Ultrapure water production device and ultrapure water production method

Abstract

Provided is an ultrapure water production device which is capable of stably supplying ultrapure water of good water quality over a long period of time. This ultrapure water production device is provided with a primary pure water production device and a secondary pure water production device. The ultrapure water production device is characterized in that: the primary pure water production device has a first ultraviolet oxidation device; the secondary pure water production device has a second ultraviolet oxidation device and a hydrogen peroxide removal device that is provided in a subsequent stage of the second ultraviolet oxidation device; the hydrogen peroxide removal device contains an ion exchanger on which a platinum group metal catalyst is supported; and the amount of ultraviolet irradiation by the second ultraviolet oxidation device is controlled so that the difference ΔTOC (TOCSUP – TOCTRE) between the TOC value (TOCSUP) of supply water to the second ultraviolet oxidation device and the TOC value (TOCTRE) of the treated water that has been treated by the second ultraviolet oxidation device is 1 ppb or less.

Description

[Technical Field]

[0001] The present invention relates to an ultrapure water production apparatus and an ultrapure water production method. [Background technology]

[0002] In recent years, as demands for higher quality ultrapure water have increased, methods for decomposing and removing trace amounts of organic matter contained in water have been investigated. TOC (Total Organic Carbon) is used as an indicator of water quality after decomposition and removal of organic matter, and TOC must be below a certain standard.

[0003] One method for decomposing and removing trace amounts of organic matter in water is ultraviolet oxidation treatment, which oxidizes and decomposes water to generate OH radicals, which then oxidize and decompose organic matter (TOC components).

[0004] However, in UV oxidation, excess OH radicals produced by water decomposition combine to produce hydrogen peroxide. Hydrogen peroxide deteriorates resin materials, such as ion exchange resins, installed downstream of the UV oxidation device, resulting in a decrease in the performance of the ultrapure water production system. Furthermore, the deterioration of resin materials, such as ion exchange resins, leads to the formation of new organic matter derived from the resins, which leads to a decrease in the quality of the ultrapure water.

[0005] Therefore, a method has been proposed for removing hydrogen peroxide from water, using a platinum group metal supported catalyst, in which a platinum group metal, such as palladium (Pd) or platinum (Pt), is supported on a carrier.By using a platinum group metal supported catalyst, hydrogen peroxide can be decomposed and removed through the reaction 2H2O2 → 2H2O + O2.

[0006] As an example of an ultrapure water production method and production apparatus using such a hydrogen peroxide removal method, Patent Document 1 discloses an ultrapure water production method and production equipment in which water to be treated is subjected to ultraviolet oxidation treatment in an ultraviolet oxidation device, and then hydrogen peroxide is removed using a hydrogen peroxide removal device that uses a specific platinum-based catalyst. More specifically, the platinum-based catalyst is a platinum-based metal colloidal particle supported on an anion exchange resin, and the pure water production method and apparatus are characterized in that the TOC of the water supplied to the ultraviolet oxidation device is 5 ppb or less, the inorganic carbonate ion concentration of the water supplied to the ultraviolet oxidation device is less than 1 ppb, and the inorganic carbonate ion concentration of the treated water treated in the ultraviolet oxidation device is 1 ppb or more. The patent document states that the purpose of the method and apparatus is to provide a pure water production method and apparatus that can stably decompose hydrogen peroxide over a long period of time by preventing (or suppressing) deterioration of the catalyst resin.

[0007] Furthermore, Patent Document 2 discloses a method and apparatus for reducing hydrogen peroxide in treated water by contacting the water containing hydrogen peroxide with a catalytic resin in which a platinum group metal is supported on a strongly basic anion exchange resin. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5854163 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-069460 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 describes, as an effect of the invention, that by keeping the TOC of the water supplied to the ultraviolet oxidation device at 5 ppb or less, the organic acid concentration is reduced, preventing poisoning (deterioration) of a platinum-based catalyst for removing hydrogen peroxide installed downstream of the ultraviolet oxidation device and extending the catalyst's life. It also describes that by setting the ultraviolet oxidation treatment conditions so that the inorganic carbonate ion concentrations of the water supplied to the ultraviolet oxidation device and the effluent water are each within a specific range, the proportion of organic matter decomposed to CO2 increases (i.e., the organic matter concentration decreases).

[0010] However, the method described in Patent Document 1 requires that the inorganic carbonate ion concentration of the treated water treated with the ultraviolet oxidation device be equal to or greater than a predetermined level, leaving room for further extension of the catalyst life. Specifically, the inventors discovered that inorganic carbonate ions affect the deterioration of platinum-based catalyst-supported resins, and that high inorganic carbonate ion concentrations result in deterioration of the platinum-based catalyst-supported resins, resulting in a decrease in the quality of the resulting ultrapure water. More specifically, they discovered that in ultraviolet oxidation treatment, organic matter (TOC components) is oxidatively decomposed to produce organic acids, which are then further oxidatively decomposed to produce CO2, which dissolves in the treated water and becomes inorganic carbonate ions, resulting in an increase in the inorganic carbonate ion concentration in the treated water and deterioration of the platinum-based catalyst-supported resins.

[0011] SUMMARY OF THE INVENTION An object of the present invention is to solve the problems encountered in light of the above circumstances, that is, to provide an ultrapure water production system and an ultrapure water production method that can stably supply ultrapure water of good quality over a long period of time. [Means for solving the problem]

