JP2018178285A - Manufacturing method of porous carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a porous carbon fiber relatively excellent in manufacturing cost and manufacturing efficiency, and large in specific surface area.SOLUTION: A manufacturing method of a porous carbon fiber has a process for depositing a fine fiber on a substrate surface by electric field spinning of a solution in which ashless coal and a high molecular compound are dissolved, and a process for heating the fine fiber obtained in the deposition process. The content of the high molecular compound based on total amount of the ashless coal and the high molecular compound is preferably 1 mass% to 15 mass%. As the deposition process, a process for mixing coal and a solvent, a process for eluting a component soluble in the solvent from the coal in a slurry obtained in the mixing process, and a process for separating the slurry after elution in the elution process into a liquid content containing a solvent soluble component and a solvent insoluble component may be included.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of producing porous carbon fibers.

  Porous carbon fibers having pores with diameters on the order of microns or nanometers on the surface and high specific surface area are useful as adsorbents. As a method of producing this porous carbon fiber, for example, a method of activating a carbon raw material with water vapor or an alkaline substance to increase a specific surface area (JP-A-2012-41199), an organic resin is an oxide such as magnesium oxide (template After mixing with carbon particles and carbonizing, the method (Unexamined-Japanese-Patent No. 2016-41656) etc. which remove the said oxide are mentioned. In the above-described conventional method for producing porous carbon fiber, in addition to the step of carbonizing the raw material, a step of performing activation treatment with an alkaline substance and removal treatment of template particles is necessary, and there is room for improvement in its production efficiency. .

  As a method of producing porous carbon fibers which does not require activation treatment or removal treatment of template particles after carbonization, a method of carbonizing fibers electrospun has been proposed (Japanese Patent Laid-Open No. 2011-157668, International Publication No. 2011/070893 reference). In this conventional electrospinning method, a pitching material is supplied with a preheating gas to be spun, or a composition containing an electrospinnable polymer material, an organic compound and a transition metal is spun. That is, in the above-mentioned conventional electrospinning method, a special material and a substance other than carbon are required for the carbon raw material. In addition, the specific surface area of the carbon fiber produced by this conventional electrospinning is lower than that of the porous carbon fiber produced by performing the activation treatment and the removal treatment of the template particles. Therefore, in the above-mentioned conventional electrospinning method, there is room for improvement in the manufacturing cost and the specific surface area.

JP, 2012-41199, A JP, 2016-41656, A JP, 2011-157668, A International Publication No. 2011/070893

  The present invention has been made based on the circumstances as described above, and an object thereof is to provide a method for producing a porous carbon fiber which is relatively excellent in production cost and production efficiency and has a large specific surface area.

  As a result of intensive studies on the method for producing porous carbon fibers, the present inventors obtain porous carbon fibers having a larger specific surface area by mixing a polymer compound with a solution in which ash-free charcoal used for electrospinning is dissolved. Have found that it is possible to complete the present invention. Although the mechanism by which the specific surface area increases is not always clear, the tendency of the formation of pores in the carbon material due to the decomposition and dissipation of the polymer compound during carbonization, and the improvement of the electrospinning property of the carbon material It is considered to be

  That is, the invention made to solve the above problems is a process of depositing fine fibers on the substrate surface by electrospinning of a solution in which ash-free charcoal and a polymer compound are dissolved, and the fine fibers obtained in the above deposition process And heating the porous carbon fiber.

  In the method of producing porous carbon fibers, ashless coal is used as a carbon material. Ashless coal is relatively inexpensive, has excellent electrospinning properties, and does not require materials other than carbon. Furthermore, the excellent electrospinning property is enhanced by mixing the polymer compound with a solution in which ash-free charcoal for electrospinning is dissolved. In addition, in the method for producing porous carbon fibers, based on the excellent graphitability of ash-free charcoal, porous carbon fibers of long fibers with high specific surface area can be easily formed by electrospinning without treatment such as activation. You can get it. In addition, when carbonizing in the heating step, the pores in the carbon material increase due to the decomposition and dissipation of the polymer compound. Therefore, by using the method for producing porous carbon fibers, carbon fibers which are relatively excellent in production cost and production efficiency and have a large specific surface area can be produced.

