Method for preparing biochar through low-temperature carbonization of furfural residues and application

Abstract

The invention discloses a method for preparing biochar through low-temperature carbonization of furfural residues and application, and the method comprises the following steps: pretreatment of furfural residues: carrying out dynamic drying by using superheated steam generated by a biomass boiler, so that the moisture content is reduced to be less than or equal to 25%; carrying out particle reinforced molding, namely mixing the furfural residues with corn straws and wheat straws, and carrying out granulation molding; carrying out segmented low-temperature carbonization, sequentially carrying out drying preheating, ash removal and carbonization stages on the particles, and enabling the hardness of the carbonized particles to reach 8MPa; by-products are recycled, pyrolysis non-condensable gas is used for boiler combustion, condensate can be used as liquid organic fertilizer, heat treatment activation is carried out, and carbonization is carried out for 2 h in a nitrogen environment at the temperature of 600 DEG C; washing and drying: washing with hydrochloric acid (HCl), and drying at 80 DEG C for 24 hours; the method solves the technical problems of high energy consumption in the furfural residue carbonization process and limited application range of carbonized products in the prior art, also solves the problems of limited adsorption capacity and difficult recovery of common charcoal, and is suitable for the environmental protection fields of heavy metal wastewater treatment, pollution remediation and the like.

Description

Technical Field

[0001] The invention relates to the technical field of biochar activation and application, and specifically to a method for preparing biochar by low-temperature carbonization of furfural residue and application thereof. Background Art

[0002] Furfural residue is a waste product obtained from plant fibers such as corn cobs and rice husks through the furfural extraction process. Furfural is an important organic chemical raw material, widely used in pharmaceuticals, pesticides and chemical synthesis. Biochar is a solid carbon material obtained from furfural residue through pyrolysis or carbonization. Biochar has good adsorption properties due to its high specific surface area, porous structure, and rich surface functional groups. It can be widely used in soil improvement, pollution control and other fields. Chinese patent application No. 202210017710X discloses a method for preparing biochar from furfural production waste. The preparation method has the following defects: ① The furfural residue needs to be fermented, and during fermentation, it needs to be adjusted to neutral with wood ash and added with bacteria, which affects the carbonization quality; ② The chemical agents of aluminum silicate, potassium chloride, and calcium sulfate are introduced to reduce the purity of organic matter; ③ Primary carbonization + secondary carbonization, the secondary carbonization increases energy consumption; ④ The biochar of this process is mainly used to improve the soil and provide plant nutrients, and the product has a single use.

[0003] In addition, with the acceleration of industrialization, a large amount of heavy metal wastewater (such as Pb²⁺, Cr 6 ⁺, Cd²⁺) seriously pollute the environment; traditional treatment methods (such as chemical precipitation and membrane separation) have problems such as high treatment cost, secondary pollution of sludge, and difficulty in recovering adsorbents; biochar is considered to be a highly potential heavy metal adsorption material due to its porous structure, high specific surface area, and rich surface functional groups. However, the adsorption capacity of ordinary biochar is limited and difficult to recover; it cannot meet the needs of actual use, so a method and application of preparing biochar by low-temperature carbonization of furfural residue is proposed to solve the above problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a method and application of preparing biochar by low-temperature carbonization of furfural residues, pretreating the furfural residues, pressing the furfural residues into pellets, low-temperature carbonizing the biomass pellets, recycling the carbonization pyrolysis gas, and reusing the condensate through deep processing, and utilizing all components of the furfural residues. After low-temperature carbonization and acid-base activation treatment of the furfural residues, the furfural residues can be used in environmental water treatment, pollution remediation, industrial wastewater purification and other fields, which can effectively solve the problems in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing biochar by low-temperature carbonization of furfural residue and its application, comprising the following steps: 1) Furfural residue pretreatment: Using the superheated steam generated by the biomass boiler as the heat source, the furfural residue is dynamically dried through hot air drying equipment to reduce its moisture content from 50% to ≤25%; During the drying process, the organic acids and light volatile components in the furfural residue evaporate with the hot air, and the evaporated gas is drained to the condensation treatment device through the waste gas collection system. The condensate obtained after condensation is reused in the furfural distillation system or as a liquid organic fertilizer raw material.

[0006] 2) Particle reinforcement molding: corn straw, wheat straw and furfural residue are mixed in a mass ratio of 5:1-2:0.8-1.2 to improve the fiber cross-linking and improve the particle molding effect; they are extruded into particles with a diameter of 5mm and a length of 15-25mm through a granulator, and the moisture content of the particles after molding is ≤15%; Considering that the cellulose chain of furfural residue is short and not easy to shape and granulate, combined with the characteristics of agricultural and forestry wastes in the surrounding area, considering that the calorific value of furfural residue is low, the furfural production system is easy to coke, and there are a lot of carbonized cokes during maintenance, corn straw and wheat straw are introduced into the furfural residue to facilitate the briquetting of furfural residue. 3) Segmented low-temperature carbonization: The formed particles are sent into the low-temperature carbonization furnace. The particles first enter the drying and preheating stage, with a temperature of 105-120°C, an oxygen content of 12-20%, and a time of 2 hours; The particles are heated up by gravity and enter the ash removal stage. The temperature in the ash removal area is 160-180°C, the oxygen content is 6-9%, and the time is 1-1.5 hours; After the ash removal is completed, the particles are continuously lowered by gravity and downward pressure to enter the carbonization stage. The temperature in the carbonization area is 240-260°C, the oxygen content is ≤3%, and the time is 2-2.5 hours. The hot steam of the carbonization furnace maintains an oxygen-free or anoxic environment. After carbonization, the biochar particles enter the temporary storage tank and cool down naturally in an oxygen-deficient environment, so that the hardness of the carbonized particles reaches 8mpa; The briquette particles are pyrolyzed at low temperature in a low temperature carbonization furnace. The released pyrolysis gas is washed with water to obtain condensate (organic acids, phenols, alcohols, etc.). The remaining non-condensable pyrolysis gas is introduced into the biomass boiler for combustion through a conveying pipeline. The heat, temperature and oxygen-poor environment required for carbonization are solved by the medium-temperature and sub-high-pressure steam provided by the biomass boiler to realize the combustion of non-condensable gas in the boiler. The steam produced by the boiler is used for the large circulation of pyrolysis gas for carbonization.

[0007] 4) By-product recovery: During carbonization, the non-condensable gas from pyrolysis is sent to the boiler for combustion to provide heat for the boiler. The heat source required for carbonization is provided by the superheated steam generated by the biomass boiler, requiring a steam temperature of 420-440°C and a pressure of 4.2-4.35 MPa. At the same time, high-temperature steam enters the carbonization furnace to provide an oxygen-free or oxygen-deficient environment for the carbonization furnace; the main components of the pyrolysis gas condensate are aldehydes, phenols, acid decomposition products and trace chemical elements required by organisms, which can be collected and temporarily stored in a liquid tank.

[0008] Furthermore, in the particle enhancement molding step, furfural coke is introduced to facilitate the carbonization of furfural residue, thereby increasing the carbon content and improving the combustion performance of biochar.

[0009] Furthermore, in the by-product recovery step, the condensate contains 12-18% organic matter, which can be used as a water dispersant and humectant or directly used as a liquid organic fertilizer during agricultural watering and fertilization to help soil moisture retention and achieve high-value utilization of components. When used as liquid organic fertilizer, nitrogen, phosphorus and potassium elements are added in a certain proportion to form liquid organic fertilizer, or it can be directly added with water flow during agricultural irrigation to achieve the effect of moisturizing crops.

[0010] Furthermore, the activation of biochar particles comprises the following steps: 1) Biochar pretreatment: Take the biochar after carbonization of furfural residue, wash it with deionized water to remove surface ash and residual organic matter, and dry it at 80℃ for 12h to ensure the biochar is dry; 2) Phosphoric acid (H3PO4) activation: The biochar was immersed in a phosphoric acid (H3PO4) solution, stirred evenly, and stirred at a constant temperature of 60°C for 2 hours to promote the phosphation reaction. The solution was allowed to stand for 12 hours to allow the phosphoric acid to fully penetrate into the pores of the biochar. 3) Potassium hydroxide (KOH) activation: The biochar impregnated in step 2 is filtered and immersed in a phosphoric acid (H3PO4) solution. Ultrasonic-assisted treatment is performed for 1 hour to enhance the etching effect of the alkaline solution on the biochar. The biochar is left standing at room temperature for 6 hours to allow potassium hydroxide to fully penetrate. 4) Heat treatment activation: After drying the biochar treated in step 3, carbonize it at 600°C in a nitrogen (N2) protected environment for 2 hours, with the heating rate controlled at 5°C / min to prevent excessive damage to the carbon structure. After activation, cool it to room temperature; 5) Washing and drying: Wash with hydrochloric acid (HCl) to remove unreacted phosphoric acid and potassium hydroxide residues, wash with deionized water to pH = 7, and dry at 80°C for 24 hours to obtain the final activated biochar.

[0011] Furthermore, in step 2, the mass of phosphoric acid (H3PO4) accounts for 10% of the mass of the entire solution.

[0012] Furthermore, the concentration of hydrochloric acid is 0.1 mol / L.

[0013] Furthermore, the pyrolysis gas produced during the carbonization process includes combustible gases such as CO, H2, and CH4, which are recovered and used for boiler combustion to reduce external fuel demand and improve energy utilization.

[0014] Furthermore, biochar was used to treat wastewater containing heavy metal ions, such as Pb²⁺, Cd²⁺ and Cr6 ⁺.

[0015] Biochar usually presents a porous surface structure under a scanning electron microscope, showing pores of various sizes. The pore structure of biochar is composed of pores of various sizes with a wide distribution of pore sizes.

[0016] Through different activation treatments (such as acid-base activation), different functional groups (such as -COOH, -OH, -C=O) will be formed on the surface; the hydrophilicity and adsorption of biochar will be improved; activated carbon particles under a scanning electron microscope are usually irregular in shape, with a rough surface and obvious microscopic cracks and voids; after acid-base activation, these surfaces will be rougher and have a higher porosity.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Pre-treat the furfural residue, press the furfural residue into pellets, low-temperature carbonize the biomass pellets, recycle the carbonization pyrolysis gas, and reuse the condensate. All components of the furfural residue are utilized. After low-temperature carbonization and acid-base activation treatment of the furfural residue, it can be used in environmental water treatment, pollution remediation, industrial wastewater purification and other fields.

[0018] 2. The present invention realizes effective carbonization of furfural residue by controlling the temperature and flow rate of high-temperature superheated steam, ensures that furfural residue is converted into biochar, and the fixed carbon content reaches more than 70%; in order to improve the molding property and carbon quality of furfural residue during carbonization, the present invention introduces corn stalks and wheat stalks to enhance the fiber cross-linking property; at the same time, furfural coking material is introduced to further increase the fixed carbon content of biochar. These technical measures optimize the quality and stability of biochar and effectively improve its market competitiveness.

[0019] In addition, the present invention has significant resource utilization and economic benefits; by recycling furfural residue as industrial solid waste, it can not only reduce excess high-temperature superheated steam, but also increase the added value of furfural residue, avoid steam waste, and improve the overall economic benefits of the furfural heat and power integration project; at the same time, the present invention provides a renewable biochar resource, which helps to reduce forest exploitation, reduce the use of petrochemical-based charcoal, and thus reduce carbon emissions.

[0020] 3. Acid-base activation can significantly improve the specific surface area and pore structure of the material; through the action of acid or alkali, the surface structure of the material changes, the pores are expanded or new pores are generated, which significantly improves the adsorption performance of biochar or carbonized materials; the optimized pore structure helps to more effectively adsorb water, gas and heavy metal ions, thereby showing higher effects in fields such as environmental purification and water treatment.

[0021] 4. Acid-base activation can also improve the adsorption capacity of materials. Acid activation enhances the hydrophilicity of the material and can more effectively adsorb water-soluble pollutants, while alkaline activation improves the material's adsorption capacity for organic or oil pollutants; this makes the activated carbon material have stronger performance in pollutant removal, wastewater treatment, etc., and enhances its potential for wide application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 This is a performance diagram showing the effect of carbonization temperature on the performance of biochar according to the present invention.

[0023] Figure 3 It is a schematic diagram of the low-temperature carbonization device of the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0025] See also Figure 1-2 The present invention provides a technical solution: a method for preparing biochar by low-temperature carbonization of furfural residue and its application. Furfural residue pretreatment: The furfural residue is dried by hot air drying equipment using superheated steam generated by a biomass boiler; the drying temperature is set at 100°C to ensure that the moisture content of the furfural residue is reduced from 50% to below 25%; the evaporated organic acids and light volatile components are drained to the condensation device through the exhaust gas collection system, and the condensate is stored for later use as a liquid organic fertilizer raw material.

[0026] Particle enhancement molding: corn straw and wheat straw are added to the furfural residue and mixed in a mass ratio of 2:1; the mixture is extruded into particles with a diameter of 5 mm and a length of 20 mm through a granulator, and the moisture content of the particles after molding is controlled at 14%.

[0027] Low temperature carbonization: The formed particles are fed into a low temperature carbonization furnace. The carbonization process is divided into three stages: 1. Preheating stage: temperature 105°C, oxygen content 20%, lasting 2 hours; 2. Ash removal stage: temperature 170°C, oxygen content 9%, lasting 1.5 hours; 3. Carbonization stage: temperature 250°C, oxygen content 2%, lasting 2 hours; After carbonization, the biochar particles naturally cool down to room temperature and the hardness reaches 8 MPa; By-product recovery: The condensate contains aldehydes, phenols, acids and trace elements required by organisms. After being collected and stored, it can be used as liquid organic fertilizer for agricultural irrigation to enhance soil moisture retention. The non-condensable gas is sent to the boiler for combustion to provide heat source.

[0028] Technical effect: The introduction of agricultural and forestry waste improves the particle molding properties and enhances the carbon content; the recycling of condensate makes the whole process have a higher resource utilization rate.

[0029] As attached Figure 2 The performance diagram shown shows the effect of carbonization temperature on the properties of biochar, mainly including: Fixed carbon content (%): As the carbonization temperature increases, the fixed carbon content increases (from 55% to 76%).

[0030] Volatile matter (%): As the temperature increases, the volatile content decreases (from 30% to 12%), indicating that the volatile components are reduced during the pyrolysis process and the carbonization is more complete.

[0031] Ash content (%): It remained relatively stable from 180°C to 260°C, and then increased slightly (10% to 12%), which may be related to the conversion of some inorganic components.

[0032] The performance diagram shows that the optimal carbonization temperature: 240-260℃ has a good fixed carbon content (more than 70%) and a low volatile matter (less than 20%), which is suitable for biofuel or activated carbon preparation.

[0033] When the temperature is too high (>280°C), the ash content increases, which may affect the purity of the carbon and reduce its adsorption capacity.

[0034] Biochar activation treatment: Take 10g of biochar after carbonization of furfural residue; wash with deionized water to remove surface ash and residual organic matter; dry at 80℃ for 12h to ensure the biochar is dry.

[0035] Phosphoric acid (H3PO4) activation: Immerse the biochar in a 10wt% H3PO4 solution and stir evenly; stir at a constant temperature of 60℃ for 2h to promote the phosphation reaction; let it stand for 12h to allow the phosphoric acid to fully penetrate into the pores of the biochar.

[0036] Potassium hydroxide (KOH) activation: The impregnated biochar was filtered and immersed in a 2M KOH solution; ultrasonic-assisted treatment was performed for 1 h to enhance the etching effect of the alkaline solution on the biochar; and the biochar was left standing at room temperature for 6 h to allow KOH to fully penetrate.

[0037] Heat treatment activation: the treated biochar is dried and transferred to a tube furnace; carbonized for 2 hours at 600°C in a nitrogen (N2) protected environment; the heating rate is controlled at 5°C / min to prevent excessive damage to the carbon structure; after activation, it is cooled to room temperature; Washing and drying: Wash with 0.1 mol / L HCl to remove unreacted KOH and H3PO4 residues; wash with deionized water to pH = 7; dry at 80°C for 24 h to obtain the final activated biochar.

[0038] Through this acid-base synergistic treatment, the specific surface area of ​​biochar is increased to 800-1200m² / g, which is suitable for applications such as heavy metal wastewater treatment, adsorption of pollutants, and catalytic carriers.

[0039] Comparison table of ordinary biochar and acid-base activated biochar

[0040] Technical effects brought by synergistic activation of H3PO4 and KOH: Through the synergistic effect of phosphoric acid (H3PO4) and potassium hydroxide (KOH), the advantages of both in different aspects can be fully utilized; phosphoric acid activation mainly optimizes the pore structure of biochar and increases the number of micropores and mesopores, while potassium hydroxide enhances the adsorption capacity of biochar, especially the adsorption effect of organic pollutants and heavy metal ions. The combination of the two can improve the pore structure and adsorption performance of biochar to varying degrees, thereby providing a more efficient adsorption effect.

[0041] Optimization of pore structure and phosphate modification: By rationally regulating the activation conditions, the biochar presents a porous structure combining micropores, mesopores and macropores, which effectively improves its adsorption rate and capacity. In addition, phosphate modification is used to introduce phosphate groups (such as P=O and P-OH) on the surface of biochar, which significantly enhances the hydrophilicity and chemical stability of biochar. This modification not only improves the adsorption capacity of water-soluble pollutants, but also improves its long-term stability in complex water environments.

[0042] Thermal treatment optimization and low-cost environmental protection characteristics: Under the heat treatment condition of 600℃, nitrogen protection is used to prevent the collapse of the carbon skeleton at high temperature, ensuring the structural stability of the biochar; this process also increases the specific surface area of ​​the biochar and enhances its adsorption effect; most importantly, this technology uses furfural residue as raw material, reduces the pollution of agricultural waste, and the process is simple to operate and low-cost, which meets the development requirements of green environmental protection and has broad practical application prospects.

[0043] Example 2: Optimizing the carbonization process to improve biochar activity Furfural residue pretreatment: Use superheated steam from a biomass boiler for hot air drying, with the drying temperature set at 110°C to ensure that the moisture content of the furfural residue is reduced to 20%. During the drying process, the light volatile components are drained to the condensation device through the exhaust gas collection system, and the condensate can be used for furfural distillation.

[0044] Particle enhancement molding: Furfural residue and corn stalks are mixed in a mass ratio of 1:1, and after mixing, they are extruded into particles using a granulator; the diameter of the particles is 5 mm, the length is 18 mm, and the moisture is controlled at 14%; this embodiment introduces part of the furfural coke to increase the calorific value of the particles.

[0045] Low temperature carbonization ： Low temperature carbonization in three stages: Preheating phase: temperature set at 105°C, oxygen content 15%, for 2 hours.

[0046] Deashing stage: The temperature was set at 180°C and the oxygen content was 7% for 1 hour.

[0047] 3. Carbonization stage: The temperature is set at 260°C and the oxygen content is less than 3% for 2.5 hours.

[0048] During the carbonization process, the hot steam is kept in an oxygen-free or anoxic environment to ensure the stability of the biochar.

[0049] By-product recovery: The condensate can be used as an organic fertilizer or water dispersant, containing 12-18% of organic matter, which is suitable for agricultural fertilization; the waste gas is guided to the boiler for combustion through the waste gas collection system to provide heat source for the carbonization process.

[0050] Advantages: This solution introduces furfural coke so that the biochar produced during the carbonization process contains a higher carbon content, thereby improving the combustion performance of the biochar.

[0051] Biochar activation treatment: Take 10g of biochar after carbonization of furfural residue; wash with deionized water to remove surface ash and residual organic matter; dry at 80℃ for 12h to ensure the biochar is dry.

[0052] Phosphoric acid (H3PO4) activation: Immerse the biochar in a 10wt% H3PO4 solution and stir evenly; stir at a constant temperature of 60℃ for 2h to promote the phosphation reaction; let it stand for 12h to allow the phosphoric acid to fully penetrate into the pores of the biochar.

[0053] Potassium hydroxide (KOH) activation: The impregnated biochar was filtered and immersed in a 2M KOH solution; ultrasonic-assisted treatment was performed for 1 h to enhance the etching effect of the alkaline solution on the biochar; and the biochar was left standing at room temperature for 6 h to allow KOH to fully penetrate.

[0054] Heat treatment activation: The treated biochar is dried and transferred to a tube furnace; carbonized for 2 hours at 600°C in a nitrogen (N2) protected environment; the heating rate is controlled at 5°C / min to prevent excessive damage to the carbon structure; after activation, it is cooled to room temperature; Washing and drying: Wash with 0.1 mol / L HCl to remove unreacted KOH and H3PO4 residues; wash with deionized water to pH = 7; dry at 80°C for 24 hours to obtain the final activated biochar.

[0055] Example 3: Enhanced environmental adaptability of carbonization effect Furfural residue pretreatment: The superheated steam temperature is set to 100°C, and the moisture content of the furfural residue is reduced to 20% through hot air drying; the evaporated light volatile components are discharged through the exhaust gas collection system and sent to the condensation equipment for treatment. The condensate can be used as liquid fertilizer or in the furfural distillation system.

[0056] Enhanced particle molding: corn straw, wheat straw and furfural residue are mixed in a mass ratio of 2:1 and formed by a granulator. The particle diameter is 5 mm, the length is 20 mm, and the moisture content is controlled below 15%. In this embodiment, considering the low calorific value of furfural residue, the proportion of straw is increased to enhance the calorific value of the particles.

[0057] Low temperature carbonization: The particles enter the carbonization furnace and are carbonized at low temperature in stages: 1. Preheating stage: temperature is 120℃, oxygen content is 18%, duration is 2 hours.

[0058] 2. Ash removal stage: temperature is 170°C, oxygen content is 8%, and duration is 1 hour.

[0059] 3. Carbonization stage: temperature is 250°C, oxygen content is 2%, and duration is 2 hours.

[0060] During the carbonization process, an oxygen-free environment is maintained in the carbonization furnace to ensure the pore structure and combustion performance of the biochar.

[0061] By-product recovery: The condensate contains organic components such as phenols and aldehydes, which can be used for agricultural fertilization after storage; the non-condensable gas in the exhaust gas is sent to the boiler to provide heat to support the carbonization process.

[0062] Advantages: The calorific value of the pellets is increased by mixing straw and furfural residue in appropriate proportions, while the stability and efficiency of biochar are effectively maintained through low-temperature carbonization; the recycling of condensate increases the economic benefits of the overall production.

[0063] These examples demonstrate different technical paths to improve the efficiency and effect of preparing biochar by low-temperature carbonization of furfural residue, especially innovations in raw material mixing, particle forming, carbonization process control, and by-product utilization. Each example adjusts the process parameters according to different application scenarios or raw material characteristics, thereby optimizing the quality and performance of biochar and maximizing the utilization of by-products.

[0064] In order to further improve the adsorption performance of biochar, magnetic iron oxide (Fe3O4) is combined with biochar for composite modification to give biochar magnetic properties, which can achieve rapid recovery after adsorption and avoid secondary pollution. The following is a composite modification method combined with Fe3O4, as well as its magnetic separation principle and advantages after adsorption.

[0065] Preparation of Fe3O4 nanoparticles First, an appropriate amount of iron salt (such as FeCl3·6H2O and FeSO4·7H2O) is dissolved in deionized water to form an iron ion solution. Then, ammonia water or sodium hydroxide solution is slowly added to allow the iron ions to combine with hydroxides in an alkaline environment to precipitate Fe3O4; by controlling the pH value and reaction temperature, the particle size and morphology of the Fe3O4 nanoparticles can be adjusted to ensure that they have good magnetism and dispersibility.

[0066] Surface modification and biochar composite The prepared Fe3O4 nanoparticles are mixed with biochar and heat treated at an appropriate temperature (such as 80-120°C) so that the Fe3O4 particles can be evenly attached to the surface of the biochar; to increase the loading amount of Fe3O4, surfactants or solvents can be used to enhance the adsorption capacity of Fe3O4 on biochar to ensure the stability of the composite effect.

[0067] Cooling and screening of magnetic biochar The composite biochar-Fe3O4 mixture is cooled to room temperature, and then the Fe3O4 nanoparticles are fixed on the surface of the biochar by magnetic separation; finally, the composite biochar is sieved to obtain particle size and morphology suitable for different application requirements.

[0068] Principle explanation: By introducing Fe3O4 nanoparticles into biochar, the biochar surface acquires magnetism, thus enabling it to have magnetic separation capabilities; Fe3O4 particles form a uniform composite structure on the biochar surface, which not only enhances the biochar's magnetism, but also improves its ability to adsorb pollutants; using an external magnetic field, the magnetic biochar that has adsorbed pollutants can be quickly recovered, avoiding the secondary pollution problem that may be caused by traditional adsorption materials, and improving the efficiency and sustainability of wastewater treatment.

[0069] A method for preparing biochar by low-temperature carbonization of furfural residues uses a low-temperature carbonization device, such as the attached Figure 3 As shown, the low-temperature carbonization device includes a feeder, a low-temperature carbonization furnace, a carbonization particle tank, and a condenser. The device is conventional technology, and the specific structure will not be described in detail.

[0070] The basic principles, main features and advantages of the present invention are shown and described above. Without departing from the spirit and scope of the present invention, the present invention may also be subject to various changes and improvements, which all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing biochar by low-temperature carbonization of furfural residue, characterized in that: The following steps are involved: 1) Furfural residue pretreatment: Using the superheated steam generated by the biomass boiler as the heat source, the furfural residue is dynamically dried through hot air drying equipment to reduce its moisture content from 50% to ≤25%; 2) Particle enhancement molding: corn straw, wheat straw and furfural residue are mixed in a mass ratio of 5:1-2:0.8-1.2, and extruded into particles with a diameter of 5mm and a length of 15-25mm through a granulator. The moisture content of the particles after molding is ≤15%; 3) Segmented low-temperature carbonization: The formed particles are sent into the low-temperature carbonization furnace. The particles first enter the drying and preheating stage, with a temperature of 105-120°C, an oxygen content of 12-20%, and a time of 2 hours; The particles are continuously heated up by gravity and enter the ash removal stage. The temperature in the ash removal area is 160-180°C, the oxygen content is 6-9%, and the time is 1-1.5 hours; After the ash removal is completed, the particles are continuously lowered by gravity and downward pressure to enter the carbonization stage. The temperature in the carbonization area is 240-260°C, the oxygen content is ≤3%, and the time is 2-2.5 hours. After carbonization, the biochar particles enter the temporary storage tank and naturally cool down in an oxygen-deficient environment, so that the hardness of the carbonized particles reaches 8mpa; 4) By-product recovery: During carbonization, the non-condensable gas from pyrolysis is sent to the boiler for combustion to provide heat for the boiler. The heat source required for carbonization is provided by the superheated steam generated by the biomass boiler, requiring a steam temperature of 420-440°C and a pressure of 4.2-4.35 MPa. At the same time, high-temperature steam enters the carbonization furnace to provide an oxygen-free or oxygen-deficient environment for the carbonization furnace; the main components of the pyrolysis gas condensate are aldehydes, phenols, acid decomposition products and trace chemical elements required by organisms, which can be collected and temporarily stored in a liquid tank.

2. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 1, characterized in that: In the particle enhancement molding step, furfural coke is introduced to facilitate the carbonization of furfural residue.

3. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 1, characterized in that: In the by-product recycling step, the condensate contains 12-18% organic matter, which can be used as a water dispersant and moisturizer or directly used as liquid organic fertilizer in agricultural watering and fertilization.

4. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 1, characterized in that: The activation of biochar particles involves the following steps: 1) Biochar pretreatment: Take the biochar after carbonization of furfural residue, wash it with deionized water to remove surface ash and residual organic matter, and dry it at 80℃ for 12h to ensure the biochar is dry; 2) Phosphoric acid (H3PO4) activation: The biochar was immersed in a phosphoric acid (H3PO4) solution, stirred evenly, and stirred at a constant temperature of 60°C for 2 hours to promote the phosphation reaction. The solution was allowed to stand for 12 hours to allow the phosphoric acid to fully penetrate into the pores of the biochar. 3) Potassium hydroxide (KOH) activation: The biochar impregnated in step 2 was filtered and immersed in phosphoric acid (H3PO4) solution, treated with ultrasound for 1 hour, and left to stand at room temperature for 6 hours to allow potassium hydroxide to fully penetrate; 4) Heat treatment activation: After drying the biochar treated in step 3, carbonize it at 600°C in a nitrogen (N2) protected environment for 2 hours, with the heating rate controlled at 5°C / min to prevent excessive damage to the carbon structure. After activation, cool it to room temperature; 5) Washing and drying: Wash with hydrochloric acid (HCl) to remove unreacted phosphoric acid and potassium hydroxide residues, wash with deionized water to pH = 7, and dry at 80°C for 24 hours to obtain the final activated biochar.

5. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 4 and its application, characterized in that: In step 2, the mass of phosphoric acid (H3PO4) accounts for 10% of the mass of the entire solution.

6. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 4, characterized in that: The concentration of hydrochloric acid is 0.1 mol / L.

7. The method for preparing biochar by low-temperature carbonization of furfural residue according to claim 1, characterized in that: The pyrolysis gas produced during the carbonization process includes combustible gases such as CO, H2, and CH4, which are recovered and used for boiler combustion.

8. The use of the biochar prepared by the method according to claim 4, characterized in that: Biochar is used to treat wastewater containing heavy metal ions, including Pb²⁺, Cd²⁺ and Cr 6 ⁺.

Images