JP2007269553A - Method of manufacturing activated carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide activated carbon capable of obtaining a high energy density electric double layer capacitor and suitably used as an electrode material. <P>SOLUTION: In the method of manufacturing activated carbon, the activated carbon having 1,200-2,500 m<SP>2</SP>/g specific surface area and suitably used for an active material of an electric double layer capacitor is obtained by activating aggregate of easily graphiting carbon having 5-50 m<SP>2</SP>/g specific surface area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to activated carbon that is suitably used as an active material of an electric double layer capacitor.

  In recent years, electric double layer capacitors have been studied as a compact backup power source with excellent charge / discharge cycle characteristics and rapid charging, and small products of 1F or less have been used in a wide range of fields, mainly for memory backup applications in AV equipment and communication equipment. . However, as the application spreads, it is expected to be a device suitable for driving motors of hybrid vehicles and fuel cell vehicles, storing regenerative energy, etc., and it is a challenge to increase the capacity and current of carbon materials as electrode materials. It has become.

  As a method for solving the above, many methods for producing activated carbon using a graphitizable raw material such as pitch and coke as a raw material have been disclosed (for example, see Patent Documents 1, 2, 3, 4, 5, etc.). . However, generally graphitizable carbon has high crystallinity, so it is difficult to form a pore structure by activation using an oxidizing gas such as water vapor or carbon dioxide, which is necessary for capacity development of electric double layer capacitors. It was difficult to increase the specific surface area. For this reason, the activation of graphitizable carbon is generally performed using a chemical such as potassium hydroxide or sodium hydroxide. However, since this method is activated, metal potassium, metal sodium, and the like are generated, so that the treatment process becomes complicated, and 2 to 5 times the weight of alkali is used with respect to the carbon of the raw material. There were many problems such as high costs. For this reason, the method of activating easily graphitizable carbon with gas was calculated | required.

JP 2005-029444 A JP 2004-273520 A JP 2004-281555 A JP 2004-203715 A JP 2004-107814 A

  An object of the present invention is to provide a method for providing activated carbon suitable as an electrode material by activation of easily graphitizable carbon with an oxidizing gas, which could not be achieved by the prior art.

As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention. That is, the activated carbon that is preferably used for the active material of the electric double layer capacitor of the present invention is manufactured by activating the aggregate of graphitizable carbon having a specific surface area of 5 to 50 m ² / g. be able to. The aggregate of graphitizable carbon evaluated by the laser diffraction scattering method satisfies the following requirements (A) and (B) simultaneously:
(A) The upper limit of the frequency curve (the derivative of the volume-under curve) is 5 μm or less.
(B) d (0.9) is 4 or less, d (0.5) is 2 or less, and d (0.1) is 0.1 or more at the same time.
[Where d (0.9) is a numerical value in μm of the particle size at which the ratio of particles below 90% is expressed, and d (0.5) is 50% larger than 50% of the particles, The number of particles smaller than this is expressed in μm, and d (0.1) indicates the number of particles whose particle ratio is 90% or less, expressed in μm. ]

In the present invention, the activated carbon obtained by the above method has a specific surface area of 1200 to 2500 m ² / g, the graphitizable carbon is fibrous, and the activation treatment is performed with an oxidizing gas. Is included.

  ADVANTAGE OF THE INVENTION According to this invention, the method of providing the activated carbon suitable as an electrode material which was not able to be achieved by the prior art can be provided.

Hereinafter, the present invention will be described in detail.
As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention. An object of the present invention is achieved by obtaining the activated carbon is a specific surface area 1200~2500m ² / g by activation treatment the aggregate of the graphitizable carbon is in a range of specific surface area 5 to 50 m ² / g Is done. When collection of the graphitizable carbon is less than ^{5 m} 2 / g, undesirably it can not be carried out activation by an oxidizing gas to obtain an activated carbon is a specific surface area 1200~2500m ² / g. On the other hand, if it exceeds 50 m ² / g, the bulk density of the graphitizable carbon aggregate becomes very large and not only is difficult to handle, but also a significant reduction in carbonization yield due to activation is not preferable. A more preferable range of the specific surface area of the aggregate of graphitizable carbon is 10 to 40 m ² / g.

