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

Ultrapure water production device and ultrapure water production method

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

[0002] In recent years, with the increasing demand for high-quality ultrapure water, methods for decomposing and removing trace amounts of organic matter contained in water have been studied. TOC (Total Organic Carbon) is used as an indicator of water quality after decomposition and removal of organic matter, and TOC is required to 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 can 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, can lead to the generation of new organic matter derived from the resins, resulting in a decrease in the quality of the ultrapure water.

[0005] Therefore, a method of 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, has been proposed as a method of removing hydrogen peroxide from water. By using a platinum group metal supported catalyst, hydrogen peroxide can be decomposed and removed by the reaction represented by 2H2O2 → 2H2O + O2.

[0006] As an example of an ultrapure water production method and apparatus using such a hydrogen peroxide removal method, Patent Document 1 discloses an ultrapure water production method and apparatus 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 using 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 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 also describes a pure water production method and apparatus that can prevent (or suppress) deterioration of the catalyst resin and stably decompose hydrogen peroxide over a long period of time.

[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 catalyst resin in which a platinum group metal is supported on a strongly basic anion exchange resin.

[0008] Japanese Patent No. 5854163 Japanese Patent Application Laid-Open No. 2010-069460

[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 is increased (i.e., the organic matter concentration is reduced).

[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 deterioration in the quality of the resulting ultrapure water. More specifically, they discovered that in ultraviolet oxidation treatment, organic matter (TOC components) is oxidized and decomposed to produce organic acids, which are then oxidized and 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.

[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, wherein 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, and the TOC value (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 [2] The ultrapure water production system is characterized in that the amount of ultraviolet irradiation of the second ultraviolet oxidation device is controlled so that the TOC value (TOC SUP ) is 0 < TOC SUPThe 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 [1] The ultrapure water production system 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 total amount of the oxidized water is 1 ppb or less. [5] The ultrapure water production system according to any one of [1] to [4], wherein a water quality meter is provided upstream and / or downstream of the second ultraviolet oxidation device. [6] The ultrapure water production system according to any one of [1] to [5], wherein a first TOC meter is provided upstream of the second ultraviolet oxidation device and a second TOC meter is 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, wherein 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, and the TOC value (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 [8] A method for producing ultrapure water, characterized in that the ultraviolet irradiation amount of the second ultraviolet oxidation device is controlled so that the TOC value (TOC SUP ) is 0 < TOC SUP[9] The method for producing ultrapure water according to [7] or [8], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb.

[10] The method for producing ultrapure water according to [7] or [8], wherein the ultraviolet irradiation amount of the first ultraviolet oxidation device is controlled so as to be greater than the ultraviolet irradiation amount of the second ultraviolet oxidation device.

[11] The method for producing ultrapure water according to [7] or [8], wherein the TOC value (TOC TRE

[11] 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 first ultraviolet oxidation device is 1 ppb or less.

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

[11] , wherein the ultrapure water production system has a water quality meter provided upstream and / or downstream of the second ultraviolet oxidation device.

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

[12] , 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.

[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.

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

[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 water purification system (make-up) and a secondary water purification system (polishing) that supplies treated water from the primary water purification system. The primary water purification system includes a first ultraviolet oxidation device, and the secondary water purification system includes a second ultraviolet oxidation device and a hydrogen peroxide removal device located downstream of the second ultraviolet oxidation device. The first and second ultraviolet oxidation devices are devices that decompose and remove trace amounts of organic matter (TOC components) in water using ultraviolet oxidation treatment. In this ultraviolet oxidation treatment, water is oxidatively decomposed to generate OH radicals, which then oxidatively decompose the organic matter (TOC components). The generated organic acids are further oxidatively decomposed to generate CO2, which forms inorganic carbonate ions in the treated water, while excess OH radicals aggregate to generate hydrogen peroxide. The hydrogen peroxide removal device is a catalytic device that includes an ion exchanger (hereinafter referred to as a "catalyst carrier") supporting a platinum group metal catalyst and decomposes and removes hydrogen peroxide. This hydrogen peroxide removal device (hereinafter referred to as "catalytic device") is a device that decomposes and removes hydrogen peroxide generated by ultraviolet oxidation treatment by the action of a catalyst.

