JP4069822B2 - Method for producing activated carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing activated carbon that is capable of reducing the amount of a magnetic heavy metal incorporated to the level of electronic materials such as an electrical double layer capacitor and the like. <P>SOLUTION: The method for manufacturing the activated carbon with a small heavy metal content comprises charging the activated carbon obtained by performing the activation treatment of a carbonaceous material using an alkali metal hydroxide into water, filtrating the resulting slurry-like substance, treating the resulting filtered slurry with a magnet having magnetic force of 5,000 gauss or more and then subjecting the same to washing. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to a method for producing activated carbon. More specifically, the activated material obtained by activating the carbonaceous material with an alkali metal hydroxide is put into water, the resulting slurry is filtered, and the resulting filtered slurry is treated with a magnet. Then, the present invention relates to a method for producing activated carbon to be washed.

  Activated carbon is widely used in the food industry, chemical industry, pharmaceutical industry, and other various industries. Conventionally, activated carbon used for these has been developed mainly by utilizing its adsorption performance. In recent years, attention has been paid to the fact that activated carbon is excellent in electrostatic capacity as a polarizable electrode for electric double layer capacitors, and activated carbon has been developed for use in electrodes for electric double layer capacitors. Growing.

  Conventionally, as such activated carbon for electric double layer capacitors, activated carbon raw materials such as coconut shell, wood powder, and coal are generally activated under acidic conditions such as water vapor and gas. Activation under conditions is also known. For example, a method for producing a carbonaceous material in which such an activated carbon raw material is heat-treated at less than 700 ° C. in an alkali metal hydroxide bath has been proposed (Patent Document 1). It is also known to use pitch or coke as a raw material for activated carbon. For example, a carbon material production method is proposed in which petroleum coke or coal pitch coke is carbonized and activated with an alkali metal hydroxide. (Patent Document 2).

  By the way, since the activated carbon obtained by the method as described above usually contains heavy metals such as Ni, Fe, Cr, etc. derived from raw materials, equipment, etc., activated carbon containing such heavy metals is used. If the electrode is molded into a polarizable electrode and used in an electric double layer capacitor, problems such as a short circuit due to dendrite formation due to reduction deposition of heavy metals, or a decrease in self-discharge retention rate may occur. Therefore, when activated carbon is used as a material for a polarizable electrode for an electric double layer capacitor, the current situation is that it has been thoroughly cleaned.

  On the other hand, from the viewpoint of removing a magnetic metal from activated carbon, techniques for treating activated carbon with a magnet are known (Patent Documents 3 and 4). This technique is a technique in which a relatively large magnetic metal is selected with a magnet using a magnetic separator when carbon is activated to obtain activated carbon by steam activation.

WO91 / 12203 Publication Japanese Patent Laid-Open No. 10-199767 JP 10-338513 A JP 2001-233610 A

  However, in order to produce activated carbon for forming polarizable electrodes for electric double layer capacitors, it is necessary to perform complicated and meticulous cleaning, which increases the cleaning cost and increases the production cost of activated carbon. There was a problem that. In addition, in the case of a technology in which activated carbon is treated with a magnet in order to remove the metal from the activated carbon, it is intended to remove the magnetic metal particles and magnetic metal powder that exist independently in the activated carbon particles and activated carbon powder. However, as in the case of a polarizable electrode for an electric double layer capacitor, there is a problem that it is not a technique that can purify the metal content to such an extent that dendrite formation does not occur. As described above, it has been pointed out that the heavy metal content of the activated carbon used for the polarizable electrode for the electric double layer capacitor should be reduced, but there is a method for reducing the heavy metal easily and at low cost. The current situation is that it has not been released.

  An object of the present invention is to provide an industrially excellent method for producing activated carbon that can easily obtain activated carbon with less heavy metal contamination.

  The inventors of the present invention can further achieve the above object by further studying, filtering the slurry of activated carbon, treating the obtained filter slurry with a magnet having a specific magnetic strength, and further washing. As a result, the inventors have found out that the present invention can be achieved.

  That is, the present invention provides an activated carbon production method for producing activated carbon by activating a carbonaceous material using an alkali metal hydroxide, and activating the activated product into water, and filtering the resulting slurry. Then, the obtained filtration slurry is treated with a magnet having a magnetic strength of 5000 gauss or more, and then subjected to washing.

