Binder pitch manufacturing method

Abstract

This provides a suitable pitch for use as a binder pitch for carbon materials. [Solution] A method for producing binder pitch for carbon materials, comprising: a step of heat-treating petroleum-based heavy oil (step 1); a step of distilling the heat-treated product obtained in step 1 to obtain a base pitch as a high-boiling point component, having a softening point of 60°C to 110°C, a fixed carbon content of 50.0% by mass or more, an initial boiling point of 320°C to 450°C, and a quinoline insoluble content (QI) of 1.0% by mass or less; and a step of adding carbon powder to the base pitch obtained in step 2 and mixing it (step 3).

Description

Technical Field

[0001] The content of the present disclosure relates to a method for producing binder pitch for carbon materials such as graphite electrodes.

Background Art

[0002] Carbon materials such as graphite electrodes used in electric furnaces for remelting iron are produced by kneading and molding aggregate such as coke and pitch (referred to as "binder pitch") at a temperature above the softening point of the binder pitch, followed by firing and then graphitization. Since carbon materials are required to have characteristics such as high mechanical strength, high electrical conductivity, and high thermal conductivity, it is preferable that they have a high density. However, due to the volatilization of low molecular weight components in the binder pitch during the firing process, the fired body has a structure with many pores. Therefore, the porosity is reduced by impregnating the fired body with pitch (referred to as "impregnating pitch") and performing re-firing several times during the manufacturing process, and the resulting carbon material is made dense.

[0003] Heavy residual oil (ethylene bottom oil) by-produced when producing olefins such as ethylene and propylene by steam cracking or thermal cracking of petroleum hydrocarbons such as naphtha is only partially used as a raw material for carbon black, and most of it is used as fuel. Therefore, converting this ethylene bottom oil into a product with high added value is an issue in the technical field. In order to solve this issue, attempts have been made to produce binder pitch for carbon materials from ethylene bottom oil, taking advantage of the characteristics of ethylene bottom oil rich in aromatic compounds. However, petroleum pitch produced from petroleum heavy oil such as ethylene bottom oil has a lower carbonization rate than coal tar pitch having the same softening point as the petroleum pitch, and thus the density of the resulting carbon material tends to be low. Therefore, petroleum pitch is not widely used at present.

[0004] Among the properties required for binder pitch, some of the most important are the carbonization rate, softening point, and initial boiling point. A higher carbonization rate is preferable because it improves the density of the resulting calcined body, thus reducing the number of subsequent impregnation and re-calcination cycles of the impregnated pitch. If the softening point is too high, the kneadability and moldability decrease, so it is preferable to keep it at around 120°C or lower. If the initial boiling point is too low, a large amount of light components volatilize during kneading, which leads to an increase in viscosity during kneading and a decrease in kneadability and moldability, so it is preferable to keep it at around 320°C or higher. Generally, one method to increase the carbonization rate and initial boiling point of binder pitch is to remove light components from the pitch by distillation, but this also has the problem of raising the softening point.

[0005] One method for improving the carbonization rate while suppressing the rise in the softening point to some extent is to add cutback oil to a pitch with a relatively high carbonization rate and a high softening point (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 6,352,637 [Overview of the project] [Problems that the invention aims to solve]

[0007] The method described in Patent Document 1 requires the addition of a cutback oil with a relatively low boiling point, which leads to a problem of a lower initial boiling point of the resulting pitch. Thus, it is difficult to independently adjust these parameters using conventional methods.

[0008] This disclosure provides a method for producing a pitch from petroleum-based heavy oil that is suitable as a binder pitch for carbon materials, having a high carbonization rate and excellent mixing stability. [Means for solving the problem]

[0009] The inventors diligently conducted research to obtain an excellent binder pitch for carbon materials from petroleum-based heavy oil. As a result, they discovered that a suitable pitch for use as a binder pitch for carbon materials can be obtained by adding carbon powder to a base pitch with a high fixed carbon content, high initial boiling point, and low softening point, which is obtained by distilling petroleum-based heavy oil after heat treatment, and mixing it, leading to the present invention.

[0010] In other words, the contents of this disclosure relate to the following [1] to [7].

