JPS59106518A - Production of carbon fiber having high modulus of elasticity - Google Patents

Abstract

PURPOSE:To improve the yield of carbon fiber, by subjecting an extract component of coal tar pitch with a benzene solvent to heat polycondensation, using a material insoluble in the benzene solvent for carbon fiber production, subjecting a material soluble in it to heat polycondensation again, using a material insoluble in the benzene solvent for carbon fiber production. CONSTITUTION:A component(component A) soluble in a benzene solvent is extracted and separated from coal tar pitch, and the component A is subjected to heat polycondensation in a condition wherein an amount of a material insoluble in nitrobenzene at 350-500 deg.C is <=3wt%. The component A subjected to heat polycondensation is extracted with the benzene solvent and separated into a soluble material(component B) and an insoluble material (component C). The component C is used as mesophase pitch for production of carbon fiber having high modulus of elasticity. The component B is again subjected to heat polycondensation wherein an amount of a material insoluble in nitrobenzene at 350- 500 deg.C is <=3wt%, and extracted with the benzene solvent. A material(component D) insoluble in the benzene solvent like the component C is used as a raw material for the mesophase pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high modulus carbon fiber using coal tar or coal tar pitch as a raw material, and more specifically to a method for producing high modulus carbon fiber using coal tar or coal tar pitch as a raw material. The present invention relates to a method for obtaining pitch containing pitch (hereinafter referred to as mesophase pitch) at a high yield and producing high modulus carbon fiber from this pitch.

Conventionally, as a method for producing high modulus carbon fiber from pitches, a method using a non-phase liquid crystal state is known. However, since this method includes a step of melt-spinning menphase pitch, the melt viscosity of the menphase pitch must be low. The method for producing this low-viscosity Menphase pitch involves heating and polycondensing petroleum-based pitch, which is a mixture of toluene-soluble and toluene-insoluble components, to increase the toluene-insoluble content, which is suitable as a raw material for low-viscosity Men7Aze pitch. There is a method of obtaining low-viscosity menphase pitch by removing this toluene-insoluble content and subjecting it to heat treatment. However, this method is effective when using petroleum-based pitch as a raw material, but when using coal tar pitch that contains many high molecular weight components (toluene-insoluble and trobenzene-insoluble), which tend to cause polycondensation. cannot be applied. Therefore, the present applicant has proposed a method for obtaining spinnable men7ase pitch with low viscosity from coal tar or coal tar pitch by using coal tar or coal tar pitch, which is produced in large amounts as a by-product from coke ovens, as a raw material.
Previously, the following four methods have been proposed.

That is, first, coal tar pitch is extracted with a benzene solvent to extract only the component (component A) that is soluble in the benzene solvent. This is to remove nitrobenzene-insoluble components that form infusible menphase as components insoluble in benzene solvents. Next, this soluble pitch is
Heat polycondensation at a temperature of 350 to 500°C under conditions where the toluene insoluble content in the pitch is 20 wt% or more and no nitrobenzene insoluble content is generated. Next, this heated pitch is extracted with a benzene solvent, and the pitch is soluble in the benzene solvent. The component (B component) is removed to obtain a pitch with a toluene soluble content of 40 wt 96 or less, which has a slow conversion rate to mesophase, and this pitch is heat-treated at a temperature of 350 to 500°C to form a pitch with a mesophase content of 150 vol or more. Get Menphase Pitch. The obtained menphase pitch is spun, infusible, and fired to produce high modulus carbon fiber.

According to this method, as a raw material for obtaining spinnable mesophase pitch with low viscosity, pitch having a nitrobenzene insoluble content of 10 wt% or less, preferably 5 wt% or less, and a toluene soluble content of 40 wt% or less is preferable. It is said that More specifically, a component soluble in nitrobenzene and insoluble in toluene, that is, pitch having a relatively uniform molecular weight, is preferred.

However, according to the inventors' experiments, the above method:
Approximately 60 wt% of the raw material coal tar pitch is soluble pitch, and the component insoluble in benzene solvents in the pitch obtained by heating and polycondensing the soluble pitch is approximately 20 to 3%.
It became clear that he was in charge of 0wt. That is, it was found that only about 15 wt% of the raw material coal tar pitch can be used as a raw material for producing menphase pitch, and the pitch yield is extremely low.

