×100(%). There is no particular limit to the EDI recovery rate, but it is preferably 90 to 95%.

The water to be treated 10 used in the present invention is not particularly limited, but includes industrial water, groundwater, surface water, tap water, seawater, desalinated water obtained by desalinating seawater by reverse osmosis or evaporation, etc. Examples include sewage, treated sewage water, various types of wastewater, such as wastewater used in semiconductor manufacturing processes, and mixed water thereof. In addition, it is preferable that the water component to be treated satisfies at least one of the following: electrical conductivity of 10 μS/cm or less, and TOC concentration of 500 ppb or less. If these conditions are not met, it is preferable to perform pretreatment such as coagulation and precipitation treatment, filtration treatment, softening treatment, decarboxylation treatment, and activated carbon treatment.

In the present invention, the TOC concentration of the treated water 20 treated by the TOC removal device is not particularly limited as long as it is lower than the TOC concentration of the water to be treated. However, from the results of Example 1 described below, the TOC concentration can be, for example, less than 2.5 ppb, more preferably less than 2 ppb, and even more preferably less than 1 ppb.

Furthermore, the TOC removal device according to the present invention includes a pH adjustment device as shown in FIG. A device 70 may also be included.
A pH adjuster is added to the water supplied from the pH adjuster 70 to the UV oxidizer 40 to adjust the pH. The upper limit of the pH of the water supplied to the UV oxidizer 40 is not particularly limited, but from the results of Example 3 described later, it is preferably 9.5 or less, and more preferably less than 8.5. It is preferably 8.0 or less, and more preferably 8.0 or less. Further, the lower limit of pH is not particularly limited, but it is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 3.0 or more.
The pH adjuster used in the present invention is not particularly limited as long as it can adjust the pH of water, and any of inorganic acids, organic acids, inorganic bases, and organic bases can be used. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, sulfonic acid, phosphoric acid, etc., and examples of organic acids include formic acid, acetic acid, oxalic acid, succinic acid, etc. Further, examples of inorganic bases include sodium hydroxide, potassium hydroxide, etc., and examples of organic bases include guanidine type organic bases.

The TOC removal device according to the present invention may further include a blow pipe 60 that blows (discharges) the treated water treated by the second electrical regeneration type deionization device 50. Blow piping 60 is connected to second electroregenerative deionization device 50 . For example, if the TOC concentration of the EDI treated water is higher than a predetermined value at the beginning of operation or restart of the TOC removal device, blowing is performed until the TOC concentration decreases to a predetermined value or less. Here, there is no particular restriction on the time during which the treated water is blown through the blow piping. However, from the results of Example 2 described later, the blowing time at the initial stage of operation is preferably 15 hours or more, more preferably 30 hours or more. Further, the blowing time at the time of restart is preferably 7 hours or more, more preferably 10 hours or more, even more preferably 15 hours or more, and particularly preferably 20 hours or more.

Note that the TOC removal device according to the present invention is equipped with a UV sterilizer (not shown) after the UV oxidation device 40 and before the second electrical regenerative deionization device (EDI-2) 50. Good too.
Here, examples of the UV sterilization device include those having a main UV wavelength of 200 to 300 nm, preferably 220 to 280 nm, more preferably 240 to 260 nm. In addition, there is no particular limit to the energy amount of the ultraviolet rays to be irradiated, and it also depends on the amount of nonionic TOC components in the water to be treated, but for example, it may be 0.01 to 0.1 kW/h/ ^m3 . be able to.

Here, as shown in FIG. 2, an ultraviolet oxidation device 40 is installed before the first electrical regenerative deionization device 30, and a second electrical regeneration deionization device 30 is installed after the first electrical regenerative deionization device 30. The configuration in which the regenerative deionization device 50 is arranged and the configuration of the present invention will be compared and described. In the configuration shown in FIG. 2, all TOC contained in the water to be treated is first decomposed in the ultraviolet oxidation device 40. Therefore, compared to the configuration of the present invention, the UV oxidation device 40 requires more energy because the TOC that has already been ionized and can be removed by the electric regenerative deionization device 30 is also subjected to UV oxidation. . Moreover, when the water to be treated contains a radical scavenger such as carbonic acid, the efficiency of the ultraviolet oxidation device 40 decreases. Then, hydrogen peroxide, which is an oxidizing substance generated by polymerization of radicals generated in the ultraviolet oxidation device 40, deteriorates the ion exchanger in the first electrically regenerative deionization device 30 in the subsequent stage, causing a decrease in performance. there is a possibility.
On the other hand, in the case of the configuration of the present invention, ionized TOC, carbonic acid, etc. are removed in the first electrical regenerative deionization device 30, and then energy is used to decompose nonionic TOC using ultraviolet rays. Since irradiation only needs to be performed using the oxidizer 40, the amount of energy irradiation can be reduced compared to the configuration shown in FIG. Furthermore, since the amount of energy irradiation can be kept low, the amount of hydrogen peroxide generated can be reduced. Therefore, in the configuration of the present invention, compared to the configuration shown in FIG. 2, it can be expected that the deterioration in performance of the second electrical regenerative deionization device 50 installed after the ultraviolet oxidation device 40 can be suppressed. Furthermore, by providing the pH adjustment device 70 before the ultraviolet oxidation device 40, it is possible to reduce alkali, which is a radical scavenger, and prevent a decrease in the TOC removal rate.

