JP3155088B2 - Method for producing lithium aluminate fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is useful as a reinforcing material for an electrolyte plate of a molten carbonate fuel cell, stable in an electrolyte,
The present invention relates to a method for producing a lithium aluminate fiber having excellent properties for maintaining the strength of an electrolyte plate.

[0002]

2. Description of the Related Art Lithium aluminate fibers have high stability against electrolytes and are useful as reinforcing materials for electrolyte plates of molten carbonate fuel cells. Conventionally, as a method for producing this lithium aluminate fiber, a method of reacting an alumina fiber with a lithium carbonate, a method of reacting a basic aluminum chloride compound fiber with lithium carbonate to produce a lithium aluminate fiber (Japanese Patent Application Laid-Open No. 61-29
No. 1414), a method of producing a fibrous lithium aluminate by heating a raw material obtained by mixing lithium hydroxide or a mixture of lithium hydroxide and sodium hydroxide with alumina (Japanese Patent Laid-Open No. 63-151614). Etc. are known.

However, according to the above method, the silica component contained in the alumina fiber reacts with the molten carbonate of lithium carbonate or potassium carbonate to dissolve the fiber, the form of the fiber is impaired, and the performance as a reinforcing material is deteriorated. It is lost and cannot be used for a long time. Further, in the method of (1), before the basic aluminum chloride compound fiber reacts with lithium carbonate, the volatile substances contained in the basic aluminum chloride fiber are thermally decomposed and volatilized, so that it is difficult to maintain the fiber form, Only those with a fiber length of 100-300 μm are obtained. Further, the method is a method in which alumina powder is reacted with lithium hydroxide. The obtained lithium aluminate is a relatively long crystal having a length of 15 to 20 μm and an aspect ratio of about 20, but a crack in the electrolyte plate is generated. It is difficult to obtain long fibrous crystals that cause sufficient fiber entanglement to prevent generation. In the conventional electrolyte plate, lithium carbonate and potassium carbonate are repeatedly melted and crystallized with the operation and shutdown cycles of the molten carbonate fuel cell, and the electrolyte plate also suffers from such melting and cooling. In some cases, cracks may occur in the electrolyte plate during the power cycle, and there is a problem that fuel gas leaks through the electrolyte plate and power generation efficiency is reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art in lithium aluminate used as a reinforcing material for an electrolyte plate of a molten carbonate fuel cell, and to reduce the silica content. An object of the present invention is to provide a method for producing a lithium aluminate fiber having a length sufficient to prevent occurrence of cracks in an electrolyte plate.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a spinning solution mainly containing a high-purity alumina fiber precursor is spun into precursor fibers, and the precursor fibers are first fired at 700 to 1200 ° C. A method for producing a lithium aluminate fiber, comprising heating the obtained high-purity intermediate alumina fiber in the range of 500 to 1000 ° C. and co-firing in the presence of a lithium compound. After passing the intermediate alumina fiber through the solution or slurry of the lithium compound to attach and impregnate the lithium compound,
A method for producing a lithium aluminate fiber, comprising heating and secondary baking in the range of 500 to 1000 ° C.

[0006] The term "high purity" used herein means a precursor fiber obtained by spinning a precursor fiber obtained by spinning a spinning solution containing this alumina fiber precursor as a main component and having an alumina content of 95% or more in the alumina fiber. Say. The term "intermediate alumina" means that as the precursor fiber is heated, volatile components such as water of crystallization and organic compounds added as a spinning aid volatilize and change into alumina, and X-ray diffraction is performed. From the peak (amorphous) peak to the thermally unstable crystalline state γ-, δ-, etc., the crystal finally becomes the only stable α-alumina as a crystal. Alumina which exists in the process of becoming α-alumina or is in a thermally unstable crystalline state.

