JPH11258191A - Method and apparatus for measurement of concentration of carbonic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus in which the concentration of carbonic acid in water with the comparatively high concentration of carbonic acid and with little salts other than carbonic acid is measured by a simple operation and quickly during the preparation process of pure water, for cleaning, which is used in a semiconductor-device manufacturing process. SOLUTION: In a measuring apparatus 10 for the concentration of carbonic acid, a sample- water introduction pipe 21 which is provided with a hydrogen ion-type strongly acidic cation- exchange resin column 3 and a sample-water flow-rate detection part 4 is provided. A dilute- water injection pipe 22 which is provided with a dilute-water flow-rate detection part 6 joining it is provided. A conductivity detection part 5 which measures the conductivity of diluted sample water is provided. A computing part 7 which computes the concentration of carbonic acid in the sample water on the basis of signals from the two flow-rate detection parts 4, 6 and from the conductivity detection part 5 is provided. A display part 8 which displays the computed concentration of the carbonic acid is provided. By using the apparatus 10, the concentration of the carbonic acid in the permeated water, in a reverse osmosis membrane device, whose concentration of carbonic acid is high and which contains little salts other than carbonic acid or in treated water in an ultraviolet oxidation device can be measured by a simple operation and quickly in the preparation process of pure water, for cleaning, which is used, e.g. in a semiconductor-device manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for producing pure water for cleaning used in a process for producing semiconductor devices, for example.
The present invention relates to a method and an apparatus for measuring the concentration of carbonic acid in water having a relatively high carbonic acid concentration and low in salts other than carbonic acid by a simple operation and quickly.

[0002]

2. Description of the Related Art There are various types of pure water producing apparatuses. Among them, there is a method in which raw water such as well water or industrial water is directly or pretreated by turbidity or the like, and then treated by a reverse osmosis membrane device. This system is called a pre-stage reverse osmosis membrane system. This system reduces the load on desalination units such as ion exchange resin units and electric deionized water production units that are further arranged at the subsequent stage, and reduces the organic matter contained in raw water. And to remove fine particles. Further, in the secondary pure water system of the ultrapure water production apparatus, an ultraviolet oxidizing apparatus and a purification column are installed, and water to be treated may be passed in this order. That is, organic substances in the water to be treated are decomposed into organic acids and carbonic acids by ultraviolet oxidation, and the organic acids are removed by a purification column.

However, a reverse osmosis membrane device cannot remove carbonic acid dissolved in the water to be treated. In the ultraviolet oxidation apparatus, carbon dioxide is discharged into the treated water. Therefore, carbonic acid is dissolved in the permeated water or the treated water. In these carbonic acids, not only ionic but also neutral molecular carbon dioxide is dissolved, and all of the carbon dioxide including the neutral molecular carbon dioxide is subjected to ionic load in the subsequent desalination apparatus. For this reason, in order to make the specifications and operation method of the subsequent desalination device appropriate, it is important to accurately grasp the carbon dioxide concentration in the permeated water of the reverse osmosis membrane device and the treated water of the ultraviolet oxidation device. .

[0004] Carbonic acid in water exists in the form of carbonate ions, bicarbonate ions, carbon dioxide as a neutral molecule, and the like. For this reason, when measuring these, in order to avoid contact with outside air, it is necessary to perform in-line measurement in which sample water is directly introduced into the measurement equipment. Conventionally, measuring devices capable of measuring carbon dioxide concentration in-line include an ion chromatography method, a method of measuring only inorganic carbon concentration using a TOC meter capable of separately measuring organic carbon and inorganic carbon, and an electric device according to carbon dioxide concentration. There is known a method using a conductivity meter that utilizes a change in resistance value.

