JP3533906B2 - Method for producing hollow oxide powder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow oxide powder that can be used as a catalyst carrier or the like. [0002] Hollow metal oxide particles have a specific surface area that is 5 to 10 times or more as large as solid particles (non-hollow particles), depending on the thickness of the particle shell. Having. For this reason, the hollow oxide particles have a larger particle diameter than solid particles and are easy to handle as long as the specific surface area is the same. Utilizing this specific surface area, the hollow oxide particles can be used as a catalyst carrier. In addition, application to concealing agents, microcapsules, and the like using the hollow shape is expected. Conventionally, as a method for producing porous particles or hollow particles of metal compound composite particles, for example, Japanese Patent Application Laid-Open No.
JP-A-7670 discloses the following method. In this method, first, spherical polymer particles serving as a core are uniformly dispersed in an aqueous solution of a hydrolyzable metal salt, and a uniform metal compound coating layer is provided on the spherical polymer particles. To obtain particles. The particle size of the obtained particles is 0.07 to 30 μm, and the ratio of the inner diameter to the outer diameter of the particles is 0.40 to 0.95. Next, this is heated to decompose the polymer forming the core and convert it into carbon to obtain spherical carbon-metal compound composite particles. This method is complicated and expensive. Further, the precipitation method is used for depositing the surface coating layer. However, in the case of the composite oxide, uniform precipitation of the composite metal oxide particles is difficult due to the difference in the precipitation rate depending on the metal species in the precipitation method. Japanese Patent Application Laid-Open No. 63-258842 discloses an O / W emulsion prepared by adding an organic solvent to an aqueous solution of an inorganic compound and mixing the O / W emulsion with an oleophilic surfactant-containing organic solvent. It is added to a solvent to prepare an O / W / O emulsion. There is disclosed a method of forming hollow particles by adding and mixing an aqueous solution of a compound capable of forming a precipitate of a water-insoluble precursor to the O / W / O emulsion. However, in this method, the precursor formed by precipitation requires calcination,
The process becomes complicated. In addition, since the precipitation method is used, there is a problem in homogeneity. Further, no hollow particles having a surface layer thickness of 20 nm or less have been obtained. [0005] Japanese Patent Application Laid-Open No. 3-47528 discloses that an emulsion is formed by mixing an aqueous solution of a metal compound with a first and a second oil, and water and oil are removed from the emulsion and decomposed to form a metal oxide. There is a disclosure of a method for obtaining ceramic hollow spheres. This method involves complicated steps and produces a hollow precursor by evaporation of water. However, in the case of a composite oxide, it is difficult to obtain homogeneous composite oxide particles due to differences in solubility depending on the metal species. Also in this case, the surface layer 20n
m or less hollow particles were not obtained. Japanese Patent Application Laid-Open No. 60-122779 discloses a method of controlling the pore diameter and the pore diameter distribution by using an alumina / magnesia spinel porous powder obtained by spray pyrolysis as a starting material, and molding and firing it. There is a disclosure that an excellent porous body can be formed. In this method, the size of water droplets to be sprayed becomes one reaction field, but the size of the spray water droplets is several tens of μm under efficient conditions, and the reaction field is one order of magnitude larger than in the emulsion combustion method. Therefore, it tends to be heterogeneous. Although there is no description regarding the thickness of the surface layer, it is considered that hollow particles having a surface layer of 20 nm or less are usually difficult to obtain, considering that one sprayed water droplet becomes one particle. Japanese Patent Application Laid-Open No. Hei 8-91821 discloses a method for producing hollow silica by an alkoxide sol-gel method. In this method, the alkoxide raw material is expensive, and there is no description about the thickness of the surface layer. However, since the obtained silica powder has a large particle size of 2 to 8 μm, it is unlikely that the particles are hollow particles having a surface layer of 20 nm or less. . Further Cera
m. Inter., vol., 14 (1988), 239-244, describes the production of hollow alumina by the emulsion evaporation method. However, in this method, calcination is necessary after preparing the precursor, and the thickness of the surface layer is several hundred nm or more as judged from the SEM photograph. SUMMARY OF THE INVENTION [0008] The present invention has been made in view of the above circumstances, and has as its object to produce a hollow oxide powder having a thin surface layer by a simple process. . [0009] The method for producing a hollow oxide powder according to the present invention is characterized in that an organic solvent is added to an aqueous solution in which at least one metal salt is dissolved and / or suspended, and water droplets are added. An emulsification step of forming a W / O emulsion having a diameter of 100 nm or more, and spraying the W / O emulsion;
A powdering step of burning to form a hollow powder of the metal oxide. The hollow oxide powder obtained by the above-mentioned production method preferably has a shell thickness of 20 nm or less.
The hollow oxide powder obtained by the above production method is preferably a hollow alnium oxide having a shell thickness of 20 nm or less, or a composite oxide containing aluminum as a main component. DETAILED DESCRIPTION OF THE INVENTION The method for producing a hollow oxide powder according to the present invention is characterized in that an organic solvent is added to an aqueous solution in which a metal salt is dissolved and / or suspended to form a W / W powder having a water droplet diameter of 100 nm or more.