  As content of the high molecular compound with respect to the total amount of the said ash-free charcoal and a high molecular compound, 1 mass% or more and 15 mass% or less are preferable. As described above, by setting the content of the polymer compound to the total amount of the above ashless coal and the polymer compound in the above range, the pores in the carbon material can be maintained while maintaining the excellent electrospinning property of the ashless coal. Can increase the effect of

  In the deposition step, a step of mixing coal and a solvent, a step of eluting a component soluble in the solvent from the coal in the slurry obtained in the mixing step, and the slurry after elution in the elution step And Separating into a liquid component containing a solvent-soluble component and a solvent-insoluble component. By using solvent-extracted coal as ashless coal in this manner, the production efficiency can be further enhanced and the production cost can be reduced.

  It is preferable to adjust the voltage of electrospinning or the content of ashless carbon and the polymer compound in the above solution so that the average diameter of the obtained carbon fiber is 0.5 μm or more and 5 μm or less. The specific surface area can be increased by adjusting the average diameter of the carbon fiber obtained in this manner within the above range.

  Here, the "polymer compound" refers to a compound having a molecular weight of 1,000 or more and 1,000,000 or less.

  As explained above, by using the method for producing porous carbon fibers of the present invention, porous carbon fibers having a large specific surface area can be produced at relatively good production cost and efficiency.

FIG. 1 is a schematic flow diagram showing a method of producing a porous carbon fiber sheet according to an embodiment of the present invention. It is a schematic flowchart of the deposition process of FIG. It is a schematic diagram which shows an electrospinning part.

  Hereinafter, an embodiment of a method of producing porous carbon fibers according to the present invention will be described.

  The method for producing the porous carbon fiber mainly includes a deposition step S1 and a heating step S2, as shown in FIG. The method for producing the porous carbon fiber mainly includes, for example, a coal supply unit, a solvent supply unit, a mixing unit, a temperature raising unit, an elution unit, a separation unit, an electrospinning unit, and a heating unit. It can be performed by a manufacturing apparatus.

[Deposition process]
In the deposition step S1, fine fibers are deposited on the substrate surface by electrospinning of a solution in which ashless coal and a polymer compound are dissolved. The deposition step S1 includes a first mixing step S11, an elution step S12, a solid-liquid separation step S13, an evaporation separation step S14, a second mixing step S15, and an electrospinning step S16 as shown in FIG. .

<First mixing step>
In the first mixing step S11, coal and a solvent are mixed. This first mixing step S11 can be performed by, for example, a coal supply unit, a solvent supply unit, and a mixing unit.

(Coal supply department)
The coal supply unit supplies coal to the mixing unit. As a coal supply part, well-known coal hoppers, such as a normal pressure hopper used by a normal pressure state, a pressurized hopper used by a normal pressure state and a pressurized state, can be used.

  Coal supplied from a coal supply part is coal used as a raw material of ash-free coal. As said coal, coal of various quality can be used. For example, bituminous coal having a high extraction ratio of ash-free coal, and cheaper low-grade coal (sub-bituminous coal or lignite) are preferably used. Also, when coal is classified by particle size, finely crushed coal is suitably used. Here, "finely pulverized coal" means coal having a mass ratio of coal having a particle size of less than 1 mm to 80% or more of the mass of the entire coal. Moreover, lump coal can also be used as coal supplied from a coal supply part. Here, "mass coal" means coal in which the mass ratio of coal having a particle size of 5 mm or more with respect to the mass of the entire coal is 50% or more. Since the particle size of undissolved solid coal is maintained large as compared with finely pulverized coal, bulk coal can streamline separation in the separation section described later. Here, “particle size (particle size)” refers to a value measured in accordance with the general rule of sieving test in JIS-Z8815: 1994. In addition, the metal mesh screen defined, for example to JIS-Z8801-1: 2006 can be used for the classification by the particle size of coal.

  As a minimum of the carbon content rate of the above-mentioned low grade coal, 70 mass% is preferred. On the other hand, as a maximum of the carbon content rate of the above-mentioned low grade coal, 85 mass% is preferred, and 82 mass% is more preferred. If the carbon content of the low-grade coal is less than the above lower limit, the elution rate of the solvent-soluble component may be reduced. On the contrary, if the carbon content of the low grade coal exceeds the upper limit, the cost of the supplied coal may be high.

  In addition, you may use the coal which mixed and slurried a small amount of solvents as coal supplied from a coal supply part to a mixing part. By supplying the slurryed coal from the coal supply unit to the mixing unit, the coal can be easily mixed with the solvent in the mixing unit, and coal can be dissolved faster. However, if the amount of the solvent to be mixed in forming the slurry is large, the amount of heat for raising the temperature of the slurry to the elution temperature in the temperature rising portion described later becomes unnecessarily large, which may increase the manufacturing cost.

