JP2001207342A - Method for producing vapor-grown carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an industrially advantageous method for producing vapor- grown carbon fibers by which the production stability enabling the continuous production and quality of the carbon fibers are remarkably improved. SOLUTION: This method comprises contact heating a pyrolytic gas of a hydrocarbon, especially at 600-1,300 deg.C in the presence of an organotransition metal compound catalyst by using the electromagnetic induction heating as a heating method. In the method, the continuous production of the vapor-grown carbon fibers can be carried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing carbon fibers in a gas phase. More specifically, the present invention relates to a method for producing a vapor-grown carbon fiber, characterized in that electromagnetic induction heating is used as a heating method when producing a carbon fiber by heating a hydrocarbon raw material.

[0002]

2. Description of the Related Art Since a vapor-grown carbon fiber has excellent crystal orientation, it has excellent mechanical properties, electrical properties, biochemical properties, etc. which are not found in conventional carbon fibers. An efficient industrial production method is desired. Conventionally, as a method for producing a vapor-grown carbon fiber, for example, a substrate such as alumina or graphite is placed in an electric furnace, and iron,
To form an ultra-fine particle catalyst such as nickel, and to introduce a mixed gas of a hydrocarbon gas such as benzene and a carrier gas such as hydrogen gas thereon to decompose the hydrocarbon at a temperature of 1010 to 1300 ° C. Thus, a method of growing carbon fibers on a substrate is known in Japanese Patent Application Laid-Open No. 48-41039, Japanese Patent Publication No. 51-33210, and the like.

However, in these methods, the length tends to be non-uniform due to minute temperature unevenness on the substrate surface and the density of the surrounding fibers, and the gas as a carbon source is consumed by the reaction. Therefore, there is a problem that the fiber diameter is considerably different near the inlet and outlet of the reaction tube, and the quality of the carbon fiber is low. In addition, since the production is carried out only on the substrate surface, the central part of the reaction tube does not contribute to the reaction and the yield is poor, and it is necessary to perform independent dispersion, reduction, growth on the ultrafine particle substrate, and then take out the fiber Therefore, there is a problem that continuous production is impossible due to the steps to be performed, and therefore, productivity is low.

Further, as for a continuous production method of carbon fiber by a gas phase method, for example, as disclosed in JP-A-60-54998, a mixed gas of a hydrocarbon compound gas, an organic transition metal compound gas and a carrier gas is used. 600 ° C ~ 130
A method of continuously producing carbon fibers by a vapor phase growth method of heating at 0 ° C. is also known. However, even with this method, a large temperature unevenness is obtained at the inlet, outlet, center, and outer wall of the reaction tube. There is a problem that the length and shape of the carbon fiber are not uniform and the quality is low. In addition, regarding the collection of carbon fibers associated with continuous production, the carbon fiber accumulates at the end of the electric furnace with the lapse of time, and the workability is poor. Heat shock occurs, and the furnace core tube is made of alumina or the like, so the durability against the temperature difference is poor and the furnace core tube may be broken, so that long-term continuous operation cannot be performed and productivity is low. The problem had not been solved.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing carbon fiber by a vapor phase growth method, which is industrially advantageous, and achieves high productivity due to continuous production stability and greatly improves the quality of carbon fiber. It is another object of the present invention to provide a production method for improving the carbon fiber quality and to supply high-quality carbon fiber by the present method.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on a continuous production method of carbon fiber by a vapor growth method capable of improving productivity and quality. As a heating method, a specific method of continuous production of carbon fibers by a specific vapor phase growth method of heating in a range of 600 ° C. to 1300 ° C. using a specific electromagnetic induction heating,
The inventors have found that high quality carbon fibers can be industrially produced with high productivity, and have completed the present invention.

