JP2012101948A - Method for producing activated carbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide activated carbon which contains few impurities, has a high specific surface area, and has a large micropore volume in a micropore size range of 1 nm or more and 2 nm or less.SOLUTION: The method for producing activated carbon includes heat-treating ashless coal at a temperature below 800°C in an inert atmosphere or without performing the heat treatment, mixing the resulting ashless coal with an alkali activator, and subjecting the mixture to activation treatment at a temperature of 600°C or higher and 950°C or lower.

Description

  The present invention relates to a method for producing activated carbon.

  Currently, activated carbon has a high specific surface area and is used for applications such as polarizable electrodes and adsorbents in electric double layer capacitors. In particular, an electric double layer capacitor using activated carbon as a polarizable electrode is required to have higher performance as the electronics field advances. In order to improve the performance of the electric double layer capacitor, in particular, to increase the capacity, it is essential to increase the specific surface area of the activated carbon used for the electrode.

  Conventionally, activated carbon used for an electric double layer capacitor is generally manufactured by steam activation and chemical activation of raw materials such as coconut shell carbide, phenol resin carbide, and coal. As a method for producing such activated carbon, for example, a solvent extract of coal (ashless coal) is heated in a temperature range of 800 ° C. to 950 ° C. in an inert atmosphere, and the resulting solid residue is alkali activated ( Patent Document 1 (see claim 1)): A method in which a coal-based pitch is heat-treated in a two-step temperature range of 400 ° C. to 600 ° C. and 600 ° C. to 900 ° C., and the heat-treated coal-based pitch is alkali-activated (Patent Document 2). (See claim 17)); a method of inactivating granular isotropic pitch and then activating with a drug (see Patent Document 3 (claim 1)).

JP 2007-142204 A JP 2004-149399 A JP 2002-104817 A

  Since the solvent extract of coal (so-called ashless coal) has a very low content of metal impurities, activated carbon can be obtained by activating this. Here, when manufacturing activated carbon by the alkali activation method, in order to raise an activation yield, the carbide | carbonized_material carbonized at the high temperature of 800 degreeC or more is normally used for the activation raw material. However, if the solvent extract of coal is carbonized at a high temperature, alkali activation is difficult to proceed, and the obtained activated carbon tends to have a low specific surface area and a small pore diameter. Moreover, when such activated carbon was used as an electrode material for an electric double layer capacitor, the expansion rate after charge / discharge tended to increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an activated carbon having a small amount of impurities, a high specific surface area, and a large pore volume in a pore diameter range of 1 nm to 2 nm. .

  The present inventors pay attention to the fact that activated carbon with a reduced impurity content can be obtained by using ashless coal as an activation raw material. Using the ashless coal as an activation raw material, a high specific surface area can be obtained. The method of producing activated carbon with further researched. As a result, the inventors have found that the activated carbon obtained can be made to have a higher specific surface by lowering the heat treatment temperature for carbonizing ashless coal, or by not performing any heat treatment, thereby completing the present invention.

  That is, the method for producing activated carbon according to the present invention that has solved the above-described problem is that alkali-activation is performed after heat treatment of ashless coal at a temperature of less than 800 ° C. in an inert atmosphere or without the heat treatment. It is characterized by being mixed with an agent and subjected to activation treatment at a temperature of 600 ° C. or more and 950 ° C. or less.

  It is preferable that the usage-amount of the said alkali activator is 150 to 550 mass parts with respect to a total of 100 mass parts of the said ashless coal and / or ashless coal heat-processed material.

  The present invention also includes activated carbon obtained by the above production method, an electrode material containing the activated carbon, an electric double layer capacitor electrode using the electrode material, and an electric double layer capacitor using the electrode.

  ADVANTAGE OF THE INVENTION According to this invention, activated carbon with few impurities, a high specific surface area, and a large pore volume in the pore diameter range of 1 nm or more and 2 nm or less is obtained. By using the activated carbon as an electrode material, an electric double layer capacitor having a high electrostatic capacity, a low internal resistance, and a low expansion coefficient after charging and discharging can be obtained.