(Solvent supply unit)
The solvent supply unit supplies the solvent to the mixing unit. The said solvent supply part has a solvent tank which stores a solvent, and supplies a solvent to a mixing part from this solvent tank. The solvent supplied from the solvent supply unit is mixed with the coal supplied from the coal supply unit in the mixing unit.

  The solvent supplied from the solvent supply unit is not particularly limited as long as it dissolves coal, and, for example, a bicyclic aromatic compound derived from coal is preferably used. The bicyclic aromatic compound has a basic structure similar to that of a structural molecule of coal, and thus has a high affinity for coal and can obtain a relatively high extraction rate. Examples of coal-derived bicyclic aromatic compounds include methyl naphthalene oil, naphthalene oil and the like, which are distillation oils of by-product oil at the time of dry distillation of coal to produce coke.

  Although the boiling point of the said solvent is not specifically limited, For example, as a minimum of the boiling point of the said solvent, 180 degreeC is preferable and 230 degreeC is more preferable. On the other hand, as a maximum of the boiling point of the above-mentioned solvent, 300 ° C is preferred and 280 ° C is more preferred. If the boiling point of the solvent is less than the above lower limit, the solvent is easily volatilized, so that adjustment and maintenance of the mixing ratio of coal to the solvent in the slurry may be difficult. Conversely, if the boiling point of the solvent exceeds the upper limit, the separation of the solvent-soluble component and the solvent becomes difficult, and the recovery rate of the solvent may be reduced.

(Mixing part)
The mixing unit mixes the coal supplied from the coal supply unit and the solvent supplied from the solvent supply unit.

  A preparation tank can be used as the said mixing part. The coal and the solvent are supplied to the preparation tank through a supply pipe. In the preparation tank, the supplied coal and solvent are mixed to prepare a slurry. Further, the preparation tank has a stirrer, and the mixed slurry is kept stirred by the stirrer to maintain the mixed state of the slurry.

  The concentration of coal on the basis of anhydrous coal in the slurry in the preparation tank is appropriately determined depending on the type of solvent and the like, but the lower limit of the concentration of coal is preferably 10% by mass, more preferably 13% by mass. On the other hand, as an upper limit of the above-mentioned coal concentration, 25 mass% is preferred and 20 mass% is more preferred. When the coal concentration is less than the above lower limit, the elution amount of the solvent-soluble component eluted in the elution step S12 decreases relative to the slurry treatment amount, so that the content of ashless coal contained in the solution is insufficient May be Conversely, if the coal concentration exceeds the upper limit, the solvent-soluble component is likely to be saturated in the solvent, and the elution rate of the solvent-soluble component may be reduced.

<Elution step>
In the elution step S12, the coal component soluble in the solvent is eluted from the coal in the slurry obtained in the first mixing step S11. The elution step S12 can be performed by, for example, a temperature rising portion and an elution portion.

(Heating section)
The temperature raising unit raises the temperature of the slurry obtained in the first mixing step S11.

  The temperature raising portion is not particularly limited as long as it can heat the slurry passing through the inside, and examples thereof include a resistance heating heater and an induction heating coil. In addition, the temperature raising unit may be configured to perform temperature raising using a heat medium, and has, for example, a heating pipe disposed around the flow path of the slurry passing through the inside, The temperature of the slurry may be increased by supplying a heat medium such as steam or oil.

  Although the temperature of the slurry after temperature rising by a temperature rising part is suitably determined according to the solvent to be used, as a lower limit of the temperature of the said slurry, 300 degreeC is preferable and 360 degreeC is more preferable. On the other hand, as a maximum of the temperature of the above-mentioned slurry, 420 ° C is preferred and 400 ° C is more preferred. When the temperature of the above-mentioned slurry is less than the above-mentioned minimum, there is a possibility that a dissolution rate may fall. Conversely, if the temperature of the above-mentioned slurry exceeds the above-mentioned upper limit, there is a possibility that it becomes difficult to control the concentration of the slurry because the solvent is excessively vaporized.

  Moreover, it does not specifically limit as a pressure of a temperature rising part, It can be set as normal pressure (0.1 MPa).

(Elution part)
The elution part is obtained in the mixing part, and the coal component soluble in the solvent is eluted from the coal in the slurry heated in the heating part.

