JPH04280868A - Production of carbonized molding of coal-based pitch - Google Patents

Abstract

PURPOSE:To thoroughly dissolve problems in production of a carbonized molding using a coal-based pitch material as the raw material, i.e., very severe problems obstructive in producing a large-sized molding, e.g. occurrence of cracks and deformation on the carbonized molding with high incidence. CONSTITUTION:The surface of a raw molding composed of a coal-based pitch is substantially prevented from contact with oxygen during carbonization reaction to inhibit the formation of the oxidized pitch. Oxidation of the raw molding is inhibited by covering the raw molding with a petroleum-based pitch powder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbonized coal-based pitch compact. More specifically, the present invention relates to a method for producing a carbonized molded body that is prevented from cracking, deformation, etc.

0002

[Prior Art] In recent years, the field of special carbon materials has required "high density", "high strength", "fine filler", "large size products", "high purity", "high electrical conductivity", and "processing". Various studies have been conducted on methods for producing carbonized molded materials that simultaneously satisfy physical properties such as "ease of molding." In particular, composite powders of coal-based pitch modified by various heat treatments and chemical treatments and finely pulverized coke, and fine self-sintering powders such as mesophase microbeads are press-molded into formed bodies. By embedding this in a filler, carbonizing it, and then graphitizing it, we have created properties that are not found in carbonized and graphitized products of conventional extrusion molded products of low-softening point coal pitch and large-particle coke kneading. Efforts have been made to impart this to carbonized molded bodies. As a result, a graphite block of approximately 30 cm square has "high density", "high strength", and "fine filler".
Products that simultaneously achieve these requirements, as well as products that simultaneously achieve "fine filler,""high electrical conductivity," and "ease of processing" have been developed and put on the market.

[0003] However, it can be easily inferred from catalogs of already marketed products that the following common problems exist even in the new coal pitch-based graphite products for which many manufacturers are competing to develop them. In other words, ■ With the low softening point pitch extrusion method, large products weighing several tons can be stably produced, whereas it is extremely difficult to produce large blocks of products using heat-treated or chemically treated coal-based pitch. This results in shape constraints on processed products and a decline in block usage efficiency, which limits market expansion.
Since it is not possible to create a product that simultaneously achieves the required performance of "ease of processing," the product is less distinguishable from pitch re-impregnated products made using conventional methods, and its price competitiveness is low.

[0004] The reason why it is difficult to manufacture large products is that product damage occurs due to cracks, fissures, and foaming during carbonization of the formed product, and the cause of damage is due to the formed product having small pores due to high density filling of fine particles. In this process, a large amount of gas components generated from the pitch used in large quantities to strongly bind the fine filler and the heavy oil added to adjust the viscosity during kneading are removed within an industrially acceptable carbonization time. It is said that this is something that cannot be completely eliminated. If we believe this thesis, there is no way to make large products with the above characteristics possible.

[0005] The present inventors investigated the possibility that the degassing rate is suppressed by a controlling factor other than the pore diameter, even if the degassing rate is the direct cause. I reconsidered the physical properties of the material and recollected the basic data. Furthermore, there is a technique that discloses that oxidation of coal pitch is involved in an increase in the defective rate during carbonization of molded bodies (Japanese Patent Laid-Open No. 58-21747). However, in this method, countermeasures are considered based on the concept that the effect of oxygen extends over the entire area of the formed form. Furthermore, it is a measure to reduce the defective rate, and nothing is discussed about drastic measures against cracks, large warpage, foaming, etc., which occur almost 100% of the time in large heat-treated pitch products.

[0006]

[Problems to be Solved by the Invention] An object of the present invention is to embed a formed body using coal tar pitch, which is commonly used in the carbon material industry, as a binder in a filler mainly composed of coke and/or graphite particles. Alternatively, in a method of producing a carbonized compact using combustion gas or electrical energy as a carbonization equipment furnace heating source after creating a non-oxidizing atmosphere with an inert gas, it is made of fine filler, which has traditionally been considered extremely difficult to carbonize. The object of the present invention is to provide a technology that can stably carbonize dense, large-sized formed bodies with good reproducibility.

