JPH0757689B2 - Method for producing porous spherical alumina - Google Patents

Description

The present invention relates to a method for producing fine porous spherical alumina.

[Conventional technology]

Alumina is naturally produced as corundum, ruby, etc.,
It can be obtained by igniting aluminum hydroxide, but they are all dense crystalline.

It is also possible to form an alumina molded body containing fine pores by molding and sintering granular alumina,
The diameter of several millimeters or more can be produced by this method. JP-A-61-174103 describes that when a slurry of a mixture of alumina sol and alumina hydrogel is spray-dried, porous true spherical alumina fine particles are obtained, but the average particle diameter is formed by this method. Is an ultrafine particle having a particle size range suitable for a pigment of about 4 μm, and is mainly used as a powder.

[Problems to be Solved by the Invention]

As is well known, alumina has excellent heat resistance and chemical stability and is widely used as a catalyst carrier, an adsorbent and the like. In the case where it is provided for these uses, it is expected that making the alumina porous and in the form of fine spheres will increase the specific surface area and improve the fluidity to produce various advantages. In addition, the use of a fine spherical shape may cause a use that could not have been considered in the conventional large porous alumina sintered body.

Then, the objective of this invention is providing the manufacturing method of porous spherical alumina which can manufacture a finer particle | grain than mechanical forming method.

[Means for Solving the Problems]

The method for producing porous spherical alumina according to the present invention comprises dissolving one or more aluminum compounds selected from the group consisting of aluminum alkoxides and aluminum phenoxides in an organic solvent, and substantially mixing the resulting solution with the solvent. It is insoluble and does not dissolve the aluminum compound and dissolves water and is added to an organic solvent having a relatively high specific gravity, and the aluminum compound solution is dispersed in fine droplets by stirring, and water is added to the formed dispersion to add aluminum. It is characterized in that the compound is hydrolyzed, and the resulting particulate aluminum hydroxide is separated and baked. Although the porous spherical alumina obtained by the production method of the present invention has a fine particle size of 100 μm or less, the pores in the sphere are also extremely fine, and all of them are open to the surface of the sphere. It is evenly distributed throughout the pores. Typical pores are elongated and extend substantially linearly from the surface portion toward the core. The amount of the pore portion is about 25 to 55 vol% depending on the production conditions, so that this porous spherical alumina has a bulk density (bulk density of individual spheres) of about 0.7 to 1.2 g / cm ^3. .

In this production method, aluminum alkoxide used as a starting material is aluminum isopropoxide,
Lower alkoxides such as methoxide, ethoxide and normal butoxide are suitable.

Hereinafter, it is referred to as aluminum alkoyside in the sense of including aluminum phenoxide.

As the organic solvent for dissolving the aluminum alkoxide, benzene, toluene, an aromatic hydrocarbon such as xylene, or a mixed solvent of an alcohol and an aromatic hydrocarbon (for example, a mixture of dehydrated methanol and tolue, methanol or ethanol and benzene and Are suitable).

The organic solvent used as the dispersion medium of the aluminum alkoxide solution must have the following properties.

Substantially incompatible with the solvent of the aluminum alkoxide solution.

 Do not dissolve aluminum alkoxide.

The above is necessary for forming a stable dispersion liquid containing the aluminum alkoxide solution as the dispersoid.

Melting water. This is necessary for the water added to cause the hydrolysis of the aluminum alkoxide to reach the dispersoid surface quickly and uniformly.
However, since very little water needs to be added for hydrolysis, the solubility of water in the solvent need not be particularly high.

High specific gravity compared to the solvent of aluminum alkoxide solution. If the specific gravity is low, the dispersoid composed of the aluminum alkoxide solution cannot maintain a suspended state and is likely to settle.

Examples of the solvent satisfying these requirements are as follows, and most preferred is formamide. Solvent Specific gravity Formamide 1.14 Ethylene glycol 1.11 Glycerin 1.26 Formamide-ethanol 1.07 A solution of aluminum alkoxide is preferably about 0.75
Adjust to a concentration of ~ 2.00 mol /. In addition to aluminum alkoxide, a small amount of other metal alkoxide such as zirconium alkoxide and calcium alkoxide can be added to this solution. This solution is added to a solvent serving as a dispersion medium and stirred. Alternatively, the aluminum alkoxide solution may be injected or dropped from a thin nozzle while stirring the dispersion medium. By selecting the stirring conditions, the aluminum alkoxide solution can be dispersed as fine droplets in the dispersion medium. The droplets naturally become spherical due to the interfacial tension. In this process, the dispersion times must be anhydrous. If water is included even if the dispersion ratio is a trace amount, the aluminum alkoxide is hydrolyzed at the same time as the mixing, and a clean spherical product cannot be obtained.

