A method for preparing coconut shell-based porous carbon materials based on co-activation

Abstract

This invention belongs to the field of carbon materials technology, specifically relating to a method for preparing coconut shell-based porous carbon materials based on co-activation. The method involves pre-treating coconut shell material to obtain pre-carbonized material, then crushing and sieving it to obtain sieved pre-carbonized material; followed by activation reaction and post-treatment to obtain coconut shell-based porous carbon materials. This invention develops a method for preparing coconut shell-based porous carbon with controllable pore structure, stable interface, and suitability for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials technology, specifically relating to a method for preparing coconut shell-based porous carbon materials based on co-activation. Background Technology

[0002] With the advancement of low-carbon energy systems, the requirements for single-cell energy density and cycle stability of power batteries and energy storage systems are constantly increasing. Commercial graphite anodes are limited to 372mAh g / L. -1 The theoretical capacity of [the material] is insufficient to meet the demands of next-generation high-energy-density batteries. Silicon materials, with their high capacity of up to 4200mAh g / g, [are also problematic]. -1 Silicon's theoretical capacity and cost advantages make it the most promising alternative anode material. However, silicon undergoes a 300% volume expansion during charging and discharging, leading to particle breakage, electrode structure instability, and repeated SEI film formation, resulting in low initial efficiency and rapid capacity decay, which severely restricts its commercial application.

[0003] Porous carbon, with its tunable pore structure, high specific surface area, and excellent conductivity, can effectively buffer silicon volume expansion, stabilize interfaces, and improve ion / electron transport, making it a key material for mitigating the volume effect and interface failure of silicon anodes. Coconut shells, as a biomass resource with high carbon content, dense structure, and low ash content, are an excellent raw material for preparing high-performance porous carbon. Currently, the main methods for preparing porous carbon materials include chemical activation and physical activation. Chemical activation typically requires activators such as potassium hydroxide, phosphoric acid, and zinc chloride. While these methods are beneficial for pore formation, they introduce impurities, increase the difficulty of post-processing, and impose a certain burden on the environment. Physical activation avoids the impurity residues and environmental burden associated with chemical activation. However, existing physical activation methods mostly rely on CO2 or water vapor alone, leading to difficulties in controlling pore size distribution, insufficient synergy between micropores and mesopores, poor structural uniformity, limited surface chemical control capabilities, and imperfect pore connectivity and conductive networks. Therefore, it is impossible to achieve synergistic optimization of pore structure and interface properties at low cost. Thus, there is an urgent need to develop a coconut shell-based porous carbon preparation method with controllable pore structure, stable interface, and suitability for large-scale production. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing coconut shell-based porous carbon materials based on joint activation, which solves the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing coconut shell-based porous carbon materials based on co-activation includes the following steps: The coconut shell material is pretreated to obtain the treated coconut shell material, pre-carbonized to obtain the pre-carbonized material, crushed and sieved to obtain the sieved pre-carbonized material; activated reaction, post-treatment, to obtain coconut shell-based porous carbon material.

[0006] Further, the natural coconut shells are pretreated to obtain processed coconut shell material, including the following steps: Select mature natural coconut shells as the coconut shell material, clean the coconut shell material, dry it at 80-120℃ for 6-24 hours, crush it, and control the particle size after crushing to 2-10mm to obtain the processed coconut shell material.

[0007] Further, pre-carbonization is performed to obtain pre-carbonized material, including the following steps: Pre-carbonization is carried out in a protective atmosphere and a batch rotary kiln, with the temperature increased to 400-500℃ at a heating rate of 3-5℃ / min and held for 30-90min. After cooling, the pre-carbonized material is obtained.

[0008] Furthermore, the activation reaction includes the following steps: The pre-carbonized material after screening is first activated with CO2 in a protective atmosphere and in an intermittent rotary kiln, then activated with steam, and cooled to room temperature.

[0009] Preferably, CO2 activation is performed first, followed by water vapor activation, including the following steps: Increase the temperature to 300-500℃ at a rate of 3-5℃ / min, hold for 20-40 min, continue increasing the temperature to 850-900℃ at a rate of 3-5℃ / min, and stabilize at 850-900℃. Then introduce CO2 at a flow rate of 5-10 L / min and maintain the activation reaction at 850-900℃ for 50-70 min. After that, stop introducing CO2, increase the temperature to 850-900℃ at a rate of 3-5℃ / min, stabilize at 850-900℃, and then introduce water vapor at a flow rate of 1.0-1.5 kg / h and maintain the activation reaction at 850-900℃ for 90-180 min.

