JPH10165956A - Method and apparatus for removing organic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose and remove TOC in nonionic water with high capacity in low cost even if an electric conductor is not added. SOLUTION: Each of electrodes 24, 26 is formed by coating the surface of a titanium plate with a titanium oxide membrane. A DC power supply device 32 is disposed outside an electrolytic oxidation apparatus 20 and the cathode and anode terminals thereof are connected to the respective electrodes 24, 26 through the connector boxes 33, 33 of both end parts of a casing 22. The DC power supply device 32 can apply voltage generating an electric field with electric field intensity of 200V/cm or more between the electrodes 24, 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for removing organic components, and more particularly to a method and an apparatus for removing organic components contained in nonionic water such as pure water or ultrapure water.

[0002]

2. Description of the Related Art Non-ionic water is used in various fields of the precision electronic industry represented by semiconductor manufacturing plants, and is required to have a very high level of purity. For example,
The total organic carbon (hereinafter referred to as TOC) is used as an index for organic components in nonionic water installed in a semiconductor manufacturing plant, and its concentration is currently controlled to a level of several ppb or less.
Non-ionic water is pure water, ultrapure water, or the like, and refers to water having a specific resistance of about 10 MΩ · cm or more.

[0003] Conventionally, an ultraviolet oxidation method using ultraviolet light has been employed to remove trace TOC components present in nonionic water. In the ultraviolet oxidation method, oxidized species such as OH radicals are generated in raw water using short-wave ultraviolet light having a wavelength of 185 nm, and TOC is decomposed and removed by the oxidizing power of the oxidized species. Since this ultraviolet oxidation method can oxidize and decompose TOC only by ultraviolet light, clean TOC
It has a high utility value as a removal device and is an indispensable device for the current ultrapure water production system.

As a method for decomposing trace organic components existing in water, there is an electrolytic oxidation method using active oxygen generated by an electrolysis reaction of water, in addition to the above-mentioned ultraviolet oxidation method using ultraviolet rays. This electrolytic oxidation method is intended to decompose organic components by applying an electrolytic voltage of several volts to several tens of volts between electrodes, and it can be said to be an inexpensive method because there is almost no cost other than the electricity cost of electrolytic oxidation.

[0005]

However, in the former method for removing trace organic components by the ultraviolet oxidation method, the short wavelength lamp used in the ultraviolet oxidation apparatus is expensive, Since the life is as short as about one year, there is a problem that the maintenance cost of the apparatus is extremely high. Furthermore, since the lamp as a constituent member is made of quartz glass, there is a concern that the silica component of the quartz glass may be dissolved in water. As described above, the conventionally used ultraviolet oxidation method is excellent in the effect of removing TOC, but has high equipment cost and maintenance cost, and has problems such as economy.

In the latter method using the electrolytic oxidation method,
If the raw water does not contain an electric conductor (various ions, conductive solids, etc.), the electrolytic reaction does not occur, so it cannot be applied to nonionic water with extremely low electric conductor concentration. . Therefore, when applying the electrolytic oxidation method to non-ionic water having a low concentration of electric conductors such as ions, an electrolyte such as hydrochloric acid or sulfuric acid is added to the non-ionic water, and the electric conductor is added. (Eg, Japanese Patent Publication No. 56-37874). However, in the field of pure water or ultrapure water to be treated in the present invention, the presence of trace ions is also a serious problem, and it is not advisable to add an electrolyte or the like. If an electrolytic oxidation treatment is performed by adding an electrolyte or the like, an ion removing device must be provided at a subsequent stage, which greatly increases equipment costs and complicates the system. Further, if the pH of the raw water is lowered by an electrolyte such as hydrochloric acid, there is a problem that metal impurities at a level of several to several hundreds of ppt are eluted from the electrodes, the catalyst or the constituent members of the apparatus, which is not preferable. As described above, it has been difficult to apply the electrolytic oxidation method to a pure water or ultrapure water production system for removing trace amounts of impurities.

The present invention has been made in view of such circumstances, and it is possible to remove TOC in nonionic water with high performance without adding an electric conductor, and to remove organic components at low cost. It is an object to provide a method and an apparatus.

[0008]

In order to achieve the above object, the present invention provides a method for removing an organic component contained in non-ionic water by oxidation using an electrolytic oxidation apparatus. And a titanium dioxide film on the surface of the cathode, and an electric field strength of 200 between the electrodes.
It is characterized by generating an electric field of V / cm or more.

In order to achieve the above object, the present invention provides an apparatus for removing an organic component contained in non-ionic water by oxidation using an electrolytic oxidation apparatus. And a power supply device capable of applying a voltage for generating an electric field having an electric field strength of 200 V / cm or more between the electrodes.

