JPH0411024A - Production of carbon fiber and graphite fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having good fiber quality, high strength and high modulus by separating a pitch containing mesophase into a mesophase component and a non-mesophase component, directly spinning the mesophase pitch in molten state, carbonizing the fiber and graphitizing the product. CONSTITUTION:The objective carbon fiber can be produced from a mesophase- containing pitch derived from a carbonaceous pitch by separating the mesophase- containing pitch with a centrifugal separator into a mesophase component and a non-mesophase component, directly supplying the mesophase pitch to a spinning device in molten state without solidifying, infusibilizing the spun fiber in oxygen atmosphere, heating up to 1500 deg.C in N2 gas and allowing to cool down. The carbon fiber can be converted to the objective graphite fiber by heating up to 2400 deg.C in argon stream and allowing to cool down.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing high performance carbon fibers and graphite fibers. More specifically, the present invention separates mesophase pitch from mesophase containing pitch.

This invention relates to a method for producing high-performance carbon fibers and graphite fibers by directly spinning these fibers without solidifying them.

[Conventional technology]

Traditionally, there has been a demand for the development of high-performance materials with light weight, high strength, and high modulus of elasticity in various industrial fields such as automobiles and aircraft, and carbon fibers (including graphite fibers) have been attracting attention from this perspective. ing.

Currently, commercially available carbon fibers are still PAN-based carbon fibers made from polyacrylonitrile, but pitch-based carbon fibers made from coal or petroleum pitches are also cheaper raw materials and have a higher yield in the carbonization process. It is regarded as important due to its advantages such as the ability to obtain fibers with high elastic modulus, and active research and development is being carried out.

Pitch-based carbon fiber is produced by first adjusting carbonaceous pitch to a preferable state as a spinning raw material (pitch for spinning).

Next, it is obtained by melt spinning to convert it into a fibrous form, followed by infusibility and carbonization. Carbon fibers obtained from optically isotropic pitch (i.e., non-mesoface pitch) have low strength and modulus, but optically anisotropic pitch obtained by heat-treating optically isotropic pitch ( Since high-performance carbon fibers can be obtained from mesoface pitch, spinning pitch made of mesoface pitch is very important.

Therefore, many proposals have been made regarding the production of mesoface pitch, but the usual method of heat-treating tar, commercially available optically isotropic pitch, etc. softens when the mesoface content approaches 100%. On the other hand, if the softening point is suppressed, the amount of non-mesophase components in the pitch will increase, making it heterogeneous, and the spinnability will deteriorate. In addition to deterioration, high-performance carbon fibers cannot be obtained.

In addition, the mesoface pitch obtained in this way is
Normally, after being taken out of the heat treatment reactor, the material is returned to room temperature to solidify and stored, and then melted again during spinning and subjected to the spinning process. Therefore, mesophase pitch has problems in that solidification/remelting causes oxidation, generation of thermal decomposition gas, changes in mesophase structure, etc., and furthermore, energy loss due to reheating and melting cannot be ignored.

In order to solve this problem, we developed a method of heat-treating carbonaceous pitch (pitch or its precursor) in a solution or molten state and then melt-spinning it without solidifying it (Japanese Patent Laid-Open No. 59-17
No. 3309) has been proposed.

However, if pitch is heat-treated and then melt-spun without being solidified, although the aforementioned drawbacks due to solidification/re-melting are eliminated, the aforementioned problem of poor spinnability still remains.

[Problem to be solved by the invention]

As mentioned above, in the conventional production of carbon fibers and graphite fibers from mesoface pitch, it is difficult to obtain mesoface pitch with good spinnability, which makes it difficult to obtain high-performance carbon fibers and graphite fibers. In addition, there are problems of quality deterioration and energy loss when the pitch is solidified and stored or remelted.

Therefore, an object of the present invention is to provide a method for producing carbon fibers and graphite fibers that overcomes these problems, that is, improves spinnability and yarn properties, and avoids deterioration of mesoface pitch performance. There is a particular thing.