  An extraction tank can be used as an elution part, and the slurry after the said temperature rise is supplied to this extraction tank. In the extraction tank, coal components soluble in the solvent are eluted from the coal while maintaining the temperature and pressure of the slurry. Moreover, the said extraction tank has a stirrer. The above elution can be promoted by stirring the slurry with this stirrer.

  The elution time in the elution portion is not particularly limited, but is preferably 10 minutes to 70 minutes from the viewpoint of the extraction amount of the solvent-soluble component and the extraction efficiency.

Solid-liquid separation process
In the solid-liquid separation step S13, the slurry after elution in the elution step S12 is separated into a liquid component containing a solvent-soluble component and a solvent-insoluble component. This solid-liquid separation step S13 can be performed by the separation unit. The solvent-insoluble component mainly refers to an extraction residue which mainly contains ash and insoluble coal which are insoluble in a solvent for extraction, and additionally contains a solvent for extraction.

(Separation section)
As a method of separating the liquid component and the solvent-insoluble component in the separation part, for example, a gravity sedimentation method, a filtration method and a centrifugal separation method can be used, and a sedimentation tank, a filter and a centrifugal separator are used respectively.

  Hereinafter, the separation method will be described by taking the gravity settling method as an example. The gravity settling method is a separation method in which solvent insoluble components are precipitated and solid-liquid separated in the settling tank using gravity. In the case of separation by gravity sedimentation, the liquid containing solvent-soluble components accumulates at the top of the sedimentation tank. The liquid component is filtered using a filter unit, if necessary, and then discharged to a spray unit described later. On the other hand, the solvent insoluble component is discharged from the lower part of the separation unit.

  In addition, when separation is performed by the gravity sedimentation method, it is possible to discharge the liquid component including the solvent-soluble component and the solvent-insoluble component from the sedimentation tank while continuously supplying the slurry into the separation unit. This enables continuous solid-liquid separation processing.

  The time for maintaining the slurry in the separation part is not particularly limited, but can be, for example, 30 minutes or more and 120 minutes or less, and within this time, sedimentation in the separation part is performed. In addition, when using lumped coal as coal, since sedimentation separation is made efficient, time to maintain a slurry in a isolation | separation part can be shortened.

  The temperature and pressure in the separation unit can be the same as the temperature and pressure of the slurry after the temperature raising by the temperature raising unit.

<Evaporation separation process>
In the evaporation separation step S14, the solvent is evaporated from the liquid separated in the solid-liquid separation step S13. Evaporative separation of this solvent gives ashless coal (HPC). The ash-free coal thus obtained has an ash content of 5% by mass or less or 3% by mass or less, hardly contains ash, and has no water.

  As a method of evaporating and separating the above-mentioned solvent, a separation method including a general distillation method or evaporation method (spray dry method etc.) can be used. By separating the solvent from the liquid, it is possible to obtain ashless coal substantially free of ash from the liquid.

  On the other hand, the solvent can be evaporated and separated from the solvent insoluble component to obtain by-product carbon. The byproduct coal does not show softening and melting properties, but the oxygen-containing functional group is eliminated. Therefore, by-produced coal does not inhibit the softening and melting properties of other coals contained in this blended coal when used as blended coal. Therefore, this blended coal can be used, for example, as a part of blended coke of coke raw material. Also, by-product coal may be used as a fuel like general coal.

<2nd mixing process>
In the second mixing step S15, the ashless carbon and the polymer compound obtained in the evaporation separation step S14 are dissolved in a solvent. As a result of this dissolution, a solution in which ashless charcoal and a polymer compound are dissolved is obtained.

  The above-mentioned polymer compound is not particularly limited as long as it has a solvent which can be dissolved together with ash-free carbon, but organic polymer compounds are preferable, among which organic polymer compounds having a lower carbon yield than ash-free charcoal preferable. Since the carbon yield of ash-free charcoal is usually 30% by mass to 70% by mass, the upper limit of the carbon yield of the above-mentioned polymer compound is preferably 25% by mass, more preferably 15% by mass, 5% by mass Is more preferred. Thus, the increase effect of the pore in heating process S2 mentioned later is easy to be promoted by using the low molecular weight compound of carbon yield. On the other hand, the lower limit of the carbon yield of the above-mentioned polymer compound is not particularly limited and may be 0% by mass. Examples of such a polymer compound include poly (methyl methacrylate) (carbon yield: 4% by mass), polyvinylpyrrolidone (carbon yield: 0% by mass), polystyrene (carbon yield: 10% by mass) and the like.

