JPH04239595A - Production of isotropic pitch for carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the title pitch rich in toluene insolubles, little in quinoline insolubles, to be used for producing carbon fibers >=180 deg.C in softening point, by starting from petroleum stock through a simple production process of few treatment steps. CONSTITUTION:Using, as raw material, a fraction obtained by catalyst elimination and preliminary distillation of the oil produced by fluidized catalytic cracking of petroleum, a centrifugal molecular distillation unit is operated at 350-450 deg.C under a pressure of 0.01-1.0Torr.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing isotropic pitch for carbon fibers, which is a petroleum-based carbon fiber precursor.

0002

2. Description of the Related Art In order to produce carbon fiber precursor pitch from petroleum-based heavy oil, it is necessary to appropriately modify the heavy oil. For example, JP-A-61-190587 proposes a method in which solvent extraction is performed after heat treatment, and a second heat treatment is performed in order to further improve the molecular weight range. Further, Japanese Patent Publication No. 60-57478 discloses a method in which pitch obtained by heat treatment is subjected to heat filtration treatment to remove insoluble components, and further subjected to reduced pressure treatment.

[0003] Using a solvent to remove insoluble components not only complicates the steps of dissolving the pitch and recovering the solvent, but is also uneconomical in all respects. In addition, hot filtration methods have problems such as unmelted components tend to clog the filter, resulting in poor productivity.

0004

[Problems to be Solved by the Invention] Conventional petroleum-based carbon fibers are inexpensive as raw materials, but they are not necessarily economical because they require complicated processes as described above. The purpose of the present invention is to produce isotropic pitch for carbon fibers starting from petroleum-based raw materials and having a softening point of 180° C. or higher, containing a large amount of toluene-insoluble matter and a small amount of quinoline-insoluble matter, through a simple manufacturing process with few processing steps. There is a particular thing.

[0005]

[Means for solving the problem] Therefore, the present inventors
The present invention was achieved as a result of selecting highly aromatic raw materials and researching methods for efficiently removing low-boiling components and thermal reforming treatments.

That is, the present invention uses a fraction obtained by decatalytizing and preliminary distilling a fluid catalytic cracked oil of petroleum as a raw material and using a centrifugal molecular distillation apparatus to reduce the pressure to 0.01 to 1.0 Torr.
r, characterized by simultaneous removal of light fractions and thermal modification treatment at a temperature of 350 to 450 ° C. Contains a large amount of components desirable for improving carbon fiber strength (toluene insoluble content) and insoluble solid content (quinoline insoluble content) The present invention relates to a method for producing an isotropic pitch for carbon fibers having a softening point of 180° C. or higher and having a low softening point.

To explain the present invention in more detail, the heavy oil catalytic cracking residue of feedstock oil usually contains a catalyst with an ash content of 0.
The ash content is about 0.01 to 2% by weight, but it is deashed to reduce the ash content to 0.005% by weight or less, and the fraction with a boiling point of 400°C or higher obtained by preliminary distillation is distilled using a centrifugal molecular distillation device. Treated at a pressure of 0.01 to 1 Torr and a temperature of 350 to 450°C to remove fractions with a boiling point of 500°C or lower,
This is a method for producing isotropic pitch for carbon fibers, which also includes thermal modification to obtain a pitch with a softening point of 180° C. or higher, which contains many components desirable for improving the strength of carbon fibers.

The raw material oil used in the method of the present invention is preferably highly aromatic. The fluid catalytic cracking oil contains a large amount of aromatic compounds, and preferably has an aromatic index of 50 or more. Coal tar pitch is superior in that it contains many aromatic compounds, but coal tar pitch contains a large amount of insoluble solids and requires a solvent extraction step to remove them, which complicates the process. Therefore, it is preferable to use residual oil obtained after treating catalytically cracked oil produced when heavy oil is catalytically cracked by distillation or the like.

[0009] The specific conditions for catalytic cracking vary depending on the type of heavy oil, etc., but usually the reaction temperature is 400 to 650°C;
The reaction pressure is from reduced pressure to several hundred atmospheres. The catalyst used in this catalytic cracking may be silica-alumina or a mixture of silica-alumina and zeolite.

Catalytic cracking oil obtained by catalytic cracking is divided into cracked gas, gasoline, light oil, residual oil, coke, etc. by distillation, etc., and the residual oil used in the present invention generally accounts for about 4 to 20% by weight of the entire catalytic cracking. It is about %. This catalytic cracking residue oil is used as a raw material oil by removing the fraction with a boiling point of 500°C or less using an ordinary vacuum distillation device, and then distilled under reduced pressure with a centrifugal molecular distillation device to remove the fraction with a boiling point of 500°C or less to obtain a softening point. 180
℃ or higher, but the properties of the residual oil change due to changes in the type of crude oil and catalytic cracking conditions, and it is difficult to stably obtain pitch containing many components desirable for spinnability, carbon fiber strength, etc. with molecular distillation. It is difficult to do this with equipment alone. Generally reduced pressure ~
The residual oil and pitch are modified by heat treatment at a temperature of 250 to 400°C under pressure.

According to research conducted by the present inventors, by using a centrifugal molecular distillation apparatus and selecting high temperature and low vacuum conditions under normal molecular distillation conditions, it is possible to not only remove light fractions but also improve spinnability and carbon. It has been discovered that a pitch containing a large amount of pitch components desirable for fiber strength and having a softening point of 180° C. or higher can be obtained.

There are no particular limitations on the centrifugal molecular distillation apparatus that can be used in the present invention. For example, the present applicant's JP-A-2-11
3089, ``Centrifugal Molecular Distillation Apparatus for Producing Pitch for Carbon Fibers'' filed on December 28, 1990 (Reference number: HP000491-1), etc. can be used.

Next, an example of a centrifugal molecular distillation apparatus will be explained with reference to FIG. The condensation dome 1 and the main body plate 2 are flange-connected via an O-ring, and the inside of the main body is maintained at a high vacuum by a vacuum pump through an exhaust hole 3. The sample is supplied to the center of the rotary evaporating dish 5 by a feed pump via a preheater, a feed pipe, etc., and a uniform thin film without mist scattering is formed by the action of centrifugal force. Subsequently, the main body sheath heater 6 provided at the lower part of the evaporating dish mainly applies latent heat of evaporation to evaporate and heat-process the evaporated portion, and the evaporated portion is condensed on the opposite condensing surface 7 and collected in the distilled gutter 8. Further, the distillation residue liquid is collected in the residue gutter 9 and discharged to the outside of the apparatus.

The pitch obtained by the above apparatus must have a softening point of 180°C or higher, and the operating conditions are a temperature of 350 to 450°C, preferably 380 to 450°C, and a pressure of 0.01 to 1.5°C. 0 Torr, preferably 0.05-1
．． Perform at 0 Torr. If the pressure is too high, the removal of light components will be insufficient, leading to a decrease in the quality of pitch for carbon fibers. On the other hand, if the temperature is too high, a large amount of insoluble solids will be produced, and the pitch will further cause coking, while if the pressure is too low, the yield of pitch will decrease, and it will be necessary to increase the size of the vacuum device.

[0015] If the isotropic pitch for carbon fiber contains a light fraction, nozzle fouling occurs during melt spinning, and yarn breakage occurs frequently during spinning, making stable spinning impossible. Furthermore, the presence of a large amount of light components makes it difficult to treat the pitch system to make it infusible, and the treatment takes a long time. Furthermore, if the high temperature state is maintained for a longer time than necessary to remove light components, insoluble solids will be generated in the pitch, so it is said that the temperature is preferably 350°C or less, but surprisingly, in a low vacuum, temperature 35
By processing at 0 to 450°C for a very short time, it is possible to obtain pitch that has extremely low insoluble solid content (quinoline insoluble content) and also contains a large amount of pitch components (toluene insoluble content) that are desirable for improving carbon fiber strength. Understood.

In other words, since the centrifugal molecular distillation apparatus forms a more uniform and extremely thin liquid film during distillation than the pot-type molecular distillation apparatus and the falling film molecular distillation apparatus, the heating can be quickly averaged and the heating time can be reduced. It can be done in a short time. As a result, low-boiling fractions quickly evaporate during operation under high-temperature conditions, and the purpose is achieved in a short enough time that insoluble solids (quinoline insolubles) are not formed during the thermal modification of pitch by heating. can be achieved. The pitch with a softening point of 180°C or higher obtained in this way can be used as isotropic pitch for carbon fibers.
It becomes carbon fiber through spinning, infusibility, and carbonization steps.

[0017]

[Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. Example 1 Fluid catalytic cracking oil was treated with electrostatic oil purification to remove the catalyst, and then the fraction with a boiling point of 400° C. or lower was removed by preliminary distillation to obtain a raw material. The properties of the raw materials are shown in Table 1. Next, the raw material was heated to a pressure of 0.05T using the centrifugal molecular distillation apparatus shown in Figure 1.
The desired isotropic pitch for carbon fibers was obtained in high yield by heat treatment at a temperature of 370°C. Table 2 shows the distillation conditions and the properties of the obtained isotropic pitch. When the obtained isotropic pitch was melt-spun at a spinning temperature of 280°C, there was no yarn breakage and the result was very good. This spinning pitch was subjected to infusibility treatment at 300° C. in air, and then carbonized at 1000° C. in a nitrogen atmosphere to obtain carbon fibers. The properties of the carbon fibers are also shown in Table 2.

Example 2 A raw material having the properties shown in Table 1 obtained by subjecting the same fluidized catalytic cracking oil as in Example 1 to electrostatic oil purification and preliminary distillation treatment was used. Using the centrifugal molecular distillation apparatus shown in Figure 1, this raw material was used at a higher pressure (0.1 Torr) and at a higher temperature (420°C) than in Example 1.
), the desired isotropic pitch was obtained with a yield almost the same as in Example 1. When the obtained isotropic pitch was melt-spun at a spinning temperature of 290° C., there was no yarn breakage, and the spinnability was very good as in Example 1. This spinning pitch was subjected to infusibility treatment at 300° C. in air, and then carbonized at 1000° C. in a nitrogen atmosphere to obtain carbon fibers. The properties of the carbon fibers are also shown in Table 2.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the pressure of centrifugal molecular distillation was 0.005 Torr. The yield of the pitch produced was significantly lower, and the toluene insoluble content in the pitch was also lower than in Example 1. The obtained isotropic pitch was spun at a spinning temperature of 28
When melt-spun at 0°C, there was no yarn breakage, but there was some adhesion between the spinning pitches. This spinning pitch was treated to be infusible at 300°C in air, and then for 1 hour under nitrogen atmosphere.
Carbonization treatment was performed at 000°C to obtain carbon fibers. Although some of the carbon fibers were slightly fused, the properties shown in Table 2 were obtained.

Comparative Example 2 The raw materials shown in Table 1 obtained by carrying out the same treatment as in Example 1 were used. When centrifugal molecular distillation was carried out at a pressure of 0.005 Torr and a temperature of 300° C., the pitch yield was close to that of Example 1, but the pitch contained less toluene insoluble matter and had a lower softening point. The obtained isotropic pitch was spun at a spinning temperature of 2
When melt spinning was performed at 60° C., the nozzle was significantly contaminated, and a lot of adhesion between spinning pitches was observed. This spinning pitch was subjected to infusibility treatment at 300° C. in air to obtain carbon fibers. Many of the carbon fibers were fused. Its properties are shown in Table 2.

Comparative Example 3 The raw materials shown in Table 1 obtained by carrying out the same treatment as in Example 1 were used. Centrifugal molecular distillation at a pressure of 2.0 Torr and a temperature of 4
When conducted at 80°C, a pitch with a softening point of 276°C, which is extremely high for an isotropic pitch, was obtained. This pitch contained a large amount of toluene insoluble matter at 58.5%.
When the pitch was observed using a polarizing microscope, mesophase spheres of several microns were observed. When this pitch was spun, the nozzle was clogged and continuous spinning was not possible. (Margin below)

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Effect] In the present invention, by selecting a fraction of 400°C or higher obtained by decatalyzing and preliminary distillation of fluidized catalytic cracking oil of petroleum as a raw material, insoluble solid content that is undesirable for carbon fibers can be avoided. This raw material is then heated using a centrifugal molecular distillation device to remove fractions with a boiling point of 500°C or lower and at the same time proceed with thermal decomposition to obtain a material with a softening point of 180°C, which contains many components desirable for improving the strength of carbon fibers and has a low content of insoluble solids.
I was able to get more pitches. The method of the present invention is simpler than conventional methods, and has fewer processing steps.
We were able to obtain highly aromatic isotropic pitch for carbon fiber. As a result, carbon fibers could be produced more economically than conventional methods.

[Brief explanation of the drawing]

FIG. 1 shows a centrifugal molecular distillation apparatus used in Examples of the present invention.

FIG. 2 is a flow sheet of a centrifugal molecular distillation apparatus used in an example of the present invention.

[Explanation of symbols]

1. Condensation dome 2 Main body plate 3 Exhaust port 4 Field nozzle 5 Evaporating dish 6 Sheath heater 7 Condensation surface 8 Distilled gutters 9. Residue Gutter 10 Distillate outlet 11 Residue extraction outlet 12 Main body drive motor 13 Motor cylinder 14 Shaft sealing device 15　Centrifugal molecular distillation device main body 16 Raw material tank 17 Residue tank 18 Distillation tank 19 Feed pump 20 Preheater 21 Cold Trap 22 Oil diffusion pump 23 Mechanical booster pump 24 Oil rotary pump 25 Thermometer 26 Vacuum gauge

Claims (1)

[Claims] Claim 1: Using a fraction obtained by removing the catalyst and pre-distilling fluid catalytic cracking oil of petroleum as a raw material, using a centrifugal molecular distillation apparatus, the pressure is 0.01 to 1.0 Torr, and the temperature is 350 to 350 Torr.
Characterized by the simultaneous removal of light fractions and thermal modification treatment at 450°C.Contains a large amount of components desirable for improving carbon fiber strength (toluene insoluble content) and has a low insoluble solid content (quinoline insoluble content) with a softening point of 180. Production method of isotropic pitch for carbon fiber at temperatures above ℃.