Method for preparing carbon microchip through supercritical composite fluid stripping

Abstract

The invention discloses a method for preparing a carbon microchip through supercritical composite fluid stripping, which comprises the following steps: adding a powdery carbon source and a dispersing agent into a high-pressure kettle, then introducing a mixed gas of He and CO2 into the high-pressure kettle, carrying out pre-intercalation and stripping treatment on carbon powder under the supercritical condition of He and CO2, and then releasing pressure to obtain the carbon microchip. According to the method, the production cost can be reduced, and meanwhile, the size of the carbon microchip product can be flexibly regulated and controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nano-carbon materials, and particularly relates to a method for preparing carbon microflakes by supercritical composite fluid exfoliation. Background Art

[0002] A supercritical fluid generally refers to a fluid whose temperature and pressure values both exceed the critical pressure and critical temperature. In this supercritical state, substances enter a special state due to their special changes. This state is different from the conventional solid, liquid, and gas phases and has many unique physical and chemical properties that are not possessed by the conventional system states. Commonly used to prepare supercritical fluids are carbon dioxide, ethanol, propane, etc. Among them, carbon dioxide (CO 2 ) has very stable chemical properties, is colorless, odorless, and non-toxic. When its temperature is higher than the critical temperature Tc = 31.26 °C and its pressure is higher than the critical pressure Pc = 7.38 MPa, its physical properties will change significantly. Its density is almost close to that of a conventional liquid, its viscosity is almost close to that of a conventional gas, and the diffusion and absorption coefficients are nearly 100 times that of the viscosity of a conventional liquid, having an extremely stable, powerful, and long-lasting adsorption and dissolution ability.

[0003] As a unique carbon nanomaterial, carbon microflakes have the characteristics of a large specific surface area, good chemical stability, high mechanical strength, good electrical conductivity, etc., and have broad application prospects. Carbon microflakes can be prepared by ultrasonic exfoliation of carbon powder in a liquid phase. The exfoliation process includes the following processes: (1) dispersing carbon powder in a solvent; (2) intercalation exfoliation; (3) separation and extraction.

[0004] Chinese Patent CN101613098A discloses a solution-phase preparation method of graphene, including the following steps: 1. Graphite oxidation; 2. Exfoliation of the graphite oxide mother liquor; 3. Reduction of graphene oxide. A polymer surfactant is added as a stabilizer and hydrazine hydrate is added as a reducing agent in the graphene oxide colloidal solution. Although this method can prepare graphene with a larger area, it introduces rich oxygen-containing functional groups on the graphite sheet layer. The oxygen-containing functional groups can be removed by reduction, but the defects such as the morphology and structure are left to damage the electronic properties of the material, resulting in lower physical and chemical properties. Chemical vapor deposition is a process technology that uses different carbon precursors to decompose into small molecules or atoms at a certain temperature and generate solid materials on a catalytic substrate, and can prepare monolayer or few-layer graphene in large quantities. However, due to high energy consumption and high cost, the process has not been widely used.

[0005] Chinese Patent CN102115078A discloses a method for preparing graphene by supercritical fluid in the field of nano-new material technology. The method realizes the preparation of graphene by performing multiple repeated cycles of high temperature and high pressure and cooling on the graphite powder dispersion. The method mixes graphite powder and organic solvent, heats them to a high temperature of 200°C to 700°C and a high pressure of 10 to 100 MPa, and then prepares graphene through the processes of cooling and depressurization. The required process conditions of the method are harsh, with high temperature and high pressure, and the solvents required are various organic solvents with high toxicity, and the steps are complex.

[0006] Chinese Patent CN102515155A discloses a method for preparing large-scale graphene by supercritical carbon dioxide exfoliation. Using supercritical CO 2 as the exfoliating agent and surfactant as the dispersant, graphite powder and dispersant are placed in an autoclave, and then CO 2 is introduced. It circulates under supercritical conditions, and then quickly depressurizes to atmospheric pressure. The above process is repeated to make the material experience multiple pressure increase and decrease processes. The number of graphene layers is controlled by controlling the number of pressure increase and decrease times, that is, large-scale graphene is prepared. During the preparation process of this technology, the CO 2 circulation times are many, the efficiency is low, the number of layers of the prepared product is large, and the effect is limited.

[0007] Chinese Patent CN110386597B discloses equipment for large-scale production of thin-layer graphene and a method for large-scale production of thin-layer graphene. The equipment includes a jet mill system, a supercritical exfoliation system, and a classification system. The method includes: 1. Jet milling, 2. Supercritical exfoliation, 3. Classification to obtain thin-layer graphene. This technology increases the pretreatment grinding of raw materials, but increases the complexity of equipment and processes.

[0008] Existing methods for preparing graphite products by supercritical fluid exfoliation are applicable to graphite raw materials with a layered structure and relatively regular structure. There are limitations in the adaptability to raw materials with low structural regularity, and the exfoliation process requires multiple reciprocations with low efficiency. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for preparing carbon microflakes by supercritical composite fluid exfoliation, which can reduce production costs and can flexibly control the scale of carbon microflake products.

[0010] To achieve the above purpose, the present invention provides a method for preparing carbon microflakes by supercritical composite fluid exfoliation, including: adding carbon powder and dispersant into a high-pressure container, and then introducing a mixed gas of He and CO 2 into the high-pressure container. Under the supercritical conditions of He and CO 2 , pre-intercalation and exfoliation treatment are performed on the carbon powder, and then the pressure is released to obtain carbon microflakes.

[0011] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the volume ratio of CO 2 and He is 10:1 to 10.

[0012] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the dispersant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

[0013] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the weight ratio of the carbon powder to the dispersant is 1:0.01 to 1:20.

[0014] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the high-pressure vessel is one of a kettle-type, tank-type, and tower-type pressure vessel.

[0015] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, when the mixed gas of He and CO 2 is used to treat the carbon powder, the temperature inside the high-pressure vessel is 40 to 100 °C, and the pressure is 10 to 20 MPa.

[0016] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, when the mixed gas of He and CO 2 is used to treat the carbon powder, the treatment time is 10 to 180 minutes.

[0017] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, when pressure relief is carried out, the pressure is reduced to atmospheric pressure within 0.5 to 5 seconds, and the material inside the high-pressure vessel is transferred from the high-pressure vessel to the recovery device along with the pressure relief gas flow, and the gas volatilizes for 10 to 60 minutes to obtain carbon microflakes.

[0018] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the carbon powder is one or more of petroleum coke, carbon black, activated carbon, artificial graphite powder, and natural graphite powder.

[0019] The method for preparing carbon microflakes by supercritical composite fluid exfoliation according to the present invention, where the thickness of the carbon microflakes is 3 - 500 nanometers, and the sheet diameter size is 1 - 100 micrometers.

[0020] Advantages of the present invention:

[0021] The present invention utilizes the dissolution and diffusion capabilities of supercritical composite fluids, enabling small-molecule supercritical He to first penetrate into the layered structure of carbon powder. By virtue of the fast diffusion rate, small molecular size, and rapid vaporization rate upon pressure reduction of small molecules, the interaction force between graphite layers is reduced. By controlling the pressure reduction within a short time, the carbon powder layers are separated from each other to form carbon microflakes. Meanwhile, the dispersant is in-situ adsorbed on the surface of the carbon powder, preventing the aggregation of the carbon powder. This method belongs to physical process exfoliation, with mild treatment conditions, without damaging the structure of the carbon powder, and the preparation process is simple and efficient. Description of the Drawings

[0022] Figure 1 Figure 1 is a scanning electron microscope image of the carbon microflake product prepared in Example 1 of the present invention at a scale of 1 μm.

[0023] Figure 2 Figure 2 is a scanning electron microscope image of the carbon microflake product prepared in Example 1 of the present invention at a scale of 200 nm. Detailed Description of the Invention

[0024] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0025] Source of raw materials or equipment: Graphite powder, petroleum coke powder, CP (Shanghai Experiment), ≥99.85%, Shanghai Experiment; Sodium dodecyl sulfate, CP (Shanghai Experiment), Shanghai Experiment; CO 2 , ≥99.99%, Mega Gas; He, ≥99.99%, Mega Gas.

[0026] The thickness and flake diameter scale of the carbon microflakes were observed and characterized by using the scanning electron microscopy method.