It is a figure which shows the pore diameter distribution of the activated carbon of manufacture examples 1-4. It is a figure which shows the pore diameter distribution of the activated carbon of the manufacture examples 5 and 6. It is a figure for demonstrating the electric double layer capacitor manufactured using the activated carbon of a manufacture example.

  In the method for producing activated carbon of the present invention, ashless charcoal is mixed with an alkali activator after heat treatment at a temperature of less than 800 ° C. in an inert atmosphere or without the heat treatment, and 600 ° C. or more and 950 ° C. or less. The activation treatment is performed at a temperature of

  The ashless coal used in the present invention is not particularly limited. Here, ashless coal is produced by extracting coal with a solvent, separating only the components soluble in the solvent, and then removing the solvent.

  The coal used as the raw material of the ashless coal is not particularly limited, and lignite (carbon content is less than 70% by mass), lignite (carbon content is 70% by mass or more and less than 78% by mass), and bituminous coal (carbon content is less than 70% by mass). 78 mass% or more and less than 90 mass%) and anthracite (carbon content is 90 mass% or more) can be used. Among these, bituminous coal and anthracite coal are preferable as coal used as a raw material for ashless coal.

  Solvents used for the extraction treatment include heterocyclic compounds such as N-methyl-2-pyrrolidone; monocyclic aromatic compounds such as benzene, toluene and xylene; naphthalene, methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene and the like Ring aromatic compounds; heterocyclic aromatic compounds such as quinoline, pyridine and tetrahydrofuran; and carbon disulfide and carbon tetrachloride. Among these, an aromatic solvent containing an aromatic compound is preferable. Moreover, you may use coal dry distillation oil (what produced | generated the byproduct oil at the time of dry distillation of coal and manufacturing coke) as a solvent. Since coal dry distillation oil is excellent in affinity with coal, the proportion of soluble components extracted into the solvent (hereinafter, sometimes referred to as “extraction rate”) is high. The boiling point of the solvent is preferably 180 ° C. or higher and 330 ° C. or lower.

  The coal extraction process may be performed at room temperature (20 ° C.), but is preferably heated. The heating temperature is preferably 300 ° C. or higher and 450 ° C. or lower. By setting the heating temperature within this range, the bonds between the molecules constituting the coal are loosened and mild thermal decomposition occurs, so that the extraction rate is increased. What is necessary is just to adjust extraction time suitably according to the particle diameter of coal, and the kind of solvent. Moreover, you may pressurize etc. as needed.

  The method for separating the solution containing the coal component extracted (dissolved) in the solvent from the solid component such as ash and insoluble coal insoluble in the solvent is not particularly limited, and is a filtration method, a pressure separation method, a centrifugal separation method. Gravity sedimentation method or the like may be employed. Moreover, in order to remove the metal (salt) contained in the solution, an ion exchange treatment may be performed as necessary. A method for removing the solvent from the obtained solution is not particularly limited, and a distillation method, an evaporation method (spray dry method or the like) may be employed.

  In the present invention, the ashless coal heat-treated at a temperature of less than 800 ° C. in an inert atmosphere or the ashless coal not subjected to the heat treatment is used as an activation raw material.

  When heat-treating the ashless coal, the heat treatment temperature is less than 800 ° C, preferably 700 ° C or less, more preferably 600 ° C or less, and still more preferably 500 ° C or less. If the heat treatment temperature applied to the ashless coal is less than 800 ° C., since the carbon crystal structure is not developed, there are many active edge surfaces that contribute to the activation reaction. Due to the presence of these edge surfaces, a high specific surface area can be achieved.

  Next, the activation process will be described. In the present invention, the activation treatment is performed by mixing and heating the ashless coal and / or the ashless coal heat-treated product and the alkali activator.

