Binder pitch for producing carbon material and method for producing carbon material

Abstract

Provided is a method for producing a carbon material using, as binder pitch, pitch that has a softening point of 70-120°C, a fixed carbon content of 50.0 mass% or greater, a quinoline-insoluble content of 18.0 mass% or less, an initial boiling point of 320°C or higher, and a Casson yield value of 0.18 Pa or higher at a temperature higher than the softening point by 100°C.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing carbon materials such as graphite electrodes and a binder pitch. [Background technology]

[0002] Carbon materials, such as graphite electrodes used in electric furnaces for remelting iron, are produced by kneading and molding aggregates such as coke with pitch (called "binder pitch") at a temperature above the softening point of the binder pitch, followed by firing and subsequent graphitization. High density is desirable for carbon materials, as they are required to have properties such as high mechanical strength, electrical conductivity, and thermal conductivity. However, due to factors such as the volatilization of low-molecular-weight components in the binder pitch during the firing process, the fired body has a highly porous structure. Therefore, the porosity is reduced by impregnating the fired body with pitch (called "impregnated pitch") and re-firing it several times during the manufacturing process, resulting in a high density of the resulting carbon material.

[0003] The carbonization yield of the binder pitch in the compact during the firing process is called the carbonization rate. The higher this carbonization rate, the higher the density of the resulting fired body, which is preferable because it reduces the number of subsequent impregnations with impregnated pitch and re-firing. Generally, pitches with a higher fixed carbon content tend to have a higher carbonization rate, so it is preferable to use such pitches as binder pitches.

[0004] One known method for increasing the fixed carbon content of binder pitch is to remove light components from the pitch by distillation, but this also increases the softening point. Generally, when mixing binder pitch with aggregate such as coke, a temperature about 50°C higher than the softening point is required, so a high softening point can lead to a problem of increased load on the equipment.

[0005] To solve this problem, there is a method of adding cutback oil to pitch with a high fixed carbon content and a high softening point (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 6,352,637 Summary of the Invention [Problem to be solved by the invention]

[0007] The method described in Patent Document 1 requires the addition of cutback oil, which has a relatively low boiling point, resulting in a problem of a lower initial boiling point of the resulting pitch. If the initial boiling point is too low, a large amount of light components volatilize during kneading, which causes an increase in viscosity during kneading and a problem of reduced kneadability. As such, it is difficult to achieve both good kneadability and a high carbonization rate solely from the perspectives of fixed carbon content and softening point, which have been particularly important until now. The present disclosure provides a binder pitch that can achieve both good kneadability and a high carbonization rate, and a method for producing a high-density carbon material using the binder pitch. [Means for solving the problem]

[0008] When a compact is fired, the binder pitch in the compact softens and its viscosity decreases as the temperature rises. If the binder pitch is washed away from the compact at this time, the carbonization rate decreases. To prevent this flow-out of binder pitch during firing, it is believed to be effective to use a pitch that can maintain a relatively high viscosity even during firing. However, such pitches generally have a high softening point, which reduces kneadability. The inventors considered that, in order to prevent the flow-out of binder pitch during firing without reducing kneadability, a binder pitch with properties that tend to reduce viscosity when the binder pitch is somewhat fluid, such as during kneading, but maintain high viscosity when the binder pitch is barely fluid, such as during firing, would be preferable. Based on this consideration, the inventors conducted extensive research by combining the fixed carbon content and softening point of the binder pitch, which have traditionally been considered important, with the new perspective of the rheological properties of the binder pitch. As a result, they found that even if the amount of fixed carbon is about the same, when a pitch having a higher Casson yield value is used as the binder pitch, a higher carbonization rate and a higher density carbon material can be obtained, which led to the present invention.

[0009] That is, the contents of the present disclosure relate to the following [1] to [4].

[0010] [1] A binder pitch for producing carbon materials, having a softening point of 70°C to 120°C, a fixed carbon content of 50.0 mass% or more, a quinoline insoluble content of 18.0 mass% or less, an initial boiling point of 320°C or more, and a Casson yield value of 0.18 Pa or more at a softening point + 100°C. [2] The binder pitch for producing a carbon material according to [1], wherein the carbon material is a graphite electrode. [3] A method for producing a carbon material using pitch as a binder pitch having a softening point of 70°C to 120°C, a fixed carbon content of 50.0 mass% or more, a quinoline insoluble content of 18.0 mass% or less, an initial boiling point of 320°C or more, and a Casson yield value of 0.18 Pa or more at a softening point + 100°C. [4] The method for producing a carbon material according to [3], wherein the carbon material is a graphite electrode. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to obtain a binder pitch that can achieve both good kneadability and a high carbonization rate. According to the present disclosure, it is possible to obtain a high-density carbon material. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flow diagram showing a petrochemical process for thermally cracking naphtha or the like and a process for producing ethylene bottom oil. [Figure 2] FIG. 1 is a graph showing the change over time in the viscosity increase rate at 170° C. of various pastes (mixtures of needle coke and various binder pitches, needle coke:binder pitch=3:7 (mass ratio)). [Figure 3] FIG. 1 is a graph showing the change in viscosity when the shear rate is changed at a softening point of the binder pitch of Example 1 +100° C. (193° C.). [Figure 4] 1 is a Casson plot (measurement temperature: 193° C.) of the binder pitch of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will be described below, but it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention.