[0012] The present invention includes the following aspects. [1] An ultrapure water production system comprising a primary pure water production system and a secondary pure water production system, the primary pure water production system has a first ultraviolet oxidation device; the secondary pure water production system has a second ultraviolet oxidation device and a hydrogen peroxide removal device provided downstream of the second ultraviolet oxidation device; the hydrogen peroxide removal device includes an ion exchanger carrying a platinum group metal catalyst; The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) and the TOC value of the treated water treated by the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE The ultrapure water production system is characterized in that the amount of ultraviolet irradiation from the second ultraviolet oxidation device is controlled so that the concentration of the ions in the ultrapure water is 1 ppb or less. [2] The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) but 0 <TOC SUP The ultrapure water production system according to [1], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb. [3] The ultrapure water production system according to [1] or [2], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device is greater than the ultraviolet irradiation amount of the second ultraviolet oxidation device. [4] The TOC value (TOC TRE The ultrapure water production apparatus according to any one of [1] to [3], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device and the ultraviolet irradiation amount of the second ultraviolet oxidation device are controlled so that the concentration of ions in the first ultraviolet oxidation device is 1 ppb or less. [5] An ultrapure water production system according to any one of [1] to [4], which has a water quality meter upstream and / or downstream of the second ultraviolet oxidation device. [6] An ultrapure water production apparatus according to any one of [1] to [5], having a first TOC meter provided upstream of the second ultraviolet oxidation device and a second TOC meter provided downstream of the second ultraviolet oxidation device. [7] A method for producing ultrapure water using an ultrapure water production system equipped with a primary pure water production system and a secondary pure water production system, the primary pure water production system has a first ultraviolet oxidation device; the secondary pure water production system has a second ultraviolet oxidation device and a hydrogen peroxide removal device provided downstream of the second ultraviolet oxidation device; the hydrogen peroxide removal device includes an ion exchanger carrying a platinum group metal catalyst; The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) and the TOC value of the treated water treated by the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE ) is 1 ppb or less. [8] The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) but 0 <TOC SUP The method for producing ultrapure water according to [7], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb. [9] The method for producing ultrapure water according to [7] or [8], wherein the first ultraviolet oxidation device is operated so that the ultraviolet irradiation amount thereof is greater than the ultraviolet irradiation amount of the second ultraviolet oxidation device.

[10] The TOC value (TOC TRE The method for producing ultrapure water according to any one of [7] to [9], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device and the ultraviolet irradiation amount of the second ultraviolet oxidation device are controlled so that the concentration of the oxidized water in the first ultraviolet oxidation device is 1 ppb or less.

[11] The method for producing ultrapure water according to any one of [7] to

[10] , wherein the ultrapure water production apparatus has a water quality meter installed upstream and / or downstream of the second ultraviolet oxidation device.

[12] The method for producing ultrapure water according to any one of [7] to

[11] , wherein the ultrapure water production apparatus has a first TOC meter provided upstream of the second ultraviolet oxidation device and a second TOC meter provided downstream of the second ultraviolet oxidation device. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an ultrapure water production apparatus and an ultrapure water production method that can stably supply ultrapure water of good quality over a long period of time. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a schematic configuration diagram of an example of an ultrapure water production system according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the correlation between the OH type proportion of the catalyst resin in the hydrogen peroxide removal device and the hydrogen peroxide removal performance. [Figure 3] FIG. 1 is a schematic diagram of an ion-exchange resin container (hydrogen peroxide removal device) filled with a catalyst resin, used in Test Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will now be described.

[0016] An ultrapure water production system according to one embodiment of the present invention includes a primary pure water production system (make-up) and a secondary pure water production system (polishing) that supplies treated water from the primary pure water production system. The primary pure water production system has a first ultraviolet oxidation device, and the secondary pure water production system has a second ultraviolet oxidation device and a hydrogen peroxide removal device installed downstream of the second ultraviolet oxidation device. The first and second UV oxidation devices are devices that decompose and remove trace amounts of organic matter (TOC components) in water through UV oxidation. In this UV oxidation process, water is oxidatively decomposed to generate OH radicals, which then oxidatively decompose the organic matter (TOC components). During this process, the generated organic acids are further oxidatively decomposed to generate CO2, which forms inorganic carbonate ions in the treated water, while the excess OH radicals combine to generate hydrogen peroxide. The hydrogen peroxide removal device is a catalytic device equipped with an ion exchanger (hereinafter referred to as "catalyst carrier") carrying a platinum group metal catalyst, which decomposes and removes hydrogen peroxide. This hydrogen peroxide removal device (hereinafter referred to as "catalyst device") uses the action of a catalyst to decompose and remove hydrogen peroxide generated by ultraviolet oxidation treatment.

[0017] The ultrapure water production system of this embodiment is configured to measure the TOC value (TOC SUP) and the TOC value of the treated water from the second UV oxidation unit (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE The amount of ultraviolet radiation emitted from the second ultraviolet oxidation device is controlled so that the concentration of the oxidized carbon dioxide becomes 1 ppb or less. Here, "control" includes both automatic control and manual control. In addition, the water supplied to the second ultraviolet oxidation device contains TOC components (TOC SUP ≠0), the TOC of this feedwater SUP and TOC of treated water TRE The relationship between TOC SUP >TOC TRE (i.e., 0<ΔTOC). Furthermore, an ultrapure water production method according to another embodiment of the present invention is a method for producing ultrapure water using such an ultrapure water production apparatus, in which the TOC value (TOC SUP ) and the TOC value of the treated water from the second UV oxidation device (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE The amount of ultraviolet irradiation from the second ultraviolet oxidation device is adjusted so that the concentration of the oxidized carbon dioxide becomes 1 ppb or less. Here, "operation" includes both automatic control operation and manual operation. As mentioned above, the water supplied to the second UV oxidation device contains TOC components (TOC SUP ≠0), the TOC of this feedwater SUP and TOC of treated water TRE The relationship between TOC SUP >TOC TRE (i.e., 0<ΔTOC).

[0018] As described above, the TOC value of the feed water to the second UV oxidation device (TOC SUP ) and the TOC value of the treated water from the second UV oxidation unit (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE) to 1 ppb or less, the inorganic carbonate ion concentration in the effluent water from the second ultraviolet oxidation device can be kept below a certain level, thereby suppressing deterioration of the catalyst support in the hydrogen peroxide removal device in the subsequent stage due to inorganic carbonate ions, and enabling a stable supply of ultrapure water with high purity (operating so that the fluctuations in water quality are not small). In the present invention, it is necessary to control or manipulate the amount of ultraviolet radiation so that ΔTOC is 1 ppb or less, preferably 0.5 ppb or less, and more preferably less than 0.2 ppb. If we assume that all 1 ppb of TOC components are decomposed, a TOC value of 1 ppb corresponds to an inorganic carbonate ion concentration of 5 ppb, according to the following: If all the organic components (TOC components) in the water are decomposed, they will eventually be decomposed into water and carbon dioxide (C x H y O z →CO2 + H2O), the carbon dioxide produced dissolves in water and forms inorganic carbonate ions (HCO3 - , CO3 2- If all of the carbon dioxide produced dissolves in water and all of the carbon dioxide dissolved in water becomes inorganic carbonate ions, the mass ratio of carbon (C) in the organic components (TOC components) to the inorganic carbonate ions produced will be approximately 1:5, as shown below. [TOC component (C)]: [Inorganic carbonate ion (HCO3 - )]=12:(1+12+16×3)≒1:5 [TOC component (C)]: [Inorganic carbonate ion (CO3 2- )]=12:(12+16×3)=1:5

