JPH0438690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alumina porous body, and more specifically, the present invention relates to a method for producing an alumina porous body, and more particularly, the present invention relates to a method for producing an alumina porous body, and more particularly, aluminum salt powder or a concentrated solution thereof having water of crystallization, such as aluminum sulfate powder, aluminum nitrate powder, or a concentrated solution thereof, is heated. The present invention relates to a method for producing an alumina porous material that is foamed to have a large amount of fine air bubbles, is extremely porous, has a very low bulk density, and is particularly suitable as a catalyst carrier, an adsorbent, a filter, and a high-temperature heat insulating material.

Alumina is widely used industrially because it has high heat resistance, chemical stability, and chemical resistance. In particular, porous alumina and alumina bubble molded products have a wide range of uses as catalysts, catalyst carriers, adsorbents, filters, and high-temperature insulation materials.

However, conventional methods for producing porous alumina bodies include the following methods, each of which has drawbacks. Namely, 1. A method in which fused alumina is blown away with an air jet to form bubbles, and the bubbles are solidified with a binder. 2. Polyaluminaxane is dropped into a medium to form spherical objects, and the spherical objects are separated and fired to form alumina micro-hollows. Method 3: Mixing a combustible material with an alumina raw material, molding it, and then firing it to burn out the combustible material. Method 4: Mixing a foaming agent with an alumina slurry raw material and firing it. Method 5 There is a method in which an alumina slurry raw material is fixed to a urethane foam and then the urethane foam is burnt out by firing, but each method has various drawbacks. A common drawback of these manufacturing methods is that they are complicated and the manufacturing costs are high. Furthermore, in 1), the alumina becomes fibrous during bubble production, resulting in a poor bubble yield, and in 2), although 1) has the same drawbacks, the final product has uniform bubbles because the bubbles are mixed with a binder and molded. The reason for this is that it is difficult to become a porous body.

The inventors of the present invention have conducted various studies on a method for producing porous alumina that does not have these drawbacks, and found that by selecting an aluminum salt containing water of crystallization as a raw material, the production process is simple, extremely stable bubbles can be introduced, and the bulk density can be reduced. The present invention was completed by discovering a method for producing an alumina porous body that is small and inexpensive to produce. The gist is a method for producing an alumina porous body by heat-treating aluminum sulfate and/or aluminum nitrate containing water of crystallization, or a concentrated solution thereof under specific conditions.

To describe the present invention in more detail, one of the aluminum salts having water of crystallization such as aluminum sulfate (Al ₂ ( _{SO 4} ) 3.3-18H ₂ O) and aluminum nitrate (Al(NO ₃ ) _{3.9H 2} O) The seeds or two seeds are crushed to less than about 300 mesh, or left in powder form without being crushed,
Alternatively, a concentrated solution by adding a solvent such as water to the salt is placed in a heat-resistant container, such as a platinum crucible, and heated in an electric furnace. The heating rate and heating temperature are 0.5 to 30°C per minute and 980°C or higher, respectively.

In the method of the present invention, various porous alumina bodies can be obtained by controlling the starting raw materials, the amount of raw materials, the heating rate, and the maximum heating temperature. For example, several grams to 10 grams of aluminum sulfate (18 hydrate) are placed in a platinum crucible with an internal volume of approximately 30 c.c. and heated at 10°C per minute.
When heated to 980℃, χ alumina porous material is obtained,
Further heating to 1100°C or higher yields an α-alumina porous material. Also aluminum nitrate (9 hydrate)
Now, keeping the other conditions the same as for aluminum sulfate,
When heated to 1000℃ or higher, an α-alumina porous material is obtained.

The atmosphere in the electric furnace during the heating process may be an oxidizing atmosphere, a reducing atmosphere, a neutral atmosphere, or a corrosive atmosphere such as hydrogen sulfide, but air is economically advantageous.