According to the present invention, a titanium dioxide film is formed on the surfaces of a cathode and an anode of an electrolytic oxidation apparatus, and an electric field having an electric field strength of 200 V / cm or more is generated between the electrodes. Thereby, the organic component contained in the nonionic water can be oxidized and removed without adding the electric conductor to the nonionic water.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method and apparatus for removing organic components according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an application example of the method and apparatus for removing an organic component according to the present invention, which is a process for producing ultrapure water for semiconductor production. The steps can be broadly divided into three steps: a pretreatment step, a pure water production step, and an ultrapure water production step.

First, raw water is pretreated in a pretreatment step by a pretreatment facility and an activated carbon tower, and preparations are made to feed the raw water to a pure water production step. The raw water that has been subjected to the pretreatment is sent to a pure water production process, and an RO (reverse osmosis membrane) unit,
Pure water is produced by passing through a membrane deaeration unit, a pure water storage tank, a mixed-bed ion exchange tower, and a filter in this order. Pure water produced in the pure water production process is generally at least 10 MΩ · cm in specific resistance, sent to the ultrapure water production process in a state where there is almost no ionic substance, an ultrapure water storage tank, an organic component removal device, Pure water passes through an ion exchange membrane and a UF (microfiltration) module in that order, and the pure water is turned into ultrapure water.

Next, prior to the configuration of the organic component removing apparatus of the present invention, the experimental basis of the organic component removing method according to the present invention will be described. FIG. 2 shows the relationship between the electric field strength generated between the electrodes of the electrolytic oxidation apparatus, which is the basic configuration of the organic component removing apparatus of the present invention, and the TOC decomposition rate in non-ionic water to be electrolytically oxidized. It is.

In FIG. 2, line A is a case where the surface of a titanium plate is coated with a titanium dioxide film as an electrode, and line B is a case where a titanium plate is used alone as an electrode. Non-ionic water has a non-resistance of 17.6 MΩ · cm and a TOC concentration of 10.2 μg / l.
Met. This nonionic water was put into an electrolytic oxidation tank having a cell volume of 1 liter, and the distance between the electrodes was set to 10 mm. As a result, as shown by the line A in the figure, even in the case of non-ionic water, a significant increase in the TOC decomposition rate was observed when the electric field intensity was around 200 V / cm to around 300 V / cm. Incidentally, when the electric field intensity is 100 V / cm, the TOC decomposition rate is 0.5 μg / l · min, at 200 V / cm, the TOC decomposition rate is 2 μg / l · min, and when the electric field strength is 300 V / cm, the TOC decomposition rate is 4 μg / l · min. TO at 1000V / cm
The C decomposition rate increased to 5 μg / l · min.

On the other hand, in the case of the line B, even when the electric field intensity is increased, the TOC decomposition rate hardly increases, and the TOC decomposition rate changes at a low level of about 0.4. No. The present invention is configured to remove organic components from non-ionic water based on the above experimental basis, and will be described below by way of an example in which an ion exchange device is incorporated in a stage subsequent to an electrolytic oxidation device. FIG. 3 is an example showing an overall configuration diagram of an organic component removing apparatus according to the present invention. As shown in FIG. 1, the organic component removing device 10 mainly includes an electrolytic oxidation device 20 and an ion exchange device 34.

In this example, the electrolytic oxidation apparatus 20 includes a flat plate-shaped cathode 2 in a box-shaped casing 22 having a rectangular parallelepiped shape.
, And plate-shaped anodes 26 are alternately arranged at equal intervals in the vertical direction. Each electrode 24, 2
6 is formed by coating the surface of a titanium plate with a titanium dioxide thin film. The titanium dioxide thin film is used as the electrode 2 during electrolytic oxidation.
While preventing impurities from being eluted from 4, 26,
The catalytic effect of titanium dioxide improves the effect of decomposing organic components. The electrodes 24, 26 have at least three to five years.
Since the lamp has a life of one year and the material cost is half as low as that of an ultraviolet lamp, the total cost can be reduced from 1/5 to 1/10 of that of the ultraviolet oxidation method.

A raw water supply pipe 28 is provided at one longitudinal end of the casing 22, and a treated water outflow pipe 3 is provided at the other longitudinal end.
0 is attached. Non-ionic water flows into the electrolytic oxidation device 20 from the raw water supply pipe 28, and the electrodes 24, 2
The treated water from which TOC is removed flows through the treated water outflow pipe 30 to the outside of the electrolytic oxidation device 20 while being electrolyzed through the space 6.

A DC power supply 32 capable of generating a high voltage is provided outside the electrolytic oxidation apparatus 20, and its cathode terminal and anode terminal are connected to each electrode via connector boxes 33 at both ends of the casing 22. 24, 26, and a voltage can be applied between the electrodes 24, 26. The DC power supply 32 can supply a high voltage that can generate an electric field of 200 V / cm or more between the electrodes 24 and 26.

The treated water flowing out of the electrolytic oxidation device 20 is
It is led to the ion exchange device 34 and impurity ions in the treated water are removed by the ion exchange action. Since the ion exchange device 34 has a mixed bed type ion exchange resin in which a cation exchange resin and an anion exchange resin are mixed,
Both cations and anions can be accommodated. The ultrapure water that has passed through the ion exchanger 34 is converted into a TOC analyzer 36
The organic component concentration is continuously measured and analyzed.

Incidentally, in order to form a titanium dioxide thin film on the surfaces of the electrodes 24 and 26, a titanium electrode plate is immersed in a TiO ₂ sol liquid tank and then naturally dried. Immersion and natural drying are repeated several times, and finally baking is performed at a high temperature. By repeating immersion and natural drying, a titanium dioxide thin film of about 0.2 μm is formed each time. Next, the operation of the organic component removing apparatus configured as described above will be described.

A state in which a high voltage of several hundred to several thousand volts is applied from the DC power supply 32 between the electrodes 24 and 26 of the electrolytic oxidation apparatus 20 and an electric field strength of 200 V / cm or more is generated between the electrodes 24 and 26. Is maintained. Then, nonionic water is supplied into the electrolytic oxidation device 20 via the raw water supply pipe 28, and the TOC in the nonionic water is oxidized and removed.
That is, when the electric field strength is large as described above, electrons are emitted from the surface of the titanium dioxide film and holes are formed on the cathode surface at the same time. These electrons and holes are called valence bodies, and the valence bodies form various oxidizing species such as OH radicals in the nonionic water, and TOC in the nonionic water is oxidized and decomposed by the oxidizing species. The method for removing an organic component according to the present invention has the same effect as the photocatalytic reaction of irradiating titanium dioxide material with light to generate electrons and holes, by covering the electrodes 24 and 26 with a titanium dioxide film and applying 200 V between the electrodes 24 and 26. / Cm
This is performed by generating the above electric field strength.

Thus, even in the case of non-ionic water, trace amounts of organic components in the non-ionic water can be oxidized and removed without adding an ionic substance to the non-ionic water. FIG. 4 shows the relationship between the thickness of the titanium dioxide film and the TOC decomposition rate over time for each electrolytic oxidation time in the method for removing an organic component of the present invention. In particular,
As for the thickness of the titanium dioxide film, an electrode having a TiO ₂ sol applied once and an average TiO ₂ thickness of 0.18 μm;
_Two sols were applied 5 times and the average TiO ₂ film thickness was 0.51 μm. The other TiO ₂ sol was applied 10 times and the average TiO ₂ film thickness was 0.95 μm. In addition, as a comparative example, an experiment was performed on an electrode made of a titanium plate alone. Non-ionic water having a specific resistance of 17.6 MΩ · cm was used.

As a result, when the TOC concentration, which was 1000 μg / l each, was subjected to electrolytic oxidation for 4 hours, the electrode of the titanium plate alone became 850 μg / l, and the electrode having an average TiO ₂ film thickness of 0.18 μm was 730 μg / l. and 250 μg / l for an electrode having an average TiO ₂ film thickness of 0.51 μm.
80 μg / l for an electrode having an average iO ₂ film thickness of 0.95 μm
become. From this result, as the TiO ₂ film thickness increases, the TOC increases.
It can be seen that the decomposition rate is high and the decomposition performance is high.

FIG. 5 is a graph showing the TOC decomposition rate with respect to the thickness of the TiO ₂ thin film based on FIG. From the figure,
When the thickness of TiO ₂ is around 0.5 μm, the TOC decomposition rate sharply increases. Therefore, the TiO ₂ film thickness of the electrode is 0.5 μm.
m or more is preferable. Figure 6 is the electrode TiO ₂ thin film is formed of the same thickness, T of the case of performing the case where only electrolytic oxidation, a further ion exchange carried out electrolytic oxidation
It shows the relationship of the OC decomposition rate over time for each electrolytic oxidation time. The average thickness of the TiO ₂ film used is 0.62 μm.

As a result, the TO of 1000 μg / l
C concentration is 300μ when only electrolytic oxidation is performed for 4 hours.
g / l for 4 hours of electrolytic oxidation followed by ion exchange to 100 μg / l. From this result, it can be seen that the TOC decomposition effect is higher when ion exchange is performed at the same film thickness. Therefore, by performing ion exchange after performing the field oxidation of the present invention, the TOC removal effect can be further improved.

FIG. 7 shows a graph of 10 m based on the TOC decomposition result.
^This is an example in which an apparatus for removing organic components on a ³ / h treatment scale is manufactured and applied to an ultrapure water production system. TOC concentration 10.2
The TOC is removed from the ppb raw water at an applied voltage of 1000 V by electrolytic oxidation. Further, an ion exchange resin device 34 was disposed at a subsequent stage of the processing tank 20, and TOC was measured over about 120 days. As a result, the TOC concentration of the treatment liquid flowing out of the electric field oxidation device 20 was 4 to 6 ppb, and was reduced to 1 ppb or less by passing through the ion exchange resin device 34 in the subsequent stage. Here, the ion exchange resin device 3
The phenomenon in which the TOC component is removed in Step 4
Means that an ionic organic component was formed therein. In any case, TOC by the conventional ultraviolet oxidation method
Considering that the residual concentration of is approximately 1 ppb, it can be seen that TOC removal performance equivalent to or higher than the conventional method can be obtained by employing the electrolytic oxidation method of the present invention.

The electrodes 24 and 26 used in the method and apparatus for removing a trace amount of organic components according to the present invention were previously subjected to a surface treatment of a titanium material to form a titanium dioxide film. 26 may be used. In this case, a film of titanium dioxide is gradually formed on the surfaces of the electrodes 24 and 26 as the electrolysis proceeds, but the time required for the film is relatively short.

[0028]

As described above, according to the method and apparatus for removing an organic component of the present invention, the removal of the organic component, which was difficult in the conventional electrolytic oxidation method, is achieved by forming a titanium dioxide film on the surface of the electrode. By forming an electric field having an electric field strength of 200 V / cm or more between the electrodes, it is possible to remove organic components at a high level without adding an electric conductor to raw water. In addition, the cost is 1/5 to 1/10 that of the ultraviolet oxidation method, which is economical.

[Brief description of the drawings]

FIG. 1 is an application example of a method and an apparatus for removing an organic component according to the present invention, and is a view illustrating a process of producing ultrapure water for producing a semiconductor.

FIG. 2 is a diagram showing the relationship between the electric field strength generated between electrodes of an electrolytic oxidation device, which is a basic configuration of the organic component removing device of the present invention, and the TOC decomposition rate in non-ionic water to be electrolytically oxidized.

FIG. 3 is an overall configuration diagram of an organic component removing apparatus according to the present invention.

FIG. 4 is a diagram showing the relationship between the thickness of a titanium dioxide film and the TOC decomposition rate over time for each electrolytic oxidation time in the method for removing an organic component according to the present invention.

FIG. 5 is a graph showing the relationship between the thickness of a TiO ₂ thin film and T
Diagram showing OC decomposition rate

FIG. 6 is a graph showing the relationship between the TOC decomposition rate in the case where only the electrolytic oxidation is performed and the case where the electrolytic oxidation is performed and the ion exchange is further performed on the electrode on which the TiO ₂ thin film having the same thickness is formed, for each electrolytic oxidation time Fig.

FIG. 7 is a diagram showing a result of continuous processing over about 120 days.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Organic component removal apparatus 20 ... Electrolytic oxidation apparatus 24 ... Cathode 26 ... Anode 28 ... Raw water supply pipe 30 ... Treated water outflow pipe 32 ... DC power supply apparatus 34 ... Ion exchange apparatus 36 ... TOC analyzer

Claims (4)

[Claims] 1. A method for removing organic components by oxidizing and removing organic substances contained in nonionic water by an electrolytic oxidation apparatus, comprising: forming a titanium dioxide film on surfaces of an anode and a cathode of the electrolytic oxidation apparatus; Electric field strength 200V /
A method for removing an organic component, which comprises generating an electric field of not less than 1 cm. 2. An organic component removing device for oxidizing and removing organic substances contained in nonionic water by an electrolytic oxidizing device, wherein a titanium dioxide film is formed on the surfaces of an anode and a cathode of the electrolytic oxidizing device. A device for applying a voltage for generating an electric field having an electric field strength of 200 V / cm or more. 3. The organic component removing apparatus according to claim 2, wherein said titanium dioxide film has a thickness of 0.5 μm or more. 4. The apparatus according to claim 2, wherein an ion exchange resin device is provided at a stage subsequent to said electrolytic oxidation device, and the treated water treated by said electrolytic oxidation device is passed through said ion exchange resin device. 3. The organic component removing device according to 3.