JPS5988922A - Preparation of pitch for spinning - Google Patents

Abstract

PURPOSE:To obtain pitch for spinning having excellent spinnability, by reducing and decomposing a pitch material with a reducing solvent, flowing down the product in the form of thin film while contacting an inert gas thereto thereby effecting the separation of the solvent and low-boiling components from the film, and thermally polymerizing the concentrated high-molecular pitch. CONSTITUTION:A pitch material such as petroleum pitch, coal tar pitch, etc. is reduced and decomposed with a reducing solvent such as tetrahydrofuran, and the obtained reduced pitch solution is supplied to a reactor by the reduced liquid feed pump 12 and flowed down in the form of a thin film along the inner wall of the evaporation tube 1. At the same time, inert gas introduced from the gas inlet 7 is contacted countercurrently or concurrently with the flowing liquid film to separate both of the solvent and the low-boiling component vapor. The concentrated pitch having relatively high molecular weight is thermally polymerized or polycondensed to obtain the objective pitch for spinning use.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing spinning pitch for producing carbon fibers, more specifically, using a thin film falling reaction method,
The present invention relates to a method for efficiently preparing pitch suitable for spinning from a reduced pitch solution.

Carbon fiber has thermal insulation properties, heat resistance, chemical resistance,
Due to its rigidity and conductivity, it is widely used as heat insulating materials, sealing materials, electromechanical parts, structural members, friction materials, carbon electrodes, etc.

Typical methods for producing this carbon fiber include a method of firing fibers such as acrylonitrile or cellulose, and a method of spinning and carbonizing a pitch-like material.
The former has a high raw material cost and low carbonization yield, making it unsuitable for industrial implementation, while the latter has the advantage of being able to use various pitches that are inexpensive and available in large quantities as raw materials. However, these methods have the drawbacks of being difficult to spin and not producing high-quality carbon fibers, and neither of these methods can be said to be satisfactory as an industrial method.

Subsequently, various studies have been conducted on methods using pitch-like materials as raw materials in order to facilitate spinning and obtain high-quality carbon fibers. A method of using a pitch-like material obtained by heat treatment as a raw material (Japanese Patent Publication No. 45'-28013, Japanese Patent Publication No. 8634-1989), a petroleum-based pitch material is first heat-treated in the presence of a Lewis acid catalyst. after,
A method in which the catalyst is removed and further heat-treated is used as a raw material (% Publication No. 7533/1983), in which membrane pitch with a predetermined membrane face content is formed under reduced pressure, and this is used as a raw material to produce carbon fibers. method (Japanese Patent Application Laid-Open No. 54-11330, Japanese Patent Publication No. 54-1810), method using mesoface pitch having a specific composition and specific physical properties as a raw material (Japanese Patent Application Laid-open No. 54-55625, U.S. Patent No. 54-55625, U.S. Patent No. No. 3,787,541) have been proposed, but even with these methods, it has not been possible to obtain high-performance grade carbon fibers with physical properties comparable to those made from polyacrylonitrile. .

Recently, pitch-like substances are first heat-treated and reductively decomposed in a solvent such as tetrahydroquinoline, which is a reducing agent and is good for pitch-like substances. After recovering the solvent, low-boiling point components are is thermally polymerized while separating to form spinning pitch, and then after spinning,
By making it infusible, carbonizing, and in some cases graphitizing,
A method for producing high-performance grade carbon fiber has been proposed and is attracting attention.

The carbon fiber obtained by this method has a tensile strength of 250 K.
g/ml or more, and the manufacturing method does not require strict spinning conditions and has high productivity, but there are 9 points that need to be improved when transferring to an industrial production process.

For example, one of the important points of this method is to distill off and recover the reducing solvent from the reduced pitch solution, as well as the low-boiling components in the raw pitch and the low-boiling components generated by reductive decomposition, before carrying out thermal polymerization or thermopolymerization. The purpose of this invention is to improve the preparation process of so-called spinning pitch, in which a high molecular weight pitch that can be spun is produced by proceeding with condensation.

The spinning pitch is prepared in a reaction vessel equipped with a stirring device and heated to a high temperature, usually 500° C., under reduced pressure or while blowing inert gas.

However, this reactor on an industrial scale has a huge heating part that can raise the temperature to high temperatures, resulting in a huge investment and equipment cost, and because the operation is batchwise, the There is a drawback that a sufficiently satisfactory result regarding the yield of pitch for spinning cannot be obtained.

Furthermore, since this spinning process requires extremely complex and delicate condition adjustment, it is necessary to obtain spinning pitch with a certain range of physical properties for each reaction, but this cannot be achieved using this batch reactor. has drawbacks such as requiring extremely complicated operations.

