JP2012117162A - Method for manufacturing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a carbon fiber by heating and dissolving a solid woody material including cellulose, hemicellulose, lignin, lignocellulose and the like, in which solubility of the material and heat stability of woody pitch are improved and a spinning step in manufacturing the carbon fiber is stably performed.SOLUTION: A method for manufacturing a carbon fiber, comprises: pressure-heating a solid woody material including at least one kind selected from cellulose, hemicellulose, lignin and lignocellulose under the presence of phenols and a hydrogen-donating solvent to form the solubilized material; and subjecting woody pitch obtained by removing a low-boiling point component from the solubilized material to melt spinning, infusibilization and carbonization. It is preferable that the hydrogen-donating solvent is tetralin, for example.

Description

The present invention relates to a technique for using a solid wood material containing cellulose, hemicellulose, lignin, lignocellulose, and the like, and more particularly to a technique for producing carbon fiber using the solid wood material.
The carbon fiber is used for, for example, a carbon fiber reinforced resin composite material, a carbon fiber reinforced carbon composite material, a heat insulating material, a soundproof material, and activated carbon fiber.

  Conventionally, there are two known methods for producing carbon fibers. In the first method, carbon fiber is produced by flameproofing and carbonizing polyacrylonitrile produced from fossil raw materials such as petroleum and coal. In the second method, carbon fiber is produced by melt spinning a pitch obtained by heat treating petroleum heavy oil and coal heavy oil and performing infusibilization treatment, carbonization treatment, and the like. However, the fossil raw materials are limited, and it is desired to reduce the amount of use.

  As an alternative to fossil raw materials, renewable biomass resources (biological raw materials) can be mentioned. Biomass resources are being researched for use as fuel, such as thermal decomposition under conditions with adjusted oxygen concentration to convert them to carbon monoxide and hydrogen gas, and examples of converting biomass resources to ethanol by fermentation, etc. In addition, applied research as a carbon fiber raw material or a resin raw material has been earnestly promoted (for example, Patent Documents 1 to 4).

  In Patent Document 1, carbon fiber is produced by hydrocracking lignin obtained by treating a wood-based resource with high-pressure saturated steam treatment and alcohol-based organic solvent treatment, spinning it by a thermal melting method, and carbonizing it. . However, the method using hydrocracking is not desirable because of the high energy consumption.

  In Patent Document 2, by heating a woody material using a mixed solvent of phenols and water as a cooking solution, pulp, an aqueous layer in which hemicellulose is decomposed and dissolved as a monosaccharide, and lignin are dissolved. After separating into three components of the organic layer, lignin obtained by concentrating the organic layer under reduced pressure is melt-spun to produce lignin fibers. However, this method is not practical because the separation and refining operation of the pulp is complicated and it is difficult to treat the waste liquid in the aqueous layer portion.

  In Patent Document 3, a lignin for carbon fiber spinning is prepared by heat-healing phenolic lignin obtained by treating lignin eluted by delignification treatment from a woody material with an acidic organic catalyst in a non-oxidizing atmosphere. Yes. However, this method is costly because the production process is complicated and the yield of carbon fibers is low.

  In Patent Document 4, a lignocellulosic material is pretreated for explosion, and a solubilized product is produced by dissolving the treated product and a phenol compound under heating. However, in this method, the explosion treatment apparatus is enormous and solid content remains in the product. Therefore, spinning is difficult and it is not suitable as a raw material for carbon fiber.

  Note that the conventional methods described above have the disadvantage that the thermal stability of the product pitch is low except for the hydrocracking method (Patent Document 1) that requires high temperature, high pressure, and high energy consumption. When the thermal stability of the pitch is low, not only a desired fiber diameter cannot be obtained due to an increase in viscosity (increase in softening point) during melt spinning, but spinning itself cannot be performed due to nozzle clogging. Therefore, improvement of thermal stability is a major problem in the process of producing carbon fibers from a wood pitch.

Japanese Unexamined Patent Publication No. Sho 62-110922 Japanese Patent Laid-Open No. 01-239114 Japanese Patent Laid-Open No. 01-306618 Japanese Patent Laid-Open No. 04-126725

  The present invention has been made paying attention to the circumstances as described above, and the object thereof is a method of heating and dissolving a solid woody material containing cellulose, hemicellulose, lignin, lignocellulose, etc. , To improve the solubility (solubility) and to improve the thermal stability of the woody pitch after removing low-boiling components, and to establish a technology that can stably carry out the spinning process when producing carbon fiber .

  As a result of intensive studies to solve the above problems, the present inventors have solubilized a solid woody material containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose with a phenol compound. The inventors have found that if a predetermined solvent is used in combination, insoluble matter (solid content) can be remarkably reduced, and thermal alteration of the woody pitch after removal of low-boiling components can be suppressed, and the present invention has been completed.

  That is, the carbon fiber according to the present invention comprises a solid woody material containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose, the presence of phenols (particularly phenol) and a hydrogen-donating solvent (particularly tetralin). It is produced by spinning, infusibilizing, and carbonizing a woody pitch obtained by solubilization by heating under pressure and solubilizing, and removing low-boiling components from the solubilized product. The wood-based raw material is preferably obtained by biologically, chemically, or mechanically degrading a wood body, for example, after producing a ethanol by treating the wood body in the order of hydrothermal treatment, saccharification treatment, and fermentation. Of the residue. The amount of the phenols is 20 to 500 parts by mass with respect to 100 parts by mass of the wooden raw material. The amount of the hydrogen donating solvent is 10 to 300 parts by mass with respect to 100 parts by mass of the wood-based raw material. In the pressurization and heating, for example, a gauge pressure of 0.2 to 10 MPa and a temperature of 230 to 430 ° C. are used. After the pressurization and heating, it is preferable to spin, infusibilize, and carbonize after removing low-boiling components in the solvent and solubilizate by distillation.

  According to the present invention, since the solid woody material is heated under pressure in the presence of phenols and a hydrogen donating solvent, insoluble matter (solid content) can be significantly reduced, and thermal alteration of the woody pitch is further suppressed. Thus, the spinning process when producing the carbon fiber can be carried out stably.

  Carbon fiber is manufactured by melt spinning a pitch and performing infusibilization treatment and carbonization treatment. The present invention is to produce the above-mentioned wood-based pitch by effectively using a solid wood-based raw material, and to produce carbon fibers from this wood-based pitch.

(1) Preparation of woody pitch In the present invention, the pitch is prepared by pressurizing and heating a solid woody raw material in the presence of a predetermined solvent described later. By using a solid woody material, the dependence of fossil materials can be reduced. Moreover, by heating under pressure in the presence of a predetermined solvent, the solid woody material can be solubilized, and the woody pitch obtained by removing low-boiling components from this solubilized product is used as a raw material for producing carbon fiber Can be used. It is generally difficult to completely dissolve a solid woody material, and the woody pitch obtained after solubilization treatment has poor thermal stability, but in the present invention, it is heated under pressure using a predetermined solvent described later. Therefore, 95% by mass or more of the solid woody material can be solubilized, and thermal alteration of the obtained pitch can be suppressed.

  The solid wood material is not particularly limited as long as it is a solid material containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose, and any material derived from plants (particularly wood) can be used. is there. For example, wood-based waste such as thinned wood, coniferous wood, hardwood residue, lumber, construction waste, pruned branches, stumps, and bark covering conifers and hardwoods is desirable as a solid woody material from the viewpoint of effective use of waste.

  The solid woody material is preferably decomposed biologically, chemically or mechanically. By decomposing in advance, the processing efficiency of solubilization by pressure heating can be increased. Biological degradation includes degradation by fungi, microorganisms, enzymes, and the like. The chemical decomposition may be a sulfuric acid / alkali method, but hydrothermal treatment or hydrolysis with superheated steam is preferable in consideration of environmental load. In addition, the mechanical decomposition includes beating, crushing, crushing, grinding, and explosion, and this mechanical decomposition may be either dry or wet.

  These biological, chemical, or mechanical degradations are desirably combined as appropriate. Typically, after mechanical degradation (such as pulverization), hydrothermal treatment (hydrolysis treatment) is performed as necessary, and then biological degradation is performed. Scientifically, saccharification treatment (eg, saccharification treatment by enzymatic method) is performed. The saccharified product is usually separated into a liquid component and a solid content by filtration. The liquid component (main component is sugar) is subjected to ethanol fermentation, and the solid is discharged as a residue (saccharification residue). In some cases, the saccharified product may be sent to the subsequent stage without filtration and subjected to ethanol fermentation with microorganisms or fungi (particularly yeast). In this fermentation treatment, usually only the sugar content in the saccharification product is converted to ethanol, and the solid content (saccharification residue) does not change. The fermented product is also separated by filtration into a liquid component (main component is an aqueous ethanol solution) and a solid content (which is basically the same component as the saccharification residue, but here referred to as “fermentation residue”). The saccharification residue or fermentation residue obtained in this way has lignin as the main component, and even if it contains cellulose and hemicellulose, it can be used as it is as a solid woody material. A preferable solid wood raw material is a saccharification residue or a fermentation residue. Details of these hydrothermal treatment, saccharification treatment, and fermentation treatment are described in detail in, for example, JP-A-2005-168335.

  In the present invention, the solid woody material as described above is solubilized by heating under pressure in the presence of a predetermined solvent. Specifically, the predetermined solvent is a combined solvent of phenols and a hydrogen donating solvent. If a solid woody material is dissolved in phenol under pressure and heating, a solid content (insoluble matter) is generated. This solid is assumed to be a recombination of unstable radicals generated by thermal decomposition, and if a hydrogen-donating solvent is used with phenols, the radicals are stabilized by donating hydrogen to unstable radicals. Therefore, it is considered that the solid content can be significantly reduced.

  Furthermore, the woody pitch after removing the low boiling point component is thermally altered in the spinning temperature region. That is, the softening point of the woody pitch becomes high and spinning becomes difficult. The increase in the softening point is thought to be due to the thermal polymerization of components with a thermally unstable phenolic skeleton in the wooden pitch. If used together with a hydrogen-donating solvent and phenols, it is presumed that oxygen is extracted from the unstable phenol skeleton that is the starting point of thermal polymerization, and thermal alteration of the resulting woody pitch is suppressed.

  The phenols mean compounds having a phenol skeleton (hydroxybenzene skeleton), for example, monohydroxybenzenes such as phenol and cresol; dihydroxybenzenes such as catechol; hydroxybenzene condensed rings such as naphthol; or coal-based Alternatively, mixed phenols derived from wood tar are included. Preferred phenols are monohydroxybenzenes, especially phenol.

  As the hydrogen-donating solvent, compounds obtained by partially hydrogenating condensed aromatic hydrocarbons can be used. For example, bicyclic compounds such as partially hydrogenated naphthalenes (tetralin, etc.); partial hydrogenation Tricyclic compounds such as anthracenes (such as 9,10-dihydroanthracene), partially hydrogenated phenanthrenes (such as 9,10-dihydrophenanthrene), and tetracyclic compounds such as partially hydrogenated fluoranthene (such as tetrahydrofluoranthene) Etc. are included. As the hydrogen-donating solvent, a hydrogenated mixture containing a condensed aromatic hydrocarbon such as anthracene oil or creosote oil can also be used. A preferred hydrogen donating solvent is a low boiling point solvent containing the bicyclic compound, particularly a solvent containing partially hydrogenated naphthalenes.

  The amount of phenols and hydrogen-donating solvent used is not particularly limited as long as it is sufficient to solubilize the solid woody material, but even if used in excess, there is no further effect, and productivity is reduced. Therefore, it is recommended to use an appropriate amount. When using a saccharification residue or fermentation residue as a solid woody material, the amount of phenol is, for example, about 20 to 500 parts by mass, preferably about 50 to 400 parts by mass, with respect to 100 parts by mass of the saccharification residue or fermentation residue. More preferably, it is about 100 to 300 parts by mass. When the amount of phenols is less than 20 parts by mass, the solubility in solid raw materials is remarkably reduced, and when the amount of phenols exceeds 500 parts by mass, the amount of phenols necessary for dissolution is sufficient, but the solvent Energy consumption required for recovery increases, leading to cost increase. The amount of the hydrogen donating solvent is, for example, about 10 to 300 parts by mass, preferably about 30 to 250 parts by mass, and more preferably about 50 to 200 parts by mass with respect to 100 parts by mass of the saccharification residue or fermentation residue. . When the amount of the hydrogen donating solvent is less than 10 parts by mass, the pitch is likely to be thermally altered, resulting in an increase in solid content and a decrease in thermal stability. On the other hand, when the amount of the hydrogen donating solvent exceeds 300 parts by mass, as in the case of the phenol, the energy consumption required for solvent recovery increases, leading to an increase in cost.

  When the solid woody material is solubilized by heating under pressure in the presence of the solvent, the heating temperature is about 230 to 430 ° C, preferably about 260 to 400 ° C, more preferably about 280 to 380 ° C. If the temperature is below 230 ° C., the solubilization is insufficient, so the amount of solids increases, and if it exceeds 430 ° C., the cyclization polycondensation reaction is promoted and the solid content as a carbon precursor increases. The gauge pressure is about 0.2 to 10 MPa. This gauge pressure is determined by the vapor pressure at a predetermined temperature of moisture in the raw material, low-boiling components generated by thermal decomposition, phenols to be used, and hydrogen donating solvent. The treatment time at the above pressure and temperature (holding time after reaching a predetermined temperature) is, for example, about 1 to 120 minutes, preferably about 5 to 60 minutes, and more preferably about 10 to 30 minutes.

After solubilizing the solid woody material as described above, the solid content remaining in the solubilizate can be separated by filtering with a paper filter (retained particle diameter of about 1 to 10 μm), and the amount can be examined. it can. The solid content contained in the solubilized product before filtration is, for example, 5% by mass or less, preferably 4% by mass or less, and more preferably 3% by mass or less, with respect to the input solid woody material (105 ° C. dry base). It is. The filtered lysate is distilled. The distillation operation consists of the moisture contained in the solid woody raw material, the solvent used for solubilization (phenols, hydrogen donating solvent, etc.), and the low-boiling decomposition products (pyrolysis oil and pyrolysis produced during pressure heat treatment) (Water generated by the above) (these are collectively referred to as low boiling point components) can be removed, and may be carried out under reduced pressure conditions or under normal pressure conditions.
The solubilized product obtained as described above can be used as a pitch (woody pitch) as a carbon fiber production raw material. The softening point of the woody pitch is usually about 170 to 230 ° C.

(2) Spinning The woody pitch can be made into various carbon materials (for example, activated carbon, carbon black, binder, etc.) by carbonization or pyrolysis, and carbon fiber is produced from the woody pitch. It is preferable. In order to produce carbon fiber, the woody pitch obtained as described above is first spun (especially melt-spun). Usually, when spinning, a metal filter is installed in order to prevent clogging of the spinning nozzle and a decrease in strength of the carbon fiber due to the mixed dust and solid content in the pitch. If the above wood pitch is used, the amount of solid content is extremely small, so the filter load is reduced and continuous spinning operation can be performed for a long time.

In spinning, deaeration is carried out by heating the pitch to the softening point or higher (preferably a temperature higher by about 30 to 120 ° C. than the softening point, particularly a temperature higher by about 50 to 100 ° C. than the softening point). If the above-mentioned wood pitch is used, an increase in the softening point due to thermal alteration of the wood pitch can be suppressed, and a continuous spinning operation can be performed for a long time.
As spinning conditions, known conditions can be appropriately employed. For example, melt spinning is performed by a method such as an extrusion method or a centrifugal method to obtain pitch fibers.

(3) Infusibilization treatment, carbonization treatment Pitch fibers obtained by melt spinning are subjected to infusibilization treatment in an oxidizing gas atmosphere. As the oxidizing gas, one or more oxidizing gases such as oxygen, ozone, air, halogen, nitrogen oxide, sulfurous acid and the like are usually used. This infusibilization treatment is performed under temperature conditions where the pitch fibers are not softened and deformed. For example, a temperature of 20 to 350 ° C, preferably 30 to 320 ° C is recommended. The infusibilized pitch fiber is then carbonized in an inert gas atmosphere to obtain the woody pitch-based carbon fiber of the present invention. The carbonization conditions are about 500 to 1300 ° C. (particularly about 800 ° C. ± 50 ° C.). You may graphitize as needed. In the graphitization treatment, for example, the carbonized fiber is heated in an inert atmosphere (particularly argon gas) at a temperature of about 1500 to 2800 ° C.

  Carbon fibers produced from the wood-based pitch obtained as described above can be used as an alternative material for conventional pitch-based carbon fibers. Therefore, the use is wide, and for example, any of tow, staple yarn, cloth, milled, felt, and mat may be used. The tensile strength of the carbon fiber is obtained according to JIS R7601.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Reference example 1
After crushing unused woody biomass of about 5-100 cm in diameter consisting of cedar stumps and branches and leaves into chips of 3-5 cm square using a crusher, it was naturally dried until the water content was about 20% by mass. Further, the powder was pulverized into a powder having an average particle size of about 20 μm and a water content of about 3% by mass. To 100 parts by mass of this wood flour, 5 parts by mass of Acremonium cellulase (Meiji Seika, trade name: Acremonium Enzyme) and 500 parts by mass of water are added, and saccharification treatment is carried out at a temperature of 55 ° C. for 40 hours (the saccharification rate is in the raw material) And 35% by mass with respect to 100% by mass of cellulose), followed by filtration to separate into liquid component (a) and solid content. The solid content was further washed with water, and the washing liquid (b) and the liquid component (a) were combined and subjected to ethanol fermentation. The solid content (saccharification treatment residue) was naturally dried and then crushed into powder, and further dried overnight at a temperature of 105 ° C. to obtain a saccharification residue as a raw material for carbon fiber pitch. The yield of the saccharification residue was 82% by mass with respect to 100% by mass of the dry mass of the raw material wood flour.

Example 1
To 50 g of saccharification residue obtained in Reference Example 1, 75 g of phenol and 75 g of tetralin were added and heated at 325 ° C. for 1 hour under a gauge pressure of 5 MPa. When the heat treatment liquid obtained by the heat treatment is filtered with a paper filter, the solid content is about trace. The solubilized product from which the solid content was removed by filtration was distilled under conditions of a temperature of 280 ° C. and an absolute pressure of 4 hPa (3 torr) to obtain a woody pitch. The softening point of the obtained woody pitch was 195 ° C.

The wood pitch is put into a single hole spinning apparatus equipped with a nozzle (D / L = 0.2 / 0.4) having a diameter of 0.2 mm and a length of 0.4 mm, and after degassing at 285 ° C. under reduced pressure, the temperature is 255. The mixture was heated to 0 ° C. and spun using a nitrogen pressure under the conditions of an extrusion amount of 0.05 g / min and a winding speed of 300 m / min to obtain a pitch fiber having a diameter of 13 μm. After spinning, the pitch softening point in the spinning machine was measured and found to be 200 ° C. The obtained pitch fiber was put into a tubular furnace, and it was made infusible by treatment under conditions of a heating rate of 1 ° C./min, a holding temperature of 270 ° C., a holding time of 1 hour, and a holding atmosphere: air. Furthermore, the infusible material was treated and carbonized under the conditions of a heating rate of 5 ° C./min, a holding temperature of 800 ° C., and a holding time of 5 minutes.
The tensile strength of the carbon fiber after carbonization was 650 MPa.

Example 2
50 g of phenol and 100 g of tetralin were added to 50 g of the cedar saccharification residue obtained in Reference Example 1, and the mixture was heated at 325 ° C. for 1 hour under a gauge pressure of 5 MPa. Solid content was not observed in the obtained heat treatment liquid. The heat treatment liquid was filtered and distilled in the same manner as in Example 1 to obtain a woody pitch (softening point 190 ° C.). This woody pitch was spun in the same manner as in Example 1 to obtain a pitch fiber having a diameter of 13 μm. After the spinning, the softening point of the pitch in the spinning machine was measured and found to be 196 ° C. The obtained pitch fiber was subjected to infusibilization treatment and carbonization treatment in the same manner as in Example 1 to obtain carbon fiber (tensile strength: 600 MPa).

Example 3
To 50 g of cedar saccharification residue obtained in Reference Example 1, 75 g of phenol and 75 g of tetralin were added and heated at 350 ° C. for 1 hour under a gauge pressure of 7 MPa. The solid content in the obtained heat treatment liquid was 2.9% by mass with respect to the charged saccharification residue raw material (105 ° C. dry base). The heat treatment liquid was filtered and distilled in the same manner as in Example 1 to obtain a woody pitch (softening point 190 ° C.). This woody pitch was spun in the same manner as in Example 1 to obtain a pitch fiber having a diameter of 13 μm. After spinning, the pitch softening point in the spinning machine was measured and found to be 198 ° C. The obtained pitch fiber was infusibilized and carbonized in the same manner as in Example 1 to obtain carbon fiber (tensile strength of 680 MPa).

Example 4
50 g of phenol and 100 g of tetralin were added to 50 g of the cedar saccharification residue obtained in Reference Example 1, and the mixture was heated at 350 ° C. for 1 hour under a gauge pressure of 7 MPa. The solid content in the obtained heat treatment liquid was 1.5% by mass with respect to the charged saccharification residue raw material (105 ° C. dry base). The heat treatment liquid was filtered and concentrated in the same manner as in Example 1 to obtain a woody pitch (softening point 184 ° C.). This woody pitch was spun in the same manner as in Example 1 to obtain a pitch fiber having a diameter of 13 μm. After spinning, the pitch softening point in the spinning machine was measured and found to be 190 ° C. The obtained pitch fiber was infusibilized and carbonized in the same manner as in Example 1 to obtain carbon fiber (tensile strength of 650 MPa).

Example 5
To 50 g of cedar saccharification residue obtained in Reference Example 1, 75 g of phenol and 75 g of tetralin were added and heated at 325 ° C. for 0.5 hours under the condition of a gauge pressure of 5 MPa. Solid content was not observed in the obtained heat treatment liquid. The heat treatment liquid was filtered and concentrated in the same manner as in Example 1 to obtain a woody pitch (softening point 195 ° C.). This woody pitch was spun in the same manner as in Example 1 to obtain a pitch fiber having a diameter of 13 μm. After spinning, the softening point of the pitch in the spinning machine was measured and found to be 202 ° C. The obtained pitch fiber was infusibilized and carbonized in the same manner as in Example 1 to obtain carbon fiber (tensile strength of 580 MPa).

Comparative Example 1
To 50 g of the cedar saccharification residue obtained in Reference Example 1, 150 g of phenol was added, and a heat treatment was performed at 325 ° C. for 1 hour under a gauge pressure of 5 MPa. The solid content in the obtained heat treatment liquid was 6.0% by mass relative to the charged saccharification residue raw material (105 ° C. dry base). The heat treatment liquid was filtered and concentrated in the same manner as in Example 1 to obtain a woody pitch (softening point 205 ° C.). An attempt was made to spin this woody pitch in the same manner as in Example 1, but the spinning nozzle was clogged and no fiber was obtained. After spinning, the softening point of the pitch in the spinning machine was measured and found to be 245 ° C.

Comparative Example 2
To 50 g of cedar saccharification residue obtained in Reference Example 1, 150 g of phenol was added, and a heat treatment was carried out at 350 ° C. for 1 hour under a gauge pressure of 7 MPa. The solid content in the obtained heat treatment liquid was 8.5% by mass with respect to the charged saccharification residue raw material (105 ° C. dry base). The heat treatment liquid was filtered and concentrated in the same manner as in Example 1 to obtain a woody pitch (softening point 210 ° C.). By spinning this woody pitch in the same manner as in Example 1, a pitch fiber having a diameter of 13 μm was obtained, but the spinning nozzle was closed in a short time. After spinning, the pitch softening point in the spinning machine was measured and found to be 230 ° C.

Claims (4)

  Solid woody material containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose is solubilized by heating under pressure in the presence of phenols and a hydrogen-donating solvent. A method for producing a carbon fiber, comprising spinning, infusibilizing, and carbonizing a wood pitch obtained by removing components.   The method for producing carbon fiber according to claim 1, wherein the solid wood-based raw material is obtained by biologically, chemically, or mechanically decomposing a wooden body.   The carbon fiber production method according to claim 1 or 2, wherein the solid wood-based material is a residue after saccharification treatment of a wood body or a residue after saccharification and fermentation treatment of a wood body.   The method for producing a carbon fiber according to any one of claims 1 to 3, wherein the phenol is phenol and the hydrogen-donating solvent is tetralin.