A palm-based carbon dioxide adsorbent, its preparation method and application

Abstract

The application discloses a palm-based carbon dioxide adsorbent and a preparation method and application thereof, and the method comprises the following steps: subjecting palm empty fruit bunch fibers to hemicellulose and lignin removal to obtain pretreated palm cellulose, then mixing the pretreated palm cellulose with a nitrogen-containing phosphorus dopant, a hard template agent and a solvent, uniformly mixing, drying to obtain a precursor, carbonizing under a protective atmosphere to obtain a first intermediate, removing the hard template agent in the first intermediate by using an acid or alkali solution to obtain a second intermediate, mixing the second intermediate with an activating agent, heating and activating under a protective atmosphere to obtain a third intermediate, and finally mixing the third intermediate with an amine-containing compound; the carbon dioxide adsorbent prepared by the method has high adsorption capacity for CO2, good cycle stability and low regeneration energy consumption, and can be used for direct air capture and flue gas capture.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a palm-based carbon dioxide adsorbent, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, the concentration of carbon dioxide in the atmosphere continues to rise, leading to severe environmental problems such as global warming and ocean acidification. Carbon capture, utilization, and storage (CCUS) technology is considered one of the key approaches to mitigate the greenhouse effect. Among these technologies, adsorption has attracted widespread attention due to its advantages such as low energy consumption, simple operation, and recyclable adsorbents.

[0003] Solid adsorbents are the core of adsorption methods. Traditional adsorbents such as zeolite, activated carbon, and metal-organic frameworks (MOFs) have a certain carbon dioxide adsorption capacity, but they generally suffer from problems such as high cost and high regeneration energy consumption.

[0004] For applications like direct air capture (DAC) with extremely low CO2 concentrations, adsorbent materials need to possess both rapid diffusion capabilities and a high specific surface area, while also having a surface rich in CO2-affinity sites to facilitate carbon dioxide capture. In recent years, biomass-derived carbon materials have become a research hotspot due to their wide availability and renewability. However, currently available carbon materials prepared from biomass are difficult to apply to DAC applications with extremely low CO2 concentrations, exhibiting poor capture efficiency and effectiveness.

[0005] It should be noted that the information disclosed in the background section above is only for understanding the background of this application. Therefore, the background section of this invention may include background information about the problems or environment of this invention, and is not necessarily a description of the prior art. Thus, the content included in the background section does not constitute an admission of the prior art by the applicant. Summary of the Invention

[0006] The purpose of this invention is to overcome one or more shortcomings in the prior art and provide a novel carbon dioxide adsorbent and its preparation method. The carbon dioxide adsorbent prepared by this method has a high adsorption capacity for CO2 and is suitable for air capture.

[0007] The present invention also provides a carbon dioxide adsorption device comprising the above-mentioned carbon dioxide adsorbent.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a carbon dioxide adsorbent, the method comprising: The empty palm fruit fibers are de-hemicelluloseed and lignin-removed to obtain pretreated palm cellulose. The pretreated palm cellulose, nitrogen- and phosphorus-containing dopants, hard template agents and solvents are mixed and dried to obtain the precursor. The precursor is carbonized under a protective atmosphere to obtain a first intermediate; The hard template agent in the first intermediate is removed by using an acid or alkali solution to obtain the second intermediate; The second intermediate is mixed with an activator and activated by heating under a protective atmosphere to prepare the third intermediate; The third intermediate is mixed with an amine-containing compound.

[0009] In some embodiments of the present invention, the pretreated palm cellulose is prepared by the following method: cleaning, drying, and crushing the empty fruit bunch fiber of palm, and then treating it sequentially with alkaline solution and sodium chlorite solution to obtain the pretreated palm cellulose.

[0010] In some embodiments of the present invention, the treatment process with alkaline solution or sodium chlorite solution can be performed once, twice, three times or more.

[0011] Palm hollow fruit clusters contain a large amount of bound lignin. Multiple treatments can effectively remove stubborn impurities, improve cellulose purity and crystallinity, and prevent residual amorphous components from damaging the subsequent ordered mesoporous structure.

[0012] Further, in the preparation process of the pretreated palm cellulose, the alkaline solution comprises an aqueous solution of an alkali metal hydroxide with a mass concentration of 0.1%-5%. According to some specific aspects of the present invention, the mass concentration of the aqueous solution of the alkali metal hydroxide is 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5.0%, etc.

[0013] Furthermore, the alkali metal hydroxide aqueous solution comprises an aqueous solution of sodium hydroxide.

[0014] In some embodiments of the present invention, the preparation process of the pretreated palm cellulose is carried out at 60-90°C, for example, at temperatures of 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0015] Further, the sodium chlorite solution is an aqueous solution of sodium chlorite with a mass concentration of 0.2%-5%. According to some specific aspects of the present invention, the mass concentration of the aqueous sodium chlorite solution is 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5.0%, etc.

[0016] Furthermore, the treatment process using the sodium chlorite solution is carried out at 60-90°C and a pH of 3.0-5.5. According to some specific aspects of the invention, the treatment process using the sodium chlorite solution is carried out at 70-80°C and a pH of 4.0-5.0.

[0017] In some embodiments of the present invention, the mass ratio of the pretreated palm cellulose to the nitrogen-phosphorus dopant is controlled to be 5-20:1. According to some specific aspects of the present invention, the mass ratio of the pretreated palm cellulose to the nitrogen-phosphorus dopant is controlled to be 5:1, 5.5:1, 6.0:1, 6.5:1, 7.0:1, 7.5:1, 8.0:1, 8.5:1, 9.0:1, 9.5:1, 10:1, 10.5:1, 11:1, 11.5:1, 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 14.5:1, 15:1, 15.5:1, 16:1, 16.5:1, 17:1, 17.5:1, 18:1, 18.5:1, 19:1, 19.5:1, 20:1, etc.

[0018] In some embodiments of the present invention, the nitrogen-phosphorus dopant is one or more selected from ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0019] In some embodiments of the present invention, the mass ratio of the pretreated palm cellulose to the hard template agent is controlled to be 1:1-5. According to some specific aspects of the present invention, the mass ratio of the pretreated palm cellulose to the hard template agent is controlled to be 1:1, 1:1.5, 1:2.0, 1:2.5, 1:3.0, 1:3.5, 1:4.0, 1:4.5, 1:5.0, etc.

[0020] In some embodiments of the present invention, the particle size of the hard template agent is 5-50 nm.

[0021] In some embodiments of the present invention, the hard template agent is one or more combinations selected from solid silica nanospheres, mesoporous silica, and molecular sieves.

[0022] In some embodiments of the present invention, the solvent is a mixed aqueous solution of an alkaline hydroxide and urea. Further, the alkaline hydroxide comprises sodium hydroxide. Even further, in the mixed aqueous solution, the mass concentration of the alkaline hydroxide is 5%-10% and the mass concentration of the urea is 10%-15% by mass percentage.

[0023] According to some specific aspects of the present invention, in the mixed aqueous solution, the mass concentration of the alkaline hydroxide is 6%-8% and the mass concentration of the urea is 11%-13% by mass percentage.

[0024] In some embodiments of the present invention, the mixing process during the preparation of the precursor is carried out at -10 to -15°C. This temperature allows the alkaline hydroxide and urea system to effectively break the hydrogen bonds between cellulose molecules, achieving homogeneous dissolution, while simultaneously inhibiting the degradation of cellulose molecular chains under alkaline conditions, ensuring uniform composite composition.

[0025] In some embodiments of the present invention, the drying process in preparing the precursor is freeze-drying. Further, the freeze-drying includes a pre-freezing stage and a vacuum sublimation stage. The temperature of the pre-freezing stage is -40°C to -60°C, and the pre-freezing time is 2 to 6 hours. The temperature of the vacuum sublimation stage is -40°C to -60°C, the vacuum degree is 0.1 to 10 Pa, and the drying time is 24 to 48 hours. In some embodiments of the present invention, the carbonization is carried out at 600-1000°C.

[0026] Furthermore, the carbonization is carried out at 700-950°C.