[0019] The TOC value of the feed water to the second UV oxidation unit (TOC SUP ) and the TOC value of the treated water from the second UV oxidation unit (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE) to 1 ppb or less, the first ultraviolet oxidation device performs ultraviolet oxidation treatment on the water to be treated with a sufficiently high irradiation dose, and the TOC value (TOC SUP ) is preferably sufficiently reduced. In this case, it is preferable to set the ultraviolet irradiation amount of the first ultraviolet oxidation device to be greater than that of the second ultraviolet oxidation device. Typically, to reduce the TOC value of the final treated water, the UV irradiation intensity of the UV oxidation device (second UV oxidation device) in the downstream secondary pure water production system is increased to sufficiently decompose the TOC components. However, if a large amount of TOC components is decomposed in this process, a large amount of inorganic carbonate ions is generated. As a result, problems caused by inorganic carbonate ions (such as deterioration of the catalyst support in the hydrogen peroxide removal device) become more likely to occur. Therefore, in the present invention, it is preferable to increase the UV irradiation dose in the UV oxidation device (first UV oxidation device) of the upstream primary pure water production system to sufficiently reduce the TOC value in advance, thereby reducing the amount of TOC components required for decomposition in the UV oxidation device (second UV oxidation device) of the downstream secondary pure water production system. This reduces the amount of inorganic carbonate ions generated in the downstream secondary pure water production system, and as a result, prevents deterioration of the catalyst support in the hydrogen peroxide removal system due to inorganic carbonate ions.

[0020] In the ultrapure water production system and method of the present invention, in order to more sufficiently reduce the amount of TOC components oxidized and decomposed in the second ultraviolet oxidation device, the TOC value (TOC SUP ) is 5 ppb or less (0 <TOC SUP ≦5ppb), preferably 3ppb or less (0 <TOC SUP It is preferable that the amount of ultraviolet irradiation from the first ultraviolet oxidation device is controlled (or manipulated) so that the concentration of the oxidized carbon dioxide becomes ≦3 ppb. In addition to sufficiently reducing the TOC of the final treated water, in order to further reduce the amount of TOC components oxidized and decomposed in the second ultraviolet oxidation device, the TOC value of the treated water treated in the second ultraviolet oxidation device (TOC TREIt is preferable that the ultraviolet irradiation amount of the first ultraviolet oxidation device and the ultraviolet irradiation amount of the second ultraviolet oxidation device are controlled (or manipulated) so that the concentration of the oxidized carbon dioxide becomes 1 ppb or less. Even if TOC is excessively reduced in the primary pure water production system, there is a possibility that organic matter may be mixed into the treated water and increase the TOC content thereafter. This increase can be removed in the secondary pure water production system, so there is no need to excessively reduce TOC in the primary pure water production system. From the viewpoint of treatment efficiency, it is preferable to reduce the TOC content appropriately according to the content of TOC components in the water to be treated. The control or operation of the ultraviolet irradiation amount of the first ultraviolet oxidation device is carried out so as to prevent excessive ultraviolet irradiation in the first ultraviolet oxidation device, and the TOC value (TOC SUP It is preferable to carry out the test within a range of ultraviolet irradiation doses such that the chromatogram of the chromatogram is 0.3 ppb or more (a range of irradiation doses that does not decrease to less than 0.3 ppb), more preferably within a range of ultraviolet irradiation doses such that the chromatogram of the chromatogram is 0.5 ppb or more (a range of irradiation doses that does not decrease to less than 0.5 ppb), or within a range of ultraviolet irradiation doses such that the chromatogram of the chromatogram is 1 ppb or more (a range of irradiation doses that does not decrease to less than 1 ppb).

[0021] TOC measurement can be performed by installing a TOC meter between the first and second ultraviolet oxidation devices and at a stage subsequent to the second ultraviolet oxidation device, respectively. This allows the TOC of the treated water between the first and second ultraviolet oxidation devices and the TOC of the treated water subsequent to the second ultraviolet oxidation device to be measured. Alternatively, a TOC meter may be provided either between the first and second ultraviolet oxidation devices or after the second ultraviolet oxidation device so that the TOC of the treated water between the first and second ultraviolet oxidation devices and the TOC of the treated water after the second ultraviolet oxidation device can be measured. This allows a single TOC meter to measure the TOC of both treated waters.

[0022] Thus, in the ultrapure water production system and ultrapure water production method of the present invention, TOC can be measured using one or two TOC meters to measure the TOC of the treated water between the first ultraviolet oxidation device and the second ultraviolet oxidation device, and the TOC of the treated water at the stage after the second ultraviolet oxidation device. Regarding the measurement of TOC in the treated water between the first and second ultraviolet oxidation devices, a more accurate measurement (TOC SUP ), it is preferable to measure the feed water immediately before it is supplied to the second ultraviolet oxidation device (i.e., the treated water between the second ultraviolet oxidation device and the treatment device located immediately before it). On the other hand, as for the measurement position of the TOC of the treated water after the second ultraviolet oxidation device, as will be described later, there is no particular limitation as long as it is after the second ultraviolet oxidation device, but from the viewpoint of simplifying the equipment, it is preferable to measure the TOC of the treated water from the final treatment device of the secondary pure water production system. This allows the TOC value (TOC TRE ) and the TOC value of the final treated water from the ultrapure water production system can be obtained simultaneously.

[0023] The TOC meter thus installed can measure the TOC of the treated water between the first ultraviolet oxidation device and the second ultraviolet oxidation device, and the TOC of the treated water at the stage subsequent to the second ultraviolet oxidation device, and the amount of ultraviolet radiation from the first and second ultraviolet oxidation devices can be controlled (or manipulated) based on these TOC measurements. For example, the first TOC value (TOC SUP ) and the second TOC value (TOC TRE The amount of ultraviolet radiation from the first and second ultraviolet oxidation devices can be controlled (or manipulated) so that the difference (ΔTOC) between the measured TOC value of the effluent water from the first ultraviolet oxidation device and the measured TOC value from the second ultraviolet oxidation device is 1 ppb or less. In this case, by performing ultraviolet oxidation treatment at a sufficiently high irradiation dose in the first ultraviolet oxidation device so that the first TOC value is a predetermined value or less (e.g., 5 ppb or less), the amount of organic matter in the feed water supplied to the downstream second ultraviolet oxidation device can be sufficiently reduced. Also, the ultraviolet irradiation doses of the first and second ultraviolet oxidation devices can be controlled (or manipulated) so that the second TOC value is a predetermined value or less (e.g., 1 ppb or less).