[0007]

[Means for Solving the Problems] (Basic idea) The present inventors have conducted intensive studies to develop a manufacturing technology for particularly large carbonized molded bodies using coal-based pitch as a material.
The following various findings were obtained. (1) In order to investigate the carbonization patterns of coal-based pitch in various atmospheres, we measured the changes in general medium pitch in air using differential thermogravimetric analysis (JIS K2439), and found that up to 350°C Heat generation and weight increase were observed. The 10 mg of finely ground pitch that had undergone heat treatment had formed a thin, hard dome similar to Carmela baked sugar that partially protruded from the aluminum container. On the other hand, when the same treatment was carried out in a high-purity nitrogen atmosphere, the finely pulverized pitch was present in the container as a lump. It was confirmed that the carbonization yield was higher for products treated in air. That is, it has been found that when medium pitch is oxidized in air, it produces a film-like carbonized product that is hard and has an extremely low gas permeability, and has the property of improving the carbonization rate compared to firing in a non-oxidizing atmosphere.

(2) Differential thermogravimetric analysis (D
When measured by TG), it was confirmed that the filler did not cause any weight change and almost no change in heat absorption or heat absorption was observed. In other words, the commonly used fillers are materials that are inert to oxygen molecules and do not cause the oxygen uptake reaction (infusibility reaction in carbon fiber manufacturing) seen in medium pitches in this temperature range and do not exhibit self-combustibility. I understand. It has also been found that in this temperature range, oxygen present in the carbonization atmosphere system or leaking in from the outside can freely move through the carbonization atmosphere system through the gaps in the filler. Therefore, when the buried formed body absorbs oxygen, the oxygen partial pressure difference generated between the surface of the formed body and the entire carbonization atmosphere system is used as a driving force.
It was found that the filler could not prevent the concentration of oxygen in the carbonization atmosphere near the formed bodies.

(3) The heat-treated pitch obtained by heat-treating medium pitch and medium pitch at 440°C for 3 hours in a nitrogen gas flowing atmosphere is pulverized and heated to 300°C at a heating rate of 10°C/hour in a hot air circulation dryer. The oxidized pitch obtained by raising the temperature to 5 hours and holding it for 5 hours was subjected to QMAS measurement. Argon gas flow bottom 1
The temperature was raised at 5°C/min to 000°C, the generation patterns of various gases were observed, and their absolute amounts were quantified.The amount of oxygen calculated from the water, carbon monoxide, and carbon dioxide generated by the heat-treated pitch It has been found that the reactivity of coal pitch with oxygen is significantly increased by heat treatment, reaching twice that of medium pitch.

[0010] From this, when a formed body containing heat-treated coal pitch as a binder component is carbonized in the same carbonization atmosphere as non-heat-treated coal pitch, the above (1) and (2)
When considered together with the knowledge of Heat-treated and/or chemically treated coal-based pitch finely pulverized powder having self-sintering components and/or a mixture of fine filler and heat-treated coal pitch (including a state in which the filler surface is coated with pitch)
When a fine-grained powder consisting of is pressure-molded and the resulting molded body, which is dense on both the inner and outer surfaces, is subjected to a carbonization reaction, unlike ordinary low-melting pitch, the pitch does not soften and melt up to the temperature range where the oxygen uptake reaction becomes active. Therefore, the oxygen uptake reaction begins in a state where oxygen has penetrated into the inside of the molded article.

When the oxygen uptake reaction becomes active, the reaction progresses rapidly because the surface layer is at a high temperature, while the amount of oxygen reaching the interior is relatively small and the reaction does not proceed. Deep inside, only oxygen taken in during molding participates in the reaction. Even if the temperature of the molded body rises to the melting temperature of the viscous component, the outer surface becomes infusible in the sense of carbon fibers and is no longer in a softened and molten state. Furthermore, the saturation region of oxidation is reached and oxygen is further supplied to the inner pitch. In the interior where infusibility has not progressed, the oxygen uptake reaction continues while softening and melting. In the formed form composed of fine filler particles, the particle spacing is small, so the softened and melted pitch forms a thin film, and the entire film undergoes an oxygen uptake reaction.

Incidentally, heat-treated pitch having a softening point is placed in a container, and once melted and solidified in a non-oxidizing atmosphere, pitch films of various thicknesses with a smooth surface without pores are prepared.
When subjected to air oxidation from one side at
Oxygenation (infusibility) progresses up to the thickness, but if the thickness is greater than that, more parts will melt during carbonization, so if an oxide film is formed on the softened and melted pitch, oxidation from that part deeper will be inhibited. be done. The degree of oxidation progress is affected by various factors such as variations in the powder packing density in the compact, variations in the particle size distribution, differences in the external environment, ie, the method of filling the filler in the firing equipment, the filling condition of the produced compact, and non-uniformity of oxygen leakage. Therefore, it is distributed randomly from the surface to the inside without stopping at a certain part of the molded body.

