Low CTE, low puffing needle coke

Abstract

To provide a method for obtaining low CTE, low puffing needle coke further consistently while adapting to changes in the properties of a raw oil.SOLUTION: The low CTE, low puffing needle coke is characterized by mixing a main raw oil for needle coke, which is a coal tar-based or petroleum-based heavy oil with low hydrogen donating ability having a PDQI value of less than 5.0 as shown in formula (1), with a secondary raw oil having high hydrogen donating ability with a PDQI value of 5.0 or more as shown in the formula (1), coking the mixture, and calcining the obtained raw coke. Formula (1) is expressed as PDQI=H%×10×(HNβ / H), where H% is the hydrogen content (wt.%) determined by elemental analysis, and HNβ / H is the ratio of β-naphthene hydrogen to total hydrogen measured by 1H-NMR.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to low CTE, low puffing needle coke and artificial graphite electrodes for electric steelmaking. [Background technology]

[0002] Needle coke is generally produced using petroleum-based heavy oil or coal tar-based heavy oil as raw materials and is used as aggregate for artificial graphite electrodes in electric steelmaking. These graphite electrodes are manufactured by adjusting needle coke to a predetermined particle size, kneading it with binder pitch, then extruding it, and subsequently performing primary calcination, impregnation, secondary calcination, and graphitization treatment.

[0003] Graphite electrodes are required to have a low coefficient of thermal expansion (CTE) to withstand harsh operating environments in high-temperature atmospheres. A low CTE reduces electrode wear during electric steelmaking, contributing to cost reduction in electric steelmaking.

[0004] The graphitization process in the manufacturing of graphite electrodes involves heat treatment at high temperatures of around 3000°C, and the most common method uses an LWG furnace (direct current furnace). When graphitizing in an LWG furnace, the heating rate is rapid, which leads to a rapid generation of gas from the graphite electrode material, making it prone to an abnormal expansion phenomenon called puffing. This puffing reduces the density of the electrode, and in some cases, can cause the electrode to break. For this reason, methods for manufacturing needle coke to reduce puffing and puffing inhibitors to be added during electrode manufacturing have been investigated.

[0005] Generally, the more uniform the microstructure orientation of needle coke and the more fine cracks it contains, the lower the CTE is considered to be. The carbon hexagonal network plane direction of the graphite structure that makes up needle coke has less thermal expansion than the stacking direction, so it is thought that when the plane direction is aligned with the longitudinal direction of the electrode, it results in an electrode with a low CTE. In addition, it is thought that the presence of fine cracks helps to mitigate thermal expansion, resulting in a low CTE. Puffing is generally thought to be caused by gas pressure resulting from the vaporization of compounds derived from nitrogen and sulfur in needle coke under high-temperature conditions.

[0006] Needle coke for artificial graphite electrodes requires low CTE during electrode use and low puffing during electrode manufacturing. Conventional methods for producing low CTE, low puffing needle coke include the following technologies.

[0007] Patent Document 1 describes a method for reducing CTE by hydrogenating the feedstock oil to remove puffing-causing substances such as nitrogen and sulfur, thereby reducing puffing, and by exhibiting favorable carbonization behavior due to reduced viscosity at high temperatures caused by reduced oxygen and sodium and increased naphthene rings. Patent Document 2 describes a cocarbonization method in which puffing is reduced by diluting nitrogen and sulfur, which are puffing-causing substances, and by obtaining a balance between carbonization rate and gas generation that produces an anisotropic structure exhibiting low CTE, by mixing coal tar pitch from which quinoline-insoluble components have been removed with petroleum-based heavy oil adjusted to specific properties and coking it. Furthermore, Patent Document 3 describes a method for obtaining needle coke with low CTE and low puffing by mixing two or more feedstock oils to generate a good bulk mesophase and gas generation for crystal orientation during solidification. Patent Document 4 and Non-Patent Document 1 describe how low CTE and low puffing can be achieved by two-stage calcination, due to changes in the coke structure that occur during calcination. Patent Document 5 describes how needle coke with low CTE and low buffing can be produced by increasing the number of fine pores by re-calcining coke that has been calcined once in an oxidizing atmosphere. Patent Document 6 describes a method for producing needle coke with low CTE and low buffing by mixing coal tar-based heavy oil and petroleum-based heavy oil from which quinoline-insoluble components have been removed, coking the mixture, and then calcining it in two stages.