For example, in the case of aluminum sulfate 18 hydrate, the raw material begins to foam when it reaches approximately 120°C after heating begins.
Foaming ends at about 380°C, but in order to complete desulfurization and create a porous alumina material, it is preferable to heat the material to 980°C or higher.

When the raw material used in the method of the present invention is used in the form of powder, it is preferably 300 mesh or less. If the particle size of the raw material is coarse, the bubbles in the porous body will become coarse and a product with small bubbles will be obtained. In addition, in order to obtain uniform bubbles, it is better to adjust the particle size of the raw material within the narrowest possible range.

The raw material may be used as a powder, or it may be heat-treated after being made into a concentrated solution by adding a solvent such as water. In addition, the solution concentration should be as high as possible.

If it is desired to obtain even finer bubbles, it is advantageous to heat the atmosphere in the electric furnace under pressure. The temperature increase rate in the electric furnace is preferably 0.5 to 30°C/min; if the temperature increase/decrease is slow, fine bubbles are obtained, and if it is fast, coarse bubbles tend to occur.

In carrying out the present invention, if inorganic fibers, such as alumina fibers cut into short lengths, are added and mixed into the raw materials in advance, an alumina porous body containing fibers can be produced.

Next, examples of the present invention will be shown.

Example 1 Aluminum sulfate 18 hydrate, a reagent, was ground to 300 mesh or less and used as a starting material.

3 g of the pulverized raw material was taken and placed in a platinum crucible with an internal volume of 10 cm ³ and inserted into a horizontal electric furnace. A porous body was obtained by heating to about 980°C at a constant heating rate of 10°C/min. The bulk density was approximately 0.08 g/ml. X
Line powder diffraction measurements showed an extremely amorphous pattern and it was identified as χ alumina.

This porous body was further heated to 1100° C. and allowed to cool, yielding an α-alumina porous body having a bulk density of about 0.14 g/ml.

Example 2 Reagent hydrated aluminum sulfate (14-18 hydrate) 50
g was crushed to 44 mm or less, placed in a sintered alumina mold with internal dimensions of 5 x 10 x 2 cm, heated at a temperature increase rate of 10°C/min to 1000°C, and held at that temperature for 30 minutes. A porous alumina material identified by diffraction as η alumina (bulk density approximately 0.06 g/ml) was obtained.

The structure of this alumina porous material is composed of bubbles with a diameter of about 0.1 mm, and the walls (1 to 3 μm thick) are made up of extremely fine η-alumina particles (estimated to be about 30 Å from the broadening of the X-ray diffraction peak). The specific surface area was relatively large, and the specific surface area measured by the BET 1-point method was 156 m ² /g. This is extremely large compared to the specific surface area of 1 m ² /g (measured by the same method as above) of expanded pearlite, which was initially thought to have a similar structure.

Moreover, since this alumina porous body is composed of independent cells, it has high heat insulation properties, and its thermal conductivity at 20 to 25°C was 0.028 Kcal/m·h·°C.

Example 3 Reagent hydrated aluminum sulfate (14-18 hydrate) 50
g was dissolved in 50 c.c. of water to make a concentrated solution, and heated in an evaporating dish to evaporate some of the water to obtain a viscous liquid.
This was poured into the same mold as in Example 2, cooled at room temperature to solidify, and then heated in the same manner as in Example 2.

The obtained porous alumina material (identified as η alumina by X-ray diffraction) had almost the same structure and properties as the porous material of Example 2, with a bulk density of 0.06 g/ml and a specific surface area of 150 m ² /g. , the thermal conductivity at 20-25℃ is
It was 0.031Kcal/m・h・℃.

Claims (1)

[Claims] 1 Aluminum sulfate powder with water of crystallization and/or
or aluminum nitrate powder, or their concentrated solutions at a heating rate of 0.5-30℃ per minute and 980℃
1. A method for producing an alumina porous material, characterized by heat treatment at a heating temperature of ℃ or higher.