[0017] The ultrapure water production system of this embodiment is configured to reduce the TOC value (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 amount of ultraviolet irradiation from the second ultraviolet oxidation device is controlled so that the TOC content is 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 feed water SUP and TOC of treated water TRE The relationship is TOC SUP >TOC TRE (i.e., 0<ΔTOC). Furthermore, an ultrapure water production method according to another embodiment of the present invention is an ultrapure water production method using such an ultrapure water production apparatus, in which the TOC value (TOCSUP ) and the TOC value of the treated water of the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC (TOC SUP -TOC TRE The ultraviolet irradiation amount of the second ultraviolet oxidation device is controlled so that the TOC content is 1 ppb or less. Here, "control" includes both automatic control and manual control. As described above, the water supplied to the second ultraviolet oxidation device contains TOC components (TOC SUP ≠0), the TOC of this feed water SUP and TOC of treated water TRE The relationship is TOC SUP >TOC TRE (i.e., 0<ΔTOC).

[0018] As described above, 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 By controlling or operating the UV irradiation amount so that ΔTOC is 1 ppb or less, the inorganic carbonate ion concentration in the water effluent 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 due to inorganic carbonate ions in the subsequent stage and enabling a stable supply of ultrapure water of high purity (operating so that fluctuations in water quality are not small). In the present invention, it is necessary to control or operate the UV irradiation amount so that ΔTOC is 1 ppb or less, and it is preferable to set ΔTOC to 0.5 ppb or less, and more preferably to set it to less than 0.2 ppb. Note that a TOC value of 1 ppb corresponds to an inorganic carbonate ion concentration of 5 ppb, assuming that 1 ppb of TOC components is completely decomposed, according to the following: If all organic components (TOC components) in the water are decomposed, they will ultimately 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 is approximately 1:5, as shown below: [TOC components (C)]:[inorganic carbonate ions (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 water fed 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 When reducing the TOC value of the water 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 of the water to be supplied to the second ultraviolet oxidation device at the subsequent stage (TOC SUP ) is preferably sufficiently reduced. In this case, it is preferable to increase the UV irradiation dose of the first ultraviolet oxidation device compared to the UV irradiation dose of the second ultraviolet oxidation device. Typically, to reduce the TOC value of the final treated water, the UV irradiation dose of the ultraviolet oxidation device (second ultraviolet 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, the amount of inorganic carbonate ions generated increases. As a result, problems caused by inorganic carbonate ions (deterioration of the catalyst support in the hydrogen peroxide removal device) are more likely to occur. Therefore, in the present invention, it is preferable to increase the UV irradiation dose of the ultraviolet oxidation device (first ultraviolet oxidation device) in 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 ultraviolet oxidation device (second ultraviolet oxidation device) in the downstream secondary pure water production system. This reduces the amount of inorganic carbonate ions generated in the downstream secondary pure water production system, thereby suppressing deterioration of the catalyst support in the hydrogen peroxide removal device caused by inorganic carbonate ions.

[0020] In the ultrapure water production apparatus 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 ≦5 ppb), preferably 3 ppb or less (0 < TOC SUP It is preferable to control (or manipulate) the amount of ultraviolet irradiation in the first ultraviolet oxidation device so that the TOC value of the treated water treated in the second ultraviolet oxidation device (TOC ≦3 ppb) is ≦3 ppb. In addition to sufficiently reducing the TOC of the final treated water, from the viewpoint of further sufficiently reducing the amount of TOC components oxidatively decomposed in the second ultraviolet oxidation device, the TOC value of the treated water treated in the second ultraviolet oxidation device (TOC TRE It is preferable to control (or manipulate) the ultraviolet irradiation dose of the first ultraviolet oxidation device and the ultraviolet irradiation dose of the second ultraviolet oxidation device so that the TOC value (TOC) of the water supplied to the second ultraviolet oxidation device is 1 ppb or less. Note that even if TOC is excessively reduced in the primary pure water production device, there is a possibility that organic matter will be mixed into the treated water later, increasing the TOC, and this increase can be removed in the secondary pure water production device. Therefore, it is not necessary to excessively reduce TOC in the primary pure water production device, and from the viewpoint of treatment efficiency, it is preferable to reduce it appropriately depending on the content of TOC components in the water to be treated. The control or manipulation of the ultraviolet irradiation dose of the first ultraviolet oxidation device is performed in order to prevent excessive ultraviolet irradiation in the first ultraviolet oxidation device, so that the TOC value (TOC SUP It is preferable to carry out the test within an ultraviolet irradiation dose range in which the concentration of β-glucan is 0.3 ppb or more (a range of irradiation dose that does not decrease to less than 0.3 ppb), more preferably within an ultraviolet irradiation dose range in which the concentration of β-glucan is 0.5 ppb or more (a range of irradiation dose that does not decrease to less than 0.5 ppb), or within an ultraviolet irradiation dose range in which the concentration of β-glucan is 1 ppb or more (a range of irradiation dose that does not decrease to less than 1 ppb).

