JPS61119713A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain a carbon fiber with high generation density, in which yield, by reacting a hydrocarbon (and a carrier medium) in the presence of a catalyst under heating, treating the reaction product with an inert gas or a mixture of inert gas and active gas, and then reacting under heating. CONSTITUTION:A hydrocarbon such as methane, benzene, naphthalene, etc. or a mixture of the hydrocarbon and a carrier medium is introduced into a reaction system, and reacted at 650-950 deg.C for >=0.5min in the presence of a metal (compound) having catalytic activity, e.g. zinc, etc., to form a fiber. The produced fiber is treated with an inert gas such as nitrogen gas or with a mixture of the inert gas and an active gas such as hydrogen, steam, etc., at 1,000-1,300 deg.C. The treated fiber is made to react at 1,000-1,300 deg.C to obtain the objective fiber. The above metal (compound) is preferably a transition metal (compound).

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for producing carbon fiber, and more specifically to a method for producing carbon fiber with high efficiency by a gas phase method using hydrocarbons as raw materials. be.

Carbon fiber has excellent properties such as high strength and high modulus of elasticity.
It is a material that has been in the spotlight in recent years as a variety of composite materials.

Conventionally, carbon fibers have been mainly produced by carbonizing organic fibers, but carbon fibers produced by thermal decomposition and catalytic reactions of hydrocarbons are also known. The latter type of vapor-grown carbon fiber has superior crystallinity and orientation compared to the former type of carbon fiber, so it is expected to be used in a variety of fields as a composite material that has both high strength and high modulus. There is.

(Prior art) Various methods have been proposed for producing carbon fibers using a vapor phase method, but generally a fiber-forming base is used, in which ultrafine particles of transition metals such as iron and nickel or their alloys are dispersed. After placing the material in the reaction tube of an electric furnace and creating an inert atmosphere,
A mixed gas of hydrocarbons and hydrogen is passed into the furnace by raising v to a predetermined temperature, and carbon fibers are produced on the base material by thermal decomposition and catalytic reaction.

(Problems to be solved by the invention) However, with this method, the density of fiber generation is not sufficient, the reproducibility of fiber generation is very poor, and there are often cases where almost no fiber is generated, and it is still difficult to produce industrially. The current situation is that we have not yet reached this stage. Ultrafine metal particles commonly used as catalysts form secondary particles in which a large number of primary particles are connected. In the production of phase-grown carbon fiber, agglomerated particles may be produced during the heating process,
Currently, the amount of carbon fiber produced is extremely small relative to the amount of catalyst present due to sintering. Particularly at temperatures of 1,000 to 1,300° C., where the growth rate of fibers is high, fine particulate metal is easily sintered, which significantly inhibits the fiber density (the number of fibers generated per unit area of profit).

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a method for producing carbon fibers with high generation density and good yield by a gas phase method.

The present inventors conducted various studies on a carbon fiber manufacturing method in which a hydrocarbon-containing gas having carbon-depositing ability is passed through a reactor of an electric furnace, and the gas is thermally decomposed and catalytically reacted. The present invention was achieved by discovering that temperature and gas treatment method are important factors.

That is, the present invention provides hydrocarbons or hydrocarbons and
A method for producing carbon fibers in which a transport medium (e.g., carrier gas) is introduced into a reactor and hydrocarbons are carbonized in the presence of a metal or metal compound that acts as a catalyst. A first step in which hydrocarbons are reacted, then a second step in which treatment is performed with an inert gas alone or a mixed gas of an inert gas and an active gas at a heating temperature of 1000 to 1300°C, and a further heating temperature of 1000 to 1300°C.
It is characterized by comprising a third step of reacting hydrocarbons at 00°C.

In the present invention, if the temperature in the first step is less than 650°C, I
Almost no J, li fibers were observed, and at 950°C
If it exceeds this limit, agglomeration of the metal fine particles will progress and a large number of micron-sized particles will be produced, and effective fibers will not be produced. By setting the heating temperature to 650 to 950°C, fibers are generated at a high density, but the growth rate of fibers only in this temperature range is extremely slow, and the diameter of the generated fibers is 0.01 to 0.1μ, and the length is Since the aspect ratio is several microns to several tens of microns, and the aspect ratio is several hundred to several thousand at most, it cannot be used practically as, for example, reinforcing fibers.