[0008] As described above, it is known that low CTE and low puffing needle coke can be obtained by modifying the feedstock oil by hydrogenation, cocarbonization by mixing two or more feedstock oils and coking them, two-stage calcination, recalcination in an oxidizing atmosphere, and combinations thereof. Although this is not a method for reducing CTE or puffing, Patent Document 7 states that by adding a hydrogen-donating solvent to low-temperature tar pitch and heat-treating it, it can be modified to a quality suitable for use as a raw material for needle coke. Non-patent document 2 proposes the PDQI (Proton Donor Quality Index) as an evaluation of hydrogen donor capacity, but it evaluates the circulating solvent in the coal hydrogenation liquefaction reaction and does not indicate that it is useful as an indicator for improving the quality of needle coke. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Unexamined Patent Publication No. 60-149690 [Patent Document 2] Japanese Patent Application Publication No. 4-145193 [Patent Document 3] WO2009 / 1610 [Patent Document 4] Japanese Patent Application Publication No. 52-29801 [Patent Document 5] Japanese Patent Application Publication No. 61-218686 [Patent Document 6] Japanese Patent Application Publication No. 5-163491 [Patent Document 7] WO2011 / 48920 issue [Non-patent literature]

[0010] [Non-Patent Document 1] Carbon Vol.19 No.5 pp.347-352 [Non-Patent Document 2] Journal of the Fuel Association, 65, 12, pp. 1012-1019, 1986.

Summary of the Invention

Problems to be Solved by the Invention

[0011] It is known that low CTE and low puffing needle coke can be obtained by using a reformed feedstock oil, co-carbonization by using two or more feedstock oils, and changing the calcination conditions. However, while corresponding to changes in the properties of the feedstock oil, it is required to obtain low CTE and low puffing needle coke more stably. In artificial graphite electrodes, needle coke exhibits low CTE and low puffing. By clarifying what kind of needle coke structure contributes to low CTE and low puffing, it is considered possible to manufacture more stable low CTE and low puffing by combining the selection of feedstock oil, coking conditions, and calcination conditions. The present invention provides low CTE and low puffing needle coke by limiting the characteristics of the main feedstock oil and the auxiliary feedstock oil when manufacturing low CTE and low puffing needle coke by mixing two or more feedstock oils and coking them. Further, the present invention provides low CTE and low puffing needle coke by controlling the needle coke structure obtained after coking and calcination to a specific structure.

Means for Solving the Problems

[0012] As a result of intensive studies to solve the above problems, the present inventor has found that in order to reduce CTE and puffing, a mixed oil obtained by mixing an auxiliary feedstock oil with a large hydrogen donating property with a needle coke main feedstock oil with a small hydrogen donating property is coked and calcined, whereby low CTE and low puffing needle coke can be obtained. Also, by controlling the obtained needle coke to have a specific structure according to the raw material selection, coking conditions, and calcination conditions, low CTE and low puffing needle coke can be obtained, and the present invention has been completed.

[0013] That is, the present invention relates to 100 parts by weight of a needle coke base raw material oil of a coal tar-based heavy oil or a petroleum-based heavy oil with a low hydrogen donating property having a PDQI value calculated by formula (1) of less than 5.0, and a by-product oil with a high hydrogen donating property having a PDQI value of 5.0 or more shown by formula (1) is mixed in an amount of 10 to 80 parts by weight, and the mixture is coked, and the obtained green coke is calcined, which is characterized by a low CTE and low puffing needle coke. [Formula (1)] PDQI = H% × 10 × (HNβ / H) Here, H% is the amount of hydrogen (wt%) determined by elemental analysis, and HNβ / H is 1 the ratio of β naphthene hydrogen to total hydrogen measured by H-NMR.

[0014] The low CTE and low puffing needle coke of the present invention preferably has a structure index for CTE (NCSIC: Needle Coke Structure Index for CTE) shown by formula (2) greater than 25.0, and a structure index for puffing (NCSIP: Needle Coke Structure Index for Puffing) shown by formula (3) greater than 5.0. [Formula (2)] NCSIC = ((Lc / d002) + (open pore ratio)) / σ(θ) Here, Lc: crystallite size, d002: interplanar spacing, σ(θ): standard deviation of the average orientation angle are shown. [Formula (3)] NCSIP = (open pore volume / closed pore volume) + (HIT / 1000) / EIT Here, HIT: indentation hardness, EIT: indentation elastic modulus are shown.

[0015] The low CTE and low puffing needle coke of the present invention preferably has a de-QI pitch with a low hydrogen donating property obtained by distilling and de-QIing coal tar as the main raw material oil. In particular, it is preferable that the main raw material oil is a de-QI pitch with a low hydrogen donating property having a PDQI value calculated by formula (1) of less than 2 obtained by distilling and de-QIing coal tar.

[0016] The low CTE, low puffing needle coke of the present invention preferably has a crystallite size Lc of 4.0 to 10.0 nm, an interplanar spacing d002 of 0.340 to 0.350 nm, an open pore ratio of 0.15 to 0.40, and a standard deviation σ(θ) of the average orientation angle of 0.01 to 0.85. Open vent area: 0.040~0.070 cm 3 The value is / g, and the pore size is 0.001~0.015cm 3 Preferably, the density is / g, the indentation hardness HIT is 800-1500 MPa, and the indentation modulus EIT is 5.0-15.0 GPa.