[0021] TOC measurement can be performed by providing a TOC meter between the first and second ultraviolet oxidation devices and at a stage subsequent to the second ultraviolet oxidation device. 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 at a stage subsequent to the second ultraviolet oxidation device so as to measure both 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. This allows the TOC of both treated waters to be measured with a single TOC meter.

[0022] In this way, in the ultrapure water production system and ultrapure water production method of the present invention, 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 can be measured by one or two TOC meters. The TOC of the treated water between the first ultraviolet oxidation device and the second ultraviolet oxidation device can be measured by a more accurate measurement value (TOC SUP ), it is preferable to measure the TOC of the feed water immediately before being supplied to the second ultraviolet oxidation device (i.e., the treated water between the second ultraviolet oxidation device and the treatment device arranged 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 provided measures 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, and the amount of ultraviolet irradiation of 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 UV irradiation doses of the first and second UV oxidation devices can be controlled (or manipulated) so that the difference (ΔTOC) between the measured TOC value of the effluent water from the first UV oxidation device and the measured TOC value of the second UV oxidation device is 1 ppb or less. By performing UV oxidation treatment at a sufficiently high irradiation dose in the first UV 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 UV oxidation device can be sufficiently reduced. Furthermore, the UV irradiation doses of the first and second UV 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 meter can be a typical TOC meter used in producing ultrapure water.For example, a complete oxidation type TOC meter 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 the time when 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 provided with various water quality meters other than TOC meters at desired locations. The water quality can be managed and various treatment devices constituting the ultrapure water production system can be controlled and operated based on the measurements of the water quality meters. For example, the water quality meters can measure electrical conductivity, 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 meters can be provided between the first and second ultraviolet oxidation devices and downstream of the second ultraviolet oxidation device, or on either one of them. A single water quality meter can also measure the quality of the treated water between the first and second ultraviolet oxidation devices and downstream of 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 Fig. 1, the ultrapure water production system comprises a primary pure water production system 1 and a secondary pure water production system 2, in this order. The primary pure water production system 1 comprises a first ultraviolet oxidation system 11, an ion exchange system 12, a boron-selective resin system 13, and a degassing system 14, in this order. The secondary pure water production system 2 comprises a second ultraviolet oxidation system 21, a hydrogen peroxide removal system (catalytic system) 22, a degassing system 23, an ion exchange system 24, and an ultrafiltration membrane system 25, in this order.

[0027] As mentioned 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 FIG. 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 TREThe 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. Since the amount of TOC eluted from each treatment device and facility in the secondary pure water production system 2 after the second ultraviolet oxidation device 21 is very small, the effect of the TOC meter's installation location on ΔTOC can be ignored. Although two TOC meters are provided in the configuration shown in FIG. 1 , the TOC meter 31 at the upstream side can be omitted, leaving only the TOC meter 32 at the downstream side, and the downstream side can be configured so that a portion of the water supplied to the second ultraviolet oxidation device 21 can be introduced into the TOC meter 32 at the downstream side. This allows a single TOC meter to measure the TOC of both the water supplied to the second ultraviolet oxidation device 21 and the water treated 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 System) The primary pure water production system of this embodiment of the ultrapure water production system includes a first ultraviolet oxidation device and may further include a suitable 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 FIG. 1 , the primary pure water production system 1 may 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. The first ultraviolet oxidation device 11 oxidatively decomposes organic matter, the ion exchange device 12 removes impurity ions from the water, the boron-selective resin device 13 removes boron from the water, and the degassing device 14 removes gases such as dissolved oxygen from the water. The boron-selective resin device 13 may be omitted if necessary. A reverse osmosis membrane device may also be provided to remove inorganic substances, organic substances, fine particles, microorganisms, etc. from the water.