  As the alkali activator, an alkali metal compound is preferable. Examples of the alkali metal compound include hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; carbonates such as sodium carbonate, potassium carbonate, and lithium carbonate; These alkali activators may be used alone or in combination of two or more. Of these, potassium hydroxide is preferred.

  The amount of the alkali activator used is preferably 150 parts by mass or more, more preferably 250 parts by mass or more, and further preferably 350 parts by mass or more with respect to 100 parts by mass in total of ashless coal and / or ashless coal carbide. Yes, 550 parts by mass or less is preferable, more preferably 500 parts by mass or less, and still more preferably 450 parts by mass or less. When the amount of the alkali activator used is 150 parts by mass or more, the specific surface area of the obtained activated carbon is further improved, and when the activated carbon is used as an electrode material, an excellent capacitance is obtained, and at 550 parts by mass or less. If it exists, the excessive density fall of the activated carbon obtained can be suppressed.

  Moreover, when adding an alkali activator, in order to fully mix with an activation raw material, you may use an alkali activator as aqueous solution. The amount of water used at this time is preferably 0.05 times by mass to 10 times by mass of the alkali activator. In addition, when using an alkali activator as an aqueous solution, before performing heating for the activation treatment, heating at a temperature lower than the heating temperature in the activation treatment is performed to prevent bumping of moisture derived from the alkaline activator aqueous solution. It is preferable to remove the moisture by performing the above.

  The heating temperature for performing the activation treatment is preferably 600 ° C. or higher, more preferably 650 ° C. or higher, preferably 950 ° C. or lower, more preferably 900 ° C. or lower. Since the alkali activator contains a small amount of moisture, it is preferable to remove the moisture contained in the alkali activator before reaching the activation treatment temperature. The heating conditions for removing moisture in the alkali activator are, for example, about 400 minutes at 400 ° C. In addition, the heating time in performing the activation treatment is preferably 0.1 hour or longer, more preferably 1.5 hours or longer, 3.5 hours or shorter, more preferably 3 hours or shorter. The atmosphere during heating is preferably an inert gas atmosphere such as argon, helium, or nitrogen.

  In the production method of the present invention, the activated product may be washed, heat-treated for adjusting the functional group amount, and pulverized. Washing is performed in order to remove such deposits because the alkali metal hydroxide used as the alkali activator is adhered to the surface of the activator.

  As washing | cleaning of an activation material (activated carbon), water washing, acid washing, etc. can be mentioned. The method for washing with water is not particularly limited, but it is preferable to carry out, for example, by putting the activated material into water, stirring and dispersing as necessary, and then collecting by filtration. The stirring and dispersion can be performed by mechanical stirring, gas blowing, and ultrasonic irradiation, but can also be performed by heating and boiling. The water temperature during washing is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher. The stirring and dispersing time is preferably 1 minute or longer, more preferably 10 minutes or longer, and further preferably 30 minutes or longer.

  In the acid cleaning, the activated carbon is cleaned using a cleaning liquid containing an inorganic acid, an organic acid, or the like. The solvent for the cleaning liquid is not particularly limited, but is usually water. By performing the acid cleaning, the alkali metal hydroxide used as the alkali activator can be efficiently removed.

  Examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and carbonic acid. These inorganic acids may be used alone or in combination of two or more. When the inorganic acid is used, the concentration of the inorganic acid in the cleaning liquid is preferably 0.5 mol / L to 3.5 mol / L. When acid cleaning is performed using an inorganic acid, for example, an activation product and a cleaning liquid containing an inorganic acid may be mixed and stirred at a temperature of 50 ° C. to 100 ° C. for 10 minutes to 120 minutes.

  Examples of the organic acid include formic acid, oxalic acid, malonic acid, succinic acid, acetic acid, propionic acid, and the like. These organic acids may be used alone or in combination of two or more. The concentration of the organic acid in the cleaning liquid containing the organic acid is preferably 1 vol% to 100 vol%. When acid cleaning is performed using an organic acid, for example, an activation product and a cleaning solution containing an organic acid are mixed, and the resulting mixture is stirred at a temperature of 20 ° C. to 80 ° C. for 1 minute to 120 minutes. Good.

