A method for preparing activated carbon based on fruit shells

Abstract

This invention discloses a method for preparing activated carbon based on fruit shells, comprising the following steps: coarsely crushing the fruit shells, then using airflow separation to separate the particles into light particles, medium particles, and heavy particles; when impregnating with an activating agent, the concentration of the activating agent for the light particles, medium particles, and heavy particles increases sequentially, as does the impregnation time for the light particles, medium particles, and heavy particles; after drying the impregnated particles, they are subjected to microwave carbonization, and after carbonization, they are subjected to steam activation; the activated carbon is washed, dried, pulverized, and sieved to obtain an activated carbon product with a set particle size.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon preparation technology, specifically relating to a method for preparing activated carbon based on fruit shells. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Activated carbon, as a porous carbon material with a highly developed pore structure and a huge specific surface area, has extremely wide applications in many fields such as environmental protection, industrial catalysis, food processing, and medical and health care. Traditional activated carbon preparation processes mostly use coal, wood, and other raw materials.

[0004] Fruit shells are waste products from fruit processing, and are widely available and inexpensive. Microwave heating has unique advantages such as rapid heating speed, good uniformity, and strong selectivity. Introducing microwave technology into the preparation of activated carbon allows water molecules and organic components inside carbon-containing raw materials such as fruit shells to be rapidly polarized and generate heat under the action of microwave electromagnetic fields, achieving rapid heating, effectively shortening activation time, and reducing energy consumption.

[0005] However, the inventors discovered that the composition of the nutshell is quite complex, including light, medium and heavy substances. If it is crushed and directly microwaved, the light and heavy particles will be mixed together, resulting in uneven reaction during impregnation and activation. The light particles are prone to over-reaction, while the heavy particles are under-reacted, ultimately affecting the pore structure and adsorption performance of the activated carbon. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing activated carbon based on fruit shells, which maintains the carbon yield, improves product quality, reduces production costs, and is environmentally friendly.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing activated carbon based on fruit shells, comprising the following steps:

[0009] After the shells are coarsely crushed, airflow separation is used to separate the particles into light particles, medium particles, and heavy particles.

[0010] When using an activator for impregnation treatment, the concentration of the activator increases sequentially for light particles, medium particles, and heavy particles, and the impregnation time also increases sequentially for light particles, medium particles, and heavy particles.

[0011] After the impregnated granules are dried, they are then microwave-carbonized, and after carbonization, they are steam-activated.

[0012] After the activated carbon is washed, dried, pulverized and sieved, an activated carbon product with a set particle size is obtained.

[0013] Lightweight particles mainly consist of fibers and impurities from the fruit shell, medium-weight particles consist of the main carbonaceous part of the fruit shell, and heavyweight particles consist of minerals and hard parts of the fruit shell.

[0014] Lightweight granules, with their high fiber content, readily adsorb activators, requiring shorter impregnation times and lower activator concentrations to avoid over-reaction. Medium-weight granules, being the primary carbonaceous component, require moderate impregnation times and activator concentrations to ensure uniform activator penetration. Heavy granules, due to their higher density, experience slower activator penetration, necessitating longer impregnation times and higher activator concentrations to ensure complete reaction. Targeted treatment of lightweight, medium-weight, and heavyweight granules can effectively improve the performance of activated carbon.

[0015] In some embodiments, the airflow separation is performed using a cyclone separator, with light particles having an airflow velocity of 5-8 m / s and a pressure of 0.1-0.3 MPa; medium particles having an airflow velocity of 8-12 m / s and a pressure of 0.3-0.5 MPa; and heavy particles having an airflow velocity of 12-15 m / s and a pressure of 0.5-0.8 MPa.

[0016] Cyclone separators can effectively separate light, medium and heavy particles by adjusting airflow speed and pressure.

[0017] In some embodiments, the particle size of the coarsely crushed fruit shell is 1-5 mm.

[0018] In some embodiments, the density of the lightweight particles is 0.2-0.5 g / cm³. 3 It has a relatively low density;

[0019] The density of the medium-density particles is 0.5-1.0 g / cm³. 3 The density is moderate;

[0020] The density of the heavy particles is 1.0-1.5 g / cm³. 3 It has a high density.

[0021] In some embodiments, when impregnating the particles with an activator, a dynamic impregnation method is employed, simultaneously applying mechanical stirring, ultrasonic and microwave assistance. This improves the uniformity and penetration efficiency of the activator.

[0022] Preferably, the mechanical stirring speed is 150-200 rpm; the microwave power is 800-1000W; the ultrasonic frequency is 20-40kHz; and the ultrasonic power is 200-300W.

[0023] The microwave and ultrasonic times are synchronized with the impregnation time, which can further improve the penetration efficiency of the activator, especially the impregnation efficiency of heavy particles.

[0024] In some embodiments, the activator is a zinc chloride solution or a phosphoric acid solution.

[0025] Preferably, when impregnating lightweight particles, the concentration of the zinc chloride solution is 10-20%;

[0026] When impregnating medium-density particles, the concentration of zinc chloride solution is 20-30%;

[0027] When impregnating heavy particles, the concentration of the zinc chloride solution is 30-40%, where % is a mass percentage.

[0028] Preferably, when impregnating lightweight particles, the concentration of the phosphoric acid solution is 20-25%;

[0029] When impregnating medium-density particles, the concentration of the phosphoric acid solution is 25-30%.

[0030] When impregnating heavy particles, the concentration of the phosphoric acid solution is 30-35%, where % is a mass percentage.

[0031] In some embodiments, the moisture content of the impregnated granules after drying is less than 20%.

[0032] In some embodiments, the microwave carbonization temperature is 600-700°C and the microwave carbonization time is 20-60 minutes.

[0033] Preferably, the microwave carbonization temperature is 615-630℃ and the microwave carbonization time is 40-50min.

[0034] In some embodiments, the steam activation temperature is 750-850°C, and the activation time is 10-60 min.

[0035] In some embodiments, the washing is countercurrent washing. The direction of the washing water flow is opposite to the direction of movement of the activated carbon precursor, which allows for more thorough removal of residual activators and impurities, reduces water consumption, and washes until the washing solution is neutral.

[0036] In some embodiments, the container is filled to 70-85% during microwave carbonization.

[0037] In some embodiments, the prepared activated carbon has a moisture content of 7%-13%.

[0038] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0039] (1) It aligns with resource recycling. Activated carbon is prepared by using widely available and inexpensive waste materials from wood and fruit processing, such as fruit shells, as well as other carbon-containing raw materials. This enables the reuse of waste materials, promotes resource recycling, and reduces resource waste.

[0040] (2) Improving the quality of activated carbon. Through airflow sorting technology, fruit shells are precisely divided into three categories: light, medium, and heavy. Targeted treatment is then applied to raw materials with different properties to ensure uniform penetration and sufficient reaction of the activator. This refined processing significantly improves the pore structure and adsorption performance of the activated carbon, enhancing product quality and consistency.

[0041] (3) Microwave technology avoids the high reaction temperature and long activation time required by traditional physical activation methods, achieving rapid heating and effectively shortening the entire activation process time, thereby reducing energy consumption. At the same time, the selection of low-cost waste materials such as fruit shells as raw materials further helps to reduce the overall cost of activated carbon preparation, enabling production at a lower cost while maintaining the same carbon yield. Attached Figure Description

[0042] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0043] Figure 1 This is a process flow diagram of a green preparation method for activated carbon based on microwave technology. Detailed Implementation

[0044] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] The present invention will be further described below with reference to the embodiments.

[0046] Example 1

[0047] a. Coconut shells were selected as the carbon-containing raw material. The coconut shells were coarsely crushed, with the particle size controlled at 2-5mm. Then, a cyclone separator was used to separate the crushed shells using airflow. By adjusting the airflow speed and pressure, the raw material was divided into three categories: light, medium, and heavy. The density of the light particles was 0.1g / cm³. 3 The density of the medium-density particles is 0.5 g / cm³. 3 The density of the heavy particles is 1.0 g / cm³. 3 Lightweight particles mainly consist of fibers and impurities from the fruit shell, medium-weight particles consist of the main carbonaceous part of the fruit shell, and heavyweight particles consist of minerals and hard parts of the fruit shell.

[0048] b. The sorted light, medium, and heavy raw materials were mixed with different concentrations of phosphoric acid activator and subjected to dynamic impregnation treatment. The light raw material was impregnated for 30 minutes with an activator concentration of 25%; the medium raw material was impregnated for 60 minutes with an activator concentration of 30%; and the heavy raw material was impregnated for 90 minutes with an activator concentration of 35% (%). Mechanical stirring, microwave, and ultrasonic assistance were combined. The mechanical stirring speed was 150 rpm; the microwave power was 800 W, and the microwave assistance time was synchronized with the impregnation time; the ultrasonic frequency was 20 kHz, and the power was 200 W, further improving the uniformity and penetration efficiency of the activator.

[0049] c. Add the impregnated raw materials to the drying device and dry them until the moisture content is below 20%;

[0050] d. Evenly fill the dried raw materials into the microwave reaction vessel, filling it to 80% of its volume, and install an inert gas (nitrogen) supply device. Turn on the microwave device, set the microwave carbonization temperature to 620℃, the carbonization time to 45 minutes, and the nitrogen flow rate to 4 m³ / min. 3 Microwave radiation treatment was carried out under a protective atmosphere of / h;

[0051] e. Increase the set temperature to 800℃ inside the reaction chamber. By precisely controlling the steam flow and pressure, steam activation is carried out for 30 minutes to fully activate the raw materials, remove impurities from the surface and inside of the raw materials, and form more micropores and mesopores on the surface of the raw materials, thereby increasing the specific surface area and adsorption performance of the raw materials.

[0052] f. After microwave radiation, the activated raw material is naturally cooled to room temperature, and the obtained activated carbon product is taken out. The cooled activated carbon precursor is washed in a rinsing tank in a countercurrent manner. The direction of the washing water flow is opposite to the direction of the movement of the activated carbon precursor. The washing liquid is washed until neutral to fully remove residual activators and impurities, while reducing the consumption of washing water.

[0053] g. After washing with water, the activated carbon is placed in a drying device at 120°C and dried again for 1 hour. After cooling, activated carbon is obtained.

[0054] h. Crushing and charcoal making: The above activated carbon is fed to a crushing device and passed through a 100-mesh sieve to obtain activated carbon with a particle size of 100 mesh.

[0055] Example 2

[0056] a. Walnut shells were selected as the carbon-containing raw material. The walnut shells were coarsely crushed, with the particle size controlled to 1-3 mm. Then, a cyclone separator was used to separate the crushed walnut shells by airflow. By adjusting the airflow speed and pressure, the raw material was divided into three categories: light, medium, and heavy. The density of the light particles was 0.4 g / cm³. 3 The density of the medium-grained particles is 1.1 g / cm³. 3 The density of the heavy particles is 1.5 g / cm³. 3 Light particles mainly consist of fibers and impurities from the walnut shell, medium particles consist of the main carbonaceous part of the walnut shell, and heavy particles consist of minerals and hard parts of the walnut shell.

[0057] b. The sorted light, medium, and heavy raw materials were mixed separately with zinc chloride activator solutions of different concentrations and subjected to dynamic impregnation treatment. The impregnation time for light raw materials was 20 minutes with an activator concentration of 15%; the impregnation time for medium raw materials was 50 minutes with an activator concentration of 25%; and the impregnation time for heavy raw materials was 80 minutes with an activator concentration of 35%. This was combined with mechanical stirring and microwave assistance. The mechanical stirring speed was 200 rpm; the microwave power was 900 W, and the microwave assistance time was synchronized with the impregnation time; the ultrasonic frequency was 40 kHz with a power of 300 W to further improve the uniformity and penetration efficiency of the activator.

[0058] c. Add the impregnated raw materials to the drying device and dry them until the moisture content is below 20%;

[0059] d. Evenly fill the dried raw materials into the microwave reaction vessel, filling it to 80% of its volume, and install an inert gas (nitrogen) supply device. Turn on the microwave device, set the microwave carbonization temperature to 620℃, the carbonization time to 50 minutes, and the nitrogen flow rate to 5 m³ / min. 3 Microwave radiation treatment was carried out under a protective atmosphere of / h;

[0060] e. Increase the set temperature to 800℃ inside the reaction chamber. By precisely controlling the steam flow and pressure, steam activation is carried out for 20 minutes to fully activate the raw materials, remove impurities from the surface and inside of the raw materials, and form more micropores and mesopores on the surface of the raw materials, thereby increasing the specific surface area and adsorption performance of the raw materials.

[0061] f. After microwave radiation, the activated raw material is naturally cooled to room temperature, and the obtained activated carbon product is taken out. The cooled activated carbon precursor is washed in a rinsing tank in a countercurrent manner. The direction of the washing water flow is opposite to the direction of the movement of the activated carbon precursor. The washing liquid is washed until neutral to fully remove residual activators and impurities, while reducing the consumption of washing water.

[0062] g. After washing with water, the activated carbon is placed in a drying device at 120°C and dried again for 1.5 hours. After cooling, activated carbon is obtained.

[0063] h. Crushing and charcoal making: The above activated carbon is fed to a crushing device and passed through a 200-mesh sieve to obtain activated carbon with a particle size of 200 mesh.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that after the coconut shell is coarsely crushed, it is directly impregnated with 30% phosphate activator without sorting. Everything else is the same as in Example 1.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that the impregnation process is a traditional impregnation process, that is, directly immersing in the activator solution for 60 minutes, with an activator concentration of 30%, without mechanical stirring, ultrasonic assistance, or microwave assistance. After impregnation, it is left to stand and drain, and then subjected to subsequent drying and carbonization treatment. Everything else is the same as in Example 1.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that ultrasonic assistance is omitted during the impregnation process, while everything else is the same as in Example 1.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that microwave assistance is omitted during the impregnation process, while everything else is the same as in Example 1.

[0072] Comparative Example 5

[0073] The difference from Example 1 is that mechanical stirring is omitted during the impregnation process, while everything else is the same as in Example 1.

[0074] Table 1. Test results of activated carbon prepared in the two examples and the comparative example.

[0075]

[0076] As shown in Table 1, the activated carbon prepared by the targeted impregnation process after airflow separation technology of the present invention has an iodine value of over 1000 mg / g and a methylene blue adsorption value of over 15 mL / 0.1 g. The indicators are ideal and the quality of the activated carbon meets the standards of many industries.

[0077] Table 2 shows the comparison results between microwave-assisted impregnation and conventional impregnation.

[0078]

[0079] As can be seen from Table 2, microwave and ultrasonic-assisted impregnation can shorten the traditional impregnation time from 8-12h to 2-5h, while increasing the utilization rate of the activator by more than 20%, and significantly improving the iodine adsorption value of activated carbon. This indicates that microwave-assisted impregnation can effectively improve the uniformity and penetration efficiency of the activator.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing activated carbon based on fruit shells, characterized in that: Includes the following steps: After the shells are coarsely crushed, airflow separation is used to separate the particles into light particles, medium particles, and heavy particles. When using an activator for impregnation treatment, the concentration of the activator increases sequentially for light particles, medium particles, and heavy particles, and the impregnation time also increases sequentially for light particles, medium particles, and heavy particles; the density of the light particles is 0.2-0.5 g / cm³, the density of the medium particles is 0.5-1.0 g / cm³, and the density of the heavy particles is 1.0-1.5 g / cm³; the activator is a zinc chloride solution or a phosphoric acid solution; When impregnating light particles, the concentration of zinc chloride solution is 10-20%; when impregnating medium particles, the concentration of zinc chloride solution is 20-30%; when impregnating heavy particles, the concentration of zinc chloride solution is 30-40%, where % is by mass. When impregnating light particles, the concentration of the phosphoric acid solution is 20-25%; when impregnating medium particles, the concentration of the phosphoric acid solution is 25-30%; when impregnating heavy particles, the concentration of the phosphoric acid solution is 30-35%, where % is a mass percentage. The soaking time for light raw materials is 20-30 minutes, the soaking time for medium raw materials is 50-60 minutes, and the soaking time for heavy raw materials is 80-90 minutes. When impregnating particles with an activator, a dynamic impregnation method is used, simultaneously applying mechanical stirring, ultrasonic assistance, and microwaves. After the impregnated granules are dried, they are then microwave-carbonized, and after carbonization, they are steam-activated. After the activated carbon is washed, dried, pulverized and sieved, an activated carbon product with a set particle size is obtained.

2. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The airflow separation is performed using a cyclone separator. Light particles: airflow velocity is 5-8 m / s, pressure is 0.1-0.3 MPa; medium particles: airflow velocity is 8-12 m / s, pressure is 0.3-0.5 MPa; heavy particles: airflow velocity is 12-15 m / s, pressure is 0.5-0.8 MPa.

3. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The particle size of the coarsely crushed fruit shells is 1-5mm.

4. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The density of the lightweight particles is 0.2-0.5 g / cm³; The density of the medium-density particles is 0.5-1.0 g / cm³; The density of the heavy particles is 1.0-1.5 g / cm³.

5. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The moisture content of the impregnated granules after drying is below 20%.

6. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The microwave carbonization temperature is 600-700℃, and the microwave carbonization time is 20-60 minutes.

7. The method for preparing activated carbon based on fruit shells according to claim 6, characterized in that: The temperature for microwave carbonization is 615-630℃, and the time for microwave carbonization is 40-50 minutes.

8. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The steam activation temperature is 750-850℃, and the activation time is 10-60 minutes.

9. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The washing process is countercurrent washing; during microwave carbonization, the container is filled to 70-85%.

Images