Preparation method and application of porous carbon with cottonseed hull as raw material

Abstract

This invention relates to the field of capacitor technology, specifically to a method for preparing porous carbon modified from cottonseed hulls and its application. The invention involves ultrasonically treating cottonseed hulls in a dilute acid solution, followed by acidification to modify the hulls. Microwave pore-forming is then used to obtain porous carbon with well-developed pores and a large specific surface area. Acid washing and water washing remove minerals and residual carbon fragments from the pores, significantly improving pore utilization. Simultaneously, the acidified cottonseed hull surface is covered with microspheres, forming porous carbon containing numerous micropores and mesopores. This provides a wider charge transport channel during subsequent charging and discharging of supercapacitors, thereby increasing the specific capacitance of the supercapacitor. Finally, the carbon skeleton structure of the acidified cottonseed hulls is more stable, and the prepared porous carbon, used as a capacitor electrode material, maintains its carbon skeleton structure unchanged after multiple charge-discharge cycles, exhibiting outstanding cycle stability.

Description

Technical Field

[0001] This invention relates to the field of capacitor technology, specifically to a method for preparing porous carbonated products using cottonseed hulls as raw material and its application. Background Technology

[0002] With the rapid development of the global economy, the consumption of fossil fuels, and increasing public awareness of environmental issues, the utilization of renewable energy has become increasingly urgent. The gradual replacement of fossil fuels with renewable energy is an inevitable trend. However, renewable energy sources are often unstable, have low energy density, and face many problems with energy storage technology, all of which hinder its large-scale application. Developing renewable energy into high-end materials for energy storage is a crucial solution for its efficient and sustainable utilization. Cottonseed hulls are a major byproduct of cotton processing, with China's annual cottonseed hull production estimated at approximately 1.9-2.1 million tons. Currently, cottonseed hulls are mainly used for cultivating fungi and as livestock feed, while a large amount is burned because it cannot be utilized, resulting in a waste of biomass resources and environmental pollution.

[0003] Supercapacitors have become a research hotspot in electrochemical energy storage devices due to their advantages such as high energy and power density, good stability, long cycle life, and fast charge and discharge speed. Biomass-based porous carbon has advantages such as abundant resources, high carbon content, large specific surface area, stable structure, low cost, and environmental friendliness, making it a commonly used electrode material for supercapacitors. However, Chinese Patent No. 201310536256.X discloses a method for preparing activated carbon, which uses physical mixing of potassium hydroxide for activation. The amount of potassium hydroxide used is 1 to 7 times that of the raw carbon, resulting in a large waste of resources. Furthermore, capacitors made from porous carbon prepared using this method have low electrochemical capacity and short service life.

[0004] To address the above problems, the present invention provides a solution. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying porous carbon modified from cottonseed hulls. The porous carbon prepared by this invention has well-developed pores, a large specific surface area, and a high pore utilization rate. At the same time, capacitors made using the porous carbon prepared by this invention have a large specific capacitance and a long service life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing porous carbonated modified cottonseed hulls includes the following steps:

[0007] A1: Place cottonseed hulls in an ultrasonic cleaner, add deionized water, set the ultrasonic frequency to 80-100kHz, and ultrasonically clean for 15-20 minutes. After ultrasonic cleaning, transfer the cottonseed hulls to an oven, set the oven wind speed to 1.5m / s, and the temperature to 60℃ to dry for 1-2 hours until the moisture content of the cottonseed hulls is 3-5%. Then place the cottonseed hulls in a crusher to crush, set the crusher particle size to 200 mesh, crush for 30 minutes, and then pass through a 200-mesh filter to obtain cottonseed hull powder.

[0008] A2: Place cottonseed hull powder in deionized water and add zinc chloride. Mix using a magnetic stirrer at 600-800 rpm for 15-20 minutes. After mixing, let stand for 1 hour. After standing, transfer the zinc chloride-cottonseed hull powder mixture to a high-pressure reactor. Adjust the pressure of the high-pressure reactor to 1.6-1.8 atm and the temperature to 120℃ for 30-45 minutes.

