JP2004324004A - Carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber having industrial utility value, simultaneously produced with hydrogen without accompanying the byproduction of carbon dioxide by decomposing hydrocarbons such as methane by using a catalyst; and to provide a method for producing the carbon fiber. <P>SOLUTION: The carbon fiber (3) is obtained by allowing a hydrocarbon molecule to be absorbed on a catalytic metal particle (2) carried by the surface of a spherical carrier (1), allowing the carbon formed by the decomposition reaction to continuously precipitate on the interface between the catalytic metal particle (2) and the carrier, and growing the fiber in a crystal shape accompanying the catalytic metal particle (2) at the tip. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for decomposing hydrocarbons using a catalyst to produce hydrogen and carbon nanotubes or ultrafine carbon fibers. More specifically, the present invention relates to a technology for efficiently pyrolyzing hydrocarbons to produce hydrogen and ultrafine carbon fibers, particularly carbon materials called carbon nanotubes.
[0002]
[Prior art]
Conventionally, as a method for producing hydrogen, a method is known in which hydrocarbons such as methane are reformed by steam using a catalyst or partially oxidized by air. Although hydrogen produced by such a method is widely consumed as a raw material for the chemical industry, it is expected that hydrogen consumption for energy use will increase in recent years. However, the conventional method of producing hydrogen has a problem that carbon dioxide, which is a greenhouse gas, is generated in large quantities at the same time, and a hydrogen producing method that does not produce carbon dioxide is strongly desired.
[0003]
On the other hand, a method for producing hydrogen and carbon by directly decomposing hydrocarbons in the presence of a catalyst has been known for a long time, and an invention relating to catalyst improvement has recently been made (Patent Document 1 below). There has been a problem that, together with the production of hydrogen, powdery or amorphous solid carbon having no usefulness is produced in large quantities.
[0004]
Various methods have been reported for producing carbon nanotubes and nanoscale carbon fibers, such as an arc discharge method, a laser ablation method, a plasma synthesis method, and a hydrocarbon catalytic decomposition method. Research and development are being actively pursued with the aim of establishing inexpensive mass synthesis technology. In the production of carbon nanotubes by the hydrocarbon catalytic decomposition method, many methods using fine particles of catalytic metal have been reported, but there is no report that the produced carbon is affected by the shape of the catalyst carrier.
[0005]
Further, there is no report that the amount, shape and other properties of carbon produced are affected by the degree of dispersion of the catalyst carrier.
[0006]
[Patent Document]
Patent No. 2838192 Specification
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems by thermally decomposing hydrocarbons such as methane using a catalyst to produce hydrogen without by-producing carbon dioxide, and at the same time, reduce the value of industrial use. An object is to provide a high carbon fiber and a method for producing the same.
[0008]
[Means for Solving the Problems]
In the carbon fiber of the present invention, hydrocarbon molecules are adsorbed to the catalyst metal particles supported on the surface of the spherical carrier, and carbon generated by causing a decomposition reaction is continuously deposited on the interface between the catalyst metal particles and the carrier. , Characterized in that it has grown into a crystal with the catalyst metal particles at the tip.
[0009]
The method for producing carbon fiber of the present invention is a method for producing carbon fiber using a hydrocarbon decomposition catalyst, in which hydrocarbon molecules are supplied to catalyst metal particles supported on a spherical carrier surface, adsorbed, and the decomposition reaction is performed. Then, carbon is continuously deposited on the interface between the catalyst metal particles and the carrier, and is grown in a crystalline state with the catalyst metal particles at the tip.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have conducted research on a catalyst for thermal decomposition of hydrocarbons, and as a result, have found a catalyst in which carbon produced simultaneously with hydrogen is converted into carbon nanotubes or ultrafine carbon fibers, and have accomplished the present invention.
[0011]
In general, a catalyst support needs to have a large surface area for supporting a catalyst, but other important factors such as physical properties such as pore diameter and acidity have been regarded as important. However, the present inventors have determined that the carbon generated together with hydrogen by the thermal decomposition of hydrocarbons is not particulate or amorphous, but rather carbon nanotubes or ultrafine carbon fibers, depending on the type of catalyst metal and the catalyst preparation method. Also found that the shape and the degree of dispersion of the catalyst carrier were important, and made the present invention based on this finding.
