JPS617386A - Pitch for making carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:A pitch as a starting material for producing carbon fibers of high strength and elasticity is obtained by heat-treating a specific heavy fraction of petroleum so that optically anisotropy does not develop, centrifuging solid or semisolid fractions, further separating into 2 phases and collecting the heavier fraction. CONSTITUTION:A petroleum heavy fraction which boils over 430 deg.C and contains less than 1.0wt% of S, less than 0.1ppm of Ni and V and less than 0.1wt% of asphalten is heat-treated in a non-oxidative atmosphere at 420-460 deg.C for 30min to 5hr so that optical anisotropy does not develop. Then, centrifugation is conducted in a non-oxidative atmosphere at 250-300 deg.C with 200-2,000G to remove solid or semisolid in the product. Further, the product is subjected to separation into 2 phases by effecting centrifugation with acceleration of 200-2,000G at 370-400 deg.C under 0.1-1.0Torr and the heavier fraction is collected as the objective pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a raw material pitch suitable for producing high-performance carbon fibers and a method for producing the same.

Many methods for manufacturing carbon II using pitch as a raw material have been disclosed for a long time, and many methods for manufacturing high-performance carbon fibers having high strength and high modulus of elasticity have also been disclosed. In order to produce such high-performance carbon fibers, the properties of the raw material pitch are extremely important, but since pitch is a mixture of molecules with large molecular weights, there are few analytical methods that can directly measure its properties. It was gllm to globally and directly define the nature of pitch. For example, JP-A-49-19127 is characterized in that pitch containing 40 to 90% by weight of mesophase is used as the raw material pitch. In this case, the mesophase is defined as one whose optical anisotropy is observed using a polarizing microscope and which is insoluble in quinoline or pyridine at 75°C. The patent states that carbon fibers are obtained by spinning and firing such pitch at a temperature that is non-thixotropic, but it is quite difficult to spin pitch containing 40% by weight or more of quinoline insoluble matter. It is expected that. In order to industrially produce high-performance carbon Alt11, the spinning process is extremely important, and the raw material pitch is also required to have good spinnability. JP-A-54-55625 discloses that the raw material pitch consists essentially of 100% mesophase, is suitable for spinning into continuous filaments, has an average molecular weight of 1000 or less, and contains a net pyridine insoluble content of no more than 60% by weight. It is disclosed to use a pitch of In this case, the mesophase is defined as a pitch sample that is embedded in epoxy resin, polished, and inspected with a polarizing microscope using an orthogonal polarizer, and found to be optically anisotropic. do not match.Unexamined Japanese Patent Publication No. 1973-
No. 160,427 discloses a method for producing raw pitch suitable for producing carbon products, in particular carbon IN. This raw material pitch is defined as neomesophase pitch, and although this pitch is highly oriented and optically anisotropic, it is said to be substantially soluble in pyridine and quinoline. JP-A-57-100186 discloses latent anisotropic pitch as a raw material pitch with good spinnability as a raw material for carbon fibers. This pitch substantially contains a quinoline-soluble polycyclic polyskeleton hydrocarbon as a potential anisotropy-forming component, and in the dissolved state substantially does not form mesophase, and is entirely homogeneous and optically isotropic. It is said that when a single phase is formed and an external force is applied, no orientation is exhibited in that direction. Furthermore, Japanese Patent Application Laid-Open No. 58-18421 discloses the use of brimesophase as a raw material for carbon fibers. This pre-mesoface pitch is optically isotropic and is soluble in quinoline, making it possible to produce carbon fibers with excellent spinnability and properties comparable to PAN-based carbon fibers. Looking at the patents that have already been disclosed, we can see that at a relatively early stage, it was possible to produce high-performance carbon fiber using pitch containing a large amount of optically anisotropic components that are insoluble in solvents, such as quinoline and pyridine. However, since the quality of spinnability is an extremely important factor in the performance of carbon fibers, the content of components insoluble in quinoline and pyridine gradually shifted to products with a low content of components insoluble in quinoline and pyridine. This is changing to the point where optically isotropic pitch is used as a raw material instead of containing pitch. That is, pitch, which is a raw material for high-performance carbon fibers, is not determined simply by the presence or absence of an optically anisotropic phase or the amount of components insoluble in solvents such as quinoline. As a result of our research on raw material pitch for producing high-strength, high-modulus carbon fibers, it became clear that the raw material pitch must satisfy at least the following conditions.

