Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2002-08-30
2003-08-05
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S210000, C423S245300, C423S447200, C423S447700, C588S253000
Reexamination Certificate
active
06602486
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for separating a reaction exhaust gas from production of carbon fiber and an apparatus used for separation of the gas, which exhaust gas is generated in a reaction furnace during production of carbon fiber, more particularly vapor-grown carbon fiber formed by thermal decomposition of an organic compound in a reducing atmosphere containing hydrogen; to a method for treating exhaust gasses and an incinerator used for treatment of the gasses, which gasses include the reaction exhaust gas and/or a thermal treatment exhaust gas generated during thermal treatment, including firing and graphitization, performed in a post-process; and to a method for producing the carbon fiber.
BACKGROUND OF THE INVENTION
Carbon fiber is produced from a variety of raw materials, and fine carbon fiber is produced through a method in which an organic compound such as methane, ethylene, benzene, or toluene is thermally decomposed at 800-1,300° C. in a thermal-decomposition furnace containing a reducing gas such as hydrogen or carbon monoxide, by use of a transition metal such as iron serving as a catalyst; i.e., a seed.
Specific examples of methods for producing carbon fiber include:
(1) a method for producing carbon fiber in which super-fine powder of a transition metal is distributed on a substrate in a thermal-decomposition furnace and used as seeds (Japanese Patent Application Laid-Open (kokai) No. 103528/1977);
(2) a method for producing carbon fiber in which a transition metal compound such as ferrocene is vaporized and introduced into a thermal-decomposition furnace to thereby form super-fine powder of a transition metal, and the powder is used as seeds (Japanese Patent Application Laid-Open (kokai) No. 54998/1985);
(3) a method for producing carbon fiber in which a transition metal such as iron is directly vaporized in a thermal-decomposition furnace to thereby form super-fine powder, and the powder is used as seeds (Japanese Patent Application Laid-Open (kokai) No. 29 1497/1986); and
(4) a method for producing carbon fiber in which a transition metal compound such as ferrocene is diffused or dissolved in an organic compound serving as a raw material, and the resultant mixture is introduced into a thermal-decomposition furnace to thereby form super-fine powder of a transition metal, and the powder is used as seeds (Japanese Patent Application Laid-Open (kokai) No. 180615/1983).
Japanese Patent No. 2778434 discloses a method for producing carbon fiber, in which an organic compound containing a transition metal such as iron, serving as a catalyst, is dissolved in a raw material liquid such as benzene, and the resultant solution is sprayed on the inner wall of a reaction furnace heated at 800-1,300° C., to thereby thermally decompose the material. Specifically, a transition metal compound such as ferrocene, serving as a catalyst, is dissolved in a liquid organic compound such as benzene, and the resultant solution is sprayed on the inner wall of a reaction tube, serving as a thermal-decomposition furnace, by use of hydrogen serving as a carrier gas, to thereby form seeds and thermally decompose the organic compound. As a result, crude carbon fiber of fine fibrous shape is produced. (Hereinafter the above process will be referred to as “the first process.”)
The thus-produced carbon fiber or the reaction furnace contains flammable gases including a carrier gas such as hydrogen, and hydrocarbon generated in a side reaction (hereinafter the flammable gases will be collectively referred to as “reaction exhaust gas”), and thus the gas must be separated. A reaction exhaust gas which is separated from carbon fiber in a reaction furnace is collected with relative ease, but a reaction exhaust gas contained in carbon fiber, or in other words, captured between filaments of the carbon fiber, is difficult to separate.
Conventionally, a reaction exhaust gas is separated from carbon fiber containing the reaction exhaust gas by means of the following methods: (1) a method in which the temperature of a thermal-decomposition furnace is lowered after completion of reaction, and the inside of the furnace is substituted by nitrogen gas, to thereby separate the reaction exhaust gas; and (2) a method in which a recovery can is provided in a lower portion of a thermal-decomposition furnace, and carbon fiber containing a reaction exhaust gas is recovered in the can and the inside of the can is substituted by nitrogen gas, to thereby separate the exhaust gas.
However, when carbon fiber is industrially produced, in the above method (1), reaction or recovery is carried out batchwise, which is disadvantageous in terms of efficiency. In addition, the temperature of a thermal-decomposition furnace must be lowered, which is unsatisfactory in consideration of energy efficiency.
In the above method (2), a large recovery tube is required, due to low bulk density of carbon fiber, which results in high cost.
In the methods (1) and (2), the produced carbon fiber has a very low bulk density of 0.001-0.005 g/cm
3
as measured immediately after production, which means a large volume of space between fibers. Thus, gas held in such space cannot be completely removed from the carbon fiber, and may directly accompany the fiber product.
In addition, the carbon fiber is detrimentally difficult to handle due to its low bulk density.
A recovered reaction exhaust gas is flammable and explosive, since the gas predominantly contains hydrogen. Therefore, conventionally, the gas is diluted in a blower in order to reduce the concentration of hydrogen below the range causing explosion, and then released in the air.
The crude carbon fiber produced in the reaction tube in the first process is usually scraped off and collected. The collected carbon fiber contains non-reacted organic substances, non-fibrous carbides, and tar, and therefore, in the next process the carbon fiber is thermally treated in a non-oxidative atmosphere. For example, the carbon fiber is subjected to thermal treatment such as firing and graphitization in a closed furnace as disclosed in Japanese Patent Application Laid-Open (kokai) No. 60444/1996, in a non-oxidative atmosphere of nitrogen, helium, or argon at a temperature which varies depending on required properties of a final product. (Hereinafter the above process will be referred to as “the second process.”)
An exhaust gas generated in the second process predominantly contains inert gasses such as argon and nitrogen. In addition, the exhaust gas contains naphthalene, anthracene, and high-molecular weight substances such as tar, and thus the gas is difficult to combust. (Hereinafter the gas will be referred to as “thermal treatment exhaust gas.”)
Since the thermal treatment exhaust gas is difficult to combust, there was no other way than releasing it as is.
The present invention contemplates provision of a method and apparatus for continuously separating a reaction exhaust gas from carbon fiber with ease and in a safe manner, which exhaust gas is generated in the first process during production of carbon fiber through the above-described vapor-growth method, as well as a method and apparatus for combusting and air-releasing exhaust gasses at low cost, which gasses include the flammable reaction exhaust gas and a thermal treatment exhaust gas which is generated during thermal treatment in the second process and is difficult to combust.
The present invention also contemplates provision of a method for producing carbon fiber, including the above methods and apparatus.
Particularly, exposure of an operator to an organic compound such as benzene is regulated by the Law on Industrial Safety and Hygiene. In addition, such an organic compound is poisonous, and thus must be prevented from being released in the air. Meanwhile, hydrogen, methane, and ethylene are flammable substances, and leakage thereof may cause explosion.
Tar is difficult to collect, because of its high viscosity. A method for condensing tar by use of activated carbon or for causing tar to be adsorbed by acti
Matsumoto Nobuhiro
Nishimura Kunio
Sakamoto Yoshihisa
Showa Denko K.K.
Silverman Stanley S.
Vanoy Timothy C
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