JPH058757B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing pitch raw material for carbon fibers, and more specifically to a method for producing pitch-based raw material pitch for carbon fibers, and more specifically, a method for producing pitch-based pitch carbon fibers with high properties at a high yield. The present invention relates to a method for producing crude raw material pitch. [Prior art] In recent years, carbon fiber has been highly evaluated for its performance as a composite material with plastic or metal.
In particular, various studies have been conducted on pitch-based carbon fibers. The improvement of the properties of pitch-based carbon fibers is achieved by heat-treating the raw pitch instead of the isotropic pitch used as the conventional spinning raw material to develop anisotropy and form molecular species that are easy to orient. A mesophasic pitch is used, and the spinning pitch is mainly controlled by adjusting the properties of the spinning pitch. However, ordinary pithus have a low content of β-resin components, which are useful components for forming mesophase produced by heat treatment.
In addition, it has a wide molecular weight distribution ranging from low molecules to polymers, so when producing a spinning pitch using this raw material pit, there are few parts involved in the formation of mesophases, and it can be reduced to a low molecular weight range by heat treatment. There was a drawback that mesophase production was different in the high molecular region and it was difficult to produce uniform mesophase. Therefore, as a method to overcome these drawbacks, a method of treating coal tar or coal tar pitch with an aromatic solvent or a mixed solvent of an aromatic solvent and an aliphatic solvent (Japanese Unexamined Patent Publication No. 160427/1989, 1978
-Refer to Publication No. 156027) has been proposed. [Problems to be Solved by the Invention] However, none of these methods is sufficient to produce components useful for forming mesophase and uniform mesophase. [Means for Solving the Problems] Therefore, as a result of intensive studies on these solvent treatment methods, the present inventors have determined that among coal tar pitches obtained by distilling coal tar, coal tar containing specific components can be used. By using a soft pit and treating with an aliphatic solvent and/or alicyclic solvent, the load on distillation to remove light boiling components from coal tar is reduced, and the simple solvent treatment is useful for forming carbon fibers. The ingredients are concentrated,
They also found that the spinnability was improved, and based on this knowledge, they completed the present invention. That is, an object of the present invention is to provide a method for producing pitch, a crude raw material for carbon fibers, which allows pitch-based carbon fibers with high properties to be obtained at a high yield.
This purpose has an initial boiling point in the temperature range of 80-270℃,
A coal tar soft pitch containing at least 25% by weight of a fraction up to 360°C is mixed with a solvent consisting of an aliphatic hydrocarbon substance and/or an alicyclic hydrocarbon substance, and the mixture is subjected to stratified separation. This is accomplished by removing the solvent from the heavy liquid layer. To explain the present invention in detail below, the coal tar soft pitch used in the present invention is obtained by removing light boiling components from coal tar, which is a coal-based raw material, through ordinary distillation, and has an initial boiling point. 80℃～270℃
A coal tar soft pitch containing at least 25% by weight of fractions up to 360°C is used. Preferably 85-260°C, more preferably 100-260°C
It is preferable to use a coal tar soft pit having an initial boiling point in the temperature range of 250°C and containing 30 to 45% by weight of distillates up to 360°C. The initial boiling point is controlled by adjusting the boiling point of light boiling components distilled from the top of the distillation column. That is, by setting the tower top temperature within the above temperature range, the initial boiling point of the coal tar soft pitch obtained from the tower bottom is determined. With such a simple operation, the content of fractions up to 360°C in the coal tar soft pitch can be controlled. That is, the light boiling point below the desired initial boiling point is removed by distillation from the top of the column, and the coal tar soft pitch whose initial boiling point is within the above range is obtained from the bottom of the column. The fraction up to this point is adjusted to at least 25% by weight, preferably 30 to 45% by weight. From this, if the initial boiling point of the coal tar soft pitch is 270℃ or higher, the distillate up to 360℃ in the pitch will decrease,
The solubility of pitch in the solvent decreases, and in layer separation of a mixture of pitch and solvent, the proportion of useful components concentrated in the lower layer decreases. Conversely, if the initial boiling point is below 80℃, the temperature in the pitch
As the fraction up to 360°C increases, effective components are carried away to the upper layer due to increased compatibility between the solvent and low boiling point substances, and the concentration ratio to the lower layer similarly decreases, so the initial boiling point should be set within the above range. is important. As the solvent, an aliphatic hydrocarbon substance or an alicyclic hydrocarbon substance having a boiling point or a distillation temperature of 95% by volume of 65 to 290°C, preferably 80 to 250°C is used. It is not advantageous to use a heavy hydrocarbon oil with a temperature of 290° C. or higher because the heat load increases in the operation of removing the solvent after the extraction process. Examples of these aliphatic hydrocarbon substances include _C6 to _C14 paraffins such as hexane, heptane, octane, decane, and tetradecane, naphtha, kerosene, and the like. In addition, examples of alicyclic hydrocarbon substances include cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, methylcycloheptane,
C ₆ - _{C 10} alicyclic hydrocarbons such as ethylcycloheptane, cyclooctane, decalin, etc. or alicyclic hydrocarbons having an alkyl group can be mentioned, but naphtha or kerosene is not used from the viewpoint of economy and operability. is preferred. It is preferable to select these solvents whose dry point is lower than the initial distillation temperature of the coal tar soft pitch used as a raw material to the extent that the two can be separated. Especially when recycling the recovered solvent,
This selection condition is important. If the recovered solvent contains a low boiling point substance, the recovered solvent may be further purified by distillation and recycled. Two or more of the above solvents may be used in combination. If the amount of solvent used is too small, stratified separation in the next step will be difficult, and if too large is used, it will take time to recover the solvent from the stratified separation liquid, making it uneconomical. It is preferable to use 1 to 10 parts by weight, preferably 2 to 6 parts by weight, per 1 part by weight of tar soft pitch. Mixing coal tar soft pitch and solvent is
Using a stirring tank, axial flow mixer, biaxial flow nozzle, ejector, static mixer, etc.,
It is preferably carried out at a temperature of 100 to 180°C. The mixing time varies depending on the type of mixer, and in the case of a stirring tank, several minutes or more is required, but in the case of other mixers, a few seconds to about one minute is sufficient. The resulting mixture is heated at a temperature at which the light liquid layer stratified from the mixture can be separated while maintaining its liquid state, such as room temperature to 200°C,
Preferably, the mixture is kept stationary at 100 to 180° C. for 0.2 to 2 hours under normal pressure or increased pressure to separate into a light liquid layer and a heavy liquid layer. The above-mentioned mixture is allowed to stand still and separated using a container equipped with a heating jacket, a thickener, or the like. The obtained heavy liquid layer is processed using an evaporator or distillation column,
Distilling off the solvent fraction by distillation under normal pressure or reduced pressure,
The distilled off solvent fraction is recycled as a solvent as it is or after being purified. The desired product obtained as a bottom fraction or bottom fraction in this distillation is:
It varies depending on the physical properties of the coal tar, but usually,
Using GPC, the number average molecular weight obtained from the calibration curve of polystyrene and toluene is 800 to 1200, and the toluene insoluble content is 25 to 45 wt%, and the quinoline insoluble content is 12 to 12%.
It is a blackish brown pitch-like substance containing 20 wt% of β-resin and 20 to 30 wt% of β-resin, and has desirable physical properties as a raw material pitch for carbon fibers. The obtained raw material pitch is subjected to meso-forming treatment according to a conventional method and then used as a pitch for spinning.
Further, hydrogenation treatment may be performed before meso conversion treatment. From the light liquid layer, the solvent fraction is removed by distillation under normal pressure or reduced pressure, or steam distillation using an evaporator or a distillation column. The bottom fraction or bottom fraction obtained by distillation of the light liquid layer components usually has an average molecular weight of 200 to 300, a maximum molecular weight of 350 to 400, and a benzene insoluble content of 0 to 5 wt%, although it varies depending on the physical properties of the coal tar. It is a blackish-brown, pitch-like substance with a melting point of about room temperature to about 50°C, and is usually used as a carbon black raw material oil in a heated and molten state. Alternatively, it can be used by mixing it with carbon oil obtained by distillation of coal tar, naphthalene oil, or carbon black raw material obtained by thermal cracking or catalytic cracking of petroleum distillation residue or by thermal cracking of naphtha. Note that the recovered solvent fraction is recycled and used as a solvent. [Effect] As described in detail above, in the present invention, the bottom fraction having a specific component obtained by removing the fraction up to a specific boiling point range from coal tar is mixed with a specific solvent, and the heavy liquid layer is separated by stratification. The simple operation of distilling off the solvent reduces the burden of coal tar distillation.
In addition, as shown in the examples below, it is possible to obtain pitch containing a component (β-resin) useful for producing mesophace at a high concentration of 25% or more, so it is extremely useful as a method for producing pitch as a crude raw material for carbon fibers. . By subjecting the crude raw material pitch obtained in the present invention to treatments such as meso-formation according to conventional methods, it is possible to obtain a spinning pitch that has excellent spinnability and provides high-quality carbon fibers. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 Coal tar soft pitch obtained by distillation of coal tar (initial boiling point 230°C, fraction up to 360°C 38.9% by weight, toluene insoluble content 7.5% by weight, quinoline insoluble content 2.8% by weight, β-resin 4.7%) (% by weight) 200 parts by weight, light kerosene with an initial boiling point of 140℃ and a 95% distillation point of 170℃
360 parts by weight at 140℃ for 20 minutes, and then at the same temperature for 20 minutes.
It was left standing for a minute. Next, the light kerosene fraction was removed from the stratified lower layer by vacuum distillation, and the physical properties of the resulting pitch were measured. The measurement results are shown in Table 1. Example 2 Coal tar soft pitch obtained by distillation of coal tar (initial boiling point 200°C, fraction up to 360°C 43.0% by weight, toluene insoluble content 6.8% by weight, quinoline insoluble content 2.5% by weight, β-resin 4.3%) (% by weight) and 360 parts by weight of the same light kerosene used in Example 1 were mixed at 130° C. for 20 minutes, and left at the same temperature for 20 minutes. Next, the light kerosene fraction was removed from the stratified lower layer by vacuum distillation, and the physical properties of the resulting pitch were measured. The measurement results are shown in Table 1. Example 3 Coal tar soft pitch obtained by distillation of coal tar (initial boiling point 260°C, fraction up to 360°C 26.5% by weight, toluene insoluble content 8.5% by weight, quinoline insoluble content 3.2% by weight, β-resin 5.3%) (% by weight) and 360 parts by weight of the same light kerosene used in Example 1 were mixed at 150° C. for 20 minutes and left at the same temperature for 20 minutes. Next, the light kerosene fraction was removed from the stratified lower layer by vacuum distillation, and the physical properties of the resulting pitch were measured. The measurement results are shown in Table 1. Comparative Example 1 Coal tar soft pitch obtained by distillation of coal tar (initial boiling point 290°C, fraction up to 360°C 20% by weight, toluene insoluble content 10.0% by weight, quinoline insoluble content)
4.0% by weight, β-resin 6.0% by weight) 200 parts by weight,
360 parts by weight of the same light kerosene used in Example 1 was mixed at 140° C. for 20 minutes, and left at the same temperature for 20 minutes. Next, the light kerosene fraction was removed from the stratified lower layer by vacuum distillation, and the physical properties of the resulting pitch were measured. The measurement results are shown in Table 1. Reference Example 1 100 parts by weight of pitch obtained in Example 1 and 100 parts by weight of tetrahydroquinoline were heated to 430° C. with stirring in a closed container and maintained at the same temperature for 10 minutes. The contents were then cooled, filtered through a filter with an average opening diameter of 5 μm, and light boiling components were removed by vacuum distillation (5 torr, 250° C.) to obtain 65 parts by weight of hydrogenated pitcher. Next, 60 parts by weight of this hydrogenated pitch was heated at 450° C. for 40 minutes while stirring and introducing nitrogen gas to obtain 23.4 parts by weight of mesophase pitch having 95% anisotropy. When this mesophase pitch was spun at a temperature of 340° C., a spinning nozzle inner diameter of 0.3 mm, and a spinning speed of 400 m/min, fibers having a thread diameter of 12 μm could be stably obtained for over 1 hour. Furthermore, by infusibleizing this pitch fiber at 310℃ and then carbonizing it at 1200℃,
Carbon fibers with a thread diameter of 9.7μ were obtained. The tensile strength and tensile modulus of this carbon fiber were measured and found to be 250 Kg/mm ² and 18100 Kg/mm ² . Reference Example 2 The pitch obtained in Example 2 was treated in the same manner as in Reference Example 1 to obtain 70 parts by weight of hydrogenated pitch and 28.5 parts by weight of mesophase pitch having 95% anisotropy. When this mesophasic pitch was spun under the same conditions as in Reference Example 1, 1 fiber with a thread diameter of 12μ was spun.
I was able to get it stable for more than an hour. The carbon fiber obtained by treating the obtained pitch fiber in the same manner as in Reference Example 1 had a tensile strength of 305 Kg/mm ² ,
The tensile modulus was 22000Kg/ ^mm2 . Reference Example 3 The pitch obtained in Example 3 was treated in the same manner as in Reference Example 1 to obtain 60 parts by weight of hydrogenated pitch and 23.0 parts by weight of mesophasic pitch having 95% anisotropy. When this mesophase pitch was spun under the same conditions as in Reference Example 1, fibers with a yarn diameter of 12μ were
I was able to get it stable for more than an hour. The carbon fiber obtained by treating the obtained pitch fiber in the same manner as in Reference Example 1 had a tensile strength of 220 Kg/mm ² ,
The tensile modulus was 16000Kg/ ^mm2 . Reference Example 4 The pitch obtained in Comparative Example 1 was treated in the same manner as in Reference Example 1 to obtain 55 parts by weight of hydrogenated pitch and 20 parts by weight of mesophasic pitch having 95% anisotropy. When this mesophase was spun under the same conditions as in Reference Example 1, spinning trouble occurred within 10 minutes and the spinning was discontinued. The carbon fiber obtained by treating the obtained pitch fiber in the same manner as in Reference Example 1 had a tensile strength of 150 Kg/mm ² and a tensile modulus of 14400 Kg/mm ² . 【table】

Claims (1)

[Claims] 1 Coal tar soft pitch having an initial boiling point in the temperature range of 80°C to 270°C and containing at least 25% by weight of a fraction up to 360°C, an aliphatic hydrocarbon substance and/or 1. A method for producing a raw material pitch for carbon fibers, which comprises mixing a raw material pitch with a solvent made of an alicyclic hydrocarbon substance, subjecting the mixture to stratified separation, and removing the solvent from the obtained heavy liquid layer. 2 The solvent has a boiling point or distillation temperature of 95% by volume of 65~
A method for producing a raw material pitch for carbon fiber according to claim 1, characterized in that the temperature is 290°C. 3. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the amount of the solvent is 1 to 10 parts by weight per 1 part by weight of the coal tar soft pitch. 4. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the stratification separation is carried out at a temperature of room temperature to 200°C. 5. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the solvent made of an aliphatic hydrocarbon substance and/or an alicyclic hydrocarbon substance is naphtha or kerosene.