JPH044964B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing ultrafine metal oxide particles, and more specifically to cosmetics, white pigments, adsorbents, catalysts,
This invention relates to an efficient method for producing ultrafine metal oxide particles that can be used in a wide range of applications such as catalyst supports. [Prior Art and Problems to be Solved by the Invention] Various methods have been known for producing fine particles of metal oxides such as titanium and zirconium. For example, titanium oxide has excellent weather resistance and strong hiding power, so it is widely used in the fields of cosmetics and paints. The sulfuric acid method, in which the resulting precipitate is then calcined, and the chlorine method, in which titanium tetrachloride is decomposed and oxidized at high temperatures, have been developed. However, in these conventional methods for producing rutile-type titanium oxide, particle growth occurs during the production process, so the particle size of the obtained titanium oxide is large, exceeding 1 μm. Furthermore, according to Funaki, Saeki et al., titanium tetrachloride and water are mixed in the gas phase at 200 to 800°C to produce anatase-type titanium oxide in the form of fine particles, and titanium tetrachloride and water are mixed in the liquid phase. It has been confirmed that it is possible to produce titanium oxide in the form of anatase or anatase type fine particles with a slight amount of rutile mixed through the reaction, but these methods have only been able to obtain particles of amorphous shape. Furthermore, according to the method of hydrolyzing by introducing water vapor as shown in JP-A-61-201604, spherical and amorphous titanium oxide fine particles can be obtained from titanium alkoxide etc., but the particle size is 200 Å. In addition, the particle size distribution was wide, and more than 1% by weight of carbonaceous matter due to unreacted alkoxide remained in the fine particles, which caused problems in terms of purity and other quality. Furthermore, in the Proceedings of the 20th Autumn Conference of the Society of Chemical Engineers (1987), p. 188, it is stated that titanium alkoxides are hydrolyzed and oxidized using an excess amount of steam that is 2 to 30 times the theoretical amount required for hydrolysis. Although it has been shown that ultrafine particles of titanium can be obtained, the particle size of the titanium oxide obtained in this case is all 200 Å or more. [Means for Solving the Problems] Therefore, the present inventors have solved the problems of the above-mentioned prior art, and have created a particle size that is extremely small, has a narrow particle size distribution, and has visible light transmittance and ultraviolet rays. We have conducted intensive research to develop a method that can produce ultrafine particles of metal oxides such as titanium oxide with excellent shielding properties, high purity, and a simple process. As a result, it has been found that the above problems can be solved by hydrolyzing a volatile metal compound in the presence of an extremely excessive amount of water vapor. The present invention was completed based on this knowledge. That is, the present invention vaporizes or atomizes a volatile metal compound and then decomposes it under heating to produce ultrafine metal oxide particles. The present invention provides a method for producing ultrafine metal oxide particles, characterized in that the volatile metal compound is hydrolyzed in an atmosphere containing twice as much water vapor. In the method of the present invention, various volatile metal compounds can be used as raw materials. For example, volatile titanium compounds such as titanium alkoxide and titanium halide; volatile zirconium compounds such as zirconium alkoxide, zirconium halide, and organic zirconium compounds; rare earth metals such as scandium, yttrium, lanthanum, and cerium. Examples include alkoxides. These can be used alone or in combination. Here, specific examples of the titanium alkoxide include titanium tetramethoxide, titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetraisopropoxide, and titanium tetrabutoxide. Further, as the titanium halide, titanium tetrahalide such as titanium tetrachloride can be mentioned as a suitable titanium halide. Furthermore, volatile titanium compounds such as trihalogenated monoalkoxytitanium, monohalogenated trialkoxytitanium, and dihalogenated dialkoxytitanium can also be used. In addition, as zirconium alkoxide,
