JP2003221227A - Method for producing boehmite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing boehmite enabling the production in a short time with short ageing time, and in a small number of process steps dispensing with washing step with water, dewatering step and filtering step, also capable of producing high purity boehmite with no residual impurities such as Na or Ca efficiently and at a low cost. <P>SOLUTION: This method for producing boehmite comprises dry ageing of an aluminum hydroxide powder under heating in a steam atmosphere using a pressure vessel. Produced boehmite according to the invention sometimes shows a plate shape. Heating temperature is preferably 140 to 300°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is used for flame retardant fillers such as plastics and rubbers, fillers for electronic materials, catalyst carriers, coating fillers for papermaking, pigments for paints, raw materials for high purity alumina, etc. The present invention relates to a method for manufacturing boehmite.

[0002]

2. Description of the Related Art Conventionally, various methods for producing boehmite have been provided, but generally, it is carried out by hydrothermally treating aluminum hydroxide as a raw material. This manufacturing method uses aluminum hydroxide and a reaction accelerator (metal compound).
It consists of a stirring and mixing process of slurry with water added, a hydrothermal treatment process of wet curing while heating in a steam atmosphere with a pressure vessel, a dehydration process of reaction products, a washing process, a filtration process, and a drying process. (For example, JP-A-6-
263437, Japanese Patent Laid-Open No. 2000-86235).

According to the conventional method for producing boehmite by hydrothermal treatment, since hydroxides, oxides, chlorides, sulfates and the like of alkaline earth metals and alkali metals are added to aluminum hydroxide as reaction accelerators, it is washed with water. Since the process is indispensable, impurities such as Na and Ca derived from the reaction accelerator are still liable to remain even after the water washing process, and it is difficult to produce high-purity boehmite. Since the slurry obtained by adding water to aluminum hydroxide is subjected to hydrothermal treatment, the amount charged per batch is restricted, and in addition to the washing step, the dehydration step,
There is a problem that the filtration process is indispensable and the process is complicated. Further, in order to obtain boehmite at a high yield, it has to be aged for a long time, and a production method that can be aged in a short time has been desired in order to improve production efficiency.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional method for producing boehmite, and is a method for efficiently producing high-purity boehmite at low cost with a short production time and a small number of steps. Regarding

[0005]

The method for producing boehmite according to the present invention for solving the above-mentioned problems is characterized in that aluminum hydroxide powder is dry-cured while being heated in a steam atmosphere using a pressure vessel. Here, the dry curing means that the starting aluminum hydroxide is cured in a powder state without adding water. Further, the wet curing used in the present specification is the opposite of dry curing and means curing by adding water to aluminum hydroxide to form a slurry (liquid state). Further, in the above invention, plate-shaped boehmite can be produced. Further, in any of the above inventions, the dry curing can be performed while heating at 140 to 300 ° C.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. Powdered aluminum hydroxide is used as a starting material. In addition, the powdery form also includes a product obtained by drying aluminum hydroxide, which is commercially available in the form of a slurry, into a powdery form. Since the particle size of boehmite produced depends on the particle size of aluminum hydroxide, aluminum hydroxide having various particle sizes can be selected and used in accordance with the required particle size of boehmite. . The particle size of aluminum hydroxide may be adjusted by crushing with a ball mill or the like. In addition, high-purity aluminum hydroxide containing few impurities such as Na and Ca can be used depending on the application.

The above aluminum hydroxide powder is filled in a container, and dry curing is carried out in a pressure container such as an autoclave under a steam atmosphere while heating. The heating temperature is 140 ~
300 degreeC is preferable, 145-250 degreeC is more preferable, 150-180 degreeC is the most preferable. Heating temperature is 1
This is because if the temperature is lower than 40 ° C, boehmite cannot be sufficiently obtained, and if the temperature is higher than 300 ° C, it is not preferable in terms of cost.

After completion of the above dry curing, the autoclave is allowed to cool and then dried to obtain boehmite.
Since the boehmite produced by the production method of the present invention has a low water content, the drying may be omitted depending on the application of the boehmite.

