JP2019044313A - Production method of carbon fiber - Google Patents

Abstract

To provide a production method of carbon fiber having comparatively excellent production cost and producibility.SOLUTION: The production method of a carbon fiber contains: a step of electrospinning of a solution containing ashless coal dissolved therein and a step of heating the spun fiber obtained in the electrospinning step; wherein the value of electric conductivity of the solution divided by an ashless coal mass rate to the solution is 0.1 mS/m or over and 0.2 mS/m or under, and a viscosity coefficient of the solution is 500 mPa s or over and 2000 mPa s or under. Preferably, the solvent used in the solution contains an organic compound containing a nitrogen atom or oxygen atom and having a boiling point at atmospheric pressure of 50°C or over and under 250°C as its principal component.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of producing carbon fiber.

  Carbon fibers are widely used as reinforcements for structural materials such as, for example, resins, concrete, ceramics and the like. In addition, carbon fibers are also used as, for example, heat insulating materials, activated carbon materials, conductive materials, heat transfer materials and the like. As a manufacturing method of carbon fiber, the method of electrospinning pitch, resin, etc. derived from petroleum or coal is known (refer Unexamined-Japanese-Patent No. 2011-157668 and international publication 2011/070893).

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

  However, in the above-mentioned method, since special treatments and materials such as surface treatment and a template material are required, there is a problem that the production cost of porous carbon fibers is increased.

JP, 2011-157668, A International Publication No. 2011/070893

  The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a carbon fiber which is relatively low in production cost and high in production efficiency.

  As a result of various investigations on the spinnability and fiber physical properties of important control factors and their control factors in the electrospinning of ash-free charcoal, the present inventors have made the solution physical properties by the interaction between ash-free charcoal and solvent. Changes over time may occur, which have been properly detected to reveal that they need to be adjusted. Specifically, in addition to the viscosity, the conductivity is easy to measure, and it is useful for spinnability and fiber physical property management as an index indicating the association state between ashless carbon molecules in a solution in which ashless carbon is dissolved. I found that.

  That is, the invention made to solve the above problems comprises the steps of: electrospinning a solution in which ash-free coal is dissolved; and heating the spun fibers obtained in the electrospinning step; Of carbon dioxide in which the viscosity ratio of the solution is from 500 mPa · s to 2000 mPa · s. It is a method.

  The manufacturing method of the said carbon fiber can manage spinnability simply by controlling the viscosity and the electric conductivity of the solution which ash-free charcoal dissolves to a fixed range. That is, according to the manufacturing method of the said carbon fiber, based on adjusting solution physical-property value, carbon fiber can be manufactured by a comparatively easy process. Therefore, the method for producing the carbon fiber is relatively low in production cost and high in production efficiency.

  It is preferable that the solvent used for the said solution has as a main component the organic compound which contains a nitrogen atom or an oxygen atom, and whose boiling point in atmospheric pressure is 50 to 250 degreeC. Ash-free charcoal can be dissolved in a high concentration in the above-mentioned solvent. In addition, in the electrospinning, since the above-mentioned solvent is rapidly detached from the state in which ashless coal is dissolved, a large number of micropores are induced in the obtained carbon fiber. Therefore, by using the above-mentioned solvent, the production efficiency of carbon fiber can be enhanced and the specific surface area can be increased.

  It is preferable that the said organic compound is a pyridine. Ashless coal can be dissolved in pyridine in high concentration. Thereby, good spinnability and fiber physical properties are realized.

  In the electrospinning step, a step of mixing coal and a solvent, a step of eluting ashless coal as a component soluble in the solvent from the coal in the slurry obtained in the mixing step, and after the elution step And separating the solution in which the ashless coal is dissolved from the slurry. Ash-free charcoal can be eluted to a solvent by the solvent extraction process of coal in the said elution process. That is, the manufacturing cost of carbon fiber can be further reduced by using the solution in which the ashless coal is dissolved as it is in the electrospinning step.

  Here, "conductivity" means a value at a reference temperature measured in accordance with JIS-K0130 (2008). "Ash-free charcoal mass ratio" means the ratio of ash-free charcoal mass to the weight of the solution in which ash-free charcoal is dissolved. "Viscosity" means a value at a reference temperature measured in accordance with JIS-Z8803 (2011). The "main component" means a component with the highest content, for example, a component with a content of 50% by mass or more. "Specific surface area" means a value measured in accordance with JIS-Z8830 (2013).

