WO2017199966A1 - Method for producing carbon fibers, carbon fibers, and electrode for electric double layer capacitors - Google Patents

Abstract

This method for producing carbon fibers comprises: a step for obtaining an ash-free coal by means of solvent extraction of a coal; a step for electrospinning the ash-free coal obtained in the ash-free coal acquisition step together with a solvent; and a step for carbonizing fibers obtained in the electrospinning step, preferably a step for heating the fibers at a temperature from 700°C to 1,200°C (inclusive). The thus-obtained carbon fibers have a specific surface area of from 300 m²/g to 3,000 m²/g (inclusive), an average diameter of from 0.5 μm to 5 μm (inclusive) and an oxygen content of 0.4% by mass or more, and are suitable as an electrode for electric double layer capacitors.

Description

Carbon fiber manufacturing method, carbon fiber, and electrode for electric double layer capacitor

The present invention relates to a carbon fiber manufacturing method, carbon fiber, and electrode for an electric double layer capacitor.

Carbon fiber is widely used as a reinforcing material for structural materials such as resin, concrete and ceramic. In addition, carbon fiber is also used as, for example, a heat insulating material, activated carbon raw material, conductive material, heat transfer material, and the like. As a method for producing carbon fiber, a method of electrospinning pitch or resin derived from petroleum or coal is known (see Japanese Patent Application Laid-Open No. 2011-157668 and International Publication No. 2011/070893).

On the other hand, porous carbon fibers having fine pores are useful as adsorbents and electrodes. As a method for producing such a porous carbon fiber, a method called so-called activation in which the surface of the carbon fiber is eroded by treatment with high-temperature steam or strong alkali, or the pitch or resin of the carbon fiber raw material such as MgO is used. There is a method of mixing and spinning fine particles as a template material.

However, the above-described method requires a special treatment or material such as a surface treatment or a template substance, which raises a problem that the manufacturing cost of the porous carbon fiber increases.

Japanese Unexamined Patent Publication No. 2011-157668 International Publication No. 2011/070893

In view of the above inconveniences, the present invention provides a carbon fiber production method capable of producing porous carbon fibers in a relatively simple process, a carbon fiber obtained in a relatively simple process, and an electric double layer capacitor using the same. It is an object to provide a working electrode.

The invention made to solve the above problems includes a step of obtaining ashless coal by solvent extraction treatment of coal, a step of electrospinning ashless coal obtained in the ashless coal acquisition step together with a solvent, and the electric field And a step of carbonizing the filament obtained in the spinning step.

The carbon fiber manufacturing method uses ashless coal as a raw material, and electrospinning ashless coal together with a solvent and then carbonizing to obtain porous carbon fibers in which fine pores are formed by volatilization of the solvent. be able to. That is, according to the carbon fiber manufacturing method, porous carbon fibers can be manufactured by a relatively simple process of carbonization after electrospinning.

The carbonization may be performed by heating the filament to 700 ° C. or more and 1200 ° C. or less. By performing carbonization in this way, porous carbon fibers can be obtained easily and reliably.

Another invention made to solve the above problems is a carbon fiber made from coal, having a specific surface area of 300 m ² / g to 3000 m ² / g, an average diameter of 0.5 μm to 5 μm, oxygen Content is 0.4 mass% or more, It is characterized by the above-mentioned.

The carbon fiber has a specific surface area and an average diameter in the above ranges, and the oxygen content is 0.4% by mass or more. Therefore, after the ashless coal is electrospun together with a solvent, the ashless coal is used as a raw material. Obtained by carbonization. Therefore, the carbon fiber can be produced by a relatively simple process and can be effectively used as a porous material having many fine pores.

Still another invention made to solve the above problems is an electrode for an electric double layer capacitor using the carbon fiber. The electric double layer capacitor electrode is excellent in manufacturing cost because the carbon fiber is used.

Here, “specific surface area” means a value measured according to JIS-Z8830 (2013). “Oxygen content” means the content of oxygen atoms including not only oxygen molecules but also atoms bonded to other atoms, and is specifically measured according to JIS-M8813 (2004). Mean value.

As described above, the carbon fiber production method can produce porous carbon fiber by a relatively simple process. Further, the carbon fiber is obtained by a relatively simple process, and the electric double layer capacitor electrode using the carbon fiber is excellent in manufacturing cost.

