Needle coke for graphite electrodes, its manufacturing method and inhibitor

Abstract

The purpose of the present invention is to provide: needle coke for graphite electrodes for which a huge cost is not required at the time of manufacturing, in which puffing of the needle coke is suppressed, and which improves manufacturing yield and properties of graphite electrodes; a manufacturing method thereof; and an inhibitor. This inhibitor for graphite electrode production is volatile at a temperature of 2100-6000°C and comprises: a metal comprising at least one element (Mβ) selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form of periodic table, and / or one oxide including the element (Mβ); or a metal comprising the element (Mβ) and / or a compound including the element (Mβ).

Description

[Technical Field]

[0001] The present invention relates to needle coke for graphite electrodes, a method for producing the same, and an inhibitor. This application claims priority based on Japanese Patent Application Nos. 2021-066201, 2021-066203, and 2021-066639, filed on April 9, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Coal tar, a by-product of coal carbonization, is largely composed of condensed polycyclic aromatic compounds (PPAs). It has long been used as a raw material for various carbon products. Approximately 30% of coal tar-based products are derived from distillate oils, such as creosote oil and naphthalene, while the remaining 70% is derived from coal tar pitch, a heavy non-distillate component. Needle coke, produced from coal tar pitch, is a particularly important high-value-added product and is primarily used as aggregate for graphite electrodes used in electric steelmaking. The graphite electrode manufacturing process begins by blending needle coke particles and binder pitch in a predetermined ratio, kneading them under heat, and then extruding the mixture to produce raw electrodes. These raw electrodes are then calcined, graphitized, and processed to produce graphite electrode products.

[0003] Because these graphite electrodes are used under severe high-temperature conditions, they require extremely high thermal shock resistance. To produce graphite electrodes with high thermal shock resistance, needle coke with a low thermal expansion coefficient is required. Needle coke made from coal tar pitch (hereinafter sometimes referred to as pitch-based needle coke) has the smallest thermal expansion coefficient of all cokes, making it the most preferable raw material for graphite electrodes. However, while pitch-based needle coke can produce high-quality graphite electrodes, it has the disadvantage of being prone to irreversible expansion, known as puffing, during the graphitization process used to produce electrodes. Rapid graphitization can result in cracks in the product, significantly reducing yield.

[0004] Therefore, in the production of graphite electrodes, the temperature must be raised for a long time for graphitization, resulting in extremely low productivity. This puffing phenomenon is thought to be caused by abnormal expansion due to the rapid desorption and volatilization of nitrogen and sulfur contained in pitch-based needle coke, mainly in the 1500 to 2100°C range and the 2500 to 2800°C range during the graphitization process.

[0005] To eliminate this puffing phenomenon, several techniques have been adopted in the graphite electrode manufacturing process. For example, one method involves adding small amounts of iron oxide, nickel, or titanium oxide as puffing inhibitors during the mixing process of pitch-based needle coke with binder pitch, which forms stable compounds of the sulfur content in the coke with the metal during graphitization, delaying the desorption timing until the decomposition temperature, thereby suppressing puffing. Another method involves adjusting the bulk density of the graphite electrode during the molding process to facilitate the volatilization of gases generated during graphitization. However, while the former method is effective in reducing sulfur-induced expansion to a certain extent, it is not effective in reducing nitrogen-induced expansion, and the latter method has the problem of reducing the mechanical strength of the graphite electrode due to a decrease in bulk density.

[0006] In addition to the above, various methods have been proposed for suppressing puffing during the production of graphite electrodes using needle coke. For example, Patent Documents 1 and 2 propose a method for reducing puffing by heat-treating pitch coke at 1500°C or higher to denitrify it. Patent Document 3 also discloses a method for pretreating raw coke, such as by oxidation, and then heat-treating it at a normal calcination temperature. These methods have the problem that the former consumes a lot of energy due to high-temperature heating, and the latter is more complicated than conventional methods. Furthermore, it has been proposed that a metal compound used as a puffing inhibitor is added in solution form only to the surface of lumpy and granular coke before it is mixed with binder pitch or the like, and then the mixture is heated, thereby increasing the puffing suppression effect despite reducing the amount of inhibitor added (Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 60-33208 [Patent Document 2] Japanese Patent Application Publication No. 60-208392 [Patent Document 3] Japanese Patent Application Laid-Open No. 63-135486 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-329271 Summary of the Invention [Problem to be solved by the invention]

[0008] However, all of these methods for producing low-puffing needle coke have problems such as being economically inefficient and not being put to practical use, or not necessarily achieving a sufficient effect of reducing puffing.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a needle coke for graphite electrodes, a method for producing the same, and an inhibitor that suppresses puffing of the needle coke and improves the production yield and properties of graphite electrodes without incurring significant costs during the production of the needle coke. [Means for solving the problem]

[0010] As a result of extensive research to solve the above-mentioned problems, the inventors have found that the puffing suppression effect can be increased by using an inhibitor for producing graphite electrodes that contains at least one of a metal consisting of the element (Mβ) described below and an oxide having the element (Mβ) described below, or by using an inhibitor for producing graphite electrodes that contains at least one of a metal consisting of the element (Mβ) described below or a compound having the element (Mβ) and that volatilizes at a temperature of 2100 to 6000°C, and have completed the present invention. In the case of an inhibitor for producing graphite electrodes that contains at least one of a metal consisting of the element (Mβ) and an oxide having the element (Mβ), the puffing suppression effect is further enhanced, so inhibitors for producing graphite electrodes that contain a composite oxide having the element (Mα) and the element (Mβ) described below, or inhibitors for producing graphite electrodes that contain an oxide having the element (Mα-1) described below and an oxide having the element (Mβ) are preferred.

[0011] That is, the present invention is summarized as follows [1] to

[24] . [1] An inhibitor for producing graphite electrodes, comprising at least one of a metal consisting of an element (Mβ) and an oxide having the element (Mβ). Element (Mβ): At least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long-form periodic table. [2] The inhibitor for producing a graphite electrode according to [1], wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe, and P. [3] The inhibitor for producing a graphite electrode according to [1] or [2], wherein the oxide having the element (Mβ) is a composite oxide having the following element (Mα) and the element (Mβ): Element (Mα): At least one metallic element (excluding element (Mβ)). [4] The inhibitor for producing a graphite electrode according to [3], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements. [5] The inhibitor for producing a graphite electrode according to [3] or [4], wherein the composition formula of the composite oxide is the following formula (1): Mα 3-x Mβ 1-y O 5-z ···(1) (Wherein, 0≦x<3, 0≦y<1, and 0≦z<5.) [6] The inhibitor for producing graphite electrodes according to [1] or [2], further comprising at least one of a metal consisting of the following element (Mα) and an oxide having the element (Mα): Element (Mα): At least one metallic element (excluding element (Mβ)). [7] The inhibitor for producing a graphite electrode according to [6], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements. [8] The inhibitor for producing a graphite electrode according to [6] or [7], wherein the composition formula of the oxide containing the element (Mα) is the following formula (2): Mα 3-x1 O 3-z1 ···(2) (In the formula, Mα is an element (Mα), 0≦x1<3, and 0≦z1<3.) [9] The inhibitor for producing a graphite electrode according to any one of [6] to [8], wherein the composition formula of the oxide containing the element (Mβ) is the following formula (3): Mβ 1-y1 O 2-z2 ···(3) (In the formula, Mβ is an element (Mβ), 0≦y1<1, and 0≦z2<2.)

[10] A metal comprising the following element (Mβ) and / or a compound having the element (Mβ), An inhibitor for graphite electrode production that volatilizes at temperatures between 2100 and 6000°C. Element (Mβ): At least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long-form periodic table.

[11] The inhibitor for producing graphite electrodes according to

[10] , wherein when the proportion (wt%) of the inhibitor added to the needle coke is X and the proportion (wt%) of the inhibitor after heat treatment at a temperature of 2800°C for 30 minutes is Y, the relationship Y / X<0.01.

[12] The inhibitor for producing graphite electrodes according to

[10] or

[11] , wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe, and P.

[13] The inhibitor for producing a graphite electrode according to any one of

[10] to

[12] , which reacts with a sulfur compound.

[14] The inhibitor for producing a graphite electrode according to any one of

[10] to

[13] , which reacts with a nitrogen compound.

