JPH0442805A - Production of fibrous carbon having high orientation property - Google Patents

Abstract

PURPOSE:To form the title carbon having controlled characteristic micro structure and high graphitizing properties by heat-treating a mixed raw material gas of carbon monoxide and hydrogen in the presence of cementite. CONSTITUTION:CO is used as a carbon raw material and is allowed to react with H2 by using cementite as a catalyst raw material for carbon precipitation. Cementite has no problem even if existing by any state and usually is put in a magnetic boat 12, etc., and placed in a reaction tube 1 laid in a furnace 2. Cementite is brought into contact with CO by sending a raw material gas containing CO to the reaction tube 1 and cementite is preferably contacted with CO by using the fluidized bed. Carbon of micro structure which is not prepared by other method is obtained by this method. Since the prepared fibrous carbon has high graphitizing properties in spite of low formation temperature, the fibrous carbon is useful as a material suitable for conductive material, thermal conductive material, catalyst carrier, etc., even without passing the fibrous material through after-heat treatment.

Description

Detailed Description of the Invention [Technical Field to which the Invention Pertains] The present invention relates to a method for producing carbon by a gas phase method, and more particularly, to a method for producing carbon from carbon monoxide using a catalytic action of a transition metal compound. The present invention relates to a method for producing vapor-grown fibrous carbon.

[Prior Art] By controlling its structure, carbon materials can be used as materials with excellent physical properties such as mechanical properties, electrical conductivity, thermal conductivity, and the like.

However, it is generally difficult to control the structure, and the structure tends to be irregular and disorderly.

In order to obtain a carbon material with a high degree of graphitization, a high temperature is usually required, and generally a heat treatment of 2500° C. or higher is required.

However, by utilizing the catalytic action of transition metals such as iron group metals, it is possible to obtain carbonaceous materials with a high degree of graphitization at lower temperatures.

For example, flaky quiche graphite, which is precipitated from molten iron, has a precipitation temperature of around 1500° C., and it is well known that it has extremely high graphitizability.

In recent years, in the thermal decomposition of hydrocarbons, the carbonaceous material known as vapor-grown carbon fiber, which is produced at 1000 to 1300°C using the catalytic action of ultrafine transition metal particles, has a relatively highly crystalline part. It has been confirmed that there are.

Furthermore, highly oriented carbon that can easily be highly graphitized in the form of a thin film or flake on the surface of a transition metal during carbon precipitation due to the disproportionation reaction of carbon monoxide that occurs at low temperatures (400 to 800°C). quality, and in recent years, G
It is known that fibrous carbon with a highly crystalline carbon layer structure resembling stacked truncated cones can be produced from o -Ni-based ultrafine particles.

Various attempts have been made to develop such a carbon precipitation reaction due to the disproportionation reaction of carbon monoxide, starting with intensive research in Germany during the Second War.

Catalytic raw materials often used in this case include electrolytic iron powder and iron oxide powder such as red red iron oxide powder, but the carbon produced is mainly crimped fibers and irregular granules, with a microstructure. It is said that it is messy and has no particular characteristics.

[Problem to be Solved by the Invention 1] However, this thin film-like or flaky carbonaceous material is generated so as to surround metal particles that serve as a catalyst, and is difficult to handle as a carbon material.

In addition, there is no established practical method for producing fibrous carbon, which has a structure of carbon layers like stacked truncated cones, and there are many issues such as yield and by-products that are not clear. There are problems in using this method industrially as a method for producing carbon.

In particular, the carbon precipitation reaction from carbon monoxide gas can produce carbon at low temperatures, but many details such as the mechanism of carbon precipitation, the form of precipitated carbon, and the microstructure are still unclear. It has been difficult to obtain a highly oriented carbon material that has a fibrous form, which is one of the useful forms as a material, and has a controlled microstructure and high graphitizability at low temperatures.

[Means for Solving the Problems] Therefore, the present inventors have developed fine fibrous materials having a unique microstructure and morphology by using carbon monoxide as a carbon raw material and, for example, using Fe(CO)5 as a catalyst raw material. The company has filed a patent application for a method for efficiently producing carbon as Japanese Patent Application No. 1-286673.

The fibrous carbon has a characteristic microstructure in which the carbon network planes are stacked perpendicularly to the fiber axis and a flat fiber cross section, and although it is produced at a low temperature of around 400 to 700°C, it has a special It is a highly oriented carbon material that exhibits high graphitizability without any post-heat treatment.

The present inventors further investigated the catalyst particles present at the tips of this highly graphitizable fibrous carbon, and found that cementite (Fe3
It has been discovered that even by using C), highly oriented fibrous carbon having a controlled microstructure and high graphitizability can be produced at a relatively low temperature and in good yield, and the present invention has been achieved.

