JPS6349540B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for obtaining highly purified water by irradiating ultraviolet light or light containing ultraviolet light to water containing trace amounts of oxidizable substances in the presence of dissolved oxygen. This invention relates to an oxidation catalyst molded body.

The oxidizable substances according to the present invention are trace organic components dissolved in water, and are mainly substances usually expressed by COD _cr (chemical oxygen demand) values.

In recent years, as technology has become more sophisticated in various industries, the water used is also required to be of high quality, and therefore there is a need for advanced water purification treatment technology. Especially in the electronic industry and pharmaceutical manufacturing industry, for example,
Highly treated water called ultrapure water with a TOC value (total organic carbon) of 0.2mg/or less is required. Removal of soluble organic matter is one of the most difficult targets to undergo high-level purification treatment, and several organic matter removal methods have been proposed, but these only require trace amounts of the substances that make up the treatment process itself. However, since these substances may be eluted into water or release decomposition products, they have the disadvantage that further treatment must be carried out in order to remove these minute amounts of eluted substances.

On the other hand, as a technology for treating contaminated wastewater, a photo-oxidation catalyst method has been proposed in which a fine powder of titanium oxide or the like is used in a suspended state. In this photo-oxidation catalyst method, water to be treated containing pollutants is treated by contacting and passing water through a photo-oxidation catalyst made of titanium oxide or the like while irradiating the water with light including ultraviolet rays.

When such a photooxidation catalyst receives energy from ultraviolet irradiation, electrons in the valence band on the surface transfer to the conduction band, and as a result, holes are generated in the valence band. These electrons and holes react with dissolved oxygen and hydroxyl groups to generate strong oxidizing superoxide (O ₂ ^- ) and hydroxyl radicals. In other words, the photooxidation catalyst method It utilizes a reaction in which organic matter is oxidized to produce carbon dioxide gas and water. Therefore, the photo-oxidation catalyst method does not require the addition of an oxidizing agent to oxidize and decompose organic substances, and can decompose organic substances into harmless carbon dioxide gas and water. Because of this structure, unlike conventional methods, the substances that make up the treatment process itself do not leach out or decomposition products are released, so it is extremely advantageous as a water purification treatment technology that removes trace amounts of organic matter. This is a great method.

However, conventionally proposed photo-oxidation catalyst methods place emphasis on the oxidation efficiency of organic substances, and use titanium oxide as a photo-oxidation catalyst in the form of fine powder. Therefore, a technical difficulty arises in separating the water and the photo-oxidation catalyst after the water to be treated is treated. Photooxidation catalysts are expensive because they contain platinum group metals, and complete separation and recovery is required to economically purify water. However, since the photooxidation catalyst is a fine powder, complete separation and recovery would unnecessarily complicate the treatment process, which would be extremely disadvantageous economically and in terms of treatment operation.

The present invention has been made in view of the above, and when purifying water containing a trace amount of oxidizable substances by irradiating it with ultraviolet rays and contacting it with a photooxidation catalyst in the presence of sufficient dissolved oxygen, it is possible to purify water containing a trace amount of oxidizable substances. The present invention uses a photooxidation catalyst in which titanium oxide or a platinum group metal is supported on titanium oxide on a molded product, and provides a photooxidation catalyst molded product that does not require separation or recovery.

The photooxidation catalyst used for water purification according to the present invention will be explained below. Titanium oxide, which serves as a photo-oxidation catalyst, is difficult to sinter between particles at low temperatures, making it difficult to obtain molded bodies with sufficient mechanical strength; However, the activity as an effective photooxidation catalyst cannot be obtained. The present inventors conducted intensive research to overcome the drawbacks of titanium oxide photooxidation catalysts, and as a result, titanium oxide was firmly attached to the surface of a molded article made of an inorganic material by the method described below, and high photocatalytic activity was achieved. It was confirmed that this photooxidation catalyst molded product is optimal for efficiently producing high-purity water. The inorganic material used to obtain the photooxidation catalyst molded body is mainly one selected from glass, alumina, silica, titanium oxide, mullite, cordierite, etc., and these are used alone or as a mixture, and in small amounts. A binder is added, and the product is molded and sintered to form a molded body. The molded body can be of any shape such as a flat plate, a cylinder, or a cylinder, and is porous or has an uneven surface.
It is preferable that the light irradiation part has a large surface area, is compatible with the device used, and has a shape that allows efficient use of the light irradiation area. In addition to the above, examples of inorganic materials include pottery made of feldspar, clay, etc.
Unglazed diaphragms for electrolysis, earthenware for roofing, bricks,
Tableware such as tiles can also be used if organic titanates are attached to them. The photooxidation catalyst can be obtained by attaching an organic titanate to the surface of the above-mentioned inorganic material molded body, treating it under certain firing conditions to form titanium oxide, and further supporting a platinum group metal if necessary.

Next, the manufacturing method will be explained in detail.

The organic titanate to be attached to the surface of the inorganic material is an alkyl titanate, an allyl titanate, a titanium acylate, or a titanium chelate, and one or more selected from these are used as a mixture. These titanates can be dissolved in diluents such as methanol, ethanol, propanol, butanol, benzene, toluene, hexane, carbon tetrachloride, methylchloroform, acetic acid, etc., and titanium chelates such as dihydroxybis(lactato)titanium monoammonium salt can be prepared. When used, it is made into an aqueous solution using water as a diluent and applied to the surface of the molded article. The method of attachment is to immerse the molded body in an organic titanate solution and take it out;
A method of applying the organic titanate solution with a brush or the like, or a method of spraying it, etc. can be used. The inorganic material molded body to which the organic titanate is attached is dried at 100°C to 110°C, and then fired in an oxidizing gas atmosphere at a temperature in the range of 350°C to 700°C, preferably 400°C.
Calcination treatment is performed in the range of ℃~500℃. As a result, the organic titanate is oxidatively decomposed and a molded body covered with titanium oxide having high photooxidation catalytic activity is obtained. As for the firing temperature, titanium oxide having photooxidation catalyst activity begins to be obtained from 350°C, and photooxidation catalyst activity is lost at high temperatures of 700°C or higher. In addition, if the amount of organic titanate coated on the surface of the inorganic material is large, cracks may occur during the drying or firing process and there is a risk of peeling from the surface of the molded product. To prevent this, the amount of organic titanate coated per coat may be The desired thickness of the titanium oxide film can be adjusted by reducing the amount of titanium oxide, that is, by repeating the coating-drying-baking process of organic titanate as many times as necessary.

Although the molded product with titanium oxide adhered to it can be used as a photo-oxidation catalyst molded product for water purification, it is possible to create an even more efficient photo-oxidation catalyst by supporting a platinum group metal on the surface of this titanium oxide. A molded body is obtained. As the supported metal, one selected from platinum, palladium, rhodium, ruthenium, etc. or a mixture of two or more thereof can be used. As a method for supporting these metals on a molded body to which titanium oxide is attached, an aqueous solution containing these metals in the form of a water-soluble inorganic compound,
This is carried out by irradiating the molded body with ultraviolet rays while it is immersed to support the metal, or by adding a reducing agent to support the metal.

The main purpose of supporting metal is to prevent recombination of electrons and holes generated on the surface of titanium oxide by ultraviolet irradiation. The smaller the coverage ratio of metal to the light irradiation area and the larger the number of metal spots per unit light irradiation area, the higher the photooxidation catalyst activity. Therefore, the metal is supported while controlling the amount and state of the metal deposited. The amount of metal is 0.01wt% to 1wt% based on titanium oxide.

The figure is a diagram explaining the basic concept when the photooxidation catalyst of the present invention is used for water purification.

