JP2003239142A - Carbon fiber by gas phase method and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a carbon fiber in a gas phase by increasing choices of transition metal compounds essential to produce the carbon fiber in the gas phase and yield of the carbon fiber. <P>SOLUTION: This method for producing the carbon fiber in the gas phase is to dissolve the transition element compound in a solvent, generate minute droplets from the solution, generate fine particles of the transition metal element by vaporizing the solvent in the droplets and feed the fine particles together with an organic compound which is a raw material to a carbon fiber-producing furnace. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine carbon fibers by vapor phase pyrolysis of organic compounds, and more particularly to a method for identifying fine particles of a transition metal compound as a catalyst for producing carbon fibers. The present invention relates to a method for efficiently producing carbon fibers by supplying the carbon fibers into a carbon fiber production furnace.

[0002]

2. Description of the Related Art So-called vapor grown carbon fibers obtained by thermal decomposition of organic compounds grow using fine particles of transition metals such as Fe and Ni as catalysts. The generation mechanism is that carbon generated by thermal decomposition of an organic compound is deposited around the fine particles and extends into a fibrous shape. Therefore, in order to obtain fine carbon fibers, the fine particles should be as small as possible. By using these fine particles and shortening the growth time, it becomes possible to manufacture fine fibers.

Vapor grown carbon fiber is a filler of synthetic resin or paint as a conductive or heat conductive filler material, a filler of lithium battery or the like, an electrode material of fuel cell, secondary battery, capacitor or the like,
It is used as an electron emission material such as a field emission display (FED). For these applications, it is preferable that the carbon fiber has a diameter as small as possible. Heretofore, various methods have been proposed as a method for allowing fine particles of a transition metal to exist in a carbon fiber production furnace (reaction furnace). One is a method in which a transition metal compound is thermally decomposed to obtain fine particles of the metal in advance, and the fine particles are allowed to exist in a reaction furnace (Japanese Patent Publication No. 58-22571). In addition, there is also a method in which an organic transition metal compound such as ferrocene having a lower evaporation temperature (vaporization temperature) than the thermal decomposition temperature is gasified and supplied to a reaction furnace, where it is thermally decomposed to produce fine particles of the transition metal ( Japanese Patent Publication No. 62-4936
3 gazette). Further, there is also a method in which a transition metal compound is dissolved in a solvent, the solution is sprayed and supplied into a reaction furnace, and the compound is decomposed in the reaction furnace to generate fine particles of a transition metal (Japanese Patent No. 2778434).

[0004]

In the above-mentioned prior art, it is difficult to obtain fine particles of transition metal by the method of previously obtaining fine particles of transition metal. There is a limit in pulverization, and it tends to agglomerate into secondary particles and coarsens. Further, even in the thermal decomposition of a gas such as ferrocene, the produced metal particles tend to aggregate and become large in the thermal decomposition temperature region. The method of supplying the transition metal compound in the form of gas to the reaction furnace requires that the compound be vaporized at a temperature lower than the thermal decomposition temperature, and the types of the compound are considerably limited. Compounds such as ferrocene satisfy this condition, but are expensive and have problems in economic efficiency. When the transition metal compound is supplied in the form of gas, the size of the fine particles tends to vary. In particular, since the compounds are supplied in the molecular state, thermal decomposition is fast, and most of them are thermally decomposed near the inlet of the reaction furnace, and the generated metal particles agglomerate along the flow of gas and often become coarse. It grows to a size that does not function as. Therefore, the production efficiency (yield) of fine carbon fibers is low. Dissolving the transition metal compound in a solvent,
The method of supplying the solution as fine droplets into the reaction furnace has an advantage that various compounds can be used in a wide range by selecting a solvent. However, since the solvent evaporates in the reaction furnace, the effect of temperature due to the latent heat of evaporation appears and the temperature in the reaction furnace cannot be kept uniform, so that there is a problem that carbon fibers having a uniform diameter cannot be obtained. . An object of the present invention is to provide a method for producing a fine vapor-phase grown carbon fiber with a transition metal compound serving as a catalyst that can be widely applied to various compounds.

