Conductive Eastern manufacturing method

Abstract

This invention provides a method for producing conductive carbon that has superior electrical conductivity compared to commercially available carbon black. [Solution] A method for producing conductive carbon, comprising the steps of: heating desalted coniferous kraft lignin powder in an oxygen-containing gas at 200°C to 350°C and finely grinding it to prepare fine heat-stabilized kraft lignin powder; and heating the fine heat-stabilized kraft lignin powder in an inert gas at 2500°C or higher and finely grinding it.

Description

Technical Field

[0001] The present invention relates to a method for producing conductive carbon.

Background Art

[0002] As conductive carbon materials, carbon black (CB) derived from fossil resources, Ketjen black, acetylene black, carbon nanotubes, etc. are widely known. As other conductive carbon materials, those made from lignocellulosic raw materials such as peat, wood, and coconut shells are known. Also, a method for producing carbonized particles from lignocellulosic materials containing lignin is known (see, for example, Patent Document 1). However, Patent Document 1 does not describe the electrical conductivity of the carbonized particles.

[0003] Lignin (kraft lignin, KL) that can be produced by the kraft method, which is a major pulping method worldwide, is a renewable resource that is only used for energy recovery by incineration. Research examples on the carbonization of hardwood kraft lignin (HKL) have been reported (see, for example, Non-Patent Document 1), but it is difficult to secure hardwood materials. On the other hand, softwoods (e.g., cedar) are abundant in artificial forests in Japan. Hardwood kraft lignin and softwood kraft lignin (SKL) are different substances, and their physical properties (e.g., ease of handling) are also different. Specifically, hardwood kraft lignin thermally melts, while softwood kraft lignin has many condensed structures in the molecule and does not thermally melt. Therefore, hardwood kraft lignin has excellent processability. On the other hand, softwood kraft lignin is relatively difficult to handle and has not been studied so far.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005] [Non-Patent Document 1] J. Rodriguez-Mirasol, T. Cordero, JJ Rodriguez, “High-temperature carbons from kraft lignin”, Science Direct, Volume 34, Issue 1, 1996, Pages 43-52. [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above circumstances, and aims to provide a method for producing conductive carbon that has better electrical conductivity than commercially available carbon black. This will ultimately contribute to energy efficiency. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A step of preparing fine powder of heat-stabilized kraft lignin by heating desalted coniferous kraft lignin powder in an oxygen-containing gas at 200°C to 350°C and then finely grinding it, A method for producing conductive carbon, comprising the steps of heating the fine powder of the heat-stabilized Kraft Lignin in an inert gas to 2500°C or higher and finely grinding it.

[0008] According to the above embodiment, by heating a fine powder of heat-stabilized Kraft Lignin to 2500°C or higher in an inert gas and then finely grinding it, conductive carbon with an electrical conductivity exceeding that of commercially available carbon black can be obtained.

[0009] [2] The method for producing conductive carbon according to [1], wherein the time for heating the desalted coniferous kraft lignin powder at 200°C to 350°C is 30 minutes to 120 minutes.

[0010] According to the above embodiment, by heating the desalted coniferous kraft lignin powder at 200°C to 350°C for 30 minutes to 120 minutes, optimally heat-stabilized kraft lignin can be obtained as a precursor for conductive carbon.

[0011] [3] The method for producing conductive carbon according to [1] or [2], wherein the time for heating the heat-stabilized Kraft Lignin fine powder to 2500°C or higher is 30 minutes or more and 120 minutes or less.

[0012] According to the above embodiment, by heating the fine powder of heat-stabilized Kraft Lignin to 2500°C or higher for 30 minutes to 120 minutes, the desired conductive carbon can be obtained more efficiently. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for producing conductive carbon that has better electrical conductivity than commercially available carbon black. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows the results of measuring the electrical resistance of the conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3. [Figure 2] This figure shows the results of Raman spectroscopy analysis of conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3. [Figure 3] This figure shows the X-ray diffraction results of conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3. [Figure 4] This figure shows the results of X-ray diffraction of conductive carbon obtained in Examples 1 and 2. [Figure 5] This figure shows the particle size distribution of conductive carbon in Example 1. [Figure 6] This figure shows the particle size distribution of conductive carbon in Example 2. [Figure 7] This figure shows the particle size distribution of conductive carbon in Comparative Example 1. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments of the present invention will be described.

[0016] [Method for producing conductive carbon] The method for producing conductive carbon according to this embodiment includes a step of heating the desalted softwood kraft lignin powder in a gas containing oxygen at 200°C or higher and 350°C or lower, and finely pulverizing it to prepare a fine powder of thermally stabilized kraft lignin (hereinafter referred to as the "preparation step"), and a step of heating the fine powder of thermally stabilized kraft lignin in an inert gas at 2500°C or higher and finely pulverizing it (hereinafter referred to as the "heating step").

