JP2009174092A - Method for producing carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a carbon fiber, by which the highly pure carbon fiber can be mass-produced in an effective utilization rate of high raw material gas. <P>SOLUTION: The method for producing the carbon fiber, includes: when annealing and activating a catalyst in a process for traveling a catalyst-attached substrate 16 in a reaction tube 12 and decomposing C<SB>2</SB>H<SB>2</SB>gas flowed in the direction opposite to the travel direction to grow CNT22 on the substrate 16, enhancing the concentration of H<SB>2</SB>gas at the substrate 16-traveling position where the catalyst 20 is annealed; and inhibiting the production of impure carbon with the C<SB>2</SB>H<SB>2</SB>gas having a high H<SB>2</SB>gas concentration in a high active catalyst region C, and enhancing the high C<SB>2</SB>H<SB>2</SB>gas concentration in a low active catalyst region D to maximize the ability of the catalyst 20 to grow the CNT22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon fiber manufacturing method in which a raw material gas is allowed to act on a catalyst on a substrate in a reaction furnace to grow carbon fiber on the substrate using the catalyst as a growth nucleus.

  Carbon fibers, such as carbon nanotubes, are nano-order thin and have a high aspect ratio, and are being widely used as electron emitter materials. In such a carbon nanotube, a raw material gas is allowed to act on the catalyst to grow the carbon nanotube (see Patent Document 1).

  As a manufacturing apparatus for manufacturing such a carbon nanotube, a raw material gas is introduced onto a substrate placed in the reaction furnace while heating the reaction furnace with a heater outside the reaction furnace, and the raw material gas is decomposed with a catalyst to be on the substrate. There is a manufacturing apparatus using a so-called thermal CVD method for manufacturing carbon nanotubes.

However, in the conventional manufacturing method using such a manufacturing apparatus, the growth of carbon nanotubes is promoted by catalytic activity, but at the same time, carbon impurities such as amorphous carbon other than carbon nanotubes are easily generated, and the yield of carbon nanotubes is increased. As a result, the mass production of carbon nanotubes becomes difficult. Further, if carbon impurities are simultaneously generated in addition to the carbon nanotubes, it becomes difficult to generate high-purity carbon nanotubes. In addition, the gas flow rate of the raw material gas that is consumed in the reaction furnace is larger than the yield of carbon nanotubes, and a large amount of raw material gas is wasted, resulting in a low effective utilization rate of the raw material gas. There was a problem.
JP 2005-145743 A

  The problem to be solved by the present invention is to provide a carbon fiber manufacturing method capable of mass-producing high-purity carbon fibers at a high yield and having a high effective utilization rate of raw material gas.

  In the carbon fiber manufacturing method according to the present invention, the catalyst is annealed and activated in the course of advancing the substrate with the catalyst in a heated atmosphere, and the raw material gas flowing in opposite to the traveling direction is decomposed on the substrate. The carbon fiber manufacturing method is for growing carbon fiber at the same time, and the hydrogen gas concentration effective for annealing of the catalyst is increased at the progress position of the substrate where the catalyst is annealed in a heated atmosphere, and the substrate is in the process of progressing. In the region where the catalytic activity is high, the generation of carbon impurities such as amorphous carbon is suppressed by the source gas having a high hydrogen gas concentration, and in the region where the catalytic activity is low due to further progress of the substrate, the high concentration source gas is supplied. It is characterized by growing the carbon fiber by maximizing the capacity of the catalyst.

  In the present invention, while the catalyst-carrying substrate is advanced in the heating atmosphere, the raw material gas flows in the direction opposite to the traveling direction of the substrate when the raw material gas flows in opposite to the traveling direction. Thus, the raw material gas reacts with the catalyst and is decomposed, and the carbon fiber is grown on the substrate and consumed. On the other hand, the concentration of hydrogen gas generated by the decomposition increases. At the initial progress position of the substrate where the catalyst is annealed, the source gas is almost consumed for the growth of the carbon fiber, and the hydrogen gas concentration is high, so that the annealing of the catalyst is efficiently performed. On the other hand, in the region where the catalytic activity is high in the course of the substrate, the decomposition of the raw material gas has progressed considerably, and the hydrogen gas concentration has increased, so that carbon fibers such as amorphous carbon are grown simultaneously with the growth of the carbon fiber with the raw material gas. The generation of impurities is suppressed by high-concentration hydrogen gas. Next, as the substrate progresses further, the catalytic activity decreases, and in the region where the catalytic activity is low, the supply concentration is high on the side where the raw material gas flows in. The carbon fiber grows with maximum.

  As described above, in the present invention, as the manufacturing method, the substrate with the catalyst is simply advanced in the heating atmosphere, and the raw material gas is simply allowed to flow in the direction of travel, so that the carbon fiber is mass-produced. It is a manufacturing method that can At the same time, in the present invention, the concentration of hydrogen gas generated when the raw material gas is decomposed by the reaction with the catalyst and consumed for the growth of the carbon fiber increases, thereby suppressing the generation of unnecessary carbon impurities on the substrate. As a result, it is possible to grow high-purity carbon fiber, and at the stage where the consumption of the source gas is sufficiently advanced, the hydrogen gas has a high concentration and is effective for the annealing of the catalyst. Can be used effectively.

  In a preferred embodiment of the present invention, the source gas flowing in the direction opposite to the advancing direction is a process in which the substrate proceeds from a region where the catalytic activity is high to a region where the catalytic activity is low in the heating atmosphere. The consumption rate in which carbon in the raw material gas is converted into carbon fibers and the carbon impurities and immobilized after being decomposed by reaction with the catalyst is 90% or more.

  The carbon fiber may include carbon nanotubes, carbon nanohorns, carbon nanocones, carbon nanobumps, and graphite nanofibers.

  The material of the catalyst is not particularly limited as long as it is a material that acts on a compound gas containing carbon as a constituent element, and examples thereof include iron, cobalt, nickel, and oxides thereof.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon fiber manufacturing method with high mass productivity of a high purity carbon fiber and a high effective utilization factor of source gas can be provided.

  Hereinafter, a carbon fiber manufacturing method according to an embodiment of the present invention will be described with reference to the accompanying drawings. This carbon fiber manufacturing apparatus manufactures carbon nanotubes (hereinafter referred to as CNT). FIG. 1 shows a schematic configuration of a carbon fiber manufacturing apparatus used for carrying out the manufacturing method according to the embodiment, and FIG. 2 (a) is an acetylene gas which is a raw material gas when manufacturing CNTs using the carbon fiber manufacturing apparatus. FIG. 2 (b) shows the change in the catalytic activity, and FIG. 2 (c) shows the growth rate of the CNTs on the substrate. Carbon impurities are carbon compounds other than CNT, which is the production purpose, and amorphous carbon and graphite carbon are reference examples.

  With reference to these drawings, a carbon fiber manufacturing apparatus 10 according to an embodiment includes a reaction tube 12 that is long in one direction, and the reaction tube 12 that surrounds the reaction tube 12 and heats the reaction tube 12 from the outside. And a heating furnace 14 that forms a heating atmosphere having a uniform temperature throughout. The reaction tube 12 is shown with both ends open for convenience of explanation. A substrate transfer table 18 in which a plurality of substrates 16 are arranged and stored in the vertical direction at equal intervals from one opening side 122 of the reaction tube is carried in. The substrate 16 mounted on the substrate carrier 18 advances in the reaction tube 12 from the one opening side 122 toward the other opening side 121 in the arrow direction P. Further, the length and the tube shape of the reaction tube 12 are also shown in the shape shown in the figure for convenience of explanation, and may not be a straight tube shape, may be a curved tube shape, and the inner diameter is uniform in the longitudinal direction. It is not limited to a simple tube shape. The illustration of the transport mechanism of the substrate transport base 18 is omitted. The heating furnace 14 has, for example, a built-in heater, and heats the reaction tube 12 at a uniform temperature in the longitudinal direction thereof, and controls the temperature inside the reaction tube 12 to an atmospheric temperature necessary for CNT growth.

A source gas from a source gas supply unit (not shown) flows into the reaction tube 12 from the other opening side 121 in the arrow direction Q so as to face the traveling direction of the substrate 16. This source gas is, for example, acetylene (C ₂ H ₂ ) gas. The source gas is not limited to this C ₂ H ₂ gas, but may be a hydrocarbon compound gas. The arrow directions P and Q indicating the moving direction of the substrate 16 and the inflow direction of the C ₂ H ₂ gas in the reaction tube 12 are shown for convenience, and the substrate 16 and the C ₂ H ₂ gas are continuous. It does not indicate the moving speed of the substrate 16, the flow rate of the C ₂ H ₂ gas, or the inflow amount.

In the carbon fiber manufacturing method according to the present embodiment, as will be described below, the C ₂ H ₂ concentration on the other opening side 121 of the reaction tube 12 is high, for example, 100%, and hydrogen (H ₂₎ the gas concentration is 0%, C2H2 gas concentration is 50% at the center side of the reaction tube 12, H2 gas concentration becomes 50%, C ₂ H ₂ gas concentration in the one open side 121 of the reaction tube 12 Becomes a low concentration, for example, 0%, and the H ₂ gas concentration becomes 100%. Therefore, in the carbon fiber manufacturing method of the embodiment, the effective utilization rate of the C ₂ H ₂ gas that is the raw material gas is almost 100%.

That is, as shown by the C2H2 and H2 concentration lines in FIG. 2A, 100% C ₂ H ₂ gas flows into the reaction tube 12 from the other opening side 121 of the reaction tube. On the other hand, the substrate 16 with catalyst is mounted on the carrier 18 from one opening side 122 of the reaction tube 12 and is carried in, and the substrate 16 is advanced in the direction of arrow P in the reaction tube 12. The C ₂ H ₂ gas is decomposed by reacting with the catalyst on the substrate 16 in the process of flowing into the reaction tube 12 in the arrow direction Q opposite to the traveling direction of the substrate 16, and the CNTs are decomposed. Growing on the substrate 16 at the growth rate indicated by the growth rate line D in (c), the C ₂ H ₂ gas is consumed in the process of flowing in the arrow direction Q. On the other hand, the C ₂ H ₂ at decomposition of gas while the concentration of C ₂ H ₂ gas flowing inside the reaction tube 12 is lowered, H ₂ gas with the decomposition of C ₂ H ₂ gas is generated, the direction of the arrow As the C ₂ H ₂ gas flows into Q, the H ₂ gas concentration increases.

Although the C ₂ H ₂ gas has a concentration of 100% on the other opening side 121 of the reaction tube, almost 100% of the C ₂ H ₂ gas is grown to the CNT growth until it flows into the opening side 122 through the reaction tube 12. %, The gas in the vicinity of the one opening side 122 of the reaction tube becomes H ₂ gas having a concentration of 100%. In the hatching region of FIG. 2 (b) on the one opening side 122 of the reaction tube, the source gas C ₂ H ₂ gas exists as shown in FIG. 2 (a), and the catalyst has a gradient indicated by the annealing line A. Is annealed and activated. In this case, since the H ₂ gas concentration is high in this hatching region as shown in FIG. 2A, the annealing of the catalyst proceeds with high efficiency.

  On the other hand, in the reaction tube 12, the left side in FIG. 2B is a region where the catalyst is annealed on the substrate 16 with the catalyst loaded and loaded on the carrier table 18, and the right side is the catalyst. As shown in the region where the substrate 16 is carried in the active state, the catalytic activity is increased as the substrate 16 advances through the reaction tube 12 for a certain distance after the catalyst is annealed and activated. Although it gradually decreases as shown by the active line C, for the convenience of explanation, the part from the vertical dotted line B to the middle part in the right direction in the figure is called a catalyst high activity region where the activity of the catalyst is high. This is referred to as a catalyst low activity region having low activity. The catalyst high activity region and the catalyst low activity region are determined by the gas flow rate or the catalyst. One of the factors that make the CNT difficult to grow due to the low activity of the catalyst is one that the catalyst size is increased or the activity of the catalyst is reduced due to reaction with the substrate, and the other is amorphous. There is a form in which carbon such as carbon or graphite carbon covers the surface of the catalyst.

Since the C ₂ H ₂ gas flows into the reaction tube 12 in the direction of the arrow Q from the direction opposite to the traveling direction of the substrate 16, initially, it reacts with the catalyst in the catalyst low activity region inside the reaction tube 12. In this case, the C ₂ H ₂ gas concentration is, for example, approximately 100% in the vicinity of the other opening side 121 of the reaction tube, and the CNT is grown with the maximum catalytic capacity. Then, even if the C ₂ H ₂ gas concentration is lowered in the process of flowing C ₂ H ₂ gas into the reaction tube 12 from the other opening side 121 of the reaction tube, a high reaction with the catalyst occurs in the catalyst high activity region. CNT is grown as shown in c). On the other hand, carbon impurities are also generated in the catalyst high activity region. In this catalyst high activity region, as shown in FIG. 2 (a), the decomposition of C ₂ H ₂ gas progresses considerably and the H ₂ gas concentration increases. Therefore, as shown in FIG. 2C, CNT is grown with C ₂ H ₂ gas, and at the same time, generation of carbon impurities such as amorphous carbon is suppressed with high concentration of H ₂ gas. Thereby, it is suppressed that a catalyst is covered with the said carbon impurity and a catalyst activity falls.

As shown in FIG. 3A, the catalyst 20 on the substrate 16 on the one opening side 122 of the reaction tube is in a film form before being annealed, and is finely divided by annealing as shown in FIG. . During this annealing, the substrate 16 has an H ₂ gas concentration of 100%, and the annealing progress is promoted.

In the catalyst high activity region, as shown in FIG. 3C, the decomposition of C ₂ H ₂ gas proceeds and the H ₂ gas concentration is high, so that the generation of carbon impurities such as amorphous carbon is suppressed, As a result of the C ₂ H ₂ gas entering between the grown CNTs 22 and acting on the catalyst, the CNTs 22 grow. Further, in the low catalyst activity region, as shown in FIG. 3 (d), since the C ₂ H ₂ gas concentration is high, even if the catalyst activity is low, its catalytic ability is exerted to the maximum, and the CNT 22 grow up.

In the present embodiment described above, the reaction tube 12, while advancing the substrate 16, in the course of facing allowed to flow into C ₂ H ₂ gas in the direction of travel, C ₂ H ₂ gas substrate 16 It is decomposed by reacting with the catalyst 20 above, and the CNTs 22 are grown on the substrate 16 and consumed. Meanwhile, the H2 gas concentration generated in the decomposition of C ₂ H ₂ gas increases. Then, the C ₂ H ₂ gas is almost consumed for the growth of the CNTs 22 at the progress position of the substrate 16 where the catalyst 20 is annealed, and the H ₂ gas concentration is high, so that the catalyst progresses efficiently.

On the other hand, the decomposition of C ₂ H ₂ gas progresses considerably in the catalyst high activity region in the course of the substrate 16, and the H ₂ gas concentration is increased. Therefore, when the CNT 22 is grown with the C ₂ H ₂ gas. At the same time, the generation of carbon impurities is suppressed by a high concentration of H ₂ gas.

Next, since the substrate 16 is further advanced and the supply concentration is high on the side where the C ₂ H ₂ gas is introduced in the low catalyst active region, even if the catalyst activity is low, the catalyst capacity is high with the high concentration C ₂ H ₂ gas. The CNT 22 grows by being maximized.

As described above, in the present embodiment, as the manufacturing method, when CNT2 is grown by catalytic activity, carbon impurities other than CNT22 are not easily generated. Therefore, the yield of CNT22 is increased and mass production is facilitated. In addition to being able to grow high-purity CNT22, C ₂ H ₂ gas consumed in the reaction tube 12 is efficiently consumed compared with the yield of CNT22, and its effective utilization rate is high. Become.

In the present embodiment, C ₂ H ₂ gas flowing in the direction opposite to the traveling direction of the substrate 16 is decomposed by reaction with the catalyst 20 in the process of the substrate 16 traveling in the reaction tube 12, thereby causing C ₂ H _2. Carbon in the gas is converted to CNT22 and carbon impurities, immobilized and consumed, and the consumption rate is 90% or more, preferably 99.9%, which is extremely high.

  The present invention is not limited to the above-described embodiment, and includes various changes or modifications within the scope described in the claims.

FIG. 1 is a diagram showing a schematic configuration of a carbon fiber manufacturing apparatus used for carrying out the manufacturing method of the embodiment. FIG. 2 is used for explaining the manufacturing method of the embodiment. FIG. 2 (a) shows the relationship between the C ₂ H ₂ gas concentration and the H ₂ gas concentration, FIG. 2 (b) shows the catalytic activity, FIG. 2C shows the growth rate of CNTs. FIG. 3 shows the CNT growth process on the substrate, FIG. 3 (a) shows a state in which the catalyst is formed in a film shape on the substrate, and FIG. 3 (b) shows the catalyst finely divided by annealing. FIG. 3C shows the growth of CNTs in the high catalytic activity region, and FIG. 3D shows the growth of CNTs in the low catalytic activity region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Carbon fiber manufacturing apparatus 12 Reaction tube 14 Heating furnace 16 Substrate 20 Catalyst 22 CNT

Claims (2)

A carbon fiber manufacturing method for growing a carbon fiber on a substrate by annealing and activating the catalyst in the process of advancing the substrate with the catalyst in a heated atmosphere and decomposing the raw material gas flowing in opposite to the traveling direction And
And in a heated atmosphere,
In the progress position of the substrate where the catalyst is annealed, the hydrogen gas concentration effective for the annealing progress of the catalyst is increased,
In the catalyst high activity region where the catalytic activity is high while the substrate is in progress, the generation of carbon impurities such as amorphous carbon is suppressed by the source gas having a high hydrogen gas concentration,
A carbon fiber manufacturing method characterized in that carbon fiber is grown by maximizing the capacity of the catalyst by supplying a high-concentration raw material gas in a catalyst low activity region where the catalytic activity is further lowered due to further progress of the substrate.   In the process of the substrate moving from the high catalyst active region to the low catalyst active region in the heating atmosphere, the raw material gas flowing in the direction opposite to the traveling direction is decomposed by the reaction with the catalyst, so that the carbon in the raw material gas is changed. The carbon fiber manufacturing method according to claim 1, wherein a consumption rate of carbon fiber or the carbon impurity converted into the carbon impurity and immobilized and consumed is 90% or more.

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