The solvent for dissolving the ashless carbon and the polymer compound is not particularly limited as long as the ashless carbon and the polymer compound dissolve, but it is preferable to use an organic compound containing an oxygen atom or a nitrogen atom as a main component. Thus, by making the main component of the solvent an organic compound containing an oxygen atom or a nitrogen atom, the affinity between the solvent and the ashless charcoal and the polymer compound is enhanced, and the ashless charcoal and the polymer in the solution for electrospinning It is easy to control the compound content. As a result, the production cost of porous carbon fibers can be reduced since the yield of porous carbon fibers is increased. Such solvents include pyridine (C ₅ H ₅ N), tetrahydrofuran (C ₄ H ₈ O), dimethylformamide ((CH ₃ ) ₂ NCHO), N-methyl pyrrolidone (C ₅ H ₉ NO), etc. Be Among them, pyridine and tetrahydrofuran having high affinity to ashless coal are preferable. The organic compound containing an oxygen atom or a nitrogen atom may be of one type, or two or more types of organic compounds may be mixed.

  As a minimum of content of ash-free charcoal in the above-mentioned solution, 20 mass% is preferred and 25 mass% is more preferred. On the other hand, as an upper limit of content of ash-free charcoal in the above-mentioned solution, 60 mass% is preferred, 50 mass% is more preferred, and 40 mass% is still more preferred. If the content of the ash-free coal is less than the above lower limit, droplets are easily formed during electrospinning, so it may be difficult to obtain fine fibers in the later-described electrospinning step S16. On the contrary, when content of the above-mentioned ash-free charcoal exceeds the above-mentioned maximum, there is a possibility that the diameter of the fine fiber obtained by electrospinning becomes too large, and the specific surface area of a porous carbon fiber sheet may fall.

  The lower limit of the content of the polymer compound with respect to the total amount of the ashless carbon and the polymer compound is preferably 1% by mass, more preferably 3% by mass, and still more preferably 5% by mass. On the other hand, as a maximum of content of a high molecular compound to a total amount of the above-mentioned ash-free charcoal and a high molecular compound, 15 mass% is preferred and 10 mass% is more preferred. If the content of the polymer compound with respect to the total amount of the ashless carbon and the polymer compound is less than the above lower limit, the pore increasing effect may be insufficient. Conversely, if the content of the polymer compound with respect to the total amount of the above ashless coal and the polymer compound exceeds the above upper limit, the layer separation from the ashless coal is likely to occur, so the pore increasing effect is insufficient May be

  In addition, as a method of dissolving ash-free charcoal and a polymer compound in a solvent, ash-free charcoal and a polymer compound may be directly dissolved in a solvent, and a solution in which ash-free charcoal is dissolved in a solvent, and a polymer It may be prepared by mixing a solution of the compound in a solvent.

<Electrospinning process>
In the electrospinning step S16, microfibers are deposited on the substrate surface by performing electrospinning using the solution obtained in the second mixing step S15.

  Electrospinning can be performed, for example, by an electrospinning unit having a syringe 1 and a substrate 2 as shown in FIG. Specifically, the electrospinning is performed by placing the solution in the syringe 1 and applying a voltage E between the nozzle 1 a of the syringe 1 and the substrate 2. When a voltage E is applied between the nozzle 1a and the substrate 2, charges are collected on the surface of the droplet at the tip of the nozzle 1a and repel each other to form a conical shape. The voltage E is further increased, and when the repulsive force of the charge exceeds the surface tension, the solution is jetted from the tip of the nozzle 1 a toward the substrate 2. Since the surface charge density is increased as the ejected solution flow 3 becomes thinner, the repulsive force of the charge is increased and the solution flow 3 is further stretched. At this time, the solvent volatilizes due to the specific surface area of the solution flow 3 rapidly increasing, and the fine fibers 4 are spun on the surface of the substrate 2. Thus, in electrospinning, the fine fibers 4 can be produced with a relatively simple device. Although one nozzle 1a is provided in FIG. 3, a plurality of nozzles 1a may be provided to simultaneously produce a plurality of fine fibers.

  The substrate 2 is not particularly limited as long as it has conductivity, but a metal plate, a metal foil, a carbon substrate or the like can be used.

