Manufacturing method of petroleum pitch and petroleum 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-based pitch suitable for impregnation pitch used in the production of carbon materials such as graphite electrodes, and a method for producing the same. [Background technology]

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

[0003] Heavy residual oil (ethylene bottom oil), a by-product of the production of olefins such as ethylene and propylene by steam cracking or thermal cracking of petroleum hydrocarbons such as naphtha, is mostly used as fuel, with only a portion being used as a raw material for carbon black. Therefore, converting this ethylene bottom oil into high-value-added products is a challenge in the technical field. To address this challenge, attempts have been made to utilize the characteristics of ethylene bottom oil, which contains a large amount of aromatic compounds, to produce impregnation pitch for carbon material production, binder pitch, and the like from ethylene bottom oil. However, petroleum pitch produced from petroleum heavy oils such as ethylene bottom oil has a lower fixed carbon content than coal tar pitch produced from coal tar, and therefore the density of the resulting carbon material tends to be lower. Therefore, petroleum pitch is not currently widely used.

[0004] Among the properties required for impregnated pitch, some of the most important are impregnation ability and fixed carbon content. Better impregnation ability allows the impregnated pitch to easily penetrate into the fine pores generated in the fired body during the impregnation process, resulting in a higher density of the resulting carbon material, which is desirable. A higher fixed carbon content reduces the amount of volatile matter produced during firing, reducing the occurrence of pores. As a result, the number of impregnation and re-firing steps can be reduced, which is economically advantageous. Various methods for improving the impregnation ability of coal tar pitch are known, including a typical method of removing or reducing quinoline insoluble matter (QI) in the pitch. Coal tar pitch typically contains several to several tens of percent by mass of QI, derived from primary QI contained in the raw coal tar and secondary QI that may be generated during the heat treatment process. This QI exists as solid fine particles even when the pitch is molten during the impregnation process, significantly inhibiting the pitch from penetrating the pores of the fired body. Therefore, it is desirable for coal tar-based impregnated pitch to be substantially free of QI (Patent Document 1).

[0005] On the other hand, petroleum heavy oils (especially ethylene bottom oils) contain almost no QI. Therefore, by heat treating petroleum heavy oils under conditions that do not produce QI, it is possible to prepare petroleum pitches that are substantially free of QI without a QI removal or reduction step. In fact, Japanese Patent Laid-Open Publication No. 60-92388 (Patent Document 2) reports that petroleum pitches with a QI content of 1% by mass or less can be produced from petroleum heavy oils without a QI removal or reduction step, and that the resulting petroleum pitches are suitable for use as impregnation pitches. However, many of the petroleum pitches reported to date, including the petroleum pitch described in Patent Document 2, have lower fixed carbon contents than coal tar pitches with equivalent softening points (Patent Document 2 and Non-Patent Document 1). One method for increasing the fixed carbon content of petroleum pitches is to remove light components from the pitch by distillation, etc., but this simultaneously increases the softening point and viscosity, resulting in a problem of reduced impregnation properties. Therefore, it is difficult to produce petroleum pitches that combine good impregnation properties with a high fixed carbon content using conventional methods. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open 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 Summary of the Invention [Problem to be solved by the invention]

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

[0009] The present inventors have conducted extensive research to achieve the above-mentioned object. Specifically, they investigated a method of subjecting petroleum heavy oil to a relatively severe heat treatment within a range of conditions that would prevent the generation of QI. However, when the present inventors investigated this method, they were able to obtain a petroleum pitch that was free of QI and had a high fixed carbon content, but it was revealed that its impregnation ability was significantly poor (see Comparative Examples 1, 3, and 4 in this specification). This suggests that factors other than QI have a significant effect on impregnation ability in petroleum pitch produced by a production method that includes a step of heat treating petroleum heavy oil under relatively severe conditions. The present inventors have discovered that toluene insoluble matter (TI), which does not affect impregnation ability in coal tar pitch, does affect impregnation ability in petroleum pitch produced by a production method that includes a step of heat treating petroleum heavy oil under relatively severe conditions, and have embodied this finding in the present invention.

[0010] That is, the present invention relates to a method for producing petroleum pitch, which includes the steps of thermally treating petroleum heavy oil (step 1), distilling the thermally treated product obtained in step 1 to obtain pitch 1 as a high-boiling component (step 2), reducing the toluene insolubles (TI) of pitch 1 obtained in step 2 (step 3), and distilling the toluene insolubles (TI-reduced) component obtained in step 3 to obtain pitch 2 as a high-boiling component (step 4).The present invention also relates to a petroleum pitch having a quinoline insolubles (QI) of 0.5% by mass or less, a toluene insolubles (TI) of 3.0% by mass or less, a softening point of 60°C to 120°C, and 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] That is, the present invention relates to the following [1] to

[10] .

[0012] [1] A method for producing petroleum pitch comprising at least the following steps 1 to 4. Process 1: Heat treatment of petroleum heavy oil Step 2: A step of distilling the heat-treated product obtained in Step 1 to obtain pitch 1 as a high-boiling point component. Step 3: Removing toluene insolubles (TI) from the pitch 1 obtained in step 2; A process for obtaining a component with reduced TI Step 4: Distilling the component with reduced toluene insolubles (TI) obtained in step 3; A process for obtaining pitch 2 as a high boiling point component [2] The method for producing petroleum pitch according to [1], wherein the petroleum heavy oil is ethylene bottom oil. [3] The method for producing petroleum pitch according to [1] or [2], wherein the heat treatment temperature in step 1 is 360°C to 500°C. [4] The method for producing a petroleum pitch according to any one of [1] to [3], wherein the removal of the toluene-insoluble matter (TI) in step 3 is carried out by adding a solvent to the pitch 1 and extracting the solvent-soluble matter of the pitch 1 into the solvent, and the solvent is at least one selected from the group consisting of benzene, alkylbenzene, cracked gasoline, and cracked kerosene. [5] The method for producing petroleum pitch according to any one of [1] to [4], wherein in step 1, the heat treatment time is 8 hours to 48 hours when the heat treatment temperature is 360°C to 390°C, 0.5 hours to 24 hours when the heat treatment temperature is above 390°C to 430°C, and 0.1 hours to 16 hours when the heat treatment temperature is above 430°C to 500°C. [6] A method for producing a graphite electrode, in which 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 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, and 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) [8] The petroleum pitch according to [7], having a fixed carbon content of 47.0% by mass or more. [9] The petroleum-based pitch according to [7] or [8], which is an impregnation pitch for producing carbon materials.

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

[0013] According to the present invention, petroleum pitch having a high fixed carbon content and excellent impregnation ability into fired bodies during the production of carbon materials such as graphite electrodes can be obtained using petroleum heavy oil as a raw material. Because this petroleum pitch can easily impregnate fired bodies and has a high fixed carbon content, the quality of the resulting carbon material can be improved. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a flow diagram showing an example of a petrochemical process for thermally cracking petroleum such as naphtha and a process for producing ethylene bottom oil. [Figure 2] FIG. 1 is a flow diagram showing one embodiment of a method for producing petroleum-based pitch. [Figure 3] FIG. 1 is a graph showing the relationship between the softening point and the fixed carbon content of various pitches produced from ethylene bottom oil under different production conditions. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will be described below, but it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention.

[0016] In this specification, when "to" is used to describe a range of values, the values ​​at both ends are the upper and lower limits, respectively, and are included in the range.

[0017] <Graphite electrode manufacturing process> Carbon materials refer to various molded carbon materials such as graphite pipes, graphite crucibles, graphite boats, graphite electrodes, etc. The general manufacturing process for graphite electrodes is described below. 1. Mixing process Mixing and kneading needle coke and binder pitch together 2. Molding process A process of molding the kneaded material to obtain a molded body of a predetermined size and shape. 3. Firing process A step of firing the compact to obtain a fired body. 4.Impregnation process A process of filling the fired body with impregnated pitch 5. Re-firing process A process of re-firing the fired body filled with impregnated pitch to obtain a re-fired body. 6.Graphitization process The process of graphitizing the refired body 7. Processing process A process in which the graphitized body is formed into a predetermined shape by cutting or the like to produce a graphite electrode.

[0018] 1. Mixing process The needle coke is crushed, classified, and blended in a predetermined particle size ratio with the binder pitch, and then mixed and kneaded together. The blending amount of the binder pitch varies depending on the blending method and molding method, but is generally about 20 to 30 parts by mass per 100 parts by mass of the needle coke.

[0019] The kneaded material may contain a puffing inhibitor such as iron oxide.

[0020] A commercially available mixer or kneader can be used for mixing and kneading. Specific examples include mixers and kneaders such as 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, more preferably 110°C or lower. When kneading at around 150°C, it is difficult to knead sufficiently if the softening point of the binder pitch is higher than 130°C. After kneading, the kneaded product is cooled to a temperature (100°C to 130°C) suitable for subsequent molding.

[0021] 2. Molding process The kneaded material is molded to obtain a molded product of a predetermined size and shape. The molding method can be appropriately selected from extrusion molding, molding, etc. depending on the target carbon material. When the target carbon material is a graphite electrode, extrusion molding into a cylindrical shape is generally used.

[0022] 3. Firing process The molded body from the previous process is heated and fired at 700°C to 1000°C to obtain a fired body. The firing process is preferably carried out in a non-oxidizing atmosphere of combustion exhaust gas. The molded body softens at the beginning of the temperature rise, and at 200°C to 500°C, a large amount of decomposition gas is generated by thermal decomposition and polycondensation of the binder pitch, resulting in the formation of pores and volume shrinkage. At 500°C to 600°C, the binder pitch carbonizes. The firing process, including cooling, often takes around one month.

[0023] 4.Impregnation process In the firing process, generally, 35% to 45% of the mass of the binder pitch is lost as volatile matter. At that time, a large number of pores are generated in the fired body. The impregnation process involves filling these pores with impregnation pitch. Impregnation is carried out, for example, by placing the fired body in an autoclave, degassing it under reduced pressure, and then injecting molten impregnation pitch into the pores at approximately 200°C and a gas pressure of approximately 1 MPa.

[0024] 5. Re-firing process The fired body filled with the impregnated pitch is fired again to obtain a refired body. The refired body can be performed under the same conditions as the firing step. The impregnation step and the refired body can be repeated as necessary.

[0025] 6.Graphitization process The re-fired body is placed in a furnace (such as an Acheson furnace or an LWG furnace) surrounded by an insulating material, and is subjected to heat treatment using packing coke or resistance heating of the re-fired body due to the passage of electricity. The graphitization temperature is 2000°C to 3000°C. This temperature is necessary to convert the amorphous carbon in the re-fired body into crystalline graphite. The re-fired body is preferably heat-treated for several days to convert it into graphite.

[0026] 7. Processing process The graphitized body is machined by cutting or other machining to produce graphite electrode products of the desired shape. The density (bulk density) of the graphite electrode varies depending on the electric furnace equipment and operating conditions used, but is generally 1.5 g / cm 3 ~1.9g / cm 3 It is preferable that:

[0027] <Method of manufacturing petroleum pitch> A method for producing petroleum pitch in one embodiment includes at least the following steps 1 to 4 in this order, and may include other steps. A method for producing petroleum pitch in another embodiment includes the following steps 1 and 2 in this order, and steps 3 and 4 can be omitted. Process 1: Heat treatment of petroleum heavy oil Step 2: A step of distilling the heat-treated product obtained in Step 1 to obtain pitch 1 as a high-boiling point component. Step 3: Removing toluene insolubles (TI) from the pitch 1 obtained in step 2; A process for obtaining a component with reduced TI Step 4: Distilling the component with reduced toluene insolubles (TI) obtained in step 3; A process for obtaining pitch 2 as a high boiling point component

[0028] In the petrochemical industry, naphtha and other materials are generally thermally cracked at high temperatures, and the resulting pyrolysis product is then distilled to separate the various fractions into products such as ethylene, propylene, and other olefins, aromatic compounds such as benzene, toluene, and xylene, cracked gasoline, and cracked kerosene. Of these fractions, the heaviest fraction with the highest boiling point is called ethylene bottoms oil, and is used as a raw material for carbon black and other products, as well as fuel (see Figure 1). Because naphtha and other thermal cracking plants are often called ethylene plants, the aforementioned heavy fraction is called ethylene bottoms oil.

[0029] The properties of ethylene bottom oil obtained by thermal cracking of naphtha-containing feedstock vary depending on the type of naphtha-containing feedstock, the thermal cracking conditions, the operating conditions of the refinery distillation column, etc., but generally, the 50% distillation temperature is 200°C to 400°C, the aromatic carbon content is 50% by mass or more, the flash point is 70°C to 100°C, and the kinematic viscosity at 50°C is 40mm 2 However, since ethylene bottom oil is a mixture of hydrocarbons, the above value may vary slightly.

[0030] The petroleum heavy oil may be ethylene bottom oil, an ethylene bottom oil heavy fraction obtained by removing any proportion (e.g., 5 to 70% by mass) of light components from ethylene bottom oil by distillation or the like, or the removed ethylene bottom oil light fraction, other petroleum heavy oils, or a mixture thereof. In one embodiment, the petroleum heavy oil is ethylene bottom oil. Furthermore, heavy oils such as coal tar may be added to the petroleum heavy oil. The other petroleum heavy oil is not particularly limited, but examples include fluid catalytic cracking oil (FCC decant oil), atmospheric distillation residue, and vacuum distillation residue. The sulfur and nitrogen contents in pitch are preferably low because they cause puffing during firing. When a graphite electrode is produced using a pitch containing a large amount of metal components, these metal components evaporate during graphitization, reducing the density of the graphite electrode, which may be undesirable in terms of product quality. From these viewpoints, fluid catalytic cracking oil (FCC decant oil) is preferred as the other petroleum heavy oil. The properties of fluid catalytic cracking oil (FCC decant oil) vary depending on the raw material and operating conditions, 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 40mm. 2 However, since fluid catalytic cracking oil (FCC decant oil) is a complex mixture, the above values ​​may vary slightly.

[0031] (Process 1) Step 1 is a step of thermally treating petroleum heavy oil. The thermal treatment is preferably carried out in a sealed container in a non-oxidizing gas atmosphere. Examples of non-oxidizing gases include nitrogen gas, argon gas, hydrogen gas, lower alkanes such as methane and ethane, and mixed gases of these non-oxidizing gases. However, nitrogen gas is preferred from the viewpoints 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 limit values ​​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 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, the time is preferably 8 hours or more, 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, the time is preferably 48 hours or less. When the heat treatment temperature is 360°C to 390°C, the time is preferably 8 hours to 48 hours, more preferably 16 to 48 hours. When the heat treatment temperature is greater than 390°C to 430°C, the time is preferably 0.5 hours or more, more preferably 1 hour or more. When the heat treatment temperature is greater than 390°C to 430°C, the time is preferably 24 hours or less, more preferably 16 hours or less. When the heat treatment temperature is greater than 390°C to 430°C, the time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 16 hours. When the heat treatment temperature is greater than 430°C to 500°C, the time is preferably 0.1 hours or more, more preferably 0.5 hours or more. When the heat treatment temperature is between 430°C and 500°C, the heat treatment time is preferably 16 hours or less, more preferably 8 hours or less. When the heat treatment temperature is between 430°C and 500°C, the heat treatment time is preferably 0.1 to 16 hours, more preferably 0.5 to 8 hours. The above upper and lower limit values ​​can be combined arbitrarily. By setting the heat treatment time within the above range, pitch with a sufficient fixed carbon content can be obtained.

[0034] The pressure at the start of the heat treatment (initial pressure) is preferably 0 MPaG, but there are no particular limitations. The pressure inside the sealed vessel rises due to hydrogen and lower alkanes such as methane and ethane generated by thermal decomposition during the heat treatment. There is no limitation on the pressure inside the sealed vessel, but pressurized conditions are preferred because TI is likely to be produced under normal pressure, which reduces the final pitch yield.

[0035] In step 1, an additive such as a solid catalyst may be added to the petroleum heavy oil. The solid catalyst referred to here is a catalyst that does not dissolve in the reaction substrate (petroleum heavy oil) and does not decompose even at the heat treatment temperature. Specific examples include solid acid catalysts such as activated clay, silica alumina, and zeolite. As described in Japanese Patent Application Laid-Open Nos. 60-179493 and 60-240790, these solid acid catalysts are known to suppress the occurrence of fouling during the heat treatment of petroleum heavy oil, and are useful when heat treatment is performed under relatively severe reaction conditions to increase the fixed carbon content of the pitch. The added solid catalyst can be removed as a solvent-insoluble component together with TI in step 3, and therefore is not mixed into the pitch finally obtained in step 4.

[0036] (Process 2) Step 2 is a step of removing low boiling components by distilling the heat-treated product obtained in Step 1 to obtain pitch 1 as a high boiling component. When Steps 3 and 4 are omitted, pitch 1 obtained in Step 2 is a petroleum 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 appropriately. The internal temperature of the distillation apparatus, although depending on the distillation pressure, is preferably not higher than 360°C. This is because temperatures above 360°C are likely to produce TIs, which may reduce the final pitch yield. The lower limit temperature does not affect the pitch characteristics, but a low temperature necessitates a lower distillation pressure to distill off low-boiling (light) fractions. Therefore, from an economical perspective, a temperature of 200°C or higher is preferable. To achieve a softening point of 120°C or lower for pitch 2 obtained in step 4, 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 heavy oil used and the heat treatment conditions in step 1. When performing reduced-pressure distillation (vacuum distillation), the pressure during distillation is preferably 100 PaA to 10,000 PaA, more preferably 300 PaA to 5,000 PaA, in order to obtain pitch 1 with a softening point of approximately 180°C or lower. The softening point of the pitch can be controlled by the amount of light components removed. Generally, the softening point increases as the amount of light components removed increases, i.e., the distillation end point increases. When ethylene bottom oil is used as the petroleum heavy oil, in order to make the softening point of pitch 1 about 180°C or lower, the distillation end point converted to atmospheric pressure is preferably 450°C or lower, more preferably 420°C or lower, and even more preferably 400°C or lower, although this depends on the heat treatment conditions and distillation apparatus in step 1.

[0038] (Step 3) Step 3 is a step in which toluene-insoluble matter (TI) is removed from the pitch 1 obtained in step 2 to obtain a component with reduced TI. The method for removing TI is not particularly limited, but examples include adding an appropriate solvent to the pitch 1 obtained in step 2, extracting the solvent-soluble matter of pitch 1 into the solvent, and then separating and removing the solvent-insoluble matter to obtain a component with reduced TI. In this case, the component with reduced TI contains both the solvent-soluble matter and the solvent used. Meanwhile, the solvent-insoluble matter contains TI and a solid catalyst added as needed.

[0039] A suitable solvent is preferably one that dissolves only the toluene-soluble fraction (TS) in the pitch but not the TI. Specifically, benzene, alkylbenzenes such as toluene and xylene, and mixtures thereof are preferred. Fractions rich in benzene and alkylbenzenes obtained from petrochemical processes can also be used. Examples of such fractions include cracked gasoline and cracked kerosene.

[0040] Cracked gasoline is a mixture of hydrocarbons, mainly containing 6 to 8 carbon atoms, produced in a petrochemical process, and is a fraction with a boiling point in the range of 65°C to 150°C at 1 atmosphere. However, because cracked gasoline is a mixture of hydrocarbons, the number of carbon atoms and boiling point may vary slightly.

[0041] The main components of cracked gasoline include, for example, benzene, toluene, ethylbenzene, xylene, styrene, and hexane.

[0042] Cracked kerosene is a mixture of hydrocarbons, mainly those with 9 or more carbon atoms, produced in petrochemical processes, and is a fraction with a boiling point in the range of 90°C to 230°C at 1 atmosphere. However, because cracked kerosene is a mixture of hydrocarbons, the number of carbon atoms and boiling point may vary slightly.

[0043] Examples of the main components of cracked kerosene include xylene, styrene, allylbenzene, propylbenzene, methylethylbenzene, trimethylbenzene, methylstyrene, dicyclopentadiene, indane, indene, methylpropylbenzene, methylpropenylbenzene, ethylstyrene, divinylbenzene, methylindene, naphthalene, and methyldicyclopentadiene.

[0044] The amount of solvent added is preferably 25 to 5,000 parts by mass, more preferably 300 to 2,000 parts by mass, per 100 parts by mass of pitch 1. Although this varies somewhat depending on the extraction conditions, an amount of 25 parts by mass or more ensures efficient extraction. If the amount exceeds 5,000 parts by mass, the extraction efficiency does not change significantly, so from the standpoints of economy and productivity, an amount of 5,000 parts by mass or less is preferred.

[0045] The extraction temperature is not particularly limited. Extraction can be performed at room temperature, but heating conditions are preferred for better extraction efficiency. When extraction is performed under heating conditions at normal pressure, it is necessary to perform the extraction at a temperature below the boiling point of the solvent used. When heating at a temperature above the boiling point, extraction can be performed under reflux conditions or under pressure using a sealed container.

[0046] The method for separating the solvent in which the solvent-soluble components are dissolved 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 step of distilling off light components by distillation from the component with reduced TI obtained in Step 3 to obtain pitch 2 as a high-boiling component. Pitch 2 obtained in Step 4 is a petroleum pitch of one embodiment.

[0048] The distillation method in step 4 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, although depending on the distillation pressure, is preferably not higher than 360°C. This is because a temperature higher than 360°C facilitates the polycondensation reaction and the production of TI. The lower limit temperature does not affect the pitch properties, but a low temperature necessitates a lower distillation pressure to distill off low-boiling substances (light fractions). Therefore, from an economical perspective, 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 less, the distillation pressure is preferably 100 PaA to 10,000 PaA, more preferably 300 PaA to 5,000 PaA. The softening point of the pitch can be controlled by the amount of light fractions removed. Generally, the softening point increases as the amount of light fractions removed increases, i.e., the distillation end point increases. When ethylene bottom oil is used as the petroleum heavy oil, in order to make the softening point of pitch 2 120°C or lower, the distillation end point when converted to atmospheric pressure is preferably 450°C or lower, more preferably 420°C or lower, and even more preferably 400°C or lower, although this depends on the heat treatment conditions and distillation apparatus in step 1. Furthermore, the distillation end point when converted to atmospheric pressure is preferably 250°C or higher, more preferably 300°C or higher, although this also depends on the heat treatment conditions and distillation apparatus in step 1. If the distillation end point is lower than 250°C, a large amount of light components will volatilize at the impregnation temperature (for example, 200°C), raising concerns that the viscosity of the pitch may abnormally increase during the impregnation step.

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

[0050] In one embodiment, the quinoline insoluble matter (QI) of the petroleum pitch is 0.5% by mass or less. Since the lower the QI, the better the pitch's impregnation ability, the QI is preferably 0.3% by mass or less, and more preferably 0.1% by mass or less. The lower limit of the QI is not particularly limited, but is, for example, 0.0% by mass or 0.001% by mass. The QI is measured by the method described in the Examples section.

[0051] In one embodiment, the toluene insolubles (TI) of the petroleum pitch is 3.0% by mass or less. Since the lower the TI, the better the pitch's impregnation ability, so 2.0% by mass or less is preferable, and 1.0% by mass or less is more preferable. The lower limit of TI is not particularly limited, but is, for example, 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 pitch in one embodiment is 60°C to 120°C. The lower the softening point, the better the fluidity of the pitch and its ability to impregnate a fired body. Therefore, 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 limit values ​​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 by the method described in the Examples section.

[0053] In one embodiment, the viscosity of the petroleum pitch at 200°C is 200 mPa·s or less. Since the lower the viscosity, the better the fluidity and impregnation properties 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. The viscosity is measured by the method described in the Examples section.

[0054] Since the density of the resulting carbon material tends to increase as the fixed carbon content increases, the fixed carbon content of the petroleum 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 pitch with a higher fixed carbon content requires more severe heat treatment conditions, which may result in 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 arbitrarily combined. 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 and fixed carbon content of pitch. Figure 3 shows the relationship between the softening point and fixed carbon content of pitch prepared by heat-treating ethylene bottom oil under different heat treatment conditions and then distilling the heat-treated product under different distillation conditions. Figure 3 shows that when the distillation conditions are changed while maintaining the same heat treatment conditions, the relationship between the softening point and fixed carbon content can be approximated by a linear equation. While the intercept value varies depending on the heat treatment conditions, the slope value is 0.2 regardless of the heat treatment conditions. Furthermore, the more severe the heat treatment conditions (higher temperature and / or longer time), the larger the intercept value, indicating that pitch with a higher fixed carbon content can be obtained at the same softening point.

[0056] The petroleum pitch of one embodiment satisfies formula (1). That is, the value of the fixed carbon content Y (mass%) of the petroleum pitch exceeds the value calculated by substituting the softening point X (°C) of the petroleum pitch into formula (1). Petroleum pitches that satisfy this condition have a larger fixed carbon content than 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 satisfying the above-mentioned requirements, petroleum pitch can achieve both good impregnation properties and a high fixed carbon content, which was difficult to achieve with conventional methods.

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

[0059] The present invention will be further described with reference to the following examples, comparative examples and reference examples. However, these examples are merely examples of the present invention, and the present invention is not limited to these examples.

[0060] <Method for measuring softening point (SP)> Measurement was performed in accordance with "8. Method for measuring the softening point of tar pitch (ring and ball method)" in JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch."

[0061] <Method for measuring fixed carbon (FC) amount> Measurement was performed in accordance with "11. Fixed carbon content determination method" in JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch."

[0062] <Method for measuring quinoline insoluble matter (QI)> Measurement was performed in accordance with the filtration method described in "15. Quantitative method for quinoline insoluble matter in tar pitch" in JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch."

[0063] <Method for measuring toluene insolubles (TI)> Measurement was performed in accordance with the filtration method described in "14.2 Quantitative method for toluene insoluble matter in processed tar and tar pitch" of JIS K 2425:2006 "Test methods for creosote oil, processed tar and tar pitch."

[0064] <Viscosity measurement method> The 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 made in accordance with ASTM D4892-14(2019) "Standard Test Method for Density of Solid Pitch (Helium Pycnometer Method)."

[0066] <Method for preparing light ethylene bottom oil fraction> Using 894 kg of ethylene bottom oil as a feedstock, it was distilled and refined in a distillation apparatus with 15 theoretical plates (Sulzer packing) at a vessel temperature of 101°C and an operating pressure of 533 to 1067 PaA, yielding 544 kg of a heavy ethylene bottom oil fraction as the bottom liquid. The initial boiling point of the obtained heavy ethylene bottom oil fraction was 218°C. Approximately 350 kg of components obtained as the distillate were used as a light ethylene bottom oil fraction.

[0067] <Filterability test> Measurements were made with reference to the methods described in Japanese Utility Model Laid-Open Publication No. 57-64743 and Japanese Patent Laid-Open Publication No. 63-97691. A piece of sintered body cut out from the sintered body described in "3. Firing step" of the above-mentioned graphite electrode manufacturing method was used as a filter plate (diameter: 50 mmφ, thickness: 30 mm), which was attached to an impregnated pitch filterability tester (Japanese Utility Model Laid-Open Publication No. 57-64743), and filtered at 210°C and a pressure of 5 kg / cm. 2The time it took for 100g of pitch to filter out under these conditions was measured, and the impregnation properties of the pitches were compared. The flow times are shown in Table 1. The shorter the flow time, the better the impregnation properties. If 100g of pitch did not completely flow out within 60 minutes, it was deemed "unfilterable," indicating extremely poor impregnation properties.

[0068] <Calculation method of formula (2) and formula (3)> The heat-treated product 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 pitch obtained were measured, and equation (2) was calculated by the least squares method. Y=0.2X+33.0 (2) The heat-treated product 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 pitch obtained were measured, and equation (3) was calculated by 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 stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the vessel was raised to 430 °C at a rate of 5 °C / min while stirring. One hour after reaching 430 °C, heating was stopped and the vessel was allowed to cool to room temperature (Step 1). The yield of the resulting heat-treated product was 2,790 g. 600 g of the resulting heat-treated product was distilled under reduced pressure (distillation pressure: 667 PaA) so that the distillation end point was 355 °C (at atmospheric pressure), yielding 222 g of pitch 1 (Step 2). The resulting pitch 1 had a softening point of 110 °C, a TI of 13.9% by mass, and a QI of 0.0% by mass. 2,220 g of toluene was added to 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 fractions by centrifugation (Step 3). The light components were removed from the resulting soluble fraction (components with reduced TI) by vacuum distillation (step 4), and 184 g of pitch 2 was obtained as the distillation residue (high boiling point component) (corresponding to a yield of 29% based on the raw ethylene bottom oil). This pitch was used to carry out the various tests described above.

[0070] Example 2-1 3,000 g of ethylene bottom oil light fraction was introduced into a 6 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the vessel was raised to 400 °C at a rate of 5 °C / min while stirring. Six hours after reaching 400 °C, heating was terminated and the vessel was allowed to cool to room temperature (Step 1). The yield of the heat-treated product obtained was 2,940 g. 2,940 g of the heat-treated product obtained was distilled under reduced pressure (distillation pressure: 667 PaA) so that the distillation end point was 390 °C (equivalent to atmospheric pressure), yielding 617 g of pitch (21% yield relative to the raw ethylene bottom oil light fraction) (Step 2). The properties of the obtained pitch were as shown in Table 1, and since it satisfied the above-mentioned preferred pitch properties, Steps 3 and 4 were omitted. This pitch was used to conduct a filterability test.

[0071] (Example 2-2) Pitch was prepared according to the method described in Example 2-1, except that the heat treatment conditions and distillation conditions were changed as shown in Table 1. The yield of pitch was 570 g (19% yield based on the light fraction of ethylene bottom oil used as the raw material) (Step 2). The properties of the obtained pitch were as shown in Table 1, and since the above-mentioned preferred pitch properties were satisfied, Steps 3 and 4 were omitted. A filterability test was carried out using this pitch.

[0072] (Example 2-3) Pitch was prepared according to the method described in Example 2-1, except that the heat treatment conditions and distillation conditions were changed as shown in Table 1. The yield of pitch was 732 g (24% yield based on the light fraction of ethylene bottom oil used as the raw material) (Step 2). The properties of the obtained pitch were as shown in Table 1, and since the above-mentioned preferred pitch properties were satisfied, Steps 3 and 4 were omitted. A filterability test was carried out using this pitch.

[0073] (Comparative Example 1) 600 g of the heat-treated product obtained in step 1 of Example 1 was distilled under reduced pressure so that the distillation end point was 335°C (at atmospheric pressure), and 234 g of pitch was obtained (corresponding to a yield of 36% based on the raw ethylene bottom oil). This pitch was used to carry out the various tests described above.

[0074] (Comparative Example 2) 500 g of ethylene bottom oil was introduced into a 1 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the vessel was raised to 380°C at a rate of 4°C / min while stirring. Four hours after reaching 380°C, heating was stopped and the vessel was allowed to cool to room temperature. The yield of the heat-treated product was 492 g. 492 g of the heat-treated product was distilled under reduced pressure (distillation pressure: 667 PaA) so that the distillation end point was 330°C (equivalent to atmospheric pressure), yielding 196 g of pitch (39% yield based on the raw ethylene bottom oil). This pitch was used to carry out the various tests described above.

[0075] (Comparative Example 3) 500 g of ethylene bottom oil was introduced into a 1 L stainless steel autoclave. The autoclave was sealed under a nitrogen gas atmosphere, and the temperature inside the vessel was raised to 380°C at a rate of 4°C / min while stirring. 24 hours after reaching 380°C, heating was stopped and the vessel was allowed to cool to room temperature. The yield of the heat-treated product was 465 g. 465 g of the heat-treated product was distilled under reduced pressure (distillation pressure: 667 PaA) so that the distillation end point was 335°C (equivalent to atmospheric pressure), yielding 214 g of pitch (43% yield based on the raw ethylene bottom oil). This pitch was used to carry out the various tests described above.

[0076] Comparative Example 4 Pitch was prepared according to the method described in Comparative Example 3, except that the vacuum distillation conditions were such that the distillation end point was 345°C converted to atmospheric pressure. The yield of pitch was 191 g (38% yield based on the raw ethylene bottom oil). This pitch was used to carry out the various tests described above.

[0077] (Reference example 1) Data for commercially available coal tar-based impregnated pitches are shown.

[0078] As shown in Table 1, the petroleum pitches of the examples have both good impregnation properties and a high fixed carbon content, and are clearly suitable as impregnation pitches for producing carbon materials.

[0079]

Table 1

Claims

1. A method for producing petroleum pitch comprising at least the following steps 1 to 4. Step 1: Heat treating petroleum heavy oil Step 2: A step of distilling the heat-treated product obtained in Step 1 to obtain pitch 1 as a high-boiling point component. Step 3: Removing toluene insolubles (TI) from the pitch 1 obtained in step 2; Step of obtaining a component with reduced TI Step 4: Distilling the component with reduced toluene insolubles (TI) obtained in Step 3; A step of obtaining pitch 2 as a high boiling point component

2. 2. The method for producing petroleum pitch according to claim 1, wherein the petroleum heavy oil is ethylene bottom oil.

3. The method for producing petroleum pitch according to claim 1 or 2, wherein the heat treatment temperature in step 1 is 360 ° C to 500 ° C.

4. 3. The method for producing petroleum pitch according to claim 1 or 2, wherein the removal of the toluene-insoluble matter (TI) in step 3 is carried out by adding a solvent to the pitch 1 and extracting the solvent-soluble matter of the pitch 1 into the solvent, and the solvent is at least one selected from the group consisting of benzene, alkylbenzene, cracked gasoline, and cracked kerosene.

5. In step 1, the heat treatment time is 8 hours to 48 hours when the heat treatment temperature is 360 ° C to 390 ° C, 0.5 hours to 24 hours when the heat treatment temperature is greater than 390 ° C to 430 ° C, and 0.1 hours to 16 hours when the heat treatment temperature is greater than 430 ° C to 500 ° C. The method for producing petroleum-based pitch according to claim 1 or 2.

6. A method for producing a graphite electrode, in which the petroleum pitch obtained by the method according to claim 1 or 2 is used as an impregnation pitch.

7. A petroleum 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, and a viscosity at 200°C of 200 mPa s or less, and a fixed carbon content Y (% by mass) that satisfies formula (1). 80.0≧Y>0.2X+29.5 (1) Y: fixed carbon amount (mass%) X: Softening point (℃) (60≦X≦120)

8. 8. The petroleum pitch according to claim 7, having a fixed carbon content of 47.0% by mass or more.

9. The petroleum pitch according to claim 7 or 8, which is an impregnation pitch for producing carbon materials.

10. The petroleum-based pitch according to claim 9, wherein the carbon material is a graphite electrode.

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