JPS6219240B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water purification method that decomposes and removes pollutants contained in water to be treated by irradiating them with ultraviolet rays in the presence of dissolved oxygen and a photo-oxidation catalyst. The substances to be decomposed and removed by the present invention are organic components dissolved in water, and are usually
Mainly substances expressed as COD _cr (chemical oxygen demand) values. Conventionally, coagulation-sedimentation methods, biological treatment methods, and the like have been popular for sewage treatment and wastewater reuse based on wastewater regulations, but more advanced purification technology is required. Removal of soluble organic matter is one of the most difficult targets to undergo advanced purification treatment, and removal methods such as activated carbon adsorption, membrane permeation, and ozone oxidation have been used in the past, but recently photo-oxidation has been used. Removal methods are also being developed. Activated carbon adsorption is the most common and widely used method, but when the molecular weight of soluble organic matter is 100
~10,000, there is no practical problem, but the adsorption capacity is small for relatively low-molecular saturated compounds and high-molecular compounds such as humic acid, and a large amount of activated carbon is required to completely remove them. is required,
If you try to actually implement it, it will be extremely expensive and uneconomical. Although the membrane permeation method is an excellent treatment method with low energy consumption, it is difficult to remove hydrophilic low-molecular compounds such as alcohol, and it may clog the permeable membrane and cause deterioration of the membrane due to microbial growth, or damage to membrane components. It has problems such as elution. Since the ozone oxidation method does not completely oxidize soluble organic matter to carbon dioxide gas and water, additional treatment is required. A photo-oxidation method that uses a halogen-based oxidizing agent, such as sodium hypochlorite, is not preferred because it produces trihalomethane, which is said to be carcinogenic, and at the same time increases chlorine ions, sodium ions, etc. in the treated water. Recently, a method using a photooxidation catalyst has been developed as a new pollutant removal method that does not have the above-mentioned drawbacks. In this photo-oxidation method, in the presence of sufficient dissolved oxygen to decompose and remove pollutants contained in the water to be treated, a photo-oxidation catalyst consisting of titanium oxide particles or titanium oxide particles supporting platinum group metals is exposed to ultraviolet light. This is done by passing water through contact while irradiating. In the photo-oxidation method for removing pollutants, holes and electrons are generated on the surface of a photo-oxidation catalyst using light energy, and the reaction between the holes and electrons generates hydroxyl radicals with high oxidizing ability. , Since it utilizes the reaction in which superoxide (O ₂ ^- ) oxidizes pollutants, it oxidizes and decomposes pollutants without adding an oxidizing agent to oxidize and decompose pollutants as in conventional methods. It can be converted into harmless carbon dioxide and water. The catalyst used is composed of titanium oxide and platinum group metals, so it is insoluble in water, and unlike conventional oxidation methods, the decomposition products of the oxidant do not remain, and the water to be treated containing dissolved oxygen can be treated. ,
Contaminants can be removed simply by contacting photo-oxidation catalyst particles under ultraviolet irradiation. Therefore, it is an extremely advantageous method for purifying water. For this reason, several purification methods using photo-oxidation catalysts have been proposed, but the photo-oxidation catalyst used in the proposed methods is in the form of powder. This is to reduce the rate of recombination of electrons and holes generated by ultraviolet irradiation on the surface of the photo-oxidation catalyst as described above. In other words, by turning the photooxidation catalyst into powder, the oxidation efficiency of organic matter is greatly increased. Therefore, it can be said that the finer the powder of the photooxidation catalyst used, the better the oxidation efficiency. However, when titanium oxide powder is used to purify water by the conventional method, there is a problem in separating the water and the photo-oxidation catalyst after purifying the water, making separation and recovery difficult. Titanium oxide and platinum group metals are expensive, and recovery and reuse of the catalyst is essential for economical water purification. However, if the photooxidation catalyst is a powder, it is impossible to completely recover and reuse it. It was recognized that this would be impossible and would pose a major practical difficulty. The present invention was made in view of the above, and it is possible to treat wastewater containing pollutants in the presence of sufficient dissolved oxygen.
