JP2004250325A - Method for manufacturing titanium oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing titanium oxide having a photocatalytic activity and a narrow particle size distribution. <P>SOLUTION: The method for manufacturing titanium oxide comprises heating a solution of a titanium compound (e.g. titanium sulfate, titanium oxysulfate, titanium trichloride, titanium tetrachloride, titanium oxychloride, titanium tetrabromide, tetraalkoxytitanium, or a titanium chelate compound) to 60°C or higher without hydrolyzing the titanium compound, reacting the titanium compound with a base (e.g. ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, or an amine) at 60°C or higher, and firing the resultant product. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

The present invention relates to a method for producing titanium oxide, and more particularly to a method for producing titanium oxide having photocatalytic activity and a small particle size distribution.

It has been studied to remove malodorous substances in the atmosphere and to impart a self-cleaning effect to window glass and road walls by the photocatalytic action of titanium oxide (see Patent Document 1: Japanese Patent Application Laid-Open No. 9-57912). ]. When a titanium oxide film is formed on a building material such as a road wall or a window glass or an automobile material, a coating is usually formed by mixing titanium oxide and a solvent, and then applying the coating. In order to form a favorable film on a building material or an automobile material, a titanium oxide having not only a photocatalytic action but also a uniform particle diameter is demanded.

JP-A-9-57912

An object of the present invention is to provide a method for producing titanium oxide having photocatalytic activity and a small particle size distribution.

The present inventors have studied the method for producing titanium oxide, and have completed the present invention.

That is, the present invention provides a method for producing titanium oxide, comprising reacting a base with a solution of a titanium compound not containing a hydrolyzate at 60 ° C. or higher and calcining the obtained product. is there.

According to the production method of the present invention, titanium oxide having photocatalytic activity and a small particle size distribution can be obtained.

The titanium compound used in the present invention is a compound containing titanium as a metal component and reacting with a base in the presence of water to produce titanium hydroxide. For example, titanium sulfate [Ti (SO ₄ ) ₂ .mH ₂ O 0 ≦ m ≦ 20], titanium oxysulfate [TiOSO ₄ .nH ₂ O, 0 ≦ n ≦ 20], titanium trichloride [TiCl ₃ ], titanium tetrachloride [TiCl ₄ ], titanium oxychloride [TiOCl ₂ ], Titanium-containing inorganic compounds such as titanium tetrabromide [TiBr ₄ ] are exemplified. The titanium compound used may be a titanium-containing organic compound in addition to the above-mentioned titanium-containing inorganic compound, for example, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, Tetraalkoxytitanium compounds such as -n-butoxytitanium, tetraisobutoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium, tetrakis-2-ethylhexyloxytitanium, tetrastearyloxytitanium;
Diisopropoxybis (acetylacetonato) titanium, diisopropoxybis (triethanolaminato) titanium, di-n-butoxybis (triethanolaminato) titanium, di (2-ethylhexyloxy) bis (2-ethyl-) Titanium chelate compounds such as 1,3-hexanediolato) titanium, isopropoxy (2-ethylhexanediolato) titanium, titanium tetraacetylacetonate, and hydroxybis (lactato) titanium. Among these, titanium oxysulfate is preferably used.

The solution used in the production method of the present invention is a solution in which a titanium compound is dissolved in a solvent, and is preferably a solution in which the titanium compound is completely dissolved. As the solvent, for example, water, aqueous medium such as aqueous hydrogen peroxide, methyl alcohol, ethyl alcohol, isopropyl alcohol, alcoholic medium such as butyl alcohol,
Examples include a ketone medium such as acetone. Usually, a titanium-containing inorganic compound such as titanium oxysulfate is preferably dissolved in an aqueous medium, and a titanium-containing organic compound such as tetraisopropoxytitanium is preferably dissolved in an alcoholic medium or a ketone medium. preferable. The amount of these solvents to be used is usually 1 mol times or more based on the titanium compound. The larger the amount of the solvent is, the more preferable it is, and it is preferable that the amount is 5 mol times or more with respect to the titanium compound. If the amount of the solvent is too large, the particle size distribution of the obtained titanium oxide becomes large. Therefore, the amount of the solvent is preferably 40 mol times or less, more preferably 25 mol times or less with respect to the titanium compound.

