Preparation method of coconut shell-based activated carbon

Abstract

The invention relates to the field of activated carbon preparation, and discloses a preparation method of coconut shell-based activated carbon. The preparation method comprises the following steps: pretreating raw materials, crushing coconut shells, sieving, washing and drying to obtain coconut shell particles; activating pretreatment: soaking the coconut shell particles into an activating agent, standing after soaking, and draining; carbonization treatment: in a nitrogen atmosphere, raising the temperature to 300 DEG C, and carrying out heat preservation and carbonization to obtain carbide; gradient activation treatment is conducted, specifically, the carbide is heated to 500 DEG C in the CO2 atmosphere, heat preservation activation is conducted, after heat preservation is finished, the carbide continues to be heated to 750 DEG C, heat preservation activation is conducted, and an activator is obtained; and carrying out post-treatment, recovering and removing the activating agent, and drying. According to the method, the pore structure of the activated carbon is optimized, the ratio of mesopores to macropores is increased while the high specific surface area is guaranteed, the adsorption capacity of the activated carbon to water COD is further improved, and sewage treatment of high-COD organic pollutants such as industrial wastewater and printing and dyeing wastewater can be met.

Description

Technical Field

[0001] This application relates to the field of activated carbon preparation, and more specifically, it relates to a method for preparing coconut shell-based activated carbon. Background Technology

[0002] Activated carbon is a porous carbon material with a well-developed pore structure, high specific surface area, and excellent adsorption performance, widely used in environmental protection, energy storage, chemical separation, and medical and health fields. In water treatment, chemical oxygen demand (COD) is an important indicator for measuring the degree of organic pollution in water bodies, and activated carbon, due to its high adsorption capacity, has become one of the key materials for COD removal. Traditional raw materials for activated carbon preparation mainly include coal, wood, and fruit shells. Among them, coconut shells are considered one of the ideal raw materials for preparing high-performance activated carbon due to their high carbon content, high density, and unique pore structure, especially suitable for high-requirement wastewater treatment scenarios.

[0003] Currently, the main methods for preparing coconut shell-based activated carbon include physical activation and chemical activation. Physical activation typically uses steam or carbon dioxide as an activating agent to activate carbonized coconut shells at high temperatures. However, this method suffers from high activation temperatures and high energy consumption, and the resulting activated carbon has a low proportion of mesopores and macropores, limiting its adsorption capacity for large-molecule organic pollutants in water. Chemical activation uses chemical reagents such as phosphoric acid, potassium hydroxide, and zinc chloride as activating agents. While this can lower the activation temperature and increase the yield, it suffers from strong corrosiveness and challenges in wastewater treatment, limiting its application in water treatment. Furthermore, coconut shell-based activated carbon prepared by traditional methods often suffers from uneven pore size distribution and insufficient specific surface area, further limiting its application in water treatment.

[0004] Chinese patent CN115974079A discloses a process for preparing activated carbon using coconut shells as raw material. This process increases the formation of micropores and voids in the activated carbon, resulting in more comprehensive contact and effectively improving the specific surface area of ​​the activated carbon, thereby increasing its COD removal efficiency from water. However, simply increasing the specific surface area of ​​activated carbon has limited effect on improving COD removal efficiency. If the pore structure of coconut shell-based activated carbon can be reasonably optimized, increasing the proportion of mesopores and macropores while maintaining a high specific surface area, it will help further improve the activated carbon's adsorption capacity for COD in water, meeting the needs of wastewater treatment for high-COD organic pollutants such as industrial wastewater and dyeing wastewater. Summary of the Invention

[0005] The purpose of this invention is to find a way to optimize the pore structure of coconut shell-based activated carbon, thereby increasing the proportion of mesopores and macropores while ensuring a high specific surface area, so as to further improve the adsorption capacity of activated carbon for COD in water and meet the needs of wastewater treatment for high COD organic pollutants such as industrial wastewater and dyeing wastewater.