[0031] (Secondary Pure Water Production System) The secondary pure water production system of this embodiment of the ultrapure water production system includes a second ultraviolet oxidation device and a hydrogen peroxide removal device (catalytic device) downstream of the second ultraviolet oxidation device. It may also include a degasser (e.g., a membrane degasser), an ion exchanger (e.g., a non-regenerative ion exchanger such as a cartridge polisher), an ultrafiltration membrane device (UF), or other treatment devices commonly used in ultrapure water production systems. For example, as shown in FIG. 1 , the secondary pure water production system 2 may have a configuration in which a second ultraviolet oxidation device 21, a hydrogen peroxide removal device 22, a degasser 23 (e.g., a membrane degasser), an ion exchanger 24 (e.g., a non-regenerative ion exchanger), and an ultrafiltration membrane device 25 are connected in this order. The order of the degasser 23 and the ion exchanger 24 may be reversed if necessary. Furthermore, a tank for temporarily storing the treated water from the primary pure water production system 1 may be provided upstream of the secondary pure water production system 2. Organic matter is oxidatively decomposed in the second ultraviolet oxidation device 21, hydrogen peroxide generated in the preceding second ultraviolet oxidation device 21 is decomposed in the hydrogen peroxide removal device 22, gases such as dissolved oxygen are removed from the water in the degassing device 23, impurity ions are removed from the water 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 stages following 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 to 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 (Catalyst Device)) The hydrogen peroxide removal device installed in the secondary pure water production system is a catalyst device for decomposing hydrogen peroxide generated in the ultraviolet oxidation device in the upstream stage, and includes an ion exchanger (catalyst support) on which a platinum group metal catalyst is supported. Examples of platinum group metal catalysts include catalytic metals such as ruthenium, rhodium, palladium, osmium, iridium, and platinum. These may be used alone or in combination of two or more, or as an alloy of two or more. Among these catalytic metals, platinum, palladium, and alloys of platinum and palladium are preferred, and these may be used alone or in combination of two or more. Palladium is particularly preferred because of its excellent catalytic activity and relatively low cost. Examples of supports 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 as ion exchangers, and the ion exchanger supporting a platinum group metal catalyst in an embodiment of the present invention is preferably a platinum group metal catalyst-supported ion exchange resin (hereinafter referred to as "catalyst resin" as appropriate). Anion exchangers are preferred as ion exchangers, and anion exchange resins are preferred as anion exchangers, with strongly basic anion exchange resins being particularly preferred. The shape of the platinum group metal catalyst support is not particularly limited, and either granular or pellet-shaped supports can be used. When an ion exchange resin such as an anion exchange resin is used as a platinum group metal catalyst support, a gel-like resin (gel-type resin) can be used. By contacting the water to be treated containing hydrogen peroxide with such a catalyst support, the hydrogen peroxide in the water to be treated is decomposed by the reaction 2H2O2 → 2H2O + O2.

[0033] As an ion exchanger (catalyst support) carrying such a platinum group metal catalyst, for example, the catalyst resin disclosed in Japanese Patent Laid-Open Publication No. 2010-069460 can be suitably used. Specifically, a strongly basic anion exchange resin carrying a platinum group metal catalyst can be suitably used, 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. The amount of platinum group metal catalyst (catalyst metal) supported on this strongly basic anion exchange resin is in the range of 10 mg-catalyst / L-R to 500 mg-catalyst / L-R, preferably 10 mg-catalyst / L-R to 170 mg-catalyst / L-R, and more preferably 10 mg-catalyst / L-R to 50 mg-catalyst / L-R. R is an abbreviation for anion exchange resin based on the OH type, and "mg-catalyst / L-R" means the mass (mg) of catalyst per 1 L of anion exchange resin based on the OH type. The strongly basic anion exchange resin is preferably in a gel state 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 a platinum group metal catalyst (catalytic metal). The catalyst resin is supported on the strongly basic anion exchange resin by passing the water to be treated at a space velocity (SV) of 30 to 2,000 hr. -1 It is preferable to contact the material within the range of SV200 to 2000 hr. -1 It is more preferable to contact the water with the hydrogen peroxide within this range. The hydrogen peroxide removal device may be provided with a hydrogen supply device to supply hydrogen to the water to be treated. This allows the hydrogen peroxide in the water to be decomposed and makes it easier to remove gas components such as oxygen produced by the decomposition of hydrogen peroxide by degassing.

