JP2016108175A - Production method of carbon nanotube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of carbon nanotubes, with which long-sized carbon nanotubes with high crystallinity are efficiently produced by effectively suppressing deactivation of a catalyst, even when acetylene of high concentration is fed.SOLUTION: In a production method of carbon nanotubes, acetylene, a catalyst for generating carbon nanotubes from the acetylene, and a support medium to carry the catalyst are used, and carbon nanotubes are synthesized on the support medium while heating the support medium in a fluidized-bed reactor. The production method of carbon nanotubes has a synthesizing step to synthesize carbon nanotubes on the support medium by feeding a raw material gas including acetylene, carbon dioxide, and a carrier gas into the fluidized-bed reactor with a linear flow rate of 10 cm/s or more, in which concentration of acetylene in the raw material gas is less than 5 vol.%, and concentration of carbon dioxide is 0.1 vol.% or more and less than 40 vol.%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing carbon nanotubes.

  A carbon nanotube is a material having a structure in which a graphene sheet is wound in a cylindrical shape and having a one-dimensional structure with a very large aspect ratio (see, for example, Non-Patent Document 1). It is known that carbon nanotubes have excellent mechanical strength, excellent flexibility, excellent semiconducting or metallic conductivity, and are extremely chemically stable. As a method for producing carbon nanotubes, an arc discharge method, a laser evaporation method, a chemical vapor deposition method (hereinafter referred to as “CVD method” (Chemical Vapor Deposition Method)) and the like have been reported. In particular, the CVD method is a synthesis method attracting attention as a synthesis method suitable for mass synthesis, continuous synthesis, and high purity (see, for example, Non-Patent Document 2).

  Among carbon nanotubes, in particular, single-walled carbon nanotubes (hereinafter referred to as “SWCNT”) are confirmed to exhibit metallic or semiconducting properties depending on how they are wound and their diameter. Application to electric and electronic devices is expected. For the synthesis of SWCNTs, a catalytic CVD method (see, for example, Non-Patent Document 3) in which nanotubes are grown using a catalyst has become the mainstream. This catalytic CVD method uses metal nanoparticles as a catalyst. Then, while supplying a gaseous carbon source, the carbon source is thermally decomposed at a high temperature, and nanotubes are grown from metal nanoparticles as a catalyst.

S. Iijima, Nature 354, 56 (1991). Co-edited by Riichiro Saito and Hissunori Shinohara “Basics and Applications of Carbon Nanotubes” Baifukan, 2004 H. Dai, A. G. Rinzler, P. Nikolaev, A. Thess, D. T. Colbert, and R.E. Smalley, Chem. Phys. Lett. 260, 471 (1996).

  When acetylene is used as the carbon source in the catalytic CVD method, if the concentration of acetylene is low, the growth of carbon nanotubes is possible, but the raw material supply amount is small, so that it is not suitable for mass production, and long carbon nanotubes It takes time to get. On the other hand, if the concentration of acetylene is high, amorphous carbon will adhere to the catalyst surface, promote carbon deactivation of the catalyst, and stop carbon nanotube growth. Cannot be obtained. As a means for suppressing carbonization deactivation of the catalyst, a method of adding a small amount of water is known, but since it is necessary to strictly control the amount of water added, carbon nanotube growth tends to be uneven. There's a problem. Moreover, when increasing the addition amount of water with acetylene in order to improve productivity, there exists a problem that crystallinity falls significantly.

  The present invention has been made in view of the above-mentioned problems of the prior art, and even when acetylene is supplied at a high concentration, catalyst deactivation can be effectively suppressed, and long carbon nanotubes with high crystallinity are efficiently used. An object of the present invention is to provide a method for producing carbon nanotubes, which can be produced in an automated manner.

  In order to achieve the above-mentioned object, the present invention uses an acetylene, a catalyst for producing carbon nanotubes from the acetylene, and a support carrying the catalyst, and supports the support in a fluidized bed reactor. A carbon nanotube production method for synthesizing the carbon nanotubes on the support while heating the body, wherein the source gas containing the acetylene, carbon dioxide and carrier gas is introduced into the fluidized bed reactor at 10 cm / s. Supplying at the above linear flow velocity has a synthesis step of synthesizing the carbon nanotube on the support, the concentration of the acetylene in the source gas is less than 5% by volume, and the carbon dioxide Provided is a carbon nanotube production method having a concentration of 0.1% by volume or more and less than 40% by volume.

According to such a production method, a raw material gas containing acetylene, carbon dioxide, and a carrier gas, and having a concentration of acetylene and carbon dioxide controlled within the above range, is supplied at a linear flow rate within the above range. Thus, even when acetylene is supplied at a high concentration (but less than 5% by volume), catalyst deactivation can be effectively suppressed, and long carbon nanotubes with high crystallinity can be efficiently produced. The present inventors infer the reason why such an effect is obtained as follows. That is, in order to suppress the catalyst deactivation, when comparing the case of using water and the case of using carbon dioxide as in the past, when water is used between the amorphous carbon causing catalyst deactivation, While the reaction of the following formula (C) occurs, when carbon dioxide is used, the reaction of the following formula (A) occurs, and in some cases, the reaction of the following formula (C) is performed after the reaction of the following formula (B). ) Reaction occurs.
CO ₂ + C → 2CO (A)
CO ₂ + H ₂ → CO + H ₂ O (B)
H ₂ O + C → H ₂ + CO (C)
Here, since water has high reactivity, the reaction of the formula (C) occurs not only with amorphous carbon but also with carbon in crystalline carbon nanotubes, leading to a decrease in yield and crystallinity of carbon nanotubes. On the other hand, since carbon dioxide is less reactive than water, it is difficult to react with carbon in crystalline carbon nanotubes, and the reaction of formula (A) occurs mainly with amorphous carbon. Further, when carbon dioxide is used, the reaction probability decreases because the reaction of the formula (C) needs to go through the reaction of the formula (B). Therefore, when carbon dioxide is used, amorphous carbon can be mainly removed while suppressing a decrease in the yield and crystallinity of the carbon nanotubes, compared with the case where water is used. Furthermore, the generation of the reaction of the formula (C) via the reaction of the formula (B) is further suppressed by increasing the linear flow velocity of the raw material gas to 10 cm / s or more and synthesizing the carbon nanotubes by the fluidized bed reactor. In addition, the yield of carbon nanotubes can be increased, and long carbon nanotubes with high crystallinity can be efficiently produced in a short time.

  Further, when water is supplied in order to suppress catalyst deactivation, bubbling is used because the supply amount is small. However, when the pressure in the reactor fluctuates, the supply amount varies and the synthesis becomes unstable. In contrast, carbon dioxide is supplied as a gas rather than bubbling, so there is little variation in the supply amount, and the reactivity with amorphous carbon is mild, so the content in the source gas can be increased. This makes it possible to stably produce long carbon nanotubes with high crystallinity.

  In the carbon nanotube production method of the present invention, the concentration of the acetylene in the raw material gas is preferably 0.1% by volume or more. Thereby, a long carbon nanotube with high crystallinity can be manufactured more efficiently.

In the carbon nanotube production method of the present invention, the source gas preferably contains hydrogen gas as the carrier gas. As a result, it is possible to suppress the generation of soot and amorphous carbon due to the reaction of acetylene gases in the gas phase in the reactor. This effect is obtained because a function of returning the equilibrium to the left is generated by increasing the H ₂ partial pressure for the reaction C ₂ H ₂ → 2C + H ₂ .

  In the method for producing carbon nanotubes of the present invention, it is preferable that the catalyst is supported on the support through a catalyst carrier layer formed on the support. Thereby, since the catalyst is fixed to the support by the catalyst carrier layer, the catalyst can be held in the fluidized bed for a long time, so that long carbon nanotubes can be synthesized. In addition, when separating and recovering the synthesized carbon nanotubes, the carbon nanotubes can be separated from the catalyst.

  According to the present invention, a method for producing carbon nanotubes that can effectively suppress catalyst deactivation even when acetylene is supplied at a high concentration, and can efficiently produce long carbon nanotubes with high crystallinity. Can be provided.

It is a figure which shows one Embodiment of the manufacturing method of a carbon nanotube. It is a schematic diagram which shows notionally the whole structure of one Embodiment of the carbon nanotube manufacturing apparatus used for manufacture of a carbon nanotube. It is a schematic diagram which shows the principal part of one Embodiment of the fluidized bed reactor used for manufacture of a carbon nanotube. 2 is a Raman spectrum of the carbon nanotube obtained in Example 1. FIG. 4 is a Raman spectrum of the carbon nanotube obtained in Example 4. 4 is a Raman spectrum of the carbon nanotube obtained in Comparative Example 2.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  The carbon nanotube production method of this embodiment is a method including a synthesis step of synthesizing carbon nanotubes on a support by supplying a raw material gas to the support supporting a catalyst in a fluidized bed reactor. FIG. 1 is a diagram showing an embodiment of a method for producing carbon nanotubes. As shown in FIG. 1, the carbon nanotube production method includes a catalyst supporting step (S1), a catalyst reduction step (S2), a carbon nanotube synthesis step (S3), a carbon nanotube separation step (S4), and a bead firing step (S5). ) In order. These steps can be repeated a plurality of times as one cycle.

  The catalyst supporting step (S1) is a step of supporting a catalyst for carbon nanotube synthesis on a granular support. In the present embodiment, the catalyst supporting step (S1) is performed by the CVD method in which the catalyst is supported on the support by supplying the catalyst gas to the reaction tube. In addition, a granular support body is also called a granular body or a bead. In this catalyst supporting step (S1), the first catalyst gas is circulated on the support to thereby form a catalyst carrier layer on the support, and the second catalyst gas is circulated on the support. Thus, the second catalyst supporting step of supporting the catalyst on the catalyst carrier layer is performed. In the following description, the “first catalyst gas” and the “second catalyst gas” are collectively referred to as “catalyst gas” unless particularly distinguished from the “first catalyst gas” and the “second catalyst gas”. That's it.

The support is composed of particulate heat-resistant beads having heat resistance. The material of the support preferably contains one or more elements selected from the group consisting of Si, Al, Mg, Zr, Ti, O, N, C, Mo, Ta, and W. Specific examples of the material include oxides such as SiO ₂ , Al ₂ O ₃ and MgO, nitrides such as SiN ₄ and AlN, and carbides such as SiC. Alternatively, a composite oxide such as Al ₂ O ₃ —SiO ₂ may be used.

  The diameter of the support is preferably 100 to 2000 μm, and more preferably 200 to 2000 μm. When the diameter of the support is 100 μm or more, the support is stably held in the reaction tube and tends to flow efficiently, and the support and the carbon nanotube are easily separated in the same reaction tube. Tend. On the other hand, when the diameter of the support is 2000 μm or less, the support tends to flow easily.

  The first catalyst gas is a gas for supporting a catalyst carrier on a support to form a catalyst carrier layer, and is composed of, for example, a catalyst carrier precursor that forms a catalyst carrier layer and a carrier gas. It is.

The catalyst carrier formed by the first catalyst gas preferably contains one or more elements selected from Si, Al, Mg, O, C, Mo, and N. In particular, the catalyst carrier precursor forms a catalyst carrier layer containing an oxide such as SiO ₂ , Al ₂ O ₃ or MgO, a nitride such as Si ₃ N ₄ or AlN, or a carbide such as SiC. It is good to be. The precursor of the catalyst carrier may form a catalyst carrier layer containing a composite oxide of Al ₂ O ₃ —SiO ₂ . In particular, the catalyst carrier precursor preferably forms a catalyst carrier layer made of Al ₂ O ₃ from the viewpoint of the stability of the catalyst particles. Specific examples of the catalyst precursor include alkoxides such as aluminum isopropoxide and aluminum sec-butoxide, alkylaluminums such as triethylaluminum and triisobutylaluminum, and aluminum chloride.

  The average thickness of the catalyst carrier layer formed on the support is preferably 1 nm to 100 nm, and more preferably 1 nm to 50 nm. When the thickness of the catalyst support layer is 1 nm or more, the catalyst particles are stably supported on the catalyst support layer, and Ostwald ripening is unlikely to occur, and carbon nanotubes tend to grow long. On the other hand, when the thickness of the catalyst carrier layer is 100 nm or less, the catalyst particles are not easily taken into the catalyst carrier layer during the synthesis, and the carbon nanotubes tend to grow long.

  The carrier gas contained in the first catalyst gas is preferably an inert gas such as argon gas or nitrogen gas. Further, hydrogen gas may be used as the carrier gas.

  In the first catalyst supporting step, the supply rate of the first catalyst gas into the reaction tube is not particularly limited, but is preferably 15 cm / s to 50 cm / s, and 20 cm / s to 40 cm / s in terms of linear flow rate. Is more preferable.

  The second catalyst gas is a gas for supporting a catalyst for carbon nanotube synthesis on a support, and is composed of, for example, a catalyst precursor that forms a catalyst for carbon nanotube synthesis and a carrier gas. .

  The catalyst precursor contained in the second catalyst gas is preferably a gas containing a metal generally used for the synthesis of carbon nanotubes, such as V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, One containing one or more elements selected from W and Au is preferable. Among these, those containing one or more elements selected from Fe, Co, and Ni having a large solid solution amount of carbon are preferable, and an organic metal vapor such as metallocene is more preferable.

  The diameter of the catalyst supported on the support is preferably 0.2 nm to 2000 nm, and more preferably 10 nm to 1000 nm. The diameter of the catalyst can be measured by an atomic force microscope (AFM).

As a combination of the catalyst carrier layer and the catalyst, it is preferable that the catalyst carrier layer is Al ₂ O ₃ and the catalyst is Fe from the viewpoint of productivity of carbon nanotubes. From the viewpoint of efficiently obtaining carbon nanotubes having a small diameter, it is preferable that the catalyst support layer is Al ₂ O ₃ and the catalyst is Co.

The carrier gas contained in the second catalyst gas is preferably an inert gas such as argon gas or nitrogen gas. A gas obtained by adding oxygen to the inert gas may be used as a carrier gas. In addition, moisture (H ₂ O) may be added to the second catalyst gas from the viewpoint of reducing the amount of the second catalyst gas used.

  In the second catalyst supporting step, the supply rate of the second catalyst gas into the reaction tube is not particularly limited, but is preferably 10 cm / s to 100 cm / s in terms of linear flow rate, and is 10 cm / s to 50 cm / s. Is more preferable. When the supply speed is 10 cm / s or more, the catalyst tends to be uniformly supported on the support. Further, when the supply rate is 100 cm / s or less, the support tends to be stably held in the reaction tube.

The catalyst reduction step (S2) is a step in which the catalyst supported on the catalyst carrier layer is reduced by heating with a reducing gas to reduce the size. The miniaturized catalyst is also referred to as catalyst particles. The reducing gas is composed of, for example, a gaseous reducing agent such as hydrogen gas and an inert gas such as argon gas or nitrogen gas as a carrier gas. In addition, moisture (H ₂ O) may be added to the reducing gas from the viewpoint of bubbling stability.

  In the catalyst reduction step (S2), the supply rate of the reducing gas into the reaction tube is not particularly limited, but is preferably 1.0 cm / s to 50 cm / s at a linear flow rate, and 3.3 cm / s to 33 cm / s. It is more preferable that

  The carbon nanotube synthesizing step (S3) is a step of synthesizing the carbon nanotubes on the catalyst particles by circulating the raw material gas on the support.

  The source gas is a mixed gas containing acetylene, carbon dioxide and a carrier gas. Acetylene is a carbon source for synthesizing carbon nanotubes, and is supplied in a gaseous state into the reactor. Acetylene may also be produced in the reactor.

  As carrier gas contained in source gas, inert gas, such as argon gas and nitrogen gas which do not affect the production | generation of a carbon nanotube, can be used conveniently. Further, hydrogen gas may be used as the carrier gas.

  Carbon dioxide removes the amorphous carbon generated on the surface of the catalyst particles during the synthesis of the carbon nanotubes to prevent catalyst deactivation, and as a result contributes to the synthesis of long carbon nanotubes with high crystallinity. In addition, since carbon dioxide can be supplied at a higher concentration than water, there is no need to control the supply amount in a trace amount like water, and catalyst deactivation is possible even when acetylene is at a high concentration. It can be effectively suppressed, and conditions suitable for mass production of long carbon nanotubes with high crystallinity can be provided.

  The content (concentration) of carbon dioxide in the source gas needs to be not less than 0.1% by volume and less than 40% by volume based on the total volume of the source gas. When the carbon dioxide content is 0.1% by volume or more, even when acetylene is supplied at a high concentration, catalyst deactivation can be effectively suppressed, and long carbon nanotubes with high crystallinity are efficiently produced. Can be manufactured. On the other hand, it can suppress that the crystallinity of a carbon nanotube falls because content of a carbon dioxide is less than 40 volume%. The content of carbon dioxide in the raw material gas is preferably 3% by volume or more, and more preferably 5% by volume or more from the viewpoint of uniformly suppressing catalyst deactivation by acetylene. Moreover, it is preferable that content of the carbon dioxide in source gas is 30 volume% or less.

  The carbon nanotube synthesis step (S3) is performed in a fluidized bed reactor. At the time of synthesis, the support is blown up and fluidized by supplying the raw material gas into the fluidized bed reactor. In this state, the raw material gas flows on the support, and the acetylene and the catalyst come into contact with each other to grow carbon nanotubes on the support. At this time, the supply speed of the source gas needs to be 10 cm / s or more in terms of the linear flow rate. When the linear flow rate is 10 cm / s or more, long carbon nanotubes with high crystallinity can be efficiently produced in a short time. From the viewpoint of more efficiently producing longer carbon nanotubes with higher crystallinity in a shorter time, the linear flow rate of the raw material gas is preferably 11 cm / s or more. On the other hand, from the viewpoint of suppressing separation of the carbon nanotubes due to collisions between the supports, the linear flow rate of the raw material gas is preferably 20 cm / s or less, and more preferably 15 cm / s or less.

  The content (concentration) of acetylene in the raw material gas needs to be less than 5% by volume based on the total volume of the raw material gas, preferably from 0.1% by volume to less than 5% by volume. It is more preferably 1% by volume to 4% by volume, still more preferably 0.2% by volume to 4% by volume, and particularly preferably 0.5% by volume to 3% by volume. When the acetylene content is 0.1% by volume or more, long carbon nanotubes with high crystallinity can be produced more efficiently. On the other hand, when the acetylene content is less than 5% by volume, long carbon nanotubes can be produced more efficiently.

  In the source gas, the partial pressure ratio of acetylene and carbon dioxide (acetylene / carbon dioxide) is preferably 0.2 to 50, more preferably 0.5 to 40, and 0.5 to 30. More preferably it is. By adjusting the partial pressure ratio between acetylene and carbon dioxide within the above range, it is possible to produce carbon nanotubes having high crystallinity and long length more efficiently in a shorter time.

  The source gas preferably contains hydrogen gas as the carrier gas. When the source gas contains hydrogen gas, the polymerization of acetylene is suppressed, and the generation of amorphous carbon that deactivates the catalyst particles tends to be suppressed. The content of the hydrogen gas in the raw material gas is preferably 0.1% by volume to 80% by volume based on the total volume of the raw material gas, more preferably 1.0% by volume to 50% by volume, More preferably, it is 5.0 volume%-30 volume%. By adjusting the hydrogen gas content within the above range, long carbon nanotubes can be easily obtained.

The carbon nanotube separation step (S4) is a step of separating the carbon nanotubes from the support by circulating a separation gas over the support on which the carbon nanotubes have been synthesized, and collecting the separated carbon nanotubes. The separation gas is composed of, for example, a carrier gas. The carrier gas constituting the separation gas is preferably an inert gas such as argon gas or nitrogen gas. Further, hydrogen gas may be used as the carrier gas. In order to promote the separation of the carbon nanotubes, moisture (H ₂ O), oxygen, or the like may be added to the separation gas.

  In the carbon nanotube separation step (S4), the supply speed of the separation gas into the reaction tube is not particularly limited as long as the carbon nanotube can be separated from the support, but the linear flow rate is 10 cm / s to 200 cm / s. Is preferable, and it is more preferable that it is 20 cm / s-100 cm / s.

  The bead firing step (S5) is a step of firing the support from which the carbon nanotubes have been separated to inactivate the catalyst. Firing is performed by heating the support while circulating an oxidizing gas containing oxygen and a carrier gas on the support. As carrier gas which comprises oxidizing gas, inert gas, such as argon gas and nitrogen gas, is preferable. Further, hydrogen gas may be used as the carrier gas.

  In the bead firing step (S5), the supply rate of the oxidizing gas into the reaction tube is not particularly limited, but is preferably 0.1 cm / s to 200 cm / s at a linear flow rate, preferably 0.1 cm / s to 100 cm / s. More preferably, it is s.

  Next, a carbon nanotube production apparatus used for producing carbon nanotubes and a carbon nanotube production method using the same will be described.

FIG. 2 is a schematic diagram conceptually showing the overall configuration of an embodiment of a carbon nanotube production apparatus used for producing carbon nanotubes. As shown in FIG. 2, the carbon nanotube production apparatus 1 includes a reaction tube 2, a gas supply source 3 that sends out various gases such as a carrier gas supplied to the reaction tube 2 by mass flow, a reaction tube 2, and a gas supply source 3. Between the bubbler 4 containing moisture (H ₂ O) in the carrier gas and the path between the reaction tube 2 and the gas supply source 3 and containing the catalyst precursor in the carrier gas. The first catalyst container 5 for generating the first catalyst gas is disposed in the path between the gas supply source 3 and the reaction tube 2 to generate the second catalyst gas by including the catalyst precursor in the carrier gas. A second catalyst container 6, a carbon nanotube recovery device 7 that recovers carbon nanotubes from the reaction tube 2, and an exhaust unit 8 that discharges gas from the carbon nanotube recovery device 7.

  The reaction tube 2 is a reaction tube used in each step of the catalyst supporting step (S1), the catalyst reduction step (S2), the carbon nanotube synthesis step (S3), the carbon nanotube separation step (S4), and the bead firing step (S5). is there. In the present embodiment, the fluidized bed reactor 20 is used as the reaction tube 2 in the carbon nanotube synthesis step (S3). The reaction tube 2 used in the steps other than the carbon nanotube synthesis step (S3) is not particularly limited, and the same reaction tube as that in the carbon nanotube synthesis step (S3) may be used. Other reaction tubes different from S3) may be used. In the present embodiment, the same fluidized bed reactor 20 is used in all steps S1 to S5.

  FIG. 3 is a schematic view showing the main part of one embodiment of a fluidized bed reactor 20 used for producing carbon nanotubes. As shown in FIG. 3, the fluidized bed reactor 20 includes a pipe part 21, a dispersion plate 22, and a heating part 23. The pipe portion 21 is formed in a straight line, is filled with a support, and is supplied with various supply gases such as a catalyst gas, a reducing gas, a raw material gas, a separation gas, or an oxidizing gas from below.

  The pipe portion 21 preferably has the same diameter (outer diameter and inner diameter) in the vertical direction from the viewpoint of ease of manufacture, but may have a different diameter in the vertical direction. The material of the tube part 21 is not particularly limited as long as it is a heat-resistant material. However, from the viewpoint of heating the support and the supply gas using the radiant heat from the heating part 23, a transparent material such as quartz is used. It is preferable to use those.

  The dispersion plate 22 is disposed at the lower end of the reaction region A in the pipe part 21, holds the support filled in the pipe part 21, and allows the supply gas to pass therethrough. The reaction region A is a region in which the supply gas supplied to the tube portion 21 is reacted on the support by thermal decomposition or the like. Any dispersion plate 22 may be used. For example, an eye plate or a porous plate in which a plurality of holes are formed may be used. In addition, since the dispersion | distribution plate 22 hold | maintains a support body, what is smaller than the outer diameter of the support body with which the internal diameter of a hole is thrown into the pipe part 21 is used.

  The heating unit 23 is a heating device that covers the reaction region A of the tube unit 21. The heating unit 23 heats the support filled in the tube unit 21 and supplies the carrier gas and the catalyst gas supplied to the reaction region A of the tube unit 21. It is for heating. As the heating unit 23, any heating device may be used, for example, an electric furnace can be used.

  Further, the heating unit 23 may cover only the reaction region A, but may cover a region that extends beyond the reaction region A and slightly below the dispersion plate 22. In other words, the heating unit 23 heats the supply gas supplied immediately before being supplied to the reaction region A, in addition to heating the supply gas supplied to the support and the reaction region A filled in the tube part 21. Good. In this case, the lower end position of the heating unit 23 is set so that the supply gas supplied to the reaction region A is lower than the decomposition temperature of the catalyst raw material charged in the tube unit 21.

  Next, the catalyst supporting step (S1) using the carbon nanotube production apparatus 1 provided with the fluidized bed reactor 20 will be described.

  In the catalyst supporting step (S1), first, the support is filled in the pipe portion 21 of the fluidized bed reactor 20, the first catalyst gas is supplied from below, and the first catalyst gas is circulated on the support, A first catalyst supporting step of forming a catalyst carrier layer on the support is performed.

  In the first catalyst supporting step (S1), a carrier gas is supplied to the first catalyst container 5, a first catalyst gas containing a catalyst precursor is generated, and this first catalyst gas is supplied to the fluidized bed reactor 20. To do. Further, the first catalyst gas may include a carrier gas that is directly supplied to the fluidized bed reactor 20 without going through the first catalyst container 5.

  The first catalyst gas supplied to the fluidized bed reactor 20 passes through the dispersion plate 22 and is supplied to the reaction zone A and rises in the reaction zone A. On the other hand, while supplying the first catalyst gas, the heating region 23 heats the reaction region A of the tube portion 21 to heat the support. At this time, the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes a temperature at which the catalyst precursor in the first catalyst gas is thermally decomposed. The heating temperature (set temperature) of the heating unit 23 is appropriately adjusted according to the catalyst precursor contained in the first catalyst gas, but is usually 700 ° C to 900 ° C, preferably 750 to 850 ° C.

  The support is held in a heated state by the heating unit 23 and is blown up and fluidized by the first catalyst gas that has passed through the dispersion plate 22. In such a state, the catalyst precursor layer in the first catalyst gas is thermally decomposed on the support, whereby a catalyst carrier layer is formed on the support. By performing the first catalyst supporting step in a state where the support is fluidized, the catalyst carrier layer can be uniformly formed on the support.

  When the above first catalyst supporting step is completed, a second catalyst supporting step of supporting the catalyst on the catalyst carrier layer by circulating the second catalyst gas on the support is then performed.

In the second catalyst supporting step, the gas supplied to the reaction zone A is switched from the first catalyst gas to the second catalyst gas. That is, in the second catalyst supporting step, the carrier gas is supplied to the second catalyst container 6 while maintaining the heating by the heating unit 23 to generate the second catalyst gas containing the catalyst precursor, and this second catalyst Gas is supplied to the fluidized bed reactor 20. The second catalyst gas may contain a carrier gas that is directly supplied to the fluidized bed reactor 20 without going through the second catalyst container 6. Further, in the second catalyst supporting step, it is preferable to include moisture (H ₂ O) in the second catalyst gas. The moisture can be supplied to the fluidized bed reactor 20 as a carrier gas containing moisture by supplying the carrier gas to the bubbler 4 to contain moisture.

  Similar to the first catalyst supporting step, the second catalyst gas supplied to the fluidized bed reactor 20 passes through the dispersion plate 22 and is supplied to the reaction zone A, and rises in the reaction zone A. On the other hand, while the second catalyst gas is being supplied, the reaction region A of the tube portion 21 is heated by the heating portion 23 to heat the support. At this time, the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes a temperature at which the catalyst precursor in the second catalyst gas is thermally decomposed. The heating temperature (set temperature) of the heating unit 23 is appropriately adjusted according to the catalyst precursor contained in the second catalyst gas, but is usually 20 ° C to 250 ° C, preferably 20 ° C to 150 ° C. .

  The support is held in a heated state by the heating unit 23 and is blown up and fluidized by the second catalyst gas that has passed through the dispersion plate 22. In such a state, the catalyst precursor in the second catalyst gas is thermally decomposed on the catalyst carrier layer formed on the support, whereby the catalyst is formed on the catalyst carrier layer formed on the support. Supported. By performing the second catalyst supporting step in a state where the support is fluidized, the catalyst can be uniformly supported on the catalyst carrier layer formed on the support.

Next, a catalyst reduction step (S2) is performed. In the catalyst reduction step (S2), the gas supplied to the reaction region A is switched from the second catalyst gas to the reducing gas. That is, in the catalyst reduction step (S2), while maintaining the heating by the heating unit 23, the reducing gas is supplied to the fluidized bed reactor 20, and the catalyst supported on the support is heated and reduced. In the catalyst reduction step (S2), it is preferable to include moisture (H ₂ O) in the reducing gas. When moisture is included in the reducing gas, the carrier gas containing moisture is supplied to the fluidized bed reactor 20 via the bubbler 4 as in the second catalyst supporting step.

  In the catalyst reduction step (S2), the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes a temperature at which the catalyst is reduced by the reducing gas. The heating temperature (set temperature) of the heating unit 23 is appropriately adjusted according to the reducing gas and the catalyst to be used, but is usually 450 ° C to 1000 ° C, preferably 600 ° C to 900 ° C.

  The support is held in a heated state by the heating unit 23, and is blown up by the reducing gas that has passed through the dispersion plate 22 to be fluidized. And in such a state, reducing gas distribute | circulates on a support body and the catalyst carry | supported on the support body is reduced. By performing the catalyst reduction step (S2) in a state where the support is fluidized, the catalyst can be uniformly reduced.

  Next, a carbon nanotube synthesis step (S3) is performed. In the carbon nanotube synthesis step (S3), the gas supplied to the reaction region A is switched from the reducing gas to the source gas. That is, in the carbon nanotube synthesis step (S3), the raw material gas is supplied to the fluidized bed reactor 20 while maintaining the heating by the heating unit 23, and the carbon nanotubes are synthesized on the support.

  In the carbon nanotube synthesis step (S3), the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes a temperature at which the carbon source in the raw material gas is thermally decomposed to generate carbon nanotubes. Although the heating temperature (setting temperature) of the heating part 23 is suitably adjusted according to the carbon source and catalyst to be used, it is usually 600 ° C to 1200 ° C, preferably 750 to 850 ° C.

  The support is held in a heated state by the heating unit 23 and is blown up and fluidized by the raw material gas that has passed through the dispersion plate 22. And in such a state, source gas distribute | circulates on a support body and a carbon nanotube grows on a support body. By performing the carbon nanotube synthesis step (S3) in a state where the support is fluidized, it is possible to efficiently synthesize long carbon nanotubes with high crystallinity in a short time.

  Next, a carbon nanotube separation step (S4) is performed. In the carbon nanotube separation step (S4), the gas supplied to the reaction region A is switched from the source gas to the separation gas. That is, in the carbon nanotube separation step (S4), while maintaining the heating by the heating unit 23, the separation gas is supplied to the fluidized bed reactor 20, and the carbon nanotubes grown on the support are separated from the support. Since the catalyst supported on the support is fixed to the support by the catalyst carrier layer, the carbon nanotubes are separated from the catalyst.

  In the carbon nanotube separation step (S4), the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes 650 ° C. or higher. The heating temperature (set temperature) of the heating unit 23 is usually 650 ° C. to 1000 ° C., preferably 650 ° C. to 900 ° C.

  The support is held in a heated state by the heating unit 23 and is blown up and fluidized by the separation gas that has passed through the dispersion plate 22. In such a state, the separation gas flows on the support, and the carbon nanotubes grown on the support are separated. By performing the carbon nanotube separation step (S4) in a state where the support is fluidized, the carbon nanotubes can be separated efficiently.

  Next, a bead firing step (S5) is performed. In the bead firing step (S5), the gas supplied to the reaction region A is switched from the separation gas to the oxidizing gas. That is, in the bead firing step (S5), while maintaining heating by the heating unit 23, an oxidizing gas is supplied to the fluidized bed reactor 20, and the catalyst supported on the support is oxidized to deactivate the catalyst.

  In the bead firing step (S5), the heating temperature of the heating unit 23 is set so that the surface temperature of the support becomes a temperature at which the catalyst is oxidized and inactivated. Although the heating temperature (setting temperature) of the heating part 23 is suitably adjusted according to the catalyst to be used, it is usually 650 ° C to 1000 ° C, preferably 700 ° C to 900 ° C.

  The support is held in a heated state by the heating unit 23, and is blown up by the oxidizing gas that has passed through the dispersion plate 22 to be fluidized. And in such a state, oxidizing gas distribute | circulates on a support body and carbon on the surface of a support body reacts. By performing the bead firing step (S5) in a state in which the support is fluidized, it can be fired uniformly and the carbon component can be removed.

  The length of the carbon nanotube is preferably 300 μm or more. The length of the carbon nanotube depends on the synthesis time, but when the catalyst is deactivated, a sufficient length cannot be obtained even if the synthesis is performed for a long time. According to the present embodiment, long carbon nanotubes of 300 μm or more can be efficiently produced in a short time.

  The carbon nanotube may be a single-walled one or may be composed of a plurality of layers. The carbon nanotubes are preferably composed of one to ten layers. The carbon nanotube production method of the present embodiment can produce carbon nanotubes having various structures, but is suitable for the production of SWCNTs. In the carbon nanotube production method of the present embodiment, carbon nanotubes having various structures can be produced by controlling the size and components of the catalyst. Although it has been difficult to efficiently produce SWCNTs with the conventional production method, according to the carbon nanotube production method of the present embodiment, the production efficiency of SWCNTs can be dramatically improved.

The crystallinity of the synthesized carbon nanotube can be evaluated by using Raman spectroscopy. In the measurement using Raman spectroscopy, the G band due to the graphite structure is observed near 1590 cm ⁻¹ , and the D band due to crystal defects is observed near 1340 cm ⁻¹ . Carbon nanotubes with high crystallinity have a low D band, and conversely, the G band has a high peak. That is, the higher the value of the intensity ratio (G / D ratio) between the G band and the D band defined by the following formula (1), the higher the crystallinity. And the higher the crystallinity, the better the conductivity of the carbon nanotube can be expected. According to the carbon nanotube production method of the present embodiment, carbon nanotubes having a high G / D ratio can be produced efficiently.
G / D ratio = (G−Bg) / (D−Bg) (1)
Here, “G” indicates the peak top value of the G band, “D” indicates the peak top value of the D band, and “Bg” is the background correction value, which is an average from 600 cm ⁻¹ to 1000 cm ^−1. Indicates the value.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  For example, in the above-described embodiment, the support has been described as having a particulate shape, but the specific shape, dimensions, and the like can be set as appropriate.

  In the above embodiment, the catalyst supporting step is described as performing the first catalyst supporting step of forming the catalyst carrier layer on the support and the second catalyst supporting step of supporting the catalyst on the catalyst carrier layer. However, only one of them may be used. For example, if the catalyst carrier layer is formed in advance on the support and the support on which the catalyst carrier layer is formed is put into the pipe portion, the first catalyst support step may not be performed. Further, when the catalyst is supported on the support without the catalyst carrier layer, the first catalyst supporting step may not be performed.

  In the above embodiment, the first catalyst supporting step, the second catalyst supporting step, the catalyst reduction step (S2), the carbon nanotube synthesis step (S3), the carbon nanotube separation step (S4), and the bead firing step (S5) are performed. Although described as being performed continuously, these steps are not necessarily performed continuously.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to a following example.

[Example 1]
In Example 1, as shown in FIG. 1, the catalyst supporting step (S1), the catalyst reduction step (S2), the carbon nanotube synthesis step (S3), the carbon nanotube separation step (S4), and the bead firing step (S5) are performed. went.

  As the reaction tube, a fluidized bed reactor 20 shown in FIG. 3 was used. The fluidized bed reactor 20 is composed of a quartz tube portion 21 having an inner diameter of 25 mm that extends linearly in the vertical direction, and a dispersion plate 22 in which a through hole is formed. It is the structure which discharges. The heating unit 23 is a heating device that covers the periphery of the section from the vicinity of the lower end of the pipe part 21 to a predetermined height position and heats the reaction region A of the pipe part 21. The heating unit 23 set the set temperature to 820 ° C. in all steps S1 to S5. In the fluidized bed reactor 20, 40 g of alumina beads having a diameter of 500 μm were charged as a support. At this time, the height of the beads on the dispersion plate 22 was 30 mm.

  In the catalyst supporting step (S1), the first catalyst supporting step and the second catalyst supporting step were performed. Note that the flow rates (sccm: Standard Cubic Centimeter per Minutes) of various supply gases shown below are values at 1 atm (101.325 kPa) and 0 ° C.

In the first catalyst supporting step, in order to form an Al catalyst carrier layer on the support, by passing the carrier gas through an Al catalyst container (first catalyst container 5 (see FIG. 2)) filled with Al, A precursor gas having Al as a catalyst precursor was generated. Aluminum isopropoxide was used as Al as the catalyst precursor. The temperature of the Al catalyst container was set to 130 ° C. Ar gas having a flow rate of 150 sccm was supplied to the Al catalyst container as a carrier gas, and Ar having a flow rate of 150 sccm was supplied from the Al catalyst container to the pipe portion 21. Further, as the other gas, a carrier gas composed of Ar having a flow rate of 8,000 sccm and O ₂ having a flow rate of 2,000 sccm was supplied to the pipe portion 21 without passing through the Al catalyst container. A first catalyst gas composed of a carrier gas and a precursor gas was supplied to the tube portion 21 for 60 seconds, and an Al catalyst support layer was formed on the support while the support was allowed to flow. The formed catalyst carrier layer was a layer mainly composed of Al ₂ O ₃ . The catalyst carrier layer may also contain aluminum oxide having a lower oxygen ratio than Al ₂ O ₃ .

In the second catalyst supporting step, in order to support the Fe catalyst on the catalyst support layer, the carrier gas is passed through the Fe catalyst container (second catalyst container 6 (see FIG. 2)) filled with Fe, thereby providing Fe. A precursor gas having a catalyst precursor was produced. Ferrocene was used as Fe as a catalyst precursor. The temperature of the Fe catalyst container was set to 120 ° C. The Fe catalyst container was supplied with Ar at a flow rate of 50 sccm as a carrier gas, and Ar was supplied at a flow rate of 50 sccm from the Fe catalyst container to the tube portion 21. Further, in the pipe portion 21, as other gases, a carrier composed of Ar having a flow rate of 8,000 sccm, O ₂ having a flow rate of 2,000 sccm, and H ₂ O directly without passing through the Fe catalyst container. Gas was supplied. H ₂ O was supplied by bubbling with Ar so that the concentration in the second catalyst gas was 400 ppmv (parts per million volume). Here, H ₂ O was supplied by bubbling in a constant temperature bath (around 25 ° C.) using dry Ar, and the concentration in the second catalyst gas was calculated based on the water vapor pressure of the constant temperature bath. A second catalyst gas composed of a carrier gas and a precursor gas was supplied to the tube portion 21 for 60 seconds, and Fe catalyst particles were supported on the catalyst support layer formed on the support while the support was flowing.

In the catalyst reduction step (S2), a reducing gas composed of Ar having a flow rate of 2,300 sccm, H ₂ having a flow rate of 900 sccm, and H ₂ O having a concentration of 600 ppmv was used. H ₂ O was supplied by bubbling with Ar. The time for heating and reducing the Fe catalyst supported on the catalyst carrier layer by supplying the reducing gas to the tube portion 21 was 10 minutes.

In the carbon nanotube synthesis step (S3), a raw material gas composed of Ar having a flow rate of 2,300 sccm, H ₂ having a flow rate of 900 sccm, CO ₂ having a flow rate of 100 sccm, and C ₂ H ₂ having a flow rate of 33 sccm. Was used. The total flow rate of the gas was 3,333 sccm, and a gas having a linear flow rate of 11.3 cm / s per cm ² was passed through the fluidized bed reactor 20. Further, the time for supplying the raw material gas to the tube portion 21 to synthesize the carbon nanotubes on the catalyst particles was 10 minutes.

  For evaluation and observation, the fluidized bed reactor 20 was once cooled after the carbon nanotube synthesis step (S3), and the beads were observed with a scanning electron microscope (SEM). ) It was confirmed that long carbon nanotubes exceeding 300 μm were growing. Then, the temperature of the heating part 23 was set to 820 degreeC again, and the following processes were performed.

  In the carbon nanotube separation step (S4), the flow rate of Ar supplied to the tube portion 21 was gradually increased from about 5,000 sccm to about 10,000 sccm, and the carbon nanotubes were separated for several minutes.

In the bead firing step (S5), the support was fired for 10 minutes while supplying Ar with a flow rate of 3,000 sccm and O ₂ with a flow rate of 1,000 sccm to the tube portion 21.

[Examples 2 to 5 and Comparative Examples 1 to 6]
In Examples 2 to 5 and Comparative Examples 1 to 6, in the carbon nanotube synthesis step (S3), the flow rates of Ar, H ₂ , CO _2, and C ₂ H ₂ constituting the source gas are changed to the flow rates shown in Table 1. A carbon nanotube was synthesized under the same conditions as in Example 1 except that. In Comparative Example 2, H ₂ O was supplied instead of CO ₂ . In Comparative Example 2, H ₂ O was supplied by bubbling using Ar so that the concentration in the reaction tube was 600 ppmv. In Examples 2 to 5 and Comparative Examples 1 to 6, as in Example 1, the beads were observed after the carbon nanotube synthesis step (S3), and the length of the carbon nanotubes grown from the bead surface was measured. The measurement results are shown in Table 1 as the CNT length.

(Evaluation of crystallinity)
Using a Raman spectrometer (trade name: HR-800, manufactured by HORIBA), the crystallinity of the synthesized carbon nanotubes was evaluated by Raman spectroscopy. The measurement wavelength was 488 nm. As a result of the measurement, in the carbon nanotubes obtained in Examples 1 to 5, Comparative Example 2 and Comparative Example 4, as shown in FIGS. 4 to 6, the G band due to the graphite structure is present in the vicinity of 1590 cm ⁻¹ . In the vicinity of 1340 cm ⁻¹ , a D band due to crystal defects could be observed. 4 is a Raman spectrum of the carbon nanotube obtained in Example 1, FIG. 5 is a Raman spectrum of the carbon nanotube obtained in Example 4, and FIG. 6 is a carbon spectrum obtained in Comparative Example 2. It is a Raman spectrum of a nanotube. The G / D ratio representing the crystallinity is obtained from the intensity ratio of the G band and the D band, and the higher this value, the higher the crystallinity. The results are shown in Table 1. In Comparative Examples 1, 3, 5 and 6, the length of the carbon nanotube grown from the bead surface is insufficient, and the carbon nanotube cannot be recovered in the carbon nanotube separation step (S4), and the crystallinity is evaluated. I couldn't.

  As shown in Table 1, in Examples 1 to 5, it was confirmed that long and highly crystalline carbon nanotubes could be synthesized. On the other hand, in Comparative Examples 1, 3, 5 and 6, long carbon nanotubes could not be synthesized, and in Comparative Examples 2 and 4, carbon nanotubes with high crystallinity could not be synthesized. In Comparative Example 2 and Comparative Example 4, the length of the carbon nanotubes grown from the bead surface was unstable and varied, and carbon nanotubes having a uniform length could not be synthesized.

  DESCRIPTION OF SYMBOLS 1 ... Carbon nanotube manufacturing apparatus, 2 ... Reaction tube, 3 ... Gas supply source, 4 ... Bubbler, 5 ... 1st catalyst container, 6 ... 2nd catalyst container, 7 ... Carbon nanotube recovery device, 8 ... Exhaust part, 20 ... Fluidized bed reactor, 21 ... pipe part, 22 ... dispersion plate, 23 ... heating part, A ... reaction zone.

Claims (4)

Using acetylene, a catalyst for producing carbon nanotubes from the acetylene, and a support supporting the catalyst, the support is heated on the support in a fluidized bed reactor, and the support is supported on the support. A method of producing a carbon nanotube for synthesizing a carbon nanotube,
A synthesis step of synthesizing the carbon nanotubes on the support by supplying a source gas containing the acetylene, carbon dioxide and carrier gas into the fluidized bed reactor at a linear flow rate of 10 cm / s or more. ,
The method for producing carbon nanotubes, wherein the concentration of the acetylene in the source gas is less than 5% by volume and the concentration of the carbon dioxide is 0.1% by volume or more and less than 40% by volume.   The method for producing carbon nanotubes according to claim 1, wherein the concentration of the acetylene in the raw material gas is 0.1% by volume or more.   The method for producing a carbon nanotube according to claim 1, wherein the source gas contains hydrogen gas as the carrier gas.   The manufacturing method of the carbon nanotube as described in any one of Claims 1-3 with which the said catalyst is carry | supported by the said support body through the catalyst support | carrier layer formed on the said support body.