In the present invention, a base is reacted with such a solution at 60 ° C. or higher. In order to cause the base to react with the solution of the titanium compound containing no hydrolyzate at 60 ° C. or higher, for example, the solution of the titanium compound may be first heated without hydrolyzing the titanium compound. In order to heat the titanium compound so as not to hydrolyze it, it is preferable to heat the titanium compound quickly at, for example, a heating rate of 5 ° C./min or more, more preferably 10 ° C./min or more, especially 15 ° C./min or more. The heating is performed at the above-mentioned heating rate until the temperature becomes 60 ° C. or higher, preferably 80 ° C. or higher, more preferably 85 ° C. or higher.

により求めることができる。溶液中に実際に含まれる水酸化チタン質量は、
(1)先ず加熱終了時、または終了直前の溶液から試料を採取し、
(2)チタン化合物を溶解しうる溶媒、例えば水などに加えたのち固形分を濾取し、
(3)得られた固形分を１００℃程度で乾燥し、
(4)乾燥後の固形分の質量から、この固形分に含まれる溶媒分の質量を差し引く
方法で、求めることができる。固形分に含まれる溶媒分は熱重量測定法、示差熱分析（ＴＧ−ＤＴＡ）法などの方法で求めることができる。 If the titanium compound in the solution is heated without being hydrolyzed, during or during the heating, the solution after the heating does not show cloudiness due to titanium hydroxide generated by hydrolysis of the titanium compound. The presence or absence of hydrolysis of the titanium compound can be determined. In a state where this opacity is not observed, the hydrolysis rate of the titanium compound is generally 5% or less, preferably 1% or less, and ideally 0%, and 95% or more, preferably 99% of the titanium compound used. As described above, ideally, 100% remains dissolved in the solution immediately after heating to 60 ° C. or higher without being changed to titanium hydroxide. Here, the hydrolysis rate of the titanium compound is calculated assuming that the mass of the titanium hydroxide actually contained in the solution (the mass of the titanium hydroxide) and that the total amount of the titanium compound used is titanium hydroxide. From the mass (theoretical mass of titanium hydroxide), the formula (A)

Can be obtained by The mass of titanium hydroxide actually contained in the solution is
(1) First, at the end of heating or immediately before taking a sample from the solution,
(2) a solvent capable of dissolving the titanium compound, such as water, and then the solids are collected by filtration,
(3) drying the obtained solid at about 100 ° C.,
(4) It can be determined by subtracting the mass of the solvent contained in the solid from the mass of the solid after drying. The solvent content in the solid content can be determined by a method such as thermogravimetry or differential thermal analysis (TG-DTA).

The heating of the solution containing the titanium compound is performed, for example, by supplying the solution of the titanium compound to the inner circular pipe of the double pipe and supplying the heating medium to the outer annular pipe, or by putting the upper solution in a container with a stirrer, It can be carried out by a method of heating using a heat medium while stirring the object.

The heated titanium compound solution is reacted with a base at 60 ° C. or higher. Examples of the base include ammonia, alkali metal hydroxide, alkaline earth metal hydroxide, and amine.Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide. Examples of the amine include hydroxylamine. Among the bases, ammonia is preferable. These bases are used alone or in combination of two or more.

The temperature at which the base is reacted is 60 ° C. or higher, preferably 80 ° C. or higher, more preferably 85 ° C. or higher. The time required for the reaction is usually about 0.1 to 60 hours, preferably about 0.5 to 24 hours. The amount of the base used is preferably at least the stoichiometric amount required to convert the titanium compound to titanium hydroxide in the presence of water, for example, at least twice the stoichiometric amount, and usually at most 40 times the stoichiometric amount. Preferably it is 20 times or less.

