JP2002104816A - Activated carbon and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode which is for a capacitor and has high affinity for water and has high electrostatic capacity per volume. SOLUTION: An activated carbon which is obtained by activating a carbonaceous material is further acid-treated at an elevated temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to activated carbon and a method for producing the same. More specifically, the present invention relates to activated carbon obtained by further activating activated carbon obtained by activating a carbonaceous material, and a method for producing the same. The activated carbon according to the present invention is suitable for water purification because of its excellent affinity with water, and is suitable as an electrode for an electric double layer capacitor because of its large capacitance.

[0002]

2. Description of the Related Art Activated carbon is widely used in the food industry, chemical industry, pharmaceutical industry and other various industries. Although these mainly utilize the adsorption performance of activated carbon, adsorbents having even better adsorption performance are being pursued.
In recent years, electric double-layer capacitors have been attracting attention as backup power supplies and auxiliary power supplies, and developments of activated carbon focusing on the performance of the electric double-layer capacitors as electrodes have been made widely. An electric double layer capacitor using activated carbon as a polarizable electrode has excellent capacitance, and the demand is rapidly growing with the development of the electronics field.
Recently, in addition to miniaturization of conventional memory backup power supplies and the like, large-capacity products used for auxiliary power supplies such as motors have been developed.

[0003] The principle of the electric double layer capacitor has been known for a long time, but it has only recently been started to use it as a device. The capacitance of the electric double layer capacitor is mainly controlled by the surface area of the polarizable electrode on which the electric double layer is formed, the electric double layer capacitance per unit area, the resistance of the electrode, and the like. In practical terms, it is also important to increase the density of the electrodes themselves in order to increase the capacitance per unit volume and reduce the volume of the electric double layer capacitor. Conventionally, as activated carbon for electric double layer capacitors, (1) activated carbon obtained by activating resin material, coconut shell, pitch and coal under acidic conditions such as steam and gas (Large-capacity capacitor technology and materials, published by CMC Corporation ( 1998)), (2) Activated carbon (WO 91) obtained by activating the above-mentioned raw material with a chemical having a strong oxidizing power such as KOH.
/ 12203, JP-A-10-199767) and the like have been used.

As an example of activating a carbonaceous material with an alkali and using it as a polarizable electrode of an electric double layer capacitor,
For example, Japanese Patent Application Laid-Open No. 1-139865 discloses that a carbon fiber is heated in an inert gas atmosphere at a temperature exceeding 500 ° C. in the presence of an excess amount of an alkali metal hydroxide to obtain a large surface area carbon fiber. A method is disclosed. Japanese Patent Application Laid-Open No. Hei 5-258996 discloses an electric element formed by melt spinning a pitch as a raw material, activating a carbonaceous fiber obtained by a heat treatment with an aqueous solution of an alkali metal hydroxide, decalcifying the powder, and then pulverizing and shaping the powder. An electrode for a multilayer capacitor is disclosed in JP-A-7-161.
No. 587 discloses an electrode for an electric double layer capacitor which is obtained by activating a carbonaceous raw material with steam, further activating it with an alkali metal hydroxide, and then pulverizing and forming the same.

[0005]

As described above, the adsorbent is required to further increase the adsorption performance, while the electrode for the capacitor is required to have a high capacitance. However, when the activated carbon obtained by the method (1) is used, a sufficient capacitance cannot be obtained, and in order to obtain a required capacitance, a large device is required. According to the method of (1), by activating at a high temperature using an activator having strong oxidizing power such as potassium hydroxide, it is possible to obtain a certain amount of high-capacity activated carbon. Is still not enough. In addition, the above-mentioned JP-A-1-139865 and JP-A-5-258
996 and JP-A-7-161587 are still not satisfactory. Accordingly, an object of the present invention is to provide an activated carbon having a high capacitance while having excellent adsorption performance for pollutants dissolved in water and a method for producing the same.

[0006]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that the above problem can be solved by further treating an activated carbon obtained by activating a carbonaceous material at an elevated temperature with an acid. Thus, the present invention has been completed. That is, the present invention is an activated carbon obtained by further activating an activated carbon obtained by activating a carbonaceous material. Another aspect of the present invention is an electrode for an electric double layer capacitor obtained by molding such activated carbon. Yet another aspect of the present invention is a method for producing activated carbon, in which activated carbon obtained by activating a carbonaceous material is further subjected to an acid treatment at an elevated temperature.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The carbonaceous material used in the present invention is not particularly limited as long as it forms activated carbon upon activation. For example, coconut shell, petroleum and / or coal pitch, coke , Phenolic resin,
PVC can be given. The shape of the carbonaceous material is not limited, and various shapes such as granular, fine powder, fibrous, and sheet shapes can be used.

