JP2001019413A - Production of carbon nanofiber and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high occluding capacity for gaseous hydrogen or Li ion per unit quantity without containing no unfaverable foreign matter by passing a product obtained by pyrolyzing ethylene or CO, or the like, by using a metallic catalyst such as Co having magneticity at a temp. equal to or above the pyrolysis temp. through a magnetic separator in a gas circulation process. SOLUTION: Valves A, D, E, and H are opened and valves B, C, F and G are closed and the formation of carbon nanofiber and the magnetic attraction in the magnetic separator 6 are performed by circulating an original starting gas through a closed circulation line connecting a gas adjusting vessel 4, a pyrolytic reaction vessel 5, the valve A, a magnetic separator 6 and the valve E. A magnetic separator 6' is demagnetized to release carbon nanofiber magnetically attracted to a wool like metal 16 in a circulation line of the magnetic separator 6', the valve H, a gas filter 7 and the valve D, and the carbon nanofiber is suspended in a gas and caught and recovered by a gas filter 7. The formation and recovery of the carbon nanofiber are completed after the elapse of a prescribed time and the magnetic separators 6, 6' are switched by reversing the opening and closing of each switching valve to be continuously operated.

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 producing carbon nanofibers used as a hydrogen storage material.

[0002]

2. Description of the Related Art A phenomenal experimental result that carbon nanofibers obtained by thermally decomposing a hydrocarbon gas such as ethylene or carbon monoxide using a metal catalyst can absorb hydrogen gas more recently than a hydrogen storage alloy. Was announced,
It is attracting attention as a hydrogen storage material. 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 manufacturing process for obtaining pure 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 provides a method and an apparatus for producing carbon nanofibers which do not contain undesired foreign substances and have a high storage capacity for hydrogen gas and lithium ions per unit volume or unit weight. The purpose is to provide.

[0006]

In order to achieve the above object, the present invention is directed to a metal catalyst having a Curie temperature higher than the thermal decomposition temperature, such as cobalt having a magnetism at a temperature higher than the thermal decomposition temperature. The product obtained by thermal decomposition of ethylene, carbon monoxide, etc. using a metal catalyst of the above is passed through a magnetic separator in the gas circulation process, so that the carbon nanofiber grown with the metal catalyst piece as a nucleus is magnetized. It is a method for producing carbon nanofibers, characterized by separating.

[0007] The invention according to claim 2 provides a gas regulating tank for adjusting at least the composition of the raw material gas, a fixed layer filled with metal catalyst particles such as cobalt having magnetism at a temperature higher than the thermal decomposition temperature, and / or A pyrolysis reaction tank composed of a fluidized bed, a plurality of magnetic separators, a gas filter, and a gas circulation circuit that connects the gas adjustment tank, the pyrolysis reaction tank and one magnetic separator, and the other magnetic field A carbon nanofiber manufacturing apparatus characterized in that a gas circulation circuit connecting a separator and a gas filter can be constructed independently of each other.

According to a third aspect of the present invention, the magnetic separator has a catalytic function by using a magnetic separator in which a high gradient magnetic field is formed by the metal catalyst by, for example, filling a wool-like metal catalyst. The apparatus for producing carbon nanofibers according to claim 2, wherein the thermal decomposition reaction tank is omitted.

[0009]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 is an explanatory view of an example, and FIG. 2 is a schematic view of a carbon nanofiber.

As shown in the schematic diagram of FIG. 2, 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. The process of forming the fine metal catalyst pieces 1 is such that the raw material gas comes into contact with the metal catalyst, the deposited carbon diffuses into the metal, and the catalyst surface breaks and collapses due to stress based on the volume change of the carbide generated in the metal. It is presumed that the metal catalyst becomes fine particles, but in any case, the metal catalyst is consumed as fine particles, and the results of observation by an electron microscope show that the fine metal catalyst piece 1 as shown in FIG. Is 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 foreign substances such as carbon and hydrocarbons in other forms.

This apparatus removes such foreign matters in the process of producing carbon nanofibers. The main elements are a gas regulating tank 4, a pyrolysis reaction tank 5, and a plurality of magnetic separators, as shown in FIG. 6, 6 'and gas filter 7
It is composed of A heater 8 is provided inside the gas regulating tank 4 in order to keep the composition and temperature of the gas in an optimum state at all times.
And a cooler 9, and an automatic regulating valve 11 for a raw material gas 10 such as a hydrocarbon gas such as ethylene or carbon monoxide.
And an automatic regulating valve 13 for hydrogen gas 12 for reduction. Note that the heater 8 and the cooler 9 can be provided inside the thermal decomposition reaction tank 5 as a matter of course. Metal catalyst particles 15 having a Curie temperature (magnetism loss temperature) equal to or higher than the thermal decomposition temperature are filled on the gas dispersion plate 14 of the thermal decomposition reaction tank 5, and the magnetic separators 6 and 6 'each apply a high gradient magnetic field. It is composed of a wool-like metal 16 to be formed and an electromagnet 17 arranged around the metal. In the figure, reference numerals 18 and 19 denote gas circulation blowers, and reference numeral 20 denotes a non-magnetic substance, that is, foreign matter generated by thermal decomposition, but illustration of a device for capturing and discharging the foreign matter 20 is omitted. The gas filter 7 is a schematic diagram of a well-known bag filter in which the filter is made of a heat-resistant fiber, and a device for discharging solid fine particles separated by the filter, that is, a carbon nanofiber 3 is not shown.

