Nitrogen-doped porous carbon material as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped porous carbon material which is prepared by taking a nitrogen-containing compound as a nitrogen source and EDTA (Ethylene Diamine Tetraacetic Acid) metal salt as an activating agent and a carbon source through pyrolysis. Through the synergistic effect of the nitrogen source and the EDTA metal salt, carbon skeleton construction, nitrogen atom in-situ doping and pore self-activation are synchronously achieved, the problems that an existing nitrogen-doped porous carbon preparation process is complex, and adsorption performance and selectivity are difficult to consider at the same time are solved, the material can be efficiently used for CO2 capture in industrial flue gas and other scenes, and the application prospect is wide. The method has a wide industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of gas adsorption and separation materials technology, specifically to a nitrogen-doped porous carbon material, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization and the massive consumption of fossil fuels, global carbon dioxide (CO2) emissions have continued to climb. Currently, CO2 accounts for more than 70% of global greenhouse gases and is the core cause of global warming. To reduce carbon emissions, carbon capture, utilization, and storage (CCUS) technologies have become a research hotspot. CO2 capture, as the primary step, directly determines the industrial feasibility of the technology system based on its efficiency and cost. The industrial sector is the main source of CO2 emissions, with coal-fired power plants and petrochemical plants accounting for 33%-40% of global anthropogenic carbon emissions. Given that the energy structure will remain dominated by fossil fuels for decades to come, the demand for efficient and low-cost CO2 capture technologies is extremely urgent.

[0003] Currently, the mainstream CO2 capture technologies include membrane separation, absorption, cryogenic separation, and adsorption. These technologies differ significantly based on different separation principles: (1) Membrane separation utilizes the difference in permeability of gas molecules to achieve separation, which has the advantages of high efficiency and low energy consumption. However, it is difficult to balance permeability and selectivity, and its thermal stability and anti-plasticity are insufficient. The preparation process of inorganic membranes and composite membranes is complex, the interface compatibility is poor, and the cost of large-scale application is high. The core reason is that the molecular structure design of the membrane material is not matched with the separation mechanism; (2) Absorption is based on the solubility or chemical reaction of gas in liquid to achieve capture. Chemical absorption (such as the amine method) has strong absorption capacity, but the absorbent is highly corrosive, has high regeneration energy consumption, and is easily volatilized and degraded. Physical absorption is suitable for high-temperature and high-temperature environments. The pressure condition is low but the separation purity is low; the low temperature separation method uses the boiling point difference to separate, which is suitable for high concentration CO2 tail gas, but requires extremely low temperature and high pressure, and the energy consumption and equipment cost are high, so it is only suitable for large-scale scenarios; (3) the adsorption method is based on the interaction between solid adsorbent and CO2 molecules to achieve separation. It has the advantages of low energy consumption, simple operation and recyclable adsorbent, and is the most promising technology. Commonly used adsorbents include porous carbon materials, zeolite molecular sieves, MOFs, COFs, etc. Among them, porous carbon materials have become the core research direction because of the wide range of raw materials, low cost and strong stability. The adsorption performance can be improved by doping with nitrogen, sulfur and other heteroatoms. Nitrogen doping can adjust the surface acidity and alkalinity and increase the active sites, making it the most effective modification method.

[0004] The synthesis methods of nitrogen-doped porous carbon materials are mainly divided into two categories: in-situ doping and post-treatment doping. In-situ doping is prepared directly by pyrolysis of nitrogen-containing carbon sources, which is simple to operate and produces uniform nitrogen distribution, but the nitrogen content and pore structure are difficult to control precisely. Post-treatment doping introduces nitrogen functional groups by chemically modifying the prepared porous carbon, which is highly flexible, but the steps are cumbersome, the nitrogen doping efficiency is low, and it is easy to damage the original pore structure. Therefore, developing nitrogen-doped porous carbon materials with simple preparation processes, low energy consumption, and excellent adsorption performance has become the key to solving the bottleneck of CO2 capture technology. Summary of the Invention

[0005] This invention aims to provide a nitrogen-doped porous carbon material, its preparation method, and its application. Through the synergistic effect of nitrogen source and EDTA metal salt, carbon framework construction, in-situ nitrogen atom doping, and pore self-activation are achieved simultaneously, solving the problems of complex preparation process and difficulty in balancing adsorption performance and selectivity in existing nitrogen-doped porous carbon materials.