1) Molecular alignment parallel to the fiber axis is created in the fiber during spinning or firing. 2) It is homogeneous and can be spun smoothly. 3) It does not cause fusion during infusibility. 4) The fiber There shall be no defects such as cracks or holes.

The present invention was achieved through research to produce a raw material pitch that satisfies these conditions. i.e. temperature 25℃
We have discovered that it is possible to produce high-performance carbon fiber by using a raw material pitch with a specific gravity of 1.290 to 1.330 and a dielectric constant of 2.9 to 3.2 at a temperature of 25°C. A method for producing raw material pitch having such properties has been discovered. As mentioned above, in order to produce high-strength, high-modulus carbon fibers, there are necessary conditions at each stage from spinning to firing, and some of these conditions have contradictory tendencies. Therefore, the properties of the pitch that satisfy these conditions must be extremely limited. First of all, if we convert the first condition, which is that molecular alignment parallel to the fiber axis is formed in the fiber during spinning or firing, to the structure of pitch, it is necessary to have a relatively large molecular structure to form molecular alignment, and spinning It is preferable that carbon atoms are arranged in process steps such as carbon fibers, etc., and that the arranged carbon atoms easily form a graphite structure as they are in the final carbon fiber stage. In other words, it contains a large amount of a compound having an aromatic ring with a relatively large molecular weight. The second condition, which is homogeneity and allows smooth spinning, is related to the fact that the content of impurities in the bit is small, the molecular weight distribution is relatively narrow, and the molecular weight is not very large. . The first condition and the second condition tend to contradict each other.The third condition, which is not to fuse during infusibility, requires relatively large molecules to avoid deformation at the infusibility temperature. It is necessary for carbon fibers to have the same structure as possible, and in the oxidative infusibility that is commonly used in the production of carbon fibers, it is necessary to minimize the content of saturated hydrocarbon compounds that have a relatively small molecular weight and are difficult to oxidize. In terms of the fourth condition, which is that fibers do not have defects such as cracks and holes, cracks are related to the molecular structure that is common to the first condition.
The defects are related to the same molecular structure as the second condition. We actually manufactured carbon fibers using various pitches and researched the relationship between pitch properties and found that preferred pitches contain aromatic ring compounds and have a relatively large molecular weight, so the dielectric constant is within a certain range. It has become clear that the value of Generally, when pitch is manufactured from the same raw material, as the heat treatment conditions become more severe, the aromatic compound content increases and the dielectric constant becomes higher. However, when excessive heat treatment is performed, the dielectric constant of the pitch decreases. Therefore, the dielectric constant of the preferred pitch is 2.
It will be limited to a narrow range of 9 to 3.2. In this way, the preferred pitch is determined by the dielectric constant, but the dielectric constant alone is insufficient to define properties related to molecular weight distribution, etc., and in that respect, in addition to the dielectric constant, the specific gravity is also limited to a limited range. It is necessary that there be. This is specific gravity 1
．． It ranges from 290 to 1.330. Currently, there is a lack of means to directly analyze the properties of pitch, both physically and chemically. Up until now, the method used for carbon fiber original pitch has been to measure the properties of one part rather than the whole, and to estimate and define the whole from this, but this method is incomplete. In the present invention, we investigated the relationship between the pitch and carbon region M properties from the properties of the pitch, such as relative permittivity and specific gravity, which represent the entire pitch, and found a raw material pitch suitable for producing high strength, high modulus carbon l1tIi. It is something that The manufacturing method is not particularly limited as long as it is possible to satisfy predetermined properties as the raw material pitch for carbon fibers, but preferred manufacturing methods include the following method. That is, it is a petroleum heavy fraction with a boiling point of 430°C or higher, a sulfur content of 1.0% by weight or less, and a N1 content of 10. l
Under p++JX, raw materials having properties of V content of 0.1 ppn+ or less and asphaltene content of 0.1% by weight or less are heated at a temperature of 420 to 420 without blowing gas in a non-oxidizing atmosphere and without reducing, pressurizing or pressurizing. Heat treatment is performed under conditions of 460''C1 heating time ranging from 30 minutes to 5 hours.

At this time, reflux is actively carried out to suppress as much as possible the low-boiling fraction generated during the heat treatment from exiting the system. Further, the heating temperature and heating time are set within a range such that no optically anisotropic phase such as menphasis is observed in the heated product when observed under a reflective polarizing microscope at room temperature (orthogonal lens, magnification: 200 times) at the end of heating.

The heat-treated product obtained in this way is centrifuged in a non-oxidizing atmosphere at a temperature of 250 to 300°C and a centrifugal effect of 200 to 2000G. Separate and remove substances that exist in the form of This centrifuged and heated product is further subjected to two-phase separation in a second-stage centrifugal separator under a vacuum of 0.1 to 1.0 Torr at a temperature of 370 to 400°C and a centrifugal effect of 100 to 2000 G. The resulting heavy liquid is used as raw material pitch for carbon fibers. The properties of the carbon fiber raw material pitch obtained in this way have a specific gravity of 1.2 at 25°C.
90~1, relative dielectric constant at 330.25℃ is 2.9
-3.2, more preferably the value obtained by subtracting the quinoline insoluble content from the toluene insoluble content is 65 to 80% by weight, and even more preferably the heptane soluble content. is 1.0% by weight or less, which is suitable as a raw material pitch for high-performance carbon fiber.

Here, the density of the raw material pitch is measured by the Barbard pycnometer specific gravity measurement method in JIS K2425.

Further, the dielectric constant is measured by the method specified in ASTM D-150. The quinoline-insoluble content and toluene-insoluble content are measured by the method specified in JIS K2425. For the heptane soluble content, 5 g of ground pitch was mixed with an average pore size of 1
The soluble components obtained by placing the sample in a μ cylindrical Hilter and performing heat extraction with n-heptane for 20 hours using a Soxhlet extractor are weighed after removing the solvent.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Atmospheric distillation residue of Middle Eastern crude oil was distilled under reduced pressure to boiling point 300-5
The atmospheric distillation fraction collected at 50°C was heated to 370°C and a pressure of J 60 in the presence of a cobalt-molybdenum catalyst.
Hydrogenation was carried out under the conditions of K9/crA G, liquid hourly space velocity of 1.9, and hydrogen/oil ratio of 36 ONTd/h, and the temperature was 500°C and the pressure was 1.59/h using a zeolite catalyst.
A catalytic cracking reaction was carried out using cIllG and Catalyst Oilification 9.

The heavy oil remaining after the catalytic cracking reaction is distilled to a boiling point of 430
The heavy fraction above ℃ was collected.

This heavy fraction has a sulfur content of 0.95% by weight, an N1 content of 0.021)Ill, a V content of 0. O5pp
It had the following properties: 10.02% by weight of asfultin. Next, this heavy fraction was heat-treated under normal pressure at a heating temperature of 435° C. for a heating time of 2.5 hours without the intrusion of air. At this time, 10 parts of the reactor are cooled and reflux is applied within a range where the heating temperature can be maintained to prevent the low boiling point fraction from exiting the system. This heated product was embedded in polyester resin and polished, and then examined using a reflective polarization microscope to obtain orthogonal lenses.
When observed at a magnification of 200 times, no optically anisotropic phase was observed. This heated product was centrifuged at a temperature of 280° C. and a centrifugal effect of 1200 G to remove solid substances at this temperature. The heat-treated product obtained in this way is further passed through a second stage centrifugal separator.
．． 2iorr vacuum temperature 390℃, centrifugal effect 1000℃
Two-phase centrifugation was performed at G, and the heavy liquid was collected to obtain raw material pitch for carbon fibers. The properties of this raw material pitch for carbon fiber are: specific gravity at 25°C: 1.314; dielectric constant at 25°C: 3.0
The value obtained by subtracting the quinoline insoluble content from the toluene insoluble content was 70% by weight, and the heptane soluble content was 0.5% by weight. This raw material pitch for carbon fiber is passed through a nozzle with a diameter of 0.5 m.
Using a φ spinning nozzle, spinning was carried out at a spinning humidity of 365°C, a winding speed of 500 m/min, and a fiber diameter of 13 μm.
It was possible to spin the yarn for more than a minute without breaking the yarn. The pitch fibers were made infusible at 300° C. in an air atmosphere, and then carbonized by raising the temperature to 1000° C. in an inert gas atmosphere to obtain carbon fibers.

A tensile test was performed on this carbon fiber in accordance with the carbon fiber tensile test method specified in JIS R-7601 in order of 25 gauge lengths, and the average of 20 samples was 10.2μ in diameter and 22゜2T in tensile strength. /cti,
The elastic modulus was 1230 T/cat and the elongation at break was 1°8%.

Comparative Example 1 The same heavy fraction as used in Example 1 was heat-treated under normal pressure at a heating temperature of 435°C and a heating time of 2.5 hours without the intrusion of air. This heat-treated material was heated to a pressure of 1.2T.
Pitch was obtained by vacuum distillation at a temperature of 410° C. above vacuum. The properties of this pitch are that the specific gravity at 25°C is 1.321.
The dielectric constant at 25°C was 2.8. The value obtained by subtracting the quinoline insoluble content from the toluene insoluble content was 52% by weight and the heptane soluble content was 2.0% by weight. Example 1 of this pitch
When spinning was performed using the same spinning nozzle as above at a spinning temperature FI of 267° C., yarn breakage was severe at a fiber diameter of 15 μm, and spinning was difficult. This pitch fiber was fired under the same conditions as in Example 1, and a tensile test was conducted to find a diameter of 12.0 μm and a tensile strength r of 1112.2 T/cd.

The elastic modulus was 980T/Q11 and the elongation at break was 1.2%.

Comparative Example 2 The same heavy fraction as used in Example 1 was heat-treated under normal pressure, heating mli/120° C., and heating time for 6 hours without the intrusion of air. This heat-treated material was heated to a pressure of 1.2T.
Pitch was obtained by vacuum distillation at a temperature of 410° C. above vacuum. The bamboo-like shape of this pitch has a specific gravity of 1.301 at 25°C.
Ratio at 25℃! ! ! The value obtained by subtracting the value of the quinoline insoluble content from the value of the quinoline insoluble content is 82% by weight,
The heptane soluble content was 2.6% by weight. When this pitch was spun at a spinning temperature of 360° C. using the same spinning nozzle as in Example 1, spinning was possible with a fiber diameter of 13 μm and yarn breakage of about 11 every 3 minutes. When this pitch fiber was fired under the same conditions as in Example 1 and subjected to a tensile test, the diameter was 1.
0.5μ. Tensile strength 11.47/d1 Elastic modulus 970T
/cd, and the elongation at break was 1.2%.

that's all

Claims (1)

[Claims] 1. Carbon fiber raw material pitch temperature 25 having the following properties:
Specific gravity at 1.290-1.330 °C, relative permittivity at 25 °C 2.9-3.2 2 In claim 1, the value obtained by subtracting the quinoline-insoluble content from the toluene-insoluble content is 65-80. weight%
Carbon fiber raw material pitch 3 characterized by having a heptane soluble content of 1.0% by weight or less in claim 1 Carbon fiber raw material pitch 4 characterized by having a heptane soluble content of 1.0% by weight or less Petroleum-based weight having a boiling point of 430°C or higher A raw material having a quality fraction of sulfur content of 1.0% by weight or less, Ni content of 0.1ppm or less, V content of 0.1ppm or less, and asphaltene content of 0.1% by weight or less is prepared in a non-oxidizing atmosphere. The heat treatment is carried out under conditions of a heating temperature of 420 to 460° C. and a heating time of 30 minutes to 5 hours without blowing gas or reducing or increasing pressure. In this heat treatment, reflux is applied to suppress the low boiling point fraction generated during the heat treatment from exiting the system. The conditions for the heat treatment are such that at the end of the heat treatment, no optically anisotropic phase is observed in the heat treated product when observed under a reflective polarizing microscope at room temperature (orthogonal lens, 200x magnification). The obtained heat-treated product was heated in a non-oxidizing atmosphere at a temperature of 250°C to 300°C and a centrifugal effect of 200 to 20°C.
Centrifugation is performed under conditions in the range of 00G to separate and remove substances present in the solid or semi-solid state in the heat-treated product in this temperature range. This centrifuged and heated product is further transferred to a second stage centrifuge under a vacuum of 0.1 to 1.0 Torr at a temperature of 3.
A method for producing raw material pitch for carbon fibers having the properties of claim 1 obtained by performing two-phase separation at 70 to 400°C and a centrifugal effect of 100 to 2000 G and collecting a heavy liquid.