[0006] To achieve the above-mentioned objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for preparing coconut shell-based activated carbon, comprising the following steps: Step 1, Raw material pretreatment: Crush coconut shells, sieve, wash, and dry to obtain coconut shell granules; Step 2, Activation Pretreatment: Immerse the coconut shell particles obtained in Step 1 in the activator, let them stand after immersion, and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C under a nitrogen atmosphere and carbonized to obtain carbonized products; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C in a CO2 atmosphere and kept at that temperature for activation. After the temperature holding period, the temperature is further increased to 750°C and kept at that temperature for activation to obtain the activated material. Step 5, post-processing: recover and remove the activator, dry, and obtain coconut shell-based activated carbon.

[0007] Furthermore, in step 2, the activator is 40 wt% H3PO4 or 30 wt% ZnCl2.

[0008] Furthermore, in step 2, the activator is a composite activator, which is obtained by mixing 40wt% H3PO4 and 30wt% ZnCl2 in a mass ratio of 1:(0.3~0.5).

[0009] Furthermore, in step 2, the coconut shell particles and the composite activator are impregnated at a mass ratio of 1:(2~2.4), and ultrasonic-assisted impregnation is used during the impregnation process.

[0010] Furthermore, in step 3, the carbonization process involves heating the coconut shell particles obtained in step 2 to 300°C at a rate of 5°C / min under a nitrogen atmosphere and holding the temperature for 20-40 minutes to obtain carbonized material.

[0011] Further, in step 4, the gradient activation process involves heating the carbide obtained in step 3 to 500°C at a rate of 3°C / min under a CO2 atmosphere, holding it at that temperature for 40-60 minutes, and then further heating it to 750°C at a rate of 5°C / min for 2-3 hours to obtain the activated material.

[0012] Furthermore, in step 1, the raw material pretreatment step involves crushing the coconut shell to 2-4 mm, washing it 2-3 times with deionized water, and drying it at 100-105°C to a constant weight to obtain coconut shell granules.

[0013] Further, in step 5, the post-processing step is to soak the activated material obtained in step 4 in 1 mol / L HCl, filter to recover the ZnCl2 solution, wash the precipitate with water at 75~80°C until the pH is 6~7 to remove residual activator, and then vacuum dry at 110~120°C for 3~4 hours to obtain coconut shell-based activated carbon.

[0014] Secondly, this application provides a coconut shell-based activated carbon prepared by any of the preparation methods described above.

[0015] Thirdly, this application provides the application of coconut shell-based activated carbon prepared by any of the above-described preparation methods in wastewater treatment, wherein wastewater treatment refers to the removal of COD from water bodies.

[0016] In summary, this application optimizes the pore structure of coconut shell-based activated carbon, achieving a synergistic improvement in both specific surface area and the proportion of high to medium porosity. This further enhances the activated carbon's adsorption capacity for COD in water, effectively meeting the needs of wastewater treatment for high-COD organic pollutants such as industrial wastewater and dyeing wastewater. The beneficial effects are manifested in at least the following aspects: 1. Through the synergistic effect of the composite activator H3PO4 and ZnCl2, H3PO4 mainly acts in the low-temperature stage, promoting the formation of micropores through dehydration reaction, thus providing a high specific surface area for activated carbon. ZnCl2 acts as a template in the intermediate-temperature stage; its molten state can penetrate into the carbon skeleton, and after volatilization at high temperature, it leaves behind a mesoporous structure, thereby increasing the proportion of mesopores. When the two are compounded at a mass ratio of 1:(0.3~0.5), the ratio of micropores to mesopores reaches the optimal balance, and the mesopore ratio in the resulting activated carbon can reach 45~50%, which is significantly higher than the mesopore ratio of samples prepared by a single activator.

[0017] The activation temperature of traditional activation systems is approximately 850~950℃, while the high-temperature activation temperature in this application is only 750℃, and the activation time can also be significantly shortened, which can significantly reduce energy consumption. In addition, the addition of ZnCl2 can significantly reduce the amount of H3PO4 used, which reduces the difficulty of subsequent acid washing and saves raw materials.

[0018] 2. This application involves phased pore development. First, carbonization is carried out at a low temperature of 300℃ to effectively stabilize the carbon skeleton structure and prevent pore collapse in the subsequent high-temperature stage. Then, the temperature is raised to 500℃ for medium-temperature activation. In this stage, ZnCl2 dominates the formation of mesopores and expands the pores through selective oxidation by CO2 to form interconnected channels. Subsequently, in a high-temperature environment of 750℃, H3PO4 creates deep pores, further generating and stabilizing the proportion of mesopores, thereby obtaining activated carbon with a high proportion of mesopores.

[0019] In addition, the reasonable setting of heating rate and holding time avoids the destruction of pore structure caused by thermal shock, ensures the specific surface area of ​​activated carbon, and increases the proportion of mesopores in the obtained activated carbon. Detailed Implementation

[0020] This application aims to optimize the pore structure of coconut shell-based activated carbon, increasing the proportion of mesopores and macropores while maintaining a high specific surface area, thereby further enhancing the activated carbon's adsorption capacity for COD in water and meeting the needs of wastewater treatment for high-COD organic pollutants such as industrial wastewater and dyeing wastewater. To this end, a method for preparing coconut shell-based activated carbon is provided, comprising the following steps: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 2-3 times, and dry at 100-105℃ to constant weight to obtain coconut shell granules; Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:(0.3~0.5) to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:(2~2.4) under ultrasonic-assisted impregnation at 50~60°C for 2~3 hours. After the impregnation is completed, let it stand for 8~12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 20~40min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 40~60min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 2~3h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 is soaked in 1 mol / L HCl, the ZnCl2 solution is recovered by filtration, the precipitate is washed with water at 75~80°C until the pH is 6~7 to remove residual activator, and then vacuum dried at 110~120°C for 3~4 hours to obtain coconut shell-based activated carbon.

[0021] The technical solutions and effects of this application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely for explaining the invention and are not intended to limit the invention. Example 1

[0022] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 2

[0023] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4mm, wash twice with deionized water, and dry at 100℃ to constant weight to obtain coconut shell granules; Step 2, Activation pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 50°C for 3 hours. After the impregnation is completed, let it stand for 8 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 75°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 110°C for 3 h to obtain coconut shell-based activated carbon. Example 3

[0024] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.4 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 4

[0025] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.5 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 5

[0026] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2.2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 6

[0027] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2.4. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 7

[0028] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 20 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 40 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 2 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon. Example 8

[0029] This embodiment discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 30 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 50 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 2.5 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0030] Comparative Example 1 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: The coconut shell particles obtained in Step 1 are impregnated with 40wt% H3PO4 activator at a mass ratio of 1:2. The impregnation is carried out at 60°C with ultrasonic assistance for 2 hours. After the impregnation is completed, the mixture is left to stand for 12 hours and then drained. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-treatment: The activated material obtained in step 4 was soaked in 1 mol / L HCl, filtered, and the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator. Then, it was vacuum dried at 120°C for 4 hours to obtain coconut shell-based activated carbon.

[0031] Comparative Example 2 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are placed in a nitrogen atmosphere and kept at 300°C for 40 minutes to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is placed in a CO2 atmosphere and kept at 500°C for 60 min. After the incubation is completed, it is placed at 750°C for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0032] Comparative Example 3 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 10°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 8°C / min under a CO2 atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 10°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0033] Comparative Example 4 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 10 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 30 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 1 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0034] Comparative Example 5 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 60 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a CO2 atmosphere and held for 2 hours. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 hours to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0035] Comparative Example 6 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, carbonization treatment: The coconut shell particles obtained in step 2 are heated to 300°C at a rate of 5°C / min under a nitrogen atmosphere and held for 40 min to obtain carbonized material; Step 4, gradient activation treatment: The carbide obtained in step 3 is heated to 500°C at 3°C / min under a nitrogen atmosphere and held for 60 min. After the holding period, the temperature is further increased to 750°C at 5°C / min and held for 3 h to obtain the activated material. Step 5, post-processing: The activated material obtained in step 4 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0036] Comparative Example 7 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, Activation treatment: The coconut shell particles obtained in step 2 are heated to 750°C at 5°C / min under a nitrogen atmosphere, then switched to a CO2 atmosphere and kept at that temperature for 3 hours to obtain the activated product; Step 4, post-processing: The activated material obtained in step 3 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0037] Comparative Example 8 This comparative example discloses a method for preparing coconut shell-based activated carbon, the steps of which are as follows: Step 1, raw material pretreatment: crush coconut shells to 2-4 mm, wash with deionized water 3 times, and dry at 105℃ to constant weight to obtain coconut shell granules. Step 2, Activation Pretreatment: Mix 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:0.3 to obtain a composite activator. Impregnate the coconut shell particles obtained in Step 1 with the composite activator at a mass ratio of 1:2. Perform ultrasonic-assisted impregnation at 60°C for 2 hours. After the impregnation is completed, let it stand for 12 hours and drain. Step 3, Activation treatment: The coconut shell particles obtained in step 2 are heated to 750°C at a rate of 5°C / min under a nitrogen atmosphere and kept at this temperature for 3 hours to obtain the activated product; Step 4, post-processing: The activated material obtained in step 3 was soaked in 1 mol / L HCl, the ZnCl2 solution was recovered by filtration, the precipitate was washed with water at 80°C until the pH was 6-7 to remove residual activator, and then vacuum dried at 120°C for 4 h to obtain coconut shell-based activated carbon.

[0038] Performance testing Pore ​​structure: ① Specific surface area: The specific surface area of ​​the activated carbon prepared in Examples 1-8 and Comparative Examples 1-8 was tested according to the method described in GB / T 19587-2017, and the results are recorded in the table below.

[0039] ② Pore size distribution: The specific surface area of ​​the activated carbons prepared in Examples 1-8 and Comparative Examples 1-8 was tested using the BJH method combined with the DFT model on a specific surface area and porosity analyzer, and the results are recorded in the table below.

[0040] COD adsorption performance test: The COD removal rates of the activated carbons prepared in Examples 1-8 and Comparative Examples 1-8 were tested according to the method described in GB / T 11914-1989, and the results are shown in the table below.

[0041] Table 1. Test results of pore structure and COD adsorption performance Specific surface area m² / g Pore ​​size distribution (percentage of mesopores) COD removal rate % Example 1 1420 45 97.2 Example 2 1380 43 96.3 Example 3 1450 50 98.3 Example 4 1410 44 97.2 Example 5 1440 47 97.6 Example 6 1430 45 97.4 Example 7 1380 44 96.4 Example 8 1440 47 97.7 Comparative Example 1 1050 30 82.5 Comparative Example 2 920 28 75.6 Comparative Example 3 980 25 77.3 Comparative Example 4 1020 35 80.5 Comparative Example 5 1080 38 82.0 Comparative Example 6 1120 26 84.3 Comparative Example 7 890 22 72.5 Comparative Example 8 840 20 70.1 As shown in the table above, this application utilizes the synergistic effect of the H3PO4 and ZnCl2 composite activators. H3PO4 primarily functions at low temperatures, promoting micropore formation through dehydration and providing a high specific surface area for the activated carbon. ZnCl2 acts as a template at intermediate temperatures, its molten state penetrating into the carbon skeleton, and leaving behind mesoporous structures after high-temperature volatilization, thereby increasing the mesopore ratio. When the two are combined at a mass ratio of 1:(0.3~0.5), especially when they are combined at a mass ratio of 1:0.4, the micropore to mesopore ratio reaches an optimal balance, and the resulting activated carbon has a mesopore ratio of up to 50%, which is significantly higher than that of samples prepared with a single activator.

[0042] This application involves phased pore development. First, carbonization is performed at a low temperature of 300℃ to effectively stabilize the carbon framework structure and prevent pore collapse in the subsequent high-temperature stage. Then, the temperature is raised to 500℃ for intermediate-temperature activation. In this stage, ZnCl2 dominates the formation of mesopores, and CO2 selectively oxidizes and expands the pores to form interconnected channels. Subsequently, at a high temperature of 750℃, H3PO4 creates deep pores, further generating and stabilizing the proportion of mesopores, thereby obtaining activated carbon with a high proportion of mesopores, which can reach 43-50%.

[0043] Furthermore, the reasonable setting of heating rate and holding time avoids the destruction of pore structure caused by thermal shock, ensuring the specific surface area of ​​activated carbon and increasing the proportion of mesopores in the obtained activated carbon. The optimal conditions for carbonization activation are: under a nitrogen atmosphere, heating to 300°C at 5°C / min and holding for 30 min to obtain carbides; then, under a CO2 atmosphere, heating the carbides to 500°C at 3°C / min and holding for 50 min; after the holding period, further heating to 750°C at 5°C / min and holding for 2.5 h.

[0044] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a coconut shell-based activated carbon, characterized by, The method comprises the following steps: Step 1, raw material pretreatment: crushing, screening, washing, and drying the coconut shell to obtain coconut shell particles; Step 2, activation pretreatment: immersing the coconut shell particles obtained in step 1 in an activating agent, standing after the immersion is completed, and draining; Step 3, carbonization treatment: heating the coconut shell particles obtained in step 2 to 300°C under a nitrogen atmosphere, and carbonizing under heat preservation to obtain carbonized substances; Step 4, gradient activation treatment: heating the carbonized substances obtained in step 3 to 500°C under a CO2 atmosphere, activating under heat preservation, continuously heating to 750°C after the heat preservation is completed, and activating under heat preservation to obtain activated substances; Step 5, post-treatment: recovering and removing the activating agent, and drying to obtain coconut shell-based activated carbon.

2. The method of claim 1, wherein the coconut shell-based activated carbon is prepared by the steps of: In the step 2, the activating agent is 40wt% H3PO4 or 30wt% ZnCl2. ​ 3. The method for preparing coconut shell-based activated carbon according to claim 1, wherein in the step 2, the activating agent is a composite activating agent obtained by mixing 40wt% H3PO4 and 30wt% ZnCl2 at a mass ratio of 1:(0.3-0.5).

4. The method of producing a coconut shell-based activated carbon according to claim 2 or 3, characterized by, In the step 2, the coconut shell particles are immersed in the composite activating agent at a mass ratio of 1:(2-2.4), and ultrasonic-assisted immersion is adopted during the immersion.

5. The method for preparing coconut shell-based activated carbon according to claim 1, characterized in that, In the step 3, the carbonization treatment is heating the coconut shell particles obtained in step 2 to 300°C at a rate of 5°C / min under a nitrogen atmosphere, and heat preserving for 20-40 min to obtain carbonized substances.

6. The method for preparing coconut shell-based activated carbon according to claim 1, characterized in that, In the step 4, the gradient activation treatment is heating the carbonized substances obtained in step 3 to 500°C at a rate of 3°C / min under a CO2 atmosphere, heat preserving for 40-60 min, continuously heating to 750°C at a rate of 5°C / min after the heat preservation is completed, and heat preserving for 2-3 h to obtain activated substances.

7. The method for preparing coconut shell-based activated carbon according to claim 1, characterized in that, In the step 1, the raw material pretreatment is crushing the coconut shell to 2-4 mm, washing with deionized water for 2-3 times, and drying at 100-105°C to constant weight to obtain coconut shell particles.

8. The method for preparing coconut shell-based activated carbon according to claim 1, characterized in that, In the step 5, the post-treatment is soaking the activated substances obtained in step 4 in 1 mol / L HCl, filtering to recover ZnCl2 solution, washing the precipitate with water at 75-80°C until the pH is 6-7 to remove residual activating agent, and then vacuum drying at 110-120°C for 3-4 h to obtain coconut shell-based activated carbon.

9. Coconut shell-based activated carbon prepared by the method according to any one of claims 1-8.

10. Use of the coconut shell-based activated carbon according to claim 9 in the treatment of sewage, characterized in that, The sewage treatment refers to removing COD in water.