JPH0680210B2 - Carbon fiber manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for producing whisker-like carbon fibers by a vapor phase method.

[Prior Art] In addition to carbon fibers obtained by a vapor phase method, carbon fibers are produced by PAN-based carbon fibers produced by firing organic fibers, mesophase pitch melt spinning, infusibilization and carbonization treatment. There are pitch-based carbon fibers and the like. Carbon fibers obtained by the vapor phase method are superior to other fibers in mechanical properties such as high tensile strength, and are also excellent in electrical conductivity and thermal conductivity. Therefore, it has recently attracted particular attention as a functional material. For example, the vapor grown carbon fiber graphitized at 2800 ° C has a tensile strength of 700 kg / mm ² and a tensile elastic modulus of 70 ton / mm ²
And the value is extremely high. These excellent properties are considered to be based on the high crystal orientation of carbon fibers.

Since the vapor grown carbon fiber has the above-mentioned properties, its field of application is wide and is used as a fiber reinforcing material for various composite materials such as FRP, FRM, FR cement and C / C composite. These are space, aviation, automobile industry,
It is a material that can be applied to many industries, such as the construction and electrical industries, and expectations for this carbon fiber are very high. Recently, the demand for electromagnetic shielding materials has increased due to the use of precision machinery in OA and FA applications, and high-quality carbon fibers are desired. Furthermore, although this carbon fiber can be easily converted into a graphite intercalation compound, it has attracted attention as a conductive material to replace the copper wire.

Conventionally, such vapor grown carbon fibers have been manufactured by a method using a substrate called a fixed bed method. But this method
Since continuous production is difficult, there is a drawback that productivity is extremely low. In order to overcome this, a fluidized bed system has been developed, in which ultrafine metal particles, which are catalysts, are suspended in a reactor to grow carbon (Japanese Patent Laid-Open No. 58-180).
See No. 615). Since this system uses the space inside the reactor three-dimensionally, the yield is high in principle and continuous production is possible. For this reason, it has become the mainstream of methods for producing vapor grown carbon fibers.

[Problems to be Solved by the Invention] However, there are still some problems in production on an industrial scale.

The first problem is that the growth rate of carbon fiber is higher than that of the fixed bed method, but the growth rate is not always satisfactory for industrial scale production, and the yield cannot be said to be sufficiently high. That's what it means. With this technology,
An organic compound such as ferrocene is pyrolyzed to produce an ultrafine particle catalyst for carbon fiber growth.However, since the thermal decomposition of an organometallic compound is complicated, its utilization rate as an iron atom is extremely low and It is very difficult to selectively generate ultrafine particles having a particle size of 300 Å or less, which works.
However, it is generally considered that the growth rate of carbon fibers is higher as the particle size of the catalyst is smaller, and the yield thereof is higher as the amount of ultrafine particles having a particle size of 300Å or less is larger. Therefore, for example, in JP-A-60-54998, ferrocene as a catalyst is used in an amount 2.5 times as much as that of benzene as a carbon fiber. In such a method, the cost of the organometallic compound product is high.

The second problem is the atmospheric gas source. As an improvement of the manufacturing method by the fluidized bed system, JP-A-60-5498 and JP-A-60-22
No. 4815, JP-A-61-108723, JP-A-61-225328 and the like have been proposed. In these methods, the atmosphere gas is mainly hydrogen gas. However, in order to obtain carbon fiber with a high yield using hydrogen gas, it is considered that hydrogen gas having a purity of 80% or more is required. Moreover, the impurities contained in the permissible gas are limited to inert gases such as nitrogen, and moisture and oxygen deactivate the catalyst, which is not preferable. When a hydrocarbon gas having a higher concentration is mixed, the heating causes thermal decomposition to generate soot. As a result, the purity of the product is lowered, which is not preferable. Also, the atmospheric gas is generally
It requires more than one time capacity, and a huge amount of gas is required for industrial scale production. When using expensive hydrogen,
It has to be reused and requires a refining device for that purpose, which is extremely economically disadvantageous.