[Means to solve the problem]

According to the present invention, mesophase-containing pitch produced from carbonaceous pitch is separated into a mesophase component and a non-mesophase component, and the separated mesophase pitch is directly spun in a molten state without solidifying, and then carbonized. , a method for producing carbon fibers and graphite fibers is provided, which further comprises optionally graphitizing the fibers.

That is, the method for producing carbon fibers and graphite fibers of the present invention involves subjecting mesoface-containing pitch produced from carbonaceous pitch to a mesoface pitch separation treatment that separates mesoface components and non-mesoface components. Men face pitch.

It is characterized by direct spinning in a molten state without solidification, and with this structure, mesoface pitch suitable for spinning is formed, and oxidation due to solidification/remelting of mesoface pitch is prevented. Since pyrolysis gas generation, mesophase structure change, etc. are prevented, spinnability and yarn physical properties are significantly improved, and energy for remelting mesophase pitch is also saved.

Note that the mesoface pitch (i.e., optically anisotropic pitch) as used in the present invention refers to a pitch in which brightness is observed by polishing the cross section of a pitch lump solidified at room temperature and rotating crossed nicols with a reflective polarizing microscope. In other words, it means a pitch in which the majority is substantially an optically anisotropic phase (referred to as a mesophase component in this specification), and a pitch in which no brilliance is observed and a pitch in which a substantially optically isotropic phase (referred to as a non-mesophase component in this specification) is present. In this specification, a pitch consisting of a non-mesophase pitch (optically isotropic pitch) is referred to as a non-mesophase pitch (optically isotropic pitch). Therefore, in this specification, mesoface pitch includes not only pure mesoface pitch, but also cases where non-mesoface components are included in the mesoface pitch in the form of a sphere or an irregularly shaped island.

Conversely, non-mesophase pitches also include those that contain small amounts of mesophase components.

Furthermore, there are two types of mesoface pitch: one that is insoluble in quinoline or pyridine, and one that contains a large amount of components that are soluble in quinoline or pyridine, and the term mesoface pitch used herein mainly refers to the latter.

Note that the mesophase content in the present invention is determined by observing and photographing a sample under crossed Nicols using a polarizing microscope and measuring the area ratio occupied by the mesophase component in the sample. The softening point of pitch as used in the present invention refers to the solid-liquid transition temperature of pitch, and the temperature at which absorption or release of latent heat peaks when pitch melts or solidifies using a differential scanning calorimeter. This is what I found from.

This temperature agrees within a range of ±10°C with those measured by other methods such as the ring and ball method and the micro melting point method.

Hereinafter, the method for producing carbon fibers and graphite fibers of the present invention will be explained in detail.

(1) Carbonaceous Pitch As the carbonaceous pitch for producing mesophase-containing pitch used in the present invention, known starting materials such as so-called heavy hydrocarbon oil, tar, or pitch can be used. For example, various petroleum-based heavy oils, pyrolysis tar, catalytic cracking residue oil, heavy oil obtained by carbonization of coal, tar, pitch, aromatic hydrocarbons, etc. can be used as starting materials, and are particularly suitable. An example of this is residual oil from catalytic cracking of petroleum. These are used after being subjected to pretreatment such as filtration, distillation, and solvent extraction, if necessary. Furthermore, in order to stabilize the quality of the mesoface pitch produced, carbonaceous pitch that already contains a small amount of mesoface pitch can also be used as a raw material.

(2) Production of mesophase-containing pitch Mesophase-containing pitch is produced using carbonaceous pitch as a raw material, and the production method thereof is not specified. For example, it can also be produced by a heat treatment process in which carbonaceous pitch is subjected to a meso conversion reaction (defined as a reaction that produces mesophase) through a pyrolysis polycondensation reaction. The term pyrolysis polycondensation reaction refers to a reaction in which a pyrolysis reaction of a heavy hydrocarbon and a polycondensation reaction occur in parallel as main reactions, thereby changing the chemical structure of pitch component molecules. As a result of this reaction, scission of the paraffin chain structure, dehydrogenation, ring closure, development of a planar structure of polycyclic condensed aromatics due to polycondensation, etc. proceed.

For this reaction, the carbonaceous pitch is about 380 to about 460
℃, preferably 400-430℃. If the reaction temperature exceeds about 460°C, the volatilization of unreacted substances in the raw materials will increase, the softening point of the carbonaceous pitch will also increase, and coking will easily occur, which is unsuitable.
If the temperature is below 0°C, the reaction will take a long time, which is not preferable.

In the heat treatment process, stirring is performed to prevent local overheating and to ensure uniform reaction, but in addition, stirring is performed under reduced pressure or as necessary to quickly remove low molecular weight substances generated as a result of thermal decomposition. This can be carried out while blowing an inert gas into the reactor. In this case, the inert gas may be one that has sufficiently low chemical reactivity with the pitch at the reaction temperature, such as nitrogen, water vapor, carbon dioxide, light hydrocarbon gas, or a mixed gas thereof.

It is preferable to preheat these inert gases before blowing them in because the reaction temperature will not be lowered.

In this heat treatment step, the pitch is brought to a state where the memphis component is contained in the pitch from about 30 to about 80%, preferably from about 380 to about 70%, excluding substantially all low molecular weight decomposition products and unreacted substances. When this occurs, it is preferable to stop the process and transfer to the next membrane pitch separation process. This is because in order to obtain a high yield of homogeneous mesophase pitch with a low softening point in the mesophase pitch separation process, the content of mesophase components in the produced pitch must be approximately 20 to 80% and the softening point must be low. This is because it is preferable that the pitch yield is high at 260° C. or lower. Memphis component in generated pitch is 20
If it is less than 80%, the yield of mesophase pitch in the next separation step will be extremely small, and conversely, if the mesophase component is
% or the softening point is higher than 260°C, the separability in the separation process will be poor, making it impossible to obtain mesoface pitch with a high concentration, and the obtained mesoface pitch will have a high softening point. becomes. The mesophase-containing pitch obtained in this step is suitably one in which most or substantially all of the mesophase components are in a spherical state with a diameter of 500 μm or less, preferably 300 μm or less.

(3) Separation of mesophase pitch In the present invention, mesophase-containing pitch produced from carbonaceous pitch is sent to the next mesophase pitch separation step, where it is separated into mesophase components and non-mesophase components. Various known solid-liquid separation methods are appropriately employed to separate mesoface pitch and non-mesoface pitch, but in particular, a separation method that utilizes the difference in specific gravity (reference: Japanese Patent Publication No. 38755/1983) , JP-A No. 58-180585, and JP-A No. 60-34619. Among them, centrifugation is preferably used, especially in industrial production.

The centrifugation method involves centrifuging the mesophase-containing pitch in its molten state.

Since the mesophase component has a higher specific gravity than the non-mesophase component, it quickly settles, grows together and accumulates in the lower layer (layer in the direction of centrifugal force), and the mesophase component forms a continuous phase with approximately 80% or more of it. The lower layer is a mesoface pitch containing a small amount of non-mesophase components in the form of islands or minute spherules, while the upper layer is mostly composed of non-mesophase components, in which the mesophase components are dispersed in the form of minute spherules. In addition, the interface between the upper layer and the lower layer is clear, and the melting state and specific gravity of the upper layer and the lower layer are significantly different. This is a method of separating and taking out the mesoface pitch and separating the mesoface pitch and non-mesoface pitch. Note that centrifugal separation is a processing operation that applies high-speed rotation to a fluid, collects a phase with a higher specific gravity in the fluid to a lower layer (in the direction of centrifugal force), and separates this, and is one of its embodiments. As such, operation using a so-called centrifugal separator, particularly a continuous type centrifugal separator that continuously separates and discharges a heavy phase and a light phase, is advantageously used.

The temperature in the centrifugation operation depends on the magnitude of the centrifugal force, but is preferably a temperature higher than the softening point of the mesophase-containing pitch, preferably 280°C to 400°C, more preferably 320°C.
-380°C. A predetermined constant temperature within this range may be used, and the temperature does not necessarily have to be constant.