Hereinafter, the method of the present invention will be described in detail. In the method of the present invention, first, a precursor fiber of a high-purity alumina fiber is manufactured, and this is primarily fired at 700 to 1200 ° C. to obtain a high-purity intermediate alumina fiber. The method for obtaining the precursor fiber is not particularly limited, and an inorganic salt method, a precursor polymer method, a slurry method, a sol method, and the like can be applied. Slurry method (Japanese Patent Publication No. 57-27210,
JP-A-63-75117) is suitable.

Hereinafter, the method of the present invention will be described in detail based on the slurry method. First, the alumina weight after firing in an aqueous solvent solution such as an aqueous solution of a basic aluminum salt or a mixed solvent of water and a water-soluble solvent such as an alcohol is 20 to 60%.
Weight% of alumina having an average particle diameter of 1 μm or less or powder of an aluminum compound which becomes alumina when fired,
A slurry containing 4 to 10% by weight of a spinning aid and, if desired, 3% by weight or less of a sintering aid on an oxide basis is used as a spinning stock solution, which is spun and dried to obtain a precursor fiber.

The basic aluminum salt used here includes basic aluminum chloride, basic aluminum nitrate, basic aluminum acetate, basic aluminum chloroacetate and the like. In addition, in addition to alumina, boehmite, bayerite, diaspore, or the like may be used as the powder added to improve the fluidity of the spinning raw material and the stability of the precursor, reduce volatile matter during firing, and improve fiber strength. An aluminum compound which becomes alumina by sintering such as pseudo-boehmite can be used.

Further, as a spinning aid for improving the spinnability of the spinning raw material, a water-soluble organic polymer compound such as polyvinyl alcohol, polyethylene oxide or polypropylene oxide is added in an amount of 0.1 to 10% by weight based on the oxide. .

Further, CuO, MgO, ZrO ₂ ,
One or more oxides selected from PbO, Cr ₂ O ₃ , Fe ₂ O ₃ , MoO ₃ and TiO ₂ or CuSO ₄ , MgCl ₂ , ZrOCl ₂ , Zr
Compounds which become these oxides by baking such as Cl ₄ may be added.

[0012] The precursor fiber thus obtained has a fiber diameter of about 5 to 20 µm.
At a relatively low temperature to produce high-purity intermediate alumina fibers. The primary firing temperature may be appropriately set within the above temperature range depending on the properties of the precursor fiber, the reaction conditions with the lithium compound, the properties of the intended lithium aluminate fiber, and the like. In the processing step (1), the high-purity intermediate alumina fiber is melted, and it becomes difficult to maintain its shape.

When the temperature exceeds 1200 ° C., the intermediate alumina component undergoes α-transformation and changes to crystalline alumina, so that the flexibility of the fiber is lost. Are easily broken, and only a lithium aluminate fiber having a short length can be obtained. Furthermore, when the crystal of alumina undergoes α-transition, the surface activity becomes lower than that of intermediate alumina, and a high temperature exceeding 1000 ° C. is required to react with the lithium compound. However, if the reaction temperature is too high, This is not preferable because lithium aluminate crystals grow and the fibers become brittle.

The high-purity intermediate alumina fiber fired in the range of 700 to 1200 ° C. has a low elasticity and flexibility, so that the fiber hardly breaks even when mixed with a lithium compound. In addition, since it has a large surface activity and is porous, it can be reacted with a lithium compound at a low temperature, so that the particle size of lithium aluminate can be easily controlled.

The high-purity intermediate alumina fiber obtained in this manner is heated at 500 to 1000 ° C. in the presence of a lithium compound.
The alumina is reacted with the lithium compound by heating in the temperature range described above and secondary firing to form lithium aluminate fibers.

The secondary firing is conveniently carried out by heating the mixture while mixing, impregnating and adhering a lithium compound to the high-purity intermediate alumina fiber. When firing in a mixed state, the high-purity intermediate alumina fiber is cut into, for example, about 5 to 50 mm, mixed with a lithium compound having an average particle diameter of 1 μm or less in a dry or wet manner, dried if necessary, and then dried in a suitable container. And fired. Further, a method is preferable in which the high-purity intermediate alumina fiber is immersed in a solution or slurry of a lithium compound and then dried to uniformly adhere and impregnate the lithium compound.

As the solvent used, water is most suitable because of its easy handling. Depending on the type of the high-purity intermediate alumina fiber, the type and the amount of the lithium compound used, etc., methanol, ethanol, diethylene glycol may be used. It is possible to use organic solvents such as alcohol solvents such as alcohols, aromatic solvents such as benzene and toluene, ketone solvents such as acetone and methyl ethyl ketone, or mixed solvents thereof, or mixed solvents of these organic solvents and water. it can.

This impregnation operation may be performed after cutting the high-purity intermediate alumina fiber into an appropriate length,
An efficient method is to continuously pass the primary-fired high-purity intermediate alumina long fibers through a solution or slurry of a lithium compound. High-purity intermediate alumina fibers impregnated with and adhered with a lithium compound in the form of long fibers, as they are, or cut into appropriate lengths and then fired to form long-fiber or short-fiber lithium of uniform length Aluminate fibers can be obtained.

As the lithium compound used here,
There is no particular limitation as long as the lithium oxide content when fired as it has a purity of 95% by weight or more and the silica content is low, but preferred examples include lithium hydroxide, lithium carbonate, lithium chloride and nitric acid. Lithium and the like. The silica content needs to be controlled so that the silica content in the obtained lithium aluminate fiber is 1% by weight or less in total with the silica content derived from the spinning raw material. The silica contained in the lithium aluminate fiber becomes lithium silicate in the molten carbonate and elutes in the molten carbonate, which lowers the strength of the lithium aluminate fiber and impairs the ability as a reinforcing material for the electrolyte plate Becomes

The amount of the lithium compound used is such that the element ratio of aluminum to lithium at the stage of secondary firing is 1: 1 to 1: 1.
The range is set to 1.5. When the element ratio is less than 1, the lithiation reaction does not proceed sufficiently. When the element ratio exceeds 1.5, a large amount of lithium oxide crystals precipitate on the fiber surface, and it becomes difficult to obtain a good lithium aluminate fiber. Absent.

The high-purity intermediate alumina fiber impregnated with the lithium compound obtained as described above is
Secondary firing is performed at a temperature of 0 ° C. to obtain a lithium aluminate fiber. If the secondary firing temperature is lower than 500 ° C., the lithiation reaction does not proceed sufficiently. If the temperature exceeds 1000 ° C., sintering of lithium aluminate proceeds too much, and crystals are grown to make the fibers brittle, which is not preferable.

The firing time depends on the properties of the high-purity intermediate alumina fiber, the type and mixing of the lithium compound used, the state of adhesion,
It may be determined as appropriate depending on the crystal grain size in the intended lithium aluminate fiber, etc., but is up to about 10 hours.

In the method of the present invention, since the lithium compound is mixed and adhered to the high-purity intermediate alumina fiber and baked, the lithium compound easily penetrates into the fiber.
Since the reactivity is high, a high-purity lithium aluminate fiber having a long fiber length can be easily produced.

In the method of the present invention, a high-purity intermediate alumina fiber cut into a length of about 5 to 50 mm from the beginning is mixed with a lithium compound and fired, or the lithium compound is impregnated and adhered in a long fiber state. If it is manufactured by the method of cutting and firing in the same manner after the above, mainly 3 to 30 m
m of lithium aluminate fiber is obtained. Also,
If the high-purity intermediate alumina fibers to which the lithium compound is attached and impregnated are fired as long fibers, lithium aluminate fibers in the form of long fibers can be obtained. Can be used as a uniform fiber. This lithium aluminate fiber has excellent performance as a reinforcing material for the electrolyte plate of a molten carbonate fuel cell, and is easy to handle by mixing with lithium aluminate powder and carbonate, molding and processing. Good,
It is possible to obtain a high-strength electrolyte plate in which cracks due to heat cycle are unlikely to occur.

Hereinafter, the method of the present invention will be described more specifically with reference to examples.

【Example】

(Example 1) Basic aluminum chloride (Al
₂ O ₃ content of 48 wt%) 214 g of a solution obtained by dissolving in water of 855g was added and the γ- alumina fine powder 50.6g of an average particle size of 0.2μm dispersed. To this slurry, 78.4 g of polyethylene oxide (average molecular weight: about 900,000) was added, mixed well, and adjusted so that the viscosity at 25 ° C. became about 2000 poise to prepare a spinning dope. The spinning solution was extruded from a 0.3 mmφ spinning nozzle into a dried spinning cylinder and spun to obtain a precursor fiber. The precursor fiber is cut into a length of about 50 mm, placed in a high-purity alumina box, heated to 1050 ° C., kept at the same temperature for 3 hours and fired, and has a fiber diameter of about 12 μm and a fiber length of about 30 mm. Purity 9
9.6% by weight of γ-alumina fiber was obtained. In addition, the silica content of this fiber was measured using a high-frequency plasma emission spectrometer (IC
As a result of analysis by P), it was 0.03% by weight.

148 g of the high-purity γ-alumina fiber,
Lithium hydroxide monohydrate 15 ground to a particle size of 1 μm or less
A mixture (Al / Li ratio 1 / 1.26) obtained by dry-mixing 3 g with a V-type mixer for 20 minutes is placed in a high-purity alumina box, heated to 750 ° C., and kept at the same temperature for 2 hours. And fired. The obtained lithium aluminate fiber was a mixture of fibers having a fiber diameter of about 10 μm and a fiber length of 50 μm to 30 mm. As a result of identification and analysis by an X-ray diffractometer, γ-LiAlO ₂ having a purity of about 92% by weight was obtained. The silica content of this fiber was 0.04% by weight. The obtained lithium aluminate fiber was added in an amount of 5% by weight based on the lithium aluminate powder, kneaded with potassium carbonate, lithium carbonate and an organic binder, and then tape-molded to a thickness of 1.2 mm. Electrolyte plates of the order were prepared. This electrolyte plate was placed on a stack of molten carbonate fuel cells,
After operating at 50 to 750 ° C., the heat cycle of cooling to room temperature was repeated 20 times, but no leakage of fuel gas from the electrolyte plate was observed, and the electrolyte plate had suitable properties as a reinforcing material. Met.

Example 2 Basic Aluminum Chloride (Al
39.6 g of γ-alumina fine powder having an average particle size of 0.1 μm was added and dispersed in a solution of 193 g of 193 g dissolved in 496 g of water ( ₂ O ₃ content: 48% by weight). To this slurry was added 43.7 g of polyethylene oxide (average molecular weight: about 900,000), mixed well, and adjusted so that the viscosity at 25 ° C. became about 3000 poise to prepare a spinning dope. The spinning solution was extruded from a 0.3 mmφ spinning nozzle into a dried spinning cylinder and spun to obtain a precursor fiber. This precursor fiber is cut into a length of about 50 mm, placed in a high-purity alumina box, heated to 1100 ° C., kept at the same temperature for 3 hours and fired, and has a fiber diameter of about 15 μm and a fiber length of about 40 mm. Purity 9
As a result, 9.5% by weight of γ-alumina fiber was obtained. The silica content of the fiber was 0.03% by weight.

106 g of this high-purity γ-alumina fiber is
480 ml of an aqueous solution of lithium hydroxide having a concentration of 5 mol / l
The mixture was put into the flask and mixed well, and then dried at a temperature of 105 ° C. The obtained lithium hydroxide monohydrate has an Al / Li ratio of 1
/1.16 High purity γ uniformly adhered at such a ratio
-Place the alumina fiber in a high-purity alumina box,
The temperature was raised to 0 ° C., and kept at the same temperature for 2 hours for firing. The obtained lithium aluminate fiber has a fiber diameter of about 12 μm,
It is a mixture of fibers having a fiber length of 50 μm to 30 mm. As a result of identification and analysis by an X-ray diffractometer, a purity of about 90% by weight is obtained.
Of γ-LiAlO ₂ . The silica content of the fiber was 0.05% by weight.

Example 3 Basic Aluminum Chloride (Al
68.5 g of γ-alumina fine powder having an average particle size of 0.1 μm was added and dispersed in a solution of 214 g of ₂ O ₃ content (48% by weight) dissolved in 500 g of water. To this slurry was added 39.0 g of polyethylene oxide (average molecular weight: about 900,000), mixed well, and adjusted so that the viscosity at 25 ° C. became about 2500 poise to prepare a spinning dope. This spinning solution was extruded from a spinning nozzle having 500 holes of 0.3 mmφ into a dried spinning cylinder and spun to obtain a precursor fiber composed of 500 filaments. This precursor fiber is
It is continuously passed through a firing furnace having a temperature gradient of from 00 ° C. to a maximum of 1200 ° C. for a residence time of 10 minutes and fired, and has a purity of 500 filaments comprising 500 filaments having a fiber diameter of about 12 μm.
9.5% by weight of γ-alumina long fiber was obtained. The silica content of the fiber was 0.02% by weight.

The long fiber is passed through an aqueous solution in which 110 g of lithium chloride and 0.5 g of polyvinyl alcohol are dissolved in 150 ml of water, and is impregnated with lithium chloride at a ratio so that the Al / Li ratio is 1 / 1.16. After adhering, it is continuously fired in a firing furnace having a temperature gradient of 500 ° C. to a maximum of 1000 ° C. for a residence time of 30 minutes and fired to form a long fiber comprising 500 filaments having a fiber diameter of about 10 μm. Was obtained. As a result of identification and analysis by an X-ray diffractometer, this fiber was γ-LiAlO ₂ having a purity of about 92% by weight. The silica content of the fiber was 0.03% by weight.

Comparative Example 1 A precursor fiber having a length of about 50 mm obtained in the same manner as in Example 1 was put into a high-purity alumina box, heated to 1300 ° C., and kept at the same temperature for 3 hours. And fired. As a result of measurement by an X-ray diffractometer, the obtained fiber was α-alumina, and was an alumina fiber having a fiber diameter of about 10 μm and a fiber length of about 25 mm and a purity of 99.6% by weight. 148 g of this crystalline high-purity alumina fiber and a particle size of 1
153 g of lithium hydroxide monohydrate pulverized to not more than μm was dry-mixed in a V-type mixer for 20 minutes. Mixture (Al
/ Li ratio 1 / 1.26) was placed in a high-purity alumina box, heated to 750 ° C., and baked at the same temperature for 2 hours.

The obtained fiber was a mixture of α-Al ₂ O ₃ , γ-LiAlO ₂ , Li ₂ O and LiAl ₅ O ₈ as a result of identification by an X-ray diffractometer, and the lithiation reaction proceeded sufficiently. I knew it wasn't. Therefore, the fiber is further heated at 750 ° C for 5
After holding for a time, γ-LiAlO ₂ having a purity of about 90% by weight was obtained. In the obtained baked product, fibers having a fiber diameter of about 10 μm and a fiber length of 20 to 70 μm accounted for about 90%, and the rest were particles having an average particle diameter of about 10 μm. However, the length of the obtained fiber is insufficient to entangle the fiber three-dimensionally when producing an electrolyte plate, and it has been difficult to produce an electrolyte plate having sufficient strength.

Comparative Example 2 A precursor fiber having a length of about 50 mm obtained in the same manner as in Example 2 was put in a high-purity alumina box, heated to 600 ° C., and kept at the same temperature for 3 hours. Baked to a purity of 9 with a fiber diameter of about 13 μm and a fiber length of about 30 mm.
9.5% by weight of alumina fiber was obtained. As a result of identification by an X-ray diffractometer, this fiber was an alumina fiber in which peaks of intermediate alumina such as γ- and δ- and peaks of brood were mixed.

106 g of the obtained alumina fiber was
The mixture was poured into 480 ml of an aqueous solution of lithium hydroxide having a concentration of 1 / l, mixed well, and then dried at a temperature of 105 ° C. The obtained lithium hydroxide monohydrate has an Al / Li ratio of 1/1.
The alumina fibers uniformly adhered at a ratio of 16 were placed in a high-purity alumina box, heated to 800 ° C., and held at the same temperature for 2 hours for firing.

As a result of identification and analysis by an X-ray diffractometer, the obtained fired product was found to be γ-LiAlO ₂ having a purity of about 90% by weight, but about 4 μm of a fiber having a fiber diameter of about 10 μm and a fiber length of 20 μm to 1 mm And the remainder were particles having an average particle size of about 10 μm. This mixture of lithium aluminate fibers and particles is insufficient in length to be entangled three-dimensionally when producing an electrolyte plate, and it is difficult to produce an electrolyte plate having sufficient strength. there were.

Comparative Example 3 A mixture of high-purity γ-alumina fiber prepared in the same manner as in Example 1 and 153 g of lithium hydroxide monohydrate (Al / Li ratio 1 / 1.26) was obtained by
Put into a high-purity alumina box, heat up to 1100 ° C,
The firing was carried out at the same temperature for 2 hours. As a result of identification and analysis by an X-ray diffractometer, the obtained lithium aluminate fiber was γ-LiAlO ₂ having a purity of about 90% by weight. However, the sintering of the crystal progressed too much, and the fibers were partially fused to each other. However, it formed block-shaped particles, and was unsuitable as an electrolyte plate reinforcing material for a molten carbonate fuel cell.

According to the method of the present invention, a high-purity intermediate alumina fiber having a low modulus of elasticity and a low silica content is used as an alumina source, so that it breaks when mixed with a lithium compound. And a lithium aluminate fiber having a high aspect ratio can be obtained.
By using long fibers of high-purity intermediate alumina, lithium aluminate fibers in the form of long fibers can also be obtained. When the lithium aluminate fiber produced by the method of the present invention is used as a reinforcing material for an electrolyte plate of a molten carbonate fuel cell, since the fiber contains almost no silica component, the fiber is converted into lithium silicate in the molten carbonate. There is no danger of elution. In addition, since the fiber length is longer than conventionally used lithium aluminate fibers, when the electrolyte plate is used, the fibers are three-dimensionally entangled with each other, and high strength is obtained. Since it is hardly affected by thermal stress and can prevent the occurrence of cracks, it has excellent performance as an electrolyte plate reinforcing material for a molten carbonate fuel cell.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsusuke Iwanaga 1, Kunifu-cho, Tochigi City, Tochigi Prefecture, Central Research Laboratory, Mitsui Mining Co., Ltd. (56) References JP-A 6-10204 (JP, A) -503027 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 9/08-9/10 H01M 8/02

Claims (2)

(57) [Claims] 1. A high-purity intermediate alumina fiber obtained by spinning a spinning solution containing a high-purity alumina fiber precursor as a main component into a precursor fiber, and primary firing the precursor fiber at 700 to 1200 ° C. , In the presence of lithium compound, 50
A method for producing a lithium aluminate fiber, comprising heating and secondary firing in the range of 0 to 1000 ° C. 2. A high-purity intermediate alumina fiber obtained by spinning a spinning solution containing a high-purity alumina fiber precursor as a main component into a precursor fiber, and subjecting the precursor fiber to primary firing at 700 to 1200 ° C. After adhering and impregnating the lithium compound by passing it through a solution or slurry of the lithium compound,
A method for producing a lithium aluminate fiber, comprising heating and secondary baking in the range of 500 to 1000C.