Preparation method of coconut shell-hydrotalcite-amino compound carbon dioxide adsorbent
By co-precipitating hydrotalcite on coconut shell biochar and modifying it with PEI, a composite carbon dioxide adsorbent with a hierarchical pore structure and amine active sites was prepared. This solved the problem of unstable performance of adsorbents at low concentrations in the prior art and achieved efficient and stable CO2 adsorption and recycling performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-02
- Publication Date
- 2026-03-13
AI Technical Summary
Existing CO2 adsorption materials have unstable adsorption capacity at low concentrations. Traditional coconut shell-based amino-modified adsorbents have low amine loading and are easily lost, and their performance degrades in humid environments. Metal-organic framework materials are structurally unstable in flue gas containing SOx/NOx.
A co-precipitation method was used to uniformly load hydrotalcite on the surface and in the pores of coconut shell biochar, and then modified with polyethyleneimine to form a coconut shell-hydrotalcite-amino composite material. Combined with the chemical adsorption properties of PEI, an organic-inorganic synergistic adsorption network was formed.
An adsorbent with abundant hierarchical pore structure and amine active sites was prepared, exhibiting excellent CO2 selective adsorption performance and cycle regeneration stability. The adsorption capacity is less affected by carbon dioxide concentration, and the components complement each other, showing significant industrialization potential.
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Figure CN121648894A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of carbon capture functional materials technology, and particularly relates to a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent. Background Technology
[0002] Since the beginning of the 21st century, the global economy has experienced rapid growth, but this rapid development has also brought global environmental problems. Against the backdrop of global warming, we believe that one of the main causes of global warming is the use and combustion of fossil fuels. Various countries and institutions have introduced strategies and policies to address the massive emissions of greenhouse gases.
[0003] Biomass-based adsorbents (such as activated carbon) have attracted attention due to their renewable raw materials and low cost; however, traditional activated carbon exhibits low selectivity for CO2 adsorption. Amine modification can introduce alkaline sites, enhancing its chemisorption capacity for CO2. Coconut shells, with their high cellulose and lignin content, are ideal raw materials for preparing high-porosity activated carbon; however, the preparation process for coconut shell-based amino-modified adsorbents is currently immature, exhibiting problems such as uneven modification, low amine loading, or pore structure collapse.
[0004] Currently, CO2 adsorption materials mainly face three major technical bottlenecks: First, although commercially available zeolite molecular sieves (such as 13X) have a regular microporous structure, their competitive adsorption of water molecules leads to a sharp drop in CO2 adsorption capacity of more than 50% in humid environments; second, although metal-organic framework materials (MOFs, such as Mg-MOF-74) exhibit extremely high theoretical adsorption capacity (>6 mmol / g), their structural stability is poor in industrial flue gas containing SOx / NOx; third, traditional amine-modified silica (such as TEPA-SBA-15) has an inherent contradiction between amine loading (usually <50 wt%) and diffusion mass transfer efficiency, and is prone to amine volatilization and degradation at flue gas temperatures exceeding 60°C.
[0005] Biomass-derived adsorbents offer a new approach to solving the aforementioned problems. Coconut shells, a major agricultural waste in tropical regions, possess unique anatomical structures that give them inherent advantages in the preparation of activated carbon: 1) native vascular bundles form naturally interconnected channels; 2) high lignin content (approximately 30%) ensures the strength of the carbon skeleton; 3) abundant oxygen-containing functional groups facilitate subsequent chemical modification. However, existing technologies have significant shortcomings: although ethylenediamine modification is introduced, the impregnation method results in the amine groups being mainly distributed on the particle surface, which are easily lost during cyclic adsorption. Furthermore, the adsorption capacity of the adsorbent for carbon dioxide is greatly affected by the carbon dioxide concentration, leading to unstable adsorbent performance. Summary of the Invention
[0006] The purpose of this invention is to provide a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent, overcoming the shortcomings of existing technologies. By using PEI to perform directional amino functionalization modification on coconut shell waste, the prepared adsorbent has a rich hierarchical pore structure and amino active sites. The obtained amino-modified coconut shell adsorbent exhibits excellent CO2 selective adsorption performance and cycle regeneration stability, solving the problem of unstable carbon dioxide adsorption capacity of adsorbents at low carbon dioxide concentrations in existing technologies.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] A method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent involves using coconut shell biochar as a porous carrier matrix, uniformly loading hydrotalcite (LDH) onto its surface and pores via a co-precipitation method, and then using polyethyleneimine (PEI) as an amino modifier for amino modification. The final product is a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with a multi-layered porous structure, abundant surface active sites, and high CO2 selective adsorption performance.
[0009] The preparation process of the coconut shell biochar is as follows: First, fresh coconut shells are repeatedly rinsed with deionized water to remove surface impurities, dried at 80-105℃ to constant weight, and then crushed into 100-200 mesh fine powder using a high-speed pulverizer; pyrolysis is carried out in a tube furnace under nitrogen protection, with the temperature increased to 650-750℃ at a rate of 8-12℃ / min and held at a constant temperature for 1.5-2.5 hours, followed by natural cooling to room temperature; the obtained coconut shell biochar is soaked in 25% dilute hydrochloric acid for 6-12 hours to remove ash, then washed with deionized water until neutral, and vacuum dried at 70-80℃ for 10-12 hours for later use. The final coconut shell biochar has a particle size of 800-1500 μm. 2 High specific surface area per g and 0.5-2.0 cm² 3 / g has a well-developed porous structure.
[0010] The hydrotalcite is a magnesium-aluminum type layered bimetallic hydroxide (MgAl-LDH), and its preparation process is as follows: magnesium nitrate hexahydrate Mg(NO3)2·6H2O and aluminum nitrate nonahydrate Al(NO3)3·9H2O are prepared into a mixed salt solution with a total metal ion concentration of 0.5-1.5 mol / L at a Mg / Al molar ratio of 2:1-3:1; a mixed alkaline solution of 1.0-2.0 mol / L NaOH and 0.2-0.5 mol / L Na2CO3 is used as a precipitant. The molar ratio of NaOH to NaCO3 is 4:1-10:1. Under nitrogen protection and vigorous stirring, the mixed salt solution and alkaline solution are slowly added dropwise to the reactor using a co-precipitation method, controlling the pH of the reaction system within the range of 9.0-11.0. After the addition is complete, the mixture is hydrothermally crystallized at 60-80℃ for 12-24 hours. The precipitate is collected by centrifugation and washed with deionized water until neutral. After vacuum drying at 60-80℃ for 12-14 hours, it is ground through a 200-mesh sieve to obtain highly crystalline LDH powder.
[0011] The polyethyleneimine (PEI) used as an amino modifier has a molecular weight of 600-1000 Da.
[0012] The specific steps of the co-precipitation method are as follows: coconut shell biochar and LDH powder are mixed at a mass ratio of 1-3:1, an appropriate amount of anhydrous ethanol is added, the mixture is heated to 50-60°C, stirred evenly at a stirring speed of 500-1000 r / min, and after stirring for 8-10 hours, it is ultrasonically dispersed for 30-60 minutes to form a stable suspension.
[0013] The specific steps of the amino modification are as follows: a mixed solution of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage or weight ratio of 40-50%:40-50%:10-20%, and reacted at a constant temperature of 60-80℃ for 4-8 hours under nitrogen protection and magnetic stirring. After the reaction, the mixture is washed repeatedly with anhydrous ethanol 3-5 times to remove unbonded free polyethyleneimine (PEI), and then vacuum dried at 60-80℃ for 12-24 hours.
[0014] The PEI-ethanol mixture has a PEI to ethanol mass ratio of 1:3 to 1:1, and the ethanol purity is 99 wt%.
[0015] The PEI ethanol mixture solution needs to be filtered through a 0.22μm microporous membrane before use to remove insoluble matter.
[0016] The washing process described above involves ultrasonic cleaning at 60-70Hz for 30-60 minutes.
[0017] The coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent is suitable for carbon dioxide concentrations ranging from 3500 to 4500 ppm.
[0018] Compared with the prior art, the beneficial effects of the present invention are:
[0019] 1) This invention is the first to use PEI to perform targeted amino functionalization modification of coconut shell waste. The prepared adsorbent has a rich hierarchical pore structure and amino active sites. The amino-modified coconut shell adsorbent exhibits excellent CO2 adsorption performance and recycling stability.
[0020] 2) This invention is the first to load magnesium-aluminum type hydrotalcite onto treated coconut shells and use PEI for amino modification to form a coconut shell-hydrotalcite-amino ternary composite material for carbon dioxide adsorption. Using waste coconut shells as raw materials, it is low-cost and realizes solid waste resource utilization. Furthermore, the coconut shell biochar carrier has a high specific surface area and hierarchical pore structure, providing a large number of CO2 adsorption sites. The aluminum-magnesium type hydrotalcite has positively charged layers, which preferentially adsorb acidic CO2 molecules through electrostatic interaction. CO2 undergoes ion exchange with CO32- between layers, enhancing chemical adsorption. Moreover, the layered structure can intercalate PEI molecules without causing a serious reduction in material porosity. PEI contains primary and secondary amines, which undergo reversible carboxylation reactions with CO2, significantly improving the chemical adsorption capacity.
[0021] 3) The treated coconut shell is simultaneously loaded with aluminum-magnesium hydrotalcite and PEI, which gives the coconut shell both strong physical adsorption properties and good chemical adsorption properties, forming an "organic-inorganic" synergistic adsorption network. This effectively improves the carbon dioxide adsorption performance, and the adsorption capacity is less affected by the carbon dioxide concentration. The adsorbent performance is stable, and the advantages of each component are complementary, showing significant industrialization potential and stability. Attached Figure Description
[0022] Figure 1 Comparison curves of CO2 adsorption capacity of materials under different carbon dioxide concentrations in embodiments of the present invention;
[0023] Figure 2 Five adsorption-desorption cycle performance test diagrams in this embodiment of the invention;
[0024] Figure 3 Comparison curves of CO2 adsorption capacity of materials at different carbon dioxide concentrations in the comparative examples of this invention;
[0025] Figure 4 The comparative example of this invention shows the performance test results of five adsorption-desorption cycles. Detailed Implementation
[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.
[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.
[0028] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.
[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.
[0030] In the following examples, the preparation process is as follows: Fresh coconut shells are first repeatedly rinsed with deionized water to remove surface impurities, dried at 80-105℃ to constant weight, and then crushed into 100-200 mesh fine powder using a high-speed pulverizer; pyrolysis is carried out in a tube furnace under nitrogen protection, with the temperature increased to 650-750℃ at a rate of 8-12℃ / min and held at that temperature for 1.5-2.5 hours, followed by natural cooling to room temperature; the obtained coconut shell biochar is treated with 25% dilute hydrochloric acid for 6-12 hours to remove ash, then washed with deionized water until neutral, and vacuum dried at 70-80℃ for 10-12 hours for later use. The final coconut shell biochar has a particle size of 800-1500 μm. 2 High specific surface area per g and 0.5-2.0 cm² 3The product has a well-developed porous structure. Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) and aluminum nitrate nonahydrate (Al(NO3)3·9H2O) were prepared into a mixed salt solution with a total metal ion concentration of 0.5-1.5 mol / L at a Mg / Al molar ratio of 2:1-3:1. A mixed alkaline solution of 1.0-2.0 mol / L NaOH and 0.2-0.5 mol / L Na2CO3 was prepared as a precipitant, with a NaOH:NaCO3 molar ratio of 4:1-10:1. Under nitrogen protection and vigorous stirring, the mixed salt solution and alkaline solution were slowly added dropwise to the reactor using a co-current co-precipitation method, controlling the pH of the reaction system within the range of 9.0-11.0. After the addition was complete, the product was hydrothermally crystallized at 60-80℃ for 12-24 hours. The precipitate was collected by centrifugation and washed with deionized water until neutral. After vacuum drying at 60-80℃ for 12-14 hours, it was ground through a 200-mesh sieve to obtain highly crystalline LDH powder. Polyethyleneimine (PEI), used as an amino modifier, has a molecular weight of 600-1000 Da.
[0031] In the following embodiments, the method for studying the CO2 adsorption performance of the obtained adsorbent is as follows: One gram of coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent sample is filled onto the catalytic column in the reactor of the carbon dioxide adsorption performance testing device. Quartz wool is filled at the upper end of the catalytic column to prevent powdery sample from entering the pipeline with the gas flow. The reaction temperature and CO2 inlet concentration are set. Then, the outlet valve of the entire system is closed, and the vacuum pump is turned on to evacuate the entire device for 3-5 minutes until the pressure gauge reading reaches -0.06 to -0.05, to reduce the influence of impurity gases on the detection results. After evacuation, the N2 valve is opened first, and gas is introduced for 15-20 minutes until the CO2 concentration in the entire system is 450-620 ppm before opening the CO2 cylinder valve. The inlet valve is opened, and N2 and CO2 are mixed in the gas mixing tank along the pipeline. The CO2 concentration is detected at the outlet using a gas detector. When the detected CO2 concentration reaches the designed CO2 concentration, adsorption is stopped. Finally, the carbon dioxide adsorption capacity is calculated.
[0032] Example 1
[0033] This invention discloses a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent. Coconut shell biochar is used as a porous carrier matrix. Hydrotalcite (LDH) is uniformly loaded onto its surface and pores via co-precipitation. Coconut shell biochar and LDH powder are mixed at a mass ratio of 1:1, and an appropriate amount of anhydrous ethanol is added. The mixture is heated to 60°C, stirred uniformly at a stirring speed of 500 r / min for 10 hours, and then ultrasonically dispersed for 50 minutes to form a stable suspension. Polyethylene imine (PEI) is then used as an amino modifier for amino modification. The specific steps of amino modification are as follows: a mixture of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage of 45%:45%:10%. Under nitrogen protection and magnetic stirring, the mixture is reacted at a constant temperature of 70°C for 6 hours. After the reaction, the mixture is repeatedly washed five times with anhydrous ethanol, each wash consisting of 60Hz ultrasonic cleaning for 60 minutes to remove unbonded free polyethyleneimine (PEI). The mixture is then vacuum dried at 80°C for 24 hours. The PEI-ethanol mixed solution has a PEI to ethanol mass ratio of 1:1, and the ethanol purity is 99 wt%. Before use, the PEI-ethanol mixed solution needs to be filtered through a 0.22 μm microporous membrane to remove insoluble matter, ultimately yielding a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with a multi-layered porous structure, abundant surface active sites, and high CO2 selective adsorption performance. When the carbon dioxide concentration is 3500 ppm, the adsorbent's carbon dioxide adsorption capacity was tested to be 1.83 mmol / g, and its adsorption curve is shown below. Figure 1 As shown.
[0034] Example 2
[0035] This invention discloses a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent. Coconut shell biochar is used as a porous carrier matrix. Hydrotalcite (LDH) is uniformly loaded onto its surface and pores via a co-precipitation method. Coconut shell biochar and LDH powder are mixed at a mass ratio of 1:1, and an appropriate amount of anhydrous ethanol is added. The mixture is heated to 50°C, stirred uniformly at a stirring speed of 500 r / min for 10 hours, and then ultrasonically dispersed for 50 minutes to form a stable suspension. Polyethylene imine (PEI) is then used as an amino modifier for amino modification. The specific steps of amino modification are as follows: a mixed solution of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage of 42.5%:42.5%:15%, and reacted at a constant temperature of 70°C for 6 hours under nitrogen protection and magnetic stirring. After the reaction, the mixture is repeatedly washed five times with anhydrous ethanol, each wash consisting of 60Hz ultrasonic cleaning for 60 minutes to remove unbonded free polyethyleneimine (PEI). The mixture is then vacuum dried at 60°C for 12 hours. The PEI-ethanol mixed solution has a PEI to ethanol mass ratio of 1:1, and the ethanol purity is 99 wt%. Before use, the PEI-ethanol mixed solution needs to be filtered through a 0.22 μm microporous membrane to remove insoluble matter, ultimately yielding a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with a multi-layered porous structure, abundant surface active sites, and high CO2 selective adsorption performance. When the carbon dioxide concentration is 4000 ppm, the adsorbent's carbon dioxide adsorption capacity was tested to be 1.99 mmol / g, and its adsorption curve is shown below. Figure 1 As shown.
[0036] Example 3
[0037] This invention discloses a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent. Coconut shell biochar is used as a porous carrier matrix. Hydrotalcite (LDH) is uniformly loaded onto its surface and pores via a co-precipitation method. Coconut shell biochar and LDH powder are mixed at a mass ratio of 1:1, and an appropriate amount of anhydrous ethanol is added. The mixture is heated to 50°C, stirred uniformly at a stirring speed of 500 r / min for 10 hours, and then ultrasonically dispersed for 50 minutes to form a stable suspension. Polyethylene imine (PEI) is then used as an amino modifier for amino modification. The specific steps of amino modification are as follows: a mixed solution of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage of 40%:40%:20%, and reacted at a constant temperature of 70°C for 6 hours under nitrogen protection and magnetic stirring. After the reaction, the mixture is repeatedly washed five times with anhydrous ethanol, each wash consisting of 60Hz ultrasonic cleaning for 60 minutes to remove unbonded free polyethyleneimine (PEI). The mixture is then vacuum dried at 60°C for 12 hours. The PEI-ethanol mixed solution has a PEI to ethanol mass ratio of 1:1, and the ethanol purity is 99 wt%. Before use, the PEI-ethanol mixed solution needs to be filtered through a 0.22 μm microporous membrane to remove insoluble matter, ultimately yielding a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with a multi-layered porous structure, abundant surface active sites, and high CO2 selective adsorption performance. When the carbon dioxide concentration is 4500 ppm, the adsorbent's carbon dioxide adsorption capacity is tested to be 2.03 mmol / g, and its adsorption curve is shown below. Figure 1 As shown.
[0038] Example 4
[0039] This invention discloses a method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent. Coconut shell biochar is used as a porous carrier matrix. Hydrotalcite (LDH) is uniformly loaded onto its surface and pores via co-precipitation. Coconut shell biochar and LDH powder are mixed at a mass ratio of 1:1, and an appropriate amount of anhydrous ethanol is added. The mixture is heated to 60°C, stirred uniformly at a stirring speed of 500 r / min for 10 hours, and then ultrasonically dispersed for 50 minutes to form a stable suspension. Polyethylene imine (PEI) is then used as an amino modifier for amino modification. The specific steps of amino modification are as follows: a mixture of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage of 45%:45%:10%. Under nitrogen protection and magnetic stirring, the mixture is reacted at a constant temperature of 70°C for 6 hours. After the reaction, the mixture is repeatedly washed five times with anhydrous ethanol, each wash consisting of 60Hz ultrasonic cleaning for 60 minutes to remove unbonded free polyethyleneimine (PEI). The mixture is then vacuum dried at 80°C for 24 hours. The PEI-ethanol mixed solution has a PEI to ethanol mass ratio of 1:1, and the ethanol purity is 99 wt%. Before use, the PEI-ethanol mixed solution needs to be filtered through a 0.22 μm microporous membrane to remove insoluble matter, ultimately yielding a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with a multi-layered porous structure, abundant surface active sites, and high CO2 selective adsorption performance. When the carbon dioxide concentration is 5000 ppm, the adsorbent's carbon dioxide adsorption capacity was tested to be 2.33 mmol / g, and its adsorption curve is shown below. Figure 1 As shown.
[0040] The carbon dioxide adsorbent of the present invention exhibits low sensitivity to changes in CO2 concentration within the CO2 concentration range of 3500-5000ppm, and its saturated adsorption capacity does not show significant differences with concentration fluctuations, maintaining stable overall adsorption performance.
[0041] Example 5
[0042] The sample that underwent adsorption in Example 4 was placed in a vacuum drying apparatus and heated to 120°C at a heating rate of 10°C / min under a nitrogen protective atmosphere. It was then held at 120°C for 12 hours to complete the desorption process. After desorption, the adsorption performance was tested again under a carbon dioxide concentration of 5000 ppm. The above adsorption-desorption operation was repeated for this adsorbent, and its carbon dioxide adsorption capacity was measured after 5 cycles. The corresponding adsorption curves are shown below. Figure 2 As shown.
[0043] After five adsorption-desorption cycles, the carbon dioxide adsorbent of the present invention can still maintain more than 95% of the initial adsorption capacity, indicating that the carbon dioxide adsorbent has good cycle regeneration stability.
[0044] Comparative Example 1
[0045] Taking traditional coconut shell activated carbon amino-modified material as an example, coconut shell biochar and PEI ethanol mixed solution were mixed at a weight percentage of 90%:10%, and reacted at a constant temperature of 70℃ for 6 hours under nitrogen protection and magnetic stirring. After the reaction, the mixture was repeatedly washed five times with anhydrous ethanol, each wash being ultrasonic cleaning at 60Hz for 60 minutes to remove unbonded free polyethyleneimine (PEI). The mixture was then vacuum dried at 80℃ for 24 hours. The mass ratio of PEI to ethanol in the PEI ethanol mixed solution was 1:1, and the purity of the ethanol was 99wt%. Before use, the PEI ethanol mixed solution was filtered through a 0.22μm microporous membrane to remove insoluble matter, finally yielding the coconut shell activated carbon amino-modified material. Its adsorption curves at carbon dioxide concentrations of 3500ppm, 4000ppm, 4500ppm, and 5000ppm are shown below. Figure 3 As shown.
[0046] Comparative Example 1 shows that the saturated adsorption capacity of traditional amino-modified biochar materials varies significantly with concentration fluctuations.
[0047] Comparative Example 2
[0048] Taking the traditional coconut shell activated carbon amino-modified material as an example, the sample from Comparative Example 1 that completed adsorption at a carbon dioxide concentration of 5000 ppm was placed in a vacuum drying apparatus and heated to 120℃ at a heating rate of 10℃ / min under a nitrogen protective atmosphere. It was then held at 120℃ for 12 hours to complete the desorption process. After desorption, the adsorption performance was tested again under the test condition of a carbon dioxide concentration of 5000 ppm. The above adsorption-desorption operation was repeated for this adsorbent, and its carbon dioxide adsorption capacity was measured after 5 cycles. The corresponding adsorption curve is shown below. Figure 4 As shown.
[0049] Comparative Example 2 shows that after five adsorption-desorption cycles, the saturated adsorption capacity of the traditional amino-modified biochar material decreased significantly, indicating that the cyclic regeneration stability of the traditional amino-modified biochar material is poor.
[0050] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.
Claims
1. A method for preparing a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent, characterized in that, Using coconut shell biochar as a porous carrier matrix, hydrotalcite (LDH) was uniformly loaded onto its surface and pores, and then polyethyleneimine (PEI) was used as an amino modifier for amino modification. Finally, a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent with multi-level pore structure, abundant surface active sites and high CO2 selective adsorption performance was obtained.
2. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The preparation process is as follows: First, fresh coconut shells are repeatedly rinsed with deionized water to remove surface impurities, dried at 80-105℃ to constant weight, and then crushed into 100-200 mesh fine powder using a high-speed pulverizer. The powder is then subjected to programmed temperature pyrolysis in a tube furnace under nitrogen protection, with the temperature increased to 650-750℃ at a rate of 8-12℃ / min and maintained at that temperature for 1.5-2.5 hours, followed by natural cooling to room temperature. The resulting coconut shell biochar is then soaked in 25% dilute hydrochloric acid for 6-12 hours to remove ash, washed with deionized water until neutral, and vacuum dried at 70-80℃ for 10-12 hours for later use. The final coconut shell biochar has a particle size of 800-1500 μm. 2 High specific surface area per g and 0.5-2.0 cm² 3 / g has a well-developed porous structure.
3. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The preparation process of the hydrotalcite is as follows: magnesium nitrate hexahydrate Mg(NO3)2·6H2O and aluminum nitrate nonahydrate Al(NO3)3·9H2O are prepared into a mixed salt solution with a total metal ion concentration of 0.5-1.5 mol / L according to the Mg / Al molar ratio of 2:1-3:1; a mixed alkaline solution of 1.0-2.0 mol / L NaOH and 0.2-0.5 mol / L Na2CO3 is prepared as a precipitant, with the NaOH:NaCO3 molar ratio of 4:1-10:1; under nitrogen protection and vigorous stirring, the mixed salt solution and alkaline solution are slowly added dropwise to the reaction vessel, and the pH value of the reaction system is controlled within the range of 9.0-11.0; after the addition is completed, hydrothermal crystallization is carried out at 60-80℃ for 12-24 hours, the precipitate is collected by centrifugation and washed with deionized water until neutral, and then vacuum dried at 60-80℃ for 12-14 hours and ground through a 200-mesh sieve to obtain highly crystalline MgAl-LDH powder.
4. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The polyethyleneimine (PEI) used as an amino modifier has a molecular weight of 600-1000 Da.
5. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The specific steps of the co-precipitation method are as follows: coconut shell biochar and LDH powder are mixed at a mass ratio of 1-3:1, an appropriate amount of anhydrous ethanol is added, the mixture is heated to 50-60°C, stirred evenly at a stirring speed of 500-1000 r / min, and after stirring for 8-10 hours, it is ultrasonically dispersed for 30-60 minutes to form a stable suspension.
6. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The specific steps of the amino modification are as follows: a mixed solution of coconut shell biochar, hydrotalcite (LDH), and PEI ethanol is prepared at a weight percentage or weight ratio of 40-50%:40-50%:10-20%, and reacted at a constant temperature of 60-80℃ for 4-8 hours under nitrogen protection and magnetic stirring. After the reaction is complete, wash repeatedly with anhydrous ethanol 3-5 times to remove unbonded free polyethyleneimine (PEI), and vacuum dry at 60-80℃ for 12-24 hours.
7. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 5, characterized in that, The PEI-ethanol mixture has a PEI to ethanol mass ratio of 1:3 to 1:1, and the ethanol purity is 99 wt%.
8. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 5, characterized in that, The PEI ethanol mixture solution needs to be filtered through a 0.22μm microporous membrane before use to remove insoluble matter.
9. The preparation method of the coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 5, characterized in that, The washing process described above involves ultrasonic cleaning at 60-70Hz for 30-60 minutes.
10. The preparation method of a coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent according to claim 1, characterized in that, The coconut shell-hydrotalcite-amino composite carbon dioxide adsorbent is suitable for carbon dioxide concentrations ranging from 3500 to 5000 ppm.