Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
1999-04-16
2001-05-08
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C502S418000
Reexamination Certificate
active
06228343
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing modified optically isotropic pitch exhibiting superior stabilization characteristics and activated carbon fibers and anode materials for secondary batteries using said modified optically isotropic pitch.
BACKGROUND OF THE INVENTION
Heretofore, optical isotropic pitch has been prepared from coal pitch or petroleum pitch. Japanese Laid Open Patent Applications 1994-256767 and 1995-18058 teach methods for obtaining superior optical isotropic pitch having excellent stabilization characteristics by particularization of low pressure distillation of and blowing gas into raw materials, such as coal tars. However, the pitch fibers obtained by spinning the optical isotropic pitch obtained from these methods require some protection where high temperatures were applied over long periods in order to stabilize the fibers, and the methods are therefore not entirely satisfactory.
In addition, U.S. Pat. No. 4,789,455 discloses that it is possible to prepare a pitch that may be suitably applied as a high performance carbon material for carbon fibers or other applications by polymerizing conjugated polycyclic hydrocarbons or materials containing them in the presence of an HF/BF, catalyst. When the isotropic pitch thus obtained is used for the manufacture of carbon fibers and the like, melt adhesion of the fibers occurs easily during spinning because of a low softening point, and it takes an extremely long time to stabilize the fibers. Where the softening point of the pitch is raised to decrease the time required to stabilize the fibers, then, as taught by U.S. Pat. No. 4,891,126, the pitch obtained has anisotropic properties and fundamentally has ceased to be an isotropic pitch.
The fact that the time required for stabilization when carbon fibers are prepared from either of the aforementioned coal type or petroleum type pitches is so long is an important problem from the standpoint of produceability. In particular, pitch fibers obtained using optically isotropic pitch as raw material require a long period of time for stabilization compared with pitch fibers obtained using optically anisotropic pitch as the raw material, and the stabilization process is difficult.
With respect to various carbon material applications, such as for use as carbon fibers, activated carbon fibers and anode materials for secondary batteries using a non-aqueous solvent, an optically isotropic pitch that can easily be stabilized as pitch fiber or pitch granules ground to various particle sizes is desired.
Accordingly, it is an object of the present invention to provide a method for making optical isotropic pitch with superior stabilization characteristics for various carbon material applications. It is a further object of the invention to provide a method for producing activated carbon fibers and amorphous type secondary battery material having superior characteristics.
SUMMARY OF THE INVENTION
The present invention is predicated on the discovery that an optically isotropic pitch with clearly superior stabilization characteristics can be obtained by polymerizing conjugated polycyclic hydrocarbons substituted with one or more low molecular weight alkyl groups, or a material containing such a conjugated polycyclic hydrocarbon, in the presence of an HF/BF
3
catalyst and treating the resulting polymerized material at elevated temperature with a flow of oxidizing gas.
In one embodiment, the present invention thus provides a method of preparing modified optically isotropic pitch characterized by the polymerization of a conjugated polycyclic hydrocarbon containing at least one low molecular weight alkyl group, or materials containing such conjugated polycyclic hydrocarbons, using an HF/BF
3
catalyst and, at elevated temperatures, passing an oxidizing gas through the pitch thus obtained. In another embodiment, the invention provides a method of preparing activated carbon fibers characterized by melt spinning the modified optically isotropic pitch obtained in accordance with the invention, and after stabilization of said modified pitch, conducting activation treatment. In yet another embodiment, the invention provides a method of preparing anode material for secondary batteries using a non-aqueous solvent characterized by conducting stabilization treatment on the said modified pitch and then calcining.
Using the modified optically isotropic pitch obtained by the method of the present invention, it has been found that activated carbons having high absorption capacity can be obtained. The activated carbon can be applied effectively to gas separation or water treatment and formed for use in secondary battery anodes in which minimization of capacity loss in the initial cycle together with large discharge capacity as compared with materials used to lithium secondary batteries heretofore is achieved.
The flow diagram for preparing the modified optically isotropic pitch, the activated carbon fiber and the anode material for a secondary battery that uses a non-aqueous solvent is as follows:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A conjugated polycyclic hydrocarbon containing at least one low molecular weight alkyl group is used as the raw material in accordance with the present invention. Conjugated polycyclic hydrocarbons suitable for use in the present invention include: derivatives of conjugated polycyclic hydrocarbons such as naphthalene, anthracene, pyrene, coronene and the like, which contain at least one low molecular weight alkyl group; derivatives of heteropolycyclic hydrocarbons such as benzofuran, quinoline, thianaphthalene, and the like, containing at least one low molecular weight alkyl group; mixtures of the heteropolycyclic hydrocarbons with the aforementioned derivatives of polycyclic hydrocarbons; or coal tar distillates, petroleum distillates, residues from petroleum processing and the like. In the present invention, low molecular weight alkyl groups refers to alkyl groups attached to the aforementioned conjugated polycyclic hydrocarbons that have between 1 and 10 carbon atoms and particularly those having between 1 and 3 carbon atoms. In particular, the methyl group is preferred as the low molecular weight alkyl group and naphthalene derivatives including methyl naphthalene or dimethyl naphthalene as well as mixtures of such compounds with the methyl naphthalene fraction of coal tar and ethylene bottom oil and the like are particularly preferred.
Isotropic pitch is prepared by polymerizing the conjugated polycyclic hydrocarbon in the presence of a suitable polymerization catalyst. The preferred catalyst used in the polymerization reaction of the conjugated polycyclic hydrocarbons containing at least one low molecular weight alkyl group is hydrofluoric acid/boron trifluoride. The amount of hydrofluoric acid used with respect to one mole of the conjugated polycyclic hydrocarbon or its equivalent is on the order of between about 0.1 to about 10 moles pet mole of conjugated polycyclic hydrocarbon or its equivalent and the amount of boron trifluoride is between about 0.05 to about 5 moles per mole of conjugated polycyclic hydrocarbon or its equivalent. The reaction temperature is between 20° C. and 250° C. and preferably between 40° C. and 220° C. If the reaction temperature is too low, the degree of polymerization is also too low, and a satisfactory optically isotropic pitch cannot be obtained. If the reaction temperature is too high, the pitch obtained has anisotropic properties and fundamentally has ceased to be an isotropic pitch. The amount of time required for the polymerization reaction is usually between 5 and 300 minutes and preferably between 30 and 240 minutes. The reaction pressure is not particularly limited and the reaction is normally conducted under self-generated pressure within the reaction vessel under the other conditions described herein.
After completing polymerization, the catalyst, the unreacted raw materials and other light fractions are removed by conventional methods, such as extraction or distillation. Fo
Higashiizumi Takaaki
Hirai Yasuhiro
Kanno Koichi
Koike Nobuyuki
Oishi Jitsuo
Hendrickson Stuart L.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Gas Chemical Company Inc.
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