Production process for preparing graphene by extracting graphite from coal

Abstract

The invention discloses a production process for preparing graphene by extracting graphite from coal, relates to the technical field of preparation of carbon nanomaterials, constructs an integrated process for extracting graphite from coal and preparing graphene, adopts composite weak oxidation mild activation, in-situ intercalation and low-energy ultrasonic synergistic turbulence stripping, and synchronously recovers resources. The method abandons the traditional strong oxidation and secondary treatment, and has the advantages that by adopting the coal raw material pretreatment-pyrolysis reduction to extract the coarse graphite and combining the integrated process of mild activation of a composite weak oxidation system, in-situ intercalation modification and low-energy ultrasonic synergistic turbulence stripping, a strong oxidant used in the traditional chemical oxidation method is abandoned; the problems of generation of a large amount of acid wastewater and equipment corrosion are avoided from the source, meanwhile, the process collaboration is optimized according to the structural characteristics of the coal derived graphite, secondary crushing and purification are not needed, the material loss is reduced, and the problems of graphene sheet layer fracture and excessive defects are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterial preparation technology, specifically a production process for preparing graphene from coal-extracted graphite. Background Technology

[0002] Graphene, as a two-dimensional carbon nanomaterial with excellent electrical conductivity, mechanical strength, thermal conductivity and ultra-large specific surface area, has shown irreplaceable application value in many strategic emerging fields such as electronic devices, new energy storage, composite material reinforcement and biomedical carriers. With the continuous increase in demand for high-performance materials from downstream industries, the large-scale and low-cost preparation of graphene has become the core key to promoting its industrialization.

[0003] Existing processes for preparing graphene from coal mainly involve obtaining graphite through coal pyrolysis, followed by oxidative exfoliation with strong oxidants or ultrasonic exfoliation alone. These processes have several drawbacks. First, they rely on strong oxidants, easily generating large amounts of acidic wastewater and corroding production equipment. Furthermore, secondary crushing and purification of intermediate products is required, leading to significant material losses and excessive graphene sheet breakage and defects. Second, the graphite extraction and graphene preparation processes are disconnected, resulting in high energy consumption during intermediate product transfer and secondary processing. Resources such as intercalating agents and oxidation systems cannot be recycled, causing serious waste. Therefore, we propose a new production process for preparing graphene from coal-extracted graphite. Summary of the Invention

[0004] The purpose of this invention is to provide a production process for preparing graphene by extracting graphite from coal.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a production process for preparing graphene by extracting graphite from coal, the production process comprising the following steps: Step 1: The coal raw material is crushed, dried and impurities are removed to obtain pretreated coal particles; Step 2: The pretreated coal particles are pyrolyzed under a protective atmosphere, and then reduced by a reducing gas to obtain crude graphite product. Step 3: Mix the coarse graphite with the composite weak oxidation system and perform a mild activation treatment to obtain activated graphite slurry; Step 4: Add an intercalating agent to the activated graphite slurry to carry out an in-situ intercalation reaction, and obtain an intercalated modified graphite slurry. Step 5: The intercalated modified graphite slurry is subjected to low-energy ultrasonic synergistic turbulent exfoliation treatment, followed by centrifugation, and the upper suspension is collected to obtain the primary graphene product. Step 6: Distill the precipitate after centrifugation to recover the intercalating agent, filter the upper suspension to recover the mother liquor of the composite oxidation system and recycle it; Step 7: Wash, dry and test the primary graphene product to obtain a graphene product that meets the requirements.

[0006] As a further aspect of the present invention: In step one, the coal raw material is either bituminous coal or anthracite with a fixed carbon content ≥75%, ash content ≤10%, and sulfur content ≤1.5%. After crushing, the particle size of the coal particles is 100-200 mesh. The drying process is carried out in a forced-air drying oven at a drying temperature of 105℃-110℃ for 4-6 hours. The impurity removal process is carried out using a plasma impurity removal device under an argon atmosphere with a plasma power of 80W-120W and a processing time of 15-20 minutes.

