JP3363113B2 - Method and apparatus for selecting carbon nanofiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for carefully selecting carbon nanofibers used as a hydrogen storage material.

[0002]

2. Description of the Related Art Carbon nanofibers obtained by thermally decomposing hydrocarbon gases such as ethylene and carbon monoxide using a metal catalyst such as iron and nickel have recently been said to absorb hydrogen gas more than hydrogen storage alloys. Astonishing experimental results have been announced and attracted attention as a hydrogen storage material. Although the mechanism of hydrogen storage is not completely clarified, hydrogen storage alloys have the drawbacks of having a high specific gravity and being pulverized by repeated use, so that storage performance equivalent to or better than that of alloys has been stably proven. For example, it can be used as a hydrogen storage material for fuel cells, etc., so its performance is being tested in many places.

Further, since the lithium ion storage capacity of carbon currently used for the cathode of a lithium ion secondary battery is an important factor that influences the capacity of the battery, the use of carbon nanofibers for this cathode will store the lithium ion. If the capacity can be increased, a dramatic increase in battery capacity can be expected.

However, since carbon nanofibers are thermal decomposition products, the production and mixing of undesired foreign substances such as carbon and hydrocarbon having other structures are unavoidable. By mixing these foreign substances,
Since the storage capacity per unit volume or unit weight naturally decreases, a process for separating and selecting only carbon nanofibers is required, but such a process has not existed in the past.

[0005]

SUMMARY OF THE INVENTION In view of the above, according to the present invention, undesired foreign substances are removed from the produced thermal decomposition product to be carefully selected, and the ability to store hydrogen gas or lithium ion per unit volume or unit weight is enhanced. The purpose is to

[0006]

The present invention has been made by paying attention to the fact that carbon nanofibers are formed by adhering to a ferromagnetic material such as iron or nickel. That is, the invention according to claim 1 is to stir a solid product obtained by thermally decomposing ethylene or carbon monoxide with a metal catalyst containing a magnetic substance such as iron or nickel together with a surfactant.
Then, the product is dispersed and made into a slurry, and then passed through a magnetic separator to cause the carbon nanofibers grown with the magnetic metal catalyst pieces as nuclei to be magnetically non-magnetic slurry.
It is a method for finely selecting carbon nanofibers, which is characterized by separating from carbon nanofibers.

The invention according to claim 2 is a solid product obtained by thermally decomposing ethylene, carbon monoxide or the like using a metal catalyst containing a magnetic substance such as iron or nickel together with a surfactant. A dispersion tank for stirring the product in the liquid to disperse the product, a magnetic separator for separating the magnetic slurry from the slurry in the dispersion tank, and a filter for separating solid particles from the separated magnetic slurry. It is a characteristic carbon nanofiber selection device.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on examples with reference to the drawings. 1 shows an example using a drum type magnetic separator, FIG. 2 shows an example using a superconducting magnetic separator, and FIG. 3 shows a schematic view of carbon nanofibers. In addition, in FIG. 2 and FIG.
The parts given the same reference numerals as in the above indicate the same or corresponding parts.

As shown in the schematic view of FIG. 3, the carbon nanofiber 3 has a thickness in which a flat carbon piece 2 is grown with a fine metal catalyst piece 1 as a nucleus with a gap of about G = 0.34 nm. D = 10 to several hundreds of nanometers, length L =
It is a minute carbon fiber of a few microns. In the process of forming the fine metal catalyst piece 1, the raw material gas comes into contact with the catalyst metal and the deposited carbon diffuses into the metal, and the catalyst surface is damaged and collapsed due to stress based on the volume change of the carbide formed on the metal surface. It is presumed that the metal catalyst is consumed in any case, but in any case, the metal catalyst is consumed, and the electron microscope observation shows that the metal catalyst piece 1 has a regular morphology with the fine metal catalyst piece 1 as a nucleus. The carbon nanofibers 3 are formed.

However, carbon nanofiber 3
Is produced by reductive thermal decomposition of hydrocarbon gas such as ethylene or carbon monoxide at a relatively low temperature of about 550 ° C. to 600 ° C. Therefore, under these conditions, the target carbon nanofiber It is difficult to prevent the simultaneous generation and mixing of other forms of carbon and hydrocarbons.

As shown in FIG. 1, the present invention is a pyrolysis product 4 containing carbon nanofibers 3 produced by pyrolysis.
Is first supplied to a dispersion tank 5 in which a liquid such as water is stored, and stirred with a surfactant 6 by a stirring blade 15 to isolate and disperse solid particles of the product in the liquid to form a slurry, The drum type magnetic separator 7 is supplied.

As shown in the figure, the drum-type magnetic separator 7 includes a drum 18 which rotates the outer periphery of a partially-fixed cylindrical fixed magnet 16 in the direction of arrow 17, a non-magnetic slurry storage tank 19, a magnetic slurry storage tank 20, and a sprayer. The magnetic material in the slurry supplied to the top of the drum 18 is adsorbed on the drum and rotated, and is detached at the defective portion of the fixed magnet 16 and washed by the spray nozzle 26 to be washed by the drum. The non-magnetic slurry 11 stored in the magnetic slurry storage tank 20 as a magnetic slurry and not affected by the magnetic force stays in the non-magnetic slurry storage tank 19.

In the magnetic slurry 8, a solid magnetic material, that is, the carbon nanofibers 3 is separated and collected by a filter 9 composed of a well-known hollow fiber membrane and the separated liquid 10 is returned to the dispersion tank 5. The non-magnetic slurry 11 is separated by the filter 12 into a solid non-magnetic material, that is, a foreign substance 13 and a separation liquid 14, and the separation liquid 14 is returned to the dispersion tank 5.

FIG. 2 shows a configuration in which a known superconducting magnetic separator 7'is used as another embodiment. As in the example of FIG. 1, the thermal decomposition product 4 is stirred with the surfactant 6 in the dispersion tank 5 to be dispersed in the liquid to make a slurry, and then supplied to the well-known superconducting magnetic separator 7 ′.

The superconducting magnetic separator 7'is composed of a superconducting magnet 21 surrounding a mesh metal material 22 and a refrigerator 23 as shown in the figure. The mesh metal material 22 may be made of a well-known high gradient magnetic type wool magnetic metal. The non-magnetic slurry 11 is separated into a solid non-magnetic material, that is, a foreign substance 13 and a separation liquid 14 by the filter 12 after passing through the mesh metal material 22, and the separation liquid 14 is returned to the dispersion tank 5. On the other hand, the magnetic substance trapped by the mesh metal material 22 is once demagnetized and then backwashed to be separated from the magnetic substance 22, and the magnetic slurry 8 containing the magnetic substance is separated by the filter 9 into the solid magnetic substance, that is, the carbon nanofibers 3. The separated liquid 10 is recovered and returned to the backwash liquid storage tank 24. In the figure, 25 indicates a replenisher for the backwash solution.

[0016]

Since the present invention is constructed as described above, it has the following effects.

Only carbon nanofibers formed by adhering to a ferromagnetic substance such as iron or nickel are separated and separated,
It is possible to remove foreign matter, which was impossible in the past. Therefore, the carbon nanofibers selected according to the present invention have remarkably high storage capacity such as hydrogen gas and lithium ion per unit volume or unit weight, such as a hydrogen storage material for a fuel cell and a cathode material for a lithium ion secondary battery. It can be used as an industrial material with high added value.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention using a drum type magnetic separator.

FIG. 2 is a diagram showing an embodiment of the present invention using a superconducting magnetic separator.

FIG. 3 shows a schematic view of carbon nanofibers.

[Explanation of symbols]

1 Metal catalyst piece 2 carbon pieces 3 Carbon nanofiber 4 Thermal decomposition products 5 dispersion tanks 6 Surfactant 7 Drum type magnetic separator 7'Superconducting magnetic separator 8 Magnetic slurry 9, 12 filters 11 Non-magnetic slurry 13 foreign matter 15 stirring blades 16 fixed magnet 18 drums 21 Superconducting magnet 22 Metal mesh material 23 refrigerator

Claims (2)

(57) [Claims] 1. A solid product obtained by thermally decomposing ethylene, carbon monoxide, or the like using a metal catalyst containing a magnetic substance such as iron or nickel is stirred with a surfactant to separate the product.
A method for finely selecting carbon nanofibers, characterized by separating carbon nanofibers grown with magnetic metal catalyst pieces as nuclei from a non-magnetic slurry by magnetic force after being dispersed and made into a slurry, and then passed through a magnetic separator. . 2. A solid product obtained by thermally decomposing ethylene, carbon monoxide or the like using a metal catalyst containing a magnetic substance such as iron or nickel, and stirring the resulting solid product in a liquid together with a surfactant. Characterized by comprising a dispersion tank for dispersing, a magnetic separator for separating the magnetic slurry from the slurry of the dispersion tank, and a filter for separating solid particles from the separated magnetic slurry, of carbon nanofibers Selector.