That is, the present invention provides: A method for producing carbon fibers, in which a gas obtained by thermal decomposition of a hydrocarbon is heated in contact with an electromagnetic induction heater in the presence of an organic transition metal compound. In addition, the thermal decomposition is characterized in that fine powder of a heated refractory metal or metal compound is suspended in a hydrocarbon thermal decomposition zone. Further, the thermal decomposition is characterized in that a mixed gas of a gas of an organic transition metal compound, a carrier gas and a hydrocarbon gas is heated. It is also characterized in that the heating is performed at 600 ° C. to 1300 ° C. Also, the electromagnetic induction heating is characterized in that a heating element made of a carbon / ceramic composite material is installed in a passage formed of a non-magnetic material through which a gas passes. In the electromagnetic induction heating, a plurality of heating stages including a heating element and its coil are provided in the direction of gas movement, and the heating element of the first heating stage is formed of metal, and the heating stages subsequent to the next heating stage are formed. It is also characterized by using a device in which the heating element is made of a carbon / ceramic composite material. Also, the ceramic composite material is characterized in that it is mainly composed of carbon and is made of a composite of boron carbide and silicon carbide. Further, the electromagnetic induction heating is characterized in that a device having a heating element formed on a member having an outer periphery fitted into the inner periphery of the gas passage and having the gas passage hole is used. Also, the electromagnetic induction heating is characterized in that a device in which the heating element is composed of a plurality of members and is supported by a non-magnetic material in the passage so as to form a gas passage is used. Also provided is a carbon fiber produced by the method according to any one of (10) to (10). In summary, the present invention provides a method for producing carbon fibers, which comprises heating a gas obtained by thermal decomposition of hydrocarbons in the presence of an organic fiber metal compound in contact with an electromagnetic induction heating body, and the high quality obtained by the method. It is intended to provide carbon fiber.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a hydrocarbon compound as a main carbon source feedstock is intended to include all hydrocarbon compounds comprising an organic chain compound or an organic cyclic compound. Are required to be aliphatic hydrocarbons and aromatic hydrocarbons. In addition, derivatives containing elements such as nitrogen, oxygen, sulfur, fluorine, bromine, iodine, phosphorus, and arsenic can also be used. Specific examples of individual compounds include alkane compounds such as methane and ethane; alkene compounds such as ethylene and butadiene; alkyne compounds such as acetylene; aryl hydrocarbon compounds such as benzene, toluene and styrene; An aromatic hydrocarbon having a condensed ring such as naphthalene and phenanthrene; a cycloparaffin compound such as cyclopropane and cyclohexane; a cycloolefin compound such as cyclopentene and cyclohexene; an alicyclic hydrocarbon compound having a condensed ring such as steroid; methylthiol; Metulethyl sulfide,
Sulfur-containing aliphatic compounds such as dimethyl thioketone; sulfur-containing aromatic compounds such as phenylthiol and diphenyl sulfide;
And sulfur-containing heterocyclic compounds such as benzothiophene and thiophene. It is also possible to use a mixture of two or more of the above compounds.

Further, the gas in the present invention means a gas in a broad sense including not only a pure gas but also a mist containing solid or liquid fine particles in the gas. The carrier gas is mainly composed of a rare gas such as argon or helium of the periodic group 0 and a gas selected from hydrogen, nitrogen or a mixed gas thereof, and hydrogen gas is most preferable for obtaining a high yield. Mainly means that other gases are allowed to be contained in addition to the above, and the ratio is within 20% of the carrier gas component. Such minor component gases are preferably hydrogen sulfide and / or carbon disulfide.

In the present invention, an organic transition metal compound used as a catalyst source includes: an alkyl metal having an alkyl group and a metal bonded; an allyl complex having an allyl group and a metal bonded; Is an organic transition metal compound typified by a π complex and a chelate-type compound or the like bonded to the compound. Among these, chelate type compounds are preferred. The transition metals here are scandium, titanium,
It refers to vanadium, chromium, manganese, iron, cobalt, nickel, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, tungsten, rhenium, iridium, and platinum. Belonging to a tribe,
Among them, iron, cobalt, and nickel are particularly preferred, and iron is most preferred. It is also possible to use these mixtures.