[0007] As a further aspect of the present invention: In step two, the protective atmosphere is a nitrogen atmosphere, the pyrolysis treatment is carried out in a continuous pyrolysis furnace, the heating rate is 5℃ / min-8℃ / min, the pyrolysis temperature is 800℃-900℃, the holding time is 2h-3h, the volatile matter removal rate is ≥90%, the reducing gas is hydrogen with a volume fraction of 5%-8%, the reduction temperature is the same as the pyrolysis temperature, the reduction time is 1h-1.5h, and the fixed carbon content of the crude graphite product is ≥92%, and the particle size is 50μm-100μm.

[0008] As a further aspect of the present invention: In step three, the composite weak oxidation system is composed of peracetic acid and phosphoric acid, wherein the mass fraction of peracetic acid is 8%-12%, the mass fraction of phosphoric acid is 3%-5%, the pH value of the composite oxidation system is 2.5-3.5, the solid-liquid ratio of crude graphite to the composite weak oxidation system is 1:15 (g / mL)-1:20 (g / mL), the mild activation treatment is carried out in a reaction vessel, the reaction temperature is 60℃-80℃, the stirring rate is 300r / min-500r / min, and the reaction time is 2h-4h.

[0009] As a further aspect of the present invention: in step four, the intercalating agent is -aminopropyltriethoxysilane, N-( -aminoethyl)- One or two of the following are selected: aminopropyltrimethoxysilane; the amount of intercalating agent added is 8%-15% of the mass of crude graphite; the temperature of the in-situ intercalation reaction is 60℃-70℃; the stirring rate is 400r / min-600r / min; the reaction time is 1.5h-2.5h; and the interlayer spacing of graphite in the intercalated modified graphite slurry is 0.5nm-0.7nm.

[0010] As a further aspect of the present invention: In step five, the low-energy ultrasonic synergistic turbulent stripping treatment is carried out in a circulating ultrasonic stripping device, with an ultrasonic power of 200W-300W, an ultrasonic frequency of 20kHz-40kHz, a slurry flow velocity of 0.8m / s-1.2m / s in the turbulent field, a stripping temperature of room temperature, a stripping time of 3h-5h, a centrifugal separation speed of 8000r / min-10000r / min, and a centrifugation time of 15min-20min.

[0011] As a further aspect of the present invention: in step six, the conditions for distilling and recovering the intercalating agent are a temperature of 120℃-150℃, a pressure of -0.08MPa to -0.09MPa, a distillation time of 2h-3h, an intercalating agent recovery rate of ≥95%, filtration using a microfiltration membrane with a pore size of 0.1μm-0.2μm, and the mother liquor of the composite oxidation system is concentrated to the initial concentration by vacuum distillation and then recycled for step three, with the number of cycles being ≥8 times.

[0012] As a further aspect of the present invention: In step seven, deionized water is used for washing, the stirring rate is 200 r / min-300 r / min, the number of washings is 3-4 times, and the washing time for each washing is 30 min-35 min. The drying process is carried out in a vacuum drying oven at a drying temperature of 60℃-80℃, a drying pressure of -0.07 MPa to -0.08 MPa, and a drying time of 8 h-10 h. The detection is performed using atomic force microscopy and Raman spectroscopy. The graphene product contains ≥90% graphene of 1-3 layers, a defect density ID / IG≤0.3, and an oxygen-containing functional group content≤5at.