Specific examples include zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, and zirconium tetrabutoxide. Further, examples of zirconium halides include tetrahalogenated zirconiums such as zirconium tetrachloride and zirconium tetrabromide, and trihalogenated monoalkoxyzirconium, monohalogenated trialkoxyzirconium, dihalogenated dialkoxyzirconium, etc. can also be used. can. It is also possible to use volatile organic zirconium compounds such as zirconium phenoxide. In the method of the present invention, the above-mentioned volatile metal compound is first vaporized or atomized. The conditions for vaporizing or atomizing the volatile metal compound, that is, evaporating or atomizing the volatile metal compound, vary depending on the type of the volatile metal compound and cannot be unambiguously determined. Here, when vaporizing or atomizing the above-mentioned volatile metal compound, it is preferable to dilute the volatile metal compound with a diluent gas to a proportion of 0.01 to 10% by volume. This diluent gas serves as a carrier gas for introducing the vaporized volatile metal compounds into the decomposition furnace where they are decomposed, and if the amount is too small, the vaporization temperature of the volatile metal compounds must be increased. First, there is a risk that the raw material (volatile metal compound) may thermally decompose before being mixed with water vapor, which will be described later, and may clog a vaporizer such as a vaporizer. The diluent gas used here includes inert gases such as argon, helium, and nitrogen, oxygen, and air, with helium and nitrogen being particularly preferred. This diluent gas may be appropriately selected depending on the type of volatile metal compound used as a raw material, the structure of the apparatus, etc. In addition, as a means to vaporize a volatile metal compound, for example, the volatile metal compound used as a raw material is heated using a vaporizer, and a diluent gas is introduced into the vaporizer to convert the volatile metal compound into a gas containing the volatile metal compound. It is introduced into the reactor described later. In addition, when using such a diluent gas (carrier gas), it is not necessary to completely vaporize the volatile metal compound used as the raw material, but some or all of it is introduced into the reactor as a mist using the carrier gas. You may. On the other hand, the amount of water vapor used to hydrolyze the vaporized or atomized volatile metal compound is at least 40 times, preferably 40 to 5000 times, the theoretical amount of water vapor required to hydrolyze the raw material volatile metal compound. , particularly preferably in a range of 40 to 1000 times, and introduced into the reactor to be included in the atmosphere during hydrolysis. The water vapor content in the atmosphere is
When the amount is less than 40 times the theoretical amount, the particle size of the obtained metal oxide fine particles becomes large and the particle size distribution becomes broad. On the other hand, although there is no upper limit to the amount of water vapor,
If it exceeds 5,000 times, the raw material concentration during reaction will inevitably be low, resulting in a decrease in production efficiency. This water vapor may be introduced into the reactor by simply heating water with a vaporizer or the like to evaporate it, or alternatively, it may be introduced into the reactor using a carrier gas as in the case of the volatile metal compound. In the method of the present invention, the volatile metal compound thus vaporized or atomized and water vapor are introduced into a reactor and mixed, and a hydrolysis reaction is performed under heating. For example, in the case of titanium tetraalkoxide (Ti(OR) ₄ ; R represents an alkyl group), this hydrolysis reaction is carried out by the reaction represented by Ti(OR) ₄ +2H ₂ O→TiO ₂ +4ROH. Titanium oxide (TiO ₂ )
is generated. The temperature during this hydrolysis is preferably 600°C or less, particularly preferably in the range of 100 to 450°C. If the temperature during hydrolysis is too low, the hydrolysis reaction will not proceed sufficiently and the amount of undecomposed raw materials remaining as hydrocarbons will increase, and if the temperature is too high, particles with a large specific surface area will not be obtained. Particularly suitable spherical amorphous particles cannot be obtained. In addition, the residence time and flow rate of the raw material (vaporized or atomized volatile metal compound) and water vapor in the reactor for hydrolysis are not particularly limited and can be set as appropriate depending on the situation, but usually It is preferred that the residence time be 0.01 to 10 seconds and the flow rate be 0.01 to 10 m/sec. There are no particular restrictions on the reactor for this hydrolysis, and any commonly used reactor may be used. In the method of the present invention, ultrafine metal oxide particles can be obtained by reacting the vaporized or atomized volatile metal compound with water vapor in a large excess of 40 times or more relative to the theoretical amount. can. These ultrafine metal oxide particles have an extremely small particle size of 50 to 200 Å, and their particle size distribution is also sharp.
It also has excellent transparency against visible light. Note that the metal oxide ultrafine particles generated in this way coalesce with each other in the gas phase while still being heated.