The reaction may be performed in the presence of water. When the reaction is carried out in the presence of water, the amount of water used is 0.3 times by mass or more, preferably 0.4 times by mass or more with respect to the titanium compound.

In order to cause the base to react, for example, the titanium compound solution and the base may be mixed at a reaction temperature, that is, at 60 ° C. or higher. The base may be used alone, may be dissolved in a solvent and used as a base solution, or may be used as an aqueous solution of a base using water as a solvent. When the titanium compound solution is a solution in which the titanium compound is dissolved in a solvent other than water, for example, an alcoholic solvent, a ketone solvent, or the like, it is preferable to use the aqueous solution as the base.

To mix the titanium compound solution and the base solution, for example, a titanium compound solution heated by a double tube and a base solution heated by another double tube are mixed in both double tubes. Can be led to a reaction tube connected to the reaction tube, and mixed in this reaction tube.

Further, before heating to 60 ° C. or higher, a base precursor may be contained in a titanium compound solution in advance, and the solution may be heated to 60 ° C. or higher. Since the titanium compound solution contains the base precursor in advance, the base precursor is decomposed by heating the solution to 60 ° C. or more to generate a base, and the generated base can be reacted with the titanium compound. . Here, the base precursor is a compound which is not itself a base but decomposes when heated to 60 ° C. or higher, preferably 80 ° C. or higher to generate a base. When a base precursor is used, the base precursor is used in such an amount that the amount of the base generated by the decomposition of the base precursor becomes the above-mentioned amount of the base used.

Specific examples of the base precursor include urea, thiourea, dimethylurea, and urea peroxide. Among these, a compound that decomposes under conditions of normal pressure and 80 ° C. or higher to generate ammonia, for example, urea is preferable. When urea (NH ₂ CONH ₂ ) is heated to 85 ° C. or more in the presence of water (H ₂ O), the formula (1)
NH ₂ CONH ₂ + 3H ₂ O → 2NH ₃ .H ₂ O + CO ₂ (1)
As shown in (1), 2 mol of ammonia (NH ₃ .H ₂ O) is generated from 1 mol of urea. When a mixed solution of urea and an aqueous solution of a titanium compound such as titanium sulfate or titanium oxysulfate is heated, the produced ammonia is converted into the formula (2)
_{NH 3 · H 2 O → NH} 4 + + OH - (2)
Dissociate as shown. The generated ammonium ion (NH ₄ ⁺ ) reacts with the acid group of the titanium compound to form a salt, and titanium hydroxide (Ti (OH) ₄ ) is generated from the titanium ion (Ti ^{4 +} ). The reaction at this time is, for example, the formula (3)
2SO ₄ ^2- + 4NH ₄ ⁺ → 2 (NH ₄ ) ₂ SO ₄ (3)
And equation (4)
^{Ti 4+ + 4OH - → Ti (} OH) 4 (4)
Can be expressed as When the titanium compound is titanium sulfate, the stoichiometric amount of the base for converting 1 mol of titanium sulfate to titanium hydroxide is 4 mol as ammonia and 2 mol as urea. When the titanium compound is titanium oxysulfate, the stoichiometric amount of the base for converting 1 mol of titanium oxysulfate to titanium hydroxide is 2 mol as ammonia and 1 mol as urea.

By reacting a titanium compound with a base, titanium hydroxide is obtained as a product. This product may be aged as needed. Aging may be performed, for example, by a method of maintaining the slurry containing the product at a temperature of 20 ° C. or higher, preferably 30 ° C. or higher, and 55 ° C. or lower, preferably 50 ° C. or lower. The holding time is usually 0.5 hours or more and 10 hours or less.

