Carbon nanotube production device and carbon nanotube manufacturing device

Abstract

A carbon nanotube production device for producing carbon nanotubes, said device comprising: a reaction tube to which a carbon nanotube starting material gas is supplied; a heater which is positioned at the periphery of the reaction tube; an insulating material which covers the outside of the heater; an enclosing case which surrounds and encloses the periphery of the reaction tube, and accommodates the heater and the insulating material; a supply port which supplies a shield gas to the interior of the enclosing case; and a discharge port which discharges the shield gas from the interior of the enclosing case.

Description

Carbon nanotube generating device and carbon nanotube manufacturing device

[0001] The present invention relates to a carbon nanotube generating apparatus and a carbon nanotube manufacturing apparatus for generating carbon nanotubes.

[0002] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are a new material that has attracted attention in many fields due to their excellent properties such as electrical conductivity, thermal conductivity, and mechanical strength. Patent Document 1 discloses a CNT manufacturing device that uses a chemical vapor deposition (CVD) method to generate CNTs by thermally decomposing a carbon-containing raw material (carbon source).

[0003] In a method for producing CNTs using chemical vapor deposition, for example, CNT raw materials and a carrier gas are supplied to the inside of a reaction tube heated to a high temperature, and CNTs are produced by passing the raw materials through the inside of the reaction tube for a certain period of time. The produced CNTs are discharged from the end of the reaction tube opposite the raw material supply side. Hydrocarbons are used as the CNT raw materials, and hydrogen gas is used as the carrier gas.

[0004] Japanese Patent Application Laid-Open No. 2019-064918

[0005] The inside of the reaction tube is the reaction generation region, and the heat source for heating the reaction tube (e.g., an electric heater) is installed outside the reaction tube, heating the reaction tube from the outside. Since CNT production must be performed at high temperatures and in a flammable gas atmosphere, the reaction tube must be made of a material that is heat-resistant, corrosion-resistant, and gas-impermeable at high temperatures. Materials that meet these conditions include heat-resistant steel, tungsten, molybdenum, carbon, alumina, zirconia, mullite, SiC, and quartz.

[0006] However, these materials have different performance and characteristics, such as heat resistance and corrosion resistance, and there are limitations on how they can be used, so the material for the reaction tube must be selected based on the CNT production conditions (temperature, gas used). Furthermore, there are limitations on the manufacturable dimensions of reaction tubes made from each material, and because reaction tube size is directly related to the amount of CNT produced, CNT production capacity is influenced by the reaction tube material. In short, CNT production is subject to certain limitations depending on the reaction tube material selected. If the reaction tube is damaged, flammable gas, which serves as the carrier gas, will leak, igniting the heating source installed outside the reaction tube and potentially causing a fire.

[0007] For example, heat-resistant steel has a limit of use temperature of 1100°C, and is prone to melting and damage due to carburization. Tungsten, molybdenum, and carbon are subject to rapid wear, thinning, and breakage in oxidizing atmospheres above 300°C. Alumina, zirconia, mullite, SiC, and quartz cannot be rapidly heated or cooled because they are susceptible to thermal shock and breakage.

[0008] Even if a reaction tube made of a material suitable for the CNT production conditions is selected, the reaction tube material will deteriorate over a long period of time and repeated use, causing the initial performance and characteristics to gradually change and deteriorate. In such cases, the reaction tube may break even under the same CNT production conditions.

[0009] If the reaction tube is damaged, the flammable carrier gas will leak, igniting the heat source installed outside the reaction tube and possibly causing a fire.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a carbon nanotube generation device and a carbon nanotube manufacturing device that can reduce the risk of fire even in the event of a flammable gas leak from the reaction system due to damage to the reaction tube, etc.

[0011] One aspect of the present invention that solves the above problem is a carbon nanotube production apparatus that produces carbon nanotubes, characterized by comprising a reaction tube to which a raw material gas for the carbon nanotubes is supplied, a heater arranged around the reaction tube, an insulating material covering the outside of the heater, a sealed case that hermetically surrounds the reaction tube and houses the heater and the insulating material, a supply port that supplies a shielding gas into the inside of the sealed case, and an exhaust port that exhausts the shielding gas from the inside of the sealed case.

[0012] In this carbon nanotube generation apparatus, the supply port may be provided at the bottom of the sealed case, and the discharge port may be provided at the top of the sealed case. Also, the carbon nanotube generation apparatus may be configured to monitor the differential pressure between the inside of the reaction tube and the space to which the shielding gas is supplied, and automatically adjust the supply flow rate of the shielding gas when the differential pressure exceeds a set range, thereby preventing leakage of the shielding gas into the reaction tube when the reaction tube is damaged.

[0013] Another aspect of the present invention is a carbon nanotube production apparatus, characterized by comprising the carbon nanotube production apparatus described above and a recovery apparatus for recovering carbon nanotubes.

[0014] According to the present invention, it is possible to provide a carbon nanotube generation apparatus and a carbon nanotube manufacturing apparatus that can reduce the risk of fire even in the event of a flammable gas leak from the reaction system due to damage to the reaction tube, etc.

[0015] The present invention relates to a carbon nanotube manufacturing apparatus and a CNT manufacturing method thereof.

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification and the drawings, elements having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0017] 1 is an explanatory diagram showing a schematic configuration of a CNT production apparatus 1 for producing carbon nanotubes (hereinafter sometimes referred to as "CNT") according to this embodiment. In this specification, CNT refers to a tubular carbon allotrope (typically a cylindrical structure with a graphite structure), and includes so-called single-walled CNT, multi-walled CNT, or carbon nanohorns with horn-shaped tube tips. The CNT production apparatus 1 is particularly suitable for use in producing single-walled CNT.

[0018] The CNT production apparatus 1 has a CNT production apparatus 2 that produces CNTs and a recovery apparatus 3 that recovers the CNTs. The recovery apparatus 3 is connected to the lower end of the CNT production apparatus 2.

[0019] The CNT generating apparatus 2 that generates CNTs is an apparatus that generates CNTs using a chemical vapor deposition method (CVD method), in which raw materials such as catalytic metals or catalytic metal compounds are thermally decomposed to generate CNTs. When CNT raw materials are supplied to the CNT generating apparatus 2, a carrier gas (e.g., hydrogen gas) is also supplied along with the raw materials. In this specification, the raw materials supplied together with the carrier gas are referred to as raw material gas.

[0020] The generating device 2 includes a reaction tube 10 to which a raw material gas for CNTs is supplied, a heater 11 arranged to surround the reaction tube 10 , and a heat insulating material 12 covering the outside of the heater 11 .

[0021] The shape of the reaction tube 10 is not limited, but is preferably a straight tube (i.e., a shape with a linear axis). The cross-sectional shape of the reaction tube 10 may be a rounded shape such as a circle, an ellipse, an oval, or an oval, or a polygonal shape. Examples of materials that can be used for the reaction tube 10 include alumina (Al2O3), mullite, silicon carbide (SiC), quartz glass, Kanthal (iron-chromium-aluminum alloy), Inconel, and carbon.

[0022] The shape and heating method of the heater 11 are not particularly limited as long as they can heat the reaction tube 10 to a temperature suitable for CNT production. The heater 11 may be capable of heating the reaction tube 10 to, for example, 500°C to 2000°C, preferably 1000°C to 1600°C. Specific examples of the heater 11 include a tungsten heater capable of heating the reaction tube 10 to 500°C to 2000°C, or a silicon carbide heater (SiC heater) capable of heating the reaction tube 10 to 600°C to 1600°C.

[0023] A sealed case 13 is provided outside the reaction tube 10 to hermetically surround the reaction tube 10. The heater 11 and the heat insulating material 12 are housed inside the sealed case 13.

[0024] An upper end 15 of the reaction tube 10 protrudes above the sealed case 13, and an inlet unit 16 is provided at the upper end 15 to supply a replacement gas and a raw material gas from the outside into the reaction tube 10. A lower end 20 of the reaction tube 10 protrudes below the sealed case 13 and opens at the top surface of the recovery device 3.

[0025] Gaskets 21 are attached to the outer circumferential surface of the upper end 15 of the reaction tube 10 and the outer circumferential surface of the lower end 20 of the reaction tube 10. The packings 21 keep the internal space of the sealed case 13 sealed around the reaction tube 10.

[0026] A supply port 25 is provided at the bottom of the sealed case 13 to supply shielding gas into the interior of the sealed case 13, and an exhaust port 26 is provided at the top of the sealed case 13 to discharge the shielding gas from the interior of the sealed case 13. The internal space of the sealed case 13 is constantly maintained in an inert gas atmosphere by flowing a constant amount of shielding gas (inert gas, nitrogen, argon, etc.) from the supply port 25 into the interior of the sealed case 13 while discharging a constant amount from the exhaust port 26. The heat insulating material 12 is also provided with holes 27 to allow the shielding gas to circulate.

[0027] The recovery device 3 has a recovery chamber 30 that recovers the CNTs produced in the CNT production device 2, and an exhaust port 31 that exhausts the atmosphere inside the recovery chamber 30 is provided on the side of the recovery chamber 30. The gas supplied from the reaction tube 10 into the recovery chamber 30 is exhausted through this exhaust port 31.

[0028] A pressure sensor 35 for measuring and monitoring the pressure inside the reaction tube 10 is installed at the upper end 15 of the reaction tube 10. A pressure sensor 36 for measuring and monitoring the pressure inside the sealed case 13 (shielded space) is installed in the sealed case 13. An oxygen concentration meter 37 for measuring and monitoring the oxygen concentration of the shielding gas discharged from the inside of the sealed case 13 and a hydrogen detector 38 for detecting hydrogen in the shielding gas are attached to the exhaust port 26 of the sealed case 13. An oxygen concentration meter 39 is attached to the recovery chamber 30.

[0029] Next, a method for producing CNTs in the CNT production apparatus 1 configured as described above will be described with reference to Fig. 2. Of the operations described below, such as supplying and stopping each gas and raw material, and recovering CNTs, those that can be performed automatically may be performed automatically via a control unit (not shown) or manually by an operator.

[0030] First, as a preparation step, replacement of the gas inside the reaction tube 10 is started (S1). That is, an inert gas is supplied into the reaction tube 10 from the inlet unit 16 provided at the upper end 15 of the reaction tube 10 (S2), and the inside of the reaction tube 10 is replaced with an inert atmosphere (S3).

[0031] Since the reaction tube 10 and the recovery chamber 30 are connected by space, replacing the inside of the reaction tube 10 with an inert atmosphere also replaces the inside of the recovery chamber 30. The replacement method includes a method of supplying an inert gas for a certain period of time and a method of restoring pressure with an inert gas after evacuation.

[0032] In the method of supplying an inert gas for a fixed time, the oxygen concentration can be reduced to a predetermined level by supplying an inert gas equivalent to four times the volume of the purged gas. The relationship between the multiple of the purged volume (multiple of the spatial volume of the reaction tube 10 and the recovery chamber 30) and the oxygen concentration in the volume when the oxygen concentration is set to 2.3% or less in the method of supplying an inert gas for a fixed time is shown below.

[0033]

[0034] In the method of restoring pressure with an inert gas after evacuation, the ultimate vacuum value when evacuating is important, and by evacuation to -90 kPaG or less, it is possible to achieve a predetermined oxygen concentration or less. The following shows the relationship between the ultimate vacuum value when evacuating and the oxygen concentration within the volume when the oxygen concentration is set to 2.3% or less in the method of restoring pressure with an inert gas after evacuation.

[0035]

[0036] Meanwhile, gas replacement within the sealed case 13 (within the shielded space) is initiated (S4). That is, a constant amount of shielding gas (inert gas) is flowed into the sealed case 13 from the supply port 25 provided at the bottom of the sealed case 13, while a constant amount is discharged from the discharge port 26 (S5), thereby replacing the internal space of the sealed case 13 with an inert atmosphere (S6).

[0037] Thereafter, in the generator 2, the temperature of the reaction tube 10 is increased by heating with the heater 11 (S7), and when the temperature of the reaction tube 10 reaches the processing temperature (S8), a carrier gas (e.g., hydrogen gas) is supplied into the reaction tube 10 through the inlet unit 16 provided at the upper end 15 of the reaction tube 10 (S9), and raw material gases such as a carbon source and a catalytic metal or catalytic metal compound are supplied (S10). In this way, the CNT processing starts (S11), and CNTs are generated.

[0038] The produced CNTs are then discharged together with the carrier gas from the lower end 20 of the reaction tube 10 and collected in the collection chamber 30. The carrier gas supplied from the reaction tube 10 into the collection chamber 30 is discharged via the exhaust port 31. The shielding gas supplied from the supply port 25 is discharged via the exhaust port 26.

[0039] On the other hand, when CNT processing is to be terminated (S12), first, the supply of raw material into the reaction tube 10 is stopped (S13), and then the supply of carrier gas is stopped (S14). Then, heating by the heater 11 is stopped, and the reaction tube 10 is cooled (S15). In this way, CNT production by the CNT production apparatus 1 is terminated, and the facility is shut down (S16). By doing as described above, even if the reaction tube 10 is damaged, the risk of a fire caused by contact between the raw material gas containing hydrogen and a gas containing oxygen, such as air, can be significantly reduced.

[0040] During the production of CNTs, the pressure inside the reaction tube 10 can be measured and monitored by a pressure sensor 35, the pressure inside the sealed case 13 (shielded space) can be measured and monitored by a pressure sensor 36, and hydrogen in the shielding gas can be detected and monitored by a hydrogen detector 38. In addition, the oxygen concentration meter 37 can measure and monitor the oxygen concentration of the shielding gas discharged from the inside of the sealed case 13, and the oxygen concentration meter 39 can measure and monitor the oxygen concentration of the carrier gas discharged to the recovery chamber 30.

[0041] If the pressure inside the sealed case 13 (shielded space) is excessively high compared to the pressure inside the reaction tube 10, the shielding gas will infiltrate into the reaction tube 10 through the sealing packings 21 attached to both ends of the reaction tube 10, affecting the production of CNTs. Therefore, when the pressure inside the sealed case 13 measured by the pressure sensor 36 becomes equal to or greater than a certain pressure difference with respect to the pressure inside the reaction tube 10 measured by the pressure sensor 35, it is preferable to perform control to notify an abnormality.

[0042] During the production of CNTs, it is advisable to set the internal pressure of the shield space higher than the internal pressure of the reaction tube 10. For example, the flow rate of the shield gas is set so that the differential pressure between the internal pressure of the reaction tube 10 and the pressure inside the sealed case 13 (shield space) is within the range of 0 to 2 kPaG.

[0043] Furthermore, when the hydrogen detector 38 is used to monitor the intrusion of hydrogen gas from the reaction tube 10 into the shield space, an abnormality may be reported when the hydrogen detector 38 detects hydrogen in the shield gas.

[0044] In addition to the above-mentioned anomaly alarm when a leak of carrier gas (hydrogen gas) from the reaction tube is detected, automatic control by constantly monitoring the differential pressure between the reaction tube and the shielded space is also possible. For example, if it is determined that the carrier gas (hydrogen gas) is leaking into the shielded space beyond the normal range, it is possible to control the system by issuing an anomaly alarm associated with the hydrogen gas detection, stopping the hydrocarbon raw material and carrier gas, and introducing nitrogen gas.

[0045] Furthermore, when an oxygen concentration meter 39 is used, when it is detected that the oxygen concentration of the carrier gas exhausted to the recovery chamber 30 has reached a set value or higher, the supply of the carrier gas may be stopped, the heating of the heater 11 may be turned off, and a large flow rate of inert gas may be supplied into the reaction tube 10 and the recovery chamber 30 to replace the gas, thereby bringing an emergency halt to the production of CNTs by the CNT production apparatus 1. During CNT production, the oxygen concentration of the carrier gas is set in the range of 0 to 4%, which is outside the explosion limit range of hydrogen gas, and is preferably set to 2.3% or less.

[0046] Furthermore, when an oxygen concentration meter 37 is used, when it is detected that the oxygen concentration of the shielding gas discharged from the inside of the sealed case 13 has reached or exceeded a set value, the supply of carrier gas may be stopped, heating by the heater 11 may be turned off, and a large flow rate of inert gas may be supplied into the reaction tube 10 and the recovery chamber 30 to replace the oxygen, thereby bringing an emergency stop to the production of CNTs by the CNT production apparatus 1. During CNT production, the oxygen concentration of the shielding gas is set in the range of 0 to 4%, which is outside the explosion limit range of hydrogen gas, and is preferably set to 2.3% or less.

[0047] In this way, by controlling the pressure sensors 35, 36, the oxygen concentration meter 37, the hydrogen detector 38, and the oxygen concentration meter 39, it is possible to enhance the effect of preventing oxidation of the reaction tube 10 made of a material that is easily oxidized at high temperatures, and even if leakage of the carrier gas from the reaction tube 10 occurs, it is possible to detect the occurrence of the leakage.

[0048] According to the CNT production apparatus 1 of the present embodiment described above, during CNT production, a constant amount of shielding gas (e.g., inert gas, nitrogen, argon, etc.) is flowed into the sealed case 13 through the supply port 25 provided at the bottom of the sealed case 13 while a constant amount is discharged through the discharge port 26, thereby maintaining an inert gas atmosphere inside the sealed case 13. This suppresses oxidation of the reaction tube 10 at high temperatures, thereby providing a carbon nanotube production apparatus 2 in which, even if carrier gas leaks from the reaction tube due to oxidation-induced deterioration, the leaked gas is safely discharged outside the apparatus. Heating the reaction tube 10 in an inert gas atmosphere increases the material options for the reaction tube 10 and eliminates constraints on CNT production conditions and equipment specifications, resulting in improved production capacity and costs. The inert gas atmosphere in the heat source space (shield space) allows the use of a heater 11 that oxidizes at high temperatures. This increases the options for the heat source (heater 11) and broadens the range of heating conditions, leading to improvements in CNT production conditions and equipment specifications.

[0049] Furthermore, even if the reaction tube 10 or related parts are damaged while the raw material and carrier gas are being supplied and the production reaction is being carried out, the flammable carrier gas can be safely discharged outside the factory together with the shielding gas without leaking.

[0050] In the example shown, the heat insulating material 12 is provided with holes 27 for circulating the shielding gas, but since the heat insulating material 12 is not airtight, the holes 27 are not particularly necessary, and the holes 27 are provided for the purpose of shortening the time required to replace atmospheric air with an inert gas atmosphere. Therefore, the holes 27 may be omitted.

[0051] The positional relationship between the supply port 25 that supplies shielding gas into the inside of the sealed case 13 and the exhaust port 26 that exhausts the shielding gas from the inside of the sealed case 13 is such that the exhaust port 26 is located at the farthest point from the supply port 25 and at the very end of the sealed space so that no atmospheric air accumulates in the sealed space and atmospheric replacement is ensured. For example, in the case of horizontal equipment, gas is supplied from below one end of the shielded sealed space and exhausted from above the opposite end of the shielded sealed space.

[0052] Although the present invention has been described above by way of example, it is understood that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and that such modifications and alterations are also within the technical scope of the present invention.

[0053] For example, the components of the above-described embodiments can be combined in any manner, and such combinations will naturally provide the functions and advantages of the individual components involved in the combination, as well as other functions and advantages that will be apparent to those skilled in the art from the description of this specification.

[0054] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that are apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0055] The present invention can be applied to a carbon nanotube production device.

[0056] REFERENCE SIGNS LIST 1 CNT production device 2 CNT production device 3 Recovery device 10 Reaction tube 11 Heater 12 Heat insulating material 13 Sealed case 15 Upper end 16 Inlet unit 20 Lower end 21 Packing 25 Supply port 26 Discharge port 27 Hole 30 Recovery chamber 31 Exhaust port 35 Pressure sensor 36 Pressure sensor 37 Oxygen concentration meter 38 Hydrogen detector 39 Oxygen concentration meter

Claims

1. A carbon nanotube generation apparatus for generating carbon nanotubes, comprising: a reaction tube to which a raw material gas for the carbon nanotubes is supplied; a heater arranged around the reaction tube; an insulating material covering the outside of the heater; a sealed case that hermetically surrounds the reaction tube and houses the heater and the insulating material; a supply port that supplies a shielding gas into the inside of the sealed case; and an exhaust port that exhausts the shielding gas from the inside of the sealed case.

2. The carbon nanotube generating apparatus according to claim 1, wherein the supply port is provided at the bottom of the sealed case, and the discharge port is provided at the top of the sealed case.

3. A carbon nanotube generation apparatus as described in claim 1, which is configured to monitor the differential pressure between the inside of the reaction tube and the space to which the shielding gas is supplied, and automatically adjust the supply flow rate of the shielding gas when this differential pressure exceeds a set range, thereby preventing leakage of the shielding gas into the reaction tube in the event of damage to the reaction tube.

4. A carbon nanotube production apparatus comprising: the carbon nanotube production apparatus according to any one of claims 1 to 3; and a recovery device for recovering carbon nanotubes.

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