It is a flow which shows the procedure of the manufacturing method of the carbon fiber of one Embodiment of this invention. 2 is a graph showing the pore distribution of the carbon fiber of Example 1. 2 is a scanning electron micrograph of the carbon fiber of Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Method for producing carbon fiber]
As shown in FIG. 1, the carbon fiber production method includes ashless coal acquisition step S1 for obtaining ashless coal by solvent extraction treatment of coal and ashless coal obtained in ashless coal acquisition step S1 together with a solvent. An electrospinning process S2 for electrospinning and a carbonization process S3 for carbonizing the filament obtained in the electrospinning process S2 are mainly provided.

<Ashless coal acquisition process>
In the ashless coal acquisition step S1, raw material coal is subjected to solvent extraction treatment to obtain ashless coal. Specifically, the slurry obtained by mixing the raw coal and the solvent is heated to a temperature equal to or higher than the pyrolysis temperature of the raw coal, the soluble component of the pyrolyzed raw coal is extracted into the solvent, and the insoluble component at this pyrolysis temperature is extracted. Ashless coal is obtained by separating from the slurry. The “ashless coal” is a modified coal obtained by modifying coal, and has an ash content of 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. “Ash” means a value measured in accordance with JIS-M8812 (2004).

Examples of coal used as raw material for ashless coal include anthracite coal, bituminous coal, subbituminous coal, lignite, etc., in descending order of degree of coalification. Of these, bituminous coal or subbituminous coal having a moderate degree of coalification is preferred.

The solvent is not particularly limited as long as it has a property of dissolving the raw material coal. For example, monocyclic aromatic compounds such as benzene, toluene and xylene, bicyclic rings such as naphthalene, methylnaphthalene, dimethylnaphthalene and trimethylnaphthalene. Aromatic compounds, tricyclic aromatic compounds such as anthracene, and the like can be used. The bicyclic aromatic compound includes naphthalenes having an aliphatic chain, biphenyls having a long aliphatic chain, and the like.

Among the above solvents, a bicyclic aromatic compound which is a coal derivative purified from a coal dry distillation product is preferable. The bicyclic aromatic compound of the coal derivative is stable even in a heated state and has an excellent affinity with coal. Therefore, by using such a bicyclic aromatic compound as a solvent, the ratio of coal components extracted into the solvent can be increased, and the solvent can be easily recovered and reused by a method such as distillation. .

The lower limit of the slurry heating temperature (pyrolysis extraction temperature) is preferably 300 ° C, more preferably 350 ° C, and even more preferably 380 ° C. On the other hand, the upper limit of the heating temperature of the slurry is preferably 450 ° C, more preferably 420 ° C. If the heating temperature of the slurry is less than the above lower limit, the bonds between the molecules constituting the coal cannot be sufficiently weakened. For example, when low grade coal is used as the raw coal, There is a possibility that the solidification temperature cannot be increased, and the yield may be low and uneconomical. On the other hand, when the heating temperature of the slurry exceeds the above upper limit, the pyrolysis reaction of coal becomes very active, so that the oxygen content of ashless coal may decrease and recombination of the generated pyrolysis radical occurs. This may reduce the extraction rate of ashless coal.

The upper limit of the slurry heating time (extraction time) is preferably 120 minutes, more preferably 60 minutes, and even more preferably 30 minutes. On the other hand, the lower limit of the slurry heating time is preferably 10 minutes. When the heating time of the slurry exceeds the above upper limit, the thermal decomposition reaction of coal proceeds too much and the radical polymerization reaction proceeds, which may reduce the extraction rate. On the contrary, when the heating time of the slurry is less than the above lower limit, extraction of soluble components of coal may be insufficient.

After heating the slurry, it is preferable to cool the slurry to suppress the thermal decomposition reaction. The cooling temperature of the slurry is preferably 300 ° C. or higher and 370 ° C. or lower. When the cooling temperature of the slurry exceeds the above upper limit, the thermal decomposition reaction may not be sufficiently suppressed. On the other hand, when the cooling temperature of the slurry is less than the lower limit, the solvent dissolving power is reduced, and re-precipitation of the extracted coal component occurs, which may reduce the recovery rate of ashless coal.

In addition, it is preferable to perform heat extraction of the slurry in a non-oxidizing atmosphere. Specifically, it is preferable to perform heat extraction of the slurry in the presence of an inert gas such as nitrogen. By using an inert gas such as nitrogen, it is possible to prevent the slurry from coming into contact with oxygen and igniting at low cost during the heat extraction.

Although the pressure at the time of heat extraction of the slurry depends on the heating temperature and the vapor pressure of the solvent used, it can be, for example, 1 MPa or more and 2 MPa or less. When the pressure at the time of heat extraction is lower than the vapor pressure of the solvent, the solvent is volatilized and the soluble component of coal cannot be confined in the liquid phase, and the soluble component cannot be extracted. On the other hand, if the pressure at the time of heating extraction is too high, the cost of the equipment, the operating cost, etc. increase.

