JPS633051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fiber from a pitch-like substance reduced with a reducing solvent,
In particular, the present invention relates to a method for producing carbon fibers that is an improved method of thermally polycondensing reduced pitch into spinning pitch. The method of producing carbon fiber using a pitch-like material as a raw material is economical because the raw material is inexpensive and the carbonization yield is high. However, spinning from optically isotropic pitch,
The fibers obtained by subsequent infusibility and carbonization have a low tensile strength of about 100 Kg/mm ² . On the other hand, fibers made of optically anisotropic pitches have a tensile strength of 300 kg/mm ²
However, the heat and pressure conditions during spinning are extremely severe.
It has the disadvantage of low productivity. Recently, a so-called reduced pitch solution, in which a pitch-like substance is once reductively decomposed by heat treatment in a reducing agent and a good pitch solvent such as tetrahydroquinoline, is produced by recovering the solvent and distilling off low-boiling components. Condensation to form spinning pitch, then spinning,
BACKGROUND ART A method for producing carbon fiber that is infusible, carbonized, and in some cases graphitized is attracting attention. The carbon fiber obtained by this method also has a tensile strength of 300
Kg/cm ² or more, and the manufacturing method requires strict spinning conditions and high productivity. However, there are many problems that must be solved before such methods can be industrialized. One of them is a thermal polycondensation process in which a reduced pitch is used as a spinning pitch. In this process, low-boiling substances that are contained in the reduced pitch and vaporize until the temperature reaches the thermal polymerization temperature are distilled off, and the long side chains on the benzene condensed rings are thermally decomposed at the thermal polymerization temperature, resulting in by-product low-boiling substances. Thermal polycondensation is carried out while distilling off the boiling point components to form a polymer. At this time, the reduced pitch is treated at a high temperature of 500℃ to induce thermal decomposition and thermal polycondensation.
Through thermal polycondensation, the molecular weight increases and an optically anisotropic liquid crystal grows. Since this liquid crystal is not compatible with the amorphous portion of pitch and has an extremely high melting point, the spinning conditions must be strict and the process must be carried out quickly. Therefore, in such a process, a method of heating while distilling under highly reduced pressure (30 mmHg or less) has been proposed. However, under reduced pressure, air sometimes enters through the gaps in the equipment, causing the reduced pit to become oxidized and inoxidized, or when the amount of vaporized components decreases, the vapor pressure is insufficient and the components cannot be distilled out of the equipment, causing the walls of the equipment to evaporate. It carbonizes and becomes infusible at the top, causing clogging of the spinning nozzle. Furthermore, this has the disadvantage that the strength and yield of carbon fibers are reduced. The present inventors conducted intensive studies to improve the thermal polycondensation process for making the reduced pitch into a spinning pitch, and as a result, they arrived at the present invention. That is, the present invention heat-treats a pitch-like material as a raw material with a reducing solvent, recovers the solvent, and contains acyclic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, heterocyclic compounds, While blowing in a non-oxidizing compound selected from halogen derivatives, hydroxyl derivatives, ether derivatives, ketone derivatives, nitrogen or sulfur derivatives, and ammonia and having a boiling point of 400°C or less at normal pressure (hereinafter simply referred to as non-oxidizing compound), The present invention relates to a method for producing carbon fibers, which comprises distilling off boiling point components, proceeding with thermal polycondensation to obtain a spinning pitch, and then spinning, infusible, carbonized, and optionally further graphitized. The pitch-like substance referred to in the present invention is petroleum pitch,
This is a general term for coal tar pitch, natural asphalt, and pitch-like substances produced as by-products during industrial production, and coal tar pitch is particularly preferred in the present invention. The reducing solvent referred to in the present invention is a solvent that dissolves pitches well and at the same time releases hydrogen at a temperature of 300°C or higher to decompose crosslinking groups between aromatic condensates, long side chains, or aromatic rings. Alternatively, it refers to a solvent that adds hydrogen to thermally decomposed radical groups to suppress excessive thermal decomposition, and after releasing hydrogen, it is automatically oxidized to a compound with double bonds that is also a good solvent. The boiling point of this solvent is preferably 200°C or higher at normal pressure. Specifically, the following can be mentioned. TetrahydronaphthaleneTetrahydroquinolineHydrogenatedpyreneHydrogenatedphenanthreneHydrogenated wash oilHydrogenated anthracene oilOf course, a mixture of these may also be used, or a mixture of tetrahydroquinoline and a solvent before hydrogenation such as quinoline. I don't mind.