The product obtained by reacting the base with the titanium compound and the product that has been further aged after the reaction are usually separated into a solid and a liquid, and the product recovered as a solid is further washed, if necessary, Dried. The separation may be performed by, for example, pressure filtration, vacuum filtration, centrifugation, decantation, or the like. The cleaning may be performed using water, aqueous hydrogen peroxide, aqueous ammonia, aqueous oxalic acid, aqueous ammonium nitrate, or water containing an amine. Drying may be performed using, for example, a flash dryer, a fluid dryer, a stationary dryer, a spray dryer, or the like.

A product obtained by reacting a titanium compound with a base, a product further aged after the reaction, and then a product recovered as a solid by separation are calcined. The sintering may be performed, for example, by a method such as an air-flow sintering furnace, a tunnel furnace, or a rotary furnace. The firing may be performed in an atmosphere containing air, water vapor, nitrogen, a rare gas or ammonia, and the temperature is preferably 300 ° C. or higher, more preferably 350 ° C. or higher, and 800 ° C. or lower, further preferably 600 ° C. or lower. Preferably, there is. The firing time varies depending on the type, atmosphere and firing temperature of the firing furnace, but is usually 0.1 hours or more and 30 hours or less.

The titanium oxide obtained by the production method of the present invention usually has an average particle diameter of 15 μm or less and a standard deviation of the particle diameter distribution of 5 or less. The titanium oxide has a photocatalytic activity and usually has an anatase crystal structure.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.
The average particle size, the standard deviation of the particle size distribution, and the crystal structure of titanium oxide were determined by the following methods.

により算出した。 Average particle diameter D ₅₀ (μm) and standard deviation SD (μm) of particle diameter distribution:
The sample is dispersed in a 0.2% by weight aqueous solution of sodium hexametaphosphate, and the dispersion is introduced into a particle size distribution measuring device (trade name “MICROTRAC HRA model 9320-X100”, manufactured by Nikkiso Co., Ltd.), and the measurement range is 0.1 to 700 μm. The particle size distribution was measured under the conditions of the number of divisions of the measurement range: 100. From this particle size distribution, calculates a cumulative 50% by volume diameter, was defined as the average particle diameter D ₅₀ of this. Further, the standard deviation SD is obtained by calculating the volume fraction at an arbitrary particle diameter D _i in the particle diameter distribution as P _i and using the equation (B)

Was calculated by

Crystal structure:
The measurement was performed using an X-ray diffractometer (trade name “RAD-IIA”, manufactured by Rigaku Corporation).

Example 1
In a 1 L (1000 cm ³ ) flask equipped with a stirrer, 340 g of an aqueous solution of titanium oxysulfate prepared by dissolving 204 g of titanium oxysulfate (trade name “TM crystal”, appearance: white solid, manufactured by Teica) in 136 g of water, urea (special grade reagent) , Manufactured by Wako Pure Chemical Industries, Ltd.) and 126 g of water. The stirrer was rotated at 400 rpm for 5 minutes to dissolve the urea. The resulting mixture had a temperature of 21.6 ° C. and a pH of 1. At this time, the amount of water was 17.3 times the molar amount of titanium oxysulfate, and the amount of urea was 4 times the stoichiometric amount required to convert titanium oxysulfate to titanium hydroxide in the presence of water. Met.

The above mixture was heated at a heating rate of 5 ° C./min while stirring. The heating at this time was performed using an oil bath at 100 ° C. When the temperature of the mixture reached 95 ° C., cloudiness was observed. Thereafter, the slurry was kept at 100 ° C. for 3 hours while stirring. The pH of the mixture after the retention was 6.9.

The above slurry was cooled to 40 ° C. while stirring. The pH of the slurry after cooling was 8.2. Next, this slurry was kept at 40 ° C. for 1 hour. The obtained slurry was filtered, washed and dried.

(Evaluation of solid-liquid separation properties of slurry)
The solid-liquid separation property of the slurry was measured using a simple device consisting of a filter equipped with filter paper (model No. “125 mm No. 5C”, Advantech) and an aspirator (model “A-3S”, Tokyo Riken). Was evaluated. The time required to filter 0.2 L of this slurry was 10 seconds.

The dried product obtained above was calcined in air at 400 ° C. for 1 hour to obtain titanium oxide. This titanium oxide had an average particle size of 11.9 μm, a standard deviation of the particle size distribution of 4.3 μm, and an anatase type crystal structure.

(Activity evaluation of titanium oxide)
A glass petri dish having a diameter of 5 cm was placed in a sealed glass reaction vessel having a diameter of 8 cm, a height of 10 cm, and a capacity of about 0.5 L, and 0.3 g of the titanium oxide obtained above was placed on the petri dish. . The inside of the reaction vessel was filled with a mixed gas in which the volume ratio of oxygen and nitrogen was 1: 4, and 13.4 μmol of acetaldehyde was sealed, and visible light was irradiated from outside the reaction vessel. For irradiation with visible light, a light source device (trade name “Optical Modlex SX-UI500XQ”, trade name “Lamp UXL-500SX”, manufactured by USHIO Inc., manufactured by USHIO Inc.) with a wavelength of about 430 nm was attached. A filter equipped with the following filter that cuts ultraviolet light (trade name "Y-45", made by Asahi Techno Glass) and a filter that cuts infrared light with a wavelength of about 830 nm or more (trade name "Super Cold Filter", made by Ushio Inc.) Was used as a light source. When acetaldehyde is decomposed by irradiation with visible light, carbon dioxide is generated. Therefore, the concentration of carbon dioxide is measured over time with a photoacoustic multi-gas monitor (Type 1312, manufactured by INNOVA), and the carbon dioxide generation rate calculated from the concentration change The photocatalytic action of titanium oxide on acetaldehyde was evaluated. The generation rate of carbon dioxide in this example was 10.4 μmol / h per 1 g of titanium oxide.

Example 2
In a 1 L flask equipped with a stirrer, 170 g of an aqueous solution of titanium oxysulfate prepared by dissolving 204 g of titanium oxysulfate (trade name “TM Crystal”, appearance: white solid, manufactured by Teica) in 136 g of water, urea (special grade reagent, Wako Pure Chemical Industries, Ltd.) (Industrial product) 404 g and water 126 g. The stirrer was rotated at 400 rpm for 5 minutes to dissolve the urea. The resulting mixture had a temperature of 18.5 ° C. and a pH of 1.8. The amount of water at this time was 17.3 mol times with respect to titanium oxysulfate, and the amount of urea was 8 with respect to the stoichiometric amount required to convert titanium oxysulfate to titanium hydroxide in the presence of water. It was twice.

The above mixture was heated at a heating rate of 5 ° C./min while stirring. The heating was performed using a 100 ° C. oil bath as in Example 1. When the temperature of the mixture reached 100 ° C., cloudiness was observed. Thereafter, the slurry was kept at 100 ° C. for 3 hours while stirring. The pH of the mixture after the retention was 7.3.

The above slurry was cooled to 40 ° C. while stirring. The pH of the slurry after cooling was 8.7. Next, this slurry was kept at 40 ° C. for 1 hour.

The obtained slurry was filtered, washed and dried, and the dried product was fired in air at 400 ° C. for 1 hour to obtain titanium oxide. This titanium oxide had an average particle diameter of 4.2 μm, a standard deviation of the particle diameter distribution of 1.8 μm, and a crystal structure of an anatase type.

The photocatalytic action of this titanium oxide was examined under the same conditions as in [Evaluation of the activity of titanium oxide] in Example 1. The generation rate of carbon dioxide in this example was 6.9 μmol / h per 1 g of titanium oxide.

Example 3
Titanium oxide was obtained by performing the same operation as in Example 2 except that the heating rate during heating was changed from 5 ° C./min to 16 ° C./min. The obtained titanium oxide had an average particle diameter of 2.3 μm, a standard deviation of the particle diameter distribution of 1.0 μm, and a crystal structure of an anatase type.

The photocatalytic action of this titanium oxide was examined under the same conditions as in [Evaluation of the activity of titanium oxide] in Example 1. The generation rate of carbon dioxide in this example was 8.8 μmol / h per 1 g of titanium oxide.

Comparative Example 1
An aqueous titanium oxysulfate solution prepared by dissolving 68 g of titanium oxysulfate (trade name “TM Crystal”, appearance: white solid, manufactured by Teica) in 272 g of water is placed in a 1 L flask equipped with a stirrer, and stirred at 400 rpm. , At a heating rate of 5 ° C./min. When the temperature of the aqueous solution reached 90 ° C., cloudiness was observed. Thereafter, the slurry was kept at 100 ° C. for 3 hours while stirring. The slurry was cooled to 40 ° C. with stirring and kept at 40 ° C. for 1 hour. The obtained slurry was filtered, washed and dried.

This slurry was evaluated under the same conditions as in [Evaluation of Solid-Liquid Separability of Slurry] in Example 1. The time required to filter 0.2 L of this slurry was 2 hours.

The dried product obtained above was calcined in air at 400 ° C. for 1 hour to obtain titanium oxide. This titanium oxide had an average particle size of 15.8 μm, a standard deviation of the particle size distribution of 12.0 μm, and an anatase type crystal structure.

The photocatalytic action of this titanium oxide was examined under the same conditions as in [Evaluation of the activity of titanium oxide] in Example 1. The generation rate of carbon dioxide in this example was 0 μmol / h per 1 g of titanium oxide.

Claims (13)

A method for producing titanium oxide, comprising reacting a base with a solution of a titanium compound containing no hydrolyzate at 60 ° C. or higher and calcining the obtained product. The production method according to claim 1, wherein the titanium compound solution is heated to 60 ° C or higher without hydrolyzing the titanium compound, and then the base is reacted with the solution at 60 ° C or higher. The method according to claim 1, wherein the titanium compound is a titanium sulfate, titanium oxysulfate, titanium trichloride, titanium tetrachloride, titanium oxychloride, titanium tetrabromide, tetraalkoxy titanium, or a titanium chelate compound. Tetraalkoxytitanium is tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetraisobutoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium 4. The production method according to claim 3, which is tetrakis-2-ethylhexyloxytitanium or tetrastearyloxytitanium. The titanium chelate compound is diisopropoxybis (acetylacetonato) titanium, diisopropoxybis (triethanolaminato) titanium, di-n-butoxybis (triethanolaminato) titanium, di (2-ethylhexyloxy) bis The method according to claim 3, which is (2-ethyl-1,3-hexanediolato) titanium, isopropoxy (2-ethylhexanediolato) titanium, titanium tetraacetylacetonate, or hydroxybis (lactato) titanium. The method according to claim 1, wherein the base is ammonia, an alkali metal hydroxide, an alkaline earth metal hydroxide or an amine. The method according to claim 1, wherein the amount of the base used is not less than the stoichiometric amount required to convert the titanium compound to titanium hydroxide in the presence of water. The method according to claim 2, wherein the titanium compound solution contains a base precursor in advance, and the titanium compound is reacted with a base generated by decomposing the base precursor by heating the solution to 60 ° C or higher. The production method according to claim 9, wherein the base precursor is an ammonium precursor. The production method according to claim 10, wherein the ammonium precursor is urea, thiourea, dimethylurea, or urea peroxide. The method according to claim 1, wherein the obtained product is calcined at 300C to 800C. A method for producing titanium hydroxide, comprising reacting a base with a solution of a titanium compound containing no hydrolyzate at 60 ° C. or higher. The method according to claim 13, wherein the titanium compound solution is heated to 60 ° C or higher without hydrolyzing the titanium compound, and then the base is reacted with the solution at 60 ° C or higher.