According to the method for producing boehmite of the present invention described above, it is not necessary to add water to make aluminum hydroxide into a slurry form, and the product can be used in the form of powder as it is, so that it can be produced per batch. The charged amount can be increased, which in turn can contribute to the improvement of productivity.
Moreover, since heating energy for water is unnecessary, it is possible to reduce energy cost. Furthermore, by not hydrothermally treating slurry aluminum hydroxide,
Since each process of dehydration, washing with water, and filtration is not required, boehmite can be produced by a simple process, and an additional facility for wastewater treatment is not required, which also reduces the production cost. Further, compared with the case where hydrothermal treatment is performed using slurry aluminum hydroxide, the boehmite obtained in the present invention has less attached water, the drying step can be completed in a short time, and the boehmite can be efficiently produced. .

Further, since a reaction accelerator is not required and only aluminum hydroxide powder as a starting material is sufficient, impurities such as Na and Ca derived from the reaction accelerator do not remain, and high-purity boehmite can be obtained. it can. Further, since a reaction accelerator is not necessary, it is possible to reduce the manufacturing cost.

According to the boehmite production method of the present invention, boehmite can be produced in a short time. The method for producing boehmite of the present invention is suitable for producing plate-like boehmite, but it is also possible to produce other forms of boehmite such as needles by examining the production conditions.

[0012]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

The relationship between the yield (%) of boehmite obtained after aging for a predetermined time and the aging (reaction) time, the particle size and the aspect ratio were examined for each Example and Comparative Example. Example 1
In Example 5, as shown in Tables 1 to 4, 1 kg of aluminum hydroxide powders each having a different particle size was filled in a container, and a dry type while heating at a predetermined temperature for a predetermined time in a saturated steam atmosphere using an autoclave. I was cured. After curing, the autoclave was naturally cooled and dried at 130 ° C to obtain a plate-shaped boehmite.

In Comparative Examples 1 to 6, as shown in Tables 1 to 4, 1 kg of aluminum hydroxide powder having different particle diameters and a predetermined amount of water were placed in a container and sufficiently stirred and mixed to form a slurry. Using an autoclave in a steam atmosphere,
Wet curing was performed while heating at a predetermined temperature for a predetermined time. After curing, plate boehmite was obtained through the steps of dehydration, washing with water, filtration and drying. In addition, about Comparative Example 3-5, the reaction accelerator was added (Comparative Example 3 and Comparative Example 4: Na.
OH, 85.5 g (versus Al (OH) ₃ 16.7 mol%,
Comparative Example 5: CaAc ₂ , 251.0 g (vs. Al (OH))
₃ 11.1 mol%)). The amount of water added to aluminum hydroxide was 5 kg in each of Comparative Example 1, Comparative Example 3, and Comparative Example 6, 10 kg in Comparative Example 2, and Comparative Example 4 and Comparative Example 5.
Then, it was 3 kg each. In Table 2, CaAc ₂ is calcium acetate monohydrate.

The results are shown in Tables 1 to 4. Example 1
The yield reached 100% in 1 hour after dry curing, but it took a long time in Comparative Example 1 and Comparative Example 2 (see Table 1). In Comparative Example 3, the yield was almost 100% in 5 hours. In Example 2 in which the particle size of aluminum hydroxide was larger than that in Example 1, the yield reached 100% in 3 hours and could be produced in a shorter time than in Comparative Examples 4 and 5 to which the reaction accelerator was added ( See Table 2). In Example 3 in which the particle size was the same as in Example 1 and the heating temperature was 150 ° C. for dry curing, the yield was 10 in 5 hours.
Comparative Example 6, which reached 0%, was wet-cured under the same conditions.
Even 6 hours was only 39% (see Table 3). Also,
From Example 5 and Example 6, it was found that the manufacturing method of the present invention can be applied even when the particle size of aluminum hydroxide is large, and plate boehmite having a large particle size can be manufactured in a short time.

Comparative Examples 3 to 5 to which a reaction accelerator was added
Then, even if the washing step is repeated, Na contained in the plate boehmite is 0.1 wt% (measured representative value in terms of Na ₂ O,
Comparative Example 3 and Comparative Example 4), Ca is 0.5 wt% (C
It is a measured representative value in terms of aO, see Comparative Example 5), and Na and Ca derived from the reaction accelerator could not be sufficiently removed. On the other hand, in Examples, since the plate-shaped boehmite does not contain Na or Ca derived from the reaction accelerator,
For example, when high-purity aluminum hydroxide having a Na content of 0.002 wt% (as Na ₂ O) is used as a starting material, extremely high-purity plate boehmite can be easily obtained.