[0014] In this specification, when "to" is used to describe a range of values, the values ​​at both ends are the upper and lower limits, respectively, and are included in the range.

[0015] <Binder pitch> The binder pitch of one embodiment has a softening point of 70°C to 120°C, a fixed carbon content of 50.0% by mass or more, a quinoline insoluble content of 18.0% by mass or less, an initial boiling point of 320°C or more, and a Casson yield value at the softening point + 100°C of 0.18 Pa or more. The softening point, fixed carbon content, quinoline insoluble content, initial boiling point, and Casson yield value are measured by the methods described in the Examples section.

[0016] The softening point of the binder pitch in one embodiment is 70°C or higher, preferably 80°C or higher, and more preferably 85°C or higher. The softening point of the binder pitch in one embodiment is 120°C or lower, preferably 110°C or lower, and more preferably 100°C or lower. These upper and lower limit values ​​can be combined arbitrarily. A softening point within the above temperature range is preferable because the binder pitch softens sufficiently at the kneading temperature (for example, 130°C to 170°C) and exhibits good kneadability.

[0017] The higher the fixed carbon content, the higher the carbonization rate and the higher the density of the resulting carbon material. In one embodiment, the fixed carbon content of the binder pitch is 50.0 mass% or more, and preferably 51.0 mass% or more. The upper limit of the fixed carbon content is not particularly limited, but is, for example, 75.0 mass% or 85.0 mass%.

[0018] In one embodiment, the quinoline insoluble content (QI) of the binder pitch is 18.0% by mass or less, preferably 15.0% by mass or less, and more preferably 10.0% by mass or less. The quinoline insoluble content of the binder pitch includes not only the quinoline insoluble content contained in the base pitch but also carbon powder added to the base pitch. The carbon powder can be added, for example, in step 3 described below. It is preferable that the components detected as quinoline insoluble content (QI) are substantially free of mesophase spherulites that may be generated during the thermal treatment of petroleum heavy oil. As long as the Casson yield value at the softening point of the binder pitch + 100°C is 0.18 Pa or more, the lower limit of the quinoline insoluble content is not particularly limited, but is, for example, 1.0% by mass or 1.5% by mass.

[0019] The initial boiling point of the binder pitch in one embodiment is 320°C or higher, preferably 340°C or higher. If the initial boiling point is 320°C or higher, the amount of light components volatilized at the kneading temperature (e.g., 130°C to 170°C) is small, so the viscosity of the pitch is less likely to increase during kneading, allowing for good kneading. As long as the softening point of the binder pitch is in the range of 70°C to 120°C, the upper limit of the initial boiling point is not particularly limited, but is, for example, 400°C or 450°C.

[0020] In one embodiment, the Casson yield value at the softening point + 100°C of the binder pitch is 0.18 Pa or more, more preferably 0.20 Pa or more, and even more preferably 0.22 Pa or more. "At the softening point + 100°C of the binder pitch" means, for example, that when the softening point of the binder pitch is 93°C, the temperature at which the yield value is measured is set to 193°C. A Casson yield value of 0.18 Pa or more at the softening point + 100°C is preferred because it suppresses loss of binder pitch from the molded body that may occur during firing and tends to increase the carbonization rate. The upper limit of the Casson yield value at the softening point + 100°C is not particularly limited, but is, for example, 1.5 Pa or 1.0 Pa.

[0021] The Casson yield value can be calculated by measuring the relationship between shear rate and shear stress at the measurement temperature according to the method described in ASTM D5018-18, and then applying the Casson formula (1) to a graph plotting the measured values. That is, S is the shear stress (Pa), and D is the shear rate (s -1 ), τ0: Casson yield value (Pa), μ0: Casson viscosity (Pa·s), the Casson yield value is D in Casson equation (1). 1 / 2 S against 1 / 2 The y-intercept of the graph (τ0 1 / 2 ) squared.

number

[0022] <Method for producing binder pitch for carbon material production> The method for producing binder pitch for producing carbon materials is not particularly limited as long as it is a method that can produce binder pitch that satisfies predetermined physical property values, and examples thereof include the following production methods. The method for producing binder pitch for producing carbon materials in one embodiment includes at least the following steps 1 to 3 in this order, and other steps may be added. Process 1 (heat treatment process): Process of heat treating petroleum heavy oil Step 2 (distillation step): A step of distilling the heat-treated product obtained in step 1 to obtain a base pitch having a softening point of 60°C to 110°C, a fixed carbon content of 49.0% by mass or more, an initial boiling point of 320°C or more, and a quinoline insoluble matter (QI) of 1.0% by mass or less as a high-boiling point component. Step 3 (carbon powder mixing step): A step of adding carbon powder to the base pitch obtained in step 2 and mixing to obtain binder pitch.