[0034] (Ultraviolet Oxidation Device) The first and second ultraviolet oxidation devices used in the present invention can be ultraviolet oxidation devices 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 light having a wavelength of at least approximately 100 to 200 nm and is capable of oxidatively decomposing organic matter in the water to be treated. From the viewpoint of decomposing organic matter in the water to be treated, the ultraviolet oxidation device is preferably equipped with an ultraviolet lamp capable of irradiating ultraviolet light having a wavelength of approximately 185 nm. The ultraviolet lamp is not particularly limited, but a low-pressure mercury lamp is preferred. Furthermore, ultraviolet oxidation devices include flow-through and immersion types, with flow-through types being preferred from the viewpoint of treatment efficiency.

[0035] The first and second ultraviolet oxidation devices measure the first TOC value (TOC SUP ) and a second TOC value (TOC TRE 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 a second TOC value (TOC TRE ) is input, and the difference ΔTOC (TOC SUP -TOC TRE The ultraviolet irradiation amount control device may be configured to control (or operate) the ultraviolet irradiation amount of the second ultraviolet oxidation device so that the TOC value (TOC) is 1 ppb or less. This ultraviolet irradiation amount control device may be configured to further control (or operate) the ultraviolet irradiation amount of the first ultraviolet oxidation device. SUPWhen 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 calculate a 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 a predetermined value or less (for example, 5 ppb or less). SUP The ultraviolet irradiation amount of the first ultraviolet oxidation device may be controlled (or manipulated) so that the first TOC value (TOC SUP When the TOC value increases and is about to exceed a predetermined value (for example, 5 ppb), the amount of ultraviolet radiation from the first ultraviolet oxidation device is increased to reduce the first TOC value (TOC SUP ) can be controlled (or manipulated) to be a predetermined value or less (for example, 5 ppb or less).

[0037] The ultraviolet irradiation amount control device also controls the second TOC value (TOC TRE The ultraviolet irradiation amount of the first and / or second ultraviolet 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 amount of ultraviolet radiation from the first ultraviolet oxidation device and / or the second ultraviolet oxidation device is increased to increase the second TOC value (TOC TREHowever, as described above, the amount of ultraviolet irradiation from the second ultraviolet oxidation device is controlled (or operated) so that ΔTOC is maintained 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 value of current passed through the multiple ultraviolet lamps provided in the ultraviolet oxidation device, etc. In addition to these methods, known methods for controlling the ultraviolet irradiation amount can also be used as appropriate.

[0039] The majority of OH radicals generated by the decomposition of water by ultraviolet irradiation in the ultraviolet oxidation device are used to decompose organic matter, but the excess OH radicals combine to form hydrogen peroxide. This hydrogen peroxide is decomposed and removed in the subsequent hydrogen peroxide removal device (catalytic device). Meanwhile, the organic matter (TOC components) contained in the water to be treated is converted by the ultraviolet oxidation device into organic acids and CO ２ The hydrogen peroxide is oxidized and decomposed to form carbon dioxide in the water, and as a result, the resulting treated water contains inorganic carbonate ions. These inorganic carbonate ions have the problem of deteriorating the catalyst carrier of the hydrogen peroxide removal device. According to an embodiment of the present invention, the TOC value (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 TREBy controlling or manipulating the UV irradiation doses of the first and second ultraviolet oxidation devices so that the TOC concentration is 1 ppb or less, the amount of TOC components oxidatively decomposed in the second ultraviolet oxidation device can be kept below a predetermined level. This makes it possible to keep the inorganic carbonate ion concentration in the effluent water from the second ultraviolet oxidation device below a predetermined 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 water quality fluctuations are not small).

[0040] (Membrane Degassing Apparatus) A membrane degassing apparatus is an apparatus in which treated water from a hydrogen peroxide removal apparatus flows into one chamber separated by a gas separation membrane, while the pressure in the other chamber is reduced, thereby transferring gas contained in the treated water through the gas separation membrane to the other chamber for removal. Examples of the gas separation membrane that can be used include hydrophobic polymer membranes, such as tetrafluoroethylene-based or polyolefin-based membranes, formed into hollow fiber membranes or other shapes. Other degassing apparatuses, such as vacuum degassing apparatuses and thermal degassing apparatuses, can be used to remove gas contained in the treated water from the hydrogen peroxide removal apparatus. However, when using such other degassing apparatuses, there is a risk of impurities being introduced into the water from these apparatuses or leaching into the water from the apparatus's packing. In contrast, a membrane degassing apparatus is particularly preferred as a degassing apparatus because it does not encounter the problems of impurities being introduced into or leaching out of the water.

[0041] (Non-regenerative ion exchange device) The non-regenerative ion exchange device (cartridge polisher) is not particularly limited as long as it removes impurities such as cations and anions from the treated water from the hydrogen peroxide removal device, but examples include an ion exchange device using a mixed bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin (mixed bed single tower type), an ion exchange device using a single bed of a strongly basic anion exchange resin (single bed single tower type), a multi-layer ion exchange device (multi-layer single tower type) with a single bed of a strongly basic anion exchange resin on the inlet side and a mixed bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin on the outlet side, and an ion exchange device (two tower type) with a resin tower with a single bed of a strongly basic anion exchange resin on the front side and a resin tower with a mixed bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin on the rear side. Of these, a mixed bed single tower type ion exchange device is preferably used because it causes little change in the pH of 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 remove hydrogen peroxide generated in an ultraviolet oxidation device while suppressing deterioration of the catalyst carrier in a downstream catalytic device, and can stably supply ultrapure water of good quality for a long period of time. The ultrapure water production apparatus and ultrapure water production method of the embodiment of the present invention can supply high-purity 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.

[0043] <Test to confirm the correlation between the OH type proportion of the catalytic resin and the 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 catalytic device (hydrogen peroxide removal device), and the test results confirmed the correlation between the OH type proportion of the catalytic resin and the hydrogen peroxide removal performance.

[0044] Test Example 1: As shown in FIG. 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 a container for filling with catalytic resin. The mesh 32 was positioned to cover the treated water outlet at the bottom of the container 30, acting as a filter to allow 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 catalytic resin 31 filled in the container 30 consisted of layers of CO3-type catalytic resin and OH-type catalytic 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 catalytic resin (CO3-type / OH-type = 100 / 0). The OH-type catalyst resin used was a Pd-supported strong basic anion exchange resin (product name: ORLITE (registered trademark) HR43-HG) manufactured by Organo Corporation. The CO3-type catalyst resin used was the OH-type catalyst resin converted to the carbonate type (CO3 type) by passing carbonated water through it. It was determined that the resin had completely become 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 packed into a container (column) 30 as described above to prepare a catalyst device.

[0045] Next, H ２ O ２ Water to be treated with a concentration of 35 ppb (μg / L) was prepared and passed through the catalyst device at a water flow rate of LV425 (water to be treated was supplied from the top of the container 30, and treated water was discharged from the bottom of the 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 phenolphthalein. 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 proportion of the ion exchange resin after water flow and the 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 proportion (Pd(OH) proportion (%)) of the catalyst resin, and the upper horizontal axis shows the CO2 concentration of the catalyst resin. ３As shown in FIG. 2, the lower the OH type ratio (Pd(OH) ratio) (i.e., the higher the CO type ratio), the higher the H in the treated water. ２ O ２ It can be seen that the concentration is high and the hydrogen peroxide removal performance is low.

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

[0047] (Test Example 2) A test was conducted using a scaled-up actual machine compared to Test Example 1 above. A tank made of FRP (Fiberglass Reinforced Plastics) with an inner diameter of 320 mm 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 (registered trademark) HR43-HG) supported with Pd manufactured by Organo Corporation was used as the catalyst resin. Water to be treated was supplied from the top of the tank, and the water was passed through the catalyst resin and then the non-regenerative ion exchange resin, and the treated water was discharged from the bottom of the tank. The carbon dioxide concentration of the water to be treated (supply 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 periodically measured by colorimetric analysis using phenolphthalein, and the OH type proportion (Pd(OH) proportion) in the catalyst resin at the time of measurement was calculated based on the carbonate 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 confirm whether there was any discrepancy 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 at this time was measured by titration. In this titration measurement, a sodium nitrate solution, hydrochloric acid, and ammonia were respectively 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 ratio (%) of the ion exchange capacity of each ionic form to the sum of these ion exchange capacities (total ion exchange capacity) was calculated, and the OH type ratio of the sample resin was determined based on the obtained values. The results of Test Example 2 are shown in Figure 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 H ２ O ２ The vertical axis of Fig. 2 shows the H2O2 concentration (µg / L) of the treated water, the lower horizontal axis shows the OH type ratio (Pd(OH) ratio (%)) of the catalyst resin, and the upper horizontal axis shows the ratio of resin in which OH of the catalyst resin has been replaced with inorganic carbonate ions (CO3 type ratio: Pd(CO ３ 2 shows that the concentration of H2O2 in the treated water increases as the OH type ratio (Pd(OH) ratio (%)) of the catalyst resin decreases (as the Pd(CO3) ratio increases), i.e., as the catalyst resin deteriorates.