[0027] Furthermore, the carbonization is carried out at 750-900°C.

[0028] In some embodiments of the present invention, the heating rate of the carbonization is 1-10°C / min, and more specifically 3-7°C / min.

[0029] In some embodiments of the present invention, the alkaline solution used in the preparation of the second intermediate is a 0.5-3 mol / L sodium hydroxide aqueous solution, and the process of removing the hard template agent is carried out at 60-90°C.

[0030] In some embodiments of the present invention, the activator comprises one or more combinations selected from potassium hydroxide, sodium hydroxide, zinc chloride, phosphoric acid, and carbon dioxide.

[0031] In some embodiments of the present invention, the mass ratio of the activator to the second intermediate is controlled to be 1-5:1. According to some specific aspects of the present invention, the mass ratio of the activator to the second intermediate is controlled to be 1:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, etc.

[0032] In some embodiments of the present invention, the heating activation process is carried out at 600-900°C.

[0033] Furthermore, the heating activation process is carried out at 600-850°C.

[0034] Furthermore, the heating activation process is carried out at 650-800°C.

[0035] In some embodiments of the present invention, the heating activation rate is 1-10°C / min, and more specifically 3-7°C / min.

[0036] In some embodiments of the present invention, during the preparation of the third intermediate, after the heating activation, the intermediate is washed until neutral.

[0037] In some embodiments of the present invention, the amine-containing compound is one or more combinations selected from polyethyleneimine, tetraethylenepentamine, triethylenetetramine, urea, and chlorocyanuric acid.

[0038] The third intermediate is impregnated in a solution containing an amine compound by means of impregnation, stirred and mixed, washed and dried to prepare the carbon dioxide adsorbent.

[0039] Another technical solution provided by the present invention: a carbon dioxide adsorbent prepared by the preparation method of the carbon dioxide adsorbent described above.

[0040] In some embodiments of the present invention, the carbon dioxide adsorbent comprises first-order pores with a pore size of 2-10 nm and second-order pores with a pore size of less than 2 nm.

[0041] In some embodiments of the present invention, the specific surface area of ​​the carbon dioxide adsorbent is 1200-2000 m². 2 / g.

[0042] In some embodiments of the present invention, the pore volume of the carbon dioxide adsorbent is 0.7-2.6 cm³. 3 / g.

[0043] Another technical solution provided by the present invention: the application of the above-mentioned carbon dioxide adsorbent in a carbon dioxide adsorption device.

[0044] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: This invention aims to address the problem that biomass carbon materials cannot meet the requirements for efficient capture of low-concentration CO2. It provides a phosphorus / nitrogen co-doped palm cellulose-based ordered mesoporous-microporous hierarchical carbon adsorbent and its preparation method. This adsorbent has highly ordered mesoporous channels and abundant micropores. The intrinsic CO2 affinity of the carbon skeleton is enhanced by phosphorus / nitrogen co-doping, and a dual nitrogen synergistic system is constructed by combining surface amine functionalization. It has a high adsorption capacity for CO2 and is suitable for direct air capture.

[0045] Furthermore, the present invention was proposed because the inventors discovered during their research that the cellulose obtained from empty palm fruit bunches after hemicellulose / lignin removal has high crystallinity and exhibits a dense structure and rough surface in its microstructure. This dense structure ensures uniform filling of the cellulose solution in the channels of the hard template, forming a high-fidelity ordered mesoporous framework after carbonization; the rough surface provides abundant physical anchor points for subsequent phosphorus / nitrogen co-doping and amine anchoring, improving the stability of surface functional groups and making them less prone to detachment during recycling. Detailed Implementation

[0046] The main inventive concept of this invention is as follows: (1) The raw materials are renewable and have a unique structure. Using palm waste as raw material, the sources are wide and the price is low, realizing the high-value utilization of agricultural waste. In particular, the extracted palm cellulose has high crystallinity, and its micro-morphology is characterized by a dense structure and a rough surface. Research and analysis suggest that this dense structure can ensure high-fidelity filling and replication of hard template pores, and the rough surface can provide strong physical anchoring points for amine loading. (2) This invention can precisely control the mesopore size (first-order pores) and arrangement order of the adsorbent through the hard template method. Further, combined with the activation method, smaller micropores (second-order pores) can be introduced on the mesopore wall to form an ordered mesopore-micropore hierarchical structure. This hierarchical structure not only ensures the channel for rapid diffusion of low-concentration CO2, but also provides high specific surface area adsorption sites, synergistically improving adsorption kinetics and capacity. (3) Phosphorus / nitrogen co-doping synergistically enhances the intrinsic activity of the carbon skeleton. This invention uses nitrogen-phosphorus dopants to achieve lattice co-doping of phosphorus and nitrogen in one step during the carbonization process. During carbonization, nitrogen and phosphorus dopants decompose to produce NH3 and H3PO4. NH3 embeds nitrogen atoms into the carbon framework to form active sites such as pyridine nitrogen and pyrrole nitrogen, while H3PO4 embeds phosphorus atoms into the carbon framework to form PC and PO bonds. Both work synergistically to enhance the intrinsic affinity of the carbon framework for CO2. Simultaneously, the doped nitrogen and phosphorus are integral components of the carbon framework, exhibiting good thermal and chemical stability, and can continue to function effectively through multiple cycles. Furthermore, the surface amino functionalization process is further combined, creating a dual nitrogen synergy between lattice doping and surface amino functionalization, further enhancing CO2 capture performance.

[0047] Practice has shown that the carbon dioxide adsorbent of this invention has an adsorption capacity of 2.5-4 mmol / g under direct air capture conditions (400 ppm CO2, 25℃), which is far superior to traditional activated carbon and most biomass carbon materials.

[0048] Meanwhile, the carbon skeleton structure is stable, and phosphorus / nitrogen co-doping further enhances the thermal and chemical stability of the carbon skeleton. The rough surface of palm cellulose provides strong physical anchoring sites for amine loading, allowing for more than 10 cycles after amine functionalization with an adsorption capacity retention rate greater than 95% and low regeneration energy consumption. The carbon dioxide adsorbent of this invention can be used for both direct air capture (DAC) and flue gas capture.

[0049] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0050] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0051] Example 1: This example provides a carbon dioxide adsorbent and its preparation method, which includes: (1) Preparation of pretreated palm cellulose: Take 500 g of commercially available palm hollow fruit bunch fiber, wash it, dry it at 60℃, and pulverize it through a 40-mesh sieve. Add the powder to 2 L of 2 wt.% NaOH aqueous solution, stir at 80℃ for 2 h, filter, and wash with water until neutral. Then add the solid to 2 L of 1.5 wt.% NaClO2 aqueous solution, adjust the pH to 4.5 with glacial acetic acid, stir at 75℃ for 2 h, filter, wash with water until neutral, and repeat the treatment twice. Wash the obtained solid with ethanol, dry it under vacuum at 60℃ to obtain pretreated palm cellulose with a yield of about 38%.

[0052] (2) Preparation of precursor: Take 10 g of the above pretreated palm cellulose and dissolve it in 100 mL of an aqueous solution containing 7 wt.% NaOH and 12 wt.% urea. Pre-cool and dissolve at -12℃. Add ammonium phosphate (mass ratio of ammonium phosphate to pretreated palm cellulose 1:15) and stir for 1 h to make the ammonium phosphate uniformly dispersed. Add hard template agent - commercially available ordered mesoporous silica SBA-15 (mass ratio of hard template agent to pretreated palm cellulose 2:1) and stir vigorously for 2 h. Then freeze dry (conditions: pre-freezing temperature is -55℃, pre-freezing time is 4 h; vacuum sublimation stage temperature is -55℃, vacuum degree is not higher than 1 Pa, drying time is 36 h) to obtain the precursor.

[0053] (3) Preparation of the first intermediate: The above precursor was placed in a tube furnace, nitrogen was introduced as a protective atmosphere, the temperature was raised to 800°C at a heating rate of 5°C / min, and the carbonization reaction was carried out by holding at the temperature for 2 h. After natural cooling, the first intermediate was obtained.

[0054] (4) Preparation of the second intermediate: The first intermediate was immersed in a 2 mol / L NaOH aqueous solution and stirred at 80°C for 12 h to completely dissolve and remove the ordered mesoporous silica SBA-15. The solution was filtered, washed with water until neutral, and dried at 80°C to obtain the second intermediate.

[0055] (5) Preparation of the third intermediate: The second intermediate was mixed with KOH at a mass ratio of 1:3, and heated to 700℃ at 5℃ / min under a nitrogen atmosphere and kept at this temperature for 1 h. After cooling, it was washed with 1 mol / L hydrochloric acid, then washed with water until neutral, and dried at 80℃ to obtain the third intermediate.

[0056] (6) Surface amine functionalization: Take 5 g of the third intermediate, add 50 mL of 10 wt.% polyethyleneimine (PEI, molecular weight about 600) methanol solution, stir at room temperature for 12 h, filter, wash with methanol, and dry under vacuum at 60℃ to obtain the final carbon dioxide adsorbent.

[0057] Example 2: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as in Example 1, except that in step (2), ammonium phosphate is replaced with ammonium dihydrogen phosphate, and the mass ratio of ammonium dihydrogen phosphate to pretreated palm cellulose is 1:10.

[0058] Example 3: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as Example 1, except that: in step (2), ammonium phosphate is replaced with diammonium hydrogen phosphate, and the mass ratio of diammonium hydrogen phosphate to pretreated palm cellulose is 1:12; in step (5), the second intermediate is mixed with KOH at a mass ratio of 1:4.

[0059] Comparative Example 1: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as in Example 1, except that ammonium phosphate is not added in step (2).

[0060] Comparative Example 2: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as in Example 1, except that: in step (2), no hard template agent - ordered mesoporous silica SBA-15 is added.

[0061] Comparative Example 3: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as in Example 1, except that step (5) is omitted and step (6) is performed directly after step (4).

[0062] Comparative Example 4: This example provides a carbon dioxide adsorbent and its preparation method, which is basically the same as in Example 1, except that in step (1), palm hollow fruit bunch fiber is replaced with commercially available bamboo pulp of the same added mass.

[0063] Performance testing: Under simulated direct air capture conditions, the adsorption capacity of the carbon dioxide adsorbents obtained in Examples 1-3 and Comparative Examples 1-4 was tested to capture CO2 from the air. The carbon dioxide capture test at atmospheric pressure was conducted on a fixed-bed device. Specifically: (1) Pack 0.2±0.002g of carbon dioxide adsorbent into a glass tube with an inner diameter of 21mm; (2) The fresh carbon dioxide adsorbent was treated in a pure N2 gas flow at 90℃ and a flow rate of 500 mL / min for 30 min to remove the adsorbed moisture and CO2. (3) When the temperature is cooled to the test temperature of 25°C, the pure N2 gas flow is switched to a dry 400ppm CO2 gas flow; (4) When CO2 adsorption reaches equilibrium, the adsorption process terminates.

[0064] The carbon dioxide adsorbent underwent a desorption process at 100℃ for 30 minutes. The cyclic CO2 adsorption capacity was tested by repeating the adsorption-desorption process.

[0065] The test results are shown in Table 1.

[0066] Table 1 Compared to Comparative Example 1, the best comparative example, the adsorption capacity of Example 1 of this invention is increased by approximately 4.3%. Analysis suggests this is due to the dense structure of palm cellulose ensuring that the SBA-15 channels are uniformly filled by the cellulose solution, forming high-fidelity ordered mesopores after carbonization, thus accelerating CO2 diffusion. Simultaneously, the rough surface of palm cellulose provides strong physical anchoring sites for PEI, making it difficult for surface amino groups to detach during cycling. Furthermore, the NH3 and H3PO4 produced by the decomposition of ammonium phosphate achieve lattice phosphorus / nitrogen co-doping, introducing pyridine nitrogen, pyrrole nitrogen, and phosphorus-containing functional groups, enhancing intrinsic CO2 affinity. This triple synergy enables the material to maintain high adsorption capacity even at low CO2 concentrations.