  As described above, the method for producing a carbon fiber of the present invention is relatively low in production cost and high in production efficiency.

FIG. 1 is a schematic flow diagram showing a method of producing carbon fiber according to an embodiment of the present invention. FIG. 2 is a schematic flow diagram of the electrospinning process of FIG. FIG. 3 is a schematic diagram showing an electrospinning unit. FIG. 4 is a schematic flow diagram of an electrospinning process of an embodiment different from that of FIG.

First Embodiment
Hereinafter, a first embodiment of a method for producing carbon fiber according to the present invention will be described.

  Ash-free coal is used as a carbon raw material in the manufacturing method of the said carbon fiber. Ashless coal is relatively inexpensive, has excellent electrospinning properties, and does not require materials other than carbon. The manufacturing method of the said carbon fiber mainly comprises an electrospinning process S1 and a heating process S2, as shown in FIG. The carbon fiber manufacturing method 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. Can be done by

[Electrospinning process]
In the electrospinning step S1, a spun fiber is formed on the substrate surface by electrospinning of a solution in which ashless coal is dissolved. The electrospinning 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 a fiber forming step S16, as shown in FIG. Prepare.

<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 lower limit, the elution amount of the solution in which the ash-free charcoal to be eluted in the elution step S12 dissolves is smaller than the slurry treatment amount, so the content of ash-free charcoal contained in the solution is It may be insufficient. Conversely, if the coal concentration exceeds the upper limit, the solution in which the ashless coal is dissolved is likely to be saturated in the solvent, and the elution rate of the solution in which the ashless coal is dissolved 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 that has been eluted in the elution step S12 is separated into a solution in which ash-free charcoal is dissolved and an extraction residue. This solid-liquid separation step S13 can be performed by the separation unit. In addition, the extraction residual component mainly refers to an extraction residue which mainly contains ash and insoluble coal which are insoluble in a solvent for extraction, and further contains a solvent for extraction in addition to these.

(Separation section)
As a method for separating the solution in which the above ashless coal is dissolved and the extraction residual component in the separation part, for example, gravity sedimentation, filtration, or centrifugation can be used, and the sedimentation tank, the filter, and the centrifugal separator respectively used.

  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 the extraction residual component is precipitated and solid-liquid separated in the settling tank using gravity. When separation is performed by gravity sedimentation, a solution in which ashless coal is dissolved is accumulated at the top of the sedimentation tank. The solution in which the ashless coal is dissolved is filtered using a filter unit as needed, and then discharged from the top of the settling tank. On the other hand, the extraction residual component is discharged from the lower part of the separation unit.

  In addition, when separation is performed by the gravity settling method, it is possible to discharge a solution in which ash-free coal is dissolved and an extraction residual 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 solution in which the ashless coal separated in the solid-liquid separation step S13 is dissolved. 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 for evaporating and separating the above-mentioned solvent, a separation method including a general distillation method and evaporation method (spray dry method etc.) can be used. By separating the solvent from the solution in which the ashless coal is dissolved, it is possible to obtain ashless coal which is substantially ash-free from the solution in which the ashless coal is dissolved.

  On the other hand, the solvent can be evaporated and separated from the above extraction residual components to obtain by-product coal. 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 coal obtained in the evaporation separation step S14 is dissolved in a solvent. By this dissolution, a solution in which ashless coal dissolves is obtained.

  The solvent for dissolving the ashless coal is not particularly limited as long as the ashless coal dissolves, but it is preferable to use a solvent containing an organic compound containing a nitrogen atom or an oxygen atom as a main component. As described above, when the main component of the solvent is an organic compound containing a nitrogen atom or an oxygen atom, the affinity between the solvent and the ashless charcoal is enhanced, and the content of ashless charcoal in the solution to be electrospinning can be easily controlled. As a result, the production cost of carbon fibers can be reduced because the yield of carbon fibers is increased. Ash-free charcoal can be dissolved in a high concentration in a solvent containing an organic compound containing nitrogen or oxygen as the main component. Therefore, the production efficiency of carbon fiber is enhanced by using the above-mentioned solvent.