However, the present inventors surprisingly found that after reacting the hydrocarbons in the first step, the heating temperature was 1000 to 1300.
We have discovered that by contacting 'C with an inert gas alone or a mixture of an inert gas and an active gas, fibers with an extremely fast growth rate can be produced without the need to supply hydrocarbons in the second step. . Furthermore, they discovered that by reacting hydrocarbons at a heating temperature of 1,000 to 1,300°C in the third step, the above-mentioned fibers can maintain a high generation density and grow at a high growth rate, producing carbon fibers with good yield. , the present invention has been achieved.

The hydrocarbons (hereinafter sometimes simply referred to as hydrocarbons) used in the present invention are not particularly limited as long as they can be used for manufacturing carbon fibers, and include, for example, aliphatic hydrocarbons (such as methane, ethane, propane, (ethylene, propylene, acetylene, etc.), aromatic hydrocarbons (such as benzene,
toluene, xylene, etc.), polycyclic aromatic hydrocarbons (e.g. naphthalene, anthracene, phenanthrene, etc.)
, alicyclic hydrocarbons (for example, cyclohexane, cyclopentadiene, etc.), and other raw materials mainly composed of hydrocarbons can be used.

An active gas, an inert gas, and a carrier medium can be added to the hydrocarbon to be reacted or adjusted as necessary.

Active gases include hydrogen, water vapor, ammonia, hydrogen chloride, chlorine, oxygen, -carbon oxide, -nitrogen oxide, sulfur, and inert gases include nitrogen, helium, neon, argon, etc., and as a carrier gas. Hydrogen, argon, nitrogen, etc. are preferably used.

In the present invention, the metal or metal compound used as a catalyst is preferably a transition metal or a transition metal compound. Transition metals include atomic numbers ranging from Sc with atomic number 21 to Zn with 30, 39
From Y to 48 Cd, from 57 La to 80 Hg
up to 89 Ac or higher elements. Transition metal compounds include inorganic compounds such as sulfates, nitrates, acetates, formates, chlorides, sulfides, hydroxides, oxides, carbides, nitrides, and silicides, as well as ferrocene, pentacarbonyl iron, etc. Examples include organometallic compounds.

A method for making metals or metal compounds present in the reaction system is to uniformly dissolve or disperse them in water and/or an organic solvent, hold or support them on a fiber-producing base material, and then place the mixture in a reactor. Highly volatile substances such as organometallic compounds, chlorides, etc. may be directly fed into the reactor as they are or in gaseous form, or the organometallic compounds, chlorides, etc. may be soluble in hydrocarbons. If the metal is dispersible in the hydrocarbon, the liquid hydrocarbon containing these may be directly blown into the reactor through a pipe or the like. The base materials for fiber production are generally pipes made of alumina, mullite, quartz, carbon, graphitic silicon carbide, etc.
Boards, fibers, granules, etc. are used. In addition, the materials of the reactor, gas introduction pipe, etc. should be adjusted to a fiber growth temperature of 1000 to 1.
Any material can be used as long as it can withstand a temperature range of 300° C. For example, ceramics such as alumina and mullite are used. Note that both the metal and metal compound and the hydrocarbon may be blown separately and mixed within the reactor.

These methods are not limited in any way and can be arbitrarily set depending on the desired fiber form, but when spraying the metal or metal compound on the fiber production substrate, it is necessary to From the viewpoint of generation density, it is 0.1 to 100 m-mo7 per unit area of the base material for fiber production! /% is preferable,
1-10 m-m.

l/bo is more preferable. If the dispersion density is too high, the metal fine particles will overlap more often, making it easier to form aggregated particles during the temperature rising process. In general, vapor-grown carbon fiber is one in which one fiber is produced and grown in one ultrafine metal particle.
When ultrafine metal particles are present in a base material for fiber production, it is preferable to disperse the fine particles in an isolated state on the base material (Japanese Patent Application No. 82815/1982).

In methods in which the metal or metal compound is fed directly into the reactor, continuous production of fibers is possible using a fluidized bed process.

In the present invention, when a mixed gas of hydrocarbon and carrier gas is used in the first step of reacting at a heating temperature of 650 to 950°C, the concentration of hydrocarbon in the gas is 0.1 to 950°C.
10% by volume is preferred, and 0.5-5% by volume is more preferred. The reaction time in the first step is preferably 0.5 minutes or more, and when the reaction time is 0.5 minutes or more, the treatment time is increased if the hydrocarbon concentration is low, and the treatment time is increased if the hydrocarbon concentration is high. Keep it short. Preferably, for example, when the concentration of hydrocarbons is 0.5 to 3% by volume, the treatment time is 3 to 3%.
By setting the time to 0 minutes, the effects of the present invention can be significantly exhibited. If the amount of hydrocarbon supplied is insufficient, fiber production will be insufficient, and if hydrocarbon is supplied in excess, fewer fibers will grow in the second step.