[0011] The heating temperature in the present invention is preferably a mixture of a hydrocarbon compound gas, an organic transition metal compound gas and a carrier gas containing a small amount of 0 to 20% of a gas.
C. to 1300 C., more preferably 1050 C. to 1200 C.
Is the temperature at which heating is performed. In this case, if the temperature is lower than 600 ° C., the organic transition metal compound is not sufficiently vaporized, so that carbon fibers are not generated. So it does not become fibrous.

As described above, when the organic transition metal compound serving also as the catalyst and the carbon supply source is heated in the above-mentioned temperature range together with the hydrocarbon compound which is the main carbon supply source, both are thermally decomposed (carbon source). The heat-melting metal or fine particles of the metal compound, which are gasified and released by the thermal decomposition of the organic transition metal compound, float in the thermal decomposition zone of the hydrocarbon compound, and the fine particles are used as catalyst points from both gases. It is considered that the carbon source is vapor grown to produce carbon fibers.

The ratio of the hydrocarbon compound and the organic transition metal compound in the mixed gas with the carrier gas is preferably 0 to 40 wt% and 0.05 to 10 w%, respectively.
t%. Here, the reason why the concentration of the carbon compound may be 0 means that when the skeleton of the organic transition metal compound contains sufficient carbon, the gas of the carbon compound is not necessarily required. The ratio of hydrocarbon compounds is 40wt%
When the amount exceeds the limit, a sufficient reaction is not performed to inhibit the growth of carbon fibers, and the catalytic activity of the organic transition metal is deactivated. Further, when the proportion of the hydrocarbon compound exceeds 40 wt%, the straightness of the carbon fiber is hindered, and the number of branched fibers increases. Further, when the ratio of the organic transition metal compound is as small as less than 0.1 wt%,
Since the starting point of fiber growth is reduced, the yield is reduced. Therefore, the ratio of the two is preferably in the above range.

The present invention is characterized in that a method using electromagnetic induction heating is employed as a method for heating the mixed gas. The principle of this heating method is that, as shown in, for example, the electromagnetic induction heating device of FIG. 1, heat is generated by electromagnetic induction in a passage made of a non-magnetic material, for example, silicon nitride, ceramics or the like so that gas basically passes through. A heating element is provided, and heat is generated by bringing a gas passing through the passage into contact with the heating element heated by electromagnetic induction. At this time, it is preferable that the heating element is a carbon / ceramic composite material. When a carbon-ceramic composite material having the necessary heat resistance, mechanical strength, and electrical resistivity is used, the composite material is heated by electromagnetic induction heating, and the temperature is set to 600 to 1300 ° C. in the atmosphere. This has the advantage that there is almost no deterioration even if the temperature is maintained for a long time. The carbon-ceramic composite material and the production method are well-known technologies.
As described in Japanese Patent No. 75, it can be produced by pressing a mixed powder of a milled coke powder and a ceramic powder in a mold and then baking the mixture at a reaction temperature or lower under an inert atmosphere. . In addition, the carbon-ceramic composite material is preferably composed mainly of carbon and composited with boron carbide and silicon carbide. In this case, by changing the mixing ratio of boron carbide and silicon carbide, the electrical resistivity and the strength against thermal shock can be changed, so that an electromagnetic induction heating device with high durability and electrical efficiency can be obtained.

[0015] The electromagnetic induction heating device may be configured, for example, by providing a plurality of heating stages each composed of the heating element and its coil in the moving direction of the gas, wherein the heating element of the first heating stage is made of metal or the like. The heating element of the heating stage after the next heating stage can be made of a carbon / ceramic composite material.
In this case, since the heating element in the first heating stage is made of metal, the temperature of the heating element in this stage has a limit temperature according to the material in consideration of the durability of the metal heating element. Assuming that the temperature is about 500 ° C., the temperature is controlled to be lower than this temperature, and after the next heating stage, using a heating element made of a carbon / ceramic composite material, the temperature is raised to 600 to 1300 ° C.
It is desirable that the temperature be raised to C before use.

