JP2520099B2 - Carbon fiber pitch manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a pitch for carbon fiber, and more particularly to a method for efficiently producing a pitch suitable for producing a high-strength pitch-based carbon fiber.

[Problems to be Solved by Conventional Techniques and Inventions] Carbon fibers, which are known as composite materials of plastics and metals, have been manufactured by firing polyacrylonitrile fibers conventionally, but the raw materials are expensive. However, there is a problem that the carbonization yield during firing is low. Therefore, in recent years, many methods for producing carbon fibers using pitch as a raw material have been proposed (JP-A-57-141488, JP-A-58-196293, JP-A-58-142976, JP-A-58-142976, 58-164687,
JP-A-63-196721).

However, JP-A-57-141488 and JP-A-58-19
In the method described in Japanese Patent No. 6293, the boiling point is 150 to 500.
Since a fraction having a relatively low boiling point of ℃ and a relatively low boiling point is used as a raw material, it takes a long time to carry out the heaviening reaction, and the resulting molecular weight distribution of the pitch is broad, so that a high strength fiber cannot be obtained.

Further, in the method described in JP-A-58-142976, a relatively high-boiling fraction having a boiling point of 540 ° C. or higher is used, but a vacuum distillation residue is used. Contaminants may remain. Further, the molecular weight distribution spreads toward the high molecular weight side, which may impair the high strength fiber and the spinnability.

Further, the methods described in JP-A-58-164687 and JP-A-63-196721, once generate a mesophase,
This is a method of separating a non-meso phase portion using a density difference or the like and using it as a carbon material, and there is a problem that the separation of the non-meso phase portion is complicated, the separation performance is poor, and the economy is poor.

An object of the present invention is to solve such conventional problems, and to provide a method for efficiently producing a pitch which is suitable for producing a carbon fiber having high strength and high elongation and is excellent in spinnability. Is.

[Means for Solving the Problems] That is, the present invention has a number-average molecular weight of 300 to 500, a weight-average molecular weight / number-average molecular weight of 1.5 to 2.2, as a raw material pitch.
Boiling point is 450 ℃ or higher, 800 at a heating rate of 10 ℃ / min in nitrogen gas
The residual content when heated to ℃ is 5% by weight or less, and 95% by volume of dichloromethane and 5% by volume of methyl alcohol.
The first stage heat treatment was performed at a temperature of 380 to 500 ° C and a pressure of 1 to 1500 mmHg, and then the second stage heat treatment was performed at a temperature of 450 to It is intended to provide a method for producing a pitch for carbon fiber, which is characterized in that it is carried out at 550 ° C. and a pressure of 0.1 coarse 20 mmHg.

As described above, the present invention is characterized by using a specific raw material pitch and performing a two-step heat treatment.

Here, the raw material pitch is number average molecular weight (VPO measurement)
Is 300 to 500, preferably 350 to 480, and the weight average molecular weight (Mw) and the number average molecular weight (Mn) (GPC measurement) are Mw / Mn.
= 1.5 to 2.2, preferably 1.5 to 2.0 is used. The maximum molecular weight is preferably 1500 or less. Homogeneity is lost when the maximum molecular weight exceeds 1500.

As the raw material pitch, one having a boiling point of 450 ° C. or higher measured according to ASTM D 1160 is used. Boiling point 4
If the temperature is lower than 50 ° C, the yield is lowered, which is not preferable.

Furthermore, when the temperature is raised to 800 ° C. at a heating rate of 10 minutes per minute (10 ° C./minute) in nitrogen gas using a thermobalance analyzer (TGA), the residual content is 5% by weight or less, preferably 4.5 to 0.5. Weight% of the material is used as the raw material pitch. Here, a large amount of the above-mentioned residue means that it contains a large amount of a high-molecular-weight substance or a component that easily forms a high-molecular-weight substance upon heat treatment, and if this residual amount exceeds 5% by weight,
It is not preferable because the homogeneity of the spun fiber is lost and the strength is lowered.

As the raw material pitch, a thin layer chromatograph / hydrogen flame ionization detector (TLC-FID) was used, and the peak area at the origin developed on a silica gel thin layer with a mixed solvent of 95% by volume of dichloromethane and 5% by volume of methyl alcohol was measured. 1%
Use the following. Here, if the peak area at the origin exceeds 1%, the content of foreign substances such as high molecular weight substances is large, the homogeneity of the fibers is lost, and the strength is lowered, which is not preferable.