In this step, the main purpose is to deposit and coalesce most of the mesophase components in the direction of centrifugal force, and it is necessary to avoid thermal decomposition and polycondensation reactions as much as possible. Therefore, temperatures above 400°C are undesirable, and temperatures higher than necessary make it difficult to operate the centrifugal separator for long periods of time, but at the above-mentioned temperature there is no such problem, and at temperatures lower than the above-mentioned range, pitch In particular, since the viscosity of mesophase pitch is high, non-mesophase components co-precipitate with mesophase components into the underlying mesophase pitch, making separation difficult even when a very large centrifugal acceleration is applied for a long time.

The centrifugal force of the centrifugation operation may be of any value, but it is possible to efficiently separate mesophase components (heavy phase) and non-mesophase components (light phase) in a short time by shortening the residence time. In order to achieve this, it is preferable to adopt a range of 1,000 OOG or more, particularly a range of 10,000 to 40,000 OOG. Note that there are restrictions in terms of equipment when using 50,000 OOG or more.

From this process, a memphithic pitch having a memphaceous component content of 90% or more, particularly 95% or more can be obtained economically in a short time.

In addition, when producing mesoface-containing pitch by heat treating carbonaceous pitch, the non-mesoface pitch separated in this process can be heat-treated again to
Since it can be converted to mesophase-containing pitch,
In a preferred embodiment, this non-mesoface pitch is recycled to the heat treatment step at a specific point in time. This circulation of the non-mesoface pitch causes the non-mesoface pitch to undergo heat treatment again, improving the final pitch yield.

In the present invention, it is also possible to add an appropriate finishing heat treatment step immediately after the mesoface pitch separation step. That is, by using a particularly short residence time in the separation step, a mesophase pitch with a sufficiently low softening point but with a slightly insufficient content of mesophase components of about 80% to 90% is produced, and then this is It is also possible to adopt a method of adding a thermogravid reaction treatment at a temperature of 300° C. to 430° C. to adjust the properties of the mesoface pitch to within narrow quality control limits. Mesophase pitch containing 80-90% mesophase components has 10% non-mesophase components.
It contains ~20%, but this non-mesophase component can be further reduced by adding a small amount of thermal weighting reaction treatment.
It is also known that the softening point gradually increases, so
The mesophase component content can be adjusted to 90% or more, preferably 95% or more, by thermograviding the separated pitch at an appropriately controlled temperature and treatment time.

In addition, in the present invention, after the mesophase pitch separation step, a solvent extraction step for removing quinoline soluble components or n-hebutane soluble components, a non-oxidizing gas blowing treatment for removing light components, or /And a vacuum degassing process etc. can be provided, and if the finishing heat treatment process is provided, a mild hydrogenation process is provided immediately after to adjust the excessive rise in the softening point of the pitch. You can also do that.

In the present invention, the mesoface pitch separated in the mesoface pitch separation step (or the mesoface pitch that has undergone the final heat treatment, etc., if the above-mentioned final heat treatment, etc., is applied) is sent to a storage tank, for example, where the softening point is lowered. It is heated and kept at a higher temperature and kept in a molten state. In this case, it is preferable to stir the pitch.

(4) Spinning The mesoface pitch maintained in a molten state can be directly spun by a known method after removing solid content by filtration if desired. In such a method, for example, pitch is placed in a metal spinning container having 1 to 2,000 spinnerets with a diameter of 0.1 mm to 0.5 m below, and the pitch is heated at 280 to 200 m in an inert gas atmosphere. The pitch is held at a constant temperature of 370°C, kept in a molten state, and the pressure of the inert gas is increased to several 100 + U + Hg to push the molten pitch out of the die, and while controlling the temperature and atmosphere, the pitch fibers that flow down are , which is wound onto a bobbin that rotates at high speed.

Alternatively, it is also possible to adopt a method in which pitch fibers spun from a spinneret are collected in a can-like manner in a lower collecting case while being collected by an air current. In this case, continuous spinning is possible by supplying pitch to the spinning container by supplying pre-melted pitch under pressure using a gear pump or the like. Furthermore, in the above method, a method can also be used in which the pitch fibers are drawn and drawn using gas that is controlled at a constant temperature and descends at high speed in the vicinity of one die to produce long fibers on the belt conveyor below. can.