  The lower limit value of the boiling point at atmospheric pressure of the solvent containing an organic compound containing a nitrogen atom or an oxygen atom as a main component is preferably 50 ° C., more preferably 60 ° C., and still more preferably 65 ° C. on the other hand. The boiling point of the solvent is preferably less than 250 ° C., more preferably less than 210 ° C., and still more preferably less than 160 ° C. If the boiling point of the solvent is less than the lower limit, ashless coal may not be sufficiently dissolved, and the content of ashless coal may not be increased. On the other hand, when the boiling point of the above-mentioned solvent is more than the above-mentioned upper limit, there is a possibility that the pore of carbon fiber may not be formed sufficiently because the pressure accompanying the desorption of the solvent is insufficient in electrospinning.

Examples of such an organic compound containing a nitrogen atom or an oxygen atom and having a boiling point of at least 50 ° C. but less than 250 ° C. include pyridine (C ₅ H ₅ N), tetrahydrofuran (C ₄ H ₈ O), and dimethylformamide _{((CH 3) 2 NCHO)} , such as N- methylpyrrolidone _{(C 5} H 9 NO) and the like. Among them, pyridine and tetrahydrofuran having high affinity to ashless coal are preferable. The organic compound containing a nitrogen atom or an oxygen atom may be of one type, or two or more types of organic compounds may be mixed.

  As a minimum of ash-free charcoal mass ratio to the above-mentioned solution, 0.2 is preferred and 0.25 is more preferred. On the other hand, as an upper limit of ash-free charcoal mass ratio to the above-mentioned solution, 0.6 is preferred, 0.5 is more preferred, and 0.4 is more preferred. When the mass ratio of ashless coal to the solution is less than the above lower limit, droplets are easily formed during electrospinning, so that it may be difficult to obtain a spun fiber in a fiber forming step S16 described later. On the contrary, when the ash-free charcoal mass ratio to the above-mentioned solution exceeds the above-mentioned upper limit, the diameter of the spinning fiber obtained by electrospinning becomes too large, and there is a possibility that the specific surface area of carbon fiber may fall.

  The lower limit of the value obtained by dividing the conductivity (reference temperature 25 ° C.) of the solution by the ash-free carbon mass ratio to the solution is 0.1 mS / m, preferably 0.12 mS / m, and 0.14 mS / m. Is more preferred. On the other hand, the upper limit of the value obtained by dividing the conductivity of the solution by the ash-free carbon mass ratio to the solution is 0.2 mS / m, preferably 0.18 mS / m, and more preferably 0.16 mS / m. If the value obtained by dividing the conductivity by the ashless coal mass ratio to the solution does not reach the above lower limit, the conductivity is insufficient and the spinnability is insufficient, which may make it difficult to produce carbon fibers. On the contrary, when the value which divided the above-mentioned conductivity by the ash-free charcoal mass ratio to the above-mentioned solution exceeds the above-mentioned upper limit, spinnability may become insufficient because conductivity becomes excessive, and manufacture of carbon fiber may become difficult. There is.

  The lower limit of the viscosity (reference temperature 25 ° C.) of the solution is 500 mPa · s, preferably 600 mPa · s, and more preferably 800 mPa · s. On the other hand, the upper limit of the viscosity of the solution is 2000 mPa · s, preferably 1800 mPa · s, more preferably 1600 mPa · s. When the viscosity is less than the above lower limit, the spinnability is insufficient due to the decrease in the association between ashless carbon molecules, and there is a possibility that the production of carbon fibers becomes difficult. On the contrary, when the above-mentioned viscosity exceeds the above-mentioned upper limit, there is a possibility that spinnability may become inadequate because association between ash-free charcoal molecules becomes excessive, and manufacture of carbon fiber may become difficult.

<Fiber forming process>
In the fiber forming step S16, electrospinning is performed using the solution obtained in the second mixing step S15 to form spun fibers on the substrate surface.