  In the washing step, it is preferable to perform acid washing and water washing, and more preferably, after acid washing, water washing is performed a plurality of times. The activated carbon after washing is preferably dried at 50 to 120 ° C. for 0.5 to 2.0 hours.

  Heat treatment for adjusting the amount of functional groups is not necessarily required. However, when the amount of functional groups on the surface of the obtained activated carbon is to be adjusted, the activated product after activation or after washing is further heat-treated in an inert gas atmosphere. May be. As said inert gas, argon, nitrogen, helium etc. can be used, for example. Moreover, the said heat processing temperature is although it does not specifically limit, Preferably it is 400 to 1200 degreeC.

  The pulverization is performed to adjust the particle size of the activated carbon. The method for pulverizing the activated carbon is not particularly limited, and may be performed using a disk mill, a ball mill, a bead mill, or the like. In addition, it is preferable that the volume average particle diameter of activated carbon shall be 1 micrometer or more, More preferably, it is 2 micrometers or more, It is preferable to set it as 15 micrometers or less, More preferably, it is 10 micrometers or less. If the average particle diameter is too small, the binding property between the current collector plate and the electrode material layer in the electrode is deteriorated, and the amount of binder required for the electrode material layer may be increased in order to maintain the practical binding property. is there.

The specific surface area of the activated carbon obtained by the production method of the present invention is preferably 2200 m ² / g or more, more preferably 2300 m ² / g or more, further preferably 2400 m ² / g or more, preferably 3500 m ² / g or less, more Preferably it is 3200 m < ² > / g or less, More preferably, it is 3000 m < ² > / g or less. Here, in the present invention, the specific surface area is a value determined by the BET method for measuring the nitrogen adsorption isotherm of activated carbon.

Pore volume in the 1nm or more 2nm or less pore size range of the activated carbon obtained by the process of the present invention is 0.35 cm ³ / g or more, more preferably 0.45 cm ³ / g or more, 1.0 cm ³ / G or less, more preferably 0.95 cm ³ / g or less. Here, in the present invention, the pore volume means the relative pressure P / P ⁰ (P: pressure of the adsorbate gas in the adsorption equilibrium, P ⁰ : saturated vapor pressure of the adsorbate at the adsorption temperature) up to 0.99. It is a value calculated | required by MP method which measures the nitrogen adsorption amount of.

  Activated carbon obtained by the production method of the present invention can be used as an electrode material for an electric double layer capacitor, and an electrode for an electric double layer capacitor or an electric double layer capacitor can be produced using the electrode material. is there. According to the production method of the present invention, activated carbon having a small amount of impurities, a high specific surface area, and a large pore volume in a pore diameter range of 1 nm to 2 nm can be obtained. If this activated carbon is used as an electrode material, an electric double layer capacitor having a large capacitance, a low internal resistance, and a small electrode expansion coefficient after charging can be obtained.

  Next, the electric double layer capacitor of the present invention will be described. The electric double layer capacitor of the present invention is characterized in that activated carbon obtained by the above-described manufacturing method is used as an electrode constituent material.

  As an electrode for an electric double layer capacitor, for example, activated carbon, a conductivity-imparting agent and a binder are kneaded, a solvent is further added to prepare a paste, and this paste is applied to a current collector plate such as an aluminum foil. Is obtained by drying and removing.

  As the binder used for the electrode for the electric double layer capacitor, fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, phenol resin, and the like can be used. As the conductivity imparting agent, acetylene black, ketjen black, or the like can be used.