Furthermore, a cylindrical spinning vessel having a spinneret on the peripheral wall is rotated at high speed, molten pitch is continuously supplied to the spinning vessel, the pitch is pushed out from the peripheral wall of the cylindrical spinner by centrifugal force, and the spinning vessel is drawn by the action of rotation. It is also possible to adopt a spinning method that accumulates pitch fibers.

(5) Adding a sizing agent (oil) The melt-spun pitch fibers are bundled through an air sucker and guided to an oiling roller, where a sizing agent (oil) is applied and further bundled.

In this case, examples of the sizing agent include ethyl alcohol,
Alcohols such as isopropyl alcohol, n-propyl alcohol, butyl alcohol or viscosity 3-300c
st, (30℃) dimethyl silicone oil, methylphenyl silicone oil, etc. diluted with a solvent such as silicone oil or paraffin oil, or dispersed in water with an emulsifier added; Similarly, graphite or polyethylene glycol or a hinderer. In addition, ordinary fibers such as those which do not damage the pitch fibers among the various oils used for polyester fibers can be used.

Methods of applying the sizing agent to the pitch fibers include a method of applying it through a 0-shaped guide, an oiling roller method,
Conventionally known application methods such as a spray method can be employed.

Furthermore, although the sizing agent can be applied at any time between the spinning process and the infusibility process, it is preferable to apply the sizing agent between the spinneret and the winder in order to stably handle the brittle pitch fibers.

The amount of sizing agent attached to the fibers is usually 0. O1 to 10 by weight, preferably 0.05 to 5 by weight2.

(6) Infusibility of pitch fibers The pitch fibers to which the above-mentioned sizing agent has been applied and are bundled are infusible by a known method. The temperature of the infusibility step is 15
The temperature is raised stepwise or gradually in the range of 0°C to 400°C, preferably 200°C to 350°C, and the treatment is usually carried out for 10 minutes to 5 hours. The treatment time may be as long as 1 to 3 days so that the infusibility reaction proceeds sufficiently and uniformly.

The infusibility can be achieved using air, oxygen, a mixed gas of air and oxygen or nitrogen, or a mixed gas containing an oxidizing agent such as NO2, ozone, or halogen.

(7) Carbonization and graphitization Next, this infusible carbonaceous pitch fiber is heated in a chemically inert atmosphere such as argon gas or nitrogen gas.
After preliminary carbonization by raising the temperature to 500 to 1,000℃,
Carbon fibers are obtained by carbonization by raising the temperature to a temperature in the range of 1,000 to 2,000°C;
The temperature is raised to a temperature in the range of -3,000°C, and graphitization treatment is performed to obtain graphite fibers.

In the present invention, the details of the carbonization and graphitization methods are not particularly limited, and generally known methods can be used.

Also, during infusibility, carbonization, and graphitization treatments, it prevents scratches from rubbing against the furnace walls and furnace bottom, avoids shrinkage and deformation of the yarn, or produces carbon fibers and graphite fibers with good appearance and high physical properties. For these purposes, when processing a fiber bundle coated with a sizing agent, it is preferable to apply a load or tension to the fiber bundle.

〔Effect of the invention〕

The method for producing carbon fibers and graphite fibers of the present invention includes subjecting mesophase-containing pitch produced from carbonaceous pitch to a mesophase pitch separation treatment that separates mesophase components and non-mesophase components, and then subjecting the obtained mesophase This is because the structure allows the pitch to be directly spun in its molten state without solidifying it.

(a) The mesoface pitch separation treatment makes it possible to form a mesoface pitch suitable for spinning. (b) As a result, spinning properties and yarn physical properties are improved.

(c) Oxidation and generation of thermal decomposition gas due to solidification/remelting.

Mesophase texture changes are avoided and remelting energy is saved.

As a result, according to the present invention,
High-strength, high-modulus carbon fibers and graphite fibers with good yarn quality can be stably produced.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is of course not limited thereto.

Example: The residual oil produced as a by-product in the catalytic cracking of petroleum is 4
Distilled under reduced pressure to 50℃, and further distilled the obtained tar to 100℃
The tar obtained by centrifuging at 10,0 OOG and then using an electrostatic precipitator and a filtration device to remove solid contents such as catalyst fine particles and solid carbon from the tar was used as a starting material.