That is, the present invention utilizes this carbon precipitation reaction from carbon monoxide that is possible at a relatively low temperature to provide highly oriented fibrous carbon with a controlled microstructure and highly graphitic properties that cannot be obtained by other methods. The purpose is to This objective can be easily achieved by heat-treating a mixed raw material gas of carbon monoxide and hydrogen in the presence of cementite.

The present invention will be explained in detail below.

The highly oriented fibrous carbon of the present invention is produced as follows.

The reaction is carried out using carbon monoxide as a carbon raw material and cementite as a catalyst raw material for carbon deposition in the presence of hydrogen.

There is no problem with cementite being present in any way, but it is usually placed in a magnetic boat or the like and placed in a reaction tube installed in a superheating furnace, and by flowing raw material gas containing carbon monoxide through this reaction tube. Preferably, contacting with carbon monoxide or using a fluidized bed is preferred.

Although the shape of the cementite used in the present invention is not particularly limited, it is desirable to use powdered cementite, preferably with a particle size of 10 μm or less, for efficient carbon precipitation.

It is necessary to coexist hydrogen gas in addition to carbon monoxide in the raw material gas.

Since the generation of highly oriented carbon is suppressed when the proportion of hydrogen is lowered, it can be seen that hydrogen plays an important role in the activity of the carbon deposition catalyst.

In addition to increasing catalytic activity, hydrogen also reduces carbon dioxide in the system by reacting with carbon dioxide, which is simultaneously produced when carbon is produced by the disproportionation reaction of carbon monoxide, to become water. It has the effect of promoting carbon precipitation reaction from carbon monoxide.

Therefore, carbon can be precipitated at a higher yield than when only carbon monoxide is used.

However, if the proportion of hydrogen gas is too large, the partial pressure of carbon monoxide will decrease and the reaction efficiency will decrease, so the practical ratio of hydrogen to carbon monoxide in the raw material gas is 0.3 to 3 ( molar ratio) is preferable, more preferably 0
．． 5 to 1.5 (molar ratio). Further, the raw material gas may contain other substances in addition to carbon monoxide, hydrogen, and catalyst raw materials.

Rare gases such as argon and helium, nitrogen, and water vapor may be contained in the raw material gas at a partial pressure higher than that of hydrogen, and other hydrocarbons or hydrocarbons containing heteroatoms such as oxygen and nitrogen may also coexist. . However, oxygen is 1
It is desirable to suppress the content to 0% by volume or less.

As mentioned above, various gases can coexist in the system, but for efficient carbon production, it is desirable to make the ratio of carbon monoxide and hydrogen in the raw material gas as high as possible.
The content is preferably 5% by volume or more.

The amount of carbon monoxide gas reacted with cementite depends on the method of contact between the two, but for efficient carbon precipitation, 0.01 carbon monoxide gas should be added to 1 g of cementite.
~10/min, more preferably 0.1~1. (M
'/min.

The appropriate reaction temperature is 400 to 1000°C, but if the temperature is low, the reaction rate of carbon precipitation is low, and if the temperature is high, the balance of the disproportionation reaction of carbon monoxide shifts to the carbon monoxide side. Therefore, in any case, the efficiency of carbon precipitation is undesirable, so the most preferable range is 500 to 800.
°C is appropriate.

The high degree of graphitization described in the present invention means that when the interplanar distance of carbon network planes is expressed as d(002), the value is 3.40 Å or less, and Mering and Maire
The following relational expression derived from the carbon structure model of %
In the formula %), it means that the degree of graphitization indicated by g is 46.5% or more, and this value means that the vapor-grown carbon fiber obtained by the most excellent Yidao black is heated to 200°C. This value corresponds to that obtained by heat treatment as described above. Moreover, high graphitization property means that such high graphitization can be easily performed.

The carbon material obtained by the present invention has a fibrous morphology and is characterized by a controlled microstructure.

That is, as mentioned above, the ribbon-like carbon fibers are those in which the carbon mesh surface is laminated perpendicular to the fiber growth direction, or those in which the carbon mesh surface is laminated in a similar shape to the fiber growth direction, or those in which the carbon mesh surface is laminated almost parallel to the fiber growth direction. There are various types of carbon fibers, but all of them have carbon layers stacked in a similar manner, without having holes in the center like vapor-grown carbon fibers obtained from hydrocarbons, for example.
The carbon has good orientation.

These carbon materials can be used as materials particularly suitable for electrical conductors, thermal conductors, catalyst carriers, graphite lubricants, host materials for graphite intercalation compounds, and the like.

[Examples] The present invention will be explained in more detail below using Examples, but the present invention is not limited to the Examples unless the gist thereof is exceeded.

The outline of the apparatus used to produce the highly graphitizable carbon material of the present invention is shown in FIG.