Among these, tetrahydroquinoline is most preferred. The heat treatment of raw material pitch in a reducing solvent is carried out by distributing 10 to 500 parts by weight of pitch to 100 parts by weight of the solvent and heating it to 300 to 550°C. heating temperature
If the temperature is less than 300°C, the reaction will be extremely slow, impairing economic efficiency, and if it exceeds 550°C, the reaction cannot be controlled. The pressure of the reaction system may be normal pressure, but if the boiling point of the solvent is lower than the thermal decomposition temperature, the reaction is often carried out in a pressure vessel. Of course, the reaction may be carried out under pressure with hydrogen gas in the presence of a reducing solvent. In the present invention, most of the reducing solvent is distilled off and recovered from the reaction system by heating under reduced pressure. Under this temperature condition, oily substances in the raw material pitch and thermally decomposed low-boiling components of low molecules are distilled out. Sometimes I do. The temperature at which such low boiling point components are distilled off is generally normal pressure.
The temperature is 200-450℃. After a series of heat treatments, the pituti are highly aromatic, but have a low molecular weight (number average molecular weight (200 to 500) and a low melting point (20 to 100°C), so-called reduced pitch). The non-oxidizing compound used in the process of manufacturing the spinning pitch from the reduced pitch of the present invention vaporizes below the thermal polymerization temperature, compensates for the vapor pressure of the low-boiling component, and accelerates the distillation of the low-boiling component. It is a compound that promotes the distillation of low-boiling components by boiling or gas-liquid dosing, and does not have the effect of oxidizing pitch. At the very least, it is a compound that does not cause any undesirable reactions.Specific examples of such non-oxidizing compounds include acyclic hydrocarbons such as n-butane, propylene, and hexane; cyclohexane, 1,3
-Cyclic hydrocarbons such as cyclohexadiene; Aromatic hydrocarbons such as benzene, toluene, and xylene; Heterocyclic compounds such as quinoline, pyridine, and dioxane; Halogen derivatives such as dichloroethane and monochlorobenzene; Hydroxy derivatives; ether derivatives such as isopropyl ether and anisole; ketone derivatives such as methyl ethyl ketone and methyl isobutyl ketone; nitrogen or sulfur derivatives such as dimethyl sulfoxide and dimethyl formamide; and ammonia. Such compounds are injected into the device in either gaseous or liquid form, but generally they are in gaseous form;
It is best to heat it to as high a temperature as possible and blow into it. The amount of such compound injected into the apparatus can be freely varied depending on the size of the reactor, the type of compound, the expected reaction rate or molecular weight, but if the amount is too large, there is a risk of bumping of the contents. If the amount is too low, low-boiling components cannot be distilled. Also, such compounds are naturally blown into the reactor at a higher pressure. The inside of the reactor may be slightly depressurized to the extent that the above-mentioned inflow of air does not occur. The blowing port may be installed below the liquid level of the contents to cause the liquid to bubble, or it may be installed above the liquid level to allow the gas in the reaction vessel to flow out. In the spinning pitch produced by this method, thermal polycondensation is easy because low-boiling components are quickly distilled off, and the molecular weight has reached a high molecular weight before the optically anisotropic liquid crystal grows. The spinning process performed is easy, and the strength of the carbon fibers finally obtained is high. The spinning, infusibility, carbonization, and optionally graphitization mentioned in the present invention may be carried out under conventional conventional manufacturing conditions for producing carbon fibers from pitch, and are not particularly limited. For example, infusibility is usually performed in air by heating at 130 to 400°C. Carbonization is usually carried out in a metal furnace or refractory brick furnace under an atmosphere of an inert gas such as nitrogen, helium, or argon at about 800 to 1500° C. for 5 to 60 minutes. Further, graphitization, if necessary, is usually carried out in a graphite furnace under an atmosphere of argon or helium at about 1500 to 3000°C for 5 to 60 minutes. Next, the present invention will be further explained with reference to Examples shown below. [Reference example] (Production of reduced pitch) Tar pitch with a softening point of 86°C, fixed carbon content of 56%, quinoline insoluble content of 6%, and benzene insoluble content of 38%.
