JP2005132702A - Method and apparatus for producing activated carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that although the activated carbon obtained by using, as a raw material, mesophase-based soft carbon and alkali-activating the raw material and having a high specific surface area is suitable as an electric double layer capacitor, the capacitor capacitance is decreased significantly over time when the activated carbon is used as the electric double layer capacitor for a long time. <P>SOLUTION: The method for producing the activated carbon comprises activating a raw material with alkali metal compounds 12, then deactivating the alkali metal compounds 12, removing the deactivated alkali metal compounds 12 to obtain activated carbon 15, and subjecting the obtained activated carbon 15 to heat treatment 6 and washing 7. In the heat treatment 6, the temperature rising rate is 0.1-100°C/min, the maximum temperature is 500-1,000°C, and the time for holding the maximum temperature is ≤10 h. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for producing activated carbon, and more particularly to activated carbon suitably used as an electrode material for an electric double layer capacitor.

  As an apparatus for producing activated carbon activated using alkali metal compounds, there is an apparatus in which a raw material supply unit, a tunnel furnace, a cooling zone, a water injection chamber, a gas replacement chamber, and a discharge unit are connected (for example, see Patent Document 1). .

  In addition, a carbon material is heated to 400 to 500 ° C., held for a certain period of time, and then activated at 600 to 900 ° C., and a raw material supply unit, a kneading low temperature heat treatment furnace, a high temperature heat treatment furnace, and an alkali deactivation zone (For example, refer to Patent Document 2).

  These technologies basically consist of a raw material supply unit that inputs raw materials of a carbon material and alkali metal compounds (potassium hydroxide, sodium hydroxide, lithium hydroxide, etc.), an activation reaction unit that makes the carbon material porous, A cooling zone (cooling part) for cooling the reaction product from a high activation reaction temperature, an inactivation zone (alkali metal inactivation part) of active alkali metals by-produced by the activation reaction, and a water injection chamber ( This is a technology for producing activated carbon having a high specific surface area.

  Activated carbon (alkali activated charcoal) having a high specific surface area produced by the above technique is excellent in initial capacitor capacity when used for an electric double layer capacitor. However, there has been a problem of deterioration over time that the capacitance of the capacitor is greatly reduced when used for a long time.

In particular, when a carbon material called mesophase-based soft carbon is used as a raw material, activated carbon having a large specific surface area suitable for an electric double layer capacitor cannot be produced unless activated by alkali. However, this alkali activated activated carbon has a problem that the performance deterioration is large.
JP-A-5-306109 (page 2-6, FIG. 1) Japanese Patent Laid-Open No. 2001-163612 (page 2-6, FIG. 1)

  Electric double layer capacitors using activated carbon, especially activated carbon obtained when mesophase soft carbon is used as the carbon material, have excellent initial capacitor capacity, but capacitor capacity when used for a long time There is a problem of so-called deterioration over time, in which the decrease in the resistance is large.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method and a manufacturing apparatus for manufacturing a highly durable activated carbon for electric double layer capacitors with little change with time.

  Activated carbon, the inventors of the present invention have made extensive studies to solve the above problems, and after the conventional normal activated carbon production process of removing by-products composed of alkali metals from activated carbon generated by alkali activation, further heat treatment is performed. By applying and washing, the inventors have obtained the knowledge that a highly durable activated carbon with little deterioration with time can be produced, and the present invention has been completed.

  That is, the present invention is to activate a carbon material using alkali metal compounds, inactivate the generated alkali metals, remove the deactivated alkali metals, and further perform heat treatment and washing. Provided is a method for producing activated carbon. As the carbon material, various activated carbon precursors can be used. In the present invention, particularly, a material that becomes high-quality activated carbon by alkali activation is targeted. The present invention is a technique for obtaining activated carbon with little deterioration over time for an electric double layer capacitor of activated carbon subjected to alkali treatment.

  The heat treatment is preferably performed at a heating rate of 0.1 to 100 ° C./min, a maximum temperature of 500 to 1000 ° C., and a maximum temperature holding time of 10 hours or less.

  In addition, a higher effect can be expected by repeatedly performing heat treatment and cleaning a plurality of times.

  The apparatus of the present invention capable of suitably carrying out the above-described method of the present invention includes a heating apparatus for charging activated carbon to be treated and heating it in atmospheric gas, a cleaning apparatus for cleaning the heated activated carbon with a cleaning liquid, and a pump And a separator for separating the washed activated carbon and the washing liquid after washing.

  ADVANTAGE OF THE INVENTION According to this invention, it became possible to manufacture the activated carbon for electric double layer capacitors with high capacity | capacitance, little deterioration with time, and high durability.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing an example of a method for producing activated carbon according to the present invention. The present invention is a technique for improving the characteristics of activated carbon produced by alkali activation. However, the present invention is not limited to FIG.

  Hereinafter, it demonstrates according to drawing. The carbon material 11 is mixed with the alkali metal compounds 12 in the raw material supply unit 1.

  As the carbon material 11 used as a raw material in the present invention, carbonized products such as coconut shells and coal, carbonized products such as mesophases prepared from petroleum and coal pitch, petroleum and coal coke, phenol resin carbonized products, carbon Examples thereof include black, fullerene black, carbon fiber, and carbon nanotube. These can be used alone or as a mixture. Moreover, what was pre-baked before the alkali activation reaction can also be used. In particular, when a mesophase-based carbonized material is used as a raw material, it is preferable to apply it to a high-quality activated carbon.

  About the shape of the carbon material 11, any shape, such as a granular form and a fibrous form, can be used. When the particle size is large, uniform activation cannot be performed. Therefore, the particle size is 500 μm or less, particularly preferably about 100 to 10 μm. Similarly, in the case of a fibrous form, the minor axis is preferably 500 μm or less, particularly about 100 to 10 μm, and the aspect ratio is preferably 1 or more and 10 or less.

  The alkali metal compounds 12 are preferably alkali metal hydroxides. Specifically, lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, rubidium hydroxide and the like can be used alone. Any of the mixtures can be used. The particle size when used as a solid may be a commercially available pellet, but from the viewpoint of improving the mixing with a solid carbon material, a finer particle size is desirable, and a particle size of 500 μm or less is suitable. It can also be used in the form of a solution, for example, it may be mixed in an aqueous solution.

  As the amount of the alkali metal compounds 12 to be mixed increases, the mixed state is improved, but preferably 1 to 5 parts by weight, preferably 1 to 3 parts by weight, particularly preferably 2 parts by weight with respect to 1 part by weight of the carbon material 11. Part. If the amount is less than 1 part by mass with respect to the carbon material, the mixed state is deteriorated, and the alkali metal compounds 12 necessary for making the porous material are insufficient, so that sufficient activation cannot be performed. If it exceeds 5 parts by mass, the proportion not contributing to the activation reaction increases, which is not preferable.

  The carbon material 11 mixed with the alkali metal compounds 12 is activated at a high temperature in the atmosphere of the inert gas 13 in the activation reaction part 2. The atmosphere may be inert, and helium, argon, or the like can be used as the inert gas 13, but nitrogen is sufficient in that it is economical.

  The temperature increase rate in the activation reaction part 2 is preferably 100 ° C./min or less in order to avoid foaming of the mixture of the carbon material 11 and the alkali metal compounds 12, and if the temperature increase rate is too small, the production efficiency is deteriorated. It is preferable to set it as ° C / min or more. More preferably, it is 10-30 degrees C / min.

  The maximum temperature of the activation reaction part 2 is preferably 600 ° C. or higher because the activation reaction does not proceed sufficiently if it is too low, and it is preferably 600 to 900 ° C. since no significant reaction progress is observed even when it exceeds 900 ° C. . The holding time at the maximum temperature is not particularly required, but holding for about 5 hours or less is preferable because the temperature distribution becomes uniform and activated carbon with uniform quality can be obtained. A more preferable holding time is 1 hour to 3 hours.

  Regarding the type of furnace that is a heating device used in the activation reaction unit 2, various types such as a continuous rotary kiln furnace, a pusher type tunnel furnace, a roller hearth type tunnel furnace can be used in addition to a batch type rotary kiln furnace. .

  The carbon material that has finished the activation reaction is cooled in the cooling unit 3 together with the alkali metal compounds. The atmosphere of the cooling unit 3 is preferably the above-described inert atmosphere, and there is no restriction on the temperature lowering rate. Usually, it is cooled by natural air cooling or forced air cooling from the outside of the apparatus.

  After cooling, active alkali metals generated by this activation reaction, for example, lithium, sodium, potassium, cedium, rubidium, and the like are inactivated by the alkali metals inactivating section 4. At this time, a reactive gas 14 such as water vapor, carbon dioxide gas, or a mixture thereof is circulated through the alkali metal deactivation section 4. For example, when potassium hydroxide is used as the alkali metal compound for the activation reaction, metal potassium is generated, so that it is converted to potassium hydroxide when flowing water vapor, and converted to potassium carbonate when flowing carbon dioxide gas. It becomes a stable compound and is inactivated. Furthermore, the mixture of the carbon material (activated carbon) and the alkali metal compound in which the alkali metal has been deactivated may be poured in the sense of complete deactivation, or conversely, the mixture may be submerged in water. It may be thrown into.

  In the alkali metal removal unit 5, the deactivated alkali metal is removed from the carbon material (activated carbon), and an activated carbon material (activated carbon) is obtained. For example, cleaning with water is effective for removing the alkali metals, but other means may be used. That is, since the above-mentioned potassium hydroxide or potassium carbonate is water-soluble, it can be easily removed by washing with water. The water used for removing the alkali metals can be filtered water or the like in addition to clean water. However, since impurities contained in a very small amount are adsorbed on the activated carbon surface, resulting in a decrease in quality. It is preferable to use distilled water. Further, the washing is preferably carried out until the pH of the washing water becomes 5.8 to 8.5, and more preferably, the washing water is washed until the pH becomes 7. The washing temperature may be room temperature, but if it is heated to around 80 ° C., the washing time is shortened.

  In addition, when producing activated carbon with a batch type apparatus, for example, when using a batch type rotary kiln furnace, as long as the carbon material and alkali metal compounds are charged, the subsequent mixing, activation, cooling, alkali metal inertness (Deactivation) can be performed only by temperature raising / lowering operation and atmosphere gas switching operation. That is, the raw material supply unit 1, the activation reaction unit 2, the cooling unit 3, and the alkali metal deactivation unit 4 can be performed by the same apparatus and do not need to be provided separately.

  The above process is a manufacturing process of the conventional activated carbon 15 manufactured by alkali activation. In the present invention, the conventional activated carbon 15 obtained by the above-described treatment is heat-treated in the heat treatment section 6. The atmosphere in the heat treatment section 6 is an inert gas atmosphere such as nitrogen, helium, argon, or a reducing gas atmosphere such as hydrogen or methane so that the activated carbon does not burn. A sufficient effect can be obtained even in a reducing gas atmosphere. These mixed gas atmospheres can also be used.

  The furnace used for the heat treatment section 6 may be any of a rotary kiln furnace, a tunnel furnace, a fixed bed furnace, a fluidized bed furnace, etc.

  Although the temperature increase rate in the heat processing part 6 is not specifically limited, It is preferable to set it as 0.1-100 degrees C / min. If the rate of temperature increase is slower than 0.1 ° C./min, the energy cost becomes excessive, and if it is faster than 100 ° C./min, it is necessary to enlarge the heating device such as an electric heater, which increases the equipment cost. More preferably, it is set to 1 to 20 ° C./min. Particularly preferred is 3 to 10 ° C./min.

  As for the maximum temperature of the heat treatment, there is no problem as long as it is 500 ° C. or higher. 500 to 1000 ° C. is preferred. The holding after reaching the maximum temperature may be omitted, but it is preferably held for 10 hours or less in order to make the activated carbon temperature uniform. This is because if the time exceeds 10 hours, the energy loss increases.

  Since the heat-treated activated carbon cannot suppress deterioration with time when it is used as an electric double layer capacitor as it is, cleaning in the cleaning unit 7 is performed. As the cleaning liquid to be used, clean water, filtered water, ion exchange water, distilled water and the like can be used as in the case of removing alkali metals. Thereafter, the cleaning liquid is removed by filtration or centrifugation and dried. This process is not particularly limited, such as atmospheric drying or vacuum drying. However, when drying at normal pressure and at a high temperature or for a long time, it is preferably performed in an inert atmosphere or a reducing atmosphere in order to avoid oxidation (combustion) loss.

