JPH06184831A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To safely operate a graphitizing furnace by introducing cyanides such as cyanide or hydrogen cyanide, if produced in a graphitizing furnace using nitrogen gas, into an oxidizing atmosphere at 200-500 deg.C, decomposing and removing the cyanides. CONSTITUTION:A waste gas, produced in a graphitizing furnace and containing cyanides is introduced through a discharge conduit into a waste gas converter of an oxidizing atmosphere at 200-500 deg.C. Air is simultaneously introduced through a conduit into the waste gas converter. Thereby, the cyanides in the waste gas are then decomposed and removed by the waste gas converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for producing carbon fibers, and particularly to a preliminary carbonization treatment, in which the preliminary carbonized fibers are heated at a temperature of 1500 ° C. to 3000 ° C. under a nitrogen gas atmosphere. The present invention relates to a method for producing carbon fiber, which comprises decomposing and removing cyanogens such as cyanogen and hydrogen cyanide in exhaust gas generated during the graphitization treatment.

[0002]

2. Description of the Related Art For example, carbon fibers produced from carbonaceous pitch such as petroleum pitch and coal pitch are currently
(1) A carbonaceous pitch, which is an organic precursor suitable for carbon fibers, is prepared from petroleum pitch, coal pitch, etc., the pitch is heated and melted and spun by a spinning machine, and the obtained pitch fibers are converged. (2) The maximum temperature of the pitch fibers is 250 to 35 in an infusible furnace under an oxidizing atmosphere.
(3) The obtained infusible fiber is heated to 0 ° C. to make it infusible, and the maximum temperature is 40 in an inert gas atmosphere in a preliminary carbonization furnace.
Manufactured by heating to 0 to 1500 ° C. to pre-carbonize, and (4) further heating the pre-carbonized fiber to 3000 ° C. or less in an inert gas atmosphere in a graphitizing furnace to graphitize. There is.

Conventionally, in the above-mentioned steps of infusibilization, preliminary carbonization, and further graphitization, a method of continuously infusibilizing pitch fibers made into a fiber bundle under tension, continuously precarbonizing, and continuously graphitizing has been used. ing.

[0004]

By the way, the graphitization of the pre-carbonized fiber in the graphitization furnace is carried out by using argon gas as an inert gas to make the inside of the furnace an inert gas atmosphere. However, since argon gas is a rare gas, it is extremely expensive, and there is a big drawback that the production cost of carbon fiber increases not a little.

On the other hand, if nitrogen gas is used as the inert gas, the above problems can be solved, but during the graphitization treatment, it reacts with the graphite heating element used as the heating element of the furnace to produce toxic cyan ( A large amount of cyanides such as dicyan C ₂ N ₂ ) and hydrogen cyanide (HCN) is generated, and the exhaust gas containing a large amount of this cyanides is discharged to the outside of the furnace, so that the operation of the graphitization furnace is safe. There was a problem with.

The object of the present invention is to remove, even if cyan or cyanides such as hydrogen cyanide are generated in a graphitization furnace using nitrogen gas, the cyanides are introduced into an oxidizing atmosphere at 200 to 500 ° C. and decomposed and removed. By doing so, it is possible to provide a method for producing carbon fiber, which enables safe operation of the graphitization furnace.

[0007]

The above object can be achieved by the method for producing carbon fiber according to the present invention. In summary, the present invention relates to a method for producing a carbon fiber in which a fiber bundle of an organic precursor is infusibilized, pre-carbonized, and the pre-carbonized fiber is graphitized in a nitrogen gas atmosphere to obtain a carbon fiber. The method for producing carbon fiber is characterized in that the exhaust gas generated in the graphitization furnace is introduced into an oxidizing atmosphere at 200 to 500 ° C. to decompose and remove cyanides in the exhaust gas. In order to accelerate the decomposition and removal of cyanides, it is preferable to carry out through an oxidation catalyst in an oxidizing atmosphere. As the oxidation catalyst, for example, silica or alumina, or a carrier made of a mixture of silica and alumina, and Pt, P as an active ingredient are used.
d, Ir, Ru, Rh, Os, Cu, Ni, V, Co,
A catalyst supporting one or a mixture thereof selected from Fe, Mn, and Ag is used.

