JP2012255223A - Method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably conduct a spinning process for producing a carbon fiber by enhancing solubilization properties (solubility) of a solid wood-based raw material and enhancing heat stability of wood-based pitch obtained by removing a low-boiling component from the raw material even in a method for heating and fusing the solid wood-based raw material including cellulose, hemicellulose, lignin and lignocellulose, and spinning the resultant material.SOLUTION: The carbon fiber is produced by the steps of: preparing the solid wood-based raw material including at least one substance selected from cellulose, hemicellulose, lignin and lignocellulose; pressurizing and heating the raw material under the existence of phenols and a thermally decomposable heavy oil to solubilize the material; removing the low-boiling component from the solubilized material to obtain the wood-based pitch; and spinning, infusibilizing and carbonizing the pitch.

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 present inventors have found that if pyrolytic heavy oil 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 is obtained by pressurizing and heating a solid woody material containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose in the presence of phenols and pyrolytic heavy oil. It is produced by spinning, infusibilizing, and carbonizing a woody pitch obtained by solubilizing and removing low-boiling components from the solubilized product. The wood-based material is preferably a material obtained by biologically, chemically, or mechanically degrading a wood body, for example, a residue after saccharification treatment of the wood body, or after saccharification and fermentation treatment of the wood body Of residues. As the phenols, phenol is preferable, and as the pyrolytic heavy oil, ethylene bottom oil, decant oil, coal tar, and the like are preferable.

According to the present invention, since the solid woody raw material is heated under pressure in the presence of phenols and pyrolysis heavy oil, insoluble matter (solid content) can be reduced, and thermal alteration of the woody pitch can be further reduced. By restraining, the spinning process when producing the carbon fiber can be carried out stably.
Furthermore, the carbon fiber which suppressed thermal change using the pyrolysis heavy oil is excellent also in the intensity | strength. In addition, pyrolytic heavy oil is inexpensive and has great cost merit.

  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. It is. For example, wood-based waste materials such as thinned wood covering conifers and broad-leaved trees, forest land residual materials, lumber residual materials, construction waste materials, pruned branches, stumps and bark are desirable as solid wood-based raw materials 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 woody 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 pyrolytic heavy oil. If a solid woody material is dissolved in phenol under pressure and heating, a solid content (insoluble matter) is generated. This solid content is assumed to be a recombination of unstable radicals generated by pyrolysis. If pyrolysis heavy oil is used with phenols, unstable radicals function as pyrolysis heavy oil. It is considered that recombination is suppressed by the above, and that the insoluble matter (solid content) can be reduced by the dispersion effect of the composite solvent and the increase in dissolving power.

  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. When used together with phenols and pyrolytic heavy oil, the viscosity resulting from the crosslinking reaction due to the extraction of oxygen from the unstable phenolic skeleton, which is the starting point of thermal polymerization, and the reaction with the pyrolytic heavy oil component. It is speculated that the rapid rise is suppressed and the thermal stability of the obtained woody pitch is improved.

  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.

  The pyrolytic heavy oil is a heavy oil that is by-produced when pyrolyzing petroleum or coal for refining, for example, heavy oil having a distillation temperature at atmospheric pressure of more than 200 ° C. It refers to quality oil. Such pyrolysis heavy oil includes ethylene bottom oil, which is a heavy oil by-product when olefins are produced by steam cracking of naphtha, and heavy oil that is a by-product when gasoline is produced by a fluid catalytic cracking unit. Examples include decant oil, which is a quality oil, coal tar produced as a by-product in the production of coal coke, creosote oil obtained by distillation of coal tar, anthracene oil, and the like. Preferable pyrolysis heavy oil is ethylene bottom oil, decant oil, coal tar, and the like, and ethylene bottom oil is particularly preferable from the viewpoint of extending the thermal stability time of the woody pitch.

  The amount of phenols and pyrolytic heavy oil used is not particularly limited as long as it is sufficient to solubilize solid woody raw materials, but even if used excessively, there is no further effect, and productivity is reversed. 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 phenols is, for example, about 20 to 400 parts by mass, preferably about 50 to 300 parts by mass with respect to 100 parts by mass of the saccharification residue or fermentation residue. It is. 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 400 parts by mass, the amount of phenols necessary for dissolution is sufficient, Energy consumption required for recovery increases, leading to cost increase. Moreover, the quantity of pyrolysis heavy oil is about 10-400 mass parts with respect to 100 mass parts of saccharification residues or fermentation residues, Preferably it is about 20-300 mass parts. If the amount of the pyrolytic heavy oil is less than 10 parts by mass, thermal alteration of the pitch is likely to occur, leading to an increase in solid content and a decrease in thermal stability. On the other hand, when the amount of the pyrolytic heavy oil exceeds 400 parts by mass, the energy consumption required for solvent recovery increases as in the case of the phenol, leading to an increase in cost.

  When the solid wood 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. 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 pyrolysis, phenols to be used, and pyrolysis heavy oil. 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.

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 amount of solid content contained in the solubilized product before filtration is, for example, 5% by mass or less with respect to the input solid woody material (105 ° C. dry base). The filtered lysate is distilled. The distillation operation consists of the moisture contained in the solid wood material, the solvent used for solubilization (phenols, light components contained in the pyrolysis heavy oil, etc.), and the low-boiling decomposition produced during pressure heat treatment Products (pyrolyzed oil and water generated by pyrolysis) and the like (these are collectively referred to as low-boiling components) may 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 70 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.

Since the carbon fiber manufactured from the woody pitch obtained as described above contains a pyrolytic heavy oil in the pitch, its tensile strength is also excellent. The tensile strength of the carbon fiber is, for example, about 600 to 900 MPa.
The carbon fiber of the present invention 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.

Raw material 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
The saccharification residue of cedar obtained in Raw Material Example 1, phenol and ethylene bottom oil are mixed in the amounts shown in Table 1, and subjected to pressure and heat treatment under the conditions shown in Table 1, so that the solid content shown in Table 1 A pressure heat treatment liquid was obtained (the solid content was determined by filtering the pressure heat treatment liquid with a paper filter and indicated by the ratio to the saccharification residue raw material (105 ° C. dry base). The same applies hereinafter). The solubilized product from which the pressure heat treatment liquid was filtered to remove the solid content 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 wood pitch was put into a single hole spinning device 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 under reduced pressure at the temperatures shown in Table 1. The mixture was heated to the temperature shown in Table 1 and spun using nitrogen pressure at the extrusion amount shown in Table 1 and at a winding speed of 300 m / min to obtain pitch fibers having the diameters shown in Table 1. 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 softening point of the woody pitch before spinning and the softening point of the woody pitch remaining in the spinning machine after spinning were examined to determine the change in softening point (ΔT). The tensile strength of the carbon fiber after carbonization was also measured. The results are shown in Table 1.

Examples 2-6
A woody pitch was obtained in the same manner as in Example 1 except that the raw materials and conditions for the pressure heat treatment were changed as shown in Table 1. This woody pitch was spun in the same manner as in Example 1 to obtain pitch fibers having a predetermined diameter. Further, the obtained pitch fibers were subjected to infusibilization treatment and carbonization treatment in the same manner as in Example 1 to obtain carbon fibers.
The results of Examples 2 to 6 are shown in Table 1.

Comparative Examples 1-2
A woody pitch was obtained in the same manner as in Example 1 except that the raw materials and conditions for the pressure heat treatment were changed as shown in Table 1. This woody pitch was spun in the same manner as in Example 1. However, in Comparative Example 1, the spinning nozzle was immediately closed and no fiber was obtained. Also in Comparative Example 2, the spinning nozzle was blocked in a short time.
The results of Comparative Examples 1 and 2 are shown in Table 1.

  As is clear from Table 1, in Examples 1 to 6 in which the saccharification residue was solubilized with phenol and ethylene bottom oil, decant oil, or coal tar oil, the solid content was higher than that of Comparative Examples 1 and 2. Further, since ΔT (change in softening point) at the time of heating the pitch (melt spinning) is very small, excellent thermal stability is confirmed, and the spinning process can be carried out stably.

Claims (4)

  Solid wood-based raw materials containing at least one selected from cellulose, hemicellulose, lignin, and lignocellulose are solubilized by pressurizing and heating in the presence of phenols and pyrolytic heavy oil. A method for producing a carbon fiber, comprising spinning, infusibilizing, and carbonizing a wood pitch obtained by removing low-boiling 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 pyrolysis heavy oil is at least one selected from ethylene bottom oil, decant oil, and coal tar. .