A method for the preparation of biomass char-based base-charge band sorbents for air direct co2 capture

Abstract

This invention discloses a method for preparing a biomass char-based base-based charged adsorbent for direct CO2 capture in air, comprising the following steps: (1) screening biomass raw materials with a lignin content ≥20wt.%, washing, drying, and sieving to obtain biomass powder; (2) heat-treating the biomass powder from step (1) at 300~400℃ for 180~300 minutes under an inert atmosphere, and then heat-treating it at 700~1000℃ for 90~180 minutes to obtain biomass char; (3) adding the biomass char from step (2) to an alkaline solution, dispersing it fully to obtain a biomass char suspension; connecting the positive and negative electrodes of the flow battery to a potentiostat, injecting an alkaline electrolyte containing an oxidant into the electrolytic cell, and injecting the biomass char suspension into the solution cell; starting the circulation pump to exchange the liquids in the two cells, and applying a constant current using a chronopotential method, so that the oxidant is oxidized on the electrode surface and enters the solution cell to oxidize the biomass char, making its surface positively charged and adsorbing OH. ‑ (4) After the electrochemical reaction, the solid product is separated from the suspension; after washing and drying, the base charged biochar adsorbent is obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing a biomass carbon-based base charged adsorbent for direct CO2 capture from air. Background Technology

[0002] In recent years, an electrochemical-based carbon capture adsorbent preparation technology has attracted widespread attention. This technology utilizes a flow battery system, applying an electric current to induce a redox reaction in an electron transfer medium (such as TEMPO), thereby inducing a positive charge on the surface of porous carbon materials in the electrode or suspension. This allows for the efficient adsorption of hydroxide ions (OH-) from the solution via electrostatic interactions. - It can directly adsorb CO2. This method can regenerate the adsorbent under mild conditions (<100℃), significantly reducing energy consumption, and has strong tolerance to humidity.

[0003] However, existing basic charged adsorbents still have obvious limitations in the selection of carbon material substrates, mainly in the following aspects: (1) High raw material cost. Existing technologies mostly use commercial conductive carbon black (such as acetylene black, Super P) or high specific surface area activated carbon as adsorbent substrates. Most of these commercial carbon materials are derived from fossil fuels such as petroleum coke, asphalt or coal. Their production process itself is accompanied by high energy consumption and high carbon emissions, which is contrary to the original intention of DAC (Direct AirCapture) technology. In addition, commercial electronic grade carbon powder with high conductivity and high purity is expensive, which greatly limits the economic feasibility of this technology in large-scale industrial applications. (2) Simple pore structure and limited mass transfer: Commercial conductive carbon black is usually composed of nanoparticles, mainly consisting of stacked pores; while ordinary activated carbon, although having well-developed micropores, often lacks interconnected macropores and mesopore channels. In the flow battery system, the adsorbent suspension needs to react with the redox medium (such as TEMPO) in the electrolyte. + Rapid ion exchange and electron transfer are necessary, while also allowing CO2 molecules in the air to diffuse quickly to the adsorption sites within the adsorbent. Different reaction pathways require pore structures of different sizes to effectively improve the utilization rate of the active sites and increase the adsorbent's adsorption capacity for CO2 in the air. However, the single or disordered pore structure of existing commercial carbon materials results in high ion transport resistance and low utilization of active sites, thus limiting their adsorption capacity for CO2 in the air. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing basic charged adsorbents based on biochar. This method can obtain biochar materials with hierarchical pore structure and large specific surface area through a specific method. The basic charged adsorbent prepared based on the biochar material has a large adsorption capacity for CO2 in the air.

[0005] Technical solution: The method for preparing basic charged adsorbents based on biochar according to the present invention includes the following steps:

[0006] (1) Select biomass raw materials with lignin content ≥20wt.% (such as hardwood chips, corn stalks, coconut shells or walnut shells) as precursors; wash the selected biomass raw materials with deionized water to remove surface mud and ash, dry them in an oven at 90~105℃ to constant weight, then crush the dried raw materials with a pulverizer and sieve them to obtain biomass powder with a particle size of 100~200 mesh (74~150μm);

[0007] (2) Place the biomass powder from step (1) into the corundum crucible of a tube furnace, seal the furnace tube and introduce high-purity inert gas (nitrogen or argon). The gas flow rate is controlled at 100-300 mL / min to exhaust the air in the furnace. Then, raise the temperature from room temperature to 300-400℃ (preferably 400℃) at a heating rate of 2-5℃ / min and hold for 180-300 minutes. This stage aims to slowly remove hemicellulose and some cellulose volatiles to avoid the rapid escape of volatiles that could cause the carbon skeleton to collapse and initially form a pore structure. Then, raise the temperature from the pre-carbonization temperature to 700-1000℃ (preferably 800℃) at a heating rate of 5-10℃ / min and hold for 90-180 minutes. This stage aims to utilize the rigid skeleton formed by high lignin content for aromatic ring reforming and graphitization transformation, significantly improving the conductivity of the material and fixing the microporous structure. After naturally cooling to room temperature, biochar with a hierarchical pore structure is obtained. A process of 400℃ pre-carbonization followed by 800℃ deep carbonization is used. At 400℃, gentle devolatilization and pore formation occur, while at 800℃, the lignin-rich framework is rearranged and graphitized, thus producing a material with both high specific surface area (≥800m²). 2 / g) and biochar with excellent electrical conductivity;

[0008] (3) Prepare an alkaline solution with a concentration of 1~2 mol / L (preferably KOH or NaOH solution), add the biochar obtained in step (2) to the alkaline solution at a solid-liquid ratio (g / mL) of 1:10~20, and disperse it for 10~30 minutes using an ultrasonic cleaner or a high-speed shear machine to make the biochar uniformly suspended in the liquid phase and form a stable biochar suspension.

[0009] (4) Construct a flow battery system, which includes an electrolytic cell (anode chamber), a solution tank (external storage tank), and a circulation pipeline connecting the two; inject an alkaline electrolyte containing an oxidant into the electrolytic cell; wherein, the bottom solution concentration of the alkaline electrolyte is consistent with that of the suspension (1~2 mol / L alkaline solution), and the oxidant is preferably 2,2,6,6-tetramethylpiperidine oxide (TEMPO), and the concentration of the oxidant in the alkaline electrolyte is 0.1~0.2 mol / L; add the biochar suspension to the solution tank;

[0010] (5) Start the circulation pump and control the flow rate to 3~10cm / s to allow the alkaline electrolyte in the electrolytic cell to exchange substances with the biochar suspension in the solution cell. Connect the positive electrode of the flow battery to the working electrode and the negative electrode to the counter electrode. Use chronopotentiometry to apply a constant current of 40~60mA (preferably 50mA) to charge the system. During this process, TEMPO is oxidized to TEMPO at the positive electrode. + Driven by a circulating pump, the ions enter the solution tank and undergo an electron transfer reaction with the biochar, causing the surface of the biochar to become positively charged. Then, the ions adsorb OH⁻ from the solution through electrostatic attraction. The reaction ends when the voltage of the flow cell rises sharply or the solution color changes from light yellow to dark orange and remains stable.

[0011] (6) After the reaction is complete, shut off the circulation system, filter or centrifuge the suspension, and collect the solid product; quickly rinse the surface of the solid with a small amount of deionized water to remove residual free TEMPO and excess alkali, then place it in a vacuum drying oven and dry it at 60~80℃ for 6~10 hours to obtain the base charged biochar adsorbent (Biochar + ·OH - ).

[0012] In this invention, biomass raw materials refer to biomass waste, such as hardwood chips, corn stalks, coconut shells, or walnut shells. Hardwood chips refer to processing scraps, waste log chips, or hardwood board offcuts from hardwoods such as oak, birch, elm, beech, and maple. These hardwood chips have a lignin content of 25-35 wt.%, possess a dense, rigid wood structure, and after staged temperature-controlled carbonization, effectively retain their multi-level porous structure and exhibit good electrical conductivity. Softwood chips such as poplar and pine, due to their lignin content being below 20 wt.%, cannot be used as biomass raw materials in this invention. Lignin content is quickly screened using conventional testing methods (such as the Van denier method and the Klason method) and can be directly selected. Mature and dried corn stalks must be selected to ensure that the lignin content meets the requirements.

[0013] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: The base-charged biochar adsorbent of the present invention has a unique hierarchical pore structure, which can significantly improve mass transfer kinetics. Compared with existing commercial carbon black, which is mainly composed of nanoparticle agglomeration and whose pores are mostly disordered pores formed by stacking, resulting in high gas diffusion resistance, the biochar adsorbent of the present invention simultaneously has a connected hierarchical pore structure of macropores (transport channels) - mesopores (diffusion channels) - micropores (adsorption sites). This structure not only facilitates the adsorption of large-sized oxidant ions (TEMPO) + During the electrochemical modification process, the adsorbent penetrates deep into the material interior and greatly accelerates the diffusion of low-concentration CO2 to the adsorption active sites in DAC applications, thereby effectively improving the utilization rate of the active sites and thus increasing the adsorption capacity of the adsorbent for CO2 in the air. The saturated adsorption capacity of the adsorbent of this invention can reach 1.8 mmol / g at a low concentration of CO2 of 440 ppm, which is superior to commercial carbon black adsorbents under the same conditions (about 1.3 mmol / g). At the same time, the adsorbent still maintains more than 95% of its performance in a high humidity environment (RH 70%). Attached Figure Description

[0014] Figure 1 Comparative diagram of pore size distribution of biochar prepared in Example 1 and Comparative Example 1;

[0015] Figure 2 The graph shows the direct air carbon capture performance of the adsorbent prepared in Example 1 at a CO2 concentration of 440 ppm.

[0016] Figure 3 The graph shows the direct air carbon capture performance of the adsorbent prepared in Example 2 at a CO2 concentration of 440 ppm.

[0017] Figure 4 A bar chart comparing the saturated CO2 adsorption capacity of the adsorbents prepared in Examples 1 and 2 with those in Comparative Examples 1, 2, 3, 4, and 5.

[0018] Figure 5 The graph shows the stability test curve of the adsorbent prepared in Example 1 under the temperature-switching adsorption mode of 25℃ adsorption-80℃ regeneration after 100 cycles.

[0019] Figure 6 The graph shows the CO2 adsorption capacity performance of the adsorbent prepared in Example 1 under different relative humidity (10%, 50%, 80%) conditions. Detailed Implementation

[0020] Example 1

[0021] This invention relates to a method for preparing basic charged adsorbents based on biochar, comprising the following steps:

[0022] (1) Raw material pretreatment: Collect waste hardwood (select birch processing scraps from wood processing plants in Suzhou City and surrounding areas of Jiangsu Province as raw materials, air-dry naturally, free of impurities), wash with tap water and deionized water alternately 3 times to wash away dirt and impurities; place in an oven at 105℃ to dry for 24 hours, crush using a high-speed pulverizer, pass through a 100-mesh sieve, and collect the powder passing through the sieve; according to the composition analysis, the lignin content in this hardwood chip raw material is about 27%;

[0023] (2) Weigh 20g of the hardwood powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, raise the temperature from room temperature to 400℃ at a rate of 5℃ / min and hold for 240 minutes. Then, raise the temperature to 800℃ at a rate of 10℃ / min and hold for 120 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 923m². 2 / g, and has a significant mesoporous distribution; through Figure 1 It can be seen that biochar materials based on hardwood chips have a richer pore structure than commercial carbon materials, with a multi-level pore structure of macropores, mesopores, and micropores, and a larger specific surface area.

[0024] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0025] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80 °C for 8 hours to finally obtain the hardwood chip-based base charged adsorbent.

[0026] Example 2

[0027] This invention relates to a method for preparing basic charged adsorbents based on biochar, comprising the following steps:

[0028] (1) Raw material pretreatment: Collect waste corn stalks (mature and dried corn stalks from farmland in Suzhou City and surrounding areas of Jiangsu Province are selected as raw materials, naturally air-dried, and free from mold), wash them three times with tap water and deionized water alternately to remove mud and impurities; dry them in an oven at 105℃ for 24 hours, crush them with a high-speed pulverizer, pass them through a 100-mesh sieve, and collect the powder that passes through the sieve; according to the composition analysis, the lignin content in the corn stalk raw material is about 22%;

[0029] (2) Weigh 20g of the corn stalk powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, raise the temperature from room temperature to 400℃ at a rate of 5℃ / min and hold for 240 minutes. Then, raise the temperature to 800℃ at a rate of 10℃ / min and hold for 120 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 814m². 2 / g, and has a significant mesoporous distribution;

[0030] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject a 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0031] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it at 80 °C for 8 hours to finally obtain corn straw-based base charged adsorbent.

[0032] Comparative Example 1: Preparation of a base-charged adsorbent based on commercially conductive carbon black, specifically:

[0033] (1) Purchase commercially available conductive carbon black (Super P) directly without undergoing tube furnace carbonization treatment;

[0034] (2) Prepare 1L of 1mol / L KOH solution; add 50g of conductive carbon black (Super P) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution tank of the flow battery; inject a 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0035] (3) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80 °C for 8 hours to finally obtain a conductive carbon black base charged adsorbent.

[0036] Comparative Example 2

[0037] A method for preparing basic charged adsorbents based on biochar includes the following steps:

[0038] (1) Raw material pretreatment: Collect waste hardwood (source and type are the same as in Example 1), wash it three times with tap water and deionized water alternately to remove dirt and impurities; dry it in an oven at 105℃ for 24 hours, crush it with a high-speed pulverizer, pass it through a 100-mesh sieve, and collect the powder that passes through the sieve; according to the composition analysis, the lignin content in this hardwood chip raw material is about 27%;

[0039] (2) Weigh 20g of the hardwood powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, continue heating to 800℃ at a rate of 10℃ / min and hold for 120 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 390m². 2 / g;

[0040] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0041] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80 °C for 8 hours to finally obtain the hardwood chip-based base charged adsorbent.

[0042] Comparative Example 3

[0043] A method for preparing basic charged adsorbents based on biochar includes the following steps:

[0044] (1) Raw material pretreatment: coffee grounds (coffee grounds are waste filter grounds after brewing coffee, coffee beans are commercial coffee beans produced in Baoshan, Yunnan, which are naturally dried after collection and are free of impurities) are collected, washed 3 times with tap water and deionized water alternately to remove dirt and impurities; placed in an oven at 105℃ to dry for 24 hours, pulverized using a high-speed pulverizer, passed through a 100-mesh sieve, and the powder passing through the sieve is collected; according to the composition analysis, the lignin content in this coffee ground raw material is about 14%;

[0045] (2) Weigh 20g of the coffee grounds powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, raise the temperature from room temperature to 400℃ at a rate of 5℃ / min and hold for 240 minutes. Then, raise the temperature to 800℃ at a rate of 10℃ / min and hold for 120 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 462m². 2 / g;

[0046] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0047] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80°C for 8 hours to finally obtain coffee grounds-based charged adsorbent.

[0048] Comparative Example 4

[0049] A method for preparing basic charged adsorbents based on biochar includes the following steps:

[0050] (1) Raw material pretreatment: Collect waste hardwood (source and type are the same as in Example 1), wash it three times with tap water and deionized water alternately to remove dirt and impurities; dry it in an oven at 105℃ for 24 hours, crush it with a high-speed pulverizer, pass it through a 100-mesh sieve, and collect the powder that passes through the sieve; according to the composition analysis, the lignin content in this hardwood chip raw material is about 27%;

[0051] (2) Weigh 20g of the hardwood powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, raise the temperature from room temperature to 400℃ at a rate of 5℃ / min and hold for 240 minutes. Then, raise the temperature to 550℃ at a rate of 10℃ / min and hold for 150 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 635m². 2 / g;

[0052] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0053] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80 °C for 8 hours to finally obtain the hardwood chip-based base charged adsorbent.

[0054] Comparative Example 5

[0055] A method for preparing basic charged adsorbents based on biochar includes the following steps:

[0056] (1) Raw material pretreatment: Collect waste hardwood (source and type are the same as in Example 1), wash it three times with tap water and deionized water alternately to remove dirt and impurities; dry it in an oven at 105℃ for 24 hours, crush it with a high-speed pulverizer, pass it through a 100-mesh sieve, and collect the powder that passes through the sieve; according to the composition analysis, the lignin content in this hardwood chip raw material is about 27%;

[0057] (2) Weigh 20g of the hardwood powder from step (1) and place it in the corundum boat of the tube furnace. Purge with high-purity nitrogen (flow rate 200mL / min) for 30 minutes to remove all air from the furnace. Then, raise the temperature from room temperature to 200℃ at a rate of 5℃ / min and hold for 240 minutes. Then, raise the temperature to 800℃ at a rate of 10℃ / min and hold for 120 minutes. Allow the furnace to cool naturally to room temperature and remove the black biochar. According to BET testing, the specific surface area of ​​the biochar is 403m². 2 / g;

[0058] (3) Prepare 1L of 1mol / L KOH solution; add 50g of the biochar prepared in step (2) to it, stir magnetically for 30 minutes to form a suspension, and inject it into the external solution pool of the flow battery; inject 1mol / L KOH solution containing 0.1mol / L TEMPO into the electrolytic cell (anode chamber) of the flow battery as the electrolyte; the flow battery uses a glass carbon plate as the working electrode (positive electrode, area 5cm²). 2 A platinum sheet serves as the counter electrode (negative electrode, area 5 cm²). 2 The two chambers are separated by an ion exchange membrane; the circulation pump is started and the flow rate is set to 5 cm / s; the electrochemical workstation is connected, the timing potential mode is set, and a constant current of 50 mA is applied; the reaction proceeds for about 60 minutes, and the color of the electrolyte changes from light yellow to dark orange, and a clear inflection point appears on the voltage curve, at which point the reaction is stopped;

[0059] (4) Filter the suspension, rinse the filter cake once with 50 mL of deionized water, and quickly transfer it to a vacuum drying oven. Dry it in a vacuum oven at 80 °C for 8 hours to finally obtain the hardwood chip-based base charged adsorbent.

[0060] Application Example 1

[0061] 0.3 g of the basic charged adsorbent prepared in Example 1 was degassed under vacuum at 100°C for 12 hours to remove residual moisture and impurities. Then, direct air carbon capture was performed in a closed container at room temperature. The experimental results are as follows: Figure 2 As shown, in the DAC performance test, the base-charged adsorbent only needed a very short time (10 min) to adsorb the carbon dioxide concentration in the container to a low level (<50 ppm). The initial carbon dioxide concentration was the atmospheric CO2 concentration (approximately 440 ppm).

[0062] Application Example 2

[0063] 0.3 g of the basic charged adsorbent prepared in Example 2 was degassed under vacuum at 100°C for 12 hours to remove residual moisture and impurities. Then, direct air carbon capture was performed in a closed container at room temperature. The experimental results are as follows: Figure 3 As shown, in the DAC performance test, the base-charged adsorbent only needed a very short time (10 min) to adsorb the carbon dioxide concentration in the container to a low level (<50 ppm). The initial carbon dioxide concentration was the atmospheric CO2 concentration (approximately 440 ppm).

[0064] Application Example 3: In the experiment corresponding to Application Example 3, the simulated humidity is 55% (the ambient air humidity during the experiment).

[0065] 0.3 g of each of the base-charged adsorbents prepared in Examples 1, 2, 1, 2, 3, 4, and 5 were placed in a fixed-bed reactor. Pretreatment degassing was performed by purging with pure nitrogen at 100°C for 2 hours. Subsequently, the temperature was lowered to 25°C, and the gas flow was switched to simulated air containing 440 ppm CO2 (equilibrium gas was N2) at a flow rate of 50 mL / min. Dynamic breakthrough adsorption tests were conducted, and the saturated adsorption capacity was calculated. The results are as follows: Figure 4 As shown, their saturated adsorption capacities at 440 ppm were 1.82 mmol / g, 1.68 mmol / g, 1.37 mmol / g, 0.61 mmol / g, 0.86 mmol / g, 0.93 mmol / g, and 0.68 mmol / g, respectively.

[0066] Application Example 4

[0067] The sample from Example 1, after adsorption saturation, was placed in an 80°C environment and purged with N2. The results showed that heating to 80°C was sufficient to desorb over 95% of the adsorbed CO2 within 20 minutes, demonstrating that its regeneration temperature is significantly lower than that of traditional chemisorbents (typically requiring >120°C), exhibiting a low-energy consumption advantage. In a temperature-switching adsorption (TSA) mode of "25°C adsorption - 80°C regeneration," the sample from Example 1 was subjected to 100 consecutive adsorption-desorption cycles. Figure 5 As shown, after 100 cycles, the CO2 adsorption capacity of the adsorbent remained above 96.5% of its initial value. This indicates that the biochar framework structure is stable and the electrochemically injected active sites were not lost during the cycles.

[0068] Application Example 5

[0069] The adsorption performance of the sample from Example 1 was tested in humidified airflows (440 ppm CO2) at relative humidity (RH) of 10%, 50%, and 80%, respectively. The test results are as follows: Figure 6 As shown: RH=10% (dry): adsorption capacity 1.72 mmol / g; RH=50% (medium humidity): adsorption capacity 1.85 mmol / g; RH=80% (high humidity): adsorption capacity 1.53 mmol / g. With increasing humidity, the adsorption capacity of the adsorbent did not show the drastic decrease seen in amine adsorbents, remaining stable. This indicates that the charged adsorbent of the present invention is less affected by competitive adsorption of water molecules, making it very suitable for direct use in humid natural air environments.

Claims

1. A method for preparing a biomass-carbon-based basic charged adsorbent for direct CO2 capture from air, characterized in that, Includes the following steps: (1) Screen biomass raw materials with lignin content ≥20wt.%, wash, dry and sieve to obtain biomass powder; (2) The biomass powder from step (1) is first heat-treated at 300~400℃ for 180~300 minutes under an inert atmosphere, and then heat-treated at 700~1000℃ for 90~180 minutes to obtain biochar. (3) Add the biochar from step (2) to an alkaline solution and disperse it fully to obtain a biochar suspension; connect the positive and negative electrodes of the flow battery to a potentiostat respectively, inject an alkaline electrolyte containing an oxidant into the electrolytic cell, and inject the biochar suspension into the solution pool. The circulation pump is started to exchange liquids between the two pools, and a constant current is applied using a chronopotential method. The oxidant is then oxidized on the electrode surface and enters the solution pool to oxidize the biochar, causing its surface to become positively charged and adsorb OH-. - ; (4) After the electrochemical reaction, the solid product is separated from the suspension; after washing and drying, the base charged biochar adsorbent is obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the biomass raw material is one of hardwood chips, corn stalks, coconut shells or walnut shells.

3. The preparation method according to claim 1, characterized in that: In step (1), the drying temperature is 90~105℃ and the drying time is 20~24h.

4. The preparation method according to claim 1, characterized in that: In step (2), the temperature is increased from room temperature to 300-400℃ at a heating rate of 2-5℃ / min; then the temperature is increased from 300-400℃ to 700-1000℃ at a heating rate of 5-10℃ / min.

5. The preparation method according to claim 1, characterized in that: In step (3), biochar is added to an alkaline solution at a solid-liquid ratio of 1g:10~20mL to obtain a biochar suspension.

6. The preparation method according to claim 5, characterized in that: The alkaline solution is a NaOH or KOH solution with a concentration of 1~2 mol / L.

7. The preparation method according to claim 1, characterized in that: In step (3), the oxidant is 2,2,6,6-tetramethylpiperidine oxide or cobalt decene; the concentration of the oxidant in the alkaline electrolyte is 0.1~0.2 mol / L.

8. The preparation method according to claim 1, characterized in that: In step (3), the positive electrode of the flow battery is a glassy carbon electrode or a titanium-based carbon coated electrode, and the negative electrode is a platinum electrode or a graphite electrode.

9. The preparation method according to claim 1, characterized in that: In step (3), start the circulation pump with a flow rate of 4~5cm / s; apply a constant current of 40~60mA.

10. The preparation method according to claim 1, characterized in that: In step (4), the drying temperature is 60~100℃ and the drying time is 6~12h.

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