WO2018186018A1 - Method of manufacturing porous carbon fiber sheet and method of manufacturing porous carbon electrode - Google Patents

Abstract

The purpose of the present invention is to provide a method of manufacturing a porous carbon fiber sheet the manufacturing cost of which is relatively low and manufacturing efficiency is high, and a method of manufacturing a porous carbon electrode using this porous carbon fiber sheet. This method of manufacturing the porous carbon fiber sheet is provided with a step for depositing fine fibers in felt form on a substrate surface by electrospinning of a solution in which ashless coal is dissolved, and a step for heating the fine fiber deposit obtained by the deposition step. The deposition step may preferably be provided with a step for mixing coal and a solvent, a step for causing a component soluble in the solvent to be eluted from the coal in a slurry obtained by the mixing step , and a step for separating the slurry after elution by the elution step into a liquid content containing the solvent-soluble component and a solvent-insoluble component. This method of manufacturing the porous carbon electrode is provided with a step for forming the porous carbon fiber sheet manufactured by the method of manufacturing the porous carbon fiber sheet into an electrode.

Description

Method for producing porous carbon fiber sheet and method for producing porous carbon electrode

The present invention relates to a method for producing a porous carbon fiber sheet and a method for producing a porous carbon electrode.

As a method for producing a porous carbon fiber sheet having gas or liquid fluid diffusibility, a method is known in which short carbon fibers are mixed with a binder substance and made into a felt shape. In this conventional method for producing a porous carbon fiber sheet, since it is necessary to perform molding with a binder substance, there is room for improvement in the production efficiency.

As a method for producing a porous carbon fiber sheet that does not require molding, methods for carbonizing electrospun fibers have been proposed (see Japanese Patent Application Laid-Open No. 2011-157668 and International Publication No. 2011/070893). In this conventional electrospinning method, spinning is performed by supplying a preheated gas to a pitch-based material, or a composition containing a polymer material that can be electrospun, an organic compound, and a transition metal is spun.

Thus, the conventional method for producing a porous carbon fiber sheet by electrospinning requires a special material and a substance other than carbon as a carbon raw material. For this reason, the manufacturing method of the porous carbon fiber sheet by the conventional electrospinning has room for improvement in manufacturing cost.

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

The present invention has been made based on the circumstances as described above, a method for producing a porous carbon fiber sheet having relatively low production cost and high production efficiency, and a porous material using the porous carbon fiber sheet. It aims at providing the manufacturing method of a carbon electrode.

The invention made in order to solve the above-mentioned problems includes a step of depositing fine fibers in a felt shape on the substrate surface by electrospinning of a solution in which ashless coal is dissolved, and a fine fiber deposit obtained in the above deposition step. It is a manufacturing method of a porous carbon fiber sheet provided with the process of heating.

In the method for producing the porous carbon fiber sheet, ashless coal is used as a carbon raw material. Ashless coal is relatively inexpensive, has excellent electrospinning properties, and does not require materials other than carbon. Further, in the method for producing the porous carbon fiber sheet, based on the excellent graphitization property of ashless coal, a fine fibrous porous carbon fiber having a high specific surface area can be obtained by electrospinning without performing processing such as molding. Can be easily obtained. Therefore, the manufacturing method of the porous carbon fiber sheet has a relatively low manufacturing cost and high manufacturing efficiency.

As the deposition step, the step of mixing coal and solvent, the step of eluting components 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 a step of separating into a liquid component containing a solvent-soluble component and a solvent-insoluble component. Thus, by using what was solvent-extracted as ashless coal, manufacturing efficiency can be improved further and manufacturing cost can be reduced.

The electrospinning voltage or the content of ashless coal in the above solution may be adjusted so that the average diameter of the obtained carbon fibers is 0.5 μm or more and 5 μm or less. By adjusting the average diameter of the carbon fibers thus obtained within the above range, the fibers are appropriately entangled during electrospinning, and fluid diffusibility is enhanced.

Another invention made to solve the above problems is a method for producing a porous carbon electrode comprising a step of forming a porous carbon fiber sheet produced by the method for producing a porous carbon fiber sheet into an electrode.