If a reduction treatment of the metal compound is required to raise the temperature up to the first step or to maintain the catalytic activity up to the first step, it is preferable that the carrier gas is hydrogen gas alone or mostly hydrogen gas.

In the second step of the present invention, the heating temperature is 1000 to 130
By treating with an inert gas alone or a mixed gas of an inert gas and an active gas at 0° C., in the first step, fibers with a length of at most about 100 μm grow into fibers with a length of several dragons to several marks. Although it is not clear why fibers grow even without a new supply of hydrocarbons, it is possible that excessive carbon or intermediates or unreacted hydrocarbons precipitated on ultrafine metal particles are a catalyst that has not lost its activity. It is assumed that the particles react and grow at a high growth rate.

The gas used in the second step is preferably an inert gas alone or mostly an inert gas in order to effectively grow the fibers. Although these can be appropriately set depending on the catalyst particles, hydrocarbon conditions, etc., the active gas concentration in the gas is generally preferably 30% by volume or less, particularly preferably 0% by volume or less. The room temperature equivalent flow velocity of the gas (the heating temperature in the reactor is 1000 to 1300°C, but the gas flow velocity value when this is converted to room temperature) is 30 to 300 cm/
minutes is preferred, and 50 to 200 cm/min is particularly preferred.

Further, the treatment time (J% residence time) is preferably 1 minute or more. In this case, when the gas flow rate is high, a short time treatment is preferred, and when the gas flow rate is low, a long time treatment is preferred.

In the present invention, after finishing the prescribed gas treatment in the second step after heating the first culm to 650 to 950°C,
The fibers are grown in the process at a heating temperature of 1000 to 1300°C, and in these steps, the fibers primarily grow in the longitudinal direction, and then grow in the thickness direction in stages. At that time, the length and thickness of the fibers can be adjusted arbitrarily by changing the heating temperature, hydrocarbon partial pressure, mixed gas flow rate, reaction time, etc. Usually, the heating temperature during length growth is 1,050 to 1,150°C, the hydrocarbon partial pressure to the carrier gas is 10% by volume or less, and the mixed gas flow rate is 1 to 1.
0 cm/min (calculated at room temperature in the reaction tube), reaction time 1
It is preferable to set it as 5 to 60 minutes. In addition, the heating temperature, hydrocarbon partial pressure, mixed gas flow rate, and reaction time during thickness growth should be set to appropriate conditions to achieve the desired fiber diameter, but it is necessary to efficiently grow the thickness. In order to achieve this, it is preferable to increase the heating temperature and increase the hydrocarbon partial pressure as the fiber diameter increases. Therefore, effective fiber growth can be achieved by increasing the heating and hydrocarbon partial pressure stepwise or continuously.

Next, an example of the apparatus and operation used in the vapor phase carbon fiber manufacturing method of the present invention will be explained with reference to FIG.

The illustrated apparatus has a reaction tube 2 installed in an electric furnace 1 equipped with a heating element, and partitioned in the length direction into a first furnace, a second furnace, and a third furnace.
A furnace is used, and the supply pipes 10.20.30 for gas 1, gas 2, and gas 3 are inserted from one end of the reaction tube 2, and the supply pipes 10.2
No. 0 and 30 tip nozzles (porous portions) are arranged in the first furnace, second furnace, and third furnace, respectively.

Temperature controllers (TIC) 14 and I5.16 are installed in the first furnace, second furnace, and third furnace, respectively. Supply pipes 10.20 and 30 are connected to evaporators 5.5A and 5B for raw materials (hydrocarbons) housed in thermostats 4.4A' and 4B via three-way cocks 3, respectively, and a bypass pipe 8.8A.
, 8B are connected, gas 1, gas 2 and gas 3
A predetermined amount of raw materials can be supplied to the reactor either alone or in combination with these gases. The fiber base material 7 connects the tungsten wire 17 and connects the speed adjustment motor 18.
It allows for intermittent or continuous movement.

In this apparatus, a fiber-producing base material 7 in which a metal or a metal compound is dispersed in advance is placed in a first furnace. Next, only the carrier gas 1 is introduced from the supply pipe 10 into the reaction tube 2 via the three-way cock 3 and the bypass pipe 8. The first furnace is 6
50-950℃, second furnace 1000-1150℃, third furnace
The furnace is set at 1150 to 1300° C., and the temperature is raised to the predetermined temperature while only carrier gas 1 is flowing. After the temperature is raised, the carrier gas is introduced into the evaporator 5 in the constant temperature bath 4 by turning the three-way cock 3, and the hydrocarbon 6 of a predetermined concentration is supplied together with the carrier gas for a predetermined time to generate fibers on the base material 7. . Next, the base material 7 is moved continuously or intermittently to the fiber growth zone (second furnace and third furnace). In the second furnace, the three-way cock 3A is operated to continuously or intermittently supply an inert gas alone or a mixed gas 2 with an active gas at a temperature of 1000 to 1150°C and a room temperature equivalent flow rate of 30 to 300.
cm/min for 3 minutes or more to cause the fibers formed on the base material 7 to grow mainly in the longitudinal direction. Next, in the third furnace, the three-way cock 3B is operated to supply hydrocarbons continuously or intermittently to grow the fibers in the thickness direction. In addition, in the second furnace, after the heat treatment with inert gas is completed, the three-way cock 3A may be operated to introduce hydrocarbons, and growth in the thickness direction may be started from the stage of the second furnace.

In FIG. 1, an embodiment is shown in which the fiber production base material 7 is pulled and moved by a tungsten wire 17 to produce vapor-grown carbon fiber in a semi-continuous or continuous manner. It is also possible to introduce the metal or metal compound together with the hydrocarbon into the reactor without using the material 7, and to produce the fibers continuously as a fluidized bed process.

(Effects of the Invention) According to the method of the present invention, vapor-grown carbon fibers having a high generation density, a long fiber length, and a desired thickness can be produced with a high yield, which is extremely advantageous industrially. . The obtained carbon fibers have excellent fiber physical properties and a high aspect ratio compared to conventional methods, and are useful as, for example, reinforcing fibers.

(Examples) Hereinafter, aspects of the present invention will be explained in detail using specific examples.

Example 1 After adsorbing oleate ions on the surface layer of iron powder (Fe) (manufactured by Shinku Yakini Co., Ltd.) with an average particle size of 100, it was uniformly dispersed in isooctane, and the dispersion was sprayed to form graphite. Fe was added to the concave part of the base material (a cylindrical material with an inner diameter of 50 mm and a length of 200 mm divided into two in the length direction to form a toy shape).
6■ was made to exist. The base material was placed in a mullite reaction tube (inner diameter 5
21111. (Length 1500mm)
After replacing the inside of the reaction tube with argon gas, hydrogen gas 100c
The temperature was raised to 800° C. while venting at a flow rate of c/min (room temperature equivalent flow rate: 4.7 Cm/min). After raising the temperature, 1.5% by volume of benzene was aerated for 10 minutes to form carbon fibers on the substrate (first step). The fibers produced at this time have a fiber diameter of 0.01
~0.05μ, length approximately 1-10μ. Thereafter, the supply of benzene was temporarily stopped, and the temperature was further raised to 1100°C. After raising the temperature, nitrogen gas was passed through at 1000 cc/min (room temperature conversion flow rate 47 marks/min) for 10 minutes (second step). Thereafter, 100 cc/min of a mixed gas of hydrogen and argon (H2/Ar-1/4) containing 3% by volume of benzene was aerated for 30 minutes to mainly grow the fiber length. The thickness of the fibers was grown by gradually raising the heating temperature from 1100°C to 1250°C and the benzene concentration from 3% by volume to 33% by volume over a further 150 minutes (3rd step).

After that, the gas in the reaction tube was replaced with argon and cooled.
The base material for fiber production was taken out of the furnace, the amount of produced carbon fibers, the fiber diameter, and the fiber length were measured, and the fiber generation density was calculated. The results are shown in Table 1.

Comparative Example 1 Carbon fibers were produced in the same manner as in Example 1 except that benzene was not aerated at 800°C. The results are shown in Table 1.

Example 2 The amount of benzene vented at 800°C was 0.25% by volume,
Carbon fibers were produced in the same manner as in Example 1 except that the ventilation time at this temperature was 180 minutes. The results are shown in Table 1.

Comparative Examples 2 to 3 The heating temperature in the first step was 600°C (Comparative Example 2) and 1
Carbon fibers were produced in the same manner as in Example 1 except that the temperature was 000°C (Comparative Example 3). The results are shown in Table 1.

Comparative Example 4 Carbon fibers were produced in the same manner as in Example 1, except that the second step of processing with nitrogen gas at 1000 cc/min at a heating temperature of 1100° C. was not performed. The results are shown in Table 1.

Example 3 Iron-Nisokel alloy powder (Fe-Ni) with an average particle size of 300
), (manufactured by Shinku Yakini Co., Ltd.), oleate ions are adsorbed on the surface layer, and then uniformly dispersed in hexane.
Fe-Ni1O■
was accommodated. Three sets of connected base materials were charged into a mullite reaction tube (inner diameter 52 mφ, length 2200+n),
As shown in FIG. 1, the base material was installed so as to be movable on the gas outlet side. After replacing the inside of the reaction tube with nitrogen gas, the first furnace is heated to 800°C and the second furnace is heated to 1100°C while passing 1QQcc/min of hydrogen gas as gas 1 into the gas supply pipe 10.
1 The third furnace is heated to 1250℃ (here, each furnace length is 400+I+1
). After raising the temperature, while moving the substrate at a speed of 0.5 cm/min to the gas outlet side, operate the three-way cock 3 when the leading substrate in the substrate advancing direction passes through the center of the first furnace,
2.0% by volume of benzene was bubbled through the evaporator 5 for 8 minutes.

Next, when the first substrate entered the second furnace, only nitrogen gas was passed through the supply pipe 10 at 100 Qcc/min for 2 minutes (after that, nitrogen gas was passed intermittently from the supply pipe 10 at 10 minute intervals).
00cc/min for 2 minutes). Next, a hydrogen/nitrogen mixed gas containing 5% by volume of benzene (H7/N 2 = 1 /
1) Fiber length growth was performed by aerating at 100 cc/min. Further, when the first base material entered the third furnace, 200 cc/min of nitrogen gas containing 18% by volume of benzene was passed through the supply pipe 30 to grow the thickness of the fiber. The second and third base materials were operated in the same manner as the first base material, and at the same time as the third base material exited the third furnace, benzene ventilation was stopped and cooled.

After cooling, the base material for fiber production was taken out, and the amount, fiber diameter, and fiber length of the produced carbon fibers were measured, and the fiber generation density was calculated. The results are shown in Table 1. The physical properties of the produced fibers are
The tensile strength was 42 T on / crA, and the tensile modulus was 4700 T on / c♂.

Comparative Example 5 Carbon fibers were produced in the same manner as in Example 2, except that benzene was not passed into the reaction tube of the first furnace.

The results are shown in Table 1. The physical properties of the produced fibers include a tensile strength of 17 T on /ca and a tensile modulus of 1900.
It was 7 on/-.

Comparative Example 6 Same as Example 2 except that benzene was not vented into the reaction tube of the first furnace and nitrogen gas treatment (intermittent aeration treatment for 2 minutes at 1000 cc/min) was not performed in the second furnace. carbon fiber was produced. The results are shown in Table 1. Physical properties of the produced fibers include tensile strength of 15 T on /c
1, and the tensile modulus was 1600 Ton/cl.

Margin below

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a carbon fiber manufacturing apparatus showing an embodiment of the present invention. 1... Electric furnace, 2... Reaction tube, 3... Three-way cock, 4.4A, 4B... Constant temperature chamber, 5.5A, 5B...
Hydrocarbon compound evaporator, 6.6A, 6B... Hydrocarbon compound, 7... Base material for fiber production, 8.8A, 8B.
...Bypass pipe, 10,20.30...Gas supply pipe. Agent Patent Attorney Takeshi Kawakita Long Procedural Amendment

Claims (4)

[Claims] (1) A carbon fiber production method in which hydrocarbons or hydrocarbons and a carrier medium are introduced into a reaction system and carbonized in the presence of a catalytic metal or metal compound, at a heating temperature of 650 to 950°C. A first step of reacting hydrocarbons, then a second step of treating with an inert gas alone or a mixed gas of an inert gas and an active gas at a heating temperature of 1000 to 1300°C, and a further heating temperature of 1000 to 1300°C.
A method for producing carbon fibers, comprising a third step of reacting hydrocarbons at °C. (2) Claim 1, wherein the metal or metal compound is a transition metal or a transition metal compound.
The method for manufacturing carbon fiber described in Section 1. (3) The concentration of hydrocarbons in the gas phase in the first step is 0.1 to 10% by volume, and the reaction time is 0.1% to 10% by volume.
Claim 1 characterized in that the duration is 5 minutes or more.
The method for manufacturing carbon fiber described in Section 1. (4) The active gas concentration in the gas phase in the second step is 3
0% by volume or less, and the room temperature equivalent flow rate of the gas is 30
300 cm/min and the processing time is 1 minute or more.