Preparation method of shell-based activated carbon

Abstract

The invention discloses a preparation method of shell-based activated carbon, which comprises the following steps: coarsely crushing shells, and separating particles into light particles, medium particles and heavy particles by adopting airflow separation; when the activating agents are adopted for dipping treatment, the concentrations of the activating agents for treating the light particles, the medium particles and the heavy particles are sequentially increased, and the dipping time of the light particles, the medium particles and the heavy particles is sequentially increased; drying the impregnated particles, performing microwave carbonization, and performing steam activation after carbonization is completed; and washing, drying, crushing and screening the activated carbon to obtain an activated carbon product with set granularity.

Description

Technical Field

[0001] The present invention belongs to the technical field of activated carbon preparation, and particularly relates to a preparation method of activated carbon based on fruit shells. Background Art

[0002] The statements herein only provide background art related to the present invention and do not necessarily constitute prior art.

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

[0004] Fruit shells are waste in the fruit processing process, with wide sources and low costs. Microwave heating has unique advantages such as fast heating speed, good uniformity, and strong selectivity. Introducing microwave technology in the process of preparing activated carbon can enable 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 a microwave electromagnetic field, achieving rapid temperature rise, effectively shortening the activation time, and reducing energy consumption.

[0005] However, the inventor found that the composition of fruit shells is relatively complex, including light, medium, and heavy substances. If they are directly microwave-treated after being crushed, the light and heavy particles are mixed together, resulting in uneven reactions during the impregnation and activation processes. 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] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a preparation method of activated carbon based on fruit shells, which can maintain the carbon yield unchanged, reduce production costs and be environmentally friendly while improving product quality.

[0007] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0008] In a first aspect, the present invention provides a preparation method of activated carbon based on fruit shells, including the following steps:

[0009] After the fruit shells are roughly crushed, air classification is adopted to divide the particles into light particles, medium particles, and heavy particles;

[0010] When using an activator for impregnation treatment, the concentrations of the activators for treating the light particles, medium particles, and heavy particles increase in sequence, and the impregnation times for the light particles, medium particles, and heavy particles increase in sequence;

[0011] After the impregnated particles are dried, microwave carbonization is carried out, and after the carbonization is completed, steam activation is carried out;

[0012] After washing, drying, crushing and screening the activated activated carbon, an activated carbon product with a set particle size is obtained.

[0013] The light particles are mainly the fibers and impurities in the fruit shell, the medium particles are the main carbonaceous part of the fruit shell, and the heavy particles are the minerals and hard parts in the fruit shell.

[0014] Due to the high fiber content of the light particles, they are easy to adsorb the activator, with a shorter impregnation time and a lower activator concentration to avoid overreaction; the medium particles, as the main carbonaceous part, have a moderate impregnation time and activator concentration to ensure uniform penetration of the activator. The heavy particles have a slow activator penetration due to their large density, a longer impregnation time, and a higher activator concentration to ensure sufficient reaction. Targeted treatment of the light particles, medium particles and heavy particles can effectively improve the performance of the activated carbon.

[0015] In some embodiments, the air classification is carried out by a cyclone separator for air classification. For light particles: the air flow velocity is 5 - 8 m / s and the pressure is 0.1 - 0.3 MPa; for medium particles: the air flow velocity is 8 - 12 m / s and the pressure is 0.3 - 0.5 MPa; for heavy particles: the air flow velocity is 12 - 15 m / s and the pressure is 0.5 - 0.8 MPa.

[0016] The cyclone separator can effectively separate light, medium and heavy particles by adjusting the air flow velocity and pressure.

[0017] In some embodiments, the particle size after rough crushing of the fruit shell is 1 - 5 mm.

[0018] In some embodiments, the density of the light particles is 0.2 - 0.5 g / cm 3 , with a lighter density;

[0019] The density of the medium particles is 0.5 - 1.0 g / cm 3 , with a moderate density;

[0020] The density of the heavy particles is 1.0 - 1.5 g / cm 3 , with a higher density.

[0021] In some embodiments, when the particles are impregnated with the activator, a dynamic impregnation treatment method is adopted, and mechanical stirring, ultrasonic and microwave assistance are applied simultaneously. This can improve the uniformity and penetration efficiency of the activator.

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

[0023] The time of both microwave and ultrasound is 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 light particles, the concentration of the zinc chloride solution is 10-20%;

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

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

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

[0029] When impregnating medium 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%, and % is the mass percentage.

[0031] In some embodiments, the water content of the impregnated particles after drying is below 20%.

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

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

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

[0035] In some embodiments, the washing is countercurrent washing. The flow direction of the washing water is opposite to the moving direction of the activated carbon precursor, so that the residual activator and impurities can be removed more fully, the consumption of washing water can be reduced, and the washing liquid is washed to neutral;

[0036] In some embodiments, during the microwave carbonization, the filling rate of the container is 70-85%.

[0037] In some embodiments, the water content of the prepared activated carbon is 7%-13%.

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

[0039] (1) Align with resource recycling. Activated carbon is prepared using waste from wood processing, fruit processing, and other carbon-containing raw materials such as fruit shells, which are widely sourced and low-cost. This realizes the reuse of waste, promotes resource circulation, and reduces resource waste.

[0040] (2) Improve the quality of activated carbon. Through air classification technology, fruit shells are accurately classified into light, medium, and heavy categories, and targeted treatment is carried out for raw materials of different properties to ensure uniform penetration of the activator and sufficient reaction. This refined treatment significantly improves the pore structure and adsorption performance of activated carbon, enhancing the quality and consistency of the product.

[0041] (3) Microwave technology avoids the high reaction temperature and long activation time required by traditional physical activation methods, enables rapid heating, and effectively shortens the entire activation process time, thus reducing energy consumption. At the same time, choosing low-cost waste such as fruit shells as raw materials further helps reduce the overall cost of activated carbon preparation, enabling production at a lower cost while maintaining the same carbon yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments and descriptions thereof of the invention are used to explain the invention and do not constitute an improper limitation of the invention.

[0043] Figure 1 It is a process flow chart of a green preparation method of activated carbon based on microwave technology. DETAILED DESCRIPTION OF THE INVENTION

[0044] It should be noted that the following detailed description is illustrative and is 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 those of ordinary skill in the technical field to which this invention belongs.

[0045] The invention will be further described below in conjunction with embodiments.

[0046] Example 1

[0047] a. Select coconut shells as the carbon-containing raw material. Coarsely crush the coconut shells, and control the particle size of the crushed particles to be 2 - 5 mm. Then use a cyclone separator to perform air classification on the crushed fruit shells. By adjusting the air flow rate and pressure, the raw materials are divided into light, medium, and heavy categories. The density of the light particles is 0.1 g / cm 3 , the density of the medium particles is 0.5 g / cm 3 , and the density of the heavy particles is 1.0 g / cm 3 . The light particles are mainly fibers and impurities in the fruit shells, the medium particles are the main carbonaceous part of the fruit shells, and the heavy particles are the minerals and hard parts in the fruit shells;

[0048] b. The sorted light, medium, and heavy raw materials are respectively mixed with phosphoric acid activators of different concentrations, and a dynamic impregnation treatment method is adopted. The impregnation time for the light raw material is 30 min, and the activator concentration is 25%; the impregnation time for the medium raw material is 60 min, and the activator concentration is 30%; the impregnation time for the heavy raw material is 90 min, and the activator concentration is 35%, where % is the mass percentage; and mechanical stirring, microwave, and ultrasonic assistance are combined. The speed of mechanical stirring is 150 rpm; the microwave power is 800 W, and the microwave assistance time is synchronized with the impregnation time; the ultrasonic frequency is 20 kHz, and the power is 200 W to further improve the uniformity and penetration efficiency of the activator;

[0049] c. The impregnated raw materials are fed into a drying device and dried to a moisture content of less than 20%;

[0050] d. The dried raw materials are evenly loaded into a microwave reaction vessel, and the loading amount is 80% of the volume of the vessel, and an inert gas (nitrogen) supply device is configured. The microwave device is turned on, and the microwave carbonization temperature is set to 620 °C, and the carbonization time is 45 min. Microwave radiation treatment is carried out under a protective atmosphere with a nitrogen flow rate of 4 m 3 / h;

[0051] e. The set temperature is increased to make the temperature in the reaction chamber reach 800 °C, and steam activation is carried out for 30 min by precisely controlling the flow rate and pressure of steam to fully activate the raw materials, remove impurities on the surface and inside of the raw materials, and at the same time 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 the microwave radiation ends, the activated raw materials are naturally cooled to room temperature, and the obtained activated carbon products are taken out; the cooled activated carbon precursor is subjected to countercurrent washing in a rinsing tank. The flow direction of the washing water is opposite to the moving direction of the activated carbon precursor. The washing liquid is washed to neutral to fully remove the residual activator and impurities, and at the same time reduce the consumption of washing water;

[0053] g. The washed activated carbon is placed in a drying device at 120 °C and dried again for 1 hour, and activated carbon is obtained after cooling;

[0054] h. Crushing to make carbon: The above-mentioned activated carbon is transported 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. Select walnut shells as the carbon-containing raw material. Coarsely crush the walnut shells, and control the particle size of the crushed particles to be 1 - 3 mm. Then use a cyclone separator to perform air classification on the crushed walnut shells. By adjusting the air flow rate and pressure, the raw materials are divided into three categories: light, medium, and heavy. The density of the light particles is 0.4 g / cm 3 , the density of the medium particles is 1.1 g / cm 3 , and the density of the heavy particles is 1.5 g / cm 3 . The light particles are mainly fibers and impurities in the walnut shells, the medium particles are the main carbonaceous part of the walnut shells, and the heavy particles are minerals and hard parts in the walnut shells;

[0057] b. Mix the sorted light, medium, and heavy raw materials with zinc chloride activator solutions of different concentrations respectively, and adopt the dynamic impregnation treatment method. The impregnation time for the light raw material is 20 min, and the activator concentration is 15%; the impregnation time for the medium raw material is 50 min, and the activator concentration is 25%; the impregnation time for the heavy raw material is 80 min, and the activator concentration is 35%; and combine mechanical stirring and microwave assistance. The speed of mechanical stirring is 200 rpm; the microwave power is 900 W, and the microwave assistance time is synchronized with the impregnation time; the ultrasonic frequency is 40 kHz, and the power is 300 W to further improve the uniformity and penetration efficiency of the activator;

[0058] c. Feed the impregnated raw materials into a drying device and dry them to a moisture content of less than 20%;

[0059] d. Uniformly load the dried raw materials into a microwave reaction container, and the loading amount is 80% of the container volume, and configure an inert gas (nitrogen) supply device. Turn on the microwave device, set the microwave carbonization temperature to 620 °C, and the carbonization time to 50 min, and perform microwave radiation treatment under a protective atmosphere with a nitrogen flow rate of 5 m 3 / h;

[0060] e. Increase the set temperature to make the temperature in the reaction chamber reach 800 °C, and perform steam activation for 20 min by precisely controlling the steam flow rate and pressure to fully activate the raw materials, remove impurities on the surface and inside of the raw materials, and at the same time 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 the microwave radiation ends, naturally cool the activated raw materials to room temperature, and take out the obtained activated carbon product; the cooled activated carbon precursor is washed in a countercurrent manner in a rinsing tank, and the flow direction of the washing water is opposite to the moving direction of the activated carbon precursor. Wash the washing liquid until it is neutral to fully remove the residual activator and impurities, and at the same time reduce the consumption of washing water;

[0062] g. Place the washed activated carbon in a drying device at 120 °C and dry it again for 1.5 hours. After cooling, activated carbon is obtained.

[0063] h. Crushing to make carbon: Transport the above-mentioned activated carbon to a crushing device and pass it 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 roughly crushed, without sorting, it is directly impregnated with a 30% phosphoric acid activator, and the others are 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 immersed in the activator solution, the impregnation time is 60 min, the activator concentration is 30%, without mechanical stirring, ultrasonic assistance and microwave assistance. After impregnation, let it stand and drain, and then carry out subsequent drying and carbonization treatments. The others are the same as in Example 1.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that during the impregnation process, ultrasonic assistance is omitted, and the others are the same as in Example 1.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that during the impregnation process, microwave assistance is omitted, and the others are the same as in Example 1.

[0072] Comparative Example 5

[0073] The difference from Example 1 is that during the impregnation process, mechanical stirring is omitted, and the others are the same as in Example 1.

[0074] Table 1 Test results of activated carbon indexes prepared by two examples and comparative examples

[0075]

[0076] It can be seen from Table 1 that after the air classification technology of the present invention, by using the process method of targeted impregnation treatment to prepare activated carbon, the iodine value of the activated carbon is above 1000 mg / g, and the methylene blue adsorption value is above 15 mL / 0.1 g. The index effect is ideal, and the quality of the activated carbon meets the use standards of many industries.

[0077] Table 2 shows the comparison results of the effects of microwave-assisted impregnation and traditional impregnation

[0078]

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

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing activated carbon based on fruit shells, characterized in that: The steps include: After the shells are roughly crushed, air flow separation is used to separate the particles into light particles, medium particles and heavy particles; When the activator is used for impregnation treatment, the concentration of the activator for treating light particles, medium particles and heavy particles increases in sequence, and the impregnation time for light particles, medium particles and heavy particles increases in sequence; After the impregnated particles are dried, microwave carbonization is performed, and after carbonization is completed, steam activation is performed; The activated carbon is washed, dried, crushed and sieved to obtain an activated carbon product with a set particle size.

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

3. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The particle size of the fruit shell after coarse crushing 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 / cm 3 ; The density of the medium particles is 0.5-1.0 g / cm 3 ; The density of the heavy particles is 1.0-1.5 g / cm 3 .

5. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: When the particles are impregnated with the activating agent, a dynamic impregnation treatment method is adopted, and mechanical stirring, ultrasonic assistance and microwaves are applied simultaneously.

6. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The activator is zinc chloride solution or phosphoric acid solution; Preferably, when impregnating lightweight particles, the concentration of the zinc chloride solution is 10-20%; When impregnating medium-quality particles, the concentration of zinc chloride solution is 20-30%; When impregnating heavy particles, the concentration of zinc chloride solution is 30-40%, % is mass percentage; Preferably, when impregnating lightweight particles, the concentration of the phosphoric acid solution is 20-25%; When impregnating medium-quality particles, the concentration of phosphoric acid solution is 25-30%; When impregnating heavy particles, the concentration of the phosphoric acid solution is 30-35%, where % is mass percentage.

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

8. The method for preparing activated carbon based on fruit shells according to claim 1, characterized in that: The temperature of the microwave carbonization is 600-700°C, and the time of the microwave carbonization is 20-60min; Preferably, the temperature of microwave carbonization is 615-630° C., and the time of microwave carbonization is 40-50 min.

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

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

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