[0012]
The method of the present invention is carried out by thermally decomposing a hydrocarbon gas such as methane on a catalyst composed of a highly dispersed spherical carrier and a metal supported on the carrier. Carbon fiber is produced. In this case, it is important that the shape of the carrier is spherical, and the effects of the present invention cannot be obtained if the shape is plate-like, scale-like, amorphous, or the like.
[0013]
Examples of the carrier include spherical zirconium (ZrO ₂ ), spherical silica (SiO ₂ ), and spherical erbium-gallium oxide (Er ₃ Ga ₅ O ₁₂ ). The average particle size of the carrier is preferably in the range of 10 to 1000 nm.
[0014]
As the metal to be supported, various known catalyst metals such as nickel and copper can be used. In addition, a carrier that is not aggregated and has better dispersibility is more suitable for producing carbon nanotubes or ultrafine carbon fibers. The size of the catalyst metal particles is preferably in the range of 5 to 100 nm. The carbon fiber that grows in a crystalline state has catalytic metal particles at its tip, and the diameter of the carbon fiber is substantially equal to the diameter of the catalytic metal particles. The diameter of the carbon fiber is also in the range of 5 to 100 nm. The length of the carbon fiber is several hundred microns or more.
[0015]
The catalyst according to the present invention can be prepared by impregnating and drying a spherical catalyst support with a salt of a catalyst metal, followed by heating. The spherical catalyst support can be synthesized by a so-called glycothermal method. Here, the glycothermal method refers to a method of forming a carrier by suspending a carrier precursor in a glycol such as 1,4-butanediol and then baking it. Taking a case where a zirconia carrier is synthesized as an example, a predetermined amount of zirconium tetrapropoxide and yttrium acetate or magnesium acetylacetonate are suspended in 1,4-butanediol and reacted at about 300 ° C. in a nitrogen atmosphere. Thereafter, the product is washed and dried, and then calcined at about 400 ° C., whereby a high-surface-area carrier having a substantially spherical shape is obtained. The degree of dispersion of the carrier is affected by the sintering temperature. For example, aggregation occurs at a high temperature of about 1200 ° C., which is inappropriate. This is impregnated with an aqueous solution of various metal salts (nickel nitrate, cobalt nitrate, iron nitrate, copper formate, ammonium molybdate, manganese chloride, etc.), dried and calcined at a temperature of about 400 ° C. to obtain the catalyst of the present invention.
[0016]
When a gas of hydrocarbons such as methane flows at a predetermined temperature over the catalyst produced as described above, hydrogen and solid carbon are generated, and the solid carbon is converted into carbon nanotubes (ultrafine carbon fibers depending on conditions). This is confirmed by observation with a transmission electron microscope. The preferred reaction temperature varies depending on the catalyst, but is generally in the range of 400 ° C. to 800 ° C., preferably 450 ° C. to 650 ° C.
[0017]
The production of carbon nanotubes or ultrafine carbon fibers by the catalyst of the present invention is based on the fact that carbon generated by the decomposition reaction of hydrocarbon molecules on the metal supported on the catalyst is dissolved in the catalyst metal, and the catalyst metal particles and the carrier It is caused by precipitation at the interface with. If carbon deposition at the catalyst metal particle-carrier interface occurs continuously, the generated carbon becomes carbon nanotubes or ultrafine carbon fibers, but if the deposition is discontinuous, powdery or amorphous carbon is formed. Generate. In the catalyst of the present invention, since the carrier shape is spherical, liberation of carrier particles proceeds with the deposition of carbon, the growth of carbon nanotubes or ultrafine carbon fibers is not hindered, and the catalyst is useful in high yield. Carbon nanotubes or ultrafine carbon fibers can be produced. In addition, when the dispersibility of the catalyst carrier is poor and the carrier particles are aggregated, the growth of carbon nanotubes or ultrafine carbon fibers is hindered.However, if a highly dispersed catalyst carrier is used, the crystallinity is improved. Long carbon nanotubes or ultrafine carbon fibers can be manufactured.
