Method for preparing graphene from graphite

Abstract

The present invention relates to a method for obtaining graphene from a graphite raw material, comprising: a purification step of obtaining purified graphite having a purity of 99.5% or higher by removing impurities from the graphite raw material in a sulfuric acid-based solvent using a Taylor-Couet reactor; and an exfoliation step of converting the purified graphite into graphene in an organic solvent and an ionic liquid-based solvent using a Taylor-Couet reactor.

Description

Technology Field

[0001] The present invention relates to a method for obtaining graphene from a graphite raw material. Background Technology

[0002] Although large quantities of waste carbon resources such as anthracite coal, graphite ore, waste cathode materials, and waste graphite refractory plates are being generated, the development of technologies for resource utilization is lacking.

[0003] To utilize waste carbon resources, it is necessary to develop refining technologies as well as technologies to produce high-value-added raw materials from refined raw materials.

[0004] Furthermore, while eco-friendly processes are required for the refining process and the production of high-value-added raw materials, conventional technologies pose a significant environmental burden due to the large-scale use of sulfuric acid and hydrofluoric acid. Prior art literature

[0005] Korean Patent Registration No. 10-2876469 (Publication Date: Oct. 27, 2025) The problem to be solved

[0006] The object of the present invention is to provide a method for obtaining graphene from a graphite raw material. means of solving the problem

[0007] The objective of the present invention is achieved by a method for obtaining graphene from a graphite raw material, comprising: a purification step of removing impurities from the graphite raw material in a sulfuric acid-based solvent using a Taylor-Couet reactor to obtain purified graphite having a purity of 99.5% or higher; and an exfoliation step of converting the purified graphite into graphene in an organic solvent and an ionic liquid-based solvent using a Taylor-Couet reactor.

[0008] Inert gas can be injected in both the purification step and the peeling step.

[0009] The above inert gas may include carbon dioxide.

[0010] The concentration of the aqueous sulfuric acid solution used in the above purification step is 1.5 to 4.0 M, and the mixture of the pretreated graphite raw material and the aqueous sulfuric acid solution can be ultrasonically dispersed before being introduced into the Taylor-Coutet reactor.

[0011] The above purification step can be performed for 100 to 150 minutes at 1500 to 3000 rpm, 10 to 50℃, a solid-liquid ratio of 7 to 15 mg / ml, and a carbon dioxide flow rate of 300 to 700 cc / min.

[0012] The method further includes a step of pre-treating the graphite raw material before the purification, wherein the pre-treatment step uses an aqueous sulfuric acid solution with a concentration of 0.3 to 1.2 M and the solid-to-liquid ratio may be 7 to 15 mg / ml.

[0013] The above organic solvent may be one of N-Methyl-2-Pyrrolidone (NMP), DMF (N,N-Dimethylformamide), DMAc (Dimethylacetamide), and DMSO (Dimethyl sulfoxide), and the above ionic liquid may be one of [EMIM][PF6](1-ethyl-3-methylimidazolium hexafluorophosphate), [EMIM][BF4], [EMIM][SO4], and [TMA][BF4](Tetramethylammonium tetrafluoroborate).

[0014] The concentration of the above ionic liquid may be 4 to 6 wt% relative to the total solvent.

[0015] In the above peeling step, the reaction time may be 80 to 160 minutes and the solid-to-liquid ratio may be 15 to 25 mg / ml.

[0016] The purified solution mixed with the above-mentioned purified graphite and solvent can be ultrasonically dispersed for 5 to 15 minutes before being introduced into a Taylor-Coute reactor.

[0017] The method further includes the step of sequentially performing low-speed centrifugation and high-speed centrifugation on the graphene, wherein the low-speed centrifugation is performed at 20 to 600XG and the high-speed centrifugation can be performed at 3,000 to 7,000XG.

[0018] The above graphite raw material may include at least one of anthracite, waste cathode material, waste graphite refractory shell, and graphite ore. Effects of the invention

[0019] According to the present invention, a method for obtaining graphene from a graphite raw material is provided. Brief explanation of the drawing

