JPH0637292B2 - Method for producing coarse particles of porous lithium aluminate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a fuel cell used in the energy sector for directly converting chemical energy of a fuel into electric energy, and in particular, molten carbonate impregnated with molten carbonate as an electrolyte. The present invention relates to a method for producing porous lithium aluminate coarse particles for use as a reinforcing material for an electrolyte plate of a salt fuel cell.

[Prior Art] As a molten carbonate fuel cell that has been proposed so far, a molten carbonate as an electrolyte is impregnated into a porous matrix tape to form an electrolyte plate, and this electrolyte plate is used as a cathode ( It is sandwiched by both electrodes (oxygen electrode) and anode (fuel electrode) from both sides, and by supplying oxidizing gas to the cathode side and supplying fuel gas to the anode side, power is generated between the cathode and the anode. One cell is used, each cell is laminated in multiple layers via a separator to form a stack, and the stack is tightened with an appropriate tightening force.

The electrolyte plate used in the molten carbonate fuel cell has been conventionally manufactured by various methods. One of the manufacturing methods is ceramic particles of several μ or less, for example, lithium aluminate (LiAlO ₂ ) There is an electrolyte plate in which a matrix having a large number of pores is formed from powder and the matrix is impregnated with an electrolyte so that the electrolyte is retained in the voids of the matrix.

The electrolyte plate obtained by such a method is used by being sandwiched between both the cathode and anode electrodes, and the oxidizing gas supplied to the cathode side and the fuel gas supplied to the anode side must be completely separated. However, the temperature of the electrolyte plate should be kept at room temperature and the operating temperature of the fuel cell (approx.
650 ° C), it receives a magnitude stress due to repeated thermal operation, and the maximum stress at this time is when the electrolyte changes from the liquid phase to the solid phase, especially when the operation is suddenly stopped. If a decrease occurs, it will occur remarkably. Along with such a phase change, the volume suddenly changes to release energy, which is released by causing cracks in the electrolyte plate. If a crack that penetrates through the electrolyte plate in the front and back direction occurs, the electrolyte plate will no longer be able to maintain the ability to separate the oxidizing gas and the fuel gas, and the oxidizing gas and the fuel gas will come into direct contact with each other, reducing the battery output. Or there is a problem of causing a risk of explosion.

Therefore, in the conventional case of producing an electrolyte plate, when forming a matrix using lithium aluminate particles having a particle size of several μ or less as a support particle, the coarse particles of lithium aluminate (50 to 150 μm) much larger than the above particles are used.
μ) to an appropriate proportion of lithium aluminate particles of several μ or less as the supporting particles (for example, 10 vol to 90 vol% of lithium aluminate particles of several μ or less).
%), The penetration cracks on both the front and back surfaces generated in the electrolyte plate are reduced by blocking the mixed lithium aluminate coarse particles, and the coarse particles of the lithium aluminate are reduced in cracking particles, That is, a material which is used as a reinforcing material for an electrolyte plate has been proposed (JP-A-57-27569).

[Problems to be Solved by the Invention] However, the lithium aluminate coarse particles as the reinforcing material (crack reducing particles) of the electrolyte plate described in JP-A-57-27569 described above are liable to be generated in the electrolyte plate. The above-mentioned conventional lithium aluminate coarse particles merely function as an object for preventing penetration cracks by blocking penetration cracks in the front and back directions, and cannot impregnate carbonate inside. Is mixed into lithium aluminate particles of several μ or less as supporting particles forming a matrix and used as a reinforcing material for an electrolyte plate, a carbonate when cooling the fuel cell from operating temperature to room temperature. At the time of solidification, a gap was formed at the interface between the carbonate and the surroundings of the lithium aluminate coarse particles as the reinforcing material, and when the carbonate solidified, it was generated in the electrolyte plate. Cracked number communicates with the gap around the coarse particles, cracks which may penetrate the electrolyte plate.

Therefore, the inventors of the present invention have conducted a device study to prevent a series of gaps from being formed around the coarse particles when the lithium aluminate coarse particles are used as the reinforcing material of the electrolyte plate. As a result, if the carbonate as the electrolyte can be impregnated inside the reinforcing material when it is used as the reinforcing plate of the electrolyte plate, the carbonate in the reinforcing material will be contained inside when the carbonate becomes solid when the fuel cell is cooled. It should be noted that porous lithium aluminate coarse particles should be used as the reinforcing material, paying attention to the fact that it becomes a solid as it enters and becomes a series with the surrounding carbonate, and a series of gaps is not formed around the reinforcing material. Found out.

Therefore, the present invention is intended to provide a method for producing the porous lithium aluminate coarse particles.

[Means for Solving the Problems] In order to solve the above problems, the present invention combines a small number of silica particles and a large number of alumina particles to form coarse particles, and then the coarse particles contain lithium ions. 500 in carbonate
The temperature is raised to ℃ ~ 1000 ℃, the silica particles in the coarse particles are eluted into carbonate and the coarse particles due to the alumina particles having pores due to the elution of the silica particles are lithiated to obtain lithium aluminate coarse particles. After that, the lithium aluminate coarse particles are cooled, and then washed with water and pickled to obtain porous lithium aluminate coarse particles.
Further, the above-mentioned washing with water and pickling do not have to be performed if the components of the initial carbonate are set.

[Operation] A single coarse particle is made by enclosing a small number of silica particles with a large number of alumina particles, and the silica particles are eluted from the coarse particles to form pores. The pore diameter can be arbitrarily changed by changing the diameter. When the obtained porous lithium aluminate coarse particles are used as a reinforcing material for the electrolyte plate, carbonate as an electrolyte enters the pores and becomes solid as it is when the fuel cell is cooled. Since the carbonate and the carbonate around the reinforcement are continuous, a series of gaps are not formed around the reinforcement.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a process for carrying out the method for producing porous lithium aluminate coarse particles of the present invention, in which 1 is a supply part of silica (SiO ₂ ) 1a and 2 is alumina (Al ₂ O ₃ ), 3 is a dispersant 3a supply part, 4 is a binder 4a supply part, 5 is a mixing treatment part for mixing silica 1a and alumina 2a with the binder 4a to form a slurry 6, and 7 is granulation. A treatment unit (granulator), 8 heats the coarse particles 7a granulated to a predetermined particle size in the granulation processing unit 7 in a carbonate 9a containing lithium ions to obtain the silica in the coarse particles 7a. A lithiation treatment unit that elutes 1a from the coarse particles 7a into the carbonate 9a and lithiates the remaining alumina 2a, 9 is a carbonate supply unit containing lithium ions, 10 is a cooling unit, and 11 is a coarse particle washed with water. , A decarbonation treatment part to remove the carbonate remaining by pickling, 12 is a porous lithium aluminate crude product It is a child.
In addition, 13 is a high temperature heating part used as needed in order to increase the strength of the porous lithium aluminate coarse particles 12, and 13a is a strong lithium aluminate coarse particle obtained in the high temperature heating part 13.

The case of producing the porous lithium aluminate coarse particles of the present invention along the above production process will be specifically described below.

First, after dispersing a large number of alumina (Al ₂ O ₃ ) 2a with a dispersant 3a, the large number of alumina 2a and a small number of silica (SiO ₂ ) 1a are dispersed.
Is mixed with a binder (for example, polyvinyl alcohol) 4a in the mixing processing section 5 to form a slurry 6, and this slurry 6
Is put into the granulation processing section 7, and the granulation processing section 7 prepares coarse particles 7a in a form in which a small number of silica 1a is mixed in a large number of particles of alumina 2a. In the above description, a small number of silicas 1a are for forming pores in the coarse particles 7a as described later, and the particle size thereof is 1 μ to 10 μ. Also, many used alumina 2a
The particle size of is from 0.01 μ to 10 μ, but 0.01 μ to 1 μ is preferable because it is easy to adjust any coarse particle size and the particle shape is likely to be spherical. Further, the above granulation processing section
The coarse particles 7a granulated in 7 have a particle size of 0.5 μ to 200 μ.

Next, the 0.5 μ to 200 μ coarse particles 7a produced above are heated to a temperature of about 500 ° C. to 1000 ° C. in the lithium ion-containing carbonate 9 in the lithiation processing unit 8 to obtain the coarse particles 7a. A small amount of silica 1a is dissolved in carbonate 9 to form pores 14 in the coarse particles 7a as shown in FIG. 2, and the remaining coarse particles composed of alumina 2a, which is the coarse particle constituent, are lithiated. , Coarse particles 7a to lithium aluminate coarse particles 7b, then, after cooling the lithium aluminate coarse particles 7b, washed with water in the decarbonation treatment section 11, pickled, porous with pores 14 Use lithium aluminate coarse particles 12.

In the above description, the lithium ion-containing carbonate 9 is usually a solid (powder) at room temperature and liquefies when heated, but a carbonate liquefied from the beginning may be used. In addition, the temperature rise during lithiation is 5
00 ℃ ~ 1000 ℃, the reaction itself is very slow below 500 ℃, above 1000 ℃, the coarse particles 7b after the reaction or the alumina 2a itself sintering proceeds, the coarse particle size becomes small. , Holes 14 formed in the lithium aluminate coarse particles 7b
The above-mentioned temperature range is optimal, because it will be crushed.
Further, as a cooling method in the cooling unit 10, forced cooling (flowing gas etc.) is carried out depending on required physical properties of coarse particles (size, pore diameter).
Or slow cooling (furnace cooling). In this case, the cooling time does not matter.

In the above example, the coarse particles 7a are heated to 500 ° C. to 1000 ° C. in a carbonate containing lithium ions in the lithiation processing unit 8 to elute the silica 1a from the coarse particles 7a to make it porous. It was lithiated with lithium aluminate coarse particles 7b, and after cooling this, a process for obtaining a porous lithium aluminate coarse particle 12 as a product by treatment with dehydrochloric acid was shown. The steps of washing with water and pickling in the decarbonation treatment section are not particularly required as long as the components of the initial carbonate are set in consideration of the composition of carbonate contained in the coarse particles, and thus may be omitted manufacturing steps. However, in the following cases, it is a necessary step, and since the surface treatment of the particles (including the surface and the pore surface) can be performed by this step, it is left inside the lithium aluminate coarse particles by incorporating such a step. Carbonate can be removed.

Explaining a specific method in the case of performing the decarbonation treatment, first, after coarse particles are washed with warm water, neutralized with acetic acid, etc.,
Then, it is impregnated with an aqueous solution of acetic acid or the like (arbitrary time, arbitrary composition), followed by alcohol cleaning, and finally drying.

When the pores 14 of the porous lithium aluminate coarse particles 12 obtained in the above manufacturing process have a large diameter, in order to increase the strength, the high temperature heating unit 13 shown in FIG. And solidify to obtain strong porous lithium aluminate coarse particles 13a.

The porous lithium aluminate coarse particles 12 or 13a produced by the above-mentioned method are used as a reinforcing material for an electrolyte plate constituting a fuel cell. In this case, when a matrix is formed by using ceramic particles such as fine lithium aluminate particles as supporting particles, a large number of voids produced by the present invention are contained in the supporting particles as shown in part in FIG. The matrix 15a of the electrolyte plate 15 containing the porous lithium aluminate coarse particles 12 or 13a having pores.
When this matrix 15a is impregnated with molten carbonate 16 as an electrolyte, the molten carbonate 16 becomes pores of the porous lithium aluminate coarse particles 12 or 13a as a reinforcing material.
When the fuel cell is cooled from the operating temperature (650 ° C.) to room temperature and the molten carbonate 16 solidifies, the molten carbonate 16 that has entered the holes 14 becomes solid and remains as it is. It may be in series with the molten carbonate 16 around the particles 12 or 13a. As a result, a series of gaps are not formed around the coarse particles 12 or 13a, and even if the cracks 17 generated from both surfaces of the electrolyte plate 15 reach the coarse particles 12 or 13a, the cracks 17
Will not penetrate.

In the embodiment shown in FIG. 1 as the manufacturing process of the present invention, a small number of silica (SiO ₂ ) 1a and a large number of alumina (Al
₂ O ₃ ) 2a was mixed with the binder 4a in the mixing treatment section 5 to form the slurry 6, but as a bonding method for the silica 1a and the alumina 2a, a method using electrostatic adsorption other than the above is used. , There is also a method that uses mechanical force.

[Effects of the Invention] As described above, according to the method for producing porous lithium aluminate coarse particles of the present invention, a small number of silica particles are wrapped with a large number of alumina particles to form coarse particles having a required diameter,
The coarse particles are heated to 500 ℃ ~ 1000 ℃, to elute the silica particles from the inside of the coarse particles to form pores and to lithiate the alumina particles to lithium aluminate, and after cooling, if necessary. Since coarse particles of porous lithium aluminate are produced by performing decarbonation treatment accordingly, lithium aluminate coarse particles having a large number of pores can be produced by a simple method, and the particle diameter of silica particles can be arbitrarily set. By changing it, coarse particles with an arbitrary pore size can be obtained, and by using these coarse particles as a reinforcing material for the electrolyte plate of the molten carbonate fuel cell, molten carbonate can penetrate into the inside of the coarse particles. Moreover, since the molten carbonate that has entered the inside can be solidified as it is when the fuel cell is cooled, the problem of the conventional reinforcing material that a series of gaps are formed around the coarse particles is eliminated. It can be erased, an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a production process for carrying out the production method of the present invention, FIG. 2 is a schematic diagram of porous lithium aluminate coarse particles produced by the production method of the present invention, and FIG. It is a schematic diagram showing the state when the porous lithium aluminate coarse particles manufactured by the manufacturing method of the invention are used as a reinforcing material of an electrolyte plate. 1 ...... Silica supply section, 1a ...... Silica, 2 ...... Alumina supply section, 2a ...... Alumina, 3 ...... Dispersant supply section, 3a ...... Dispersant, 4 ...... Binder supply section, 4a ...... Bind Agent, 5 ... Mixing processing part, 6 ... Slurry, 7 ... Granulation processing part (granulator), 7a ... Coarse particles, 8 ... Lithiation processing part, 9 ...
Carbonate supply unit containing lithium ions, 9a ... Carbonate containing lithium ions, 10 ... Cooling unit, 11 ... Decarbonation treatment unit, 12 ... Porous lithium aluminate coarse particles (product).

Claims (1)

[Claims] 1. A coarse particle is produced by combining a small number of silica particles and a large number of alumina particles, and then the coarse particles are heated in a carbonate containing lithium ions to 500 ° C. to 1000 ° C. The silica particles therein are dissolved in carbonate to form vacancies, and the coarse particles made of alumina in which the vacancies are formed are lithiated to obtain lithium aluminate coarse particles. A method for producing porous lithium aluminate coarse particles, which comprises cooling the nate coarse particles to obtain porous lithium aluminate coarse particles.