[0018]
Next, FIGS. 1 (a) to 1 (c) are drawings illustrating the mechanism of producing the carbon fiber of the present invention. First, as shown in FIG. 1 (a), for example, methane (CH ₄ ) hydrocarbon molecules are supplied to the catalyst metal 2 supported on the surface of the spherical carrier 1 and adsorbed to cause a thermal decomposition reaction. As shown in FIG. 1 (b), carbon (C) produced by the dehydrogenation reaction is dissolved in the catalyst metal 2, and as shown in FIG. 1 (c), the interface between the catalyst metal particles 2 and the carrier 1 is formed. The carbon fiber 3 is continuously precipitated. The carbon fiber 3 grows in a crystalline state with the catalyst metal particles 2 at the tip. The portion indicated by the arrow in FIG. 2 is the catalytic metal particle at the tip of the carbon fiber.
[0019]
FIG. 3 shows a state in which a large number of carbon fibers have grown from the central black spherical carrier. FIG. 4 is an enlarged view of the spherical carrier in FIG. 3, and FIG. 5 is an enlarged view of the carbon fiber portion in FIG.
[0020]
FIG. 6 is an enlarged view of the carbon fiber in FIG. 3, and the graphene carbon layer is shown in parallel lines. Here, the graphene carbon layer refers to a layer having a six-membered ring network structure made of graphite. In addition, when attention is paid to the right fiber in FIG. 6, a white line is seen in the central longitudinal direction. The fibers are hollow, indicating the structure of the carbon nanotube. The carbon nanotube is formed such that a long layer of a 6-membered ring network structure made of graphite is rolled in a single layer or in multiple layers, or wound obliquely in a bamboo shoot shape.
[0021]
The carbon fibers and carbon nanotubes of the present invention can be applied to applications such as batteries, fuel cells, electrodes of electric double layer capacitors, and conductive fillers.
[0022]
【Example】
Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In order to further clarify the effects of the present invention, comparative examples will be described.
[0023]
(Example 1)
A predetermined amount of zirconium tetrapropoxide and yttrium acetate are suspended in 1,4-butanediol, heated at a rate of 2.5 degrees per minute in a reaction system purged with nitrogen, and kept at about 300 degrees Celsius for 2 hours. Reacted. The product was washed with methanol, air-dried, and calcined at about 400 ° C. to obtain a carrier according to an example of the present invention. When the obtained carrier was observed using a scanning electron microscope, it was confirmed that the carrier was substantially spherical and highly dispersed.
[0024]
The carrier was impregnated with an aqueous solution of nickel nitrate, dried, and calcined at 400 ° C. to obtain a Ni / ZrCo ₂ catalyst. The nickel loading was adjusted to 10% by weight.
[0025]
The temperature of the Ni / ZrCo ₂ catalyst produced as described above was raised in argon gas, and when the temperature reached a predetermined temperature, the flow of argon gas was stopped and the flow of methane gas was switched to produce hydrogen and carbon nanotubes. The production of hydrogen and the level at which by-products of carbon dioxide do not pose any problems were confirmed by gas chromatographic analysis of the gas after the reaction. The deposited solid carbon was observed with a transmission electron microscope and an X-ray diffractometer to confirm that carbon nanotubes were produced. 2 to 5 show carbon fibers obtained according to this example. FIG. 6 shows a transmission electron micrograph of the carbon nanotube.
[0026]
When the reaction was repeated while changing the temperature variously, the production efficiency of the carbon nanotube was highest at around 500 ° C.
[0027]
(Example 2)
A predetermined amount of erbium acetate tetrahydrate, tris-acetylacetonatogallium, and 1,4-butanediol were suspended, reacted at 300 ° C for 2 hours, washed with methanol, air-dried, and calcined at 300 ° C. Thus, a catalyst carrier Er ₃ Ga ₅ O ₁₂ was obtained. It was confirmed by electron microscope observation that the spherical carrier Er ₃ Ga ₅ O ₁₂ prepared by the glycothermal method was spherical and highly dispersed. When a methane decomposition reaction was carried out at 650 ° C. using a catalyst prepared by supporting 5% by weight of Ni on this carrier, the production of hydrogen was confirmed by gas chromatography. In addition, transmission electron microscopy confirmed that the generated carbon was a carbon nanotube, as shown in FIGS.