[0017] The method for producing conductive carbon according to this embodiment may include a step of desalting the softwood kraft lignin powder (hereinafter referred to as the "desalting step"). Further, the method for producing conductive carbon according to this embodiment may use the desalted softwood kraft lignin powder in advance.

[0018] Lignin is one of the main components of wood, a phenolic polymer, and plays a role in adhering fibers in wood. Lignin is removed from wood chips according to the required paper quality. The lignin extracted in the kraft pulp manufacturing process is called kraft lignin. Softwood kraft lignin is the kraft lignin extracted when producing kraft pulp from softwood.

[0019] "Desalting step" The method for desalting the softwood kraft lignin powder is as follows. The softwood kraft lignin powder is added to an aqueous hydrochloric acid solution, stirred at room temperature, and then suction filtered to separate the solid content by filtration. The obtained solid content is thoroughly washed with pure water (the criterion for "thoroughly" is based on whether the washing liquid becomes "neutral"), and freeze-dried to obtain a desalted softwood kraft lignin powder.

[0020] "Preparation step" In the preparation process, desalted coniferous kraft lignin powder is heated in an oxygen-containing gas at a temperature between 200°C and 350°C, and then finely ground to prepare heat-stabilized kraft lignin fine powder. As the oxygen-containing gas, for example, air or oxygen can be used.

[0021] The heating temperature for the coniferous kraft lignin powder is between 200°C and 350°C, preferably between 250°C and 300°C. When the heating temperature is above the lower limit, the crosslinking reaction by oxygen proceeds gradually, and a sufficient thermal stabilization effect can be obtained (eliminating the possibility of particle shape being damaged by glass transition during the subsequent carbonization treatment). When the heating temperature is below the upper limit, the thermal stabilization treatment can be performed while suppressing changes (loss) in particle shape due to glass transition of the sample that may occur under high-temperature heating.

[0022] The average particle size of the desalted coniferous kraft lignin powder is not particularly limited, but is preferably between 10 μm and 200 μm, and more preferably between 50 μm and 100 μm. When the average particle size is above the lower limit, the powder's scattering is reduced, resulting in excellent handling. When the average particle size is below the upper limit, a sufficient thermal stabilization effect can be obtained in a relatively short time, enabling an efficient process.

[0023] The method for heating the desalted coniferous kraft lignin powder at a temperature between 200°C and 350°C is not particularly limited, but for example, a heating method using an electric furnace can be used.

[0024] When heating desalted coniferous kraft lignin powder at 200°C to 350°C, the heating rate is preferably 0.1°C / min to 5°C / min, more preferably 0.1°C / min to 1°C / min, and even more preferably 0.1°C / min to 0.5°C / min. If the heating rate is above the lower limit, the target temperature can be reached in a relatively short time, thus enabling an efficient process. If the heating rate is below the upper limit, changes (loss) in particle shape due to glass transition of the sample that may occur under rapid high-temperature heating can be suppressed, and the difference between the set temperature and the temperature inside the furnace (actual temperature) is reduced, resulting in a uniform thermal stabilization effect. The temperature at which heating of the desalted coniferous kraft lignin powder is started is, for example, room temperature.

[0025] The heating time (holding time) of the desalted coniferous kraft lignin powder at 200°C to 350°C is preferably 30 minutes to 120 minutes, and more preferably 45 minutes to 75 minutes. If the holding time at the heating temperature is above the lower limit, the crosslinking reaction by oxygen proceeds gradually, and a sufficient thermal stabilization effect can be obtained (eliminating the possibility of particle shape being damaged by glass transition during the subsequent carbonization treatment). If the holding time at the heating temperature is below the upper limit, a sufficient thermal stabilization effect can be obtained in a relatively short time, thus enabling an efficient process.

[0026] The heated coniferous kraft lignin (heat-stabilized kraft lignin) powder is finely ground. The method for finely grinding the heat-stabilized kraft lignin powder involves grinding the powder in a mortar and pestle, and collecting the fine powder that passes through a sieve. The resulting fine powder is considered to be the fine powder of heat-stabilized kraft lignin.

[0027] "Heating process" In the heating process, the fine powder of heat-stabilized Kraft Lignin is heated to over 2500°C in an inert gas and then finely ground. Preferably, the heating temperature of the fine powder of heat-stabilized Kraft Lignin is 2800°C or higher. When the heating temperature is above the lower limit, the graphene structure responsible for conductivity is sufficiently formed and developed, and a small amount of graphite structure is also formed, resulting in electrical conductivity exceeding that of commercially available carbon black.