Moreover, it is preferable that the aggregate of graphitizable carbon of the present invention satisfies the following requirements (A) and (B) simultaneously.
(A) The upper limit of the frequency curve (the derivative of the volume-under curve) is 5 μm or less.
(B) d (0.9) is 4 or less, d (0.5) is 2 or less, and d (0.1) is 0.1 or more at the same time.
[Where d (0.9) is a numerical value in μm of the particle size at which the ratio of particles below 90% is expressed, and d (0.5) is 50% larger than 50% of the particles, The number of particles smaller than this is expressed in μm, and d (0.1) indicates the number of particles whose particle ratio is 90% or less, expressed in μm. ]

If the upper limit of the frequency curve (derivative of the volume-under curve) exceeds 5 μm, it is not preferable because activated carbon having a specific surface area of 1200 to 2500 m ² / g cannot be produced. In the present invention, in addition to the above conditions, it is necessary that d (0.9) is 4 or less, d (0.5) is 2 or less, and d (0.1) is 0.1 or more at the same time. Even if an aggregate of graphitizable carbon in a range deviating from this condition is activated, activated carbon having a specific surface area of 1200 to 2500 m ² / g cannot be produced, which is not preferable. More preferable values for the condition (B) include d (0.9) of 0.1 to 3 or less, d (0.5) of 0.1 to 1 or less, and d (0.1) of 0.1 or more. is there. In order to activate the graphitizable carbon to obtain activated carbon having a specific surface area of 1200 to 2500 m ² / g, the smaller the particle size, the better, but d (0.9), d (0.5) and d ( If any of 0.1) is less than 0.1, the bulk density of the activated carbon finally obtained increases, and as a result, the weight of the activated carbon that can be packed per unit volume decreases. Absent.

In the method of the present invention, it is preferable to activate the aggregate of graphitizable carbon until the BET specific surface area estimated from the nitrogen adsorption amount is in the range of 1200 to 2500 m ² / g. If the specific surface area of the obtained activated carbon is less than 1200 m ² / g, the double layer capacity sufficient as the active material of the electric double layer capacitor cannot be provided, which is not preferable. On the other hand, if it is 2500 m ² / g or more, the weight of the activated carbon that can be packed per unit volume is lowered, which causes a decrease in the double layer capacity per volume, which is not preferable. A preferable range of the specific surface area is in the range of 1500 to 2300 m ² / g.

The raw material of the aggregate of graphitizable carbon used in the present invention is particularly limited as long as it can be a carbon precursor such as pitch, coke, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, and aramids. However, it is preferable to use pitch, coke, and aramid from the viewpoint of required characteristics such as higher capacity and higher current of the electric double layer capacitor. It is particularly preferable to use mesophase pitch among graphitizable carbons. The graphitizable carbon referred to here is carbon having a structure in which the hexagonal network layer has anisotropy and is appropriately arranged in one direction. A substance having an estimated d002 value of 0.350 nm or less. Further, the aggregate of graphitizable carbon used in the present invention may be a fibrous nanofiber in the range of a specific surface area of 5 to 50 m ² / g. The fiber has an average fiber diameter of 10 to 1000 nm, an average fiber length of 200 nm to 5000 μm, more preferably a fiber diameter of 50 to 800 nm, and an average fiber length of 500 nm to 3000 μm.

  The aggregate of graphitizable carbon of the present invention is preferably subjected to infusibilization and firing treatment before the activation treatment. Infusibilization is a process necessary to suppress melt due to firing and activation of an aggregate of graphitizable carbon. As a method for infusibilization treatment, for example, a method of performing heat treatment at a temperature lower than the melting point of the graphitizable carbon aggregate is preferable. Although the melting point of the graphitizable carbon aggregate depends on its structure, it is generally 100 ° C. or higher and lower than 500 ° C. Some graphitizable carbon structures do not have a melting point. In such a case, it is preferable to perform an infusibilization treatment at a temperature lower than the softening point temperature. In the infusible treatment, the treatment is preferably performed in an oxygen or oxygen / halogen mixed gas atmosphere. As the halogen gas, bromine or iodine is preferably used, and iodine is particularly preferable. The infusibilization time is 10 minutes to less than 24 hours. When the infusibilization time is less than 10 minutes, the infusibilization is insufficient, and the melt of the activated carbon precursor aggregate proceeds by firing and activation, which is not preferable. On the other hand, when the infusibilization treatment time exceeds 24 hours, it is not preferable because the productivity is remarkably reduced. The time required for the infusibilization treatment is preferably 10 minutes or more and 20 hours or less. The infusibilization treatment is a necessary step when the aggregate of graphitizable carbon melts during firing or activation, but is accompanied by melt during firing or activation even if this treatment is not performed. There is no need for a graphitizable carbon aggregate. The firing process is a process necessary for improving the yield by activation by further heat treating the aggregate of graphitizable carbon that has been infusibilized in advance at about 300 to 1000 ° C. in an inert gas atmosphere. It is. When the firing temperature is less than 300 ° C., the yield due to the activation of the graphitizable carbon aggregate is remarkably lowered, which is not preferable. On the other hand, if it exceeds 1000 ° C., it takes a lot of time for activation, which is not preferable from the viewpoint of productivity. A more preferable range of the firing temperature is 350 to 800 ° C.

  The above-mentioned graphitizable carbon aggregates are pulverized after firing carbon precursors such as pitch, coke, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, and aramids at 300 to 1000 ° C. You can get it. The method of pulverization is not particularly limited, but in the dry method, for example, a method using a ball mill, a claw-shaped stator (fixed platen) in which the raw material sent to the pulverization chamber is attached to an impact claw (pin) and a lid As a result of the rotation, a method of pulverizing by impact and shearing action (impact mill), a method of powder colliding with compressed air, and a method of pulverizing by mutual friction (jet mill) can be exemplified. On the other hand, examples of the wet method include a method of charging together with zirconia balls and the like in water or an organic solvent such as N-methylpyrrolidone and dimethylacetamide, and pulverizing the burned charcoal by collision and shearing.

  The activated carbon preferably used for the active material of the electric double layer capacitor of the present invention can be produced by activating the aggregate of carbon particles obtained above. Examples of the activation method include a method using a chemical such as zinc chloride, potassium hydroxide, and sodium hydroxide, a method using an oxidizing gas such as water vapor and carbon dioxide, or a combination thereof.

  Activation using a chemical is a method of activating carbon particles by heat treating the chemical with a carbon material. For example, alkali activation is an example of chemical activation. The alkali activation method is a method of obtaining activated carbon by impregnating a raw material with an alkali hydroxide or an alkali carbonate and activating in a predetermined temperature range. Examples of the activator used in the alkali activation include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkaline earth metal hydroxides such as barium hydroxide, and the like. Potassium oxide and sodium hydroxide are preferred. The conditions for alkali activation differ depending on the activator to be used, and thus cannot be generally stated. For example, when potassium hydroxide is used, the reaction is preferably performed at a temperature of 300 to 1000 ° C, preferably 350 to 900 ° C. . What is necessary is just to select the process time of alkali activation suitably according to a temperature increase rate and process temperature. The activator is usually used in the form of an aqueous solution, and a concentration of about 0.1 to 90 wt% is employed. When the concentration of the aqueous solution of the activator is less than 0.1 wt%, it is not preferable because activated carbon having a high specific surface area cannot be produced. On the other hand, if it exceeds 90 wt%, it is not preferable because activated carbon having a high specific surface area cannot be produced and the carbonization yield is reduced. More preferably, it is 1-50 wt%. Alkali metals, alkali salts, hydroxides, and the like may be present on the surface of the activated carbon material obtained by the above method. Therefore, treatments such as washing with water and drying may be performed.

  Activation using an oxidizing gas is a gas activation method for ordinary granular activated carbon, and is performed at a temperature of 700 ° C. to 1500 ° C. in the presence of an oxidizing gas such as water vapor, carbon dioxide, or air. A more preferable temperature range is 800 ° C to 1200 ° C. The activation treatment time is preferably 3 to 500 minutes. When the activation treatment time is less than 3 minutes, the specific surface area of the obtained activated carbon is remarkably lowered, which is not preferable. On the other hand, when the time is longer than 500 minutes, not only the productivity is lowered, but also the carbonization yield is remarkably lowered.

  In the activation using chemicals, especially the activation using alkali, metal potassium, metal sodium, and the like are generated, so that the treatment process becomes complicated, and the alkali used is 2 to 5 times the weight of the raw material carbon. There are many problems such as the fact that the sum processing is very expensive. For this reason, activation with an oxidizing gas is more preferable. In the present invention, the activated carbon obtained by the activation treatment is preferably further pulverized and classified.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention does not receive any limitation by this.
The specific surface area of the activated carbon was determined from the amount of nitrogen adsorbed evaluated with NOVA1200 (manufactured by Yua Sionics). The particle size distribution of carbon particles or activated carbon was evaluated using a laser diffraction / scattering device (SYSMEX 2000).

[Example 1]
After pulverizing mesophase pitch AR-MP (manufactured by Mitsubishi Gas Chemical Co., Inc.) as a raw material for carbon particles with a mortar, AR-MP particles of less than 300 μm were obtained with a sieve. 10 parts by weight of these particles and 10 parts by weight of water were charged into a 500 cc stainless steel container together with 350 parts by weight of 1 mm zirconia balls, and pulverized using a planetary ball mill apparatus at 200 rpm for 10 hours. The obtained carbon particles were heated in air to 200 ° C. over 1 hour, and then heated from 200 ° C. to 400 ° C. over 3 hours to obtain 400 ° C. calcined charcoal. The obtained calcined charcoal had a BET specific surface area of 12 m ² / g according to the nitrogen adsorption method. Further, when the carbon particles were measured using a laser diffraction / scattering apparatus, the upper limit of the frequency curve (differentiation of the volume-under curve) was 3.3 μm, and d (0.9) was 2.7. d (0.5) was 1.2 or less, and d (0.1) was 0.3. Activated carbon was obtained by introducing the carbon particles into a tubular furnace in which carbon dioxide gas was circulated at 2 L / min for 2 hours. The specific surface area of the obtained activated carbon was 1480 m ² / g.