[0027] Example 1

[0028] A certain amount of sodium dodecyl sulfate was mixed with natural graphite powder, and the weight ratio of graphite powder to sodium dodecyl sulfate was 1:5, and then added into an autoclave. The autoclave was controlled at a temperature of 40°C. CO 2 and He were pumped into the autoclave at a ratio of 1:1 by a compression pump, and the pressure in the autoclave was controlled at 18 MPa. The material was kept in the autoclave for 120 minutes. The pressure relief rate was controlled, and the pressure was reduced to atmospheric pressure within 2 s. The material was transferred to the recovery tower along with the pressure relief gas stream. After the gas volatilized for 25 minutes, carbon microflakes were obtained. Through testing and characterization, the carbon microflake products with less than 10 layers in the product accounted for 82%, and there was no aggregation phenomenon in the product.

[0029] Example 2

[0030] A certain amount of sodium dodecyl sulfate was mixed with natural graphite powder, and the weight ratio of graphite powder to sodium dodecyl sulfate was 1:6. They were added into an autoclave. The autoclave was controlled at a temperature of 45 °C. CO 2 and He were pumped into the autoclave in a ratio of 1:1, and the pressure in the autoclave was controlled at 15 MPa. The material stayed in the autoclave for 120 minutes. The pressure relief rate was controlled, and the pressure was reduced to atmospheric pressure within 3.2 s. The material was transferred to the recovery tower along with the pressure relief gas flow. After the gas volatilized for 40 minutes, carbon microflakes were obtained. Through test characterization, the carbon microflakes with less than 10 layers in the product accounted for 75%, and there was no agglomeration phenomenon in the product.

[0031] Example 3

[0032] A certain amount of sodium dodecyl sulfate was mixed with natural graphite powder, and the weight ratio of graphite powder to sodium dodecyl sulfate was 1:5. They were added into an autoclave. The autoclave was controlled at a temperature of 55 °C. CO 2 and He were pumped into the autoclave in a ratio of 2:1, and the pressure in the autoclave was controlled at 12 MPa. The material stayed in the autoclave for 120 minutes. The pressure relief rate was controlled, and the pressure was reduced to atmospheric pressure within 2.8 s. The material was transferred to the recovery tower along with the pressure relief gas flow. After the gas volatilized for 35 minutes, carbon microflakes were obtained. Through test characterization, the carbon microflakes with less than 10 layers in the product accounted for 78%, and there was no agglomeration phenomenon in the product.

[0033] Example 4

[0034] A certain amount of sodium dodecyl sulfate was mixed with natural graphite powder, and the weight ratio of graphite powder to sodium dodecyl sulfate was 1:5. They were added into an autoclave. The temperature of the autoclave was controlled at 40 °C. CO 2 and He were pumped into the autoclave in a ratio of 1:1, and the pressure in the autoclave was controlled at 18 MPa. The material stayed in the autoclave for 120 minutes. The pressure relief rate was controlled, and the pressure was reduced to atmospheric pressure within 1.5 s. The material was transferred to the recovery tower along with the pressure relief gas flow. After the gas volatilized for 60 minutes, carbon microflakes were obtained. Through test characterization, the carbon microflakes with less than 10 layers in the product accounted for 76%, and there was no agglomeration phenomenon in the product.

[0035] Example 5

[0036] A certain amount of sodium dodecyl sulfate was mixed with natural graphite powder, and the weight ratio of graphite powder to sodium dodecyl sulfate was 1:20. They were added into an autoclave. The autoclave was controlled at a temperature of 50 °C. CO 2Mix with He in a ratio of 1:2 and pump them into the autoclave, controlling the pressure in the autoclave at 10 MPa. The material stays in the autoclave for 10 minutes. Control the pressure relief speed and reduce the pressure to atmospheric pressure within 5 s. The material is transferred to the recovery tower along with the pressure relief gas flow. After 40 minutes of gas volatilization, carbon microflakes are obtained. Through testing and characterization, the carbon microflakes with less than 10 layers in the product account for 75%, and there is no agglomeration phenomenon in the product.

[0037] Example 6

[0038] Mix a certain amount of sodium dodecyl sulfate with natural graphite powder. The weight ratio of graphite powder to sodium dodecyl sulfate is 1:0.1, and add them into the autoclave. The autoclave is controlled at a temperature of 100 °C. Pump CO 2 and He into the autoclave in a ratio of 1:1, controlling the pressure in the autoclave at 20 MPa. The material stays in the autoclave for 180 minutes. Control the pressure relief speed and reduce the pressure to atmospheric pressure within 2.5 s. The material is transferred to the recovery tower along with the pressure relief gas flow. After 20 minutes of gas volatilization, carbon microflakes are obtained. Through testing and characterization, the carbon microflakes with less than 10 layers in the product account for 83%, and there is no agglomeration phenomenon in the product.

[0039] Example 7

[0040] Mix sodium dodecyl sulfate with petroleum coke powder in a ratio of 1:20 (mass ratio), add them into a tower-type high-pressure vessel, and heat up the temperature to 100 °C. Pump CO 2 and He into the high-pressure vessel in a ratio of 10:1 (volume ratio), controlling the pressure in the controller at 15 MPa. The material stays under constant conditions for 120 minutes. Control the pressure relief speed and reduce the pressure to atmospheric pressure within 3 s. The material is transferred to the recovery tower along with the pressure relief gas flow. After 30 minutes of gas volatilization, carbon microflakes are obtained. Through testing and characterization, the coke microflakes with less than 10 layers in the product account for 70%, and there is no agglomeration phenomenon in the product.

[0041] Comparative Example 1

[0042] Mix a certain amount of sodium dodecyl sulfate with graphite powder. The weight ratio of graphite powder to sodium dodecyl sulfate is 1:5, and add them into the autoclave. The autoclave temperature is set at 65 °C and the temperature is controlled at 40 °C. Pump carbon dioxide into the autoclave through a pump, controlling the pressure in the autoclave at 18 MPa. The material stays in the autoclave for 120 minutes. Through testing and characterization, the graphene with less than 10 layers in the product accounts for 42%.

[0043] Comparative Example 2

[0044] A certain amount of sodium dodecylbenzenesulfonate is mixed with graphite powder, and the weight ratio of graphite powder to sodium dodecylbenzenesulfonate is 1:6, and then added into an autoclave. Heat the materials in the autoclave and control the temperature at 45 °C. Pump carbon dioxide into the autoclave through a pump, and control the pressure in the autoclave at 10 MPa. The materials stay in the autoclave for 60 minutes. After rapid pressure relief, pump carbon dioxide into the autoclave again through a pump. Repeat the pressurization and pressure relief process three times. Through test characterization, graphene with less than 10 layers accounts for 63% in the product.

[0045] Comparative Example 3

[0046] Add artificial graphite powder directly into a high-pressure tank-type container, and set the temperature of the high-pressure container at 100 °C. Pump CO 2 and He into the high-pressure container in a ratio of 1:1 through a compression pump, and control the pressure at 20 MPa. The materials stay in the high-pressure container for 180 minutes. After separation and extraction, it is observed that obvious agglomeration of graphite micropieces occurs, and graphite micropiece products with less than 10 layers account for 77% in the product.

[0047]

[0048] Of course, the present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing carbon microsheets by supercritical composite fluid exfoliation, characterized in that: include: The carbon powder and the dispersant are added into a high-pressure container, and then a mixed gas of He and CO2 is introduced into the high-pressure container. The carbon powder is pre-intercalated and stripped under supercritical conditions of He and CO2, and then the pressure is released to obtain carbon microsheets.

2. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The volume ratio of CO2 and He is 10:1~10.

3. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The dispersant is sodium dodecyl sulfate and / or sodium dodecylbenzene sulfonate.

4. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The weight ratio of the carbon powder to the dispersant is 1:0.01 to 1:

20.

5. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The high-pressure container is one of kettle-type, tank-type and tower-type pressure containers.

6. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: When the mixed gas of He and CO2 is used to treat the carbon powder, the temperature in the high-pressure container is 40-100°C and the pressure is 10-20MPa.

7. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The treatment time of the mixed gas of He and CO2 on the carbon powder is 10 to 180 minutes.

8. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The carbon powder is one or more of petroleum coke, carbon black, artificial graphite powder and natural graphite powder.

9. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: During the pressure relief treatment, the pressure is reduced to normal pressure within 0.5 to 5 seconds, and the material in the high-pressure container is transferred from the high-pressure container to the recovery device along with the pressure relief gas flow. The gas evaporates for 10 to 60 minutes to obtain carbon micro-flakes.

10. The method for preparing carbon microsheets by supercritical composite fluid exfoliation according to claim 1, characterized in that: The carbon microsheet has a thickness of 3-500 nanometers and a sheet diameter of 1-100 micrometers.

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