Carbon nanotube production device and carbon nanotube production method

Abstract

Provided is, in relation to the technology of producing carbon nanotubes through chemical vapor deposition in the presence of an alkali metal compound, a new carbon nanotube production device that can efficiently produce carbon nanotubes continuously for a long period of time.　This carbon nanotube production device is for producing carbon nanotubes through chemical vapor deposition, and comprises: a reaction container; a carbon material supply nozzle 1 for supplying a carbon material into the reaction container; and an alkali metal compound aqueous solution supply nozzle 2 for supplying an alkali metal compound aqueous solution into the reaction container. The alkali metal compound aqueous solution supply nozzle 2 is an ultrasonic wave atomization-type nozzle. When producing carbon nanotubes by supplying the carbon material into the reaction container from the carbon material supply nozzle 1, by supplying the alkali metal compound aqueous solution into the reaction container from the alkali metal compound aqueous solution supply nozzle 2 and by heating the carbon material inside the reaction container, the leading end of the alkali metal compound aqueous solution supply nozzle 2 is disposed at a position where the temperature inside the reaction container becomes 120°C or lower.

Description

Carbon nanotube manufacturing apparatus and method for manufacturing carbon nanotubes

[0001] The present invention relates to an apparatus and method for producing carbon nanotubes, and more particularly to an apparatus and method for producing carbon nanotubes that can produce carbon nanotubes efficiently and continuously for a long period of time.

[0002] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are cylindrical substances composed entirely of carbon and with a diameter of nanometers. They have attracted attention due to their structural characteristics, such as electrical conductivity, thermal conductivity, mechanical strength, and chemical properties, and their practical use in a variety of fields, including electronics and energy, is being considered.

[0003] Carbon nanotube synthesis methods are broadly classified into three categories: arc discharge, laser vaporization, and chemical vapor deposition (CVD). CVD, unlike arc discharge and laser vaporization, uses gaseous carbon raw materials instead of solid carbon raw materials, making it suitable for mass synthesis because it allows the carbon raw materials to be continuously injected into the reactor. Furthermore, CVD is an excellent synthesis method because the resulting carbon nanotubes are highly pure and the production costs are low.

[0004] Among these, the floating catalyst CVD method (FC-CVD method) is a method particularly suitable for synthesizing single-walled carbon nanotubes, which have many excellent properties such as extremely high electrical and thermal conductivity compared to multi-walled carbon nanotubes.

[0005] More specific examples of methods for producing carbon nanotubes using the floating catalyst CVD method include a method for producing single-walled carbon nanotubes that suppresses the by-production of amorphous carbon (Patent Document 1), a method for producing high-purity single-walled carbon nanotubes (Patent Document 2), and a method for producing single-walled carbon nanotubes with a high yield (Patent Document 3).

[0006] These carbon nanotube production methods can produce high-purity single-walled carbon nanotubes, but the yield of carbon nanotubes is only a few percent, making it impossible to mass-produce single-walled carbon nanotubes.

[0007] Japanese Patent No. 5046078 Japanese Patent No. 4968643 Japanese Patent Application Laid-Open No. 2007-246309

[0008] "The effect of alkaline doped catalysts on the CVD synthesis of carbon nanotubes" Phys. Status Solidi B 248, No.11 2471-2474(2011)"CVD-synthesis of multiwall carbon nanotubes over potassium-doped supported catalysts" Applied Catalysis A: General 344, 191-197(2008)" Carbon nanotube synthesis and spinning as macroscopic fibers assisted by the ceramic reactor tube" Scientific Reports volume 9, Article number: 9239 (2019)

[0009] The present inventors have developed a technology for producing carbon nanotubes (CNTs) with high efficiency by chemical vapor deposition in the presence of an alkali metal compound. This technology is a production method characterized by supplying an aqueous alkali metal compound solution to a reaction system in addition to a mixture (raw material solution) of a carbon raw material for carbon nanotubes, an iron catalyst (e.g., ferrocene), and a sulfur compound.

[0010] In this production method, the effect of alkali metal compounds on CNT production is not entirely clear. However, similar to iron-based catalysts (Mittasch catalysts), which are well known as industrial ammonia synthesis catalysts, it is thought that alkali metals act as electron donors to iron atoms, and act as promoters that promote the dissociation of hydrocarbon molecules, which are the carbon raw material for CNTs.

[0011] On the other hand, industrial mass production of CNTs requires continuous and stable operation of a synthesis apparatus for extended periods of time. When using the aforementioned production method, there is a problem in that when an aqueous alkali metal compound solution is supplied from a nozzle, the compound precipitates and easily clogs the nozzle. For this reason, the continuous operation time of a carbon nanotube production apparatus is limited to a maximum of about three hours, and stable continuous operation for longer periods of time is required. Even when the nozzle does not clog, there is a problem in that reaction products and the like accumulate at the nozzle tip. The accumulation of reaction products and the like at the nozzle tip not only causes an unstable spray state of the aqueous alkali metal compound solution from the nozzle, but also may cause clogging at the tip as the deposition progresses, potentially hindering longer continuous operation.

