JPH0247190A - Manufacture of anisotropic pitch for carbon fiber - Google Patents

Abstract

PURPOSE: To provide a high anisotropic intermediate product for manufacturing carbon fiber, by injecting oxygen containing gas into coal tar pitch and by heating solvable pitch fraction under a specific condition.

CONSTITUTION: Gas which contains oxygen of 1-10×10^-3kg per hour for 1kg of pitch, preferably air, is injected into a coal tar pitch at temperature 330-400°C for 8-12 hours. After pitch fraction is extracted with pitch solvent, the solvent is separated with evaporation, and solvable pitch fraction is heated at 1-50k/min. of heating rate, under pressure of 0.5-50mbar, and to 400-480°C. Then, by keeping the final temperature for 50min., the aimed anisotropic pitch is provided. The coal tar pitch is residual products from evaporation process of high temperature coal tar, preferably that having softening point of about 70°C (by Kraemer- Sarnow method).

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION The subject of the invention is a process for the production of highly anisotropic intermediates for carbon fibers from coal tar pitch.

The production of carbon fibers from coal tar pitch is known per se. Fibers made therefrom were expected to be made at very low costs compared to those from polyacrylonitrile due to lower raw material costs and higher yields. However, from the isotropic pitch, 1%
It is not possible to produce high tensile strength carbon fibers, such as those from polyacrylonitrile, with a tensile strength greater than 2 GPa at higher elongations at break. For that purpose, only anisotropic pitches are suitable. For this reason, there is a strong research effort worldwide to develop such pitches.

Such a pitch has a macroplanar azimuthal arrangement of aromatic molecules while retaining liquid crystal properties, particularly fluidity. Such pitches are referred to as "interphase pitches", in which, together with the predominant anisotropic phase, an isotropic phase can also be present. Anisotropy is determined by observing the polished pitch surface using a polarizing microscope.

In addition to anisotropy, a pitch suitable for the production of high-strength carbon fibers must exhibit the following properties: The content of solid particles should be as low as possible to avoid the formation of roughness in the fibers. - lower flow temperatures to avoid polymerization during processing; - higher and less volatile carbon content and coking residues to achieve higher yields and easier spinning, stabilization and carbonization; and a higher content of components insoluble in toluene and a lower content of components insoluble in quinoline (high β-span = TI
It is clear that in order to achieve such properties it is necessary to carry out a rectification of the multicomponent mixture pitch.

Careful separation of the solid particles present in the pitch is natural and belongs to the known state of the art.

It is known from the literature that only moderate results are obtained by direct production of mesophase pitch by heat treatment of filtered coal tar pitch or petroleum pitch.

In the case of relatively short treatment times, a higher isotropic fraction is present, which reduces the yield and impairs the strength of the fiber. If the processing is overdone, infusible particles are formed from the polymeric pitch component, which makes spinning difficult and deteriorates fiber quality.

The rectification of pitch for the purpose of narrowing the molecular weight distribution has been described in numerous publications.

In the method according to European Patent Application No. 172.955 (known method 1), starting from a soft pitch, a mesophase is formed in a first heat treatment and by extraction with an aromatic solvent and subsequent filtration. ,
Separate the insoluble pitch components formed. To separate the solvent, the filtrate is treated by distillation and subjected to a second heat treatment, thereby producing a highly anisotropic pitch for carbon fiber production, which, however, has a high pour point and a quinoline-soluble component. Has a high content. The strength properties of carbonized fibers are not sufficient.

Another method for producing spinnable mesophase pitch involves hydrogenation of the pitch. German Patent No. 3.330
．． In the process according to No. 575 (known process 2), the pitch is hydrogenated with a hydrogenating agent, for example tetrahydroquinoline, and after separation of the solvent by filtration and distillation, it is heat treated under reduced pressure until an intermediate phase forms.

By this means the pour point is lowered and 1.500°C
The strength properties of the carbonized fibers are improved.

A complex method for the production of spinning pitch is described in European Patent Application No. 247,565 (Known Method 3): After extraction with xylene from the coal tar, the insoluble components are filtered off. . The soluble components are subjected to heat and pressure treatment, flashed for distillative separation of low molecular weight components and the heavy phase is hydrogenated. After the distillative separation of the hydrogenating agent, the intermediate phase is produced by heat treatment.

A disadvantage of the last two methods mentioned above for producing spinning pitch is the high technical outlay due to the high pressures and temperatures required for the hydrogenation of the pitch.

In particular, the last method, which involves additional heat-pressure-treatment, flashing and distillation, is expensive and thus the low-cost advantage obtained with low-order raw materials is again offset.

The properties of the spun pitch and carbonized pitch fibers produced according to the above-mentioned known methods selected as examples are as follows:
It is clear from Table 1: Table 1: Pour point according to the following known method 350 Optical anisotropy Volume % 94 Toluene insoluble component Weight % 93.7 Quinoline insoluble component Weight % 45 Next! 1 m row 1 tensile strength elastic modulus carbonization final temperature °C Pa Pa 1.3 2.76 2.67 2 Carbonized pitch fibers with tensile strength greater than 2 GPa and elongation at break greater than 1% It is clear from the prior art that this could hitherto only be achieved using hydrogenated pitch.

Therefore, an hour wheel for producing anisotropic pitch, which can be spun from fibers without hydrogenation, has a tensile strength of more than 2 GPa at an elongation at break of more than 1% after carbonization. The challenge was to develop a method.

According to the present invention, the above problem has been solved by reducing coal tar pitch from 8 to 1 in the temperature range of 330 to 400 °C.
Pitch 1 to 10.10 per kg per hour for 2 hours
-' kg of oxygen-containing gas and then extraction with pitch solvent and, after separation of the solvent by distillation, the soluble pitch fraction at a heating rate of 1 to 50 K/win and a pressure of 0.5 to 50 mbar. 40 below
This is achieved by heating to a temperature of 0 to 480° C. and holding the final temperature for up to 50 min.

Blowing air into coal tar pitch is known per se. It serves to increase the softening point and coking residue. The pitch so treated is used, for example, as a charge for the coking of pitch in horizontal furnaces. It has also been proposed to filter coal tar pitch, blow air into it and then spin it [Fuel, 1981, Vol. 60, No. 84]
See pages 8-850]. Again, the blowing is
The purpose is to increase the softening point so that the pitch fibers do not stick during subsequent processing. Furthermore, the pitch obtained is isotropic and therefore not suitable for the production of high-tensile fibers.

By coal tar pitch is meant the residue from the distillation process of hot coal tar, preferably having a softening point (according to the Kraemer-5arnow method) of about 70"C.

As solvents used are all pitch solvents which correspond in their solubility properties to pyridine, quinoline or anthracene oils.

The invention is explained in more detail by the following example: Example Coal tar pitch 500 k with a softening point of 70° C. (according to the Kremer-Zarnow method) in a heated retort
g to 335 °C under stirring and at a pitch of 6·10- per kg per hour until the temperature rises to 393 °C.
Blow 3 kg of air for 10 hours. Air is forced into the liquid pitch via a somewhat protruding tube on the bottom of the retort.

The pitch thus aerated has the following physical properties: Pour point: 160°C Toluene-insoluble components: 52% by weight Quinoline-soluble components
21% by weight coking residue (according to Alcan method) 68% by weight ash (
900 DEG C.) The 0.2% by weight injected pitch is ground and 1 part by weight of pitch is dissolved in 2 parts by weight of quinoline at 180 DEG C. with stirring. After about 2 hours, the insoluble adult bones of the pitch are separated from the soluble components by sedimentation.

The liquid phase is aspirated and filtered through a sintered metal filter (pore size: 1 μm) to separate the finest solid particles. 30 under a pressure of 200 mbar from the pitch solution
Distill to a bottom temperature of 0°C.

The remaining pitch fraction has the following physical properties: Pour point 170"C Toluene insoluble components 46 Weight large quinoline soluble components
< 1% by weight coking residue 65% by weight ash (900 °C) trace pitch fraction from 250 to 4 in 60 minutes under a pressure of 5 mbar
Heat to 40°C and hold this final temperature for 20 minutes.

The mesophase pitch thus produced has the following properties: Pour point 320″C Optical anisotropy 〉90% by volume toluene insoluble components
85% by weight quinoline soluble component 18% by weight coking residue (alkanes) 94% by weight pressure filter test (1 μm) Practically no infusible particles present and the mesophase pitch described above does not result in thread breakage (380
Spun at ℃. This pitch fiber is 3
It is stabilized to a temperature of 50°C and then carbonized to 1.200°C. The carbon fibers obtained in this way are characterized by the following data: diameter 9-10 μm tensile strength 2.4 GPa elastic modulus
The 210 GPa strength properties exceed those of fibers obtained from twice heat-treated pitch (see European Patent Application Publication No. 172,955) and fibers produced from hydrogenated and heat-treated pitch. It is almost equivalent to that of .

The influence of blowing on pitch and fiber properties is illustrated by the following comparative example: Comparative Example The same starting pitch as in the above example is filtered at 270° C. after dosing with filter aid. The filtrate has the following properties: Softening point (according to Kremer-Zarnow method) 70"C Toluene-insoluble components 22% by weight Quinoline-soluble components <0.1% by weight Ash content
The trace filtered pitch is heat treated under the same conditions as in the examples. To obtain an optical anisotropy of at least 90% by volume, the final temperature was increased to 465°C and the holding time was 3.
The mesophase pitch thus produced, which must be increased to 0 min, has the following properties: Pour point 340 °C optical anisotropy
90% by volume toluene insoluble component 8
8% by weight quinoline soluble component 51% by weight coking residue (according to the alkane method) 95% by weight Filter test (1 μm) 0.5% by weight infusible particles The above mesophase pitch can only be spun at 405°C. Cutting of the thread often appears. Filter elements placed before the spinneret have a short useful life.

1. Carbon fibers carbonized to 200°C are characterized by the following typical properties: Diameter 9-111tm Tensile strength 1.6 GPa Modulus of elasticity
230 GPa or tensile strength is 2
Comparable to that of reheat-treated pitch. However, the elongation at break is 1% or less.

Comparing the analytical data clearly shows that the formation of the mesophase is favorably influenced by air blowing as a pretreatment of the pitch. The mesophase pitch according to the invention surprisingly has a relatively low pour point at a relatively high anisotropy and a lower content of quinoline-soluble components. As a result, spinning becomes easier and the strength properties of the carbonized fibers are significantly improved.

Claims (1)

[Claims] 1. A method for producing anisotropic pitch for producing carbon fibers, in which coal tar pitch is heated at a temperature of 330 to 400°C for 8 to 12 hours to produce an anisotropic pitch of 1 to 10.10% per kg of pitch per hour. ^-^ 3 kg of oxygen-containing gas is bubbled in and then extracted with pitch solvent and after separation of the solvent by distillation the soluble pitch fraction is extracted from 1 to 5 kg.
The method for producing anisotropic pitch as described above, characterized in that it is heated to a temperature of 400 to 480° C. under a pressure of 0.5 to 50 mbar at a heating rate of 0 K/min, and the final temperature is maintained for up to 50 min. 2. The softening point of coal tar pitch is approximately 70°C [Kraemer-Sarnow method (Kraemer-Sarnow met
2. A process according to claim 1, wherein the residue is obtained from the distillative treatment of a hot tar. 3. The method according to claim 1 or 2, wherein pyridine, quinoline or anthracene oil is used as the pitch solvent. 4. The method according to any one of claims 1 to 3, wherein the oxygen-containing gas is air.