[0005]

The present invention has been made to solve the above-mentioned problems and comprises the following items. (1) A transition metal compound is dissolved in a solvent, fine droplets are generated from the solution, and then the solvent in the droplets is evaporated to form fine particles of the transition metal compound, and the fine particles are suspended in a gas of an organic compound. And a method for producing vapor grown carbon fiber, characterized in that the carbon fiber is supplied to a carbon fiber production furnace together with the carbon fiber production furnace. (2) A transition metal compound is dissolved in a solvent, fine droplets are generated from the solution, and then the solvent in the droplets is evaporated to form fine particles of the transition metal compound, and the fine particles are suspended in a gas of an organic compound. And a method for producing a vapor grown carbon fiber, which comprises supplying a transition metal compound gas together with a gas to a carbon fiber production furnace. (3) The method for producing a vapor grown carbon fiber according to the above (1) or (2), wherein the droplets contain two or more kinds of transition metal compounds having different thermal decomposition temperatures or reduction temperatures with hydrogen. (4) Production of the vapor grown carbon fiber according to the above (1) or (2), wherein there are two or more kinds of liquid droplets, and each liquid droplet contains a transition metal compound having a different thermal decomposition temperature or reduction temperature with hydrogen. Method. (5) The gas according to any one of (1) to (4) above, wherein the concentration of the transition metal compound in the droplets (the total amount of two or more kinds) is 0.01 to 40 mass%. Phased carbon fiber manufacturing method. (6) The transition metal compound is iron, nickel, cobalt, molybdenum, platinum, palladium, rhodium, ruthenium,
Titanium and vanadium oxides, hydroxides, sulfides, fluorides, fluoro complexes, chlorides, chloro complexes,
The gas phase method according to any one of (1) to (5) above, which is one selected from bromide, iodide, perchlorate, nitrate, double sulfate, carbonate, cyano complex, and metallocene. Carbon fiber manufacturing method.

(7) The method for producing a vapor grown carbon fiber according to any one of (1) to (6) above, wherein the transition metal compound has a thermal decomposition temperature lower than the evaporation temperature. (8) A method of generating droplets of a transition metal compound solution is
At least one selected from the pressure atomization method, the two-fluid atomization method, the centrifugal atomization method, the vibration method, the ultrasonic method, the acoustic atomization method, and the electric force atomization method (1) to ( 7. The method for producing a vapor grown carbon fiber according to any one of 7). (9) The method for producing carbon fiber according to any one of (1) to (8) above, wherein the solvent of the transition metal compound is water, an organic solvent, or a water-containing organic solvent. (10) Any one of the above (1) to (9), wherein the solvent of the transition metal compound is at least one selected from water, methanol, ethanol, propanol, benzene, toluene, xylene, acetone, ether and hexane. The method for producing a carbon fiber according to item. (11) A vapor grown carbon fiber produced by the production method described in (1) to (10) above. (12) Fiber outer diameter is 1 to 500 nm, fiber length is 0.5
The vapor grown carbon fiber according to (11) above, which has a thickness of -100 μm. (13) A resin composition containing the vapor grown carbon fiber according to (11) above in a resin.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a method for producing a vapor grown carbon fiber, wherein droplets are generated from a solution containing a transition metal compound and the solvent is evaporated from the droplets to produce fine particles of the transition metal compound. And supplying the fine particles into the reaction furnace. As the transition metal compound, either an inorganic or organic transition metal compound can be used. These compounds include iron, nickel, cobalt, molybdenum, platinum, palladium, rhodium, ruthenium, titanium, vanadium oxides, hydroxides, sulfides, fluorides, fluorocomplexes, chlorides, chlorocomplexes, bromides. , Iodide, perchlorate, nitrate, double sulfate, carbonate, cyano complex, metallocene, etc., such as FeF ₂ , Fe
Cl ₂ , FeCl ₃ , FeSO ₄ , FeNO ₃ , Fe (C
O) ₅ , Fe (C ₅ H ₅ ) ₂ , FeS, FeS ₂ , NiC
l ₂ , K ₃ [NiF ₆ ], K ₃ [CoF ₆ ], MoCl ₂ , R
Examples thereof include hCl ₂ , RuCl ₂ , TiCl _{4 and the} like. Further, these may be anhydrate or hydrate. Of these, for example, many compounds other than iron chloride, ferrocene, and the like are difficult to vaporize or have a thermal decomposition temperature lower than the vaporization temperature, so that they cannot be gasified and led to a reaction furnace. Therefore, these transition metal compounds are particularly useful in the present invention.