It is considered that hydrogen, which is a conventional atmosphere gas, is for reducing ultrafine iron particles as a catalyst, cleaning the surface, and gasifying generated carbon. Therefore, the present inventor has selected and examined carbon monoxide as an atmosphere gas as an alternative to hydrogen, and as a result, a converter gas can be used, and fine particle dust contained in the converter gas has a catalytic ability. The inventors have found that exhaust heat can be used as a heat source, and applied for a patent for an invention that directly uses a high-temperature converter gas as an atmospheric gas (see Japanese Patent Laid-Open No. 63-12720). This converter gas is a gas generated in the process of manufacturing steel by adjusting the components such as carbon and silicon by oxygen from the hot metal produced in the blast furnace, and has been used as a fuel at most in the steel industry so far. , Its composition varies depending on operating conditions, but it is approximately 60-80% carbon monoxide, 10-20% carbon dioxide, 5-20 nitrogen.
%, Hydrogen 0.5 to 2%, and oxygen 1.0% or less.

However, in this method, since the converter gas is used as it is, it is difficult to separate the coarse particles contained in the high temperature converter gas and the gas fluctuation in the initial and final operations of the converter. Moreover, it cannot be said that the yield of carbon fiber is high enough, and there are problems such as variations in quality.

The third problem is the problem of heat source. The gas phase method requires a high temperature of 1000 ° C. or more, and when it is produced on an industrial scale, its energy is enormous, and an electric furnace cannot be economically adopted as its heating method. An internal heating method using a combustion exhaust gas of fuel is also conceivable, but in this case, there is a disadvantage in that the combustion exhaust gas contains water and soot, which hinders the production of carbon fibers.

The fourth problem is the problem of surface modification. In general, carbon fibers obtained by the vapor phase method have graphite crystals oriented in an annual ring shape, so when used as a reinforcing material for composites, their surface needs to be modified. There is a drawback that the process takes time.

[Means for Solving the Problems] As a result of intensive studies for solving the above problems, the present inventor has found that the addition of a metal compound as a decomposition catalyst for the organometallic compound produces the organometallic compound by thermal decomposition. The first problem relating to the growth rate of carbon fiber was solved by including many fine metal particles for growing carbon fiber having a particle size of 300 Å or less.

As atmospheric gas, carbon monoxide 50-80% such as converter gas
And at least 5 to 30% of carbon dioxide are used, the atmospheric gas is stored directly in the gas holder without directly introducing it into the reaction vessel at a high temperature, and the gas from the gas holder is heated. By performing at least two hot blast stoves alternately,
And the third problem related to the heat source have been solved.

Further, by using the atmospheric gas having the above composition, not only the atmospheric gas functions as a carrier gas, but also carbon dioxide performs a gasification action of carbon to form a surface modification of carbon fiber, and carbon monoxide serves a surface modification. It has a function of depositing carbon on the surface of the formed carbon fiber, and thereby solves the fourth problem relating to surface modification.

Hereinafter, the present invention will be specifically described.

The present invention introduces a hydrocarbon (raw carbon source) and an organometallic compound into a reaction vessel, and grows carbon obtained by pyrolysis of the hydrocarbon on fine particles produced by pyrolysis of the organometallic compound. In the method, a metal compound is introduced into the reaction vessel as a decomposition catalyst for the organometallic compound.

Hydrocarbons used in the present invention include aliphatic hydrocarbons such as methane, ethane, propane, ethylene, propylene and phthalicene, monocyclic aromatic hydrocarbons such as benzene, toluene and xylene, naphthalene and anthracene. Polycyclic aromatic hydrocarbons, or a mixture thereof can be applied, but crude gas oils, absorption oils, carbole oils, anthracene oils, heavy oils, pitches, and their mixtures, which are by-products from a coke oven, are cheap and large in amount. The sulfur-containing thiophenes, thiols, and thiophenols are particularly useful because the production rate of carbon fiber is high.

As the organometallic compound, any known one can be used as long as it has a carbon-metal bond, but when it is used by dissolving it in a raw material hydrocarbon, it is soluble, and when it is used in a gaseous state, it is sublimated. It is desirable that it has the property. Specifically, an organic transition metal compound containing titanium, vanadium, chromium, manganese, iron, cobalt, nickel, rubidium, rhodium, tungsten, palladium,
Of these, organometallic compounds containing iron, nickel, and cobalt are particularly preferable, and organometallic compounds containing iron are most preferable.

The metal compound, which is a decomposition catalyst for the organometallic compound, is added in order to decompose the organometallic compound to generate a large amount of fine metal particles for carbon fiber growth of 300 liters or less. The metal compound may be added in an amount of about 0.01 to 50 mol per mol of the organometallic compound used. Further, the transition metal compound can be used in any complex as long as it has the same or different metal atom as the organometallic compound used. The metals include titanium, vanadium, chromium, molybdenum,
Tungsten, manganese, iron, cobalt, nickel, ruthenium, rhodium, osmium, and iridium are preferable, and manganese, iron, cobalt, and nickel are particularly preferable. The compound may be in any form, for example, sulfate,
Inorganic compounds such as nitrates, acetates, chlorides, sulfides, oxides, carbides, nitrides, acetylacetonate salts, and organic transition metal complexes such as carbonyl compounds are used.

In the present invention, carbon monoxide 50-80% and carbon dioxide 5-30%
A gas containing at least and is used as an atmospheric gas, and in particular, in a volume ratio, carbon dioxide 0.06 per 1 part of carbon monoxide.
A composition containing .about.0.6 and hydrogen 0.001 to 0.2 is preferable. The reason for limiting the composition range of carbon monoxide, carbon dioxide and hydrogen is that it is set by the combination of carbon dioxide and hydrogen gasification action of carbon fiber and carbon deposition action of carbon monoxide. This is because the balance of each gas is lost and the desired carbon fiber shown below cannot be obtained. Specifically, this atmosphere gas is a converter gas, a blast furnace gas, a mixed gas thereof, or a gas obtained by mixing a hydrogen-containing gas such as a coke oven gas. However, the composition of the converter gas alone can satisfy the above composition,
It is suitable. In the present invention, when the atmospheric gas is preheated and kept at 600 to 1300 ° C. which is the reaction zone, a method using a hot stove system used in a blast furnace or the like is adopted. That is, the converter gas or the like at high temperature is not directly introduced into the reaction vessel but is temporarily stored in the gas holder and the gas from the gas holder is heated in the heating furnace. According to this method, coarse particles are removed, and a converter gas or the like having a stable gas composition can be used from the gas holder. In the present invention, at least two hot air stoves (heat storage furnaces) are connected to the reaction vessel. In the hot-blast stove, the combustion gas is burned to heat the filling material filled in the furnace to 1000 to 1600 ° C, and the temperature of the atmospheric gas introduced into the reactor from the hot-blast stove is 600 ° C.
Atmosphere gas is heated and introduced so that the temperature becomes ~ 1300 ° C. At this time, moisture and soot contained in the combustion exhaust gas can be obtained by replacing the combustion exhaust gas with the atmospheric gas. Also,
Since at least two hot blast stoves are provided, a cycle of combustion, flue gas replacement, and atmosphere gas circulation is possible, and atmosphere gas heated to 600 to 1300 ° C can be continuously introduced into the reaction vessel. Here, the fuel gas used in the present invention is hydrogen, propane, naphtha, LNG, petroleum gas,
The mixture, blast furnace gas generated in a steel mill, converter gas, coke oven gas, and the mixture can be used,
Blast furnace gas, converter gas, coke oven gas, and a mixture thereof are particularly useful for suppressing generation of water and soot. A known method can be applied to the combustion of the fuel gas. Various kinds of burners can also be used.
Any packing can be used as long as it is stable at a high temperature of about 1600 ° C. Ceramic pebble is especially desirable.

