JP4110859B2 - 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 electric double layer capacitor electrode using the activated carbon. More specifically, after mixing the carbonaceous material and the liquid alkali metal hydroxide at a low temperature, the mixture is cooled and solidified to form a solid mixture, and the solid mixture is activated in an inert gas atmosphere while maintaining the solid state. The present invention relates to an activated carbon manufacturing method and an electric double layer capacitor electrode formed by molding 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 capacitance, and an electrode for an electric double layer capacitor formed with the activated carbon.
[0006]
[Means for Solving the Problems]
When the present inventors alkali-treat the carbonaceous material, the carbonaceous material and the liquid alkali metal hydroxide are mixed at a low temperature, and then activated in a solid state under an inert gas atmosphere. The present inventors have found that the above problems can be solved, and have completed the present invention. That is, in the present invention, a carbonaceous material and a liquid alkali metal hydroxide liquefied by melting are mixed at 100 ° C. or higher and 300 ° C. or lower , and then cooled and solidified to form a solid mixture. It is a manufacturing method of activated carbon characterized by activating under an inert gas atmosphere, maintaining a state .
[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 mixing with 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]
The present invention has a great feature in that a carbonaceous material and these liquid alkali metal hydroxides are mixed at a low temperature. The low temperature referred to in the present invention is 400 ° C. or lower, and it is desirable to carry out at a temperature at which the alkali metal hydroxide does not solidify, preferably 100 ° C. or higher and 300 ° C. or lower. In the present invention, the carbonaceous material and the liquid alkali metal hydroxide are mixed at a low temperature, solidified by cooling to form a solid mixture, and then the solid mixture is preferably 0.1 mm to 10 mm in size. Then, activation treatment is performed in an inert gas atmosphere while maintaining a solid state. In many cases, the solid mixture is usually formed into a spherical shape or a cylindrical shape by a known forming means. In this case, the size means the maximum diameter or the maximum length. Say. In the present invention, the solid mixture is activated while maintaining a solid state, but the solid state means that at least the surface of the carbonaceous material is maintained in a solid state.
[0011]
If the mixing ratio of the carbonaceous material and the liquid alkali metal hydroxide is too large, the raw material cost will be high, and it may become overactive. It is preferable to carry out with a quality material: alkali metal hydroxide = 1: 0.3-1: 5 (weight ratio). The mixing treatment is performed in an air and / or inert gas atmosphere, but when air is used, it is preferable to use it with a water content as low as possible.
[0012]
The apparatus used for mixing is not particularly limited, and a stirring tank, an extrusion-type kneader, a rotary kiln, or the like can be used. As the material of the apparatus, stainless steel, hastelloy, nickel or the like is used, but nickel is preferably used in terms of relatively little corrosion. Teflon (registered trademark) or the like can be used by lining it.
[0013]
Next, the solid mixture is activated 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 it is dried by normal temperature or heating under atmospheric pressure and / or 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
An nickel autoclave having an internal volume of 200 mL (milliliter) equipped with an inert gas inlet, outlet, temperature sensor, pressure gauge, liquid discharge valve and stirring device was set in an electric furnace. The autoclave was charged with 20 g of a pitch-based fibrous carbon material having a length of about 15 μm and a diameter of about 12 μm obtained in the above reference example, and 40 g of potassium hydroxide powder (purity: 95%) previously pulverized to 10 μm, and autoclaved with nitrogen. The inside gas was replaced, and then the temperature was raised under stirring at 50 rpm while flowing nitrogen gas at 250 mL / min. The contents were found to be liquefied from the vicinity of 240 ° C. due to melting of potassium hydroxide, and existed as a slurry with the fibrous carbon material. After the internal temperature reached 260 ° C., stirring was continued for 30 minutes under a nitrogen flow.
[0019]
Then, stop the flow of nitrogen, open the discharge valve installed at the bottom of the autoclave under the condition of slight nitrogen pressurization, drop out the slurry-like mixture, and cool it with nitrogen stream Gave a granular solid of about 3 mmΦ. 30 g of the granular solid was loaded into a cylindrical processing apparatus having an internal volume of 100 ml having a pan capable of circulating nitrogen from the bottom of the apparatus, set in a 230 ° C. bath, and nitrogen gas preheated to 230 ° C. was added at 300 mL / min. The mixture was allowed to flow for 4 hours at a flow rate and processed while maintaining a solid state. Then, it cooled under nitrogen circulation and preserve | saved in the desiccator.
[0020]
The granular solid 10g obtained by the above operation was prepared in an electric furnace, heated to 700 ° C. at a temperature rising rate of 200 ° C./hour, and activated. 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 15 ppm.
[0021]
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 using a punching device. Subsequently, it dried at 150 degreeC under pressure reduction for 4 hours, and obtained the sheet electrode.
[0022]
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, a constant current up to 2.5 V and a charge / discharge cycle test were performed 10 times at room temperature. The average value of the capacity was 30.4 F / CC.
[0023]
Example 3
Activated carbon was obtained by the same operation as in Example 1 except that coconut shell charcoal was used instead of the pitch-based fibrous carbon material used in Example 1. The specific surface area of the activated carbon was 1500 m ² / g, and the contained nickel was 19 ppm. Moreover, the electrostatic capacitance calculated | required similarly to Example 2 was 26.5 F / cc.
[0024]
Example 4
The carbonaceous material was converted to 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 17 ppm. Moreover, the electrostatic capacitance calculated | required similarly to Example 2 was 27.5 F / cc.
[0025]
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 13 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 capacitance measured by producing an electric double layer capacitor in the same manner as in Example 2 was 38.1 F / g.
[0026]
Example 6
Using a nickel twin screw extruder equipped with a feed port and a vent port equipped with a meter for activated carbon material and potassium hydroxide, the zone temperature was set to 250 ° C for the first zone, The third zone was set to 300 ° C and the fourth zone was set to 100 ° C. After replacing the inside of the system with nitrogen, a pitch-type fibrous carbon material was used as the carbon material and continuously supplied at 1 kg / hr, while potassium hydroxide was continuously supplied at 2 kg / hr.
[0027]
The residence time in the extruder was 20 minutes, and a granular molded product having a diameter of about 5 mmΦ was discharged from a discharge port provided with a forming nozzle. This discharged product 0.5kg was charged into a nickel vibratory dryer with an internal volume of 3L, heated to 230 ° C while nitrogen was circulated at 10L / min, and the nitrogen flow was continued for 4 hours after reaching it. The solid state was maintained. Then, it cooled under nitrogen circulation and preserve | saved in the desiccator. The following operations were carried out as in Example 1 to obtain the target activated carbon. The specific surface area of the obtained activated carbon was 1200 m ² / g, and the contained nickel was 14 ppm.
[0028]
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 430 ° C. The nickel contained in this activated carbon was 53 ppm.
[0029]
Comparative Example 2
In Example 6, activated carbon was obtained in exactly the same manner except that the mixing of the pitch-based fibrous carbon material and potassium hydroxide was performed at 450 ° C. in the second and third zones of a twin-screw extruder. The nickel contained in this activated carbon was 47 ppm.
[0030]
【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 of an electric double layer 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 (5)

In the method of producing activated carbon by subjecting a carbonaceous material to an alkali treatment, the carbonaceous material and a liquid alkali metal hydroxide liquefied by melting are mixed at 100 ° C. or higher and 300 ° C. or lower , then solidified by cooling and solidified. A method for producing activated carbon, characterized by forming a mixture and activating the solid mixture in an inert gas atmosphere while maintaining a solid state.   The method for producing activated carbon according to claim 1, wherein the alkali metal hydroxide is potassium hydroxide. The method for producing activated carbon according to claim 1 or 2, wherein the water content of the alkali metal hydroxide is 20% by weight or less.   The method for producing activated carbon according to any one of claims 1 to 3, wherein the solid mixture is formed into a size of 0.1 mm to 10 mm.   The method for producing activated carbon according to any one of claims 1 to 4, wherein the activation temperature is 350C to 800C.

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