The above-mentioned transition metal compound is thermally decomposed in the reaction furnace, or hydrogen gas which is usually used as a carrier gas exists in the reaction furnace and is reduced by the hydrogen gas to form fine particles of transition metal. . In the present invention, two or more transition metal compounds can be used in combination, and it is particularly preferable to use two or more compounds having different thermal decomposition temperatures or reduction temperatures with hydrogen. By this combined use, it is possible to prevent the fine particles of the transition metal from being concentrated and produced in a narrow range zone in the reaction furnace, and to produce them in a wide range of zones, thereby improving the utilization efficiency of the fine particles. As a method of using two or more kinds of transition metal compounds, one is a method of dissolving two or more kinds of transition metal compounds in a solvent and using them as droplets. In this case, one droplet contains two or more kinds of transition metal compounds having different thermal decomposition temperatures or hydrogen reduction temperatures (collectively referred to as thermal decomposition temperatures). Another method is to generate two or more kinds of separate droplets from two or more kinds of transition metal compounds having different thermal decomposition temperatures and supply them to the reaction furnace. In the present invention,
The concentration of the transition metal compound in the solvent for forming the droplets is not particularly limited, but if it is too low, the production amount of the compound fine particles is small, and if it is too high, the fine particles tend to become large. The degree is suitable, preferably 0.
It is 1 to 30% by mass, more preferably 1 to 15% by mass.

The solvent used for forming the liquid droplets may be any one capable of dissolving the transition metal compound, and water, an organic solvent, a water-containing organic solvent, preferably water, alcohols, aromatic compounds,
It is selected and used from ketones, ethers, chain hydrocarbons such as water, methanol, ethanol, propanol, benzene, hexene, toluene, xylene, acetone, ether, and hexane. The solvent may be one kind or a mixture of two or more kinds. Generally, water is used for the inorganic transition metal compound and an organic solvent is used for the organic transition metal compound. A method for generating droplets from a transition metal compound-containing solution is a known pressure atomization method, two-fluid atomization method,
A centrifugal atomization method, a vibration method, an ultrasonic method, an acoustic atomization method, an electric force atomization method, or the like can be used. Devices belonging to these methods include an air jet spraying device, a Ruskin nozzle, a spray nozzle, and an ultrasonic atomizer. It is necessary to generate droplets as fine as possible using these devices. A preferred device that meets that requirement is an air jet atomizer. The droplets are generated in an atmosphere of nitrogen, helium, argon or hydrogen gas.

In general, droplets having a size of several microns or less are affected by Brownian motion, and gravitational sedimentation is less likely to occur, so that aggregation is less likely to occur. In the present invention, in order to obtain fine particles having a desired diameter of the transition metal compound, it is necessary to control the solution concentration of the transition metal compound and the diameter of droplets to be generated.
The droplet diameter can be controlled by changing the type of droplet generator. For example, in the case of generating the above-mentioned ferrous sulfate fine particles as an example, in the case of using an apparatus for generating droplets having a diameter of 0.3 to 0.8 μm, for example, when using a constant output atomizer, By using the iron aqueous solution, it is possible to generate fine particles of ferrous sulfate having a diameter of about 50 to 140 nanometers. In this case, if a 5 mass% ferrous sulfate aqueous solution is used, fine particles having a diameter of about 40 to 110 nanometers can be generated. To obtain fine particles of the transition metal compound from the droplet, the solvent in the droplet may be evaporated. Evaporation of the solvent is also possible by passing the droplets through, for example, a heating tube, but since hydrogen gas is usually preheated and used as a carrier gas in the production of vapor grown carbon fiber, the carrier gas is mixed with the droplets. However, it is efficient to evaporate the solvent in the droplets by the heat of the carrier gas. When the solvent evaporates, fine particles of the transition metal compound are generated and float in the gas. Since these fine particles are very small, no sedimentation occurs, and neither thermal decomposition nor aggregation occurs at a temperature about the evaporation of the solvent. Further, since the droplets are obtained in a state in which the particle diameters are considerably uniform, the generated fine particles also have a uniform particle diameter and the particle size distribution is narrow.

Next, the fine particles are supplied to a reaction furnace together with an organic compound as a raw material. As a supply method, it is preferable that a gas in which fine particles are suspended, a carrier gas, and an organic compound as a raw material are sent to, for example, a line mixer, sufficiently mixed and supplied to a reaction furnace. Hydrogen gas is usually used as the carrier gas and is preheated to about 200 to 400 ° C. Organic compounds are generally used in the production of vapor grown carbon fibers, and are aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene and phenanthrene, alicyclic hydrocarbons such as cyclopropane, cyclopentene and cyclohexane, methane and ethane. , Chain hydrocarbons such as acetylene, butadiene, and ethylene, oxygen-containing compounds such as methanol and ethanol, and mixtures thereof can be used. Among these, benzene, toluene, cyclohexane, acetylene, butadiene and ethylene are preferable, and benzene is particularly preferable. The ratio of the gas supplied to the reaction is generally 30 to 60 carrier gas to 1 mol of the organic compound.
Good molarity. The fine particles of the transition metal compound are used in an amount of about 1 to 10% by mass based on the organic compound.