Furthermore, since oxygen has to diffuse inside the pores, which are extremely small compared to the conventional graphite material, the oxygen intake temperature and the oxygen partial pressure at that time are all different, so the oxygen in the pitch The compound also -COOH, -C
The main selection of various functional groups such as HO, -OH, -C-O-C-, =C=O, etc. differs greatly depending on the part of the molded product, that is, the decomposition temperature at the stage of carbonization and It can be easily inferred that the degree of crosslinking of the residual carbon content is different. This means that the temperature at which the carbonization shrinkage reaction occurs and the amount of shrinkage are completely different in the molded article after the oxygen uptake reaction.

Therefore, by controlling factors such as volatile content, quinoline insoluble content, molding pressure, particle size distribution, and β component, and by slowing down the temperature increase rate, uniform heating of the molded body and adjustment of the amount of degassing can improve the shape of the formed body. Efforts to achieve uniform shrinkage result in a situation where the entire pitch is attributable to blisters due to the addition of previously unforeseen factors such as faster oxidation rate than conventional pitch, close packing due to fine fillers, and increased pitch melting and softening temperature. Furthermore, it was found that when only the lower half of the molded body was coated with the material of the present invention and subjected to carbonization, the amount of shrinkage of the upper half was smaller than that of the lower half, and large deep cracks ran along the upper surface. This means that as oxidation progresses, the shrinkage rate becomes lower than that of non-oxidized pitch. Therefore, when a formed body formed by fine filler is subjected to a carbonization reaction using the conventional method, the carbonization shrinkage rate differs between the non-oxidized pitch inside and the oxidized pitch on the outer surface, and depending on the situation, the oxidized pitch with different oxidation depth However, since the shrinkage rates are different, a huge stress will be generated, which will cause large cracks in the carbonized molded body.

(Detailed Description of the Invention) The coal-based pitch used in the present invention has a history of heat treatment with a softening point of 80° C. or higher, and exhibits self-sintering properties during the carbonization reaction. For example, asphalt vacuum residue oil, ethylene heavy end oil, catalytic cracking decant oil, pitch coke, raw coke, etc. can be obtained as starting materials. It is preferable that the pitch is melted and softened in the equipment and subjected to as mild a heat treatment or chemical treatment as possible to the extent that the filler does not stick. In addition, the pitch is heat-treated to a degree that does not cause it to lose its oxygen activity as coke, and has side chains and naphthene rings, and is highly polymerized, which increases its reactivity with oxygen. is valid.

The present invention is not only extremely effective for carbonizing heat-treated coal-based pitch single powder represented by mesocarbon microbeads, but also for carbonizing the coal-based pitch and graphitic carbon,
The present invention is extremely effective for carbonizing a formed body composed of a mixture with at least one aggregate component selected from the group consisting of carbonaceous carbon, ceramics, metals, and metal compounds. Graphitic carbon refers to natural graphite, artificial graphite, vapor-grown graphite, graphitized fiber, expanded graphite, etc., and there are wide differences in crystallinity and content of various impurities, from natural flake graphite to graphitized glassy carbon. Regardless of the size, the size (from several mm to submicron) and shape of the aggregate can be set arbitrarily.

Examples of carbonaceous carbon include coal-based and petroleum-based coke, carbon black, glassy carbon, carbon fibers, mesocarbon microbeads, and the like. Ceramics include silicon carbide, boron carbide, silicon nitride, boron nitride, aluminum nitride, titanium carbide, tungsten carbide, zirconium carbide, titanium boride, zirconium boride, zirconium nitride, titanium nitride, tantalum carbide, niobium carbide, iron carbide. , tantalum carbide, uranium carbide, etc., and as mentioned above, there are no restrictions on particle size or shape. Metals include tungsten, iron,
Examples include cobalt, niobium, nickel, aluminum, cadmium, silicone, titanium, zircon, manganese, chromium, copper, gold, silver, boron platinum, zinc, tin, and lead. The metal compound is a general term for compounds consisting of at least one metal oxide selected from the above metal group, phosphates, sulfates, and combinations thereof, such as silica and alumina. In addition, oxides such as sodium, potassium, aluminum, barium, and strontium,
Examples include phosphates and sulfates. Further examples include various glasses, ceramics, refractories (for example, silica bricks, clay bricks, waxite bricks, chrome bricks, falstenite bricks, chrome-magnesia bricks, and dolomite bricks), and clay.