The present inventors have conducted intensive research to provide a method for preparing pitch for spinning that overcomes these drawbacks, and have found that the objective can be achieved by treating a reduced pitch solution using a thin film falling reaction method. The present invention was completed based on this finding.

That is, in the present invention, after reductively decomposing a pitch-like substance with a reducing solvent, the resulting reduced pitch solution is spread out in a thin film and simultaneously brought into contact with an inert gas in a countercurrent or cocurrent manner. The present invention provides a method for preparing pitch for spinning, which is characterized by carrying out thermal polymerization while separating both the pitch and the low-boiling point components.

Examples of pitch-like substances used in the method of the present invention include petroleum pitch, coal tar pitch, natural asphalt,
Other examples include pitch-like substances produced as by-products during industrial production such as thermal cracking of naphtha and fluid catalytic cracking of light oil, among which coal tar pitch is particularly preferred.

The reducing solvent used in the method of the present invention is one that dissolves pitch-like substances well and releases hydrogen to decompose crosslinking groups between aromatic condensates, long side chains, or aromatic rings at a temperature of 300°C or higher. Or, it suppresses excessive thermal decomposition by adding hydrogen to the thermally decomposed radical group, and after releasing the hydrogen, it oxidizes itself to a compound with a double bond that is also a good solvent. The boiling point is preferably 200°C or higher at normal pressure. Examples of such oils include tetrahydronaphthalene, tetrahydroquinoline, hydrogenated pyrene, hydrogenated phenanthrene, hydrogenated wash oil, and hydrogenated anthracene oil. These reducing solvents may be used alone or in combination of two or more, and for example, a mixed solvent of tetrahydroquinoline and quinoline,
It may be a mixture of reducing agent and its solvent before hydrogenation. Among these solvents, tetrahydroquinoline is the most preferred.

The reductive decomposition of the raw material pitch-like material in the method of the present invention is carried out, for example, by blending 10 to 500 parts by weight of the pitch-like material to 100 parts by weight of the above-mentioned reducing solvent and heating the mixture to 300 to 550°C. If the heating temperature is less than 300°C, the reaction will be extremely slow and impractical, while if it exceeds 550°C, it will be difficult to suppress the reaction. In addition, there are no particular restrictions on the pressure of the reaction system, and normal pressure may be used, but if the boiling point of the solvent is lower than the reductive decomposition temperature, it is preferable to perform the reductive decomposition in a pressure vessel, and furthermore, in the presence of a reducing solvent. The reaction may be carried out under pressure with hydrogen gas.

The reduced pitch solution obtained by such reductive decomposition treatment contains a reducing solvent, an oily substance contained in the raw material pitch-like substance, a low-molecular low-boiling point component produced by reductive decomposition, and reduced pitch. . Although this reduced pitch is highly aromatic, it has a low molecular weight (thermal average molecular weight 200-500).
, and has a low melting point (20 to 100°C).

Next, specific embodiments of the present invention will be described with reference to the accompanying drawings. The figure is a cross-sectional view of one example of a thin film falling type reactor used in the present invention, and a reduced pitch solution is supplied to the reactor by a reducing solution injection pump 12. This reduced pitch solution flows up the tube kept warm by the heat insulating material 11 by the liquid circulation pump 5, enters the upper liquid reservoir 6, and flows down as a thin film on the inner wall of the many evaporation tubes 1 as an overflow 17. do.

This evaporator tube is heated either directly with an electric heating coil 2 or indirectly via a salt bath. On the other hand, inert gas heated by the heating heater 13 is injected from the gas blowing lower, flows downward into the evaporator, and comes into contact with the flowing liquid film in a countercurrent manner. The solvent, low-boiling point component vapor, and any liquid droplets are removed from the gas outlet 8, but a portion of the condensed liquid is separated by the shielding plate 9 and removed to the outside of the can via the outlet 10. .

On the other hand, the treated reduced pitch solution is mainly desolventized in the upper part of the evaporator tube 1, delighted pitch in the middle part,
In the lower part, the concentrated relatively high molecular weight pitch is thermally polymerized or thermally polycondensed to become high molecular weight pitch.

This high molecular weight pinch (pitch for spinning) accumulates in the lower liquid reservoir 3, and the salt 9 is taken out of the system by the liquid extraction pump 4.
A portion of it is sent through distributor 14 to liquid mixer 15 for processing again.

However, the preparation of this pitch for spinning can also be carried out, if necessary, by using a multiplicity of systems in which the liquid outlet of one reaction can is directly connected to the input port of another reaction can.

