JP4284931B2 - Method for producing activated carbon and electrode for electric double layer capacitor using the activated carbon - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing activated carbon and an electrode for an electric double layer capacitor using the activated carbon. More specifically, a liquid alkali metal hydroxide is added to a carbonaceous material heated in an inert gas atmosphere at a low temperature while maintaining the solid state of the carbonaceous material, and then in an inert gas atmosphere. The present invention relates to a method for producing activated carbon that activates the carbonaceous material, and an electrode for an electric double layer capacitor formed with the activated carbon.
[0002]
[Prior art]
Activated carbon is widely used in food industry, chemical industry, pharmaceutical industry, and other various industries. Conventionally, activated carbon used in these has been developed mainly by utilizing its adsorption performance, but in recent years, development focusing on the performance of activated carbon as an electrode of an electric double layer capacitor has been widely made. This is a development focusing on the fact that activated carbon is excellent in capacitance as a polarizable electrode for an electric double layer capacitor, and the demand is growing rapidly with the development of the electronics field. Recently, in addition to the miniaturization of the conventional memory backup power source and the like, a large-capacity product that is used for an auxiliary power source such as a motor has been developed.
[0003]
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. For example, WO91 / 12203 The publication discloses a carbonaceous material obtained by heat-treating such an activated carbon raw material at less than 700 ° C. in an alkali metal hydroxide bath. On the other hand, it is also known to use pitch or coke as a raw material for activated carbon. For example, JP-A-10-1997767 discloses carbonization of petroleum coke or coal pitch coke and activation treatment with alkali metal hydroxide. A method for producing a carbon material is disclosed.
[0004]
As another example of using activated carbon obtained by activating a carbonaceous material with an alkali as a polarizable electrode for an electric double layer capacitor, JP-A-1-139865 discloses an excessive amount of alkali metal hydroxide. In the presence, a method of heating a carbon fiber in an inert gas atmosphere at a temperature exceeding 500 ° C. to obtain a large surface area carbon fiber is disclosed. In JP-A-5-258996, a carbon fiber obtained by melt spinning and heat-treating pitch as a raw material was activated with an aqueous solution of an alkali metal hydroxide, deashed, pulverized and molded. An electrode for a multilayer capacitor is disclosed, and Japanese Patent Application Laid-Open No. 7-161587 discloses an electrode for an electric double layer capacitor formed by activating and pulverizing a carbonaceous raw material with water vapor and further with an alkali metal hydroxide. Has been.
[0005]
[Problems to be solved by the invention]
As described above, with respect to the activated carbon for producing the electrode for the electric double layer capacitor, activated carbon having a certain high capacity by being activated at a high temperature using an alkali activator having strong oxidizing power such as potassium hydroxide. Although it is known that the corrosion of the equipment due to the use of alkali is severe, the corrosion due to alkali is a big problem even if the equipment made of nickel is used, which is a major factor that hinders industrialization It has become. Accordingly, an object of the present invention is to provide a method for producing activated carbon that can reduce corrosion of the device due to alkali and is excellent in electrostatic capacity, and an electrode for an electric double layer capacitor formed with the activated carbon.
[0006]
[Means for Solving the Problems]
The inventors of the present invention have used a nickel-based device to perform an alkali treatment on a carbonaceous material, and the carbonaceous material heated in an inert gas atmosphere is liquid while maintaining the solid state of the carbonaceous material. In order to complete the present invention, the above-mentioned problems can be solved by adding the alkali metal hydroxide at a temperature of 100 ° C. to 300 ° C. and then activating the carbonaceous material in an inert gas atmosphere. It came. That is, the present invention relates to a method for producing activated carbon by subjecting a carbonaceous material to an alkali treatment , using a nickel-based apparatus and heating the carbonaceous material in an inert gas atmosphere to at least the carbonaceous material. Activated carbon characterized in that a liquid alkali metal hydroxide is added at a temperature of 100 ° C. or higher and 300 ° C. or lower with the surface kept in a solid state, and then the carbonaceous material is activated in an inert gas atmosphere. It is a manufacturing method.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The carbonaceous material used in the present invention is not particularly limited as long as activated carbon is formed by activation. Examples thereof include coconut shell, petroleum-based and / or coal-based pitch, coke, phenolic resin, vinyl chloride and the like. Can give. The shape of the carbonaceous material is not limited, and various shapes such as granular, fine powder, fiber, and sheet can be used.
[0008]
Examples of fibrous or sheet-like carbonaceous materials include natural cellulose fibers such as cotton, regenerated cellulose fibers such as viscose rayon and polynosic rayon, synthetic fibers such as pulp fibers, polyvinyl alcohol fibers, ethylene vinyl alcohol fibers, and phenol fibers. Examples thereof include woven or non-woven fabrics, films, felts, and sheet-like materials.
[0009]
In the present invention, a liquid alkali metal hydroxide is used for addition to the carbonaceous material. Examples of the alkali metal hydroxide include alkali metal water such as potassium hydroxide, sodium hydroxide, and lithium hydroxide. Oxides can be mentioned. Of these, the use of liquid potassium hydroxide is preferable because the effects of the present invention are remarkably exhibited. The water content of the alkali metal hydroxide is preferably 20% by weight or less.
[0010]
In the present invention, firstly, nitrogen, carbonaceous material in an inert gas atmosphere such as argon and heated, the carbonaceous material, while maintaining the solid phase state, A alkali metal of an alkali metal hydroxide liquid hydroxides you out at a temperature below 300 ° C. have 1 00 ° C. or more, such solidified. The solid state as referred to in the present invention means that at least the surface of the carbonaceous material maintains a solid state. If the mixing ratio of the carbonaceous material and the alkali metal hydroxide is too large, the raw material cost will be high, and it may become overactive. : Alkali metal hydroxide = 1: 0.3-1: 5 (weight ratio) is preferable.
[0011]
The apparatus used for adding the alkali metal hydroxide is not particularly limited, and the carbonaceous material is sequentially fed by a moving device such as a belt conveyor type, and the liquid alkali metal hydroxide is added at a low temperature. That's fine. The liquid alkali metal hydroxide may be added continuously, but it is preferable to add the liquid alkali metal hydroxide sequentially and appropriately after knowing the drying state of the carbonaceous material surface. As the material of the apparatus, a material with relatively little corrosion, such as stainless steel, hastelloy, or nickel, is used. Teflon (registered trademark) or the like can be used by lining it.
[0012]
When the carbonaceous material is molded to a size of 0.1 mm to 10 mm and used, it is preferable that the liquid alkali metal hydroxide is easily impregnated. The molding is often formed into a spherical or cylindrical shape by a known means, and the size in that case means the maximum diameter or the maximum length, and when it is formed in an indefinite shape, it means an equivalent diameter.
[0013]
The carbonaceous material impregnated with the alkali metal hydroxide is then subjected to an activation treatment. The activation process is performed in an atmosphere of an inert gas such as nitrogen, argon, helium, or a mixed gas thereof. The activation temperature is 350 ° C to 800 ° C, preferably 400 ° C to 700 ° C. In order to raise the temperature, various methods such as a method of raising the temperature linearly, a method of holding for a certain time after reaching a certain temperature, and a method of raising the temperature stepwise are adopted. The obtained activated carbon is washed by being poured into water, and further, acid washing and water washing are repeated, and dried by heating at normal temperature or under reduced pressure.
[0014]
According to the present invention, corrosion of the device due to alkali can be greatly reduced. The reason for this cannot always be clearly explained, but the carbonaceous material and the liquid alkali metal hydroxide are mixed at a low temperature, and the subsequent activation treatment is carried out in a solid state. It is conceivable that the opportunity for direct contact with the apparatus for the solid mixture of alkali metal hydroxides has been reduced.
[0015]
The activated carbon obtained by the present invention is preferably molded into a polarizable electrode for an electric double layer capacitor. A known method may be adopted as a method for forming the electrode. Briefly speaking, after adding about 0 to several percent of a substance known as a binder such as commercially available polytetrafluoroethylene to activated carbon powder and mixing it well, it is put into a mold and pressed or rolled. It can be formed into an electrode by forming it into a sheet and punching it into the required shape. At that time, it is possible to apply heat as necessary, but it should be understood that it should be stopped to such an extent that it does not affect the surface structure such as deterioration of the binder component and specific surface area of the activated carbon component.
[0016]
Further, at the time of molding, a conductive substance such as conductive carbon or metal fine particles may be added to reduce the resistance of the electrode. This is effective in reducing the internal resistance of the polarizable electrode and reducing the electrode volume. The polarizable electrode is preferably used for an electric double layer capacitor. A schematic diagram of the electric double layer capacitor is shown in FIG. 1 and 2 are current collecting members, 3 and 4 are polarizable electrodes made of activated carbon of the present invention, 5 is a separator made of polypropylene nonwoven fabric, and 6 is a lid made of a material such as stainless steel. EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
[0017]
【Example】
Reference Example Melt blow spinning of an optically anisotropic pitch having a Mettler softening point of 285 ° C. obtained by heat-treating a cracked residue of petroleum using a nozzle having 1000 spinning holes having a diameter of 0.2 mm in a slit having a width of 2 mm, A mesophase pitch-based fibrous carbon material was produced by infusibilization and carbonization.