[Example 2]
100 parts by weight of poly-4-methylpentene-1 (TPX: Grade RT-18 [manufactured by Mitsui Chemicals, Inc.) as a thermoplastic resin and mesophase pitch AR-HP (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a thermoplastic carbon precursor 11.1 parts were melt-kneaded with the same direction twin screw extruder (TEX-30 manufactured by Nippon Steel Works, barrel temperature 320 ° C., under nitrogen stream) to prepare a mixture. The dispersion diameter of the mixture obtained under these conditions into the thermoplastic resin of the thermoplastic carbon precursor was 0.05 to 2 μm. Further, this mixture was held at 300 ° C. for 10 minutes, but aggregation of the thermoplastic carbon precursor was not observed, and the dispersion diameter was 0.05 to 2 μm.

  Next, the mixture was discharged and spun from a discharge hole at 330 ° C. to prepare a precursor fiber having a fiber diameter of 15 μm. 1 part by weight of this precursor fiber was immersed in 200 parts by weight of decalin heated to 150 ° C. to dissolve the thermoplastic resin. Subsequently, the thermoplastic resin was removed by filtration to obtain a carbon nanofiber precursor. After the carbon nanofiber precursor is washed several times with acetone and dried, the temperature is raised from room temperature to 200 ° C. in air for 1 hour, and then heated from 200 ° C. to 400 ° C. in 3 hours, so that the carbon nanofiber precursor is heated at 400 ° C. I got a fiber. The obtained carbon nanofibers were in an apparent powder form, but it was confirmed by electron microscope observation that the average fiber diameter was 200 nm and the average fiber length was 2 μm (see FIG. 1).

Moreover, the BET specific surface area by a nitrogen adsorption method is 23 m < ² > / g, The upper limit of the frequency curve (Volume-under curve derivative) evaluated with the laser diffraction / scattering apparatus is 4.2 micrometers, d (0.9) Was 3.8, d (0.5) was 0.8 or less, and d (0.1) was 0.2. Activated carbon was obtained by introducing the carbon particles into a tubular furnace in which carbon dioxide gas was circulated at 2 L / min for 2 hours. The specific surface area of the obtained activated carbon was 1856 m ² / g.

[Comparative Example 1]
After pulverizing mesophase pitch AR-MP (manufactured by Mitsubishi Gas Chemical Co., Inc.) as a raw material for carbon particles with a mortar, AR-MP particles of less than 300 μm were obtained with a sieve. 10 parts by weight of these particles were charged in a 500 cc stainless steel container together with 50 parts by weight of 10 mm zirconia balls, and pulverized using a planetary ball mill apparatus at 200 rpm for 15 minutes. The obtained carbon particles were heated in air to 200 ° C. over 1 hour, and then heated from 200 ° C. to 400 ° C. over 3 hours to obtain 400 ° C. calcined charcoal. The resulting calcined charcoal had a BET specific surface area of 0.3 m ² / g as determined by the nitrogen adsorption method. Further, when the carbon particles were measured using a laser diffraction / scattering apparatus, the upper limit of the frequency curve (derivation of the volume-under curve) was 154 μm, d (0.9) was 122, and d (0. 5) was 56 or less, and d (0.1) was 7. Activated carbon was obtained by introducing the carbon particles into a tubular furnace which was circulated at 2 L / min of carbon dioxide gas for 6 hours. The specific surface area of the obtained activated carbon was 168 m ² / g.

3 is an electron micrograph (photographing magnification: 5000 times) of carbon nanofibers (powder) obtained by the operation of Example 2. FIG.

Claims (4)

Obtained by activation treatment of the aggregate of the graphitizable carbon is in a range of specific surface area 5 to 50 m ² / g, a specific surface area 1200~2500m ² / g, good to the active material of the electric double layer capacitor Method for producing activated carbon used. The method for producing activated carbon according to claim 1, wherein the aggregate of graphitizable carbon evaluated by a laser diffraction scattering method satisfies the following requirements (A) and (B) simultaneously.
(A) The upper limit of the frequency curve (the derivative of the volume-under curve) is 5 μm or less.
(B) d (0.9) is 4 or less, d (0.5) is 2 or less, and d (0.1) is 0.1 or more at the same time.
[Where d (0.9) is a numerical value in μm of the particle size at which the ratio of particles below 90% is expressed, and d (0.5) is 50% larger than 50% of the particles, The number of particles smaller than this is expressed in μm, and d (0.1) indicates the number of particles whose particle ratio is 90% or less, expressed in μm. ]   The method for producing activated carbon according to claim 1, wherein the graphitizable carbon is fibrous.   The method for producing activated carbon according to claim 1, wherein the activation treatment is performed with an oxidizing gas.

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