  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 rapid increase of the specific surface area of the solution flow 3, and the spun fibers 4 are formed on the surface of the substrate 2. Thus, in electrospinning, the spun fiber 4 can be formed with a relatively simple apparatus. Although only one nozzle 1a is shown in FIG. 3, a plurality of nozzles 1a may be provided to simultaneously form a plurality of spun 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 resulting spun fibers 4 become thin and thus easily broken, which may make it 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 spun fiber 4 obtained becomes large, there is a possibility that the specific surface area of the 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, if the inter-spinning distance exceeds the above-mentioned upper limit, the resulting spun 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 spun fiber 4 may not be stably formed. Conversely, if the applied voltage E exceeds the upper limit, the distribution of the diameters of the resulting spun fibers 4 is likely to spread, and the 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 spun fiber 4 may not be stably formed. Conversely, if the flow rate of the solution flow 3 exceeds the upper limit, the diameter of the spun fiber 4 increases, and the specific surface area of the carbon fiber to be produced 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 spun fibers 4 formed on the surface of the substrate 2 is preferably 0.5 μm, more preferably 0.7 μm. On the other hand, the upper limit of the average diameter of the spun fibers 4 is preferably 5 μm, more preferably 3 μm. If the average diameter of the spun fiber 4 is less than the above lower limit, the spun fiber 4 is likely to be broken, which may make it difficult to obtain long fibers. Conversely, if the average diameter of the spun fibers 4 exceeds the upper limit, the specific surface area of the carbon fibers to be produced may be reduced. From the viewpoint of controllability, the average diameter of the spun fiber 4 is mainly controlled by the applied voltage E of electrospinning or the content of ashless coal in the solution. Also, the average diameter of the spun fibers 4 can be adjusted by the inner diameter of the nozzle and the distance between spinnings.

  The spun fibers 4 formed on the surface of the substrate 2 are peeled off from the substrate 2. In the carbon fiber manufacturing method, the spun fibers 4 are continuously and randomly formed on the substrate 2 without being cut due to the excellent electrospinning property of ashless coal. Therefore, the carbon fiber of a long fiber is easy to be obtained by using the manufacturing method of the said carbon fiber.

[Heating process]
In the heating step S2, the spun fiber obtained in the electrospinning step S1 is heated. The heating step S2 can be performed by the heating unit.

(Heating unit)
The heating unit carbonizes the spun fiber by heating. Carbon fiber is obtained by this carbonization.

  As the heating unit, for example, a known electric furnace or the like can be used, and the spun fiber is inserted into the heating unit, the inside is replaced with an inert gas, and heating is performed while blowing the inert gas into the heating unit. Can carbonize the spun fiber. 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 carbon fibers may be reduced.

The lower limit of the specific surface area of the 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 carbon fiber 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.

<Advantage>
In the method for producing a carbon fiber, the electrospinning property is enhanced based on controlling the solution physical property value by controlling the conductivity and the viscosity of the solution in which the ashless coal is dissolved in a certain range. On the other hand, when the solvent of the solution in which ashless coal dissolves contains an organic compound containing a nitrogen atom or an oxygen atom as a main component, the electrospinning property is enhanced. Moreover, in the manufacturing method of the said carbon fiber, the kind of solvent used when extracting ash-free charcoal and the solvent used for the solution of electrospinning can be changed. Therefore, since the ashless coal extraction and electrospinning can be respectively optimized, the yield of carbon fibers can be increased. Therefore, by using the method for producing carbon fibers, carbon fibers having relatively low production cost and high production efficiency can be produced.

Second Embodiment
Hereinafter, a second embodiment of the method for producing carbon fiber according to the present invention will be described.

  The manufacturing method of the said carbon fiber mainly comprises an electrospinning process S1 and a heating process S2 similarly to the manufacturing method of the carbon fiber of FIG. The carbon fiber manufacturing method also includes, as electrospinning step S1, mixing step S21, elution step S22, solid-liquid separation step S23, and fiber forming step S24, as shown in FIG.

<Mixing process>
In the mixing step S21, coal and a solvent are mixed. In the second embodiment, since ashless coal is not isolated as a solid, it is necessary to use a solvent for extracting ashless coal from coal and a solvent for a solution to be electrospun as the same kind of solvent. Other than the type of the solvent, the method can be similarly performed by the method described in regard to the first mixing step S11 of the first embodiment.

  As a solvent for extracting ashless coal from coal, a solvent containing an organic compound containing nitrogen atom or oxygen atom as a main component and having an organic compound boiling point at atmospheric pressure of 50 ° C. or more and less than 250 ° C. is used Is preferred.