In the method for producing the porous carbon electrode, since the porous carbon fiber sheet produced by the method for producing the porous carbon fiber sheet is formed into an electrode, an electrode having fluid diffusibility can be produced at a relatively low production cost. It can be manufactured efficiently.

As described above, the method for producing a porous carbon fiber sheet of the present invention and the method for producing a porous carbon electrode using the porous carbon fiber sheet have relatively low production costs and high production efficiency.

FIG. 1 is a schematic flow diagram showing a method for 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 typical schematic diagram showing an electrospinning part. 2 is an optical micrograph of a porous carbon fiber sheet of Example 1. FIG. 2 is a scanning electron micrograph of carbon fibers of the porous carbon fiber sheet of Example 1. FIG. 3 is a graph showing the pore size distribution of the porous carbon fiber sheet of Example 1. FIG.

Hereinafter, an embodiment of a method for producing a porous carbon fiber sheet and a method for producing a porous carbon electrode according to the present invention will be described.

[Method for producing porous carbon fiber sheet]
As shown in FIG. 1, the method for producing the porous carbon fiber sheet mainly includes a deposition step S1 and a heating step S2. The method for producing the porous carbon fiber sheet 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 carry out with the manufacturing apparatus provided.

[Deposition process]
In the deposition step S1, fine fibers are deposited in a felt shape on the substrate surface by electrospinning of a solution in which ashless coal is dissolved. As shown in FIG. 2, 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. .

<First mixing step>
In the first mixing step S11, coal and a solvent are mixed. This 1st mixing process S11 can be performed by a coal supply part, a solvent supply part, and a mixing part, for example.

(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 in a normal pressure state, a pressure hopper used in a normal pressure state and a pressurization state, can be used.

Coal supplied from the coal supply unit is coal that is a raw material for ashless coal. As the coal, various quality coals can be used. For example, bituminous coal with a high extraction rate of ashless coal or cheaper low-grade coal (subbituminous coal or lignite) is preferably used. Further, when coal is classified by particle size, finely pulverized coal is preferably 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, “coal” means coal in which the mass ratio of coal having a particle size of 5 mm or more to the mass of the entire coal is 50% or more. The lump coal can maintain the particle size of undissolved solid coal larger than that of finely pulverized coal, so that the separation in the separation unit described later can be made more efficient. Here, “particle size (particle size)” refers to a value measured in accordance with JIS-Z8815: 1994 general screening test rules. For sorting according to the particle size of coal, for example, a metal net sieve specified in JIS-Z8801-1: 2006 can be used.

The lower limit of the carbon content of the low-grade coal is preferably 70% by mass. On the other hand, the upper limit of the carbon content of the low-grade coal is preferably 85% by mass, and more preferably 82% by mass. There exists a possibility that the elution rate of a solvent soluble component may fall that the carbon content rate of the said low grade coal is less than the said minimum. Conversely, if the carbon content of the low-grade coal exceeds the upper limit, the cost of the coal to be supplied may increase.

In addition, as a coal supplied to a mixing part from a coal supply part, you may use the coal which mixed a small amount of solvent and made it slurry. By supplying the slurried coal from the coal supply unit to the mixing unit, the coal is easily mixed with the solvent in the mixing unit, and the coal can be dissolved more quickly. However, if the amount of the solvent to be mixed at the time of forming the slurry is large, the amount of heat for raising the slurry to the elution temperature in the temperature raising 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 from this solvent tank to a mixing part. The solvent supplied from the solvent supply unit is mixed with 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. For example, a bicyclic aromatic compound derived from coal is preferably used. Since this bicyclic aromatic compound has a basic structure similar to the structural molecule of coal, it has a high affinity with coal and can obtain a relatively high extraction rate. Examples of the bicyclic aromatic compound derived from coal include methyl naphthalene oil and naphthalene oil, which are distilled oils of by-products when carbon is produced by carbonization to produce coke.

The boiling point of the solvent is not particularly limited. For example, the lower limit of the boiling point of the solvent at normal pressure (0.1 MPa) is preferably 180 ° C., more preferably 230 ° C. On the other hand, the upper limit of the boiling point of the solvent at normal pressure is preferably 300 ° C. and more preferably 280 ° C. If the boiling point of the solvent is less than the above lower limit, the solvent is likely to volatilize, and thus it may be difficult to adjust and maintain the mixing ratio of coal and solvent in the slurry. Conversely, if the boiling point of the solvent exceeds the upper limit, it is difficult to separate the solvent-soluble component from the solvent, and the solvent recovery rate 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 mixing unit. The coal and 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. Moreover, the said preparation tank has a stirrer, and maintains the mixing state of a slurry by hold | maintaining the mixed slurry, stirring with a stirrer.

Although the coal concentration on the basis of anhydrous carbon in the slurry in the preparation tank is appropriately determined depending on the type of solvent, the lower limit of the coal concentration is preferably 10% by mass, and more preferably 13% by mass. On the other hand, the upper limit of the coal concentration is preferably 25% by mass, and more preferably 20% by mass. If the coal concentration is less than the lower limit, the elution amount of the solvent-soluble component eluted in the elution step S12 is less than the slurry processing amount, and therefore the content of ashless coal contained in the solution is insufficient. There is a risk. 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 process>
In the elution step S12, coal components soluble in the solvent are 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 raising part and an elution part.

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

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

Although the temperature of the slurry after the temperature rise by the temperature raising unit is appropriately determined according to the solvent used, the lower limit of the temperature of the slurry is preferably 300 ° C, more preferably 360 ° C. On the other hand, the upper limit of the temperature of the slurry is preferably 420 ° C., more preferably 400 ° C. If the temperature of the slurry is less than the lower limit, the elution rate may decrease. On the other hand, if the temperature of the slurry exceeds the upper limit, the solvent is excessively vaporized, which may make it difficult to control the concentration of the slurry.

Further, the pressure of the temperature raising portion is not particularly limited, but can be normal pressure (0.1 MPa).

(Elution part)
An elution part elutes a coal component soluble in a solvent from coal in a slurry obtained by the above-mentioned mixing part and heated at the above-mentioned temperature raising part.

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

The elution time at the elution part is not particularly limited, but is preferably 10 minutes or more and 70 minutes or less 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 liquid component containing a solvent-soluble component and a solvent-insoluble component. This solid-liquid separation step S13 can be performed by a separation unit. The solvent-insoluble component refers to an extraction residue that mainly contains ash and insoluble coal insoluble in the extraction solvent, and further contains an extraction solvent in addition to these.

(Separation part)
As a method for separating the liquid component and the solvent-insoluble component in the separation unit, 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 sedimentation method as an example. The gravitational sedimentation method is a separation method in which a solvent-insoluble component is settled by using gravity in a sedimentation tank to separate it into solid and liquid. When the separation is performed by the gravity sedimentation method, the liquid component containing the solvent-soluble component is accumulated in the upper part of the sedimentation tank. This liquid content is filtered using a filter unit as necessary, and then discharged to a spraying section to be described later. On the other hand, the solvent-insoluble component is discharged from the lower part of the separation part.

Further, when separation is performed by the gravity sedimentation method, the liquid component including the solvent-soluble component and the solvent-insoluble component can be discharged from the sedimentation tank while continuously supplying the slurry into the separation unit. Thereby, continuous solid-liquid separation processing becomes possible.

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 sedimentation separation in the separation part is performed within this time. In addition, when using lump coal as coal, since sedimentation separation is made efficient, the time which maintains a slurry in a 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 is raised by the temperature raising unit.

<Evaporation separation process>
In the evaporation separation step S14, the solvent is evaporated from the liquid component separated in the solid-liquid separation step S13. Ashless coal (HPC) is obtained by evaporating and separating the solvent. The ashless coal thus obtained has an ash content of 5% by mass or less or 3% by mass or less, contains almost no ash, and has no moisture.

As a method for evaporating and separating the solvent, a separation method including a general distillation method or an evaporation method (spray drying method or the like) can be used. By separating the solvent from the liquid, ashless coal substantially free of ash can be obtained from the liquid.

On the other hand, by-product coal can be obtained by evaporating and separating the solvent from the solvent-insoluble component. By-product charcoal does not show softening and melting properties, but the oxygen-containing functional groups are eliminated. Therefore, by-product coal does not inhibit the softening and melting properties of other coals contained in this blended coal when used as a blended coal. Therefore, this blended coal can be used, for example, as a part of the blended coal of the coke raw material. Further, by-product coal may be used as fuel in the same manner as general coal.

