JPH058756B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing raw material pitch for carbon fibers, and more specifically, a method for producing raw material pitch for carbon fibers that can obtain high-quality pitch-based carbon fibers at a high yield. It is related to. [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 a component useful for forming mesophase produced by heat treatment, that is, a β-resin component, and have a wide molecular weight distribution from low molecules to high molecules. When producing a spinning pitch using these raw material pits, there are few parts involved in the formation of mesophases, and the mesophase production differs in the low-molecular and high-molecular regions due to heat treatment, making it difficult to produce uniform mesophases. There was a drawback. Therefore, as a method to overcome these drawbacks, there is a method of treating coal tar or coal tar soft pitch with an aromatic solvent or a mixed solvent of an aromatic solvent and an aliphatic solvent (Japanese Patent Application Laid-open No. 16047/1983,
(See Japanese Patent Application Laid-Open No. 156027/1983) has been proposed. [Problems to be Solved by the Invention] However, none of these methods is sufficient to efficiently obtain components useful for forming carbon fibers and to produce uniform mesophase. [Means for Solving the Problems] The present inventors have conducted further studies on these solvent treatment methods, and have developed a coal tar pitch having an initial boiling point within a specific range obtained by removing light boiling components from coal tar. By using a two-stage extraction method in combination with a specific type of solvent, components useful for forming carbon fibers are concentrated, improving the yield of carbon fibers, and narrowing the molecular weight distribution and improving spinnability. Heading: The present invention was completed based on this finding. That is, an object of the present invention is to provide a method for producing pitch, a crude raw material for carbon fibers, which can yield pitch-based carbon fibers with high properties. The coal tar pitch having the dots is mixed with a first solvent consisting of an aliphatic hydrocarbon substance and/or an alicyclic hydrocarbon substance, and the obtained first mixture is divided into a first light liquid layer and a first heavy liquid layer. A first stratified separation is performed into a liquid layer, and then a second solvent consisting of a mixture of the obtained first heavy liquid layer and an aromatic hydrocarbon substance, an aliphatic hydrocarbon substance, and/or an alicyclic hydrocarbon substance. mixing the obtained secondary mixture into a secondary light liquid layer and a secondary heavy liquid layer, and removing the solvent from the obtained secondary light liquid layer. This is achieved by The present invention will be described in detail below. Coal tar pitch, which is the starting material of the present invention, is obtained by removing light-boiling components from coal tar using ordinary pressure distillation or vacuum distillation. Those with an initial boiling point of 190 to 400℃, preferably 200 to 350℃,
More preferred is coal tar pitch at 220-270°C. Specifically, regular road tar, tar pitch,
There are various types of pitches called soft pitches, hard pitches, etc. The initial boiling point is controlled by the boiling point of the light boiler to be removed. That is, by setting the distillation temperature at the top of the distillation column within the above temperature range, the initial boiling point of the coal tar pitch obtained from the bottom of the column is determined. In particular, when the distillation temperature range is selected from the range of 220 to 270°C, the concentration ratio of components useful for forming carbon fibers is improved. That is, by adjusting the top temperature, the fraction up to 360°C in the pitch of the extraction raw material obtained as the bottom fraction changes, but if the amount of this fraction is small, the dissolution of the pitch in the solvent will be affected. In the stratified separation of the mixture of pitch and solvent, the proportion of useful components concentrated in the lower layer decreases, and the concentration of useful components decreases during two-stage extraction. On the other hand, when the amount increases, the effective components are carried away to the upper layer due to increased compatibility with the solvent and low-boiling substances, and the concentration ratio to the lower layer decreases, which is undesirable because the concentration of useful components during two-stage extraction becomes low. As the first solvent used in the present invention, an aliphatic hydrocarbon substance or an alicyclic hydrocarbon substance having a boiling point or distillation temperature of 95% by volume of 65 to 290°C, preferably 80 to 250°C is used. If heavy hydrocarbon oil with a temperature of 290℃ or higher is used, the heat load will be large in the operation of removing the solvent after the extraction process.