  An electric double layer capacitor generally has a structure in which an electrode, an electrolytic solution, and a separator are main components, and a separator is disposed between a pair of electrodes. Examples of the electrolytic solution include an electrolytic solution in which an amidine salt is dissolved in an organic solvent such as propylene carbonate, ethylene carbonate, and methyl ethyl carbonate; an electrolytic solution in which a quaternary ammonium salt of perchloric acid is dissolved; quaternary ammonium or lithium An electrolytic solution in which an alkali metal boron tetrafluoride salt or phosphorous hexafluoride salt is dissolved; an electrolytic solution in which a quaternary phosphonium salt is dissolved may be mentioned. Examples of the separator include cellulose, glass fiber, or a nonwoven fabric, cloth, or microporous film mainly composed of polyolefin such as polyethylene or polypropylene.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

Evaluation Method Specific Surface Area, Pore Volume After 0.2 g of activated carbon was vacuum heated at 300 ° C., an adsorption isotherm was determined using a nitrogen adsorption device (“BELSORP-max” manufactured by Nippon Bell Co., Ltd.), and the BET method was used. The specific surface area was calculated. Further, assuming that the shape of the pores formed in the activated carbon is a slit shape, the pore size distribution was calculated by the MP method to obtain the pore volume.

Capacitance, internal resistance, electrode expansion rate The charge / discharge terminal of the charge / discharge device (“ETAC (registered trademark) Ver. 4.4” manufactured by Enomoto Kasei Co., Ltd.) is connected to the current collector plate of the electric double layer capacitor, The battery was charged at a constant current of 40 mA until the voltage between the electric plates reached 2.5 V, and then charged at a constant voltage of 2.5 V for 30 minutes. After charging, the electric double layer capacitor was discharged with a constant current (discharge current 10 mA). At this time, the discharge times t1 and t2 required until the voltage between the current collector plates became V1 and V2 were measured, and the capacitance was obtained using the following formula (1). The obtained capacitance was divided by the mass of activated carbon in the electrode material layer in the capacitor electrode to calculate a mass-based capacitance (F / g). Moreover, internal resistance was calculated | required using following formula (2). The capacitance and internal resistance were measured at 25 ° C. and −30 ° C. For the electric double layer capacitor, the expansion coefficient was determined from the change in electrode thickness before and after applying the voltage.

I: 10 (mA)
t1: Discharge time required for the electric double layer capacitor voltage to reach V1 (sec)
t2: Discharge time (sec) required for the electric double layer capacitor voltage to reach V2
V0: 2.5 (V)
V1: 2.0 (V)
V2: 1.0 (V)

1. Production method 1 of activated carbon
100 parts by mass of ashless coal, 400 parts by mass of potassium hydroxide (potassium hydroxide / ashless coal (mass ratio) = 4) are mixed, and the mixture is heated to 800 ° C. at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere. The mixture was heated and heat treated at 800 ° C. for 2 hours to activate the alkali.
Water and hydrochloric acid were added to the obtained mixture of the activated product and the potassium component, and after heating at 100 ° C. for 2 hours, the activated product was collected by filtration to wash with hydrochloric acid. Thereafter, water was added to the activated product after washing with hydrochloric acid, heated to 100 ° C. and boiled for 2 hours, and then washed with warm water by filtering the activated product. The same operation was repeated, and washing with warm water was performed until the pH of the filtrate reached 6 or more. The activated product that had been washed once with hydrochloric acid and washed with warm water was dried at 110 ° C. for 2 hours. The activated product after drying was pulverized with a ball mill and adjusted so that the average particle size was 3 μm, to obtain activated carbon.

Production Example 2
Ashless charcoal was heat-treated at 500 ° C. for 7 minutes in a nitrogen atmosphere to obtain a heat-treated ashless charcoal. 400 parts by mass of potassium hydroxide is mixed with 100 parts by mass of the heat-treated ashless coal, and the mixture is heated to 800 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere, and at 800 ° C. for 2 hours. It heat-processed and alkali activation was performed. The mixture of the obtained activated substance and potassium component was washed with hydrochloric acid, washed with warm water, dried and ground in the same manner as in Production Example 1 to obtain activated carbon having an average particle diameter of 3 μm.