[15] The inhibitor for producing a graphite electrode according to any one of

[10] to

[14] , wherein the oxide having the element (Mβ) further has the following element (Mα-1): Element (Mα-1): One or more metal elements including at least alkaline earth metal elements (but excluding element (Mβ)).

[16] The inhibitor for producing graphite electrodes according to any one of

[10] to

[15] , further comprising at least one of a metal consisting of the following element (Mα-1) or a compound having the element (Mα-1): Element (Mα-1): One or more metal elements including at least alkaline earth metal elements (but excluding element (Mβ)).

[17] The inhibitor for producing a graphite electrode according to any one of

[10] to

[16] , wherein the element (Mα-1) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements.

[18] The puffing value P of the test piece prepared in the following evaluation test (i) is calculated by the following formula (I): 2100 The inhibitor for producing a graphite electrode according to any one of [1] to

[17] , wherein the amount of ZnO in the inhibitor is 1.00% or less. P 2100 =(L2-L1) / L1×100 (I) In the formula (I), L1 and L2 have the following meanings. L1: Thickness of test piece before firing (mm) L2: Thickness of the test piece after firing to 2100°C (mm) <Evaluation Test (i)> Coal-based needle coke, 30% by weight of binder pitch relative to the coke, and an inhibitor were mixed and kneaded for 5 minutes while heating at 165°C. This was then molded into a 20mm diameter x 3-15mm disk and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch, creating a test piece. The test piece was then heated to 2100°C at a rate of 20°C / min and calcined, and the L1 and L2 of the test piece were measured before and after calcination.

[19] A composition containing the inhibitor for producing graphite electrodes according to any one of [1] to

[18] and needle coke.

[20]

[19] A needle coke for graphite electrodes comprising the composition according to

[19] .

[21] A graphite electrode obtained by firing the needle coke for graphite electrodes according to

[20] .

[22] A method for producing needle coke for graphite electrodes, comprising a composition in which an inhibitor is directly attached to the surface of the needle coke, A method for producing needle coke for graphite electrodes, comprising adding the inhibitor for graphite electrode production according to any one of [1] to

[18] in a solution or molten state to needle coke before kneading with binder pitch, thereby allowing the inhibitor for graphite electrode production to adhere directly to the surface of the needle coke.

[23] A method for producing a graphite electrode, comprising calcining the needle coke for graphite electrodes according to

[20] .

[24] The method for producing a graphite electrode according to

[23] , wherein the firing temperature is 300 to 1500°C. [Effects of the Invention]

[0012] According to the present invention, by producing a graphite electrode using a specific inhibitor, it is possible to provide a graphite electrode that maintains low thermal expansion and exhibits low puffing. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the results of plotting the cold puffing value versus the amount of Ca3SiO5 added for Examples A3, A12 to A14, and Comparative Example A1. [Figure 2] FIG. 1 shows the results of TPD-MS measurements of nitrogen in Examples A3, A12 to A14, and Comparative Example A1, where the temperature was raised to 1700° C. [Figure 3] FIG. 1 shows the results of powder X-ray diffraction normalized by the peak top from 2θ=24° to 27° after TPD-MS measurement in Examples A3, A12 to A14, and Comparative Example A1. [Figure 4] FIG. 10 is a graph showing the results of measuring puffing values ​​at 1000° C. to 2650° C. in Example A21 and Comparative Example A8. [Figure 5] FIG. 1 is a graph showing the cold puffing values ​​of Examples B1 and B2 and Comparative Examples B1 and B2 when fired up to 2100° C. and when fired up to 2800° C. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below, but the present invention is not limited to the following description and can be practiced with any modifications within the scope of the gist of the present invention. In the following description, "% by weight" is synonymous with "% by mass," and "parts by weight" is synonymous with "parts by mass." In the present invention, "pitch-based" and "coal-based" are treated as synonymous terms. The "sulfur content of coke" in the present invention means a value measured in accordance with JIS M8813. The "nitrogen content of coke" in the present invention means a value measured in accordance with JIS M8819.

[0015] 1. Inhibitor for graphite electrode production The inhibitor for producing graphite electrodes of the present invention (hereinafter sometimes simply referred to as "inhibitor") is used for obtaining graphite electrodes by firing it together with needle coke.

[0016] The inhibitor according to one embodiment of the present invention comprises at least one of a metal consisting of the element (Mβ) and an oxide having the element (Mβ). Element (Mβ): At least one element selected from the group consisting of Group 4 elements (Ti, Zr, Hf), Group 8 elements (Fe, Ru, Os), Group 9 elements (Co, Rh, Ir), Group 10 elements (Ni, Pr, Pt), Group 13 elements (B, Al, Ga, In), Group 14 elements (Si, Ge, Sn), and Group 15 elements (P, Sb, Bi) of the long-form periodic table.

[0017] 1.1. First embodiment The inhibitor of the first embodiment includes a complex oxide having an element (Mα) and an element (Mβ). Element (Mα): At least one metal element (excluding element (Mβ)). Element (Mβ): At least one element selected from the group consisting of Group 4 elements (Ti, Zr, Hf), Group 8 elements (Fe, Ru, Os), Group 9 elements (Co, Rh, Ir), Group 10 elements (Ni, Pr, Pt), Group 13 elements (B, Al, Ga, In), Group 14 elements (Si, Ge, Sn), and Group 15 elements (P, Sb, Bi) of the long-form periodic table.

[0018] As the element (Mα), at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements (Mg, Ca, Sr, Ba) and rare earth metal elements (Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is preferred, as it is more likely to reduce puffing, at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements is more preferred, at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements is particularly preferred, and an alkaline earth metal is most preferred.

[0019] The element (Mβ) is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P, as this element is likely to reduce puffing, more preferably at least one element of Si and Ge, and most preferably Si.

[0020] The composition formula of the inhibitor of the first embodiment is not particularly limited, but is preferably the following formula (1) because it is easy to reduce puffing. Mα 3-x Mβ 1-y O 5-z ···(1) (Wherein, 0≦x<3, 0≦y<1, and 0≦z<5.)

[0021] In the formula, x is preferably 0≦x<3, more preferably 0.05≦x≦2.5, and particularly preferably 0.1≦x≦2, since this tends to reduce puffing. In the formula, y is preferably 0≦y<1, more preferably 0.01≦y≦0.8, and particularly preferably 0.1≦y≦0.5, since this facilitates reduction of puffing. In the formula, z is preferably 0≦z<5, more preferably 0.05≦z≦4, and particularly preferably 0.1≦z≦3, since this tends to reduce puffing.

[0022] Specific examples of composite oxides having elements (Mα) and (Mβ) include MgSiO, MgSiO, Mg 14 SiO 24 , MgO, Ca3SiO5, Ca2SiO4, CaSiO3, Ca8Si5O 18 , CaSi2O5, CaO, CaCO3, Ca(OH)2, SrSiO3, Sr3SiO5, SrSi2O5, Sr2SiO4, Ba3SiO5, Ba2SiO4, BaSiO3, BaSi2O5, Ba2Si3O8, Ba5Si8O 21 , Ba3Si5O 13 , Ba2SiO4, BaO, BaCO3, Ce2SiO5, Ce2Si2O7, Ce2Si4O 11 , CeSi3O8, Ce3SiO8, Ce6Si6O 21 , La5Si3O 13.5 , La6Si6O 21 , La2SiO5, La2Si4O 11 , La2Si6O 16 , Pr 4.67 SiO 13 , Pr2Si2O7, Pr6Si2, Pr6Si12 O 25 Eu5Si3O 13 Eu2Si2O7, Eu2SiO4, Eu6Si 12 O 33 、CaGe2O5、Ca3GeO5、Ca2GeO4、Ca5Ge3O 11 CaGeO3, Ca2Ge7O 16 CaAl 12 O 19 CaAl4O7, Ca4Al6O 13 Ca5Al6O 14 Ca6Al7O 16 Ca2Al2O5, Ca3Al2O6, CaFeO2, Ca2Fe2O5, CaFeO3, CaFe2O4, CaFe3O5, CaFe4O6, CaFe5O7, CaFe6O8, CaTi2O4, CaTi2O5, Ca3Ti2O7, Ca4Ti3O 10 CaTiO3, CaTi5O 11 、Mg2Al4O8、MgAl2O4、Mg2Al2O5、MgGe2O4、Mg2TiO4、MgTiO3、MgTi2O4、MgTi2O5、MgFe2O4、SrAl 12 O 19 SrAl4O7 Sr4Al 14 O 25 Sr 12 Al 14 O 33 Sr3Al2O6 Sr 10 Al6O 19 、Sr3GeO、SrGe4O9、SrGeO3、Sr3GeO5、SrTi 11 O 20 Sr2Ti6O 13 SrTiO3, Sr4Ti3O 10 Sr3Ti2O7, Sr2TiO4, SrFe 12 O9, SrFe2O4, Sr2Fe3O6, SrFeO2, Sr4Fe6O 13 Sr2Fe2O5, Sr3Fe2O5, Sr4Fe4O 11 、SrFeO3、Sr3Fe2O6、Sr2FeO3、Sr3Fe2O7、SrFeO4、Sr2FeO4、BaAl 12 O 19,BaAl4O7, BaAl2O4, Ba3Al2O6, Ba4Al2O7, Ba7A l2 O 10 , Ba 17 Al3O7, Ba 21 Ge2O5, Ba3GeO, Ba3GeO5, Ba 10 Ge7O3, BaGeO3, BaGe2O5, Ba2Ge5O 12 , BaGe4O9, Ba3TiO5, Ba2TiO4, Ba4Ti5O 10 , Ba4Ti4O 11 , BaTiO3, BaTi2O5, BaTi4O9, Ba2Ti9O 20 , BaTi5O 11 , Ba2Ti 13 O 22 , Ba3FeO5, Ba2FeO4, BaFeO2, Ba2Fe2O5, Ba8Fe8O 21 , Ba5Fe5O 14 , BaFeO3, BaFe2O4, Ba2Fe6O 11 , BaFe4O7, BaFe7O 11 , BaFe 12 O 19 , BaFe 15 O 23 The inhibitor of the first embodiment may contain one type of composite oxide or two or more types of composite oxides.

[0023] Since the inhibitor of the first embodiment is easy to suppress needle coke puffing during the production of graphite electrodes, the puffing value P calculated by the following formula (I) of the test piece prepared in the following evaluation test (i) is 2100 is preferably 1.00% or less. P 2100 =(L2-L1) / L1×100 (I) In the formula (I), L1 and L2 have the following meanings. L1: Thickness of test piece before firing (mm) L2: Thickness of the test piece after firing to 2100°C (mm)

[0024] <Evaluation Test (i)> Coal-based needle coke, 30% by weight of binder pitch relative to the coal-based needle coke (i.e., 30 parts by weight of binder pitch per 100 parts by weight of coal-based needle coke), and an inhibitor are mixed and kneaded for 5 minutes while heating at 165°C. This is molded into a 20 mm diameter x 3 to 15 mm disk and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch, producing a test piece. The test piece is then heated to 2100°C at a rate of 20°C / min and calcined, and L1 and L2 of the test piece are measured before and after calcination.

[0025] Puffing value P 2100 is preferably 1.00% or less, more preferably 0.00% or less, even more preferably -1.00% or less, particularly preferably -2.00% or less, and most preferably -3.00% or less. 2100 The lower limit of the puffing value P is not particularly limited, but is preferably −30% or more, more preferably −20% or more, particularly preferably −15% or more, and most preferably −10% or more. 2100 The lower and upper limits can be arbitrarily combined, and are preferably, for example, −30% or more and 1.00% or less.

[0026] Since the inhibitor of the first embodiment is easy to suppress needle coke puffing during the production of graphite electrodes, the puffing value P calculated by the following formula (II) of the test piece prepared in the following evaluation test (ii) is 2800 is preferably 2.9% or less. P 2800 =(L3-L1) / L1×100 (II) In the formula (II), L1 and L3 have the following meanings. L1: Thickness of test piece before firing (mm) L3: Thickness of the test piece after firing to 2800°C (mm)

[0027] <Evaluation Test (ii)> Coal-based needle coke, binder pitch (30% by weight of the total weight of the coke) and an inhibitor were mixed and kneaded for 5 minutes while heating at 165°C. This was then molded into a 20mm diameter x 3-15mm disc and calcined in a firing furnace at 1300°C for 3 hours to burn off the binder pitch, creating a test piece. The test piece was then heated to 2800°C at a rate of 20°C / min and calcined, and the L1 and L3 of the test piece were measured before and after calcination.

[0028] Puffing value P 2800 is preferably 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. 2800 The lower limit of the puffing value P is not particularly limited, but is preferably −5.0% or more, more preferably −3.0% or more, particularly preferably −1.0% or more, and most preferably 0% or more. 2800 The lower and upper limits can be arbitrarily combined, and for example, it is preferable that the range is from −5.0% to 2.9%.

[0029] The method for producing the inhibitor of the first embodiment is not particularly limited, and an example thereof is a method in which raw material compounds are weighed and mixed to achieve the composition ratio of the target composite oxide, and then calcined in an air atmosphere or a reducing atmosphere at a temperature range of 1000°C to 1500°C. The upper limit of the particle size of the resulting inhibitor is not particularly limited, but is more preferably 10,000 μm or less, particularly preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm or more, and most preferably 100 nm or more. Controlling the particle size within this range facilitates uniform dispersion, maintains the crystallinity of the resulting inhibitor, and is expected to enhance the puffing effect. In this specification, the "particle size of the inhibitor" means the mode diameter measured by a method using a laser diffraction particle size distribution analyzer MT3300EX (manufactured by Microtrack Bell) and ethanol as the dispersion medium.

[0030] The use of the inhibitor of the first embodiment, which contains a composite oxide having elements (Mα) and (Mβ), enhances the puffing suppression effect, improving the production yield and characteristics of the graphite electrode. The reason why the inhibitor of the first embodiment exhibits such an effect is not yet clear, but is presumed to be as follows. It is presumed that adding the inhibitor of the first embodiment during the calcination of needle coke for graphite electrodes forms a nitrogen-containing complex compound or a sulfur-containing complex compound at a temperature lower than the temperature at which nitrogen desorbs from the graphite electrode, and that the timing of nitrogen desorption or sulfur desorption is shifted compared to a system without the inhibitor added, thereby suppressing the puffing phenomenon. That is, since the inhibitor of the first embodiment contains a complex oxide having elements (Mα) and (Mβ), it reacts with nitrogen or sulfur in the coke during the temperature rise process during calcination to form complex compounds (nitrides, oxynitrides, sulfides, oxysulfides), and therefore the effect of the first embodiment is achieved.

[0031] 1.2. Second embodiment The inhibitor of the second embodiment includes a metal consisting of the element (Mα) or an oxide having the element (Mα), and a metal consisting of the element (Mβ) or an oxide having the element (Mβ). The inhibitor of the second embodiment preferably includes an oxide having the element (Mα) and an oxide having the element (Mβ), since this is likely to reduce puffing. Element (Mα): At least one metal element (excluding element (Mβ)). Element (Mβ): At least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long-form periodic table.

[0032] (Metal consisting of element (Mα) or oxide containing element (Mα)) The element (Mα) is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements, as this easily reduces puffing, more preferably at least one metal element selected from the group consisting of Sc, alkaline earth metals, and rare earth metal elements, particularly preferably at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements, and most preferably an alkaline earth metal.

[0033] The composition formula of the oxide containing the element (Mα) is not particularly limited, but is preferably the following formula (2) because it is easy to reduce puffing. Mα 3-x1 O 3-z1 ···(2) (In the formula, Mα is an element (Mα), 0≦x1<3, and 0≦z1<3.)

[0034] In the formula, x1 is preferably 0≦x1<3, more preferably 0.05≦x1≦2.5, and particularly preferably 0.1≦x1≦2, since this tends to reduce puffing. In the formula, z1 is preferably 0≦z1<3, more preferably 0.05≦z1≦2.5, and particularly preferably 0.1≦z1≦2, since this facilitates reduction of puffing.

[0035] Specific examples of metals consisting of element (Mα) or oxides containing element (Mα) include CaO, Ca(OH)2, CaCO3, Ca, MgO, MgCO3, Mg(OH)2, Mg, SrO, SrCO3, Sr(OH)2, Sr, BaO, BaCO3, Ba(OH)2, Ba, CeO2, Ce, and Pr6O 11 , Pr, Eu2O3, and Eu. The oxide having the element (Mα) contained in the inhibitor of the second embodiment may be one type or two or more types.

[0036] (Metal consisting of element (Mβ) or oxide containing element (Mβ)) As the element (Mβ), since it is easy to reduce puffing, it is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe, and P, more preferably at least one element of Si and Ge, and most preferably Si.

[0037] The composition formula of the oxide having the element (Mβ) is not particularly limited, but since it is easy to reduce puffing, the following formula (3) is preferable. Mβ 1-y1 O 2-z2 ···(3) (In the formula, Mβ is the element (Mβ), 0 ≦ y1 < 1, and 0 ≦ z2 < 2.)

[0038] In the formula, since it is easy to reduce puffing, 0 ≦ y1 < 1 is preferable, 0.01 ≦ y1 ≦ 0.8 is more preferable, and 0.1 ≦ y1 ≦ 0.5 is particularly preferable. In the formula, since it is easy to reduce puffing, 0 < z2 ≦ 2 is preferable, 0.05 ≦ z2 ≦ 0.15 is more preferable, and 0.1 ≦ z2 ≦ 0.2 is particularly preferable.

[0039] Specific examples of the metal composed of the element (Mβ) or the oxide having the element (Mβ) include, for example, SiO2, Si, SiO x , GeO2, Ge, Al2O3, Al, B2O3, P2O5. The oxide having the element (Mβ) contained in the inhibitor of the second embodiment may be one kind or two or more kinds.

[0040] Since the inhibitor of the second embodiment is likely to suppress the puffing of needle coke during the production of the graphite electrode, the puffing value P calculated by the above formula (I) of the test piece prepared in the evaluation test (i) 2100 is preferably 1.00% or less.

[0041] Puffing value P 2100is preferably 1.00% or less, more preferably 0.50% or less, even more preferably 0.00% or less, particularly preferably -1.00% or less, and most preferably -2.00% or less. 2100 The lower limit of the puffing value P is not particularly limited, but is preferably −30% or more, more preferably −20% or more, particularly preferably −15% or more, and most preferably −10% or more. 2100 The lower and upper limits can be arbitrarily combined, and are preferably, for example, −30% or more and 1.00% or less.

[0042] Since the inhibitor of the second embodiment is easy to suppress needle coke puffing during the production of graphite electrodes, the puffing value P calculated by the formula (II) of the test piece prepared in the evaluation test (ii) is 2800 is preferably 2.9% or less.

[0043] Puffing value P 2800 is preferably 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. 2800 The lower limit of the puffing value P is not particularly limited, but is preferably −5.0% or more, more preferably −3.0% or more, particularly preferably −1.0% or more, and most preferably 0% or more. 2800 The lower and upper limits can be arbitrarily combined, and for example, it is preferable that the range is from −5.0% to 2.9%.

[0044] The method for producing the inhibitor of the second embodiment is not particularly limited. For example, the inhibitor may be produced by weighing and mixing the elements (Mα) and (Mβ) in a desired ratio, followed by firing at a temperature range of 1000°C to 1500°C in air or a reducing atmosphere to obtain an inhibitor in which an oxide containing the element (Mα) and an oxide containing the element (Mβ) are composited. Alternatively, the inhibitor may be prepared by mixing an oxide containing the element (Mα) with an oxide containing the element (Mβ). The particle size of the composite inhibitor is not particularly limited, but is preferably 10,000 μm or less, more preferably 1,000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, more preferably 10 nm, and most preferably 100 nm or more. Controlling the particle size within this range facilitates uniform dispersion and is expected to enhance the puffing effect.

[0045] The mixing ratio of the oxide having the element (Mα) and the oxide having the element (Mβ) (the oxide having the element (Mα) and the oxide having the element (Mβ)) is not particularly limited, but in order to achieve low puffing, the lower limit of the weight ratio of the oxide having the element (Mβ) to the oxide having the element (Mα) is usually 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more, while the upper limit is usually 1 or less, preferably 0.7 or less, and more preferably 0.5 or less.

[0046] By using the inhibitor of the second embodiment, which contains a metal consisting of the element (Mβ) or an oxide having the element (Mα), and a metal consisting of the element (Mβ) or an oxide having the element (Mβ), the puffing suppression effect is enhanced, and the production yield and characteristics of the graphite electrode are improved. The reason why the inhibitor of the second embodiment exhibits such an effect is not yet clear, but is presumed to be as follows. It is presumed that adding the inhibitor of the second embodiment during the calcination of needle coke for graphite electrodes forms a nitrogen-containing complex compound or a sulfur-containing complex compound at a temperature lower than the temperature at which nitrogen desorbs from the graphite electrode, and that the timing of nitrogen desorption or sulfur desorption is shifted compared to a system without the inhibitor added, thereby suppressing the puffing phenomenon. That is, since the inhibitor of the second embodiment contains an oxide having the element (Mα) and an oxide having the element (Mβ), it reacts with nitrogen or sulfur in the coke during the temperature rise process during calcination to form a complex compound (nitride, oxynitride, sulfide, oxysulfide), thereby achieving the effect of the second embodiment.

[0047] 1.3. Third Embodiment Another embodiment of the inhibitor of the present invention will now be described. The inhibitor of the third embodiment of the present invention contains at least one of a metal consisting of the element (Mβ) or a compound having the element (Mβ), and is volatilized at a temperature of 2100 to 6000°C. Element (Mβ): At least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long-form periodic table.

[0048] The temperature at which the inhibitor volatilizes is preferably 2100°C or higher, more preferably 2400°C or higher, even more preferably 2600°C or higher, particularly preferably 2700°C or higher, and most preferably 2800°C or higher, because this tends to reduce puffing. The upper limit of the temperature at which the inhibitor volatilizes is preferably 6000°C or lower, more preferably 5000°C or lower, even more preferably 4000°C or lower, particularly preferably 3500°C or lower, and most preferably 3000°C or lower, because this tends to reduce puffing. The lower and upper limits of the temperature at which the inhibitor volatilizes can be combined in any combination.

[0049] The inhibitor of the third embodiment is added to needle coke, and the ratio (wt%) of the inhibitor to the total amount of needle coke is X, and the ratio (wt%) of the inhibitor to the total amount of needle coke after heat treatment at a temperature of 2800°C for 30 minutes is Y. In this case, it is preferable that Y / X<0.01, as this facilitates the reduction of puffing. The value of Y / X is more preferably 0.004 or less, particularly preferably 0.0005 or less. The lower limit of the value of Y / X is preferably 0.000001 or more, more preferably 0.00001 or more, since puffing can be easily reduced.

[0050] The element (Mβ) is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P, as this element is likely to reduce puffing, more preferably at least one element of Si and Ge, and most preferably Si.

[0051] The compound having the element (Mβ) is preferably an oxide having the element (Mβ) because it is easy to reduce puffing. The composition formula of the oxide having the element (Mβ) is not particularly limited, but it is preferably the following formula (4) because it is easy to reduce puffing. Mβ 1-y2 O 2-z3 ···(4) (In the formula, Mβ is the element (Mβ), 0≦y2<1, and 0≦z3<2.)

[0052] In the formula, y2 is preferably 0≦y2<1, and more preferably 0.001≦y2≦0.1, since this facilitates reduction of puffing. In the formula, z3 is preferably 0≦z3<2, more preferably 0.001≦z3≦0.1, since this makes it easier to reduce puffing.

[0053] Specific examples of oxides containing the element (Mβ) include SiO2, Si, SiO xExamples include GeO2, Ge, Al2O3, Al, B2O3, and P2O5. The compound having the element (Mβ) contained in the inhibitor of the third embodiment may be one type, or two or more types.

[0054] The compound having the element (Mβ) may further have the following element (Mα-1). Element (Mα-1): One or more metal elements including at least alkaline earth metal elements (but excluding element (Mβ)).

[0055] The element (Mα-1) is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements, as this element is likely to reduce puffing, more preferably at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements, and most preferably an alkaline earth metal.

[0056] As the compound having the element (Mα-1) and the element (Mβ), a composite oxide having the element (Mα-1) and the element (Mβ) is preferred because it is easy to reduce puffing. The composition formula of the composite oxide having the element (Mα-1) and the element (Mβ) is not particularly limited, but it is preferably the following formula (5) because it is easy to reduce puffing. Mα 3-x2 Mβ 1-y3 O 5-z4 ···(5) (In the formula, Mα is an element (Mα-1), Mβ is an element (Mβ), 0≦x2<3, 0≦y3<1, and 0≦z4<5.)

[0057] In the formula, x2 is preferably 0≦x2<3, more preferably 0.05≦x2≦2.5, and particularly preferably 0.1≦x2≦2, since this easily reduces puffing. In the formula, y3 is preferably 0≦y3<1, more preferably 0.01≦y3≦0.8, and particularly preferably 0.1≦y3≦0.5, since puffing is easily reduced. In the formula, z4 is preferably 0≦z4<5, more preferably 0.05≦z4≦4, and particularly preferably 0.1≦z4≦3, since this facilitates reduction of puffing.

[0058] Specific examples of composite oxides having an element (Mα-1) and an element (Mβ) include MgSiO, MgSiO, Mg 14 SiO 24 , MgO, Ca3SiO5, Ca2SiO4, CaSiO3, Ca8Si5O 18 , CaSi2O5, CaO, CaCO3, Ca(OH)2, SrSiO3, Sr3SiO5, SrSi2O5, Sr2SiO4, Ba3SiO5, Ba2SiO4, BaSiO3, BaSi2O5, Ba2Si3O8, Ba5Si8O 21 , Ba3Si5O 13 , Ba2SiO4, BaO, BaCO3, Ce2SiO5, Ce2Si2O7, Ce2Si4O 11 , CeSi3O8, Ce3SiO8, Ce6Si6O 21 , La5Si3O 13.5 , La6Si6O 21 , La2SiO5, La2Si4O 11 , La2Si6O 16 , Pr 4.67 SiO 13 , Pr2Si2O7, Pr6Si2, Pr6Si 12 O 25 , Eu5Si3O 13 , Eu2Si2O7, Eu2SiO4, Eu6Si 12 O 33 , CaGe2O5, Ca3GeO5, Ca2GeO4, Ca5Ge3O 11 , CaGeO3, Ca2Ge7O 16 , CaAl 12 O 19 , CaAl4O7, Ca4Al6O 13 , Ca5Al6O 14 , Ca6Al7O 16Ca2Al2O5, Ca3Al2O6, CaFeO2, Ca2Fe2O5, CaFeO3, CaFe2O4, CaFe3O5, CaFe4O6, CaFe5O7, CaFe6O8, CaTi2O4, CaTi2O5, Ca3Ti2O7, Ca4Ti3O 10 CaTiO3, CaTi5O 11 、Mg2Al4O8、MgAl2O4、Mg2Al2O5、MgGe2O4、Mg2TiO4、MgTiO3、MgTi2O4、MgTi2O5、MgFe2O4、SrAl 12 O 19 SrAl4O7 Sr4Al 14 O 25 Sr 12 Al 14 O 33 Sr3Al2O6 Sr 10 Al6O 19 、Sr3GeO、SrGe4O9、SrGeO3、Sr3GeO5、SrTi 11 O 20 Sr2Ti6O 13 SrTiO3, Sr4Ti3O 10 Sr3Ti2O7, Sr2TiO4, SrFe 12 O9, SrFe2O4, Sr2Fe3O6, SrFeO2, Sr4Fe6O 13 Sr2Fe2O5, Sr3Fe2O5, Sr4Fe4O 11 、SrFeO3、Sr3Fe2O6、Sr2FeO3、Sr3Fe2O7、SrFeO4、Sr2FeO4、BaAl 12 O 19 ,BaAl4O7、BaAl2O4、Ba3Al2O6、Ba4Al2O7、Ba7A l2 O 10 Ba 17 Al3O7、Ba 21 Ge2O5, Ba3GeO, Ba3GeO5, Ba 10 Ge7O3, BaGeO3, BaGe2O5, Ba2Ge5O 12 BaGe4O9, Ba3TiO5, Ba2TiO4, Ba4Ti5O 10 Ba4Ti4O 11 BaTiO3, BaTi2O5, BaTi4O9, Ba2Ti9O 20 BaTi5O11 , Ba2Ti 13 O 22 , Ba3FeO5, Ba2FeO4, BaFeO2, Ba2Fe2O5, Ba8Fe8O 21 , Ba5Fe5O 14 , BaFeO3, BaFe2O4, Ba2Fe6O 11 , BaFe4O7, BaFe7O 11 , BaFe 12 O 19 , BaFe 15 O 23 The inhibitor of the third embodiment may contain one type of compound or two or more types of compounds.

[0059] The inhibitor of the third embodiment may further contain at least one metal consisting of element (Mβ) or compound having element (Mβ), and at least one metal consisting of element (Mα-1) or compound having element (Mα-1). In this case, the preferred element (Mα-1) is the same as the preferred element (Mα-1) in the compound having element (Mα-1) and element (Mβ).

[0060] The compound having the element (Mα) is preferably an oxide having the element (Mα-1) because it is easy to reduce puffing. The composition formula of the oxide having the element (Mα-1) is not particularly limited, but it is preferably the following formula (6) because it is easy to reduce puffing. Mα 3-x3 O 3-z5 ···(6) (In the formula, Mα is an element (Mα-1), 0≦x3<3, and 0≦z5<3.)

[0061] In the formula, x3 is preferably 0≦x3<3, more preferably 0.05≦x3≦2.5, and particularly preferably 0.1≦x3≦2, since this easily reduces puffing. In the formula, z5 is preferably 0≦z5<3, more preferably 0.05≦z5≦2.5, and particularly preferably 0.1≦z5≦2, since this makes it easier to reduce puffing.

[0062] Specific examples of oxides containing the element (Mα-1) include CaO, Ca(OH)2, CaCO3, Ca, MgO, MgCO3, Mg(OH)2, Mg, SrO, SrCO3, Sr(OH)2, Sr, BaO, BaCO3, Ba(OH)2, Ba, CeO2, Ce, and Pr6O 11 , Pr, Eu2O3, and Eu. The compound having the element (Mα-1) contained in the inhibitor of the third embodiment may be one type, or two or more types.

[0063] In the third embodiment, the inhibitor preferably reacts with sulfur compounds because this tends to reduce puffing, but the phrase "the inhibitor reacts with sulfur compounds" means that under conditions where the inhibitor is added to the needle coke, a different compound is formed by the reaction between the inhibitor and the sulfur compounds. In the third embodiment, the inhibitor is preferably reactive with a nitrogen compound to reduce puffing, but "the inhibitor reacts with a sulfur compound" means that under the conditions in which the inhibitor is added to the needle coke, a different compound is formed by the reaction between the inhibitor and the nitrogen compound.

[0064] Since the inhibitor of the third embodiment is easy to suppress needle coke puffing during the production of graphite electrodes, the puffing value P calculated by the formula (I) of the test piece prepared in the evaluation test (i) is 2100 is preferably 1.00% or less.

[0065] Puffing value P 2100 is preferably 1.00% or less, more preferably 0.50% or less, even more preferably 0.00% or less, particularly preferably -1.00% or less, and most preferably -2.00% or less. 2100The lower limit of the puffing value P is not particularly limited, but is preferably −30% or more, more preferably −20% or more, particularly preferably −15% or more, and most preferably −10% or more. 2100 The lower and upper limits can be arbitrarily combined, and are preferably, for example, between −30% and 1.00.

[0066] Since the inhibitor of the third embodiment is easy to suppress needle coke puffing during the production of graphite electrodes, the puffing value P calculated by the formula (II) of the test piece prepared in the evaluation test (ii) is 2800 is preferably 2.9% or less. P 2800 =(L3-L1) / L1×100 (II) In the formula (II), L1 and L3 have the following meanings. L1: Thickness of test piece before firing (mm) L3: Thickness of the test piece after firing to 2800°C (mm)

[0067] Puffing value P 2800 is preferably 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. 2800 The lower limit of the puffing value P is not particularly limited, but is preferably −5.0% or more, more preferably −3.0% or more, particularly preferably −1.0% or more, and most preferably 0% or more. 2800 The lower and upper limits can be arbitrarily combined, and for example, it is preferable that the range is from −5.0% to 2.9%.

[0068] The method for producing the inhibitor of the third embodiment is not particularly limited. For example, in the case of an oxide, raw materials are weighed and mixed to achieve the desired oxide composition ratio, and the mixture is fired in an air atmosphere or a reducing atmosphere at a temperature ranging from 1000°C to 1500°C. The upper limit of the particle size of the resulting inhibitor is not particularly limited, but is preferably 10,000 μm or less, more preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, more preferably 10 nm or less, and most preferably 100 nm or more. Controlling the particle size within this range facilitates uniform dispersion, maintains the crystallinity of the resulting inhibitor, and is expected to enhance the puffing effect.

[0069] 2.Needle coke for graphite electrodes The needle coke for graphite electrodes of the present invention comprises a composition containing one or more inhibitors according to embodiments of the present invention and needle coke.

[0070] 2.1. Composition The composition of the present invention is not particularly limited as long as it contains one or more inhibitors according to the embodiments of the present invention and needle coke. A composition in which one or more inhibitors according to the embodiments of the present invention are directly attached to the surface of needle coke is preferred, as this allows for an increased puffing suppression effect while reducing the amount of inhibitor added.

[0071] The content of the inhibitor in the composition is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 3 parts by weight, in terms of the ash content (metal component or metal oxide) per 100 parts by weight of needle coke. When the content of the inhibitor is within the above range, a sufficient puffing reduction effect is easily obtained, and the remaining ash hardly affects the electrode product.

[0072] The method for producing the composition is not particularly limited, but a preferred method is to add the inhibitor of the present invention in a solution or molten state to needle coke before mixing with binder pitch, directly adhere the inhibitor to the surface of the needle coke, and then heat-treat the needle coke at 300 to 1500°C. As the needle coke, lump or granular calcined coke, i.e., coarse coke whose particle size has not been adjusted, can be used. When the inhibitor is added in solution, it may be added as an aqueous solution. If the inhibitor is insoluble in water, it may be added by dissolving it in a volatile solvent such as alcohol or benzene.

[0073] Since the composition obtained by the above-mentioned production method has not been subjected to particle size adjustment, it is preferable to mix the obtained composition with fine coke or the like to obtain needle coke for graphite electrodes, the particle size of which has been adjusted before kneading with the binder pitch. In this case, the amount of the fine coke mixed is preferably 50% by weight or less, more preferably 30% by weight or less, of the total amount of needle coke for graphite electrodes.

[0074] Alternatively, an inhibitor may be added to coarse coke that has not been particle-sized, and the coarse coke may be subjected to a pulverization process after heat treatment. Fine coke is generated by the pulverization process, and in this case, fine coke to which no inhibitor has been added may be further mixed, or not. Since the fine coke is not directly related to the puffing reduction effect, the amount of fine coke to be mixed may be determined appropriately, taking into consideration the electrode quality, such as the ash content, and economic efficiency.

[0075] 2.2.Needle coke The needle coke used in the present invention will be described in further detail below. The needle coke used in the present invention is not particularly limited, but pitch-based needle coke is preferred because it has a low sulfur and nitrogen content, a small thermal expansion coefficient, and is likely to sufficiently suppress puffing. Pitch-based needle coke can be suitably used as an aggregate for graphite electrodes for electric furnace steelmaking. Pitch-based needle coke can be produced by hydrogenating raw coal tar pitch to obtain hydrogenated coal tar pitch, and then coking the hydrogenated coal tar pitch.

[0076] Hydrogenated coal tar pitch is obtained by hydrogenating a raw coal tar pitch (hydrogenation step) and separating light oil from the resulting hydrogenated coal tar pitch (separation step). The light oil separated in the separation step can be recycled by supplying it to the hydrogenation step. The method for hydrogenating the raw coal tar pitch and the method for separating the light oil from the hydrogenated coal tar pitch are not particularly limited, and known methods can be applied.

[0077] The raw coal tar pitch is not particularly limited. The method for producing raw coal tar pitch (pre-conditioning method) is not particularly limited, and examples include a method in which quinoline insoluble matter is substantially removed from coal tar-based heavy oil. While known methods can be used to remove quinoline insoluble matter, treatment with an aromatic oil or aliphatic oil solvent, or treatment with a mixed solvent of aromatic oil and aliphatic oil, is preferred. Specifically, the solvent is mixed with coal tar-based heavy oil under appropriate conditions, heated, and then allowed to stand as needed. The mixture is then distilled to remove low-boiling components, thereby obtaining raw coal tar pitch that is almost free of quinoline insoluble matter. Examples of aliphatic oils that can be used include alicyclic compounds such as cyclohexane and cyclopentane, compounds with carbonyl groups such as acetone and ether, and diesel oils. Examples of aromatic oils that can be used include tar-based wash oils and anthracene oils.

[0078] In the production of hydrogenated coal tar pitch, petroleum heavy oil may be mixed with the raw coal tar pitch. When petroleum heavy oil is mixed, the coal tar heavy oil and the petroleum heavy oil may be mixed, and then the quinoline insoluble matter may be removed to obtain a mixture of raw coal tar pitch and petroleum heavy oil. Alternatively, the raw coal tar pitch and petroleum heavy oil may be mixed, and the light oil may be separated and used in the hydrogenation step. Furthermore, the light oil-separated coal tar pitch obtained by separating the light oil may be mixed with the petroleum heavy oil and used in the hydrogenation step.

[0079] The petroleum heavy oil is not particularly limited, and examples thereof include fluid catalytic cracking oil, atmospheric distillation residue, vacuum distillation residue, shale oil, tar sand bitumen, Orinoco tar, coal liquefaction oil, ethylene bottom oil, and heavy oils obtained by hydrorefining these. In addition to these, the petroleum heavy oil may further contain relatively light oils such as straight-run diesel, vacuum diesel, desulfurized diesel, and desulfurized vacuum diesel.

[0080] The method for converting the hydrogenated coal tar pitch into coke is not particularly limited, and examples thereof include delayed coking, visbreaking, flexicoking, and the Eureka process. Among these, the delayed coking method is preferred from the viewpoints of productivity and quality stability of needle coke.

[0081] In the delayed coking method, hydrogenated coal tar pitch is rapidly heated and passed through a heating tube, and then introduced into a coke drum where coking occurs. The coking conditions are not particularly limited, but the temperature is preferably 400 to 600°C, and the coking time is preferably 18 to 72 hours.

[0082] The coke thus obtained is preferably calcined in a rotary kiln, shaft furnace, etc. The calcination temperature is preferably 1000 to 1500° C., and the calcination time is preferably 1 to 6 hours. The raw material for coking may be other raw materials in addition to the hydrogenated coal tar pitch, and such raw materials include, but are not limited to, heavy petroleum oil.

[0083] 3.Graphite electrodes The graphite electrode of the present invention is a graphite electrode obtained by calcining the needle coke for graphite electrodes of the present invention. The graphite electrode of the present invention can be obtained, for example, by kneading a raw material obtained by adding an appropriate amount of binder pitch to the needle coke for graphite electrodes of the present invention, molding the mixture, and calcining the resulting green electrode to graphitize it. In producing the graphite electrode, processing may be performed after graphitization as necessary.

[0084] A specific example of a method for producing a graphite electrode of the present invention is a method in which binder pitch is kneaded (mixed) with the needle coke for graphite electrodes of the present invention, iron oxide is further added and kneaded as necessary, and then extrusion molding, primary firing, impregnation, secondary firing, graphitization, etc. The use of iron oxide may be omitted, but the use of iron oxide can provide a further puffing reduction effect, so the amount of iron oxide may be appropriately determined taking into consideration the required quality and economic efficiency.

[0085] The temperature during firing is not particularly limited, but is preferably 300 to 1500°C, more preferably 400 to 1400°C, for the purpose of burning off the binder pitch.

[0086] 4. Experimental Results The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following descriptions.

[0087] (1) Inhibitor synthesis method Each compound was weighed out to achieve the composition ratio of each example, mixed in a mortar, and fired in air and reducing atmospheres at temperatures ranging from 1000° C. to 1500° C. The resulting compound was pulverized in the mortar to particles of 100 μm or less, and used as an inhibitor.

[0088] (2) Puffing measurement method 1 (cold puffing method) In each example, coal-based needle coke crushed to a specified particle size, 30% by weight of binder pitch relative to the coal-based needle coke, and the inhibitor additive amounts listed in Tables 1 to 3 were mixed and kneaded for 5 minutes while heating at 165°C. This mixture was molded into a 20 mm diameter x 3 to 15 mm disk and calcined in a calcination furnace at 1000°C or 1300°C for 3 hours to burn off the binder pitch, yielding a test piece for puffing measurement. The test piece was calcined (main calcination) by heating to 2100°C or 2800°C at a heating rate of 20°C / min. The irreversible expansion and contraction ratios before and after calcination were calculated using the above-mentioned formula (I) or formula (II) and expressed as the cold puffing value. The cold puffing value when the calcination temperature is 1000°C and the firing temperature (maximum firing temperature) is 2100°C is the puffing value P 2100 The cold puffing value when the calcination temperature is 1300°C and the firing temperature (maximum firing temperature) is 2800°C is the puffing value P 2800 is.

[0089] (3) Puffing Measurement-2 (Hot Puffing) Calcined coke was crushed and adjusted to a certain particle size. Coal-based binder pitch was added to the mixture in an amount of 30% by weight based on the calcined coke, and the mixture was kneaded at 165°C. A cylindrical compact was then produced using an extrusion molding machine. The compact was then fired in a firing furnace at 1000°C for 3 hours to produce a test piece (cylinder). The test piece was heated from room temperature to 2800°C at a heating rate of 20°C / min. The elongation of the length of the sample during this period was measured using a push rod type dilatometer and calculated using the following formula to indicate the hot puffing value. The elongation of the length of the test piece (cylinder) corresponds to the elongation in the direction perpendicular to the extrusion direction of the extrusion molding. A lower hot puffing value is preferable. Hot puffing value (%) = (△L / L) x 100 (In the formula, L is the length of the test piece before the test, and ΔL is the elongation in the longitudinal direction of the test piece during the temperature rise up to 2800°C.)

[0090] (4) Measurement method for graphitized BD For the test pieces after firing using the measurement method (2) above, the volume was calculated from their diameter and thickness, and the weight of the test piece was measured. The weight was divided by the volume to calculate the bulk density, which was taken as the compact density BD (bulk density; BD).

[0091] (5)TPD-MS method A test piece calcined at 1300°C, obtained using the same method as in (2) above, was placed in a W crucible and precisely weighed. It was then placed in a quartz TPD tube set in an infrared heating furnace. The temperature was increased to 1700°C at 100°C / min while flowing He at 100 ccm. The temperature was maintained at 1700°C for 3 minutes, and the sample was then allowed to cool. During this time, gases exiting the quartz TPD tube were introduced into a time-of-flight mass spectrometer, and the trends of each gas component were monitored. Quantitation was performed using the area above the background of the obtained trend as a function of the trend area-to-substance ratio of a separately measured standard sample, or a calibration curve for a standard gas.

[0092] (6) Powder X-ray diffraction method The test pieces after the TPD-MS measurement in (5) above were measured using an X-ray diffractometer. The measurement conditions were CuKα, 40 kV, 50 mA, and 2θ = 10-90°, and a sealed tube X-ray diffractometer (Rigaku Smart Lab SE) was used.

[0093] [Examples A1 to A20, Comparative Examples A1 to A7] The inhibitor was synthesized by method (1), and a test piece was prepared by method (2), and the cold puffing value and compact density BD were measured. In Comparative Example A1, the test piece was prepared by the same method as in (2), except that no inhibitor was added. The inhibitor composition, amount added, calcination temperature, and main calcination temperature for each example were as shown in Tables 1 to 3. The measurement results of the cold puffing value and compact density BD for each example are shown in Tables 1 to 3. Furthermore, for Examples A3, A12 to A14 and Comparative Example A1, the cold puffing value versus the amount of Ca3SiO5 added is plotted in Figure 1. Furthermore, the TPD-MS measurement results after heating to 1700°C are shown in Figure 2, and the powder X-ray diffraction results after the TPD-MS measurement are shown in Figure 3.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] As shown in Table 1, Examples A1 to A11, in which the inhibitor of the first embodiment was added, had smaller cold puffing values ​​and a higher puffing suppression effect than Comparative Example A1, in which no inhibitor was added, and Comparative Examples A2 to A5, in which other inhibitors were added. As shown in Table 3, Examples A15 to A20, in which the inhibitor of the first embodiment was added, also had smaller cold puffing values ​​and a higher puffing suppression effect than Comparative Example A6, in which no inhibitor was added, and Comparative Example A7, in which other inhibitors were added. Furthermore, as shown in Table 2 and FIG. 1, when comparing Comparative Example A1, Examples A3, and A12 to A14, the cold puffing value decreased as the amount of inhibitor added increased, and the puffing suppression effect increased. Furthermore, in Examples A1 to A20, the compact density BD was also sufficiently high.

[0098] As shown in Figure 2, the TPD-MS results indicate that the nitrogen desorption temperature shifts toward a lower temperature as the amount of the inhibitor of the first embodiment increases. Furthermore, as shown in Figure 3, the powder X-ray diffraction spectrum was normalized based on the peak tops at 2θ = 24° to 27°, and the changes in the diffraction peaks were observed. As the amount of the inhibitor of the first embodiment increased, the half-width narrowed. It was confirmed that, in Example A14, a peak corresponding to the 002 plane of the graphite crystals appeared. From these results, it is inferred that the addition of the inhibitor of the first embodiment promotes graphite crystallization, and as graphite crystallization progresses, nitrogen is desorbed, resulting in a reduction in the puffing phenomenon.

[0099] [Example A21, Comparative Example A8] Test pieces were prepared by adding 2 wt% of Ca3SiO5 synthesized by method (1) to method (2), and the cold puffing value was measured. In Comparative Example A8, a test piece was prepared by method (3) without adding an inhibitor, and the hot puffing temperature was measured. The measurement results of the puffing value from 1000°C to 2650°C are shown in Figure 4. In addition, since the temperature at which nitrogen puffing occurs is between 1700°C and 2100°C, in order to distinguish between nitrogen puffing and sulfur puffing, the rate of change in expansion / contraction ratio at firing temperatures between 1700°C and 2100°C and the rate of change in expansion / contraction ratio from 1700°C to 2600°C were calculated. The results are shown in Table 4.

[0100] [Table 4]

[0101] As shown in Figure 4 and Table 4, in Comparative Example A8, puffing occurred suddenly from around 1900°C, whereas in Example A21, puffing did not occur in the temperature range in which puffing normally occurs, confirming that the inhibitor of the first embodiment suppresses puffing.

[0102] [Examples A22 to A25] The inhibitor was synthesized by method (1), and test pieces were prepared by method (2), and the cold puffing value and compact density BD were measured. The inhibitor composition, amount added, calcination temperature, and main firing temperature for each example were as shown in Table 5. Table 5 shows the measurement results of the cold puffing value and compact density BD for each example.

[0103] [Table 5]

[0104] As shown in Table 5, even in Examples A22 to A25 in which the inhibitor of the first embodiment was added, the cold puffing value was small and the puffing suppression effect was high.

[0105] (7) Puffing measurement method (cold puffing method) In each example, coal-based needle coke crushed to a predetermined particle size was mixed with 30% by weight of binder pitch and 2% by weight of inhibitor, based on the total weight of the coal-based needle coke, and kneaded for 5 minutes while heating at 165°C. This mixture was molded into a 20mm diameter x 3-15mm disc and calcined in a calcination furnace at 1000°C or 1300°C for 3 hours to burn off the binder pitch, yielding a test piece for puffing measurement. The test piece was calcined (main calcination) by heating to 2100°C or 2800°C at a heating rate of 20°C / min. The irreversible expansion and contraction ratios before and after calcination were calculated using the above-mentioned formula (I) or (II) and expressed as the cold puffing value. The cold puffing value when the calcination temperature was 1000°C and the main calcination temperature (maximum temperature of main calcination) was 2100°C was the puffing value P. 2100 The cold puffing value when the calcination temperature is 1300°C and the firing temperature (maximum firing temperature) is 2800°C is the puffing value P 2800 is.

[0106] [Example B1] Ca and Si were mixed to obtain the molar ratio shown in Table 6, and an inhibitor in which CaO and SiO2 were composited was synthesized by method (1). Two test pieces were prepared using the obtained inhibitor by method (7), and measurements were performed using the cold puffing method. In order to distinguish between nitrogen puffing and sulfur puffing, one test piece was stopped from being fired at 2100°C, where nitrogen puffing is thought to occur, and the other was fired up to 2800°C, and the 2100°C cold puffing value (P 2100 ) and 2800℃ cold puffing value (P 2800 ) was sought.

[0107] [Example B2] Two test pieces were prepared in the same manner as in Example B1, except that CaO and SiO2 were mixed in a ratio of 75 mol% CaO and 25 mol% SiO2, and the mixed powder was used as the inhibitor. The 2100°C cold puffing value (P 2100 ) and 2800℃ cold puffing value (P 2800 ) was sought.

[0108] [Comparative Example B1] Two test pieces were prepared in the same manner as in Example B1, except that the inhibitor consisted of only CaO, and the 2100°C cold puffing value (P 2100 ) and 2800℃ cold puffing value (P 2800 ) was sought.

[0109] [Comparative example B2] Two test pieces were prepared in the same manner as in Example B1, except that the inhibitor consisted of only SiO2, and the 2100°C cold puffing value (P 2100 ) and 2800℃ cold puffing value (P 2800 ) was sought. The results of measuring the cold puffing values ​​at 2100°C and 2800°C for each example are shown in Table 6 and FIG.

[0110] [Table 6]

[0111] As shown in Table 6 and FIG. 5, in Examples B1 and B2 in which the inhibitor of the second embodiment was added, puffing at both 2100° C. and 2800° C. was suppressed. Furthermore, as shown in Comparative Examples B1 and B2, when only a single element metal was added, it was not possible to suppress both puffing at 2100°C and 2800°C. For example, Comparative Example B1 only demonstrated the effect of suppressing nitrogen puffing at 2100°C. In other words, since the inhibitor of the second embodiment contains an oxide having the element (Mα) and an oxide having the element (Mβ), it reacts with nitrogen or sulfur in the coke during the temperature rise process during firing to form complex compounds (nitrides, oxynitrides, sulfides, oxysulfides), and it is therefore presumed that this is why the effects of the second embodiment are achieved.

[0112] (8) Puffing measurement method-3 (cold puffing method) In each example, coal-based needle coke crushed to a specified particle size was mixed with 30% by weight of binder pitch and 2% by weight of inhibitor, and the mixture was heated to 165°C for 5 minutes. This mixture was molded into a 20mm diameter x 3-15mm disc and calcined in a kiln at 1000°C for 3 hours to burn off the binder pitch, creating a test piece for puffing measurement. The test piece was then heated to 2100°C, 2650°C, or 2800°C at a heating rate of 20°C / min (main calcination). The irreversible expansion and contraction ratio before and after calcination was expressed as the cold puffing value. The cold puffing value when the temperature was raised to 2100°C was calculated using the above formula (I), and the cold puffing value when the temperature was raised to 2650°C or 2800°C was calculated by substituting the thickness (mm) of the test piece after firing to 2650°C or 2800°C as L2 in the above formula (I).

[0113] (9) Measurement method for graphitized BD For the test piece after firing by the measurement method (8) above, the volume was calculated from its diameter and thickness, and the weight of the test piece was measured. The weight was divided by the volume to calculate the bulk density, which was the compact density BD (bulk density; BD).

[0114] (10) Composition analysis method The composition of the test pieces after calcination or firing in each example was analyzed. The metal elements (Ca, Si) in the test pieces were analyzed by dry ashing at a maximum temperature of 750 °C, followed by alkali salt fusion decomposition, dissolving in dilute hydrochloric acid to a constant volume, and then diluting appropriately. The solution was analyzed using an inductively coupled plasma (ICP) optical emission spectrometer (Thermo Fischer Scientific, iCAP7600 duo) and quantified using the matrix matching calibration method. Nitrogen and oxygen in the test pieces were analyzed by heating and extracting them in an impulse furnace under an inert gas atmosphere using an oxygen-nitrogen analyzer (LECO TCH600). Oxygen was quantified using the NIR detection calibration method, and nitrogen was quantified using the thermal conductivity detection calibration method. Sulfur in the test pieces was analyzed by burning the test pieces in a high-frequency furnace in an oxygen stream using a carbon-sulfur analyzer (LECO CS600). The NIR detection calibration method was used.

[0115] [Example C1] Using Ca3SiO5 synthesized by method (1) as the inhibitor, test pieces were prepared by method (8), and the composition of the test pieces after calcination was analyzed by method (10). The results are shown in Table 7.

[0116] [Examples C2 to C4] Using the Ca3SiO5 synthesized by method (1) as the inhibitor, test pieces were prepared by method (8). After calcination, the test pieces were heated to 2100°C, 2650°C, or 2800°C and sintered to measure the cold puffing value. The green density BD of these test pieces was measured by method (9), and composition analysis was performed by method (10). The results are shown in Table 7. The unit of each component in the composition analysis results in Table 6 is μmol / g.

[0117] [Table 7]

[0118] As shown in Table 7, puffing was suppressed in Examples C1 to C4, which used the inhibitor of the third embodiment. Furthermore, in Example B4, the amount of inhibitor-derived substances remaining after graphitization was extremely small. While this depends on the application of the graphite electrode, having fewer inhibitor-derived substances remaining on the graphite electrode is advantageous in that it can reduce the deterioration of the product performance of the graphite electrode and adverse effects on the environment.

Claims

1. An inhibitor for graphite electrode production for suppressing puffing of needle coke, comprising a composite oxide having the following elements (Mα) and (Mβ): Element (Mβ): Si, Ge, Al, Ti, or Fe. Element (Mα): Mg, Ca, Sr, Ba, or Ce.

2. 2. The inhibitor for producing graphite electrodes according to claim 1, wherein the composite oxide has a composition formula represented by the following formula (1): Ma ３－ｘ Mβ １－ｙ O ５－ｚ ・・・(1) (Wherein, 0≦x<3, 0≦y<1, and 0≦z<5.)

3. The compound oxide includes the following elements (Mα-1) and (Mβ): An inhibitor for graphite electrode production to suppress needle coke puffing, which volatilizes at temperatures between 2100 and 6000°C. Element (Mβ): Si, Ge, Al, Ti, or Fe. Element (Mα-1): Mg, Ca, Sr, Ba, or Ce.

4. 4. The inhibitor for producing graphite electrodes according to claim 3, wherein Y / X<0.01, where X is the percentage (wt%) of the inhibitor added to the needle coke and Y is the percentage (wt%) of the inhibitor after heat treatment at 2800°C for 30 minutes.

5. 4. The inhibitor for producing graphite electrodes according to claim 3, which reacts with a sulfur compound.

6. 4. The inhibitor for producing graphite electrodes according to claim 3, which reacts with a nitrogen compound.

7. The puffing value P of the test piece prepared in the following evaluation test (i) is calculated by the following formula (I). ２１００ 2. The inhibitor for producing graphite electrodes according to claim 1, wherein the amount of ZnO in the inhibitor is 1.00% or less. P ２１００ =(L2-L1) / L1×100 ・・・(I) In the formula (I), L1 and L2 have the following meanings. L1: Thickness of test piece before firing (mm) L2: Thickness (mm) of the test piece after firing to 2100 ° C. <Evaluation test (i)> Coal-based needle coke, binder pitch (external ratio of 30% by weight based on the coal-based needle coke), and an inhibitor were mixed and kneaded for 5 minutes while heating at 165°C. This was molded into a disk of 20 mm diameter x 3 to 15 mm, and calcined in a calcination furnace at 1000°C for 3 hours to burn off the binder pitch, yielding a test piece. The test piece was calcined by heating it up to 2100°C at a rate of 20°C / min, and L1 and L2 of the test piece were measured before and after calcination.

8. A composition comprising the inhibitor for producing graphite electrodes according to any one of claims 1 to 7 and needle coke.

9. A needle coke for graphite electrodes comprising the composition of claim 8.

10. A graphite electrode obtained by firing the needle coke for graphite electrodes according to claim 9.

11. A method for producing needle coke for graphite electrodes, comprising: a composition in which an inhibitor is directly attached to the surface of the needle coke; A method for producing needle coke for graphite electrodes, comprising adding the inhibitor for graphite electrode production according to any one of claims 1 to 7 in a solution or molten state to needle coke before kneading with binder pitch, thereby directly adhering the inhibitor for graphite electrode production to the surface of the needle coke.

12. A method for producing a graphite electrode, comprising calcining the needle coke for graphite electrodes according to claim 9.

13. The method for producing a graphite electrode according to claim 12, wherein the firing temperature is 300 to 1500°C.

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