Provides a water purification method that uses a photooxidation catalyst in the form of a molded body when irradiating ultraviolet rays and removing pollutants using a photooxidation catalyst, and does not require separation or recovery of the photooxidation catalyst after use. It is something to do. The water purification method according to the present invention will be explained below. When using titanium oxide as a catalyst, it is possible to form the titanium oxide into a compact in order to avoid the disadvantages of being a powder, but since titanium oxide does not easily cause sintering between particles at low temperatures, it cannot be It is difficult to obtain a molded body with mechanical strength, and on the other hand, if sintered at a high temperature, a molded body with mechanical strength can be obtained, but effective photocatalytic activity 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 product made of an inorganic material using the method described below, and the result was a high photocatalytic activity. It was discovered that a molded body could be obtained, and it was confirmed that pollutants in wastewater can be efficiently removed by using this photooxidation catalyst. The inorganic material is mainly selected from glass, alumina, silica, titanium oxide, mullite, and cordierite, and these are used alone or as a mixture, and are formed and sintered with the addition of a small amount of binder. Make it into a molded body. The molded object can be flat, cylindrical,
Choose any shape such as a cylinder, and make it porous or have an uneven surface and have a large surface area for the light irradiation part, and be compatible with the equipment used and have a shape that allows efficient use of the light irradiation area. It is preferable that In addition to the above-mentioned inorganic materials, pottery made of feldspar, clay, etc., unglazed diaphragms for electrolysis, earthenware such as roof tiles, and vessels such as bricks and tiles can also be used if organic titanates are attached to them. The photooxidation catalyst can be obtained by depositing an organic titanate on the surface of the above-mentioned inorganic material molding, 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 titanates to be attached to the surface of the inorganic material are alkyl titanates, allyl titanates, titanium acylates, and titanium chelates, 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. When used, it is made into an aqueous solution using water as a diluent and applied to the surface of the molded article. As a method for adhesion, the molded body may be immersed in an organic titanate solution and taken out, the organic titanate solution may be applied with a brush or the like, or the organic titanate solution may be sprayed. The inorganic material molded body to which the organic titanate is attached is dried at 100°C to 110°C, and then fired at a temperature of 350°C to 700°C in an oxidizing gas atmosphere.
Preferably, the firing treatment is performed at a temperature in the range of 400°C to 500°C. As a result, the organic titanate is oxidatively decomposed and a molded body covered with titanium oxide having high photooxidation catalytic activity is obtained. The firing temperature is 350
Titanium oxide with photooxidation catalytic activity begins to be obtained at temperatures above 700°C, and photooxidation catalytic 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. In other words, by repeating the organic titanate coating-drying-baking process as many times as necessary, the desired thickness of the titanium oxide film can be obtained. Although the molded product with titanium oxide adhered to it can be used as a photo-oxidation catalyst molded product for water purification, even more efficient photo-oxidation catalyst molding can be achieved by supporting a platinum group metal on the surface of this titanium oxide. You get a body. As the supported metal, one or a mixture of two or more selected from platinum, palladium, rhodium, ruthenium, etc. can be used. A method for supporting these metals on a molded body to which titanium oxide is attached is to irradiate the molded body with ultraviolet rays while the molded body is immersed in an aqueous solution containing these metals in the form of a water-soluble inorganic compound. This is carried out by a method of supporting a metal or a method of adding a reducing agent to support a 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 of a water purification device using the photo-oxidation catalyst of the present invention. A reaction tank 3 has a flat photooxidation catalyst molded body 2 coated with titanium oxide or platinum-supported titanium oxide, and a light source 1 is installed above it. The light source is a high-pressure mercury lamp, low-pressure mercury lamp, Bratz lamp, xenon lamp, etc. that emits light with a wavelength of about 420 nm or less, and sunlight can also be used as a light source. When using the light source in a immersed state, insert it into a quartz tube to protect the light source. When using a high-pressure mercury lamp, Pyrex glass can also be used. The water to be treated enters the reaction tank 3 through the inlet 6 by the pump 7, air or oxygen is introduced through the aeration tube 4, is irradiated by the light source 1, impurities are oxidized by the photo-oxidation catalyst, and the water is discharged as treated water to the drain port. It is discharged from 5. The waste water is again circulated to the reaction tank 3 by the pump 7 as required. According to this method of water purification, titanium oxide is not in powder form, so there is no need to separate or recover it, and because it is firmly attached to the molded object, it will not fall off even after long-term use. Because it maintains a highly active oxidizing ability, it is possible to efficiently treat contaminated water.Also, by irradiating it with a light source that includes ultraviolet rays, it can simultaneously sterilize mold, bacteria, viruses, etc. Extremely large. Examples are shown below. Example 1 A glass plate of 5 x 5 cm was immersed in a mixed solution consisting of di-isopropoxy, 10 parts of bis(acetylacetonata) titanium, 90 parts of isopropyl alcohol, and 200 parts of methanol, then taken out and dried at 110°C for 30 minutes. A glass plate coated with titanium oxide was obtained by firing at 500°C for 30 minutes in an oxygen atmosphere. After immersing it in an aqueous palladium nitrate solution, ascorbic acid was added as a reducing agent and a heating treatment was performed to support palladium. The photooxidation catalyst thus obtained was added to a dextran solution.