[0011] [1] The process involves heat treatment of petroleum-based heavy oil (Process 1), Step 2 involves distilling the heat-treated product obtained in Step 1 to obtain a base pitch as a high-boiling point component, which has a softening point of 60°C to 110°C, a fixed carbon content of 50.0% by mass or more, an initial boiling point of 320°C to 450°C, and a quinoline insoluble content (QI) of 1.0% by mass or less. Step 3 involves adding carbon powder to the base pitch obtained in Step 2 and mixing it, A method for manufacturing binder pitch for carbon materials, including [the specified component]. [2] A method for manufacturing a binder pitch for carbon materials according to [1], wherein the 3% distillation temperature of the base pitch is 340°C or higher and 470°C or lower. [3] A method for producing binder pitch for carbon materials according to [1] or [2], wherein the petroleum-based heavy oil is the light component of ethylene bottom oil. [4] A method for producing binder pitch for carbon materials according to any one of the following [1] to [3], wherein the carbon powder is at least one selected from the group consisting of graphite powder, coke powder, carbon black powder, and free carbon powder in coal tar. [5] A method for manufacturing a binder pitch for carbon materials according to any one of [1] to [4], wherein the amount of carbon powder added is 1.0 part by mass or more and 22.0 parts by mass or less per 100 parts by mass of the base pitch. [6] The method for producing a binder pitch for carbon materials according to any one of [1] to [5], wherein the softening point of the binder pitch for carbon materials obtained in Step 3 is 80°C or higher and 120°C or lower, and the quinoline insoluble content is 18.0% by mass or lower. [7] The method for producing a binder pitch for carbon materials according to any one of [1] to [6], wherein the carbon material is a graphite electrode.

Advantages of the Invention

[0012] According to the present disclosure, a pitch suitable as a binder pitch for carbon materials can be obtained from petroleum heavy oil. Specifically, a binder pitch for carbon materials having a high carbonization rate and excellent kneading stability can be obtained. By using this binder pitch in the production of carbon materials, a high-density carbon material can be obtained.

Brief Description of the Drawings

[0013] [Figure 1] It is a flow chart showing a petrochemical process for thermally decomposing naphtha or the like and a production process of ethylene bottom oil. [Figure 2] It is a diagram showing the change over time of the viscosity increase rate at 170°C of various pastes (kneaded product of needle coke and various binder pitches, needle coke:binder pitch = 3:7 (mass ratio)).

Embodiments for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described, but it should be understood that the present invention is not limited only to these embodiments, and various applications are possible within the spirit and scope of implementation.

[0015] In this specification, when "~" is used for a numerical range, the numerical values at both ends are the upper limit value and the lower limit value, respectively, and are included in the numerical range. Each value such as the softening point, fixed carbon content, quinoline insoluble content, initial boiling point, etc. is measured by the method described in the section of the examples.

[0016] <Method for Producing Binder Pitch> The manufacturing method of the binder pitch of one embodiment includes at least the following steps 1 to 3 in this order, and other steps may be added. Step 1 (heat treatment step): A step of heat-treating petroleum heavy oil Step 2 (distillation step): Distilling the heat-treated product obtained in Step 1 to obtain a base pitch having a softening point of 60°C or higher and 110°C or lower, a fixed carbon content of 50.0% by mass or higher, an initial boiling point of 320°C or higher and 450°C or lower, and a quinoline insoluble content (QI) of 1.0% by mass or lower as a high-boiling 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 a binder pitch

[0017] The petroleum heavy oil used as a raw material is not particularly limited as long as a base pitch having desired properties can be obtained in Step 2, but it preferably has the following composition. That is, the content of the fraction 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 still more preferably 1% by mass or less. The content of the fraction having a boiling point of 150°C or higher and less than 450°C in the petroleum heavy oil is preferably 75% by mass or higher, more preferably 85% by mass or higher, and still more preferably 90% by mass or higher. The content of the fraction having a boiling point of 450°C or higher and less than 550°C in the petroleum heavy oil is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less. The content of the fraction having a boiling point of 550°C or higher in the petroleum heavy oil is preferably 5% by mass or less, preferably 3% by mass or less, and still more preferably 1% by mass or less. The content of the fraction in each temperature range mentioned here means the distillation amount in each temperature range when the distillation curve of the petroleum heavy oil is determined. The calculation method of the distillation curve can be appropriately selected from JIS K 2254:2018, ASTM D7500-15, and ASTM D7169-16 according to the type of the petroleum heavy oil and measured.

[0018] An example of a petroleum-based heavy oil having the above composition is the light component of ethylene bottom oil. In the petrochemical industry, naphtha and the like are generally pyrolyzed at high temperatures, and the resulting pyrolysis products are distilled to separate them 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 it is used as a raw material and fuel for carbon black and other products (see Figure 1). Since pyrolysis plants for naphtha and the like are often called ethylene plants, the aforementioned heavy fraction is called ethylene bottom oil.

[0019] The properties of ethylene bottom oil obtained by the thermal decomposition of naphtha-containing raw materials depend on the type of naphtha-containing raw material, thermal decomposition conditions, and operating conditions of the refining distillation column, 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 40 mmHg. 2 It is less than / s. However, since ethylene bottom oil is a mixture of hydrocarbons, the above value may vary slightly.