The method for separating the insoluble component from the slurry is not particularly limited, and a known separation method such as a filtration method, a centrifugal separation method, a gravity sedimentation method, or a combination of these two methods can be employed. Among these, a combination of a centrifugal separation method and a filtration method that can continuously operate a fluid, is suitable for a large amount of processing at low cost, and can reliably remove insoluble components is preferable.

The extraction rate (yield) of ashless coal from coal is, for example, 20% by mass to 60% by mass in the case of bituminous coal or sub-bituminous coal, although it depends on the quality of the raw coal.

As a minimum of oxygen content of ashless coal, 1 mass% is preferred, 1.5 mass% is more preferred, and 2 mass% is still more preferred. On the other hand, as an upper limit of oxygen content of ashless coal, 5 mass% is preferable, 4 mass% is more preferable, and 3.5 mass% is further more preferable. When the oxygen content of ashless coal is less than the above lower limit, it is not possible to sufficiently suppress crystal development in electrospinning due to an increase in aromatic compounds, and the resulting carbon fiber is insufficiently porous There is a risk. Conversely, when the oxygen content of ashless coal exceeds the above upper limit, the mass reduction rate during carbonization is large, and the carbon fiber production cost may increase due to a decrease in the carbon fiber yield.

<Electrospinning process>
In the electrospinning step S2, electrospinning is performed using the mixed solution of ashless coal and a solvent (solution of ashless coal) obtained in the ashless coal acquisition step S1 as a raw material liquid.

As the solvent, the ashless coal extraction solvent used in the ashless coal acquisition step S1 may be used as it is. That is, it is good to use for electrospinning the solvent which isolate | separated the insoluble component after heating by ashless coal acquisition process S1 (after ashless coal extraction) as the said liquid mixture. Thereby, the process can be simplified.

Also, solid ashless coal may be separated from the solvent from which insoluble components have been separated in the ashless coal acquisition step S1, and the solvent may be mixed with the separated ashless coal. As this solvent, the same solvents that can be used for extraction of ashless coal can be used. As the separation method, a general distillation method, evaporation method (for example, spray drying method) or the like can be used.

The lower limit of the boiling point of the solvent used in the mixed solution is preferably 50 ° C, more preferably 100 ° C. On the other hand, as an upper limit of the boiling point of a solvent, 150 degreeC is preferable and 130 degreeC is more preferable. By making the boiling point of the solvent within the above range, the carbon fiber can be made porous. Examples of such a solvent include pyridine and tetrahydrofuran.

The lower limit of the content of ashless coal in the mixed solution is preferably 3% by mass, more preferably 5% by mass, and even more preferably 10% by mass. On the other hand, as an upper limit of the content rate of ashless coal in the said liquid mixture, 50 mass% is preferable and 40 mass% is more preferable. When the content rate of ashless coal in the said mixed liquid is less than the said minimum, there exists a possibility that the manufacturing efficiency of carbon fiber may fall and it may become uneconomical. Conversely, if the content of ashless coal in the mixed solution exceeds the above upper limit, spinning may be difficult, or the carbon fiber may become insufficiently porous.

Electrospinning is a known method for obtaining a filament by spinning a raw material liquid with electric charge repulsion while spinning the raw material liquid in an electric field. Specifically, a nozzle for jetting the raw material liquid and a drum-shaped collector facing the nozzle are used as a pair of electrodes, and a high voltage is applied to the raw material liquid by these electrodes, so that A filamentous body having a skeleton of carbon derived from ashless coal contained in the raw material liquid is formed.

As conditions for the electrospinning, for example, the voltage is 1 kV to 50 kV, the raw material liquid flow rate is 0.1 ml / h to 2 ml / h, the distance between the nozzle and the collector is 1 cm to 50 cm, and the nozzle diameter is 0.1 mm or more. It can be 1 mm or less.

The filament is made porous by volatilizing the solvent at the time of ejection from the nozzle and laminating molecules constituting ashless coal randomly. In addition, when the filamentous body is formed on the collector, it contains a part of the solvent that has not volatilized after ejection together with the carbon skeleton. This solvent is removed by the next carbonization step S3.

<Carbonization process>
In the carbonization step S3, porous carbon fibers are obtained by heating and carbonizing (graphitizing) the filament containing the solvent obtained in the electrospinning step S2.

Specifically, after the filamentous body is inserted into an arbitrary heating device such as an electric furnace and the inside is replaced with a non-oxidizing gas, the filament is heated to a constant temperature while blowing the non-oxidizing gas into the heating device.

As a minimum of heating temperature in a carbonization process, 700 ° C is preferred and 800 ° C is more preferred. On the other hand, as an upper limit of heating temperature, 1200 degreeC is preferable and 1000 degreeC is more preferable. When heating temperature is less than the said minimum, carbonization may become inadequate. On the other hand, when the heating temperature exceeds the above upper limit, the production cost may increase from the viewpoint of improving the heat resistance of the equipment and fuel consumption.

The heating time including the temperature increase in the carbonization step is preferably 15 minutes or more and 10 hours or less. Moreover, as a temperature increase rate, 1 degreeC / min or more and 5 degrees C / min or less are preferable.

The non-oxidizing gas is not particularly limited as long as it can suppress the oxidation of the carbon material, but nitrogen gas is preferable from the economical viewpoint.

In addition, in order to prevent the deformation | transformation and fusion | melting of a fiber, the manufacturing method of the said carbon fiber may be provided with the oxidation process process which lightly oxidizes a filament before carbonization process S3. As this oxidation treatment, for example, heating in an atmosphere containing oxygen of 300 ° C. or lower, treatment with an oxidizing agent, or the like can be used.

[Carbon fiber]
The carbon fiber is made of coal, has a specific surface area of 300 m ² / g to 3000 m ² / g, an average diameter of 0.5 μm to 5 μm, and an oxygen content of 0.4% by mass or more. The said carbon fiber can be obtained with the manufacturing method of the said carbon fiber mentioned above.

The carbon fiber has a small proportion of polycyclic aromatic compounds because the oxygen content is not less than the above lower limit. Therefore, in the carbon fiber, since the planarity of the molecule of the compound contained is low and the ring size is small, the molecule is difficult to orient. That is, since the molecules are randomly stacked during electrospinning as described above, the carbon fiber is excellent in porosity.

The lower limit of the specific surface area of the carbon fiber, 350m ² / g are preferred, 400m ² / g is more preferable. On the other hand, the upper limit of the specific surface area is preferably 2500 m ² / g, and more preferably 1000 m ² / g. When the specific surface area is less than the above lower limit, the number of pores becomes insufficient, and the suitability as an adsorbent may be reduced. Conversely, when the specific surface area exceeds the above upper limit, the strength of the carbon fiber may be insufficient.

The lower limit of the average diameter of the carbon fiber is preferably 0.8 μm. On the other hand, the upper limit of the average diameter is preferably 1.5 μm. When the average diameter is less than the above lower limit, the strength of the carbon fiber may be insufficient. Conversely, if the average diameter exceeds the above upper limit, the suitability as a constituent material such as an adsorbent may be reduced.

The lower limit of the oxygen content of the carbon fiber is preferably 0.5% by mass. On the other hand, the upper limit of the oxygen content is not particularly limited, but is, for example, 5% by mass. When the oxygen content is less than the above lower limit, the carbon fiber becomes difficult to be porous due to the increase of the aromatic compound, and the suitability as an adsorbent may be lowered. Conversely, when the oxygen content exceeds the above upper limit, it may be difficult to produce carbon fibers.

[Electric double layer capacitor electrode]
The electric double layer capacitor electrode is formed using the carbon fiber. Specifically, the electrode for the electric double layer capacitor is obtained by mixing the carbon fiber with a binding aid and laminating the fibers so that the fibers are entangled with each other.

[advantage]
The carbon fiber manufacturing method uses ashless coal as a raw material, and electrospinning ashless coal together with a solvent and then carbonizing to obtain porous carbon fibers in which fine pores are formed by volatilization of the solvent. be able to. That is, according to the carbon fiber manufacturing method, porous carbon fibers can be manufactured by a relatively simple process of carbonization after electrospinning.

Further, the carbon fiber can be produced by a relatively simple process and can be effectively used as a porous material having many fine pores. Furthermore, since the said electrode for electric double layer capacitors uses the said carbon fiber, it is excellent in manufacturing cost.

[Other Embodiments]
The method for producing the carbon fiber is not limited to the above embodiment.

The carbon fiber manufacturing method may include steps other than those described above as necessary. Specifically, within a range that does not adversely affect each step, there may be a step such as a step of pulverizing raw coal, a step of removing foreign matters, or the like between or before and after each step.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not construed as being limited based on the description of the examples.