[0023] The petroleum heavy oil used as the feedstock is not particularly limited as long as it can produce a base pitch having the desired properties in step 2, but preferably has the following composition. That is, the content of fractions having a boiling point of less than 150°C in the petroleum heavy oil is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The content of fractions having a boiling point of 150°C or more but less than 450°C in the petroleum heavy oil is preferably 75% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. The content of fractions having a boiling point of 450°C or more but less than 550°C in the petroleum heavy oil is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. The content of fractions having a boiling point of 550°C or more in the petroleum heavy oil is preferably 5% by mass or less, preferably 3% by mass or less, and even more preferably 1% by mass or less. The content of fractions in each temperature range referred to here means the distillate amount in each temperature range when the distillation curve of the petroleum heavy oil is determined. The distillation curve can be calculated by selecting an appropriate method from JIS K 2254:2018, ASTM D7500-15, and ASTM D7169-16 depending on the type of petroleum heavy oil.

[0024] An example of a petroleum heavy oil having the above composition is ethylene bottom oil light fraction. In the petrochemical industry, naphtha or the like is generally thermally cracked at high temperatures, and the resulting pyrolysis product is distilled to separate it into various fractions, such as ethylene, propylene, and other olefins, aromatic compounds such as benzene, toluene, and xylene, cracked gasoline, and cracked kerosene, which are then used as products. Of these fractions, the heavy fraction with the highest boiling point is called ethylene bottom oil, and is used as a raw material and fuel for carbon black, etc. (See Figure 1). Since plants for thermally cracking naphtha and the like are often called ethylene plants, the above-mentioned heavy fraction is called ethylene bottom oil.

[0025] The properties of ethylene bottom oil obtained by thermal cracking of naphtha-containing feedstock vary depending on the type of naphtha-containing feedstock, the thermal cracking conditions, the operating conditions of the refinery distillation column, etc., but generally, the 50% distillation temperature is 200°C to 400°C, the aromatic carbon content is 50% by mass or more, the flash point is 70°C to 100°C, and the kinematic viscosity at 50°C is 40mm 2 However, since ethylene bottom oil is a mixture of hydrocarbons, the above value may vary slightly.

[0026] Ethylene bottom oil light fraction refers to a distillate obtained by distilling off a desired proportion (e.g., 5% to 70% by mass) of light fractions from ethylene bottom oil by distillation or the like. The high-boiling point components obtained in this process are called ethylene bottom oil heavy fraction. Ethylene bottom oil, ethylene bottom oil heavy fraction, or other heavy oils may be added to the ethylene bottom oil light fraction as long as the above-mentioned preferred composition is satisfied. Examples of other heavy oils include, but are not limited to, fluid catalytic cracking oil (FCC decant oil), atmospheric distillation residue, vacuum distillation residue, various petroleum heavy oils hydrotreated, cracked kerosene, and coal tar. Sulfur and nitrogen contents in pitch are preferably low because they cause puffing during firing. When graphite electrodes are produced using pitch containing a high content of metal components, these metal components evaporate during graphitization, reducing the density of the graphite electrode, which may be undesirable in terms of product quality. From these perspectives, other heavy oils with low sulfur, nitrogen, and metal contents are preferred. As such other heavy oils, fluid catalytic cracking oil (FCC decant oil) and cracked kerosene are preferred. The properties of fluid catalytic cracking oil (FCC decant oil) vary depending on the raw material, operating conditions, etc., but generally, the 50% distillation temperature is 300°C to 450°C, the flash point is 60°C to 160°C, and the kinematic viscosity at 40°C is 40mm. 2 / s. However, since fluid catalytic cracking oil (FCC decant oil) is a complex mixture, the above values ​​may vary slightly. In one embodiment, the petroleum heavy oil is an ethylene bottoms light fraction.

[0027] Cracked kerosene is a mixture of hydrocarbons, mainly those with 9 or more carbon atoms, produced in petrochemical processes, and is a fraction with a boiling point in the range of 90°C to 230°C at 1 atmosphere. However, because cracked kerosene is a mixture of hydrocarbons, the number of carbon atoms and boiling point may vary slightly.

[0028] Examples of the main components of cracked kerosene include xylene, styrene, allylbenzene, propylbenzene, methylethylbenzene, trimethylbenzene, methylstyrene, dicyclopentadiene, indane, indene, methylpropylbenzene, methylpropenylbenzene, ethylstyrene, divinylbenzene, methylindene, naphthalene, and methyldicyclopentadiene.

[0029] (Process 1: Heat treatment process) Step 1 is a step of heat treating petroleum heavy oil. The heat treatment is preferably carried out in a sealed container in a non-oxidizing gas atmosphere. Examples of non-oxidizing gases include nitrogen gas, argon gas, hydrogen gas, lower alkanes such as methane and ethane, and mixed gases of these non-oxidizing gases. Nitrogen gas is preferred from the viewpoints of cost and ease of handling.

[0030] The heat treatment temperature is preferably 380°C or higher, more preferably 400°C or higher, and even more preferably 410°C or higher. The heat treatment temperature is preferably 500°C or lower, more preferably 480°C or lower, and even more preferably 450°C or lower. These upper and lower limit values ​​can be combined arbitrarily. A preferred range is 380°C to 500°C, more preferably 400°C to 480°C, and even more preferably 410°C to 450°C.

[0031] The appropriate heat treatment time varies depending on the heat treatment temperature. When the heat treatment temperature is 380°C to 400°C, the time from when the predetermined heat treatment temperature is reached (the same applies below) is preferably 8 to 48 hours, more preferably 16 to 48 hours. When the heat treatment temperature is above 400°C to 430°C, the time is preferably 1 to 24 hours, more preferably 3 to 16 hours. When the heat treatment temperature is above 430°C to 500°C, the time is preferably 0.1 to 16 hours, more preferably 0.5 to 8 hours. The upper and lower limit values ​​for the appropriate heat treatment time under each heat treatment temperature condition can be combined arbitrarily.

[0032] The pressure at the start of the heat treatment (initial pressure) is preferably 0 MPaG, but is not particularly limited. The pressure inside the sealed container rises due to hydrogen and lower alkanes such as methane and ethane generated by thermal decomposition during the heat treatment. There is no limit to the pressure inside the sealed container, and it is possible to release the pressure as needed. However, carrying out the heat treatment under pressurized conditions is preferred because this tends to increase the yield of base pitch obtained in step 2. When carrying out the heat treatment under pressurized conditions, the preferred pressure range is, for example, about 0.1 MPaG to 15 MPaG.

[0033] As described in JP-A-60-179493 and JP-A-60-240790, a solid catalyst or the like may be added during the heat treatment, but in that case, a step of removing the solid catalyst must be added before step 3.

[0034] (Process 2: Distillation process) Step 2 is a step in which the heat-treated product obtained in Step 1 is distilled to remove low-boiling components and obtain a pitch (base pitch) with the desired properties as a high-boiling component. The distillation method in Step 2 may be atmospheric distillation, reduced-pressure distillation (vacuum distillation), or a combination of atmospheric distillation and reduced-pressure distillation, and can be selected appropriately. The internal temperature of the distillation apparatus preferably does not exceed 360°C. This is because, if the temperature exceeds 360°C, reactions such as polymerization are likely to occur, and coking may occur on the inner walls of the distillation apparatus. The lower limit temperature does not affect the pitch properties, but a low temperature requires a low distillation pressure to distill off the low-boiling components, so from an economical perspective, a temperature of 200°C or higher is preferable. When performing reduced-pressure distillation (vacuum distillation), in order to obtain a base pitch with an initial boiling point of 320°C or higher, the distillation pressure is preferably 100 PaA to 10,000 PaA, more preferably 500 PaA to 3,000 PaA, and even more preferably 800 PaA to 2,000 PaA. In general, the higher the distillation end point, the higher the initial boiling point. Although it depends on the type of petroleum heavy oil used, the heat treatment conditions in step 1, and the distillation conditions in step 2, in order to make the initial boiling point of the obtained base pitch 320°C or higher, the distillation end point converted to atmospheric pressure is preferably 320°C or higher, and more preferably 330°C or higher.

[0035] The softening point of the base pitch of one embodiment obtained in step 2 is preferably 60°C or higher, more preferably 65°C or higher. The softening point of the base pitch of one embodiment obtained in step 2 is preferably 110°C or lower, more preferably 100°C or lower. These upper and lower limit values ​​can be combined as desired. A preferred range is 60°C to 110°C, more preferably 65°C to 100°C. Although this depends on the type and amount of carbon powder added and mixed in step 3, a softening point of 60°C to 110°C is preferred because the softening point of the resulting binder pitch will be 70°C to 120°C. The softening point is measured by the method described in the Examples section.

[0036] The fixed carbon content of the base pitch in one embodiment obtained in step 2 is preferably 49.0% by mass or more, and more preferably 50.0% by mass or more. Although it depends on the type and amount of carbon powder added and mixed in step 3, a fixed carbon content of 49.0% by mass or more is preferable because the fixed carbon content of the resulting binder pitch will be 50.0% by mass or more. The upper limit of the fixed carbon content is not particularly limited, but is, for example, 75.0% by mass or 85.0% by mass. The fixed carbon content is measured by the method described in the Examples section.

[0037] The initial boiling point of the base pitch in one embodiment is preferably 320°C or higher, more preferably 330°C or higher. Although it depends on the conditions of step 3, if the initial boiling point of the base pitch is 320°C or higher, the initial boiling point of the resulting binder pitch will also be 320°C or higher, which is preferable. The upper limit of the initial boiling point of the base pitch in one embodiment is not particularly limited as long as the softening point of the resulting base pitch is 60°C to 110°C, but is preferably 450°C or lower, more preferably 400°C or lower. These upper and lower limit values ​​can be arbitrarily combined. A preferred range is 320 to 450°C, more preferably 330 to 400°C. The initial boiling point is measured by the method described in the Examples section.

[0038] Quinoline insolubles (QI) (mesophase spherulites) formed by heat treatment of petroleum-based heavy oils cause a decrease in kneadability (Light Metals 2006, pp. 535-540). Therefore, the quinoline insolubles (QI) of the base pitch in one embodiment is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The lower limit of the QI of the base pitch is not particularly limited, but is, for example, 0.0% by mass or 0.001% by mass. The QI is measured by the method described in the Examples section.

[0039] (Process 3: Carbon powder mixing process) Step 3 is a step of adding and mixing carbon powder with the base pitch obtained in Step 2. The carbon powder used is not particularly limited as long as it improves the Casson yield value of the binder pitch without impairing the kneadability of the resulting binder pitch. For example, carbon powder with a particle size of approximately 1 nm to 20 μm can be used. Here, within the above particle size range, the particle size of particles 10 nm or more refers to the average particle size (median diameter: D50) measured by laser diffraction / scattering, and the particle size of particles less than 10 nm refers to the arithmetic mean diameter measured by electron microscope observation. Examples of such carbon powder include graphite powders such as artificial graphite powder and natural graphite powder, coke powder, and free carbon powder in coal tar (primary QI), with artificial graphite powder and coke powder being preferred. Carbon powder by-produced during the production of graphite electrodes can also be used. The carbon powder can be used alone or in a mixture of two or more types. In one embodiment, the carbon powder is artificial graphite powder.

[0040] The amount of carbon powder added is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, per 100 parts by mass of base pitch. The amount of carbon powder added is preferably 22.0 parts by mass or less, more preferably 18.0 parts by mass or less, and even more preferably 11.0 parts by mass or less, per 100 parts by mass of base pitch. These upper and lower limits can be arbitrarily combined. A preferred range is 1.0 part by mass or more and 22.0 parts by mass or less, more preferably 3.0 parts by mass or more and 18.0 parts by mass or less, and even more preferably 5.0 parts by mass or more and 11.0 parts by mass or less, per 100 parts by mass of base pitch. Although this range depends on the amount of quinoline insoluble matter in the base pitch, within the above range, the quinoline insoluble matter in the resulting binder pitch will be 18.0 mass% or less, which allows for an improvement in the Casson yield value without impairing kneadability, thereby improving the carbonization rate.

[0041] The method for mixing the base pitch and the carbon powder is not particularly limited, but a method that allows the carbon powder to be well dispersed in the base pitch is preferred.

[0042] For example, a method of mixing base pitch and carbon powder at a temperature equal to or higher than the softening point of the base pitch can be used. When mixing base pitch and carbon powder at a temperature equal to or higher than the softening point of the base pitch, the mixing temperature is preferably 350°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower. Although depending on the mixing conditions, a temperature of 350°C or lower can minimize deterioration of the base pitch that may occur during mixing. The mixing time is not particularly limited, but is, for example, 5 minutes to 24 hours. Although depending on the mixing conditions, within the above range, the carbon powder can be well dispersed in the base pitch. The mixing atmosphere is not particularly limited, and can be performed in air or a non-oxidizing gas atmosphere. However, from the viewpoint of minimizing deterioration of the base pitch that may occur during mixing, a non-oxidizing gas atmosphere is preferred. Examples of non-oxidizing gases include nitrogen gas, argon, hydrogen gas, lower alkane gases such as methane and ethane, and mixtures of these non-oxidizing gases. Among these, nitrogen gas is preferred from the viewpoints of cost and ease of handling. The mixing device is not particularly limited, but for example, a heatable mixer, kneader, etc. can be used.

[0043] Another example of a mixing method is to dissolve the base pitch in a suitable solvent and mix it with carbon powder. In this case, a step of removing the solvent by vacuum distillation or the like is required after mixing. Suitable solvents are not particularly limited as long as they can dissolve the base pitch well, but benzene, toluene, xylene, quinoline, pyridine, and mixtures thereof are preferred. Fractions containing large amounts of benzene and toluene obtained from petrochemical processes can also be used. Examples of such fractions include cracked gasoline and cracked kerosene.

[0044] Cracked gasoline is a mixture of hydrocarbons, mainly containing 6 to 8 carbon atoms, produced in a petrochemical process, and is a fraction with a boiling point in the range of 65°C to 150°C at 1 atmosphere. However, because cracked gasoline is a mixture of hydrocarbons, the number of carbon atoms and boiling point may vary slightly.

[0045] The main components of cracked gasoline include, for example, benzene, toluene, ethylbenzene, xylene, styrene, and hexane.

[0046] The cracked kerosene is as described above.