When the carbon fiber is grown under such conditions, the carbon fiber having an uneven surface is obtained. Such properties are
It is not recognized by the method of directly introducing the high temperature converter exhaust gas into the reaction vessel. The inventor believes that carbon monoxide contained in the atmospheric gas contributes to carbon deposition on the carbon fiber, while carbon dioxide contributes to gasification of carbon to size the surface. That is, carbon dioxide has a gasification rate sensitive to the structure of carbon, and for example, the gasification rate of charcoal with respect to graphite is said to be 10,000 times. Therefore, the gasification rate for the non-crystalline carbon present on the surface is faster than that for the crystalline carbon, and a crystalline carbon fiber having irregularities, which is extremely useful as a reinforcing fiber for a composite material, is formed on the surface of the carbon fiber. It is possible to produce. It is known that carbon monoxide precipitates carbon due to its disproportionation reaction, and it is possible to further deposit carbon on the uneven surface of the crystalline carbon fiber surface having unevenness by the pyrolytic carbon. it can. On the other hand, with hydrogen which has been conventionally used as the atmospheric gas, the carbon fiber obtained is smooth and its fiber diameter is extremely small. The reason why the composition range of carbon monoxide and carbon dioxide is limited as described above in the present invention is that it is difficult to obtain a desired carbon fiber if the composition range deviates from the above range.

[Effects of the Invention] According to the present invention, since a metal compound is added as a decomposition catalyst of an organometallic compound, most of the particle size of fine metal particles generated by thermal decomposition of an organometallic compound can be 300 Å or less, As a result, the growth rate of carbon fiber was remarkably increased, enabling production on an industrial scale. Further, since the gas containing carbon monoxide and carbon dioxide was used as the atmospheric gas, the atmospheric gas not only functions as a carrier gas, but also has the function of modifying the surface of the carbon fiber, and the characteristics of the obtained carbon fiber are excellent. Can be one. Further, since this atmosphere gas is heated by a hot-blast stove, it is possible to solve the problem of the property of the gas and the problem of the heat source and to stably produce good quality carbon fiber.

[Examples] The present invention will be described below with reference to Examples.

Example 1 Carbon fiber was manufactured using the apparatus shown in FIG. In the figure, reference numeral 11 is a gas cylinder filled with argon gas. 12 is a gas cylinder filled with converter gas, and the converter gas is a gas having a composition of carbon monoxide gas 70% by volume, carbon dioxide gas 15% by volume, hydrogen gas 1.1% by volume, and nitrogen gas 15% by volume. Is introduced into the reaction vessel as an atmospheric gas. Flowmeters 13 and 14 are connected to the cylinders 11 and 12, respectively, to control the gas flow rate. Numeral 15 is a raw material tank in which benzene was added as a raw material oil. Ferrocene, thiophene, and Mn (II) acetylacetonate salt, which is a decomposition catalyst for ferrocene, are dissolved in this benzene, and the weight composition ratio is such that ferrocene, thiophene, and Mn (II) are mixed with 100 parts by weight of benzene. Acetylacetonate salts are in proportions of 0.4, 0.2 and 0.1 respectively. These cylinders 11 and 12 are connected to a reaction tube 20 via a stainless pipe 16, and the raw material tank 15 is connected to a reaction tube 20 (reaction vessel) via a stainless pipe 17. The reaction tube 20 is an alumina tube having an inner diameter of 90 mm and a length of 1000 mm, and an electric furnace 23 is installed on the outer circumference over the length of 800 mm. The temperature of the electric furnace 23 is detected by the thermocouple 24 and is controlled to a constant temperature by the temperature controller 25. In this example, the temperature during the operation of the electric furnace 23 was set to 1150 ° C.

In operation, first, argon gas is supplied from the cylinder 11 into the reaction tube, and the inside of the reaction tube is replaced with argon gas.
Subsequently, the converter gas stored in the cylinder 12 was used as a reaction tube at 300 ml / min.
Shed within 20. Further, the raw material oil was supplied into the reaction tube 20 at a rate of 2 ml / min by using the chemical pump 22. In the reaction tube, pyrolysis of the raw material oil and catalytic reaction occurred, whereby whisker-like carbon fibers were continuously produced and collected by the collector 21. The obtained carbon fibers had an average diameter of 1 μm and an average length of 2000 μm, and as a result of observation with a transmission electron microscope, the surface was rough and fluffy. The yield was 68% based on benzene.

