JP4006516B2 - Carbon fiber manufacturing method - Google Patents

Description

【００２２】
供試体Ｎｏ．１〜７のように、反応温度が高温であったり、反応時間が長過ぎたりすると、木タールは炭化してしまい、繊維状に成形可能なピッチは得られなかった。しかし、供試体Ｎｏ．６、７のように、高い炭素含有率を持つことも明らかになった。これに対して、供試体Ｎｏ．８、９のように、反応温度を２００℃とし、３０分間加熱を続ける条件では、炭素含有率が約６０％と相当高いにも拘わらず、繊維状に成形可能なピッチが得られることが判明した。
【００２３】
得られたピッチ（以後、木タールピッチと呼ぶ）は光沢があり、その外観は石炭から得られるピッチとよく似ている。なお、液体成分は、水分及び低沸点カルボン酸を主成分とする。
【００２４】
図１に、木タールピッチの示差熱分析（ＤＳＣ）の結果を示す。得られた木タールピッチの軟化点は、ＤＳＣ曲線の形状から、約７０℃付近と考えられる。また、１８９℃から不連続な吸熱ピークが見られ、炭化が始まったと考えられる。従って、実際の炭素繊維製造の際に前駆体として繊維状に成形する温度は、１５０℃程度が適当であると考えられる。
【００２５】
なお、石炭から製造したピッチを原料とした場合の繊維製造の際の成形温度は３００℃程度であるので、これと比べて、木タールピッチの成形温度はかなり低い。高強度・高弾性率炭素繊維を、縮合した芳香環構造の少ない木タールピッチから製造することは容易ではないが、高い強度が要求されない活性炭素繊維などを製造する際には、プロセスの簡素化を考慮すれば、紡糸温度は１５０℃程度でも問題はない。２００℃になると炭化が始まり、糸状繊維に成形することが困難になるため、１４０℃から１８０℃の範囲で紡糸し、ピッチ繊維化する。そのピッチ繊維を既存の炭素繊維化プロセス、即ち、高温処理と水蒸気などによる賦活化処理などにより、活性炭素繊維へと導く。そのような活性炭素繊維の用途として、高性能二次電池の電極やキャパシタ、水質浄化分野などが考えられる。
【００２６】
図２に、木タールピッチの熱重量分析（ＴＧＡ）の結果を示す。熱重量分析では、２０％質量減少は３０１℃、５０％減少は４２７℃であり、８００℃では６６％の質量減少となった。５００℃での炭素分析値（表１）は約８７％であるので、８００℃では木タールチップは完全に炭化していることになる。なお、８００℃で残存重量が３４％あることは、繊維状に成形できれば炭素繊維化が可能であることを示している。
【００２７】
木タールピッチを細砕した後、以下の方法で溶融紡糸を行い、木タールピッチを繊維化した。使用された装置は、内径１０ｍｍのパイレックス製ガラス管で、先端に約１ｍｍの細孔が設けられ、外側にリボンヒータが巻き付けられたもので、熱電対と温度制御装置によって温度調整が可能である。このガラス管の中に、細かく砕かれた木タールピッチ２ｇを入れ、１６５℃に加熱して溶融した。ガラス管の上部から窒素ガスを用いて加圧し、下部の細孔からピッチ繊維を押し出した。木タールピッチは、繊維状によく延び、空気中で速やかに固化した。また、少なくとも１０ｍの長さのピッチ繊維が切れずに得られることも判明した。
【００２８】
なお、このピッチ繊維から、不融化及び高温での炭化の工程を経て、炭素繊維を製造することができる。
【００２９】
【発明の効果】
本発明に基づく炭素繊維の製造方法によれば、従来、炭素製造プロセスの副生物として廃棄されていた木タールを、炭素繊維の製造工程の出発原料として使用することができる。また、本発明に基づく製造方法によれば、比較的低い温度でピッチ繊維の炭化を行うことが可能であり、石油ピッチを原料とする従来の方法と比べて簡単な装置を用いて実施することができる。更に、本発明は、いわゆるゼロ・エミッションの手法に合致し、環境保護の対策に貢献するものである。
【図面の簡単な説明】
【図１】木タールピッチの示差熱分析（ＤＳＣ）の結果を示す図。
【図２】木タールピッチの熱重量分析（ＴＧＡ）の結果を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing carbon fiber, and more particularly to a method for producing carbon fiber using wood tar as a raw material.