[0018]
Example 1
A nickel autoclave (V-1) with an internal volume of 100 mL (milliliter) equipped with a gas inlet, outlet, temperature sensor, pressure gauge, liquid discharge valve and stirring device is set in the electric furnace. did. First, 50 g of potassium hydroxide powder finely pulverized to about 10 μm (purity: 95%) was charged, nitrogen was circulated to replace the gas in the autoclave, and then nitrogen gas was circulated at 100 mL / min. Heating was started under stirring at 100 rpm. The liquefaction assumed to be due to melting of potassium hydroxide was observed from around 240 ° C. in the contents. Even after the internal temperature reached 260 ° C., stirring was continued under a nitrogen flow.
[0019]
A 200 mL nickel autoclave (V-2) equipped with a gas inlet, outlet, temperature sensor, pressure gauge, liquid sample inlet and stirring device was set in an electric furnace separately, The V-1 liquid discharge valve was connected to the V-2 liquid sample inlet. V-2 was charged with 25 g of the pitch-based fibrous carbon material obtained in the above reference example, the gas in the autoclave was replaced under a nitrogen flow, and then the nitrogen gas was circulated at 100 mL / min. Heating was started under stirring. After the internal temperature reaches 280 ° C., the flow of nitrogen gas of V-1 is stopped, the inside of the system is slightly pressurized, the liquid material discharge valve is opened, and about half amount of liquid potassium hydroxide (25 g) is added in 30 minutes. It was dripped in V-2.
[0020]
From the start of dropping, the nitrogen flow rate in V-2 was increased to 300 mL / min. The pitch-based fibrous carbon material after dropping was kept in a solid state, and liquefaction with molten potassium hydroxide was not observed. Stirring was continued for 90 minutes at the same temperature under a nitrogen flow, and then the remaining half of potassium hydroxide (25 g) contained in V-1 was dropped in 30 minutes, and stirring was continued for 90 minutes in the same manner. Meanwhile, the pitch-based fibrous carbon material maintained a solid state, and liquefaction with molten potassium hydroxide was not observed. The resulting carbon material powder was cooled while flowing nitrogen at 50 mL / min, and stored in a desiccator.
[0021]
10 g of the powdered solid obtained by the above operation was charged into an activated electric furnace, and the activation treatment was performed by raising the temperature to 700 ° C. at a rate of temperature increase of 200 ° C./hour. During this time, nitrogen was circulated at 300 mL / min up to 400 ° C. and 100 mL / min after reaching 400 ° C. The alkali activated product was washed with water, washed with acid, washed with water and then dried. The specific surface area of the obtained activated carbon was 1200 m ² / g, and the contained nickel was 18 ppm.
[0022]
Example 2
The activated carbon obtained in Example 1 was pulverized to an average particle size of 5 to 20 μm to obtain powdered activated carbon, and a mixture comprising 80% by weight of the powdered activated carbon, 10% by weight of conductive carbon, and 10% by weight of polytetrafluoroethylene was prepared. Kneaded. Next, the mixture was formed into a sheet having a thickness of 300 μm by roll rolling, and punched into a circle having a diameter of 2 cm by a punching device. Subsequently, it dried at 150 degreeC under pressure reduction for 4 hours, and obtained the sheet electrode.
[0023]
In a glow box having a dew point of −80 ° C. or lower, a collector electrode, a polarizable electrode sheet, a polypropylene nonwoven fabric, a polarizable electrode, and a collector electrode were laminated on a stainless steel lid, and then 1 mol of tetraethylammonium tetrafluoro A propylene carbonate solution containing borate was impregnated into a polarizable electrode and caulked and sealed on a stainless steel upper lid using an insulating gasket made of polypropylene to produce an electric double layer capacitor as shown in FIG. Using an electric double layer capacitor evaluation device manufactured by Hioki Electric Co., Ltd., a constant current up to 2.5 V and 10 charge / discharge cycle tests were performed at room temperature, and the capacitance was measured. The average value of the electrostatic capacity obtained from the discharge curve by a conventional method was 29.7 F / CC.
[0024]
Example 3
Activated carbon was obtained by the same operation as in Example 1 except that coconut shell charcoal was used in place of the pitch-based fibrous activated carbon material of Example 1. The specific surface area of the activated carbon was 1500 m ² / g, and the contained nickel was 15 ppm. Further, the capacitance measured in the same manner as in Example 2 was 26.0 F / cc.
[0025]
Example 4
Activated carbon was converted into a phenol resin carbide and treated at a low temperature in the same manner as in Example 1 to obtain activated carbon. The specific surface area of the activated carbon was 1500 m ² / g, and the contained nickel was 19 ppm. Further, the capacitance measured in the same manner as in Example 2 was 27.0 F / cc.
[0026]
Example 5
The phenol-based nonwoven fabric carbide was treated at a low temperature in the same manner as in Example 1 to obtain activated carbon. The specific surface area of the activated carbon was 1500 m ² / g, and the contained nickel was 14 ppm. This activated carbon nonwoven fabric was formed into a circular shape having a diameter of 2 cm using a punch, and then dried at 150 ° C. for 4 hours under reduced pressure to produce a polarizable electrode. The average value of the capacitance measured by producing an electric double layer capacitor in the same manner as in Example 2 was 37.5 F / g.
[0027]
Example 6
A nickel disk type dryer equipped with a carbon material introduction port, molten potassium hydroxide addition port (front and middle stages of the apparatus) and an exhaust port is maintained at 280 ° C. with a heating medium, and nitrogen is circulated at 10 L / min. Replaced with nitrogen. After that, the apparatus was started and pitch-based fibrous carbon material was introduced at a rate of 1 kg / hr from the carbon material inlet under nitrogen flow, and 95% molten potassium hydroxide was introduced at 1 kg / hr from the previous molten potassium hydroxide addition port. The 95% molten potassium hydroxide was added at a rate of 0.5 kg / hr from the middle portion of the molten potassium hydroxide addition port.
[0028]
The average residence time of the mixture was 3 hours, and the pitch-based fibrous activated carbon material maintained a solid state even when discharged, and no liquefaction with molten potassium hydroxide was observed. The discharged product was stored in a desiccator under a nitrogen stream. The operation after activation was carried out according to Example 1 to obtain activated carbon having a specific surface area of 1200 m ² / g and a nickel content of 18 ppm.
[0029]
Comparative Example 1
Activated carbon was obtained in exactly the same manner as in Example 1 except that the pitch-based fibrous carbon material and potassium hydroxide were mixed at 450 ° C. The nickel contained in this activated carbon was 55 ppm.
[0030]
Comparative Example 2
In Example 6, activated carbon was obtained in exactly the same manner except that the pitch-based fibrous carbon material and potassium hydroxide were mixed at 420 ° C. The nickel contained in this activated carbon was 58 ppm.
[0031]
【The invention's effect】
According to the present invention, it is possible to provide a method for producing activated carbon that can remarkably reduce corrosion of an apparatus due to alkali. According to the present invention, activated carbon that is excellent in capacitance and suitable as an electrode for an electric double layer capacitor can be manufactured with less corrosion of the device due to alkali, and industrial utility is great.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example in which the activated carbon of the present invention is applied to an electrode of a capacitor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Current collection member 2 Current collection member 3 Polarization electrode 4 Polarization electrode 5 Separator 6 Lid

Claims (6)

In a method for producing activated carbon by treating a carbonaceous material with an alkali, a carbonaceous material heated in an inert gas atmosphere using an apparatus made of nickel, and at least the surface of the carbonaceous material is in a solid state A method for producing activated carbon, comprising adding a liquid alkali metal hydroxide at 100 ° C. or higher and 300 ° C. or lower while maintaining the temperature, and then activating the carbonaceous material in an inert gas atmosphere. Preparation of activated carbon of claim 1 Symbol mounting said alkali metal hydroxide is potassium hydroxide. The method for producing activated carbon according to claim 1 or 2 , wherein the alkali metal hydroxide is an alkali metal hydroxide having a water content of 20% by weight or less. The method for producing activated carbon according to any one of claims 1 to 3, wherein the carbonaceous material is formed into a size of 0.1 mm to 10 mm. Preparation of activated carbon according to any one of claims 1 to 4 for sequentially adding the liquid alkali metal hydroxide. The method for producing activated carbon according to any one of claims 1 to 5, wherein the activation temperature is 350 ° C to 800 ° C.

Images