Forming an O-type emulsion and spraying and burning the W / O-type emulsion to form a hollow powder of the metal oxide. In the emulsification step of forming an emulsion, a metal forming an oxide is dissolved and an organic solvent is added to an ionic or fine suspension aqueous solution and mixed, and the W / O using an organic solvent as a matrix is used. This is a step of forming a mold emulsion. In order to make the water droplet diameter of this W / O emulsion 100 nm or more, the particle diameter of the water droplet is adjusted by using a surfactant as necessary. The diameter of the water droplet containing the metal forming the oxide in the emulsion is maintained during spraying and combustion, and the reaction field at the time of oxide formation can be controlled. The kind of the metal salt used in the present invention is not particularly limited. For example, any water-soluble metal salt such as metal nitrate, metal acetate, metal sulfate and metal chloride can be used. Further, when the metal salt is in a suspended state, the particle size of the metal salt is 1 μm or less, more preferably 0.1 μm. The type of the organic solvent used is not limited as long as it is hardly soluble in water and can form a W / O emulsion. For example, hydrocarbon-based organic solvents such as hexane, octane, kerosene, and gasoline are preferable. The kind and amount of the dispersing agent added for keeping the W / O emulsion stable are not limited. For example, any of a cationic surfactant, an anionic surfactant, and a nonionic surfactant can be used, and the type and amount of the dispersant are changed according to the type of the aqueous solution, the organic solvent, and the required droplet diameter. Can be used. The pulverization step is a step of spraying and burning the W / O emulsion to form a hollow powder of the metal oxide. When the W / O emulsion is sprayed into the heated reactor, the water droplets containing the sprayed metal are coated with the organic solvent on the outside, so that the organic solvent burns and the metal salt on the organic solvent side is discharged. Oxidation and evaporation of water occur, so that the oxide is formed in a shell shape to form a hollow oxide. The droplet size of the emulsion when sprayed is
It is necessary that the thickness be 100 nm or more in order to form a hollow shape. If the water droplet diameter is less than 100 nm, the water droplet completely contracts before the formation of the oxide crust on the surface side of the water droplet,
The oxide is not preferred because it does not become hollow but solid particles. On the other hand, if the water droplet diameter is larger than 100 μm, the reaction field becomes too large, and it takes time to form an oxide, and the composition of the product may be non-uniform. According to the production method of the present invention, a homogeneous hollow oxide powder having a shell thickness of about 20 nm or less can be easily produced. According to the production method of the present invention, a desired homogeneous, hollow oxide powder having a shell thickness of about 20 nm or less can be directly synthesized from a W / O emulsion of a metal salt solution. The production method of the present invention does not require steps such as drying, calcination, and pulverization as compared with the conventional precipitation method, so that the steps are simple and low cost. Further, in the production method of the present invention, the water droplets of the metal ion solution or the metal ion suspension are oxidized and evaporated instantaneously by combustion, so that powder having the same homogeneity as the water droplet composition is obtained. be able to. Furthermore, in the present production method, the diameter of one water droplet (several nm to several μm) in the W / O emulsion, microemulsion or reverse micelle is the size of one reaction field, and the diameter of the spray water droplet is the size of one reaction field. As compared with the spray pyrolysis method of an aqueous metal ion solution, generation of a temperature distribution can be suppressed, and a more uniform oxide powder can be obtained. When the metal compound is alumina or a composite oxide containing aluminum as a main component, very thin hollow particles are formed. Although the cause is not clear at present, it is presumed that the aluminum oxide has a high rate of forming a surface oxide film, so that a surface oxide film is formed at a stage where water droplet shrinkage is small, and as a result, it becomes extremely thin. The hollow particles obtained by the production method of the present invention have a specific surface area 5 to 10 times or more that of the spherical real particles, depending on the thickness of the surface layer. Therefore, compared to solid particles having the same specific surface area, the particle size is large and easy to handle. The present invention will be described more specifically with reference to the following examples. (Example 1) (Emulsification step) As the aqueous phase, an aqueous solution of aluminum nitrate obtained by dissolving commercially available aluminum nitrate nonahydrate in deionized water at a concentration of 0.1 to 2 mol / L was used. Commercial kerosene was used as the organic solvent. As a dispersant for forming an emulsion, Sunsoft N Co., Ltd.
o818H was used in an amount of 5 to 10% by weight based on kerosene.
The kerosene containing the dispersant was used as an oil phase. The ratio of the water phase to the oil phase is as follows: water phase / oil phase = 40 to
It was mixed so as to be 70/60 to 30 (% by volume). The mixed solution is 1000 to 20,000 using a homogenizer.
The mixture was stirred at a rotation speed of rpm for 5 to 30 minutes to obtain a W / O emulsion. From the result of observation with an optical microscope, the water droplet diameter in the above emulsion was about 1 to 2 μm. (Powdering step) The obtained W / O emulsion is converted into an emulsion combustion reactor developed by the inventors (Japanese Patent Laid-Open No.