[0017] In this invention, the crystallite size Lc and interplanar spacing d002 in formula (2) are obtained by measuring with XRD and analyzing with the JSPS method, the open pore ratio is calculated as the ratio of the pore volume of pores with a diameter of 1 to 10 μm to the pore volume of pores with a diameter of 120 μm or less, measured by mercury porosimetry, and the standard deviation σ(θ) of the average orientation angle is calculated as the standard deviation, which is an indicator of the variation in orientation angle, measured using a birefringent. [Effects of the Invention]

[0018] According to the present invention, low CTE and low puffing needle coke can be stably obtained by coking a secondary raw material oil with high hydrogen-donating properties with a main raw material oil with low hydrogen-donating properties, calcining the resulting green coke, and controlling the pore structure and microstructure to achieve a specific coke structure. [Brief explanation of the drawing]

[0019] [Figure 1] This is the displacement-load curve obtained from measurements using a microhardness tester. [Figure 2] This is the displacement-load curve of the needle coke in Example 1. [Figure 3] This is the displacement-load curve for needle coke in Comparative Example 1. [Modes for carrying out the invention]

[0020] The key factors influencing the CTE of needle coke are thought to be crystallinity, pore size, and microstructure orientation. These are mostly formed during the coking process. During the coking process, when raw material oil is heated, organic molecules undergo repeated dehydrogenation polycondensation reactions. As these molecules stack, optically anisotropic mesophase spherulites are formed, which then grow and coalesce to develop an optically anisotropic structure. While it is known that the viscosity of the system increases with the progression of mesophase growth and coalescence during the coking process, an imbalance between the viscosity increase and mesophase growth and coalescence is crucial. If the viscosity increase occurs first, sufficient mesophase growth is not possible, resulting in low crystallinity. Conversely, crystallinity develops when the low viscosity range persists, allowing sufficient mesophase growth and coalescence. Furthermore, just before the end of coking, shear forces from generated and introduced gases orient the microstructure uniaxially, improving the orientation of the optically anisotropic structure. Hydrogenated raw material oil is effective in addressing these CTE-influencing factors. A study examining the differences between hydrogenated and non-hydrogenated feed oils revealed that hydrogenated feed oils have a larger PDQI value, as shown in equation (1), than non-hydrogenated feed oils. In other words, hydrogenated feed oils are characterized by their high hydrogen-donating capacity. It was found that by preparing hydrogenated feed oils with particularly high hydrogen-donating capacity, needle coke with a lower CTE can be produced. Although the exact reason why using feed oils with high hydrogen-donating capacity yields low CTE needle coke is unclear, it is thought that using feed oils with high hydrogen-donating capacity allows naphthenic hydrogen to migrate during coking, maintaining a low viscosity region during coking, promoting sufficient mesophase growth and coalescence, increasing the amount of generated gas, and improving the orientation of the optically anisotropic structure due to the shear of these gases just before the end of coking. However, if a feed oil with high hydrogen-donating properties is used alone as a feed oil, its boiling point will be lower than that of the main feed oil with low hydrogen-donating properties, resulting in excessive gas generation. This is expected to result in either no green coke being obtained, or only a low yield. On the other hand, by using a mixed feed oil in which a feed oil with low hydrogen-donating properties is used as the main feed oil and a feed oil with high hydrogen-donating properties is used as a secondary feed oil, the naphthenic hydrogens in the secondary feed oil can be transferred to the aromatic rings of the main feed oil. This allows the main feed oil, which did not develop sufficiently in terms of mesophase growth and coalescence when used alone, to maintain a low viscosity region where it can develop sufficiently. Furthermore, the gas generated from the secondary feed oil with high hydrogen-donating properties is also expected to improve orientation. In addition, the secondary feed oil with high hydrogen-donating properties acts as a reaction modifier, and its amount can be increased or decreased to adjust the improvement of properties. Therefore, it is preferable that the amount of secondary feed oil with high hydrogen-donating properties mixed with 100 parts by weight of the main feed oil with low hydrogen-donating properties is between 10 parts by weight and 80 parts by weight. More preferably, the amount is 20 parts by weight or more and 50 parts by weight or less, and even more preferably, 25 parts by weight or more and 45 parts by weight or less. By selecting the needle coke raw material oil and simultaneously adjusting the coking and calcination conditions as appropriate to prepare the needle coke structure, and creating a structure suitable for low CTE and low puffing, further improvements in properties can be expected in addition to the improvements made by the raw material oil.

