JPH068173B2 - Method for producing lithium aluminum powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing lithium aluminate powder.

More specifically, it relates to a method for producing a fine high surface area lithium aluminate powder used as a raw material for an electrolyte tile of a molten carbonate fuel cell.

(Prior Art) Since an electrolyte tile of a molten carbonate fuel cell holds an alkali carbonate melt (Li ₂ CO ₃ / K ₂ CO ₃ ) at around 650 ° C., its raw material is a fine powder having heat resistance and alkali resistance. A high surface area powder is required. At present, lithium aluminate (LiAlO ₂ ) is selected from the viewpoint of melt resistance stability, and γ-type lithium aluminate having a surface area of 15 m ² / g or more is desired from the viewpoints of electrolyte retention and thermal stability.

The following methods are known as methods for producing lithium aluminate used for electrolyte tiles.

(1) Alumina (γ-Al ₂ O ₃ or α-Al ₂ O ₃ ) and Li ₂ CO ₃ are dry-mixed and heat-treated (JP-A-52-48600).

(2) Alumina (γ-Al ₂ O ₃ or α-Al ₂ O ₃ ) and lithium hydroxide are wet-mixed, dried and heat-treated (JP-A-53-53).
136638).

(3) Flux of alumina and lithium hydroxide (NaCl / KCl
Alternatively, it is heat-treated in LiCl / KCl) (JP-A-58-45118).

(4) A powder obtained by hydrolyzing a mixture of aluminum alkoxide and lithium alkoxide is heat-treated (Japanese Patent Laid-Open No. 53-87772).

The γ-type lithium aluminate obtained by the methods (1) and (2) has a drawback that only particles having a large particle size and a small surface area can be produced.

The lithium aluminate powder obtained from the direction of (3) is γ
A mold having a relatively high surface area of 10 to 20 m ² / g can be obtained, but it has a drawback that the chloride used in the flux cannot be completely removed.

The lithium aluminate powder obtained from the method (4) is fine γ type having a high surface area, but it is difficult to handle because the raw material lithium alkoxide has large hygroscopicity and easily aggregates, and it is expensive and available. It has the drawback of being difficult to do.

(Problems to be Solved by the Invention) As a result of various studies to improve the above-mentioned inconvenience, the present inventors have wet-mixed a specific alumina hydrate and lithium hydroxide, and calcined this mixture. The obtained lithium aluminate powder was fine and had a high surface area, and was found to be suitable as a material for an electrolyte tile of a molten carbonate fuel cell, and completed the present invention.

(Means for Solving Problems) The present invention provides boehmite, pseudo-boehmite, diaspore,
One or two or more kinds of alumina hydrate selected from the group consisting of gibbsite and bayerite and lithium hydroxide are wet-mixed in the presence of a solvent, and then the dissolution ratio is removed to obtain a solid content of 650 A method for producing a γ-type lithium aluminate powder, which comprises firing at a temperature in the range of ℃ to 1000 ℃.

The alumina hydrate used in carrying out the method of the present invention is
One or more selected from boehmite, pseudo-boehmite, diaspore, gibbsite and bayerite. These alumina hydrates can be obtained by methods such as hydrolysis of alkali aluminate, aging of aluminogel and hydrolysis of aluminum alkoxide. Boehmite, pseudo-boehmite, diaspore, gibbsite or alumina hydrate having a crystal structure other than bayerite, for example, when γ-alumina or α-alumina is used as a raw material, the activity of alumina may be low, so that the powder after firing has a There are disadvantages that unreacted alumina remains and only γ-type lithium aluminate having a large particle size and a small surface area can be obtained.

The solvent used in the present invention is water; saturated aliphatic hydrocarbons such as hexane, heptane, octane, paraffin oil and kerosene;
Unsaturated aliphatic hydrocarbons such as pentene, hexene, heptene, octene, decene; alicyclic compounds such as cyclopentane, cyclohexane, cyclohexene; aromatic hydrocarbons such as benzene, toluene; methanol, ethanol, propanol, butanol, etc. One or more selected from alcohols; ketones such as acetone methyl ethyl ketone and methyl isobutyl ketone; ethers such as diethyl ether, tetrahydrofuran and dioxane. In particular, water, methanol, etc. in which lithium hydroxide is dissolved are preferably used because the surface area of the obtained lithium aluminate becomes particularly large.

The lithium hydroxide used in the present invention is preferably a powder or a monohydrate which becomes powder when wet mixed.

In practicing the present invention, alumina hydrate and lithium hydroxide are wet mixed in the presence of a solvent. As a means for wet mixing, a mixing tank equipped with a stirrer, a ball mill, a vibration mill, a V-type mixer, an ultrasonic peptizer or the like is used. If the mixing conditions are not wet conditions but dry conditions, the dispersion may not be uniform between the alumina hydrate and lithium hydroxide, the reaction may not proceed sufficiently, or the lithium aluminate with a large particle size and a small surface area may be used. I can only get it.

The wet mix of hydrated alumina and lithium hydroxide is then stripped of solvent.

As a method for removing the solvent, known techniques such as evaporation removal, filtration, centrifugation, and spray drying can be used. However, when the lithium compound dissolves in the solvent, the evaporation removal method or the spray drying method is used.

When the solvent is removed from the wet mixture by these methods, the solid content is obtained in powder form.

The firing in the present invention is usually carried out at a temperature within the range of 650 ° C to 1000 ° C, preferably 700 ° C to 950 ° C. When fired at a temperature lower than 650 ° C, the main structure becomes amorphous or β-type lithium aluminate, and 1000 ° C
The lithium aluminate obtained by firing at a higher temperature has a large particle size and a small surface area, which is not preferable.

In carrying out the present invention, the powdery solid matter obtained by removing the solvent from the wet mixture of alumina hydrate and lithium hydroxide may be immediately calcined, but before that, it may be pulverized or mixed. The pulverization and homogenization of the secondary agglomerates, followed by calcination, are preferable because γ-type lithium aluminate having a small particle size and a large surface area can be obtained. A ball mill, a vibration mill, an attritor, a raider, a V-type mixer, or the like is used as an apparatus used for the pulverization or mixing treatment.

(Effect of the Invention) The lithium aluminate obtained by the method of the present invention is 7
Since 0% or more has a γ-type crystal form and the rest has a β-type crystal form, and has a small particle size and a large surface area of about 15 m ² / g or more, an electrolyte tile for a molten carbonate fuel cell. It is preferably used as a raw material.

(Examples) Hereinafter, the method of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 Pseudo-boehmite 2550 g (2040 g as Al ₂ O ₃ ), lithium hydroxide monohydrate (LiOH.H ₂ O) 1680 g and water 10 Kg were charged into 20 mixing tanks that exceeded a stirrer, a condenser and the like, 2 at 100 rpm while keeping the temperature at 95-100 ° C
Stir and mix for hours. Then, water was removed by evaporation at 100 ° C. to obtain 3000 g of a dry powder. The dried powder was treated with a vibration mill for 2 hours and then fired under the conditions shown in Table 1.

The physical properties of the obtained fired product were as shown in the column of physical properties of product in Table 1.

Examples 2 to 8 In the same manner as in Example 1, various alumina hydrates, lithium hydroxide-hydrates and various solvents were wet-mixed under the conditions shown in Table 1, the solvent was removed, and the dried powders were obtained. Dry pulverization treatment was carried out under the conditions shown in Table 1 (Example 8 was not treated),
Then, it was fired under the conditions shown in Table 1 to obtain a fine powder of lithium aluminate. The crystal form and BET specific surface area of this lithium aluminate were measured and are shown in Table 1.

Example 9 2550 g of the same pseudo-boehmite as in Example 1 (2040 g as Al ₂ O ₃ ), 1680 g of lithium hydroxide hydrate,
And 10 kg of water into a 30 ball mill, temperature 2
Mix by rotation at 0 ° C to 30 ° C. This mixed slurry was charged into the same mixing tank as in Example-1, water was evaporated and removed at 100 ° C. and dried to obtain 3000 g of a dry powder. The dried powder was treated with a vibration mill for 2 hours and then calcined at 800 ° C. for 1 hour. The physical properties of the obtained baked product were as shown in the column of physical properties of product in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated except that the firing was performed at 600 ° C. or 1100 ° C. for 1 hour each. The physical properties of the obtained fired product were as shown in the product physical properties column of Table 2.

Comparative Example 2 The procedure of Example 2 was repeated except that the firing was performed at 600 ° C. or 1100 ° C. for 1 hour each. The physical properties of the obtained fired product were as shown in the product physical properties column of Table 2.

Comparative Example 3 γ-Al ₂ O ₃ 2150 was added to the same mixing tank used in Example 1.
g (2040 g as Al ₂ O ₃ ), lithium hydroxide monohydrate (LiOH.H ₂ O) 1680 g and water 10 kg were charged, and the mixture was stirred and mixed at 100 rpm for 2 hours while maintaining the temperature at 95 ° C. to 100 ° C. Then, water was removed by evaporation at 100 ° C. to obtain a dry powder. This dry powder was mixed for 2 hours in a vibration mill and then fired under the conditions shown in Table 2.

As for the physical properties of the obtained fired product, as shown in the column of physical properties of product in Table 2, unreacted γ-Al ₂ O ₃ remained, and only γ-type lithium aluminate having a small surface area was obtained.

Comparative Example 4 In the same manner as in Example 1, α-Al ₂ O ₃ and lithium hydroxide monohydrate were wet mixed in the presence of water under the conditions shown in Table 2, the solvent was removed, and the dried powder was dried. Dry pulverization was performed under the conditions shown in Table 2, and then firing was performed under the conditions shown in Table 2. The physical properties of the obtained fired product are shown in Table 2.

Comparative Example 5 2550 g of the same pseudo-boehmite as Example 1 (2040 g as Al ₂ O ₃ ) and lithium hydroxide monohydrate 1680
g was dry mixed in a 30 ball mill for 8 hours in the absence of solvent. This powder was fired under the conditions shown in Table 2.

As for the physical properties of the obtained fired product, only γ-type lithium aluminate having a small surface area was obtained as shown in Table 2.

From the above Examples and Comparative Examples, it is clear that fine and high surface area γ-type lithium aluminate can be stably produced by the method of the present invention.

Claims (4)

[Claims] 1. A mixture of one or more alumina hydrates selected from the group consisting of boehmite, pseudoboehmite, diaspore, gibbsite and bayerite and lithium hydroxide in the presence of a solvent, and then the solvent. A method for producing a γ-type lithium aluminate powder, characterized in that the solid content obtained by the removal is fired at a temperature in the range of 650 ° C to 1000 ° C. 2. The production method according to claim 1, wherein the firing temperature is in the range of 700 ° C. to 950 ° C. 3. The production method according to claim 1, wherein the solid component is subjected to pulverization or mixing treatment before being subjected to firing. 4. The method according to claim 1, 2, or 3, wherein the solvent is one or more selected from water or alcohols.