JPH01229818A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To readily control quality and efficiently obtain carbon fibers at a low cost by generating a plasma containing a transition metal using an electrode of the transition metal (compound), passing the resultant plasma through a reaction zone, simultaneously feeding a hydrocarbon and growing carbon into the fibers. CONSTITUTION:An electrode 3 consisting of a transition metal or a compound thereof is used to pass a DC current across the electrodes (anode and cathode) 4 and 3. A plasma gas 5, such as H2, is introduced into an arc plasma torch 2 to generate an arc plasma jet 10, which is then used to generate ultrafine particles of the transition metal from the cathode 3. The obtained plasma is subsequently made to flow to a reaction zone (vessel) 1 and a hydrocarbon is simultaneously fed from an introduction port 6 into the reaction zone 1, excited and decomposed to grow carbon into a fibrous form using the ultrafine particles of the transition metal as a growth point. The grown fibers are then collected in a carbon fiber collector 7 to afford the aimed carbon fibers 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing carbon fibers, and more particularly to a method for efficiently manufacturing carbon fibers by vapor phase growth using arc plasma.

[Prior Art] Conventionally, PAN-based and pitch-based carbon fibers have been commercially produced. However, the PAN system is expensive, and the pitch system has fatal drawbacks such as complicated processes and difficult quality control.

On the other hand, a vapor phase growth method has been proposed in recent years. Conventionally, vapor-grown carbon fibers are produced by placing a substrate made of porcelain such as alumina or graphite in an electric furnace, forming carbon growth nuclei, ultrafine particle catalysts such as iron or nickel on this, and then forming carbonization particles such as benzene on this. A method is known in which carbon fibers are grown on a substrate by introducing a mixed gas of hydrogen gas and hydrogen carrier gas and decomposing hydrocarbons at a temperature of 950 to 1300°C.

However, with this method, there are two issues: (1) the length is likely to be non-uniform due to subtle temperature irregularities on the substrate surface and the density of the surrounding fibers, and (2) the gas that serves as a carbon source is consumed by the reaction. As a result, the fiber diameter is considerably different between the part near the population of the reaction tube and the part near the outlet. ■Since the fiber is produced only on the surface of the substrate, the central part of the reaction tube does not participate in the reaction and the yield is poor. , (2) Since there are processes that must be carried out independently, such as dispersion of ultrafine particles onto a substrate, reduction, growth, and extraction of fibers, continuous production is impossible, and therefore there are problems such as poor productivity.

Therefore, a method for manufacturing carbon fiber was proposed in which a mixed gas of a carbon compound gas as a raw material, an inorganic or organic transition metal compound gas as a catalyst, and a carrier gas is reacted at high temperature (JP-A-60-54998.60- 224816 etc.)
.

[Problem to be solved by the invention] However, Japanese Patent Application Laid-Open No. 60-54998.6°-224
Methods such as 816 have problems such as line blockage and the inability to feed quantitatively.Furthermore, since the reaction vessel is also heated, by-products adhere to the vessel wall, reducing yield. Problems such as continuous operation were difficult. In addition, it is not easy to scale up, making it unsuitable for mass production, and requires an electric furnace for heating, resulting in high energy costs.

The present invention solves the above-mentioned conventional problems and provides a method that can produce carbon fibers extremely efficiently.

[Means for Solving the Problems] The method for producing carbon fiber of the present invention provides a method for producing carbon fibers using transition metals or if
The method is characterized by generating plasma containing a transition metal using an electrode made of a metal compound, flowing this plasma toward a reaction zone, and supplying hydrocarbons to the reaction zone to grow carbon in the form of fibers. do.

Conventionally, methods for producing carbon fiber using arc plasma have already been proposed (Japanese Patent Laid-Open Nos. 59-152298 and 1986-6).
O-231822). However, all of these methods use carbon electrodes, and a catalyst such as a transition metal compound is separately supplied in the form of a gas by heating.

For this reason, problems arise in that quantitative feeding is difficult and continuous production is difficult.

The method of the present invention solves these problems by using an electrode made of a transition metal or its compound and generating and injecting extra-transition ultrafine particles by an arc plasma jet in a carbon fiber manufacturing method using arc plasma. This is to solve the problem.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view illustrating the configuration of a carbon fiber manufacturing apparatus suitable for implementing the carbon fiber manufacturing method of the present invention.

In the apparatus shown in FIG. 1, reference numeral 1 denotes a reaction vessel (in this example, a reaction tube), and an arc plasma torch 2 for generating an arc plasma jet is installed at one end of the reaction vessel. The arc plasma torch 2 of this device is of a type that generates an arc plasma jet using a DC power source, and the cathode 3 is made of a transition metal or a compound thereof, and the anode 4 is an ordinary carbon electrode. Anode 4
Plasma gas is introduced from a gas inlet 5 formed in the .

An inlet 6 for introducing hydrocarbons as a raw material is provided near the arc plasma torch 2 of the reaction vessel 1, and a carbon fiber collector 7 is provided at the other end of the reaction vessel 1 (the side opposite to the arc plasma torch 2). is connected to the carbon fiber collector 7, and an exhaust gas extraction pipe 8 is connected to the carbon fiber collector 7. A cooling gas inlet 9 is provided between the hydrocarbon inlet 6 of the reaction vessel 1 and the connection portion with the carbon fiber collector 7 .

In the carbon fiber manufacturing apparatus configured as described above, a direct current is passed between the electrodes 3 and 4, and a plasma gas such as H2 or a mixed gas of H2 and a rare gas is introduced into the torch 2. arc plasma jet 10
As a result, ultrafine particles of transf3 metal or transition metal compound are generated and injected from the cathode 3 (zone A).

The ultrafine particles of the transition metal or transition metal compound are ejected into the reaction vessel 1, excite the hydrocarbon gas coming from the inlet 6, and decompose it. According to the arc plasma jet 10, reaction temperature conditions of approximately 950 to 1300°C can be easily obtained, and carbon iA! l fibers grow (zone B).

A cooling gas such as H2 or H2O is introduced from the inlet 9 as necessary to the rear of zone B, which is the carbon fiber production zone, to prevent the reverse reaction from proceeding (zone C).

The carbon fibers ii [i
30 is introduced into the carbon fiber collector 7. As this collection method, various conventionally known methods such as gravity sedimentation method and electric condensation method can be employed.

When H, O (water vapor) is used as the cooling gas, it can also be condensed and collected in the liquid phase. Note that the carbon fiber collector 7 also plays the role of cooling the generated carbon fibers.

FIG. 2 is a schematic cross-sectional view showing the configuration of another example of a carbon fiber manufacturing apparatus suitable for carrying out the present invention, and FIG.
It is a sectional view along line -III.

This manufacturing apparatus differs from the one shown in FIG. 1 in the configuration of one end side of the reaction vessel 11, the arc plasma jet generation zone A, and the carbon fiber generation zone B, but the structure of the collector side of the generated carbon J51 fibers is different from that shown in FIG. Since it is similar to the device shown in FIG. 1, illustration is omitted.

In the apparatus shown in FIGS. 2 and 3, an arc plasma torch 12 is connected to one end of a reaction vessel 11. This arc plasma torch 12 is also powered by a DC power source, and the cathode 13 is a normal carbon electrode, and the anodes 14a, 14b, 1
4c and 14d are composed of a transition metal or a transition metal compound.

A plasma gas inlet 15 is provided on one end surface of the arc plasma torch 12, and a hydrocarbon inlet 16 is provided in the vicinity of the arc plasma torch 12 in the reaction vessel 11. Furthermore, the introduction port 1 of the reaction vessel 11
A heater 20 is provided downstream of the heater 6 .

In the apparatus of this embodiment as well, when plasma gas is introduced from the inlet 15 and a current is supplied between the cathode 13 and the anodes 14a to 14d, an arc plasma jet is generated within the torch 2, causing the holes 8i14 Ultrafine particles of transition metals or transition metal compounds are generated and injected from a to 14d (zone A).

The ultrafine particles of the transition metal or transition metal compound are introduced into the inlet 1.
Hydrocarbons supplied from 6 are excited, and carbon fibers grow in the same way as in the apparatus shown in FIG. 1 (zone B). This growth zone B is heated from outside the reaction vessel by a heater 2° as required.

In this device, the cathode 13 may be a transition metal or a transition metal compound 'ti, and the anodes 14a to 14d may be carbon electrodes. In addition, the cathode 13 and the anodes 14a to 14
Both d and transition metal or transition metal compound electrodes may be used.

In this embodiment, four anodes are provided in order to increase the plasma jet generation efficiency, but the number of anodes is not limited to this.

Furthermore, although a heater 20 is attached to the reaction vessel 11, the heater 20 is not necessarily required, and is unnecessary when a high temperature sufficient for the reaction can be obtained by the arc plasma jet.

In the present invention, the raw material hydrocarbons include methane (natural gas may also be used), alkane compounds such as ethane, alkene compounds such as ethylene and butadiene, alkyne compounds such as acetylene, and aryl compounds such as benzene, toluene, and styrene. Hydrocarbon compounds, indene, naphthalene,
Examples include aromatic hydrocarbons having condensed rings such as phenanthrene, cycloparaffin compounds such as cyclopropane and cyclohexane, cycloolefin compounds such as cyclopentene and cyclohexene, and alicyclic hydrocarbon compounds having condensed rings such as steroids.

In addition, as the plasma gas, N2, N2 or N2
．． A mixed gas of N2 and a rare gas such as H″e%Ar can be used. When using a mixed gas, it is preferable that the N2 or N2 gas concentration is 60% or more.

In addition, the transition metals used for the electrode include scandium,
This refers to titanium, vanadium, chromium, manganese, iron, cobalt, nickel, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tantalum, tungsten, rhenium, iridium, and platinum. %Ni, Co.

Pt, Ag%Pd%Ti%Cr, etc. are easily formed into ultrafine particles, and Fe, Ni, and Co are particularly preferred.

Further, as the transition metal compound, an alloy of two or more transition metals, or Fe(No)4, FeCjZ
3, Fe (No)3cjZ, Fe (No)2, F
e (No)2I, FeF3, Fe (NOs)z,
FeBr3, Fe (HCOO)3, C27H, 2F
eN9012, Fe(SO4)3, Fe'(SC
N)s, Fe (No)3NH3, Co (NO2)C
A, N1 (No) Cf2, Pd (No) zcJ! 2,
Examples include inorganic transition metal compounds such as N i Cftz.

In the present invention, the setting conditions for the carbon fiber production zone (zone B) are normal pressure of 1 atm, temperature of 950 to 1300°C,
Preferably it is 1000-1100°C. If the temperature conditions are outside this range, carbon fibers will not be produced well. Such temperature conditions can be easily obtained using an arc plasma jet, but if the temperature does not rise sufficiently, external heating may be used as necessary.

Conditions such as plasma gas supply amount, arc current, voltage, etc. for generating an arc plasma jet are based on the type of transition metal or transition metal compound in the electrode, the type of raw material hydrocarbon to be subjected to the reaction, and other conditions. To be determined accordingly.

In normal cases, it is preferable to set various conditions within the following ranges.

Arc plasma torch internal pressure Normal pressure plasma gas supply speed: 10 cm/s ~ 100 m/s Arc current: 100 mA ~ 100 A Arc voltage = 1 ~ 200 V Normally, under these setting conditions, the particle size is 50 ~ 5
Ultrafine particles of transition metals or transition metal compounds are generated.

According to such a method of the present invention, the length usually ranges from 10 μm to
It is about 100 μm, and carbon fibers with a diameter of about 0.1 to 1 μm can be easily produced.

[Function] In the method of the present invention, carbon fibers are produced by generating and heating catalyst fine particles using an arc plasma jet.

That is, diatomic molecular gases such as N2 and N2 are used at high pressures (10
0 torr or more) and at low voltage (50 Vcm or less), it dissociates into a high-temperature plasma-like gas in the form of atoms or ions. For example, the temperature of an H2 plasma arc is as high as about 10,000"K, and the transition metal or transition metal compound of the electrode is melted by the arc. The dissociated atomic and ionic H2 in the arc is highly reactive. , is sufficiently activated, so molecular H2
A larger amount of N3 is dissolved in the molten transition metal or transition metal compound, but when the N3 in the molten transition metal or transition metal compound becomes supersaturated, it is released. At this time, by entraining the molten transition metal or transition metal compound, ultrafine particles of the transition metal or transition metal compound are formed. In particular, H
2 arc is the ultrafine particleization of metals, especially Fe%Ni,
It is effective for making ultrafine particles of noble metals such as Co, Pt, Ag, and Pd, as well as Ti and Cr.