[0016] This allows the metal heating element to generate heat within the reasonable range of durability in the first heating stage, thereby heating the gas to a predetermined temperature. , The load after the next heating stage is reduced by that much, the temperature can be raised to the maximum temperature at once in the first heating stage, and the gas temperature can be raised in a short time, improving durability and electrical efficiency I do. Further, the heating element made of the carbon / ceramic composite material may be formed as a member having an outer periphery fitted to the inner periphery of the passage and having the gas passage hole, and the outer periphery of the heating element may be formed in the passage. The gas is uniformly heated by passing through the gas passage hole with little gas passing therethrough because it fits around the circumference. Further, the heating element made of the carbon / ceramic composite material can be made up of a plurality of members. Since the heating element is supported by a non-magnetic material in the passage forming the gas passage, the gas passage is bent. The gas passing through the gas passage can be sufficiently contacted with the heating element, and the temperature can be effectively raised for a predetermined length of the passage. Can be.

The electromagnetic induction heating apparatus used for electromagnetic induction heating in the present invention is not particularly limited as long as it can exhibit its function, but it is preferable to use the apparatus shown in FIG. FIG.
The outline of the electromagnetic induction heating device shown in FIG.
In FIG. 1, 1 is a raw material liquid container containing a hydrocarbon compound and a catalyst as a carbon supply source, an organic transition metal compound also serving as a carbon supply source, 2 is a liquid addition pump for sending a raw material liquid, 3 is a flow control valve, 4 is a hydrogen gas cylinder as a carrier gas, 5 is a flow control valve, 6 is a raw material liquid supply pipe, 7 is a hydrogen gas supply pipe, 8 is a heat resistant silicon nitride furnace core pipe,
9 pyrolysis gas residual discharge pipe 10 N ₂ inlet for the explosion-proof equipment, 11 argon gas inlet, 12 is the flow rate adjusting valve, 13 is an argon gas cylinder as a carrier gas, 14 push rod, Reference numeral 15 denotes a vapor growth carbon fiber collection box, and reference numeral 16 denotes an electromagnetic coil.

The mechanism of the electromagnetic induction heating device of the present invention will be described. A raw material liquid is sent from a raw material liquid container 1 containing a hydrocarbon compound as a carbon supply source and an organic transition metal compound as a catalyst source to an electromagnetic induction heating zone by a liquid addition pump 2 and a liquid supply pipe 6. The electromagnetic induction heating zone includes a heating element 1 made of a metal material such as an Fe alloy and a heating element 2 made of the carbon / ceramic composite material. Is an electromagnetic induction heating furnace. A gas introduction pipe 7 and a liquid supply pipe 6 are connected to one end of a silicon nitride furnace core pipe (inner diameter 60 mm, length 2000 mm) 8 horizontally installed in the heating furnace, and a gas residue discharge pipe 9 is connected to the other end. Argon gas cylinder 13 in tube 8
After the hydrogen gas from the hydrogen gas cylinder 4 is introduced into the heating element 1 at a predetermined flow rate (usually 20 to 60 L / min), the temperature of the heating element 2 is raised to 1100 ° C. did. After the temperature is raised, the raw material liquid is supplied at a predetermined flow rate (usually 7
-20 g / min), and a carbon source from a hydrocarbon compound gas is grown with a fine powder of a heated refractory metal or metal compound formed from an organic transition metal compound floating in a pyrolysis heating zone as a growth point. Growing sequentially, carbon fiber flocs are generated in the heating zone, scraped out with an extrusion rod 14, and stored in a recovery box 15 provided with a gas residue discharge pipe 9 above and a nitrogen gas inlet 10 for explosion proof below. . Of course, the production of carbon fibers may be either batch operation or continuous operation.

As shown in FIG. 2, the structure of the heating element 17 includes a plurality of heating elements 17 so that a pyrolysis gas from a hydrocarbon compound or the like is sufficiently heated by contact with the electromagnetic induction heating element. And a gas passage 18 composed of a hole may be formed between the heating elements. In FIG. 2, 8 is a furnace core tube, 16 is a coil, 17 is a heating element, 18 is a gas passage, 1
9 is a high frequency power supply.

The carbon fiber produced by the method of the present invention can be used as a reinforcing material, a conductive material, an easily coated material, an antistatic material, etc. by kneading with various resins. Can be applied. The present invention will be described below based on examples.