[0013] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows: 1. This invention employs a coal raw material pretreatment-pyrolysis reduction extraction of crude graphite, combined with a composite weak oxidation system for mild activation, in-situ intercalation modification, and low-energy ultrasonic synergistic turbulent exfoliation integrated process. This eliminates the strong oxidants used in traditional chemical oxidation methods, thus avoiding the generation of large amounts of acidic wastewater and equipment corrosion problems from the source. At the same time, the process synergy is optimized for the structural characteristics of coal-derived graphite, eliminating the need for secondary crushing and purification, reducing material loss, and effectively improving the problems of graphene sheet breakage and excessive defects. 2. This invention constructs an integrated and continuous process for extracting graphite from coal and preparing graphene, seamlessly connecting the pyrolysis reduction, mild activation, in-situ intercalation, and synergistic exfoliation steps. This eliminates the secondary processing steps of intermediate products in traditional processes. At the same time, it achieves efficient recycling of intercalating agents and composite oxidation systems through distillation and filtration, which reduces material loss during transportation and secondary processing, avoids resource waste, and significantly reduces energy input in the production process. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the process flow in an embodiment of the present invention. Detailed Implementation

[0015] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0016] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Please see the appendix Figure 1 This invention discloses a production process for preparing graphene by extracting graphite from coal, the production process comprising the following steps: Step 1: The coal raw material is crushed, dried and impurities are removed to obtain pretreated coal particles; Step 2: The pretreated coal particles are pyrolyzed under a protective atmosphere, and then reduced by a reducing gas to obtain crude graphite product. Step 3: Mix the coarse graphite with the composite weak oxidation system and perform a mild activation treatment to obtain activated graphite slurry; Step 4: Add an intercalating agent to the activated graphite slurry to carry out an in-situ intercalation reaction, and obtain an intercalated modified graphite slurry. Step 5: The intercalated modified graphite slurry is subjected to low-energy ultrasonic synergistic turbulent exfoliation treatment, followed by centrifugation, and the upper suspension is collected to obtain the primary graphene product. Step 6: Distill the precipitate after centrifugation to recover the intercalating agent, filter the upper suspension to recover the mother liquor of the composite oxidation system and recycle it; Step 7: Wash, dry and test the primary graphene product to obtain a graphene product that meets the requirements.

[0018] Example 1, please refer to the appendix. Figure 1Bituminous coal with a fixed carbon content of 78%, ash content of 8%, and sulfur content of 1.2% was selected as raw material. After being crushed to 150 mesh, it was placed in a forced-air drying oven and dried at 108℃ for 5 hours. Then, it was placed in an argon-atmosphere plasma purification device and treated at 100W power for 18 minutes to obtain pretreated coal particles. These particles were then fed into a continuous pyrolysis furnace and heated to 850℃ at 6.5℃ / min under nitrogen protection, and held at that temperature for 2.5 hours to complete the pyrolysis. Subsequently, 6.5% hydrogen (by volume) was introduced, and reduction was carried out at the same temperature for 1.2 hours to obtain coarse graphite with a fixed carbon content of 94% and a particle size of 75μm. The coarse graphite was added to a reaction vessel at a solid-liquid ratio of 1:18 (g / mL), along with a composite weak oxidizing system consisting of 10% peracetic acid (by mass), 4% phosphoric acid (by mass), and a pH of 3.0. The reaction was carried out at 70℃ and 400r / min for 3 hours to obtain activated graphite slurry. 12% by mass of coarse graphite was then added to the slurry. -Aminopropyltriethoxysilane was reacted at 65℃ and 500 r / min for 2 h to obtain intercalated modified graphite slurry with an interlayer spacing of 0.6 nm. The slurry was fed into a circulating ultrasonic exfoliation device with an ultrasonic power of 250 W and a frequency of 30 kHz. The slurry flow rate was controlled at 1.0 m / s to form a turbulent field. After exfoliation at room temperature for 4 h, the slurry was centrifuged at 9000 r / min for 18 min, and the supernatant was collected. The centrifuged precipitate was distilled at 135℃ and -0.085 MPa for 2.5 h to recover the precipitate. The intercalating agent and the upper suspension were filtered through a 0.15 μm microfiltration membrane. The separated mother liquor of the composite oxidation system was concentrated and recycled. The graphene primary product was washed three times with deionized water at 250 r / min for 32 min each time. Then it was dried in a vacuum drying oven at 70℃ and -0.075 MPa for 9 h. The product was detected by atomic force microscopy and Raman spectroscopy. The proportion of 1-3 layers of graphene in the product was 93%, the defect density ID / IG=0.25, and the oxygen-containing functional group content was 3.8 at, which met the requirements.

