Preparation method of light-weight high-strength high-adsorption biomass activated carbon

Abstract

The present application relates to a kind of preparation method of lightweight high-strength high adsorption biomass activated carbon, belong to activated carbon material technical field.The present application is by ammonium bicarbonate chemical foaming and sodium chloride salt template double macropore creation, soluble starch pyrolysis and zinc acetate reduction double mesopore creation, the fourfold pore creation strategy of compound activation of micropore creation of reduced pressure carbon dioxide, in combination with alkali lignin self-enhancing carbon skeleton and boron acid chemical crosslinking enhancement mechanism, the integration of lightweight, high-strength, high adsorption three integrations is realized.Specifically, alkali lignin, soluble starch, sodium chloride, zinc acetate, boric acid, urea are obtained by spray drying to obtain composite microspheres, then mixed with ammonium bicarbonate and foamed, treated by staged pre-carbonization, salt removal by washing, zinc acetate activation and reduced pressure CO2 activation, to obtain biomass activated carbon.The present application does not need additional binder, raw material source is extensive, process is environmental protection.

Description

Technical Field

[0001] This invention relates to the field of activated carbon materials technology, and more particularly to a method for preparing lightweight, high-strength, and highly adsorbent biomass activated carbon. Background Technology

[0002] Activated carbon is a porous material with a well-developed pore structure and a large specific surface area, widely used in water purification, air purification, solvent recovery, and catalyst support. With the continuous expansion of application scenarios, the market demands increasingly higher performance from activated carbon. Especially in weight-sensitive fields such as aerospace, automotive exhaust treatment, and portable purification equipment, activated carbon is required not only to possess excellent adsorption performance but also to have low bulk density and good mechanical strength to meet the demands of lightweight, high efficiency, and long service life. Therefore, developing activated carbon materials that simultaneously possess lightweight, high strength, and high adsorption performance has become an urgent technical problem to be solved in this field.

[0003] To obtain high-strength molded activated carbon, existing technologies typically add binders during the preparation process. For example, coal tar, pitch, and phenolic resins are used as binders to bond activated carbon powder or carbonized materials into shape, followed by carbonization and activation to obtain molded activated carbon with a certain mechanical strength. In recent years, to address the problems of high pollution and cost associated with external binders, self-bonding technologies utilizing the inherent properties of biomass raw materials have emerged. For example, plant fibers can be used as binders, or modified bamboo tar byproducts can be used as adhesives. Furthermore, to achieve high adsorption performance, existing technologies typically employ chemical or physical activation methods to create pores in carbon materials. Chemical activation methods commonly use KOH and H3PO4 as activating agents, generating numerous micropores by etching the carbon framework; physical activation methods use water vapor or CO2 as activating gases, reacting with carbon at high temperatures to create pores.

[0004] However, existing technologies still have significant drawbacks in achieving the aforementioned performance: First, while adding binders can improve strength, it can clog the pore structure of activated carbon, leading to a significant decrease in specific surface area and adsorption capacity. Over-activation, while improving adsorption performance, can severely erode the carbon skeleton, resulting in reduced mechanical strength. Second, existing technologies lack active means to control the bulk density of activated carbon, resulting in generally high product bulk density, making it difficult to meet the demands of lightweight applications. Finally, even with self-adhesive technology, specific forms of plant fibers or byproduct tar are still required as binding media, making it difficult to achieve completely "zero binder" preparation. Furthermore, some technologies still rely on fossil-based raw materials such as coal tar and pitch, posing environmental pollution and unsustainability issues. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a method for preparing lightweight, high-strength, and high-adsorption biomass activated carbon. Through a multi-level pore construction strategy involving chemical foaming and salt template for creating macropores, starch pyrolysis and zinc source reduction for creating mesopores, and reduced-pressure CO2 composite activation for creating micropores, combined with a lignin self-reinforcing framework and boric acid chemical cross-linking enhancement mechanism, the method achieves an integrated synergistic effect of lightweight, high strength, and high adsorption.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a method for preparing lightweight, high-strength, and highly adsorbent biomass activated carbon is provided, comprising the following steps: (1) Dissolve the alkali-free lignin in an alkaline aqueous solution, add soluble starch and heat to dissolve, cool and add sodium chloride, boric acid and urea and mix evenly, adjust the pH value and add zinc acetate and mix evenly, spray dry to obtain composite microspheres with uniformly distributed salt template, mix the composite microspheres with ammonium bicarbonate, place at 80-100℃ and heat to decompose and foam the ammonium bicarbonate to obtain a porous precursor; Spray drying involves atomizing a liquid mixture into tiny droplets, which are then rapidly evaporated by hot air. The solute precipitates to form solid microspheres, and NaCl crystallizes during the drying process, distributing evenly within the microspheres.

[0007] Ammonium bicarbonate foaming produces large pores (>50μm).

[0008] Porous precursors are intermediate products that have completed foaming (with macropores) but have not yet been carbonized.

[0009] (2) The porous precursor obtained in step (1) is pre-carbonized in stages under an inert atmosphere: first, the temperature is raised to 300-350℃ and held for 0.5-1h, then the temperature is raised to 420-450℃ and held for 0.5-1h to obtain the pre-carbonized product with a strengthened framework; then, sodium chloride is removed by washing with deionized water to obtain a precursor with both salt template macropores and starch pyrolysis mesopores. The 300-350℃ heat preservation process achieves the following: starch pyrolysis, decomposition into gas that escapes, leaving mesopores (10-50nm); urea decomposition releases NH3, which reacts with the carbon skeleton to introduce nitrogen doping; lignin begins to soften and crosslink.

[0010] Insulation at 420-450℃ achieves: deep condensation and cross-linking of lignin, with aromatic rings interconnected to form a three-dimensional network skeleton; dehydration of boric acid to generate B2O3, and esterification reaction of B2O3 with hydroxyl groups at the edge of the carbon skeleton to form BOC covalent bonds, so that boron atoms are covalently bonded to the carbon skeleton, filling microcracks and structural defects.

[0011] Pre-carbonized products after skeleton reinforcement: At this stage, lignin is not completely carbonized, but deep cross-linking has occurred, forming a preliminary carbon network structure; after being kept at 420-450℃, the condensation reaction between lignin molecules is fully carried out, and aromatic rings are interconnected to form a three-dimensional network skeleton with high mechanical strength.

[0012] After washing with deionized water to remove NaCl, the space occupied by the original NaCl crystals is left with macropores (1-10 μm). At the same time, starch pyrolysis at 300-350℃ has left mesopores (10-50 nm). Therefore, the precursor obtained after washing with water is called a "precursor with both salt template macropores and starch pyrolysis mesopores".

[0013] (3) The precursor obtained in step (2) with both salt template macropores and starch pyrolysis mesopores is heated to 650-750℃ in an inert atmosphere and kept at that temperature for 0.5-1.5h to activate zinc acetate to form pores. Then, under reduced pressure, the temperature is further increased to 850-950℃ and carbon dioxide is introduced for activation for 1-2h to obtain the activated product. The activated product is an intermediate product that has been fully carbonized, has formed a hierarchical porous structure, but contains zinc and boron residues.

[0014] Zinc acetate decomposes into zinc oxide during heating, and then is reduced by a carbon skeleton at 650-750℃ to generate metallic zinc vapor. The zinc vapor diffuses out of the carbon skeleton, leaving behind mainly mesopores (2-10 nm) and a small number of micropores, which serve as the "basic channels" for subsequent CO2 activation. CO2 can then enter the carbon skeleton along the channels created by zinc acetate, further etching the inner walls of the channels to form micropores (<2 nm).

[0015] Under reduced pressure, the concentration of CO2 molecules decreases, slowing down the etching reaction rate. This gentle etching process creates pores while protecting the carbon framework from excessive damage, thus achieving a balance between high adsorption and high strength.

[0016] During the high-temperature activation stage at 850-950℃, some of the BOC bonds formed in the pre-carbonization stage are converted into BC bonds. Boron is doped into the carbon skeleton and forms BC bonds with carbon atoms, making the carbon network more compact and further improving the mechanical strength of the carbon skeleton.

[0017] (4) The activated product obtained in step (3) is first washed with dilute acid and then washed with deionized water until neutral, and then dried to obtain the biomass activated carbon.

[0018] Pickling can remove residues such as ZnO and B2O3, while washing with water can further remove residual acid and soluble salts.

[0019] Further, the components in step (1) are in the following weights on a dry basis: 40-50 parts of dealkalized lignin, 20-30 parts of soluble starch, 8-12 parts of ammonium bicarbonate, 5-10 parts of zinc acetate, 5-8 parts of boric acid, 2-5 parts of urea, and 10-15 parts of sodium chloride.

[0020] Further, in step (1), the pH is adjusted to 5.5-6.0; the inlet temperature of the spray dryer is 180-220℃, the outlet temperature is 60-70℃, and the material residence time is 5-15 seconds.

[0021] Further, in step (2), the heating rate of the segmented pre-carbonization is 2-5℃ / min; the washing is to repeatedly wash with deionized water 2-4 times until no chloride ions are detected in the washing solution.

[0022] Further, in step (3), the inert atmosphere is nitrogen or argon, with a flow rate of 0.5-1.0 L / min.

[0023] Further, in step (3), the heating rate to 650-750℃ is 3-8℃ / min, and the heating rate to 850-950℃ is 2-5℃ / min.

[0024] Further, in step (3), the absolute pressure of the depressurizing atmosphere is 0.05-0.08 MPa.

[0025] Further, in step (3), the flow rate of the carbon dioxide is 0.5-1.0 L / min.

[0026] Further, in step (4), the dilute acid is 1M hydrochloric acid, and the washing is performed 2-3 times to remove zinc and boron residues; the drying is performed at 100-110℃ for 11-13 hours.

[0027] Secondly, a lightweight, high-strength, high-adsorption biomass activated carbon is provided, obtained by the preparation method of the lightweight, high-strength, high-adsorption biomass activated carbon described in the first aspect, with a bulk density of 0.24-0.35 g / cm³. 3 Wear resistance strength 95.5%-97.5%, specific surface area 1650-1860 m² 2 / g.

[0028] The beneficial effects of this invention are as follows: (1) This invention achieves a synergistic four-stage pore-forming process by using ammonium bicarbonate chemical foaming and sodium chloride salt template to create macropores, combined with soluble starch pyrolysis and zinc acetate reduction to create mesopores. Specifically, ammonium bicarbonate is heated and decomposed before the carbon skeleton is formed to produce gas, which expands and leaves macropores (>50 μm). Sodium chloride, as a salt template, is uniformly distributed in the composite microspheres during spray drying. After pre-carbonization is completed and the carbon skeleton is initially solidified, sodium chloride crystals are washed away with water, leaving micron-sized macropores (1-10 μm) in the space it originally occupied. Soluble starch is pyrolyzed and volatilized during the pre-carbonization stage at 300-350℃, leaving mesopores (10-50 nm). Zinc acetate is reduced by the carbon skeleton at 650-750℃ to generate zinc vapor, which diffuses out and forms mesopores (2-10 nm). The four pore-forming methods are staggered in time and are all completed without damaging the carbon skeleton, synergistically achieving a balance between lightweight and high strength.

[0029] (2) This invention uses lignin as the main carbon source, which is rich in aromatic ring structures. After carbonization, it naturally forms a continuous rigid carbon skeleton, completely independent of any external binder. A segmented pre-carbonization process is adopted, firstly, starch is pyrolyzed at 300-350℃ to create pores, and then the temperature is raised to 420-450℃ to deeply cross-link and solidify lignin, forming a three-dimensional network carbon skeleton. Boric acid, as a chemical reinforcing agent, dehydrates to generate B2O3 during the pre-carbonization stage at 420-450℃, forming BOC covalent bonds with the carbon skeleton and filling microcracks and structural defects. During the high-temperature activation stage at 850-950℃, it is converted into BC bonds, and boron doping enters the carbon skeleton, forming BC bonds with carbon atoms, enhancing the mechanical strength and structural stability of the carbon skeleton. At the same time, reduced pressure CO2 activation is used to reduce the etching rate, gently creating pores while protecting the carbon skeleton. The above mechanisms work together to achieve high strength of biomass activated carbon.

[0030] (3) In this invention, zinc acetate is reduced to zinc vapor at 650-750℃, creating initial micropores and mesopores, providing gas diffusion channels for CO2 activation; CO2 enters the carbon skeleton along the initial channels at 850-950℃, further etching the inner walls of the channels to generate more micropores (<2nm). Simultaneously, the macropores left by chemical foaming and salt templates serve as rapid diffusion channels, while the mesopores left by starch pyrolysis and zinc source reduction serve as mass transfer channels, together forming a three-level pore system to achieve rapid diffusion and efficient adsorption of pollutants. The decomposition of urea releases NH3, introducing nitrogen-containing functional groups and enhancing the chemical adsorption capacity for polar pollutants. These mechanisms synergistically achieve the high adsorption performance of biomass activated carbon.

[0031] (4) This invention uses dealkalized lignin, a byproduct of the papermaking industry, as the main raw material. No fossil-based binder is required. Sodium chloride template and dilute acid can be recycled and reused, which meets the requirements of low carbon, environmental protection and sustainable development. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0033] Example 1 Step (1): Preparation of porous precursor Weigh out 45 parts of dealkalized lignin, 25 parts of soluble starch, 10 parts of ammonium bicarbonate, 7.5 parts of zinc acetate, 6.5 parts of boric acid, 3.5 parts of urea, and 12.5 parts of sodium chloride on a dry basis.

[0034] 1.1 Lignin alkali solubility Add 45 parts of dealkalized lignin to 200 parts of deionized water, add 10% NaOH solution dropwise to adjust the pH to 11, stir for 45 minutes until completely dissolved, and obtain a brownish-brown transparent solution.

[0035] 1.2 Starch dissolution Add 25 parts of soluble starch to the above solution, heat to 75°C and stir for 30 minutes until completely dissolved to obtain a viscous and transparent solution.

[0036] 1.3 Adding other components Cool the above solution to 35°C, add 12.5 parts sodium chloride, 6.5 parts boric acid, and 3.5 parts urea, and stir for 30 minutes until completely dissolved to form a homogeneous mixture.

[0037] 1.4 Adjusting pH Add 10% dilute hydrochloric acid to adjust the pH to 5.8, and lignin will be uniformly precipitated as nano / micron-sized fine particles, forming a uniform suspension.

[0038] 1.5 Spray drying Add 7.5 parts of zinc acetate to the above suspension, stir for 10 minutes until completely dissolved, and then spray dry at an inlet temperature of 200℃, an outlet temperature of 65℃, and a material residence time of 10 seconds to obtain composite microspheres with uniformly distributed NaCl salt template.

[0039] 1.6 Ammonium bicarbonate loading and foaming The composite microspheres obtained by spray drying were mixed evenly with ammonium bicarbonate and heated in a 90℃ oven for 3 hours. The ammonium bicarbonate was completely decomposed and foamed to obtain a porous precursor containing foamed macropores (>50μm).

[0040] Step (2): Segmented pre-carbonization and water washing to remove salt 2.1 Segmented pre-carbonization The porous precursor obtained in step (1) was placed in a tube furnace and pre-carbonized in stages under a nitrogen atmosphere (flow rate 0.8 L / min): The temperature was increased to 325℃ at 3.5℃ / min and held for 45min to allow starch to pyrolyze and create pores (producing 10-50nm mesopores), while urea decomposed to release NH3 to achieve nitrogen doping. The temperature was increased to 435℃ at 3.5℃ / min and held for 45min to allow the lignin to undergo deep cross-linking and curing, forming a three-dimensional network skeleton, thus obtaining a pre-carbonized product with a skeleton-reinforced structure.

[0041] 2.2 Wash away salt with water The pre-carbonized product was washed three times with deionized water, stirring for 10 minutes each time, until no white precipitate (no chloride ions detected) was found when AgNO3 solution was added to the wash solution, thus removing the NaCl crystals. The space occupied by the NaCl crystals left micron-sized macropores (1-10 μm), resulting in a precursor with both salt template macropores and starch pyrolysis mesopores.

[0042] Step (3): Composite Activation 3.1 Activation of Zinc Acetate The precursor obtained in step (2) was placed in a tube furnace and heated to 700°C at a rate of 5°C / min under a nitrogen atmosphere (flow rate 0.8 L / min) and held for 1 h. Zinc acetate first decomposes into ZnO, and then ZnO is reduced by carbon to generate Zn vapor, which escapes, creating initial micropores and mesopores.

[0043] 3.2 Activation by Reduced Pressure CO2 The temperature was increased to 900℃ at a rate of 3.5℃ / min, while the vacuum pump was started to reduce the absolute pressure of the system to 0.06 MPa. CO2 was introduced (flow rate 0.8 L / min) for activation for 1.5 h. The CO2 reacted with the carbon skeleton in a vaporization reaction, and further etching was performed on the inner wall of the existing channels to create more micropores (<2 nm), thus obtaining the activated product.

[0044] Step (4): Post-processing The activated product obtained in step (3) was cooled to room temperature and washed three times with 1M hydrochloric acid (soaking for 30 minutes and stirring for 10 minutes each time) to remove zinc and boron residues; then washed with deionized water until pH=7; and finally dried at 105℃ for 12 hours to obtain lightweight, high-strength, and highly adsorbent biomass activated carbon.

[0045] Example 2 Step (1): Preparation of porous precursor Weigh out 40 parts of dealkalized lignin, 20 parts of soluble starch, 8 parts of ammonium bicarbonate, 5 parts of zinc acetate, 5 parts of boric acid, 2 parts of urea, and 10 parts of sodium chloride on a dry basis.

[0046] 1.1 Lignin alkali solubility Add 40 parts of dealkalized lignin to 200 parts of deionized water, add 10% NaOH solution dropwise to adjust the pH to 10, stir for 60 minutes until completely dissolved.

[0047] 1.2 Starch dissolution Add 20 parts of soluble starch to the above solution, heat to 70°C and stir for 45 minutes until completely dissolved.

[0048] 1.3 Adding other components Cool the above solution to 30°C, add 10 parts sodium chloride, 5 parts boric acid, and 2 parts urea, and stir for 45 minutes until completely mixed.

[0049] 1.4 Adjusting pH Add 10% dilute hydrochloric acid to adjust the pH to 5.6, and lignin will precipitate uniformly.

[0050] 1.5 Spray drying Add 5 parts of zinc acetate to the above suspension, stir until completely dissolved, and then spray dry at an inlet temperature of 180°C, an outlet temperature of 60°C, and a material residence time of 15 seconds.

[0051] 1.6 Ammonium bicarbonate loading and foaming The composite microspheres obtained by spray drying were mixed evenly with ammonium bicarbonate and heated in an 80°C oven for 4 hours to ensure complete decomposition of ammonium bicarbonate.

[0052] Step (2): Segmented pre-carbonization and water washing to remove salt 2.1 Segmented pre-carbonization Heat to 300℃ at a rate of 2℃ / min and hold for 1 hour; Increase the temperature to 420℃ at a rate of 2℃ / min and hold for 1 hour.

[0053] 2.2 Wash away salt with water Wash repeatedly with deionized water 4 times, stirring for 15 minutes each time, until no chloride ions are detected.

[0054] Step (3): Composite Activation 3.1 Activation of Zinc Acetate The temperature was increased to 650℃ at a rate of 3℃ / min and held for 1.3 hours.

[0055] 3.2 Activation by Reduced Pressure CO2 The temperature was increased to 850℃ at a rate of 2℃ / min, the absolute pressure was reduced to 0.05 MPa, the CO2 flow rate was 0.5 L / min, and the activation time was 2h.

[0056] Step (4): Post-processing Wash three times with 1M hydrochloric acid, then wash with deionized water until neutral, and dry at 100℃ for 13 hours.

[0057] Example 3 Step (1): Preparation of porous precursor Weigh out 50 parts of dealkalized lignin, 30 parts of soluble starch, 12 parts of ammonium bicarbonate, 10 parts of zinc acetate, 8 parts of boric acid, 5 parts of urea, and 15 parts of sodium chloride on a dry basis.

[0058] 1.1 Lignin alkali solubility Add 50 parts of dealkalized lignin to 250 parts of deionized water, add 10% NaOH solution dropwise to adjust the pH to 12, stir for 30 minutes until completely dissolved.

[0059] 1.2 Starch dissolution Add 30 parts of soluble starch to the above solution, heat to 80°C and stir for 20 minutes until completely dissolved.

[0060] 1.3 Adding other components Cool the above solution to 40°C, add 15 parts sodium chloride, 8 parts boric acid, and 5 parts urea, and stir for 20 minutes until completely mixed.

[0061] 1.4 Adjusting pH Add 10% dilute hydrochloric acid to adjust the pH to 5.9, and lignin will precipitate uniformly.

[0062] 1.5 Spray drying Add 10 parts of zinc acetate to the above suspension, stir until completely dissolved, and then spray dry at an inlet temperature of 220°C, an outlet temperature of 70°C, and a material residence time of 5 seconds.

[0063] 1.6 Ammonium bicarbonate loading and foaming The composite microspheres obtained by spray drying were mixed evenly with ammonium bicarbonate and heated in an oven at 100°C for 2 hours to ensure complete decomposition of ammonium bicarbonate.

[0064] Step (2): Segmented pre-carbonization and water washing to remove salt 2.1 Segmented pre-carbonization The temperature was increased to 350℃ at a rate of 5℃ / min and held for 0.5 hours. The temperature was increased to 450℃ at a rate of 5℃ / min and held for 0.5h.

[0065] 2.2 Wash away salt with water Wash twice with deionized water, stirring for 8 minutes each time, until no chloride ions are detected.

[0066] Step (3): Composite Activation 3.1 Activation of Zinc Acetate The temperature was increased to 750℃ at a rate of 8℃ / min and held for 0.7h.

[0067] 3.2 Activation by Reduced Pressure CO2 The temperature was increased to 950℃ at a rate of 5℃ / min, the absolute pressure was reduced to 0.08 MPa, the CO2 flow rate was 1.0 L / min, and the activation time was 1h.

[0068] Step (4): Post-processing Wash twice with 1M hydrochloric acid, then wash with deionized water until neutral, and dry at 110℃ for 11 hours.

[0069] Comparative Example 1 Based on Example 1, ammonium bicarbonate and sodium chloride are not added in step (1) (i.e., foaming agent and salt template are missing at the same time), and the other conditions are the same as in Example 1.

[0070] Comparative Example 2 Based on Example 1, boric acid is not added in step (1), and the other conditions are the same as in Example 1.

[0071] Comparative Example 3 Based on Example 1, in step (1), boric acid was replaced with 6.5% sodium carboxymethyl cellulose (CMC), and the other conditions were the same as in Example 1.

[0072] Comparative Example 4 Based on Example 1, zinc acetate is not added in step (1), and CO2 activation is performed directly in step (3) without heat preservation at 650-750℃. The other conditions are the same as in Example 1.

[0073] Comparative Example 5 Based on Example 1, in step (1), the dealkalized lignin is replaced with phenolic resin, and the other conditions are the same as in Example 1.

[0074] Comparative Example 6 Based on Example 1, in step (1), soluble starch is not added, and the other conditions are the same as in Example 1.

[0075] Comparative Example 7 Based on Example 1, in step (2), the segmented pre-carbonization is cancelled and replaced with direct heating to 300-350℃ and holding for 1.5h, with the other conditions being the same as in Example 1.

[0076] Comparative Example 8 Based on Example 1, in step (3), the carbon dioxide activation pressure is changed to atmospheric pressure (0.101 MPa), and the other conditions are the same as in Example 1.

[0077] Comparative Example 9 Based on Example 1, in step (3), only zinc acetate activation at 650-750℃ is performed, without subsequent CO2 activation, and the other conditions are the same as in Example 1.

[0078] Performance testing To further verify the effects achieved by the present invention, the samples obtained in the examples and comparative examples were tested. The tested performance indicators included bulk density, wear resistance, specific surface area and iodine adsorption value.

[0079] I. Testing Methods (1) Bulk density determination According to GB / T 7702.4-1997 standard, the sample is loaded into a graduated cylinder, and the sample is compacted under vibration conditions. The mass of the sample in the graduated cylinder is weighed, and the mass per unit volume is calculated.

[0080] (2) Abrasion resistance test Referring to GB / T 12496.6-1999 standard, the sample is placed in a strength tester, steel balls are added, and the sample is vibrated under specified conditions to determine the retained mass fraction of the sample after wear.

[0081] (3) Specific surface area determination Referring to GB / T 7702.20-2008 standard, the nitrogen adsorption method was used to determine the amount of nitrogen adsorbed by activated carbon at liquid nitrogen temperature, and the specific surface area was calculated using the BET equation.

[0082] (4) Determination of iodine adsorption value According to GB / T 12496.8-2015 standard, the sample was thoroughly mixed with iodine solution to allow iodine to be adsorbed by activated carbon. After filtration, the concentration of residual iodine in the filtrate was titrated with sodium thiosulfate standard solution, and the iodine adsorption value was calculated.

[0083] II. Test Results The performance of the samples obtained in Examples 1-3 and Comparative Examples 1-9 was tested according to the above test method, and the results are as follows.

[0084] Table 1. Performance test results of the examples and comparative examples.

[0085] The test results show that Examples 1-3 all exhibit excellent lightweight, high strength, and high adsorption performance, with a bulk density of 0.24-0.32 g / cm³. 3 Its wear resistance is 95.5%-97.5%, and its specific surface area is 1650-1860 m². 2 / g, iodine adsorption value 1160-1300 mg / g. Comparative Example 1 lacks both ammonium bicarbonate foaming and sodium chloride salt template, failing to form a macroporous structure, resulting in a higher bulk density. The absence of macroporous mass transfer channels also reduces specific surface area and iodine adsorption value, leading to lower lightweighting and high adsorption performance compared to the Example. Comparative Example 2, without boric acid, exhibits lower wear resistance and lower high-strength performance compared to the Example. Comparative Example 3, replacing boric acid with traditional CMC binder, significantly reduces specific surface area and iodine adsorption value, resulting in lower high adsorption performance compared to the Example. Comparative Example 4, without zinc acetate, has lower specific surface area and iodine adsorption value, resulting in lower high adsorption performance compared to the Example. Comparative Example 5, replacing lignin with phenolic resin, exhibits lower wear resistance and lower high-strength performance compared to the Example. Comparative Example 6, without soluble starch, slightly increases bulk density, but decreases specific surface area and iodine adsorption value, resulting in slightly lower lightweighting and high adsorption performance compared to the Example. Comparative Example 7, omitting the segmented pre-carbonization high-temperature section, exhibits lower wear resistance and lower high-strength performance compared to the Example. Comparative Example 8, by changing the CO2 activation pressure to atmospheric pressure, intensified the etching reaction and increased the specific surface area, but significantly reduced the wear resistance, and its high-strength performance was inferior to that of the Example. Comparative Example 9, without CO2 activation, had a lower specific surface area and iodine adsorption value, and its high adsorption performance was inferior to that of the Example.

[0086] The above results indicate that the present invention achieves lightweight, high strength, and high adsorption performance through a pore-forming strategy of creating macropores by ammonium bicarbonate foaming and sodium chloride salt template, creating mesopores by soluble starch pyrolysis and zinc acetate reduction, and creating micropores by reduced pressure CO2 composite activation, combined with the lignin self-reinforcing framework and the boric acid chemical cross-linking enhancement mechanism.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing lightweight, high-strength, high-adsorption biomass activated carbon, characterized in that, Includes the following steps: (1) Dissolve the alkali-free lignin in an alkaline aqueous solution, add soluble starch and heat to dissolve, cool and add sodium chloride, boric acid and urea and mix evenly, adjust the pH value and add zinc acetate and mix evenly, spray dry to obtain composite microspheres with uniformly distributed salt template, mix the composite microspheres with ammonium bicarbonate, place at 80-100℃ and heat to decompose and foam the ammonium bicarbonate to obtain a porous precursor; (2) The porous precursor obtained in step (1) is pre-carbonized in stages under an inert atmosphere: first, the temperature is raised to 300-350℃ and held for 0.5-1h, then the temperature is raised to 420-450℃ and held for 0.5-1h to obtain the pre-carbonized product with a strengthened framework; then, sodium chloride is removed by washing with deionized water to obtain a precursor with both salt template macropores and starch pyrolysis mesopores. (3) The precursor obtained in step (2) with both salt template macropores and starch pyrolysis mesopores is heated to 650-750℃ in an inert atmosphere and kept at that temperature for 0.5-1.5h to activate zinc acetate to form pores. Then, under reduced pressure, the temperature is further increased to 850-950℃ and carbon dioxide is introduced for activation for 1-2h to obtain the activated product. (4) The activated product obtained in step (3) is first washed with dilute acid and then washed with deionized water until neutral, and then dried to obtain the biomass activated carbon.

2. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, The components in step (1) are in the following weights on a dry basis: 40-50 parts of dealkalized lignin, 20-30 parts of soluble starch, 8-12 parts of ammonium bicarbonate, 5-10 parts of zinc acetate, 5-8 parts of boric acid, 2-5 parts of urea, and 10-15 parts of sodium chloride.

3. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (1), the pH is adjusted to 5.5-6.0; the inlet temperature of the spray dryer is 180-220℃, the outlet temperature is 60-70℃, and the material residence time is 5-15 seconds.

4. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (2), the heating rate of the segmented pre-carbonization is 2-5℃ / min; the washing is to repeatedly wash with deionized water 2-4 times until no chloride ions are detected in the washing solution.

5. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (3), the inert atmosphere is nitrogen or argon, and the flow rate is 0.5-1.0 L / min.

6. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (3), the heating rate to 650-750℃ is 3-8℃ / min, and the heating rate to 850-950℃ is 2-5℃ / min.

7. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (3), the absolute pressure of the depressurization atmosphere is 0.05-0.08 MPa.

8. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (3), the carbon dioxide flow rate is 0.5-1.0 L / min.

9. The method for preparing lightweight, high-strength, high-adsorption biomass activated carbon according to claim 1, characterized in that, In step (4), the dilute acid is 1M hydrochloric acid, and the washing is performed 2-3 times to remove zinc and boron residues; the drying is performed at 100-110℃ for 11-13 hours.

10. A lightweight, high-strength, high-adsorption biomass activated carbon, characterized in that, The lightweight, high-strength, high-adsorption biomass activated carbon obtained by the preparation method according to any one of claims 1-9 has a bulk density of 0.24-0.32 g / cm³. 3 Wear resistance strength 95.5%-97.5%, specific surface area 1650-1860 m² 2 / g.

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