No. 81905), the emulsion was sprayed, the oil phase was burned, and the metal ions present in the aqueous phase were oxidized to form oxide powder. The synthesis conditions are controlled in such a manner that the spray flow rate of the emulsion, the amount of air (the amount of oxygen), and the like are controlled so that the sprayed emulsion completely burns and the flame temperature becomes a constant temperature of 700 to 1000 ° C. Was. The obtained powder was collected by a bag filter installed at the rear of the reaction tube. The shape of the obtained oxide powder was examined with a transmission electron microscope (T
(EM). Fig. 1 shows the low magnification TE of the produced powder.
An M image is shown. As shown in FIG. 1, the produced powder was clearly observed to be a very thin hollow particle because the back side of the particle could be clearly observed. FIG. 2 shows a high magnification TEM image of the produced powder. The hollow particles had a surface layer thickness of 10 nm. (Example 2) (Synthesis of spinel powder) Commercially available aluminum nitrate nonahydrate and magnesium nitrate hexahydrate were mixed with Al / Mg = 2/1.
(Molar ratio). This was dissolved in deionized water to prepare an aqueous solution of a mixed solution of aluminum nitrate and magnesium nitrate having a concentration of 0.1 to 2 mol / liter, which was used as an aqueous phase. Oil phase and emulsification process, powdering process,
An oxide powder was synthesized under the same conditions as in Example 1. FIG. 3 shows a high magnification TE of the produced oxide powder.
An M image is shown. As in Example 1, the produced oxide powder was very thin hollow particles, and the thickness of the surface phase was 20 nm.
It was weak. (Example 3) (Synthesis of zirconia powder) A concentration of 0.1 to 2 prepared by diluting a commercially available zirconium oxynitrate solution with deionized water.
A mol / L aqueous solution of zirconium nitrate was used as the aqueous phase. In the oil phase, the emulsifying step, and the powdering step, powder synthesis was performed under the same conditions as in Example 1. FIG. 4 shows a high magnification TEM image of the produced powder. As in Examples 1 and 2, the produced powder was hollow particles. The thickness of the surface phase is slightly thicker than that of Examples 1 and 2, and
〜30 nm. Example 4 (Synthesis of Other Oxide Powders) Commercially available magnesium nitrate hexahydrate, iron nitrate nonahydrate, yttrium nitrate hexahydrate was dissolved in deionized water, and commercially available titanium tetrachloride was used. Was diluted with deionized water to prepare aqueous 0.1 to 2 mol / L metal solutions. In the oil phase, the emulsifying step, and the powdering step, powder synthesis was performed under the same conditions as in Example 1. As a result, it was confirmed that similar hollow particles were obtained for magnesium oxide, iron oxide, yttrium oxide, and titanium oxide. (Example 5) The aqueous phase and the organic solvent of Example 1 were used, and NP6 (polyoxyethylene (6) nonylphenyl ether) was used as a dispersant to be added. Water and NP
By adjusting the molar ratio of 6 between water / NP6 = 10-100, a microemulsion having a water droplet diameter of 100-400 nm was obtained. The powdering step was performed under the same conditions as in Example 1. As a result, similarly to Example 1, it was confirmed that hollow alumina particles having a surface thickness of 20 nm or less were obtained. Therefore, if the water droplet diameter of the emulsion is 100 nm or more, hollow particles can be obtained. (Comparative Example) (Synthesis of alumina powder in a region where water droplet diameter is smaller than 100 nm) As a dispersant, NP6 (polyoxyethylene (6) nonylphenyl ether) was used. Example 5
In the same emulsion preparation step as described above, the molar ratio of water to NP6 was adjusted between water / NP6 = 10 to 100 to obtain a microemulsion having a water droplet diameter of 30 to 80 nm. The powdering step was performed under the same conditions as in Example 1. As a result, the obtained particles did not become hollow. The hollow particles obtained by the production method of the present invention have a specific surface area that is 5 to 10 times or more that of the spherical solid particles. It can be used as a catalyst carrier and the like. Moreover, since it is hollow, it is considered that the thermal conductivity is low, and it can be used as a heat insulating material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a low-magnification T of alumina particles synthesized in Example 1.
3 shows an EM image. FIG. 2 shows a high-magnification T of the alumina particles synthesized in Example 1.
3 shows an EM image. FIG. 3 shows a TEM image of the spinel powder synthesized in Example 2. FIG. 4 shows a TEM image of the zirconia powder obtained in Example 3.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-81905 (JP, A) JP-A-7-96165 (JP, A) JP-A-62-53701 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) C01B 13/34 B01J 13/00

Claims (1)

(57) Claims 1. An organic solvent is added to an aqueous solution in which at least one kind of metal salt is dissolved and / or suspended to form a water droplet having a diameter of 1%.
An emulsification step of forming a W / O emulsion having a size of at least 00 nm; and a pulverization step of spraying and burning the W / O emulsion to form metal oxide hollow powder particles. Of producing hollow oxide powder.