[0008]

EXAMPLES Next, the method for producing carbon fibers of the present invention will be described in more detail.

As the organic precursor, for example, a carbonaceous pitch prepared from petroleum pitch, coal pitch or the like is used, and this pitch is heated and melted and spun by a spinning machine, and the obtained pitch fibers are bundled. To make a pitch fiber bundle. After this, the pitch fiber bundle is passed through the infusibilizing furnace and the maximum temperature 2
It is made infusible by heating in an oxidizing gas atmosphere at 50 to 350 ° C. Next, the infusible fiber is fed to a preliminary carbonization furnace and heated to a maximum temperature of 400 to 1500 ° C. in an inert gas atmosphere such as nitrogen or argon to be precarbonized.

Next, the pre-carbonized fiber obtained as described above is introduced into a graphitizing furnace in a nitrogen gas atmosphere. The maximum temperature in the graphitization furnace is 15 due to the graphite heating element.
The pre-carbonized fiber, which is maintained at a predetermined temperature of 00 to 3000 ° C. and thus introduced into the graphitization furnace, is heated and graphitized while passing through the graphitization furnace, and carbon fiber (graphite fiber) It is said that

As described above, in the graphitization furnace using nitrogen gas as the inert gas, the nitrogen in the furnace reacts with the carbon of the graphite heating element and the hydrocarbons and hydrogens emitted from the fibers to cause toxicity. Cyan (dicyan C ₂ N ₂ ) and hydrogen cyanide (HC
N) and other cyanides are produced. Since these reactions reach equilibrium in a very short time, when the supply of nitrogen gas to the heating element is increased, a large amount of them are generated.

Therefore, according to the present invention, an exhaust pipe for connecting the exhaust gas of cyanides generated in the graphitization furnace to the outside is connected. This discharge conduit contains 200-500
An exhaust gas converter in an oxidizing atmosphere at ℃ is connected. Therefore, the exhaust gas from the graphitization furnace is discharged to the outside, that is, to the atmosphere through the exhaust gas converter.

The exhaust gas converter is preferably filled with an oxidation catalyst, and the filled catalyst is a carrier made of silica or alumina, or a mixture of silica and alumina, and Pt, Pd, Ir, Ru, Rh, Os as an active ingredient. , Cu, N
It is a catalyst supporting one or a mixture of i, V, Co, Fe, Mn, and Ag. The amount of the active ingredient supported is 0.
It is 5 g or more, preferably 1.0 to 3 g.

The catalyst shape may be pellet type (granular type), monolith type (integral type or honeycomb type), or the like.

In order to effectively carry out the present invention, the reaction temperature in the exhaust gas converter is 200 to 500 ° C., preferably 300 to 400 ° C., and the ratio of the volume of gas flowing per hour to the catalyst volume, that is, Space velocity is 10
50,000 Hr ^-1 or less, preferably 50,000 Hr
^-1 or less.

Further, if the exhaust gas is deficient in oxygen, good oxidation performance cannot be obtained. Therefore, the exhaust gas converter is supplied with air which is approximately 10 times the exhaust gas capacity from the graphitization furnace fed to the exhaust gas converter. It is preferably introduced via a conduit.

With the above construction, cyan (dicyan C ₂ N ₂ ) and hydrogen cyanide (HCN) generated in the graphitization furnace are generated.
The cyanides are converted into CO ₂ , N ₂ , H ₂ O, etc. by the oxidizing action of the exhaust gas converter, become harmless, and are discharged to the outside.

In the above description, the production of pitch-based carbon fibers was described as an example. However, the present invention is not limited to pitch, but carbon fibers are also started from organic precursors such as polyacrylonitrile and rayon, which are organic fibers. It can also be applied to the case of manufacturing.

Next, the present invention will be described in more detail by way of examples.

Example 1 Using catalytic cracking tar as a raw material, 5 pitches of carbon fiber pitch consisting of 98% of an optically anisotropic phase obtained by thermal decomposition polycondensation were obtained.
The melt was spun through a melt spinning machine (nozzle hole: diameter 0.3 mm) having a spinneret with 00 holes.