[0006] To achieve the above objectives, this application provides the following technical solution: The first aspect of this invention provides a nitrogen-doped porous carbon material, which is prepared by pyrolysis using a nitrogen-containing compound as the nitrogen source and EDTA metal salt as the activator and carbon source.

[0007] Optimally, the nitrogen source is selected from at least one of melamine, cyanamide, melamine-formaldehyde resin, and polyacrylonitrile; the EDTA metal salt is selected from at least one of EDTA dipotassium salt, EDTA disodium salt, and EDTA diammonium salt.

[0008] Ideally, the nitrogen source is melamine, and the EDTA metal salt is EDTA dipotassium salt.

[0009] A second aspect of this invention provides a method for preparing nitrogen-doped porous carbon materials, comprising the following steps: S1. Mix the nitrogen source and EDTA metal salt at a mass ratio of 1:1 to 10, and grind them into a uniform powder. S2. Place the obtained mixture in an inert atmosphere and heat it to 700-900℃ at a heating rate of 2-5℃ / min, and keep it at that temperature for 1-3 hours to carry out the pyrolysis self-activation reaction. S3. After cooling the product obtained in S2 to room temperature, wash it several times and then dry it under vacuum to obtain nitrogen-doped porous carbon material.

[0010] Ideally, in step S1, the nitrogen source and EDTA metal salt are mixed at a mass ratio of 1:1 to 5 and heated to 800°C.

[0011] Ideally, in step S1, the nitrogen source and EDTA metal salt are mixed at a mass ratio of 1:5.

[0012] The third aspect of this invention provides an application of nitrogen-doped porous carbon materials in CO2 adsorption.

[0013] Working principle and beneficial effects of the present invention: Using nitrogen-containing compounds (such as melamine) as a nitrogen source, nitrogen-containing reactive species (such as NH3 and CN) are easily decomposed during pyrolysis. - EDTA metal salts (such as dipotassium EDTA) can be uniformly incorporated into the carbon framework. EDTA metal salt molecules contain abundant carbon chain structures, which can form a carbon framework upon pyrolysis. Simultaneously, the metal ions they contain (such as K+) can also be incorporated into the carbon framework. + During pyrolysis, a reduction reaction occurs, and the generated elemental metals or oxides can act as self-activating agents to etch the carbon skeleton, forming a rich microporous and mesoporous structure.

[0014] Compared with traditional methods, this invention does not require the addition of an activator. The EDTA metal salt simultaneously serves as both a carbon source and an activator, avoiding environmental problems and increased costs caused by excessive activator. At the same time, the etching effect of metal ions and the doping process of nitrogen source are carried out simultaneously, ensuring that nitrogen atoms are evenly distributed on the pore surface to form active adsorption sites. Attached Figure Description

[0015] Figure 1 This is a flowchart of the preparation process for EDTA-X series materials; Figure 2 The CO2 adsorption isotherm of EDTA-X at 273.15 K is shown. Figure 3 The synthetic route for Example 2; Figure 4 SEM image of nitrogen-doped adsorbent; Figure 5 X-ray diffraction pattern; Figure 6 The Raman spectrum of QC-(x:y)-z; Figure 7 XPS spectral investigation of QC-(x:y)-z sample; Figure 8 The C1s spectrum of the QC-(x:y)-z sample; Figure 9 The N1s spectrum of the QC-(x:y)-z sample; Figure 10 The N2 adsorption / desorption isotherm of the QC-(x:y)-z sample at 77 K; Figure 11 The NLDFT pore size distribution of the C-(x:y)-z sample; Figure 12The CO2 adsorption isotherm for the QC-(x:y)-z sample; Figure 13 These are adsorption isotherms for CO2 and N2. Figure 14 The adsorption breakthrough curve for QC-(1:5)-800; Figure 15 The isothermal adsorption heat curve of CO2; Figure 16 The graph shows the cycling stability of QC-(1:5)-800 against CO2 at 298.15 K. Detailed Implementation