Example 2 Mn used in Example 1 as a ferrocene decomposition catalyst
Instead of the (II) acetylacetonate salt, a cobalt (II) acetylacetonate salt was used, and the other conditions were the same as in Example 1. As a result, the obtained carbon fiber had an average diameter of 1 μm and an average length of 3000 μm. As a result of observation with a transmission electron microscope, the surface was rough and fluffy as in Example 1. The yield was as high as 70% with respect to benzene.

Example 3 An apparatus similar to that of Example 1 was used, but the cylinder 12 was filled with an atmospheric gas mainly containing carbon monoxide gas. The composition of the atmosphere gas is 76% by volume of carbon monoxide gas, 19% by volume of carbon dioxide gas, 2.8% by volume of hydrogen gas, 1.5% by volume of methane gas, and the balance nitrogen gas. And as a result of carrying out under the same conditions as in the example, the obtained carbon fiber has an average diameter of 1 μm,
The average length was 3000 μm, and as a result of observation with a transmission electron microscope, the surface was rough and fluffy. The yield was as high as 70% with respect to benzene.

Example 4 An apparatus similar to that of Example 1 was used, but the cylinder 12 was filled with an atmospheric gas mainly containing carbon monoxide gas. This atmosphere gas composition uses a mixed gas of 97% by volume of converter gas and 3% by volume of coke oven gas. Its composition is 68% by volume of carbon monoxide gas, 13% by volume of carbon dioxide gas, and 4.
0% by volume, 1.0% by volume of methane gas and 14% by volume of nitrogen gas. Then, as a result of carrying out under the same conditions as in Example 1, the obtained carbon fibers have an average diameter of 1 μm and an average length of 3000 μm, and as a result of observation with a transmission electron microscope, the surface is rough,
It had a fluffy appearance. Yield is 65 relative to benzene
%Met.

Comparative Example 1 The same apparatus as in Example 1 was used, but the cylinder 12 was filled with an atmospheric gas mainly containing carbon monoxide gas. The composition of the atmosphere gas is 21% by volume of carbon monoxide gas, 20% by volume of carbon dioxide gas, 4.0% by volume of hydrogen gas, and 55% by volume of nitrogen gas. And as a result of carrying out under the same conditions as in Example 1,
The obtained carbon fiber has an average diameter of 1 μm and an average length of 1500.
The surface was smooth as a result of observation with a transmission electron microscope. The yield was 23% based on benzene.

Comparative Example 2 Example 1 except that no ferrocene decomposition catalyst was added.
As a result of carrying out under the same conditions as above, the yield of the obtained carbon fiber was 40%, the average diameter was 1 μm, and the average length was 250 μm.
The yield and growth rate were low.

Comparative Example 3 The same apparatus as in Example 1 was used, and the cylinder 12 used was one filled with high-purity hydrogen gas as an atmosphere gas. Example 1 was repeated without adding a ferrocene decomposition catalyst.
As a result of carrying out under the same conditions as above, the obtained carbon fiber had an average diameter of 0.5 μm and an average length of 500 μm, and the surface was smooth as a result of observation with a transmission electron microscope. The yield was 40% based on benzene.

In Comparative Example 2, when 0.1% by weight of cobalt (II) acetylacetonate salt was added as a ferrocene decomposition catalyst, the obtained carbon fiber had an average diameter of 0.5 μm.
m, the average length was 2000 μm, and the yield was 60% based on benzene. However, the surface of the obtained carbon fiber is
It was smooth.

Fifth Embodiment FIG. 2 is an explanatory diagram showing a schematic configuration of an apparatus for carrying out the present invention. Reference numeral 31 in the drawing is a converter gas holder. The converter gas 32 discharged from the gas holder 31 is dehydrated by the dehumidifier 33, passes through the heat exchanger 34, and enters the hot stove 36 through the burner 35. The burner 35 is charged with combustion air, the converter gas is burned to heat the hot stove, the converter gas is again introduced into the furnace, and the inside of the furnace is replaced with the converter gas. Raise to ~ 1300 ° C. The heated converter gas was coke oven gas 38 and crude benzene.
It is introduced into the reactor 37 together with 39. This crude benzene is
Ferrocene 0.4% by weight, cobalt acetylacetonate salt 0.1% by weight, and thiophene 0.2% by weight are dissolved. Then, carbon fiber is produced in this reactor. Reactor 37
The outlet and the heat exchanger 34 are connected and communicate with the filter 40. In the filter, the carbon fiber 43 produced is exhaust gas 42
And separated.

Convert the converter gas 32 and air 41 into a hot air stove that has been replaced with nitrogen 2.
It was introduced at a flow rate of ⁵ Nm ³ / hr and 3.8 Nm ³ / hr and added to the burner. At this time, the temperature in the furnace was 1400 ° C. Then, the converter gas was introduced into the furnace at a flow rate of 0/5 Nm ³ / hr to replace the combustion exhaust gas. Next, the converter gas mixed with the unheated converter gas and heated to 1150 ° C. was introduced into the reactor at a flow rate of 10 Nm ³ / hr. When the temperature inside the hot blast stove reaches 1200 ° C, the cycle of combustion of the hot blast stove, converter gas replacement, and blast are alternately repeated in the two tower hot blast stoves under the same conditions, and the temperature of the converter gas introduced into the reactor is changed. Hold at 1150 ° C. After the reactor was preheated, coke oven gas was blown into the oven at a flow rate of 0.5 Nm ³ / hr. Thereafter, 0.4% by weight of ferrocene, 0.1% by weight of cobalt acetylacetonate salt, and 0.2% by weight of thiophene dissolved in crude benzene were blown at a flow rate of 3.3 kg / hr. When the fine cotton-like material obtained from the lower part of the filter 40 was pulled out, the thread diameter was 1
It was a carbon fiber having a micrometer and a fiber length of 1000 μm or more. After operating for 1 hour, 1.32 kg of carbon fiber was obtained. As a result of observation with a transmission electron microscope, the surface was rough and fluffy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an apparatus for carrying out the method of the present invention, and FIG. 2 is an explanatory diagram showing an outline of another apparatus for carrying out the method of the present invention. 11 …… Argon gas cylinder, 12 …… Carrier gas cylinder, 13,14 …… Flowmeter, 15 …… Material tank, 16,17 …… Stainless steel pipe, 20 …… Reaction tube, 21 …… Collector, 22…
… Chemical pumps, 23 …… Electric furnaces, 24 …… Thermocouples, 25…
… Temperature controller, 31… Gas holder, 32… Converter gas,
33 …… Dehumidifier, 34 …… Heat exchanger, 35 …… Burner, 36
...... Hot air stove, 37 …… Reactor, 38 …… Coke oven gas, 39
…… Raw oil, 40 …… Filter, 41 …… Combustion air, 42
...... Combustion exhaust gas, 43 …… Vapor grown carbon fiber

Front Page Continuation (72) Inventor Hidetoshi Morotomi 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (56) Reference JP-A-61-225320 (JP, A) JP-A-60-181319 (JP, A) JP 63-12720 (JP, A) JP 62-250225 (JP, A) JP 62-238826 (JP, A)

Claims (3)

[Claims] 1. A carbon fiber in which a hydrocarbon and an organometallic compound are introduced into a reaction vessel and carbon obtained by pyrolysis of the hydrocarbon is grown on suspended fine particles produced by the pyrolysis of the organometallic compound. In the method for producing, in the vessel, a metal compound that is a decomposition catalyst of the organometallic compound is added, and the composition of the atmosphere gas to be introduced into the reaction vessel is 50 to 80% by volume of carbon monoxide. % And carbon dioxide 5-30%
A method for producing a carbon fiber, wherein the carbon fiber is surface-modified with the atmosphere gas as a composition containing at least. 2. The method for producing carbon fiber according to claim 1, wherein 0.01 to 50 mol of the metal compound is added to 1 mol of the organometallic compound. 3. The composition of the atmosphere gas is, by volume ratio, carbon dioxide 0.06 to 0.6 part and hydrogen 0.001 to 1 part carbon monoxide.
Claim 1 with a composition containing at least 0.2 parts
A method for producing a carbon fiber according to item.