The amount of transition metals or transition metal compounds generated varies depending on their type, melting point, H2 concentration, etc. Generally, H2? I
The higher the 4 degree (60 to ioo%), the higher the melting point of the transition metal or transition metal compound, the lower the amount. Further, the particle size of the generated fine particles is greatly influenced by arc atmospheric pressure, H2 concentration, plasma gas flow rate, arc current, voltage, type of transition metal or transition metal compound, etc. Therefore,
By appropriately controlling these parameters, it is possible to efficiently generate a desired amount of ultrafine particles of a transition metal or transition metal compound having a desired particle size.

According to the method of the present invention, (1) using an electrode made of a transition metal or a transition metal compound;
Ultrafine particles of transition metals or transition metal compounds can be generated directly from electrodes by arc discharge, and the particle size and amount generated can be adjusted as appropriate.
Catalyst feed problem can be solved and catalyst supply can be carried out.

(2) Using a plasma jet, a reaction temperature of 950 to 1300° C. can be easily obtained, eliminating the need for external heating or reducing the proportion of external heating. Therefore, energy efficiency can be improved, heating temperature can be lowered, and yield can be improved.

■ In plasma jet, radicals are easily generated and the reaction rate is high.

■ The catalyst fine particle density and radical density are large, the reaction zone can be locally concentrated, and the throughput is large.

■ Plasma gas can be used as a carrier gas, and catalyst particles can be reduced at the same time.

■ Due to the presence of catalyst fine particles, the production of carbon fibers outweighs the production of acetylene, suppressing the production of acetylene.

Effects such as these are achieved, and it becomes possible to produce uniform carbon ia fibers extremely efficiently and easily.

[Example code] Hereinafter, preferred manufacturing examples will be described.

Capacity 5 pieces 1 Carbon fibers were manufactured using the apparatus shown in Figure 1 under the following conditions.

Arc plasma torch (DC) Pole: Graphite cathode: Carbon steel rod (cylindrical) Plasma gas: Hydrogen Plasma gas supply speed: 1 m/s Current: 4 A Voltage: 10 V Pressure Crab normal pressure carbon fiber production zone raw material carbonization Hydrogen: Benzene supply amount: 1 mu/min Temperature: 950-1100°C Pressure Crab is normal pressure cooling condition Cooling gas dihydrogen (25°C) Cooling gas supply fi: 10 It/min As a result, diameter 0.1 ~1μm, length 100~toooo
It was possible to obtain carbon ia fibers of μm size in a high yield (yield: 53%).

[Effects of the Invention] As described above, the method for producing carbon fiber of the present invention utilizes arc discharge to generate catalyst fine particles, heat them, etc., so that ■ The problems of conventional catalyst feeding are solved. , it is possible to generate and supply a desired amount of catalyst fine particles having a desired particle size.

■ Low energy consumption and low manufacturing costs.

■ The inner wall surface of the reaction vessel is at a low temperature, and its material can be made of an inexpensive material.

(2) It is difficult for by-products to adhere to the inner surface of the reaction vessel, making it suitable for continuous operation and operation of large reaction vessels.

(2) The quality of the carbon 1a fibers obtained can be easily controlled by adjusting the arc plasma jet generation conditions.

■ Mass production and scale-up are easy.

■ Due to the high activation efficiency and thermal efficiency of the catalyst, the yield, reaction rate, and energy efficiency are extremely high.

Excellent effects such as these can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of a device suitable for carrying out the present invention, FIG. 2 is a schematic sectional view showing another example of a device suitable for carrying out the present invention, and FIG. Figure 2 III-II
It is a sectional view along I line. . 1.10... Reaction vessel, 2.12... Arc plasma torch, 3.13...
Cathode, 4.14a, 14b, 14c, 14d---Anode, 7.
...Carbon fiber collector. Agent Patent Attorney Tsuyoshi Shigeno Figure 2 Figure 3

Claims (1)

[Claims] (1) Using an electrode made of a transition metal or a transition metal compound, generate plasma containing a transition metal, flow this plasma toward a reaction zone, and supply hydrocarbons to the reaction zone to turn carbon into fibers. A method for producing carbon fiber, which comprises growing carbon fiber.