Once the aluminum alkoxide solution is dispersed in sufficiently fine droplets, the amount of water required to hydrolyze the aluminum alkoxide is added in small portions with continued stirring. The added water molecules, after being dissolved in the dispersion medium, reach the droplet surface of the aluminum alkoxide solution and react with the aluminum alkoxide to hydrolyze it. Hydrolysis starts from the entire surface of the spherical droplet, and the aluminum hydroxide mass that is produced grows while squeezing out the alkoxide solvent, leaving innumerable minute gaps from which the solvent has escaped. To form a set of columns extending radially from. After the hydrolysis, the aluminum hydroxide mass formed is heavy and settles in the dispersion medium.

The precipitated aluminum hydroxide lumps are separated from the dispersion medium so as not to be crushed, washed, and dried. Furthermore, about 1000
When dehydration, crystallization and sintering are performed by heating to ℃ or more, preferably 1200 to 1600 ℃, alumina is generated while maintaining the structure with the gaps of the aluminum hydroxide lumps, and porous spherical alumina is obtained. To be

〔Example〕

Example 1 100 ml of a benzene solution containing 124 mmol of aluminum isopropoxide was added to 200 ml of formamide, treated with a disperser for 1 minute and dispersed, and then 200 ml of water sufficient for hydrolysis of aluminum isopropoxide was added. . Then, a lump of aluminum hydroxide generated by hydrolysis was separated by decantation, washed with acetone, and then dried. This was further baked at 1500 ° C. for 1 hour.

The obtained alumina particles were spherical and had an average diameter of about 20 μm. In addition, a structure in which alumina particles of about 0.5 to 2 μm were aggregated was recognized, and continuous air holes were formed as gaps between the particles. As a result of powder X-ray analysis, it was confirmed to be alumina α-alumina.

Example 2 Benzene solution containing 6.20 mmol aluminum isopropoxide and 1.55 mmol calcium ethoxide.
Add 5 ml into 150 ml of formamide and mix at 70-75 ° C for 15 minutes.
Stir with a stirrer to disperse. Then 1 ml of water sufficient for hydrolysis was added. Spherical aluminum hydroxide produced by hydrolysis of aluminum isoproxide was separated by decantation, washed with formamide, and further washed with acetone and water. When dried and calcined at 1500 ° C., spherical porous alumina having an average particle size of about 100 μm was obtained. The stomata extended randomly in the sphere.

Example 3 6.20 mmol aluminum isopropoxide, 0.705
Benzene solution containing 5 mM calcium ethoxide and 0.321 mM zirconium butoxide 5 m
l was added to 150 ml of formamide and dispersed by stirring with a stirrer at 70 to 75 ° C for 15 minutes. Then 1 ml of water sufficient for hydrolysis was added. Spherical aluminum hydroxide produced by hydrolysis of aluminum isopropoxide was separated by decantation, washed with formamide, and further washed with acetone and water. When dried and calcined at 1500 ° C., spherical porous alumina having an average particle diameter of about 60 μm was obtained. The pores were elongated and arranged radially.

〔The invention's effect〕

Although the porous spherical alumina according to the present invention has a fine particle size of 100 μm or less, the pores in the sphere are also very fine, and all of them have the diameter of the continuous ventilation hole that opens on the surface of the sphere. The specific surface area is extremely large because it is evenly distributed over, and therefore, it exhibits superior performance to conventional alumina when used as a catalyst carrier or adsorbent.

Also, by being made of alumina with excellent heat resistance and chemical stability, and having a high percentage of fine pores,
It is an extremely versatile material that can be used for heat insulating materials, fillers, filter media, etc.

According to the production method of the present invention, it is possible to easily produce this fine porous spherical alumina, which cannot be produced by a mechanical forming method. It is also an advantage of the production method of the present invention that the shape and orientation of the pores can be easily changed by using a small amount of another metal compound together with the aluminum compound or adjusting the hydrolysis conditions.

Claims (2)

[Claims] 1. An aluminum compound in which one or more kinds of aluminum compounds selected from the group consisting of aluminum alkoxides and aluminum phenoxides are dissolved in an organic agent, and the resulting solution is substantially incompatible with the solvent. Is added to an organic solvent of relatively high specific gravity that does not dissolve and dissolves water, and the aluminum compound solution is dispersed in fine droplets by stirring, and water is added to the formed dispersion liquid to hydrolyze the aluminum compound, A method for producing a porous spherical alumina, characterized in that the produced particulate aluminum hydroxide is collected and calcined. 2. One or more aluminum compounds selected from the group consisting of aluminum alkoxides and aluminum phenoxides are dissolved in an organic solvent substantially incompatible with formamide, and the resulting aluminum compound solution is added to formamide. The aluminum compound solution is dispersed in the form of fine droplets by stirring, water is added to the formed dispersion liquid to hydrolyze the aluminum compound, and the resulting particulate aluminum hydroxide is fractionated and baked. Method for producing porous spherical alumina.