[0021] The structure of needle coke obtained through raw material selection, coking, and calcination is considered to be most closely related to CTE and puffing characteristics. Coke structure evaluation is performed using XRD to assess the degree of crystallinity development, birefringence to assess the orientation of the optical anisotropy structure, and mercury porosimetry to assess the pore size. By using the needle coke structure index (Equation (2)) related to CTE obtained from the results of each evaluation, it is possible to quantify the structure of low CTE needle coke. When crystallinity is well-developed, the crystallite size Lc is large and the interplanar spacing d002 is narrow; therefore, a large Lc / d002 indicates well-developed crystallinity. The crystallite size Lc is preferably 5.5 nm or larger, more preferably 6.0 nm or larger. The standard deviation σ(θ) of the average orientation angle θav measured from the birefringence is smaller when the orientation is high, indicating that the orientation is uniform. Therefore, the smaller σ(θ), the more uniformly oriented the coke is considered to be. The standard deviation σ(θ) is preferably less than 0.80, and more preferably less than 0.70. A high ratio of 1-10 μm pores to 120 μm or smaller pores is thought to contribute to low CTE by acting as a relaxation area during expansion. The ratio of 1-10 μm pores to 120 μm or smaller pores is called the open pore ratio. The open pore ratio is preferably in the range of 0.15 to 0.40, more preferably 0.30 or higher, and even more preferably 0.33 or higher.

[0022] NCSIC is a numerical representation of a coke structure suitable for low CTE, using crystallinity, orientation, and pore size. A higher NCSIC value (indicating well-developed crystallinity, high orientation, and high pore size) suggests a lower CTE needle coke.

[0023] The key factors in needle coke puffing are nitrogen and sulfur, which are the causative substances in the needle coke. It is known that puffing can be reduced by reducing nitrogen and sulfur, which are the gas-causing substances, but while it is known that a large number of pores is useful, other structures were not clearly defined as being effective in reducing puffing. The inventors of this invention have found that the number of pores, which provide an escape route for the generated gas, and the coke strength that can withstand the gas pressure are important, and that the coke structure of needle coke for low puffing needs to be optimized in both the pore structure that allows the gas generated during puffing to escape and the structural structure that can withstand the gas pressure.

[0024] Since nitrogen and sulfur content originates from the raw oil, low-nitrogen and low-sulfur raw oils are required. However, in recent years, the nitrogen and sulfur content in raw oils has increased, making raw oil selection difficult. Adding auxiliary raw oils with high hydrogen-donating properties can be expected to cause mild hydrodesulfurization and denitrification during coking, making the hydrogen-donating properties of auxiliary raw oils an important factor in their selection.

[0025] Pore ​​density and strength can be appropriately modified depending on the coking or calcination conditions. It is believed that a coke structure suitable for low buffing can be quantified by using two pore density values—open pore density obtained from mercury porosimetry and closed pore density calculated from true density and apparent density—along with the indentation hardness (HIT) calculated from the applied load and depth of indentation obtained from a microhardness tester, and the coke strength calculated from the indentation modulus (EIT), which represents the degree of recovery after unloading. In the present invention, the indentation hardness HIT is preferably 800 to 1500 MPa, more preferably 900 to 1400 MPa. The indentation modulus EIT is preferably 5.0 to 15.0 GPa, more preferably 8.0 to 13.0 GPa.

[0026] Optimizing the microstructure related to pore size and strength results in needle coke suitable for low buffing. Specifically, the pore size should have a large number of open pores connecting to the outside of the coke and a small number of closed pores not connecting to the outside. The microstructure related to strength, which can withstand gas pressure, should have high resistance to deformation by external forces (hard structure) and flexibility to easily recover after deformation (low modulus of elasticity). More precisely, this coke structure should have disordered optical anisotropy at the micron size, but uniform optical anisotropy at the submicron to nanoscale. Regarding the pore size, a large number of pores that allow gases to escape during graphitization (when nitrogen and sulfur volatilize as gas) is thought to reduce buffing. A small number of closed pores reduces the amount of gas remaining in the coke, thus reducing buffing. On the other hand, a coke microstructure with high strength can withstand gas pressure during graphitization, or easily recover after deformation by gas pressure, thus reducing buffing. In coking, methods include developing submicron to nanoscale optical anisotropy by coking at low temperatures in the initial stages or by developing the mesophase while maintaining a low viscosity state using hydrogenated raw materials, and in the later stages of coking by changing the coking conditions during the process to disrupt the orientation of the micron-scale optical anisotropy structure by increasing the temperature, pressure, and steam amount, or by changing a combination of these factors. By changing coking conditions such as temperature, pressure, and steam amount during the process, the optical anisotropy structure from submicron to nanoscale and from micron to millimeter scale can be altered, leading to an increase or decrease in the amount of closed pores in the coke obtained by the orientation of the microstructure. In calcination, methods such as calcination in two or more stages, high-temperature calcination, and oxidation calcination can be used to increase the amount of open pores. In calcination in two or more stages, calcination is performed at a low temperature in the first stage, and after cooling, subsequent calcinations are performed. This causes fine cracks to form due to cooling and heating, resulting in an increase in open pores and a decrease in closed pores.Furthermore, in high-temperature calcination, calcining at a higher temperature than usual results in greater shrinkage than normal calcination, leading to stress-induced crack formation and an increase in the amount of open pores. In oxidative calcination, introducing an oxidizing gas during calcination oxidizes the surface of the needle coke, creating pores and increasing the amount of open pores. The amount of open vents is 0.040-0.070 cm. 3 It is in the range of / g, preferably 0.050~0.065cm 3 The value is / g. On the other hand, the pore size is 0.001~0.015cm 3 The range is / g, preferably 0.005~0.009cm 3 It is within the range of / g.