In the method of the present invention, the input amount of the reduced pitch solution, the inner diameter and length of the evaporation tube, the heating temperature, the film thickness, the flow rate of inert gas blowing, or the distribution ratio by the distributor are determined so that the desired amount of spinning pitch can be taken out. It is selected as appropriate depending on the material, physical properties, or other conditions. As such conditions, for example, a heating temperature of 150 DEG to 550 DEG C., a film thickness of 0.01 to 1 mm, and an inert gas blowing flow rate of 0.05 to 10 t/pitch solution IK9.min can be selected.

In addition, as the inert gas used in the method of the present invention,
There are no particular restrictions on the gas as long as it does not substantially make the reduced pitch an acid, but steam, nitrogen gas, argon gas, helium gas, hydrogen scum, butane, etc. are generally suitable.

The spinning pitch thus obtained is spun, made infusible, carbonized, and optionally graphitized using a conventionally known method to obtain carbon fibers. This infusibility is usually carried out by heating in air to a temperature of 130 to 400°C. Further, carbonization is usually performed by heating at a temperature of 800 to 1500° C. for 5 to 60 minutes in a metal furnace or a refractory brick furnace under an inert gas atmosphere such as nitrogen, helium, or argon. Further, graphitization is usually carried out in a graphite furnace under an atmosphere of argon or helium gas at 150 °C.
It is carried out by heating at a temperature of 0 to 3000°C for 5 to 60 minutes.

The spinning pitch obtained by the preparation method of the present invention has a relatively uniform molecular structure and exhibits good spinnability. Therefore, it is possible to spin into thin fibers, and the physical properties of the obtained carbon fibers are also excellent.

Further, according to the method for preparing spinning pitch of the present invention, continuous production is possible and a large amount of spinning pitch can be prepared using small equipment, which is extremely advantageous for industrial implementation.

Next, the present invention will be explained in more detail with reference to Examples.

Example Evaporation tube with inner diameter of 40 mm and length of 1000 mm3. Prepare a thin film descent type reactor as shown in the attached drawing, which has a built-in reactor L~. The amount of liquid retained in the upper liquid reservoir 6 is 1000 ml.
It is. The temperature of the evaporation tube was adjusted to 480:423°C by winding it in a coil shape with a heating filament.

On the other hand, tetrahydroquinoline 250Of and coal tar pitch c high pitch, softening point 89.6℃) 2500 it
' in an autoclave at 430°C for 30 minutes with stirring, then cooled to 100-150°C,
Filter through a glass filter to obtain a reduced pitch solution. This reduced pitch solution was put into the upper liquid reservoir 6, and the remainder was pressurized into the injection pump 12 in an amount of 1 mL, and then sent by the circulation pump 5. Nitrogen gas was heated to about 200° C. and blown through the blowing lower at an amount of 1 OOJ/min. The obtained spinning pitch was circulated in the system in an amount of 0.03 ml, and then taken out from the pump 4. When the steady state is reached, the pitch has a softening point of 223°C and a quinoline solubility of 28.
The content was 4% by weight and the benzene insoluble content was 92.3% by weight.

This spinning pitch was heated at 380°C with nitrogen gas Q, l I
(When spun on a single hole melt spinning machine at 7/ctl,
The yarn could be spun continuously at 800 m/min, and the yarn diameter was 9 μm.

This thread was carbonized according to a conventional method [7], and the tensile strength was 21
8 Kg/myA, elastic modulus 18 Ton/mi
A carbon fiber having a breaking elongation of 1.4 was obtained.

[Brief explanation of the drawing]

The figure is a sectional view of one example of a thin film descending reactor used in the present invention, in which reference numeral 1 is an evaporation tube, 3 is a lower liquid reservoir, 4 is a liquid take-out pump, 5 is a liquid circulation pump, and 6 is upper liquid reservoir 2
, 7 is a gas inlet, 8 is a gas JiP air port, 1o is a concentrated liquid outlet, and 12 is a reducing liquid input pump. Patent Applicant Makoto Ishiita, Director of the Agency of Industrial Science and Technology (and 1 other person) Sub-Agent Akira Agata Continued from page 1 Applicant Dainippon Ink & Chemicals Co., Ltd. 3-35-58 Sakashita, Itabashi-ku, Tokyo

Claims (1)

[Scope of Claims] 1. After reductively decomposing a pitch-like substance with a reducing solvent, the resulting reduced pitch solution is developed into a thin film and flowed down, and at the same time is brought into contact with an inert gas countercurrently or cocurrently, 1. A method for preparing spinning pinches, which comprises carrying out thermal polymerization while separating the solvent or both the solvent and low-boiling components. 2 The reducing solvent is tetrahydroquinoline, tetrahydronaphthalene, hydrogenated pyrene, hydrogenated phenanthrene,
Claim 1, which is at least one selected from hydrogenated wash oil and hydrogenated anthracene oil.
Method 0 described in section 0