JP2001010809A - Method and apparatus for carefully selecting carbon nano-fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To select/separate carbon nano-fibers which have grown up on catalyst fragments as nuclei made of a magnetic metal by thermally decomposing ethylene, etc., in the presence of a metal catalyst comprising a magnetic substance such as iron and then by making obtained solid products pass through a magnetic separator. SOLUTION: Ethylene, carbon monoxide or the like is thermally decomposed in the presence of a metal catalyst containing a magnetic substance such as iron and/or nickel, and thermally decomposed products 4 containing formed carbon nano-fibers 3 are fed into a separation vessel 5 where liquid is stored, followed by being agitated together with a surfactant 6 so as to form slurry. The slurry is fed on the top of a drum 18 rotating in the direction of an arrow 17 around the peripheral surface of a fixed cylindrical magnet 16 having a defective part in a drum-type magnetic separator 7. Magnetic substances in the slurry are adsorbed on the drum 18 and are rotated toward the defective part of the magnet 16, in which the magnetic substances are desorbed from the drum 18, are washed by means of a spray nozzle 26 and are stored as magnetic slurry in a storage tank 20. Nonmagnetic slurry 11 is made to stay in a storage tank 19. Carbon nano-fibers 3 are separated and recovered through a filter 9 from the magnetic slurry and separated liquid 10 is returned to the separation vessel 5.

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 finely selecting carbon nanofibers used as a hydrogen storage material.

[0002]

2. Description of the Related Art Carbon nanofibers obtained by thermally decomposing a hydrocarbon gas such as ethylene or carbon monoxide using a metal catalyst such as iron or nickel have recently absorbed hydrogen gas more than a hydrogen storage alloy. Astonishing experimental results have been announced and are attracting attention as hydrogen storage materials. Although the mechanism of hydrogen storage has not been fully elucidated, hydrogen storage alloys have the drawbacks of heavy specific gravity and powdering due to repeated use. For example, it can be used as a hydrogen storage material for fuel cells and the like.

[0003] Further, the capacity of carbon, which is currently used for the cathode of a lithium ion secondary battery, to absorb lithium, is an important factor influencing the capacity of the battery. If capacity can be increased, a dramatic improvement in battery capacity can be expected.

[0004] However, since carbon nanofibers are pyrolysis products, generation and mixing of undesirable foreign substances such as carbon and hydrocarbons having other structures cannot be avoided. By mixing these foreign substances,
Since the storage capacity per unit volume or unit weight is naturally reduced, a process of separating and selecting only carbon nanofibers is required, but such a process has not existed conventionally.

[0005]

SUMMARY OF THE INVENTION In view of the above, the present invention removes undesired foreign substances from a produced pyrolysis product and carefully selects the same to increase the storage capacity of hydrogen gas and lithium ions per unit volume or unit weight. The purpose is to:

[0006]

Means for Solving the Problems 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 pass a solid product obtained by thermally decomposing ethylene, carbon monoxide, and the like using a metal catalyst containing a magnetic substance such as iron or nickel, by passing through a magnetic separator. A method for selectively selecting carbon nanofibers, comprising separating magnetically grown carbon nanofibers using magnetic metal catalyst pieces as nuclei.

[0007] The invention according to claim 2 provides a solid product obtained by thermally decomposing ethylene or carbon monoxide using a metal catalyst containing a magnetic substance such as iron or nickel together with a surfactant. A dispersion tank that disperses the product by stirring in a liquid, a magnetic separator that separates a magnetic slurry from a slurry in the dispersion tank, and a filter that separates solid particles from the separated magnetic slurry. The feature is a selective device for carbon nanofiber.

[0008]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 shows an embodiment using a drum-type magnetic separator, FIG. 2 shows an embodiment using a superconducting magnetic separator, and FIG. 3 shows a schematic diagram of carbon nanofibers. 2 and 3, FIG.
The same reference numerals denote the same or corresponding parts.