The basic concept of the present invention is to reduce the oxygen uptake reaction to substantially zero during carbonization of coal-based pitch, or, if not to reduce it to zero, to form oxidized pitch into a compact by the reaction between oxygen and coal-based pitch. The purpose is to prevent the incorporation of oxygen to a level that does not cause phenomena such as cracking and deformation of the carbonized molded product. In order to achieve this objective, in the present invention, the surface of the formed body is coated with a material that undergoes an oxygen uptake reaction pattern in the same or somewhat broader temperature range as the oxygen uptake reaction pattern of the coal-based pitch that constitutes the formed form, and carbonized. From the temperature range where the reaction of coal-based pitch with oxygen forms oxygen compounds to produce oxidized pitch, oxidized pitch begins to release decomposition products such as carbon monoxide, carbon dioxide, and water; A method is adopted in which the supply of oxygen to the surface of the compact is kept to virtually zero until the combustion temperature range is reached, where it directly reacts with carbon monoxide, water, etc. and decomposes.

[0019] Therefore, the material covering the surface of the formed body is
The reactivity with oxygen needs to be selected according to the oxygen uptake behavior of the coal-based pitch. According to the invention,
Differential thermogravimetric analysis of the coal-based pitch used in the present invention is performed under air circulation, the heat generation and weight change patterns are measured, and the DTG of the material that is desired to be used as a protective material for the formed form is compared to determine whether the weight increases. If the temperature at which heat generation starts is lower than or equal to the pitch, and the temperature at which weight increase changes to weight loss is higher than or equal to the pitch, it can be applied to protective materials.
We have made it possible to select materials using an extremely simple evaluation method.

[0020] As a material that satisfies this condition, petroleum-based pitch-containing compositions can be mentioned. A petroleum-based pitch-containing composition is one in which the starting material for pitch is asphalt fraction or vacuum residue obtained by distilling crude oil, ethylene heavy end oil which is a residue fraction of naphtha thermal cracking, catalytic cracking residue, etc. at least one selected composition. It also includes pitches with high infusibility reactivity obtained by polycondensing naphthalene in strong acids. In general, petroleum-based pitch that satisfies the above conditions is suitable in terms of its fast oxidation reaction rate, but coal-based pitch, particularly coal-based pitch powder used in the formed form, is also sufficiently effective. Also suitable are wood chips, paper, sugar, coal, etc. These coating materials may be used alone, but coke, graphite, silica sand, etc., which do not have the function of coating materials,
It can also be used to protect the surface of a formed body by mixing an appropriate amount with concrete or the like.

[0021] Metal particles can play a similar role, but under conditions where the carbonization temperature is 1000°C to 1300°C, they can be used to reduce hydrogen gas and monoxide generated during oxidation-reduction reactions, especially during carbonization. Many materials melt and agglomerate when reduced with carbon, which not only makes repeated use difficult, but also causes problems such as the agglomerates melting and penetrating into the carbonized molded body, so it is not a preferable material. The material that forms carbide does not fuse to the compact (possibly because it does not go through the molten state due to carbonization via oxidized pitch), and even if it is included in coke, the coke can be used repeatedly without separate separation. There are advantages that can be achieved. In order to fully utilize the oxygen reactivity of the material, it is preferable to pulverize the material to increase the surface area as much as possible and then use it as a coating material.

[0022] The amount of the material to be used is determined by the structure of the carbonization furnace, the size of the filler, the size and shape of the formed bodies, the furnace packing conditions, etc., and the amount per weight of the formed bodies is determined. Can not. For example, if the formed body has a complex shape with many irregularities and a large surface area, a large amount will be required to protect the outer surface. Furthermore, when packing small compacts into a large furnace, it is necessary to form a fairly thick protective layer on the surface of the compacts, considering the oxygen supply capacity of the carbonization atmosphere. In furnaces where a large amount of filler material is burned during carbonization, it may not be possible to prevent oxygen from leaking in from the outside. It is necessary to measure the formation of On the other hand, in the case of a large, simple shaped molded article, the surface area/weight ratio is small, so the amount of the material used is relatively reduced. In the present invention, all commonly used fillers such as cement powder, sand, coke, and graphite can be used as the furnace filler without any restrictions. However, the furnace packing is done in such a way that the furnace filling function does not change significantly during the carbonization reaction, and the coating between the protective material and the formed body is broken, and the formed body is not exposed to the filler layer. It is necessary.

[0023]

[Effects of the Invention] As described above, according to the present invention, it is possible to produce a large carbonized molded body made of coal-based pitch with good properties, and the industrial significance of the present invention is extremely large. . According to the method of the present invention, a clean carbon molded body with no black scale components can be obtained, and the unexpected effect that hard element conductivity and graphite crystallinity are improved compared to conventional products also appears.

[0024] The method of the present invention completely eliminates irreparable cracks and bulges in carbon molded bodies, which are caused by the oxygenate-forming reaction between oxygen and binder pitch being concentrated in localized areas of the formed body. Can be suppressed. however,
Even if the method of the present invention is adopted, if the pressure during molding is uneven, cracks may occur due to non-uniform shrinkage caused by differences in the degree of compaction of the formed compact, or the shrinkage characteristic value of the pitch itself may be affected. volatile matter, quinoline insoluble matter, toluene insoluble matter,
Since uneven shrinkage cracking of the non-oxidized pitch itself is observed due to non-uniformity of physical property values represented by indicators such as β component, it is necessary to pay sufficient attention to these. Examples and comparative examples will be described below for the purpose of disclosing the contents of the present invention in more detail.

【Example】

[Example 1] JIS standard K2439 medium pitch (manufactured by Osaka Gas; thermal pitch) was heated at 440°C under nitrogen flow.
A heat treated pitch was obtained by heat treatment for a period of time. Average particle size 10μm
Finely pulverized into a powder of 1.5 tons/cm2 molding pressure,
A formed body with a diameter of 35 mm and a thickness of 20 mm was obtained. The five generated shapes were made of stainless steel (height 28cm, width 40cm).
cm, depth 9cm) in a container with coal coke grains (1~2
On top of that, petroleum-based pitch powder with an average diameter of 10 μm obtained by heat-treating ethylene heavy end pitch (manufactured by Mitsubishi Yuka) at 430°C for 3 hours was spread to a thickness of 3 mm with sufficient margin to form the formed shape. I laid it out as wide as I could. The formed bodies were placed on a firing bed at a distance of about 3 mm from each other, and the surfaces of the formed bodies were coated with the ethylene heavy end pitch to a thickness of 3 mm. Next, this was buried with coal coke grains to a thickness of 2 cm, and the inner volume was 150 with a lid on.
The container was placed in a muffle furnace of 100 ml, and subjected to a carbonization reaction while nitrogen gas was fed at 200 ml per minute from the upper part of the muffle furnace to prevent excessive oxidative deterioration of the container. Heating rate 15℃/hour, maximum temperature 1000℃, 1000℃
The carbonization reaction was carried out with a holding time of 2 hours at °C, and after cooling in the furnace, the carbonized molded body was taken out. All five of the obtained carbonized molded bodies had no black spots on the surface layer, and no cracks were observed throughout. The bending strength of the cut pieces from the two molded bodies was 1450 kg/cm2 on average.

[Comparative Example 1] A carbonization reaction was carried out in the same manner as in Example 1, except that the operation of coating the surface of the molded product with ethylene heavy end pitch was omitted. A black crust with a thickness of 1 to 3 mm was formed on the surface of the five carbonized molded bodies obtained, and all of them were
Peeling and cracking had occurred. In addition, due to the structure of the mold (the joint of the four-part outer core), a blackened part of about 10 mm protrudes into the inside of the molded product from the part where the molded density at the outer periphery is lower than the other parts (due to burr generation). Starting from this, large cracks were observed to develop internally, and all of the compacts could not be subjected to the subsequent graphitization.

Claims (4)

[Claims] [Claim 1] A formed body composed of coal-based pitch or a mixture of it and an aggregate component is buried in a filler, or a non-oxidizing atmosphere is created with an inert gas and subjected to a carbonization reaction. , a method for producing a carbonized molded body, which substantially blocks contact between the surface layer of the formed body and oxygen during the carbonization reaction, and prevents the formation of oxidized pitch in a part or local part of the molded body. A method for producing a carbonized molded body, which is characterized by suppressing cracking, deformation, etc. of the carbonized molded body. 2. Contact between the surface of the formed body and oxygen is interrupted by starting a reaction with oxygen at a temperature equal to or lower than that of the coal-based pitch, and removing the oxygen taken up by the coal-based pitch in the form of an oxygen-containing compound. The method described in item 1 is carried out by coating the surface of the formed body with a material that starts releasing the absorbed oxygen in the form of carbon monoxide or carbon dioxide at a temperature equal to or higher than the temperature at which it is released in the form of carbon oxide or carbon dioxide. Method. 3. The material reacts preferentially with oxygen present in the carbonization reaction atmosphere and the coal-based pitch, and the absolute amount of oxygen that reaches the surface of the formed body from the carbonization reaction atmosphere is controlled by the coal-based pitch. 2. The method according to item 2, which serves to reduce cracking, deformation, etc. of the carbonized molded product due to the formation of oxygen-containing compounds to a negligible range. 4. The method according to claim 2 or 3, wherein the material is a petroleum pitch-containing composition.