[0024] The TOC analyzer can be a conventional TOC analyzer used in the production of ultrapure water.For example, a complete oxidation TOC analyzer can be used, in which a portion of the treated water is introduced into a measurement cell, a valve is closed, ultraviolet light is irradiated, and the difference between the conductivity before ultraviolet light irradiation and the conductivity at which the oxidation is complete and the conductivity becomes constant can be converted into a TOC value.

[0025] The ultrapure water production system of the present invention can be equipped with various water quality meters other than TOC meters at desired locations. Based on the measurements of the water quality meters, water quality can be managed and various processing devices constituting the ultrapure water production system can be controlled and operated. For example, the electrical conductivity can be measured using a water quality meter, and the UV irradiation dose of the first ultraviolet oxidation device and / or the UV irradiation dose of the second ultraviolet oxidation device can be controlled based on the measured value. In this case, the water quality meter may be installed between the first and second ultraviolet oxidation devices and after the second ultraviolet oxidation device, or may be installed on either one of them. A single water quality meter can also measure the water quality of the treated water between the first and second ultraviolet oxidation devices and the water quality of the treated water after the second ultraviolet oxidation device.

[0026] The configuration of the ultrapure water production system of the present invention will be further described below. FIG. 1 shows an example of the configuration of an ultrapure water production system according to one embodiment of the present invention, but the present invention is not limited to this configuration. As shown in Figure 1, the ultrapure water production system comprises, in this order, a primary pure water production system 1 and a secondary pure water production system 2. The primary pure water production system 1 comprises, in this order, a first ultraviolet oxidation system 11, an ion exchange system 12, a boron-selective resin system 13, and a degassing system 14. The secondary pure water production system 2 comprises, in this order, a second ultraviolet oxidation system 21, a hydrogen peroxide removal system (catalyst system) 22, a degassing system 23, an ion exchange system 24, and an ultrafiltration membrane system 25.

[0027] As described above, the TOC meter can be provided between the first ultraviolet oxidation device 11 and the second ultraviolet oxidation device 21 and / or after the second ultraviolet oxidation device 21. In the ultrapure water production system shown in Figure 1, a TOC meter 31 is provided before the second ultraviolet oxidation device 21, and a TOC meter 32 is provided after the final treatment device of the secondary pure water production system 2. In the TOC measurement, the first TOC value (TOC SUP ) is calculated by using the measured value of the water supplied to the second ultraviolet oxidation device 21 as the second TOC value (TOC TRE The measured value of the treated water treated in the second ultraviolet oxidation device 21 (the measured value of the effluent water from the second ultraviolet oxidation device 21 or the measured value of the effluent water from each treatment device provided downstream of the second ultraviolet oxidation device) can be used as the TOC value. The difference between the first TOC value and the second TOC value is defined as ΔTOC, and the ultraviolet irradiation amount of the first and second ultraviolet oxidation devices can be controlled or manipulated so that this ΔTOC is 1 ppb or less.

[0028] The location of the downstream TOC meter is not particularly limited as long as it is located downstream of the second ultraviolet oxidation device 21 or later. However, from the viewpoint of simplifying the equipment, it is preferable to install the TOC meter 32 downstream of the final treatment device of the secondary pure water production system 2, as shown in FIG. 1. This allows the TOC value of the final treated water from the ultrapure water production system to be measured, and this measurement value can be used as the second TOC value (TOC TRE ) can be used as In addition, since the amount of TOC eluted from each processing device and equipment within the secondary pure water production system 2 is small in the stages subsequent to the second ultraviolet oxidation device 21 in the secondary pure water production system 2, the effect on ΔTOC due to the installation position of the TOC meter can be ignored. 1, two TOC meters are provided, but the upstream TOC meter 31 can be omitted, leaving only the downstream TOC meter 32, and the downstream TOC meter 32 can be configured to introduce a portion of the water supplied to the second ultraviolet oxidation device 21. This allows a single TOC meter to measure the TOC of the water supplied to the second ultraviolet oxidation device 21 and the TOC of the treated water after treatment by the second ultraviolet oxidation device 21.

[0029] 1 does not show a pretreatment device (pretreatment system), but it may be provided as part of the ultrapure water production system if necessary, or treated water pretreated in the pretreatment device (pretreatment system) may be supplied to the primary pure water production system of the ultrapure water production system. In the pretreatment device (pretreatment system), pretreatments such as coagulation, flotation, and filtration can be performed.

[0030] (Primary pure water production equipment) The primary pure water production system of the ultrapure water production system of this embodiment has a first ultraviolet oxidation device, and can further be equipped with an appropriate selection of treatment devices commonly used in ultrapure water production systems, such as an ion exchange device (e.g., a regenerative ion exchange device), a boron-selective resin device, a degassing device (e.g., a membrane degassing device), and a reverse osmosis membrane device (RO device). For example, as shown in the aforementioned FIG. 1, the primary pure water production system 1 can have a configuration in which a first ultraviolet oxidation device 11, an ion exchange device 12 (e.g., a regenerative ion exchange resin), a boron-selective resin device 13, and a degassing device 14 (e.g., a membrane degassing device) are connected in this order. Organic matter is oxidatively decomposed in the first ultraviolet oxidation device 11, impurity ions in the water are removed in the ion exchange device 12, boron in the water is removed in the boron-selective resin device 13, and gases such as dissolved oxygen in the water are removed in the degassing device 14. If necessary, the boron-selective resin device 13 may be omitted. A reverse osmosis membrane device may also be provided to remove inorganic matter, organic matter, fine particles, microorganisms, etc. from the water.