As shown in the schematic diagram of FIG. 3, the carbon nanofibers 3 are formed by growing flat carbon pieces 2 with a gap of approximately G = 0.34 nm with the fine metal catalyst pieces 1 as nuclei. D = 10 to several hundred nanometers, length L =
It is a fine carbon fiber of several microns. In the process of forming the fine metal catalyst pieces 1, the carbon deposited on contact of the raw material gas with the catalyst metal diffuses into the metal, and the catalyst surface is broken and collapsed by stress based on the volume change of the carbide generated on the metal surface. In any case, the metal catalyst is depleted, and according to the results of observation with an electron microscope, the metal catalyst has a regular shape with the fine metal catalyst piece 1 as a nucleus as shown in FIG. Carbon nanofibers 3 are formed.

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

According to the present invention, as shown in FIG. 1, a pyrolysis product 4 containing carbon nanofibers 3 generated by pyrolysis is used.
Is supplied to a dispersion tank 5 storing a liquid such as water, and stirred with a stirring blade 15 together with a surfactant 6. The solid particles of the product are isolated and dispersed in the liquid to form a slurry. It is supplied to the drum type magnetic separator 7.

As shown in the figure, a 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 an 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, rotates, is desorbed at the defective portion of the fixed magnet 16, is washed by the spray nozzle 26, and is cleaned by the spray nozzle 26. The non-magnetic slurry 11 which is stored as a magnetic slurry in the magnetic slurry storage tank 20 and is not affected by the magnetic force stays in the non-magnetic slurry storage tank 19.

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

FIG. 2 shows a configuration in which a well-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 a surfactant 6 in a dispersion tank 5 to be dispersed in a liquid to form a slurry, and then supplied to a well-known superconducting magnetic separator 7 '.

The superconducting magnetic separator 7 'is composed of a superconducting magnet 21 surrounding a mesh-like metal member 22 and a refrigerator 23 as shown. The mesh-like metal material 22 may be made of a well-known high gradient magnetic wool-like 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-like metal material 22. The separation liquid 14 is returned to the dispersion tank 5. On the other hand, the magnetic material captured by the mesh-like metal material 22 is once cut off the magnetism, backwashed and separated from the magnetic material, and the magnetic slurry 8 containing the magnetic material is separated from the solid magnetic material, ie, the carbon nanofibers 3 by the filter 9. The recovered liquid 10 is returned to the backwashing liquid storage tank 24. In the drawing, reference numeral 25 denotes a replenisher of the backwashing liquid.

[0016]

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

Only carbon nanofibers formed by adhering to ferromagnetic materials such as iron and nickel are sorted and separated,
It is possible to remove foreign substances that were not possible conventionally. Therefore, the carbon nanofiber selected according to the present invention has a remarkably high occlusion capacity of hydrogen gas or lithium ion per unit volume or unit weight, such as a hydrogen storage material for a fuel cell or a cathode material for a lithium ion secondary battery. It can be used as a high value-added industrial material.

[Brief description of the 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 diagram of a carbon nanofiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal catalyst piece 2 Carbon piece 3 Carbon nanofiber 4 Thermal decomposition product 5 Dispersion tank 6 Surfactant 7 Drum type magnetic separator 7'Superconducting magnetic separator 8 Magnetic slurry 9, 12 Filter 11 Non-magnetic slurry 13 Foreign material 15 Stirring Blade 16 Fixed magnet 18 Drum 21 Superconducting magnet 22 Reticulated metal material 23 Refrigerator

Claims (2)

[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 passed through a magnetic separator to form a magnetic metal catalyst. A method for selecting carbon nanofibers, which comprises separating magnetically grown carbon nanofibers using pieces as nuclei. 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 is stirred together with a surfactant in a liquid to obtain a product. , A magnetic separator that separates the magnetic slurry from the slurry in the dispersion tank, and a filter that separates solid particles from the separated magnetic slurry, characterized in that the carbon nanofiber Selection equipment.