Method for manufacturing petroleum-based pitch

Abstract

This invention provides a method for producing high-performance petroleum-based pitch using petroleum-based heavy oil as a raw material, more easily than conventional technologies. [Solution] A method for producing petroleum-based pitch, comprising at least the following steps 1 to 3. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A process to separate toluene-insoluble matter (TI) by adding a poor solvent to the heat-treated product obtained in Step 1. Step 3: A step in which the heat-treated product with reduced TI content obtained in Step 2 is distilled to obtain pitch as a high-boiling point component.

Description

Technical Field

[0001] The present disclosure relates to a method for producing petroleum pitch.

Background Art

[0002] Carbon materials such as graphite electrodes used in electric furnaces for remelting iron are produced by kneading aggregates such as coke and pitch (referred to as "binder pitch") at a temperature not lower than the softening point of the binder pitch, molding, firing, and then graphitizing. Since carbon materials are required to have properties such as high mechanical strength, high electric conductivity, and high thermal conductivity, they are preferably of 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 re-firing several times during the manufacturing process, and the resulting carbon material is made dense. Therefore, impregnating pitch is essential for the production of high-quality carbon materials.

[0003] When producing olefins such as ethylene and propylene by steam cracking or thermal cracking of petroleum hydrocarbons such as naphtha, the heavy residual oil (ethylene bottom oil) by-produced 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. To solve this issue, attempts have been made to produce impregnating pitch from ethylene bottom oil, taking advantage of the characteristics of ethylene bottom oil containing a large amount of aromatic compounds. However, due to performance problems, the impregnating pitch mainly commonly used is coal tar pitch produced from coal tar, and at present, petroleum pitch produced from petroleum heavy oils such as ethylene bottom oil is not used very much.

[0004] Among the properties required for impregnated pitch, some of the most important are impregnation and fixed carbon content. The better the impregnation, the easier it is for the impregnated pitch to penetrate even the fine pores formed in the calcined body during the impregnation process, resulting in a higher density carbon material, which is preferable. The higher the fixed carbon content, the less volatile matter is released during calcination, reducing the generation of pores. As a result, the number of impregnation and re-calcination processes can be reduced, which is economically preferable. In coal tar pitch, various methods are known to improve its impregnation, and a typical example is the removal or reduction of quinoline insoluble matter (QI) in the pitch. Coal tar pitch usually contains several mass% to tens of mass% of QI, derived from primary QI contained in the raw material coal tar and secondary QI that can be generated during the heat treatment process. This QI exists as solid fine particles even when the impregnated pitch is molten during the impregnation process, and therefore significantly inhibits the impregnation of the pitch into the pores of the calcined body. For this reason, it is known that removing or reducing QI in coal tar pitch improves its impregnation. For example, Patent Document 1 reports that impregnation is improved by reducing the QI in coal tar pitch from 5.2% by mass to 0.9% by mass.

[0005] Patent Document 2 describes how impregnation can be significantly improved while maintaining a high fixed carbon content by appropriately adjusting the amount of toluene-insoluble matter (TI) in petroleum-based pitch. Specifically, it describes how a petroleum-based pitch having a quinoline-insoluble matter (QI) of 0.5% by mass or less, a toluene-insoluble matter (TI) of 3.0% by mass or less, a softening point of 60°C to 120°C, a viscosity of 200 mPa·s or less at 200°C, and a fixed carbon content Y (mass%) that satisfies formula (*) can achieve both good impregnation and a high fixed carbon content. 80.0 ≥ Y > 0.2X + 29.5 (*) Y: Fixed carbon amount (mass%) X: Softening point (℃) (60≦X≦120)

[0006] Patent Document 2 describes a method for producing petroleum-based pitch that satisfies all of the aforementioned requirements, comprising the steps of: heat-treating petroleum-based heavy oil (step 1); distilling the heat-treated product to obtain pitch as a high-boiling point component (step 2); reducing toluene-insoluble content from the pitch obtained in step 2 (step 3); and distilling the component with reduced toluene-insoluble content (TI) obtained in step 3 to adjust the softening point (step 4). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Unexamined Patent Publication No. 168691 / 1983 [Patent Document 2] International Publication No. 2023 / 233847 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] This disclosure provides a method for producing high-performance petroleum-based pitch using petroleum-based heavy oil as a raw material, more easily than conventional technologies. [Means for solving the problem]

[0009] This disclosure relates to the following [1] to

[11] . [1] A method for producing petroleum-based pitch, comprising at least the following steps 1 to 3. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A step to precipitate TI by adding a poor solvent to the heat-treated product obtained in Step 1, and then separate the TI. Step 3: A step in which the heat-treated product with reduced TI content obtained in Step 2 is distilled to obtain pitch as a high-boiling point component. [2] A method for producing petroleum-based pitch according to [1], wherein the poor solvent is at least one selected from the group consisting of alkanes having 3 to 20 carbon atoms and cycloalkanes having 3 to 20 carbon atoms. [3] A method for producing petroleum-based pitch according to [1], wherein the poor solvent is at least one selected from the group consisting of alkanes having 5 to 20 carbon atoms and cycloalkanes having 5 to 20 carbon atoms. [4] A method for producing petroleum-based pitch according to [1], wherein the poor solvent is at least one selected from n-pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, cyclohexane, methylcyclohexane, n-heptane, and n-octane. [5] A method for producing petroleum-based pitch according to [1], wherein the poor solvent is at least one selected from liquefied petroleum gas, petroleum ether, petroleum benzine, ligroin, whole range naphtha, light naphtha, heavy naphtha, kerosene, and diesel fuel. [6] A method for producing petroleum-based pitch according to [5], wherein the upper limit of the boiling point range of the poor solvent at 1 atmosphere is 110°C. [7] A method for producing petroleum-based pitch according to any one of [1] to [6], wherein in step 2, the amount of poor solvent added is 5 to 200 parts by mass per 100 parts by mass of the heat-treated product. [8] A method for producing petroleum-based pitch according to any one of [1] to [7], wherein the petroleum-based heavy oil is ethylene bottom oil. [9] A method for manufacturing petroleum-based pitch as described in any of [1] to [8], wherein the manufactured petroleum-based pitch satisfies the following conditions. Quinoline insoluble matter (QI) is 0.5% by mass or less. Toluene-insoluble content (TI) is 3.0% by mass or less. Softening point is below 120°C. Viscosity at 200°C is 200 mPa·s or less. The fixed carbon content Y (mass%) satisfies equation (1). 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃)

[10] The production method of the petroleum pitch according to any one of [1] to [9], wherein the petroleum pitch is an impregnation pitch for carbon materials.

[11] A method for producing a graphite electrode using the petroleum pitch obtained by the production method according to any one of [1] to [9] as an impregnation pitch.

Advantages of the Invention

[0010] According to the present disclosure, a high-performance petroleum pitch can be produced more simply than in the prior art using petroleum heavy oil as a raw material. Examples of the high-performance petroleum pitch include those having a quinoline insoluble content (QI) of 0.5% by mass or less, a toluene insoluble content (TI) of 3.0% by mass or less, a softening point of 60°C to 120°C, a viscosity at 200°C of 200 mPa·s or less, and a fixed carbon content Y (mass%) satisfying the formula (1). 80.0≧Y>0.2X + 29.5 (1) Y: Fixed carbon content (mass%) X: Softening point (°C) This petroleum pitch is excellent in impregnability into a fired body and has a high fixed carbon content, so that the density of the obtained carbon material can be improved and the quality of the carbon material can be made excellent.

Brief Description of the Drawings

[0011] [Figure 1] It is a flowchart showing a petrochemical process for pyrolyzing naphtha or the like and a production process of ethylene bottom oil. [Figure 2] It is a flowchart showing an embodiment of a production method of petroleum pitch.

Modes for Carrying Out the Invention

[0012] 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.

[0013] <Production Method of Petroleum Pitch> One embodiment of the method for producing petroleum-based pitch includes at least the following steps 1 to 3 in this order. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A step to precipitate TI by adding a poor solvent to the heat-treated product obtained in Step 1, and then separate the TI. Step 3: A step in which the heat-treated product with reduced TI content obtained in Step 2 is distilled to obtain pitch as a high-boiling point component.

[0014] In the petrochemical industry, naphtha and other materials 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 is used as a raw material for carbon black and as fuel (see Figure 1). Since the pyrolysis plants for naphtha and other materials are often called ethylene plants, the aforementioned heavy fraction is called ethylene bottom oil.

[0015] 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. Generally, however, the 50% distillation temperature is 200°C to 400°C, the aromatic hydrocarbon 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.

[0016] Examples of petroleum-based heavy oils used in step 1 include ethylene bottom oil, ethylene bottom oil heavy component obtained by removing an arbitrary proportion (e.g., 5-70% by mass) of light component from ethylene bottom oil by distillation, ethylene bottom oil light component obtained by removing an arbitrary proportion (e.g., 5-60% by mass) of heavy component from ethylene bottom oil by distillation, other petroleum-based heavy oils such as heavy oil produced during catalytic cracking of petroleum products, and mixtures thereof. In one embodiment, the petroleum-based heavy oil is ethylene bottom oil. In addition, heavy oils such as coal tar may be added to the petroleum-based heavy oil. Other petroleum-based heavy oils are not particularly limited, but examples include fluid catalytic cracking oil (FCC decanted oil), atmospheric distillation residue, and vacuum distillation residue. The sulfur and nitrogen content in the pitch obtained in step 3 is preferably low because it can cause buffing during calcination. 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 perspectives, other petroleum-based heavy oils are preferred if they have low sulfur, nitrogen, and metallic content, and fluid catalytic cracking oil (FCC decant oil) is preferred. The properties of fluid catalytic cracking oil (FCC decant oil) depend on the raw materials, operating conditions, etc., but generally, the 50% distillation temperature is 300-450°C, the flash point is 60-160°C, and the kinematic viscosity at 40°C is 40 mmHg. 2 It is less than / s. However, since fluid catalytic cracking oil (FCC decanted oil) is a complex mixture, the above value may vary slightly.

[0017] (Process 1) 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, but nitrogen gas is preferred from the viewpoint of cost and ease of handling.

[0018] The heat treatment temperature is preferably 360°C to 500°C, more preferably 380°C to 450°C, and even more preferably 400°C to 450°C.

[0019] The appropriate heat treatment time varies depending on the heat treatment temperature. When the heat treatment temperature is 360°C to 390°C, the treatment time is preferably 3 to 48 hours, and more preferably 4 to 36 hours, from the time the predetermined heat treatment temperature is reached (the same applies hereinafter). When the heat treatment temperature is above 390°C to 430°C, the treatment time is preferably 0.5 to 24 hours, and more preferably 1 to 16 hours. When the heat treatment temperature is above 430°C to 500°C, the treatment time is preferably 0.1 to 16 hours, and more preferably 0.5 to 8 hours. By setting the heat treatment time within the above ranges, a pitch with a sufficient amount of fixed carbon can be obtained.

[0020] 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, but pressurized conditions are preferred because TI is easily generated under atmospheric pressure, which reduces the final pitch yield. When performing heat treatment under pressure, it is preferable to raise the pressure to a predetermined level with a non-oxidizing gas before starting the heat treatment. During the heat treatment, the pressure will rise due to the generation of decomposition gases associated with thermal decomposition, so it is preferable to perform the heat treatment while depressurizing as needed.

[0021] The reactor is not particularly limited as long as it can perform heat treatment under the above conditions. Specific examples of reactors include batch reactors such as autoclaves, and continuous reactors such as tubular reactors (PFRs) and continuous tank reactors (CSTRs). A reactor combining a batch reactor and a continuous reactor is also acceptable. In one embodiment, the reactor is an autoclave.

[0022] In step 1, additives such as solid catalysts may be added to the petroleum-based heavy oil. The solid catalyst referred to here is a catalyst that does not dissolve in the reaction substrate (i.e., petroleum-based heavy oil) and does not decompose even at the heat treatment temperature. Specifically, examples include activated clay, silica alumina, zeolite, and other solid acid catalysts. As described in Japanese Patent Publication No. 60-179493 and Japanese Patent Publication No. 60-240790, these solid acid catalysts are known to suppress the occurrence of fouling during the heat treatment of petroleum-based heavy oil and are useful when heat treatment is performed under relatively harsh reaction conditions with the aim of improving the fixed carbon content of pitch. The added solid catalyst can be removed as insoluble matter along with TI in step 2 and is therefore not mixed into the pitch finally obtained in step 3.

[0023] (Process 2) Step 2 is a step in which TI is precipitated and separated from the heat-treated product obtained in Step 1. In Step 2, a liquid component from which TI has been separated, i.e., a heat-treated product with a reduced TI content, is obtained. In Step 2, when a poor solvent is mixed with the heat-treated product, the solubility of TI in the mixture with respect to components other than TI (components other than TI in the heat-treated product + poor solvent) decreases, causing TI to precipitate and the mixture to become a slurry. The solid catalyst, which may be added as needed, does not dissolve in the components other than TI in the mixture (components other than TI in the heat-treated product + poor solvent). TI is a solid component at room temperature (25°C) on its own. The heat-treated product is a complex mixture containing components with relatively low molecular weight (low molecular weight components) such as toluene, components with medium molecular weight (medium molecular weight components), and components with relatively high molecular weight (high molecular weight components) such as TI. While not bound by any particular theory, it is presumed that the reason heat-treated materials are liquid at room temperature (25°C) is that low molecular weight components dissolve medium molecular weight components, and these (low molecular weight components + medium molecular weight components) dissolve high molecular weight components. Therefore, factors contributing to the solubility of TI include not only the solubility of TI for individual components, but also the solubility of medium molecular weight components for low molecular weight components and the solubility of high molecular weight components for "low molecular weight components + medium molecular weight components". When a poor solvent is added to the heat-treated material, the components other than high molecular weight components become "low molecular weight components + medium molecular weight components + poor solvent", changing the balance of solubility, so it is presumed that the solubility of high molecular weight components decreases and high molecular weight components precipitate. Therefore, as a poor solvent, it is not necessarily preferable to use a solvent that does not dissolve TI on its own, but rather a solvent that reduces the solubility of TI when mixed with the heat-treated material.

[0024] In this disclosure, "poor solvent" means a solvent that, when added to the heat-treated product obtained in step 1 to form a mixture, reduces the solubility of TI in the mixture and allows TI to precipitate. The poor solvent may be a mixed solvent.

[0025] The poor solvent is preferably at least one selected from the group consisting of alkanes having 3 to 20 carbon atoms and cycloalkanes having 3 to 20 carbon atoms, and more preferably at least one selected from the group consisting of alkanes having 5 to 20 carbon atoms and cycloalkanes having 5 to 20 carbon atoms. The poor solvent may be a mixture of these. The number of carbon atoms in the alkane may be 3 or more, or 5 or more, and may be 20 or less, 10 or less, or 7 or less. Among the alkanes having 3 to 20 carbon atoms, those having 5 to 20 carbon atoms are preferred, those having 5 to 10 carbon atoms are more preferred, and those having 5 to 7 carbon atoms are even more preferred. The alkanes may be linear or branched. The number of carbon atoms in the cycloalkane may be 3 or more, 5 or more, or 6 or more, and may be 20 or less, 15 or less, or 10 or less. Among the cycloalkanes having 3 to 20 carbon atoms, those having 5 to 20 carbon atoms are preferred, those having 5 to 15 carbon atoms are more preferred, and those having 6 to 10 carbon atoms are even more preferred. Cycloalkanes may have branching. From the viewpoint of ease of handling, among alkanes having 3 to 20 carbon atoms and cycloalkanes having 3 to 20 carbon atoms, those with a boiling point of 40 to 130°C at 1 atmosphere are preferred.

[0026] As an alkane having 3 to 20 carbon atoms, specifically, at least one selected from propane, butane, n-pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, n-octane, n-nonane, and n-decane is preferred, at least one selected from n-pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, and n-octane is more preferred, and at least one selected from n-pentane and n-hexane is even more preferred.

[0027] As a cycloalkane having 3 to 20 carbon atoms, specifically, at least one selected from cyclopentane, cyclohexane, and methylcyclohexane is preferred, at least one selected from cyclohexane and methylcyclohexane is more preferred, and cyclohexane is even more preferred.

[0028] Poor solvents can be used individually or as a mixture of two or more of these.

[0029] As a poor solvent, fractions containing a large amount (for example, 70% or more by mass in total) of alkanes and / or cycloalkanes with 3 to 20 carbon atoms, obtained from petroleum refining processes, can also be used. Examples of such fractions include liquefied petroleum gas, petroleum ether, petroleum benzine, ligroin, whole range naphtha, light naphtha, heavy naphtha, kerosene, and diesel fuel. Preferably, the upper limit of the boiling point range at 1 atmosphere is 110°C. Preferably, the lower limit of the boiling point range at 1 atmosphere is 50°C.

[0030] You can also use the recycled poor solvent described in section (Step 3).

[0031] Even if the poor solvent contains impurities such as water and alcohol, there are no quality issues with the resulting pitch. However, if the impurity content is high, the relative content of the poor solvent decreases, and the precipitation efficiency of TI decreases, so it is preferable to have a low impurity content. The total content of water and alcohol in the poor solvent is, for example, 0% to 10% by mass, or 0% to 5% by mass.

[0032] Liquefied petroleum gas is a mixture primarily composed of hydrocarbons with 3 to 4 carbon atoms. Examples of compounds it contains include propane, propylene, butane, and butene.

[0033] Petroleum ether is a mixture primarily composed of hydrocarbons with 3 to 8 carbon atoms. Examples of compounds it contains include hexane, pentane, heptane, and methylcyclohexane. Its boiling point range at 1 atmosphere is approximately 30°C to 60°C. However, because petroleum ether is a complex mixture, the above values ​​may vary somewhat.

[0034] Petroleum benzine is a mixture primarily composed of hydrocarbons with 5 to 6 carbon atoms. Examples of compounds it contains include hexane and heptane. Its boiling point range at 1 atmosphere is approximately 50°C to 80°C. However, because petroleum benzine is a complex mixture, the above values ​​may vary somewhat.

[0035] Ligroin is a mixture primarily composed of hydrocarbons with 7 to 8 carbon atoms. Examples of compounds it contains include hexane, heptane, octane, and toluene. Its boiling point range at 1 atmosphere is approximately 80°C to 110°C. However, because ligroin is a complex mixture, the above values ​​may vary somewhat.

[0036] Light naphtha is a fraction obtained from the atmospheric distillation process of crude oil, with a boiling point of 30°C to 90°C at 1 atm, and its main components are hydrocarbons with 5 to 6 carbon atoms. The total content of alkanes and cycloalkanes in light naphtha is 80% to 100% by mass, and the content of aromatic hydrocarbons is 0% to 20% by mass. However, because light naphtha is a complex mixture, and its boiling point range and composition are influenced by the origin of the crude oil, the type of atmospheric distillation process, and the operating conditions, the above values ​​may vary somewhat.

[0037] Heavy naphtha is a fraction obtained from the atmospheric distillation process of crude oil, with a boiling point of 90°C to 200°C at 1 atm, and its main components are hydrocarbons with 6 to 12 carbon atoms. The total content of alkanes and cycloalkanes in heavy naphtha is 80% to 100% by mass, and the content of aromatic hydrocarbons is 0% to 20% by mass. However, since heavy naphtha is a complex mixture, and its boiling point range and composition are influenced by the origin of the crude oil, the type of atmospheric distillation process, and the operating conditions, the above values ​​may vary somewhat.

[0038] Whole range naphtha is a fraction obtained from the atmospheric distillation process of crude oil, with a boiling point of 30°C to 200°C at 1 atm, and its main components are hydrocarbons with 5 to 12 carbon atoms. The total content of alkanes and cycloalkanes in whole range naphtha is 80% to 100% by mass, and the content of aromatic hydrocarbons is 0% to 20% by mass. However, since whole range naphtha is a complex mixture, and its boiling point range and composition are influenced by the origin of the crude oil, the type of atmospheric distillation process, and the operating conditions, the above values ​​may vary somewhat.

[0039] Kerosene is a fraction obtained from the atmospheric distillation process of crude oil, with a boiling point of 170°C to 250°C at 1 atmosphere, and its main components are hydrocarbons with 9 to 15 carbon atoms. The total content of alkanes and cycloalkanes in kerosene is 70% to 90% by mass, and the content of aromatic hydrocarbons is 10% to 30% by mass. However, since kerosene is a complex mixture, and its boiling point range and composition are influenced by the origin of the crude oil, the type of atmospheric distillation process, and the operating conditions, the above values ​​may vary somewhat.

[0040] Diesel fuel is a fraction obtained from the atmospheric distillation process of crude oil, with a boiling point of 180°C to 350°C at 1 atmosphere, and its main components are hydrocarbons with 10 to 20 carbon atoms. The total content of alkanes and cycloalkanes in diesel fuel is 70% to 90% by mass, and the content of aromatic hydrocarbons is 10% to 30% by mass. However, since diesel fuel is a complex mixture, and its boiling point range and composition are influenced by the origin of the crude oil, the type of atmospheric distillation process, and the operating conditions, the above values ​​may vary somewhat.

[0041] The amount of poor solvent added may be 5 parts by mass or more, 10 parts by mass or more, or 15 parts by mass or more, and may be 200 parts by mass or less, 100 parts by mass or less, or 80 parts by mass or less, per 100 parts by mass of the heat-treated product. Preferably, the amount of poor solvent added is 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 15 to 80 parts by mass, per 100 parts by mass of the heat-treated product. Although it also depends on the extraction conditions, when the amount of poor solvent added is 5 parts by mass or more, TI precipitates easily and can be separated efficiently. Since the precipitation efficiency does not change much when it exceeds 200 parts by mass, it is preferable to add 200 parts by mass or less from the viewpoint of economy and productivity.

[0042] The method for mixing the poor solvent and the heat-treated product is not particularly limited as long as it allows for sufficient mixing of the poor solvent and the heat-treated product, and can be appropriately selected depending on the mixing conditions. When mixing is performed at atmospheric pressure, it must be carried out at a temperature below the boiling point of the lower of the two components used (the poor solvent and the heat-treated product). When mixing is performed at a temperature above the boiling point, it can be done under pressure using a sealed container. If the poor solvent used is waxy at room temperature or has high viscosity, heating during mixing is preferable. The apparatus for mixing is not particularly limited, but a heat-sensitive mixer or the like can be used.

[0043] The method for separating the solid containing TI precipitated by the addition of a poor solvent from the liquid is not particularly limited. For example, centrifugation, static separation, filtration, and combinations thereof can be used. In one embodiment, the separation method is a combination of centrifugation and filter filtration. In this case, the solid catalyst optionally added in step 1 can also be separated at the same time. The separation temperature is not particularly limited as long as it is a temperature at which the solid can be efficiently removed. If the separation is performed at atmospheric pressure, it must be carried out at a temperature below the boiling point of the slurry obtained by the addition of the poor solvent. If the separation is carried out at a temperature above the boiling point of the slurry, it can be carried out under pressure using a sealed apparatus. If the viscosity of the slurry is high, heating conditions can separate the solid more effectively.

[0044] (Step 3) Step 3 is a step in which the heat-treated product with reduced TI content obtained in Step 2 is distilled, the low-boiling point components including the poor solvent added in Step 2 are separated, and pitch is obtained as a high-boiling point component. The low-boiling point components include not only the poor solvent added in Step 2, but also components with low boiling points (light components) from the heat-treated product with reduced TI content. In Step 3, the poor solvent may be further separated and recovered. In this disclosure, the poor solvent recovered in Step 3 is called recycled poor solvent. One embodiment of a method for producing petroleum-based pitch includes the above Steps 1 to 3, wherein the poor solvent is further separated in Step 3 to obtain recycled poor solvent, and the obtained recycled poor solvent is reused as the poor solvent in Step 2.

[0045] The distillation method in step 3 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, although this depends on the distillation pressure. This is because if it exceeds 360°C, the polycondensation reaction proceeds easily, and TI is more likely to be generated. The lower limit temperature does not affect the characteristics of the pitch, but if the temperature is low, the distillation pressure must be lowered to remove low-boiling point components, so from an economic standpoint, a temperature of 200°C or higher is preferable. When performing reduced pressure distillation (vacuum distillation), in order to obtain a pitch with a softening point of 120°C or lower, the distillation pressure is preferably 100 PaA to 10,000 PaA, and more preferably 300 PaA to 5,000 PaA. The softening point of the pitch can be controlled by the amount of low-boiling point components removed. Generally, the more low-boiling point components are removed, that is, the higher the distillation endpoint, the higher the softening point. When ethylene bottom oil is used as the petroleum-based heavy oil, obtaining pitch with a softening point of 60-120°C depends on the heat treatment conditions in step 1 and the distillation apparatus in step 3, but the distillation endpoint is preferably 250°C-450°C, more preferably 280°C-400°C, and even more preferably 320°C-380°C. Here, the distillation endpoint is the temperature converted to atmospheric pressure calculated from the operating pressure and the temperature at the top of the distillation column at the end of distillation. If the distillation endpoint is below 250°C, there is a concern that a large amount of low-boiling point components will volatilize at the impregnation temperature (e.g., 200°C), leading to an abnormal increase in the viscosity of the pitch during the impregnation process of carbon material production.

[0046] In step 3, the low-boiling point component containing the poor solvent added in step 2 is separated. The low-boiling point component is a fraction containing a large amount of the poor solvent added in step 2. If the low-boiling point component is further separated into the poor solvent and the light component derived from the heat-treated product, the separated poor solvent (i.e., recycled poor solvent) can be reused, for example, as the poor solvent added in step 2. From this viewpoint, the poor solvent used in step 2 is preferably a poor solvent with a certain boiling point difference from the heat-treated product, and more preferably a poor solvent having a boiling point lower than the lower limit of the boiling point range of the light component in the heat-treated product. Depending on the petroleum-based heavy oil and heat treatment conditions in step 1, the initial boiling point (at atmospheric pressure) of the heat-treated product obtained in step 1 is about 100-110°C, so the boiling point (at atmospheric pressure) of the poor solvent used in step 2 is preferably 110°C or lower, more preferably 100°C or lower, and even more preferably 85°C or lower. From this viewpoint, the poor solvents used in step 2 are preferably n-pentane (boiling point 36.1°C), isopentane (boiling point 27.8°C), n-hexane (boiling point 68.7°C), 2-methylpentane (boiling point 60.0°C), 3-methylpentane (boiling point 63.0°C), cyclohexane (boiling point 80.8°C), n-heptane (boiling point 98.4°C), petroleum benzine (boiling point 50°C to 80°C), and ligroin (boiling point 80°C to 110°C).

[0047] Figure 2 is a flow chart showing one embodiment of a method for producing petroleum-based pitch when the poor solvent is separated in step 3. In Figure 2, the distillation step in step 3 is performed in a distillation column, and the poor solvent with the lowest boiling point is recovered as the top liquid and reused as the poor solvent in step 2. Low-boiling point components other than the poor solvent (light components) are obtained as the side liquid of the distillation column, and pitch, which is the high-boiling point component, is obtained as the bottom liquid. When separating the poor solvent in step 3, the separation of the high-boiling point component, pitch, the poor solvent, and the low-boiling point components other than the poor solvent can be performed in a single distillation apparatus as shown in Figure 2, or the separation of the high-boiling point component, pitch, and the separation of the poor solvent and the low-boiling point components other than the poor solvent can be performed in separate distillation apparatuses. The separation of the high-boiling point component, pitch, the poor solvent, and the low-boiling point components other than the poor solvent can be performed simultaneously as shown in Figure 2, or the separation of the poor solvent and the separation of the high-boiling point component, pitch, can be performed in stages.

[0048] <Petroleum-based pitch> The pitch obtained by the manufacturing method of one embodiment can be used in the manufacture of various carbon materials. Specific examples of carbon materials include graphite electrodes. The pitch obtained by the manufacturing method of one embodiment can be used as impregnated pitch or binder pitch.

[0049] The quinoline-insoluble content (QI) of the petroleum-based pitch obtained by the manufacturing method of one embodiment is preferably 0.5% by mass or less. Since a lower QI improves the impregnation of the pitch, it is more preferably 0.3% by mass or less, and even more preferably 0.1% by mass or less. The lower limit of QI is not particularly limited, but for example, it is 0.0% by mass or 0.001% by mass. QI is measured by the method described in the Examples section.

[0050] The toluene-insoluble content (TI) of the petroleum-based pitch obtained by the manufacturing method of one embodiment is preferably 3.0% by mass or less. Since a lower TI improves the impregnation of the pitch, 2.0% by mass or less is more preferable, and 1.0% by mass or less is even more preferable. The lower limit of TI is not particularly limited, but for example, it is 0.0% by mass or 0.1% by mass. TI is measured by the method described in the Examples section.

[0051] The softening point of petroleum-based pitch obtained by the manufacturing method of one embodiment is preferably 120°C or lower. A lower softening point improves the fluidity of the pitch and its impregnation into the calcined body, so a softening point of 110°C or lower is more preferable, and 100°C or lower is even more preferable. The lower limit of the softening point is not particularly limited, but for example, it is 50°C or 60°C. The softening point is measured by the method described in the Examples section.

[0052] The viscosity of the petroleum-based pitch obtained by the manufacturing method of one embodiment is preferably 200 mPa·s or less at 200°C. Since lower viscosity improves the fluidity and impregnation of the pitch, the viscosity at 200°C is more preferably 100 mPa·s or less, and even more preferably 70 mPa·s or less. The lower limit of the viscosity at 200°C is not particularly limited, but is, for example, 10 mPa·s or 15 mPa·s. The viscosity is measured by the method described in the Examples section.

[0053] Since a higher fixed carbon content tends to result in a higher density of the resulting carbon material, the fixed carbon content of the petroleum-based pitch obtained by the manufacturing method of one embodiment is preferably 47.0% by mass or more, more preferably 48.0% by mass or more, and even more preferably 50.0% 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, 80.0% by mass, or 85.0% by mass. The fixed carbon content is measured by the method described in the Examples section.

[0054] The petroleum-based pitch obtained by the manufacturing method of one embodiment preferably satisfies equation (1). That is, the value of the fixed carbon content Y (mass%) of the petroleum-based pitch is greater than the value calculated by substituting the softening point X (°C) of the petroleum-based pitch into equation (1). Petroleum-based pitch that satisfies this condition has a larger fixed carbon content compared to pitches having a similar softening point. 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃)

[0055] <Manufacturing process for graphite electrodes> In this disclosure, "carbon material" refers 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 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 The process of graphitizing re-fired bodies. 7. Processing process The process of shaping a graphitized material into a predetermined shape by cutting or other means to create a graphite electrode.

[0056] 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.

[0057] The kneaded mixture may contain puffing inhibitors such as iron oxide.

[0058] Commercially available mixers or kneaders can be used for mixing and kneading. Specific examples include mixers and kneaders. The kneading temperature varies depending on the binder pitch used, but is generally around 150°C. The softening point of the binder pitch is preferably 130°C or lower, and more preferably 110°C or lower. When kneading at around 150°C, if the softening point of the binder pitch is higher than 130°C, it is difficult to knead sufficiently. After kneading, the mixture is cooled to a temperature suitable for subsequent molding (100°C to 130°C).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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 to graphite.

[0064] 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]

[0065] The present invention will be further described with reference to the following examples, comparative examples, and reference examples, but these examples are merely illustrations of the present invention and the present invention is not limited to these examples.

[0066] <Method for measuring the softening point (SP)> The measurement was performed in accordance with "8. Method for measuring the softening point of tar pitch (ring-ball method)" of JIS K 2425:2006 "Test methods for creosote oil, processed tar, and tar pitch".

[0067] <Method for measuring fixed carbon (FC) content> The measurements were taken 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".

[0068] <Method for measuring toluene-insoluble content (TI)> The measurements were performed 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".

[0069] <Method for measuring quinoline insoluble matter (QI)> The measurement was performed 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".

[0070] <Method for measuring viscosity> The viscosity at 200°C was measured in accordance with ASTM D5018-18 "Standard Test Method for Shear Viscosity of Coal-Tar and Petroleum Pitches".

[0071] (Example 1) 3000g of ethylene bottom oil was introduced into a 6L 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 5°C / min while stirring. After 80 minutes had elapsed since reaching 430°C, heating was stopped and the autoclave was allowed to cool to room temperature (Step 1). The yield of the heat-treated product obtained was 2738g (heat treatment recovery rate: 91%). The unrecovered portion consists of vaporized gas, recovery leakage, etc. 200g of the obtained heat-treated product was transferred to a 500mL beaker, 60g of n-hexane (Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred for 5 minutes at room temperature (25°C) using a magnetic stirrer to precipitate TI. The obtained slurry was divided into six 50mL centrifuge tubes and centrifuged (6000rpm, 5min) (LCX-100, Tommy Seiki Co., Ltd.), and the insoluble components were separated by decantation (Step 2). The obtained supernatant was subjected to two-stage vacuum distillation to obtain 52 g of pitch (24% yield relative to the raw material ethylene bottom oil). In the first stage of vacuum distillation, a fraction rich in n-hexane (recycled hexane) was obtained as the distillate by performing vacuum distillation at a bottom temperature of 120°C and a pressure of 30 hPa. Subsequently, vacuum distillation was performed at a distillation pressure of 5 mmHg up to the distillation endpoint of 350°C to remove light components, and the pitch of Example 1 was obtained as the distillation residue (Step 3). The distillation conditions listed in Table 1 are the conditions for the second stage of vacuum distillation. The distillation endpoint is the temperature at the top of the distillation column at the end of distillation, converted to atmospheric pressure.

[0072] (Example 2) For 200 g of the heat-treated product obtained in Step 1 of Example 1, the same procedure as in Step 2 of Example 1 was performed, except that 50 g of recycled hexane obtained in the first stage of distillation in Step 3 of Example 1 was used instead of n-hexane, and the insoluble components were separated. From the obtained supernatant, recycled hexane and light components were removed by vacuum distillation (distillation pressure: 5 mmHg, distillation endpoint: 360°C, one-stage distillation), and 52 g of pitch (yield 24% relative to the raw material ethylene bottom oil) was obtained as the distillation residue. The distillation endpoint is the temperature at the top of the distillation column at the end of distillation, converted to atmospheric pressure.

[0073] (Example 3) Pitch was prepared according to the method described in Example 2, except that the conditions for steps 2 and 3 were changed as shown in Table 1. The pitch yield was 50 g (23% yield relative to the raw material ethylene bottom oil). Cyclohexane was obtained from Fujifilm Wako Pure Chemical Industries, Ltd.

[0074] (Example 4) Pitch was prepared according to the method described in Example 2, except that the conditions for steps 2 and 3 were changed as shown in Table 1. The pitch yield was 50 g (23% yield relative to the raw material ethylene bottom oil). Petroleum benzine was obtained from Fujifilm Wako Pure Chemical Industries, Ltd.

[0075] (Example 5) Except for changing the heat treatment conditions in Step 1 as shown in Table 1, the heat treatment was carried out according to the method described in Example 1 to obtain a heat-treated product (heat treatment yield: 95%). 200 g of the obtained heat-treated product was taken out into a 500 mL beaker, 20 g of n-hexane (Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto, and the mixture was stirred at room temperature for 5 minutes to precipitate TI. The obtained slurry was filtered (filter paper: GA-55, ADVANTEC) to separate the insoluble components (Step 2). Low-boiling point components including n-hexane were removed from the obtained filtrate by vacuum distillation (distillation pressure: 5 mmHg, distillation endpoint: 350°C, one-stage distillation), and 79 g of pitch from Example 5 (yield 38% relative to the raw material ethylene bottom oil) was obtained as the distillation residue (Step 3). The distillation endpoint is the temperature at the top of the distillation column at the end of distillation converted to atmospheric pressure.

[0076] (Example 6) Except for changing the heat treatment conditions in Step 1 as shown in Table 1, the heat treatment was carried out according to the method described in Example 1 to obtain a heat-treated product (heat treatment yield: 89%). Using the obtained heat-treated product, pitch was prepared according to the method described in Example 2, except for changing the conditions in Steps 2 and 3 as shown in Table 1. The yield of pitch was 45 g (20% yield relative to the raw material ethylene bottom oil). n-heptane was obtained from Fujifilm Wako Pure Chemical Industries, Ltd.

[0077] (Comparative Example 1) 600 g of the heat-treated product obtained in Step 1 of Example 1 was subjected to vacuum distillation (distillation pressure: 7 mmHg, distillation endpoint: 340°C, one-stage distillation) to obtain 234 g of pitch of Comparative Example 1 (yield 35% relative to the raw material ethylene bottom oil). The distillation endpoint is the temperature at the top of the distillation column at the end of distillation, converted to atmospheric pressure.

[0078] (Comparative Example 2) Pitch was prepared according to the method described in Example 5, except that the solvent in Step 2 was changed to toluene and the conditions in Steps 1-3 were changed as shown in Table 1. No insoluble matter was recovered by filter filtration. The pitch yield was 80 g (36% yield relative to the raw material ethylene bottom oil). Toluene was obtained from Fujifilm Wako Pure Chemical Industries, Ltd.

[0079] (Reference example 1) Table 1 shows the pitch data obtained in Example 1, as described in Table 1 of Patent Document 2. The number of steps required to obtain the pitch is 4, which is one more step than in Examples 1 to 6.

[0080] Table 1 shows the conditions for each step in the Examples, Comparative Examples, and Reference Examples, as well as the physical properties of the obtained pitch. By preparing the pitch using the method according to one embodiment of this disclosure, a petroleum-based pitch suitable as an impregnated pitch can be obtained with fewer steps (3 steps) than the prior art (Reference Example 1, 4 steps), having a quinoline-insoluble content (QI) of 0.5% by mass or less, a toluene-insoluble content (TI) of 3.0% by mass or less, a softening point of 60°C to 120°C, a viscosity of 200 mPa·s or less at 200°C, and a fixed carbon content Y (mass%) that satisfies formula (1). 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃)

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

Claims

1. A method for producing petroleum-based pitch, comprising at least the following steps 1 to 3. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A step to precipitate TI and separate TI by adding a poor solvent to the heat-treated product obtained in Step 1. Step 3: A step in which the heat-treated product with reduced TI content obtained in Step 2 is distilled to obtain pitch as a high-boiling point component.

2. The method for producing petroleum-based pitch according to claim 1, wherein the poor solvent is at least one selected from the group consisting of alkanes having 3 to 20 carbon atoms and cycloalkanes having 3 to 20 carbon atoms.

3. The method for producing petroleum-based pitch according to claim 1, wherein the poor solvent is at least one selected from the group consisting of alkanes having 5 to 20 carbon atoms and cycloalkanes having 5 to 20 carbon atoms.

4. The method for producing petroleum-based pitch according to claim 1, wherein the poor solvent is at least one selected from n-pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, cyclohexane, methylcyclohexane, n-heptane, and n-octane.

5. The method for producing petroleum-based pitch according to claim 1, wherein the poor solvent is at least one selected from liquefied petroleum gas, petroleum ether, petroleum benzine, ligroin, whole range naphtha, light naphtha, heavy naphtha, kerosene, and diesel fuel.

6. The method for producing petroleum-based pitch according to claim 5, wherein the upper limit of the boiling point range of the poor solvent at 1 atmosphere is 110°C.

7. A method for producing petroleum-based pitch according to any one of claims 1 to 6, wherein in step 2, the amount of poor solvent added is 5 to 200 parts by mass per 100 parts by mass of the heat-treated product.

8. A method for producing petroleum-based pitch according to any one of claims 1 to 6, wherein the petroleum-based heavy oil is ethylene bottom oil.

9. A method for manufacturing petroleum-based pitch according to any one of claims 1 to 6, wherein the manufactured petroleum-based pitch satisfies the following conditions. Quinoline insoluble matter (QI) is 0.5% by mass or less. Toluene-insoluble content (TI) is 3.0% by mass or less. Softening point is below 120°C. The viscosity at 200°C is 200 mPa·s or less. The fixed carbon content Y (mass%) satisfies equation (1). 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃)

10. A method for manufacturing petroleum-based pitch according to any one of claims 1 to 6, wherein the petroleum-based pitch is impregnated pitch for carbon materials.

11. A method for manufacturing a graphite electrode using petroleum-based pitch obtained by the manufacturing method described in any one of claims 1 to 6 as the impregnated pitch.

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