As is clear from Tables 1 to 4, the particle size of the plate-shaped boehmite obtained by the production method of the present invention corresponds well to the particle size of aluminum hydroxide as a starting material and has a desired particle size. Plate boehmite can be easily manufactured.

Further, comparing the dry-cured example without adding the reaction accelerator and the wet-cured comparative example, a plate-shaped boehmite having a relatively large aspect ratio was obtained in the example (Example 1). And Comparative Example 1, Comparative Example 2, Example 3 and Comparative Example 6). From this, according to the method for producing plate-like boehmite of the present invention, it is possible to produce high-purity plate-like boehmite having a large aspect ratio without adding a reaction accelerator. The aspect ratio is the ratio of the major axis and the thickness of the plate boehmite.

The plate boehmite was identified by X-ray diffraction. In addition, FIGS.
The electron micrograph images of Example 3 are shown, and FIGS. 4 and 5 show the electron micrograph images of Comparative Example 1 and Comparative Example 5, respectively, in which plate-shaped boehmite was observed. The yield of plate boehmite was derived by X-ray diffraction and thermogravimetric analysis (TG).

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

Since the present invention is configured as described above, it has the following effects. According to the present invention, aluminum hydroxide can be used as a powder as it is without adding water to the production, so that the amount of charge per batch can be increased, and thus the production of boehmite that contributes to the improvement of productivity. A method can be provided. Further, it is possible to reduce the energy cost by not requiring heating energy for water and the manufacturing cost by not requiring an auxiliary facility for wastewater treatment, and it is possible to provide an inexpensive method for producing boehmite. It is possible to provide an efficient method for producing boehmite with simple steps, since each step of dehydration, washing with water, and filtration is unnecessary. Further, since the amount of water attached to the obtained boehmite is small, the drying step can be completed in a short time, and the boehmite can be efficiently produced.

Further, according to the present invention, since the reaction accelerator is not necessary and only the aluminum hydroxide powder as the starting material is sufficient,
High-purity boehmite can be produced without leaving impurities such as Na and Ca derived from the reaction accelerator. Also,
Since a reaction accelerator is unnecessary, it is possible to reduce the manufacturing cost.

Further, according to the present invention, since boehmite can be produced in a short time, it is possible to provide an inexpensive method for producing boehmite which is excellent in productivity.

From the above, it goes without saying that the boehmite produced by the production method of the present invention can be used as a flame-retardant filler such as plastic or rubber, a catalyst carrier, an internal filler for papermaking coatings, a pigment for coatings and the like. Therefore, since high-purity boehmite can be obtained, it can be used as a filler of an electronic material, an insulating material, a raw material of high-purity alumina, and the like.

[Brief description of drawings]

FIG. 1 shows an electron micrograph image of the plate-shaped boehmite produced in Example 1.

FIG. 2 shows an electron micrograph image of the plate-shaped boehmite produced in Example 2.

FIG. 3 shows an electron micrograph image of a plate-shaped boehmite produced in Example 3.

FIG. 4 shows an electron micrograph image of the plate-shaped boehmite produced in Comparative Example 1.

FIG. 5 shows an electron micrograph image of the plate-shaped boehmite produced in Comparative Example 5.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirokazu Kikata             Kawai Lime Works, 2093 Akasaka-cho, Ogaki City, Gifu Prefecture             Business F-term (reference) 4G076 AA10 AB06 BA24 BA43 BA45                       BD02 CA08 DA01 DA02 DA15                       FA08

Claims (3)

[Claims] 1. A method for producing boehmite, which comprises subjecting aluminum hydroxide powder to dry curing while heating in a steam atmosphere in a pressure vessel. 2. The method for producing boehmite according to claim 1, wherein the boehmite produced is plate-shaped. 3. The method for producing boehmite according to claim 1 or 2, wherein the heating temperature is 140 to 300 ° C.