The 500 spun filaments were substantially bundled by an air sucker and led to an oil ring roller, and a focusing oil agent was supplied at a ratio of about 0.1% by weight to the yarn,
A pitch fiber yarn consisting of 500 filaments was formed. As the oil agent, methylphenylpolysiloxanexane having a viscosity of 13 cst at 25 ° C. was used.

The above pitch fiber was wound on a bobbin rotating at a high speed provided under the nozzle and spun at a winding speed of about 500 m / min for 10 minutes.

Next, the above-mentioned 6 bobbins wound with the pitch fiber bundle are unwound, and they are combined while applying a heat-resistant oil agent using an oil ring roller to form a pitch fiber bundle of 3000 filaments. , Wound on another bobbin.

Methylphenylpolysiloxane (35 mol% of phenyl groups) of 30 cst at 25 ° C. was used as an oil agent at the time of forming yarn. The applied amount was 0.5% based on the yarn.

While releasing the bobbin-wound pitch fiber bundle thus obtained from the bobbin, the furnace inlet temperature is 190 ° C. and the maximum temperature is 300 ° C. in an oxygen-rich atmosphere of oxygen / nitrogen = 60/40 as an oxidizing gas atmosphere. The pitch fiber was made infusible by continuously feeding it linearly to the infusibilizing furnace having a temperature gradient of.

The infusibilization time was 18 minutes. When infusibilized, the pitch fiber was tensioned at 0.007 g per filament.

The infusibilized fiber obtained by infusibilization was continuously introduced into a pre-carbonization furnace and pre-carbonized at a maximum temperature of 1000.degree. The pre-carbonization furnace is 400, 500, 60 from the inlet.
It was heated and held in a mode in which the temperature was raised stepwise to 0, 700, and 1000 ° C., and nitrogen gas was supplied to maintain the inside of the furnace in a nitrogen gas atmosphere. The time required for pre-carbonization was 7 minutes.

The pre-carbonized fiber obtained by the above-mentioned pre-carbonization was then continuously passed through a graphitizing furnace and graphitized in a nitrogen gas atmosphere. The temperature of the graphitization furnace is 25
At 00 ° C., the treatment time was 120 seconds. When graphitized, 1
A tension of 0.1 g was applied per filament.

Nitrogen gas was supplied into the graphitization furnace from a gas supply port at a supply rate of 9.5 m ³ / hr, and was discharged from an exhaust conduit at an emission rate of 5 m ³ / hr to an exhaust gas converter. The concentration of hydrogen cyanide (HCN) in the exhaust gas is 9
It was 1 ppm.

At the same time, air was supplied to the exhaust gas converter at a rate of 50 m ³ / hr, which corresponds to 10 times the amount of exhaust gas, via a conduit.

In this example, the catalyst used silica as a carrier, and Pt as an active component was loaded at a ratio of 1.0 g per 1 liter of the carrier.

The amount of catalyst in the exhaust gas converter is 2.
The reaction temperature was 320 ° C., and the space velocity was 20,000 Hr ⁻¹ . The thickness of the catalyst layer is 6c
m, the catalyst shape was pellet type.

The concentration of hydrogen cyanide in the clean exhaust gas discharged from the exhaust gas converter into the external atmosphere is 0 pp.
It was m.

[0034]

As described above, according to the manufacturing method of the present invention, even if cyan or cyanides such as hydrogen cyanide are generated in the graphitization furnace using nitrogen gas, the cyanides are heated to 200 to 500 ° C. Since it is configured to be introduced into an oxidizing atmosphere and decomposed and removed, the graphitization treatment can be safely performed.

Claims (1)

[Claims] 1. A method for producing a carbon fiber, wherein a fiber bundle of an organic precursor is infusibilized, pre-carbonized, and the pre-carbonized fiber is graphitized in a nitrogen gas atmosphere to obtain a carbon fiber. Exhaust gas generated in graphitization furnace is 200 to 5
A method for producing carbon fiber, which comprises leading to an oxidizing atmosphere at 00 ° C. to decompose and remove cyanides in the exhaust gas.