Hereinafter, the present invention will be explained in more detail using examples, but the present invention is not limited to the examples.

(Example 1)
A TOC removal test was conducted using the apparatus shown in FIG. 1 on treated water containing a conductivity of 1 to 2 μS/cm, a boron concentration of 14 ppb, a silica concentration of 23 ppb, a TOC concentration of 13 ppb, and a dissolved oxygen (DO) of 8 ppm. The UV irradiation energy was 0.33 kW·h/m ³ , and a water flow test was conducted for 100 hours with a water flow rate of 1 m ³ /h. EDI-XP (trade name, manufactured by Organo Inc.) was used as both the first electrical regenerative deionization device (EDI-1) and the second electrical regenerative deionization device (EDI-2). The operating current value was set to 5A. As the ultraviolet oxidation device, JPW (trade name, manufactured by Nippon Photoscience Co., Ltd., wavelength: 185 nm) was used. Table 1 shows the TOC concentrations at the respective outlets of the treated water, EDI-1 treated water, UV oxidizer treated water, and EDI-2 treated water. Note that the pH of the water supplied to the UV oxidation device was adjusted to 5.5 to 6.0 using a pH adjustment device.

(Comparative example 1)
A TOC removal test was conducted under the same conditions as in Example 1, except that the device configuration was changed to the configuration shown in FIG. 2. Note that the pH of the water supplied to the UV oxidizer was 5.5 to 6.0, as in Example 1. The results are shown in Table 2.

As is clear from the above Example 1 and Comparative Example 1, even if the same irradiation energy was used in the UV oxidation device, in Example 1, the treatment was performed in the second electroregenerative deionization device (EDI-2). The TOC concentration of the treated water was <1 ppb, whereas in Comparative Example 1 it was 3 ppb.
In order to make the TOC concentration of the treated water treated with EDI-2 <1 ppb in Comparative Example 1, it is necessary to increase the irradiation energy in the UV oxidation device. This not only deteriorates energy efficiency, but also causes hydrogen peroxide etc. generated by large amounts of UV irradiation to damage the first electrically regenerative deionization device (EDI-1) installed at the subsequent stage, and even the second This may lead to deterioration of the electrical regenerative deionization device (EDI-2).

(Example 2)
After regeneration, ultrapure water (UPW) was passed through the electric regeneration deionization device (product name: EDI-XP, manufactured by Organo), and a current of 5 A was applied to confirm the change in TOC concentration in the EDI-treated water. . The results are shown in Figure 3. In FIG. 3, ΔTOC refers to a value obtained by subtracting the measured value of TOC concentration in UPW as an instrument blank from the measured value of TOC concentration.
The test was conducted under the following conditions.
0 to 47 hours: UPW water flow + current application 47 to 65 hours: UPW water flow only (no current application)
65 to 73 hours: UPW water flow + current application 73 to 161 hours: Neither UPW water flow nor current application 161 hours or later: UPW water flow + current application

The ΔTOC was approximately 9 ppb immediately after the start of energization, but gradually decreased to 1 ppb or less after 30 hours had passed. After 47 hours and until 65 hours had elapsed, the application of current was stopped while water flow through the UPW was continued, and the current was applied again after 65 hours and until 73 hours had elapsed, but in both cases the change in ΔTOC at the outlet was There was no change (verification of changes in TOC concentration when applying or not applying current while flowing water through UPW).
After 73 hours had elapsed, the apparatus was stopped, and the UPW water flow and current application were stopped. Then, after 161 hours had elapsed, the system was restarted and the transition of ΔTOC was observed. Then, ΔTOC increased again to 9 ppb, which is the same as at 0 hours, and it took about 7 hours to reach 1 ppb or less, and about 15 hours to stabilize at 1 ppb or less.

The high TOC concentration at the beginning of operation is due to TOC derived from the ion exchanger leaking into the demineralized water. Therefore, when producing low TOC water, the EDI treated water at the initial stage of operation is blown until the TOC is reduced, preferably for 15 hours or more, more preferably for about 30 hours, and then the water is passed to the subsequent equipment. This is desirable.
This test revealed that even when EDI is restarted after it has been stopped, the TOC concentration rises to the same level as the initial level. Therefore, when EDI is restarted, it is desirable to perform an initial blow, and the blowing time is preferably 7 hours or more, more preferably 10 hours or more, even more preferably 15 hours or more, and particularly preferably 20 hours or more. It is.

Furthermore, when producing water with a low TOC concentration using two-stage EDI, it is desirable that the second-stage EDI be operated continuously. As described above, whether or not current is applied does not affect the TOC concentration of EDI-treated water, but whether or not ultrapure water is passed has a large effect on the TOC concentration of EDI-treated water. Therefore, even if the first stage EDI of the two-stage EDI is operated intermittently (operation in which UPW water flow and current application are turned ON/OFF at arbitrary intervals), at least the second stage EDI near the point of use If the EDI is in continuous operation (operation in which UPW water flow and current application are continuously turned on without a break in time), the first stage EDI is in a stopped state (UPW water flow and current application are turned OFF). Even when switching from the operating state (with UPW water flow and current application ON), the TOC generated in the first stage EDI can be removed in the second stage EDI, resulting in low TOC. You can get concentrated water.

(Example 3)
Pure water (pH 6.5), water added with NaOH (pH 8.0 and pH 9.6), and water added with H ₂ SO ₄ (pH 4.0) were each treated with an ultraviolet oxidation device (trade name: JPW, Japan). The ultraviolet oxidation device-treated water was passed through an electric regeneration deionization device (trade name: EDI-XP, manufactured by Organo Inc.). The TOC concentration of the water supplied to the ultraviolet oxidation device was adjusted by adding IPA, and the TOC concentration was set to 1 ppm in water at each pH. Note that each TOC concentration was measured using a TOC meter (trade name: Sievers M9e, manufactured by SUEZ WTS Analytical Instruments). The test was conducted at an ultraviolet irradiation energy of 0.88 kW·h/m ³ from the ultraviolet oxidizer.
Table 3 shows the results of measuring the TOC concentration of the EDI treated water and calculating the TOC removal rate.

It can be seen that when water with a pH of 9.6 is passed through the ultraviolet oxidation device, the TOC removal rate is significantly reduced. From this, in order to obtain water with a low TOC concentration, it is necessary to adjust the pH of the water supplied to the ultraviolet oxidation device to an appropriate value (range).

10 Water to be treated 20 Treated water 30 First electrical regeneration deionization device (EDI-1)
40 UV oxidizer 45 Pump 50 Second electro-regenerative deionizer (EDI-2)
60 Blow piping 70 pH adjustment device 100 TOC removal device

Claims (10)

a first electroregenerative deionization device to which water to be treated is supplied;
an ultraviolet oxidation device to which treated water treated by the first electric regenerative deionization device is supplied;
a second electrically regenerative deionization device to which treated water treated by the ultraviolet oxidation device is supplied;
A TOC removal device as a primary pure water system . The TOC removal device according to claim 1, wherein the TOC concentration of the treated water treated by the TOC removal device is less than 1 ppb. The TOC removal device according to claim 1 or 2, wherein the pH of the water supplied to the ultraviolet oxidation device is 1.0 or more and less than 8.5. The TOC removal device according to any one of claims 1 to 3, further comprising a pH adjustment device upstream of the first electroregenerative deionization device . The TOC removal device according to any one of claims 1 to 4, further comprising a blow pipe for blowing the treated water treated by the second electrical regeneration type deionization device. The TOC according to claim 5, wherein the treated water treated by the second electric regenerative deionization device is blown for 15 hours or more through the blow piping at the beginning of operation or at the time of restart of the TOC removal device. removal device. The TOC removal device according to any one of claims 1 to 6, wherein the first electro-regenerative deionization device is operated intermittently, and the second electro-regeneration deionization device is operated continuously. The TOC removal device according to any one of claims 1 to 7, wherein the power consumption of the second electrical regenerative deionization device is lower than the power consumption of the first electrical regenerative deionization device. A TOC removal method that removes TOC using a TOC removal device as a primary pure water system having a first electrical regenerative deionization device, an ultraviolet oxidation device, and a second electrical regeneration deionization device. hand,
(a) supplying the water to be treated to the first electroregenerative deionization device for treatment;
(b) supplying the treated water from the first electrical regenerative deionization device to the ultraviolet oxidation device for treatment;
(c) supplying the treated water from the ultraviolet oxidation device to the second electroregenerative deionization device for treatment;
A TOC removal method having The TOC removal method according to claim 9, further comprising the step of adjusting the pH of the water supplied to the ultraviolet oxidation device to 1.0 or more and less than 8.5, before the step (a ) .

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