[0005]

However, both the ion chromatography method and the method using a TOC meter require an expensive measuring device, and in order to operate the device, calibration work and preparation of necessary reagents are required. Complicated work such as work was required. In particular, when an abnormality occurs in the operation of the pure water production equipment, it is necessary to quickly analyze the water quality at various points in the equipment in order to minimize the impact on the production of the factory and achieve an early recovery. However, in these conventional methods, the preparation work is complicated, and it is difficult to respond quickly. In addition, although the method using a conductivity meter is a simple method, there are problems such as the influence of other salts coexisting with carbonic acid, and a large error in a non-dilute system having a large amount of carbonic acid. was there.

Accordingly, an object of the present invention is to reduce the concentration of carbonic acid in water having a relatively high concentration of carbonic acid and a small amount of salts other than carbonic acid during the manufacturing process of pure water for cleaning used in the semiconductor device manufacturing process. Another object of the present invention is to provide a method and an apparatus for performing simple and quick measurement.

[0007]

Under such circumstances, the present inventors have conducted intensive studies. As a result, during the pure water production process, the permeated water of the reverse osmosis membrane device and the treated water of the ultraviolet irradiation device have a high carbon dioxide concentration. The present invention has been found that the amount of other salts coexisting with carbonic acid is small, and that the carbonic acid concentration can be accurately measured by a conductivity meter if the carbonic acid concentration in the permeated water and the treated water is adjusted to a specific concentration range. Was completed. That is, the present invention provides a method for measuring the concentration of carbonic acid in permeated water of a reverse osmosis membrane device, wherein the permeated water is brought into contact with a hydrogen ion type strongly acidic cation exchange resin, and then the contact water is purified with high-purity water. An object of the present invention is to provide a method for measuring the concentration of carbonic acid which is diluted and calculates carbonate ions from the value of the conductivity of the diluted solution. Note that the reciprocal of the conductivity is the resistivity.
1 μS / cm corresponds to a resistivity of 10 MΩ · cm. Water of relatively high purity may be represented by a resistivity capable of expressing a large number, but in the present invention, conductivity and resistivity are treated as synonyms. According to the present invention, the permeated water of the reverse osmosis membrane device,
Among the carbon dioxide gas, carbonate ions, sodium hydrogen carbonate, and the like, which are the load ions of the subsequent desalination apparatus, sodium hydrogen carbonate is converted into carbon dioxide by the hydrogen ion type strongly acidic cation exchange resin. The measured values can be converted to carbon dioxide concentration more accurately. Therefore, the accuracy of determining the load of the subsequent desalination apparatus is improved. The anion components other than carbonic acid in the sample water are negligible compared to the carbonic acid concentration. However, the dilution of the high-purity water further reduces the anion components, so that the measurement accuracy with the conductivity meter is reduced. Is further enhanced.

Further, the present invention relates to a method for measuring the concentration of carbonic acid in treated water of an ultraviolet oxidizing apparatus, wherein the treated water is diluted with high-purity water, and the carbonate ion is calculated from the value of the conductivity of the diluted liquid. The present invention provides a method for measuring the concentration. ADVANTAGE OF THE INVENTION According to this invention, the concentration of carbonic acid in the treated water of an ultraviolet oxidation device can be measured quickly and simply. Therefore, the accuracy of determining the load of the subsequent desalination apparatus is improved.

[0009]

Next, a method of measuring a carbon dioxide concentration according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a partial pure water producing apparatus 9 incorporating a carbon dioxide concentration measuring apparatus 10 according to the first embodiment of the present invention.
FIG. The pure water production device 9 includes a reverse osmosis membrane device 1 and a desalination device 2. The water to be treated is supplied to the reverse osmosis membrane device 1 to remove organic substances and fine particles. Next, the permeated water is supplied to a desalination device 2 such as an ion-exchange resin or an electric deionized water producing device, where it is treated to become pure water.