[0027] The needle coke of the present invention is obtained by coking a mixed raw material oil, which is a mixture of a main raw material oil with low hydrogen-donating properties and a secondary raw material oil with high hydrogen-donating properties, and then calcining the resulting green coke.

[0028] The main raw materials for needle coke include coal tar-based heavy oil and petroleum-based heavy oil.

[0029] Examples of coal tar-based heavy oils include coal tar produced as a by-product during coke manufacturing, coal tar pitch obtained by distilling coal tar, and liquefied coal oil obtained by liquefying coal. For coal tar pitch, it is preferable to remove quinoline-insoluble components, and generally, use pitch with a quinoline-insoluble component content of 0.1% or less. Pitch obtained by distilling and thermally reforming coal tar pitch from which quinoline-insoluble components have been removed may also be used as a raw material oil. Examples of petroleum-based heavy oils include catalytic cracking oil, pyrolysis oil, atmospheric residue, vacuum residue, and ethylene bottom oil, but decant oil (FCC-DO), which is the heavy component of catalytic cracking oil, is particularly preferred. A mixture of coal tar-based heavy oil and petroleum-based heavy oil, or a mixture of by-product oils obtained during the coking process, or a mixture of oils that have been thermally reformed may be used as the raw material oil. These main raw material oils have a PDQI value indicating hydrogen donation capacity of less than 5.0, preferably less than 1.0, and usually around 0.001, indicating low hydrogen donation capacity.

[0030] This invention uses a secondary raw material oil with high hydrogen-donating properties along with a main raw material oil, and uses a mixture of the main raw material oil and the secondary raw material oil. As described above, the secondary raw material oil used has a high PDQI value. The PDQI value is preferably 5.0 or higher, more preferably 8.0 or higher, and even more preferably 10.0 or higher. As auxiliary raw material oils, hydrogenated coal tar-based heavy oil or petroleum-based heavy oil, which are the main raw material oils, can be used. Preferred heavy oils are coal tar or its distilled components. More preferably, the 300-600°C fraction obtained by distilling the main raw material oil is partially hydrogenated. Furthermore, even if the main raw material oil of needle coke is not the starting raw material oil, any oil adjusted to have a hydrogen donor capacity of 5 or higher, preferably 10 or higher, is suitable as an auxiliary raw material oil. The hydrogenation treatment conditions are preferably 100°C or higher and below 300°C, with a hydrogen partial pressure of less than 5 MPa, and the use of a hydrogenation reactor with a hydrogenation catalyst. However, the treatment method is not limited to these conditions as long as it satisfies the PDQI value.

[0031] The blending ratio of the main raw material oil to the auxiliary raw material oil is preferably 10 to 80 parts by weight of auxiliary raw material oil per 100 parts by weight of main raw material oil. More preferably, it is 20 to 50 parts by weight of auxiliary raw material oil, and more preferably, 25 to 45 parts by weight. If the amount of auxiliary raw material oil is too small, the hydrogen donation is low, and it is not possible to obtain the desired low CTE, low puffing needle coke. On the other hand, if the amount of auxiliary raw material oil is too large, the decomposition reaction of the auxiliary raw material oil becomes dominant over the reaction between the main raw material oil and the auxiliary raw material oil, and the hydrogen from the auxiliary raw material oil cannot be used to promote the growth and coalescence of the mesophase of the main raw material oil, so it is not possible to obtain the desired low CTE, low puffing needle coke.

[0032] For coking mixed raw material oils, known delayed coking methods can be employed. For example, green coke is obtained by coking at 450-550°C and a pressure of 0.2-0.8 MPa for 18-48 hours. As for coking methods, instead of keeping the coking conditions constant from the start to the end of raw material charging, methods such as gradually changing the charging temperature during coking, gradually changing the coking pressure, gradually changing the amount of water vapor charged during coking, dividing the raw material oil into two and supplying one raw material oil into the coker from the bottom at a low temperature and the other raw material oil into the coker from the side at a high temperature, increasing the pressure and increasing the amount of water vapor during coking, or combinations thereof can be employed.

[0033] Known methods can be used to calcine green coke. For example, calcination can be performed at 800-1600°C using a rotary kiln, shaft furnace, or siliconite furnace. Calcination may be performed in one stage or in two or more stages. Calcination may be performed at high temperatures, or by blowing in an oxidizing gas.

[0034] The method for producing artificial graphite electrodes for electric steelmaking from the above-mentioned low CTE, low puffing needle coke may be a known method, for example, by kneading with binder pitch, molding, primary calcination, impregnation, secondary calcination, and graphitization.

[0035] Next, I will explain the measurement conditions. Needle coke's auxiliary oils contain condensed polycyclic aromatic hydrocarbons having a naphthenic ring structure. The hydrogen atoms in the naphthenic ring include hydrogen atoms bonded to the α-position carbon of the aromatic ring (HNα) and hydrogen atoms bonded to the β-position or higher carbons (HNβ). In addition, there are hydrogen atoms derived from alkyl groups and other substituents attached to the condensed polycyclic aromatics, which also include hydrogen atoms bonded to the α-position carbon (Hα) and hydrogen atoms bonded to the β-position or higher carbons (Hβ, etc.). Furthermore, there are hydrogen atoms bonded to the carbon of the aromatic ring (Ha).

[0036] The identification of these hydrogens, etc. 1 This is performed by measuring using H-NMR. 1 For the measurement of 1H-NMR, chloroform was used as the solvent, the standard substance was TMS (tetramethylsilane), and the measurement was carried out using JNM-LA400 manufactured by JEOL Ltd. The hydrogen fraction was calculated from the integration value in the obtained 1H-NMR spectrum. Hα, HNα, and HNβ were obtained from the 1 The chemical shifts of the H-NMR spectrum at 2.0 - 4.2, 3.0 - 4.2, and 1.5 - 2.0 were integrated and calculated respectively.

[0037] The analysis of carbon and hydrogen (elemental analysis) of the main feedstock oil and the by-feedstock oil was calculated in accordance with JIS M 8819, nitrogen was calculated in accordance with JIS K 2609, oxygen was calculated in accordance with JIS M 8813, and sulfur was calculated in accordance with JIS K 2541.

[0038] PDQI is calculated by Equation (1). H% is the amount of hydrogen (wt%) determined by elemental analysis, and HNβ / H is 1 The ratio of β-naphthene hydrogen to total hydrogen measured by 1H-NMR. PDQI represents the maximum available hydrogen amount (mg) of naphthene rings contained in 1 g of the solvent, and the unit is mg / g.

[0039] The crystallite size Lc and the interplanar spacing d002 obtained from XRD were measured at an angle of 20 - 30° using an XRD instrument manufactured by Rigaku Corporation, and calculated by crystallite size analysis using the Gakushin method.

[0040] The standard deviation σ(θ) of the orientation angle obtained from the measurement using a birefringence meter was obtained by embedding needle coke particles with a size of 1 - 2 cm in resin, polishing with a polishing machine, and using a test piece with a thickness of 8 mm with the needle coke exposed on the surface. The surface of the exposed needle coke was measured using a birefringence meter PI-micro manufactured by Photonic Lattice Co., Ltd. at 0.9 μm or 2.7 μm per pixel. The retardation Re, the average orientation angle θav, and the standard deviation σ(θ) of the average orientation angle for one field of view were obtained from the values of Re and the orientation angle θ for each pixel, and multiple fields of view were measured. The numerical value averaged for all the measured fields of view was used as the evaluation value.

[0041] For the mercury porosimetry of needle coke, needle coke was reduced to 2-5 mm sections, and pressures from 1.9 to 14400 psi (equivalent to pore diameters of 0.017-120 μm) were measured using a Micromeritics Autopore IV. The pore volume relative to the pore diameter was calculated from the obtained pressure and mercury content, and the pore volume for 1-10 μm was calculated and used as the open pore volume of the needle coke. The open pore ratio was calculated by dividing the pore volume for 1-10 μm by the pore volume for pores 120 μm and smaller. In Tables 1 and 2, the pore volume values ​​represent the total pore volume and are the pore volumes for pores 120 μm and smaller used to calculate the open pore ratio.

[0042] The true density of needle coke was measured in accordance with JIS K 2151. The apparent density was measured using the same procedure as for true density after crushing needle coke with a jaw crusher and sieving the 8-16 mesh. The number of closed pores was calculated using the following formula (4). [Formula (4)] Closed pore volume (cm 3 / g)= (1 / apparent density (g / cm³) 3 )―(1 / true density(g / cm 3 ))

[0043] For the microhardness test, needle coke particles measuring 1-2 cm in size were embedded in resin, polished with a polishing machine, and the resulting 8 mm thick specimen with the needle coke exposed on the surface was used as the test piece, and the measurement was performed on the surface of the exposed needle coke. The specific test conditions were as follows: using a Fischer Instruments FISHERSCOPE HM2000 with a Vickers indenter as the measuring probe, a maximum load of 2000 mN, a loading speed of 300 mN / s, a creep time of 2 seconds, and unloading at the same speed as loading. Ten measurements were taken for each specimen, and the average value was adopted as the value for that specimen. Figure 1 shows a typical displacement-load curve. To measure the microstructure of needle coke, it is necessary to measure in the region where the needle coke does not undergo plastic deformation (fracture) (elastic deformation region). In the displacement-load curve obtained from the test, the displacement must return to the origin after unloading, as shown in Figure 1. The indentation depth is the displacement at the maximum load of the indentation test, and varies depending on the test conditions and the material being measured. The ideal depth is just before the needle coke breaks, but when measuring the needle coke of the present invention under the test conditions of this study, 8 to 15 μm is desirable.