[0010] In a further preferred embodiment, the activation reaction of introducing CO2 lasts for 50-70 minutes, the activation reaction of introducing water vapor lasts for 90-180 minutes, and the total time for the CO2 activation reaction and the water vapor activation reaction is 120-180 minutes.

[0011] Further post-processing includes the following steps: After the activation reaction, the steam supply was stopped, the heating was turned off, and the material was kept under a protective atmosphere and allowed to cool naturally to room temperature. The material was then removed, crushed, and sieved, with the particle size D50 controlled at 6-8 μm. After drying, coconut shell-based porous carbon material was obtained.

[0012] In a further preferred embodiment, the activation reaction of introducing CO2 lasts for 50-70 minutes, the activation reaction of introducing water vapor lasts for 90-180 minutes, and the total time for the CO2 activation reaction and the water vapor activation reaction is 120-180 minutes.

[0013] Furthermore, the particle size D50 of the pre-carbonized material after screening is 1-2 mm.

[0014] Preferably, the protective atmosphere includes argon and / or nitrogen.

[0015] The beneficial effects of this invention are: 1. Precise and controllable hole structure This invention constructs a CO2 and water vapor co-activation system, utilizing the difference in reactivity of the two activation gases at high temperatures to achieve progressive etching of the coconut shell carbon skeleton through a weak oxidation and strong oxidation coupling mechanism. This method can control micropore formation and pore continuity, improve pore structure uniformity, and simultaneously maintain the integrity of the carbon skeleton and the stability of the pore walls.

[0016] 2. High specific surface area and uniform porosity The combined CO2 and water vapor activation system enhances the etching uniformity of the carbon framework, enabling porous carbon materials to achieve high specific surface area and high pore volume, while maintaining stable pore walls and concentrated pore size distribution. The material surface is rich in appropriate amounts of active functional groups and defect structures, providing adjustable space for subsequent surface chemical modification or interface control, while ensuring the continuity and permeability of the pore structure.

[0017] 3. Green, efficient, and scalable process This invention uses inexpensive and renewable coconut shells as raw materials, achieving efficient preparation through physical activation, with no chemical residue pollution and avoiding the generation of wastewater and solid waste. CO2 and water vapor are widely available, low in cost, and the process is safe and reliable; the process parameter window is wide and highly repeatable, suitable for large-scale industrial preparation. At the same time, the pore structure and surface chemistry of the material can be precisely controlled by adjusting the activation temperature, time, and gas ratio.

[0018] 4. Existing physical activation methods mostly use single CO2 or water vapor, or a mixture of gases for simultaneous activation, but they have the following drawbacks: single CO2 activation results in insufficient pore expansion and limited improvement in specific surface area; single water vapor activation results in severe etching and uneven pore structure; although mixed activation can combine the advantages of both, it is difficult to achieve staged control of micropore generation and pore expansion, resulting in poor pore structure uniformity and insufficient framework stability.

[0019] This application achieves a specific surface area and pore volume comparable to those obtained by doping methods by controlling the gas activation sequence and parameters without relying on doping.

[0020] This invention discovers that the activation sequence affects the pore structure; and that sequential activation is superior to mixed activation, with CO2 and water vapor exhibiting a synergistic effect. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the nitrogen adsorption / desorption isotherm for preparing coconut shell-based porous carbon in Example 1 of the present invention; Figure 2 This is a schematic diagram of the pore size distribution of coconut shell-based porous carbon prepared in Example 1 of the present invention; Figure 3 This is a schematic diagram of the nitrogen adsorption / desorption isotherms for preparing coconut shell-based porous carbon in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0024] Unless otherwise specified, the equipment and materials used in the embodiments can be readily obtained from commercial companies.

[0025] Example 1 A method for preparing coconut shell-based porous carbon materials based on co-activation, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0026] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0027] S3. Crush and sieve the pre-carbonized material, controlling the particle size D50 to about 2mm, to obtain the sieved pre-carbonized material.

[0028] S4. Place 2 kg of the sieved pre-carbonized material in a batch rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 850°C at a rate of 3°C / min and stabilize at 850°C. Simultaneously introduce CO2 at a flow rate of 10 L / min and maintain the activation reaction at 850°C for 60 min. Then stop the CO2 gas supply and raise the temperature to 900°C at a rate of 3°C / min. Stabilize at 900°C and simultaneously introduce water vapor at a flow rate of approximately 1.2 kg / h and maintain the activation reaction at 900°C for 120 min.

[0029] S5. After the steam activation reaction is complete, stop the steam supply, turn off the heating, keep under a nitrogen atmosphere, and allow it to cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8 μm, and dry it at 80℃ for 12 h to obtain coconut shell-based porous carbon material.

[0030] Example 2 A method for preparing coconut shell-based porous carbon materials based on co-activation, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0031] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0032] S3. The pre-carbonized material is crushed and sieved. The particle size D50 after sieving is controlled at about 2mm to obtain the sieved pre-carbonized material.

[0033] S4. Place 2 kg of the sieved pre-carbonized material in an intermittent rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 850°C at a rate of 3°C / min and stabilize at 850°C. Simultaneously introduce CO2 at a flow rate of 5 L / min and maintain the activation reaction at 850°C for 60 min. Then stop the CO2 supply and raise the temperature to 900°C at a rate of 3°C / min. Stabilize at 900°C and simultaneously introduce steam at a flow rate of 1.2 kg / h and maintain the activation reaction at 900°C for 120 min.

[0034] S5. After the steam activation reaction is complete, stop the steam supply, turn off the heating, keep under a nitrogen atmosphere, and allow it to cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8 μm, and dry it at 80℃ for 12 h to obtain coconut shell-based porous carbon material.

[0035] Example 3 A method for preparing coconut shell-based porous carbon materials based on co-activation, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0036] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0037] S3. The pre-carbonized material is crushed and sieved. The particle size D50 after sieving is controlled at about 2mm to obtain the sieved pre-carbonized material.

[0038] S4. Place 2 kg of the sieved pre-carbonized material in a batch rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 850°C at a rate of 3°C / min and stabilize at 850°C. Simultaneously introduce CO2 at a flow rate of 10 L / min and maintain the activation reaction at 850°C for 60 min. Then stop the CO2 gas supply and raise the temperature to 900°C at a rate of 3°C / min. Stabilize at 900°C and simultaneously introduce water vapor at a flow rate of 1.2 kg / h and maintain the activation reaction at 900°C for 90 min.

[0039] S5. After the steam activation reaction is complete, stop the steam supply, turn off the heating, keep under a nitrogen atmosphere, and allow it to cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8 μm, and dry it at 80℃ for 12 h to obtain coconut shell-based porous carbon material.

[0040] Example 4 A method for preparing coconut shell-based porous carbon materials based on co-activation, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0041] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0042] S3. The pre-carbonized material is crushed and sieved. The particle size D50 after sieving is controlled at about 2mm to obtain the sieved pre-carbonized material.

[0043] S4. Place 2 kg of the sieved pre-carbonized material in an intermittent rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 850°C at a rate of 3°C / min and stabilize at 850°C. Simultaneously introduce CO2 at a flow rate of 10 L / min and maintain the activation reaction at 850°C for 60 min. Then stop the CO2 gas supply and raise the temperature to 900°C at a rate of 3°C / min. Stabilize at 900°C and simultaneously introduce water vapor at a flow rate of 1.0 kg / h and maintain the activation reaction at 900°C for 120 min.

[0044] S5. After the steam activation reaction is complete, stop the steam supply, turn off the heating, keep under a nitrogen atmosphere, and allow it to cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8 μm, and dry it at 80℃ for 12 h to obtain coconut shell-based porous carbon material.

[0045] Comparative Example 1 A method for preparing coconut shell-based porous carbon material differs from Example 1 in that the activation reaction in S4 is not performed, while the rest of the steps are the same as in Example 1.

[0046] Comparative Example 2 A method for preparing coconut shell-based porous carbon material differs from Example 1 in that: in step S4, when the temperature is stable at 850°C, CO2 is introduced at a flow rate of 10 L / min for 60 min; when the temperature is stable at 900°C, CO2 is introduced at a flow rate of 10 L / min for 120 min. The rest of the steps are the same as in Example 1.

