JPS6264889A - Purification of pitch - Google Patents

Abstract

PURPOSE:To obtain an optically anisotropic pitch free from an excessively polycondensed portion and an optically isotropic pitch at low cost through separation and purification of pitch, by filtering pitch contg. both an optically isotropic phase and an optically anisotropic phase in an inert atmosphere through two stages. CONSTITUTION:Pitch contg. both an optically isotropic phase and an optically anisotropic phase is passed through a filtering medium at a temperature higher than the softening point of the pitch and lower than 320 deg.C to recover a filtrate as a first component pitch (first step). The component which is flowable in this stage is comprised essentially of an optically isotropic pitch, so that the first component pitch is an optically isotropic pitch. The pitch which has been left on the filtering medium in the first step is passed through the filtering medium at 320-400 deg.C in an inert atmosphere to recover a filtrate as second component pitch (second step). In the second step, an optically anisotropic pitch free from an excessively polycondensed portion is obtained. The second component pitch is used for production of a carbon fiber, while the first component pitch is recycled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for producing carbon materials, particularly carbon fibers, from a pitch in which an optically isotropic phase and an optically anisotropic phase coexist. Concerning how to separate pitches.

[Conventional technology]

In recent years, materials suitable for various uses have been developed, one of which is carbon-based materials.

Carbon-based materials (carbon, graphite materials) include coke,
Graphite electrodes are well known, and new products are being developed that take advantage of the material's characteristics such as heat resistance, conductivity, light weight, and corrosion resistance. Among them, pitch-based carbon ml is an inexpensive and high-performance material. It has attracted attention because of its potential to yield new products, and many studies have been published.

The present invention will now be described using carbon 11N as a representative.

Conventionally, methods for producing carbon fiber include firing synthetic fibers such as polyacrylonitrile and rayon, and natural fibers such as cellulose, and spinning fibers using carbon-based or petroleum-based bits as raw materials and subjecting them to treatments such as heat treatment. Methods for producing the material using various materials as raw materials have been announced, such as a method of spinning and firing the pitch as a commercial pitch.

Recently, since pitch is particularly inexpensive, various methods have been proposed for producing carbon II fibers using pitch as a raw material.

In general, the process of making carbon fiber from pitch can be roughly divided into (a) a process of treating coal pitch or petroleum pitch by heat treatment etc. to make pitch for spinning, (b) a process of spinning the pitch for spinning, and (C ) A process of making the spun yarn into a solid form, and (d) a process of firing the infusible yarn and carbonizing it or further graphitizing it.

Each of the above steps has points that need to be improved, but there is a particular problem in the step (a) of producing pitch for spinning. Unlike polyacrylonitrile and its similar synthetic resins, pitch is a mixture of various compounds, so it has a wide molecular weight distribution and the properties of each constituent component are different.

Therefore, when making pitch for spinning, slight differences in processing conditions affect the properties of the resulting spinning pitch, changing its spinnability and optimum spinning conditions, and in extreme cases, making stable spinning impossible. It becomes possible.

For example, if the change in pitch during heat treatment is small, the entire surface first exhibits optical isotropy, then an optically anisotropic mesophase occurs, and finally a 100% optically anisotropic pitch. and changes. Although it is easy to obtain a pitch with 100% optical anisotropy by simple heat treatment, due to the wide molecular weight distribution and the difference in the degree of polycondensation of each component that makes up the pitch, some of the components have high The molecularization progresses too much and the pitch has poor fluidity as a spinning pitch, causing blockage of the nozzle during spinning, making stable spinning impossible. On the other hand, if the heat treatment is terminated before such a component is generated, a so-called two-phase component is formed, in which an unripe optically isotropic pitch component and an optically anisotropic mesophase component coexist. This results in a separated state, and during spinning, the difference in viscoelastic behavior between the two phases causes yarn breakage to occur frequently. Further, even if the spinning conditions are set so as not to break the yarn, the yarn diameter varies widely and it is not possible to obtain carbon fibers of stable quality. Furthermore, if the heat treatment is completed when the pitch is optically isotropic over the entire surface, a pitch with good spinnability can be obtained, but a high-performance m-sodium cannot be obtained.

Therefore, various proposals have been made regarding pitch processing methods that yield spinning pitch, which is a raw material for carbon fibers with high performance and stable quality. For example, a method of heat treatment after hydrogenation (JP-A-57-179285, JP-A-58-184)
21), a method of further heat-treating the pitch that has been precipitated and separated after heat treatment (JP-A-57-88016.), a method of using a solvent instead of the above-mentioned sedimentation separation (JP-A-54-16042).
7) and many others.

All of these methods involve optical anisotropy, and the bits behave as a homogeneous system during spinning.

[Problem that the invention seeks to solve]

Incidentally, a pitch that is a mixture of optically isotropic pitch and optically anisotropic pitch appears to have fluidity as a whole when the temperature is increased to exceed the softening point. However, at this stage, only the optically isotropic pitch exhibits fluidity, and the optically anisotropic bit shows no fluidity. When the temperature is further increased, the optically anisotropic pitch also begins to exhibit fluidity, but there is a large difference in fluidity, and it has been difficult to make this behave as a completely homogeneous system.

The inventor of the present invention has been conducting intensive research to create high-performance carbon fibers or carbon materials using pitch as a raw material, but in the process, he discovered that there is a difference in fluidity between optically isotropic pitch and optically anisotropic pitch. By focusing on this and using this, we can separate each pitch component.

We found that it is possible to purify it.

The present invention was made based on the above findings, and it is possible to convert a pitch in which an optically anisotropic pitch and an optically isotropic pitch are mixed into an optically anisotropic pitch that contains almost no portion where polycondensation has progressed excessively. The present invention aims to provide a method for separating and purifying optically isotropic pitch and optically isotropic pitch.

[Means for solving problems]

The present invention has been made to achieve the above objects, and
The gist is that pitch in which an optically isotropic phase and an optically anisotropic phase coexist is passed through a filter medium in an inert atmosphere at a temperature above the softening point and below 320°C, and this is used as the first component pitch. A first step of recovering the pitch remaining on the filter material in the first step is heated at 320° C. or higher at 400° C. in an inert atmosphere.
A pitch purification method that sequentially processes pitch by passing it through a filter medium at a temperature below ℃ and a second step of recovering it as a second component pitch, and a pitch purification method used for high performance carbon fibers or carbon materials. After removing the pitch in which both the optically isotropic phase and the optically anisotropic phase coexist by passing it through a filter medium at a temperature above the softening point and below 320°C in an inert atmosphere, the remaining pitch remains on the filter medium. The prepared pitch is placed under an inert atmosphere.
The pitch purification method involves passing the pitch at a temperature of 320° C. or higher and 400° C. or lower and collecting it.

[Specific structure and operation of the invention]

The method of the present invention is comprised of a first step and a second step.

Among pitches, optically anisotropic pitch has low fluidity, and optically isotropic pitch has high fluidity. The fluidity of a mixed pitch in which both of these pitches coexist is largely dependent on the optically isotropic pitch. The first culm of the present invention is filtered under this mixed state to remove optically isotropic pitch. The above situation is similar to the relationship between a polymer and a gel in a polymer, apart from the quantitative ratio. At this time, the filtration temperature is extremely important, and the viscosity of the pitch that exhibits an optically anisotropic phase changes depending on the pitch treatment method described in (a) above when making carbon fibers, so the optimal temperature in the first step also changes. . However, when the temperature exceeds 320° C., not only the optically isotropic pitch but also the optically anisotropic bit shows considerable fluidity, so that the separation between the two pitches deteriorates.

In the second step, the remaining optically anisotropic pitch captured by the filter material in the first culm is removed at 40°C and above 320°C.
When heated to a temperature below 0°C, preferably above 320°C and below 380°C, the pitch that had low fluidity in the first step and did not pass through the filter medium will have sufficient fluidity to pass through the filter medium. become. The temperature in the second step is desirably set to the temperature in the final step of the operation using the bitge, that is, in the case of producing carbon fibers, the spinning temperature.

By filtering at the spinning temperature, it is possible to remove components that have poor fluidity during spinning and have undergone excessive polycondensation, which causes nozzle clogging. However, when the temperature is set to 400° C. or higher, polycondensation of pitch proceeds in the second step. Therefore, from a safety standpoint, the temperature is preferably 380°C or lower.

When applying water droplets at an intermediate stage of spinning pitch, it is preferable to use a water droplet below the expected spinning temperature. In addition, when the temperature is used for carbon materials, the temperature may be appropriately selected from the above temperature range depending on the desired characteristics or manufacturing conditions.

Each pitch separated and purified by the method of the present invention is not strictly separated into both pitches, but when melted,
Since it behaves as a uniform one-phase pitch, it is excellent as a pitch for spinning.

The greatest advantage of the method of the present invention is that efficient separation can be achieved by only performing two steps of pressure filtration under an inert gas atmosphere. The second component pitch obtained from the second step (2) is used as spinning pitch, and the first component pitch obtained from the first step is returned as a raw material for the pitch processing in (a) above, so There is no significant yield loss.

Also, 1st. The yield in the second step varies depending on the processing method, but in general, when comparing the first component pitch and the second component pitch, the first component pitch is 5 to 50wt.
%, and the second component pitch is 95 to 50 wt%.

Further, as the filter material, a filter filled with metal particles having a uniform diameter, a filter made of overlapping mesh nets, a sintered metal filter, a glass filter, a carbon filter, etc. are used. The filter has a porosity of 40
% or more, particularly preferably 50% or more. If it is less than 40%, the pitch component captured by the filter will increase unnecessarily, and if it is less than 40%, the filtering effect will decrease.

The present invention will be explained below with reference to Examples and Comparative Examples.

[Example 1] Two autoclaves were filled with tetrahydroquinoline as a solvent at a weight ratio of coal tar pitch:solvent-1=1, and heated at 470°C under a hydrogen pressure of 90 K9/cM.
The pitch was held for 1 hour to perform hydrogenation treatment. The obtained hydrogenated pitch was filtered and treated under reduced pressure under heating to obtain heat-treated raw pitch. This heat-treated raw material pitch was placed in a flask and treated at 470°C under a nitrogen atmosphere.
A pitch containing a mixture of isotropic phase and anisotropic phase was obtained.

Next, a monohole spinning tube having a nozzle with a diameter of 0.311111 was filled with 40 to 60% porosity to form a porosity of 67 to 72%.
0 mesh metal powder (M etallwrai
(manufactured by Cal Industries, JNC), and the ground pitch described above was set thereon.

In that case, the layer thicknesses of the metal powder and pitch were 1 cm and 10 cttr, respectively.

This spinning tube was heated under a nitrogen atmosphere until the pitch temperature reached 30
After the temperature was stabilized at 8° C., the pressure was increased to 1 Kg/d using nitrogen to carry out the first step. The pitch extruded from the nozzle by this operation is defined as the first component pitch.

After the first component pitch is completely extruded, the pitch remaining in the metal powder is heated to 345℃, and the pitch is heated to 4 to 9/c.
Pressure was applied to d for the second step. The pitch extruded by this operation is defined as the second component pitch. The second component pitch extruded from this nozzle is passed through a winder for 1000m/
It was wound at a speed of 1 minute. Its spinnability is extremely good, with 30
I was able to spin yarn for more than a minute without breaking the yarn. After making the pitch fiber infusible by a conventional method, it was fired and carbonized at 1000°C.

The obtained carbon fiber had a thread diameter of 8 μm and a tensile strength of 310.
ni'J/lttm2. Elastic modulus: 20T/am2. Elongation at break: 1.55%. Table 1 shows the properties of the pitch in each step.

Table 1 (Comparative Example 1) Same as Example 1 except that the pitch was set in the spinning tube and the second step was directly performed without going through the first step.
Spinning was carried out in the same manner as in Example 1.

The extruded pitch is non-uniform and exhibits a two-phase separation state, with 10
At a winding speed of 00 m/min, continuous spinning was possible for only a few seconds at most, and even at 300 m/min, spinning was only possible for a maximum of about 10 seconds.

[Example 2] The heat-treated raw material pitch of Example 1 was passed through a 480° C. zone as a first-stage treatment using a gear pump, and then fed into a reactor equipped with a stirrer for a second-stage treatment. The average residence time in this reactor was 2 hours, and the treatment temperature was 420°C. Pitch is continuously extracted from the bottom of this reactor, and 3
It was placed in a vessel kept at 00°C. The pitch received in this vessel was maintained at 300° C. and sent to a filter equipped with a sintered metal filter (Fuji Metal Fiber, manufactured by Fuji Filter Corporation) with a porosity of 70 to 80% as a filter layer. The pitch was then filtered with a nitrogen pressure of 1.5 to 9/ci, and the filtrate that passed through the sintered metal filter was filtered into the first
component pitch. After the first component pitch had completely flowed out, the pressure was increased to 10 Kg/c#i, but no pitch was observed to flow out. The filter was then warmed to 330°C and pressurized with a nitrogen pressure of 7 Kfl/crir.
1! A second component pitch was obtained.

This second component pitch was put into the same spinning tube as in Example 1, and
It was heated to 40°C and spun at a nitrogen pressure of 7 Kg/cM, and wound up at a speed of 900 m/min. The spinning properties were good, and the yarn could be spun for more than 30 minutes without breaking.

After making this pitch yarn infusible by a conventional method,
It was fired and carbonized. The obtained carbon fiber had a thread diameter of 9μ,
Tensile strength 11: 290Kg/cl, elastic modulus 18T/#
2. The elongation at break was 6%. Table 2 shows the properties of each pitch.

Table 2 [Comparative Example 2] Using the pitch extracted from the vessel in Example 2, spinning was carried out under the same conditions and operations as in Example 2. As a result, the pitch pulsation at the nozzle exit was severe, and the longest continuous spinning time was 20 seconds.

〔effect〕

As described above, the method of the present invention uses a simple device.

Pitch that behaves as a homogeneous phase is obtained through the operation, and since the removed pitch is recycled and used, there is no drop in yield and it has many advantages such as being able to obtain excellent products at low cost. .

Claims (4)

[Claims] (1) Pitch in which an optically isotropic phase and an optically anisotropic phase coexist is passed through a filter medium at a temperature above the softening point and below 320°C in an inert atmosphere and is recovered as the first component pitch. A second step in which the pitch remaining in the filter medium in the first step is passed through the filter medium at a temperature of 320° C. or higher and 400° C. or lower under an inert atmosphere and recovered as a second component pitch. A pitch purification method characterized by sequential processing. (2) The porosity of the filter medium in the filled state is at least 4
The pitch refining method according to claim 1, wherein the pitch is 0%. (3) In a method for refining pitch used for high-performance carbon fibers or carbon materials, pitch in which an optically isotropic phase and an optically anisotropic phase coexist is heated under an inert atmosphere to a temperature above the softening point of 32
The pitch is removed by passing through a filter medium at a temperature of 0° C. or lower, and then the pitch remaining on the filter medium is recovered by passing through the filter medium at a temperature of 320° C. or higher and 400° C. or lower in an inert atmosphere. Method for refining pitch. (4) The porosity of the filter medium in the filled state is at least 4
The pitch refining method according to claim 3, wherein the pitch is 0%.