[0002]
[Prior art]
The carbon fiber is a fiber having a high strength and a high elastic modulus composed of almost carbon, in which a benzene ring is condensed to develop a graphite structure. Carbon fiber is manufactured from a polymer such as pitch obtained from petroleum or coal, or a polymer such as PAN (polyacrylonitrile). Currently, carbon fibers are mainly produced from polyacrylonitrile fibers, rayon, and petroleum distillation residues (pitch).
[0003]
High-elasticity carbon fibers are manufactured based on the principle of liquid crystal spinning using a pitched petroleum or coal tar as a raw material. That is, the pitch is heated at a temperature of 350 ° C. or more to cause a dehydration condensation reaction to produce a liquid crystal, and spinning is performed while applying a shearing force to form a fiber having an orientation along the fiber axis. The fiber (pitch fiber) thus obtained is infusible and then carbonized to obtain a high elastic modulus carbon fiber. Carbon fiber using petroleum or coal tar as a raw material has a problem that its strength is lower than that of PAN, and improvement of the strength is a future problem. In the method of producing from PAN, acrylic fiber for clothing or special grade acrylic fiber for carbon fiber is used as a starting material. After a stabilization process in which dehydrogenation or a cross-linking reaction is performed, the product is heated in an inert gas to a few hundreds of degrees and further subjected to a surface treatment process to obtain a product. The high-strength carbon fiber obtained by this method has a high elastic modulus and elongation, and has a good balance between tensile and compression properties, and is expected to expand its application as a structural material. In addition, when the carbonization temperature is set to 2,000 and several hundred degrees, a high elastic modulus carbon fiber is obtained. By the way, wood tar generated as a by-product in the process of charcoal production is an aromatic produced by depolymerizing and dehydrogenating cellulose, which is a constituent of wood, or an aromatic derived from a lignin decomposition product having a benzene ring. Many are included. However, at present, wood tar has no industrial use and is treated as industrial waste. Furthermore, the problem of environmental pollution associated with the disposal and incineration of wood tar is also increasing. For this reason, development of the use which uses wood tar effectively was desired.
[0004]
There has been no report that pitch fibers, which are precursors of carbon fibers, have been produced using biomass resources such as wood tar as starting materials.
[Problems to be solved by the invention]
The present invention has been made in view of the environmental problems associated with the disposal of wood tar as described above, and an object of the present invention is to provide a method for producing carbon fiber using wood tar as a raw material.
[0006]
[Means for Solving the Problems]
In the method for producing carbon fiber of the present invention , THF (tetrahydrofuran) is added to wood tar, insoluble matter is filtered off, and then THF is evaporated and removed to obtain purified wood tar. heating instead of solid wood tar pitch, and the pitch fibers of this wood tar pitch by melt spinning, characterized in that the change in the carbon fiber by carbonizing pitch fibers.
[0007]
Preferably, the purified wood tar is heated and pitched in a reduced pressure atmosphere of pressure: 2 mmHg (267 Pa) to 10 mmHg (1330 Pa) and temperature: 100 ° C. to 200 ° C.
[0008]
Preferably, after the pitch thus obtained is pulverized, melt spinning is performed using a nitrogen gas pressure at a temperature of 140 ° C. or higher and 180 ° C. or lower to obtain pitch fibers.
[0009]
In addition, about the process which carbonizes the obtained pitch fiber and changes into carbon fiber, the conditions similar to the conventional process which uses the pitch obtained from petroleum or coal as a raw material are applicable.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
When producing the charcoal, if the liquid to be distilled is allowed to stand, it is divided into three layers. A small amount of essential oil and oily components float in the upper layer, water-soluble components (wood vinegar) in the middle layer, and tar-like components in the lower layer. Tar separated into lower layers is called sedimentation tar, and tar dissolved in wood vinegar is called dissolved tar. When conifers are used as raw materials, a relatively large amount of essential oil / oil components are produced. On the other hand, when hardwood is used as a raw material, there are many sedimentation tars, and for example, 9.2% sedimentation tar is obtained with respect to the total dry wood weight.
[0011]
The dissolved tar contains levoglucosan (1,6-anhydroglucose), furfural and other phenol components (phenol, guaiacol, creosote, etc.), and also contains a trace amount of 3,4-benzpyrene. Dissolved tar is hard and brittle and used for fuel.