[0012] The main object of the present invention is to provide a novel carbon nanotube production apparatus that can produce carbon nanotubes efficiently and continuously for a long period of time in a technology for producing carbon nanotubes by chemical vapor deposition in the presence of an alkali metal compound.

[0013] The present inventors have discovered that a carbon nanotube production apparatus for producing carbon nanotubes by chemical vapor deposition comprises a reaction vessel, a carbon raw material supply nozzle 1 for supplying a carbon raw material into the reaction vessel, and an alkali metal compound aqueous solution supply nozzle 2 for supplying an alkali metal compound aqueous solution into the reaction vessel, wherein the alkali metal compound aqueous solution supply nozzle 2 is an ultrasonic atomization type nozzle, and when the carbon raw material is heated in the reaction vessel to produce carbon nanotubes, the tip of the alkali metal compound aqueous solution supply nozzle 2 is positioned at a position where the temperature inside the reaction vessel is 120°C or below, thereby enabling carbon nanotubes to be produced efficiently and continuously for a long period of time.

[0014] The present invention was completed based on these findings and through further investigation.

[0015] That is, the present invention provides the following aspects: Item 1. A carbon nanotube production apparatus for producing carbon nanotubes by chemical vapor deposition, comprising a reaction vessel, a carbon raw material supply nozzle 1 for supplying a carbon raw material into the reaction vessel, and an alkali metal compound aqueous solution supply nozzle 2 for supplying an alkali metal compound aqueous solution into the reaction vessel, the alkali metal compound aqueous solution supply nozzle 2 being a nozzle of an ultrasonic atomization type, and the carbon raw material is supplied from the carbon raw material supply nozzle 1 into the reaction vessel, the alkali metal compound aqueous solution is supplied from the alkali metal compound aqueous solution supply nozzle 2 into the reaction vessel, and the carbon raw material is heated in the reaction vessel to produce carbon nanotubes, the tip of the alkali metal compound aqueous solution supply nozzle 2 being positioned at a position where the temperature inside the reaction vessel is 120°C or less. Item 2. The carbon nanotube production apparatus according to Item 1, further comprising a supply channel for supplying a carrier gas for the alkali metal compound aqueous solution to the reaction vessel, coaxially and externally provided around the alkali metal compound aqueous solution supply nozzle 2. Item 3. Item 3. A method for producing carbon nanotubes using the carbon nanotube production apparatus according to Item 1 or 2.

[0016] According to the present invention, it is possible to provide a novel carbon nanotube production apparatus that can efficiently and continuously produce carbon nanotubes for a long period of time in a technique for producing carbon nanotubes by chemical vapor deposition in the presence of an alkali metal compound. Furthermore, it is also possible to provide a carbon nanotube production method that utilizes the production of carbon nanotubes.

[0017] 1 is a schematic diagram of a carbon nanotube synthesis apparatus according to an embodiment of the present invention, and is a schematic diagram of the periphery of an inlet flange of the apparatus shown in FIG.

[0018] The carbon nanotube production apparatus of the present invention is an apparatus for producing carbon nanotubes by chemical vapor deposition. The carbon nanotube production apparatus of the present invention includes a reaction vessel, a carbon raw material supply nozzle 1 for supplying a carbon raw material into the reaction vessel, and an alkali metal compound aqueous solution supply nozzle 2 for supplying an alkali metal compound aqueous solution into the reaction vessel. The alkali metal compound aqueous solution supply nozzle 2 is an ultrasonic atomization type nozzle.

[0019] In the carbon nanotube production apparatus of the present invention, a carbon raw material is supplied into a reaction vessel from a carbon raw material supply nozzle 1, an aqueous alkali metal compound solution is supplied into the reaction vessel from an aqueous alkali metal compound solution supply nozzle 2, and the carbon raw material is heated in the reaction vessel to produce carbon nanotubes. The present invention is characterized in that the tip of the aqueous alkali metal compound solution supply nozzle 2 is positioned at a position where the temperature inside the reaction vessel becomes 120° C. or less when the carbon raw material is heated in the reaction vessel to produce carbon nanotubes.

[0020] By having such a configuration, the carbon nanotube manufacturing apparatus of the present invention can provide a novel carbon nanotube manufacturing apparatus that can efficiently and continuously produce carbon nanotubes for long periods of time in a technology for producing carbon nanotubes by chemical vapor deposition in the presence of an alkali metal compound.

[0021] Hereinafter, one embodiment of the carbon nanotube production apparatus according to the present invention will be described in detail with reference to Figures 1 and 2. Figure 1 is a schematic diagram of the carbon nanotube production apparatus according to one embodiment of the present invention. Figure 2 is a schematic diagram of the periphery of the inlet flange of the apparatus shown in Figure 1. The carbon nanotube production apparatus shown in Figures 1 and 2 is merely one embodiment showing a specific aspect of the carbon nanotube production apparatus according to the present invention, and the carbon nanotube production apparatus according to the present invention is not limited to this embodiment.

[0022] The carbon nanotube production apparatus according to this embodiment is a carbon nanotube production apparatus for producing carbon nanotubes by chemical vapor deposition, and more specifically, is an apparatus for producing carbon nanotubes by floating catalyst chemical vapor deposition (FC-CVD). Floating catalyst chemical vapor deposition (FC-CVD) is a type of CVD method in which, without using a substrate to support the catalyst, a catalyst is introduced into a heated reaction vessel, and the catalyst is chemically reacted with a carbon raw material in a suspended and fluidized state in a gas phase in which a carrier gas flows, thereby growing carbon nanotubes (CNTs) in a suspended state.

[0023] 1, an inlet flange 6 is attached to the opening on the upstream side (the side where the carbon raw material is supplied) of a reaction vessel 5, and a carbon nanotube collector 4 is attached to the downstream side. The carbon raw material supplied to the upstream side of the reaction vessel 5 reacts in the reaction vessel 5 to produce carbon nanotubes, which are then collected in the collector 4 on the downstream side.

[0024] The shape, material, size, etc. of the reaction vessel 5 may be selected as appropriate, as long as it provides a reaction system (reaction field) in which the carbon raw material reacts to produce carbon nanotubes. There are no particular limitations on the reaction vessel 5 as long as it can efficiently produce carbon nanotubes, and it is preferable to use either a horizontal reactor or a vertical reactor for the reaction, and it is more preferable to use a vertical reactor for the reaction. As the shape of the reactor, for example, a reactor having a tubular shape can be preferably used. The reaction vessel 5 is typically a straight tube with a hollow cylindrical shape.

[0025] A specific example of the reaction vessel 5 is a straight pipe having an inner diameter of about 50 mm to 200 mm and a length of about 500 mm to 2,000 mm.

[0026] The material of the reaction vessel 5 is not particularly limited as long as it has excellent strength even in high temperature regions (for example, the temperature region of 1200°C or higher at which CNTs are produced, as described below), and examples thereof include ceramics such as alumina, silica, silicon carbide, silicon nitride, aluminum nitride, mullite, and ferrite; glasses such as soda glass, lead glass, borosilicate glass, and quartz glass; and metals such as stainless steel and carbon steel. In the present invention, it is preferable to use ceramics, and specific materials are preferably alumina, silicon carbide, and mullite, more preferably alumina and silicon carbide, and even more preferably silicon carbide.

[0027] The inlet flange 6 serves as an upper lid that surrounds the reaction system in the reaction vessel 5, and is equipped with a carbon raw material supply nozzle 1 (hereinafter sometimes simply referred to as "nozzle 1"), an aqueous alkali metal compound solution supply nozzle 2 (hereinafter sometimes simply referred to as "nozzle 2"), and a pedestal 7 (nozzle pedestal) for fixing instruments, etc. In the production apparatus of Figures 1 and 2, the nozzle 1 that supplies a carbon raw material into the reaction vessel 5 and the nozzle 2 that supplies an aqueous alkali metal compound solution into the reaction vessel 5 are attached to the reaction vessel 5 via the inlet flange 6.

[0028] The aqueous alkali metal compound solution supply nozzle 2 is an ultrasonic atomization type nozzle. Nozzles for spraying a liquid generally include one-fluid nozzles that supply the liquid to be sprayed at high pressure and two-fluid nozzles that atomize the liquid using a carrier gas flow. In contrast, ultrasonic atomization type nozzles have the advantage over these nozzles of being able to spray a small flow rate with high precision. For this reason, in this embodiment, an ultrasonic atomization type nozzle that uses ultrasonic vibrations to spray the aqueous alkali metal compound solution from the nozzle tip is used as the nozzle 2 for supplying the aqueous alkali metal compound solution into the reaction vessel 5.

[0029] Furthermore, there are two main types of known ultrasonic atomization methods: the "nebulizer type," in which a vibrator is placed on the bottom of a container containing liquid to atomize it, and the "Langevin type," in which vibrations from a piezoelectric element are transmitted to the atomization surface at the tip of the nozzle. In this embodiment, a Langevin ultrasonic spray nozzle is suitable, as it is small and has high directionality for atomized droplets. A commercially available liquid pump can be used to supply liquid to the ultrasonic spray nozzle. For example, a syringe pump, which is small and has a fixed volume, is preferred.

[0030] In FIG. 1 , the base 7 of the inlet flange 6 has a hollow structure, and a supply channel through which a carrier gas B of an alkali metal compound aqueous solution is supplied into the reaction vessel 5 is connected to the base 7. Between the base 7 and the reaction vessel 5, the supply channel for the carrier gas B is provided coaxially outside the nozzle 2. In FIG. 2 , the supply channel is formed along the outer side surface of the nozzle 2 and is configured to allow the carrier gas B to pass through. In FIG. 2 , the carrier gas B is supplied from the outside of the manufacturing apparatus toward the nozzle 2, then changes direction inside the base 7, travels coaxially with the nozzle 2, and passes through the supply channel (cylindrical space) provided in the inlet flange 6. The carrier gas B entrains droplets of the alkali metal compound aqueous solution atomized at the tip of the nozzle 2 and is introduced into the reaction field in the reaction vessel 5.

[0031] The carbon raw material supply nozzle 1 is not particularly limited as long as it can supply the carbon raw material into the reaction vessel 5, and a known two-fluid spray nozzle can be used. By using a two-fluid spray nozzle, the carbon raw material can be atomized and sprayed by the energy of the carrier gas A and supplied into the reaction vessel 5.

[0032] The carrier gas A used in the nozzle 1 may be any gas that does not affect the CNT synthesis reaction, and argon or nitrogen, which are generally used as inert gases, or hydrogen, which is commonly used as a carrier gas in CNT synthesis reactions, are suitable.

[0033] 1 and 2, a thermocouple 8 is attached to the inlet flange 6. The thermocouple 8 is provided to measure the temperature near the tip of the aqueous alkali metal compound solution supply nozzle 2 so that the nozzle 2 does not overheat to a temperature exceeding 120°C. The thermocouple 8 is placed in the reaction vessel 5 at the same insertion depth h as the tip of the nozzle 2 and at a distance of approximately 20 mm horizontally from the tip of the nozzle 2. The temperature near the tip of the nozzle 2 is substantially the same as the temperature at the tip of the nozzle 2, and the position of the thermocouple 8 is adjusted so that this temperature is maintained.

[0034] A heater 3 is attached to the outside of the reaction vessel 5, and by heating the reaction vessel 5, the carbon raw material supplied inside the reaction vessel 5 is heated to produce carbon nanotubes. A carbon nanotube collector 4 that collects the produced carbon nanotubes is connected to the downstream side of the reaction vessel 5. The carbon raw material supplied from the upstream side of the reaction vessel 5 reacts with the heat of the heater 3 as it moves downstream to produce carbon nanotubes, which are then collected by the carbon nanotube collector 4 on the downstream side.

[0035] In this embodiment, the installation position of the tip of nozzle 2 is adjusted, for example, by appropriately setting the distance from heater 3. As a result, when carbon raw material is heated in reaction vessel 5 to produce carbon nanotubes, the tip of nozzle 2 can be positioned at a position where the temperature inside reaction vessel 5 is 120°C or less. By positioning the tip of nozzle 2 at a position where the temperature inside reaction vessel 5 is 120°C or less, clogging of the flow path due to overheating of nozzle 2 caused mainly by radiant heat from heater 3 is prevented, and the supply of alkali metal compound from nozzle 2 can be stabilized for a long period of time, allowing carbon nanotubes to be produced efficiently and continuously for a long period of time.

[0036] Note that because the tip of the nozzle 2 vibrates at high speed due to ultrasonic waves, it is difficult to directly measure the temperature by contacting it with a measurement probe. Therefore, a thermocouple 8 is placed in the reaction vessel 5 at the same insertion depth as the tip of the nozzle 2 and approximately 20 mm horizontally from the tip of the nozzle 2 to measure the temperature near the tip of the nozzle 2. If the temperature exceeds 120°C, clogging inside the nozzle 2 is likely to occur. Clogging of the nozzle 2 is caused by rapid evaporation of water due to overheating. When producing carbon nanotubes by heating a carbon raw material in the reaction vessel 5, the temperature of the tip of the nozzle 2 should be 120°C or less, but is preferably 100°C or less, and even more preferably 90°C or less. There is no particular lower limit, but if the tip of the nozzle 2 is too far from the reaction field of the carbon raw material, the reaction efficiency may decrease. Therefore, the temperature is preferably 40°C or more, more preferably 60°C or more, and even more preferably 70°C or more.

[0037] During carbon nanotube production, the temperature inside the reaction vessel 5 is controlled by radiant heat from the heater 3. When the heating temperature of the heater 3 is fixed, the temperature of the tip of the nozzle 2 can be adjusted by adjusting the distance from the heater 3. In a carbon nanotube production apparatus, the temperature of the tip of the nozzle 2 can be kept below 120°C by adjusting the distance between the tip of the nozzle 2 and the heater 3 in millimeters. For convenience, the inner surface of the inlet flange 6 (the surface on the reaction vessel 5 side) can be used as a reference, and the insertion depth of the tip of the nozzle 2 from that surface can be used as an index. The optimal value of the nozzle insertion depth h varies depending on heat dissipation from the apparatus (which depends on the size and structure of the apparatus) and the presence or absence of a cooling mechanism, so the numerical value is essentially meaningless. In this embodiment, it is important to maintain the temperature at the tip of the nozzle 2 below 120°C, and the position of the tip of the nozzle 2 is adjusted using that temperature as an index.

[0038] 2, in this embodiment, by supplying carrier gas B into reaction vessel 5 from the coaxial outside of nozzle 2, the temperature of the tip of nozzle 2 can be kept lower and adhesion of alkali metal compounds to the tip of nozzle 2 can be more effectively suppressed. Carrier gas B is a medium for cooling the tip of nozzle 2 and also has the effect of constantly purging the tip, thereby suppressing the deposition of alkali metal compounds.

[0039] The carrier gas B used in the nozzle 2 may be any gas that does not affect the CNT synthesis reaction, and argon or nitrogen, which are generally used as inert gases, or hydrogen, which is commonly used as a carrier gas in CNT synthesis reactions, are suitable.