<Second mixing step>
In the second mixing step S15, the ashless coal obtained in the evaporation separation step S14 is dissolved in a solvent. By dissolving the ashless coal, a solution in which the ashless coal is dissolved is obtained.

The solvent for dissolving the ashless coal is not particularly limited as long as the ashless coal is dissolved, but an organic compound containing an oxygen atom or a nitrogen atom may be a main component. Thus, by making the main component of the said solvent into the organic compound containing an oxygen atom or a nitrogen atom, the affinity of a solvent and ashless coal increases, and it is easy to raise the content of ashless coal in the solution to be electrospun. As a result, the yield of the porous carbon fiber increases, so that the manufacturing cost of the porous carbon fiber sheet can be reduced. Examples of such a solvent include 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. It is done. Of these, pyridine and tetrahydrofuran having high affinity with ashless coal are preferred. In addition, the organic compound containing an oxygen atom or a nitrogen atom may be one kind, and two or more kinds of organic compounds may be mixed.

The lower limit of the content of ashless coal in the above solution is preferably 20% by mass, and more preferably 25% by mass. On the other hand, as an upper limit of content of ashless coal in the said solution, 60 mass% is preferable, 50 mass% is more preferable, and 40 mass% is further more preferable. If the content of the ashless coal is less than the lower limit, droplets are easily formed during electrospinning, and it may be difficult to obtain fine fibers in the electrospinning step S16 described later. Conversely, if the content of the ashless coal exceeds the upper limit, the diameter of the fine fiber obtained by electrospinning becomes too large, and the specific surface area of the porous carbon fiber sheet may be reduced.

<Electrospinning process>
In the electrospinning step S16, electrospinning is performed using the solution obtained in the second mixing step S15, thereby depositing fine fibers in a felt shape on the substrate surface.

Electrospinning can be performed by, for example, an electrospinning unit having a syringe 1 and a substrate 2 as shown in FIG. Specifically, the electrospinning is performed by putting the above solution into 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 droplet surface at the tip of the nozzle 1a, repel each other, and become conical. When the voltage E is further increased and the repulsive force of the charges exceeds the surface tension, the solution is ejected from the tip of the nozzle 1a toward the substrate 2. When the jetted solution stream 3 becomes thin, the surface charge density increases, so that the repulsive force of charges increases and the solution stream 3 is further stretched. At that time, the specific surface area of the solution stream 3 rapidly increases, whereby the solvent is volatilized and the fine fibers 4 are spun on the surface of the substrate 2. Thus, in electrospinning, the fine fiber 4 can be produced with a relatively simple device. In FIG. 3, the number of nozzles 1 a is one, but a plurality of nozzles 1 a 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 (nozzle inner diameter) of the tip of the nozzle 1a is preferably 0.2 mm, and more preferably 0.4 mm. On the other hand, the upper limit of the nozzle inner diameter is preferably 0.7 mm, more preferably 0.6 mm. When the nozzle inner diameter is less than the above lower limit, the resulting fine fiber 4 becomes thin, so that it is easily cut and becomes a short fiber. For this reason, it may be difficult to deposit the fine fibers 4 on the surface of the substrate 2 in a felt shape. On the other hand, when the nozzle inner diameter exceeds the upper limit, the diameter of the fine fiber 4 to be obtained increases, so that the specific surface area of the produced porous carbon fiber sheet may decrease.

The lower limit of the interspinning distance (the distance between the tip of the nozzle 1a and the substrate 2) is preferably 10 cm, and more preferably 12 cm. On the other hand, the upper limit of the interspinning distance is preferably 20 cm, and more preferably 18 cm. If the interspinning distance is less than the above lower limit, the solvent does not volatilize sufficiently, and electrospinning may be difficult. On the contrary, if the interspinning distance exceeds the above upper limit, the resulting fine fiber 4 becomes thin, so that it is easily cut and becomes a short fiber. For this reason, it may be difficult to deposit the fine fibers 4 on the surface of the substrate 2 in a felt shape.

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, the upper limit of the applied voltage E is preferably 30 kV, and more preferably 20 kV. 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 be widened, so that the produced porous carbon fiber sheet may be inhomogeneous.