[0020] FIG. 1 shows a flowchart of purification in a method according to one embodiment of the present invention, and FIG. 2 shows a flowchart of the peeling process in a method according to an embodiment of the present invention, and FIG. 3 is an image of the unused graphite raw material used in the present invention, and FIG. 4 schematically illustrates a purification reaction in a method according to one embodiment of the present invention, and FIG. 5 schematically illustrates the peeling reaction in a method according to one embodiment of the present invention, and Figure 6 shows the purification efficiency according to the solid-liquid ratio in the pretreatment of the purification experimental example of the present invention, and Figure 7 shows the purification efficiency according to the sulfuric acid concentration in the pretreatment of the purification experimental example of the present invention, and Figure 8 shows the purification efficiency according to ultrasonic treatment in the pretreatment of the purification experimental example of the present invention, and FIG. 9 shows the purification efficiency according to the type of reactor in the purification experimental example of the present invention, and Figure 10 shows the purification efficiency according to the reaction time of the TC reaction in the purification experimental example of the present invention, and Figure 11 shows the purification efficiency according to the temperature of the TC reaction in the purification experimental example of the present invention, and Figure 12 shows the purification efficiency according to the RPM of the TC reaction in the purification experimental example of the present invention, and Figure 13 shows the purification efficiency according to the solid-liquid ratio of the TC reaction in the purification experimental example of the present invention, and Figure 14 shows the purification efficiency according to the sulfuric acid concentration of the TC reaction in the purification experimental example of the present invention, and FIG. 15 shows the purification efficiency according to the type of inert gas in the TC reaction in the purification experimental example of the present invention, and Figure 16 shows the purification efficiency according to the CO2 gas flow rate of the TC reaction in the purification experimental example of the present invention, and FIGS. 17a and 17b are SEM images of graphite ore before and after purification in the purification experimental example of the present invention, and FIGS. 18a and 18b are SEM images of anthracite coal before and after purification in the purification experimental example of the present invention, and FIGS. 19a and 19b are SEM images of a waste graphite refractory case before and after purification in the purification experimental example of the present invention, and FIGS. 20a and 20b are SEM images of waste cathode material before and after purification in the purification experimental example of the present invention, and FIG. 21 is an XRD graph of purified graphite in the purification experimental example of the present invention, and FIG. 22 is an XPS graph of purified graphite in the purification experimental example of the present invention, and FIGS. 23 to 26 are graphs of particle size analysis of purified graphite in the purification experimental examples of the present invention, and FIG. 27 shows the graphene yield according to the solvent of the TC reaction in the exfoliation experimental example of the present invention, and FIG. 28 shows the graphene yield according to the concentration of the ionic liquid in the TC reaction in the exfoliation experimental example of the present invention, and FIG. 29 shows the graphene yield according to the reaction time of the TC reaction in the exfoliation experimental example of the present invention, and FIG. 30 shows the graphene yield according to the solid-liquid ratio of the TC reaction in the exfoliation experimental example of the present invention, and FIG. 31 shows the graphene yield according to the type of inert gas in the TC reaction in the exfoliation experimental example of the present invention, and FIG. 32 shows the graphene yield according to the CO2 gas flow rate of the TC reaction in the exfoliation experimental example of the present invention, and FIG. 33 is an XPS graph of graphene obtained in the exfoliation experimental example of the present invention, and FIG. 34 is an SEM image of graphene obtained in an exfoliation experimental example of the present invention, and FIG. 35 is a TEM image of graphene obtained in an exfoliation experimental example of the present invention, and Figures 36a and 36b are BET graphs for purified graphite and graphene obtained in the experimental examples of the present invention, respectively. Specific details for implementing the invention

[0021] The present invention relates to obtaining graphene from unused graphite raw materials and includes a purification method and an exfoliation method.

[0022] The present invention will be described in more detail below with reference to the drawings.

[0023] Unless otherwise noted in the following description, % refers to weight %.

[0024] The attached drawings are merely examples illustrated to further explain the technical concept of the present invention, and therefore the concept of the present invention is not limited to the attached drawings.

[0025] FIG. 1 shows a flowchart of purification in a method according to one embodiment of the present invention, FIG. 2 shows a flowchart of exfoliation in a method according to one embodiment of the present invention, FIG. 3 is an image of an unused graphite raw material used in the present invention, FIG. 4 schematically shows a purification reaction in a method according to one embodiment of the present invention, and FIG. 5 schematically shows an exfoliation reaction in a method according to one embodiment of the present invention.

[0026] The purification and exfoliation method according to the present invention includes purification (S11 to S15) shown in FIG. 1 and exfoliation (S21 to S24) shown in FIG. 2. In purification, high-purity purified graphite is produced from low-grade graphite raw materials, and in exfoliation, high-quality graphene is produced from high-purity purified graphite. However, the high-purity purified graphite produced in the purification method of the present invention may be used for other purposes, and in the exfoliation method of the present invention, high-purity purified graphite produced by other methods may be used.

[0027] In the purification process, the low-grade graphite raw material is first crushed and acid-treated (S11).

[0028] As shown in FIG. 3, low-grade graphite raw materials may include natural graphite (raw ore), anthracite, waste graphite refractory plates, and waste cathode materials, but are not limited thereto. Low-grade graphite raw materials may be referred to as unused graphite raw materials or graphite raw materials.

[0029] Grinding can be performed using various methods to convert graphite raw materials into powder form.

[0030] Acid treatment can be performed by mixing the crushed graphite raw material with an aqueous sulfuric acid solution, dispersing the solution using ultrasound, and then stirring.

[0031] The solid-to-liquid ratio in acid treatment may be 7 to 15 mg / ml, 6 to 18 mg / ml, or 8 to 12 mg / ml. Ultrasonic dispersion may be performed for 5 to 30 minutes, and stirring may be performed for 5 to 30 minutes at 100 to 500 rpm. Ultrasonic dispersion and stirring may be performed at 10 to 50°C, 10 to 40°C, 15 to 30°C, or room temperature.