Not advantageous. These aliphatic hydrocarbons include hexane, heptane, octane, decane,
Examples include C ₆ to C ₁₅ paraffins such as pentadecane, naphtha, kerosene, and the like. In addition, examples of alicyclic hydrocarbon substances include cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane,
Methylcycloheptane, ethylcycloheptane,
Examples include _C6 to _C10 alicyclic hydrocarbons such as cyclooctane and decalin, or alicyclic hydrocarbons having an alkyl group, but naphtha or kerosene is preferably used from the viewpoint of economy and operability. It is preferable to select these solvents whose dry point is several degrees Celsius or more lower than the initial distillation temperature of the coal tar pitch used as the extraction raw material. This selection condition is especially important when recycling the recovered solvent. If the recovered solvent contains a low boiling point substance, the recovered solvent may be further purified by distillation and recycled. Two or more kinds of the above-mentioned first solvents can be used in combination. If the amount of the first 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 first solvent from the stratified separation liquid, making it uneconomical. It is used in an amount of 1 to 10 parts by weight, preferably 2 to 6 parts by weight, per 1 part by weight of coal tar pitch used as a starting material. The coal tar pitch and the solvent are mixed using a stirring tank, an axial flow mixer, a biaxial flow nozzle, an ejector, a static mixer, etc. at a temperature of room temperature to 200°C, preferably 100 to 180°C. Mixing time varies depending on the type of mixer, with stirring tanks requiring several minutes or more, but with other mixers,
A few seconds to one minute is sufficient. The obtained primary 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 100 to 180°C, for 0.2 to 2 hours under normal pressure or pressurization. By holding the liquid at rest, primary stratification separation is performed into a primary light liquid layer and a primary 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 first heavy liquid layer is then mixed with a second solvent, which has a boiling point or distillation temperature of 95% by volume of 65 to 400°C, preferably 80 to 400°C.
A mixture of an aliphatic hydrocarbon substance and/or an alicyclic hydrocarbon substance having a temperature of 250°C and an aromatic hydrocarbon substance having a boiling point or 95% volume distillation temperature of 200 to 400°C, preferably 210 to 300°C. use As these aliphatic hydrocarbon substances and/or alicyclic hydrocarbon substances, the same substances as those mentioned above as the first solvent can be used. In addition, as aromatic hydrocarbon substances, hydrocarbon substances having carbon monocycles or carbon polycycles such as naphthalene, methylnaphthalene, and anthracene, medium oil obtained by distillation of coal tar, heavy oil, anthracene oil, etc. are used. However, if the boiling point of the aromatic solvent is too low, the yield will decrease, which is not preferable. The proportion of the aromatic hydrocarbon substance in the second solvent is selected such that the proportion of the aromatic hydrocarbon substance in the total solvent after mixing with the first heavy liquid layer is 30 to 60% by volume, Usually 0.5 to 1.5 parts by weight of aliphatic and/or cycloaliphatic hydrocarbon substances.
Parts by weight are mixed. That is, the second solvent is mixed so that the proportion of the aromatic hydrocarbon substance in the second solvent is 30 to 60 parts by weight. If the mixing ratio of aromatic hydrogenated hydrogen is too high, quinoline insoluble matter will increase in the hydrogenation pitch, which will put a burden on the overprocessing, and if it is too low, the effective ingredient β-resin will be reduced, and an appropriate amount will be added. It is necessary to select the proportion. Next, regarding the amount of the second solvent used, as with the above aromatic component mixing ratio, if it is too small, the removal rate of quinoline insoluble matter will be low, and if it is used too large, the amount of β-resin, which is the active ingredient, will decrease, and at the same time, the stratified separation liquid will decrease. Since it takes time to recover the solvent from the liquid and is not economical, it is usually 0.3 parts by weight for 1 part by weight of the primary heavy liquid layer.
~1.5 parts by weight, preferably 0.5 to 1.0 parts by weight, and must be selected appropriately. The first heavy liquid layer and the second solvent are mixed and left to stand at a temperature of 200 to 350°C, preferably 220 to 330°C, and a standing time of 30 minutes or less. However, if the standing time is too long, β
- Resin sedimentation occurs, which is not good. After that, a second stratification separation is performed into a second light liquid layer and a second heavy liquid layer. The obtained second light liquid layer is subjected to distillation under normal pressure or reduced pressure to remove the solvent fraction using an evaporator or a distillation column. The distilled off solvent fraction is recycled as a solvent as it is or after being purified. The desired product obtained as a residue or bottom fraction in this distillation varies depending on the quality of the coal tar used as a starting material, but is usually determined by the number average obtained from a calibration curve of polystyrene and toluene using GPC. Molecular weight is 650-850℃, toluene insoluble content 20-25wt%, quinoline insoluble content 0-1wt%, β-resin 20-25wt%
It is a blackish-brown pitch-like substance 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. The first light liquid layer obtained by the first stratified separation can be used as carbon black raw material oil by appropriately treating it, but it is difficult to obtain coal tar pitch having an initial boiling point of 190 to 400°C. Used by mixing with carbon oil obtained by distillation of distilled fraction and/or coal tar, naphthalene oil, or carbon flak raw material obtained by thermal cracking or catalytic cracking of petroleum distillation residue or thermal cracking of naphtha. You can also do that. In addition, the second heavy liquid layer obtained by the second stratified separation can be used as fuel or other purposes, or it can be stored under normal pressure or reduced pressure using a distiller or distillation column and an extruder such as an extri-user. The solvent fraction is removed by distillation or steam distillation, and then, after cooling, it is cut with high-pressure steam and used as fuel, pitch coke, and raw materials for various carbon materials. The recovered solvent fraction is recycled and used as a solvent. Furthermore, the first heavy liquid layer to be extracted with the second solvent may be mixed with the second solvent after removing the solvent fraction by distillation under normal pressure or reduced pressure using an evaporator or distillation column. good. The distilled off solvent fraction is recycled and used as a solvent. [Effects] As detailed above, in the present invention, the bottom fraction from which the light boiling point fraction below 190°C is removed from coal tar is extracted in two stages using a specific solvent, and the light liquid layer obtained by stratified separation is extracted. By a simple operation of distilling off the solvent, it is possible to obtain a component (β-resin) useful for mesophase production at a high concentration of 20% or more and a narrow pitch in molecular weight, as shown in the examples below. This method is extremely useful as a method for producing raw material pitch for carbon fibers. Further, by subjecting the crude raw material pitch obtained in the present invention to a meso-forming treatment according to a conventional method, a spinning pitch with good spinnability can be easily obtained. Moreover, after hydrogenation treatment, meso-forming treatment may be performed as necessary. Pitch-based carbon fibers with high properties can be obtained by melt-spinning the spinning pitch obtained in this way according to a conventional method, and subjecting it to infusibility treatment, carbonization treatment, and graphitization treatment if necessary. [Examples] 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 pitch obtained by distillation of coal tar (initial boiling point 230°C, fraction up to 360°C 38.9% by weight,
200 parts by weight of toluene insolubles (7.5% by weight, 2.8% by weight of quinoline insolubles, 4.7% by weight of β-resin) and 360 parts by weight of light kerosene (first solvent) with an initial boiling point of 140°C and a 95% distillation point of 170°C. were mixed at 140°C for 20 minutes, and left at the same temperature for 20 minutes. Next, 100 parts by weight of the lower layer that was subjected to the primary stratification separation and the initial boiling point of 140°C and 95% distillation point.
Mix 90 parts by weight of a mixture of light kerosene at 170°C and naphthalene oil in a 1:1.25 weight ratio (second solvent).
The mixture was stirred at 300°C for 15 minutes, and then left at the same temperature for 0.5 hour. 151 parts by weight of the upper layer after the second stratified separation was collected, and the solvent was removed from the collected product by distillation under reduced pressure to obtain 60 parts by weight of pitch. The substances in the resulting pitch were measured and the results are shown in Table 1. Example 3 Coat tar pitch obtained by distillation of coal tar (initial boiling point 260°C, fraction up to 360°C 26.5% by weight, toluene insolubles 8.5% by weight, quinoline insolubles 3.2% by weight, β-resin 5.3% by weight) 200 parts by weight and Example 1
400 parts by weight of the same first solvent used in 140°C.
The mixture was mixed for 20 minutes and left at the same temperature for 20 minutes. Next, 100 parts by weight of the lower layer after the primary stratification separation and 90 parts by weight of the same second solvent used in Example 1 were mixed, stirred at 300°C for 15 minutes, and then left at the same temperature for 0.5 hour. I placed it. 151 parts by weight of the upper layer after the second stratified separation was collected, and the solvent was removed from the collected product by distillation under reduced pressure to obtain 60 parts by weight of pitch. The substances in the resulting pitch were measured and the results are shown in Table 1. Comparative Example 1 100 parts by weight of the heavy liquid layer subjected to the primary stratification separation at 140° C. in Example 1 was distilled under reduced pressure to remove the solvent to obtain 85 parts by weight. The physical properties of the obtained pitch 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. After the contents were filtered, light boiling components were removed by vacuum distillation. 60 parts by weight of the obtained hydrogenated pitch was heated at 450° C. for 40 minutes while stirring and introducing nitrogen gas to obtain a 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 with a thread diameter of 12 μm were stably obtained for a long time (over 1 hour). was completed. Furthermore, by infusible treatment of this pitch fiber at 310℃ and then carbonization treatment 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 270 Kg/mm ² and 24500 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 a mesophase pitch having 95% anisotropy. When this mesophasic pitch fiber was spun under the same conditions as Reference Example 1, fibers with a thread diameter of 12μ could be stably obtained for a long time (more than 1 hour). Carbon fibers obtained by the same treatment had a tensile strength of 260 Kg/mm ² and a tensile modulus of 22,600 Kg/mm ² . Reference Example 3 The pitch obtained in Comparative Example 1 was treated in the same manner as in Reference Example 1 to obtain mesophase pitch having 95% anisotropy. When this mesophasic pitch was spun under the same conditions as in Reference Example 1, fibers with a thread diameter of 12μ could be obtained stably for more than 1 hour. , the properties of the yarn are reduced, tensile strength 250Kg/mm ² , tensile modulus 18100
It was Kg/ ^mm2 .

[Table] * Spinnability ◎ Stable spinning for over 1 hour

Claims (1)

[Claims] 1. A first solvent obtained by mixing coal tar pitch having an initial boiling point of 190 to 400°C and a first solvent consisting of an aliphatic hydrocarbon substance and/or an alicyclic hydrocarbon substance. The mixture is subjected to first stratification separation into a first light liquid layer and a first heavy liquid layer, and then the obtained first heavy liquid layer contains aromatic hydrocarbon substances, aliphatic hydrocarbon substances and/or or a second solvent consisting of a mixture of alicyclic hydrocarbon substances, and the obtained second solvent
The second mixture is divided into a second light liquid layer and a second heavy liquid layer.
A method for producing a raw material pitch for carbon fibers, which comprises performing stratification separation and removing the solvent from the obtained second light liquid layer. 2 The boiling point of the first solvent or the distillation temperature of 95% by volume is 65
A method for producing a raw material pitch for carbon fiber according to claim 1, wherein the temperature is 290°C. 3 The boiling point of the second solvent or the distillation temperature of 95% by volume is 65
A method for producing a raw material pitch for carbon fibers according to claim 1, wherein the temperature is 400°C. 4 The aromatic hydrocarbon substance contained in the second solvent
The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the content is 30 to 60% by weight. 5. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the amount of the first solvent used is 1 to 10 parts by weight per 1 part by weight of the coal tar pitch. 6. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the amount of the second solvent used is 0.3 to 1.5 parts by weight per 1 part by weight of the first heavy liquid layer. . 7. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the first stratification separation is carried out at a temperature of room temperature to 200°C. 8. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the secondary stratification separation is carried out at a temperature of 200 to 350°C. 9. The method for producing a raw material pitch for carbon fibers according to claim 1, characterized in that the first heavy liquid layer that does not substantially contain the first solvent is mixed with the second solvent. 10. The method for producing a raw material pitch for carbon fibers according to claim 1, wherein the first solvent is naphtha or kerosene.