JP2009112941A - Ultrapure water production system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrapure water production system where UV is securely emitted to TOC (total organic carbon) concentration in inflow water by the right amount, thus TOC is securely oxidized and decomposed away, further, the increase of DO (dissolved oxygen) is prevented, and ultrapure water of low TOC and low DO can be stably produced. <P>SOLUTION: An ultrapure water production system 1 including: an ultraviolet ray oxidizing means 2 decomposing a TOC component in treatment water; and an ion exchange tower 3 removing the TOC component decomposed by the ultraviolet ray oxidizing means 2, has a peroxide concentration measuring means 4 measuring the concentration of peroxide in outlet water in the ultraviolet ray oxidizing means 2; and an ultraviolet ray irradiation amount controlling means 5 controlling an ultraviolet ray irradiation amount in the ultraviolet ray oxidizing means 2 according to the measured result from the peroxide concentration measuring means 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrapure water production apparatus, and more particularly, in an ultrapure water production apparatus comprising an ultraviolet (UV) oxidation means and an ion exchange tower, by controlling the amount of ultraviolet irradiation by the ultraviolet oxidation means, the TOC (total organic matter) The present invention relates to an ultrapure water production apparatus that can efficiently decompose and remove carbon.

  A general production system for producing ultrapure water used in semiconductor production processes, etc. from raw water such as river water, industrial water, tap water, etc. is a pretreatment process, primary pure water production process and secondary pure water. It consists of a manufacturing process (subsystem).

  The ultraviolet oxidation means is applied to a primary pure water production process and a secondary pure water production process in such an ultrapure water production system in order to oxidize and decompose organic substances in water. Further, the ion exchange tower is filled with an anion exchange resin and / or a cation exchange resin, and in order to remove ionic substances in the water, an ultraviolet oxidation means in the primary pure water production process and the secondary pure water production process. It is installed in the rear stage.

  In the conventional ultrapure water production system, the maximum content of the TOC concentration of the inflow water (inlet water) of the ultraviolet oxidation means is set, and the amount of OH radicals necessary for oxidative decomposition removal of the set TOC content is generated. An ultraviolet oxidation means for generating an ultraviolet irradiation amount as a fixed value is installed. That is, in the past, TOC remaining after UV oxidation is prevented by always irradiating the amount of UV light that can oxidatively decompose and remove the TOC with the maximum TOC setting concentration regardless of fluctuations in the TOC concentration of the influent water. .

  In such an ultrapure water production system, in order to prevent TOC remaining after UV oxidation, the UV irradiation amount of the UV oxidation means is fixed to a high value corresponding to the maximum TOC setting concentration. In such an ultraviolet oxidation means, when water having a TOC concentration lower than the maximum TOC setting concentration flows, an excessive amount of ultraviolet rays is irradiated, resulting in high cost of ultraviolet rays and the following problems.

  That is, when the TOC concentration in the inflowing water of the ultraviolet oxidation means is lower than the maximum TOC setting concentration, surplus OH radicals that have not been used for the ultraviolet oxidation decomposition of TOC remain as DO (dissolved oxygen) components in the treated water. It is presumed that this is because hydrogen peroxide is generated from surplus OH radicals, and this generates oxygen when it comes into contact with the ion exchange resin of the ion exchange tower at the latter stage of the ultraviolet oxidation means, particularly an anion exchange resin.

  For this reason, when the water whose TOC concentration is lower than the maximum TOC setting concentration is treated by the ultraviolet oxidation means and the ion exchange tower, the DO of the effluent of the ion exchange tower is higher than the DO of the ultraviolet oxidation means inflow. Therefore, in such a case, DO of the ultrapure water of the final treated water also becomes high.

  If DO is present in ultrapure water, when this is used as wafer cleaning water in a semiconductor manufacturing process, there is a high possibility that harmful effects such as formation of an oxide film on the silicon wafer surface will occur.

In order to avoid such adverse effects, the TOC concentration of the influent water is irradiated with ultraviolet rays without excess or deficiency, so that the TOC is surely oxidized and removed and the increase in DO is prevented. An ultrapure water production apparatus capable of stably producing ultrapure water has been proposed (see, for example, Patent Document 1).
JP-A-10-123118

  However, when measuring the TOC, since the TOC is generally a mixture of various organic components and the ease of decomposition differs depending on the type of organic matter in the ultraviolet oxidation means, a TOC meter is placed at the inlet of the ultraviolet oxidation means. Even if it is installed, since it is affected by the type of TOC component, it is difficult to control it uniformly.