The lower limit of the flow rate of the solution flow 3 (the amount of solution discharged from one nozzle 1a) is preferably 1 ml / h, and more preferably 1.5 ml / h. On the other hand, the upper limit of the flow rate of the solution stream 3 is preferably 3 ml / h, more preferably 2.5 ml / h. If the flow rate of the solution stream 3 is less than the lower limit, the fine fibers 4 may not be stably formed. Conversely, if the flow rate of the solution stream 3 exceeds the upper limit, the diameter of the resulting fine fiber 4 increases, and the specific surface area of the produced porous carbon fiber sheet may decrease. 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, and more preferably 0.7 μm. On the other hand, the upper limit of the average diameter of the fine fibers 4 is preferably 5 μm and more preferably 3 μm. If the average diameter of the fine fibers 4 is less than the lower limit, the fine fibers 4 are easily cut and become short fibers, and it may be difficult to deposit the fine fibers 4 on the surface of the substrate 2 in a felt shape. Conversely, if the average diameter of the fine fibers 4 exceeds the upper limit, the specific surface area of the produced porous carbon fiber sheet may be reduced. The average diameter of the fine fibers 4 is controlled mainly by the applied voltage E of electrospinning from the viewpoint of controllability. The average diameter of the fine fibers 4 can also be adjusted by the nozzle inner diameter and the interspinning distance.

The fine fibers 4 deposited in a felt shape on the surface of the substrate 2 are peeled off from the substrate 2. In the method for producing the porous carbon fiber sheet, the fine fibers 4 are continuously and randomly deposited on the substrate 2 without being cut by the excellent electrospinning property of ashless coal. For this reason, since the fine fibers 4 are intertwined moderately, the felt shape after peeling can be maintained without using, for example, a binder substance. Moreover, in the manufacturing method of the said porous carbon fiber sheet, carbonization of the fine fiber 4 can be performed by heating process S2 mentioned later, maintaining this felt shape.

[Heating process]
In the heating step S2, the fine fiber deposit obtained in the deposition step S1 is heated. This heating process S2 can be performed by a heating part.

(Heating part)
A heating part carbonizes the said fine fiber deposit, maintaining the aggregate state substantially by heating. A porous carbon fiber sheet is obtained by this carbonization.

As the heating unit, for example, a known electric furnace or the like can be used. After inserting the fine fiber deposit into the heating unit and replacing the inside with an inert gas, heating is performed while blowing an inert gas into the heating unit. By doing so, carbonization of the fine fiber deposit can be performed. Although it does not specifically limit as said inert gas, For example, nitrogen, argon, etc. can be mentioned. Of these, inexpensive nitrogen is preferred.

The lower limit of the heating temperature is preferably 500 ° C, more preferably 700 ° C. On the other hand, the upper limit of the heating temperature is preferably 3000 ° C and more preferably 2800 ° C. There exists a possibility that carbonization may become inadequate that the said heating temperature is less than the said minimum. Conversely, if 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. In addition, as a temperature increase rate, it can be 0.01 degree-C / min or more and 10 degree-C / min or less, for example.

Further, the lower limit of the heating time is preferably 10 minutes, and more preferably 20 minutes. On the other hand, the upper limit of the heating time is preferably 10 hours, more preferably 8 hours. There exists a possibility that carbonization may become inadequate that heating temperature is less than the said minimum. Conversely, if the heating time exceeds the above upper limit, the production efficiency of the porous carbon fiber sheet may be reduced.

The present inventors have known that the carbon fibers constituting the porous carbon fiber sheet thus obtained are mainly composed of fine pores having a pore diameter of 10 nm or less and have a high specific surface area. The mechanism by which such fine pores are formed is not always clear, but ashless coal has a higher oxygen content and a lower carbon content than, for example, coal pitch. For this reason, ashless coal is considered to have low molecular planarity and a small ring size as a mixture of polycyclic aromatic compounds, and it is considered that molecular orientation is difficult. In other words, when the solution is ejected from the nozzle 1a by electrospinning in the deposition step S1 and the solvent is rapidly volatilized, the ashless coal is condensed, but the molecules are stacked randomly. In the heating step S2, since carbonization is performed while maintaining a random structure without such molecules being oriented, it is considered that porous carbon is generated. On the other hand, when coal pitch with high aromaticity is condensed while forming a molecular orientation in which molecules are stacked in parallel to each other, when carbon with relatively high crystallinity, that is, carbon fiber without developing micropores, is generated. Conceivable.

The upper limit of the oxygen content of the carbon fibers constituting the porous carbon fiber sheet is preferably 0.6% by mass, and more preferably 0.55% by mass. When the oxygen content of the carbon fiber exceeds the upper limit, the strength of the carbon fiber may be insufficient.

As a minimum of the specific surface area of the porous carbon fiber sheet manufactured, 300 m < ² > / g is preferable, 400 m < ² > / g is more preferable, 450 m < ² > / g is further more preferable. If the specific surface area is less than the lower limit, it may be difficult to use as the porous material. On the other hand, the upper limit of the specific surface area is not particularly limited, but is usually about 3000 m ² / g.

The lower limit of the average diameter of the obtained carbon fiber is preferably 0.5 μm, more preferably 0.7 μm. On the other hand, the upper limit of the average diameter of the carbon fibers is preferably 5 μm and more preferably 3 μm. If the average diameter of the carbon fibers is less than the lower limit, the carbon fibers are easily cut and become short fibers, and it may be difficult to obtain a felt-like carbon fiber sheet. Conversely, if the average diameter of the carbon fibers exceeds the upper limit, the specific surface area of the produced porous carbon fiber sheet 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 determined by the applied voltage E of electrospinning or the content of ashless coal in the solution from the viewpoint of controllability. Be controlled. The average diameter of the fine fibers 4 can also be adjusted by the nozzle inner diameter and the interspinning distance.

[advantage]
In the method for producing the porous carbon fiber sheet, ashless coal is used as a carbon raw material. Ashless coal is relatively inexpensive, has excellent electrospinning properties, and does not require materials other than carbon. Further, in the method for producing the porous carbon fiber sheet, based on the excellent graphitization property of ashless coal, a fine fibrous porous carbon fiber having a high specific surface area can be obtained by electrospinning without performing processing such as molding. Can be easily obtained. Therefore, the manufacturing method of the porous carbon fiber sheet has a relatively low manufacturing cost and high manufacturing efficiency.

Further, in the method for producing the porous carbon fiber sheet, by using a solvent-extracted ashless coal, the production efficiency can be further increased and the production cost can be reduced.

[Method for producing porous carbon electrode]
The method for producing the porous carbon electrode includes a forming step. In the forming step, the porous carbon fiber sheet manufactured by the method for manufacturing the porous carbon fiber sheet is formed into an electrode. Thereby, an electrode having fluid diffusibility can be efficiently manufactured at a relatively low manufacturing cost. Although it does not specifically limit as a shaping | molding method, For example, the method by the punching of the said porous carbon fiber sheet is mentioned.

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

In the above embodiment, a method for producing ashless coal by solvent extraction has been described as a method for producing a porous carbon fiber sheet. However, the method for producing ashless coal is not limited to this, for example, coal and hydrogen donating solvent. Ashless coal produced by mixing and heating with can also be used.

Moreover, in the said embodiment, although the ashless coal was solvent-extracted by the evaporative separation process as a manufacturing method of a porous carbon fiber sheet, the ashless charcoal was dissolved and electrospun in the second mixing process. The evaporative separation step and the second mixing step may be omitted by making the solvent for extracting ashless coal and the solvent for the solution for electrospinning the same type of solvent. In this case, the liquid obtained in the solid-liquid separation step can be used as an electrospinning solution.

In the said embodiment, although the mixing part of the 1st mixing process demonstrated the structure which has a preparation tank as a manufacturing method of a porous carbon fiber sheet, if not only this structure but mixing of a solvent and coal can be performed, 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 apparatus structure used at each process is not limited to the said embodiment.

In addition, the use of the porous carbon fiber sheet produced by the method for producing a porous carbon fiber sheet is not limited to an electrode, and for example, it is preferably used for a sheet requiring a porous property such as an adsorbent or a catalyst carrier. Can do.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
Ashless coal produced by solvent extraction of bituminous coal was prepared as a carbon raw material. The elemental analysis values of the ashless coal are shown in Table 1 as “ashless coal A”. Moreover, pyridine was prepared as a solvent.

A solution in which the ashless coal was dissolved in the solvent was prepared by mixing the ashless coal and the solvent so that the content of the ashless coal in the solution was 39% by mass.

Using this solution, electrospinning was performed under the conditions shown in Table 2, and fine fibers were deposited on the aluminum foil substrate. After the fine fiber deposit was peeled from the aluminum foil, the temperature was raised to 900 ° C. at a rate of 3.3 ° C./min, and heat treatment (carbonization) was performed for 30 minutes. A carbon fiber sheet was produced. An optical micrograph of the obtained porous carbon fiber sheet is shown in FIG.

[Example 2]
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 values of the ashless coal are shown in Table 1 as “ashless coal B”. A porous carbon fiber sheet of Example 2 was produced in the same manner as Example 1 except that this ashless coal was used.

[Comparative Example 1]
A coal-based pitch produced from tar produced as a by-product in the coal hot distillation process was prepared. Table 1 shows the elemental analysis values of this coal-based pitch. A porous carbon fiber sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that this coal-based pitch was used as a carbon raw material.

In Table 1, the amount of oxygen means the amount of components other than carbon, hydrogen, nitrogen and sulfur, and is obtained by subtracting the components of carbon, hydrogen, nitrogen and sulfur from 100% by mass.

[Evaluation methods]
About the said Example 1, 2 and the comparative example 1, the following measurements were performed.

<Average fiber diameter>
The average diameter (average fiber diameter) of the carbon fibers was measured with a scanning electron microscope. The measurement was performed by measuring the diameters of any ten fibers in the field of view of the scanning electron microscope and calculating the average. The scanning electron micrograph of the carbon fiber of the porous carbon fiber sheet of Example 1 is shown in FIG. The measurement results are shown in Table 3.

<Specific surface area>
The specific surface area of the porous carbon fiber sheet was measured using “BELSOR-max” of Microtrack Bell Co., Ltd. Table 3 shows the measurement results.

<Pore distribution>
About the porous carbon fiber sheet of Example 1, the pore distribution of the carbon fiber was measured using the HK method. The measurement results are shown in FIG.

From Table 3, it can be seen that Examples 1 and 2 using ashless coal as the carbon material have a larger specific surface area than Comparative Example 1. Moreover, it can be seen from FIG. 6 that the carbon fibers of the porous carbon fiber sheet of Example 1 are mainly composed of fine pores having a pore diameter of 10 nm or less, and the individual carbon fibers have high porosity. Further, from FIG. 5, the carbon fibers are continuously and randomly assembled without being cut, and the porous carbon fiber sheet of Example 1 can maintain this felt shape without using a binder or the like, It can be seen that it is excellent in fluid diffusibility of liquid and liquid.

On the other hand, Comparative Example 1 using coal pitch as the carbon material is considered to have a small specific surface area and no fine pores. Therefore, it is possible to easily obtain a fine fibrous porous carbon fiber with a high specific surface area by electrospinning without performing a treatment such as molding by the method for producing the porous carbon fiber sheet using ashless coal as a carbon raw material. I understand.

As described above, the method for producing a porous carbon fiber sheet of the present invention and the method for producing a porous carbon electrode using the porous carbon fiber sheet have relatively low production costs and high production 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)

A process of depositing fine fibers in a felt shape on the substrate surface by electrospinning of a solution in which ashless coal is dissolved;
And a step of heating the fine fiber deposit obtained in the deposition step. As the deposition process,
Mixing coal and solvent;
Eluting components soluble in the solvent from the coal in the slurry obtained in the mixing step;
The method for producing a porous carbon fiber sheet according to claim 1, 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. The method for producing a porous carbon fiber sheet according to claim 1, wherein the electrospinning voltage or the content of ashless coal in the solution is adjusted so that the average diameter of the obtained carbon fibers is 0.5 µm or more and 5 µm or less. The manufacturing method of a porous carbon electrode provided with the process of shape | molding the porous carbon fiber sheet manufactured by the manufacturing method of the porous carbon fiber sheet of Claim 1, Claim 2 or Claim 3 to an electrode.

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