JPS6257678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to carbon fiber raw material pitch using petroleum-based heavy residual oil and a method for producing pitch.

Currently, in order to produce carbon fibers with excellent strength and elastic modulus using pitches as raw materials, (1) carbon fibers made of isotropic carbon are stretched under high temperature conditions of 2500°C or higher. (2) Use anisotropic pitch as raw material. It is roughly divided into two methods.

A typical method (2) is to produce carbon fibers using pitch containing a large amount of mesophase as a raw material. A method for producing pitches containing a large amount of mesophase is as shown in Japanese Patent Publication No. 55-37611, in which precursor raw materials (substances used as raw materials for producing pitches) are heated while being blown with an inert gas, etc. to produce mesophases. A method for generating is disclosed.

Further, JP-A-57-88016 discloses a method of heating a precursor raw material and then concentrating mesophase by a method such as gravity sedimentation to obtain mesophase-containing pitch. Further, JP-A-56-57881 discloses a method for separating a component containing a large amount of mesophase from pitch, which is a complete raw material, by an extraction operation using a solvent. However, in this case as well, "the carbonaceous precursor material pitch is the conventional method (USP-
4005183), the precursor material pitch must be capable of forming an extensive pitch of the mesophase."

In any case, these methods include a heat treatment operation in the pitch manufacturing process.
In general, there are few cases in which chemically pure compounds are used as precursor raw materials, and in most cases petroleum-based or coal-based heavy oils are used as precursor raw materials. These petroleum-based or coal-based heavy oils usually contain some impurities, even if only in trace amounts, and when they are heated, a dehydrogenation reaction proceeds, making them similar to carbon, and even when heated. Substances that are difficult to melt are produced. Regarding this point, as disclosed in the above-mentioned Japanese Patent Publication No. 55-37611, it is common practice to lower the heat treatment temperature as much as possible and lengthen the heat treatment time, but it is still difficult to melt a certain amount. The generation of such substances is an unavoidable problem.

If carbon fibers are produced using pitch containing such difficult-to-melt substances, problems such as yarn breakage and blockage of the spinning nozzle holes may occur during spinning of the pitch. Of course, it is possible to remove such impurities from the raw material pitch before spinning by means such as filtration, but if the amount is large, it may be difficult to filter due to the high viscosity of the raw material pitch, and it may be necessary to clean the filter. It is necessary to carry out this process frequently, which requires a lot of effort and is uneconomical from an industrial point of view. On the other hand, when a molded pitch is carbonized, it is customary to make it infusible to prevent the pitch from deforming due to melting. Particularly in the case of carbon fibers, spun pitch fibers are often oxidized and rendered infusible in an oxidizing atmosphere such as air. At this time, if the infusibility is insufficient, fibers may fuse together or shrink, and even if such infusible fibers are carbonized and fired, carbon fibers with excellent strength and elastic modulus will not be produced. It won't be.

As a result of intensive research on this point, we have discovered that it is possible to economically produce pitches that have excellent processability, particularly spinnability, and are less prone to fusion during infusibility by a method different from conventional methods.

The details of the invention are as follows. In other words, the yield of heat-treated oil becomes 80% by weight or more at a temperature of 420 to 450°C and a heating time of 1 to 10 hours without pressurizing heavy petroleum residual oil with a boiling point of 410°C or higher and a sulfur content of 1.5% by weight or less. After heat treatment under the following conditions, insoluble substances in the heat-treated oil are separated in this temperature range by heating at a temperature of 350°C or lower, preferably 200 to 350°C, and using separation means that utilizes the action of gravity or centrifugal force. Remove.

Next, the material from which insoluble substances have been separated is removed under pressure.
1.0Torr or less, preferably 0.5Torr or less, liquid temperature in the system
By removing low boiling point substances by vacuum distillation under conditions in the range of 370 to 390°C, the n-heptane soluble content is 1.0% by weight or less, and the quinoline insoluble content is 7 to 7% by weight.
18% by weight and a toluene insoluble content of 75-90% by weight.

