KR100864418B1 - Vapor grown carbon fiber and its manufacturing method - Google Patents

Abstract

The present invention provides a method for producing vapor-grown carbon fibers in which carbon fibers are produced in a gas phase by contacting a carbon source in a feedstock with a catalyst and / or catalyst precursor compound in a heating zone, wherein the carbon source contains at least methane, and the feedstock Provided is a method for producing a vapor-grown carbon fiber in which the concentration of methane in the mixture is from 15 mCO% to less than 100 mCO%, and the temperature of the hot zone of the heating zone is 1,100 ° C to 1500 ° C. The production method of the present invention is simple and effective, the utilization efficiency of the catalyst or catalyst precursor is remarkably improved, and carbon fibers can be produced at low cost.

Description

Vapor-grown carbon fiber and its manufacturing method {VAPOR-GROWN CARBON FIBER AND PRODUCTIION PROCESS THEREOF}

The present invention relates to a method for efficiently producing vapor-grown carbon fibers such as carbon nanotubes.

The carbon fibers (phase grown carbon fibers) obtained by the vapor phase growth method can have a large aspect ratio relatively easily. Therefore, there have been many studies on the manufacturing method of the related art, and have studied hard. In recent years, carbon nanotubes (ie, carbon fibers having nanometer orders of fiber diameter) have attracted special attention, and can be synthesized by applying this vapor phase growth method.

1 is a schematic diagram showing an example of a reaction apparatus for continuously producing carbon fibers by the vapor phase growth method. In an example of a general manufacturing method, CO, methane, acetylene, ethylene, benzene, toluene, etc. are used as a carbon source which is a raw material of carbon fiber. The carbon source which is gas at normal temperature and normal pressure is supplied by mixing with a carrier gas in a gaseous phase. In the case of liquid, the carbon source is vaporized with the vaporizer 4, and then mixed with the carrier gas and supplied or sprayed into the heating zone 1 in the liquid phase. As a carrier gas, nitrogen gas which is an inert gas, hydrogen gas which is a reducing gas, etc. are used. In some cases, a carbon source may be supplied into the decompression device. As the catalyst, a supported catalyst having a metal supported on a carrier such as alumina or an organometallic compound such as ferrocene is used. In the case of using a supported catalyst, the supported catalyst is placed in the heating zone 1 in advance, heated, and subjected to necessary pretreatment, followed by supplying a carbon source for reaction (example shown in FIG. 1). Furthermore, the reaction is carried out by supplying the supported catalyst which has been pretreated in a continuous or pulse manner from the outside of the apparatus. In addition, an organometallic compound such as ferrocene, which can be easily dissolved in a carbon source, is used as a catalyst precursor, and a metal particle generated by pyrolysis of the catalyst precursor is used as a catalyst by supplying it continuously or pulsed with a carbon source in a heating zone. It is also possible to produce carbon fibers. The product is collected in the collector 3 at the end of the heating zone 1 or at the end of the heating zone 1 which is heated by the heater 2, and is recovered after the reaction is completed after a predetermined time.

Methods for producing carbon fibers by the gas phase method are roughly classified into the following three forms depending on the catalyst or the method of supplying the precursor compound of the catalyst.

(1) a method in which a substrate or boat made of alumina or graphite carrying a catalyst or a precursor compound thereof is placed in a heating zone and brought into contact with a gas of a carbon source supplied in a gas phase;

(2) a method in which particles of a catalyst or a precursor compound thereof are dispersed in a liquid carbon source or the like, continuously or pulsedly supplied into a heating zone from outside the apparatus, and contacted with a carbon source at a high temperature; And

(3) By using a metallocene or carbonyl compound which can be dissolved in a liquid carbon source as a catalyst precursor compound, and supplying a carbon source in which the catalyst precursor compound is dissolved in a heating zone, A method of contacting a carbon source at high temperature.

In the method of (1), applying a catalyst or a precursor thereof to a substrate, performing a pretreatment such as reduction, if necessary, preparing a carbon fiber, and taking out the prepared carbon fiber after lowering the temperature Because it includes steps to be performed independently, such as, it is not preferable because it is difficult to manufacture continuously and the productivity is bad. On the other hand, in the method of said (2) and (3), continuous manufacture is possible and productivity is high. Therefore, the method generally classified industrially as (2) or (3) is used. However, it is not possible to obtain a sufficiently large amount of carbon fiber without using a catalyst or its precursor compound in excess of the amount required for the growth of the carbon fiber as a product. Therefore, it is a present state that the expensive catalyst or catalyst precursor compound is consumed in large quantities, and the step of removing the by-product by the catalyst added excessively is provided. The reason why a large amount of carbon fiber cannot be obtained sufficiently is that the catalyst having high activity aggregates and becomes coarse and loses the ability to grow carbon fiber. This tendency is serious when a catalyst which is not supported on a carrier or the like, for example, a catalyst precursor such as ferrocene or the like is produced by supplying a catalyst precursor suspended in a gaseous or source gas in a heating zone.

When inorganic or non-aromatic compounds such as CO, ethane, acetylene, and ethylene are used as the carbon source, these compounds have a low rate of carbon fiber production, and therefore the method of (1) is often used. In this case, the contact time between the catalyst and the carbon source is extended from several minutes to several tens of minutes, so the productivity is low.

When aromatic compounds, such as benzene and toluene, are used as a carbon source, continuous manufacture is possible by the method of said (2) and (3). However, as mentioned above, the effective utilization rate of a catalyst or its precursor compound is low, and an excess catalyst or its precursor compound is needed, and it is expensive.

When methane is used as a raw material of carbon fiber, the method of said (1) is used in many cases as mentioned above. In addition, in the case of a method capable of continuous production, the yield or productivity is low.

For example J. Phys. Chem. In B, 1999, 103, 6484-6492, since the method of said (1) is used, continuous manufacture is difficult. In addition, the method has a low reaction temperature, and carbon fiber production amount per methane usage and carbon fiber production amount per catalyst are very small.

Japanese Patent Laid-Open No. 62-49363 discloses a method of using methane as a raw material of carbon fiber, but the yield is low as low as 0.1% because the methane concentration is low and the reaction temperature is low.

Japanese Unexamined Patent Application Publication No. Hei 1-92423 discloses a method of using a mixed gas of H ₂ , CO and CO ₂ as a carrier gas in producing carbon fibers by the gas phase method. Japanese Unexamined Patent Publication No. Hei 1-92423 uses methane as a raw material of carbon fiber, but the main carbon source is benzene, the amount of catalyst used is large, and the effectiveness of using methane is not described.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a vapor-grown carbon fiber, in which the effective utilization rate of the catalyst or catalyst precursor is remarkably improved, and as a result, a carbon fiber can be produced at low cost, and a simple and effective method is provided. . Another object of the present invention is to provide a method for producing a vapor-grown carbon fiber in which carbon fibers having a long average fiber length can be obtained.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, when using methane as a main carbon source in the atmosphere of the temperature of 1,100 degreeC or more, and introducing into high concentration, reaction time becomes short and the effective utilization rate of a catalyst or a catalyst precursor increases. I found something. The present invention has been accomplished based on this finding. That is, according to the method of the present invention, even in the case of using a very small amount of catalyst which has not been able to form fibers conventionally, carbon fibers can be obtained in high yield.

That is, this invention relates to the following (1)-(25).

(1) A method for producing vapor-grown carbon fibers in which carbon fibers are produced in a gas phase by contacting a carbon source in a feedstock with a catalyst and / or catalyst precursor compound in a heating zone, wherein the carbon source contains at least methane, and the feedstock The concentration of methane in the mixture is 15 m% or more and less than 100 m%, and the temperature of the high temperature portion of the heating zone is 1,100 ° C to 1,500 ° C.

(2) The method for producing a vapor-grown carbon fiber according to (1), wherein the temperature of the raw material introduction portion of the heating zone is 700 ° C or less.

(3) The above (1) or (2), wherein the feedstock stays in the low temperature portion of the heating zone at a temperature of 600 ° C to 1,000 ° C for at least 0.05 seconds before reaching the high temperature portion of the heating zone. Method for producing a vapor-grown carbon fiber, characterized in that.

(4) The method for producing a vapor-grown carbon fiber according to any one of (1) to (3), wherein in the heating zone, a residence time at a temperature of 1,100 ° C or higher is 0.001 second or more.

(5) The vapor-grown carbon fiber according to any one of (1) to (4), wherein the total amount of carbon atoms contained in the carbon source other than methane is 60% or less of the total amount of carbon atoms contained in methane. Manufacturing method.

(6) The method for producing vapor-grown carbon fiber according to (5), wherein the total amount of carbon atoms contained in the carbon source other than methane is 10% or less of the total amount of carbon atoms contained in methane.

(7) In any one of said (1)-(6), the ratio of the number of atoms of a catalyst element and the number of carbon atoms in a carbon source is

(Atomic number of catalyst element)

/ (Number of carbon atoms)

= 0.000005 to 0.0015

Method for producing a vapor-grown carbon fiber, characterized in that.

(8) The method for producing a vapor-grown carbon fiber according to any one of (1) to (7), wherein the catalyst precursor compound is dissolved in a liquid compound at normal temperature and normal pressure and then introduced into a heating zone.

(9) The method according to any one of the above (1) to (7), wherein the catalyst precursor compound is dissolved in a liquid compound at normal temperature and normal pressure, and all the obtained solutions are vaporized, and then introduced into the heating zone. The manufacturing method of vapor-grown carbon fiber made into.

(10) The method according to any one of (1) to (7), wherein the catalyst precursor compound is dissolved in a liquid compound at room temperature and atmospheric pressure, and all the obtained solutions are vaporized, and the obtained gas is mixed with a methane-containing gas. And then introducing into the heating zone.

(11) The method for producing a vapor-grown carbon fiber according to any one of (8) to (10), wherein the compound which is liquid at room temperature and atmospheric pressure is a carbon source.

(12) The solubility at 25 ° C. of the catalyst precursor compound in the compound which is liquid at normal temperature and normal pressure is at least 10 g per 100 g of the compound which is liquid at normal temperature and normal pressure in any one of the above (8) to (10). Method for producing a vapor-grown carbon fiber, characterized in that.

(13) The gas phase growth according to any one of (8) to (10), wherein the compound which is liquid at normal temperature and normal pressure is at least one compound selected from the group consisting of benzene, toluene and tetrahydrofuran. Method for producing carbon fiber.

(14) One of the above (1) to (13), wherein the catalyst and / or catalyst precursor compound is one selected from Groups 3, 5, 6, 8, 9, and 10 of the Group 18 Periodic Table of the Elements. A method for producing a vapor-grown carbon fiber, characterized in that the compound containing at least one metal and / or at least one of the metals.

(15) The method for producing a vapor-grown carbon fiber according to any one of (1) to (14), wherein all or part of the gas after the reaction is circulated and reused.

(16) The method for producing a vapor-grown carbon fiber according to any one of (1) to (15), wherein the carbon fiber has an average fiber diameter of 10 nm or more.

(17) The vapor phase growth carbon fiber manufactured by the manufacturing method of vapor phase growth carbon fiber in any one of said (1)-(16).

(18) The vapor-grown carbon fiber according to (17), wherein the average fiber length is 10 µm or more.

(19) The vapor-grown carbon fiber according to (18), wherein the average fiber length is 13 µm or more.

(20) The solubility at 25 ° C of the catalyst precursor in the compound which is liquid at room temperature and atmospheric pressure is at least 1 g per 100 g of the compound which is liquid at room temperature and atmospheric pressure, in any one of (8) to (10) above, The boiling point of the compound which is liquid at room temperature and atmospheric pressure, the manufacturing method of the vapor-grown carbon fiber, characterized in that more than 115 ℃.

(21) The compound according to (20), wherein the compound which is liquid at room temperature and atmospheric pressure is o-xylene, m-xylene, p-xylene, ethylbenzene, styrene, methyl lactate, methyl pyruvate, 4-methyl-2 1 type selected from the group consisting of -pentanone, 2-hexanone, 3-hexanone, cyclopentanone, hydroxyacetone, 3-heptanone, 4-heptanone, propylene glycol monomethyl ether and propylene glycol monoethyl ether It is a compound of the above, The manufacturing method of vapor-grown carbon fiber characterized by the above-mentioned.

(22) The solubility at 25 ° C of the catalyst precursor compound with respect to the compound which is liquid at room temperature and atmospheric pressure is at least 1 g per 100 g of the compound which is liquid at room temperature and atmospheric pressure in any one of (8) to (10). The boiling point of the compound in the liquid phase at normal temperature and pressure, the method of producing a vapor-grown carbon fiber, characterized in that more than 150 ℃.

(23) The compound according to the above (22), wherein the compound which is liquid at normal temperature and normal pressure is cumene, anisole, 4-methoxy toluene, ethyl lactate, 2-ethoxyethyl acetate, propylene glycol monoethyl ether acetate, Dimethyl malonate, propylene glycol diacetate, γ-butylollactone, 4-methoxy-4-methyl-2-pentanone, 4-hydroxy-4-methyl-2-pentanone, cyclohexanone, 2,6 -Dimethyl-4-heptanone, 3-methyl cyclohexanone, 3-methoxy-1-butanol, ethylene glycol monoisobutyl ether, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol mono-n-butyl Ether, ethylene glycol mono-n-butyl ether, 3-methoxy-3-methyl-1-butanol, tetrahydrofurfuryl alcohol, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, trie Method for producing a polyalkylene glycol dimethyl ether, dimethylformamide, vapor-grown carbon fiber, characterized in that at least one compound selected from the group consisting of amides.

(24) The method for producing a vapor-grown carbon fiber according to any one of (1) to (23), wherein the feedstock contains a sulfur compound.

(25) The method for producing a vapor-grown carbon fiber according to (24), wherein the sulfur compound is at least one compound selected from the group consisting of dimethyl sulfide and dimethyl disulfide.

According to the present invention, by introducing a high concentration of methane under a high temperature atmosphere of 1,100 ° C or higher, carbon fibers of high productivity can be obtained with a very small amount of catalyst.

The mechanism for providing the effect of the present invention is not clearly known, but it is considered as follows from the results of the inventor's examination and the prior patents, the literature, and the like.

In J. Phys. Chem. B, 1999, 103, 6484-6492, where methane is used as a raw material of carbon fiber, carbon fiber is produced at a temperature lower than 1000 ° C, in particular about 900 ° C, resulting in low productivity. In addition, the catalyst is, for example, supported on a carrier, injected into the reactor in advance, and carbon catalyst is produced by reacting a catalyst heated to a temperature in the reactor with similarly heated methane.

In this method, when the temperature of the reaction furnace is heated to 1,100 ° C. or more, the catalyst supported on the carrier may aggregate. In addition, when only methane is used as a raw material of carbon fiber, some methane is thermally decomposed to produce aliphatic hydrocarbons such as ethylene and propylene, or aromatic compounds having aromatic rings.

Many patent documents disclose techniques for producing carbon fibers at high temperatures of 1,100 ° C. or higher using aromatic compounds. However, in the patent literature and non-patent literature, there is no specific indication that the aliphatic hydrocarbon can be used to produce carbon fibers at a high temperature of 1,100 ° C. or higher, and in particular, a mass can be produced. It is assumed that aliphatic hydrocarbons such as ethylene and propylene do not produce carbon fibers successfully when contacted with a catalyst at a high temperature of 1,100 ° C or higher.

That is, also in this invention, it is not necessary to introduce a catalyst into a reactor beforehand, and to manufacture, but it is necessary to introduce the carbon source containing at least methane from the outside, and a catalyst and / or a catalyst precursor compound together in the heated reactor. By this introduction, during the temperature rise of the raw material mixture prepared at low temperature, carbon fibers are produced by contacting methane and a catalyst at a temperature of 1,000 ° C. or lower, and carbon fibers obtained by a carbon source other than methane and methane at a temperature of 1,000 ° C. or higher To grow. In order to obtain a high productivity carbon fiber, it is necessary to promote growth at a temperature of 1,100 ° C or higher.

The production of carbon fibers from methane starts at a low temperature, that is, the production of fibers before the catalyst particles agglomerate and coarsen and lose their catalytic capability, thereby significantly improving the effective utilization of the catalyst or catalyst precursor, and at high temperatures. It grows continuously in the radial direction of the fiber. As a result, even if the methane concentration is high, production of non-fibrous materials can be suppressed and high productivity can be achieved.

In addition, since the production of carbon fibers from methane starts at a low temperature, carbon fibers having a longer fiber length can be obtained as compared with the case of using an aromatic compound as a raw material carbon source of the carbon fibers.

Hereinafter, the components of the present invention will be described in detail.

(Carbon source)

In the method for producing a carbon fiber of the present invention, the carbon source contains at least methane, and preferably the main carbon source is methane. "Carbon source" means a compound having a carbon atom. Therefore, when the catalyst precursor compound has a carbon atom, the catalyst precursor compound is also included in the "carbon source". However, since carbon monoxide and carbon dioxide exhibit different behavior from aliphatic hydrocarbons or aromatic hydrocarbons, the present invention is not included in the "carbon source", and the "main carbon source" is carbon in each carbon source contained in the feedstock. When the total amount of is compared, it means the carbon source having the most carbon, of course, only methane may be used as the carbon source.

In the production of carbon fibers by the method of the present invention, a carbon source other than methane cannot be used as the main carbon source. For example, when aliphatic hydrocarbons such as ethane, propane and butane are used as the main carbon source, a mixture of fine carbon fibers and non-fibrous products is obtained, the yield of carbon fibers is lowered, and a large amount of non-fibrous material is contained. When aromatic hydrocarbons such as benzene and toluene are used, carbon fibers cannot be obtained without using a large amount of catalyst.

The methane concentration in the feedstock is preferably 15% or more but less than 100%, more preferably 30% to 95%, and even more preferably 45% to 90%. If the methane concentration in the raw material is too low, the productivity of the carbon fiber is low, while if the methane concentration is very high, nonfibrous products may be produced. A "feedstock" is a composition containing a carbon source, a catalyst and / or a catalyst precursor compound, a carrier gas, etc. which are mentioned later and contain all the components supplied to a heating zone regarding this invention.

Carbon sources other than methane used in combination with methane inhibit the methane properties when used in large quantities, so it is not preferable to use an excessively large amount. For carbon sources other than methane, the total amount of carbon atoms contained in these carbon sources is preferably 60% or less, more preferably 40% or less, even more preferably 20% or less, furthermore, based on the total amount of carbon atoms contained in methane. More preferably, it is used in an amount of 10% or less, most preferably 5% or less. When an excessive amount of carbon source other than methane is used, the amount of nonfibrous solids produced increases rapidly.

(catalyst)

The catalyst used in the present invention is not particularly limited as long as it is a substance capable of promoting the growth of carbon fibers. This catalyst is, for example, at least one metal selected from the group consisting of Groups 3 to 12 of the Group 18 periodic table recommended by IPCAC in 1990, and particularly (particularly its fine particles), preferably 3, 5, 6, At least one metal selected from the group consisting of Groups 8, 9, and 10, more preferably iron, nickel, cobalt, ruthenium, rhodium, palladium, platinum, or rare earth elements.

(Catalyst precursor compound)

By "catalyst precursor compound" is meant a compound which is thermally decomposed at the time of heating and optionally further reduced to provide the catalyst. An organometallic compound, a metal salt, etc. are mentioned as a catalyst precursor compound. For example, ferrocene, a catalyst precursor compound, thermally decomposes upon heating to produce iron fine particles that act as a catalyst. Therefore, a compound providing such a metal as the catalyst precursor compound can be suitably used. More specifically, for example, the catalyst precursor compound is a metal compound containing at least one element selected from the group consisting of Groups 3 to 12, preferably Groups 3, 5, 6, 8, 9, and 10 A compound containing at least one element selected from the group consisting of, and most preferably, a compound containing iron, nickel, cobalt, ruthenium, rhodium, palladium, platinum and rare earth elements.

It is also possible to modify the catalytic performance of the metal as the main component by adding a metal compound containing at least one element selected from the group consisting of Groups 1 to 17 to the main component as a modifying component (so-called cocatalyst).

(carrier)

It is also possible to use the said catalyst and / or catalyst precursor compound on a support | carrier as needed. The carrier is preferably a compound that is stable in the heating zone, and examples of such a compound include alumina, silica, zeolite, magnesia, titania, zirconia, graphite, activated carbon, carbon fiber and the like. However, the carrier compound needs to be introduced together with a carbon source or the like into the heated furnace, rather than previously injected into the reactor.

(Consumption such as catalyst)

The amount of the catalyst or catalyst precursor compound used is preferably 0.000005 to 0.0015, more preferably 0.00001 to 0.001, more preferably 0.00002 to 0.0005, in the ratio of the number of atoms of the catalyst element (e.g. Fe) to the number of carbon atoms in the carbon source. Preferably, 0.00004-0.0004 are the most preferable. If less than 0.000005, the number of fibers decreases or the fiber diameter increases due to lack of catalyst, while if this ratio is larger than 0.0015, coarse catalyst particles which are not economical and do not function as catalysts will be mixed in the fibers. The total number of carbon atoms of the carbon source in the raw material includes the carbon atoms as long as the catalyst precursor compound contains carbon. That is, the total amount of carbon atoms is the total amount of all carbon atoms except carbon monoxide and carbon contained in the feedstock.

(Feeding method of raw materials)

The supply method of a raw material is not specifically limited. Carbon sources other than methane and / or methane, catalysts and / or catalyst precursor compounds may be vaporized and supplied in the gas phase, or some or all of them may be supplied in the liquid phase. In order to efficiently produce the carbon fibers, it is particularly preferable to supply these raw materials by vaporizing and mixing them sufficiently with gaseous substances before the production of the carbon fibers starts. It is preferable that this gaseous substance is fully mixed at 700 degrees C or less, 600 degrees C or less is more preferable, and 400 degrees C or less is the most preferable.

The catalyst and / or catalyst precursor compound is often solid or liquid at normal temperature and atmospheric pressure. Since the catalyst utilization efficiency is high, the amount thereof may be used in a small amount, and even in the case of liquid phase, it may be difficult to supply the catalyst or the catalyst precursor compound directly to the heating zone. In such a case, the catalyst and / or catalyst precursor compound or the like may be dissolved or dispersed and supplied to the compound which is liquid at normal temperature and normal pressure. As this compound which is liquid at normal temperature and normal pressure, a carbon source which is liquid at normal temperature and normal pressure may be used. When dissolving a catalyst and / or a catalyst precursor compound in a compound that is liquid at room temperature and atmospheric pressure, the solubility thereof is preferably high.

As the compound which is liquid at normal temperature and normal pressure, the solubility at 25 ° C. of the catalyst precursor compound per 100 g of the compound which is liquid at normal temperature and normal pressure and liquid at normal temperature and normal pressure is preferably 1 g or more, more preferably 5 g. As mentioned above, More preferably, it is 10 g or more. For example, in the case of using ferrocene which is frequently used as a catalyst precursor compound, the solubility of ferrocene per 100 g of the compound which is a liquid at normal temperature and normal pressure and a liquid at normal temperature and normal pressure is 5 g at 25 ° C. It is preferable to use the above compound, and specifically, benzene, toluene, tetrahydrofuran, etc. can be used.

As a compound which is liquid at normal temperature and normal pressure, the solubility in 25 degreeC of a catalyst precursor compound per 100 g of a compound which is liquid at normal temperature and normal pressure is 1 g or more, and the compound whose boiling point is 115 degreeC or more is preferable. Specific examples of such a compound include aromatic compounds such as o-xylene, m-xylene, p-xylene, ethylbenzene and styrene; Esters such as methyl lactate and methylpyruvate; Ketone compounds such as 4-methyl-2-pentanone, 2-hexanone, 3-hexanone, cyclopentanone, hydroxyacetone, 3-heptanone, 4-heptanone; And ether compounds such as propylene glycol monomethyl ether and propylene glycol monoethyl ether.

As a compound which is liquid at normal temperature and normal pressure, the compound whose solubility in 25 degreeC of a catalyst precursor per 100 g of a compound which is liquid at normal temperature and normal pressure is 1 g or more, and the compound whose boiling point is 150 degreeC or more is preferable. Specifically, Aromatic compounds, such as cumene, anisole, 4-methoxy toluene; Ester compounds such as ethyl lactate, 2-ethoxyethyl acetate, propylene glycol monoethyl ether acetate, dimethyl malonate, propylene glycol diacetate, γ-butylollactone, and 4-methoxy-4-methyl-2-penta Ketone compounds, such as 4-hydroxy-4-methyl-2-pentanone, cyclohexanone, 2,6-dimethyl-4-heptanone, 3-methyl cyclohexanone, and 3-methoxy-1-butanol , Ethylene glycol monoisobutyl ether, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol mono-n-butyl ether, ethylene glycol mono-n-butyl ether, 3-methoxy-3-methyl-1-butanol Ether compounds such as tetrahydrofurfuryl alcohol, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol dimethyl ether, and dimethyl Amide compounds, such as formamide, are mentioned.

The method of dissolving or dispersing a catalyst and / or a catalyst precursor compound and the like to supply a compound which is liquid at normal temperature and normal pressure is not particularly limited. For example, the compound may be sprayed into a liquid phase using a nozzle or the like to be supplied, but in order to sufficiently mix gas components such as methane at a lower temperature, it is preferable to introduce the compound after vaporizing at a temperature where all components can be sufficiently vaporized. And it is more preferable to introduce in the state mixed sufficiently before introduction.

(Carrier gas)

In the production of the vapor-grown carbon fiber of the present invention, it is recommended to use a carrier gas in addition to the above composition. As the carrier gas, hydrogen, nitrogen, helium, argon, krypton, or a mixed gas thereof can be used, but a gas containing oxygen molecules such as air (that is, molecular oxygen (O ₂ )) is not suitable. The catalyst precursor compound used in the present invention may be in an oxidized state, and in this case, it is preferable to use a gas containing hydrogen as the carrier gas. Therefore, a preferable carrier gas is a gas containing 1% or more of hydrogen, more preferably 30% or more, most preferably 85% or more, and is a gas obtained by diluting 100% hydrogen or hydrogen with nitrogen. The hydrogen gas concentration used here is the concentration of only the carrier gas, but carbon sources other than methane and / or methane, gasified catalysts and / or catalyst precursor compounds and the like are not considered.

(Sulfur compound)

In the production of the vapor-grown carbon fiber of the present invention, a sulfur compound which is considered to be effective in controlling the carbon fiber diameter may be used in combination. As a sulfur compound which can be used by this invention, Sulfur; Thiophene; Hydrogen sulfide; Carbon sulfide; Mercaptans such as methyl mercaptan and tert-butyl mercaptan; Sulfides such as dimethyl sulfide; And disulfides such as dimethyl disulfide and the like. Sulfur compounds are preferably thiophene, carbon disulfide, dimethyl sulfide and dimethyl disulfide, more preferably dimethyl sulfide and dimethyl disulfide.

Compounds such as sulfur, thiophene, hydrogen sulfide, carbon sulfide, mercaptans such as tert-butyl mercaptan, sulfides such as dimethyl sulfide, and disulfides such as dimethyl disulfide are present in the gas phase. You may supply or it may melt | dissolve in a solvent and supply. The total number of moles of sulfur to be supplied is preferably 100 times or less, preferably 10 times or less, and more preferably 2 times or less of the number of moles of the catalyst element. Too much sulfur supply is not economical and is not preferable because it does not inhibit the growth of carbon fibers.

(Synthesis of carbon fiber)

Synthesis of gaseous growth carbon fibers is accomplished by supplying a carrier gas to a heating zone and contacting under heating as necessary for the above-described raw materials and necessity. The reactor (heating zone) is not particularly limited as long as a predetermined residence time and heating temperature can be obtained, but a vertical or horizontal tubular furnace is preferable in view of raw material supply and residence time control.

Since methane, which is a stable compound as a carbon source, preferably a main carbon source, is used, when the temperature of the heating zone is too low, not only carbon fibers but also solid products are not completely produced or are produced in very small amounts. Carbon fibers do not grow or only coarse fibers are obtained. Therefore, it is preferable that the temperature of the high temperature part of a heating zone is 1,100 degreeC or more and 1,500 degreeC or less, More preferably, it is 1,150 degreeC or more and 1,350 degreeC or less.

It is preferable that the main component of the carbon source in the gas after reaction is methane. When the oxygen-containing compound is contained in the reaction gas, some of the carbon becomes carbon monoxide or carbon dioxide, but is not included in the carbon source as described above. The gas after the reaction satisfies the composition containing the methane and a carbon source other than methane, circulating by supplying all or part of it as it is, or adding a carbon source other than methane and / or methane to the heating zone and then supplying it to the heating zone again. Can be reused. When the gas after this reaction is circulated and reused, the combination of the gas to be reused and the component to be added becomes a reaction raw material, and this raw material needs to satisfy the raw material composition of the present invention.

2 shows an example of a reactor. In this case, the quartz reaction tube 1 used as the heating zone has a heater 2, and contains a catalyst gas and / or a catalyst precursor compound as well as a carrier gas and raw material components such as methane. Connect to the supply line to mix and supply the liquid components. The vaporizer | carburetor 4 is arrange | positioned in this supply line. In the lower part of the reaction tube 1, there exists a collector 3 which collects the produced carbon fiber. Using such a device, the heater 2 is brought to a predetermined temperature of 1,100 ° C or higher, and the raw material is introduced into the introduction line 4 to react.

It is a feature of the present invention to efficiently recover a carbon source supplied as carbon fiber. The basic mechanism is that the carbon fibers produced during the contact of methane and the catalyst at a low temperature of 1,000 ° C. or lower are mainly aliphatic hydrocarbons such as methane, methane, ethylene, and propylene, which are decomposition products of methane, and / or propylene. It grows effectively in the radial direction using carbon sources, such as aromatic hydrocarbons, such as benzene.

In order to realize the above state, it is necessary to keep the temperature of the reaction tube, that is, the raw material introduction portion for introducing the raw material into the heating zone, at a lower temperature than the high temperature portion of the heating zone. 700 degrees C or less is preferable, as for the temperature of this raw material introduction part, 600 degrees C or less is more preferable, and 400 degrees C or less is further more preferable. It is necessary to introduce the raw material into the low temperature region and to maintain the residence time to some extent at 1,000 ° C. or lower. In particular, the residence time is important at 600 ° C. to 1,000 ° C., so that the residence time is 0.05 seconds or more, preferably 0.5 seconds or more, and more preferably 1.0 second to 30 seconds. However, this residence time can be arbitrarily determined according to the desired fiber length, raw material concentration, feedstock temperature, catalyst concentration and the like.

In this case, it is difficult to measure the actual gas temperature. Therefore, the temperature used here is a value obtained by inserting the platinum-platinum 13% rhodium alloy thermocouple which can measure a temperature of 1,000 degreeC or more, for example in a heating zone. To be precise, this measurement is affected by radiation and does not necessarily correspond to the gas temperature, but can be satisfactorily used as an indicator for defining the preferred conditions of the invention.

The residence time in the temperature range of 600 degreeC-1,000 degreeC is the time which passed source gas through the area | region where the temperature measured as mentioned above at the reaction apparatus entrance side rose from 600 degreeC to 1,000 degreeC. In this region, the residence time is calculated assuming that the source gas is a plug flow and the temperature of the source gas is raised to the temperature measured as described above. Moreover, when the temperature of the ejection part, such as the nozzle inserted in the heating zone by the piping which has an internal diameter smaller than 1/5 compared with the temperature upstream of the heating zone or the heating zone, exceeds 600 degreeC, the residence time Is the residence time in the region from the upstream end of the heating zone or up to 1,000 ° C. at a jet such as a nozzle. In this case, the residence time is calculated assuming that the source gas is a plug flow in this region, and that the source gas is heated up to the temperature measured as described above.

The residence time at a temperature of 1,100 ° C. or more can be determined by the same method as the residence time in the temperature range of 600 ° C. to 1,000 ° C., for example, 0.001 second or more, preferably 0.01 second or more, more preferably 0.1 to 30 Second. However, the residence time at a temperature of more than 1,100 ℃ can be arbitrarily determined according to the desired fiber thickness, raw material concentration, temperature of the hot portion and the like.

As described above, the basic mechanism of the present invention is to grow carbon fibers produced at a low temperature of 1,000 ° C. or lower mainly in a radial direction at a high temperature of 1,000 ° C. or higher. In order to grow the fibers effectively, high temperatures of 1,100 ° C. or higher are used here. Therefore, it is particularly suitable for the production of relatively coarse fibers, compared to the production of carbon fibers having very small outer diameters such as single-walled or double-walled carbon fibers. More specifically, the production method of the present invention is optimal as a method for producing carbon fibers having an average outer diameter of the fiber of 10 nm or more, preferably 50 nm or more, and most preferably 100 nm or more. The outer diameter of the carbon fiber used here can be determined, for example, by measuring the outer diameter of about 100 fibers in the SEM photograph.

In addition, the present invention is characterized in that the carbon fiber having a longer fiber length can be produced compared to the case of using a carbon source, such as benzene, which can produce a carbon fiber having a high productivity while having a high productivity. do. That is, the average fiber length is 10 micrometers or more, Preferably it is 13 micrometers or more, Most preferably, it is optimal as a manufacturing method of the carbon fiber of 15 micrometers or more. The length of the carbon fiber used herein can be determined by measuring the length of about 100 fibers in the photograph of the SEM, for example, similarly to the case of the outer diameter.

According to this invention, the utilization efficiency of a catalyst or a catalyst precursor can be improved significantly. In other words, carbon fibers can be efficiently obtained even with a small amount of catalyst. In general, about 50,000 mass ppm of catalyst (iron, etc.) remain in the carbon fiber manufactured by the conventional method. Therefore, in order to improve the physical properties, the produced carbon fiber is subjected to calcining (before and after 1500 ° C) or graphitization treatment under inert gas (2000 to 3000 ° C). By this treatment, a part of iron or the like, which is a catalyst, is vaporized or evaporated, and the catalyst residual amount of carbon fibers after graphitization treatment is reduced. On the other hand, according to the manufacturing method of this invention, content of the catalyst in carbon fiber can be reduced extremely even in the state which does not process, such as baking and graphitization. For example, carbon fiber having a catalyst content of 5,000 mm or less and 500 mm or less can be obtained under preferable conditions without performing treatment such as calcination and graphitization, and no graphitization treatment is required depending on the application.

In addition, in the method of the present invention, the average outer diameter of the obtained fiber tends to be changed by changing the ratio of the catalyst to the methane and / or the catalyst precursor compound. That is, as the ratio of catalyst and / or catalyst precursor compound increases, the fiber diameter decreases, and when the ratio decreases, the fiber diameter increases. This shows that the average outer diameter of the obtained carbon fiber can be controlled by simply changing the composition of the carbon source and the catalyst of the raw material without changing the reaction apparatus or the detailed conditions. For example, it becomes possible to manufacture carbon fiber in the range of 80-150 nm of fiber outer diameters very easily.

1 is a schematic diagram showing a general example of a horizontal reactor for producing vapor-grown carbon fiber.

Fig. 2 is a schematic diagram showing an example of a vertical reactor for producing vapor grown carbon fibers.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited to these.

The reagents used in the following Examples and Comparative Examples are as follows.

Reagents

1. Carbon source

Methane: Products of Takachiho Trading Co., Ltd.

Benzene: Products of Wako Pure Chemical Industries, Ltd.

Toluene: Product from Wako Pure Chemical Industries, Ltd.

Tetrahydrofuran: Product of Wako Pure Chemical Industries, Ltd.

2. Catalyst precursor compound

Ferrocene: Product of Nippon Zeon Co., Ltd.

3.Other ingredients

Thiophene: Product of Wako Pure Chemical Industries, Ltd.

Dimethyl sulfide: Products of Wako Pure Chemical Industries, Ltd.

Dimethyl Disulfide: Product from Wako Pure Chemical Industries, Ltd.

Carbon Disulfide: Products of Wako Pure Chemical Industries, Ltd.

Synthesis of Carbon Fiber

Example 1

A vertical furnace having a heating zone 1 (inner diameter 31 mm, outer diameter 36 mm, length of the heating zone about 400 mm) of the quartz reaction tube shown in FIG. 2 was used. The temperature of the heating zone 1 was raised to 1200 ° C. under N ₂ airflow, thereafter, the supply of N ₂ was stopped, and instead, H ₂ was flowed into the heating zone 1 at 1 NL / mSi as a carrier gas. . After the temperature is stable, benzene, ferrocene and thiophene are dissolved and mixed with each other, the resulting solution is introduced into a vaporizer 4 heated to 200 ° C, each component is introduced in the amounts shown in Table 1, and vaporized, H _2. Introduced. In this state, no solid product was produced. Thereafter, the flow rate of H ₂ was lowered to 0.5 NL / mI, and methane was mixed with hydrogen at a flow rate of 0.5 NL / mI. In this way, all compounds were fed into the reaction tube in the gas phase. The unit "NL" used here represents the volume in the standard state (0 degreeC, 1 atmosphere).

In order to determine the residence time, the temperature of the quartz tube was measured using a platinum-platinum · 13% rhodium alloy thermocouple when the temperature was raised to 1,200 ° C. together with 1NL Hem air and the temperature was stabilized. As a result, the temperature at 24 cm from the top of the quartz tube was 600 ° C. and 1,000 ° C. at 29 cm. The residence time between them was determined to be 0.59 seconds. In addition, it exceeded 1,100 degreeC at 33cm from the top of a quartz tube, and it was lower than 1,100 degreeC at 60cm. The residence time between them was determined to be 2.25 seconds.

As a result of the reaction, a grayish cobweb-like deposit was produced between the reaction tube bottom and the collector 3. After the temperature was lowered, the deposit was recovered, and the carbon recovery rate was determined by dividing the recovered deposit by the amount of carbon included in the originally used carbon source. The conditions and results of the experiment are shown in Table 1.

The concentration of methane is determined by the formula:

Methane Concentration

= [Methane supply amount (MM) / MII]

/ [Supply amount of raw material (ｍｍｏｌ / ｍｉｎ)]

× 100

Supply of raw materials (ｍｍｏｌ / ｍｉｎ)

= Supply of Methane (ｍｍｏｌ / ｍｉｎ)

+ Carrier Gas Supply (ｍｍｏｌ / ｍｉｎ)

Supply of carbon sources other than methane (ｍｍｏｌ / ｍｉｎ)

Supply of ferrocene (ｍｍｏｌ / ｍｉｎ)

Supply of sulfur compounds (ｍｍｏｌ / ｍｉｎ)

As to the experimental conditions, the ratio (%) of the total amount of carbon atoms other than methane in the supplied carbon source to the total amount of carbon atoms in the supplied methane was calculated from the following equation, and is shown in Table 2:

Ratio (%) of the total amount of carbon atoms other than methane in the supplied carbon source to the total amount of carbon atoms in the supplied methane

[Carbon atomic weight in carrier gas (ｍｍｏｌ / ｍｉｎ)

Carbon atoms in carbon sources other than methane (ｍｍｏｌ / ｍｉｎ)

Carbon atoms in ferrocene (ｍｍｏｌ / ｍｉｎ) +

Carbon Atomic Weight in Sulfur Compounds

/ [Carbon atom in methane (ｍｍｏｌ / ｍｉｎ)]

× 100

In addition, the product of cobweb was observed with the scanning electron microscope. In the product, about 100 average outer diameters and average lengths were examined, and it was a fibrous material having an average outer diameter of 200 nm and an average length of 20 µm.

Example 2

The reaction was carried out according to the method of Example 1 except that the reaction temperature was 1,250 ° C, and the composition of the solution prepared by dissolving and mixing benzene, ferrocene and thiophene together was changed. The experimental conditions and the results are shown in Tables 1 and 2. The carbon recovery was 53%, and the product was a fibrous material having an average outer diameter of 170 nm and an average length of 15 μm.

Example 3

The reaction was carried out in accordance with the method of Example 2, except that the flow rates of H ₂ and methane were 0.64 NL / mI and 0.36 NL / mI, respectively. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 34%, and the product was a fibrous material with an average outer diameter of 170 nm.

Example 4

The reaction was carried out according to the method of Example 2 except that the flow rates of H ₂ and methane were respectively 0.82 NL / mI and 0.18 NL / mI. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery rate was 15%, and the product was a fibrous material having an average outer diameter of 150 nm.

Example 5

The reaction was carried out in accordance with the method of Example 1 except that the flow rates of H ₂ and methane were 0.25 NL / mI and 0.75 NL / mI, respectively. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 45% and the product was a fibrous material with an average outer diameter of 250 nm.

Example 6

The reaction was carried out in accordance with the method of Example 2, except for the flow rate of the solution prepared by dissolving and mixing benzene, ferrocene and thiophene with each other. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 55% and the product was a fibrous material with an average outer diameter of 200 nm.

Example 7

Toluene was used in place of benzene, and the reaction was carried out in accordance with the method of Example 6, except that the introduction amount thereof was 0.10 mM / mL. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 56%, and the product was a fibrous material with an average outer diameter of 200 nm.

Example 8

Tetrahydrofuran was used in place of benzene, and the reaction was carried out in accordance with the method of Example 6, except that the introduction amount was 0.13 mM / mni. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 51% and the product was a fibrous material with an average outer diameter of 200 nm.

Example 9

The reaction was carried out in accordance with the method of Example 2, except that dimethyl sulfide was used instead of thiophene. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 55% and the product was a fibrous material with an average outer diameter of 250 nm and an average length of 32 μm.

Example 10

The reaction was carried out in accordance with the method of Example 2, except that dimethyl disulfide was used instead of thiophene. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 51% and the product was a fibrous material with an average outer diameter of 200 nm and an average length of 18 μm.

Example 11

The reaction was carried out according to the method of Example 2, except that hydrogen disulfide was used instead of thiophene. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 54% and the product was a fibrous material with an average outer diameter of 250 nm.

Comparative Example 1

A vertical furnace having a heating zone 1 (inner diameter 31 mm, outer diameter 36 mm, length of the heating zone about 400 mm) of the quartz reaction tube shown in FIG. 2 was used. The temperature of the heating zone was raised to 1200 ° C. under N ₂ air flow, and then the supply of N ₂ was stopped. Instead, H ₂ was flowed into the reaction tube as a carrier gas at 1 NL / mSi. After the temperature was stabilized, benzene, ferrocene and thiophene were dissolved and mixed together, the obtained solution was introduced into a vaporizer 4 heated to 200 ° C, each component was introduced in the amounts shown in Table 1, and after vaporizing, H ₂ Introduced. In this way, all the compounds were supplied to the reaction tube in the gas phase.

As a result of the reaction, a black powdery deposit was formed between the bottom of the reaction tube and the collector. After the temperature was lowered, the deposit was recovered, and the carbon recovery rate was determined by dividing the recovered amount by the amount of carbon contained in the originally used carbon source, which was 30%. The conditions and results of the experiment are shown in Table 1 and Table 2.

In addition, the product in the powder state was observed with a scanning electron microscope. Most of the solids were spherical particles, and almost no fibrous substance was obtained with the catalytic amount similar to that of Examples 1 to 5.

Comparative Example 2

The reaction was carried out in accordance with the method of Comparative Example 1, except that the composition of the solution prepared by dissolving and mixing benzene, ferrocene and thiophene with each other was changed. The conditions and results of the experiment are shown in Table 1 and Table 2. The carbon recovery was 39% and the product was a fibrous material with an average outer diameter of 100 nm and an average length of 7 μm. By increasing the amount of catalyst, a fibrous material was obtained, but the length of the fiber was short.

Comparative Example 3

The reaction was carried out in accordance with the method of Example 2 except that the flow rates of H ₂ and methane were 0.91 NL / mI and 0.09 NL / mI. The conditions and results of the experiment are shown in Table 1 and Table 2. As a result of the reaction, no solid deposit was obtained. That is, the carbon recovery rate was 0%. This is because methane concentration is too low.

Comparative Example 4

The reaction was carried out in accordance with the method of Example 2, except that the reaction temperature was set at 1,000 ° C. The conditions and results of the experiment are shown in Table 1 and Table 2. As a result of the reaction, a solid deposit could not be obtained. That is, the carbon recovery rate was 0%. This is because reaction temperature is too low.

Comparative Example 5

The reaction was carried out in accordance with the method of Comparative Example 4, except that the methane flow rate was 1 NL / mIin without flowing H ₂ . The conditions and results of the experiment are shown in Table 1 and Table 2. As a result of the reaction, a brown smoke-like substance was formed in the gas at the exit of the reactor, and a black sticky substance was attached to the inner wall of the reaction tube, but a recoverable solid deposit was not obtained. That is, the carbon recovery rate was 0%. If the reaction temperature is too low, carbon fibers cannot be obtained even with a high methane concentration.

Table 1

Experiment Conditions and Results

Table 2

Conditions of experiment

Claims (19)

A method for producing vapor-grown carbon fibers in which carbon fibers are produced in the gas phase by contacting a carbon source in a feedstock with at least one of a catalyst and a catalyst precursor compound in a heating zone, wherein the carbon source contains at least methane, The production of vapor-grown carbon fiber, characterized in that the concentration of methane is more than 15m% and less than 100m%, the temperature of the hot portion of the heating zone is 1,100 ℃ ~ 1500 ℃, the temperature of the raw material introduction portion of the heating zone is 700 ℃ or less. Way. delete The vapor-grown carbon fiber of claim 1, wherein the feedstock stays in the low temperature portion of the heating zone at a temperature of 600 ° C to 1,000 ° C for at least 0.05 seconds before reaching the high temperature portion of the heating zone. Method of preparation. The method for producing a vapor-grown carbon fiber according to claim 1, wherein in the heating zone, a residence time at a temperature of 1,100 ° C or more is 0.001 second or more. The method for producing a vapor-grown carbon fiber according to claim 1, wherein the total amount of carbon atoms contained in the carbon source other than methane is 60% or less of the total amount of carbon atoms contained in methane. The method for producing vapor-grown carbon fibers according to claim 5, wherein the total amount of carbon atoms contained in the carbon source other than methane is 10% or less of the total amount of carbon atoms contained in methane. The ratio of the number of atoms of the catalytic element to the number of carbon atoms in the carbon source, (Atomic number of catalyst element) / (Number of carbon atoms) = 0.000005 to 0.0015 Method for producing a vapor-grown carbon fiber, characterized in that. The method of claim 1, wherein the catalyst precursor compound is dissolved in a liquid compound at room temperature and atmospheric pressure, and then introduced into a heating zone. The method for producing a vapor-grown carbon fiber according to claim 1, wherein the catalyst precursor compound is dissolved in a liquid compound at normal temperature and normal pressure, and all the obtained solutions are vaporized and then introduced into the heating zone. The method according to claim 1, wherein the catalyst precursor compound is dissolved in a liquid compound at room temperature and atmospheric pressure, and all the obtained solutions are vaporized, and the obtained gas is mixed with a methane-containing gas and then introduced into the heating zone. The manufacturing method of vapor-grown carbon fiber made into. The method for producing a vapor-grown carbon fiber according to claim 8, wherein the compound which is liquid at room temperature and atmospheric pressure is a carbon source. The method for producing a vapor-grown carbon fiber according to claim 8, wherein the solubility at 25 DEG C of the catalyst precursor compound is at least 10 g per 100 g of the compound which is liquid at normal temperature and normal pressure. . The method for producing a vapor-grown carbon fiber according to claim 8, wherein the compound which is liquid at normal temperature and atmospheric pressure is at least one compound selected from the group consisting of benzene, toluene and tetrahydrofuran. The method of claim 1, wherein at least one of the catalyst and the catalyst precursor compound comprises at least one metal selected from Groups 3, 5, 6, 8, 9, and 10 of the Group 18 Periodic Table of the Elements; And at least one selected from compounds containing at least one of the above metals. The method for producing a vapor-grown carbon fiber according to claim 1, wherein all or part of the gas is circulated and reused after the reaction. The method for producing a vapor-grown carbon fiber according to claim 1, wherein a carbon fiber having an average fiber diameter of 10 nm or more is produced. The vapor-growth carbon fiber manufactured by the manufacturing method of the vapor-growth carbon fiber of Claim 1. 18. The vapor-grown carbon fiber according to claim 17, wherein the average fiber length is 10 m or more. 19. The vapor-grown carbon fiber according to claim 18, wherein the average fiber length is 13 µm or more.

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