[0009] A3: After the high temperature and high pressure reaction is completed, cottonseed hull powder is separated by a 200-mesh filter screen and transferred to an oven. The air velocity is set to 1.5 m / s and the temperature is set to 60℃ for drying for 20-30 minutes. Then, the cottonseed hull powder is transferred to a 5% phosphoric acid solution for ultrasonic treatment. After ultrasonic treatment, acidified cottonseed hull powder is obtained.

[0010] A4: Transfer the acidified cottonseed hull powder to a microwave pyrolysis reactor, then fill the microwave pyrolysis reactor with nitrogen, adjust the pressure of the microwave pyrolysis reactor to 1.2-1.3 atm using nitrogen, set the power of the microwave pyrolysis reactor to 500W, and increase the temperature by 10℃ per minute to heat the acidified cottonseed hull powder to 200℃. Then set the power of the microwave pyrolysis reactor to 800W, and increase the temperature by 30℃ per minute to heat the acidified cottonseed hull powder to 800℃, and maintain the temperature at 800℃. Microwave pyrolysis for 90 minutes to obtain the pyrolysis acidified modified material.

[0011] A5: Wash the pyrolysis acidified modified material with deionized water until the pH value is 7, then transfer it to an oven. Set the oven temperature to 65℃ and the air velocity to 2m / s to obtain pre-porous carbon. Then add the pre-porous carbon to a tubular activation furnace, along with potassium hydroxide and potassium carbonate. Stir with a magnetic stirrer at a speed of 200-300rpm for 1.5-2 hours to obtain activated porous carbon.

[0012] A6: After activation, immerse the activated porous carbon in a 0.1M dilute hydrochloric acid solution for 25-30 minutes, and then wash the activated porous carbon with distilled water until the pH value is 7 to obtain porous carbon.

[0013] Furthermore, in step A2, the mass ratio of cottonseed hull powder to zinc chloride is 20:1; in step A3, the ultrasonic treatment program is set to ultrasonic once every 10s, ultrasonic for 1.5s, and ultrasonic cycle every 11.5s for a total of 30min; in step A5, the mass ratio of pre-processed porous carbon, potassium hydroxide and potassium carbonate is 15:6:4.

[0014] Furthermore, a method for preparing porous carbon using cottonseed hulls as raw material through acid modification for use in supercapacitors includes the following steps:

[0015] B1: A porous carbon prepared by acid modification of cottonseed hulls was added to a spherical grinder and ground for 15 minutes. Then it was transferred to an ultrasonic grinder, the ultrasonic power was set to 320W, and ground for 15 minutes to obtain porous carbon powder.

[0016] B2: Mix porous carbon powder, graphene powder and polytetrafluoroethylene and add to a homogenizer, homogenize for 30 minutes to obtain mixed porous carbon powder;

[0017] B3: The mixed porous carbon powder is coated on nickel foam, placed in an oven, and dried at a wind speed of 0.5 m / s and a temperature of 45°C for 30 min. Then, it is pressed into tablets using a tablet press. After the tablets are pressed, the electrode material is obtained. The electrode material is then placed in an electrolyte to obtain a supercapacitor.

[0018] Furthermore, the porous carbon powder in step B1 has a particle size of 1000 mesh; the graphene powder in step B2 is a black powder with a particle size of 300 mesh; the mass ratio of the porous carbon powder, graphene powder, and polytetrafluoroethylene in step B2 is 8:1:1; the coating thickness of the mixed porous carbon powder in step B3 is 0.3 mm; and the electrolyte is a 6 mol / L potassium hydroxide solution.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of this invention are as follows: This invention involves ultrasonically treating cottonseed hulls in a dilute acid solution, followed by acidification to modify the hulls, and then microwave-assisted pore formation to obtain porous carbon with well-developed pores and a large specific surface area. Acid washing and water washing remove minerals and residual carbon fragments from the pores, significantly improving pore utilization. Simultaneously, the acidified surface of the cottonseed hulls is covered with microspheres, forming porous carbon containing numerous micropores and mesopores, providing a wider charge transport channel during subsequent charging and discharging of the supercapacitor, thereby increasing the specific capacitance of the supercapacitor. Finally, the carbon skeleton structure of the acidified cottonseed hulls is more stable, and the porous carbon prepared from it can maintain its carbon skeleton structure after multiple charge-discharge cycles, exhibiting outstanding cycle stability. Attached Figure Description

[0020] Figure 1This is the nitrogen adsorption / desorption isotherm of Example 1.

[0021] Figure 2 This is the nitrogen adsorption / desorption isotherm of Example 2.

[0022] Figure 3 This is the GCD curve of Example 3 at 1A / g.

[0023] Figure 4 This is the rate performance curve of Example 3.

[0024] Figure 5 This is the GCD curve of Example 4 at 1A / g.

[0025] Figure 6 This is the rate performance curve of Example 4. Detailed Implementation

[0026] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. Example

[0028] 1. Place 25g of cottonseed hulls in an ultrasonic cleaner, add deionized water, set the ultrasonic frequency to 100kHz, and ultrasonically clean for 20 minutes. After ultrasonic cleaning, transfer the cottonseed hulls to an oven, set the oven wind speed to 1.5m / s, and the temperature to 60℃ to dry for 2 hours until the moisture content of the cottonseed hulls is 5%. Then place the cottonseed hulls in a crusher to crush, set the crusher particle size to 200 mesh, crush for 30 minutes, and then pass through a 200-mesh filter to obtain cottonseed hull powder.

[0029] 2: Place 20g of cottonseed hull powder in deionized water and add 1g of zinc chloride. Mix using a magnetic stirrer at 800rpm for 20 minutes. After mixing, let stand for 1 hour. After standing, transfer the zinc chloride-cottonseed hull powder mixture to a high-pressure reactor. Adjust the pressure of the high-pressure reactor to 1.6atm and the temperature to 120℃ for 45 minutes.

[0030] 3: After the high temperature and high pressure reaction is completed, cottonseed hull powder is separated using a 200-mesh filter sieve and transferred to an oven. The air velocity is set at 1.5 m / s and the temperature at 60℃ for 30 min. Then, the cottonseed hull powder is transferred to a 5% phosphoric acid solution for ultrasonic treatment. Ultrasonic treatment is performed once every 10 s for 1.5 s, and an ultrasonic cycle is performed every 11.5 s for a total of 30 min. After ultrasonic treatment, acidified cottonseed hull powder is obtained.

[0031] 4. Transfer the acidified cottonseed hull powder to a microwave pyrolysis reactor, then fill the microwave pyrolysis reactor with nitrogen and adjust the pressure of the microwave pyrolysis reactor to 1.3 atm. Set the power of the microwave pyrolysis reactor to 500W and increase the temperature by 10°C per minute to heat the acidified cottonseed hull powder to 200°C. Then set the power of the microwave pyrolysis reactor to 800W and increase the temperature by 30°C per minute to heat the acidified cottonseed hull powder to 800°C and maintain it at 800°C. Microwave pyrolysis for 90 minutes to obtain the pyrolysis acidified modified material.

[0032] 5: Wash the pyrolysis acidified modified material with deionized water until the pH value is 7, then transfer it to an oven. Set the oven temperature to 65℃ and the air velocity to 2m / s to obtain pre-porous carbon. Then add 15g of pre-porous carbon to a tubular activation furnace, along with 6g of potassium hydroxide and 4g of potassium carbonate. Stir with a magnetic stirrer at 300rpm for 1.5h to obtain activated porous carbon.

[0033] 6: After activation, the activated porous carbon is immersed in 0.1M dilute hydrochloric acid solution for 30 minutes, and then washed with distilled water until the pH value is 7 to obtain the porous carbon prepared in Example 1.

[0034] Table 1. Reagent parameters used in Example 1

[0035] Example

[0036] 1. Place 25g of cottonseed hulls in an ultrasonic cleaner, add deionized water, set the ultrasonic frequency to 80kHz, and ultrasonically clean for 20 minutes. After ultrasonic cleaning, transfer the cottonseed hulls to an oven, set the oven wind speed to 1.5m / s, and the temperature to 60℃, and dry for 1-2 hours until the moisture content of the cottonseed hulls is 3%. Then, place the cottonseed hulls in a crusher and crush them. Set the crusher particle size to 200 mesh and crush for 30 minutes. Then, filter through a 200-mesh sieve to obtain cottonseed hull powder.

[0037] 2: Place 20g of cottonseed hull powder in deionized water and add 1g of zinc chloride. Mix using a magnetic stirrer at 600rpm for 15 minutes. After mixing, let stand for 1 hour. After standing, transfer the zinc chloride-cottonseed hull powder mixture to a high-pressure reactor. Adjust the pressure of the high-pressure reactor to 1.8atm and the temperature to 120℃ for 30 minutes.

[0038] 3: After the high temperature and high pressure reaction is completed, cottonseed hull powder is separated using a 200-mesh filter sieve and transferred to an oven. The air velocity is set at 1.5 m / s and the temperature at 60℃ for 30 min. Then, the cottonseed hull powder is transferred to a 5% phosphoric acid solution for ultrasonic treatment. Ultrasonic treatment is performed once every 10 s for 1.5 s, and an ultrasonic cycle is performed every 11.5 s for a total of 30 min. After ultrasonic treatment, acidified cottonseed hull powder is obtained.

[0039] 4. Transfer the acidified cottonseed hull powder to a microwave pyrolysis reactor, then fill the microwave pyrolysis reactor with nitrogen and adjust the pressure of the microwave pyrolysis reactor to 1.2 atm. Set the power of the microwave pyrolysis reactor to 500W and the temperature to rise by 10°C per minute to heat the acidified cottonseed hull powder to 200°C. Then set the power of the microwave pyrolysis reactor to 800W and the temperature to rise by 30°C per minute to heat the acidified cottonseed hull powder to 800°C and maintain it at 800°C. Microwave pyrolysis for 90 minutes to obtain the pyrolysis acidified modified material.

[0040] 5: Wash the pyrolysis acidified modified material with deionized water until the pH value is 7, then transfer it to an oven. Set the oven temperature to 65℃ and the air velocity to 2m / s to obtain pre-porous carbon. Then add 15g of pre-porous carbon to a tubular activation furnace, along with 6g of potassium hydroxide and 4g of potassium carbonate. Stir with a magnetic stirrer at 200rpm for 2 hours to obtain activated porous carbon.

[0041] 6: After activation, the activated porous carbon is immersed in 0.1M dilute hydrochloric acid solution for 25 minutes, and then washed with distilled water until the pH value is 7 to obtain the porous carbon prepared in Example 2.

[0042] Table 2, Reagent Parameters Used in Example 2

[0043] Example

[0044] 1: The porous carbon prepared in Example 1 was added to a spherical grinder and ground for 15 minutes, and then transferred to an ultrasonic grinder. The ultrasonic power was set to 320W and ground for 15 minutes to obtain 1000 mesh porous carbon powder.

[0045] 2: Mix 8g of porous carbon powder, 1g of graphene powder and 1g of polytetrafluoroethylene and add them to a homogenizer. Homogenize for 30 minutes to obtain mixed porous carbon powder.

[0046] 3: The mixed porous carbon powder was coated on the nickel foam to a thickness of 0.3 mm. Then the nickel foam was placed in an oven and dried at a wind speed of 0.5 m / s and a temperature of 45 °C for 30 min. Then the foam was pressed into tablets using a tablet press. After pressing, the electrode material was obtained. The electrode material was placed in a 6 mol / L potassium hydroxide solution to obtain the supercapacitor prepared in Example 3.

[0047] Table 3. Reagent parameters used in Example 3

[0048] Example

[0049] 1: The porous carbon prepared in Example 2 was added to a spherical grinder and ground for 15 minutes. Then it was transferred to an ultrasonic grinder, the ultrasonic power was set to 320W, and it was ground for 15 minutes to obtain 1000 mesh porous carbon powder.

[0050] 2: Mix 8g of porous carbon powder, 1g of graphene powder and 1g of polytetrafluoroethylene and add them to a homogenizer. Homogenize for 30 minutes to obtain mixed porous carbon powder.

[0051] 3: The mixed porous carbon powder was coated on the nickel foam to a thickness of 0.3 mm. Then the nickel foam was placed in an oven and dried at a wind speed of 0.5 m / s and a temperature of 45 °C for 30 min. Then the foam was pressed into tablets using a tablet press. After pressing, the electrode material was obtained. The electrode material was placed in a 6 mol / L potassium hydroxide solution to obtain the supercapacitor prepared in Example 4.

[0052] Table 4. Reagent parameters used in Example 4

[0053]

[0054] Comparative Example 1

[0055] Example 1 of publication number CN109231204A was selected as Comparative Example 1.

[0056] Comparative Example 2

[0057] Using Ag / AgCl as the reference electrode and a platinum sheet as the counter electrode, the supercapacitor prepared in Comparative Example 2 was obtained by placing it in a 6 mol / L potassium hydroxide solution.

[0058] Physical performance testing:

[0059] The physical properties of the porous carbon prepared in Examples 1, 2 and 1 were tested.

[0060] Table 5. Results of Physical Performance Tests

[0061]

[0062] As can be seen from the analysis of Table 5, the porous carbon prepared by the present invention has better physical properties. Among them, the porous carbon prepared in Example 2 has well-developed pores and a larger specific surface area. It has a large number of micropores and a large amount of stored charge, making it suitable for preparing supercapacitors.

[0063] Electrochemical testing:

[0064] Electrochemical tests were performed on the supercapacitors prepared in Examples 3, 4 and Comparative Example 2, with a current density of 1 A / g.

[0065] Table 6. Electrochemical test results

[0066]

[0067] Analysis of Table 6 shows that the supercapacitors prepared using the porous carbon prepared in Examples 1 and 2 have a larger specific capacitance and good capacitance retention after cyclic charging. Among them, the supercapacitor prepared in Example 4 has the best specific capacitance because it uses the porous carbon prepared in Example 2.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing porous carbonated products using cottonseed hulls as raw material, characterized in that, Includes the following steps: A1: Place cottonseed hulls in an ultrasonic cleaner, add deionized water, set the ultrasonic frequency to 80-100kHz, and ultrasonically clean for 15-20 minutes. After ultrasonic cleaning, transfer the cottonseed hulls to an oven, set the oven wind speed to 1.5m / s, and the temperature to 60℃ to dry for 1-2 hours until the moisture content of the cottonseed hulls is 3-5%. Then place the cottonseed hulls in a crusher to crush, set the crusher particle size to 200 mesh, crush for 30 minutes, and then pass through a 200-mesh filter to obtain cottonseed hull powder. A2: Place cottonseed hull powder in deionized water and add zinc chloride. Mix using a magnetic stirrer at 600-800 rpm for 15-20 minutes. After mixing, let stand for 1 hour. After standing, transfer the zinc chloride-cottonseed hull powder mixture to a high-pressure reactor. Adjust the pressure of the high-pressure reactor to 1.6-1.8 atm and the temperature to 120℃ for 30-45 minutes. A3: After the high temperature and high pressure reaction is completed, cottonseed hull powder is separated by a 200-mesh filter screen and transferred to an oven. The air velocity is set to 1.5 m / s and the temperature is set to 60℃ for drying for 20-30 minutes. Then, the cottonseed hull powder is transferred to a 5% phosphoric acid solution for ultrasonic treatment. After ultrasonic treatment, acidified cottonseed hull powder is obtained. A4: Transfer the acidified cottonseed hull powder to a microwave pyrolysis reactor, then fill the microwave pyrolysis reactor with nitrogen, adjust the pressure of the microwave pyrolysis reactor to 1.2-1.3 atm using nitrogen, set the power of the microwave pyrolysis reactor to 500W, and increase the temperature by 10℃ per minute to heat the acidified cottonseed hull powder to 200℃. Then set the power of the microwave pyrolysis reactor to 800W, and increase the temperature by 30℃ per minute to heat the acidified cottonseed hull powder to 800℃, and maintain the temperature at 800℃. Microwave pyrolysis for 90 minutes to obtain the pyrolysis acidified modified material. A5: Wash the pyrolysis acidified modified material with deionized water until the pH value is 7, then transfer it to an oven. Set the oven temperature to 65℃ and the air velocity to 2m / s to obtain pre-porous carbon. Then add the pre-porous carbon to a tubular activation furnace, along with potassium hydroxide and potassium carbonate. Stir with a magnetic stirrer at a speed of 200-300rpm for 1.5-2 hours to obtain activated porous carbon. A6: After activation, immerse the activated porous carbon in a 0.1M dilute hydrochloric acid solution for 25-30 minutes, and then wash the activated porous carbon with distilled water until the pH value is 7 to obtain porous carbon.

2. The method for preparing porous carbonated material using cottonseed hulls as raw material according to claim 1, characterized in that, In step A2, the mass ratio of cottonseed hull powder to zinc chloride is 20:

1.

3. The method for preparing porous carbonated material using cottonseed hulls as raw material according to claim 1, characterized in that, In step A3, the ultrasound treatment program is set to perform ultrasound once every 10 seconds, with each ultrasound session lasting 1.5 seconds. Each ultrasound cycle lasts 11.5 seconds, for a total of 30 minutes.

4. The method for preparing porous carbonated material using cottonseed hulls as raw material according to claim 1, characterized in that, In step A5, the mass ratio of pre-porous carbon, potassium hydroxide, and potassium carbonate is 15:6:

4.

5. A method for preparing porous carbon obtained by any one of claims 1-4 in the fabrication of a supercapacitor, characterized in that, Includes the following steps: B1: A porous carbon prepared by acid modification of cottonseed hulls was added to a spherical grinder and ground for 15 minutes. Then it was transferred to an ultrasonic grinder, the ultrasonic power was set to 320W, and ground for 15 minutes to obtain porous carbon powder. B2: Mix porous carbon powder, graphene powder and polytetrafluoroethylene and add to a homogenizer, homogenize for 30 minutes to obtain mixed porous carbon powder; B3: The mixed porous carbon powder is coated on nickel foam, placed in an oven, and dried at a wind speed of 0.5 m / s and a temperature of 45°C for 30 min. Then, it is pressed into tablets using a tablet press. After the tablets are pressed, the electrode material is obtained. The electrode material is then placed in an electrolyte to obtain a supercapacitor.

6. The preparation method according to claim 5, characterized in that, The porous carbon powder mentioned in step B1 has a particle size of 1000 mesh.

7. The preparation method according to claim 5, characterized in that, The graphene powder mentioned in step B2 is a black powder with a particle size of 300 mesh.

8. The preparation method according to claim 5, characterized in that, The mass ratio of porous carbon powder, graphene powder and polytetrafluoroethylene mentioned in step B2 is 8:1:

1.

9. The preparation method according to claim 5, characterized in that, The coating thickness of the mixed porous carbon powder mentioned in step B3 is 0.3 mm, and the electrolyte is a 6 mol / L potassium hydroxide solution.

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