[0012]
The sedimentation tar is fractionated into light oil (boiling point 200 ° C. or less), heavy oil (boiling point 200 to 360 ° C.) and pitch by distillation. In the case of wood tar from hardwood, examples of its composition are: acetic acid 2%, methanol 0.65%, water 17.75%, light oil (specific gravity 0.97) 5%, heavy oil (specific gravity 1.043) 10 %, And the soft pitch is 64.60%. A 200-220 degreeC fraction (specific gravity 1.03-1.09) of heavy oil is called creosote oil, and it has guaiacol and creosote as a main component, and becomes a manufacturing raw material of a wood preservative and guaiacol.
[0013]
In this experiment, wood tar derived from hardwood was used as a starting material. From alder, charcoal as a carbon raw material and agricultural vinegar are produced, and a large amount of wood tar is generated as a by-product.
[0014]
3 L of THF (tetrahydrofuran) was added to 1 kg of wood tar and stirred well. A brown precipitate (80 g) was separated by suction filtration of a THF solution of wood tar using a filter paper to remove insoluble matters. The filtrate was sent to a rotary evaporator, and a low-boiling solution such as THF and moisture was collected using a water pump and subsequently a vacuum pump to concentrate tar. As a result, 450 g of black thick purified tar was obtained.
[0015]
The composition of the raw hardwood is:
C: 49.0 wt%
H: 6.1 wt%
N: 0.1 wt%
And the composition of the resulting purified tar is:
C: 55.9 wt%
H: 6.4 wt%
N: 1.5 wt%
Met.
[0016]
Refined tar is obtained by thermally decomposing cellulose and lignin in wood and reducing the molecular weight. As a result of the removal of low-boiling components such as methanol, water, and acetic acid, the analytical value of carbon element is somewhat increased.
[0017]
Next, using an autoclave, the low-boiling liquid component was distilled off from the purified tar to pitch the purified tar. In addition, the used autoclave fixed the lid | cover with the screw to the stainless steel container with an internal capacity of 500 mL, and wound the heater around the outer wall. Further, this autoclave is provided with a liquid nitrogen trap for collecting the flowing liquid component, and further provided with a pressure gauge, a thermocouple, a nitrogen introduction hole, and a vacuum pump. The pressure resistance temperature is 300 ° C. and 400 atmospheres.
[0018]
100 g of purified tar was weighed into this autoclave and the atmosphere was purged with nitrogen. After raising the temperature to 200 ° C. under vacuum (5 to 8 mmHg) over about 2 hours, the heating was further continued at 200 ° C. for 30 minutes to distill off the low-boiling liquid component and perform pitching. During the heating process, a brown liquid began to be trapped at around 180 ° C. The reaction was stopped after the outflow of the liquid component was stopped (approximately two and a half hours after the start of temperature increase).
[0019]
After cooling the autoclave, the pitched contents were taken out. The yield was 28 g (28%) of the liquid component and 63 g (63%) of pitched wood tar. The remaining 9% is considered a gas component.
[0020]
Table 1 shows the reaction conditions using the autoclave and the results (products and their analytical values, etc.). In this table, for comparison, the results of reaction under various conditions are also shown. In this table, those corresponding to the production method of the present invention are specimen Nos. 8 and 9.
[0021]

[0022]
Specimen No. As in 1 to 7, when the reaction temperature was high or the reaction time was too long, the wood tar was carbonized, and a pitch that could be formed into a fiber was not obtained. However, specimen no. It became clear that it has high carbon content like 6 and 7. In contrast, the specimen No. 8 and 9, when the reaction temperature is 200 ° C. and heating is continued for 30 minutes, it is found that a pitch that can be formed into a fiber is obtained even though the carbon content is considerably high at about 60%. did.
[0023]
The resulting pitch (hereinafter referred to as wood tar pitch) is glossy and its appearance is very similar to that obtained from coal. In addition, a liquid component has a water | moisture content and a low boiling-point carboxylic acid as a main component.
[0024]
FIG. 1 shows the results of differential thermal analysis (DSC) of wood tar pitch. The softening point of the obtained wood tar pitch is considered to be about 70 ° C. from the shape of the DSC curve. Further, a discontinuous endothermic peak was observed from 189 ° C., and it is considered that carbonization started. Therefore, it is considered that an appropriate temperature for forming into a fibrous form as a precursor during actual carbon fiber production is about 150 ° C.
[0025]
In addition, since the shaping | molding temperature in the case of the fiber manufacture at the time of using the pitch manufactured from coal as a raw material is compared with this, the shaping | molding temperature of a wood tar pitch is quite low. It is not easy to produce high-strength and high-modulus carbon fiber from wood tar pitch with few condensed aromatic ring structures, but simplification of the process when producing activated carbon fiber that does not require high strength. Is considered, there is no problem even if the spinning temperature is about 150 ° C. When the temperature reaches 200 ° C., carbonization starts and it becomes difficult to form into a filamentous fiber. Therefore, the fiber is spun in a range of 140 ° C. to 180 ° C. to form a pitch fiber. The pitch fibers are led to activated carbon fibers by an existing carbon fiber forming process, that is, an activation treatment with high temperature treatment and steam. Possible applications of such activated carbon fibers include high performance secondary battery electrodes and capacitors, and water purification fields.
[0026]
FIG. 2 shows the results of thermogravimetric analysis (TGA) of wood tar pitch. In thermogravimetric analysis, a 20% mass reduction was 301 ° C., a 50% reduction was 427 ° C., and a 800% mass reduction was 66%. Since the carbon analysis value at 500 ° C. (Table 1) is about 87%, the wood tar chips are completely carbonized at 800 ° C. The residual weight of 34% at 800 ° C. indicates that carbon fiber can be formed if it can be formed into a fiber.
[0027]
After pulverizing the wood tar pitch, melt spinning was carried out by the following method to fiberize the wood tar pitch. The apparatus used was a Pyrex glass tube with an inner diameter of 10 mm, with a 1 mm pore at the tip, and a ribbon heater wound around the outside. The temperature can be adjusted by a thermocouple and temperature controller. . In this glass tube, 2 g of finely crushed wood tar pitch was placed and heated to 165 ° C. to melt. Pressurization was performed using nitrogen gas from the upper part of the glass tube, and pitch fibers were extruded from the lower pores. The wood tar pitch extended well in a fiber form and quickly solidified in the air. It has also been found that pitch fibers having a length of at least 10 m can be obtained without breaking.
[0028]
In addition, a carbon fiber can be manufactured from this pitch fiber through the process of infusibilization and carbonization at high temperature.
[0029]
【The invention's effect】
According to the carbon fiber production method of the present invention, wood tar that has been conventionally discarded as a by-product of the carbon production process can be used as a starting material for the carbon fiber production process. Moreover, according to the manufacturing method based on this invention, it is possible to carbonize pitch fiber at a comparatively low temperature, and it implements using a simple apparatus compared with the conventional method which uses petroleum pitch as a raw material. Can do. Furthermore, the present invention is consistent with the so-called zero emission technique and contributes to environmental protection measures.
[Brief description of the drawings]
FIG. 1 is a diagram showing the results of differential thermal analysis (DSC) of wood tar pitch.
FIG. 2 is a graph showing the results of thermogravimetric analysis (TGA) of wood tar pitch.

Claims (4)

THF is added to the wood tar to filter out insoluble matters, and then THF is evaporated to remove it to obtain a purified wood tar.
This refined wood tar is heated under reduced pressure to change it into a solid wood tar pitch,
This wood tar pitch is made into a pitch fiber by melt spinning,
Carbonizing this pitch fiber into carbon fiber ,
A carbon fiber production method characterized by the above. The purified wood tar, Pressure: 2 mmHg above 10mmHg or less, temperature: 100 ° C. by heating in a reduced pressure atmosphere of 200 ° C. inclusive carbon fiber according to claim 1, characterized in that changing to solid wood tar pitch Manufacturing method. 2. The method for producing carbon fiber according to claim 1, wherein after the wood tar pitch is pulverized, melt spinning is performed in an inert atmosphere at a temperature of 140 ° C. or higher and 180 ° C. or lower to form pitch fibers. 3. A method for producing pitch fiber, which is a precursor of carbon fiber,
THF is added to the wood tar to filter out insoluble matters, and then THF is evaporated to remove it to obtain a purified wood tar.
This purified wood tar is heated in a reduced pressure atmosphere of pressure: 2 mmHg or more and 10 mmHg or less, temperature: 100 ° C. or more and 200 ° C. or less to change to a solid wood tar pitch,
After pulverizing the wood tar pitch, the temperature: 140 ° C. or higher and 180 ° C. or lower, and pitch spinning by melt spinning in an inert atmosphere ,
A method for producing pitch fibers characterized by the above .

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