  According to the method for producing activated carbon of the present invention, activated carbon with a reduced amount of magnetic heavy metal mixed can be produced by a simple operation.

  In the present invention, the carbonaceous material is activated using an alkali metal hydroxide, the obtained activated product is put into water, the obtained slurry is filtered, and the obtained filtered slurry is magnetically treated. It is a method for producing activated carbon, characterized by subjecting it to washing after treatment with a magnet having a strength of 5000 gauss or more.

  In the production method of the present invention, first, the carbonaceous material is activated using an alkali metal hydroxide to obtain an activated product. More specifically, the alkali metal hydroxide such as a lump or flake is finely pulverized, the obtained finely pulverized product is uniformly mixed at a predetermined blending ratio, and the resulting mixture is maintained in a solid state. It is preferable to perform the granulation treatment as it is, dehydrate the obtained granulated product, and activate the obtained dehydrated product.

  The carbonaceous material used in the present invention is not particularly limited as long as activated carbon is formed by activation. For example, coconut shell, petroleum-based and / or coal-based pitch, coke, phenolic resin, vinyl chloride. And so on. Of these, an easily graphite-based carbonaceous material is preferable. Examples of the easily graphite-based carbonaceous material include mesophase pitch-based carbon materials. Of these, mesophase pitch-based carbon fibers are preferred. The shape of the carbonaceous material is not limited, and various shapes such as a granular shape, a fine powder shape, a fiber shape, and a sheet shape can be used.

  Examples of the alkali metal hydroxide used in the present invention include particulates of alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide and cesium hydroxide, or mixtures thereof. From the viewpoint of obtaining a large capacitance, it is preferable to use sodium hydroxide and / or potassium hydroxide. Of these, potassium hydroxide is preferable. As these alkali metal hydroxides, commercially available ones can be used. The water content of the metal hydroxide can be 1 to 20% by weight, but is preferably 1 to 10% by weight from the viewpoint of handling. In the case where the alkali metal hydroxide is a lump, it is preferably pulverized by the pulverizer as described above to have a particle size of about 100 μm or less.

  The method for pulverizing the alkali metal hydroxide such as a lump or flake is not particularly limited, but the carbonaceous material is added to the alkali metal hydroxide in an amount of 0.5 to 10% by weight, preferably 1 to 5% by weight. When added in a batch or continuous mode using a known pulverizer such as a ball mill or a dynamic mill, the pulverization can be efficiently performed, which is preferable from the viewpoint of the manufacturing process. Since alkali metal hydroxide generally has moisture absorption and deliquescence properties, it is preferably carried out in a low dew point air of about −10 ° C. or less or in an inert gas atmosphere such as nitrogen, helium, or argon that does not contain moisture.

  The alkali metal hydroxide finely pulverized by the above pulverization process is uniformly mixed with a carbonaceous material at a predetermined mixing ratio. In this treatment, it is preferable in terms of activation efficiency that the carbonaceous material and the alkali metal hydroxide are sufficiently mixed so as to be as uniform as possible. In consideration of variation in activation and prevention of overactivation, the alkali metal hydroxide is generally blended at a weight ratio of preferably 1.2 to 4, more preferably 1.3 to 3 with respect to the carbonaceous material 1. Is done. It is preferable to use fine particles of alkali metal hydroxide finely pulverized in the coexistence of a carbonaceous material as the alkali metal hydroxide, because the mixing property is improved and a uniform mixture with little variation in composition ratio is obtained.

  The mixing temperature is not particularly limited, and is usually sufficient at room temperature. The type of the mixer is not particularly limited, and a known rotary container type mixer or a fixed container type mixer can be used, but the rotary container type mixer is used in that a more uniform mixing can be obtained. Is good. The material of the mixer is preferably nickel from the viewpoint of reducing corrosion as much as possible.

  Next, a granulating process is performed on the carbonaceous material and the alkali metal hydroxide in order to facilitate handling in dehydration described later. The particle size of the resulting granulated product is not particularly limited, but a diameter of 0.2 mm to 10 mm is preferable for handling. The granulation is preferably carried out while maintaining a solid state by raising the temperature to 120 ° C. to 140 ° C. under a reduced pressure of 0.01 to 300 Torr (1.33 to 40000 Pa). Although the rate of temperature increase is not limited, it is preferably about 0.1 to 10 ° C./min. Granulation can be carried out with a double cone type mixer, etc., but considering the particle size of the granulated product, particle size distribution, deterring of adhesion to the machine wall, etc., it should be carried out under the above conditions with the rotational speed taken into account. preferable.

  A dehydration process is performed on the granulated product (ie, the carbonaceous material / alkali metal hydroxide mixture) obtained by the granulation process. In this case, there is a close relationship between the melting temperature of the granulated product and its moisture content, and the temperature is raised at an appropriate rate of temperature while maintaining the system pressure at an appropriate pressure below atmospheric pressure. The carbonaceous material / alkali metal hydroxide mixture can be dehydrated in the solid state without melting and its water content can be lowered.

  Next, an activation treatment is performed on the dehydrated product (that is, the granular mixture of carbonaceous material / alkali metal hydroxide). Specifically, the granular mixture may be heat-treated in batch or continuously in an inert gas such as nitrogen or argon. As the temperature of heat treatment (activation temperature), when potassium hydroxide is used, the capacitance increases unexpectedly in a region exceeding 700 ° C., so that it may be 700 ° C. to 850 ° C. preferable.

  The granular mixture of carbonaceous material / alkali metal hydroxide obtained through the above pulverization, mixing, and dehydration processes is used in each process (particularly activation process) in order to avoid corrosion of the apparatus due to alkali melting in the activation process. It is preferable to strictly control the temperature rising rate. According to the results of detailed studies by the present inventors, the initial purpose can be reached by maintaining the temperature rising rate at 5 ° C./min or less. Moreover, since the holding time after temperature rising influences the performance of activated carbon together with the temperature rising rate, the holding time at 700 ° C. or higher is preferably 0.5 to 8 hours.

  As an apparatus (activation apparatus) for performing heat treatment, conventionally known activation apparatuses such as a rotary type, a fluid type, and a mobile type are adopted. It is preferable to use a material mainly composed of nickel from the viewpoint of reducing corrosion as much as possible. With regard to the activation device and the processing method, the industrial superiority is taken into consideration, and as the activation device, the rotary kiln is preferable in the above category, and as the processing method, the continuous method is from both the productivity and the activated carbon performance. preferable.

  In addition, it is preferable to cool the activation treatment product obtained by the activation treatment to a predetermined temperature (for example, room temperature) prior to preparation of a slurry-like material described later. Cooling is preferably performed under a stream of inert gas such as nitrogen, argon, carbon dioxide, etc., in order to suppress the combustion of the activated product.

  Next, the obtained activation treatment product is put into water, and the obtained slurry is filtered. Filtration treatment is performed by sieving such as poorly shaped materials contained in carbonaceous materials, impurities, and bulk by-products generated during mixing, dehydration and activation treatments, and mixtures of metal masses and carbonaceous materials derived from equipment corrosion. Effective for removal.

  Preparation of the slurry-like material from the activation treatment product may be performed by putting the activation treatment product into the stirring water. Further, if the amount of water relative to 100 parts by weight of the activated product is too small, the viscosity will be too high, the filtration process will not proceed smoothly, and if it is too large, the filtration process and the wastewater treatment will be complicated. Parts by weight. As water to be used, purified water or ion exchange water containing no metal ions is particularly preferable.

  In addition, a filtration device, a filtration material, and the like used for the filtration treatment can be selected from conventionally known ones, but considering that there are cases where washing is performed using acids (for example, hydrochloric acid) in the subsequent washing treatment, alkali resistance, It is preferable to select an acid-resistant material. It is preferable to employ a filtration device using a corrosion-resistant metal material or a filtration device coated with a corrosion-resistant fluororesin.

  The opening of the filtering material is preferably 75 μm or less, more preferably 60 μm or less, because activated carbon particles containing metals are not captured if it is too large, although it depends on the shape of the carbonaceous material. The lower limit of the spread is preferably 10 μm or more because if it is too small, the filtration pressure is high and the filtration takes a long time.

  Next, the obtained filtered slurry is treated with a magnet to remove magnetic heavy metals (eg, iron, nickel, cobalt, etc.). As described above, the activated carbon for the electric double layer capacitor needs to extremely reduce the content of magnetic heavy metal, and the magnet used in the present invention preferably has a magnetic strength in terms of the effect of improving the removal of magnetic heavy metal. Is 5000 Gauss or more, more preferably 8000 Gauss or more. Moreover, it is desirable to arrange several magnets in series in consideration of the contact efficiency with the filtration slurry. Moreover, a permanent magnet and an electromagnet can be used suitably for a magnet. The adhesion efficiency of magnetic metals to the magnet is also affected by the contact time between the filtration slurry and the magnet. According to the detailed study by the present inventors, the moving speed of the filtration slurry is preferably 10 cm / second or less, more preferably 5 cm / second or less.

  Next, as explained above, the filtration slurry treated with a magnet is subjected to a washing treatment. The washing treatment can be performed by a conventional method. For example, the filter slurry is filtered with a relatively fine filter medium, and the activated carbon is collected, washed with water, pickled as necessary, washed with water, and washed with alkali. The target activated carbon is obtained by removing metals and impurities and drying at room temperature or under reduced pressure at atmospheric pressure or under heating.

  The activated carbon obtained by the production method of the present invention described above is useful as a material for a polarizable electrode particularly suitable for an electric double layer capacitor.

  Such a polarizable electrode is obtained by mixing and molding at least a binder such as polyvinylidene fluoride and polytetrafluoroethylene and a conductive material such as carbon black into the activated carbon obtained by the production method of the present invention. It is. By mixing the conductive material, the resistance of the electrode can be reduced, which is effective in reducing the internal resistance of the polarizable electrode and reducing the electrode volume.

  In order to manufacture a polarizable electrode suitable for such an electric double layer capacitor, a generally known method can be applied. For example, commercially available materials known as binders such as polyvinylidene fluoride and polytetrafluoroethylene, and conductive materials such as carbon black are added to a few percent as necessary, and kneaded well, then the mold It can be molded into an electrode by pressing it into a mold or rolling it into a sheet and punching it into the required shape. Alternatively, the kneaded product may be applied to a current collector to form a coated electrode. When forming an electrode, if necessary, an organic compound such as alcohol or N-methylpyrrolidone, a solvent such as water, a dispersant, or various additives may be used. It is also possible to apply heat within a range that does not impair the effects of the invention.

  The polarizable electrode described above is useful as an electrode of an electric double layer capacitor as shown in FIG. 1 (schematic cross-sectional view). Each component constituting the capacitor of FIG. 1 can have the same configuration as a known electric double layer capacitor except that the polarizable electrode according to the present invention is used. For example, in the figure, 1 and 2 are aluminum. Current collecting members made of, etc., 3 and 4 are polarizable electrodes made of activated carbon of the present invention, 5 is a separator made of polypropylene nonwoven fabric, 6 is a battery lid made of a material such as stainless steel, 7 is made of stainless steel, etc. A case made of a material, 8 is a gasket made of polypropylene, polyethylene, polyamide, polyamideimide, polybutylene or the like, and 9 is an electrolyte.

  In order to function as an electric double layer capacitor, a known electrolyte such as tetraethylammonium tetrafluoroborate or tetramethylammonium tetrafluoroborate is placed in case 7 with a carbonate such as ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate. It is necessary to enclose an electrolytic solution dissolved in a solvent such as nitriles such as acetonitrile, lactones such as α-methyl-γ-butyrolactone, sulfoxides such as dimethyl sulfoxide, amides such as dimethylformamide.

  Since the electric double layer capacitor having the configuration shown in FIG. 1 uses the activated carbon of the present invention, it has a small capacitance and a high capacitance.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Reference example 1

  Melt blow spinning using an optically anisotropic pitch with a Mettler softening point of 285 ° C obtained by heat treatment of petroleum cracking residue using a nozzle having 1,000 spinning holes with a diameter of 0.2 mm in a slit with a width of 2 mm, and infusible The mesophase pitch carbon fiber was produced by treatment and carbonization.

  A mesophase pitch-based carbon fiber produced in Reference Example 1 is pulverized into a nickel batch external heat type rotary kiln with a diameter of 400 mm and a length of 300 mm equipped with a thermometer so that the maximum length in the major axis direction is 200 μm or less. A pitch of 0.7 kg and 1.3 kg of 95% potassium hydroxide pulverized to an average particle size of 1 mm or less were added, and a rotary kiln was rotated at 30 rpm under a reduced pressure of 0.3 Torr (40.0 Pa). After heating the mixture of mesophase pitch-based carbon fiber and potassium hydroxide from room temperature to 100 ° C at a rate of 0.5 ° C / min, the power is turned off while maintaining the rotational speed of the rotary kiln and the decompression condition as it is, cooling To obtain a granulated product. The granulated product had a size of 10 mm or less.

  Using the same rotary kiln, the granulated product was heated from room temperature to 320 ° C. at a rate of 0.5 ° C./min under reduced pressure of 0.3 Torr (40.0 Pa) while rotating at 30 rpm. After holding for 1 hour, dehydration was performed.

  As an activation furnace, an externally heated rotary kiln type electric furnace having a thermometer, a nitrogen introduction port, a gas discharge port having a water trap, and a temperature variable activation zone (activation zone inner diameter 100 mm, inner volume 400 ml (mL)) used. Under nitrogen flow, 50 g of the dehydrated product was charged into the activation zone.

  The activation zone was heated from room temperature to 730 ° C. at a rate of 200 ° C./hour while flowing nitrogen at 300 mL / min, and held for 3 hours after reaching the predetermined temperature. Then, it cooled to 50 degrees C or less under nitrogen flow, and after that, the activated carbon raw material obtained by activating was processed under the flow of the mixed gas of a carbon dioxide gas and water vapor | steam, and the residual metal potassium was deactivated. The above activation operation was repeated 16 times.

  The activated carbon and potassium carbonate-based mixture obtained by activation was added to and stirred in distilled water to prepare a slurry containing 10% activated carbon, and this slurry was filtered through a nylon resin filter having an opening of 45 μm. Subsequently, the obtained filtration slurry was passed through a tank in which three 8000 Gauss rod-shaped magnets were arranged in series at a flow rate of 2 cm / second to remove contained metals. About 0.4% by weight of defectives in the activated carbon was removed by this filtration operation and metal removal operation with a magnet. This defect contained about 30% by weight of iron (Fe) and nickel (Ni).

  The activated carbon from which the defectives were removed was then washed with water, acid washed with 0.5 N (N) hydrochloric acid solution (95 ° C.), hot water washed (95 ° C.), dried at 110 ° C. and commercialized. The contents of Ni and Fe in the product were 5 ppm and 3 ppm, respectively.

  The obtained activated carbon was pulverized to an average particle size of 5 to 30 μm by a vibration mill to obtain powdered activated carbon. 80 parts by weight of the powdered activated carbon, 10 parts by weight of conductive carbon and 10 parts by weight of polytetrafluoroethylene (PTFE) And kneaded in an agate mortar. Subsequently, the obtained kneaded material was formed into a sheet having a thickness of about 200 μm by roll rolling, punched into a circle having a diameter of 2 cm, and dried under reduced pressure at 150 ° C. for 4 hours to produce a polarizable electrode.

  Propylene containing tetraethylammonium tetrafluoroborate was assembled in a cell using a stainless steel case and an aluminum collector electrode and a glass separator in a clove box having a dew point of −50 ° C. or less, as shown in FIG. The carbonate solution was impregnated and caulked and sealed in a glove box to obtain 10 electric double layer capacitors. The obtained electric double layer capacitor was subjected to a 2.7 V constant current and charge / discharge cycle test at room temperature using a power system electric double layer capacitor evaluation apparatus to test whether or not a short circuit occurred. As a result, in the charge / discharge cycle test of 1000 times, there was no electric double layer capacitor in which a short-circuit phenomenon was recognized.

  A slurry having an activated carbon concentration of 20% by weight made of a mixture of activated carbon and potassium carbonate mainly prepared according to Example 1 was filtered through a filter made of nylon resin having an opening of 70 μm. Next, the same operation as in Example 1 was carried out except that the filtrate was passed through a tank in which three 6000 Gauss rod-shaped magnets were arranged in series at a flow rate of 4 cm / sec and the contained metals were removed by the magnet. Was repeated. About 0.25% by weight of defectives in the activated carbon was removed by this filtration operation and metal removal operation with a magnet. The defective product contained about 20% by weight of Fe and Ni. The activated carbon thus treated was washed with water, acid washed with 0.5N hydrochloric acid solution (95 ° C.) and hot water washed (95 ° C.), and then dried at 110 ° C. to obtain a product. The contents of Ni and Fe in the product were 7 ppm and 5 ppm, respectively.

  An electric double layer capacitor was prepared from the obtained activated carbon in the same manner as in Example 1, and a charge / discharge cycle test was conducted. As a result, in the 500 charge / discharge cycle tests, there was no electric double layer capacitor in which a short-circuit phenomenon was observed.

Comparative Example 1

  A mixture mainly containing activated carbon and potassium carbonate obtained by activation in Example 1 was added to distilled water to prepare a slurry containing 10 wt% activated carbon. The slurry was washed with water, acid washed with 0.5N hydrochloric acid solution (95 ° C.) and hot water washed (95 ° C.) without filtration and removal of metals with a magnet, and then dried at 110 ° C. to produce a product. did. The contents of Ni and Fe in the product were 20 ppm and 15 ppm, respectively.

  Ten electric double layer capacitors were produced from the obtained activated carbon in the same manner as in Example 1, and a charge / discharge cycle test was conducted. As a result, there were three electric double layer capacitors in which a short-circuit phenomenon was observed in 100 charge / discharge cycles.

Comparative Example 2

  In Example 1, the slurry was not filtered and only the magnet treatment was performed. About 0.1% by weight of defectives in the activated carbon was removed by a metal removal operation with a magnet. The activated carbon subjected to this operation was washed with water, acid washed with a 0.5N hydrochloric acid solution (95 ° C.), and washed with hot water (95 ° C.), and then dried at 110 ° C. to obtain a product. This defective contained about 50% by weight of Fe and Ni. The contents of Ni and Fe in the product were 15 ppm and 10 ppm, respectively.

  Ten electric double layer capacitors were produced from the obtained activated carbon in the same manner as in Example 1, and a charge / discharge cycle test was conducted. As a result, there were two electric double layer capacitors in which a short-circuit phenomenon was observed in 100 charge / discharge cycles.

Comparative Example 3

  In Example 1, only the slurry filtration operation was performed, and the magnet treatment was not performed. About 0.03% by weight of defectives in the activated carbon was removed by filtration. This defective contained about 20% by weight of Fe and Ni. The activated carbon subjected to this operation was washed with water, acid washed with a 0.5N hydrochloric acid solution (95 ° C.), and washed with hot water (95 ° C.), and then dried at 110 ° C. to obtain a product. The contents of Ni and Fe in the product were 18 ppm and 13 ppm, respectively.

  From the obtained activated carbon, 100 electric double layer capacitors were prepared in the same manner as in Example 1, and a charge / discharge cycle test was performed. As a result, there was one electric double layer capacitor in which a short-circuit phenomenon was observed in 100 charge / discharge cycles.

  According to the production method of the present invention, it is possible to easily obtain activated carbon with a reduced amount of magnetic heavy metal mixed therein. In addition, when activated carbon obtained by the production method of the present invention is used to form a polarizable electrode and used for an electric double layer capacitor, the content of magnetic heavy metal is low, so short due to dendrite formation due to reduction precipitation of magnetic heavy metal, etc. The self-discharge retention rate does not decrease. Therefore, the electric double layer capacitor can be used in a wide range from a small-capacity memory backup application to a large-capacity motor auxiliary power supply application.

It is a schematic sectional drawing which shows an example of an electrical double layer capacitor.

Explanation of symbols

1, 2 Current collecting member 3, 4 Polarized electrode 5 Separator 6 Battery cover 7 Case 8 Gasket 9 Electrolyte

Claims (5)

  In the method for producing activated carbon in which activated carbon is produced by activating a carbonaceous material using an alkali metal hydroxide, the activated material obtained by activating the carbonaceous material using an alkali metal hydroxide is submerged in water. A method for producing activated carbon, wherein the obtained slurry is subjected to filtration treatment, the obtained filtration slurry is treated with a magnet having a magnetic strength of 5000 gauss or more, and then subjected to washing.   The method for producing activated carbon according to claim 1, wherein the opening of the filter medium is 75 μm or less.   The method for producing activated carbon according to claim 1 or 2, wherein the alkali metal hydroxide is potassium hydroxide.   The method for producing activated carbon according to any one of claims 1 to 3, wherein the carbonaceous material is an easily graphite-based carbonaceous material.   The method for producing activated carbon according to claim 4, wherein the easily graphite-based carbonaceous material is mesophase pitch-based carbon fiber.

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