As an organic compound containing such a nitrogen atom or an oxygen atom, pyridine (C ₅ H ₅ N), tetrahydrofuran (C ₄ H ₈ O), dimethylformamide ((CH ₃ ) ₂ NCHO), N-methylpyrrolidone (C) ₅ H ₉ NO) and the like. Among them, pyridine and tetrahydrofuran having high affinity to ashless coal are preferable. The organic compound containing a nitrogen atom or an oxygen atom may be of one type, or two or more types of organic compounds may be mixed.

<Elution step>
In the elution step S22, the coal component soluble in the solvent is eluted from the coal in the slurry obtained in the mixing step S21. The elution step can be similarly performed by the method described for the elution step S12 of the first embodiment.

  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, 80 degreeC is preferable and 90 degreeC is more preferable. On the other hand, as an upper limit of the temperature of the above-mentioned slurry, 120 ° C is preferred and 110 ° 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).

  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 solution in which ash-free charcoal is dissolved and the extraction efficiency.

Solid-liquid separation process
In the solid-liquid separation step S23, the slurry that has been eluted in the elution step S22 is separated into a solution in which ash-free charcoal is dissolved and an extraction residual component. This solid-liquid separation step can be carried out in the same manner by the method described for the solid-liquid separation step S13 of the first embodiment.

  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.

  In the second embodiment, the evaporation separation step and the second mixing step can be omitted by using the solvent for extracting ashless coal and the solvent for the solution to be electrospinning the same type of solvent. In this case, the liquid obtained by solid-liquid separation can be used as a solution for electrospinning.

<Fiber forming process>
In the fiber forming step S24, electro spinning is performed using the solution obtained in the solid-liquid separation step S23 to form spun fibers on the substrate surface. This electrospinning can be similarly performed by the method described for the electrospinning of the first embodiment.

[Heating process]
In the heating step S2, the spun fibers obtained in the fiber forming step S24 are heat-treated. This heating process S2 can be similarly performed by the method described regarding the heating process S2 of the first embodiment.

<Advantage>
In the second embodiment, since ashless coal is not isolated as a solid, the liquid obtained in the solid-liquid separation step can be used as a solution for electrospinning. Therefore, it is necessary to make the solvent for extracting ashless coal from coal and the solvent for the solution to be electrospun the same kind of solvent. Thereby, since the evaporation separation step and the second mixing step can be omitted, the production efficiency can be further enhanced and the production cost can be reduced as a method for producing a carbon fiber.

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

  Although the said 1st embodiment demonstrated the structure which the mixing part of a 1st mixing process has a preparation tank, if a solvent and coal can be mixed not only in this structure, a preparation tank may be abbreviate | 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.

  In the first embodiment, the method for producing ash-free charcoal by solvent extraction has been described, but the use of separately produced ash-free charcoal omits the production of ash-free charcoal by solvent extraction. You can also.

  EXAMPLES The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[Examples 1 and 2, Comparative Examples 1 and 2]
Ashless coal manufactured by solvent extraction of bituminous coal was prepared as a carbon raw material. The elemental analysis value of this ashless coal is shown as "HPC-A" in Table 1.

  As a solvent, pyridine having a boiling point of 115 ° C. at atmospheric pressure was prepared. Pyridine is an organic compound containing nitrogen.

  Ash-free charcoal was dissolved in this solvent, and it was prepared so that ash-free charcoal mass ratio in a solution might be 0.30-0.40.

  Using this solution, electrospinning was performed under the conditions shown in Table 2 to form spun fibers on an aluminum foil substrate. The spun fiber-formed product is peeled off from the aluminum foil, heated to 900 ° C. at a temperature rising rate of 3.3 ° C./min, and subjected to heat treatment (carbonization) for 30 minutes. Carbon fibers of Comparative Examples 1 and 2 were produced.

[Examples 3 and 4, Comparative Examples 3 to 5]
Ashless coal having a composition different from that of Example 1 was prepared as a carbon raw material by solvent extraction of bituminous coal. The elemental analysis value of this ashless coal is shown as "HPC-B" in Table 1. Carbon fibers of Examples 3 and 4 and Comparative Examples 3 to 5 were produced in the same manner as Example 1 except that the ash-free charcoal mass ratio in the solution was changed to 0, 30 to 0.45.