  Moreover, it is preferable to repeat this heat treatment and cleaning a plurality of times, since the effect of improving deterioration with time when used as an electric double layer capacitor is further increased.

  FIG. 3 is a schematic diagram showing an apparatus 20 according to an embodiment of the present invention. This device 20 includes a heating device 21 that heats activated carbon, a cleaning device 22 that cleans the heated activated carbon, a pump 23 that extracts and sends the slurry containing activated carbon from the cleaning device 22, and the cleaned activated carbon and the cleaning liquid after washing (drainage). ) Are separated from each other.

  The heating device 21 is a heating device provided with a hopper for charging the activated carbon 31 to be processed and a gas blowing port for feeding the atmospheric gas 32. The heating device 21 may be a continuous furnace or a batch furnace, and the type and shape of the furnace are not limited. A temperature measuring device, a temperature adjusting device, a flow rate control device, etc., not shown, are provided. The heating device 21 is also provided with a gas discharge port for discharging the exhaust gas 33 and a delivery path for discharging the heat-treated activated carbon and sending it to the cleaning device 22.

  The cleaning device 22 cleans the heated activated carbon. The cleaning liquid 34 is supplied, and cleaning is performed in a state where the activated carbon is immersed in the cleaning liquid in the tank. The size and type of the tank are not limited. The container may be a self-rotating container, may be equipped with a stirring device, and may be a batch type or a continuous type.

  The pump 23 sends the slurry containing activated carbon in the cleaning device 22 to the separation device 24. The separation device 24 separates the washed cleaning liquid (drainage) 35 and the washed activated carbon 36. The type and structure of the separation device 24 are not limited. A centrifuge or other solid-liquid separation device can be used.

  A carbon material was obtained by grinding 24 kg of mesophase pitch to a particle size of 30 μm or less. To this, 48 kg of potassium hydroxide whose particle size was adjusted so as to be 500 μm or less was added and mixed. The mixture was charged into a muffle furnace in which nitrogen was circulated, heated to 700 ° C. at a heating rate of 10 ° C./min, held for 1 hour, and the carbon material was activated. Then, it stood to cool naturally, and when it became 150 degreeC, water vapor | steam was supplied and the inactivation process of alkali metals was performed. Ion exchanged water was added to the obtained mixture of activated carbon and inactivated alkali metals to form a slurry state and washed at 75 to 85 ° C. to remove the produced alkali metals. Removal of alkali metals was performed 5 times using ion-exchanged water, and it was confirmed to be neutral (pH = 7). Thereafter, the activated carbon was recovered by filtration.

  The obtained activated carbon was further processed using the apparatus shown in FIG. The muffle furnace (heating device 21) was charged, heated to 700 ° C. at a rate of 10 ° C./min under a nitrogen stream, and heat-treated for 1 hour. After cooling to room temperature by natural cooling, the activated carbon was sent to the washing device 22 and washed with ion exchange water, and the pump 23 was sent to the separation device 24 to separate the washing solution and activated carbon by filtration. The obtained activated carbon was dried.

  About a part of activated carbon of the said Example 1, the heat processing and washing | cleaning which used the apparatus shown in the said FIG. 3 were performed again, the washing | cleaning liquid and activated carbon were isolate | separated by filtration, and the obtained activated carbon was dried.

Comparative Example 1

  The activated carbon obtained by performing the same operation as in Example 1 except that the heat treatment and cleaning using the apparatus shown in FIG.

[Production and evaluation of capacitors]
Using each activated carbon obtained in Examples 1 and 2 and Comparative Example 1, an electric double layer capacitor was produced as follows and its performance was evaluated. First, the electrode was produced as follows. 10 parts by mass of carbon black and 10 parts by mass of PTFE (polytetrafluoroethylene) are added to 80 parts by mass of activated carbon, and after dry mixing, the aluminum mesh is used as a current collector and pressed into a disk with a diameter of 13 mm at room temperature (50 MPa). A polarizable electrode material was obtained.