[0047] Mixing using a solvent can be carried out at room temperature or under heated conditions. When mixing at normal pressure, mixing is preferably carried out at or below the boiling point of the solvent used. When mixing at a temperature above the boiling point of the solvent used, mixing can be carried out under reflux conditions or under pressure using a sealed container. Depending on the mixing conditions, the mixing temperature is preferably 350°C or less, more preferably 250°C or less, and even more preferably 200°C or less. Although depending on the mixing conditions, a temperature of 350°C or less can minimize deterioration of the base pitch that may occur during mixing. The mixing time is not particularly limited, but is, for example, 5 minutes to 24 hours. Depending on the mixing conditions, the carbon powder can be well dispersed in the base pitch within the above range. The mixing atmosphere is not particularly limited, and can be carried out in air or a non-oxidizing gas atmosphere. However, from the viewpoint of minimizing deterioration of the base pitch that may occur during mixing, it is preferable to carry out the mixing in a non-oxidizing gas atmosphere. Examples of non-oxidizing gases include nitrogen gas, argon gas, hydrogen gas, lower alkanes such as methane and ethane, and mixed gases of these non-oxidizing gases. Among these, nitrogen gas is preferred from the viewpoints of cost and ease of handling.

[0048] If the base pitch and carbon powder are mixed using a solvent, a solvent removal step is required after step 3. The solvent removal method is not particularly limited, but a method that can efficiently remove the solvent without altering the base pitch is preferred. Examples of such solvent removal methods include distillation. The distillation method in this case may be atmospheric distillation, reduced-pressure distillation (vacuum distillation), or a combination of atmospheric distillation and reduced-pressure distillation, and can be selected appropriately. It is preferable that the internal temperature of the distillation apparatus does not exceed 360°C. This is because, if the temperature exceeds 360°C, reactions such as polymerization are likely to occur, which may result in alteration of the base pitch. The lower limit temperature and the pressure when performing reduced-pressure distillation (vacuum distillation) do not affect the physical properties of the base pitch, so the conditions can be selected appropriately depending on the type of solvent used.

[0049] <Method of manufacturing carbon materials> In one embodiment, a method for producing a carbon material uses, as binder pitch, pitch having a softening point of 70°C to 120°C, a fixed carbon content of 50.0% by mass or more, a quinoline insoluble content of 18.0% by mass or less, an initial boiling point of 320°C or more, and a Casson yield value of 0.18 Pa or more at a softening point +100°C. The carbon material refers to various molded carbon materials such as graphite tubing, graphite crucibles, graphite boats, and graphite electrodes. An exemplary process for producing a carbon material such as a graphite electrode is described below. 1. Mixing process Mixing and kneading needle coke and binder pitch together 2. Molding process A process of molding the kneaded material to obtain a molded body of a predetermined size and shape. 3. Firing process A step of firing the compact to obtain a fired body. 4.Impregnation process A process of filling the fired body with impregnated pitch 5. Re-firing process A process of re-firing the fired body filled with impregnated pitch to obtain a re-fired body. 6.Graphitization process A step of graphitizing the re-fired body to obtain a graphitized body. 7. Processing process A process in which the graphitized body is formed into a predetermined shape by cutting or the like to produce carbon materials such as graphite electrodes.

[0050] 1. Mixing process The needle coke is crushed, classified, and blended in a predetermined particle size ratio with the binder pitch, and then mixed and kneaded together. The blending amount of the binder pitch varies depending on the blending method and molding method, but is generally about 20 to 30 parts by mass per 100 parts by mass of the needle coke.

[0051] The kneaded material may contain a puffing inhibitor such as iron oxide.

[0052] Commercially available mixers or kneaders can be used for mixing and kneading. Specific examples include mixers, kneaders, and other mixers and kneaders. The kneading temperature varies depending on the binder pitch used, but is generally about 130°C to 170°C. After kneading, the kneaded mixture is cooled to a temperature suitable for subsequent molding (for example, 100°C to 130°C).

[0053] In this step, the binder pitch used has a softening point of 70°C to 120°C, a fixed carbon content of 50.0% by mass or more, a quinoline insoluble content of 18.0% by mass or less, an initial boiling point of 320°C or more, and a Casson yield value of 0.18 Pa or more at a softening point + 100°C. Details of the pitch are as described above.

[0054] 2. Molding process The kneaded material is molded to obtain a molded product of a predetermined size and shape. The molding method can be appropriately selected from extrusion molding, molding, etc. depending on the target carbon material. When the target carbon material is a graphite electrode, extrusion molding into a cylindrical shape is generally used.

[0055] 3. Firing process The molded body from the previous process is heated and fired at 700°C to 1000°C to obtain a fired body. The firing process is preferably carried out in a non-oxidizing atmosphere of combustion exhaust gas. The molded body softens at the beginning of the temperature rise, and at 200°C to 500°C, a large amount of decomposition gas is generated by thermal decomposition and polycondensation of the binder pitch, resulting in the formation of pores and volume shrinkage. At 500°C to 600°C, the binder pitch carbonizes. The firing process, including cooling, often takes around one month.

[0056] 4.Impregnation process In the firing process, generally, 35% to 45% of the mass of the binder pitch is lost as volatile matter. At that time, a large number of pores are generated in the fired body. The impregnation process involves filling these pores with impregnation pitch. Impregnation is carried out, for example, by placing the fired body in an autoclave, degassing it under reduced pressure, and then injecting molten impregnation pitch into the pores at approximately 200°C and a gas pressure of approximately 1 MPa.

[0057] Although it differs depending on the type of carbon material to be produced and the production method, the softening point of the impregnation pitch used is preferably 80° C. to 120° C. The fixed carbon content is preferably 45.0 mass % or more, more preferably 50.0 mass % or more.

[0058] 5. Re-firing process The fired body filled with the impregnated pitch is fired again to obtain a refired body. The refired body can be performed under the same conditions as the firing step. The impregnation step and the refired body can be repeated as necessary.

[0059] 6.Graphitization process The re-fired body is placed in a furnace (such as an Acheson furnace or an LWG furnace) surrounded by an insulating material, and is subjected to heat treatment by applying current to packing coke or by resistance heating of the re-fired body. The graphitization temperature is 2000°C to 3000°C. This temperature is necessary to convert the amorphous carbon in the re-fired body into crystalline graphite. It is preferable to heat treat the re-fired body for several days to convert it into a graphitized body.

[0060] 7. Processing process The graphitized body is made into a carbon material with a predetermined shape, such as a graphite electrode product, by machining such as cutting. The density (bulk density) of the graphite electrode varies depending on the electric furnace equipment used and the operating conditions of the electric furnace, but is preferably 1.5 g / cm 3 ~1.9 g / cm 3 It is preferable that it is.

Example

[0061] The present invention will be further described with reference to the following examples and comparative examples. However, these examples show an example of the present invention, and the present invention is not limited to these examples.

[0062] <Method for measuring softening point (SP)> The softening point was measured in accordance with "8. Method for measuring softening point of tar pitch (ring and ball method)" of JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch".

[0063] <Method for measuring fixed carbon content> The fixed carbon content was measured in accordance with "11. Method for determining fixed carbon content" of JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch".

[0064] <Method for measuring quinoline insoluble content (QI)> The quinoline insoluble content (QI) was measured in accordance with the filtration method described in "15. Method for quantifying quinoline insoluble content of tar pitch" of JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch".

[0065] <Method for measuring initial boiling point> The initial boiling point of the pitch was measured in accordance with the "6. Vacuum method" described in JIS K 2254:2018 "Petroleum products - Method for determining distillation properties".

[0066] <Method for measuring Casson yield value> The relationship between shear rate and shear stress at each temperature was measured according to the method described in ASTM D5018-18. The shear rate was changed so that the torque was in the range of 10% to 90%, and the viscosity at each shear rate was recorded. As an example of the measurement results, the measurement results of Example 1 are shown in Figure 3. The yield value was calculated using the Casson formula (1) based on the measured data. As an example of how to calculate the yield value, the Casson plot of Example 1 is shown in Figure 4. The equipment used for the measurement is as follows: Rotational viscometer (Brookfield, DV-II +Pro) Thermosel (Brookfield, HT-110115 ADP) Spindle (Brookfield, SC4-21) Chamber (Brookfield, HT-2DB-100)

[0067] <Method for measuring pitch true density> The true density of the pitch was measured by a constant volume expansion method using an Accupyc II 1340 (Micromeritics) at 25°C using helium as the replacement gas.

[0068] <Electrode evaluation> Binder pitch and needle coke were mixed (needle coke:binder pitch = 8:2, mass ratio) using a laboratory kneader (Toshin Corporation, TDR200-3 model) and molded into the shape of an electrode piece (cylindrical; 50 mmΦ x 35 mm) to produce a green body. The green body was fired at approximately 1000 °C to produce a fired body. The densities of the green body and fired body were measured in accordance with JIS R 7222:2017 "Methods for measuring physical properties of graphite materials, 7. Method for measuring bulk density." The carbonization rate was calculated using equation (2).

[0069]

number

[0070] <Carbon powder> The artificial graphite powder used was fine artificial graphite powder (UF-G5) (Resonac Corporation, particle size: 3 μm), and the carbon black powder used was carbon black (MA230) (Mitsubishi Chemical Corporation, particle size: 30 nm).

[0071] <Stability evaluation at mixing temperature> The binder pitch and needle coke of the examples and comparative examples were mixed at 150°C for 5 minutes (needle coke:binder pitch = 3:7, mass ratio) to prepare a paste, which was used as a measurement sample for evaluation. This measurement sample was subjected to a measurement temperature of 170°C and a shear rate of 10 s -1 The viscosity was measured for 1 hour at 100°C, and the change in viscosity over time was recorded. An MCR72 (Anton Paar) was used for the viscosity measurement. The viscosity 10 minutes after the start of measurement was used as the reference viscosity, and the viscosity increase rate (%) was calculated using equation (3). If the viscosity increase rate 60 minutes after the start of measurement was 1.0% or less, the sample was judged to be stable at the kneading temperature (170°C in this case). If the viscosity increase rate 60 minutes after the start of measurement was 1.0% or less, the sample was judged to be "good," and if the viscosity increase rate exceeded 1.0%, the sample was judged to be "poor." The results are summarized in Table 1. The change in viscosity increase rate over time is shown in Figure 2.

[0072]

number

[0073] <Heavy and light ethylene bottoms> Using 894 kg of ethylene bottom oil (5% by mass distillation temperature: 196°C, 90% by mass distillation temperature: 575°C) as a raw material, it was purified by distillation in a distillation apparatus with 15 theoretical plates (Sulzer packing) at a pot temperature of 101°C and an operating pressure of 533 to 1067 PaA, yielding 544 kg of a heavy ethylene bottom oil fraction as a pot residue. The initial boiling point of the obtained heavy ethylene bottom oil fraction was 218°C. The component obtained as a distillate was used as a light ethylene bottom oil fraction.

[0074] <Method for measuring raw material composition (boiling point range)> The feedstock compositions (boiling point ranges) of the ethylene bottom oil and the light ethylene bottom oil fraction were measured in accordance with the method described in ASTM D7500-15 "Standard Test Method for Determination of Boiling Range Distribution of Distillates and Lubricating Base Oils - in Boiling Range from 100°C to 735°C by Gas Chromatography." An AC SIMDIS Analyzer (PAC) was used for the measurements.

[0075] Example 1 3,000 g of ethylene bottom oil light fraction was introduced into a 6.0 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the container was raised to 430 °C at a rate of 4 °C / min while stirring, and heat treatment was performed. Six hours after reaching 430 °C, the mixture was allowed to cool to room temperature, and the heat-treated product was removed. The heat-treated product was subjected to vacuum distillation using a vacuum distillation apparatus to remove low-boiling point components, yielding 720 g of base pitch A (yield 24%) as a high-boiling point component. 110.4 g of the obtained base pitch A and 9.6 g of artificial graphite powder were placed in a metal beaker and heated to 140 °C in an oil bath. The mixture was then heated and mixed for 30 minutes using a three-one motor to prepare 120 g of binder pitch, which was then subjected to various evaluations.

[0076] (Comparative Example 1) The base pitch A obtained in Example 1 was used as a binder pitch and various evaluations were carried out.

[0077] (Comparative Example 2) 114 g of the base pitch A obtained in Example 1 and 6 g of carbon black powder were placed in a metal beaker, heated to 140°C in an oil bath, and mixed with heating for 30 minutes using a Three-One Motor to prepare 120 g of binder pitch, which was then subjected to various evaluations.

[0078] (Comparative Example 3) 550 g of ethylene bottom oil (5% by mass distillation temperature: 196°C, 90% by mass distillation temperature: 575°C) was introduced into a 1.0 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the container was raised to 380°C at a rate of 4°C / min while stirring, thereby carrying out heat treatment. 36 hours after reaching 380°C, the mixture was allowed to cool to room temperature, and the heat-treated product was removed. The heat-treated product was subjected to vacuum distillation using a vacuum distillation apparatus to remove low-boiling components, yielding 226 g of base pitch B as a high-boiling component (41% yield). 110.4 g of the resulting base pitch B and 9.6 g of artificial graphite powder were placed in a metal beaker and heated to 140°C in an oil bath. The mixture was then heated and mixed for 30 minutes using a three-one motor to prepare 120 g of binder pitch, which was then subjected to various evaluations.

[0079] [Table 1-1] [Table 1-2]

[0080] Comparing the Examples and Comparative Examples, it can be seen that even though the softening points and fixed carbon contents are similar, a significantly higher carbonization rate can be obtained when a binder pitch with a Casson yield value of 0.18 Pa or higher is used. As mentioned above, this is thought to be due in part to the suppression of binder pitch loss from the compact during firing. Comparative Example 3 has a Casson yield value of 0.18 Pa or higher, which tends to result in a higher carbonization rate, but the initial boiling point is low, causing an increase in viscosity during kneading. This results in poor kneadability, a tendency for the compact density to be low, and therefore the density of the fired product to be low. From the above, it is clear that using a binder pitch with an appropriate softening point, fixed carbon content, quinoline insoluble content, initial boiling point, and Casson yield value at softening point + 100°C is effective in obtaining a carbon material with a higher density.

Claims

1. A binder pitch for producing carbon materials, having a softening point of 70°C to 120°C, a fixed carbon content of 50.0% by mass or more, a quinoline insoluble content of 10.0% by mass or less, an initial boiling point of 320°C or more, and a Casson yield value at the softening point + 100°C of 0.18 Pa or more.

2. 2. The binder pitch for producing a carbon material according to claim 1, wherein the carbon material is a graphite electrode.

3. A method for producing a carbon material using, as a binder pitch, pitch having a softening point of 70°C to 120°C, a fixed carbon content of 50.0 mass% or more, a quinoline insoluble content of 10.0 mass% or less, an initial boiling point of 320°C or more, and a Casson yield value of 0.18 Pa or more at a temperature 100°C above the softening point.

4. The method for producing a carbon material according to claim 3, wherein the carbon material is a graphite electrode.

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