Petroleum-based heavy residual oils that are precursor raw materials (substances that serve as raw materials for manufacturing pitucci) include atmospheric distillation residual oil of crude oil, hydrodesulfurization residual oil, hydrocracked residual oil, pyrolysis residual oil, and contact oil. It may originate from cracked residual oil, solvent extracted oil by-produced during lubricant production, etc., but it must have a boiling point of 410°C or higher and a sulfur content of 1.5% by weight or less. Otherwise, it will be difficult to perform the necessary heating under normal pressure, and the properties of the produced pitches will be poor. In particular, the sulfur content contained in pitch is an undesirable substance when producing high-strength, high-modulus carbon fibers, but it is extremely difficult and uneconomical to remove the sulfur content after producing pitch. Therefore, the sulfur content of the precursor material is 1.5
It is effective and economical to keep the sulfur content of the pitch produced below a certain limit by limiting the sulfur content to below a certain weight percent. Here the sulfur content is
Measure according to the method specified in JIS K-2541. The heat treatment is performed without applying pressure at a temperature of 420 to 450 °C and a heating time of 1 to 10 hours. At this time, operations such as blowing gas or reducing pressure are not performed, and the top of the heat treatment container is heated. The yield of heat-treated oil remaining in the heating device is 80% by weight by cooling as long as the heat treatment temperature can be maintained at a specified temperature and by avoiding light fractions generated during heat treatment from exiting the system. %
The heat treatment is preferably performed so that the amount becomes 90% by weight or more. In this case, heat treatment under pressure in order to increase the yield is not preferable because the thermal reforming reaction that progresses due to the heat treatment is suppressed. When such a heat treatment is performed, substantially no optically anisotropic phase is observed even when the material after the heat treatment is polished and observed under a reflective polarizing microscope. The following method is used to determine whether optical anisotropy occurs in the substance remaining in the system after heat treatment. After pulverizing the heat-treated product to a diameter of approximately 3 mm, it is reduced and a sample is collected.The sample of the heat-treated product is embedded in a resin such as unsaturated polyester and cured, and after polishing, a reflective polarizing microscope is used. Observe at a magnification of 250 times or more under crossed Nicols using a microscope to determine the presence or absence of optical anisotropy.

If the light fraction is taken out of the system, it will be difficult to separate insoluble substances later, and if an optically anisotropic phase is developed, necessary components of the pitch will be removed. Become.

Next, heat-treated material (heat-treated oil) is heated to
While heating to a temperature below 350°C, preferably in the range of 200 to 350°C, substances that are insoluble in this temperature range are separated and removed using separation means that utilizes gravity or centrifugal force. The reason why the heating temperature was set at 350° C. or lower in this case is to prevent the formation of optically anisotropic substances due to heating. On the other hand, below 200°C, the viscosity of the heat-treated oil increases, making it difficult to separate and remove insoluble substances. Of course, it is not absolutely impossible to separate and remove insoluble substances at temperatures below this temperature, but it is not economical and undesirable from an industrial standpoint. In any case, it is very easy to remove insoluble substances at this stage because the viscosity of the heat-treated oil is much lower than the viscosity of the final pitch. Separating and removing these insoluble substances results in the removal of substances that do not melt during spinning, significantly reducing yarn breakage and making it possible to perform spinning stably. Next, the material from which insoluble substances have been separated is vacuum distilled to remove low-boiling fractions. In this case, preferably a fraction having a boiling point of 750°C (converted to normal pressure) or lower is removed. i.e. boiling point of at least 750℃
The fraction above (converted to normal pressure) is vacuum distilled so that it remains. At this time, when using a batch type vacuum distillation apparatus, vacuum distillation is performed under conditions of a pressure of 1.0 Torr or less, preferably 0.5 Torr or less, and a bottom liquid temperature of 370 to 390°C, and when using a continuous type vacuum distillation apparatus, the pressure is
1.0 Torr or less, preferably 0.5 Torr or less, liquid temperature in the flash zone and at the bottom of the distillation column 370-390℃
Vacuum distillation is carried out under conditions within the range of . These pressure and liquid temperature conditions are limited to extremely narrow ranges, and if they deviate from these ranges, it is difficult to obtain pitches with desirable properties.
In other words, the pressure is 1.0 Torr or more and the liquid temperature is 370℃.
In the following cases, it is difficult for the n-heptane soluble content to fall below 1.0% by weight, and the toluene insoluble content falls below the specified range of the present invention, 80% by weight. Furthermore, if the liquid temperature is 390° C. or higher, the amount of quinoline insolubles increases and exceeds the range of 18% by weight of the present invention, and at the same time, insoluble substances also occur in this step.

Although within the extremely narrow range of conditions described above, the conditions for each step were set while taking into consideration the properties of the precursor raw materials, and the n-heptane soluble content was 1.0% by weight or less, the quinoline insoluble content was 7 to 18% by weight, Pitch is produced having a toluene insoluble content of 75 to 90% by weight, preferably 80 to 90% by weight.

If the n-heptane soluble content is 1.0% by weight or more, infusibility will not be good. This is because the components soluble in n-heptane are mainly saturated hydrocarbons with low molecular weights, and this component is chemically stable compared to other components, so it is difficult to oxidize at low temperatures such as infusibility. Therefore, pitches containing many such components are more likely to cause fusion during infusibility. Therefore, it is preferable to remove components soluble in n-heptane as much as possible, and it has been found in the present invention that this amount is preferably 1.0% by weight or less.

On the other hand, the following can be said about the amounts of quinoline-insoluble matter and toluene-insoluble matter. Conventionally, in the case of carbon fibers, especially high-strength, high-modulus carbon fibers, the raw material pitch is often specified by the amount of optically anisotropic components measured using a polarizing microscope, but if the amount of optically anisotropic components is large, However, the quality is a problem, and if the optical anisotropic structure is highly developed, such as coke, where the shape is not a big issue, there is no problem, but if the pitch is made into fibers, such as carbon fiber, If delicate processing is required, the problem arises that spinning is difficult. On the other hand, JP-A-57-
100186, "In the molten state, mesophases are not substantially formed, but a single phase that is homogeneous and optically isotropic is formed as a whole, and when an external force is applied, it shows orientation in that direction." A potential anisotropic pitch has also been disclosed, and it has become clear that it is difficult to control the properties of the pitch simply by the amount of optically anisotropic component recognized by a polarizing microscope. Regarding this point, we made various pitches and examined the relationship between spinnability, fusion problems, and the properties of the finished carbon fibers. As a result, we found that good pitch properties include n-heptane soluble content and quinoline. It has been found that it can be quantitatively defined by the amount of insoluble matter and toluene insoluble matter. n-heptane soluble content 1.0% by weight or less, quinoline insoluble content 7~
The properties of 18% by weight and 75-90% by weight of toluene insoluble matter cannot be easily obtained by normal methods, but can be achieved through each process and its limited conditions as in the present invention. In pitches having properties within such limited ranges of each component, it is possible to produce carbon fibers that have excellent spinnability, are resistant to fusion, and have high strength and high elastic modulus.

To measure the n-heptane soluble content, put 5 g of crushed pitch into a cylindrical filter with an average pore size of 1 μm, and extract it with n-heptane using a Soxhlet extractor.
It is measured by removing the solvent and then weighing the soluble components obtained by heat extraction for 20 hours. Quinoline insoluble content and toluene insoluble content are JIS
Measured by the method specified in K-2425.
The present invention provides a pitch with excellent spinnability and good infusibility, removes insoluble substances from an intermediate product with relatively low viscosity, and then generates insoluble substances that cause yarn breakage during spinning. This makes it possible to manufacture pitches that can be easily made infusible while avoiding the occurrence of carbon fibers, and the properties of the final carbon fibers obtained can be high strength and high elasticity.

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

Example 1 The residual oil produced as a by-product from the catalytic cracking process was vacuum distilled to remove the fraction with a boiling point of 415°C or lower to obtain a heavy residual oil with a boiling point of 415°C or higher. The sulfur content of this heavy residual oil is
It was 1.25% by weight. This heavy residual oil with a boiling point of 415°C or higher was heat-treated at 420°C for 10 hours, and the yield of the heat-treated oil was 85.5% by weight. This heat treated oil
Static separation was performed while heating at 340°C to remove insoluble substances by sedimentation. Subsequently, the supernatant liquid from which insoluble substances had been removed was vacuum distilled using a batch vacuum distillation device at a lower liquid temperature of 385°C and a pressure of 0.2 Torr to remove the low boiling point fraction with a boiling point of 720°C or less to obtain pitch. . The n-heptane soluble content of this pitch was 0.5% by weight, the quinoline insoluble content was 15.6% by weight, and the toluene insoluble content was 88.5% by weight.

When this pitch was melt-spun at a spinning temperature of 365°C using a spinning nozzle with a nozzle hole diameter of 0.5 mmφ, it was possible to spin the yarn at a winding speed of 500 m/min and a fiber diameter of 20 μ without causing even one yarn breakage in 10 minutes. Ta.

After making this pitch fiber infusible at 300℃ in an air atmosphere, it reached a maximum temperature of 2500℃ in an inert gas atmosphere.
The tensile strength of the fired product was 21.0Ton/cm ² and the elastic modulus was 6100Ton/cm ² .

Example 2 The boiling point of solvent-extracted oil produced as a by-product during lubricating oil refining
When oil with a sulfur content of 0.5% by weight was heat-treated at 430°C or higher for 4 hours, the yield of heat-treated oil was 88.9.
It was %. During this heat treatment, centrifugation was performed while heating at 300°C, and insoluble substances were sedimented and removed. Next, the supernatant liquid from which insoluble substances have been removed is heated to the bottom liquid temperature using a batch vacuum distillation device.
Pitch was obtained by vacuum distillation at 383°C and a pressure of 0.3 Torr to remove the low boiling point fraction below 702°C. The n-heptane soluble content of this pitch was 0.5% by weight, the quinoline insoluble content was 16.7% by weight, and the toluene insoluble content was 87.8% by weight. When this pitch was melt-spun at a spinning temperature of 370°C using a spinning nozzle with a nozzle hole diameter of 0.5 mmφ, spinning was possible at a winding speed of 500 m/min and a fiber diameter of 20 μ without a single yarn breakage occurring in 10 minutes. .
After making this pitch fiber infusible at 300℃ in an air atmosphere and then firing it at a maximum temperature of 2500℃ in an inert gas atmosphere, it has a tensile strength of 18.4Ton/cm ² and an elastic modulus.
It was 5900Ton/ ^cm2 .

Comparative Example 1 The same catalytic cracking heavy residual oil (boiling point 415°C or higher) as used in Example 1 was heated while blowing N gas.
The yield of the heat-treated oil heated at 410°C for 20 hours was 76.7% by weight. This heat-treated oil is heated to a bottom liquid temperature of 410℃ and a pressure of 410℃ using a batch vacuum distillation device.
Vacuum distilled at 10 Torr. The n-heptane soluble content of this pitch was 3.5% by weight, the quinoline insoluble content was 29.7% by weight, and the toluene insoluble content was 62.4% by weight. When this pitch was melt-spun using a spinning nozzle with a nozzle hole diameter of 0.5 mmφ at a spinning temperature of 365°C, the winding speed was
At 500 m/min and a fiber diameter of 20 μm, thread breakage occurred an average of 8 times in 10 minutes. This pitch fiber is made infusible at 300°C in an air atmosphere and then fired at a maximum temperature of 2500°C in an inert gas atmosphere, resulting in tensile strength.
The elasticity was 7.0Ton/cm ² and the elastic modulus was 4100Ton/cm ² .

Comparative Example 2 The same catalytic cracking heavy residual oil (boiling point 415°C or higher) used in Example 1 was heat-treated at 410°C for 8 hours, and the yield of the heat-treated oil was 89.1% by weight. This heat-treated oil was vacuum distilled using a batch vacuum distillation apparatus at a bottom liquid temperature of 400°C and a pressure of 10 Torr. The n-heptane soluble content of this pitch was 4.7% by weight, the quinoline insoluble content was 5.9% by weight, and the toluene insoluble content was 49.6% by weight.

When this pitch was melt-spun at a spinning temperature of 362° C. using a spinning nozzle with a nozzle hole diameter of 0.5 mmφ, yarn breakage occurred on average twice in 10 minutes at a winding speed of 500 m/min and a fiber diameter of 20 μm. This pitch fiber is made infusible at 300°C in an air atmosphere and then fired at a maximum temperature of 2500°C in an inert gas atmosphere, resulting in tensile strength.
The elasticity was 5.4Ton/cm ² and the elastic modulus was 500Ton/cm ² .

Claims (1)

[Claims] 1. Petroleum-based heavy residual oil with a boiling point of 410°C or higher and a sulfur content of 1.5% by weight or less is heated to a temperature of 420°C or higher without pressurizing it.
After heat treatment at 450°C for 1 to 10 hours, the yield of heat-treated oil is 80% by weight or more,
Separate and remove insoluble substances while heating at a temperature of 350°C or less, then reduce the liquid temperature in the system to 370°C at a pressure of 1.0 Torr or less.
It consists of vacuum distillation under conditions in the range of -390℃ to remove low boiling point fractions, and n-heptane solubles.
1.0% by weight or less, quinoline insoluble content 7-18% by weight,
A method for producing carbon fiber raw material pitch having a toluene insoluble content of 75 to 95% by weight. 2 In claim 1, heat-treated oil is heated to a temperature
A method for producing carbon fiber raw material pitch, characterized by separating and removing insoluble substances using the action of gravity or centrifugal force at 200 to 350°C. 3 In Claim 1, the substance from which insoluble substances have been separated is subjected to pressure using a batch vacuum distillation apparatus.
A method for producing a carbon fiber raw material pit, which comprises vacuum distilling under conditions of 1.0 Torr or less and a system bottom liquid temperature of 370 to 390°C to remove a low boiling point fraction. 4 In Claim 1, the substance from which insoluble substances have been separated is subjected to pressure using a continuous vacuum distillation apparatus.
1. A method for producing carbon fiber raw material pitch, which comprises vacuum distilling under conditions of 1.0 Torr or less and a liquid temperature of 370 to 390° C. in the flash zone in the system and at the bottom of the distillation column to remove low boiling point fractions.