[0020] Ethylene bottom oil light component refers to the distillate obtained by removing a desired proportion (e.g., 5% to 70% by mass) of the light component from ethylene bottom oil through distillation or other operations. The high-boiling point component obtained at this time is called the ethylene bottom oil heavy component. Within the range of the preferred composition described above, ethylene bottom oil, ethylene bottom oil heavy component, and other heavy oils may be added to the ethylene bottom oil light component. Other heavy oils are not particularly limited, but examples include fluid catalytic cracking oil (FCC decanted oil), atmospheric distillation residue, vacuum distillation residue, hydrogenated petroleum-based heavy oils, cracked kerosene, coal tar, etc. Since the sulfur and nitrogen content in the pitch can cause buffing during calcination, it is preferable to have low levels of these. When graphite electrodes are manufactured using pitch containing a large amount of metal components, these metal components evaporate during graphitization, reducing the density of the graphite electrodes, which may be undesirable in terms of product quality. From these viewpoints, other heavy oils with low sulfur, nitrogen, and metal content are preferred. Other preferred heavy oils include fluid catalytic cracking oil (FCC decant oil) and cracked kerosene. The properties of fluid catalytic cracking oil (FCC decant oil) depend on the raw materials, operating conditions, etc., but generally they have a 50% distillation temperature of 300°C to 450°C, a flash point of 60°C to 160°C, and a kinematic viscosity of 40 mmHg at 40°C. 2 It is less than / s. However, since fluid catalytic cracking oil (FCC decanted oil) is a complex mixture, the above value may vary somewhat. In one embodiment, the petroleum-based heavy oil is the light component of ethylene bottom oil.

[0021] Decomposed 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, since decomposed kerosene is a mixture of hydrocarbons, the number of carbon atoms and the boiling point may vary somewhat.

[0022] Examples of the main components of decomposed kerosene include xylene, styrene, allylbenzene, propylbenzene, methylethylbenzene, trimethylbenzene, methylstyrene, dicyclopentadiene, indane, indene, methylpropylbenzene, methylpropenylbenzene, ethylstyrene, divinylbenzene, methylindene, naphthalene, and methyldicyclopentadiene.

[0023] (Process 1: Heat treatment process) Step 1 is a process of heat-treating petroleum-based 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, hydrogen gas, lower alkanes such as methane and ethane, and mixtures of these non-oxidizing gases. Nitrogen gas is preferred from the viewpoint of cost and ease of handling.

[0024] 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 limits can be combined in any way. The preferred range is 380°C to 500°C, more preferably 400°C to 480°C, and even more preferably 410°C to 450°C.

[0025] The appropriate heat treatment time varies depending on the heat treatment temperature. When the heat treatment temperature is 380°C to 400°C, 3 to 48 hours are preferred, and 6 to 48 hours are more preferred, from the time the predetermined heat treatment temperature is reached (the same applies hereinafter). When the heat treatment temperature is over 400°C to 430°C, 1 to 24 hours are preferred, and 3 to 16 hours are more preferred. When the heat treatment temperature is over 430°C to 500°C, 0.1 to 16 hours are preferred, and 0.5 to 8 hours are more preferred. The upper and lower limits of the appropriate heat treatment time for each heat treatment temperature condition can be arbitrarily combined.

[0026] By heat-treating a petroleum-based heavy oil having the above-mentioned preferred composition under conditions that satisfy the above-mentioned heat treatment temperature and heat treatment time, a base pitch with physical properties particularly suitable for the manufacture of carbon materials such as graphite electrodes can be obtained. This base pitch can be used as a binder pitch and impregnation pitch when manufacturing carbon materials such as graphite electrodes.

[0027] The pressure at the start of the heat treatment (initial pressure) is preferably 0 MPaG, but there are no particular restrictions. The pressure inside the sealed container will rise due to hydrogen and lower alkanes such as methane and ethane generated by thermal decomposition during the heat treatment. There are no restrictions on the pressure inside the sealed container, and depressurization is possible if necessary. However, it is preferable to carry out the process under pressurized conditions because the yield of base pitch obtained in step 2 tends to increase. A preferred pressure range when carrying out the process under pressurized conditions is, for example, about 0.1 MPaG to 15 MPaG.

[0028] As described in Japanese Patent Publication No. 60-179493 and Japanese Patent Publication No. 60-240790, additives such as solid catalysts may be added during the heat treatment of petroleum-based heavy oil, but in that case, an additive removal step must be added before step 3.

[0029] (Step 2: Distillation process) Step 2 is a process in which the heat-treated product obtained in Step 1 is distilled to remove low-boiling-point substances and obtain pitch having the desired properties as a high-boiling-point component. The pitch having the desired properties is called "base pitch". The distillation method in Step 2 may be atmospheric pressure distillation, reduced pressure distillation (vacuum distillation), or a combination of atmospheric pressure distillation and reduced pressure distillation, and can be selected as appropriate. The internal temperature of the distillation apparatus is preferably not to exceed 360°C. This is because reactions such as polymerization are likely to occur if the temperature exceeds 360°C, and coking may occur on the inner wall of the distillation apparatus. The lower limit temperature does not affect the properties of the pitch, but if the temperature is low, the distillation pressure must be lowered in order to remove low-boiling-point substances, so from an economic standpoint, 200°C or higher is preferable. When performing reduced pressure distillation (vacuum distillation), in order to obtain base pitch with an initial boiling point of 320°C or higher, the distillation pressure is preferably 100 PaA to 10000 PaA, more preferably 500 PaA to 3000 PaA, and even more preferably 800 PaA to 2000 PaA. Generally, the higher the distillation endpoint, the higher the initial boiling point. Depending on the type of petroleum-based heavy oil used, the heat treatment conditions in step 1, and the distillation conditions in step 2, etc., in order to obtain an initial boiling point of 320°C or higher for the base pitch and a 3% distillation temperature of 340°C or higher, the distillation endpoint at atmospheric pressure should preferably be 320°C or higher, and more preferably 330°C or higher.

[0030] The softening point of the base pitch of one embodiment obtained in step 2 is 60°C or higher, more preferably 70°C or higher. The softening point of the base pitch of one embodiment obtained in step 2 is 110°C or lower, more preferably 100°C or lower. These upper and lower limits can be combined arbitrarily. The preferred range is 60°C to 110°C, more preferably 70°C to 100°C. Depending on the type and amount of carbon powder added and mixed in step 3, if the softening point is 60°C to 110°C, the softening point of the resulting binder pitch will be 80°C to 120°C, which is preferable. The softening point is measured by the method described in the Examples section.

[0031] Since a higher fixed carbon content tends to result in a higher carbonization rate, the fixed carbon content of the base pitch in one embodiment is 50.0% by mass or more, and more preferably 51.0% by mass or more. The upper limit of the fixed carbon content is not particularly limited, but for example, it is 75.0% by mass or 85.0% by mass. The fixed carbon content is measured by the method described in the Examples section.

[0032] In one embodiment, the initial boiling point of the base pitch is 320°C or higher, more preferably 350°C or higher. In another embodiment, the initial boiling point of the base pitch is 450°C or lower, more preferably 400°C or lower. These upper and lower limits can be combined arbitrarily. The preferred range is 320°C to 450°C, more preferably 350°C to 400°C. If the initial boiling point is 320°C or higher, the amount of volatilization of light components at the kneading temperature (e.g., 140°C to 180°C) is small, so the viscosity of the pitch is less likely to increase during kneading, and kneading can be performed well. On the other hand, if the initial boiling point exceeds 450°C, depending on the raw materials and heat treatment conditions in step 1, the softening point of the base pitch may exceed 110°C, so an initial boiling point of 450°C or lower is preferable. The initial boiling point is measured by the method described in the Examples section.

[0033] In one embodiment, the quinoline-insoluble content (QI) of the base pitch is 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. If the QI of the base pitch is 1.0% by mass or less, the QI of the resulting binder pitch will be 18.0% by mass or less, which is preferable, depending on the type and amount of carbon powder added and mixed in step 3. The lower limit of the QI of the base pitch is not particularly limited, but for example, it is 0.0% by mass or 0.001% by mass. The QI is measured by the method described in the Examples section.

[0034] In one embodiment, the 3% distillation temperature of the base pitch is preferably 340°C or higher, and more preferably 380°C or higher. In another embodiment, the 3% distillation temperature of the base pitch is preferably 470°C or lower, and more preferably 450°C or lower. These upper and lower limits can be combined arbitrarily. The preferred range is 340°C to 470°C, and more preferably 380°C to 450°C. If the 3% distillation temperature is 340°C or higher, the amount of volatilization of light components at the kneading temperature (e.g., 150°C to 170°C) is small, so the viscosity of the pitch is less likely to increase during kneading, and kneading can be performed well. On the other hand, if the 3% distillation temperature exceeds 470°C, depending on the raw materials and heat treatment conditions in step 1, the softening point of the base pitch may exceed 110°C, so a 3% distillation temperature of 470°C or lower is preferred. The 3% distillation temperature is measured by the method described in the Examples section.

[0035] (Process 3: Carbon powder mixing process) Step 3 is a step of adding carbon powder to the base pitch obtained in Step 2 and mixing it. The carbon powder used is not particularly limited as long as it improves the carbonization rate without degrading the kneadability and moldability of the resulting binder pitch. For example, carbon powder with a particle size of about 1 nm to 20 μm can be used. Here, within the above particle size range, the particle size of particles 10 nm or larger refers to the average particle size (median diameter: D50) measured by laser diffraction and 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 powders include graphite powder such as artificial graphite powder and natural graphite powder, coke powder, carbon black powder, and free carbon powder in coal tar, but at least one selected from the group consisting of artificial graphite powder, coke powder, and carbon black powder is preferred. The carbon powder can be used alone or as a mixture of two or more. In one embodiment, the carbon powder is at least one selected from the group consisting of artificial graphite powder and carbon black powder.

[0036] 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 combined arbitrarily. The 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. Depending on the amount of quinoline insoluble matter in the base pitch, if the above range is used, the quinoline insoluble matter in the resulting binder pitch will be 18.0% by mass or less, and the carbonization rate can be improved without worsening the kneadability and moldability.

[0037] The method of mixing the base pitch and carbon powder is not particularly limited, but a method that well disperses the carbon powder in the base pitch is preferred.

[0038] For example, a method of mixing base pitch and carbon powder at a temperature above the softening point of the base pitch can be used. When mixing base pitch and carbon powder at a temperature above 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. Depending on the mixing conditions, a temperature of 350°C or lower can minimize the deterioration of the base pitch that may occur during mixing. The mixing time is not particularly limited, but for example, it is 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, but from the viewpoint of minimizing the deterioration of the base pitch that may occur during mixing, it is preferable to carry it out in a non-oxidizing gas atmosphere. 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 viewpoint of cost and ease of handling. The mixing apparatus is not particularly limited, but for example, a mixer, kneader, etc., that can be heated can be used.

[0039] Other mixing methods include dissolving the base pitch in a suitable solvent and mixing it with carbon powder. In this case, a step to remove the solvent after mixing, such as by vacuum distillation, is necessary. The suitable solvent is not particularly limited as long as it can dissolve the base pitch well, but benzene, toluene, xylene, quinoline, pyridine, and mixtures thereof can be used. 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.

[0040] Cracking gasoline is a mixture of hydrocarbons, mainly with 6 to 8 carbon atoms, produced in petrochemical processes, and is a fraction with a boiling point in the range of 65°C to 150°C at 1 atmosphere. However, since cracking gasoline is a mixture of hydrocarbons, the number of carbon atoms and the boiling point may vary somewhat.

[0041] Examples of the main components of cracked gasoline include benzene, toluene, ethylbenzene, xylene, styrene, and hexane.

[0042] The details regarding decomposed kerosene are as described above.

[0043] Mixing with a solvent can be carried out at room temperature or under heated conditions. When mixing at atmospheric pressure, it is preferable to perform the mixing below the boiling point of the solvent used. When mixing at a temperature above the boiling point of the solvent used, it 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 lower, more preferably 250°C or lower, and even more preferably 200°C or lower. Depending on the mixing conditions, if the temperature is 350°C or lower, the deterioration of the base pitch that may occur during mixing can be minimized. The mixing time is not particularly limited, but for example, it is 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, but from the viewpoint of minimizing the deterioration of the base pitch that may occur during mixing, it is preferable to carry it out in a non-oxidizing gas atmosphere. Examples of non-oxidizing gases include nitrogen gas, argon, hydrogen gas, lower alkanes such as methane and ethane, and mixtures of these non-oxidizing gases. Among these, nitrogen gas is preferred from the viewpoint of cost and ease of handling.

[0044] If a solvent is used to mix the base pitch and carbon powder, a solvent removal step is required from step 3 onward. The method of solvent removal is not particularly limited, but a method that can efficiently remove the solvent without altering the base pitch is preferred. Such solvent removal methods include distillation. In this case, the distillation method can be atmospheric pressure distillation, reduced pressure distillation (vacuum distillation), or a combination of atmospheric pressure distillation and reduced pressure distillation, and can be selected as appropriate. The internal temperature of the distillation apparatus should preferably not exceed 360°C. This is because reactions such as polymerization are likely to occur if the temperature exceeds 360°C, which may cause 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 as appropriate depending on the type of solvent used.

[0045] The total carbon powder content in the binder pitch of one embodiment obtained in step 3 is preferably 1.0 to 18.0% by mass, more preferably 3.0 to 15.0% by mass, and even more preferably 5.0 to 10.0% by mass.

[0046] The softening point of the binder pitch of one embodiment obtained in step 3 is preferably 80°C or higher, and more preferably 90°C or higher. The softening point of the binder pitch of one embodiment obtained in step 3 is preferably 120°C or lower, and more preferably 110°C or lower. These upper and lower limits can be combined arbitrarily. The preferred range is 80°C to 120°C, and more preferably 90°C to 110°C. If the softening point is between 80°C and 120°C, it can soften sufficiently at the kneading temperature (e.g., 140°C to 180°C), thus exhibiting good kneadability. The softening point is measured by the method described in the Examples section.

[0047] The quinoline-insoluble content of the binder pitch of one embodiment obtained in step 3 is preferably 18.0% by mass or less, more preferably 15.0% by mass or less, and even more preferably 10.0% by mass or less. If it is 18.0% by mass or less, the binder pitch can sufficiently wet the surface of the needle coke in the kneading step, which is one of the manufacturing steps of the graphite electrode, and thus exhibits good moldability. The quinoline-insoluble content of the binder pitch of one embodiment obtained in step 3 is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more. The quinoline-insoluble content of the binder pitch includes the quinoline-insoluble content contained in the base pitch, as well as the carbon powder added in step 3. The quinoline-insoluble content is measured by the method described in the Examples section.

[0048] <Manufacturing process for graphite electrodes> Carbon materials refer to various molded carbon materials such as graphite tubes, graphite crucibles, graphite boats, and graphite electrodes. The general manufacturing process for graphite electrodes is described below. 1. Mixing process The process of mixing and kneading needle coke and binder pitch together. 2. Molding process A process of molding a kneaded material to obtain a molded body of a predetermined size and shape. 3. Firing process A process of firing a molded body to obtain a fired body. 4.Impregnation process Process of filling the fired body with impregnated pitch 5. Re-firing process A process to obtain a re-fired body by firing a fired body filled with impregnated pitch again. 6. Graphitization process A process of obtaining a graphitized body by graphitizing a re-fired body. 7. Processing process The process of shaping a graphitized material into a predetermined shape by cutting or other means to create a graphite electrode.

[0049] 1. Mixing process The needle coke, which has been crushed, classified, and mixed to a predetermined particle size ratio, is mixed and kneaded together with the binder pitch. The amount of binder pitch varies depending on the kneading and molding methods, but is generally about 20 to 30 parts by mass per 100 parts by mass of needle coke.

[0050] The kneaded mixture may contain puffing inhibitors such as iron oxide.

[0051] Commercially available mixers or kneaders can be used for mixing and kneading. Specific examples include mixers, kneaders, and other types of mixers and kneaders. The kneading temperature varies depending on the binder pitch used, but is generally around 140°C to 180°C. After kneading, the mixture is cooled to a temperature suitable for subsequent molding (e.g., 100°C to 130°C).

[0052] The softening point of the binder pitch used is preferably 80°C to 120°C, although this varies depending on the type of carbon material manufactured and the manufacturing method. The fixed carbon content is preferably 45.0% by mass or more, and more preferably 50.0% by mass or more.

[0053] 2. Molding process The kneaded material is molded to obtain a molded body of a predetermined size and shape. The molding method can be appropriately selected from extrusion molding, mold molding, etc., depending on the target carbon material. When the target carbon material is a graphite electrode, extrusion molding into a cylindrical shape is common.

[0054] 3. Firing process The molded body from the previous step 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 in the initial stages of heating, and at 200°C to 500°C, a large amount of decomposition gas is generated by thermal decomposition and polycondensation of the binder pitch, causing pore formation and volume shrinkage. At 500°C to 600°C, the binder pitch carbonizes. The firing process, including cooling, often takes about one month.

[0055] 4.Impregnation process During the firing process, generally 35% to 45% of the binder pitch mass is lost as volatile matter. At this time, a large number of pores are generated in the fired body. The impregnation process is to fill these pores with impregnation pitch. Impregnation is carried out, for example, by placing the fired body in an autoclave, degassing it under reduced pressure, injecting molten impregnation pitch, and injecting the impregnation pitch into the pores at a gas pressure of about 1 MPa at approximately 200°C.

[0056] The softening point of the impregnating pitch used is preferably 80°C to 120°C, although this varies depending on the type of carbon material manufactured and the manufacturing method. The fixed carbon content is preferably 45.0% by mass or more, and more preferably 50.0% by mass or more.

[0057] 5. Re-firing process A re-fired body is obtained by firing the fired body filled with impregnated pitch again. The re-fired process can be carried out under the same conditions as the firing process described above. The impregnation process and the re-fired process may be repeated as needed.

[0058] 6. Graphitization process The re-calcined body is placed in a furnace (such as an Acheson furnace or LWG furnace) surrounded by insulating material, and heat treatment is applied to the re-calcined body by applying an electric current to the packing coke or by resistance heating of the re-calcined body. The temperature for graphitization is 2000°C to 3000°C. This temperature is necessary to convert amorphous carbon in the re-calcined body into crystalline graphite. It is preferable to heat-treat the re-calcined body for several days to convert it into a graphitized body.

[0059] 7. Processing process The graphitized material is processed by machining, such as cutting, to produce graphite electrode products of a predetermined shape. The density (bulk density) of the graphite electrode varies depending on the electric furnace equipment and operating conditions used, but is generally around 1.5 g / cm³. 3 ~1.9g / cm 3 It is preferable that this be the case. [Examples]

[0060] The present invention will be further described with reference to the following examples and comparative examples, but these examples are merely illustrations of the present invention and the present invention is not limited to these examples.

[0061] <Method for measuring the softening point (SP)> The softening point was measured in accordance with JIS K 2425:2006 "Test Methods for Creosote Oil, Processed Tar, and Tar Pitch," specifically "8. Method for Measuring the Softening Point of Tar Pitch (Ring-Ball Method)."

[0062] <Method for measuring fixed carbon (FC) 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".

[0063] <Method for measuring toluene-insoluble content (TI)> Toluene-insoluble content (TI) was measured in accordance with the filtration method described in "14.2 Method for Determining Toluene-Insoluble Content of Processed Tar and Tar Pitch" of JIS K 2425:2006 "Test Methods for Creosote Oil, Processed Tar, and Tar Pitch".

[0064] <Method for measuring quinoline insoluble matter (QI)> The quinoline insoluble content (QI) was measured in accordance with the filtration method described in "15. Method for Determining 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 the distillation properties of base pitch> The initial boiling point and 3% distillation temperature of the base pitch were measured in accordance with "6. Reduced pressure method" described in JIS K 2254:2018 "Petroleum products - Method for determining distillation properties".

[0066] <Method for measuring true pitch density> The true density of the pitch was measured using the constant volume expansion method with an Accupic II 1340 (Micromeritics). The measurement was performed at 25°C using helium as the displacement gas.

[0067] <Electrode Evaluation> Binder pitch and needle coke were mixed using a laboratory kneader (Toshin Corporation, TDR200-3 model) (needle coke:binder pitch = 8:2, mass ratio), and molded into the shape of an electrode piece (cylindrical; 50mmΦ × 35mm) by molding to produce a molded body. The molded body was fired at approximately 1000°C to produce a fired body. The density of the molded body and the fired body was measured in accordance with JIS R 7222:2017 "Method for measuring the physical properties of graphite materials 7. Method for measuring bulk density". The carbonization rate was calculated using formula (1).

[0068]

number

[0069] <Carbon powder> The artificial graphite powder used was artificial graphite fine powder (UF-G5) (Resonac Co., Ltd., particle size: 3 μm). The carbon black powder used was carbon black (MA230) (Mitsubishi Chemical Corporation, particle size: 30 nm).

[0070] <Method for mixing carbon powder and base pitch> Base pitch was placed in a beaker and heated to a predetermined temperature in an oil bath to dissolve it. Carbon powder was then added and mixed using a three-one motor to prepare binder pitch. The type of carbon powder used, the amount of carbon powder added, the mixing temperature, and the mixing time are as described in the Examples and Comparative Examples sections.

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

[0072]

number

[0073] <Ethylene bottom oil: heavy and light components> Using 894 kg of ethylene bottom oil (5% by mass distillation temperature: 196°C, 90% by mass distillation temperature: 575°C) as raw material, distillation and purification were performed in a 15-stage theoretical stage (Sulzer packing) distillation apparatus at a kettle temperature of 101°C and an operating pressure of 533-1067 PaA, yielding 544 kg of heavy ethylene bottom oil residue. The initial boiling point of the obtained heavy ethylene bottom oil was 218°C. The components obtained as distillates were used as light ethylene bottom oil.

[0074] <Method for measuring raw material composition (boiling point range)> The raw material composition (boiling point range) of ethylene bottom oil and ethylene bottom oil light component was 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℃ to 735℃ by Gas Chromatography". An AC SIMDIS Analyzer (PAC Corporation) was used for the measurements.

[0075] (Example 1) 3000 g of ethylene bottom oil light component 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 to perform heat treatment. After 6 hours from reaching 430°C, it was allowed to cool to room temperature, and the heat-treated material was removed. The heat-treated material was subjected to vacuum distillation using a vacuum distillation apparatus to remove low-boiling-point components, yielding 720 g of base pitch (yield 24%) as the high-boiling-point component. The physical properties of the obtained base pitch are shown in Table 1. 120 g of binder pitch was prepared by adding 9.6 g of artificial graphite powder to 110.4 g of the base pitch and heating and mixing at 140°C for 30 minutes using a three-one motor, and various evaluations were performed.

[0076] (Example 2) 120 g of binder pitch was prepared by adding 6 g of carbon black powder to 114 g of base pitch obtained in Example 1 and heating and mixing it at 140°C for 30 minutes using a three-one motor, and various evaluations were performed.

[0077] (Comparative Example 1) 550 g of ethylene bottom oil 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 to perform heat treatment. After 36 hours from reaching 380°C, the contents were allowed to cool to room temperature, and the heat-treated material was removed. The heat-treated material was then subjected to vacuum distillation in a vacuum distillation apparatus to remove the low-boiling-point components, yielding 226 g of pitch (yield 41%) as the high-boiling-point component. The physical properties of the obtained pitch are shown in Table 1. 120 g of pitch was obtained by adding 9.6 g of artificial graphite powder to 110.4 g of this pitch and heating and mixing at 140°C for 30 minutes, and various evaluations were performed using this pitch as a binder pitch.

[0078] (Comparative Example 2) Pitch was obtained by vacuum distillation of ethylene bottom oil without heat treatment. The physical properties of the obtained pitch are shown in Table 1. 120 g of the obtained pitch was prepared by adding 9.6 g of artificial graphite powder to 110.4 g of this pitch and heating and mixing at 140°C for 30 minutes. This was used as a binder pitch for various evaluations.

[0079] (Comparative Example 3) The base pitch obtained in Example 1 was used as the binder pitch for various evaluations.

[0080] (Reference example 1) The data for commercially available coal tar-based binder pitch is shown.

[0081] [Table 1-1] [Table 1-2]

[0082] A comparison of the electrode evaluation results for Example 1, Example 2, and Comparative Example 3 shows that the addition of carbon powder improves the carbonization rate and thus the density of the resulting calcined body. Furthermore, a comparison of Example 1 and Comparative Example 1 reveals that even when using the same carbon powder, the effect cannot be fully obtained if the physical properties of the base pitch are not appropriate. Specifically, the binder pitch of Comparative Example 1 has a fixed carbon content and true density similar to that of Example 1, but the initial boiling point of the base pitch is low. As a result, the stability at the mixing temperature is low, and viscosity increases during mixing (see Figure 2). Consequently, the kneadability and moldability decrease, resulting in a relatively low density of the molded body, as well as low carbonization rate and calcined body density. The base pitch of Comparative Example 2 has an inappropriate softening point, fixed carbon content, and initial boiling point, resulting in poor stability during mixing, and significantly lower carbonization rate and calcined body density. From the above, it is clear that it is important to add carbon powder to a base pitch that has an appropriate softening point, fixed carbon content, initial boiling point, and quinoline insoluble matter (QI).

Claims

1. The process of heat-treating petroleum-based heavy oil (Process 1), Step 2 involves distilling the heat-treated product obtained in Step 1 to obtain a base pitch as a high-boiling point component, which has a softening point of 60°C to 110°C, a fixed carbon content of 50.0% by mass or more, an initial boiling point of 320°C to 450°C, and a quinoline insoluble content (QI) of 1.0% by mass or less. Step 3 involves adding carbon powder to the base pitch obtained in Step 2 and mixing it, A method for manufacturing binder pitch for carbon materials, including [the specified component].

2. A method for manufacturing a binder pitch for carbon materials according to claim 1, wherein the 3% distillation temperature of the base pitch is 340°C or higher and 470°C or lower.

3. A method for producing binder pitch for carbon materials according to claim 1 or 2, wherein the petroleum-based heavy oil is ethylene bottom oil light component.

4. A method for producing binder pitch for carbon materials according to claim 1 or 2, wherein the carbon powder is at least one selected from the group consisting of graphite powder, coke powder, carbon black powder, and free carbon powder in coal tar.

5. A method for manufacturing a binder pitch for carbon material according to claim 1 or 2, wherein the amount of carbon powder added is 1.0 part by mass or more and 22.0 parts by mass or less with respect to 100 parts by mass of the base pitch.

6. A method for producing binder pitch for carbon materials according to claim 1 or 2, wherein the binder pitch for carbon materials obtained in step 3 has a softening point of 80°C or higher and 120°C or lower, and a quinoline insoluble content of 18.0% by mass or less.

7. A method for manufacturing a binder pitch for a carbon material according to claim 1 or 2, wherein the carbon material is a graphite electrode.

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