[0032] The sulfuric acid concentration may be 0.3 to 1.2 M, 0.8 to 1.2 M, or 0.9 to 1.1 M.

[0033] Afterwards, the pre-treated graphite raw material is prepared by separating the solid and liquid, washing, and drying (S12).

[0034] Solid-liquid separation can be performed using a vacuum filtration device, etc. Deionized water and ethanol can be used for washing, and drying can be performed under vacuum conditions at 100 to 250°C for 4 to 8 hours.

[0035] Pretreatment is performed to remove electrolytes, binders, glassy and fluorinated impurities that are not removed by acid leaching, and to make them easier to dissolve in sulfuric acid.

[0036] Next, a raw material solution is prepared by mixing the pretreated graphite raw material and an aqueous sulfuric acid solution, and then dispersed (S13).

[0037] The solid-liquid ratio of the graphite raw material and the aqueous sulfuric acid solution may be 7 to 15 mg / ml, 6 to 18 mg / ml, or 8 to 12 mg / ml, and the concentration of the aqueous sulfuric acid solution may be 1.5 to 4.0 M, 2.0 to 4.0 M, or 2.5 to 3.5 M.

[0038] The raw material solution is dispersed by ultrasound for 5 to 15 minutes at 10 to 50°C, 10 to 40°C, 15 to 30°C, or room temperature.

[0039] Sulfuric acid is a strong acidic liquid compound that dissolves and removes impurities (such as metal ions), and is subject to weaker treatment regulations compared to nitric acid or hydrofluoric acid. Sulfuric acid is used in both pretreatment and purification, and the concentration in purification can be 2 to 10 times higher than the concentration in pretreatment.

[0040] Then, the dispersed raw material solution is introduced into a TC reactor and purified while injecting an inert gas (S14).

[0041] A schematic diagram of this step is shown in Fig. 4.

[0042] The TC reactor may be made of stainless steel, but is not limited to this, and may have a radius ratio of 0.85 to 0.95 and an aspect ratio of 2.0 to 6.0. The volume may be 0.5 to 5 L, and the gap may be 0.6 to 6 cm. In addition, the temperature can be controlled using a constant temperature bath.

[0043] The TC reactor conditions may be such that the time is 100 to 150 minutes, 80 to 200 minutes, or 110 to 130 minutes, and the temperature is 10 to 50°C, 10 to 40°C, 15 to 30°C, or room temperature. The RPM may be 1500 to 3000 or 1800 to 2200.

[0044] In the TC reaction, an inert gas is introduced to utilize a high-shear flow, and in particular, carbon dioxide can be introduced. The flow rate of carbon dioxide can be 300 to 700 cc / min, 200 to 800 cc / min, or 400 to 600 cc / min.

[0045] Acid ions are rapidly inserted into the graphite raw material by the shear force of the fluidized bed reactor (TC reactor), and the rapid penetration of acid ions improves the impurity purification efficiency.

[0046] Next, the refined graphite raw material is separated into solid and liquid phases, washed, and dried to obtain high-purity refined graphite (S15).

[0047] Solid-liquid separation can be performed using a vacuum filtration device, etc. Deionized water and ethanol can be used for washing, and drying can be performed under vacuum conditions at 100 to 250°C for 4 to 8 hours.

[0048] The purity of the refined graphite may be 99.5% by weight to 99.99% by weight or 99.6% by weight to 99.99% by weight.

[0049] In the exfoliation step, first, a purified solution is dispersed by mixing purified graphite with a mixed solvent (an organic solvent and an ionic liquid) (S21).

[0050] Polar non-protic organic solvents can be used as organic solvents. Polar non-protic organic solvents have high dielectric constants and surface energies similar to graphene / graphite, so they provide good surface energy matching, which can improve dispersion stability after exfoliation. In particular, cyclic amide-based polar solvents or N-alkyl pyrillidone can be used.

[0051] Specifically, one of N-Methyl-2-Pyrrolidone (NMP), DMF (N,N-Dimethylformamide), DMAc (Dimethylacetamide), and DMSO (Dimethyl sulfoxide) may be used.

[0052] NMP is an organic solvent with a high boiling point and low volatility. It possesses surface energy similar to graphite and stabilizes the surface of exfoliated graphene. Its high viscosity results in high shear force transfer efficiency, and its low reactivity with graphite prevents graphite damage.

[0053] Ionic liquids (ILs) are salts that are in a liquid state at room temperature. Due to their high thermal / chemical stability and strong ionic interactions, they rapidly penetrate between layers within the interlayer bonds of graphite, thereby increasing exfoliation efficiency.

[0054] Specifically, one of [EMIM][PF6](1-ethyl-3-methylimidazolium hexafluorophosphate), [EMIM][BF4], [EMIM][SO4], and [TMA][BF4](Tetramethylammonium tetrafluoroborate) can be used.

[0055] In the mixed solvent, the ionic liquid may be 4 to 6 weight%, 3 to 7 weight%, or 4.5 to 5.5 weight%.

[0056] In dispersion, the purified solution is dispersed by ultrasound for 5 to 15 minutes at 10 to 50°C, 10 to 40°C, 15 to 30°C, or room temperature.

[0057] Next, the purified solution is introduced into the TC reactor and stripping is performed while injecting an inert gas (S22).

[0058] A schematic diagram of this step is shown in Fig. 5. Exfoliation of the graphite layer is induced by a high shear flow, and the solid-liquid separated purified graphite is dissolved in NMP to improve dispersion stability.

[0059] The TC reactor can use a reactor with the same specifications as the purification process.

[0060] The reaction time may be 30 to 180 minutes, 80 to 160 minutes, 70 to 170 minutes, or 100 to 140 minutes, the RPM may be 1000 to 5000 or 2000 to 4000, and the temperature may be 10 to 50℃, 10 to 40℃, 15 to 30℃ or room temperature.

[0061] In the TC reaction in the separation process, an inert gas is introduced to utilize a high-shear flow, and in particular, carbon dioxide can be introduced. The flow rate of carbon dioxide can be 100 to 500 cc / min, 300 to 700 cc / min, 200 to 800 cc / min, or 400 to 600 cc / min.

[0062] Inert gases, such as carbon dioxide, are gases that are difficult to chemically react with other elements; they suppress crystal structure defects caused by oxidation throughout the graphite purification and exfoliation process, increase the efficiency of impurity removal, and create an environment that facilitates the breakdown of graphite's interlayer bonds during the exfoliation process. In addition to carbon dioxide, nitrogen or argon gases may be used.

[0063] Afterwards, the quality of the graphene is improved using centrifugation (S23).

[0064] In the centrifugation process, low-speed centrifugation and high-speed centrifugation are performed sequentially on the exfoliated graphene.

[0065] Low-speed centrifugation is performed at 20 to 600XG or 200 to 500XG for 5 to 30 minutes or 10 to 20 minutes to remove unexfoliated graphite through solid-liquid separation and obtain the supernatant (graphene).

[0066] High-speed centrifugation of the supernatant is performed at 3,000 to 7,000XG or 4,000 to 6,000XG for 10 to 180 minutes or 60 to 90 minutes to remove damaged graphene and carbon fragments to obtain high-quality graphene.

[0067] Finally, washing, solid-liquid separation, and drying are performed (S24).

[0068] Washing is performed by washing the obtained graphene in the order of IPA (isopropyl alcohol), acetone, and ethanol to remove residual organic solvent. Specifically, the graphene is mixed with IPA and mixed in a ball mill for 3 to 10 minutes to wash away the remaining organic solvent in the graphene, and then washed in the same manner using acetone and ethanol.

[0069] Solid-liquid separation can be performed using a vacuum filtration device, etc. Drying can be performed under vacuum conditions at 100 to 250°C for 4 to 8 hours.

[0070] The present invention will be explained in detail through the following experimental examples.

[0071] The TC reactor used in the experiment is made of stainless steel, has a radius ratio of 0.92 and an aspect ratio of 2.3. Its volume is 0.6L and its gap is 0.68cm. In addition, the temperature can be controlled using a thermostatic bath.

[0072] Purification-Pretreatment. Variance Experiment on Pretreatment of Unused Graphite Raw Material (Solid-to-Liquid Ratio)

[0073] A variable experiment on high-liquidity ratios was conducted under the following conditions.

[0074] Graphite solid-to-liquid ratio: 1 to 20 mg / ml

[0075] Sulfuric acid concentration: 1M

[0076] Cleaning conditions: Deionized water 500ml / Ethanol 500ml

[0077] Sonication (ultrasonic dispersion): 15 min (O)

[0078] Stirring time (300 RPM): 15 min

[0079] Graphite purity was calculated after graphite purity analysis through TGA analysis, and purity was calculated through the residual material flame-retardant residue (ash) remaining after maintaining at 1,000℃ for 2 hours at a heating rate of 10℃ / min.

[0080] The calculation formula is as follows.

[0081]

[0082] As shown in Table 1 and Figure 6, it was confirmed through experiments that the pretreatment purification efficiency drops sharply when the solid-to-liquid ratio (graphite concentration) increases to 20 mg / ml or higher, and the optimal condition is determined to be 10 mg / ml.

[0083]

[0084]

[0085] Purification-Pretreatment. Variance Experiment on Pretreatment of Unused Graphite Raw Material (Sulfuric Acid Concentration)

[0086] The sulfuric acid concentration was varied under the following conditions.

[0087] Graphite solid-to-liquid ratio: 10 mg / ml

[0088] Sulfuric acid concentration: 0.1 to 1 M

[0089] Cleaning conditions: Deionized water 500ml / Ethanol 500ml

[0090] Sonication (ultrasonic dispersion): 15 min (O)

[0091] Stirring time (300 RPM): 15 min

[0092] As shown in Table 2 and Figure 7, when comparing the pretreatment purification efficiency according to the concentration of sulfuric acid (0.1 to 1 M) used for pretreatment, it was found that the purification efficiency increased as the sulfuric acid concentration increased, and the purification efficiency was highest at a concentration of 1 M.

[0093] Table 2

[0094]

[0095] Purification-Pretreatment. Variance Experiment on Pretreatment of Unused Graphite Raw Material (Sonication)

[0096] The effect of ultrasonic treatment was verified under the following conditions.

[0097] Graphite solid-to-liquid ratio: 10 mg / ml

[0098] Sulfuric acid concentration: 1M

[0099] Cleaning conditions: Deionized water 500ml / Ethanol 500ml

[0100] Sonication (ultrasonic dispersion): 15 min (O / X)

[0101] Stirring time (300 RPM): 15 min

[0102] As shown in Table 3 and Figure 8, when comparing the pretreatment purification efficiency according to whether ultrasonic treatment (dispersion) was performed during the pretreatment process, it was confirmed that the purification efficiency was higher when dispersion treatment was performed.

[0103] Table 3

[0104]

[0105] Purification-TC Reaction. Variance Experiment on Unutilized Graphite TC Fluid Purification Process (Reactor Type)

[0106] The effects according to the type of reactor were verified under the following conditions.

[0107] Reactor Type: Batch / Rotor-stator / TC

[0108] Reaction time: 1 hr (60 min)

[0109] Reaction speed: 1,000 RPM

[0110] Sodium-to-liquid ratio: 10 mg / ml

[0111] Sulfuric acid concentration: 1M

[0112] Reaction temperature: 25 ℃

[0113] As shown in Table 4 and Figure 9, it was confirmed that the efficiency of TC purification is higher when purified under the same conditions as the Batch / rotor-stator method used for graphite purification in the prior art.

[0114] Table 4

[0115]

[0116] Purification-TC Reaction. Variance Experiment on Unused Graphite TC Flow Purification Process (Reaction Time)

[0117] The effect of reaction time was verified under the following conditions.

[0118] Reaction time: 30 to 180 min

[0119] Reaction temperature: 25 ℃

[0120] Reaction speed: 1,000 RPM

[0121] Sodium-to-liquid ratio: 10 mg / ml

[0122] Sulfuric acid concentration: 1M

[0123] As shown in Table 5 and Figure 10, it was confirmed that purification efficiency increases as reaction time increases, and that the 120 min condition has the highest purification efficiency with no significant change thereafter.

[0124] Table 5

[0125]

[0126] Purification-TC Reaction. Variation Experiment on Unutilized Graphite TC Fluid Purification Process (Reaction Temperature)

[0127] The effect of reaction temperature was verified under the following conditions.

[0128] Reaction time: 120 min

[0129] Reaction temperature: 10 to 60 ℃

[0130] Reaction speed: 1,000 RPM

[0131] Sodium-to-liquid ratio: 10 mg / ml

[0132] Sulfuric acid concentration: 1M

[0133] As shown in Table 6 and Figure 11, the purification efficiency according to the reaction temperature was confirmed, and since there was no significant difference from the reaction conditions at room temperature, sufficiently high purification efficiency was shown even at room temperature.

[0134] Table 6

[0135]

[0136] Purification-TC Reaction. Variance Experiment (rpm) on Unutilized Graphite TC Flow Purification Process

[0137] The effect according to rpm was verified under the following conditions.

[0138] Reaction time: 120 min

[0139] Reaction temperature: 25 ℃

[0140] Reaction speed: 500 to 3,000 RPM

[0141] Sodium-to-liquid ratio: 10 mg / ml

[0142] Sulfuric acid concentration: 1M

[0143] As shown in Table 7 and Figure 12, experiments were conducted according to reaction rate, and the highest purification efficiency was confirmed at 2,000 RPM. It was also confirmed that when the speed increased beyond this level, turbulence occurred within the TC flow, causing the purification efficiency to decrease.

[0144] Table 7

[0145]

[0146] Purification-TC Reaction. Variance Experiment (Solid-Liquid Ratio) of Unutilized Graphite TC Fluid Purification Process

[0147] The effect of high costs was confirmed under the following conditions.

[0148] Reaction time: 120 min

[0149] Reaction temperature: 25 ℃

[0150] Response speed: 2,000 RPM

[0151] Solid-to-liquid ratio: 1 to 20 mg / ml

[0152] Sulfuric acid concentration: 1M

[0153] As shown in Table 8 and Figure 13, the purification efficiency increases as the concentration of graphite in the sulfuric acid solution decreases, and experimental results showed that there was no significant difference in purification efficiency up to a concentration of 10 mg / ml, and that the purification efficiency decreased sharply from 20 mg / ml or higher.

[0154] Table 8

[0155]

[0156] Purification-TC Reaction. Variance Experiment of Unutilized Graphite TC Fluid Purification Process (Sulfuric Acid Concentration)

[0157] The effect of sulfuric acid concentration was verified under the following conditions.

[0158] Reaction time: 120 min

[0159] Reaction temperature: 25 ℃

[0160] Response speed: 2,000 RPM

[0161] Sodium-to-liquid ratio: 10 mg / ml

[0162] Sulfuric acid concentration: 0.5 to 3 M

[0163] As shown in Table 9 and Figure 14, the graphite purification efficiency according to sulfuric acid concentration was verified through experiments, and it was confirmed that the purification efficiency increased as the concentration of sulfuric acid increased, and the highest purity was confirmed in 3M sulfuric acid.

[0164] Table 9

[0165]

[0166] Purification-TC Reaction. Variance Experiment on Unutilized Graphite TC Fluid Purification Process (Types of Inert Gases)

[0167] The effects of the type of inert gas were verified under the following conditions.

[0168] Reaction time: 120 min

[0169] Reaction temperature: 25 ℃

[0170] Response speed: 2,000 RPM

[0171] Sodium-to-liquid ratio: 10 mg / ml

[0172] Sulfuric acid concentration: 3 M

[0173] Gas Type: CO2 / N2 / Ar

[0174] Gas flow rate: 100 cc / min

[0175] As shown in Table 10 and Figure 15, the results confirmed that CO2 gas is most effective in increasing the graphite purification efficiency.

[0176] Table 10

[0177]

[0178] Purification-TC Reaction. Variability Experiment of Unused Graphite TC Fluid Purification Process (CO2 Gas Flow Rate)

[0179] The effect of CO2 gas flow rate was verified under the following conditions.

[0180] Reaction time: 120 min

[0181] Reaction temperature: 25 ℃

[0182] Response speed: 2,000 RPM

[0183] Sodium-to-liquid ratio: 10 mg / ml

[0184] Sulfuric acid concentration: 3 M

[0185] Gas Type: CO2

[0186] Gas flow rate: 100 to 500 cc / min

[0187] As shown in Table 11 and Figure 16, it was confirmed that all four types of graphite raw materials had a purity of 99.5% or higher at a flow rate of 500 cc / min.

[0188]

[0189]

[0190] Analysis of purified graphite. SEM analysis of high-purity graphite after purification of underutilized graphite.

[0191] Figures 17a and 17b are SEM images of raw graphite ore before and after purification, and Tables 12 and 13 are the chemical composition of raw graphite ore before and after purification. The chemical composition of the graphite surface was analyzed by averaging 50 graphite surface images using SEM-EDS analysis. The surface chemical composition after purification was confirmed by comparing the same average values ​​before and after purification.

[0192] The purification conditions are as follows.

[0193] Reaction time: 120 min

[0194] Reaction temperature: 25 ℃

[0195] Response speed: 2,000 RPM

[0196] Sodium-to-liquid ratio: 10 mg / ml

[0197] Sulfuric acid concentration: 3 M

[0198] Table 12

[0199]

[0200]

[0201]

[0202] Figures 18a and 18b are SEM images of anthracite coal before and after purification, and Tables 14 and 15 are the chemical composition of anthracite coal before and after purification.

[0203]

[0204]

[0205]

[0206]

[0207] Figures 19a and 19b are SEM images of waste graphite refractory plates before and after purification, and Tables 16 and 17 are the chemical composition of waste graphite refractory plates before and after purification.

[0208] Table 16

[0209]

[0210] Table 17

[0211]

[0212] Figures 20a and 20b are SEM images of the waste cathode material before and after purification, and Tables 18 and 19 are the chemical composition of the waste cathode material before and after purification. The purification conditions and chemical composition analysis methods are the same as those for the graphite ore.

[0213]

[0214]

[0215]

[0216]

[0217] The surface chemical composition of four types of purified graphite purified under optimized conditions was analyzed via SEM-EDS analysis to confirm whether it was similar to the calculated graphite purity. As a result, the purity was confirmed to be 99.5% or higher.

[0218] Analysis of purified graphite. ICP analysis of high-purity graphite after purification of underutilized graphite.

[0219] Table 20 shows the results of ICP analysis after purification for four types of unused graphite.

[0220] Through ICP analysis of the graphite obtained after purification, the impurity concentration dropped below the detection limit as shown in Table 20, and when the filtrate was analyzed together with the graphite after purification, the impurity concentration was found to be almost similar to that of the raw material, confirming that the impurities were effectively purified and dissolved and removed in the solvent.

[0221] Table 20

[0222]

[0223] Analysis of purified graphite. XRD / XPS analysis of high-purity graphite after purification of underutilized graphite.

[0224] Figure 21 shows the results of XRD analysis after purification for four types of unused graphite, and Figure 22 shows the results of XPS analysis.

[0225] As shown in FIG. 21, the same crystal structure and elemental composition as high-purity commercial graphite is confirmed. As the purity increased to 99.5% or higher, the diffraction peak (26.3) of the graphite was clearly observed, similar to commercial graphite.

[0226] As shown in Figure 22, XPS peaks similar to those of high-purity commercial graphite were observed in the purified graphite. Since the C 1s intensity is high and the O 1s peak intensity is similar to that of graphite with 99.99% purity, it is determined that there are fewer defects in the graphite due to oxidation during the graphite purification process.

[0227] Analysis of purified graphite. Particle size analysis of high-purity graphite after purification of underutilized graphite.

[0228] Figures 23 to 26 show the particle size analysis of four types of unused graphite after purification.

[0229] Particle size analysis of graphite with a purity of 99.5% or higher obtained after purification confirmed that the average particle size is 10㎛ or less.

[0230] Exfoliation TC Reaction. Variation Experiment on Unutilized Graphite TC Flow Exfoliation Process (Solvent Change)

[0231] Changes in the effect according to changes in the solvent were observed under the following conditions.

[0232] Reaction time: 120 min

[0233] Reaction temperature: 25 ℃

[0234] Response speed: 2,000 RPM

[0235] Solid-liquid ratio: 0.1 mg / ml

[0236] Solvent Type: Organic solvent / Ionic liquid / Aqueous acid-base solution

[0237] The graphene yield was calculated based on the mass of the final graphene obtained by drying the solution acquired after exfoliation, after filtering out unexfoliated graphite and damaged carbon particles through centrifugation; the calculation formula is as follows.

[0238]

[0239] As shown in Table 21 and Figure 27, the highest yield was confirmed in the solvent used by mixing the ionic liquid [EMIM][PF6] and the organic solvent NMP.

[0240] Table 21

[0241]

[0242] Exfoliation TC Reaction. Variance Experiment on Unused Graphite TC Flow Exfoliation Process (Ionic Liquid Concentration)

[0243] Changes in the effect according to changes in ionic liquid concentration were observed under the following conditions.

[0244] Reaction time: 120 min

[0245] Reaction temperature: 25 ℃

[0246] Response speed: 2,000 RPM

[0247] Solid-liquid ratio: 0.1 mg / ml

[0248] Solvent concentration: [EMIM][PF6] + NMP

[0249] Experiments were conducted to determine the yield according to the concentration of the ionic liquid used to exfoliate high-purity graphite, and as shown in Table 22 and Figure 28, the highest yield was confirmed at 5 wt%.

[0250] Table 22

[0251]

[0252] Exfoliation TC Reaction. Variation Experiment on Unused Graphite TC Flow Exfoliation Process (Reaction Time)

[0253] Changes in the effect according to changes in reaction time were observed under the following conditions.

[0254] Reaction time: 30 to 180 min

[0255] Reaction temperature: 25 ℃

[0256] Response speed: 2,000 RPM

[0257] Sodium-to-liquid ratio: 20 mg / ml

[0258] Solvent concentration: [EMIM][PF6] (5 wt%) + NMP

[0259] When the graphene exfoliation yield according to reaction time was experimentally verified for exfoliating high-purity graphite, as shown in Table 23 and Figure 29, it was confirmed that the yield increased up to 120 minutes, but as it went beyond 180 minutes, the yield remained similar or decreased.

[0260] Table 23

[0261]

[0262] Exfoliation TC Reaction. Variation Experiment on Unused Graphite TC Flow Exfoliation Process (Solid-to-Liquid Ratio Variation)

[0263] Changes in the effect of changes in the high-amount ratio were observed under the following conditions.

[0264] Reaction time: 120 min

[0265] Reaction temperature: 25 ℃

[0266] Response speed: 2,000 RPM

[0267] Solid-to-liquid ratio: 0.1 to 30 mg / ml

[0268] Solvent concentration: [EMIM][PF6] (5 wt%) + NMP

[0269] When the graphene exfoliation yield according to the solid-to-liquid ratio was experimentally verified for exfoliating high-purity graphite, as shown in Table 24 and Figure 30, it was confirmed that the yield decreased rapidly when the graphite concentration increased to 30 mg / ml or higher.

[0270] Table 24

[0271]

[0272] Exfoliation TC Reaction. Variance Experiment on Unutilized Graphite TC Flow Exfoliation Process (Type of Inert Gas)

[0273] Changes in the effect according to the type of inert gas were observed under the following conditions.

[0274] Reaction time: 120 min

[0275] Reaction temperature: 25 ℃

[0276] Response speed: 2,000 RPM

[0277] Sodium-to-liquid ratio: 20 mg / ml

[0278] Solvent concentration: [EMIM][PF6] (5 wt%) + NMP

[0279] Gas Type: CO2 / N2 / Ar

[0280] Gas flow rate: 100 cc / min

[0281] Experiments were conducted to determine whether the graphene exfoliation yield could be increased by introducing an inert gas to exfoliate high-purity graphite, and as shown in Table 25 and Figure 31, it was confirmed that CO2 gas increased the exfoliation yield the most by widening the interlayer distance of the graphite.

[0282] Table 25

[0283]

[0284] Exfoliation TC Reaction. Variation Experiment on Unused Graphite TC Flow Exfoliation Process (Variation in CO2 Gas Flow Rate)

[0285] Changes in the effect of changes in CO2 gas flow rate were observed under the following conditions.

[0286] Reaction time: 120 min

[0287] Reaction temperature: 25 ℃

[0288] Response speed: 2,000 RPM

[0289] Sodium-to-liquid ratio: 20 mg / ml

[0290] Solvent concentration: [EMIM][PF6] (5 wt%) + NMP

[0291] Gas Type: CO2

[0292] Gas flow rate: 100 to 500 cc / min

[0293] The peeling yield according to the CO2 gas flow rate for peeling high-purity graphite was verified through experiments. As shown in Table 26 and Figure 32, the highest peeling yield was confirmed under the condition of 500 cc / min.

[0294] Table 26

[0295]

[0296] Graphene Analysis. High-purity graphene ICP after purification of underutilized graphite

[0297] ICP analysis was performed to check for the detection of impurities and to verify whether it possesses a purity similar to commercial graphene (>99%).

[0298] As shown in Table 27, it was confirmed that the impurities in the graphene were below the detection limit, indicating that it is high-purity graphene.

[0299] Table 27

[0300]

[0301] Graphene Analysis. High-purity graphene C 1s XPS after purification of underutilized graphite

[0302] The C 1s Peak of exfoliated graphene after purification by raw material was analyzed and compared using HR XPS. As shown in Figure 33, the CO / OC=O peak, which indicates oxidation, defects, and surface functional groups, was weak or insignificant, and the bonding between CC carbons was dominant. This suggests that structural damage to the graphene after exfoliation was minimized, indicating that the graphene was successfully exfoliated.

[0303] In addition, based on the weak sp2 bonding observed at 290.5 to 291.5 (eV), it was determined that the interlayer stacking disappeared and the peak decreased, thereby confirming that graphite was exfoliated into graphene.

[0304] Graphene Analysis. High-purity graphene BET after purification of underutilized graphite

[0305] As graphite is exfoliated into graphene, the layered structure collapses, and as surface exposure increases, the specific surface area increases.

[0306] Accordingly, the specific surface area of ​​purified graphite and graphene was compared using BET. As shown in Table 28, Figures 36a and 36b, the specific surface area increased under optimization conditions. This indicates that the number of graphite layers decreased, and the specific surface area, which was low due to the layered structure, increased as it was exposed to the outside. Therefore, it can be concluded that graphene was formed through the exfoliation of graphite.

[0307] <표 28>

[0308]

Claims

Claim 1 A method for obtaining graphene from a graphite raw material comprises: a purification step of removing impurities from the graphite raw material in a sulfuric acid-based solvent using a Taylor-Couet reactor to obtain purified graphite having a purity of 99.5% or higher; and an exfoliation step of converting the purified graphite into graphene in an organic solvent and an ionic liquid-based solvent using a Taylor-Couet reactor, wherein an inert gas is injected in both the purification step and the exfoliation step, and the inert gas comprises carbon dioxide. Claim 2 delete Claim 3 delete Claim 4 A method according to claim 1, wherein the concentration of the aqueous sulfuric acid solution used in the purification step is 1.5 to 4.0 M, and the mixture of the graphite raw material and the aqueous sulfuric acid solution is ultrasonically dispersed before being introduced into the Taylor-Couet reactor. Claim 5 A method according to claim 4, wherein the purification step is performed for 100 to 150 minutes at 1500 to 3000 rpm, 10 to 50℃, a solid-liquid ratio of 7 to 15 mg / ml, and a carbon dioxide flow rate of 300 to 700 cc / min. Claim 6 A method according to claim 1, further comprising a step of pre-treating the graphite raw material before purification, wherein the pre-treatment step uses an aqueous sulfuric acid solution with a concentration of 0.3 to 1.2 M and the solid-to-liquid ratio is 7 to 15 mg / ml. Claim 7 A method according to claim 1, wherein the organic solvent is one of N-Methyl-2-Pyrrolidone (NMP), DMF (N,N-Dimethylformamide), DMAc (Dimethylacetamide), and DMSO (Dimethyl sulfoxide), and the ionic liquid is one of [EMIM][PF6](1-ethyl-3-methylimidazolium hexafluorophosphate), [EMIM][BF4], [EMIM][SO4], and [TMA][BF4](Tetramethylammonium tetrafluoroborate). Claim 8 A method according to claim 7, wherein the concentration of the ionic liquid is 4 to 6 wt% relative to the total solvent. Claim 9 A method according to claim 8, wherein in the peeling step, the reaction time is 80 to 160 minutes and the solid-to-liquid ratio is 15 to 25 mg / ml. Claim 10 In claim 9, a method of ultrasonically dispersing the purified solution mixed with the purified graphite and solvent for 5 to 15 minutes before introducing it into a Taylor-Couet reactor. Claim 11 A method according to claim 10, further comprising the step of sequentially performing low-speed centrifugation and high-speed centrifugation on the graphene, wherein the low-speed centrifugation is performed at 20 to 600XG and the high-speed centrifugation is performed at 3,000 to 7,000XG. Claim 12 A method according to claim 1, wherein the graphite raw material comprises at least one of anthracite, waste cathode material, waste graphite refractory shell, and graphite ore.

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