[0049] In addition, the H ２ O ２The concentration was below 1 ppb (μg / L), and the Pd(OH) ratio at that time was 60%. This indicates that if the carbon dioxide concentration in the treated water is below 5 ppb, the H2O2 concentration can be sufficiently reduced for a long period of time, i.e., the deterioration of the catalytic resin can be sufficiently suppressed. As mentioned above, since the ratio of the TOC value to the inorganic carbonate ion concentration (TOC value:inorganic carbonate ion concentration) is 1:5, a carbon dioxide 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 decomposition amount of TOC components (corresponding to ΔTOC) in the ultraviolet oxidation device upstream of the catalytic device is below 1 ppb, the deterioration of the catalytic device downstream can be sufficiently suppressed.

[0050] REFERENCE SIGNS LIST 1 Primary pure water production apparatus 2 Secondary pure water production apparatus 11 First ultraviolet oxidation apparatus 12 Ion exchange apparatus 13 Boron selective resin apparatus 14 Degassing apparatus 21 Second ultraviolet oxidation apparatus 22 Hydrogen peroxide removal apparatus (catalytic apparatus) 23 Degassing apparatus 24 Ion exchange apparatus 25 Ultrafiltration membrane apparatus 30 Ion exchange resin container (column) 31 Catalytic resin 32 Mesh

Claims

1. An ultrapure water production system comprising a primary pure water production system and a secondary pure water production system, wherein the primary pure water production system has a first ultraviolet oxidation system, the secondary pure water production system has a second ultraviolet oxidation system and a hydrogen peroxide removal system provided downstream of the second ultraviolet oxidation system, the hydrogen peroxide removal system includes an ion exchanger carrying a platinum group metal catalyst, and the TOC value (TOC SUP ) and the TOC value of the water treated by the second ultraviolet oxidation device (TOC TRE ) and the difference ΔTOC (TOC SUP -TOC TRE The ultrapure water producing apparatus is characterized in that the amount of ultraviolet radiation emitted by 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 ) is 0 < TOC SUP 2. The ultrapure water producing 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. The ultrapure water production system according to claim 1, wherein the amount of ultraviolet irradiation from said first ultraviolet oxidation device is greater than the amount of ultraviolet irradiation from said second ultraviolet oxidation device.

4. The TOC value of the 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 ultrapure water is 1 ppb or less.

5. The ultrapure water production system according to claim 1, further comprising a water quality meter provided upstream and / or downstream of said second ultraviolet oxidation device.

6. The ultrapure water producing apparatus as described in claim 1, further comprising 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 having a primary pure water production system and a secondary pure water production system, wherein the primary pure water production system has a first ultraviolet oxidation system, the secondary pure water production system has a second ultraviolet oxidation system and a hydrogen peroxide removal system provided downstream of the second ultraviolet oxidation system, the hydrogen peroxide removal system includes an ion exchanger carrying a platinum group metal catalyst, and the TOC value (TOC SUP ) and the TOC value of the water treated by 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 from the second ultraviolet oxidation device so that the concentration of ions in the ultrapure water 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 amount of ultraviolet radiation emitted by said first ultraviolet oxidation device is controlled so as to satisfy the condition of ≦5 ppb.

9. A method for producing ultrapure water as set forth in claim 7, wherein the amount of ultraviolet irradiation from said first ultraviolet oxidation device is operated to be greater than the amount of ultraviolet irradiation from said second ultraviolet oxidation device.

10. The method for producing ultrapure water as described in claim 7, wherein the ultrapure water producing 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.

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