[0040] A carbon nanotube manufacturing method using the carbon nanotube manufacturing apparatus according to this embodiment (a carbon nanotube manufacturing method using the carbon nanotube manufacturing apparatus according to this embodiment) will be described in detail below.

[0041] The carbon nanotube manufacturing method according to this embodiment is a method for manufacturing carbon nanotubes by chemical vapor deposition using the carbon nanotube manufacturing apparatus according to this embodiment. More specifically, as described above, this is a method for manufacturing carbon nanotubes by floating catalyst chemical vapor deposition (FC-CVD).

[0042] The method for producing carbon nanotubes of this embodiment preferably includes a step of heating a raw material for carbon nanotubes in the presence of an iron-containing catalyst and an alkali metal compound to produce carbon nanotubes.

[0043] High-purity single-walled carbon nanotubes can be produced efficiently by heating the carbon nanotube raw material in the presence of an iron-containing catalyst and an alkali metal compound (i.e., by contacting the carbon nanotube raw material with the iron-containing catalyst and the alkali metal compound in a heated environment).

[0044] A carbon raw material, which is the raw material for carbon nanotubes, is supplied (introduced) into a reaction vessel 5 of the carbon nanotube manufacturing apparatus of the present invention using a nozzle 1, and in the heated environment inside the reaction vessel 5 heated by a heater 3, the carbon raw material is brought into contact with an iron-containing catalyst and an alkali metal compound to produce carbon nanotubes.

[0045] Liquid or gaseous carbon compounds can be used as raw materials (carbon raw materials) for carbon nanotubes. Specific examples of gaseous carbon compounds that are preferably used include methane, ethane, propane, ethylene, propylene, and acetylene. Liquid carbon compounds that are preferably used include alcohols such as methanol and ethanol, aliphatic hydrocarbons such as hexane, cyclohexane, and decalin, and aromatic hydrocarbons such as benzene, toluene, and xylene. Ethylene, benzene, toluene, and decalin are particularly preferred. Any of these carbon compounds may be mixed or used in combination.

[0046] The iron-containing catalyst is preferably a metallocene compound such as ferrocene, a metal acetylacetonate such as iron chloride or iron acetylacetonate, or a metal carbonyl such as iron carbonyl, more preferably a metallocene compound such as ferrocene, and particularly preferably ferrocene. Only one type of iron-containing catalyst may be used, or two or more types may be used.

[0047] In this embodiment, the lower limit of the supply amount of the iron-containing catalyst relative to 100 parts by mass of the carbon raw material is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 parts by mass or more. The upper limit is preferably 14 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less. Preferred ranges of the supply amount of the iron-containing catalyst relative to 100 parts by mass of the carbon raw material include 2 to 14 parts by mass, 2 to 12 parts by mass, 2 to 10 parts by mass, 4 to 14 parts by mass, 4 to 12 parts by mass, 4 to 10 parts by mass, 6 to 14 parts by mass, 6 to 12 parts by mass, and 6 to 10 parts by mass.

[0048] Further, other catalysts can be used in combination with the iron-containing catalyst. The other catalysts are preferably transition metal compounds or transition metal fine particles. The transition metals are preferably cobalt, nickel, palladium, platinum, or rhodium, and more preferably cobalt or nickel. The transition metal compounds in the other catalysts are preferably metallocene compounds such as cobaltocene or nickellocene, chlorides such as cobalt chloride, metal acetylacetonates, or metal carbonyls, and more preferably metallocene compounds such as cobaltocene or nickellocene. The other catalysts used may be one type only, or two or more types.

[0049] The particle size of the iron-containing catalyst and the transition metal particles is preferably 0.1 to 50 nm, more preferably 0.3 to 15 nm. The particle size of the particles can be measured using a transmission electron microscope.

[0050] The method for supplying the iron-containing catalyst is not particularly limited as long as it can supply the iron-containing catalyst into the system (into the reaction vessel 5), and examples thereof include a method for supplying the iron-containing catalyst in a state where it is dissolved in a solvent, and a method for introducing the iron-containing catalyst in a vaporized state into the reaction tube. In this embodiment, a method for supplying the iron-containing catalyst in a state where it is dissolved in a solvent is preferred. The same method can be used when using other catalysts in combination. The iron-containing catalyst can be prepared as a mixed liquid together with the carbon raw material, and the mixed liquid can be supplied into the reaction vessel 5 from the nozzle 1, for example.

[0051] In the method of supplying the iron-containing catalyst in a state of being dissolved in a solvent, the solvent is not particularly limited, but is preferably a liquid carbon compound used as a carbon raw material.

[0052] In the manufacturing method of this embodiment, it is preferable to further add a sulfur compound to promote the carbon nanotube production reaction. Examples of the sulfur compound include organic sulfur compounds and inorganic sulfur compounds. Examples of the organic sulfur compound include thiol, thiophene, thianaphthene, and benzothiophene, and examples of the inorganic sulfur compound include elemental sulfur, carbon disulfide, and hydrogen sulfide. Only one type of sulfur compound may be used, or two or more types may be used.