Next, the concentration of carbonic acid in the permeated water of the reverse osmosis membrane device 1 is measured. That is, a part of the permeated water of the reverse osmosis membrane device 1 is guided to the carbon dioxide concentration measuring device 10 as sample water. The water quality of the permeated water of the reverse osmosis membrane device 1 is typically about 10 ppm of carbon dioxide, 2 ppm or less of Na, 0.5 ppm or less of Ca, M
g 0.5 ppm or less and mineral acid 2 ppm or less. The carbonic acid concentration measuring device 10 includes a sample water introduction pipe 21 provided with a hydrogen ion type strongly acidic cation exchange resin tower 3 and a sample water flow rate detection unit 4.
A diluting water injection pipe 22 having a diluting water flow detecting unit 6 to be joined thereto, a conductivity meter 5 for measuring the conductivity of the diluted sample water, and the two flow detecting units 4 and 6; A calculation unit 7 for calculating the concentration of carbonic acid in the sample from the signal of the conductivity meter 5,
A display unit 8 for displaying the calculated carbon dioxide concentration. First, the sample water is supplied to the hydrogen ion type strongly acidic cation exchange resin tower 3 through the sample water introduction pipe 21.
Here, sodium hydrogen carbonate is converted to carbonic acid by ion exchange of sodium ions. The outlet water of the hydrogen ion type strongly acidic cation exchange resin tower 3 is diluted water injection pipe 2
The conductivity of the sample water that has been combined with the dilution water supplied through 2 and diluted by the conductivity detection unit 5 is measured. As the dilution water, high-purity water may be used.
Pure water of Ω · cm or more, especially 17.5 MΩ · cm or more is preferable. The installation position of the hydrogen ion type strongly acidic cation exchange resin tower 3 may be between the junction of the sample water and the dilution water and the conductivity meter 5 in addition to the above.

A method for calculating the dilution ratio and the conductivity will be described below. 2a, 2b and 2c are diagrams showing the relationship between the concentration of carbonic acid and the conductivity or resistivity of water. This relationship diagram is generally known, and is created from the ionic product of water and the dissociation equilibrium of carbonic acid when only carbonic acid is dissolved in pure water. The conductivity of the permeated water of the reverse osmosis membrane device 1 according to the first embodiment is indicated by a point A in FIG. 2A. That is, the vicinity of the point A is in a saturated state (flat curve with no slope) between the carbonic acid concentration and the electrical conductivity, and is in a region where there is a large error in which the carbonic acid concentration greatly changes due to a slight change in electrical conductivity. In the present invention, by diluting the sample water with high-purity water, the change in the conductivity is large with respect to the change in the carbonic acid concentration, in other words, the conductivity in the concentration region where the contribution of the conductivity by carbonic acid is large. Measurement of
Furthermore, by such dilution, by making water of low conductivity, it is possible to use a resistivity meter having higher measurement accuracy in the conductivity detection unit, thereby improving the quantitative accuracy of the carbonic acid concentration. At the same time, since other coexisting anions are diluted to a concentration that does not affect the conductivity (resistivity), measurement with less interference by coexisting ions is possible. As for the degree of dilution, for example, in FIG.
It may be diluted so as to fall within a region of 25 μS / cm or less (carbonic acid concentration is 1 ppm or less), preferably in FIG. 2b, so as to have a carbonic acid concentration of 0.250 ppm or less, and more preferably, in FIG. Joint water resistivity 7.00-17.00 MΩ
It may be diluted so as to be in the range of cm (the range of 0.0025 to 0.0250 ppm of carbon dioxide). Specifically, when the permeated water of the reverse osmosis membrane device is diluted with pure water having a resistivity of 18 MΩ · cm, the dilution ratio is about 5 to 4000 times.

The carbonic acid concentration value of the combined water obtained by the conductivity meter 5 is input to the arithmetic unit 7 to calculate the carbonic acid concentration of the sample water. That is, the carbon dioxide concentration of the sample water is calculated by multiplying the carbon dioxide concentration calculated from the conductivity of the combined water by the value of (V ₁ + V ₂ ) / V ₁ , which is the dilution factor of the sample water. V ₁ (L / h)
Denotes the flow rate obtained by the sample water flow rate detection unit 4;
₂ (L / h) indicates the flow rate obtained by the flow rate detection unit 6 for the dilution water. The carbonic acid concentration value and the like are displayed on the display unit 8.