[0067] Compared to Comparative Example 1, which was the best among the comparative examples, the adsorption capacity of Example 2 of the present invention was improved. Analysis suggests this is because ammonium dihydrogen phosphate decomposes during carbonization to produce NH3 and H3PO4, which, similar to ammonium phosphate, can simultaneously introduce lattice nitrogen and lattice phosphorus into the carbon framework, forming a phosphorus / nitrogen co-doping synergistic effect. Since the nitrogen content of ammonium dihydrogen phosphate is slightly lower than that of ammonium phosphate, its doping effect is slightly worse than that of Example 1, but still significantly better than the undoped sample.

[0068] Example 3 showed an improved adsorption capacity compared to Example 1. Analysis suggests that diammonium hydrogen phosphate has similar decomposition characteristics to ammonium phosphate, effectively achieving lattice phosphorus / nitrogen co-doping. Simultaneously, increasing the KOH activation ratio further increased microporosity and specific surface area, thereby enhancing the contribution of physical adsorption. Due to the dense structure of palm cellulose, the additional KOH etching can occur uniformly, avoiding localized over-etching. Therefore, the synergistic effect of lattice doping and higher specific surface area resulted in the optimal adsorption performance in this series of examples.

[0069] Compared to Example 1, the sample in Comparative Example 1 without lattice phosphorus / nitrogen co-doping showed a significant decrease in adsorption capacity. Analysis suggests this is because the carbon framework lacking lattice doping has a weak intrinsic affinity for CO2, relying primarily on surface amine functionalization to provide chemisorption sites. In contrast, lattice phosphorus / nitrogen co-doping introduces pyridine nitrogen, pyrrole nitrogen, and phosphorus-containing functional groups into the carbon framework. These sites, in synergy with surface amines, significantly enhance adsorption performance.

[0070] Compared to Example 1, the adsorption capacity of Comparative Example 2 was significantly reduced. Analysis suggests that although this example involved lattice phosphorus / nitrogen co-doping and surface amine functionalization, the lack of a hard template method to construct an ordered mesoporous structure resulted in random and disordered pores, lacking rapid diffusion channels. Under low CO2 concentrations, gas molecules struggled to quickly reach the doping sites and surface amine sites, thus limiting the effective adsorption capacity.

[0071] Compared to Example 1, the adsorption capacity of Comparative Example 3 decreased significantly. Analysis suggests that by omitting the activation and micropore-forming step, the material in this case retained only an ordered mesoporous structure, lacking the physical adsorption sites provided by the micropores. Furthermore, the absence of micropores meant that PEI was primarily loaded onto the mesoporous surface during surface amine functionalization, resulting in limited loading and easy pore blockage. The active sites generated by lattice doping also failed to fully function due to the lack of micropore confinement effect.

[0072] Compared to Example 1 (3.98 mmol / g, 95), the adsorption capacity of Comparative Example 4 was significantly lower. After 10 adsorption-desorption cycles, the adsorption capacity retention rate of Comparative Example 4 was approximately 90%, lower than the 97% of Example 1. Analysis suggests that the microstructure of bamboo cellulose differs significantly from that of palm cellulose: the surface of bamboo fiber is relatively smooth, lacking the rough structure similar to palm cellulose, resulting in insufficient physical anchoring strength of PEI and decreased cycle stability; simultaneously, bamboo cellulose has lower density, leading to slightly poorer uniformity during hard template filling, and reduced mesoporous order after carbonization, affecting CO2 diffusion efficiency. Furthermore, although bamboo cellulose also has high crystallinity, its interaction strength with PEI is weaker than that of the rough surface of palm cellulose.

[0073] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0074] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing a carbon dioxide adsorbent, characterized in that, The preparation method includes: Pretreated palm cellulose is obtained by removing hemicellulose and lignin from the fibers of empty palm fruit bunches. The pretreated palm cellulose, nitrogen- and phosphorus-containing dopants, hard template agents and solvents are mixed and dried to obtain the precursor. The precursor is carbonized under a protective atmosphere to obtain a first intermediate; The hard template agent in the first intermediate is removed by using an acid or alkali solution to obtain the second intermediate; The second intermediate is mixed with an activator and activated by heating under a protective atmosphere to prepare the third intermediate; The third intermediate is mixed with an amine-containing compound.

2. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The pretreated palm cellulose is prepared by the following method: cleaning, drying, and crushing the fibers of empty palm fruit bunches, and then treating them successively with alkaline solution and sodium chlorite solution to obtain the pretreated palm cellulose; Further, the alkaline solution comprises an aqueous solution of alkali metal hydroxide with a mass concentration of 0.1%-5%, and even further, the aqueous solution of alkali metal hydroxide comprises an aqueous solution of sodium hydroxide. Preferably, the process of treatment with the alkaline solution is carried out at 60-90°C. Furthermore, the sodium chlorite solution is an aqueous solution of sodium chlorite with a mass concentration of 0.2%-5%, and even further, the treatment process using the sodium chlorite solution is carried out at 60-90°C and at a pH value of 3.0-5.

5.

3. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The mass ratio of the pretreated palm cellulose to the nitrogen- and phosphorus-containing dopant is controlled to be 5-20:1; and / or the nitrogen- and phosphorus-containing dopant is one or more of ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

4. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The feeding mass ratio of the pretreated palm cellulose to the hard template agent is controlled to be 1:1-5; and / or, the particle size of the hard template agent is 5-50 nm; and / or, the hard template agent is one or more of the following: solid silica nanospheres, mesoporous silica, and molecular sieves.

5. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The solvent is a mixed aqueous solution of alkaline hydroxide and urea; further, the alkaline hydroxide comprises sodium hydroxide; even further, by mass percentage, the mass concentration of the alkaline hydroxide in the mixed aqueous solution is 5%-10%, and the mass concentration of the urea is 10%-15%; and / or, During the preparation of the precursor, the mixing and homogenization process is carried out at -10 to -15°C; and / or, In the process of preparing the precursor, the drying is freeze drying. Further, the freeze drying includes a pre-freezing stage and a vacuum sublimation stage. The temperature of the pre-freezing stage is -40℃ to -60℃, and the pre-freezing time is 2 to 6 hours. The temperature of the vacuum sublimation stage is -40℃ to -60℃, the vacuum degree is 0.1 to 10 Pa, and the drying time is 24 to 48 hours.

6. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The carbonization is carried out at 600-1000°C; and / or, The heating rate for carbonization is 1-10 °C / min, more specifically 3-7 °C / min; and / or, In the preparation of the second intermediate, the alkaline solution used is a 0.5-3 mol / L sodium hydroxide aqueous solution, and the removal of the hard template agent is carried out at 60-90°C.

7. The method for preparing the carbon dioxide adsorbent according to claim 1, characterized in that, The activator comprises one or more combinations selected from potassium hydroxide, sodium hydroxide, zinc chloride, phosphoric acid, and carbon dioxide; and / or, The mass ratio of the activator to the second intermediate is controlled to be 1-5:1; and / or, The heating activation process is carried out at 600-900°C; and / or, The heating activation rate is 1-10 °C / min, more specifically 3-7 °C / min; and / or, In the preparation of the third intermediate, after the heating activation, the product is washed until neutral. And / or, The amine-containing compound is selected from one or more combinations of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, urea, and cyanamide; and / or, The third intermediate is impregnated in a solution containing an amine compound by means of impregnation, stirred and mixed, washed and dried to prepare the carbon dioxide adsorbent.

8. A carbon dioxide adsorbent prepared by the method of preparing the carbon dioxide adsorbent according to any one of claims 1-7.

9. The carbon dioxide adsorbent according to claim 8, characterized in that, The carbon dioxide adsorbent comprises first-order pores with a pore size of 2-10 nm and second-order pores with a pore size of less than 2 nm; and / or, the specific surface area of ​​the carbon dioxide adsorbent is 1200-2000 m². 2 / g; and / or, the pore volume of the carbon dioxide adsorbent is 0.7-2.6 cm³. 3 / g.

10. The application of the carbon dioxide adsorbent of claim 9 in a carbon dioxide adsorption device.

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