It was placed in a reaction tank with 100ml (COD _cr concentration 50mg/) and irradiated with a 100W high pressure mercury lamp for 12 hours while blowing oxygen. As a result, the COD _cr concentration was 14mg/
It was hot. Example 2 A porous cylindrical body (trade name: Kerami Filter) made of alumina coated with glass and having a diameter of 4.3 cm, a thickness of 4 mm, and a length of 20.0 cm was mixed with 30 parts of isopropyl titanate, 130 parts of isopropyl alcohol, and acetic acid. A molded article coated with titanium oxide was obtained by immersing it in a mixed solution consisting of 10 parts, taking it out, drying it at 110°C for 1 hour, and then firing it at 400°C for 5 hours in an air atmosphere. After that, ultrasonic cleaning was performed to remove titanium oxide with weak adhesive strength, and then the molded body coated with titanium oxide was immersed in an aqueous solution containing acetic acid, sodium acetate, and chloroplatinic acid, and 100 W was applied from the inside. Platinum was supported by irradiation using a high-pressure mercury lamp. The thus obtained photooxidation catalyst molded body was again subjected to ultrasonic cleaning, and then treated with 500 ml of dextran solution.
ml (COD _cr 43 mg/) and irradiated with a 100 W high pressure mercury lamp for 6 hours while blowing air. As a result, the COD _cr concentration decreased to 7 mg/. At this time, generation of carbon dioxide gas was also observed. Example 3 Using the photooxidation catalyst molded body used in Example 2, 500 ml of an aqueous solution containing various organic substances was irradiated with light using a 6W ultraviolet germicidal lamp while blowing air into a reaction tank. The results are shown in the table below.

[Front] Na〓
Example 4 Made of mullite (2Al ₂ O ₃・5SiO ₂ ) with a diameter of 4.0
A circular molded body with a diameter of 5 mm and a thickness of 5 mm was immersed in a mixed solution consisting of 20 parts of hydroxytitanium stearate, 10 parts of phenyl titanate, and 130 parts of toluene, then taken out and dried at 110°C for 1 hour.
A molded body coated with titanium oxide was obtained by firing at a temperature of 1 hour. Using this molded body as a photo-oxidation catalyst, 100 ml of dextran solution (COD _cr 40
mg/) and irradiated with a 100W high-pressure mercury lamp for 15 hours while blowing air. As a result, the COD _cr concentration decreased to 20mg/.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of the basic concept of a water purification device using the photo-oxidation catalyst of the present invention. 1...Light source, 2...Photooxidation catalyst, 3...Reaction tank, 4...
Diffuser pipe, 5...drain port, 6...inlet, 7...pump.

Claims (1)

[Claims] 1. Irradiating the water to be treated containing pollutants with ultraviolet rays or light containing ultraviolet rays in the presence of a photo-oxidation catalyst,
In the method of oxidizing and removing contaminants, an organic titanate is attached to the surface of a molded body made of an inorganic material, and then a firing treatment is performed to form titanium oxide on the surface of the molded body, or a platinum group metal is further added to the titanium oxide. A water purification method characterized in that pollutants are oxidized and removed using a photooxidation catalyst obtained by supporting. 2 The organic titanate is an alkyl titanate,
Claim 1 is one or a mixture of two or more selected from allyl titanate, titanium acylate, and titanium chelate.
Water purification method described in section. 3. The water purification method according to claim 1, wherein the firing treatment is performed in an oxidizing gas atmosphere at a firing temperature in the range of 350°C to 700°C. 4. The platinum group metal is any one selected from platinum, palladium, rhodium, and ruthenium.
The method for purifying water according to claim 1, wherein the water purification method is a species or a mixture of two or more species. 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 materials, and forming the molded body. The water purification method according to claim 1, wherein the water purification method is a sintered molded body.