The raw material tar after solid content removal was heated to 350° C. with a preheater, and then 100 kg was poured into a heat treatment reactor with a stirrer (with a peripheral heater) having a diameter of 40 cm+++ and an internal capacity of 15 oQ. 415 while blowing nitrogen gas from the bottom of the reactor.
The mixture was heat-treated at a temperature of 4 hours to obtain mesophase-containing pitch containing 50% of the mesophase component.

The pitch yield was 33% by weight.

Immediately after the heat treatment reaction in the reactor was completed, extraction of mesophase-containing pitch from the bottom of the reactor was started and sent to a mesophase-containing pitch tank.

The membrane-containing pitch produced by the above heat treatment has a softening point of 233°C, contains 16.9% by weight of quinolinated content, and has a viscosity of 2.7 in the melted state at 370°C.
Poise was shown.

The pitch in the mesoface-containing pitch tank is sent in its molten state to a cylindrical continuous centrifugal separator, and while the rotor temperature is controlled at 350°C, the molten mesoface pitch ( It was separated into A pitch) and non-mesoface pitch (■ pitch). The entire amount of the separated I pitch was recycled and injected again as a raw material for the heat treatment reactor.

Under the above centrifugation conditions, the yield of A pitch is approximately 49wt≦
Met. The softening point of A pitch was about 264°C, the quinolinated content was 29.3 to 30.1% by weight, and the content of memphis component was about 98%.

Next, the obtained A pitch was directly injected in the molten state into a diameter of 0.
．． Used in a spinning machine with 3-1 nozzle at a temperature of 355°C.
, about 200 mm1 (H), extruded with nitrogen pressure, wound around a bobbin that rotates at high speed installed at the bottom of the nozzle, and about 500 mm
When the yarn was spun at a take-up speed of 11/min, the frequency of yarn breakage was low, less than once per hour, and there was almost no increase in pressure loss over time in the spinning nozzle, resulting in extremely good spinnability. Met.

Next, the spun pitch fibers were heated at 230° C. in an oxygen atmosphere.
℃ for 1 hour to infusible, then in N2 gas at 25℃
Heating to 1,500℃ at a heating rate of 1/min and cooling it,
Carbon fiber was obtained. Further, a part of this carbon fiber was heated in an argon stream at a heating rate of 50°C/min up to 1,100°C, and at a heating rate of 100°C/min from 1,100°C, 2.
It was heated to 400°C and allowed to cool to obtain graphite fibers.

The characteristics of carbon fiber are fiber diameter, tensile strength, and tensile modulus of 10.0 pm, 3 GPa, and 260 GPa, respectively.
a, and the characteristics of graphite fiber are fiber diameter, tensile strength, and tensile modulus of 9.7 [, 3, 8 GPa, and 59
It was 0 GPa.

Comparative Example The same heat treatment reaction as in Example was carried out, only the reaction time was increased to 10 hours, and the mesophase component content was 98.
%, softening point approximately 328°C, quinoline solubility 65% by weight
A mesophase-containing pitch was obtained.

1 kg of this pitch was taken and spun (
However, when spinning was carried out at a spinning temperature of 420°C, the frequency of yarn breakage was as high as 3 to 5 times per 10 minutes, and the spinnability was poor.

This pitch fiber was treated to be infusible in the same manner as in the example,
When carbon fibers and graphite fibers were produced by carbonization and graphitization, the characteristics of the carbon fibers were as follows: fiber diameter, tensile strength, and tensile modulus of 10.0 μs, 2.2 GPa, and 2.
50GPa, the characteristics of graphite fiber are fiber diameter, tensile strength, and tensile modulus of 9.71.2, 3GPa, and 5.
30 GPa, and the yarn physical properties were worse than those of the Examples.

Claims (1)

[Claims] (1) Mesophase-containing pitch produced from carbonaceous pitch is separated into mesophase components and non-mesophase components, and the separated mesophase pitch is directly spun in a molten state without solidifying, carbonized, and further A method for producing carbon fibers and graphite fibers, which comprises graphitizing them by.