JPH0457611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing boehmite. Boehmite is usually produced by hydrothermally treating gibbsite. Therefore, in order to economically advantageously produce boehmite on an industrial scale, it is important to keep the temperature of the hydrothermal treatment low to reduce utility.

The inventors of the present invention have conducted intensive studies in view of the above circumstances, and have found that the temperature of this reaction can be significantly lowered if a specific compound is present in the aqueous slurry of boehmite-forming compounds and hydrothermal treatment is carried out. The present invention was completed based on these findings.

That is, the gist of the present invention is to provide an aqueous slurry of a boehmite-forming compound to a water slurry containing the boehmite-forming compound.
A method for producing _boehmite , which comprises hydrothermally treating 100 parts by weight of boehmite in the presence of at least 0.05 parts by weight of a calcium compound in terms of _Ca. The present invention will be explained in detail below.

Boehmite-forming compounds used in the present invention include, for example, gibbsite, bayerite, ρ-alumina, etc. under hydrothermal treatment conditions at a temperature of 100°C or higher.
Aluminum-containing compounds are used that produce boehmite. These can be used alone or as a mixture of two or more. The amount of water used is usually selected from the range of 30 to 300 parts by weight per 100 parts by weight of the boehmite-forming compound. If the amount of water is too small, the viscosity of the water slurry will become high, making operations such as stirring difficult, while if it is too large, an unnecessary heat source will increase during the hydrothermal treatment, which is not economical.

Calcium compounds include CaO, Ca(CH) ₂ ,
A calcium compound is used that supplies calcium ions into the water slurry during the hydrothermal treatment of CaAl ₂ O ₄ , etc., and the amount thereof is at least 0.05 parts by weight in terms of Ca per 100 parts by weight in terms of Al ₂ O ₃ of the boehmite-forming compound. Department. If the boehmite obtained is made into a molded product if the amount of Ca is too large, its heat resistance and chemical resistance will decrease, so the amount of Ca should be 0.05 to 20.
parts by weight, preferably 0.1 to 10 parts by weight.

Hydrothermal treatment is usually 1Kg/ ^cm2G at 100℃ to 400℃
When hydrothermally treating an aqueous slurry of a boehmite-forming compound in the presence of a calcium compound according to the method of the present invention, the aqueous slurry of a boehmite ^- forming compound is treated with calcium. The temperature, pressure, and time during treatment can be reduced compared to when hydrothermal treatment is performed in the absence of a compound.

For example, when gibbsite is hydrothermally treated without the presence of calcium compounds, it usually takes several hours at a temperature of 180°C or higher, but according to the method of the present invention,
Hydrothermal treatment can be carried out for 3 to 4 hours even at temperatures lower than 180°C.

Furthermore, in the present invention, the crystal shape of the boehmite obtained can be changed by hydrothermally treating the boehmite-forming compound in the presence of an organic compound having an alcoholic hydroxyl group in addition to a calcium compound.

That is, normally, the crystal external shape of boehmite is monoclinic columnar, and the longest length in the a-axis direction is the length between opposing crystal planes perpendicular to the c-axis direction (hereinafter referred to as the length in the c-axis direction). Boehmite or pseudo-boehmite with a large ratio (hereinafter referred to as a-axis length/c-axis length ratio) had poor crystallinity. Boehmite with good crystallinity could not have an a-axis length/c-axis length ratio of 10 or more and a longest length in the a-axis direction of 2000 Å or more. (In other words, in conventionally known boehmite, the longest length in the a-axis direction is
When the thickness was 2000 Å or more, the a-axis length/c-axis length ratio was 5 or less. ) However, in the present invention, by making a calcium compound and an organic compound having an alcoholic hydroxyl group exist during hydrothermal treatment, the a-axis length/c-axis length ratio is 10 or more and the longest length in the a-axis direction is Boehmite with a thickness of over 2000Å can be obtained.

Various organic compounds can be used as the organic compound having an alcoholic hydroxyl group, but usually a compound having a boiling point higher than the temperature during hydrothermal treatment is used. Furthermore, although those having one hydroxyl group may be used, those having two or more hydroxyl groups are preferable. Specific examples include ethylene glycol, polyvinyl alcohol, hydroxyethyl cellulose, etc., and the amount used is determined to form boehmite. It is selected from the range of 0.01 to 100 parts by weight, preferably 0.1 to 50 parts by weight, based on 100 parts by weight of the compound in terms of Al ₂ O ₃ . When the boehmite obtained by the method of the present invention is made into a molded product, it has excellent heat resistance and high strength. Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 100 parts by weight of gibbsite, 0.8 parts by weight of calcium hydroxide and 90 parts by weight of water were stirred at room temperature to obtain a water slurry. After this water slurry was cast into a mold, it was subjected to hydrothermal treatment at 167°C and 6.5 kg/cm ² G for 4 hours, and then dried at 100°C for 24 hours to obtain a boehmite molded body. The remaining amount of gibbsite in the molded body was determined by X-ray diffraction, and it was only a trace.
The entire amount of gibbsite was converted to boehmite by hydrothermal treatment at 167°C for 4 hours.

Example 2 100 parts by weight of gibbsite, 0.8 parts by weight of calcium hydroxide and 10% aqueous solution of polyvinyl alcohol
100 parts by weight was stirred at room temperature to obtain a water slurry.
This water slurry was treated in the same manner as in Example 1 to obtain a boehmite molded body. When the remaining amount of gibbsite in the molded article was determined in the same manner as in Example 1, it was found that substantially no gibbsite remained.

In addition, the crystal outline of the boehmite obtained in this way has a length between opposing crystal planes perpendicular to the c-axis of approximately
800 Å, and the longest length in the a-axis direction is approximately
20000 Å, and the ratio of the latter to the former is 25.0.

Comparative Example 1 100 parts by weight of gibbsite and 90 parts by weight of water were stirred at room temperature to obtain a water slurry. This slurry was treated in the same manner as in Example 1, but no boehmite was obtained, and gibbsite remained.

Note that the treatment temperature when this water slurry was converted to boehmite by hydrothermal treatment for 4 hours was 183°C.

Claims (1)

[Claims] 1. The water slurry of the boehmite-forming compound is converted into 100% of the boehmite-forming compound in terms of _{Al2O3 .}
A method for producing boehmite, which comprises hydrothermally treating the boehmite in the presence of at least 0.05 parts by weight of a calcium compound calculated as Ca.