A porous cylindrical photo-oxidation catalyst molded body 3 coated with titanium oxide or platinum-supported titanium oxide is located in the center of the reaction tank 4, and inside thereof is a quartz tube 2 containing a light source 1. The light source may be a high-pressure mercury lamp, a low-pressure mercury lamp, a Bratz lamp, a xenon lamp, etc. that emit light with a wavelength of about 420 nm or less, and sunlight can also be used as a light source. The light source is inserted into a quartz tube 2 for protection, but if a high-pressure mercury lamp is used, Pyrex glass or the like can also be used.

The water to be treated enters the reaction tank 4 through the inlet 7 by the pump 8, air or oxygen is introduced through the aeration tube 5, and is irradiated by the light source 1. A trace amount of the substance to be oxidized is oxidized by the photo-oxidation catalyst 3. It can be taken out from the drain port 6 as high purity water. Irradiation can also be performed while circulating the treated water using the pump 8, if necessary.

If this photo-oxidation catalyst molded body is used, titanium oxide is not a powder, so there is no need to separate or recover it, and since it is firmly attached to the molded body, it will not fall off even after long-term use. Not only can highly active oxidizing ability be maintained, but there is no fear of impurities being dissolved, so extremely high purity water can be obtained.In addition, if a light source containing ultraviolet rays is used at this time, mold, bacteria, viruses, etc. can be sterilized at the same time. Because it can be done, the effect is extremely large.

Examples are shown below.

Example 1 A porous cylindrical body (trade name: Kerami Filter) made of alumina coated with glass and having a diameter of 4.3 cm, thickness of 4 mm, and length of 20.0 cm was mixed with 30 parts of isopropyl titanate, 130 parts of isopropyl alcohol, and 10 parts of acetic acid, then taken out, dried at 110°C for 1 hour, and then calcined at 400°C for 5 hours in an air atmosphere to obtain a titanium oxide coated molded body. After that, the titanium oxide with weak adhesion strength was removed by ultrasonic cleaning, and then the molded body coated with titanium oxide was immersed in an aqueous solution containing acetic acid, sodium acetate, and chloroplatinic acid using a 6W low-pressure mercury lamp. Platinum was supported by internal irradiation. After ultrasonically cleaning the photooxidation catalyst molded body thus obtained, 500 ml of dextran aqueous solution was added.
(COD _cr 6.8mg/) was placed in a reaction tank and irradiated for 20 hours using a 6W ultraviolet germicidal lamp as a light source while blowing air, the COD _cr concentration was 0.
It became mg/.

Example 2 Made of silica fiber, inner diameter 6.0cm, length 20.0cm
cm water-permeable cylindrical molded body with di-isopropoxy,
The silica surface was immersed in a mixed solution consisting of 10 parts of bis(acetylacetonata) titanium, 90 parts of isopropyl alcohol, and 400 parts of methanol, then taken out, dried at 110°C, and fired at 500°C for 3 hours in an air atmosphere to form a silica surface. coated with titanium oxide. After repeating this process (immersion-drying-firing) three times, ultrasonic cleaning was performed, and then a low-pressure mercury lamp was inserted inside the molded body while it was immersed in a mixture of acetic acid, sodium carbonate, and chloroplatinic acid. Platinum was supported on the inner wall by light irradiation.

After ultrasonically cleaning the obtained platinum-supported titanium oxide coated molded body, 700 ml of dextran solution (COD _cr concentration 6.8 mg/) was added at a flow rate of 100 ml/min.
Circulate with a pump while blowing air for 8.0 hours.
When irradiated with a 6W ultraviolet germicidal lamp,
The COD _cr concentration was 0 mg/.

Example 3 Glass tube (inner diameter 4.8cm, thickness 2mm, length 30.0cm)
20 parts of isopropyl titanate, 10 parts of di-isopropoxy, bis(acetylacetonata) titanium,
Immerse in a mixed solution consisting of 130 parts of isopropyl alcohol and 10 parts of acetic acid, then remove and heat at 110°C.
After drying for 1 hour, the molded body was fired at 400° C. for 1 hour in an air atmosphere to obtain a titanium oxide coated molded body. Next, after immersing in a palladium nitrate aqueous solution, ascorbic acid was added as a reducing agent, and a heat treatment was performed to support palladium.
After ultrasonically cleaning the photooxidation catalyst molded article obtained in this way, 800 ml of dextran solution was added.
(COD _cr 5.5mg/) and irradiated with a 10W ultraviolet germicidal lamp for 2.0 hours while blowing oxygen. As a result, the COD _cr concentration was 0 mg/.

Example 4 Using a brush, 30 parts of isopropyl titanate and 130 parts of isopropyl alcohol were applied to the inside of a porous cylindrical molded body (trade name: Kerami Filter) made of alumina particles coated with glass and having an inner diameter of 4.3 cm and a length of 20.0 cm. After drying at 110°C, baking was performed at 500°C for 3 hours in an air atmosphere to coat the surface with titanium oxide. After repeating this process (immersion-drying-calcination) three times, ultrasonic cleaning was performed, and then a low-pressure mercury lamp was inserted inside the molded body while it was immersed in a mixture of acetic acid, sodium carbonate, and chloroplatinate. Platinum was deposited on the inner wall by irradiation with light. The obtained platinum-supported titanium oxide coated molded body was again subjected to ultrasonic cleaning, and then 700 ml of dextran solution (COD _cr concentration 6.8 mg/min) was circulated with a pump at a flow rate of 100 ml/min for 2.0 hours while blowing air. When irradiated with a 100W high-pressure mercury lamp, the COD _cr concentration was 0mg/.

Example 5 A cylindrical shaped body made of cordierite (2MgO・2Al ₂ O ₃・5SiO ₂ ) with a diameter of 4.0 cm, a thickness of 5 mm, and a length of 20.0 cm was mixed with 30 parts of hydroxytitanium stearate and
A molded body coated with titanium oxide was obtained by immersing it in a mixed solution consisting of 20 parts of phenyl titanate and 130 parts of toluene, drying it, and then firing it at 500°C for 1 hour. This molded body was subjected to ultrasonic cleaning and then treated with 500% dextran solution as a photooxidation catalyst.
ml (COD _cr 4.0mg/) into a reaction tank,
A 6W low-pressure mercury lamp was irradiated for 2.0 hours while blowing air. As a result, the COD _cr concentration was 0 mg/.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of the basic concept of producing high purity water using the photooxidation catalyst of the present invention. 1...Light source, 2...Quartz tube, 3...Photooxidation catalyst, 4...
Reaction tank, 5... Diffusion pipe, 6... Drain port, 7... Inlet port,
8...Pump.

Claims (1)

[Scope of Claims] 1. A photo-oxidation catalyst used in a method for purifying water by irradiating ultraviolet rays or light containing ultraviolet rays to water containing trace amounts of oxidizable substances, in which an organic titanate is attached to the surface of a molded body made of an inorganic material. 1. A photo-oxidation catalyst molded body, characterized in that the molded body is subjected to a firing treatment to form titanium oxide on the surface of the molded body, or further has a platinum group metal supported on the titanium oxide. 2 The organic titanate is an alkyl titanate,
The photooxidation catalyst molded article according to claim 1, which is one or a mixture of two or more selected from allyl titanate, titanium acylate, and titanium chelate. 3. The photo-oxidation catalyst molded article according to claim 1, wherein the firing treatment is performed at a firing temperature in the range of 350°C to 700°C in an oxidizing gas atmosphere. 4. The photooxidation catalyst molded article according to claim 1, wherein the platinum group metal is one or a mixture of two or more selected from platinum, palladium, rhodium, and ruthenium. 5 The molded body made of the inorganic material is mainly made of one selected from glass, alumina, silica, titanium oxide, mullite, and cordierite, and is formed by adding a small amount of a binder to a mixture of these, The photo-oxidation catalyst molded body according to claim 1, which is a sintered molded body.