It may not be possible to maintain the ultrafine particle state. Therefore, it is desirable to cool the metal oxide superparticles produced by hydrolysis in the reactor immediately after the reaction to prevent the above-mentioned coalescence. This cooling is carried out to a temperature below which the obtained ultrafine metal oxide particles do not coalesce.It varies depending on the type of product, but usually
The temperature may be 100° C. or less, and it is desirable to install a cooler using air, nitrogen, water, etc. as a cooling source downstream of the reactor, and to continuously introduce the product after the reaction. By such a method, the generated ultrafine metal oxide particles can be collected in their ultrafine form, that is, as primary particles, without being combined. Collection of the metal oxide ultrafine particles can be carried out by common means, such as a membrane filter, a bag filter, an electrostatic precipitator, or the like. [Example] Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1 Ultrafine metal oxide particles were produced using the reaction apparatus shown in FIG. In other words, the raw material titanium tetraisopropoxide (Ti(OC ₃ H ₇ ) ₄ ) was
g/hr, nitrogen gas as carrier gas
The raw material was introduced into a vaporizer 6 heated to 130° C. with a flow rate of 1.05 Nm ³ /hr to completely vaporize the raw material. On the other hand, 880 g/hr of water and 2.65 Nm ³ /hr of nitrogen gas were introduced into the vaporizer 5 heated to 450° C. to prepare heated steam. The amount of steam relative to the raw material at this time was 157 times the theoretical amount required to hydrolyze the raw material. This superheated steam was introduced into the reactor 8 at the same time as the vaporized raw material, and a hydrolysis reaction was carried out at 260°C to obtain ultrafine titanium oxide particles. The flow rate introduced into the reactor at this time was 1.3 m/s on the raw material side and 2.6 m/s on the steam side.
m/s, and the flow rate in the reactor is 0.32
m/sec. Table 1 shows the yield and physical properties of the obtained product. Example 2 In Example 1, the raw material titanium tetraisopropoxide was 189 g/hr, and the water
The same operation as in Example 1 was performed except that 1200 g/hr was replaced with superheated steam along with 2.26 Nm ³ /hr of nitrogen gas. The amount of water vapor relative to the raw material at this time was 50 times the theoretical amount. Table 1 shows the yield and physical properties of the obtained product. Comparative Example 1 In Example 1, water 5.6g/hr nitrogen gas 3.75N
The same operation as in Example 1 was performed except that m ³ /hr and superheated steam were used, that is, the amount of steam was the theoretical amount required for hydrolysis of the raw material. Table 1 shows the yield and physical properties of the obtained product. Comparative Example 2 In Example 1, nitrogen gas 3.75N was applied to the water vapor side.
The same operation as in Example 1 was carried out except that only m ³ /hr was used, that is, no water vapor was introduced. Table 1 shows the yield and physical properties of the obtained product. Comparative Example 3 In Example 2, nitrogen gas 3.75N was applied to the water vapor side.
The same operation as Example 2 was carried out except that only m ³ /hr was used, that is, no water vapor was introduced. Table 1 shows the yield and physical properties of the obtained product. Comparative Example 4 In Example 2, 803g/hr of water was replaced with nitrogen gas.
The same operation as in Example 2 was performed except that superheated steam was used at 2.75 Nm ³ /hr. At this time, the amount of steam relative to the raw material was 33 times the theoretical amount. Table 1 shows the yield and physical properties of the obtained product.

〔Effect of the invention〕

As mentioned above, according to the method of the present invention, the particle size is 50
It is possible to efficiently produce ultrafine metal oxide particles that are extremely small at ~200 Å, have a sharp particle size distribution, and have excellent transparency to visible light and shielding properties to ultraviolet rays. Moreover, the obtained ultrafine metal oxide particles have a small amount of residual unreacted hydrocarbons and the like, and are of high purity and extremely good quality. Furthermore, since it is only necessary to introduce a large excess of water vapor, it is possible to easily produce ultrafine metal oxide particles with desired properties using equipment with a simple configuration, and the amount of carrier gas used can be reduced. Costs can be reduced significantly. Therefore, the metal oxide ultrafine particles obtained by the method of the present invention can be effectively used in various industries as high-quality cosmetics, paints, adsorbents, catalysts, catalyst carriers, etc.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of a reaction apparatus used in the method of the present invention. 1... Nitrogen cylinder, 2... Flow meter, 3
... Water charge pump, 5 ... Water vaporizer, 6 ... Raw material vaporizer, 7 ... Heater, 8 ... Reactor, 9 ... Cooling room, 10 ... Bag filter.

Claims (1)

[Claims] 1. The theoretical amount of water vapor necessary to hydrolyze a volatile metal compound when the volatile metal compound is vaporized or atomized and then decomposed under heating to produce ultrafine metal oxide particles. 1. A method for producing ultrafine metal oxide particles, which comprises hydrolyzing the volatile metal compound in an atmosphere containing 40 times or more water vapor. 2. The method according to claim 1, wherein after hydrolysis, the produced ultrafine metal oxide particles are cooled to a temperature at which they do not coalesce again. 3. The manufacturing method according to claim 1, wherein the hydrolysis is carried out at a temperature of 600°C or lower.