EXAMPLES The weight of the carbon fibers produced in the present invention was weighed, and the yield based on the weight of the raw materials was determined. In addition, the diameter of the carbon fiber and the length were measured using a transmission electron microscope (Hitachi HF-200: accelerating voltage 200 kv) and a digital microscope (Keyence VH6300), respectively, and an X-ray diffractometer (Max Science) The crystallinity was evaluated from an area value of 2θ = 25.5, which is a peak derived from carbon, using MXP-18). Example 1 1% by weight of ferrocene and 1.1% by weight of thiophene were mixed in toluene using the apparatus shown in FIG. 1, and the mixture was stirred until it became uniform. This raw material liquid is transferred to the raw material liquid container 1 connected to the liquid addition pump 2 and the liquid supply pipe 6. A silicon nitride furnace core tube (inner diameter 60 mm, length 200 mm) installed horizontally in an electromagnetic induction heating furnace equipped with the heating elements 1 and 2
0 mm) 8 is connected to a gas introduction pipe 7 and a liquid supply pipe 6 at one end, and a gas residue discharge pipe 9 to the other end. After the inside of the furnace core tube 8 is replaced with argon gas, hydrogen gas is introduced at 60 L / min. While heating, the temperature of the heating element 2 was raised to 1100 ° C. After the temperature was raised, the raw material liquid was fed at 20 g / min for 30 minutes, and a batch operation was performed. Thereafter, the gas was switched to argon gas and cooled, and the produced carbon fibers were taken out and the yield was measured. Table 1 shows the evaluation results of the obtained carbon fibers. FIG. 3 shows a transmission electron micrograph of a cross section of the obtained carbon fiber, and FIG. 5 shows the result of X-ray diffraction measurement.

(Comparative Example 1) In the apparatus shown in FIG. 1, a normal electric furnace having a silicon unit heating element as a heating element was changed to a furnace core tube made of mullite material (inner diameter: 60 mm, inner diameter: 60 mm).
The length was changed to 2000 mm) and it was installed horizontally. After the same raw material as in Example 1 was treated for the same time to take out the produced carbon fiber, the yield was measured and evaluated in the same manner as in Example 1. Table 1 shows the results. FIG. 4 shows a transmission electron micrograph and FIG. 6 shows the results of X-ray diffraction measurement.

(Example 2) An extruding rod 14 for extruding the carbon fiber mass accumulated at the end of the furnace core tube into the apparatus shown in FIG.
And a collection box 15 for collecting the produced carbon fiber
, A continuous operation was performed for 2 hours at the operating method, the processing temperature and the raw material introduction amount shown in Example 1. During the experiment, carbon fiber lump is generated at the end of the furnace core tube. Therefore, whenever the accumulated amount increases, the carbon fiber lump is inserted at a speed of 0.5 m / hr using an extruder rod, and the carbon fiber lump is removed. Continuous operation was carried out while dropping into the collection box, and after the produced fiber was taken out, the yield was measured and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0023]

Comparative Example 2 In the apparatus shown in FIG. 1, the heating element was changed to an electric furnace equipped with a silicon unit heating element, the furnace core tube was changed to a mullite material furnace core tube (inner diameter 60 mm, length 2000 mm), and the furnace was horizontally moved. installed. In addition, an extruding rod and a collection box were installed at the end of the furnace core tube in the same manner as in Example 2, and the same raw material as in Example 2 was used to produce carbon fiber lump using an extruding rod as in Example 2. Attempting to drop it in the collection box, the experiment was stopped at 78 minutes due to cracks in the furnace core tube during the first collection. After taking out the produced carbon fiber, the yield was measured and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0024]

[Table 1] In Comparative Example 2, the furnace core tube cracked, and the operation time was 78 minutes. The fluctuation rate is standard deviation / average value × 10
It was determined at 0. The X-ray diffraction area value is a Net-BG value, and a larger value indicates a sharper peak. As is clear from the above, the carbon fiber prototyped by electric furnace heating has a large average variation rate and large variation in both length and diameter, whereas the carbon fiber prototyped by electromagnetic induction heating has both length and diameter. Since the average fluctuation rate is small, uniform carbon fibers can be obtained.
Also, from the results of the X-ray diffraction measurement and the transmission electron micrograph,
Higher crystallinity and higher quality than carbon fibers produced by conventional methods. Further, in a long-time operation, when a prototype is manufactured by heating in an electric furnace, the furnace core tube is cracked by the heat shock of the extrusion rod. From the above results, carbon fiber obtained by electromagnetic induction heating is higher quality than that obtained by electric furnace heating,
It is clear that the production method is highly stable.