  The lower limit of the inner diameter (the inner diameter of the nozzle) of the tip end portion of the nozzle 1a is preferably 0.2 mm, more preferably 0.4 mm. On the other hand, as an upper limit of the above-mentioned nozzle inner diameter, 0.7 mm is preferred and 0.6 mm is more preferred. If the inside diameter of the nozzle is less than the above lower limit, the fine fibers 4 to be obtained become thin, so they are easily cut, and it may be difficult to obtain long fibers. On the contrary, when the above-mentioned nozzle internal diameter exceeds the above-mentioned maximum, since the diameter of the fine fiber 4 obtained becomes large, there is a possibility that the specific surface area of the porous carbon fiber manufactured may fall.

  The lower limit of the interspinning distance (the distance between the tip of the nozzle 1a and the substrate 2) is preferably 10 cm, more preferably 12 cm. On the other hand, as an upper limit of the distance between spinnings, 20 cm is preferable and 18 cm is more preferable. If the distance between spinning is less than the above lower limit, the solvent may not be sufficiently evaporated, which may make electrospinning difficult. On the other hand, when the distance between the spinnings exceeds the above-mentioned upper limit, the resulting fine fibers 4 become thin and therefore easily cut, which may make it difficult to obtain long fibers.

  The lower limit of the applied voltage E between the nozzle 1a and the substrate 2 is preferably 10 kV, more preferably 12 kV. On the other hand, as an upper limit of the said applied voltage E, 30 kV is preferable and 20 kV is more preferable. If the applied voltage E is less than the lower limit, the fine fibers 4 may not be stably formed. On the contrary, when the applied voltage E exceeds the upper limit, the distribution of the diameters of the obtained fine fibers 4 is likely to spread, and the porous carbon fibers to be produced may be inhomogeneous.

  The lower limit of the flow rate of the solution flow 3 (the discharge amount of the solution from one nozzle 1a) is preferably 1 ml / h, more preferably 1.5 ml / h. On the other hand, the upper limit of the flow rate of the solution flow 3 is preferably 3 ml / h, more preferably 2.5 ml / h. If the flow rate of the solution flow 3 is less than the lower limit, the fine fibers 4 may not be stably formed. Conversely, if the flow rate of the solution flow 3 exceeds the upper limit, the diameter of the fine fibers 4 becomes large, and the specific surface area of the produced porous carbon fibers may be reduced. The flow rate of the solution flow 3 can be controlled by the nozzle inner diameter and the applied voltage E.

  The lower limit of the average diameter of the fine fibers 4 deposited on the surface of the substrate 2 is preferably 0.5 μm, more preferably 0.7 μm. On the other hand, as a maximum of the mean diameter of the above-mentioned fine fiber 4, 5 micrometers is preferred and 3 micrometers is more preferred. If the average diameter of the fine fibers 4 is less than the above lower limit, the fine fibers 4 may be easily broken, and it may be difficult to obtain long fibers. Conversely, when the average diameter of the fine fibers 4 exceeds the upper limit, the specific surface area of the porous carbon fibers to be produced may be reduced. From the viewpoint of controllability, the average diameter of the fine fibers 4 is mainly controlled by the applied voltage E of electrospinning or the content of ashless coal and polymer compound in the solution. Moreover, the average diameter of the said fine fiber 4 can also be adjusted with the nozzle internal diameter and the distance between spinnings.

  The fine fibers 4 deposited on the surface of the substrate 2 are peeled off from the substrate 2. In the method of manufacturing the porous carbon fiber, the fine fibers 4 are continuously and randomly deposited on the substrate 2 without being cut due to the excellent electrospinning property of ashless coal. Therefore, it is easy to obtain porous carbon fibers of long fibers by using the method of producing porous carbon fibers.

[Heating process]
In the heating step S2, the fine fibers obtained in the deposition step S1 are heated. The heating step S2 can be performed by the heating unit.

(Heating unit)
The heating unit carbonizes the fine fibers by heating.

  For example, a known electric furnace or the like can be used as the heating unit, and fine fibers are inserted into the heating unit, the inside is replaced with inert gas, and heating is performed while blowing inert gas into the heating unit. Carbonization of fine fibers. The inert gas is not particularly limited, and examples thereof include nitrogen and argon. Among them, inexpensive nitrogen is preferable.

  As a minimum of the above-mentioned heating temperature, 500 ° C is preferred and 700 ° C is more preferred. On the other hand, as an upper limit of the above-mentioned heating temperature, 3000 ° C is preferred and 2800 ° C is more preferred. If the heating temperature is below the lower limit, carbonization may be insufficient. On the other hand, if the heating temperature exceeds the above upper limit, the manufacturing cost may increase from the viewpoint of improving the heat resistance of the equipment and the fuel consumption. In addition, as a temperature rising rate, it can be set, for example as 0.01 degrees C / min or more and 10 degrees C / min or less.

  Moreover, as a minimum of heating time, 10 minutes are preferable and 20 minutes are more preferable. On the other hand, as an upper limit of heating time, 10 hours are preferable and 8 hours are more preferable. If the heating temperature is less than the above lower limit, carbonization may be insufficient. Conversely, if the heating time exceeds the above upper limit, the production efficiency of the porous carbon fiber may be reduced.

The lower limit of the specific surface area of the porous carbon fibers produced, preferably from 700 meters ² / g, more preferably 800 m ² / g, more preferably 1000 m ² / g. There exists a possibility that it may become difficult to use as a porous material as the said specific surface area is less than the said minimum. On the other hand, the upper limit of the specific surface area is not particularly limited, but is usually about 3000 m ² / g.

  As a lower limit of the mean diameter of carbon fiber obtained, 0.5 micrometer is preferred and 0.7 micrometer is more preferred. On the other hand, as an upper limit of the mean diameter of the above-mentioned carbon fiber, 5 micrometers is preferred and 3 micrometers is more preferred. If the average diameter of the carbon fiber is less than the above lower limit, the carbon fiber may be easily cut, and it may be difficult to obtain long fibers. Conversely, if the average diameter of the carbon fibers exceeds the upper limit, the specific surface area of the porous carbon fibers to be produced may be reduced. The average diameter of the carbon fibers is determined by the average diameter of the fine fibers 4, and the average diameter of the fine fibers 4 is mainly controlled by the applied voltage E of electrospinning from the viewpoint of controllability. Moreover, the average diameter of the said fine fiber 4 can also be adjusted with the nozzle internal diameter and the distance between spinnings.

[advantage]
In the method of producing porous carbon fibers, ashless coal is used as a carbon material. Ashless coal is relatively inexpensive, has excellent electrospinning properties, and does not require materials other than carbon. Furthermore, the excellent electrospinning property is enhanced by mixing the polymer compound with a solution in which ash-free charcoal for electrospinning is dissolved. In addition, in the method for producing porous carbon fibers, based on the excellent graphitability of ash-free charcoal, porous carbon fibers of long fibers with high specific surface area can be easily formed by electrospinning without treatment such as activation. You can get it. In addition, when carbonizing in the heating step, the pores in the carbon material increase due to the decomposition and dissipation of the polymer compound. Therefore, by using the method for producing porous carbon fibers, carbon fibers which are relatively excellent in production cost and production efficiency and have a large specific surface area can be produced.

  Moreover, in the manufacturing method of the said porous carbon fiber, manufacturing efficiency can be further improved and manufacturing cost can be reduced by using what was solvent-extracted as ash-free charcoal.

Other Embodiments
The present invention is not limited to the above embodiment.

  Although the method of producing ash-free charcoal by solvent extraction has been described in the above embodiment, the method of producing ash-free charcoal is not limited thereto, and for example, ash-free produced by mixed heating of coal and a hydrogen donating solvent Charcoal can also be used.

  Furthermore, in the above embodiment, after ash-free charcoal is subjected to solvent extraction in the evaporation separation step, a solution in which the ash-free charcoal is dissolved and electrospinning is prepared in the second mixing step. The evaporation separation step may be omitted by using the same solvent as the solvent of the solution to be spun. In this case, in the second mixing step, for example, the polymer compound may be dissolved in the liquid component obtained in the solid-liquid separation step. A solution in which the polymer compound is dissolved in the liquid can be used as a solution for electrospinning. In the second mixing step, a solution in which the polymer compound is dissolved in the same solvent as the solvent for extracting ash-free charcoal is prepared, and a solution containing the polymer compound is mixed with the liquid to obtain an electrospinning solution. Can also be prepared.

  Although the above-mentioned embodiment explained the composition which a mixing part of the 1st mixing process has a preparation tank, if a solvent and coal can be mixed not only in this composition, a preparation tank may be omitted. For example, when the above mixing is completed by a line mixer, the preparation tank may be omitted and a line mixer may be provided between the supply pipe and the separation unit. Thus, the device configuration used in each process is not limited to the above embodiment.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1
Ashless coal manufactured by solvent extraction of bituminous coal was prepared as a carbon raw material. Elemental analysis values of this ashless coal are shown in Table 1. Moreover, the carbon yield of this ash-free charcoal was 55 mass%.