Therefore, the present inventors conducted research on a method for preparing menphasic pitch, which is suitable for producing high-modulus carbon fibers, at a high yield using coal tar pitch as a raw material, and based on the results of various experiments, the following was discovered. I gained a lot of knowledge.

That is, a component soluble in benzene solvents (component A) is extracted and separated from coal tar pitch, and this component A is
Thermal polycondensation is carried out at a temperature of ~500°C so that the nitrobenzene insoluble content is 3 wt% or less.-1 This heated pitch is extracted with a benzene solvent to form a soluble content (component B) and an insoluble content (component C). After separation, only component B was thermally polycondensed again at a temperature of 350 to 500°C so that the nitrobenzene insoluble content was 3 wt% or less, and the resulting heated pitch was further extracted with a benzene solvent. It was found that the component insoluble in (D component), like component C, contains almost no nitrobenzene insoluble matter and has a toluene soluble component of 40 wt% or less, and is suitable as a raw material for menphase pitch.

Furthermore, when component B was mixed with component A and subjected to thermal polycondensation, it was found that the benzene solvent-insoluble content in the resulting pitch was also suitable as a raw material for menphase pitch, just like component D. Based on the above facts, the inventors of the present invention maintained the quality of high-modulus carbon fiber by returning component B, which was discarded outside the system in the conventional method, to the thermal polymerization process and recycling it. The present inventors have discovered that the yield can be improved while maintaining the same conditions, and have accomplished the present invention.

That is, the present invention extracts coal tar or coal tar pitch with a benzene solvent to extract components soluble in the benzene solvent, and extracts the soluble components from 350 to 50%.
At a temperature of 00°C, the amount of nitrobenzene insoluble matter generated is 3wt.
% or less, preferably 1 wt % or less, and then the obtained heated pitch is extracted with a benzene solvent to extract components soluble in the benzene solvent and 40 wt % or less.
The components insoluble in benzene solvents containing toluene soluble content of 35% or less are separated, and the components insoluble in benzenes are separated into
Heat-treated at a temperature of 0 to 500℃ to obtain a menphase content of 5
0% or more pitch is obtained, the pitch is melt-spun, infusible,
While producing high modulus carbon fiber by firing,
The components soluble in benzenes are returned to the thermopolycondensation step and subjected to thermoelectric condensation again, and the resulting heated pitch is
It is insoluble in benzene solvents containing toluene soluble content of 0wt1 or less.

The benzene solvent used in the present invention refers to monocyclic aromatic nonpolar solvents such as benzene, toluene, and xylene, and mixtures thereof.
- Measured according to the toluene insoluble content determination method such as tar pitch of K.2425, and the nitrobenzene insoluble content is determined by JI
Measured by using nitrobenzene in quinoline glue 9 as a solvent in the S-K 2425 tar pitch quinoline dissolved content determination method (centrifugation method).According to a series of studies by the applicant, heat treatment lowers the viscosity. The mesophase pitch that can be formed is a toluene soluble content of 40 wt or less and a nitrobenzene insoluble content of 10 wt.
% or less, preferably 5 wt% or less. Therefore, first, the raw coal tar pitch is extracted with a benzene solvent to remove the nitrobenzene-insoluble components along with the components insoluble in the benzene/benzene solvent. At this stage, substantially all of the nitrobenzene insoluble content in the coal tar pitch is removed. Next, the components soluble in base/cene solvents (
Component A) is subjected to heating polycondensation at a temperature of 350 to 500°C,
Increases toluene insoluble content in pitch.

In this case, the polycondensation must be stopped before 3 wt%, preferably 1 wt%, of nitrobenzene insolubles are formed in the pitch.
This is because the polycondensation reaction does not occur at temperatures below 350°C, while infusible coking products are formed at temperatures above 500°C.
In addition, if the nitrobenzene insoluble content in the heated pitch exceeds 3 wt%, the nitrobenzene insoluble content in the insoluble pitch prepared by extracting the heated pitch with a benzene solvent becomes 10 wt % or more. The infusible membrane phase produced from the insoluble components significantly increases the viscosity, making spinning difficult. ) is separated from components soluble in benzene solvents to obtain pitch with a toluene soluble content of 4 Qwt% or less. This separation operation involves, for example, pulverizing the heated pitch containing toluene-insoluble matter to 1 mvt or less, and mixing the pulverized pitch with at least 5 parts by volume of a minzene solvent per 1 part by weight of the pulverized pitch. After that,
This is carried out by centrifugation at a centrifugal efficiency of 1 x 1040-8 eC or higher, and separation into a clear liquid which does not substantially contain toluene-insoluble matter and a precipitate whose main component is toluene-insoluble matter. The thus obtained pitch having a toluene soluble content of 4 wt % or less is heat treated at a temperature of 350 to 500° C. 7 to prepare a pitch having a mesophase content of 5 o vol 1 or more. If the toluene soluble content exceeds 4wt%, it will take a long time to produce mesophase pitch, and the initially formed mesophase will become highly viscous and infusible, making spinning difficult. The reason for heat treatment is that if the temperature is lower than 35°C, mesophase will not be generated, and if the temperature is higher than 500°C, an infusible coking substance will be generated in the pitch, making spinning difficult. In addition, the reason why mesophase-containing pitch containing 50 vol or more of mesophase is produced from component C is that if the mesophase content is less than 50 vol, the pitch becomes slurry and spinning is difficult. .

On the other hand, according to the present invention, the benzene solvent-soluble component (B component) separated from the heated pitch is returned to the thermal polycondensation step and is again thermally polycondensed together with the A component. In this case, there is no particular limitation on the mixing ratio of component A and component B.

The mixing ratio is determined by the mass balance, and by selecting heating conditions according to the mass balance in a steady state, it is possible to manufacture a heating pitch that satisfies the above condition 3.

Component B may be separately thermally condensed while being thermally condensed in a mixed state with component A. When reheating and polymerizing component B alone, returning the amount of component B to zero can be repeated. When reheating and polymerizing after mixing components A and B, in industrial processes, when the mass balance reaches a steady state, the quality of the components (A-1-B) becomes constant, so the number of times the components are returned is There are no limits. Also, (A
+B') Since the quality of the component is constant, the energy applied in the heating polymerization process is also constant, that is, the pitch yield is also constant. At this time, as can be seen from the typical example of mass balance shown in the drawing, in the raw material subjected to the thermal polymerization process, there is a component B whose molecular weight distribution has shifted from component A to the high molecular weight side after the thermal polymerization process. %. Therefore, the pitch yield is higher than in Example 1, in which only component A is thermally polymerized. The temperature and other conditions for thermal polycondensation in the recycling are the same as above. The treatment after the thermal polycondensation can be carried out in the same manner as above, by extraction treatment with a benzene solvent, and by ordinary melt spinning at a temperature below the insoluble content, long fibers with a diameter of 15 μm or less can be obtained. The obtained 1" pitch yarn can be easily made infusible by a normal infusible method, such as heating in air. This infusible yarn can be carbonized and graphitized even after being subjected to tension treatment, resulting in 3Q It exhibits a high monomerity rate of more than 71 torb/m and a high strength of more than 200 kg/77177/m.

Next, the effects of the present invention will be illustrated by examples.

Example 1 Crude tar was distilled at a normal pressure equivalent cut point of 350°C,
Got coal tar pitch. Add this pitch to 5 times the amount of benzene, toluene, and pynodine! After extraction at 1180°C and cooling to room temperature, insoluble matter was removed by passing through a filter with a particle size of 0.5μ, and the solvent was removed by distillation to obtain three types of soluble pitch. The properties and yield of the pitch are shown in Table 1.

Table 1 When these three types of pitches were thermally polycondensed at 430℃,
Thermal polycondensation pitches with properties as shown in Table 2 were obtained. Table 2 From these results, in the case of the benzene-soluble pitch of I and the toluene-soluble pitch of Higashi, the toluene-insoluble content was reduced to 30 wt.
Even if the amount is increased to about 1%, the nitrobenzene insoluble content is still 1wt.
% whereas ff1lll of pyridine i:
As the toluene-insoluble content of iT-soluble pitch increases, the nitrobenzene-insoluble content also increases, and it is difficult to produce a pitch containing a high concentration of toluene-insoluble content and with a nitrobenzene-insoluble content of 1 wt% or less. It can be seen that the raw material of the present invention containing no insoluble matter is suitable for producing a component insoluble in toluene and soluble in nitrobenzene with good yield.

Next, the thermally polycondensed pitches shown in Table 2, No. 2 and No. 7, were extracted with 5 times the amount of benzene and heptane at 80°C, and after cooling to room temperature, P was separated using a filter with a pore size of 0.5μ, and the soluble content was extracted. and an insoluble fraction.

The insoluble matter is heat treated at 430℃ to reduce the menphase content to 75.
A vol % menphase pitch was produced and a spinning test was conducted. Soluble content is 430℃.

After thermal polycondensation for 90 minutes at 80°C with 5 times the amount of benzene
It was extracted with water, cooled to room temperature, filtered through a filter with a pore size of 0.5μ to remove the soluble content, and the insoluble content was heat-treated at 430°C to produce mesophase pitch with a mesophase content of 75 vol 1%. The yield, properties, and results of the spinning test for each pitch were reported in the third
Shown in the table.

This result shows that mesophase pitch with good spinnability can be obtained by heat-treating the benzene-insoluble content in thermal polycondensation pitch.
I can understand that. In addition, it can be seen that the benzene-insoluble content in the pitch obtained by thermal lightning condensation of the benzene-soluble content in the thermally polycondensed pitch can also be turned into mesophase pitch with good spinnability by heat treatment. By returning the fraction to the thermal polycondensation process and recycling it, the conventional method could use only a small amount of pitch, and the yield was about 22 wt % based on the coal tar pitch, but the method of the present invention uses only a small amount of pitch. You can also use the pitch of about 63w.
It is also seen that the yield can be improved to t%/coal tar pitch.

Here, the pitches of Arashi ■, ■, and No also show good spinnability, but all have the disadvantage of low yields.Example 2 ■, ■, A 2:1 mixture of Menphase pitch (1) and (2) was melt-spun at 360°C to obtain a pitch yarn with a diameter of 15μ. These pitch yarns were heated to 280° C. in air at a rate of 0.5° C./min and then held for 30 minutes to make them infusible.

Next, these infusible yarns were heated to 1000°C in Ar at a heating rate of 1°C/min, and then held for 5 minutes to carbonize them.
The temperature was raised to 2000° C. for 5 minutes and then maintained for 5 minutes to graphitize.

Table 4 shows the physical properties of the obtained carbon fiber.

From Table 4, it can be seen that carbon fibers with high elastic modulus and strength can be produced by the method of this invention.

As is clear from the above, the present invention can achieve high quality by simply adding an extremely simple process of recycling the benzene solvent-soluble components of thermal polycondensation pitch by returning them to the thermal polycondensation process. Elastic carbon fibers can be produced at a high yield, that is, about three times as much as the conventional technology.

[Brief explanation of drawings]

The drawings are explanatory diagrams showing a processing process according to an embodiment of the present invention.

Claims (1)

[Claims] (1) Extract the components soluble in the benzene solvent by extracting with coal tar or coal tar pitch solvent, and heat the soluble components at a temperature of 350 to 500°C to generate nitrobenzene insoluble components. After thermal polycondensation under conditions such that the amount is 3 wt% or less, the resulting heated pitch is extracted with a benzene solvent to contain components soluble in benzene solvents and toluene soluble components of 40 wt% or less. A pitch with a mesophase content of 50 volqb or more is obtained by separating the benzene-based solvent-insoluble components and heat-treating the benzene-insoluble components at a temperature of 350 to 500°C.
While producing high elastic carbon fiber by melt-spinning, infusible, and firing the pinch, the components soluble in benzenes are returned to the thermal polycondensation process and subjected to thermal polycondensation again,
A method for producing high modulus carbon fibers, characterized in that the heated pitch obtained is used to obtain a component insoluble in benzene solvents containing a toluene soluble content of 40wt4 or less.