The reaction furnace is generally 1000 to 1500 ° C.
To be heated. At this temperature, the organic compound is thermally decomposed, and the fine particles of the transition metal compound are thermally decomposed or reduced by hydrogen to produce fine particles of the transition metal. When the organic compound is decomposed, carbon atoms and carbon clusters are generated. Then, the carbon clusters are extended into fibrous shapes with the fine particles as nuclei to become carbon fibers. At this time, when the thermal decomposition temperature of the transition metal compound is low, decomposition of the transition metal compound and formation of the metal fine particles occur near the inlet of the reaction furnace, but the supply of carbon clusters that form carbon fibers is not possible there. Since it is sufficient, the number of carbon fibers produced will be small,
This leads to a decrease in reaction yield. Excess transition metal fine particles and clusters that have not become catalysts here grow and become huge, and therefore cannot be catalysts even in the downstream region of the reactor where carbon clusters are sufficiently supplied. Therefore, in order to increase the number of carbon fibers produced and improve the reaction yield, it is preferable that the transition metal fine particles and clusters be released over the entire area of the reaction furnace. . As one of the methods, it is effective to use a plurality of transition metal compounds having different thermal decomposition temperatures. Further, according to the present invention, since the transition metal compound is supplied as fine particles to the reaction furnace, the ratio of decomposition in the vicinity of the inlet of the reaction furnace is smaller than that in the case where the compound is supplied as a gas (molecule), and the reaction furnace is wide. Fine particles of the desired transition metal can be provided in the region.

The present invention can be used in combination with a conventional method for producing fine particles of transition metal. For example, by utilizing the sublimability of ferrocene, the method of the present invention is combined with the method of dissolving ferrocene in a raw material (organic compound serving as a carbon source) in advance, and then evaporating and supplying the ferrocene to the reaction furnace. It is possible to feed the transition metal compound not having it to the reaction furnace at the same time. By using the method of the present invention in combination with the conventional method, it is possible to generate the transition metal fine particles in a wider area in the reaction furnace, and thus the reaction yield is improved. When they are used in combination, the ratio thereof is preferably 1 mol or less of a gaseous transition metal compound based on 1 mol of the transition metal compound in the liquid droplets in terms of the transition metal element of the transition metal compound. The carbon fibers obtained by this method are typically 1 to 500 nm in diameter and 0.5 to 10 in length.
It is 0 μm.

[0014]

Embodiments will be specifically described below with reference to embodiments. (Example 1) Carbon fiber was manufactured using an apparatus as shown in FIG. In FIG. 1, 1 is a carrier gas heating furnace, 2 is an organic compound heating furnace, 3 is a reaction furnace (reaction tube), 32 is an expansion tube whose diameter increases toward the reaction tube, and 31 is a rectifier having many small holes. The plates 31 and 32 are for uniform supply of gas to the reaction tube. 4 is a collector, 5 is a droplet generator,
6 is a solution bath of the transition metal compound. 11, 21, 33
Each is for heating the inside of the furnace to a predetermined temperature with a heater. Benzene, which is a raw material of carbon fiber, was fed through the inlet 22. Hydrogen as the carrier gas is the hydrogen gas inlet 12
Sent in. Further, ferrous sulfate and ferric chloride were used as the transition metal compounds, an aqueous solution thereof was prepared, and droplets were generated by a droplet generator using nitrogen gas as a driving source. The droplets, the heated carrier gas and the raw material gas were instantaneously mixed by the line mixer 7. The carbon fiber 42 produced in the reaction tube 3 entered the collector 4 and was collected by the filter 41. The carrier gas was discharged from the gas discharge port 43. The operating conditions and results are as follows. (1) Carrier gas heating furnace Temperature: approx. 300 ° C Hydrogen gas feed rate: 150 L / min. (Standard condition: 0 ° C, 1 atm) (2) Organic compound heating furnace Type of organic compound Benzene temperature: approx. 300 ° C Feed organic compound Amount 10g / min. (3) Droplet generator Constant output atomizer (MODEL3076, Japan Canomax Co., Ltd.) Droplet type Mixed aqueous solution of ferrous sulfate and ferric chloride Concentration of mixed aqueous solution Ferrous sulfate 4% by mass, Ferric chloride 4 mass% Droplet supply rate 0.6 × 10 ^-3 L / min. Droplet size about 0.3 μm (measured by microscope. Number average particle size) Driving nitrogen supply rate 3.5 L / min. ( 2.5 Kg / cm ² G) (4) Reaction conditions Reaction temperature Approx. 1200 ° C (maximum temperature range) Reaction time 1 sec (average residence time in reaction tube) (5) Results Carbon fiber yield 0.92 g / min. (yield ^* 10%) carbon fiber shapes thickness 0.03 .mu.m, a length 15 [mu] m (both flat ) (* The yield is intended to carbon in benzene)

(Example 2) Example 2 was repeated except that ferrocene was dissolved in benzene in an amount of 0.5% by mass, and one kind of an aqueous solution of a transition metal compound having 7% by mass of ferrous sulfate was used. A carbon fiber was produced in the same manner as in 1. Results Carbon fiber yield 0.74 g / min. (Yield 8%) Carbon fiber shape Thickness 0.03 μm, length 15 μm (all average)

[0016]

EFFECTS OF THE INVENTION According to the present invention, the number of choices of transition metal compounds increases, and inexpensive inorganic compounds can be used. Further, the yields of the transition metal compound and the organic compound as a raw material are also improved as compared with the conventional method. Further, it becomes possible to manufacture carbon fibers which are thinner and have a uniform diameter.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

1 Carrier gas heating furnace 2 Organic compound heating furnace 3 Reactor (reaction tube) 4 collector 5 Droplet generator 6 Transition metal compound solution tank 7 line mixer 11,21,31 heater 12 Carrier gas inlet 22 Raw material inlet 31 Current plate 32 Expansion tube 41 Filter 42 carbon fiber 43 gas outlet

Claims (13)

[Claims] 1. A transition metal compound is dissolved in a solvent, fine droplets are generated from the solution, and then the solvent in the droplets is evaporated to form fine particles of the transition metal compound. The fine particles are suspended in an organic compound. A method for producing a vapor grown carbon fiber, which comprises supplying the carbon fiber together with the gas to a carbon fiber production furnace. 2. A transition metal compound is dissolved in a solvent, fine droplets are generated from the solution, and then the solvent in the droplets is evaporated to form fine particles of the transition metal compound, and the fine particles are suspended in an organic compound. And a gas of a transition metal compound are supplied to a carbon fiber production furnace, and a method for producing a vapor grown carbon fiber. 3. The method for producing a vapor grown carbon fiber according to claim 1, wherein the droplets contain two or more kinds of transition metal compounds having different thermal decomposition temperatures or reduction temperatures with hydrogen. 4. The method for producing a vapor grown carbon fiber according to claim 1, wherein there are two or more kinds of liquid droplets, and each liquid droplet contains a transition metal compound having a different thermal decomposition temperature or reduction temperature with hydrogen. . 5. The vapor phase according to claim 1, wherein the concentration of the transition metal compound in the liquid droplet (the total amount of two or more kinds) is 0.01 to 40 mass%. Method of producing carbon fiber. 6. The transition metal compound is an oxide, hydroxide, sulfide, fluoride, fluoro complex or chloride of iron, nickel, cobalt, molybdenum, platinum, palladium, rhodium, ruthenium, titanium or vanadium. 6. The gas according to claim 1, which is at least one selected from the group consisting of a chloro complex, a bromide, an iodide, a perchlorate, a nitrate, a double sulfate, a carbonate, a cyano complex and a metallocene. Phased carbon fiber manufacturing method. 7. The method for producing a vapor grown carbon fiber according to claim 1, wherein the transition metal compound has a thermal decomposition temperature lower than an evaporation temperature. 8. A method for generating droplets of a transition metal compound solution is a pressure atomization method, a two-fluid atomization method, a centrifugal atomization method, a vibration method, an ultrasonic method, an acoustic atomization method, or an electric force. The method for producing a vapor grown carbon fiber according to any one of claims 1 to 7, wherein the method is at least one selected from atomization methods. 9. The method for producing carbon fiber according to claim 1, wherein the solvent of the transition metal compound is water, an organic solvent, or a water-containing organic solvent. 10. The solvent of the transition metal compound is at least one selected from water, methanol, ethanol, propanol, benzene, toluene, xylene, acetone, ether, and hexane. The method for producing carbon fiber according to 1. 11. A vapor grown carbon fiber produced by the production method according to claim 1. 12. The vapor grown carbon fiber according to claim 11, wherein the fiber outer diameter is 1 to 500 nm and the fiber length is 0.5 to 100 μm. 13. A resin composition containing a vapor grown carbon fiber according to claim 11 in a resin.