[0031] (Secondary pure water production equipment) The secondary pure water production system of the ultrapure water production system of this embodiment has a second ultraviolet oxidation device and a hydrogen peroxide removal device (catalytic device) downstream of it, and can further be equipped with an appropriate selection of treatment devices commonly used in ultrapure water production systems, such as a degassing device (e.g., a membrane degassing device), an ion exchange device (e.g., a non-regenerative ion exchange device such as a cartridge polisher), and an ultrafiltration membrane device (UF). For example, as shown in Figure 1, the secondary water purification system 2 can have a configuration in which a second ultraviolet oxidation device 21, a hydrogen peroxide removal device 22, a degassing device 23 (e.g., a membrane degassing device), an ion exchange device 24 (e.g., a non-regenerative ion exchange device), and an ultrafiltration membrane device 25 are connected in this order. If necessary, the order of the degassing device 23 and the ion exchange device 24 may be reversed. Furthermore, a tank for temporarily storing the treated water treated in the primary water purification system 1 may be provided upstream of the secondary water purification system 2. Organic matter is oxidized and decomposed in the second ultraviolet oxidation device 21, the hydrogen peroxide generated in the previous second ultraviolet oxidation device 21 is decomposed in the hydrogen peroxide removal device 22, gases such as dissolved oxygen in the water are removed in the degassing device 23, impurity ions in the water are removed in the ion exchange device 24, and fine particles generated from ion exchange resins and the like are removed in the ultrafiltration membrane device 25. Any of the above devices may be omitted if necessary in the downstream of the hydrogen peroxide removal device 22, but it is preferable to provide at least one of a degassing device (e.g., a membrane degassing device) 23 and an ion exchange device 24 (e.g., a non-regenerative ion exchange device) and subject the treated water from the hydrogen peroxide removal device to at least one of a degassing treatment and an ion exchange treatment.

[0032] (Hydrogen peroxide removal device (catalytic device)) The hydrogen peroxide removal device installed in the secondary pure water production system is a catalytic device for decomposing the hydrogen peroxide generated in the upstream ultraviolet oxidation device, and includes an ion exchanger (catalyst carrier) carrying a platinum group metal catalyst. Examples of platinum group metal catalysts include catalytic metals such as ruthenium, rhodium, palladium, osmium, iridium, and platinum, and one type can be used alone or two or more types can be combined, or two or more types can be used as an alloy. Among these catalytic metals, platinum, palladium, and alloys of platinum and palladium are preferred, and these can be used alone or two or more types can be combined. Palladium is particularly preferred because it has excellent catalytic activity and is available relatively cheaply. Examples of carriers for platinum group metal catalysts include metal oxides such as magnesia, titania, alumina, silica-alumina, and zirconia, activated carbon, zeolite, diatomaceous earth, and ion exchangers (ion exchange resins, monolithic organic porous anion exchangers, etc.). Among these, the use of ion exchangers is preferred. Ion exchange resins are preferred, and the ion exchanger supporting the platinum group metal catalyst in the embodiment of the present invention is preferably an ion exchange resin supporting the platinum group metal catalyst (hereinafter referred to as "catalyst resin"). Anion exchangers are preferred, and anion exchange resins are preferred, with strongly basic anion exchange resins being particularly preferred. The shape of the carrier for the platinum group metal catalyst is not particularly limited, and either granular or pellet-shaped carriers can be used. When using an ion exchange resin such as an anion exchange resin as a carrier for the platinum group metal catalyst, a gel-like resin (gel-type resin) can be used. When water to be treated that contains hydrogen peroxide is brought into contact with such a catalyst carrier, the hydrogen peroxide in the water to be treated is decomposed by the reaction 2H2O2 → 2H2O + O2.

[0033] As such an ion exchanger (catalyst support) on which a platinum group metal catalyst is supported, for example, the catalyst resin disclosed in JP-A-2010-069460 can be suitably used. Specifically, a catalyst resin that is a strongly basic anion exchange resin carrying a platinum group metal catalyst, in which 70% or more, preferably 90% or more, and more preferably 95% or more of the total exchange capacity of the strongly basic anion exchange resin is in the OH type, can be preferably used. The amount of platinum group metal catalyst (catalytic metal) supported on this strongly basic anion exchange resin is in the range of 10 mg-catalyst / LR to 500 mg-catalyst / LR, preferably 10 mg-catalyst / LR to 170 mg-catalyst / LR, and more preferably 10 mg-catalyst / LR to 50 mg-catalyst / LR. R is the abbreviation for OH-type anion exchange resin, and "mg-catalyst / LR" means the mass (mg) of catalyst per 1 L of OH-type anion exchange resin. The strongly basic anion exchange resin is preferably in a gel form from the viewpoint of hydrogen peroxide decomposition efficiency. The catalyst resin can be prepared by passing a platinum group metal ion solution through the strongly basic anion exchange resin, followed by passing a reducing agent such as formalin through the strongly basic anion exchange resin to support the platinum group metal catalyst (catalytic metal). This catalytic resin is passed through the treated water at a space velocity of SV30 to 2000hr -1 It is preferable to contact the material within the range of SV200 to 2000hr. -1 It is more preferable to contact the metal ions in the range of 100 to 2000. The hydrogen peroxide removal device may be provided with a hydrogen supply device to supply hydrogen to the water to be treated, which decomposes the hydrogen peroxide in the water to be treated and makes it easier to remove gas components such as oxygen produced by the decomposition of hydrogen peroxide through degassing.

[0034] (Ultraviolet oxidation equipment) The first and second ultraviolet oxidation devices used in the present invention may be ultraviolet oxidation devices that are commonly used in ultrapure water production equipment. The ultraviolet oxidation device is not particularly limited as long as it is equipped with an ultraviolet lamp capable of irradiating the water to be treated with ultraviolet rays having a wavelength of at least about 100 to 200 nm and can oxidize and decompose organic matter in the water to be treated. In order to decompose organic matter in the water to be treated, the ultraviolet oxidation device is preferably equipped with an ultraviolet lamp capable of irradiating ultraviolet light with a wavelength of around 185 nm. The ultraviolet lamp is not particularly limited, but a low-pressure mercury lamp is preferred. Furthermore, ultraviolet oxidation devices are available in flow-through and immersion types, with flow-through types being preferred in terms of treatment efficiency.

[0035] The first and second ultraviolet oxidation devices measure the first TOC value (TOC SUP ) and the second TOC value (TOC TRE ) and is configured so that the amount of ultraviolet light irradiation can be controlled (or manipulated) according to the The ultrapure water production system according to the embodiment of the present invention can have an ultraviolet irradiation amount control device attached to the second ultraviolet oxidation device, and this ultraviolet irradiation amount control device is configured to be able to control (or operate) the ultraviolet irradiation amount of the second ultraviolet oxidation device based on the input TOC value. Specifically, this ultraviolet irradiation amount control device controls (or operates) the ultraviolet irradiation amount of the second ultraviolet oxidation device based on the first TOC value (TOC SUP ) and the second TOC value (TOC TRE ) is entered, and the difference ΔTOC (TOC SUP -TOC TRE The ultraviolet irradiation amount control device may be configured to control (or manipulate) the ultraviolet irradiation amount of the second ultraviolet oxidation device so that the concentration of the ultraviolet ray emitted from the second ultraviolet oxidation device is 1 ppb or less. The ultraviolet irradiation amount control device may be further configured to control (or manipulate) the ultraviolet irradiation amount of the first ultraviolet oxidation device. First TOC value (TOC SUP When the TOC value (TOC) of the ultrapure water obtained from the ultrapure water production system increases, if the amount of ultraviolet irradiation of the second ultraviolet oxidation device is simply increased to reduce the TOC, ΔTOC may exceed 1 ppb. Therefore, it is necessary to control (or operate) the amount of ultraviolet irradiation of the second ultraviolet oxidation device so that ΔTOC is maintained at 1 ppb or less. In this case, the amount of ultraviolet irradiation of the second ultraviolet oxidation device is controlled (or operated) and the amount of ultraviolet irradiation of the first ultraviolet oxidation device is increased to reduce the first TOC value (TOC SUP ) may be reduced.

[0036] The ultraviolet irradiation amount control device is configured to control the first TOC value (TOC SUP The first ultraviolet oxidation device may be configured to control (or operate) the ultraviolet irradiation amount of the first ultraviolet oxidation device so that the TOC value (TOC) is equal to or less than a predetermined value (for example, 5 ppb or less). A separate ultraviolet irradiation amount control device may be provided attached to the first ultraviolet oxidation device, and this control device may control (or operate) the input first TOC value (TOC SUP The first ultraviolet oxidation device may be configured to control (or manipulate) the amount of ultraviolet irradiation so that the first TOC value (TOC SUP When the TOC value increases and exceeds a predetermined value (for example, 5 ppb), the UV irradiation amount of the first UV oxidation device is increased to increase the first TOC value (TOC SUP ) can be controlled (or manipulated) to be below a predetermined value (for example, below 5 ppb).

[0037] The ultraviolet irradiation amount control device also controls the second TOC value (TOC TRE The UV irradiation amount of the first and / or second UV oxidation device may be controlled (or manipulated) so that the second TOC value (TOC TRE When the TOC value increases and is about to exceed a predetermined value (for example, 1 ppb), the UV irradiation amount of the first UV oxidation device and / or the second UV oxidation device is increased to reach a second TOC value (TOC TRE ) can be controlled (or operated) to be a predetermined value or less (for example, 1 ppb or less). However, as described above, the amount of ultraviolet irradiation from the second ultraviolet oxidation device is controlled (or operated) to maintain ΔTOC at 1 ppb or less.

[0038] Methods for controlling the ultraviolet irradiation amount of an ultraviolet oxidation device using an ultraviolet irradiation amount control device include, for example, a method in which the ultraviolet irradiation amount control device controls the number of lit ultraviolet lamps provided in the ultraviolet oxidation device, a method in which the ultraviolet irradiation amount control device controls the lighting positions of the ultraviolet lamps provided in the ultraviolet oxidation device (which ultraviolet lamps among the multiple ultraviolet lamps are turned on or off), a method in which the ultraviolet irradiation amount control device controls the current value passed through the multiple ultraviolet lamps provided in the ultraviolet oxidation device, etc. In addition to these methods, any known method for controlling the ultraviolet irradiation amount can be used as appropriate.

[0039] The majority of OH radicals generated by water decomposition due to UV irradiation in the UV oxidation device are used to decompose organic matter, but excess OH radicals combine to form hydrogen peroxide. This hydrogen peroxide is decomposed and removed in the downstream hydrogen peroxide removal device (catalytic device). Meanwhile, the UV oxidation device oxidizes and decomposes the organic matter (TOC components) contained in the water to be treated into organic acids and even CO2, forming carbon dioxide in the water. As a result, the resulting treated water contains inorganic carbonate ions. These inorganic carbonate ions have the problem of degrading the catalyst support in the hydrogen peroxide removal device. According to an embodiment of the present invention, the TOC value of the feed water to the second ultraviolet oxidation device (TOC SUP ) and the TOC value of the treated water from the second UV oxidation unit (TOC TRE ) and the difference ΔTOC(TOC SUP -TOC TRE By controlling or manipulating the UV irradiation doses of the first and second UV oxidation devices so that the TOC concentration is 1 ppb or less, the amount of TOC components oxidatively decomposed in the second UV oxidation device can be reduced to a predetermined level or less. This makes it possible to suppress the concentration of inorganic carbonate ions in the effluent water from the second UV oxidation device to a predetermined level or less, thereby suppressing deterioration of the catalyst support in the hydrogen peroxide removal device in the subsequent stage due to inorganic carbonate ions, and enabling a stable supply of ultrapure water with high purity (operating so that water quality fluctuations are not small).

[0040] (Membrane degassing device) A membrane degassing device is a device that separates two chambers by a gas separation membrane, and flows treated water from a hydrogen peroxide removal device into one chamber, while reducing the pressure in the other chamber, thereby transferring gas contained in the treated water through the gas separation membrane to the other chamber and removing it. The gas separation membrane can be, for example, a hydrophobic polymer membrane such as a tetrafluoroethylene-based or polyolefin-based membrane formed into a hollow fiber membrane or the like. Other degassing devices, such as a vacuum degassing device or a thermal degassing device, can be used to remove gases contained in the treated water from the hydrogen peroxide removal device. However, when such other degassing devices are used, there is a risk that impurities may be mixed into the water from the device or may leach into the water from the packing of the device. In contrast, a membrane degassing device is particularly preferred as a degassing device because it does not cause the problems of impurities being mixed into or leached out of the water.

[0041] (Non-regenerative ion exchange device) Non-regenerative ion exchange devices (cartridge polishers) are not particularly limited as long as they remove impurities such as cations and anions from the treated water from the hydrogen peroxide removal device, but examples include ion exchange devices using a mixed bed of strongly acidic cation exchange resin and strongly basic anion exchange resin (mixed-bed, single-tower type), ion exchange devices using a single bed of strongly basic anion exchange resin (single-bed, single-tower type), multi-layer ion exchange devices with a single bed of strongly basic anion exchange resin at the inlet side and a mixed bed of strongly acidic cation exchange resin and strongly basic anion exchange resin at the outlet side (multi-layer, single-tower type), and ion exchange devices with a single bed of strongly basic anion exchange resin at the front end and a mixed bed of strongly acidic cation exchange resin and strongly basic anion exchange resin at the rear end (two-tower type). Among these, the mixed-bed, single-tower type ion exchange device is preferred because it reduces pH changes in the treated water at any position within the device and enables efficient ion exchange.

[0042] According to the ultrapure water production apparatus and ultrapure water production method of the embodiment of the present invention described above, it is possible to provide an ultrapure water production apparatus and ultrapure water production method that can stably supply ultrapure water of good quality for a long period of time, by removing hydrogen peroxide generated in the ultraviolet oxidation device while suppressing deterioration of the catalyst support in the downstream catalytic device. The ultrapure water production apparatus and ultrapure water production method according to the embodiments of the present invention can supply highly pure ultrapure water from which impurities such as organic matter, hydrogen peroxide, dissolved gases, ionic substances, and particulates have been removed, and such ultrapure water is suitable for cleaning electronic components and electronic component manufacturing tools. [Example]

[0043] <Confirmation test of the correlation between the OH type ratio of catalyst resin and hydrogen peroxide removal performance> As shown in the following Test Example 1, a test was conducted in which water to be treated containing hydrogen peroxide was passed through a catalyst device (hydrogen peroxide removal device), and the test results confirmed the correlation between the OH type proportion of the catalyst resin and the hydrogen peroxide removal performance.

[0044] (Test Example 1) As shown in Figure 3, an ion exchange resin container (column) 30 with an inner diameter of 31 mm and a height of 1 m and equipped with a mesh 32 on the bottom was prepared as the container to be filled with the catalytic resin. The mesh 32 was placed so as to cover the outlet for treated water at the bottom of the container 30, and served as a filter that allowed water to pass through while preventing the catalytic resin filled in the container from leaking out of the container. Next, catalytic resin 31 was filled to a height (layer height) of 10 cm. A test was conducted using the container filled with catalytic resin 31 as a catalytic device (hydrogen peroxide removal device). The catalyst resin 31 filled in the container 30 was prepared by stacking CO₃-type catalyst resin and OH-type catalyst resin in different mass ratios (CO₃-type / OH-type = 30 / 70, 50 / 50, 70 / 30, 90 / 10), as well as a single layer of CO₃-type catalyst resin (CO₃-type / OH-type = 100 / 0). The OH-type catalyst resin was a Pd-loaded strongly basic anion exchange resin (product name: ORLITE® HR43-HG) manufactured by Organo Corporation. The CO₃-type catalyst resin was converted to the carbonate type (CO₃-type) by passing carbonated water through the OH-type catalyst resin. The catalyst resin was determined to have completely converted to the carbonate type (CO₃-type) when the specific resistance values ​​at the inlet and outlet during water passage became the same. Each of these catalyst resins was filled into the container (column) 30 as described above to prepare a catalyst device.

[0045] Next, water to be treated with an H2O2 concentration of 35 ppb (μg / L) was prepared and passed through the catalyst device at a water flow rate of LV425 (the water to be treated was supplied from the top of container 30 and the treated water was discharged from the bottom of container 30). One hour after the start of water flow, the H2O2 concentration of the effluent water (treated water) was measured by colorimetric analysis using phenolphthaline. The results of Test Example 1 are shown in Figure 2 (the curve shows the results of Test Example 1). Figure 2 shows the correlation between the OH type fraction of the ion exchange resin after water flow and hydrogen peroxide removal performance. The vertical axis of Figure 2 shows the H2O2 concentration (μg / L) of the treated water, the horizontal axis (lower horizontal axis) shows the OH type fraction of the catalyst resin (Pd(OH) fraction (%)), and the upper horizontal axis shows the CO3 type fraction of the catalyst resin (Pd(CO3) fraction (%)). As shown in Figure 2, the lower the OH type ratio (Pd(OH) ratio) (i.e., the higher the CO3 type ratio), the higher the H2O2 concentration in the treated water and the lower the hydrogen peroxide removal performance.

[0046] <Confirmation test of catalyst resin deterioration due to inorganic carbonate ions and ultraviolet irradiation conditions (ΔTOC below 1 ppb)> As shown in the following Test Example 2, a test was conducted in which water to be treated containing hydrogen peroxide and carbonic acid (inorganic carbonate ions) was passed through a catalyst device (hydrogen peroxide removal device), and it was confirmed that the catalyst resin deteriorated. Furthermore, the results of this test confirmed that if the amount of TOC component decomposition (equivalent to ΔTOC) in the ultraviolet oxidation device (second ultraviolet oxidation device) upstream of the catalytic device is 1 ppb or less, the deterioration of the catalytic resin in the downstream catalytic device can be sufficiently suppressed.

[0047] (Test Example 2) The test was carried out using a scaled-up actual machine in comparison with the above Test Example 1. A 320 mm inner diameter FRP (Fiberglass Reinforced Plastics) tank was filled with a non-regenerative ion exchange resin to a height of 80 cm and a catalyst resin to a height of 10 cm, in that order. A strainer was provided at the bottom of the tank to allow water to pass through while preventing the ion exchange resin from leaking. A purified ion exchange resin (product name: ESP-2) manufactured by Organo Corporation was used as the non-regenerative ion exchange resin, and a strongly basic anion exchange resin (product name: ORLITE® HR43-HG) supported with Pd, manufactured by Organo Corporation, was used as the catalyst resin. The water to be treated was fed from the top of the tank, passed through the catalytic resin and non-regenerative ion exchange resin in that order, and the treated water was discharged from the bottom of the tank. The carbon dioxide concentration of the water to be treated (feed water) was 5 ppb (μg / L), the H2O2 concentration was 35 ppb (μg / L), and the flow rate was 3.4 m 3 / h. The H2O2 concentration of the water effluent from the tank (treated water) was measured periodically by colorimetric analysis using phenolphthaline, and the OH type proportion (Pd(OH) proportion) in the catalyst resin at the time of measurement was calculated based on the carbon dioxide concentration of the water to be treated (feed water), the amount of water flowing, the exchange capacity of the catalyst resin, etc. In order to check for discrepancies between the calculated value and the actual measured value, the OH type proportion of the catalyst resin was measured at one point to confirm that there was no discrepancy. The OH type proportion of the catalyst resin was measured by titration. In this titration measurement, sodium nitrate solution, hydrochloric acid, and ammonia were passed through each sample resin that had been collected and divided, and the OH type and CO3 2- Shape, Cl -The ion exchange capacities of the ionic forms were measured individually, and the proportion (%) of the ion exchange capacity of each ionic form relative to the sum of these ion exchange capacities (total ion exchange capacity) was calculated. Based on the obtained values, the proportion of the OH type of the sample resin was determined. The results of Test Example 2 are shown in FIG. 2 (the broken line shows the results of Test Example 2).

[0048] Figure 2 shows the relationship between the OH type ratio (Pd(OH) ratio) in the catalyst resin after water flow and the H2O2 concentration in the treated water. The vertical axis of Figure 2 shows the H2O2 concentration (μg / L) of the treated water, the lower horizontal axis shows the OH type ratio (Pd(OH) ratio (%)) in the catalyst resin, and the upper horizontal axis shows the ratio of resin in which OH in the catalyst resin has been replaced with inorganic carbonate ions (CO3 type ratio: Pd(CO3) ratio (%)). As shown in Figure 2, as the OH type proportion (Pd(OH) proportion (%)) of the catalyst resin decreases (the Pd(CO3) proportion increases), that is, as the catalyst resin deteriorates, the H2O2 concentration in the treated water increases.

[0049] Furthermore, the H2O2 concentration was below 1 ppb (μg / L) after the water had been treated for 8 months, and the Pd(OH) ratio was 60%. This shows that if the carbon dioxide concentration in the water to be treated is 5 ppb or less, the H2O2 concentration can be sufficiently reduced for a long period of time, that is, deterioration of the catalyst resin can be sufficiently suppressed. As mentioned above, the ratio of TOC value to inorganic carbonate ion concentration (TOC value:inorganic carbonate ion concentration) is 1:5, so a carbonic acid concentration of 5 ppb (corresponding to the maximum concentration of dissociated inorganic carbonate ions) corresponds to a TOC value of 1 ppb. Therefore, if the amount of TOC component decomposition (corresponding to ΔTOC) in the ultraviolet oxidation device upstream of the catalytic device is 1 ppb or less, it can be said that deterioration of the catalytic device downstream can be sufficiently suppressed. [Explanation of symbols]

[0050] 1 Primary water purification equipment 2 Secondary pure water production equipment 11 First UV oxidation device 12 Ion exchange unit 13 Boron-selective resin device 14 Degassing device 21 Second UV oxidation device 22 Hydrogen peroxide removal device (catalytic device) 23 Degassing device 24 Ion exchange unit 25 Ultrafiltration membrane device 30 Ion exchange resin container (column) 31 Catalyst Resin 32 mesh

Claims

1. An ultrapure water production system including a primary pure water production system and a secondary pure water production system, the primary pure water production system has a first ultraviolet oxidation device, the secondary pure water production system has a second ultraviolet oxidation device and a hydrogen peroxide removal device provided downstream of the second ultraviolet oxidation device, the hydrogen peroxide removal device includes an ion exchanger carrying a platinum group metal catalyst; The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) and the TOC value of the treated water treated in the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC (TOC SUP -TOC TRE The ultrapure water production system is characterized in that the amount of ultraviolet irradiation from the second ultraviolet oxidation device is controlled so that the concentration of ions in the ultrapure water is 1 ppb or less.

2. The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) is 0 < TOC SUP 2. The ultrapure water production system according to claim 1, wherein the amount of ultraviolet radiation emitted by said first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb.

3. 2. The ultrapure water production system according to claim 1, wherein the ultraviolet irradiation amount of said first ultraviolet oxidation device is greater than the ultraviolet irradiation amount of said second ultraviolet oxidation device.

4. The TOC value of the treated water treated by the second ultraviolet oxidation device (TOC TRE 2. The ultrapure water producing system according to claim 1, wherein the amount of ultraviolet irradiation from said first ultraviolet oxidation device and the amount of ultraviolet irradiation from said second ultraviolet oxidation device are controlled so that the concentration of ions in said first ultraviolet oxidation device is 1 ppb or less.

5. 2. The ultrapure water producing system according to claim 1, further comprising a water quality meter provided at a stage preceding and / or following the second ultraviolet oxidation device.

6. 2. The ultrapure water producing system according to claim 1, further comprising: a first TOC meter provided upstream of said second ultraviolet oxidation device; and a second TOC meter provided downstream of said second ultraviolet oxidation device.

7. 1. A method for producing ultrapure water using an ultrapure water production system including a primary pure water production system and a secondary pure water production system, the primary pure water production system has a first ultraviolet oxidation device, the secondary pure water production system has a second ultraviolet oxidation device and a hydrogen peroxide removal device provided downstream of the second ultraviolet oxidation device, the hydrogen peroxide removal device includes an ion exchanger carrying a platinum group metal catalyst; The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) and the TOC value of the treated water treated in the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC (TOC SUP -TOC TRE 2. A method for producing ultrapure water, comprising controlling the amount of ultraviolet irradiation in the second ultraviolet oxidation device so that the concentration of ions in the second ultraviolet oxidation device is 1 ppb or less.

8. The TOC value of the water supplied to the second ultraviolet oxidation device (TOC SUP ) is 0 < TOC SUP 8. The method for producing ultrapure water according to claim 7, wherein the ultraviolet irradiation amount of said first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb.

9. 8. The method for producing ultrapure water according to claim 7, wherein the first ultraviolet oxidation device is operated so that the ultraviolet irradiation amount thereof is greater than the ultraviolet irradiation amount of the second ultraviolet oxidation device.

10. 8. The method for producing ultrapure water according to claim 7, wherein the ultrapure water production system has a first TOC meter provided upstream of the second ultraviolet oxidation device and a second TOC meter provided downstream of the second ultraviolet oxidation device.

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