[0028] Examples of inert gases that can be used include nitrogen gas and argon gas.

[0029] The average particle size of the heat-stabilized kraft lignin fine powder is not particularly limited, but is preferably 10 μm to 200 μm, and more preferably 50 μm to 100 μm. When the average particle size is above the lower limit, the powder's scattering is reduced, resulting in excellent handling properties, and conductive carbon can be obtained in good yield. When the average particle size is below the upper limit, a homogeneous carbonization effect can be obtained.

[0030] The method for heating the heat-stabilized Kraft Lignin fine powder to 2500°C or higher is not particularly limited, but for example, a heating method using an electric furnace can be used.

[0031] When heating the fine powder of heat-stabilized kraft lignin to 2500°C or higher, the heating rate is preferably 0.5°C / min to 10°C / min, and more preferably 1°C / min to 5°C / min. If the heating rate is above the lower limit, the target temperature is reached in a relatively short time, thus enabling an efficient process. If the heating rate is below the upper limit, the difference between the set temperature and the temperature inside the furnace (actual temperature) is reduced, resulting in a uniform carbonization effect. The temperature at which heating of the fine powder of heat-stabilized kraft lignin is started is, for example, room temperature, or the temperature of the heat-stabilized kraft lignin obtained by heating the desalted coniferous kraft lignin in the above preparation step.

[0032] The heating time (holding time at a temperature of 2500°C or higher) of the heat-stabilized Kraft Lignin fine powder is preferably 30 minutes to 120 minutes, and more preferably 45 minutes to 75 minutes. If the time is above the lower limit, a sufficient carbonization effect can be obtained. If the time is below the upper limit, a sufficient carbonization effect can be obtained in a relatively short time, thus enabling an efficient process.

[0033] The heated, heat-stabilized Kraft Lignin (conductive carbon) is finely ground. The method for finely grinding conductive carbon involves grinding the conductive carbon powder using a mortar and pestle, and then collecting the fine powder that has passed through a sieve.

[0034] The conductive carbon of this embodiment is obtained through the above steps.

[0035] The resulting conductive carbon primarily has a graphene structure, with some parts having developed into a graphite structure.

[0036] The method for producing conductive carbon according to this embodiment includes the steps of: heating desalted coniferous kraft lignin powder in an oxygen-containing gas at 200°C to 350°C and finely grinding it to prepare fine heat-stabilized kraft lignin powder; and heating the fine heat-stabilized kraft lignin powder in an inert gas from room temperature to 2500°C or higher and finely grinding it. Thus, conductive carbon derived from coniferous kraft lignin can be produced. The obtained conductive carbon has conductivity equivalent to or better than that of carbon black.

[0037] The conductive carbon obtained by the conductive carbon manufacturing method of this embodiment showed a value of 2700 cm in Raman spectroscopy. -1 A 2D band is observed. The 2D band indicates the presence of graphene. Furthermore, in Raman spectroscopy, the conductive carbon was found to have a capacitance of 1350 cm⁻¹. -1 A D-band was detected at 1580cm. -1 A G-band is observed. The ratio of the peak intensity of the D-band to the peak intensity of the G-band (D / G) is 1.5 or less. Furthermore, the conductive carbon obtained by the method for producing conductive carbon in this embodiment shows a peak near 26.0° in wide-angle X-ray diffraction. This peak indicates the presence of a turbostratic (T) structure. In addition, the conductive carbon of Example 1, described later, also shows a peak near 26.5°. This peak indicates the presence of a graphite (G) structure. From the above, it is considered that the conductive carbon in Example 1, described later, is a mixture of graphite and a randomized graphite structure, while the conductive carbon in Example 2, described later, consists only of a randomized graphite structure.

[0038] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Examples]

[0039] 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 the following examples.

[0040] [Examples] Desalted coniferous kraft lignin powder was placed in an electric furnace and heated in air at a heating rate of 0.5°C / min to 250°C, and then maintained at 250°C for 60 minutes to prepare heat-stabilized kraft lignin. The obtained heat-stabilized Kraft lignin was ground in a mortar and pestle, placed in an electric furnace, heated to 2800°C in argon, and maintained at 2800°C for 60 minutes to prepare conductive carbon. The obtained conductive carbon was ground using a mortar and pestle to obtain a fine powder of conductive carbon with an average particle size of 0.77 ± 0.19 μm. The heating rate when heating the fine powder of heat-stabilized Kraft Lignin was set to 5°C / min.

[0041] [Example 2] Conductive carbon in the form of fine powder with an average particle size of 0.80 ± 0.22 μm was obtained in the same manner as in Example 1, except that the fine powder of heat-stabilized Kraft Lignin was heated to 2500°C and held at 2500°C for 60 minutes.

[0042] [Comparative Example 1] Conductive carbon in the form of fine powder with an average particle size of 0.84 ± 0.17 μm was obtained in the same manner as in Example 1, except that the fine powder of heat-stabilized Kraft Lignin was heated to 2000°C and held at 2000°C for 60 minutes.

[0043] [Comparative Example 2] Conductive carbon in powder form was obtained in the same manner as in Example 1, except that the fine powder of heat-stabilized Kraft Lignin was heated to 1300°C and held at 1300°C for 60 minutes.

[0044] [Comparative Example 3] Fine powder of heat-stabilized Kraft Lignin was placed in an electric furnace and heated to 900°C in nitrogen, and the temperature was maintained at 900°C for 60 minutes to obtain fine powdered conductive carbon. The heating rate when heating the fine powder of heat-stabilized Kraft Lignin was set to 3°C / min.

[0045] [evaluation] "Evaluation of the conductivity of conductive carbon" The conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3 was sandwiched between aluminum foil and set in an electrochemical measurement cell. An applied voltage of 10 mV was applied, and the electrical resistance (complex real term) in the frequency range of 400 kHz to 600 kHz was measured. Electrical conductivity was calculated from the obtained electrical resistance. Note that electrical conductivity is the reciprocal of electrical resistance. The results are shown in Figure 1. As shown in Figure 1, the electrical conductivity of commercially available carbon black used as a positive control was 0.21 Scm. -1 In contrast, the electrical conductivity of the conductive carbon in the example is 0.54 Scm. -1 This was more than twice the electrical conductivity of commercially available carbon black. Furthermore, the electrical conductivity of the conductive carbon in Example 2 was 0.22 Scm. -1 The electrical conductivity was equivalent to or better than that of commercially available carbon black.

[0046] "Raman spectroscopy analysis of conductive carbon" Raman spectroscopy was performed on the conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3. A Raman spectrometer (product name: Renishaw inVia™, manufactured by Renishaw) was used for the Raman spectroscopy. The results are shown in Figure 2. The results shown in Figure 2 indicate that the conductive carbon in the example has a graphene structure, and that the higher the temperature of the heating process, the fewer defects and more homogeneous the structure formed.

[0047] "X-ray diffraction of conductive carbon" Wide-angle X-ray diffraction was performed on the conductive carbon obtained in Examples 1-2 and Comparative Examples 1-3. A wide-angle X-ray diffractometer (product name: SmartLab, manufactured by Rigaku Corporation) was used for wide-angle X-ray diffraction. The results are shown in Figures 3 and 4. Figure 4 is an enlarged view of a portion of the profiles of KL-2800 (Example 1) and KL-2500 (Example 2) shown in Figure 3. The results shown in Figures 3 and 4 suggest that the conductive carbon obtained in Examples 1 and 2 mainly consisted of a randomly layered graphite structure, with only Example 1 exhibiting a structure in which a portion had developed into a graphite structure.

[0048] "Particle size distribution of conductive carbon" The particle size distribution of the conductive carbon obtained by the conductive carbon manufacturing method of this embodiment was measured using a digital microscope (product name: VHX-970F, manufactured by Keyence Corporation). The results are shown in Figures 5 to 7. Figure 5 shows the particle size distribution of conductive carbon from Example 1, Figure 6 shows the particle size distribution of conductive carbon from Example 2, and Figure 7 shows the particle size distribution of conductive carbon from Comparative Example 1. The average particle size and standard deviation were, respectively, 0.77 ± 0.19 μm for Example 1, 0.80 ± 0.22 μm for Example 2, and 0.84 ± 0.17 μm for Comparative Example 1. The average particle size listed in the catalog of the commercially available carbon black (CB; manufactured by Thermo Fisher Scientific) used as a reference sample was 0.042 μm.

Claims

1. The process involves heating desalted coniferous kraft lignin powder in an oxygen-containing gas at a temperature between 200°C and 350°C, and then finely grinding it to prepare heat-stabilized kraft lignin fine powder. A method for producing conductive carbon, comprising the steps of heating the fine powder of the heat-stabilized Kraft Lignin in an inert gas to 2500°C or higher and finely grinding it.

2. The method for producing conductive carbon according to claim 1, wherein the time for heating the desalted coniferous kraft lignin powder at 200°C to 350°C is 30 minutes to 120 minutes.

3. The method for producing conductive carbon according to claim 1, wherein the time for heating the heat-stabilized Kraft Lignin fine powder to 2500°C or higher is 30 minutes or more and 120 minutes or less.

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