[0008] The fibrous or sheet-like material is not particularly limited as long as it forms activated carbon upon activation. For example, coconut shell, petroleum and / or coal pitch, coke, phenolic resin, etc. Fibrous or sheet-like carbonaceous materials. Specifically, natural cellulose fiber such as cotton, viscose rayon, regenerated cellulose fiber such as polynosic rayon, pulp fiber, polyvinyl alcohol fiber, woven or non-woven fabric such as synthetic fiber such as ethylene vinyl alcohol fiber, film, felt, A sheet-like material can be exemplified.

[0009] Activated carbon can be obtained by activating and activating these carbonaceous materials. Conventionally known activation methods include zinc chloride, phosphoric acid, sulfuric acid, calcium chloride, sodium hydroxide, and bichromium. A chemical activation method using an oxidizing chemical such as potassium acid or potassium permanganate, or a gas activation method such as steam, propane gas, combustion waste gas, or carbon dioxide gas is employed.

As the activation method, it is preferable to use an alkali activation method from the viewpoint of exhibiting a high capacitance. As the alkali activation method, for example, DENKI KAGAKU,
12 (1998) p. 1311-1317, carbon, 17
7 (1997) p. Known methods specifically shown in 76-79 and the like may be used. As the alkali,
Examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth hydroxides such as calcium hydroxide and magnesium hydroxide. Particularly preferred are sodium hydroxide and potassium hydroxide. The amount of the alkali used is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the carbonaceous material, and more preferably 0.1 to 10 parts by weight in terms of operability and safety.

The activated carbon of the present invention can be obtained, for example, by further treating the activated carbon obtained as described above with an acid at an elevated temperature. Examples of the acid include mineral acids such as concentrated sulfuric acid, fuming sulfuric acid, diluted nitric acid, phosphoric acid, polyphosphoric acid, pyrophosphoric acid, and metaphosphoric acid, and sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid. Although it can be used, it is particularly preferable to use concentrated sulfuric acid, phosphoric acid or polyphosphoric acid. Among them, polyphosphoric acid is preferable. These acids are usually used alone, but may be used in combination.

As the activation method, there are conventionally known chemical activation excluding alkali activation, steam, propane gas, combustion waste gas, and the like.
When gas activation such as carbon dioxide is employed, an acid such as sulfuric acid or phosphoric acid may be used in an aqueous solution. In this case, the acid concentration is 0.01 to 100% by weight, and the reaction efficiency, operability, From the viewpoint of safety, it is preferably used at 0.1 to 80% by weight, more preferably 0.5 to 60% by weight. When the above-mentioned diluted nitric acid is used, it is preferable to use a 5 to 20% by weight aqueous solution.

The amount of the acid used is 0.01 to 100 times the weight of activated carbon. Reaction processing efficiency,
From the viewpoint of operability and safety, the operation is preferably performed at 0.1 to 50 times by weight, and more preferably at 0.5 to 20 times by weight. The treatment temperature varies depending on the type of acid used and cannot be unconditionally determined, but is lower than the temperature at the time of activation and higher than room temperature, that is, 30 ° C.
It is desirable to carry out at a temperature of 500 ° C, preferably 40 ° C to 300 ° C. The acid treatment can be carried out in an air atmosphere, but it is safe and preferable to carry out the treatment in an atmosphere of an inert gas such as nitrogen or argon. Although it can be carried out under any pressure, it is generally carried out under atmospheric pressure.

The acid-treated activated carbon is introduced into water to remove the acid. Washing treatment such as washing with water is sufficient for removing the acid. When the surplus acid remains on the activated carbon performance, it can be removed by a treatment such as neutralization. The activated carbon from which the acid has been removed is dried by heating at normal temperature or under atmospheric pressure and / or reduced pressure. However, in the case of manufacturing an electrode, extreme drying at this point does not have a significant meaning, so that it is sufficient to perform drying to such an extent that no trouble is caused.