  In addition, in Table 1, the amount of oxygen means the amount of components other than carbon, hydrogen, nitrogen, and sulfur, and subtracts the amount of components of carbon, hydrogen, nitrogen, and sulfur from 100 mass%.

  As a polymer compound, polymethyl methacrylate (PMMA, carbon yield 4% by mass) was prepared.

  Pyridine was prepared as a solvent. The ashless coal and the polymer compound are dissolved in this solvent, and the content of the ashless coal in the solution is 30% by mass, and the content of the polymer compound is 2% by mass with respect to the total amount of the ashless coal and the polymer compound. Prepared as follows.

  Using this solution, electrospinning was performed under the conditions shown in Table 2 to deposit fine fibers on an aluminum foil substrate. The fine fibers are peeled off from the aluminum foil, heated to 900 ° C. at a temperature rising rate of 3.3 ° C./min, heat-treated (carbonized) for 30 minutes, and the porous carbon fibers of Example 1 Manufactured.

[Examples 2 to 6, Comparative Example 1]
As polymer compounds, PMMA is used in Examples 2 and 3, polyvinyl pyrrolidone (PVP, carbon yield 0 mass%) in Examples 4 and 5, and polystyrene (PSt, carbon mass 10 mass%) in Example 6 A solution used for electrospinning was prepared such that the content of the molecular compound was as shown in Table 3. In Comparative Example 1, the polymer compound was not dissolved in the solution used for electrospinning. The porous carbon fibers of Examples 2 to 6 and Comparative Example 1 were produced in the same manner as Example 1 except for the above.

[Evaluation method]
The following measurements were performed on Examples 1 to 6 and Comparative Example 1 described above.

<Average fiber diameter>
The average diameter (average fiber diameter) of carbon fibers was measured by a scanning electron microscope. The measurement measured the diameter of 10 arbitrary fibers in the visual field of a scanning electron microscope, and calculated the average. The measurement results are shown in Table 3.

<Specific surface area>
The specific surface area of the porous carbon fiber was measured by nitrogen adsorption (BET method). The measurement results are shown in Table 3.

  In Table 3, "-" means that the polymer compound was not dissolved in the solution used for electrospinning.

  From the results of Table 3, in Examples 1 to 6 in which the polymer compound was dissolved in the solution used for electrospinning, regardless of the type and the content of the polymer compound, Comparative Example 1 in which the polymer compound was not dissolved was used. The specific surface area is larger than that. From this, it is understood that by mixing the polymer compound with the solution for electrospinning, the electrospinning property of the carbon raw material can be enhanced, and the specific surface area of the obtained carbon fiber can be increased.

  Moreover, the specific surface area of the carbon fiber of Example 2 and Example 5 in which the content of the polymer compound is in the range of 3% by mass to 10% by mass is higher than those of the other examples using the same polymer compound. large. That is, it is understood that the specific surface area of the carbon fiber can be further enhanced by setting the content of the polymer compound to 3% by mass or more and 10% by mass or less.

  As explained above, by using the method for producing porous carbon fibers of the present invention, porous carbon fibers having a large specific surface area can be produced at relatively good production cost and efficiency.

S1 deposition step S2 heating step S11 first mixing step S12 elution step S13 solid-liquid separation step S14 evaporation separation step S15 second mixing step S16 electrospinning step 1 syringe 1a nozzle 2 substrate 3 solution flow 4 fine fiber E voltage

Claims (4)

Depositing fine fibers on a substrate surface by electrospinning of a solution in which ash-free charcoal and a polymer compound are dissolved;
Heating the fine fibers obtained in the deposition step.   The method for producing a porous carbon fiber according to claim 1, wherein the content of the polymer compound is 1% by mass or more and 15% by mass or less based on the total amount of the ashless carbon and the polymer compound. As the above deposition process,
Mixing the coal and the solvent;
Eluting the component soluble in the solvent from the coal in the slurry obtained in the mixing step;
The method for producing porous carbon fiber according to claim 1 or 2, further comprising: separating the slurry after elution in the elution step into a liquid component containing a solvent soluble component and a solvent insoluble component. 4. The voltage of electrospinning or the content of ash-free charcoal and polymer compound in the above solution is adjusted so that the average diameter of the obtained carbon fiber is 0.5 μm or more and 5 μm or less. The manufacturing method of the porous carbon fiber as described in-.

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