According to the method for measuring the concentration of carbonic acid in the first embodiment, the permeated water of the reverse osmosis membrane device 1 and the carbon dioxide, carbonate ion and sodium hydrogencarbonate which are the load ions of the subsequent desalination device 2 are used. Of which, sodium bicarbonate
Since the hydrogen ion type strongly acidic cation exchange resin 3 changes to carbonic acid, the value measured by the conductivity meter 5 can be more accurately converted to carbonic acid concentration. Therefore, the accuracy of determining the load of the subsequent desalination device 2 is improved. The anion component other than carbonic acid in the sample water has a negligible concentration as compared with the carbonic acid concentration. However, the concentration of the anion component is further reduced by dilution with high-purity water. Accuracy is further improved.

A method for measuring the concentration of carbonic acid according to the second embodiment of the present invention will be described with reference to FIG. FIG.
FIG. 7 is a block diagram showing a part of a purified water producing apparatus 19 incorporating a carbon dioxide concentration measuring apparatus 20 according to a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, description thereof will be omitted, and different points will be mainly described. That is, FIG. 3 differs from FIG. 1 in that the purified water production step 19 is a specific step of the secondary pure water system and that the hydrogen ion type strongly acidic cation exchange resin tower is not used in the carbon dioxide concentration measuring device 20. It is in. The purified water producing step 19 is used for a part of a secondary pure water system of a cleaning ultrapure water producing apparatus used in a semiconductor producing step, for example. Polisher 12). The water to be treated containing organic matter is irradiated with an ultraviolet oxidizer 11 capable of irradiating a wavelength around 185 nm.
, It is decomposed into organic acid and carbonic acid. UV oxidation device 1
A part of the treated water 1 is guided to the carbon dioxide concentration measuring device 20 as sample water.

Next, the concentration of carbonic acid in the treated water of the ultraviolet oxidation device 11 is measured. The quality of the treated water of the ultraviolet oxidizer 11 is typically about 0.05 ppm for carbonic acid and 0.005 ppm or less for other salts. The carbon dioxide concentration measuring device 20 includes a sample water introduction pipe 2 having a sample water flow rate detection unit 4.
1, a dilution water injection pipe 22 provided with a dilution water flow detecting unit 6 to be joined thereto, a conductivity meter 5 for measuring the conductivity of the diluted sample water, and the two flow detecting units 4, 6. A calculation unit 7 for calculating the concentration of carbonic acid in the sample from the signal of the conductivity meter 5
And a display unit 8 for displaying the calculated carbon dioxide concentration. The sample water supplied through the sample water introduction pipe 21 is combined with the dilution water supplied through the dilution water injection pipe 22, and the conductivity detection unit 5 measures the conductivity of the combined water. Subsequent methods for measuring the concentration of carbon dioxide are the same as in the first embodiment. When the treated water of the ultraviolet oxidizer 11 is diluted with pure water having a resistivity of 18 MΩ · cm, the dilution ratio is 2 to 2.
It is about 0 times.

According to the method for measuring the concentration of carbonic acid in the second embodiment, the concentration of carbonic acid in the treated water of the ultraviolet oxidizing apparatus 11 can be quickly obtained by a simple operation method. Therefore, the accuracy of determining the load of the purification column 12 at the subsequent stage is improved.

The carbon dioxide concentration measuring device of the present invention is used by being incorporated in a desired place in a pure water production process. An example of its use will be described with reference to FIG. FIG. 4 is a block diagram of a pure water producing apparatus 29 incorporating the carbon dioxide concentration measuring apparatus 10 of the present invention. The water to be treated is passed through the reverse osmosis membrane device 13, the reverse osmosis membrane device 1, and the desalination device 2 in this order. In addition, an alkali addition means 14 for adding alkali is provided in a joining pipe 23 between the first-stage reverse osmosis membrane device 13 and the second-stage reverse osmosis membrane device 1 to neutralize carbonic acid in the water to be treated. In addition, a part of the outlet water of the latter reverse osmosis membrane device 1 is introduced as sample water into the carbon dioxide concentration measuring device 10, and the measurement result is fed back to the controller 15 to adjust the amount of alkali to be added. As the carbon dioxide concentration measuring device 10, the same device as used in the first embodiment can be used. Although the alkali adding means 14 is not shown in the figure, any means may be used as long as the means comprises, for example, an alkaline solution storage tank and an injection pump. As the alkali, a substance which exhibits alkalinity when dissolved in water, such as an alkali metal or an amine, can be arbitrarily selected. For example, sodium hydroxide and potassium hydroxide are preferable.

According to this application example, the pre-stage reverse osmosis membrane device 13
By adding an alkali to the permeated water to increase the pH, carbon dioxide can be efficiently removed by the reverse osmosis membrane device 1 in the latter stage. Then, even if the amount of carbonic acid increases or decreases due to fluctuations in raw water, the measured value of the carbonic acid concentration measurement device is fed back to control the alkali adding means, so that ideal alkali addition can be performed, and waste of chemicals can be achieved. The consumption is eliminated, and the amount of ions in the permeated water of the latter reverse osmosis membrane device 1 can be set to the minimum value.

In this application example, the reverse osmosis membrane device is
In addition to stages, three or more stages may be provided. In this case, the place where the sample water to be introduced into the carbon dioxide concentration measuring device 10 is collected may be the treated water of the reverse osmosis membrane device in the second and subsequent stages.

[0020]

Next, the present invention will be described more specifically with reference to examples. Example 1 The carbon dioxide concentration measuring device shown in FIG. 1 was configured by using the devices, devices and dilution water having the following specifications. In order to reproduce the typical composition of the permeated water of the reverse osmosis membrane apparatus, the sample water was dissolved in carbon dioxide in the atmosphere at a saturated concentration, and a pure carbon solution with a carbon dioxide concentration of 0.5 ppm and a resistivity of 1.2 MΩ · cm. One piece of sodium bicarbonate in water
Add 9.1 ppm, 1.37 ppm of sodium nitrate,
What was prepared beforehand so that the carbonic acid concentration was about 10 ppm was used. The flow rate of the sample water was 0.1 L / h, and the flow rate of the dilution water was 300 L / h (dilution factor 3001). As a result of the measurement, the resistivity of the combined water was 15.5 MΩ · cm, and the carbonic acid concentration calculated from the sample water was 10.5 ppm, which closely approximated the actual value.

(Carbonic acid concentration measuring device) Hydrogen ion type cation exchange resin tower; Amberlite ES
GK, water flow velocity SV100 ・ Conductivity meter; AQ-11 (manufactured by Electrochemical Instruments) ・ Flow measurement unit; trace flow sensor (manufactured by Nippon Flowcell) ・ Dilution water: pure water of 18.2 MΩ · cm ・ Calculation unit And display unit; personal computer

Comparative Example 1 The same procedure as in Example 1 was carried out except that the hydrogen ion type cation exchange resin tower was omitted. As a result of the measurement, the resistivity of the combined water was 17.2 MΩ · cm, and the carbonic acid concentration of the sample water calculated from the resistivity was 3.96 ppm, and the error was larger than that in Example 1. Was.

Example 2 In order to reproduce a typical composition of the treated water of the ultraviolet oxidizing apparatus in the secondary pure water system of the ultrapure water producing apparatus,
Methanol is added to ultrapure water having a TOC of 1.00 ppb and a resistivity of 18.2 MΩ · cm to reduce the TOC concentration to 19.2 MΩ · cm.
4 ppb, water was passed through an ultraviolet oxidizer (TDFL-4; manufactured by Chiyoda Kohan Co., Ltd.) at an irradiation dose of 0.48 kW · h / m ³ to treat water having a TOC concentration of 1.54 ppb and a resistivity of 4.12 MΩ · cm The procedure was performed in the same manner as in Example 1 except that the sample water was used, the hydrogen ion type strongly acidic cation exchange resin tower was omitted, and the dilution water flow rate was reduced and the dilution ratio was set to 5 times. . Assuming that all the decrease in TOC before and after the ultraviolet oxidizing device is decomposed into carbonic acid, the calculated value is that 0.0649 ppm of carbonic acid is contained in the treated water. As a result of the measurement, the resistivity of the combined water was 10.2 MΩ · cm, and the carbonic acid concentration was 0.063.
It was 4 ppm, which was a good approximation.

[0024]

According to the present invention, for example, during the process of producing pure water for cleaning used in the process of producing semiconductor devices, the permeation of a reverse osmosis membrane apparatus having a relatively high carbon dioxide concentration and a small amount of salts other than carbon dioxide. The concentration of the carbonic acid in the water or the treated water of the ultraviolet oxidizing apparatus can be quickly measured by a simple operation. For this reason, the accuracy of determining the load of the subsequent desalination apparatus is improved, and useful information such as the design and replacement timing of the desalination apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a pure water producing apparatus incorporating a carbon dioxide concentration measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the carbon dioxide concentration and the electrical conductivity or resistivity. FIG. 2a is a graph in which the carbon dioxide concentration on the horizontal axis is 0 to 10 ppm, and FIG. Figure 2c
Is a diagram in which the horizontal axis is 0 to 0.1 ppm.

FIG. 3 shows a block diagram of a purified water producing apparatus incorporating a carbon dioxide concentration measuring apparatus according to a second embodiment of the present invention.

FIG. 4 is a block diagram of a pure water producing apparatus using the carbon dioxide concentration measuring apparatus according to the first embodiment of the present invention.

[Explanation of symbols]

 1, 13 reverse osmosis membrane device 2 desalination device 3 hydrogen ion type cation exchange resin 4, 6 flow rate detection unit 5 conductivity meter 7 calculation unit 8 display unit 9 pure water production device 10, 20 carbon dioxide concentration measurement device 11 ultraviolet oxidation Apparatus 12 Purification column 14 Alkali addition means 15 Controller 21 Sample water introduction pipe 22 Dilution water injection pipe

Claims (5)

[Claims] In a method for measuring the concentration of carbonic acid in permeated water of a reverse osmosis membrane device, the permeated water is contacted with a hydrogen ion type strongly acidic cation exchange resin, and then the contact water is diluted with high-purity water. And calculating a carbonate ion from the value of the conductivity of the diluted solution. 2. A method for measuring the concentration of carbonic acid in treated water of an ultraviolet oxidizer, wherein the treated water is diluted with high-purity water,
A method for measuring the concentration of carbonic acid, comprising calculating carbonate ions from the value of the conductivity of the diluent. 3. The method for measuring the concentration of carbonic acid according to claim 2, wherein the treated water of the ultraviolet oxidizing apparatus is treated water of a secondary pure water-based ultraviolet oxidizing apparatus of the ultrapure water producing apparatus. 4. A sample water introduction pipe having a sample water flow rate detection section, a dilution water injection pipe having a dilution water flow rate detection section which joins the sample water introduction pipe, and a conductivity for measuring the conductivity of the diluted sample water. A carbon dioxide detector, comprising: a detector, a calculator for calculating the concentration of carbonic acid in the sample water from the signals of the two flow rate detectors and the conductivity detector, and a display for displaying the calculated carbonic acid concentration. Concentration measuring device. 5. A hydrogen ion type strongly acidic cation exchange resin tower is installed at any position in the sample water introduction pipe up to the conductivity detecting section.
The carbon dioxide concentration measuring device according to the above.