The activated carbon of the present invention preferably has an absorption spectrum at 1600 to 1800 cm ^-1 in infrared spectroscopy. In order to analyze the activated carbon by infrared spectroscopy, a known method such as a method of measuring a powder or a solid by a reflection method, a method of dispersing in a liquid paraffin, and a KBr tablet method (hereinafter abbreviated as KBr method) may be used. . The amount of activated carbon used for the measurement may be such that infrared light can be transmitted therethrough, and its concentration is not particularly limited.
It is carried out at 01 to 10% by weight, preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight. FIG.
Is an infrared absorption spectrum of the activated carbon obtained in Example 3 described below, FIG. 2 is an infrared absorption spectrum of the activated carbon obtained in Example 5, and FIG. 3 is an acid treatment with 10% nitric acid at 120 ° C. for 6 hours. FIG. 4 is an infrared absorption spectrum of activated carbon obtained by performing the method.
Is an infrared absorption spectrum of phenolic activated carbon (BP-20 manufactured by Kuraray Chemical Co., Ltd.) before acid treatment.

The obtained activated carbon has excellent affinity for water, and is used as it is or molded, and is used for water treatment such as a water purifier for removing trace harmful substances in water such as free chlorine, trihalomethane and chloroform. You. Further, for a capacitor, it is preferably formed into an electrode. As a method of forming an electrode, a generally known method can be applied. That is, if necessary, commercially available materials known as binders such as polytetrafluoroethylene,
After adding 0 to several percent and mixing well, it can be formed into an electrode by placing it in a mold and performing pressure molding or rolling to form a sheet and punching it into a required shape. At that time, if necessary, heat can be applied. An unnecessarily high temperature affects not only the deterioration of the binder component used but also the physical properties due to the surface structure of the activated carbon component, for example, the specific surface area. Therefore, it is needless to say that the temperature condition must be considered.

Further, at the time of molding, a conductive substance such as conductive carbon or metal fine particles may be added to lower the resistance of the electrode. This is effective in lowering the internal resistance of the polarizable electrode and reducing the electrode volume. The electrodes are preferably incorporated into an electric double layer capacitor and used as a capacitor. A schematic diagram of the capacitor is shown in FIG. Reference numerals 1 and 2 denote current collecting members, reference numerals 3 and 4 denote polarizable electrodes made of the activated carbon of the present invention, reference numeral 5 denotes a separator made of a polypropylene non-woven fabric or the like, and reference numeral 6 denotes a lid made of a material such as stainless steel. Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In addition,
Infrared spectroscopy in Examples and Comparative Examples was performed by the KBr method. That is, 10 mg of activated carbon and 1 g of KBr were mixed, tablet-molded using a pressure molding machine under a pressure of 1000 kg / cm2 for 1 hour, and the spectrum of the obtained tablet was measured by an infrared absorption spectrometer.

[0018]

EXAMPLES Reference Experimental Example 1 Coconut shell charcoal (YP-Kuraray Chemical Co., Ltd.) activated in a three-neck flask equipped with a thermometer and a stirrer under a combustion waste gas atmosphere.
17) 10 g was added, 20 g of concentrated sulfuric acid was added, and the inside of the reactor was replaced with nitrogen. While stirring, the mixture was placed in an oil bath heated to 200 ° C. and stirred with heating for 2 hours. The obtained mixture was poured into 500 g of ice water. After the activated carbon was sufficiently dispersed, the mixture was filtered and washed with 2 liters (L) of ion-exchanged water. After washing, it was dried by heating at 100 ° C. under reduced pressure to obtain 10.7 g of activated carbon.

REFERENCE EXPERIMENTAL EXAMPLE 2 A coal pitch (MPM-BL manufactured by Adchemco) was placed in a 2-inch Hastelloy reactor equipped with a thermometer and a stirrer.
g and 85% potassium hydroxide were added, and the system was replaced with nitrogen. Then, the temperature was increased to 700 ° C. at a rate of 200 ° C./hour under a nitrogen stream. After reaching 700 ° C., stirring was continued for 2 hours, and then cooled to room temperature over 2 hours. Nitrogen was passed through a distilled water bubbler for 1 hour, washed neutralized with 10% hydrochloric acid, washed with distilled water to remove salts, and dried to obtain 6.8 g of pitch charcoal.

Into a three-necked flask, put 6 g of the above pitch charcoal,
20 g of concentrated sulfuric acid was added, and the inside of the reactor was replaced with nitrogen. While stirring, the mixture was placed in an oil bath heated to 200 ° C. and stirred with heating for 2 hours. The obtained mixture was poured into 500 g of ice water. After the activated carbon was sufficiently dispersed, the mixture was filtered and washed with 2 L of ion-exchanged water. After washing, it was dried by heating at 100 ° C. under reduced pressure to obtain 5.8 g of pitch charcoal.

Reference Experimental Example 3 4.1 g of phenolic resin charcoal was obtained in the same manner as in Reference Experimental Example 2, except that a phenolic resole resin (BBL141B manufactured by Showa Kobunshi) was used in place of the coal pitch.

REFERENCE EXPERIMENTAL EXAMPLE 4 A glass vat was charged with 50 g of sulfuric acid and 20 g of activated carbon nonwoven fabric (ACF made by Kuraray Chemical Co., Ltd.), and immersed at room temperature for 30 minutes to impregnate the activated carbon nonwoven fabric with sulfuric acid. After dewatering at room temperature for 30 minutes, drying under a nitrogen stream for 15 minutes,
The temperature was further raised to 220 ° C., and drying was performed for 15 minutes in a drying oven. The dried activated carbon nonwoven fabric was placed in 200 g of purified water to remove the acid. This operation was repeated three times, and it was confirmed that the purified water did not show acidity. After draining, 50
C., and further vacuum-dried at the same temperature for 10 hours to obtain 19.3 g of activated carbon nonwoven fabric treated with sulfuric acid.

Example 1, Comparative Example 1 200 g of the activated carbon obtained in Reference Experimental Example 1 was charged into a cylindrical container having an inner diameter of 40 mm and a length of 90 mm, and the total organic carbon (TO) was measured.
C) Sodium hypochlorite was added to the river water having a concentration of 2.5 ppm so that the free chlorine concentration became 2 ppm, and chloroform, bromoform, bromodichloromethane and dibromochloromethane were added at 50 ppb and 20 pp, respectively.
b, 20 ppb, and 20 ppb of the raw test water added thereto were passed at SV 600 hr ^{- 1} for 2 hours. When the amount of chloroform in the water after the treatment and the total amount of the above four types of trihalomethanes were analyzed according to JIS K 0125, chloroform was 2 ppb or less, and the total of trihalomethanes was 8 ppb or less. For comparison, coconut shell charcoal (YP-17 Kuraray Chemical Co., Ltd.) not subjected to acid treatment was passed through, and the same measurement was performed.
The total of 0 ppb and trihalomethane was 90 ppb.

Example 2 The activated carbon obtained in Reference Example 1 was pulverized to an average particle size of 5 to 20 μm to obtain powdered activated carbon. The powdered activated carbon was 80% by weight, the conductive carbon was 10% by weight, and the polytetrafluoroethylene 10% was used.
A mixture consisting of% by weight was prepared and kneaded. Next, the mixture was formed into a sheet having a thickness of 300 μm by roll rolling, and formed into a circular shape having a diameter of 2 cm using a punch. Then, drying was performed at 150 ° C. under reduced pressure for 4 hours to obtain a sheet electrode.

As shown in FIG. 5, a current collecting electrode, a polarizable electrode sheet, a polypropylene nonwoven fabric, a polarizable electrode, and a current collecting electrode were laminated on a stainless steel lid in a glow box having a dew point of -80 ° C. or less. After that, the polarizable electrode was impregnated with a propylene carbonate solution containing 1 mol of tetraethylammonium tetrafluoroborate, and was caulked and sealed on a stainless steel upper lid using a polypropylene insulating gasket. Using a Hioki Electric Double Layer Capacitor Evaluation Apparatus, a constant current up to 2.5 V and 10 charge / discharge cycle tests were performed at room temperature to measure the capacitance. The average value of the capacitance obtained from the discharge curve by an ordinary method was 15.4 F / CC.

Examples 3 to 10 and Comparative Examples 2 to 3 Activated carbon was converted to a phenolic resin (BP-2 manufactured by Kuraray Chemical Co., Ltd.).
0) and acid treatment was performed in the same manner as in Reference Experimental Example 1 (Examples 3 to 5, 7 to 8, and 10). Activated carbon YP-17 was treated with acid in the same manner as in Reference Example 1 (Examples 6 and 9). Those not subjected to the acid treatment were referred to as Comparative Examples 2 and 3, respectively.
The measurement results of the capacitance and the spectrum by infrared spectroscopy are shown in Table 1, and the spectra obtained by infrared spectroscopy of the activated carbons of Example 3, Example 5, Example 10 and Comparative Example 2 are shown in FIGS. Indicated.

[0027]

[Table 1]

Example 11 Using the pitch charcoal obtained in Reference Experimental Example 2, the capacitance and the spectrum by infrared spectroscopy were measured in the same manner as in Example 2. Table 1 shows the results.

Examples 12 to 14 The carbonaceous materials obtained in Reference Examples 2 and 3 were subjected to an acid treatment under the conditions shown in Table 2, and the capacitance and the spectrum by infrared spectroscopy were measured in the same manner as in Example 2. . Table 2 shows the results.

Comparative Examples 4 and 5 For the pitch coal and the resin coal not subjected to the acid treatment, the capacitance and the spectrum by infrared spectroscopy were measured in the same manner as in Example 2. Table 2 shows the results.

[0031]

[Table 2]

Example 15 The activated carbon nonwoven fabric obtained in Reference Experimental Example 4 was formed into a circular shape having a diameter of 2 cm using a punching machine, and then 150 ° C. under reduced pressure.
For 4 hours to produce a polarizable electrode. In a glow box having a dew point of −80 ° C. or less, the current collecting electrode 5, the polarizable electrode sheet 3, the polypropylene nonwoven fabric 2, the polarizable electrode 1, and the current collecting electrode 4 are placed on a stainless steel lid 6 as shown in FIG. The laminate was laminated, a polarizable electrode was impregnated with a propylene carbonate solution containing 1 mol of tetraethylammonium tetrafluoroborate, and the stainless steel upper lid was caulked and sealed using a polypropylene insulating gasket.
Using an electric double layer capacitor evaluation device manufactured by Hioki Electric Co., a constant current up to 2.5 V and a charge / discharge cycle test were performed 10 times at room temperature to measure the capacitance. The average value of the capacitance obtained from the discharge curve by an ordinary method is 40.1 F / g.
Met. The spectrum was measured by infrared spectroscopy, and the results are shown in Table 2.

Example 16 A polarizable electrode was prepared in the same manner as in Example 15 except that phosphoric acid was used as the acid, and the capacitance and the spectrum by infrared spectroscopy were measured. Table 3 shows the results.

Example 17 A polarizable electrode was prepared in the same manner as in Example 15 except that drying after impregnation with sulfuric acid was performed at 200 ° C. for 2 hours, and a capacitance and a spectrum by infrared spectroscopy were measured. Table 3 shows the results.

Comparative Example 6 A polarizable electrode was made of an activated carbon nonwoven fabric which was not subjected to an acid treatment.
The capacitance and the spectrum by infrared spectroscopy were measured. Table 3 shows the results.

[0036]

[Table 3]

[0037]

According to the present invention, the affinity with water is high,
Activated carbon with a large capacitance can be obtained. Such activated carbon is suitable for water treatment, and is preferably molded and used as an electrode for a capacitor.

[Brief description of the drawings]

FIG. 1 is an infrared absorption spectrum of activated carbon obtained by treating carbonaceous material BP-20 with sulfuric acid.

FIG. 2 is an infrared absorption spectrum of another activated carbon obtained by treating a carbonaceous material BP-20 with sulfuric acid.

FIG. 3 is an infrared absorption spectrum of activated carbon obtained by treating carbonaceous material BP-20 with 10% nitric acid.

FIG. 4 is an infrared absorption spectrum of a carbonaceous material BP-20.

FIG. 5 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 Polarized electrode 4 Polarized electrode 5 Separator 6 Lid

 ──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 2000-221784 (P2000-221784) (32) Priority date July 24, 2000 (July 24, 2000) (33) Countries claiming priority Japan (JP) (72) Inventor Shuji Nishimura 4342 Tsuruumi, Bizen City, Okayama Prefecture Inside Kuraray Chemical Co., Ltd. (72) Inventor Yoshifumi Egawa 4342 Tsuruumi, Bizen City, Okayama Prefecture Inside Kuraray Chemical Co., Ltd. (72) Inventor Motoki Aoki Okayama 4342 Tsuruumi, Bizen Prefecture Kuraray Chemical Co., Ltd. F-term (reference) 4D024 AA05 AB11 BA02 BB01 BC01 4G046 HC03 HC05 HC07 HC14 4G066 AA04A AA05B AA13D AA47D AA50D AA53D AC25A AE05B BA03 DA08 FA12

Claims (8)

[Claims] An activated carbon obtained by further treating an activated carbon obtained by activating a carbonaceous material with an acid. 2. The activated carbon according to claim 1, wherein the activation is an alkali activation. 3. The activated carbon according to claim 1, wherein the acid is a mineral acid. 4. The method according to claim 3, wherein said mineral acid is sulfuric acid or dilute nitric acid.
Activated carbon as described. 5. The activated carbon according to claim 3, wherein said mineral acid is a phosphoric acid. 6. An infrared spectroscopic analysis of 1600 to 18
6. The activated carbon according to claim 1, which has an absorption spectrum at 00 cm ^-1 . 7. An electrode for an electric double layer capacitor obtained by molding the activated carbon according to claim 1. 8. A method for producing activated carbon, wherein the activated carbon obtained by activating the carbonaceous material is further subjected to an acid treatment at an elevated temperature.