[Comparative Examples 6 to 8]
Ash-free coal having a composition different from that of Examples 1 and 3 was prepared as a carbon raw material by solvent extraction of bituminous coal. The elemental analysis value of this ashless coal is shown as "HPC-C" in Table 1. Carbon fibers of Comparative Examples 6 to 8 were produced in the same manner as Example 1 except that the ash-free charcoal mass ratio in the solution was 0.40 to 0.60.

  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%.

<Evaluation method>
The following measurements were performed about the said Examples 1-4 and Comparative Examples 1-8.

<Conductivity>
It measured by JIS-K0130 (2008). The reference temperature is 25 ° C.
<Viscosity>
It measured by JIS-Z8803 (2011). The reference temperature is 25 ° C.

<Electrospinability>
The spinnability in electrospinning was evaluated according to the following criteria.
A: The fiber diameter is uniformly controlled, electrospinning with few thread breakage is possible, and the spinnability is excellent. B: The solution flow to be jetted is in the form of droplets, causing uneven fiber diameter or clogging of the nozzle. , Inferior in spinnability

<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.

  In Table 3, "-" in the column of average fiber diameter means that the measurement was not performed.

  From the results in Table 3, the value σ / c obtained by dividing the conductivity of the solution in which ash-free coal is dissolved by the ash-free charcoal mass ratio is 0.1 mS / m or more and 0.2 mS / m or less, and the viscosity of the solution It is understood that Examples 1 to 4 having a rate of 500 mPa · s or more and 2000 mPa · s or less are superior in electrospinning property to Comparative Examples 1 to 8.

  On the other hand, in Comparative Example 1, Comparative Example 3, Comparative Example 6, Comparative Example 7, and Comparative Example 8, since the above-mentioned σ / c exceeds 0.2 mS / m, the conductivity becomes excessive, so that spinning is performed. It is considered that the properties were insufficient and electrospinning could not be performed.

  It is considered that in Comparative Example 5, the above σ / c was less than 0.1 mS / m, and the electrospinning could not be performed because the spinnability was insufficient due to the insufficient conductivity.

  In Comparative Example 2, it is considered that electrospinning could not be performed because the viscosity was more than 2000 mPa · s and the association between ashless carbon molecules was excessive.

  It is considered that in Comparative Example 4, electrospinning could not be performed because the viscosity was less than 500 mPa · s and the association between ashless carbon molecules was insufficient.

  From the above, the electrospinning property of carbon fibers can be controlled by controlling the σ / c and the viscosity of the solution in a predetermined range by adjusting the conductivity of the solution and the ash-free carbon mass ratio. It can be said that it can be managed easily and simply.

  The method for producing carbon fiber of the present invention is relatively low in production cost and high in production efficiency.

S1, electrospinning step S2, heating step S11 first mixing step S12, mixing step S12, S22 elution step S13, S23 solid-liquid separation step S14 evaporation separation step S15 second mixing step S16, S24 fiber formation step 1 syringe 1a nozzle 2 substrate 3 solution flow 4 spinning fiber E voltage

Claims (4)

Electrospinning a solution in which ashless coal is dissolved;
Heating the spun fiber obtained in the electrospinning step;
The value obtained by dividing the conductivity of the solution by the ashless coal mass ratio to the solution is 0.1 mS / m or more and 0.2 mS / m or less,
The manufacturing method of the carbon fiber whose viscosity of the said solution is 500 mPa * s or more and 2000 mPa * s or less.   The method for producing a carbon fiber according to claim 1, wherein the solvent used in the solution contains an nitrogen atom or an oxygen atom and an organic compound having a boiling point of 50 ° C to less than 250 ° C at atmospheric pressure as a main component.   The method for producing carbon fiber according to claim 2, wherein the organic compound is pyridine. As said electrospinning process,
Mixing the coal and the solvent;
Eluting the ashless coal as a component soluble in the solvent from the coal in the slurry obtained in the mixing step;
A process of separating a solution in which the ash-free charcoal is dissolved from the slurry after the elution process, The method for producing a carbon fiber according to claim 1, 2 or 3.

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