<Examples 1 and 2>
1 kg of bituminous coal pulverized to 1 mm or less as raw material coal was mixed with 5 kg of methylnaphthalene, charged in an autoclave, held at 400 ° C. for 1 hour in a nitrogen atmosphere, and then cooled to obtain a pyrolyzate. Next, this pyrolyzate was filtered, and the obtained filtrate was distilled under reduced pressure to separate soluble components, thereby obtaining solid ashless coal. Table 1 shows the elemental analysis values of the ashless coal. The oxygen content was calculated from the difference from the content of other elements.

The resulting ashless coal was mixed with pyridine to obtain an ashless coal solution having a concentration of 35.9% by mass. Using this ashless coal solution, electrospinning was performed at a voltage of 14 to 18 kV, a flow rate of 0.7 to 0.9 ml / h, a distance between the nozzle and the collector (inter-spinning distance) of 15 cm, and an inner diameter of the nozzle of 0.48 mm. A filamentous body was formed on the aluminum foil. In Example 1 and Example 2, electrospinning was performed by changing the yarn conditions.

After the filament was peeled from the aluminum foil, it was heated to 900 ° C. at a heating rate of 3.3 ° C./min to carbonize to obtain carbon fibers having an average diameter of 1 μm.

<Comparative example>
Using a commercially available coal-based pitch produced from tar produced as a by-product in the high-temperature coal distillation process (steel coke production process) as the raw material for electrospinning, electrospinning is performed under the same conditions as in the examples, and the average diameter is 1 μm. Carbon fiber was obtained. In addition, Table 1 shows elemental analysis values of the coal-based pitch used as a raw material.

<Reference example>
Powdered activated carbon having a diameter of 50 μm or less was obtained by using coconut shell as a raw material and making it porous by a steam activation method.

<Evaluation>
The oxygen content of the carbon fibers of the above examples and comparative examples was measured. Moreover, the specific surface area and the electrostatic capacity of the carbon fibers of the examples and comparative examples and the activated carbon of the reference example were measured. These results are shown in Table 2. Moreover, about the carbon fiber of Example 1, the measurement result of pore distribution is shown in FIG. 2, and a scanning electron micrograph is shown in FIG.

The specific surface area was measured using “BELSORP-max” manufactured by Microtrac Bell. In addition, the capacitance is obtained by creating an electrode for an electric double layer capacitor using carbon fiber or activated carbon, and measuring the charge / discharge characteristics in a 1 M H ₂ SO ₄ electrolyte in a capacitor using this electrode, The capacitance at 100 mA / g was determined.

From Table 2, the carbon fibers of Examples 1 and 2, which were carbonized after electrospinning ashless coal with a solvent using ashless coal as a raw material, had a large specific surface area compared to the comparative example and were sufficiently porous. You can see that In Example 1, as can be seen from FIG. 2, the diameter of the micropores is approximately 10 nm or less. Furthermore, the average fiber diameter determined from FIG. 3 was 1.1 μm. Further, the carbon fibers of Examples 1 and 2 are excellent in capacitance as compared with the carbon fiber of the comparative example and the activated carbon of the reference example.

The carbon fiber of the comparative example uses a coal-based pitch with a high ratio of aromatic compounds, and therefore, by condensing while forming an orientation in which molecules are stacked in parallel in electrospinning, a structure with high crystallinity and no development of pores It is speculated that it became.

On the other hand, the activated carbon of the reference example is larger in specific surface area than the carbon fibers of Examples 1 and 2, but has a small capacitance. This is thought to be due to the difference in pore structure.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on May 19, 2016 (Japanese Patent Application No. 2016-100345), the contents of which are incorporated herein by reference.

Since the carbon fiber obtained by the carbon fiber production method and the carbon fiber can produce porous carbon fiber by a relatively simple process, they can be suitably used as an adsorbent or an electrode raw material.

S1 Ashless coal acquisition process S2 Electrospinning process S3 Carbonization process

Claims (4)

1. Obtaining ashless coal by solvent extraction treatment of coal;
   A step of electrospinning the ashless coal obtained in the ashless coal acquisition step together with a solvent;
   A carbon fiber manufacturing method comprising: carbonizing the filament obtained in the electrospinning step.
2. The method for producing carbon fiber according to claim 1, wherein the carbonization is performed by heating the filament to 700 ° C or more and 1200 ° C or less.
3. Carbon fiber made from coal,
   A carbon fiber having a specific surface area of 300 m ² / g to 3000 m ² / g, an average diameter of 0.5 μm to 5 μm, and an oxygen content of 0.4% by mass or more.
4. An electrode for an electric double layer capacitor using the carbon fiber according to claim 3.

Images