[0016] The following detailed description illustrates the specific implementation method: Example 1: Preparation and Performance Testing of EDTA-X Series Materials Raw material preparation: melamine (99% purity), ethylenediaminetetraacetic acid dipotassium dihydrate (EDTA-2K, 99% purity), nitrogen (99.5% purity); Material preparation: such as Figure 1 As shown, 5.0g of melamine and 5.0g of EDTA-2K were mixed, ground into a uniform powder, placed in a quartz boat, and transferred to a nitrogen gas flow rate of 100mL. min -1 In a tubular furnace, at 2°C min -1 The temperature was raised to 700℃, 800℃ and 900℃ respectively, and held for 2 hours. After cooling, the materials were washed with distilled water until the washing solution was neutral, and then vacuum dried at 80℃ for 12 hours to obtain three materials: EDTA-700, EDTA-800 and EDTA-900. Performance testing: by Figure 2 It can be seen that EDTA-800 exhibits the highest CO2 adsorption capacity, reaching 2.80 mmol, under the conditions of 273.15 K and 1 bar. g -1 The optimal carbonization temperature was determined to be 800℃.

[0017] Example 2: Preparation and performance testing of QC-(x:y)-z series materials (x:y represents the mass ratio of melamine and EDTA-2K, and z represents the carbonization temperature).

[0018] Raw material preparation: Same as in Example 1; Material preparation: such as Figure 3 As shown, melamine and EDTA-2K were mixed at mass ratios of 1:0, 1:1, 1:3, and 1:5, ground evenly, and then placed in a quartz boat under nitrogen gas at a flow rate of 100 mL / min. min -1 In a tubular furnace, at 2°C min -1 The temperature was increased to 800℃ at a heating rate and held for 2 h. After cooling, the materials were washed and dried to obtain four materials: QC-(1:0)-700 (blank control group), QC-(1:1)-800, QC-(1:3)-800 and QC-(1:5)-800.

[0019] Performance testing: (1) Material properties: like Figure 4 As shown in the figure, SEM observation shows that after adding the activator EDTA-2K, the surface pore structure of the material is richer, and the surface of QC-(1:1)-800 is uniformly dense. like Figure 5 As shown, XRD confirmed that QC-(1:1)-800, QC-(1:3)-800, and QC-(1:5)-800 have graphitic carbon and amorphous carbon characteristics, and nitrogen doping destroys the graphitized structure. like Figure 6 As shown, Raman spectra reveal that the ID / IG values ​​of the three are similar (0.85-0.86), indicating a consistent degree of disorder. like Figure 7 , Figure 8 and Figure 9 As shown, XPS indicates that the material contains C, N, and O elements, with nitrogen existing in the form of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. Furthermore, the abundance of pyrrole nitrogen increases when the mass ratio of melamine to EDTA-2K increases, thereby enhancing the CO2 adsorption capacity.

[0020] (2) Pore structure: such as Figure 10 As shown, the N2 adsorption-desorption isotherms of all materials are type I, containing H4 hysteresis loops, and possessing both abundant micropores and a certain degree of mesopores; the adsorption of N2 also significantly increases with the increase of activator EDTA-2K, indicating that these porous carbons have abundant microporous structures.

[0021] like Figure 11 As shown in Table 1, with the increase of activator EDTA-2K, the pore size of the material increases, the distribution becomes wider, and the specific surface area (S) increases. BET ), total pore volume (V Total ) and micropore volume (V Micro Significant improvement, QC-(1:5)-800 S BET Reaching 2435.9 m 2 g -1 Furthermore, all materials contain ultramicroporous structures centered at 0.50 nm.

[0022] Table 1 - Pore structure characteristics of porous carbon prepared under different activator dosages

[0023] a Brunauer-Emmett-Teller ( BET Specific surface area, b Total pore volume, c Micropore volume, d Average aperture.

[0024] (3) CO2 adsorption performance: Combined with Table 2 and Table 3, Figure 12 It can be seen that at 273.15 K and 1 bar, QC-(1:5)-800 has the highest adsorption capacity (5.15 mmol). g -1 The adsorption capacity gradually decreased with increasing temperature (from 273.15K to 328.15K), indicating that physical adsorption was the main process. The CO2 adsorption capacity of the material was positively correlated with the specific surface area and micropore volume.

[0025] Table 2. CO2 adsorption capacity (1 bar) of QC-(x:y)-z samples at various temperatures.

[0026] Table 3 - Comparison of carbon dioxide adsorption capacity of different adsorbents (1 bar, 273.15 K)

[0027] The references [1] to [8] are as follows: [1]J Shi, N Yan, H Cui, et al. Nitrogen doped hierarchically porouscarbon derived from glucosamine hydrochloride for CO2adsorption[J]. Journal of CO2Utilization, 2017, 21: 444-449. [2]J Xu, J Shi, H Cui, et al. Preparation of nitrogen doped carbon from tree leaves as efficient CO2adsorbent[J]. Chemical Physics Letters, 2018, 711: 107-112. [3]H Cui, J Xu, J Shi, et al. Facile fabrication of nitrogen dopedcarbon from filter paper for CO2adsorption[J]. Energy, 2019, 187: 115936-115936. [4]Z Yang, X Guo, G Zhang, et al. One-pot synthesis of high N-dopedporous carbons derived from a N-rich oil palm biomass residue in lowtemperature for CO2capture[J]. International Journal of Energy Research,2020, 44: 4875-4887. [5]S Shuo, L Yangxian. Nitrogen-doped activated carbons derived frommicroalgae pyrolysis by-products by microwave / KOH activation forCO2adsorption[J]. Fuel, 2021, 306. [6]Y Chunliang, Z Tianxiang, P Hongyan, et al. Facile preparation ofN-doped porous carbon from chitosan and NaNH2for CO2adsorption and conversion[J]. Chemical Engineering Journal, 2022, 432. [7]T Duanlian, L Xiaoying, H Zhixian, et al. Nitrogen-dopedmicroporous carbons as highly efficient adsorbents for CO2and Hg(II) capture[J]. Powder Technology, 2023, 427. [8]W Wu, C Wu, J Liu, et al. Nitrogen-doped porous carbon throughK2CO3-activated bamboo shoot shell for an efficient CO2adsorption[J]. Fuel, 2024, 363: 130937-. (4) CO2 adsorption selectivity: (Refer to Table 4) Figure 13 (a) and (b) CO2 and N2 adsorption isotherms of QC-(x:y)-z sample at 298.15 K, (c) IAST selectivity) The adsorption capacity of the material for CO2 is significantly higher than that for N2. The CO2 / N2 (15:85) IAST selectivity of QC-(1:5)-800 reaches 45. Figure 14 The penetration experiment confirmed that it preferentially adsorbs CO2.

[0028] Table 4. Comparison of adsorption and separation performance of different nitrogen-doped adsorbents (1 bar, 298.15 K)

[0029] (5) Adsorption heat and recycling: such as Figure 15 and Figure 16 As shown, the heat of CO2 adsorption of the material is 18-28 kJ. mol -1 It is a physical adsorption process with low regeneration energy consumption; after 5 adsorption-desorption cycles, QC-(1:5)-800 still achieves a CO2 adsorption capacity of 2.80 mmol. g -1 It has a capacity retention rate of approximately 95% and good cycle stability.

[0030] In summary, this application systematically compares it with several reported porous carbon materials and inorganic adsorbents. Regarding CO2 adsorption capacity, QC-(1:5)-800 exhibits 5.2 mmol·g⁻¹ at 273.15 K and 1 bar. -1 Its high adsorption capacity is significantly superior to most reported carbon-based adsorbents. For example, the adsorption capacity of N / O / S triple-doped porous carbon is only about 3.0 mmol·g. -1 [9] The oxygen and nitrogen enrichment of pectin-derived porous carbon was only ~3.1 mmol·g. -1

[10] , while the adsorption capacity of general nitrogen-doped carbon materials is usually less than 3.0 mmol·g due to insufficient microporous structure. -1

[11] . Furthermore, even the structurally regular carbonized PAF-1 tested at lower temperatures had a CO2 adsorption capacity of approximately 4.5 mmol·g. -1

[12] , still not as good as the materials in this application.

[0031] [9] to

[12] References are as follows: [9] Tian Z, Lai F, Heil T, et al. Synthesis of carbon frameworks withN, O and S-lined pores from gallic acid and thiourea for superiorCO2adsorption and supercapacitors[J]. Science China Materials, 2020, 63(5):748-757.

[10] Vafaeinia M, Khosrowshahi M S, Mashhadimoslem H, et al. Oxygenand nitrogen enriched pectin-derived micro-meso porous carbon for CO2uptake[J]. RSC advances, 2022, 12(1): 546-560.

[11] Zheng L, Li W B, Chen J L. Nitrogen doped hierarchical activatedcarbons derived from polyacrylonitrile fibers for CO2adsorption andsupercapacitor electrodes[J]. RSC advances, 2018, 8(52): 29767-29774.

[12] Wang J, Huang L, Yang R, et al. Recent advances in solidsorbents for CO2capture and new development trends[J]. Energy&EnvironmentalScience, 2014, 7(11): 3478-3518. In terms of separation performance, the QC-(1:5)-800 material of this application exhibits a CO2 / N2 selectivity as high as 45, demonstrating excellent gas separation capability. In contrast, most porous carbon materials reported in the literature, although varying in adsorption capacity, generally have lower CO2 / N2 selectivity, with only a few materials (such as triple-doped porous carbon) achieving similar selectivity levels. However, these materials often suffer from insufficient adsorption capacity, making it difficult to simultaneously achieve both high capacity and high selectivity.

[0032] In summary, the QC-(1:5)-800 prepared in this study demonstrates outstanding performance in terms of microporous structure optimization, nitrogen content regulation, and synergistic improvement of adsorption capacity and selectivity. Its overall performance is significantly better than that of many previously reported adsorbents, showing potential advantages in practical CO2 capture and separation applications.

[0033] It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of this invention. These modifications and improvements should also be considered within the scope of protection of this invention, and will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A nitrogen-doped porous carbon material, characterized in that, It is prepared by pyrolysis using nitrogen-containing compounds as nitrogen source and EDTA metal salt as activator and carbon source.

2. The doped porous carbon material according to claim 1, characterized in that, The nitrogen source is selected from at least one of melamine, cyanamide, melamine-formaldehyde resin, and polyacrylonitrile; the EDTA metal salt is selected from at least one of EDTA dipotassium salt, EDTA disodium salt, and EDTA diammonium salt.

3. The doped porous carbon material according to claim 2, characterized in that, The nitrogen source is melamine, and the EDTA metal salt is EDTA dipotassium salt.

4. A method for preparing nitrogen-doped porous carbon material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Mix the nitrogen source and EDTA metal salt at a mass ratio of 1:1 to 10, and grind them into a uniform powder. S2. Place the obtained mixture in an inert atmosphere and heat it to 700-900℃ at a heating rate of 2-5℃ / min, and keep it at that temperature for 1-3 hours to carry out the pyrolysis self-activation reaction. S3. After cooling the product obtained in S2 to room temperature, wash it several times and then dry it under vacuum to obtain nitrogen-doped porous carbon material.

5. The preparation method according to claim 4, characterized in that, In step S1, the nitrogen source and EDTA metal salt are mixed at a mass ratio of 1:1 to 5 and heated to 800°C.

6. The preparation method according to claim 5, characterized in that, In step S1, the nitrogen source and EDTA metal salt are mixed at a mass ratio of 1:

5.

7. The application of a nitrogen-doped porous carbon material as described in any one of claims 1 to 3 in the adsorption of CO2.

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