  In addition, when measuring DO, the DO rise does not occur at the UV exit, but passes through the ion exchange tower in the subsequent stage, and the DO meter to be controlled needs to be measured after passing through the ion exchange tower. There is a problem that the responsiveness becomes slow. Furthermore, since the original purpose is to manage the DO value at the outlet of the ion exchange tower, using the DO value for the management itself will solve the problem of preventing the DO value from rising. There was no problem.

  Therefore, the present invention solves the above-mentioned conventional problems, irradiates the TOC concentration of the inflowing water with ultraviolet rays without excess or deficiency, and reliably oxidatively removes the TOC and prevents an increase in DO. An object of the present invention is to provide an ultrapure water production apparatus capable of stably producing TOC and low DO ultrapure water.

  The ultrapure water production apparatus of the present invention is an ultrapure water production apparatus comprising: an ultraviolet oxidation means for decomposing a TOC component in treated water; and an ion exchange tower for removing the TOC component decomposed by the ultraviolet oxidation means. , Having an peroxide concentration measuring means for measuring the peroxide concentration of the outlet water of the ultraviolet oxidizing means, and controlling the ultraviolet irradiation amount of the ultraviolet oxidizing means based on the measurement result of the peroxide concentration measuring means It has quantity control means.

  When the ultraviolet irradiation amount in the ultraviolet oxidation means is constant, the TOC decomposition amount decreases when the TOC concentration of the ultraviolet oxidation means inlet water decreases. In the conventional ultraviolet oxidation means, since the ultraviolet irradiation amount is set so that the preset maximum TOC setting concentration of the ultraviolet oxidation means inlet water can be decomposed, the actual TOC concentration of the ultraviolet oxidation means inlet water is the maximum TOC setting concentration. If it is smaller, the amount of UV irradiation becomes excessive with respect to the amount of TOC present. Peroxide is generated by this excessive amount, and the DO component increases.

  In order to suppress the increase in the DO component, the present inventors measure the concentration of the peroxide that seems to be the causative substance at the outlet of the ultraviolet oxidation means, and feed back the measurement result to thereby measure the ultraviolet oxidation means. The present invention has been completed by finding that the DO value at the outlet of the ion exchange resin can be effectively suppressed by controlling the irradiation amount of the ultraviolet rays.

  However, since the amount of peroxide that appears to be the causative substance is very small, it is difficult to specify the substance strictly, but as shown in FIG. The relationship between the concentration and the DO value at the ion exchange resin outlet is generally causal, and a correlation that can be sufficiently used for controlling the ultraviolet irradiation amount can be read.

  In FIG. 1, an ultrapure water production apparatus for treating pure water having a TOC concentration of 2.1 ppb, which has been treated in the pretreatment process and the primary pure water production process, in an ion exchange tower (MB polisher) after the ultraviolet oxidation means. FIG. 2 shows the relationship between the amount of ultraviolet irradiation in the ultraviolet oxidation means, the peroxide concentration at the outlet of the ultraviolet oxidation means, and the DO value at the outlet of the ion exchange tower.

  In general, when the TOC concentration of the inlet water is constant in the ultraviolet oxidation means, there is a linear relationship between the ultraviolet irradiation amount and the TOC removal amount. When the ultraviolet irradiation amount increases, the TOC removal amount is proportional to it. To increase. Therefore, the TOC removal amount per unit power consumption can be calculated based on the TOC concentration of the ultraviolet oxidation means inlet water, and based on this, the ultraviolet irradiation amount necessary for removing the TOC (the electric energy to the ultraviolet oxidation means or the UV to be lit) Lamp number).

  However, depending on the type of TOC, etc., the amount of UV irradiation required for the decomposition process may differ, and even if the TOC amount of the inlet water of the UV oxidation means is simply measured, it does not cause an appropriate DO value. In some cases, the amount of UV irradiation is controlled by the concentration of peroxide, which is considered to be the direct cause of increasing the DO value in the present invention. it can.

  According to the ultrapure water production apparatus of the present invention, it is possible to perform an appropriate amount of ultraviolet irradiation according to fluctuations in the TOC concentration of the influent water. The increase can be prevented, and high purity ultrapure water with low TOC and low DO can be produced stably and efficiently.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

A schematic configuration of an apparatus showing an embodiment of the ultrapure water production apparatus of the present invention is shown in FIG.
The ultrapure water production apparatus 1 shown in FIG. 2 has an ultraviolet oxidation means 2 for decomposing the TOC component in the treated water subjected to the primary pure water treatment, and an ion for removing the TOC component decomposed by the ultraviolet oxidation means 2. Based on the measurement result of the exchange tower 3, the peroxide concentration measuring means 4 for measuring the peroxide concentration in the outlet water of the ultraviolet oxidizing means, and the measurement result of the peroxide concentration measuring means, the ultraviolet irradiation amount of the ultraviolet slope means 2 is controlled. And an ultraviolet irradiation amount control means 5 for performing the above.

  In addition, the ultrapure water manufacturing apparatus 1 shown here is an apparatus which processes primary pure water and manufactures ultrapure water, and is called a so-called secondary pure water manufacturing apparatus or subsystem. Accordingly, the primary pure water is obtained by treating raw water with a so-called pretreatment system and a primary pure water system. Specifically, for example, raw water such as industrial water once stored in the raw water storage tank is passed through the pretreatment system to remove part of the suspended matter and organic matter in the raw water, and after passing through the filtered water tank, the primary pure water Desalination equipment that supplies pretreated water to the water system and removes impurity ions in water, reverse osmosis membrane equipment that removes inorganic ions, organic substances, fine particles, etc. in water, dissolved oxygen in water, etc. High-purity water obtained by sequentially passing water through a vacuum deaerator that removes the dissolved gas and a regenerative mixed-bed demineralizer that removes remaining ions and the like. This primary pure water is usually sent to the primary pure water storage tank and then processed by the secondary pure water production apparatus.

  The ultraviolet oxidation means 2 may be any one that is normally used in an ultrapure water production apparatus. For example, an apparatus equipped with an ultraviolet lamp capable of irradiating a wavelength near 185 nm is suitable for decomposing organic substances in the water to be treated. This is preferable. The ultraviolet lamp to be used is not particularly limited, but a low-pressure mercury lamp is preferable. In addition, examples of the ultraviolet irradiation device include a distribution type or an immersion type, and among these, the distribution type is preferable from the viewpoint of processing efficiency.

  The ion exchange column 3 is not particularly limited, and examples thereof include a non-regenerative ion exchange column (also called a cartridge polisher) and an ion adsorption membrane column. These ion exchange towers can be used singly or in combination of two or more, but even when used alone, an extremely small amount of metal can be sufficiently removed and pressure loss can be minimized. This is preferable.

  The non-regenerative ion exchange column is not particularly limited. For example, an ion exchange column (mixed-bed type) having a strongly acidic cation exchange resin and a strongly basic anion exchange resin, or a strongly basic anion exchange column. Ion exchange tower with single bed of ion exchange resin (single-bed type), ion-exchange tower with single bed of strong acidic cation exchange resin (single-bed type), single bed layer of strong basic anion exchange resin By a multi-layer ion exchange tower (multi-layer 1-column system) in which a mixed bed layer of strong acidic cation exchange resin and strongly basic anion exchange resin is provided on the outlet side, and a single bed of chelate resin An ion exchange tower (single-bed single tower type) is mentioned.

  Among these, when a mixed bed 1-column type ion exchange tower is used, there is no change in the pH of water at any position in the mixed bed layer, so that there is an advantage that efficient ion exchange can be performed.

  Although it does not specifically limit as an ion adsorption membrane column, It consists of what used the anion adsorption membrane, the cation adsorption membrane, and the chelate membrane suitably according to use conditions like the said non-regenerative type ion exchange column. Examples of the anion adsorption membrane include a porous membrane having a quaternary amine group as an anion exchange group and a sintered porous body. Examples of the cation adsorption membrane include a sulfone group, a phosphate group or a carboxyl group as a cation exchange group. Examples of the chelate film include a porous film and a sintered porous body having ethylenediamine capable of forming a chelate with metal ions in water. Examples of the membrane shape include a hollow fiber shape, a flat membrane shape, a pleated shape, a tube shape, and a fiber shape.

  The ion exchange column 3 includes an oxidant removing resin that captures peroxide and does not increase the DO value inside the ion exchange column at the upstream stage or the inflow side of the water to be treated inside the ion exchange column. It can also be set as the structure which provided. At this time, the treated water finally obtained has a favorable water quality without increasing the DO value, but the oxidant removing resin captures the peroxide and removes the peroxide from the treated water. Therefore, since the lifetime of the resin depends on the amount of the treated peroxide, even when the ion exchange tower having such a configuration is used, the amount of ultraviolet rays to be irradiated is controlled as in the present invention. In addition, by reducing the generation of peroxide, the life of the oxidant removing resin can be dramatically extended, and the production of ultrapure water can be efficiently performed at low cost. Here, as the oxidizing agent removing resin, for example, ANP (manufactured by Nomura Micro Science Co., Ltd.) or the like can be used.

  The peroxide concentration measuring means 4 may be a known peroxide measuring means, and those utilizing oxidation / reduction reactions are used. For example, potassium iodide, potassium permanganate, dichromic acid are used. The total amount of peroxide is obtained by reacting with these compounds using potassium or the like. Of these, the iodine coulometric titration method using potassium iodide is preferable.

  Here, most of the peroxide is considered to be hydrogen peroxide, but since the peroxide concentration in the production of such ultrapure water is several tens of ppb or less, such a low concentration peroxide is used. Unless it is possible to measure with high sensitivity, it cannot be applied to the ultrapure water production apparatus of the present invention.

The ultraviolet irradiation amount control means 5 calculates an appropriate ultraviolet irradiation amount based on the input measurement value of the peroxide concentration, and controls the ultraviolet irradiation amount of the ultraviolet oxidation means 2 based on the calculation result.
For example, in this embodiment, based on the measured value of the peroxide concentration of the outlet water of the ultraviolet oxidation means 2 input from the peroxide concentration measuring means 4, the ultraviolet irradiation amount is changed until this measured value tends to increase. The ultraviolet ray irradiation amount of the ultraviolet ray oxidizing means 2 may be controlled so that the ultraviolet ray irradiation amount immediately before the measurement value increases and increases.

  In addition, a reference value of the DO amount of the outlet water of the ion exchange tower 3 is determined in advance, and how the measured value of the peroxide concentration at the outlet of the ultraviolet oxidation means 2 fluctuates when this reference value is exceeded. If the measured value of the peroxide concentration at the time of exceeding this reference value is detected, the amount of ultraviolet irradiation of the ultraviolet oxidation means 2 is reduced, and if the measured value is lower than this reference value, the ultraviolet oxidation means 2 Increase the amount of UV irradiation. This reference value may be determined as appropriate depending on the water quality to be obtained. For example, in the case of semiconductor cleaning water, the DO value may be set to about 1 to 10 ppb.

  Examples of the method for controlling the amount of ultraviolet irradiation of the ultraviolet oxidation means in the present embodiment include the following methods.

(1) An ultraviolet lamp lighting number controller is used as the ultraviolet irradiation amount control means, and the number of lighting of the ultraviolet lamp is controlled according to the desired ultraviolet irradiation amount. For example, in the case of an ultraviolet oxidation means having a plurality of cylinders provided with a plurality of arbitrary (for example, 10) ultraviolet lamps per cylinder, the number of cylinders to be lit is controlled.
(2) Using an ultraviolet lamp current controller as the ultraviolet irradiation amount control means, the current value of the ultraviolet lamp is controlled according to the desired ultraviolet irradiation amount. For example, the current value is controlled for some specific cylinders or all cylinders.
(3) An ultraviolet lamp lighting number controller and an ultraviolet lamp current controller are used as the ultraviolet irradiation amount control means, and the above (1) and (2) are combined and controlled according to the desired ultraviolet irradiation amount. For example, a certain cylinder is turned on or off at a steady current value, and the other cylinders increase or decrease the current value.

  Such an ultrapure water production apparatus of the present invention can be applied to both the primary pure water production process and the secondary pure water production process of the ultrapure water production system, and particularly to the secondary pure water production process. It is possible to suppress the DO increase of ultrapure water of final treated water due to conventional ultraviolet irradiation corresponding to the maximum TOC setting concentration, and to stably produce high purity ultrapure water.

  In the above embodiment, the case where the peroxide concentration is measured only at the outlet of the ultraviolet irradiation means 2 has been described, but a peroxide concentration measuring means is also provided at the inlet of the ultraviolet irradiation means 2. In this case, it is possible to determine whether the peroxide is originally contained in the water to be treated or whether the peroxide is generated due to excessive UV irradiation. , More appropriate processing can be performed.

  In addition, when the peroxide is contained in to-be-processed water, it is preferable to remove a peroxide before the process with the ultrapure water manufacturing apparatus of this invention. If this is not removed, even if the UV irradiation amount is appropriate, it is determined that the irradiation amount is excessive and the irradiation amount is reduced. However, this time, the UV irradiation amount becomes insufficient, and the TOC is sufficiently decomposed. Without such a problem, the TOC value of the treated water will increase.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  Using the ultrapure water production apparatus shown in FIG. 1, pure water itself (treated water A) treated in the pretreatment and primary pure water production processes, and 3 ppb of isopropyl alcohol (IPA) as a TOC component are added to this pure water. The treated water (treated water B) was used as treated water. At this time, the TOC concentration of the water to be treated was 2.1 ppb for the water to be treated A and 5.1 ppb for the water to be treated B.

Moreover, each apparatus which comprises the ultrapure water manufacturing apparatus used for the Example is as follows.
Ultraviolet oxidation means: low-pressure ultraviolet oxidation apparatus (manufactured by Nippon Photoscience Co., Ltd., trade name: NN-UV, lamp model: AY-6; 0.091 kW × 4)
Ion exchange tower: Mixed bed type ion exchange resin (MB) (Rohm & Haas, trade name: MBGP; filling resin amount: 28 L)
Peroxide concentration measurement means: ultra-low concentration peroxide automatic analyzer (trade name: NOXIA-L, manufactured by Nomura Micro Science Co., Ltd.) [Measurement method: iodine coulometric titration method, measurement range: 10 to 200 ppb]

First, the water to be treated B is treated in turn at a flow rate of 0.8 m ³ / hr in the ultraviolet irradiation means and the ion exchange tower. At this time, the peroxide concentration of the outlet water of the ultraviolet irradiation means is measured by the peroxide concentration measuring means. The measurement was carried out while feeding back the measured value at this time to the UV irradiation amount control means. Next, when only the water to be treated was changed to the water to be treated A and the same treatment was performed, the peroxide concentration at the outlet of the ultraviolet oxidation means increased and exceeded the set value. The number of UV lamps for UV irradiation means was reduced from 4 to 2.

Here the amount of UV irradiation, at the time of four lights in 0.45kWh ^{/ m} 3, 2 present during lighting was 0.22kWh / ^{m 3.} Further, based on FIG. 1, the set value of the peroxide concentration was 25 ppb (DO value was 5 ppb).

  At this time, the TOC value, DO value, peroxide concentration, peroxide concentration at the outlet of the ultraviolet oxidation means, TOC value, DO value at the outlet of the ion exchange tower of the water to be treated (inlet of the ultraviolet irradiation means) are measured. The results are summarized in Table 1.

  As a result, the DO value can be suppressed to 2.1 to 2.6 ppb, and can be stabilized at a low value.

(Comparative example)
Next, with the ultrapure water production apparatus having the same configuration as in the above embodiment except that the ultraviolet irradiation amount control means is not provided, the water to be treated B and A are similarly flowed, and the water to be treated at that time (ultraviolet irradiation means) TOC value, DO value, peroxide concentration, peroxide concentration at the outlet of the ultraviolet oxidation means, TOC value and DO value at the outlet of the ion exchange tower were measured and shown in Table 2.

  In the comparative example, when the TOC concentration in the water to be treated decreases, the amount of ultraviolet irradiation becomes excessive, and the DO value of the finally obtained treated water has increased to 5.8 ppb. I understand.

  From the above-described Examples and Comparative Examples, it was confirmed that the present invention is extremely effective in reducing the DO value of the obtained ultrapure water in the production of ultrapure water.

In addition, the following apparatus was used for the measurement of DO value and TOC value in an Example and a comparative example.
DO value measurement: “Orbisphere MOCA3600” manufactured by Hack Ultra Analytics
TOC value measurement: “Anatel A-1000XP” manufactured by Hack Ultra Analytics

It is the figure which showed the relationship between the amount of ultraviolet irradiation, the peroxide density | concentration in the exit of an ultraviolet-ray oxidation means, and DO value in the exit of an ion exchange tower. It is a schematic block diagram of the ultrapure water manufacturing apparatus which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ultrapure water manufacturing apparatus, 2 ... Ultraviolet irradiation means, 3 ... Ion exchange tower, 4 ... Peroxide concentration measurement means, 5 ... Ultraviolet irradiation amount control means

Claims (4)

In an ultrapure water production apparatus comprising: an ultraviolet oxidation means for decomposing a TOC component in treated water; and an ion exchange tower for removing the TOC component decomposed by the ultraviolet oxidation means,
Ultraviolet light having a peroxide concentration measuring means for measuring the peroxide concentration in the outlet water of the ultraviolet oxidizing means, and controlling the ultraviolet irradiation amount of the ultraviolet oxidizing means based on the measurement result of the peroxide concentration measuring means An ultrapure water production apparatus having an irradiation amount control means.   2. The apparatus for producing ultrapure water according to claim 1, further comprising a second peroxide concentration measuring means for measuring the peroxide concentration of the inlet water of the ultraviolet oxidation means.   3. The apparatus for producing ultrapure water according to claim 1, wherein an oxidant removing resin is provided at a front stage of the ion exchange tower or an inflow side of water to be treated inside the ion exchange tower.   The ultrapure water production apparatus according to any one of claims 1 to 3, wherein the measurement by the peroxide concentration measuring means is performed by an iodine coulometric titration method.

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