This TLC-FID method is outlined. This test method specifies a method for determining saturated components, aromatic components, resins and asphaltene in hydrocarbons of heavy oil with an initial boiling point of 200 ° C or higher. First, a sample diluted with an appropriate solvent was spotted on the base point of the activated silica gel thin-layer rod, and this thin-layer rod was changed to a development tank (first tank: n-hexane, second tank). : n-hexane 20% by volume and toluene 80% by volume, the third tank: dichloromethane 95% by volume and methyl alcohol 5% by volume) were sequentially developed to separate saturated components, aromatic components, and resin in this order, and spot residue, That is, the peak that appears at the origin is asphaltene. Next, after the solvent is removed by drying, the spot is detected by a spot detector, and the spot is detected under prescribed conditions. The area percentage of each component is calculated from the height of the integral curve drawn simultaneously with the chromatogram.

The raw material pitch used in the method of the present invention may basically have all the above conditions, but the softening point is 50 to 150 ° C., Si and Al are each 3 ppm or less, and the aromatic index. It is preferable that (fa) is 0.75 or more, n-heptane insoluble matter is 25 to 80% by weight, and toluene insoluble matter is close to 0% by weight.

Such a raw material pitch is obtained by distilling a petroleum-based residual oil having a high aromatic hydrocarbon content such as a catalytic cracking residual oil of petroleum and a thermal cracking residual oil of naphtha under a reduced pressure to obtain a fraction having a boiling point of about 400 ° C or higher. After removing the obtained pitch by extraction with a mixed solvent of toluene and hexane, or by supercritical extraction to remove heavy components, or in a batch reactor at 380 ~ 500 ℃, 1 ~ 500mmHg It can be obtained by reacting for 0.05 to 30 hours and recovering a relatively heavy cracked oil generated in the latter stage of the reaction. Furthermore, using a continuous two-stage reactor, 380 ~ 500 ℃ in the first stage reactor, after reacting for 0.5 to 10 hours at atmospheric pressure or less, 420 ~ 550 ℃ in the second stage reactor, 0.05 at 20mmHg or less. A pitch composed of cracked oil obtained by reacting for 6 hours can be used.

In the present invention, the above-mentioned raw material pitch is heat treated in two stages.

The first stage heat treatment is temperature 380 ~ 500 ℃, pressure 1 ~ 1500mmH
g, heat treatment time 0.1 to 10 hours, preferably temperature 390 to 480
℃, pressure 5mmHg-atmospheric pressure, heat treatment time 0.2-8 hours, no optically anisotropic phase (mesophase) is formed, and toluene insoluble content becomes 5 to 35% by weight. Is desirable. If the temperature of the first-stage heat treatment is lower than 380 ° C, the reaction is slow and the heat treatment requires a long time. On the other hand, if it exceeds 500 ° C, the amount of volatile components removed increases and the yield decreases, causing coking. In addition, a high molecular weight product is generated, which is not preferable. If the pressure of the first-stage heat treatment is less than 1 mmHg, the amount of volatile components removed increases and the yield decreases.
If it exceeds, the removal of light components becomes insufficient and the molecular weight distribution becomes broad, which is not preferable.

Next, the isotropic pitch obtained by making the structure heavy by the first-stage heat treatment in this manner is subjected to the second-stage heat treatment to form a mesophase pitch.

This second-stage heat treatment is performed at an isotropic pitch (which may contain a slight amount of mesophase pitch) under stricter conditions than the first-stage heat treatment, at a temperature of 450 to 550 ° C.
The pressure is 0.1 to 20 mmHg, the heat treatment time is 0.2 to 30 minutes, preferably the temperature is 460 to 500 ° C., the pressure is 0.1 to 10 mmHg, and the heat treatment time is 1 to 20 minutes. 90% or more, preferably 95 to 100% mesophase pitch Make a change. Where the temperature of the second stage heat treatment is
If the temperature is lower than 450 ° C, it will be difficult to remove light components and the heat treatment time will be long, while if it exceeds 550 ° C, the yield will decrease.
It is not preferable because coking occurs and it becomes difficult to control the reaction rate. Further, if the pressure of the second-stage heat treatment is less than 0.1 mmHg, the yield will be reduced and the vacuum apparatus will be large-scaled.

In this way, the mesophase pitch content is 90% or more, the quinoline insoluble content is 5 to 50% by weight, and the toluene insoluble content is
60-95% by weight, softening point 280-380 ℃, number average molecular weight 90
0 to 1200, and weight average molecular weight / number average molecular weight of 1.3 to
A carbon fiber pitch of 1.8 can be produced.

In order to produce a pitch-based carbon fiber from the pitch obtained in this way, by a conventional method, first, this pitch is spun,
Next, infusibilization treatment may be performed, and further firing (carbonization, graphitization) may be performed.

[Examples] Next, the present invention will be described with reference to Examples.

Example 1 The catalytically cracked residual oil of petroleum was distilled under reduced pressure to remove the fraction at 466 ° C. or higher to obtain pitch. This pitch was extracted with a mixed solvent of toluene: n-hexane = 7: 3 to remove heavy components, and the solvent was dried to be used as the raw material pitch.
The properties of this raw material pitch were as follows. The measuring method is the same as described below.

(1) Number average molecular weight: 440 (VPO measurement) (2) Weight average molecular weight / number average molecular weight = 1.77 (GPC measurement) (3) Maximum molecular weight: 1420 (4) Distillation property (based on ASTM D 1160) Initial boiling point 5% 10% 20% 30% 40% 50% 466 ° C 480 ° C 491 ° C 504 ° C 520 ° C 537 ° C 559 ° C (5) Use TGA to raise the temperature to 800 ° C in nitrogen gas at a rate of 10 ° C / min. Residue when heated: 4.3% by weight (6) TLC-FID (developed into a silica gel thin layer with a mixed solvent of 95% by volume of dichloromethane and 5% by volume of methyl alcohol)
Peak area at the origin in the analysis: 0.8% (7) Softening point: 105 ° C (8) fa: 0.789 (9) n-Heptane insoluble matter: 65 wt% (10) Toluene insoluble matter: 0 wt% (11) Si : 1ppm or less (12) Al: 1ppm or less The raw material pitch having the above properties is subjected to a first stage heat treatment of holding at 420 ° C and 10mmHg for 1 hour to make it heavy, with a toluene insoluble content of 17.0% by weight and a softening point of 183 ° C. A mesophase precursor pitch, which was present and was substantially free of mesophase, was obtained.

Subsequently, the precursor pitch was subjected to a second stage heat treatment at 460 ° C. and 1 mmHg for 15 minutes to obtain 100% mesophase pitch having a quinoline insoluble content of 34.5% by weight and a softening point of 330 ° C. The properties of this mesophase pitch are as follows: toluene insoluble content 89% by weight, number average molecular weight 11
The value of 30, weight average molecular weight / number average molecular weight was 1.57.

40% of the obtained 100% mesophase pitch with a nozzle having an inner diameter of 0.2 mm
Spinning was performed at a take-up speed of 0 m / min to obtain pitch fibers having a warp of 11 μm.

This pitch fiber is heated in air from 200 ℃ to 360
The temperature was raised to ℃ and kept at 360 ℃ for 10 minutes to infusibilize. Next, it was carbonized by holding it at 1500 ° C. for 5 minutes. Furthermore, it was graphitized at 2400 ℃ for 5 minutes. The tensile strength and tensile elastic modulus of the obtained carbon fiber were as follows.

Example 2 Catalytic cracking residual oil of petroleum was heated in a batch reactor at a heating rate of 2 ° C./min, and finally reacted at 420 ° C. and 2 mmHg for 1 hour to produce a mesophase pitch.

At this time, a relatively heavy fraction generated in the latter stage of the reaction was recovered and used as a raw material pitch. The properties of this raw material pitch were as follows.

(1) Number average molecular weight: 380 (2) Weight average molecular weight / number average molecular weight = 1.92 (3) Maximum molecular weight: 1030 (4) Distillation property %%%%%%%% Initial boiling point 10 20 30 40 50 60 70 ℃ ℃ ℃ ℃ ℃ ℃ ℃ 453 487 495 505 517 532 548 568 (5) Residue when heated to 800 ℃ in nitrogen gas using TGA at a heating rate of 10 ℃ / min: 3.2 wt% ( 6) Peak area at the origin in TLC-FID analysis: 0.3
% (7) Softening point: 73 ° C (8) fa: 0.75 (9) Insoluble matter in n-heptane: 32% by weight (10) Insoluble matter in toluene: 0% by weight (11) Si: 2ppm (12) Al: 1ppm or less The raw material pitch having the above properties was held at 400 ° C. and 40 mmHg for 4 hours to perform the first stage heat treatment. At this time, the toluene insoluble content was 20.3% by weight and the softening point was 152 ° C.

Then, the quinoline insoluble matter was 25.5% by weight and the softening point was 322 ° C.
A mesophase pitch was obtained. The properties of this mesophase pitch were as follows: toluene insoluble content 78% by weight, number average molecular weight 1070, weight average molecular weight / number average molecular weight 1.67.

The obtained 100% mesophase pitch was spun, infusibilized and fired in the same manner as in Example 1 to obtain a carbonized fiber. The tensile strength and tensile elastic modulus of the obtained carbon fiber were as follows.

As described above, in both Examples 1 and 2, the carbonized products at 1500 ° C. had a large strength relative to the tensile elastic modulus, so that the elongation was as large as about 2%. The graphitized product at 2400 ° C also had a large tensile modulus. From this result, according to the present invention, high strength,
It is clear that carbon fibers with high elasticity and high elongation can be obtained.

Comparative Example 1 The catalytic cracking residual oil of petroleum was distilled under reduced pressure in the same manner as in Example 1,
Fractions above 455 ° C were removed to obtain residual pitch. The properties of this pitch were as follows.

(1) Number average molecular weight: 420 (2) Weight average molecular weight / number average molecular weight = 2.36 (3) Maximum molecular weight: 2500 (4) Distillation property %%%%%%%% Initial boiling point 5 10 20 30 40 50 60 ℃ ℃ ℃ ℃ ℃ ℃ ℃ 455 ℃ 503 508 517 527 540 553 573 (5) Residue when heated to 800 ℃ in nitrogen gas using TGA at a heating rate of 10 ℃ / min: 11 wt% ( 6) Peak area at the origin in TLC-FID analysis: 2.3
% (7) Softening point: 104 ° C (8) fa: 0.779 (9) n-heptane insoluble matter: 63 wt% (10) Toluene insoluble matter: 1.3 wt% (11) Si: 2ppm (12) Al: 1ppm or less The raw material pitch having the above properties is 4.5 at 10 ℃ and 420 ℃.
A first-stage heat treatment for holding for a time was carried out to obtain a mesophase precursor pitch having a toluene insoluble content of 16.3% by weight, a softening point of 181 ° C. and substantially not containing a mesophase.

Then, the precursor pitch was subjected to a second stage heat treatment under the same conditions as in Example 1 to obtain 100% mesophase pitch having a quinoline insoluble content of 36.3% by weight and a softening point of 335 ° C. What is the nature of this mesophase pitch? Toluene insoluble content 68% by weight, number average molecular weight 11
50, and the value of weight average molecular weight / number average molecular weight was 1.83.

The obtained 100% mesophase pitch was spun, infusibilized and fired in the same manner as in Example 1 to obtain a carbon fiber. The tensile strength and tensile elastic modulus of the obtained carbon fiber were as follows.

According to the method of the present invention, the tensile strength after firing is 400 kg / mm.
^It is possible to obtain a carbon fiber pitch capable of producing a carbon fiber having a high strength of ² or more.

In addition, this carbon fiber has a high elongation and has excellent performance overcoming the brittleness which was a difficulty of the carbon fiber using the raw material pitch obtained by the conventional method.

Moreover, in the method of the present invention, it is not necessary to perform the separation operation of the mesophase pitch and the isotropic pitch, and since the second stage heat treatment is performed under severe conditions, the softening point of the pitch is relatively high,
Manufacturing efficiency is high, such as shortening the infusibilization time.

Furthermore, the pitch obtained by the method of the present invention has a narrow molecular weight distribution, is homogeneous, and has good fluidity. Therefore, it is possible to produce a high-strength fiber with good spinnability.

Claims (1)

(57) [Claims] 1. A raw material pitch having a number average molecular weight of 300 to 5
00, weight average molecular weight / number average molecular weight 1.5 to 2.2, boiling point 45
Silica gel with a residual solvent of 5% by weight or less when heated to 800 ° C at a heating rate of 0 ° C or higher in nitrogen gas at 10 ° C / min, and a mixed solvent of 95% by volume of dichloromethane and 5% by volume of methyl alcohol. The first-stage heat treatment was performed at a temperature of 380 using a thin layer with a peak area of 1% or less at the origin.
A method for producing a pitch for carbon fibers, characterized in that the second stage heat treatment is carried out at a temperature of 450 to 55 ° C. and a pressure of 0.1 to 20 mmHg at ˜500 ° C. and a pressure of 1 to 1500 mmHg.