[0047] Comparative Example 3 A method for preparing coconut shell-based porous carbon material, compared with Example 1, differs in that: in S4, when the temperature is stable at 850℃, water vapor is introduced at a flow rate of 1.2 kg / h and the activation time is 60 min; when the temperature is stable at 900℃, water vapor is introduced at a flow rate of 1.2 kg / h and the activation time is 120 min. The rest of the steps are the same as those in Example 1.

[0048] Comparative Example 4 A method for preparing coconut shell-based porous carbon material differs from Example 1 in that: in step S4, no CO2 activation reaction is carried out at 850℃; water vapor is introduced only when the temperature stabilizes at 900℃, with a flow rate of 1.2 kg / h and an activation time of 120 min; the rest of the steps are the same as in Example 1.

[0049] Comparative Example 5 A method for preparing coconut shell-based porous carbon material, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0050] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0051] S3. Crush and sieve the pre-carbonized material, controlling the particle size D50 to about 2mm, to obtain the sieved pre-carbonized material.

[0052] S4. Place 2 kg of the sieved pre-carbonized material in a batch rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 850°C at a rate of 3°C / min and stabilize at 850°C. Simultaneously introduce steam at a flow rate of 1.2 kg / h and maintain the activation reaction at 850°C for 60 min. Then stop introducing steam and raise the temperature to 900°C at a rate of 3°C / min. Stabilize at 900°C and simultaneously introduce CO2 gas at a flow rate of approximately 10 L / min and maintain the activation reaction at 900°C for 120 min.

[0053] S5. After the CO2 activation reaction is complete, stop the CO2 gas supply, turn off the heating, maintain in a nitrogen atmosphere, and allow it to cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8 μm, and dry it at 80℃ for 12 h to obtain coconut shell-based porous carbon material.

[0054] Comparative Example 6 A method for preparing coconut shell-based porous carbon material, the specific steps of which are as follows: S1. Rinse the mature natural coconut shells with water, then place them in an oven and dry them at 80℃ for 24 hours. After drying, use a pulverizer to crush the coconut shells. The particle size after crushing should be controlled at 2-10mm to obtain the processed coconut shell material.

[0055] S2. Place the pretreated coconut shell material in an intermittent rotary kiln and pre-carbonize it by heating it to 500°C at a rate of 3°C / min under a nitrogen atmosphere and holding it at that temperature for 1 hour. After cooling to room temperature, the pre-carbonized material is obtained.

[0056] S3. Crush and sieve the pre-carbonized material, controlling the particle size D50 to about 2mm, to obtain the sieved pre-carbonized material.

[0057] S4. Place 2 kg of pre-carbonized material after sieving in an intermittent rotary kiln. Under a nitrogen atmosphere, raise the temperature to 400°C at a rate of 3°C / min and hold for 30 min. Continue raising the temperature to 900°C at a rate of 3°C / min and stabilize at 900°C. Simultaneously introduce steam and CO2. The flow rate of CO2 is 10 L / min and the flow rate of steam is approximately 1.2 kg / h. Maintain the activation reaction at 900°C for 120 min.

[0058] S5. After the activation reaction is complete, stop the introduction of CO2 gas and water vapor, turn off the heating, keep under nitrogen atmosphere, and let it cool naturally to room temperature. Take out the sample, crush and sieve the activated carbon material, control the particle size D50 to 6-8μm, and dry it at 80℃ for 12h to obtain coconut shell-based porous carbon material.

[0059] The performance of the coconut shell-based porous carbon materials prepared in Examples 1-4 and Comparative Examples 1-6 was tested, and the results are shown in Table 1.

[0060] Table 1. Test results of the properties of coconut shell-based porous carbon

[0061] According to the test results of Examples 1-4 in Table 1, the present invention uses coconut shell raw materials for pretreatment, precarbonization, CO2 / water vapor combined activation, and posttreatment to obtain coconut shell-based porous carbon materials with controllable specific surface area, total pore volume, and average pore diameter.

[0062] According to Table 1, the specific surface area of ​​the coconut shell-based porous carbon material obtained by CO2 / water vapor co-activation in Example 1 is 1938.864 m². 2 / g, total pore volume is 0.934cm³ 3 The average pore size was 1.928 nm. Compared to Example 1, the CO2 flow rate was reduced to 5 L / min in Example 2, resulting in a weaker CO2 activation reaction. Nevertheless, the specific surface area of ​​the obtained porous carbon material was 1915.567 m² / g. 2 The change in g / g was not significant, but the total pore volume decreased to 0.832 cm³. 3The average pore size decreased to 1.737 nm, indicating that the overall pore expansion and pore volume were less affected by the decrease in CO2 etching intensity. Therefore, changes in CO2 flow rate mainly affect the pore etching depth and pore volume, while the specific surface area remains relatively stable under the activation effect of water vapor.

[0063] According to Table 1, compared with Example 1, Example 3 shortened the steam activation time to 90 min, significantly weakening the etching effect of steam on coconut shell carbon. Due to the shortened activation time, the steam could not fully penetrate and react within the carbon framework, resulting in insufficient micropore formation and channel expansion. Therefore, the specific surface area of ​​the obtained porous carbon material decreased to 1690.688 m². 2 / g, total pore volume decreased to 0.726cm³. 3 / g, with the average pore size reduced to 1.718nm. Water vapor activation time is a crucial factor in regulating the development of the pore structure in coconut shell-based carbon materials, directly affecting the number, volume, and size of pores.

[0064] According to Table 1, compared with Example 1, the water vapor flow rate in Example 4 was reduced to 1.0 kg / h, resulting in a weakened activation etching intensity of the coconut shell carbon skeleton by the water vapor. The reduced activation intensity of the water vapor resulted in insufficient micropore formation and pore expansion on the surface and interior of the carbon material, thus slightly decreasing the specific surface area of ​​the obtained porous carbon material to 1846.875 m². 2 / g, total pore volume is 0.831cm³ 3 / g, with an average pore size of 1.800 nm. This indicates that the water vapor flow rate directly affects the activation depth and pore development of the carbon framework, thereby regulating the pore structure parameters of the material.

[0065] According to Table 1, compared with Example 1, Comparative Example 1 did not undergo CO2 / water vapor combined activation, and its specific surface area was 84.487 m². 2 / g, total pore volume is 0.064cm³ 3 The carbon skeleton lacks effective oxidation etching under conditions without co-activation, resulting in insufficient micropore formation and channel expansion, leading to inadequate overall pore structure development and thus failing to achieve a high specific surface area and large total pore volume. Therefore, CO2 / water vapor co-activation is a crucial step in forming carbon materials with high specific surface area and porous structure.

[0066] According to Table 1, compared with Example 1, Comparative Example 2 only underwent single CO2 activation, specifically CO2 activation at 850°C for 60 min and at 900°C for 120 min, for a total activation time of 180 min. The specific surface area of ​​the obtained material was 762.867 m². 2 / g, total pore volume is 0.307cm³3 The average pore size and pore diameter were 1.610 nm, both significantly lower than those in Example 1. Therefore, the oxidation etching intensity activated by CO2 alone was limited, water vapor did not participate in etching and pore expansion, the generation of micropores inside the carbon framework was insufficient, pore expansion was restricted, and the overall pore structure was underdeveloped, resulting in a significant decrease in total pore volume and specific surface area.

[0067] According to Table 1, compared with Example 1, Comparative Example 3 only underwent single steam activation, specifically steam activation at 850°C for 60 min and at 900°C for 120 min, for a total activation time of 180 min. The specific surface area of ​​the obtained material was 2196.873 m². 2 / g, total pore volume is 1.210cm³ 3 The surface area per unit weight (S / g) and average pore size (2.204 nm) are significantly higher than those in Example 1. This indicates that single-phase steam activation possesses strong oxidative etching capabilities, rapidly generating numerous micropores and expanding pore channels. However, excessive etching leads to over-etching of the internal structure of the carbon framework, resulting in excessively large pore volumes and increased average pore size, thus reducing the overall stability of the carbon framework. While single-phase steam activation can increase specific surface area, it lacks a balanced control over pore structure and framework stability, making it difficult to obtain porous carbon materials with uniform and stable structures.

[0068] According to Table 1, compared with Example 1, Comparative Example 4 only underwent steam activation at 900°C for 120 min, and the resulting material had a specific surface area of ​​1728.361 m². 2 / g, total pore volume is 0.749cm³ 3 The surface area and average pore size were 1.707 nm, both lower than in Example 1. Therefore, in the absence of CO2-assisted oxidation, activation of coconut shell carbon by single steam for 120 min was weakened, failing to provide a larger total pore volume, resulting in a significant reduction in specific surface area and total pore volume.

[0069] According to Table 1, the present invention, through comparative examples 5 and 6, found that the activation sequence affects the pore structure of coconut shell-based porous carbon: (1) The order cannot be changed: Comparative Example 5 adopted the activation order of steam first and then CO2, and the specific surface area of ​​the obtained material was <1500 m². 2 / g, total pore volume <0.7 cm³ 3 / g, lower than in Example 1. This is because the reactivity of water vapor with carbon is much higher than that of CO2. In the early stage, water vapor excessively etches and destroys the carbon skeleton and consumes active sites. Subsequently, CO2 cannot effectively construct pores, making it difficult to accurately construct microporous structures with high specific surface area.

[0070] (2) Separate introduction is better than mixed introduction: Comparative Example 6 uses mixed activation by simultaneously introducing CO2 and water vapor. The resulting material has an uneven pore structure and poor pore wall integrity, and cannot achieve the pore structure controllability of Example 1. This is because the two gases compete for reaction in mixed activation, making it impossible to achieve the staged control of first constructing micropores and then expanding the pore channels.

[0071] (3) Synergistic effect: The order of CO2 first and then water vapor is used to construct a microporous framework by using the mild etching of CO2, and then the strong oxidation effect of water vapor is used to expand the pores, so as to achieve progressive etching and obtain porous carbon materials with controllable pore structure and complete framework.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing coconut shell-based porous carbon materials based on co-activation, characterized in that, Includes the following steps: The coconut shell material is pretreated to obtain the treated coconut shell material, pre-carbonized to obtain the pre-carbonized material, crushed and sieved to obtain the sieved pre-carbonized material; activated reaction, post-treatment, to obtain coconut shell-based porous carbon material.

2. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 1, characterized in that, Pre-treatment of natural coconut shells to obtain processed coconut shell material includes the following steps: Select mature natural coconut shells as the coconut shell material, clean the coconut shell material, dry it at 80-120℃ for 6-24 hours, crush it, and control the particle size after crushing to 2-10mm to obtain the processed coconut shell material.

3. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 1, characterized in that, Pre-carbonization, to obtain pre-carbonized material, includes the following steps: Pre-carbonization is carried out in a protective atmosphere and a batch rotary kiln, with the temperature increased to 400-500℃ at a heating rate of 3-5℃ / min and held for 30-90min. After cooling, the pre-carbonized material is obtained.

4. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 1, characterized in that, The activation reaction includes the following steps: The pre-carbonized material after screening is first activated with CO2 in a protective atmosphere and in an intermittent rotary kiln, then activated with steam, and cooled to room temperature.

5. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 4, characterized in that, First, CO2 activation is performed, followed by water vapor activation, including the following steps: Increase the temperature to 300-500℃ at a rate of 3-5℃ / min, hold for 20-40 min, continue increasing the temperature to 850-900℃ at a rate of 3-5℃ / min, and stabilize at 850-900℃. Then introduce CO2 and maintain the activation reaction at 850-900℃ for 50-70 min. After that, stop introducing CO2, increase the temperature to 850-900℃ at a rate of 3-5℃ / min, stabilize at 850-900℃, and then introduce water vapor and maintain the activation reaction at 850-900℃ for 90-180 min.

6. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 1, characterized in that, Post-processing includes the following steps: After the activation reaction, the steam supply was stopped, the heating was turned off, and the material was kept under a protective atmosphere and allowed to cool naturally to room temperature. The material was then removed, crushed, and sieved, with the particle size D50 controlled at 6-8 μm. After drying, coconut shell-based porous carbon material was obtained.

7. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 5, characterized in that, When CO2 is introduced, the CO2 flow rate is 5-10 L / min.

8. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 5, characterized in that, Steam is introduced at a flow rate of 1.0-1.5 kg / h.

9. The method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 1, characterized in that, The particle size D50 of the pre-carbonized material after screening is 1-2 mm.

10. A method for preparing coconut shell-based porous carbon materials based on co-activation according to claim 3, 4, or 6, characterized in that, The protective atmosphere includes argon and / or nitrogen.

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