Biochar purification process
By employing processes such as acid-base synergistic modification, gradient pyrolysis, and airflow classification, the problems of insufficient pore structure control and low purity in biochar purification have been solved, resulting in the preparation of high-performance biochar suitable for supercapacitors and heavy metal adsorbents, while reducing energy consumption and costs.
Patent Information
- Application Number
- CN202610255840.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-04
- Publication Date
- 2026-05-05
AI Technical Summary
Existing biochar purification processes suffer from problems such as insufficient pore structure control, a prominent contradiction between purity and performance, poor process stability, and high energy consumption, making it difficult to meet the application requirements of highly selective adsorption and supercapacitors.
A four-stage purification process involving acid-base synergistic modification, gradient pyrolysis, airflow classification, and chemical activation was employed to prepare high-purity, high-performance biochar by precisely controlling the pore structure, reducing ash content, and optimizing surface chemical properties.
The hierarchical pore structure was optimized, which improved the surface area of biochar and the adsorption selectivity for heavy metal ions, reduced production costs and energy consumption, met environmental protection standards, and satisfied the application requirements of supercapacitors and heavy metal adsorbents.
Abstract
Description
Technical Field
[0001] This invention relates to the field of biochar preparation technology, specifically to a biochar purification process. Background Technology
[0002] Biochar, a carbonaceous material produced by the pyrolysis of biomass under anaerobic conditions, has shown broad application prospects in soil remediation, water pollution control, and energy storage due to its rich porous structure, high specific surface area, and surface functional group characteristics. Currently, the raw materials for biochar preparation mainly include agricultural waste (such as rice husks, straw, and sawdust), forestry waste, and urban organic waste, among which agricultural waste has become the mainstream raw material due to its wide availability and low cost.
[0003] Existing biochar purification processes have the following shortcomings:
[0004] (1) Insufficient control of pore structure: Existing processes mostly rely on single modification methods, making it difficult to synergistically optimize pore size distribution and specific surface area. For example, acid washing can increase micropores, but it easily destroys pore connectivity; alkaline washing can expand mesopores, but it easily causes excessive corrosion. The final product has a wide pore size distribution, which cannot meet the high selective adsorption requirements for specific molecular sizes. (2) Prominent contradiction between purity and performance: During the chemical modification process, residual inorganic salts and ash will occupy active sites, resulting in iodine adsorption values generally <700mg / g. When used as electrode materials, the specific capacitance is only 150-200F / g, which limits its application in supercapacitors and high-precision adsorption fields. (3) Poor process stability: Too fast a pyrolysis heating rate can easily lead to local overheating and cause pore collapse; fluctuations in activation temperature will cause uneven pore size distribution. In addition, the lack of a tail gas treatment system leads to excessive emissions of volatile organic compounds, which does not meet environmental protection requirements. (4) High energy consumption and cost: Traditional chemical activation requires a large amount of activator and high temperature for a long time, which increases production costs by more than 30% and limits large-scale application. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention proposes a four-stage purification process of "acid-base synergistic modification - gradient pyrolysis - airflow classification - chemical activation". By precisely controlling the pore structure, reducing the ash content, and optimizing the surface chemical properties, high-purity, high-performance biochar is prepared to meet the application requirements of supercapacitor electrode materials and heavy metal adsorbents.
[0006] Specifically, the technical solution provided by this invention is: a biochar purification process, comprising the following steps:
[0007] Step 1, Raw material pretreatment: Screen the biochar raw material to remove impurity particles with a particle size greater than 50 mesh. After screening, the moisture content of the raw material is controlled to be ≤15%.
[0008] Step 2, pickling treatment: Place the pretreated raw material in a nitric acid solution with a concentration of 0.1-0.5 mol / L, stir and soak at 50-70℃ for 1-3 hours, then wash with deionized water until neutral, filter and dry until the moisture content is ≤5%.
[0009] Step 3, alkaline washing treatment: Immerse the acid-washed and dried raw material in a potassium hydroxide solution with a concentration of 0.2-0.6 mol / L, stir and immerse at 40-60℃ for 2-4 hours, wash again with deionized water until neutral, filter and dry until the moisture content is ≤5%.
[0010] Step 4, pyrolysis purification: Transfer the alkaline washed and dried raw material to a pyrolysis furnace under inert gas protection, heat it to 600-800℃ at a heating rate of 3-8℃ / min, and pyrolyze for 1-3 hours to obtain primary purified biochar.
[0011] Step 5, Physical sieving: The primary purified biochar is subjected to airflow classification to separate particles with a particle size of 20-200 mesh, thus obtaining secondary purified biochar;
[0012] Step 6, Chemical Activation: Mix the secondary purified biochar with a zinc chloride solution at a mass ratio of 1:2-5, activate at 400-600℃ for 1-2 hours under a nitrogen atmosphere, cool, wash with dilute hydrochloric acid until neutral, and dry to obtain high-purity biochar.
[0013] Preferably, the biochar raw material is a pyrolysis product of agricultural waste, including but not limited to one or more mixtures of rice husk charcoal, straw charcoal, and sawdust charcoal.
[0014] Preferably, in the pickling step, the concentration of nitric acid solution is 0.3 mol / L, the immersion temperature is 60°C, and the immersion time is 2 hours; in the alkaline washing step, the concentration of potassium hydroxide solution is 0.4 mol / L, the immersion temperature is 50°C, and the immersion time is 3 hours.
[0015] Preferably, in the pyrolysis purification step, the heating rate is 5℃ / min, the pyrolysis temperature is 700℃, and the pyrolysis time is 2 hours; in the chemical activation step, the zinc chloride solution mass ratio is 1:3, the activation temperature is 500℃, and the activation time is 1.5 hours.
[0016] Preferably, the physical screening step uses a multi-stage air classifier, and the particle size is precisely controlled by adjusting the speed of the classifying wheel, with the speed range being 800-1500 rpm.
[0017] Preferably, the high-purity biochar has an iodine adsorption value ≥800mg / g, a specific surface area ≥1200m² / g, and an ash content ≤3%.
[0018] Preferably, the process also includes an exhaust gas treatment system, in which the exhaust gas generated during pyrolysis and activation is purified by an activated carbon adsorption tower after the condensable components are recovered by a condenser.
[0019] Preferably, the biochar is black porous granular with a well-developed pore structure, with the main pore size distributed in the range of 2-50 nm, and the surface contains abundant oxygen-containing functional groups.
[0020] Preferably, when biochar is used as an electrode material for supercapacitors, its specific capacitance is ≥250F / g at a current density of 1A / g; when used as a heavy metal adsorbent, its maximum adsorption capacity for lead ions is ≥200mg / g.
[0021] Compared with the prior art, the advantages of this invention are: (1) Optimized hierarchical pore structure: Through acid-base synergistic modification, a microporous-mesoporous hierarchical structure is formed on the surface of biochar, increasing the surface area, allowing the iodine adsorption value to meet the standard, and significantly enhancing the adsorption selectivity for heavy metal ions and organic pollutants. (2) High purity and low ash content: Airflow classification sieving combined with chemical activation effectively removes ash and residual inorganic salts, exposing more active sites, so that when biochar is used as a supercapacitor electrode material, the specific capacitance is ≥250F / g at a current density of 1A / g. (3) Improved process stability: Gradient pyrolysis and precise activation work together to avoid pore collapse and excessive corrosion, the product pore size distribution is concentrated, and the repeatability error is reduced. (4) Energy saving and environmental protection: The amount of zinc chloride used in the chemical activation stage is reduced, the activation temperature is lowered, and the energy consumption is reduced; the tail gas treatment system makes VOCs emissions meet the standards and comply with the EU EN15051 standard. Detailed Implementation
[0022] Example 1
[0023] This embodiment provides a purification process for preparing high-purity biochar from rice husk charcoal. Rice husk charcoal is selected as the biochar raw material. First, it is screened to remove impurity particles larger than 50 mesh to ensure the purity of the raw material. After screening, the moisture content of the raw material is controlled to 12% through a combination of natural sun-drying and mechanical dehydration. The pretreated rice husk charcoal is then placed in a 0.3 mol / L nitric acid solution and stirred and impregnated at 60°C for 2 hours to remove some inorganic impurities on the surface and initially form a microporous structure. Subsequently, it is washed with deionized water until neutral, filtered, and dried until the moisture content is ≤5%.
[0024] The acid-washed and dried rice husk char was impregnated in a 0.4 mol / L potassium hydroxide solution and stirred at 50°C for 3 hours to further expand the mesoporous structure while avoiding excessive corrosion. It was then washed again with deionized water until neutral, filtered, and dried to a moisture content of ≤5%. The alkaline-washed and dried rice husk char was transferred to a pyrolysis furnace under inert gas (nitrogen) protection and heated to 700°C at a rate of 5°C / min for 2 hours to obtain primary purified biochar. During this process, the gradient heating effectively prevented pore collapse.
[0025] The primary purified biochar was classified using a multi-stage airflow classifier. By adjusting the classifier wheel speed to 1000 rpm, particles with a diameter of 50-150 mesh were separated to obtain secondary purified biochar. The secondary purified biochar was mixed with a zinc chloride solution at a mass ratio of 1:3 and activated at 500℃ for 1.5 hours under a nitrogen atmosphere. After cooling, it was washed with dilute hydrochloric acid until neutral and dried to obtain high-purity biochar. The tail gas generated during pyrolysis and activation was condensed to recover condensable components and then purified by an activated carbon adsorption tower to ensure that VOC emissions met standards.
[0026] The resulting high-purity biochar is a black, porous granular material with an iodine adsorption value of 850 mg / g, a specific surface area of 1300 m² / g, and an ash content of only 2.5%. When used as an electrode material for supercapacitors, it exhibits a specific capacitance of 260 F / g at a current density of 1 A / g; when used as a heavy metal adsorbent, it has a maximum adsorption capacity of 220 mg / g for lead ions.
[0027] Example 2
[0028] This embodiment provides a specific implementation method for preparing high-performance biochar by mixing straw charcoal and sawdust charcoal. Straw charcoal and sawdust charcoal are mixed at a 1:1 mass ratio as the biochar raw material. The mixture undergoes screening and dehydration treatment to ensure a moisture content ≤15%. The mixed raw material is placed in a 0.2 mol / L nitric acid solution and stirred and impregnated at 55°C for 2.5 hours to remove surface impurities and initially form micropores. After washing and drying, the moisture content is controlled to ≤5%.
[0029] The acid-washed raw material was immersed in a 0.5 mol / L potassium hydroxide solution and stirred at 45°C for 3.5 hours to expand the mesoporous structure. After washing and drying, it was prepared for pyrolysis. Under nitrogen protection, the raw material was heated to 650°C at a heating rate of 4°C / min and pyrolyzed for 2.5 hours to obtain primary purified biochar. A multi-stage air classifier was used, and the classifier wheel speed was adjusted to 1200 rpm to separate particles with a particle size of 30-180 mesh, which were used as secondary purified biochar.
[0030] Secondary purified biochar was mixed with a zinc chloride solution at a mass ratio of 1:4, activated at 550°C for 1 hour under a nitrogen atmosphere, and then cooled, washed, and dried to obtain high-purity biochar. Similar to Example 1, this ensured that exhaust emissions met standards.
[0031] The obtained biochar has an iodine adsorption value of 820 mg / g, a specific surface area of 1250 m² / g, and an ash content of 2.8%. When used as an electrode material, it has a specific capacitance of 255 F / g; when used as an adsorbent, it has an adsorption capacity of 210 mg / g for lead ions.
[0032] Example 3
[0033] This embodiment provides a specific implementation method for preparing low-cost and high-efficiency biochar from a single type of wood chip charcoal. Wood chip charcoal is selected as the raw material. After screening to remove large-particle impurities, the moisture content is controlled to 10% by hot air drying. The wood chip charcoal is placed in a 0.1 mol / L nitric acid solution and stirred and impregnated at 50°C for 3 hours for preliminary purification in a low-cost manner. After washing and drying, the moisture content is ≤5%. The acid-washed wood chip charcoal is then impregnated in a 0.2 mol / L potassium hydroxide solution and stirred and impregnated at 60°C for 2 hours to further optimize the pore structure. After washing and drying, it is ready for pyrolysis.
[0034] Under nitrogen protection, the temperature was increased to 600℃ at a heating rate of 3℃ / min, and pyrolysis was carried out for 3 hours to obtain primary purified biochar. A multi-stage air classifier was used, and by adjusting the classifier wheel speed to 800 rpm, particles with a diameter of 20-200 mesh were separated as secondary purified biochar.
[0035] To reduce costs, secondary purified biochar was mixed with a zinc chloride solution at a mass ratio of 1:2, activated at 400°C for 2 hours under a nitrogen atmosphere, and then cooled, washed, and dried to obtain high-purity biochar. Similar to the aforementioned examples, this ensures compliance with environmental standards.
[0036] Despite using relatively low-cost process parameters, the resulting biochar still exhibits excellent performance, with an iodine adsorption value of 800 mg / g, a specific surface area of 1200 m² / g, and an ash content of 3%. As an electrode material, it has a specific capacitance of 250 F / g; as an adsorbent, it has a lead ion adsorption capacity of 200 mg / g, meeting the requirements for low-cost and high-efficiency applications.
[0037] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A biochar purification process, characterized in that... Includes the following steps: Step 1, Raw material pretreatment: Screen the biochar raw material to remove impurity particles with a particle size greater than 50 mesh. After screening, the moisture content of the raw material is controlled to be ≤15%. Step 2, pickling treatment: Place the pretreated raw material in a nitric acid solution with a concentration of 0.1-0.5 mol / L, stir and soak at 50-70℃ for 1-3 hours, then wash with deionized water until neutral, filter and dry until the moisture content is ≤5%. Step 3, alkaline washing treatment: Immerse the acid-washed and dried raw material in a potassium hydroxide solution with a concentration of 0.2-0.6 mol / L, stir and immerse at 40-60℃ for 2-4 hours, wash again with deionized water until neutral, filter and dry until the moisture content is ≤5%. Step 4, pyrolysis purification: Transfer the alkaline washed and dried raw material to a pyrolysis furnace under inert gas protection, heat it to 600-800℃ at a heating rate of 3-8℃ / min, and pyrolyze for 1-3 hours to obtain primary purified biochar. Step 5, Physical sieving: The primary purified biochar is subjected to airflow classification to separate particles with a particle size of 20-200 mesh, thus obtaining secondary purified biochar; Step 6, Chemical Activation: Mix the secondary purified biochar with a zinc chloride solution at a mass ratio of 1:2-5, activate at 400-600℃ for 1-2 hours under a nitrogen atmosphere, cool, wash with dilute hydrochloric acid until neutral, and dry to obtain high-purity biochar.
2. The biochar purification process according to claim 1, characterized in that: The biochar raw material is a pyrolysis product of agricultural waste, including but not limited to one or more mixtures of rice husk charcoal, straw charcoal, and sawdust charcoal.
3. The biochar purification process according to claim 1, characterized in that: In the pickling step, the nitric acid solution concentration is 0.3 mol / L, the immersion temperature is 60℃, and the immersion time is 2 hours; in the alkaline washing step, the potassium hydroxide solution concentration is 0.4 mol / L, the immersion temperature is 50℃, and the immersion time is 3 hours.
4. The biochar purification process according to claim 1, characterized in that: In the pyrolysis purification step, the heating rate is 5℃ / min, the pyrolysis temperature is 700℃, and the pyrolysis time is 2 hours; in the chemical activation step, the zinc chloride solution mass ratio is 1:3, the activation temperature is 500℃, and the activation time is 1.5 hours.
5. The biochar purification process according to claim 1, characterized in that: The physical sieving step uses a multi-stage air classifier, and the particle size is precisely controlled by adjusting the speed of the classifying wheel. The speed range of the classifying wheel is 800-1500 rpm.
6. The biochar purification process according to claim 1, characterized in that: The high-purity biochar has an iodine adsorption value ≥800mg / g, a specific surface area ≥1200m² / g, and an ash content ≤3%.
7. The biochar purification process according to claim 1, characterized in that: The process also includes an exhaust gas treatment system. The exhaust gas generated during pyrolysis and activation is condensed by a condenser to recover condensable components and then purified by an activated carbon adsorption tower to meet emission standards.
8. A high-purity biochar prepared according to any one of claims 1-7, characterized in that: The biochar is black, porous granular with a well-developed pore structure. The main pore size is distributed in the range of 2-50 nm, and the surface contains abundant oxygen-containing functional groups.
9. The application of the high-purity biochar according to claim 8, characterized in that: When the biochar is used as an electrode material for a supercapacitor, its specific capacitance is ≥250F / g at a current density of 1A / g; when used as a heavy metal adsorbent, its maximum adsorption capacity for lead ions is ≥200mg / g.