[0028]
An electron microscope observation confirmed that the carrier produced in exactly the same manner except that the sintering temperature was 1200 ° C. had a spherical shape but was aggregated. Hydrogen and carbon nanotubes were generated from the decomposition reaction of methane on the catalyst prepared by supporting the catalyst metal in the same manner as above, but the production amount of carbon nanotubes was reduced to ２ or less. .
[0029]
(Comparative Example 1)
A catalyst was produced in the same manner as in the example except that commercially available zirconia which was not spherical was used as a carrier, and was reacted with methane gas in the same manner as in the example. Production of hydrogen gas was confirmed by gas chromatography, but the precipitated solid carbon contained a large amount of particulate or amorphous carbon, and the yield of carbon nanotubes and carbon fibers was small.
[0030]
(Comparative Example 2)
A catalyst was produced in the same manner as in the example except that commercially available titania having a non-spherical shape was used as a carrier, and reacted with methane gas in the same manner as in the example. Production of hydrogen gas was confirmed by gas chromatography, but observation of the precipitated solid carbon with a transmission electron microscope showed only onion-like particles, and no effective production of carbon nanotubes or carbon fibers was observed.
[0031]
【The invention's effect】
According to the present invention, by reacting hydrocarbons such as methane on a catalyst using a spherical carrier with good dispersibility, by-product carbon dioxide is suppressed, hydrogen and carbon nanotubes or ultrafine Carbon fibers can be produced.
[Brief description of the drawings]
1 (a) to 1 (c) are drawings for explaining a carbon fiber generation mechanism in Example 1 of the present invention.
FIG. 2 is a drawing showing catalytic metal particles at the tip of a carbon fiber.
FIG. 3 is a drawing showing a state in which a large number of carbon fibers have grown from a central black spherical carrier.
FIG. 4 is an enlarged view of the spherical carrier in FIG.
FIG. 5 is an enlarged view of a carbon fiber portion in FIG.
FIG. 6 is an enlarged view of the carbon fiber in FIG. 3, showing a graphene layer structure and a carbon nanotube structure.
[Explanation of symbols]
1 spherical carrier 2 catalytic metal 3 carbon fiber

Claims (11)

Hydrocarbon molecules are adsorbed on the catalyst metal particles supported on the surface of the spherical carrier, carbon generated by causing a decomposition reaction is continuously deposited at the interface between the catalyst metal particles and the carrier, and the catalyst metal particles are formed at the tip. Carbon fiber grown in a crystalline state with The carbon fiber according to claim 1, wherein the carbon fiber has a graphene layer structure. The carbon fiber according to claim 1, wherein the carbon fiber is a carbon nanotube. The carbon fiber according to any one of claims 1 to 3, wherein a diameter of the carbon fiber is in a range of 5 to 100 nm. The carbon fiber according to claim 1, wherein the spherical carrier is formed by suspending a carrier precursor in glycol and then baking the suspension. A method for producing carbon fibers using a hydrocarbon cracking catalyst,
Hydrocarbon molecules are supplied to the catalyst metal particles supported on the surface of the spherical carrier, adsorbed, decomposed, and carbon is continuously deposited on the interface between the catalyst metal particles and the carrier. A method for producing a carbon fiber, wherein the carbon fiber is grown together with the crystal. The method for producing carbon fibers according to claim 6, wherein the spherical carrier is formed by suspending a carrier precursor in glycol and then baking it. The method for producing a carbon fiber according to claim 6, wherein the spherical carrier is highly dispersible. The method for producing carbon fibers according to any one of claims 6 to 8, wherein the spherical carrier has an average particle diameter in a range of 10 to 1000 nm. The method for producing carbon fibers according to claim 6, wherein the catalytic metal particles are Ni, Cu, or a composition containing these. The method for producing a carbon fiber according to claim 6, wherein the size of the catalyst metal particles is in a range of 5 to 100 nm.

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