[0019] Example 2, please refer to the appendix. Figure 1 Mild activation of the composite weak oxidation system: Pretreated crude graphite was added to a reaction vessel at a solid-liquid ratio of 1:18 (g / mL) to prepare a composite weak oxidation system of 10% peracetic acid and 4% phosphoric acid. The pH was adjusted to 3.0, the stirring device was started, and the stirring speed was controlled at 400 r / min. The reaction vessel was heated to 70℃ and reacted at a constant temperature for 3 h. In this process, a small number of hydroxyl functional groups were introduced between the graphite layers through the weak oxidation system, avoiding the sheet breakage caused by strong oxidants. At the same time, the buffering effect of phosphoric acid stabilized the reaction environment, ensuring that the content of oxygen-containing functional groups in the activated graphite was controlled within a limited range, providing sufficient binding sites for subsequent intercalation reactions, and solving the problem of many defects in products from traditional oxidation methods.

[0020] Example 3, please refer to the appendix. Figure 1 Specific implementation of in-situ intercalation modification: Take the obtained activated graphite slurry and add it at 12% of the mass of crude graphite. -Umamidotriethoxysilane was used as an intercalating agent. The reaction temperature was maintained at 65℃ and the stirring rate at 500r / min for 2 hours. The intercalating agent molecules formed chemical bonds with the intercalation hydroxyl groups of graphite through amino groups, and were oriented and anchored in the interlayer region, widening the graphite interlayer spacing from the original 0.335nm to 0.6nm. This in-situ reaction does not require the separation of intermediate products and the modification is completed directly in the activated slurry, avoiding material loss caused by secondary processing. At the same time, the widened interlayer spacing greatly reduces the difficulty of subsequent stripping and solves the problem of the separation between the traditional intercalation and activation processes.

[0021] Example 4, please refer to the appendix. Figure 1 Implementation of low-energy ultrasound-assisted turbulent stripping and resource recycling: The intercalated modified graphite slurry was fed into a circulating ultrasonic exfoliation device with an ultrasonic power of 250W and a frequency of 30kHz. The turbulence generator was turned on to make the slurry flow rate 1.0m / s. After exfoliation at room temperature for 4 hours, the supernatant was collected by centrifugation at 9000r / min for 18min. The centrifuged precipitate was sent to a vacuum distillation device at 135℃ and -0.085MPa to recover 96% of the intercalating agent. The supernatant was filtered through a 0.15μm microfiltration membrane, and the separated mother liquor of the composite oxidation system was concentrated to the initial concentration under vacuum.

[0022] Specifically, the selection of coal raw materials focuses on limiting the fixed carbon, ash, and sulfur content because the carbon structure of these bituminous or anthracite coals is more easily converted into graphite through pyrolysis. Furthermore, the low ash and low sulfur characteristics reduce the pressure of subsequent impurity removal. Crushing treatment can increase the specific surface area of ​​the raw materials and improve the efficiency of pyrolysis and impurity removal. Drying treatment aims to remove free moisture and prevent moisture from affecting the removal of volatiles during pyrolysis. Plasma impurity removal uses an argon atmosphere to utilize the inert properties of argon to prevent the oxidation of the raw materials. At the same time, the high-energy action of plasma precisely removes impurities such as sulfur oxides adsorbed on the surface, laying the foundation for the subsequent preparation of high-purity graphite.

[0023] Specifically, nitrogen is used as a protective atmosphere in the pyrolysis process, which can effectively isolate air, prevent the coal raw material and pyrolysis intermediate products from being oxidized, and ensure the effective retention of fixed carbon. The design of the connection between the pyrolysis and reduction steps is based on the characteristic that there are a few defects in the carbon structure after pyrolysis. These defects are repaired by the reduction effect of hydrogen, thereby improving the crystallinity of graphite.

[0024] Specifically, the composite weak oxidation system uses a combination of peracetic acid and phosphoric acid. The core reason is that peracetic acid has a mild oxidizing strength, which can only introduce a small number of hydroxyl functional groups between graphite layers, thus avoiding damage to the integrity of the graphite sheet structure. Phosphoric acid plays a buffering role, stabilizing the pH value of the system and preventing excessive local oxidation. The purpose of this system in the mixed reaction with coarse graphite is to reduce the interlayer forces of graphite through mild oxidation, while providing chemical bonding sites for subsequent intercalation agents.

[0025] Specifically, in the molecular structure of aminosilane intercalating agents, the amino group can form a stable chemical bond with the hydroxyl groups between the layers of activated graphite, ensuring that the intercalating agent can be directionally anchored in the interlayer region rather than simply physically adsorbed, thereby stably widening the interlayer spacing. The in-situ intercalation reaction is designed to be carried out directly in the activated graphite slurry without the need to separate intermediate products, which reduces material loss and ensures the continuity of the intercalation reaction.

[0026] Specifically, the design of low-energy ultrasound-assisted turbulent exfoliation utilizes the vibration of ultrasound to disrupt the weak interactions between graphene layers, while the shear force generated by the turbulent field assists in the separation of the layers. The two work together to achieve a "gentle exfoliation" effect. The selection of low-energy ultrasound can avoid the tearing of graphene sheets caused by high-energy input. The circulating device can ensure that the slurry is uniformly stressed, improving the uniformity of exfoliation. The centrifugal separation step is specifically designed to separate the primary graphene product from the incompletely exfoliated graphite.

[0027] Specifically, the recycling design of the intercalating agent and the composite oxidation system is based on their physicochemical properties: the intercalating agent has a specific boiling point and can be separated from other substances by vacuum distillation. After recycling, its chemical properties remain stable. After the composite oxidation system is filtered through a microfiltration membrane and concentrated under reduced pressure, its concentration can be restored to the initial state without affecting the subsequent activation reaction effect.

[0028] Working principle: First, the qualified coal raw materials are crushed, dried, and subjected to plasma purification to remove moisture and surface impurities, resulting in clean pretreated coal particles. Next, the pretreated coal particles are pyrolyzed under a nitrogen protective atmosphere to remove volatiles, followed by hydrogen reduction to repair carbon structural defects and obtain high-purity coarse graphite. Subsequently, the coarse graphite is mixed with a peracetic acid-phosphoric acid composite weak oxidation system for gentle activation, introducing a small amount of hydroxyl functional groups without damaging the graphite sheets, creating conditions for intercalation reactions. Finally, aminosilicone is added to the activated graphite slurry. An alkyl intercalating agent is used to orient and widen the interlayer spacing of graphite through in-situ chemical bonding, reducing the difficulty of subsequent exfoliation. Then, low-energy ultrasound and turbulence are used to gently exfoliate the intercalated modified graphite. The graphene primary product is obtained by centrifugation. At the same time, the intercalating agent and the mother liquor of the composite oxidation system are recovered by distillation and filtration, respectively, and recycled for corresponding process steps to improve resource utilization. Finally, the graphene primary product is washed with deionized water and vacuum dried. The product meets the standards by atomic force microscopy and Raman spectroscopy. The entire process is then completed.

[0029] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A production process for preparing graphene by extracting graphite from coal, characterized in that, The production process includes the following steps: Step 1: The coal raw material is crushed, dried and impurities are removed to obtain pretreated coal particles; Step 2: The pretreated coal particles are pyrolyzed under a protective atmosphere, and then reduced by a reducing gas to obtain crude graphite product. Step 3: Mix the coarse graphite with the composite weak oxidation system and perform a mild activation treatment to obtain activated graphite slurry; Step 4: Add an intercalating agent to the activated graphite slurry to carry out an in-situ intercalation reaction, and obtain an intercalated modified graphite slurry. Step 5: The intercalated modified graphite slurry is subjected to low-energy ultrasonic synergistic turbulent exfoliation treatment, followed by centrifugation, and the upper suspension is collected to obtain the primary graphene product. Step 6: Distill the precipitate after centrifugation to recover the intercalating agent, filter the upper suspension to recover the mother liquor of the composite oxidation system and recycle it; Step 7: Wash, dry and test the primary graphene product to obtain a graphene product that meets the requirements.

2. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step one, the coal raw material is either bituminous coal or anthracite with a fixed carbon content ≥75%, ash content ≤10%, and sulfur content ≤1.5%. After crushing, the coal particles have a particle size of 100-200 mesh. The drying process is carried out in a forced-air drying oven at a temperature of 105℃-110℃ for 4-6 hours. The impurity removal process is carried out using a plasma impurity removal device under an argon atmosphere with a plasma power of 80W-120W for 15-20 minutes.

3. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step two, the protective atmosphere is a nitrogen atmosphere, the pyrolysis treatment is carried out in a continuous pyrolysis furnace, the heating rate is 5℃ / min-8℃ / min, the pyrolysis temperature is 800℃-900℃, the holding time is 2h-3h, the reducing gas is hydrogen with a volume fraction of 5%-8%, the reduction temperature is the same as the pyrolysis temperature, the reduction time is 1h-1.5h, and the particle size of the crude graphite product is 50μm-100μm.

4. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step three, the composite weak oxidation system is composed of peracetic acid and phosphoric acid, wherein the mass fraction of peracetic acid is 8%-12% and the mass fraction of phosphoric acid is 3%-5%. The pH value of the composite oxidation system is 2.5-3.

5. The solid-liquid ratio of crude graphite to the composite weak oxidation system is 1:15-1:

20. The mild activation treatment is carried out in a reaction vessel at a reaction temperature of 60℃-80℃, a stirring rate of 300r / min-500r / min, and a reaction time of 2h-4h.

5. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step four, the intercalating agent is -aminopropyltriethoxysilane, N-( -aminoethyl)- One or two of the following are selected: aminopropyltrimethoxysilanes; the amount of intercalating agent added is 8%-15% of the mass of crude graphite; the temperature of the in-situ intercalation reaction is 60℃-70℃; the stirring rate is 400r / min-600r / min; and the reaction time is 1.5h-2.5h.

6. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step five, the low-energy ultrasonic-assisted turbulent stripping treatment is carried out in a circulating ultrasonic stripping device. The ultrasonic power is 200W-300W, the ultrasonic frequency is 20kHz-40kHz, the slurry flow velocity in the turbulent field is 0.8m / s-1.2m / s, the stripping temperature is room temperature, the stripping time is 3h-5h, the centrifugation speed is 8000r / min-10000r / min, and the centrifugation time is 15min-20min.

7. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step six, the conditions for distilling and recovering the intercalating agent are: temperature 120℃-150℃, pressure -0.08MPa to -0.09MPa, distillation time 2h-3h, filtration using a microfiltration membrane with a pore size of 0.1μm-0.2μm, and the mother liquor of the composite oxidation system is concentrated to the initial concentration by vacuum distillation and then recycled for step three, with the number of cycles ≥8 times.

8. The production process for preparing graphene by extracting graphite from coal according to claim 1, characterized in that: In step seven, deionized water is used for washing, the stirring rate is 200r / min-300r / min, the number of washings is 3-4 times, and the washing time is 30min-35min each time. The drying process is carried out in a vacuum drying oven at a drying temperature of 60℃-80℃, a drying pressure of -0.07MPa to -0.08MPa, and a drying time of 8h-10h.

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