In Figure 3, (3), (4) and (5) indicate gas cylinders, cylinder (3) contains nitrogen gas, (4) high purity hydrogen gas, and (5) high purity carbon monoxide gas. Filled. The flow rates of these gases are adjusted by flow meters (6), (7) and (8), respectively. Gas supplied from the cylinder is charged into the reaction tube (1) through the pipe (9).

The reaction tube (1) is a quartz tube with an inner diameter of 47 mm and a length of 100 mm, and is installed in an electric furnace (2) equipped with a 400 mm heating section.

At the center of reaction (1) is a magnetic ball containing cementite)
(12) is placed. Off gas is filtered (10
) through the gas outlet (11). The reaction system is initially purged with nitrogen gas during operation to prevent the risk of explosion.

After that, the electric furnace (2) is heated to a predetermined temperature, and the cylinder (4) is heated to a predetermined temperature.
) and (5), the mixed gas of hydrogen and carbon monoxide is charged into the reaction tube (1) via the pipe (9).

When the inside of the reaction tube becomes a C0IH2 mixed gas atmosphere, a predetermined amount of C0IH2 gas is supplied to the reaction tube (1) and brought into contact with cementite to start a reaction.

Example 1 Highly oriented fibrous carbon was produced using the apparatus shown in FIG.

Cementite powder (manufactured by Rare Metallic Co., Ltd., purity 99.9%, particle size 10 pm or less) was used as the catalyst raw material. 0.5039 g of this powder was placed in a magnetic boat, placed in the center of the electric furnace, and placed in the reaction tube. installed inside.

After purging the reaction tube with nitrogen and raising the temperature of the system to 550°C,
H2 and CO are derived from cylinders (4) and (5), and Co/
0.5/hr (2
5°C (converted to 11at) for 2 hours.

As a result, 2.1621 g of carbonaceous material was obtained.

As a result of observing this carbonaceous material with a scanning electron microscope and a transmission electron microscope, the width was less than lpm, and the length was several yen to several tens of meters.
pm, highly oriented fibrous carbon with carbon mesh planes stacked perpendicular to the fiber growth direction, and fine fibrous carbon with a cylindrical shape with a diameter of about 0.1 pm and no orientation. In the mixture with carbon, the ratio was estimated to be approximately 6:4.

According to X-ray diffraction, the value of the interplanar distance d(002) of the carbon layer was 3.385 to 3.398. The highly oriented fibrous carbon obtained is shown in FIG.

Example 2 Highly oriented fibrous carbon was produced using the apparatus shown in FIG.

Cementite powder (manufactured by Rare Metallic Co., Ltd., purity 99.9%, particle size 10 pm or less) was used as the catalyst raw material. 0.5721 g of this powder was placed in a magnetic boat, placed in the center of the electric furnace, and placed inside the reaction tube. It was installed in

After replacing the inside of the reaction tube with nitrogen and raising the temperature of the system to 700°C, H2 and CO are extracted from the cylinders (4) and (5), and CO/H
0.5e/hr (as a mixed gas of 2=50150
25°C (calculated at 11at) for 2 hours.

As a result, 1.5582 g of carbonaceous material was obtained.

When this carbon material was observed using a scanning electron microscope and a transmission electron microscope, it was found that highly oriented fibrous carbon with a diameter of about 0.2 pm and carbon mesh planes stacked parallel to the fiber growth direction was gathered. It is a mixture of fibrous carbon in the form of bundles with a diameter of several pm and fine fibrous carbon in the form of columns with a diameter of about 0.1 pm with no visible orientation, and the ratio is approximately 8: It was estimated to be around 2.

According to X-ray diffraction, the value of the interplanar distance d(002) of the carbon layer was 3.366 to 3.377.

The highly oriented fibrous carbon obtained is shown in FIG.

[Effects of the Invention] According to the present invention, carbon having a characteristic microstructure can be obtained, and since the obtained fibrous carbon has a high degree of graphitization despite its low production temperature, it does not require post-heat treatment that is normally required. Even without going through this process, it can be used as a material particularly suitable for electrical conductors, thermal conductors, catalyst carriers, graphite lubricants, host materials for graphite intercalation compounds, and the like.

[Brief explanation of the drawing]

Figure 1 shows the shape of ribbon-like carbon fibers in which the carbon mesh surface is stacked almost perpendicular to the fiber growth direction, and Figure 2 shows the ribbon-like carbon fibers in which the carbon mesh surface is stacked almost parallel to the fiber growth direction. Fig. 3 is a schematic diagram of the apparatus used in the example. 1: Reaction tube 2: Electric furnace

Claims (1)

[Claims] (1) A method for producing highly oriented fibrous carbon characterized by heat-treating a mixed raw material gas of carbon monoxide and hydrogen in the presence of cementite (Fe_3C)