[0053] The method for adding the sulfur compound is not particularly limited, but an example thereof is to add the sulfur compound by dissolving it in a liquid carbon compound used as the carbon raw material. That is, the sulfur compound can be mixed with the carbon raw material to form a liquid mixture, and the liquid mixture can be supplied into the reaction vessel 5 from the nozzle 1.

[0054] In this embodiment, the supply amount of the sulfur compound is preferably 0.1 parts by mass or more, more preferably 0.25 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the carbon raw material. The upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less. If the supply amount is below the lower limit, the promotion effect cannot be obtained, while if the supply amount is above the upper limit, a large amount of sulfur compound may remain in the carbon nanotubes, resulting in a decrease in quality and a decrease in yield due to an increased load in the purification process. Preferred supply amounts of the sulfur compound are 0.1 to 5 parts by mass, 0.1 to 3 parts by mass, 0.1 to 2 parts by mass, 0.25 to 5 parts by mass, 0.25 to 3 parts by mass, 0.25 to 2 parts by mass, 0.5 to 5 parts by mass, 0.5 to 3 parts by mass, and 0.5 to 2 parts by mass, relative to 100 parts by mass of the carbon raw material.

[0055] The alkali metal compound in the production method of this embodiment is preferably a phosphate, acetate, chloride, sulfate, carbonate, or tetraborate hydrate, silicate, or hydroxide of lithium, sodium, potassium, or cesium, more preferably a chloride, sulfate, carbonate, or tetraborate hydrate, silicate, or hydroxide of lithium, sodium, potassium, or cesium, even more preferably a chloride, sulfate, carbonate, or tetraborate hydrate, silicate, or hydroxide of sodium, potassium, or cesium, and particularly preferably a chloride, carbonate, or hydroxide of potassium or cesium. Only one type of alkali metal compound may be used, or two or more types may be used.

[0056] In the production method of this embodiment, the alkali metal compound is supplied by preparing an aqueous solution of the alkali metal compound and spraying it into the reaction vessel 5 from the nozzle 2 .

[0057] In this embodiment, the supply amount of the alkali metal compound is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, even more preferably 0.05 parts by mass or more, and particularly preferably 0.07 parts by mass or more, relative to 100 parts by mass of the carbon raw material. The upper limit is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 8 parts by mass or less. Below the lower limit, the promotion effect cannot be obtained, whereas above the upper limit, a large amount of alkali metal compound remains in the carbon nanotubes, which may lead to a decrease in quality and a decrease in yield due to an increased load on the purification process. Preferred ranges of the supply amount of the alkali metal compound relative to 100 parts by mass of the carbon raw material include 0.01 to 15 parts by mass, 0.01 to 12 parts by mass, 0.01 to 10 parts by mass, 0.01 to 8 parts by mass, 0.03 to 15 parts by mass, 0.03 to 12 parts by mass, 0.03 to 10 parts by mass, 0.03 to 8 parts by mass, 0.05 to 15 parts by mass, 0.05 to 12 parts by mass, 0.05 to 10 parts by mass, 0.05 to 8 parts by mass, 0.07 to 15 parts by mass, 0.07 to 12 parts by mass, 0.07 to 10 parts by mass, and 0.07 to 8 parts by mass.

[0058] In this embodiment, the carbon nanotube production process is carried out in the reaction vessel 5. The reaction vessel 5 is as described above.

[0059] The reaction temperature of the carbon raw material heated by the heater 3 is preferably a temperature at which the iron-containing catalyst and the carbon raw material can react efficiently, for example, 1200 to 1800°C, more preferably 1200 to 1500°C, more preferably 1200 to 1350°C, and even more preferably 1250 to 1350°C. This reaction temperature range is advantageous in that it improves the G / D ratio, which indicates the defect rate of carbon nanotubes, and the abundance ratio of single-walled carbon nanotubes. On the other hand, if the temperature is too high, the abundance ratio of single-walled carbon nanotubes decreases, and if the temperature is too low, the carbon nanotube yield decreases significantly. In the carbon nanotube production apparatus of this embodiment, the temperature of the carbon raw material heated by the heater 3 is preferably set within this temperature range. Assuming that the carbon raw material is heated within this temperature range, it is preferable to position the tip of the nozzle 2 at a position where the temperature inside the reaction vessel 5 is 120°C or less.

[0060] The carbon purity of the carbon nanotubes produced by the production method of this embodiment is preferably 80% or more, more preferably 84% or more, and particularly preferably 88% or more.

[0061] The G / D ratio of the G band to the D band of the carbon nanotubes produced by the production method of this embodiment is preferably 40 or more, more preferably 60 or more, and particularly preferably 70 or more. G / D is measured by a Raman spectrometer, and in a Raman spectrum measured by resonance Raman scattering (excitation wavelength 532 nm), the G band (1590 cm -1 around 1300 cm -1 The higher the G / D ratio, the fewer the defects in the carbon nanotube structure.

[0062] The diameter of the carbon nanotubes produced by the production method of this embodiment is preferably 3.0 nm or less, and more preferably 2.5 nm or less.

[0063] The carbon nanotubes of this embodiment may be single-walled carbon nanotubes or multi-walled carbon nanotubes, but the manufacturing method of this embodiment makes it possible to more suitably manufacture high-purity single-walled carbon nanotubes.

[0064] The abundance ratio of single-walled carbon nanotubes (SWCNTs) in the carbon nanotubes obtained by the manufacturing method of this embodiment is preferably 75 mass% or more, more preferably 80 mass% or more, even more preferably 85 mass% or more, and particularly preferably 90 mass% or more.

[0065] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0066] Example 1: Manufacturing of Carbon Nanotube Manufacturing Apparatus A carbon nanotube manufacturing apparatus having the structure shown in Figures 1 and 2 was manufactured. The carbon nanotube manufacturing apparatus was a vertical tubular furnace, specifically configured as follows: Reaction vessel 5: A tube made of atmospheric sintered silicon carbide (SiC) with an inner diameter of 100 mm, an outer diameter of 110 mm, and a length of 2,000 mm. Carbon source supply nozzle 1: A commercially available two-fluid nozzle made of stainless steel, with a structure in which the carbon source liquid passes through the center and the carrier gas passes through the outside. Alkali metal compound aqueous solution supply nozzle 2: A commercially available Langevin-type ultrasonic spray nozzle with a nozzle tip made of titanium alloy. Heater 3: A stainless steel housing containing multiple carbon heating elements, with ceramic heat insulating material placed in the gap between the housing and the heating elements, and the center of the housing housing housing the reaction tube 5. Carbon nanotube collector 4: A stainless steel cylindrical vessel with an inner diameter of 900 mm and a height of 1,100 mm, equipped with a carrier gas outlet on the side. The top of the cylindrical vessel is connected to reactor 5. Inlet flange 6: A stainless steel inlet flange with an outer diameter of 220 mm, connected to the top of reactor 5, serves as a lid to increase the airtightness of the reactor. A through-hole is drilled in part of the inlet flange to allow nozzles 1 and 2 to be inserted into the reactor tube. A fitting for securing the carbon feedstock spray nozzle is provided near the center of the flange, and a female thread is provided for securing nozzle base 7. Nozzle base 7: A stainless steel component equipped with a mechanism for adjusting and securing the insertion depth of nozzle 2 (pipe thread type). Base 7 is hollow, and carrier gas B is supplied into reactor 5 through the space formed between the inlet flange 6 and the outer periphery of nozzle 2. Thermocouple 8 (for measuring the temperature near the tip of the alkali metal compound aqueous solution supply nozzle 2): K-type thermocouple with a stainless steel sheath tube (Φ1.6 mm x length 150 mm)

[0067] <Production of Carbon Nanotubes> The following reagents were used to produce carbon nanotubes. Toluene: Kanto Chemical Co., Ltd. Ferrocene: Fujifilm Wako Pure Chemical Industries, Ltd. Thiophene: Tokyo Chemical Industry Co., Ltd. Hydrogen: Iwatani Industrial Gases Corporation Nitrogen: Iwatani Industrial Gases Corporation Potassium chloride: Fujifilm Wako Pure Chemical Industries, Ltd. Potassium carbonate: Fujifilm Wako Pure Chemical Industries, Ltd.

[0068] Carbon nanotubes were synthesized using a carbon nanotube production apparatus. Argon gas was flowed into a reaction vessel 5 through a carbon raw material supply nozzle 1. The insertion depth h of the alkali metal compound aqueous solution supply nozzle 2 was set to 0 mm. In the argon gas flow, the reaction vessel was heated to 1,300°C using a heater 3, which was the reaction temperature of the carbon raw material. Instead of argon, 90 SLM of hydrogen gas was supplied as a carrier gas [A] through the carbon raw material supply nozzle 1. Carrier gas B was not supplied. A raw material mixture containing 100 parts by mass of toluene as a carbon raw material, 8.08 parts by mass of ferrocene as an iron-containing catalyst, and 0.91 parts by mass of thiophene as a sulfur compound was sprayed (supplied) into the reaction vessel through the carbon raw material supply nozzle 1. Furthermore, a 15 wt % potassium chloride aqueous solution (0.46 parts by mass of potassium chloride) was sprayed (supplied) into the reaction vessel through the alkali metal compound aqueous solution supply nozzle 2 as an alkali metal compound aqueous solution. As a result of the reaction of the carbon raw material in a 1300°C environment, a deposit of black carbon nanotubes was formed in the carbon nanotube recovery vessel 4 installed at the bottom of the reaction vessel. The carbon nanotube production apparatus was operated continuously for 7 hours in this state, and carbon nanotube production continued. A thermocouple was placed at the position where the tip of the aqueous alkali metal compound solution supply nozzle 2 was located, and the temperature inside the reaction vessel near that position was measured. Thereafter, the supply of the raw material mixture and aqueous alkali metal compound solution from nozzles 1 and 2 was stopped, and the carrier gas was changed from hydrogen to argon. After the temperature was lowered to room temperature, the deposit was recovered from the recovery vessel and evaluated as follows, and the results are shown in Table 1.

[0069] <Yield> The yield was calculated by dividing the mass of the collected carbon nanotubes by the mass of the supplied carbon raw material. The calculation formula is as follows: Yield (%) = (mass of collected carbon nanotubes / mass of carbon raw material) x 100

[0070] <G / D ratio> Measurement was performed using a laser Raman microscope (RAMANTouch VIS-NIR-DIS, Nanophoton Co., Ltd.) at a laser wavelength of 532 nm. The intensity ratio G / D of the G band to the D band, which indicates the crystallinity of the carbon nanotubes, was calculated by dividing the G band (1590 cm -1 around 1300 cm -1 The peak intensity was calculated from the peak intensity ratio of the

[0071] <Carbon Purity> Using a thermogravimetric differential thermal analyzer (STA7200RV, Hitachi High-Tech Science Corporation), approximately 7 mg of a sample was heated from room temperature to 900°C at a temperature increase rate of 10°C / min with an air flow rate of 200 cc / min, and the weight loss rate in the temperature range from room temperature to 900°C was evaluated.

[0072] <Internal state of the aqueous alkali metal compound solution supply nozzle 2> After the production was completed, the nozzle 2 was removed. When water was poured into the rear of the nozzle and discharged smoothly, the state was marked with a circle (legend ◯). On the other hand, when the inside of the nozzle was clogged with the alkali metal compound and the water poured into the rear of the nozzle could not be discharged, the state was marked with an x ​​(legend ×).

[0073] <Surface condition of aqueous alkali metal compound solution supply nozzle 2> After completion of production, the nozzle 2 was removed and the tip was visually observed. A state in which there was almost no adhesion of alkali metal compound and the metal surface portion of the nozzle tip could be visually confirmed was marked with a circle (legend). On the other hand, a state in which the nozzle tip was covered with alkali metal compound and the metal surface could not be visually confirmed was marked with an x ​​(legend).

[0074] Example 2 The carbon nanotube production apparatus and carbon nanotubes were produced in the same manner as in Example 1, except that the insertion depth h of the aqueous alkali metal compound solution supply nozzle 2 of the carbon nanotube production apparatus was set to 5 mm.

[0075] Example 3 Carbon nanotubes were produced in the same manner as in Example 1, except that 2 SLM of nitrogen gas was supplied as carrier gas B from the aqueous alkali metal compound solution supply nozzle 2 during the production of carbon nanotubes.

[0076] Example 4 Carbon nanotubes were produced in the same manner as in Example 1, except that a 15 wt % aqueous potassium carbonate solution (0.46 parts by mass as the supply amount of potassium carbonate) was used as the aqueous alkali metal compound solution instead of a 15 wt % aqueous potassium chloride solution (0.46 parts by mass as the supply amount of potassium chloride).

[0077] Comparative Example 1 A carbon nanotube production apparatus and carbon nanotubes were produced in the same manner as in Example 1, except that the insertion depth h of the alkali metal compound aqueous solution supply nozzle 2 was set to 10 mm. After 1.1 hours of continuous operation, the pressure in the alkali metal compound aqueous solution supply line connected to the alkali metal compound aqueous solution supply nozzle 2 rose sharply, so the operation was stopped. After cooling, the nozzle 2 was removed and checked, and it was found that a blockage had occurred inside the nozzle.

[0078]

[0079] 1... Carbon raw material supply nozzle 2... Alkali metal compound aqueous solution supply nozzle (ultrasonic atomization method) 2a... Ultrasonic vibrator (Landivin type) 3... Heater 4... Carbon nanotube collector 5... Reaction vessel 6... Inlet flange 7... Nozzle base 8... Thermocouple (for measuring temperature near nozzle 2)

[0080] According to the present invention, it is possible to provide an apparatus and a manufacturing method for efficiently manufacturing carbon nanotubes by applying a CVD method, particularly a floating catalyst chemical vapor deposition method (FC-CVD method).

Claims

1. A carbon nanotube production apparatus for producing carbon nanotubes by chemical vapor deposition, comprising a reaction vessel, a carbon raw material supply nozzle 1 for supplying a carbon raw material into the reaction vessel, and an alkali metal compound aqueous solution supply nozzle 2 for supplying an alkali metal compound aqueous solution into the reaction vessel, the alkali metal compound aqueous solution supply nozzle 2 being an ultrasonic atomization type nozzle, the carbon raw material being supplied from the carbon raw material supply nozzle 1 into the reaction vessel, the alkali metal compound aqueous solution being supplied from the alkali metal compound aqueous solution supply nozzle 2 into the reaction vessel, the carbon raw material being heated in the reaction vessel, and carbon nanotubes being produced, the tip of the alkali metal compound aqueous solution supply nozzle 2 being positioned at a position where the temperature inside the reaction vessel is 120°C or lower.

2. The carbon nanotube manufacturing apparatus according to claim 1, further comprising a supply passage provided coaxially outside said alkali metal compound aqueous solution supply nozzle 2 for supplying a carrier gas for said alkali metal compound aqueous solution to said reaction vessel.

3. A method for producing carbon nanotubes, comprising using the carbon nanotube production apparatus according to claim 1 or 2.

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