A process for refining biomass char

Abstract

The application discloses a refining process of biomass charcoal, and belongs to the technical field of deep processing of biomass charcoal. The process takes biomass residues discharged by a biomass power plant and a cement plant as raw materials, and comprises pretreatment, acid pickling and ash removal, three-stage atmosphere heat treatment, segmented cooling, surface oxidation, zirconate coupling agent modification and screening. The acid pickling and ash removal adopts different kinds of acids for acid pickling in sequence; the heat treatment is divided into three stages; the cooling is segmented cooling and constant temperature; and the zirconate coupling agent modification is performed on the surface of the charcoal after the surface oxidation. The application can effectively reduce the ash content of the product, control the pore structure, improve the surface chemical properties, and improve the safety performance. The obtained refined biomass charcoal can be applied to the fields of mosquito-repellent incense products, firework fuse, smelting heat preservation filler, activated carbon and sodium negative electrode material, etc.

Description

Technical Field

[0001] This invention belongs to the technical field of deep processing of biochar, specifically relating to a refining process for biochar. Background Technology

[0002] Biomass residues produced by biomass power plants and cement plants contain a large amount of incompletely burned charcoal components, which have high recycling and reuse value. However, these raw materials generally have problems such as high moisture content, ash content mixed with sand, gravel, and metal impurities, and active chemical properties that make them prone to oxidation and spontaneous combustion.

[0003] Traditional refining processes have many shortcomings: conventional dryers have uneven feeding and low heat exchange efficiency, which can easily lead to spontaneous combustion of materials; traditional grinding equipment lacks a dedicated impurity removal mechanism, making it impossible to effectively separate ash from heavy impurities, and the sieving fineness is difficult to meet the customized needs of customers; traditional manual packaging is inefficient, causes serious dust pollution on site, and the finished charcoal is prone to oxidation and spontaneous combustion.

[0004] More importantly, as new energy materials (such as sodium-ion battery anodes) and high-end environmentally friendly materials place higher demands on the purity, surface chemical properties, and pore structure of carbon materials, traditional processes that rely solely on physical purification (dehydration, impurity removal, and pulverization) can no longer meet the needs of downstream high-end applications. Current technology lacks an integrated process that can achieve both safe industrial-scale production and deep chemical modification of biochar. Summary of the Invention

[0005] In response to the comprehensive problems of existing biochar refining processes, such as safety hazards, incomplete impurity removal, and product performance failing to meet the needs of high-end applications, this invention provides a biochar refining process that integrates physical purification, chemical modification, heat treatment, and safety control.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A refining process for biochar, using biomass residue from biomass power plants and / or cement plants as raw material, includes the following steps:

[0008] Step 1: Pretreatment: The biomass residue is washed with water to separate the incompletely burned charcoal components, remove soil and water-soluble impurities, drain and dry at 200℃ to a moisture content of less than 8%. The drying equipment is equipped with an air separation and impurity removal system, and the furnace temperature can be adjusted in the range of 400-780℃. Then it is sent to a cooling silo with a pipeline air cooling system to cool to room temperature.

[0009] Step 2: Acid washing and deashing: Perform pre-washing with dilute acid and acid washing with wood vinegar in sequence. Add dilute acid at a liquid-to-solid ratio of 5:1, stir at 600 rpm for 30-60 min at room temperature, and wash with water until the pH is 5. Then add wood vinegar at a liquid-to-solid ratio of 4:1-6:1, stir at 500 rpm for 1-2 h at 60℃, and wash with water until the pH of the washing solution is 5-6.

[0010] Step 3: Heat treatment: Under nitrogen protection, first perform nitrogen atmosphere heat treatment at 200-400℃, then perform heat treatment at 400-650℃ in a nitrogen mixed atmosphere containing carbon dioxide, and finally perform heat treatment at 700-800℃ in a nitrogen mixed atmosphere containing water vapor.

[0011] Step 4: Cooling: The heat-treated charcoal is cooled in stages and kept at a constant temperature under nitrogen protection;

[0012] Step 5: Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 5%-10%, the oxidation temperature at 250-300℃, and the oxidation time at 30-60 minutes.

[0013] Step 6: Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Then, a coupling agent is used to modify the surface of the carbon material.

[0014] Step 7: Screening: Feed the material into the gyratory screening system and screen it to 80-400 mesh to obtain refined charcoal powder.

[0015] Furthermore, the pickling in step 2 specifically includes: the dilute acid being a 0.5 mol / L dilute hydrochloric acid solution or a 1 mol / L citric acid solution; the wood vinegar solution having a pH of 3 and an organic acid content of 10% or more.

[0016] Further, in the heat treatment described in step 3, the heating rate is 5-10℃ / min. The first stage involves heating to 200-400℃ and holding in a nitrogen atmosphere for 30min. The second stage involves heating to 400-650℃ and switching the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holding for 60min. The third stage involves heating to 700-800℃ and switching the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holding for 30min.

[0017] Further, the cooling described in step 4 is as follows: under nitrogen atmosphere protection, firstly, the temperature is reduced from the final temperature of the third stage of heat treatment to 500±10℃ at a cooling rate of 15℃ / min, and held at a constant temperature for 5 minutes; then, the temperature is reduced to 300±10℃ at a cooling rate of 10℃ / min, and held at a constant temperature for 5 minutes; finally, the temperature is naturally cooled to below 60℃ in a nitrogen atmosphere.

[0018] Further, the coupling agent mentioned in step 6 is a zirconate ester coupling agent. The specific modification process includes: adding anhydrous isopropanol to the oxidized carbon material at a liquid-to-solid ratio of 3:1, purging with nitrogen for protection, starting stirring at a speed of 400 rpm, adding the zirconate ester coupling agent at a rate of 3-5% of the carbon material mass, heating to 60-80℃, continuing stirring for 1.5-2 hours, filtering after the reaction is complete, washing 2-3 times with anhydrous ethanol, and then drying under vacuum at 80℃ for 2 hours.

[0019] This invention also protects the application of the refined biochar prepared by the above process in the preparation of mosquito coil products, fireworks fuses, smelting insulation fillers, activated carbon, and sodium electrode anode materials.

[0020] The advantages and beneficial effects of this invention are as follows:

[0021] 1. First, this invention employs a three-stage chemical deashing process—water washing, dilute acid pre-washing, and wood vinegar acid washing—to effectively remove stubborn impurities such as carbonates, metal oxides, and silicon and aluminum from biochar, reducing the ash content from 15%–20% in traditional processes to below 3%–5%. This low ash content allows the product to meet the purity requirements of sodium-ion battery anode materials and facilitates the subsequent direct preparation of high specific surface area activated carbon. Furthermore, it enables more stable combustion performance in civilian products such as mosquito coils and fireworks fuses.

[0022] 2. This invention employs a combination of pre-washing with dilute hydrochloric acid or citric acid and acid washing with wood vinegar in the acid washing and deashing stage. Dilute hydrochloric acid effectively removes carbonate impurities, while citric acid is suitable for chelating and removing metal ions; both are conventional acid washing methods. Unlike the aforementioned inorganic or organic acids, wood vinegar is an acidic mixture produced by biomass pyrolysis, containing various organic acids such as acetic acid and propionic acid, as well as phenolic substances. Wood vinegar has a unique complexing and dissolving ability for impurities such as silicon and aluminum that are tightly bound to the carbon skeleton. Furthermore, it originates from the biomass itself and has natural compatibility with the biochar system, achieving deep deashing under mild heating conditions, avoiding equipment corrosion and wastewater treatment burdens associated with using strong acids. Using the three acids in sequence ensures both effective deashing and the environmental friendliness and economy of the process.

[0023] 3. Secondly, acid washing removes inorganic impurities and opens the closed pores on the surface of the carbon particles, creating conditions for subsequent heat treatment. This invention employs a three-stage atmosphere heat treatment: first, preliminary stabilization is performed under a nitrogen atmosphere to remove residual volatiles and prevent excessive oxidation during subsequent heating; then, a mild carbonization reaction is carried out in a mixed atmosphere of carbon dioxide and nitrogen, increasing the micropore volume through etching; finally, further pore formation and the introduction of oxygen-containing functional groups are performed in a mixed atmosphere of water vapor and nitrogen, which helps to form a mesoporous-microporous composite structure and enhance surface reactivity. This segmented treatment method allows for flexible adjustment of the product's specific surface area within the range of 500~2000 m² / g, meeting different needs such as activated carbon adsorption and sodium electrode ion transport.

[0024] 4. Furthermore, this invention introduces a two-step chemical modification process: surface oxidation and zirconate ester coupling agent modification. Surface oxidation generates polar groups such as hydroxyl and carboxyl groups on the surface of carbon particles. After chemical bonding with these groups, the zirconate ester coupling agent forms an organic modified layer on the outer layer of the carbon powder. This modified layer improves the dispersibility of the carbon powder in organic solvents or polymer matrices. When used in sodium electrode anodes, it enhances the bonding force with binders, suppresses volume expansion during charge and discharge, and significantly improves cycle stability. When used in mosquito coils or fireworks fuses, it also helps improve material uniformity and processing performance.

[0025] 5. Regarding safety in production, this invention addresses the issue of biochar's susceptibility to oxidation and spontaneous combustion by incorporating a flame-retardant and explosion-proof system at the drying discharge end, adding a piped air-cooling system to the cooling silo to control the temperature below 80℃, and employing a nano-extraction system in the automatic packaging process to reduce residual oxygen in the packaging bags. These three measures reduce the risk of spontaneous combustion and dust explosions at the source, enabling continuous and stable operation of the process.

[0026] 6. Regarding production efficiency and product adaptability, the addition of an air-classifying impurity removal system to the dryer expands the furnace temperature control range to 400~780℃, increasing the hourly capacity of a single unit from 3 tons to 6 tons, while maintaining a stable discharge moisture content below 8%. The Raymond mill's negative pressure cyclone impurity removal system simultaneously operates during the grinding process, separating impurities such as sand and metal with an efficiency exceeding 90%. The gyratory screening system covers a screening range of 80~400 mesh, with convenient screen replacement, meeting the customized needs of different customers for product fineness. The continuous operation throughout the entire process reduces material transfer links, significantly lowering labor costs.

[0027] 7. Based on the above improvements, the refined biochar prepared by this invention has low ash content, controllable moisture content, and adjustable porosity and surface properties. It can be used in mosquito coil products, fireworks fuses, smelting insulation fillers, activated carbon base materials, and precursors for sodium anode materials. While maintaining safe and efficient industrial production, it broadens the resource utilization pathways of biomass residue. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments. The biomass used in the following embodiments is all based on biomass residue discharged from biomass power plants and / or cement plants. Pre-treatment is performed first: the biomass residue is washed with water to separate incompletely burned charcoal components, removes soil and water-soluble impurities, drains, and then dried at 200℃ to a moisture content of less than 8%. It is then sent to a cooling silo with a piped air-cooling system to cool to room temperature for later use. The wood vinegar used below is industrial-grade wood vinegar, purchased from Jinan Hairuisen Chemical Co., Ltd., with a pH of 2.8-3.5 and an organic acid content of over 10%. The zirconate coupling agent is NDZ-04 zirconate coupling agent, purchased from Shenzhen Binku Chemical Co., Ltd.

[0029] Example 1

[0030] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 45 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 5:1 and stir at 500 rpm for 1.5 h at 60℃. Wash with water until the pH of the washing solution is 5.5.

[0031] Heat treatment: The heating rate is 8℃ / min. The first stage heats up to 300℃ and holds in a nitrogen atmosphere for 30min. The second stage heats up to 550℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 750℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0032] Cooling: Under nitrogen atmosphere protection, first cool from 750℃ to 500℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 750℃ to 500℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0033] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0034] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 4% of the carbon material mass. The temperature is raised to 70°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0035] Screening: The material is fed into a gyratory screening system and screened to 100 mesh to obtain refined charcoal powder.

[0036] Example 2

[0037] Acid washing and deashing: Take 40 kg of pretreated biomass material and prewash it with 1 mol / L citric acid solution and then acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 60 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 4:1 and stir at 500 rpm for 2 h at 60℃. Wash with water until the pH of the washing solution is 5.

[0038] Heat treatment: The heating rate is 10℃ / min. The first stage heats up to 200℃ and holds at a nitrogen atmosphere for 30min. The second stage heats up to 400℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 800℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0039] Cooling: Under nitrogen atmosphere protection, first cool from 800℃ to 510℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 800℃ to 510℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0040] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 10%, the oxidation temperature at 250℃, and the oxidation time at 30 minutes;

[0041] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 5% of the carbon material mass. The temperature is raised to 60°C, and stirring is continued for 2 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0042] Screening: The material is fed into a gyratory screening system and screened to 400 mesh to obtain refined charcoal powder.

[0043] Example 3

[0044] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 30 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 6:1 and stir at 500 rpm for 1 h at 60℃. Wash with water until the pH of the wash solution is 6.

[0045] Heat treatment: The heating rate is 5℃ / min. The first stage heats up to 400℃ and holds at this temperature in a nitrogen atmosphere for 30min. The second stage heats up to 650℃ and switches the furnace atmosphere to a mixture of carbon dioxide and nitrogen, with a volume ratio of 3:7, and holds for 60min. The third stage heats up to 700℃ and switches the furnace atmosphere to a mixture of water vapor and nitrogen, with a volume ratio of 2:8, and holds for 30min.

[0046] Cooling: Under nitrogen atmosphere protection, first cool from 700℃ to 490℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 700℃ to 490℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0047] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 5%, the oxidation temperature at 300℃, and the oxidation time at 60 minutes;

[0048] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 3% of the carbon material mass. The temperature is raised to 80°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed three times with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0049] Screening: The material is fed into a gyratory screening system and screened to 80 mesh to obtain refined charcoal powder.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the acid washing and deashing steps in this comparative example are as follows: citric acid is added at a liquid-to-solid ratio of 5:1, and the mixture is stirred at 600 rpm for 3 hours at room temperature. The mixture is then washed with water until the pH reaches 5. The remaining heat treatment, cooling, surface oxidation, coupling agent modification, and sieving steps are the same as in Example 1.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the acid washing and deashing steps in this comparative example are as follows: citric acid is added at a liquid-to-solid ratio of 5:1, and the mixture is stirred at 600 rpm for 60 min at room temperature, then washed with water until the pH is 5; then 0.5 mol / L dilute hydrochloric acid solution is added at a liquid-to-solid ratio of 4:1, and the mixture is stirred at 500 rpm for 2 h at 60°C, then washed with water until the pH of the washing solution is 5; the rest is the same as in Example 1.

[0054] Comparative Example 3

[0055] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 45 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 5:1 and stir at 500 rpm for 1.5 h at 60℃. Wash with water until the pH of the washing solution is 5.5.

[0056] Heat treatment: The heating rate is 8℃ / min. The first stage heats up to 300℃ and holds in a nitrogen atmosphere for 30min. The second stage heats up to 550℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 750℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0057] Cooling: Under nitrogen atmosphere protection, first cool from 750℃ to 500℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 750℃ to 500℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0058] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0059] Screening: The oxidized charcoal is fed into a Raymond mill for crushing. During the crushing process, a negative pressure cyclone cleaning system is activated simultaneously to send the material into a gyratory screening system and screen it to 100 mesh to obtain refined charcoal powder.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is that the zirconate coupling agent is replaced with silane coupling agent KH550 in this comparative example; otherwise, it is the same as Example 1.

[0062] Comparative Example 5

[0063] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 45 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 5:1 and stir at 500 rpm for 1.5 h at 60℃. Wash with water until the pH of the washing solution is 5.5.

[0064] Heat treatment: The heating rate is 8℃ / min. The first stage heats up to 300℃ and holds in a nitrogen atmosphere for 30min. The second stage heats up to 550℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 750℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0065] Cooling: Under nitrogen atmosphere protection, first cool from 750℃ to 500℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 750℃ to 500℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0066] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0067] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 8% of the carbon material mass. The temperature is raised to 70°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0068] Screening: The material is fed into a gyratory screening system and screened to 100 mesh to obtain refined charcoal powder.

[0069] Comparative Example 6

[0070] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 45 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 5:1 and stir at 500 rpm for 1.5 h at 60℃. Wash with water until the pH of the washing solution is 5.5.

[0071] Heat treatment: The heating rate is 8℃ / min. The first stage heats up to 300℃ and holds in a nitrogen atmosphere for 30min. The second stage heats up to 550℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 750℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0072] Cooling: Under nitrogen atmosphere protection, first cool from 750℃ to 500℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 750℃ to 500℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0073] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0074] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate ester coupling agent is added at a rate of 1% of the carbon material mass. The temperature is raised to 70°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0075] Screening: The material is fed into a gyratory screening system and screened to 100 mesh to obtain refined charcoal powder.

[0076] Comparative Example 7

[0077] Acid washing and deashing: Take 40 kg of pretreated biomass material and pre-wash it with 1 mol / L citric acid solution and acid wash it with wood vinegar solution. Add citric acid at a liquid-to-solid ratio of 5:1 and stir at 600 rpm for 45 min at room temperature. Wash with water until the pH is 5. Then add wood vinegar solution at a liquid-to-solid ratio of 5:1 and stir at 500 rpm for 1.5 h at 60℃. Wash with water until the pH of the washing solution is 5.5.

[0078] Heat treatment: The heating rate is 8℃ / min, the temperature is raised to 750℃, the atmosphere in the furnace is nitrogen, and the temperature is held for 120min.

[0079] Cooling: Under nitrogen atmosphere protection, the temperature was reduced from 750°C to 300°C at a cooling rate of 15°C / min and held constant for 10 minutes; finally, it was allowed to cool naturally to below 60°C in nitrogen atmosphere.

[0080] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0081] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 4% of the carbon material mass. The temperature is raised to 70°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0082] Screening: The material is fed into a gyratory screening system and screened to 100 mesh to obtain refined charcoal powder.

[0083] Comparative Example 8

[0084] Acid washing and deashing: Take 40 kg of pretreated biomass material, add wood vinegar at a liquid-to-solid ratio of 5:1, stir at 500 rpm for 1.5 h at 60℃, wash with water until the pH of the wash solution is 5.5, then perform acid washing with 1 mol / L citric acid solution, add citric acid at a liquid-to-solid ratio of 5:1, stir at 600 rpm for 45 min at room temperature, and wash with water until the pH is 5.

[0085] Heat treatment: The heating rate is 8℃ / min. The first stage heats up to 300℃ and holds in a nitrogen atmosphere for 30min. The second stage heats up to 550℃ and switches the furnace atmosphere to a mixed atmosphere of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holds for 60min. The third stage heats up to 750℃ and switches the furnace atmosphere to a mixed atmosphere of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holds for 30min.

[0086] Cooling: Under nitrogen atmosphere protection, first cool from 750℃ to 500℃ at a cooling rate of 15℃ / min and hold at a constant temperature for 5 minutes; then cool from 750℃ to 500℃ at a cooling rate of 10℃ / min and hold at a constant temperature for 5 minutes; finally, allow to cool naturally to below 60℃ in nitrogen atmosphere.

[0087] Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 8%, the oxidation temperature at 280℃, and the oxidation time at 45 minutes;

[0088] Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Anhydrous isopropanol is then added to the pulverized carbon material at a liquid-to-solid ratio of 3:1. Nitrogen gas is introduced for protection, and stirring is started at a speed of 400 rpm. Zirconate coupling agent is added at a rate of 4% of the carbon material mass. The temperature is raised to 70°C, and stirring is continued for 1.5 hours. After the reaction is completed, the mixture is filtered, washed twice with anhydrous ethanol, and then dried under vacuum at 80°C for 2 hours.

[0089] Screening: The material is fed into a gyratory screening system and screened to 100 mesh to obtain refined charcoal powder.

[0090] Experiment 1: Performance Testing

[0091] (1) Weight loss rate: 10g samples were taken from each group of Examples 1-3 and Comparative Examples 1-8 and dried to constant weight in an oven at 105℃. The initial temperature was room temperature. A thermogravimetric analyzer was used to heat the samples to 950℃ at a rate of 10℃ / min under a nitrogen atmosphere (flow rate 50mL / min) until the samples reached constant weight. Two to three parallel samples were prepared for each group, and the average value was taken. Weight loss rate = (initial mass - residual mass) / initial mass × 100%. The original untreated biomass raw material was used as the control group.

[0092] (2) Ash content: Weigh 10g of dried refined biochar sample (accurate to 0.0001 g) and place it in a pre-weighed porcelain crucible. Calcinate the sample in a muffle furnace at 815℃ until constant weight, then cool and weigh. Ash content = (m2 - m0) / (m1 - m0) × 100%, where m0 is the mass of the empty crucible, m1 is the mass of the crucible + sample before calcination, and m2 is the mass of the crucible + ash after calcination. Use untreated, unprocessed biomass as a control group.

[0093] (3) Oxidation index determination: Differential scanning calorimetry was used. 10 mg of sample was heated to a set temperature of 200 °C at a rate of 20 °C / min under an inert atmosphere and held at that temperature for 5 minutes. The atmosphere was then switched to oxygen (flow rate 50 ml / min), and the time from switching to the appearance of the oxidation exothermic peak (OIT) was recorded. Commercially available high-purity graphite (99.9% purity, 10 μm particle size) was used as the standard reference sample, and its average OIT was 10.0 min after 5 measurements. The test results are expressed as OIT (min). Oxidation index = Sample OIT / Reference sample OIT × 100%. Untreated biomass raw materials were used as the control group.

[0094] (4) Determination of heavy metal residues (Cd, Pb): Weigh 5g of dried and refined biochar sample, digest it with a mixture of nitric acid and perchloric acid, and then bring the volume to a final volume. The concentrations of Cd and Pb in the solution are determined by inductively coupled plasma mass spectrometry. Heavy metal content (mg / kg) = (concentration measured × final volume) / sample mass. Untreated, unprocessed biomass raw material is used as a control group.

[0095] The results are shown in Table 1 below:

[0096] Table 1

[0097] control group 38.7 20.4 64.7 2.5 18.4 Example 1 11.5 3.8 89.7 ≤0.2 ≤5 Example 2 12.0 4.3 88.1 ≤0.3 ≤5 Example 3 12.3 4.9 87.6 ≤0.3 ≤5 Comparative Example 1 30.3 11.6 72.4 ≤0.5 ≤10 Comparative Example 2 25.8 9.2 76.8 ≤0.5 ≤10 Comparative Example 3 12.5 2.6 74.3 ≤0.5 ≤10 Comparative Example 4 22.3 8.9 78.4 ≤0.5 ≤10 Comparative Example 5 16.0 6.6 82.5 ≤0.4 ≤6 Comparative Example 6 14.5 5.3 80.1 ≤0.4 ≤8 Comparative Example 7 18.0 5.8 83.7 ≤0.5 ≤10 Comparative Example 8 14.2 6.5 82.3 ≤0.4 ≤8

[0098] As shown in Table 1, compared with the untreated control group, the refined biochar of Examples 1-3 showed significant reductions in weight loss (11.5%-12.3%), ash content (3.8%-4.9%), and heavy metal residue, while the oxidation index was significantly increased (87.6%-89.7%). This indicates that the process of the present invention can effectively remove inorganic impurities and thermally unstable components, reduce ash content, and improve antioxidant capacity.

[0099] Comparative Example 1 (single citric acid pickling only) still had an ash content of 11.6% due to the lack of wood vinegar to synergistically remove silicon and aluminum impurities; Comparative Example 2 (dilute hydrochloric acid instead of wood vinegar) had insufficient ability to remove stubborn impurities bound to the carbon skeleton, with an ash content of 9.2%; Comparative Example 3 (without coupling agent modification) lacked an organic protective layer on the surface, and although its ash content (2.6%) was lower than that of the example, its weight loss rate (12.5%) was slightly higher than that of the example, and its oxidation index was only 74.3%, significantly lower than that of the example; Comparative Example 4 (The silane coupling agent used instead of zirconate ester had lower bonding efficiency with the polar groups on the carbon surface, resulting in lower ash content and oxidation index compared to the example.) Comparative Example 5 (coupling agent excess up to 8%) and Comparative Example 6 (coupling agent only 1%) had lower oxidation index (82.5%) and ash content control compared to the example due to excessively thick or thin modified layers, respectively. Comparative Example 7 (heat treatment with nitrogen at a single temperature) had insufficient pore structure development, high residual volatile matter, and a weight loss of 18.0%. Comparative Example 8 (acid washing order reversed, wood vinegar first followed by citric acid) had ash content of 6.5% and an oxidation index of 82.3%, both lower than Example 1 (3.8% and 89.7%), demonstrating that the order of pre-washing with dilute acid followed by acid washing with wood vinegar has a synergistic effect.

[0100] In contrast, the example achieves low ash content (≤4.9%) through "dilute acid pre-washing + deep deashing with wood vinegar". It precisely controls the pore structure and surface chemical properties using a three-stage atmosphere heat treatment, followed by surface oxidation and modification with an appropriate amount of zirconate ester coupling agent (3%~5%), forming a stable organic-inorganic hybrid layer on the carbon particle surface. The weight loss rate of the example is lower than that of Comparative Example 3, while the ash content is slightly higher. This is a normal phenomenon due to the pyrolysis of the coupling agent producing residual carbon and ZrO2, precisely demonstrating the successful bonding of the modified layer. Considering the ash content, oxidation index, and heavy metal residue data, the example is still significantly superior to the unmodified or other control group. The technical solution of this application significantly enhances the antioxidant stability while meeting the stringent requirements of high purity and low heavy metal residue for sodium electrode anode materials, exhibiting excellent comprehensive performance.

Claims

1. A refining process for biochar, characterized in that, Using biomass residue from biomass power plants and cement plants as raw materials, the process includes the following steps: Step 1: Pretreatment: The biomass residue is washed with water to separate the incompletely burned charcoal components, remove soil and water-soluble impurities, drain and dry at 200℃ until the moisture content is below 8%, and then sent to a cooling silo with a piped air-cooling system to cool to room temperature. Step 2: Acid washing and deashing: Perform pre-washing with dilute acid and acid washing with wood vinegar in sequence. Add dilute acid at a liquid-to-solid ratio of 5:1, stir at 600 rpm for 30-60 min at room temperature, and wash with water until the pH is 5. Then add wood vinegar at a liquid-to-solid ratio of 4:1-6:1, stir at 500 rpm for 1-2 h at 60℃, and wash with water until the pH of the washing solution is 5-6. Step 3: Heat treatment: Under nitrogen protection, first perform nitrogen atmosphere heat treatment at 200-400℃, then perform heat treatment at 400-650℃ in a nitrogen mixed atmosphere containing carbon dioxide, and finally perform heat treatment at 700-800℃ in a nitrogen mixed atmosphere containing water vapor. Step 4: Cooling: The heat-treated charcoal is cooled in stages and kept at a constant temperature under nitrogen protection; Step 5: Surface oxidation: Oxidation treatment is carried out in an oxygen-containing atmosphere, with the oxygen content controlled at 5%-10%, the oxidation temperature at 250-300℃, and the oxidation time at 30-60 minutes. Step 6: Coupling agent modification: The dried carbon material is fed into a Raymond mill for pulverization. During the pulverization process, a negative pressure sacrificial impurity removal system is started simultaneously. Then, a coupling agent is used to modify the surface of the carbon material. Step 7: Screening: Feed the material into the gyratory screening system and screen it to 80-400 mesh to obtain refined charcoal powder.

2. The refining process according to claim 1, characterized in that, The pickling process described in step 2 specifically includes: The dilute acid is a 0.5 mol / L dilute hydrochloric acid solution or a 1 mol / L citric acid solution; the wood vinegar has a pH of 3 and an organic acid content of 10% or more.

3. The refining process according to claim 1, characterized in that, In the heat treatment described in step 3, the heating rate is 5-10℃ / min. The first stage involves heating to 200-400℃ and holding at a nitrogen atmosphere for 30 minutes. The second stage involves heating to 400-650℃ and switching the furnace atmosphere to a mixture of carbon dioxide and nitrogen, with a volume ratio of carbon dioxide to nitrogen of 3:7, and holding at this temperature for 60 minutes. The third stage involves heating to 700-800℃ and switching the furnace atmosphere to a mixture of water vapor and nitrogen, with a volume ratio of water vapor to nitrogen of 2:8, and holding at this temperature for 30 minutes.

4. The refining process according to claim 1, characterized in that, The cooling process described in step 4 is as follows: Under nitrogen atmosphere protection, the temperature is first reduced from the final temperature of the third stage of heat treatment to 500±10℃ at a cooling rate of 15℃ / min and held at a constant temperature for 5 minutes; then the temperature is reduced to 300±10℃ at a cooling rate of 10℃ / min and held at a constant temperature for 5 minutes; finally, the temperature is naturally cooled to below 60℃ in a nitrogen atmosphere.

5. The refining process according to claim 1, characterized in that, The coupling agent mentioned in step 6 is a zirconate ester coupling agent. The specific modification process includes: adding anhydrous isopropanol to the oxidized carbon material at a liquid-to-solid ratio of 3:1, purging with nitrogen for protection, starting stirring at a speed of 400 rpm, adding the zirconate ester coupling agent at a rate of 3-5% of the carbon material mass, heating to 60-80℃, continuing stirring for 1.5-2 hours, filtering after the reaction is complete, washing 2-3 times with anhydrous ethanol, and then drying under vacuum at 80℃ for 2 hours.

6. The application of biochar prepared by the refining process according to any one of claims 1-5 in the preparation of mosquito coil products, fireworks fuses, smelting insulation fillers, activated carbon, and sodium electrode anode materials.