In the above configuration, an operation method will be described below. At the time of startup, the automatic regulating valve 13 is opened to introduce the hydrogen gas 12 into the system, and the system including the metal catalyst particles 15 is maintained in a reduced state. Next, the automatic regulating valve 11 is opened, and the raw material gas 10 such as hydrocarbon gas or carbon monoxide is introduced. Since the gas composition in the gas regulating tank 4 constantly changes with the progress of the thermal decomposition, the gas regulating composition is automatically adjusted by the automatic regulating valves 11 and 13 so as to maintain the gas composition at the optimum value, and the heater 8 and / or the cooling unit are cooled. The temperature of the gas is adjusted to the optimum pyrolysis temperature (for example, 600 ° C.) by the vessel 9. The raw material gas adjusted in the adjustment tank 4 is supplied to the gas dispersion plate 14 of the pyrolysis reaction tank 5.
The carbon nanofibers 3 are formed by contacting and reacting with the fixed layer and / or the fluidized bed formed of the metal catalyst particles 15, where the metal catalyst pieces 1 generated by the collapse of the surface of the metal catalyst particles 15 are used as nuclei. grow up.

After a suitable time has elapsed in the above-mentioned growth process, the number of revolutions of the gas circulation blower 18 is switched to increase the gas flow rate to fluidize the metal catalyst particles 15.
The grown carbon nanofibers float in the gas and are captured by the magnetic separator 6. The non-magnetic substance, that is, the foreign matter 20 passes through the magnetic separator 6 and is removed from the gas regulating tank 4. The metal catalyst particles 15 are usually a fixed bed, but may be a weak fluidized bed as long as the growth of carbon nanofibers is not hindered.

However, the inlets and outlets of the magnetic separators 6 and 6 'are arranged as shown in the figure, and A, B, C, D, E, F, G,
H eight switching valves are provided. In the illustrated example, the valve in the closed state is painted black for easy understanding. That is, the valves A, D, E, and H are opened as shown in the illustrated example,
By closing the valves B, C, F, and G, the carbon nanofibers are circulated by circulating the raw material gas in a closed circuit connecting the gas regulating tank 4, the pyrolysis reaction tank 5, the valve A, the magnetic separator 6, and the valve E. And magnetic adsorption in the magnetic separator 6 are performed. In a closed circuit connecting the magnetic separator 6 ', the valve H, the gas filter 7, and the valve D, the magnetic separator 6'
Is demagnetized to release the carbon nanofibers magnetically adsorbed to the wool-like metal 16 to float in the gas, which is captured and recovered by the gas filter 7. After a certain period of time has elapsed and the generation and recovery cycle of the carbon nanofibers is completed, the same operation is continuously repeated by switching the magnetic separators 6 and 6 'by reversing the opening and closing of each switching valve.

As described above, the magnetic separators 6 and 6 'are composed of the wool-like metal 16 forming a high gradient magnetic field and the electromagnet 17 disposed therearound. By increasing the specific surface area by reducing the wire diameter to the same as that of the metal, the thermal decomposition reaction tank 4 can be omitted by providing a catalytic function, and the apparatus can be simplified.

[0017]

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

[0018] Only carbon nanofibers formed by using a metal such as cobalt having magnetic properties at the pyrolysis temperature as a nucleus are selectively produced, thereby enabling foreign matter removal which has been impossible in the past. Therefore, the carbon nanofibers manufactured according to the present invention do not contain foreign matter, so that the hydrogen gas or lithium ion storage capacity per unit volume or unit weight is increased, and the hydrogen storage material of a fuel cell and the cathode of a lithium ion secondary battery are increased. It can be used as high value-added industrial materials such as materials.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a schematic view of a carbon nanofiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal catalyst piece 2 Carbon piece 3 Carbon nanofiber 4 Gas adjustment tank 5 Pyrolysis reaction tank 6, 6 'Magnetic separator 7 Gas filter 10 Raw material gas 11, 13 Automatic adjustment valve 15 Metal catalyst particles 16 Wool-like metal 17 Electromagnet 20 Foreign matter

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[Procedure amendment]

[Submission date] May 26, 2000 (2005.2.
6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008] Further, the invention according to claim 3 has at least
A gas regulating tank for adjusting the composition of the raw material gas
Woollike metal catalysts such as cobalt that are magnetic at high temperatures
A plurality of magnetic separators filled with to form a high gradient magnetic field,
In addition to having a gas filter,
Gas circulation circuit connecting the magnetic separator and the other magnetic separator
Independent gas circulation circuits connecting gas filters
An apparatus for producing carbon nanofibers , characterized in that the apparatus can be constructed by performing the following steps .

Claims (3)

[Claims] A product obtained by thermally decomposing ethylene, carbon monoxide or the like using a metal catalyst such as cobalt having a magnetism at a temperature higher than the thermal decomposition temperature is passed through a magnetic separator in a gas circulation process. Wherein the carbon nanofiber grown with the metal catalyst piece as a nucleus is separated by magnetic force. 2. Pyrolysis comprising at least a gas adjusting tank for adjusting the composition of a raw material gas, and a fixed bed and / or a fluidized bed filled with metal catalyst particles such as cobalt having magnetism at a temperature not lower than the pyrolysis temperature. A reaction vessel, a plurality of magnetic separators,
In addition to having a gas filter, a gas circulation circuit connecting the gas conditioning tank, the pyrolysis reaction tank and one magnetic separator, and a gas circulation circuit connecting the other magnetic separator and the gas filter can be independently constructed. An apparatus for producing carbon nanofibers, characterized in that: 3. The use of a magnetic separator in which a high gradient magnetic field is formed by a metal catalyst by filling a wool-like metal catalyst or the like, so that the magnetic separator has a catalytic function and the thermal decomposition reaction tank is omitted. The apparatus for producing carbon nanofibers according to claim 2, wherein: