Method for manufacturing petroleum-based pitch and petroleum-based pitch

Abstract

To provide a petroleum pitch having excellent impregnation property to a fired body on manufacturing a carbon material such as a graphite electrode and having a high fixed carbon content.SOLUTION: A petroleum pitch has a quinoline insoluble (QI) of 0.5 mass% or under, a toluene insoluble (TI) of 3.0 mass% or under, a softening point of 60°C-120°C, and a viscosity at 200°C of 200 mPa s or under, where a fixed carbon content Y (mass%) satisfies the formula (1): 80.0≥Y>0.2X+29.5 (1). Here, Y is a fixed carbon content (mass%) and X is a softening point (°C) (60≤X≤120).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a petroleum pitch suitable for impregnation pitch used in the production of carbon materials such as graphite electrodes, and a method for producing the same. Background Art

[0002] Carbon materials such as graphite electrodes used in electric furnaces for remelting iron are produced by kneading and molding an aggregate such as coke and pitch (referred to as "binder pitch") at a temperature equal to or higher than the softening point of the binder pitch, followed by firing and then graphitization. Carbon materials are required to have characteristics such as high mechanical strength, high electrical conductivity and high thermal conductivity, and therefore are preferably highly dense. However, due to factors such as volatilization of low molecular weight components in the binder pitch during the firing step, the fired body has a structure with many pores. Therefore, in the production process, impregnation of the fired body with pitch (referred to as "impregnation pitch") and refiring are performed several times to reduce the porosity and increase the density of the obtained carbon material. Accordingly, impregnation pitch is indispensable for the production of high-quality carbon materials.

[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 high value-added products is a problem in the art. To solve this problem, attempts have been made to produce impregnation pitch for carbon material production, binder pitch for carbon material production, and the like from ethylene bottom oil, utilizing the property of ethylene bottom oil that it contains a large amount of aromatic compounds. However, petroleum pitch produced from petroleum heavy oil such as ethylene bottom oil has a lower fixed carbon content than coal tar pitch produced from coal tar, so the density of the obtained carbon material tends to be low. Therefore, the current situation is that petroleum pitch is not widely used.

[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 pitch is molten during the impregnation process, and therefore significantly inhibits the penetration of the pitch into the pores of the calcined body. For this reason, it is desirable for coal tar-based impregnated pitch to be substantially free of QI (Patent Document 1).

[0005] On the other hand, since petroleum-based heavy oils (especially ethylene bottom oil) contain almost no QI, it is possible to prepare petroleum-based pitch that is substantially QI-free without a QI removal or reduction step by heat-treating petroleum-based heavy oil under conditions that do not generate QI. In fact, Japanese Patent Publication No. 60-92388 (Patent Document 2) reports that it is possible to produce petroleum-based pitch with a QI content of 1% by mass or less from petroleum-based heavy oil without a QI removal or reduction step, and that the resulting petroleum-based pitch can be suitably used as an impregnating pitch. However, many of the petroleum-based pitches reported to date, including the petroleum-based pitch described in Patent Document 2, have a lower fixed carbon content compared to coal tar pitch with a comparable softening point (Patent Document 2 and Non-Patent Document 1). One method to improve the fixed carbon content of petroleum-based pitch is to remove light components from the pitch by distillation, etc., but this also increases the softening point and viscosity, which reduces the impregnation properties. Therefore, it is difficult to produce petroleum-based pitch that achieves both good impregnation properties and a high fixed carbon content using conventional methods. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-2124 [Patent Document 2] Japanese Patent Application Publication No. 60-92388 [Non-patent literature]

[0007] [Non-Patent Document 1] Petroleum Derived Carbons Chapter 5 p.52~p.62 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a petroleum-based pitch that exhibits excellent impregnation properties into calcined bodies during the production of carbon materials such as graphite electrodes, and has a high fixed carbon content, as well as a method for producing the same. "Petroleum-based pitch" refers to pitch produced from heavy oil derived from petroleum. [Means for solving the problem]

[0009] The inventors diligently conducted research to achieve the above objectives. Specifically, they investigated a method of subjecting petroleum-based heavy oil to relatively severe heat treatment within a range of conditions that do not generate QI. However, when the inventors investigated this method, they found that although they were able to obtain petroleum-based pitch that was QI-free and had a high fixed carbon content, its impregnation properties were remarkably poor (see Comparative Examples 1, 3, and 4 of this specification). This suggests that in petroleum-based pitch produced by a manufacturing method that includes a step of heat-treating petroleum-based heavy oil under relatively severe conditions, factors other than QI have a significant impact on impregnation properties. The inventors discovered that toluene-insoluble matter (TI), which does not affect impregnation properties in coal tar pitch, does affect impregnation properties in petroleum-based pitch produced by a manufacturing method that includes a step of heat-treating petroleum-based heavy oil under relatively severe conditions, and they have embodied this finding in the present invention.

[0010] In other words, the present invention relates to a method for producing petroleum-based pitch, comprising the steps of: heat-treating a petroleum-based heavy oil (step 1); distilling the heat-treated product obtained in step 1 to obtain pitch 1 as a high-boiling point component (step 2); reducing the toluene-insoluble content (TI) of pitch 1 obtained in step 2 (step 3); and distilling the component with reduced toluene-insoluble content (TI) obtained in step 3 to obtain pitch 2 as a high-boiling point component (step 4). Furthermore, the present invention relates to a petroleum-based pitch 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%) that satisfies formula (1). 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃) (60≦X≦120)

[0011] In other words, the present invention relates to the following [1] to

[10] .

[0012] [1] A method for producing petroleum-based pitch, comprising at least the following steps 1 to 4. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A step in which the heat-treated product obtained in Step 1 is distilled to obtain pitch 1 as a high-boiling point component. Step 3: Remove toluene-insoluble matter (TI) from pitch 1 obtained in Step 2. Process for obtaining a component with reduced TI Step 4: The toluene-insoluble (TI) component obtained in Step 3 is distilled. The process of obtaining pitch 2 as a high-boiling point component. [2] A method for producing petroleum pitch according to [1], wherein the petroleum heavy oil is ethylene bottom oil. [3] A method for producing petroleum-based pitch according to [1] or [2], wherein the heat treatment temperature of step 1 is 360°C to 500°C. [4] The method for producing petroleum pitch according to any one of [1] to [3], wherein the removal of toluene insoluble content (TI) in the step 3 is performed by adding a solvent to the pitch 1 and extracting a solvent-soluble content of the pitch 1 into the solvent, and the solvent is at least one selected from the group consisting of benzene, alkylbenzenes, cracked gasoline and cracked kerosene. [5] The method for producing petroleum pitch according to any one of [1] to [4], wherein in the step 1, when the heat treatment temperature is 360°C to 390°C, the heat treatment time is 8 hours to 48 hours; when the heat treatment temperature is higher than 390°C to 430°C, the heat treatment time is 0.5 hours to 24 hours; and when the heat treatment temperature is higher than 430°C to 500°C, the heat treatment time is 0.1 hours to 16 hours. [6] A method for producing a graphite electrode, wherein the petroleum pitch obtained by the production method according to any one of [1] to [5] is used as an impregnation pitch. [7] A petroleum pitch, wherein a quinoline insoluble content (QI) is 0.5 mass% or less, a toluene insoluble content (TI) is 3.0 mass% or less, a softening point is 60°C to 120°C, a viscosity at 200°C is 200 mPa·s or less, and a fixed carbon content Y (mass%) satisfies formula (1). 80.0≧Y>0.2X+29.5 (1) Y: fixed carbon content (mass%) X: softening point (°C) (60≦X≦120) [8] The petroleum pitch according to [7], wherein a fixed carbon content is 47.0 mass% or more. [9] The petroleum pitch according to [7] or [8], which is an impregnation pitch for producing a carbon material.

[10] The petroleum pitch according to [9], wherein the carbon material is a graphite electrode.

Effect of the Invention

[0013] According to the present invention, a petroleum-based pitch can be obtained using petroleum-based heavy oil as a raw material, which exhibits excellent impregnation properties into calcined bodies during the production of carbon materials such as graphite electrodes, and has a high fixed carbon content. Because this petroleum-based pitch is easily impregnated into calcined bodies and has a high fixed carbon content, the quality of the resulting carbon material can be improved. [Brief explanation of the drawing]

[0014] [Figure 1] This flowchart shows an example of a petrochemical process for the thermal decomposition of petroleum products such as naphtha, and a production process for ethylene bottom oil. [Figure 2] This is a flowchart illustrating one embodiment of a method for manufacturing petroleum-based pitch. [Figure 3] This figure shows the relationship between the softening point and the amount of fixed carbon in various pitches produced from ethylene bottom oil under different manufacturing conditions. [Modes for carrying out the invention]

[0015] The following describes preferred embodiments of the present invention, but it should be understood that the present invention is not limited to these forms and can be applied in various ways within its spirit and scope.

[0016] In this specification, when "~" is used for a numerical range, the numbers at both ends are the upper and lower limits, respectively, and are included within the numerical range.

[0017] <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 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.

[0018] 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.

[0019] The kneaded mixture may contain puffing inhibitors such as iron oxide.

[0020] 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).

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] <Method for manufacturing petroleum-based pitch> A method for manufacturing petroleum-based pitch according to one embodiment includes at least the following steps 1 to 4 in this order, and may include other steps. A method for manufacturing petroleum-based pitch according to another embodiment includes the following steps 1 and 2 in this order, and steps 3 and 4 may be omitted. Process 1: Process of heat-treating petroleum-based heavy oil. Step 2: A step in which the heat-treated product obtained in Step 1 is distilled to obtain pitch 1 as a high-boiling point component. Step 3: Remove toluene-insoluble matter (TI) from pitch 1 obtained in Step 2. Process for obtaining a component with reduced TI Step 4: The toluene-insoluble (TI) component obtained in Step 3 is distilled. The process of obtaining pitch 2 as a high-boiling point component.

[0028] 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 referred to as ethylene bottom oil.

[0029] 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.

[0030] The petroleum-based heavy oil may be ethylene bottom oil, ethylene bottom oil heavy component obtained by removing any proportion (e.g., 5-70% by mass) of light components from ethylene bottom oil by distillation or the like, other petroleum-based heavy oils, or 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. It is preferable to have low sulfur and nitrogen content in the pitch, as these can cause buffing during firing. 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, fluid catalytic cracking oil (FCC decanted oil) is preferred as the other petroleum-based heavy oil. The properties of fluid catalytic cracking oil (FCC decant oil) vary depending 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.

[0031] (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.

[0032] The heat treatment temperature is preferably 360°C or higher, more preferably 390°C or higher, and even more preferably 410°C or higher. The heat treatment temperature is preferably 500°C or lower, and more preferably 450°C or lower. These upper and lower limits can be combined arbitrarily. The heat treatment temperature is preferably 360°C to 500°C, more preferably 390°C to 500°C, and even more preferably 410°C to 450°C.

[0033] The appropriate heat treatment time varies depending on the heat treatment temperature. When the heat treatment temperature is 360°C to 390°C, it is preferable to have 8 hours or more, and more preferably 16 hours or more, from the time the predetermined heat treatment temperature is reached (the same applies below). When the heat treatment temperature is 360°C to 390°C, it is preferable to have 48 hours or less. When the heat treatment temperature is 360°C to 390°C, it is preferable to have 8 hours to 48 hours, and more preferably 16 hours to 48 hours. When the heat treatment temperature is above 390°C to 430°C, it is preferable to have 0.5 hours or more, and more preferably 1 hour or more. When the heat treatment temperature is above 390°C to 430°C, it is preferable to have 24 hours or less, and more preferably 16 hours or less. When the heat treatment temperature is above 390°C to 430°C, it is preferable to have 0.5 hours to 24 hours, and more preferably 1 hour to 16 hours. When the heat treatment temperature is above 430°C to 500°C, it is preferable to have 0.1 hours or more, and more preferably 0.5 hours or more. When the heat treatment temperature is greater than 430°C to 500°C, the treatment time is preferably 16 hours or less, and more preferably 8 hours or less. When the heat treatment temperature is greater than 430°C to 500°C, the treatment time is preferably 0.1 hours to 16 hours, and more preferably 0.5 hours to 8 hours. The above upper and lower limits can be combined arbitrarily. By setting the heat treatment time within the above range, a pitch with a sufficient amount of fixed carbon can be obtained.

[0034] 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 formed under atmospheric pressure, which reduces the final pitch yield.

[0035] 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 (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 solvent-insoluble matter along with TI in step 3, and is therefore not mixed into the pitch finally obtained in step 4.

[0036] (Process 2) Step 2 is a process of removing low-boiling-point substances by distilling the heat-treated product obtained in Step 1, thereby obtaining pitch 1 as a high-boiling-point component. If Steps 3 and 4 are omitted, the pitch 1 obtained in Step 2 is the petroleum-based pitch of one embodiment.

[0037] The distillation method in step 2 may be atmospheric distillation, reduced-pressure distillation (vacuum distillation), or a combination of atmospheric distillation and reduced-pressure distillation, and can be selected 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 temperatures above 360°C tend to generate TI, which can reduce the final pitch yield. The lower limit temperature does not affect the pitch characteristics, but if the temperature is low, the distillation pressure must be lowered to remove low-boiling-point substances (light components), so from an economic standpoint, a temperature of 200°C or higher is preferable. In order to make the softening point of pitch 2 obtained in step 4 120°C or lower, it is preferable to obtain pitch 1 with a softening point of approximately 180°C or lower in step 2, although this depends on the petroleum-based heavy oil used and the heat treatment conditions in step 1. When performing reduced-pressure distillation (vacuum distillation), in order to obtain pitch 1 with a softening point of approximately 180°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 pitch can be controlled by the amount of light components removed. Generally, the more light components 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, in order to lower the softening point of pitch 1 to approximately 180°C or below, the distillation endpoint at atmospheric pressure should preferably be 450°C or below, more preferably 420°C or below, and even more preferably 400°C or below, although this depends on the heat treatment conditions in step 1 and the distillation apparatus.

[0038] (Step 3) Step 3 is a step to remove toluene-insoluble matter (TI) from pitch 1 obtained in step 2 to obtain a component with reduced TI. The method for removing TI is not particularly limited, but for example, a suitable solvent can be added to pitch 1 obtained in step 2, the solvent-soluble portion of pitch 1 can be extracted into the solvent, the solvent-insoluble portion can be separated and removed, and a component with reduced TI can be obtained. In this case, the component with reduced TI includes the solvent-soluble portion and the solvent used. On the other hand, the solvent-insoluble portion includes TI and a solid catalyst added as needed.

[0039] As a suitable solvent, one that dissolves only the toluene-soluble components (TS) in the pitch without dissolving the TI is preferred. Specifically, benzene and alkylbenzenes such as toluene and xylene, and mixtures thereof are preferred. Fractions containing large amounts of benzene and alkylbenzene 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] 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.

[0043] 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.

[0044] The amount of solvent added is preferably 25 to 5,000 parts by mass, and more preferably 300 to 2,000 parts by mass, per 100 parts by mass of pitch 1. Although it may vary slightly depending on the extraction conditions, efficient extraction can be achieved with 25 parts by mass or more. Since the extraction efficiency does not change much beyond 5,000 parts by mass, it is preferable to keep it at 5,000 parts by mass or less from the viewpoint of economy and productivity.

[0045] The extraction temperature is not particularly limited. Extraction can be carried out at room temperature, but heating conditions that provide better extraction efficiency are preferable. When performing extraction under heating conditions at atmospheric pressure, the extraction must be carried out below the boiling point of the solvent used. When heating at a temperature above the boiling point, the extraction can be carried out under reflux conditions or under pressure using a sealed container.

[0046] The method for separating the solvent-soluble components from the solvent-insoluble components is not particularly limited, but for example, centrifugation, filtration, or a combination thereof can be used.

[0047] (Step 4) Step 4 is a process in which light components are removed by distillation from the TI-reduced component obtained in Step 3 to obtain pitch 2 as a high-boiling point component. The pitch 2 obtained in Step 4 is a petroleum-based pitch according to one embodiment.

[0048] The distillation method in step 4 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 formed. The lower limit temperature does not affect the characteristics of the pitch, but if the temperature is low, the distillation pressure must be lowered in order to remove low-boiling point substances (light 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 pitch 2 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 light components removed. Generally, the more light 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, in order to lower the softening point of pitch 2 to 120°C or below, the distillation endpoint at atmospheric pressure is preferably 450°C or below, more preferably 420°C or below, and even more preferably 400°C or below, although this depends on the heat treatment conditions and distillation apparatus in step 1. Furthermore, depending on the heat treatment conditions and distillation apparatus in step 1, the distillation endpoint at atmospheric pressure is preferably 250°C or higher, and more preferably 300°C or higher. If the distillation endpoint is below 250°C, there is a concern that a large amount of light 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.

[0049] <Petroleum-based pitch> The petroleum-based pitch of one embodiment can be suitably used as an impregnation pitch used in the manufacture of carbon materials. The petroleum-based pitch of one embodiment can be suitably used as an impregnation pitch used in the manufacture of graphite electrodes. The petroleum-based pitch of one embodiment can be used as a binder pitch used in the manufacture of graphite electrodes. The petroleum-based pitch of one embodiment can also be used as an impregnation pitch and binder pitch for the manufacture of carbon materials other than graphite electrodes.

[0050] In one embodiment, the quinoline-insoluble content (QI) of the petroleum-based pitch is 0.5% by mass or less. Since a lower QI improves the impregnation of the pitch, 0.3% by mass or less is preferred, and 0.1% by mass or less is more preferred. 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.

[0051] The toluene-insoluble content (TI) of the petroleum-based pitch in one embodiment is 3.0% by mass or less. Since a lower TI improves the impregnation of the pitch, 2.0% by mass or less is preferred, and 1.0% by mass or less is more preferred. 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.

[0052] The softening point of the petroleum-based pitch in one embodiment is 60°C to 120°C. Since a lower softening point improves the fluidity of the pitch and its impregnation into the calcined body, the softening point is 120°C or lower, preferably 110°C or lower, and more preferably 100°C or lower. The softening point is 60°C or higher, preferably 70°C or higher, and more preferably 75°C or higher. These upper and lower limits can be combined arbitrarily. The softening point is preferably 70°C to 110°C, and more preferably 75°C to 100°C. The softening point is measured according to the method described in the Examples section.

[0053] The viscosity of the petroleum-based pitch in one embodiment at 200°C is 200 mPa·s or less. Since lower viscosity improves the fluidity and impregnation of the pitch, the viscosity at 200°C is preferably 100 mPa·s or less, more preferably 70 mPa·s or less, and even more preferably 40 mPa·s or less. The lower limit of the viscosity at 200°C is not particularly limited, but is, for example, 5 mPa·s or 10 mPa·s. Viscosity is measured by the method described in the Examples section.

[0054] As the density of the resulting carbon material tends to increase with higher fixed carbon content, the fixed carbon content of the petroleum-based pitch in 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. As mentioned above, a higher fixed carbon content is preferable, but obtaining a pitch with a higher fixed carbon content requires more stringent heat treatment conditions, which may lead to problems such as coking during heat treatment. Therefore, the fixed carbon content is preferably 80.0% by mass or less, preferably 70.0% by mass or less, and even more preferably 65.0% by mass or less. These upper and lower limits can be combined arbitrarily. The fixed carbon content is preferably 47.0% by mass to 80.0% by mass, more preferably 48.0% by mass to 70.0% by mass, and even more preferably 50.0% by mass to 65.0% by mass. The fixed carbon content is measured by the method described in the Examples section.

[0055] It is generally known that there is a proportional relationship between the softening point of pitch and the amount of fixed carbon. Figure 3 shows the relationship between the softening point and the amount of fixed carbon of pitch prepared by distilling heat-treated products obtained by heat-treating ethylene bottom oil under different heat treatment conditions under different distillation conditions. Figure 3 shows that when the distillation conditions are changed while the heat treatment conditions are the same, the relationship between the softening point and the amount of fixed carbon can be approximated by a linear equation. It can be seen that the intercept value changes depending on the heat treatment conditions, but the slope value is 0.2 regardless of the heat treatment conditions. Furthermore, it can be seen that the more severe the heat treatment conditions (high temperature and / or long duration), the larger the intercept value, and the higher the amount of fixed carbon of pitch obtained at the same softening point.

[0056] One embodiment of the petroleum-based pitch satisfies equation (1). That is, 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 with similar softening points. 80.0≧Y>0.2X+29.5 (1) Y: Fixed carbon amount (mass%) X: Softening point (℃) (60≦X≦120)

[0057] By simultaneously meeting the requirements described above, petroleum-based pitch can achieve both good impregnation and a high fixed carbon content, which was difficult to achieve with conventional methods.

[0058] The method for manufacturing petroleum-based pitch is not particularly limited as long as it is a method that can produce pitch that satisfies the characteristics described above, but a manufacturing method including steps 1 to 4 described above is preferred. If the pitch obtained in step 2 satisfies the characteristics described above, steps 3 and 4 may be omitted. [Examples]

[0059] 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.

[0060] <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".

[0061] <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".

[0062] <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".

[0063] <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".

[0064] <Method for measuring viscosity> Viscosity was measured at 160°C, 180°C, 200°C, 210°C, and 220°C in accordance with ASTM D5018-18 "Standard Test Method for Shear Viscosity of Coal-Tar and Petroleum Pitches".

[0065] <Method for measuring true density> Measurements were taken in accordance with ASTM D4892-14 (2019) "Standard Test Method for Density of Solid Pitch (Helium Pycnometer Method)".

[0066] <Method for preparing the light component of ethylene bottom oil> Using 894 kg of ethylene bottom oil 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. Approximately 350 kg of the distillate was used as the light ethylene bottom oil component.

[0067] <Filtration Test> Measurements were taken with reference to the methods described in Japanese Utility Model Publication No. 57-64743 and Japanese Patent Publication No. 63-97691. A piece of calcined body cut from the calcined body described in "3. Calcination Process" of the aforementioned graphite electrode manufacturing method was used as a filter plate (diameter: 50 mmφ, thickness: 30 mm), and this was attached to an impregnated pitch filterability test apparatus (Japanese Utility Model Publication No. 57-64743) at 210°C and a pressure of 5 kg / cm². 2The time it took for 100g of pitch to filter out under these conditions was measured to compare the impregnation properties of the pitch. The filtering times are shown in Table 1. A shorter filtering time indicates better impregnation. If 100g of pitch did not filter out completely within 60 minutes, it was considered "unfilterable," meaning the impregnation properties were extremely poor.

[0068] <Method for calculating equations (2) and (3)> The heat-treated material obtained in Step 1 of Comparative Example 1 was distilled under different distillation conditions to prepare pitches with different softening points. The softening point and fixed carbon content of each obtained pitch were measured, and equation (2) was calculated using the least squares method. Y = 0.2X + 33.0 (2) The heat-treated material obtained in Step 1 of Comparative Example 2 was distilled under different distillation conditions to prepare pitches with different softening points. The softening point and fixed carbon content of each obtained pitch were measured, and equation (3) was calculated using the least squares method. Y = 0.2X + 29.5 (3)

[0069] (Example 1-1) 3,000 g of ethylene bottom oil was introduced into a 6 L capacity 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 1 hour 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 2,790 g. 600 g of the obtained heat-treated product was subjected to vacuum distillation (distillation pressure: 667 PaA) so that the distillation endpoint was 355°C at atmospheric pressure, yielding 222 g of pitch 1 (Step 2). The softening point of the obtained pitch 1 was 110°C, TI was 13.9 mass%, and QI was 0.0 mass%. 2,220 g of toluene was added to the 222 g of pitch 1, and the mixture was heated and stirred at 130°C for 1 hour. The mixture was then separated into soluble and insoluble components by centrifugation (Step 3). The light components were removed from the obtained soluble matter (components with reduced TI) by vacuum distillation (step 4), yielding 184 g of pitch 2 as the distillation residue (high-boiling point components) (equivalent to a yield of 29% relative to the raw material ethylene bottom oil). The above-mentioned tests were carried out using this pitch.

[0070] (Example 2-1) 3,000 g of ethylene bottom oil light component was introduced into a 6 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the container was raised to 400°C at a rate of 5°C / min while stirring. After 6 hours had elapsed since reaching 400°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 2,940 g. The obtained 2,940 g of heat-treated product was subjected to vacuum distillation (distillation pressure: 667 PaA) so that the distillation endpoint was 390°C at atmospheric pressure, and 617 g of pitch was obtained (yield of 21% relative to the raw material ethylene bottom oil light component) (Step 2). The characteristics of the obtained pitch are as shown in Table 1, and since it satisfied the above-mentioned desirable pitch characteristics, Steps 3 and 4 were omitted. A filterability test was performed using this pitch.

[0071] (Example 2-2) Except for changing the heat treatment and distillation conditions as shown in Table 1, pitch was prepared according to the method described in Example 2-1. The yield of pitch was 570 g (19% yield relative to the light component of the raw material ethylene bottom oil) (Step 2). The properties of the obtained pitch were as shown in Table 1 and satisfied the above-mentioned preferred pitch properties, so Steps 3 and 4 were omitted. A filterability test was performed using this pitch.

[0072] (Examples 2-3) Except for changing the heat treatment and distillation conditions as shown in Table 1, pitch was prepared according to the method described in Example 2-1. The yield of pitch was 732 g (24% yield relative to the light component of the raw material ethylene bottom oil) (Step 2). The properties of the obtained pitch were as shown in Table 1 and satisfied the above-mentioned preferred pitch properties, so Steps 3 and 4 were omitted. A filterability test was performed using this pitch.

[0073] (Comparative Example 1) 600 g of the heat-treated product obtained in Step 1 of Example 1 was subjected to vacuum distillation so that the distillation endpoint was 335°C at atmospheric pressure, yielding 234 g of pitch (equivalent to a yield of 36% relative to the raw material ethylene bottom oil). The above-mentioned tests were carried out using this pitch.

[0074] (Comparative Example 2) 500 g of ethylene bottom oil was introduced into a 1 L capacity 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. After 4 hours had elapsed since reaching 380°C, heating was stopped, and the autoclave was allowed to cool to room temperature. The yield of the heat-treated product obtained was 492 g. The obtained 492 g of heat-treated product was subjected to vacuum distillation (distillation pressure: 667 PaA) so that the distillation endpoint was 330°C at atmospheric pressure, and 196 g of pitch was obtained (yield 39% relative to the raw material ethylene bottom oil). The various tests described above were carried out using this pitch.

[0075] (Comparative Example 3) 500 g of ethylene bottom oil was introduced into a 1 L capacity 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. After 24 hours had elapsed since reaching 380°C, heating was stopped, and the autoclave was allowed to cool to room temperature. The yield of the heat-treated product obtained was 465 g. The 465 g of heat-treated product was subjected to vacuum distillation (distillation pressure: 667 PaA) so that the distillation endpoint was 335°C at atmospheric pressure, and 214 g of pitch was obtained (yield 43% relative to the raw material ethylene bottom oil). The various tests described above were carried out using this pitch.

[0076] (Comparative Example 4) Pitch was prepared according to the method described in Comparative Example 3, except that the conditions for vacuum distillation were adjusted so that the distillation endpoint was 345°C at atmospheric pressure. The yield of pitch was 191 g (38% yield relative to the raw material ethylene bottom oil). The above-mentioned tests were carried out using this pitch.

[0077] (Reference example 1) The data for commercially available coal tar-based impregnated pitch is shown.

[0078] As shown in Table 1, the petroleum-based pitches in the examples exhibit both good impregnation properties and a high fixed carbon content, making them clearly suitable as impregnation pitches for carbon material production.

[0079] Table 1

Claims

1. A petroleum-based pitch 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%) that satisfies formula (1). 80.0≧Y>0.2X+29.5 (1) Y: fixed carbon amount (mass%) X: Softening point (℃) (60≦X≦120)

2. The petroleum-based pitch according to claim 1, wherein the fixed carbon content is 47.0% by mass or more.

3. The petroleum-based pitch according to claim 1 or 2, which is an impregnating pitch for carbon material production.

4. The petroleum-based pitch according to claim 3, wherein the carbon material is a graphite electrode.

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