This was dried at 160 ° C. for 6 hours under reduced pressure (0.13 kPa: 1 Torr). Next, in a glove box in which high-purity argon is circulated at a dew point temperature of −60 ° C., porous polypropylene (pore diameter 0.20 μm) is sandwiched between a pair of polarizable electrode materials produced as described above, The cell was manufactured by incorporating it into a bipolar cell manufactured by Co., Ltd. and filling the electrolyte. Here, an electrolytic solution in which tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved in propylene carbonate (PC) at a concentration of 1M was used.

The charge / discharge measurement is performed by using a charge / discharge test apparatus (HJ1001SM8) manufactured by Hokuto Denko Corporation, performing a constant current charge with a current density of 0.5 mA / cm ² , and after reaching a potential of 2.4 V, a constant voltage It shifted to charge and charged for 2 hours. Thereafter, constant current discharge with a current density of 0.5 mA / cm ² was performed, and the final voltage was set to 0V. This was carried out for 3 cycles, and the capacitance obtained from the discharge curve of the third cycle was defined as “capacity before deterioration treatment”.

The cell was transferred to a constant temperature bath at 60 ° C., left for 1 hour, and then 2.4 V at a current density of 0.5 mA / cm ² . After reaching 2.4V, applying a current to maintain 2.4V, holding in a constant temperature bath at 60 ° C. for 1000 hours to perform “deterioration treatment”, constant current discharge with a current density of 0.5 mA / cm ² The final voltage was set to 0V.

The cell subjected to deterioration treatment was taken out from the thermostatic chamber, left at room temperature for 1 hour, charged and discharged at a current density of 0.5 mA / cm ² , and the capacitance obtained from this discharge curve was defined as “capacity after deterioration treatment”.

The capacitance was calculated as follows. The total discharge energy (W · s) is obtained as a time integral of discharge energy (discharge voltage × current) from the discharge curve (discharge voltage−discharge time),
Capacitance (F) = 2 × total discharge energy (W · s) / (discharge start voltage (V)) ²
The capacitance was calculated using the relational expression. This capacitance was divided by the carbon material weight of the polarizable electrode material (positive electrode + negative electrode, unit: g) to obtain a capacitance per unit weight.

Capacity degradation is indicated by the ratio of the capacitance after degradation processing to the capacitance before degradation processing,
Capacity after degradation processing (F / g) / capacity before degradation processing (F / g) × 100
The capacity reduction rate was obtained using the relational expression. The results are shown in FIG. The rate of decrease in capacity after 1000 hours was 68% in the comparative example, but improved to 86% in Example 1 and 93% in Example 2.

It is a flowchart which shows the carbon fine particle manufacturing method of this invention. It is a graph which shows the effect of the present invention. It is a figure which shows an example of the apparatus of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material supply part 2 Activation reaction part 3 Cooling part 4 Alkali metal inactivation part 5 Alkali metal removal part 6 Heat processing part 7 Cleaning part 11 Carbon material 12 Alkali metal compounds 13 Inactive gas 14 Reactive gas 15 Conventional Activated carbon 16 Activated carbon of the present invention 20 Example device 21 Heating device 22 Cleaning device 23 Pump 24 Separation device 31 Activated carbon to be treated 32 Atmospheric gas 33 Waste gas 34 Cleaning solution 35 Cleaning solution after washing (drainage)
36 Activated activated carbon

Claims (4)

  After activating the carbon material using alkali metal compounds, the generated alkali metals are deactivated, the deactivated alkali metal compounds are removed, and further, heat treatment and washing are performed. Production method.   The method for producing activated carbon according to claim 1, wherein the heat treatment is performed at a temperature rising rate of 0.1 to 100 ° C / min, a maximum temperature of 500 to 1000 ° C, and a maximum temperature holding time of 10 hours or less.   The method for producing activated carbon according to claim 1 or 2, wherein the heat treatment and washing are repeated a plurality of times.   From a heating device for charging activated carbon to be treated and heating in an atmospheric gas, a cleaning device for cleaning the heated activated carbon with a cleaning liquid, a pump, and a separation device for separating the cleaned activated carbon and the cleaning liquid after cleaning An activated carbon production apparatus characterized by comprising:

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