[0025]

According to the present invention, as compared with the conventional production method, the reaction is uniform, the whole area is obtained, a high yield is obtained, and since there is no temperature unevenness, each fiber has a uniform length and diameter. It also has high crystallinity and high quality. In addition, the electromagnetic induction heating method enables the furnace core tube and the heating element to be continuously operated because they are resistant to heat shock. Continuous operation becomes possible and high productivity is developed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of an electromagnetic induction heating device according to the present invention.

FIG. 2 is a schematic view showing a side structure of a suitable heating element in the electromagnetic induction heating device used in the present invention.

FIG. 3 shows a transmission electron micrograph of a cross section of the carbon fiber obtained in Example 1.

FIG. 4 shows a transmission electron micrograph of a cross section of the carbon fiber obtained in Comparative Example 1.

FIG. 5 is a graph showing the results of X-ray diffraction measurement of the carbon fiber obtained in Example 1.

FIG. 6 is a graph showing the results of X-ray diffraction measurement of the carbon fiber obtained in Comparative Example 1.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 raw material liquid container 2 liquid addition pump 3 flow rate control valve 4 hydrogen gas cylinder 5 flow rate control valve 6 raw material liquid supply pipe 7 hydrogen gas supply pipe 8 silicon nitride furnace core pipe 9 gas residual discharge pipe 10 N ₂ inlet 11 argon gas introduction Mouth 12 Flow control valve 13 Argon gas cylinder 14 Extrusion rod 15 Collection box 16 Coil 17 Heating element 18 Gas passage 19 High frequency power supply

Claims (10)

[Claims] 1. A method for producing carbon fiber, comprising heating a gas obtained by thermal decomposition of a hydrocarbon in contact with an electromagnetic induction heater in the presence of an organic transition metal compound. 2. The method for producing carbon fibers according to claim 1, wherein the pyrolysis is carried out by floating fine powder of a high-melting metal or a metal compound in a hydrocarbon pyrolysis zone. . 3. The method for producing carbon fibers according to claim 1, wherein the thermal decomposition is performed by heating a mixed gas of an organic transition metal compound gas, a carrier gas and a hydrocarbon gas. 4. The method for producing carbon fibers according to claim 1, wherein the heating is performed at a temperature of 600 ° C. to 1300 ° C. 5. A heating element made of a carbon / ceramic composite material is installed in a passage formed of a non-magnetic material through which a gas passes, in the electromagnetic induction heating.
The method for producing a carbon fiber according to any one of the above. 6. In the electromagnetic induction heating, a plurality of heating stages including a heating element and a coil thereof are provided in a moving direction of the gas, a heating element of a first heating stage is formed of metal, The method for producing carbon fibers according to any one of claims 1 to 5, wherein an apparatus in which the heating element of the heating stage is made of a carbon / ceramic composite material is used. 7. The method for producing carbon fibers according to claim 5, wherein said ceramics composite material is mainly composed of carbon and composited with boron carbide and silicon carbide. 8. The apparatus according to claim 1, wherein the electromagnetic induction heating uses an apparatus having a heating element formed on a member having an outer periphery fitted into an inner periphery of a gas passage and having a hole for gas passage.
A method for producing a carbon fiber according to any one of claims 5 to 7. 9. The electromagnetic induction heating using a device in which the heating element is composed of a plurality of members and is supported by a non-magnetic material in the passage so as to form a gas passage. A method for producing a carbon fiber according to any one of claims 5 to 8. 10. A carbon fiber produced by the method according to claim 1. Description: