JPH0144753B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing pitch, which has excellent performance as a raw material for producing carbon fibers. Currently, carbon fiber is mainly manufactured using polyacrylonitrile as a raw material. However, when polyacrylonitrile is used as a raw material, there are disadvantages in that the raw material is expensive, the original fibrous shape is easily destroyed during heating and carbonization, and the carbonization yield is also poor. In recent years, focusing on this point, many methods have been reported for producing carbon fibers using pitch as a raw material.
When pitch is used as a raw material, it is expected that carbon fibers can be produced at low cost because the raw material is inexpensive and the carbonization yield is usually as high as 85 to 95%. However, compared to polyacrylonitrile-based carbon fiber, carbon fiber obtained from pitch is
Although it has a high elastic modulus, it has a problem of poor strength. Therefore, if this problem could be solved and the modulus of elasticity could be further improved, it would be possible to produce carbon fibers with high strength and high modulus at low cost from pitch. Recently, commercially available petroleum pits have been heat-treated to obtain pitches containing optically anisotropic liquid crystals called mesophases, and pitches containing this mesophases have been converted into precursor pits (hereinafter referred to as molten). Carbon fibers with improved elastic modulus and strength can be obtained by melt-spinning this precursor pitch, making it infusible, and then carbonizing or graphitizing it. It was reported (Japanese Unexamined Patent Publication No. 19127-1983). However, whether a pitch can form a liquid crystal is determined by various factors, and the structure, softening point, viscosity, and other physical properties of the liquid crystal greatly depend on the raw material pitch. Said Japanese Unexamined Patent Publication No. 49-19127
This issue relates to a method for preparing pitch containing mesophase (hereinafter abbreviated as mesophase pitch), but does not mention anything about the raw material pitch for forming high quality mesophase pitch. As mentioned above,
A high-quality mesophase pitch largely depends on the raw material pitch, and if an optimal raw material pitch can be found, it will be possible to produce carbon fibers with even better elastic modulus and strength. Therefore, finding this optimal raw material pitch is an important challenge in this technical field. For example, coal tar pitch contains substances that are insoluble and infusible in carbon black-like quinoline, and these not only cause non-uniformity of the precursor pitch and deteriorate spinnability, but also reduce the strength and strength of carbon fibers. Adversely affects elastic modulus. On the other hand, many commercially available petroleum pitches and other synthetic pitches contain almost no substances that are insoluble and infusible in quinoline. Insoluble high molecular weight components are produced. In other words, when these pitches are heat-treated, thermal decomposition and polycondensation reactions occur simultaneously, and the low molecular weight components gradually become high molecular weight.
It becomes a high molecular weight component that is insoluble in quinoline, and at the same time, the high molecular weight component further increases in molecular weight. Along with this, the softening point of pitch also increases. If this quinoline insoluble matter is similar to the carbon black-like substance in coal tar, it will have an adverse effect on the steps after spinning as described above. Furthermore, even if the substance is different from the carbon black-like substance mentioned above,
The presence of a large amount of quinoline insolubles and a high softening point have an adverse effect on the melt spinning stage. In other words, in order to melt-spun a precursor pitch, it is necessary to raise the spinning temperature until the precursor pitch has a viscosity that allows spinning, and if the softening point of the precursor pitch is too high, the spinning temperature may As a result, the molecular weight of the insoluble portion of quinoline becomes even higher, and the pitch is thermally decomposed and light gas is generated, making it impossible to form a uniform precursor pitch and making it difficult to spin. It becomes virtually impossible. Thus, the precursor pitch must have a relatively low softening point and a suitable viscosity for spinning. Furthermore, it must not substantially contain volatile components during spinning or carbonization. For this reason, precursor pitch for carbon fiber production is prepared by removing the generated quinoline insoluble matter by means such as pressurization and solvent separation (Japanese Patent Application Laid-Open No. 47-9804, 50 −142820,
55-1342, 55-5954). however,
When these means are used, the processing equipment becomes complicated and the processing cost increases, which is not preferable from an economic point of view. It would be most preferable if a pitch having excellent performance could be used as the raw material pitch to prevent the formation of high molecular weight components that would be insoluble in quinoline during the heating step of mesophase formation. The present inventors have completed the present invention as a result of intensive research into these problems. That is, the present inventors suppressed the formation of high molecular weight components at the stage of preparing the precursor pitch, had an optimal viscosity, and created a composition in which the aromatic planes were easily arranged in an orderly manner at the early stage of carbonization. We have discovered a raw material pitch with excellent performance. In other words, the present invention provides a method for producing a raw material pitch in which the softening point is kept relatively low and the mesophase is easily formed. That is, in the present invention, in producing carbon fiber by melt-spinning a precursor pitch obtained by heating a raw material pitch, and then subjecting it to infusibility treatment and carbonization or further graphitization treatment, the raw material pitch is (1) petroleum A mixture of (2) heavy oil with a boiling point of 200°C or more obtained when hydrocatalytic cracking of petroleum and (2) heavy oil with a boiling point of 200°C or more obtained when petroleum is subjected to fluid catalytic cracking.
Regarding a method for producing a raw material pitch for carbon fiber, which is obtained by heat treatment at a temperature of 400 to 500°C under hydrogen pressure of cm ² G or more, the raw material pitch obtained according to the present invention is used. As a result, carbon fibers with high elastic modulus and high strength can be obtained. On the other hand, as a method for producing raw material pitch by heat-treating heavy oil in the presence of hydrogen, the method disclosed in Japanese Patent Publication No. 45-28013 is known. However,
The method of No. 28013 hydrogenates heavy oil in the presence of a catalyst, and it has disadvantages in terms of economy, such as the complexity of operations such as catalyst separation associated with the use of a catalyst, and the high cost of the catalyst. is difficult to avoid. Furthermore, the obtained carbon fibers cannot necessarily be said to have high elastic modulus and high strength. As a result of detailed studies, the present inventors found that the optimal pitch as a raw material for carbon fiber with high elastic modulus and high strength is to use a specific heavy oil under extremely limited heat treatment conditions using a hydrogenation catalyst. I discovered that I had to do it without any problems. That is, (1)
Boiling point of 200°C obtained when petroleum is steam decomposed
A mixture of the above heavy oils and (2) heavy oil with a boiling point of 200℃ or higher obtained when fluid catalytic cracking of petroleum is
Under hydrogen pressure of Kg/ ^cm2・G or more, at a temperature of 400 to 500℃
When a mesophase reaction is carried out using the raw material pitch of the present invention obtained by heat treatment with It was completely unexpected that a higher modulus of elasticity and higher strength could be achieved. On the other hand, when coal tar pitch, commercially available petroleum pitch, or synthetic pitch was heat-treated to form a mesophase according to the method of JP-A-49-19127, the resulting pitch had a softening point of 340°C or higher. thing,
In many cases, melt spinning was virtually impossible, such as in cases where solids were deposited, or even if solids were not deposited, the quinoline insoluble content reached 70 wt% or more. Even if melt spinning is possible, the strength of the carbon fiber obtained by further infusibility, carbonization, and graphitization is 120 to 200 Kg/ml, and the elastic modulus is 12 to 200 kg/ml.
It was ^around 20ton/mm2. Furthermore, when a material with a high softening point was spun, pores were present in the spun material due to the generation of thermal decomposition gas. The present invention will be explained in detail below. The heavy oil with a boiling point of 200°C or higher obtained by steam cracking petroleum used in the present invention is:
Usually 700% of petroleum such as naphtha, kerosene or light oil
It is a heavy oil that is produced by steam cracking at ~1200°C to produce olefins such as ethylene and propylene, and has a boiling point substantially within the range of 200~450°C. The heavy oil with a boiling point of 200°C or higher obtained by fluid catalytic cracking of petroleum used in the present invention is:
Petroleum such as kerosene, light oil or atmospheric residual oil is heated at 450 to 550℃ and at normal pressure to 20 kg/kg in the presence of a natural or synthetic silica/alumina catalyst or zeolite catalyst.
It is a heavy oil that is produced as a by-product when producing light oil such as gasoline by fluid catalytic cracking at cm ² G, and it is a heavy oil with a substantially boiling point within the range of 200 to 450℃. . The method for producing the raw material pitch of the present invention consists of (1) heavy oil with a boiling point of 200°C or higher obtained when petroleum is steam cracked and (2) a boiling point of 200°C or higher obtained when petroleum is subjected to fluid catalytic cracking. of heavy oil at 20Kg/ ^cm2・
G or more, for example 20-350Kg/ ^cm2・G, preferably
Under hydrogen pressure of 50-300Kg/ ^cm2・G, temperature 400-
It is obtained by heat treatment at 500°C, preferably 405-450°C. The mixing ratio of component (1) and component (2) above is component (1):
Component (2) in a weight ratio of 1:0.1 to 9, preferably 1:0.2
~4. If the heat treatment temperature is lower than 400°C, a large amount of quinoline insoluble matter will be generated in the resulting pitch during mesophase formation, resulting in coking and coking during the melt spinning process.
Problems such as phase separation and increase in softening point are likely to occur, and the performance of the resulting carbon fibers is also poor, which is undesirable. Also, if the heat treatment temperature is higher than 500℃, problems such as coking will occur during the raw material pitch manufacturing stage.
In fact, it becomes difficult to produce raw material pitches. After the heat treatment, it is also preferable to remove light components by distillation or the like, if necessary. By using the raw material pitch of the present invention thus obtained, when heat-treated to form a mesophase, the production of high molecular weight components that are insoluble in quinoline is suppressed, and at the same time, the softening point of the pitch is prevented from increasing. Furthermore, it becomes a good precursor pitch having a composition in which the aromatic planes are easily arranged in an orderly manner. As a result, carbon fibers with extremely excellent elastic modulus and strength can be obtained. A known method can be used to produce carbon fiber using the raw material pitch obtained according to the present invention. That is, a raw material pitch is heat-treated to form a mesophase, the resulting precursor pitch is melt-spun, and then subjected to infusibility treatment and carbonization or further graphitization treatment to produce carbon fibers. The reaction at the stage of heat-treating the raw material pitch to convert it into a mesophase to obtain the precursor pitch is usually carried out at a temperature
The reaction is carried out at a temperature of 340 to 450°C, preferably 370 to 420°C, by bubbling an inert gas such as nitrogen under normal pressure or reduced pressure. The heat treatment time at this time can be arbitrarily determined depending on conditions such as temperature and amount of inert gas aeration, but it is usually carried out for 1 to 50 hours, preferably 3 to 20 hours. The amount of inert gas ventilation is
A pitch of 0.7 to 5.0 scfh/1b is preferred. As a method for melt-spinning the precursor pitch, known methods such as an extrusion method, a centrifugation method, and an atomization method can be used. The pitch fiber obtained by melt spinning is then subjected to an infusible treatment in an oxidizing gas atmosphere. As the oxidizing gas, one or more of oxidizing gases such as oxygen, ozone, air, nitrogen oxide, halogen, and sulfur dioxide gas are usually used. This infusibility treatment is carried out under temperature conditions that do not soften or deform the melt-spun pitch fibers to be treated. for example
Temperatures of 20-360°C, preferably 20-300°C are employed. Further, the treatment time is usually 5 minutes to 10 hours. The infusible pitch fibers are then carbonized or further graphitized in an inert gas atmosphere to obtain carbon fibers. Carbonization is usually performed at a temperature of 800 to 2500℃, and the processing time generally required for carbonization is 0.5 minutes to
It is 10 hours. Further, when graphitizing is carried out, it is carried out at a temperature of 2500 to 3500°C, usually for 1 second to 1 hour. In addition, during infusibility, carbonization or graphitization treatment,
If necessary, a slight load or tension may be applied to the object to be processed in order to prevent shrinkage, deformation, etc. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. Example 1 Heavy oil with a boiling point of 200°C or higher (hereinafter abbreviated as heavy oil (1)) was produced as a by-product when naphtha was steam cracked at 830°C.
The properties are shown in Table 1) and hydrotreated vacuum gas oil (VGO) of Arabian crude oil were catalytically cracked at 500℃ using a silica-alumina catalyst. A mixture of 50 g of heavy oil (hereinafter abbreviated as heavy oil (2), whose properties are shown in Table 2) was heated at an initial hydrogen pressure of 100 Kg/cm ² G in an autoclave with an internal volume of 300 ml and equipped with a stirrer. Heating rate 3
Heat to 435°C at °C/min and hold at 435°C for 2.5 hours. Thereafter, heating was stopped and the mixture was cooled to room temperature. The obtained liquid product was distilled at 250° C./1 mmHg to remove light components and obtain raw material pitch. The softening point of this pitch was 63°C, the quinoline insoluble content was 0%, and the yield was 35 wt%. Next, add 600 g of nitrogen to 30 g of this raw material pitch.
Stir with ventilation at ml/min, heat treatment at 400℃ for 10 hours, softening point 268℃, quinoline insoluble content.
Pitch with a mesophase content of 27 wt% and 88% was obtained in a yield of 47%. Set this pitch to a nozzle diameter of 0.3mmφ, L/
Melt-spun at 320℃ using a D=2 spinner, and
Pitch fibers with a diameter of 15 μm were produced, and further subjected to infusible, carbonized and graphitized treatments under the conditions shown below to obtain carbon fibers. ΓInfusibility conditions: 3 in air atmosphere up to 200℃
℃/min, heat at a rate of 1℃/min up to 300℃, and hold at 300℃ for 15 minutes. Γ Carbonization conditions: In a nitrogen atmosphere, temperature was increased at 5°C/min.
Hold at 1000℃ for 30 minutes. Γ Graphitization conditions: Heat treatment in an argon stream at a heating rate of 25°C/min to 2500°C. The obtained carbon fiber had a tensile strength of 285 Kg/mm ² and a Young's modulus of 47 ton/mm ² . As shown in Comparative Example 1, the carbon fiber obtained using the raw material pitch of the present invention has higher strength and It is clear that the elastic modulus is high.

【table】

【table】

[Table] Comparative Example 1 In place of the raw material pitch of the present invention used in Example 1, Ashland 240LS (softening point 120°C), which is a commercially available petroleum pitcher, was used in the same manner as in Example 1. After heat treatment, a pitch with a mesophase content of 50% was obtained. This pitch was subjected to melt spinning, infusibility treatment, carbonization and graphitization treatment in the same manner as in Example 1 to obtain carbon fibers. The obtained carbon fiber had a tensile strength of 137 Kg/mm ² and a Young's modulus of 23 ton/mm ² . Comparative example 2 100 g of heavy oil (1) used in Example 1 and 50 g of heavy oil (2)
In an autoclave with an internal volume of 300 ml and equipped with a stirrer, the mixture was heated to 340°C at a temperature increase rate of 3°C/min at an initial hydrogen pressure of 100 kg/cm ² ·G, and maintained at 340°C for 3 hours. Thereafter, heating was stopped and the mixture was cooled to room temperature. The obtained liquid product was distilled at 250° C./1 mmHg to remove light components and obtain raw material pitch. The softening point of this pitch was 49°C, the quinoline insoluble content was 0%, and the yield was 52 wt%. Next, add 600 g of nitrogen to 30 g of this raw material pitch.
Stir with ventilation at a rate of ml/min, heat treat at 400℃ for 8 hours, softening point: 325℃, quinoline insoluble content
Pitch with a mesophase content of 53 wt% and 90% was obtained in a yield of 34%. When an attempt was made to melt-spun this pitch in the same manner as in Example 1, the yarn became non-uniform and continuous spinning was impossible.

Claims (1)

[Claims] 1. After melt-spinning a precursor pitch obtained by heating a raw material pitch, infusibility treatment and carbonization or further graphitization treatment to produce carbon fibers, the raw material pitch is subjected to (1) steam decomposition of petroleum. (2) Heavy oil with a boiling point of 200°C or higher obtained when performing fluid catalytic cracking of petroleum
A method for producing raw material pitch for carbon fiber, characterized in that it is obtained by heat-treating the above mixture with heavy oil at a temperature of 400 to 500°C under hydrogen pressure of 20 kg/cm ² ·G or more. .