[0044] The indentation hardness (HIT) is calculated in accordance with ISO 14577, using the following formula (5) from the maximum load and indentation depth of the indentation test, and is performed using the analysis software attached to the device. HIT indicates a coke structure that is highly resistant to the indenter, as hard coke will not be indented during the test. An example of a hard coke structure is thought to be caused by a disruption in the orientation of the optical anisotropy of the coke structure. [Formula (5)] Indentation hardness HIT (MPa) = Fmax / Ap Here, Fmax represents the maximum load, and Ap represents the projected area where the indenter and the test specimen are in contact.

[0045] The indentation modulus (EIT) is calculated using the analysis software attached to the device based on the slope at the initial stage of unloading from the maximum load of the indentation test, in accordance with ISO 14577, using the following equation (6). This EIT is thought to be due to the fact that coke with a low modulus of elasticity is more easily restored after unloading, and an example of a coke structure with a low modulus of elasticity is the well-developed optical anisotropy of the coke structure. [Formula (6)] Compression modulus EIT(GPa) = (1-(Vs) 2 ) / (1 / Er-1-(Vi) 2 / (Ei) Here, Vs is the Poisson's ratio of the sample, Vi is the Poisson's ratio of the indenter, Er is the decreasing modulus of elasticity at the indentation contact, and Ei is the modulus of elasticity of the indenter.

[0046] The NCSIC structural index for CTE is a measure that indicates the needle coke is more suitable for lower CTE, as its graphite crystallinity is more developed, the proportion of open pores is higher, and the orientation is more uniform. As mentioned above, NCSIC is preferably greater than 25.0, more preferably 27.0 or higher, and even more preferably 29.0 or higher.

[0047] The NCSIP structural index for buffing is an index that indicates needle coke is more suitable for low buffing as it has more open pores, fewer closed pores, a harder structure, and a lower modulus of elasticity. As described above, NCSIP is preferably greater than 5.0, more preferably 6.0 or higher, and even more preferably 7.0 or higher.

[0048] The nitrogen content in green coke and needle coke was measured in accordance with JIS M 8819. The sulfur content in green coke and needle coke was measured in accordance with JIS M 8813.

[0049] For the preparation of CTE and puffing specimens, needle coke was crushed using a jaw crusher, and the 8-16 mesh was sieved off. The sieved and unsieved portions were then mixed and crushed using a hammer crusher, and sieved into 48-200 mesh and 200 mesh or less. These were then blended at particle sizes of 40 wt%, 35 wt%, and 25 wt%, respectively, and kneaded with binder pitch (BP97, manufactured by C-Chem Co., Ltd.). The kneading was performed using a kneader, with a ratio of 30 wt% binder pitch to 100 wt% needle coke, and kneaded at 160°C for 20 minutes to obtain the mixture.

[0050] For puffing, a molded body with a diameter of 20 mm and a length of 100 mm was obtained by molding the kneaded mixture. This molded body was then fired at 900°C, impregnated with impregnation pitch (IP78, manufactured by C-Chem Co., Ltd.), and fired again at 900°C to create a test piece for puffing measurement. Puffing was measured by heating the test specimen in a Tammann furnace under an argon atmosphere at a heating rate of 10°C / min from room temperature to 2550°C, measuring the elongation in the longitudinal direction of the test specimen at 1500°C and 2500°C, and calculating the puffing from the following equation (7). [Formula (7)] Puffing (%) = (L2500 - L1500) / L × 100 Here, L represents the initial length of the specimen, L1500 represents the length at a temperature of 1500°C, and L2500 represents the length at a temperature of 2500°C.

[0051] For CTE, the kneaded material was extruded and molded to a size of 20 mm in diameter and 100 mm in length. The molded body was fired at 900°C, and then graphitized in a Tamman furnace under an argon atmosphere at 2550°C to prepare the test specimen. CTE was measured by determining the average thermal expansion coefficient of the prepared test specimen from room temperature to 500°C. [Examples]

[0052] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0053] Example 1 Coal tar was distilled, and the heavy component, coal tar pitch, was removed by solvent separation to obtain pitch, which was used as the main raw material oil. Coal tar pitch, from which quinoline-insoluble components had been removed in a similar manner, was distilled at atmospheric pressure to obtain a fraction at 300-600°C. This fraction was then batch hydrogenated at 200°C and 4.5 MPa in the presence of a hydrogenation catalyst (stabilized Ni) to obtain the secondary raw material oil. 35 parts by weight of the secondary raw material oil were mixed with 100 parts by weight of the main raw material oil. The mixed raw material oil was coked at 0.6 MPa, with the coking charge temperature gradually increased from 470°C to 530°C, and the steam ratio (amount of water vapor (g) / amount of raw material oil (g)) gradually increased from 0.15 to 0.30 to obtain green coke. The obtained green coke was calcined at 700°C under a nitrogen atmosphere, cooled, and then calcined again at 1400°C to obtain needle coke. CTE and puffing specimens were prepared from this needle coke. Furthermore, the characteristic values ​​of the obtained needle coke and test specimens are shown in Table 1.

[0054] Example 2 Using the same coal tar pitch as in Example 1 as the main raw material, the 300-600°C fraction obtained by atmospheric distillation of coal tar was batch hydrogenated at 200°C and 4.5 MPa in the presence of a hydrogenation catalyst (stabilized Ni) to obtain the secondary raw material oil. 43 parts by weight of the secondary raw material oil were mixed with 100 parts by weight of the main raw material oil. The mixed raw material oil was coked by gradually increasing the coking temperature from 460°C to 550°C, gradually increasing the pressure from 0.5 MPa to 0.65 MPa, and gradually increasing the steam ratio from 0.10 to 0.35 to obtain green coke. The same procedure as in Example 1 was followed thereafter.

[0055] Example 3 Using the same coal tar pitch as in Example 1 as the main raw material oil, the fluid catalytic cracking oil was distilled at atmospheric pressure to obtain a fraction with a boiling point of 300-600°C. This fraction was then batch hydrogenated at a temperature of 250°C and a pressure of 4.5 MPa in the presence of a hydrogenation catalyst (stabilized Ni) to obtain the secondary raw material oil. 100 parts by weight of the main raw material oil and 45 parts by weight of the secondary raw material oil were mixed, the pressure was set to 0.5 MPa, and the coking charge temperature was gradually increased from 470°C to 500°C while the steam ratio was gradually increased from 0.15 to 0.35 to obtain green coke. The same procedure as in Example 1 was followed thereafter.

[0056] Comparative Example 1 In Example 1, coal tar pitch was used as the main raw material, and the 300-600°C fraction obtained by atmospheric distillation of coal tar was used as the secondary raw material. 100 parts by weight of the main raw material and 45 parts by weight of the secondary raw material were mixed and coked under constant conditions of 500°C, 0.4 MPa, and a steam ratio of 0.12 to obtain green coke. The same procedure as in Example 1 was followed thereafter.

[0057] Comparative Example 2 Using the same main raw material oil as in Example 1, a fraction at 300-600°C was obtained by atmospheric distillation of a mixture of 70% by weight of coal tar pitch (used as the main raw material oil in Example 1) and 30% by weight of fluid catalytic cracking oil as the secondary raw material oil. 100 parts by weight of the main raw material oil and 45 parts by weight of the secondary raw material oil were mixed and coked at 490°C, 0.4 MPa, and a steam ratio of 0.12 under constant conditions to obtain green coke. The same procedure as in Example 1 was followed thereafter.

[0058] Comparative Example 3 100 parts by weight of the main raw material oil used in Example 1 was mixed with 100 parts by weight of the auxiliary raw material oil used in Example 1. The mixed raw material oil was coked at 530°C, 0.5 MPa, and a steam ratio of 0.10 under constant conditions to obtain green coke. Thereafter, the same procedure as in Example 1 was carried out.

[0059] Tables 1 and 2 show the types and properties of the raw oils, as well as the characteristics of the green coke and needle coke.

[0060] [Table 1]

[0061] [Table 2]

Claims

1. Low CTE, low puffing needle coke characterized by a structural index for CTE (NCSIC) shown in formula (2) exceeding 25.0 and a structural index for puffing (NCSIP) shown in formula (3) being greater than 5.

0. [Formula (2)] NCSIC=((Lc / d002)+(open pore ratio)) / (σ(θ)) Here, Lc: crystallite size, d002: interplanar spacing, open pore ratio: the ratio of pore volume between 1 and 10 μm in diameter to pore volume of pores with a diameter of 120 μm or less, as measured by mercury porosimetry, and σ(θ): standard deviation of the average orientation angle. [Formula (3)] NCSIP=(open pore amount / closed pore amount)+(HIT / 1000) / EIT Here, HIT represents indentation hardness (MPa) and EIT represents indentation modulus (GPa).

2. The low CTE, low puffing needle coke according to claim 1, wherein the crystallite size Lc is 4.0 to 10.0 nm, the interplanar spacing d002 is 0.340 to 0.350 nm, the open pore ratio is 0.15 to 0.40, and the standard deviation σ(θ) of the average orientation angle is 0.01 to 0.

85.

3. Open pore size: 0.040–0.070 cm ３ The value is / g, and the pore size is 0.001 to 0.015 cm. ３ The low CTE, low puffing needle coke according to claim 1, wherein the density is / g, the indentation hardness HIT is 800 to 1500 MPa, and the indentation modulus EIT is 5.0 to 15.0 GPa.

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