Production Examples 3-6
Activated carbon was obtained in the same manner as in Production Example 2 except that the heat treatment temperature of ashless coal was changed to the temperature shown in Table 1.

2. Production of Electric Double Layer Capacitor An electric double layer capacitor was produced using the activated carbon obtained in Production Examples 1-6. Specifically, polytetrafluoroethylene (PTFE) powder and acetylene black are mixed with activated carbon so that activated carbon: PTFE: acetylene black = 8: 1: 1 (mass ratio), and this is press-molded. Thus, an electrode for a capacitor was prepared.

  The obtained capacitor electrode was dried under vacuum conditions at 200 ° C. for 1 hour, and then an electrolyte (1M tetraethylammonium tetrafluoroborate propylene carbonate solution) was used as an electrode in a glove box in which nitrogen gas was circulated. Vacuum impregnated. Using this electrode, an electric double layer capacitor was assembled as shown in FIG. The electric double layer capacitor shown in FIG. 3 has a separator (Celgard, “Celguard (registered trademark) # 3501”) 1 impregnated with the electrolytic solution sandwiched between the capacitor electrodes 2, and the electrodes are surrounded by an O-ring 3. Then, it was further sandwiched between aluminum plates 4 as current collector plates.

Table 1 shows the evaluation results of the activated carbon obtained in Production Examples 1 to 6 and the evaluation results of the electric double layer capacitor produced using these activated carbons. Moreover, the pore diameter distribution of the activated carbon obtained in Production Examples 1 to 6 is shown in FIGS. In the pore diameter distribution chart, the vertical axis is log differential pore volume dV / dlogD (cm ³ / g) (V is the pore volume), and the horizontal axis is pore diameter D (nm).

In Production Examples 1 to 4, ashless coal that has not been heat-treated (Production Example 1) or ashless coal heat-treated product that has been heat-treated at less than 800 ° C. (Production Examples 2 to 4) is used as the activation raw material. It is. In these cases, the specific surface area of the obtained activated carbon was as high as 2450 m ² / g, and the pore volume in the pore diameter range of 1 nm to 2 nm in the pore diameter distribution was as large as 0.38 cm ³ / g or more. . On the other hand, when an ashless coal heat-treated product obtained by heat treating ashless coal at 800 ° C. or higher is used as the activation raw material, the specific surface area is a low value of 1820 m ² / g or less, and the pore size distribution is 1 nm to 2 nm. The pore volume in the following pore diameter range was a small value of 0.20 cm ³ / g or less.

  In the electric double layer capacitors using the activated carbons of Production Examples 1 to 4, the capacitance is larger and the internal resistance is lower than when the activated carbons of Production Examples 5 and 6 are used. It can be seen that the electrode expansion coefficient is reduced.

  The present invention is useful for producing activated carbon having a pore size distribution suitable for an electric double layer capacitor and having a high specific surface area.

1: Separator, 2: Electrode for capacitor, 3: O-ring, 4: Aluminum plate, 5: Polytetrafluoroethylene plate, 6: Stainless steel plate

Claims (6)

  The ashless charcoal is heat-treated at a temperature of less than 800 ° C. under an inert atmosphere, or without heat treatment, and mixed with an alkali activator and activated at a temperature of 600 ° C. or higher and 950 ° C. or lower. To produce activated carbon.   2. The method for producing activated carbon according to claim 1, wherein the amount of the alkali activator used is 150 parts by mass or more and 550 parts by mass or less with respect to a total of 100 parts by mass of the ashless coal and / or heat treated ashless coal.   Activated carbon obtained by the production method according to claim 1 or 2.   An electrode material for an electric double layer capacitor, comprising the activated carbon according to claim 3.   An electrode for an electric double layer capacitor, wherein the electrode material according to claim 4 is used.   An electric double layer capacitor comprising the electrode according to claim 5.