Mix 450g and 450g of tetrahydroquinoline, 200g
When heated and stirred at around ℃, it became a uniform slurry. This was filtered while hot using a G-3 glass filter, and insoluble matter was washed with 100 g of freshly heated tetrahydroquinoline. The entire filtrate was placed in an autoclave, heated and stirred at 430°C for 60 minutes, and then heated to 200°C under a 25mmHg vacuum to remove tetrahydroquinoline, reduced decomposition products with boiling points around that level, and the raw material contained in the pitch. This was continued until no more low-boiling components were distilled out. This reduced pitch has a melting point of 42°C, has a quinoline insoluble content of only 0.7%, and a benzene insoluble content of only 2.9%, and as a result of gel permeation chromatography, the molecular weight is 220 to 320, clearly indicating that the raw material pitch has been reductively decomposed. It turned out that there was. [Examples 1 to 3] 70 g of the reduced pitch of the reference example was placed in a 200 ml two-necked quartz eggplant flask, and a gas inlet tube was attached to one neck and a Liepitz condenser was attached to the other mouth.
Thermal polycondensation was continued while the pitch was heated in a salt bath at the heating temperature and heating time shown in the reduced pitch column shown in Table 1, and while introducing the non-oxidizing compound and its blown amount shown in Table 1. Table 1 shows the properties of the spinning pitch obtained. In Examples 2 and 3, the non-oxidizing compound was injected in liquid form. Next, pour the pitch through a 0.5mm diameter nozzle.
The fibers were spun while being stretched at 290°C and 1.5 nitrogen gas pressure, heated to 250°C in air to make them infusible, and further heated to 1400°C in nitrogen to carbonize to obtain fibers with a diameter of 11 to 18 microns. . Table 1 shows the tensile strength of the obtained fibers.
Shown below. [Comparative Examples 1 and 2] Weigh out 70 g of the reduced pitch of the reference example into a 200 ml two-necked quartz eggplant flask, attach a Liebig condenser via a capillary to one neck and a connecting pipe with a branch to the other neck, and attach an adapter. was set up so that it could be suctioned with an oil rotary pump. In Comparative Example 1, heating was performed at 510° C. for 18 minutes under a reduced pressure of 27 mmHg, but nothing was introduced from the capillary. In Comparative Example 2, heating was performed at 510° C. for 15 minutes under reduced pressure of 31 mmHg while introducing a small amount of nitrogen gas from the capillary. In both comparative examples, infusible powder was observed on the walls of the glassware, and convex portions were formed even after being made into fibers, and when pulled, the fibers were cut at the front and rear portions, which caused the fibers to have low strength. The results are also listed in Table-1. 【table】

Claims (1)

[Claims] 1 Heat-treating the raw material pitch-like substance with a reducing solvent and recovering the solvent.In the reduced pitch obtained, acyclic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, heterocyclic compounds, halogen derivatives, At normal pressure selected from hydroxy derivatives, ether derivatives, ketone derivatives, nitrogen or sulfur derivatives and ammonia
While blowing in a non-oxidizing compound with a boiling point of 400℃ or less, low-boiling components are distilled off, thermal polycondensation is performed to obtain a spinning pitch, and then spinning, infusibility, carbonization, and in some cases further graphitization. A method for producing pitch-based carbon fiber, which is characterized by: