Application of polar carbon adsorbent in enhanced CO2 capture in the presence of water vapor

Abstract

The application discloses application of a polar carbon adsorbent in enhanced CO2 capture in the presence of water vapor, wherein the polar carbon adsorbent has a nitrogen atom content of 5-15 at.%, an oxygen atom content of 5-15 at.%, and a micropore aperture distribution concentrated in 0.3-0.7 nm; the polar carbon adsorbent is obtained by taking a nitrogen-containing organic coordination polymer as a carbon source and performing carbonization and drying. In a dynamic breakthrough test at 25 DEG C, with 75% RH and 3000 ppm CO2 as a humid raw material gas, compared with a dry state, the CO2 breakthrough time of the adsorbent in a humid atmosphere is prolonged by 70%, the CO2 diffusion rate is obviously increased, the mass transfer zone is reduced, and regeneration is simple. Finally, the polar carbon adsorbent realizes efficient removal of low-concentration CO2 without pre-removal of water vapor in the raw material gas in a humid atmosphere, even with a promoting effect of water vapor, and long-term stable cyclic capture.

Description

Technical Field

[0001] This invention belongs to the field of CO2 capture technology and relates to the application of polar carbon adsorbents in enhanced CO2 capture in the presence of water vapor. Background Technology

[0002] Low-concentration CO2 capture and removal is an urgent area of ​​development in the chemical and environmental fields. Its main applications include direct airborne carbon capture and enclosed spaces used by humans. These environments are characterized by low CO2 concentrations and high humidity, placing more stringent requirements on the moisture resistance, cycle stability, and regeneration energy consumption of the capture materials.

[0003] Compared with methods for removing low-concentration CO2 through chemical reactions, physical adsorption removal technology has advantages such as reusable capture materials and simple equipment and process flow. Currently, physical adsorbents suitable for CO2 adsorption at low concentrations mainly include zeolite molecular sieves, metal-organic frameworks (MOFs), and porous carbon materials. Although molecular sieves and MOFs exhibit high CO2 adsorption capacity, their water resistance is poor, requiring pre-dehydration in environments with water vapor before CO2 adsorption and removal (Chem.Rev.,2021,121(13):7280-7345.). At the same time, the high activation and regeneration temperature (200-300℃) also reduces the economic efficiency of the process. Porous carbon materials have advantages such as wide availability, high specific surface area, tunable pore structure and surface chemistry, and excellent water vapor stability, and are often used for CO2 capture in different scenarios (Adv.Funct.Mater.,2020,30(17):1909265.). Common microporous carbon can be used for adsorption and capture of CO2 at high partial pressures, such as in flue gas (J. Am. Chem. Soc. 2011, 133, 11378–11388.). However, due to the low affinity of the inert surface of carbon materials for CO2, the selective adsorption effect for low-concentration CO2 is not good. Therefore, amine compounds with chemisorption properties for CO2 are usually loaded to improve the removal effect of low-concentration CO2. However, this sacrifices the advantages of easy regeneration and strong cycle stability of physical adsorption (Chem. Eng. J., 2022, 437: 135378.). In summary, the common problem is that the separation performance of adsorbents is low or even disappears under real working conditions containing water vapor; even porous carbon materials with relatively good water vapor stability will still weaken or even disappear after adsorbing water vapor during long-term cycle capture. Developing adsorbents that are not affected by water vapor, or even have enhanced capture performance in the presence of water vapor, will open up a completely new technical route for the capture and removal of low-concentration CO2. Summary of the Invention

[0004] To address the problems of poor stability of CO2 adsorbents in the presence of water vapor, severe performance degradation under water vapor conditions, and stringent activation and regeneration conditions, this invention aims to provide an application of polar carbon adsorbents in enhanced CO2 capture in the presence of water vapor. To achieve the above-mentioned objective, the technical solution adopted by this invention is as follows:

[0005] An application of a polar carbon adsorbent in enhanced CO2 capture in the presence of water vapor, wherein the polar carbon adsorbent has a nitrogen atom content ranging from 5-15 at.%, an oxygen atom content ranging from 5-15 at.%, and a micropore size concentrated in the range of 0.30-0.70 nm.

[0006] It is suitable for use in humid conditions with a humidity of 10-80%RH.

[0007] The preparation method of the polar carbon adsorbent includes using a nitrogen-containing organic coordination polymer as a carbon source, carbonizing it at 400-800℃ and drying it; the polymer is a nitrogen-containing Schiff base polymer or a nitrogen-containing polyacrylonitrile polymer.

[0008] The method for preparing the nitrogen-containing Schiff base polymer includes dissolving a nitrogen-source amine ligand in a solvent, adding an aqueous formaldehyde solution, mixing thoroughly and uniformly, pouring the mixture into a reactor for a coordination reaction, and obtaining the nitrogen-containing Schiff base polymer by centrifugation and drying. The nitrogen-source amine ligand includes one or more of hexamethylenediamine, aniline, p-phenylenediamine, and o-phenylenediamine. The solvent includes one or more of water, ethanol, methanol, and dimethylformamide. The molar ratio of nitrogen-source amine ligand:solvent:formaldehyde is (0.5-5):(1-3):(1-10).

[0009] The method for preparing the nitrogen-containing polyacrylonitrile polymer includes uniformly mixing a nitrogen-source nitrile ligand with a solvent, adding an azobisisobutyronitrile initiator, mixing thoroughly, pouring into a reactor for coordination reaction, and obtaining the nitrogen-containing polyacrylonitrile polymer by centrifugation and drying; the nitrogen-source nitrile ligand includes one or more of acrylonitrile, ethylene acetonitrile, and styrene acrylonitrile; the solvent includes one or more of water, ethanol, methanol, acetone, acetonitrile, and tetrahydrofuran; the molar ratio of nitrogen-source nitrile ligand:solvent:initiator is (0.5-5):(1-2):(1-10).

[0010] The coordination reaction temperature is 10-100℃, and the coordination reaction time is 1-40h.

[0011] The drying temperature is 0-150℃, and the drying time is 2-96h.

[0012] The carbonization process is carried out at room temperature for 0.5-5℃ min. -1 Heat to 50-150℃ and hold for 0.5-4 hours, then pass through a 1-10℃ filter for 1 minute. -1Heat to 400-800℃ and hold for 0.5-4 hours.

[0013] It is used for the adsorption and capture of low concentrations of CO2 in enclosed spaces.

[0014] The adsorption temperature is 0-50℃, and the adsorption pressure is 1-8 bar; the volume ratio of CO2 to N2 treated by the polar carbon adsorbent is (0.04-3):(99.96-97).

[0015] CO2 adsorption is a fixed-bed process, and the adsorbent is activated before adsorption.

[0016] The components of the exhaust gas after adsorption are detected by mass spectrometry. When the concentrations of N2 and CO2 reach 0.5% of the saturation concentration, it is considered as breakthrough.

[0017] The regeneration method for the carbonaceous adsorbent includes the following steps: After adsorption is completed, the adsorbent is purged and regenerated for 0.5-5 hours under normal pressure (1 bar) at 20-50℃ using an inert gas (such as Ar or N2), or under vacuum conditions at 20-50℃ with an absolute pressure equal to or lower than 0.05 bar for 0.5-5 hours to completely restore the adsorption and capture performance of low-concentration CO2, and then dynamic breakthrough adsorption is performed.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The carbonaceous adsorbent prepared in this invention alters the microporous structure of the final adsorbent by controlling the synthesis raw materials, synthesis conditions, and carbonization temperature of the nitrogen-containing organic coordination polymer precursor. This results in a highly polar chemical surface with slit-type micropores predominantly 0.3-0.7 nm and abundant N and O heteroatom doping. Unlike non-polar carbonaceous adsorbents, its polar carbon layer surface and pores exhibit strong adsorption of CO2 gas molecules, thereby achieving CO2 adsorption and capture at low concentrations.

[0020] 2. The carbonaceous adsorbent of this invention can simultaneously achieve highly efficient low-concentration CO2 capture and high water vapor stability. This physical adsorbent achieves highly efficient CO2 capture through van der Waals forces and pore size control, with a capture efficiency exceeding 99%. Simultaneously, its strong water vapor stability ensures that the material maintains good adsorption performance even under 75% RH humidity conditions, and significantly increases the CO2 diffusion rate and reduces the mass transfer zone, greatly improving the material's service life and the stable operation time of the device.

[0021] 3. The carbonaceous adsorbent of this invention, when simulated under real-world conditions and operating for an extended period in a hydrated state, exhibits a unique behavior of prolonged breakthrough time, i.e., water vapor promotes CO2 adsorption. This invention represents the first discovery of this unique phenomenon of water vapor promoting low-concentration CO2, which is of great significance for CO2 capture under practical conditions.

[0022] 4. The carbonaceous adsorbent of this invention can fully restore its low-concentration CO2 adsorption and capture performance by purging and regenerating it for 0.5-5 hours with an inert gas (such as Ar or N2) at atmospheric pressure (1 bar) at 20-50°C, or by regenerating it for 0.5-5 hours under vacuum conditions at an absolute pressure equal to or lower than 0.05 bar at 20-50°C. Simultaneously, the material does not require pretreatment of water vapor before the adsorption bed or high-temperature dehydration during regeneration, further reducing operating energy consumption, simplifying the process, and reducing equipment complexity. Attached Figure Description

[0023] Figure 1 The H2O adsorption isotherm of the adsorbent in Example 1 is shown.

[0024] Figure 2 The adsorbent of Example 1 and its N2 adsorption isotherm after being saturated with water vapor in a humid Ar atmosphere of 75% RH are shown.

[0025] Figure 3 The image shows the pore size distribution of Example 1 and Example 1 after being saturated with water vapor adsorbed in a humid Ar atmosphere at 75% RH.

[0026] Figure 4 For Example 1, the adsorbent was tested at 25°C, 1 bar, CO2 / N2 (0.3:99.7), and a total flow rate of 10 mL / min. -1 Breakthrough test curves under the following conditions: fresh adsorbent in a dry atmosphere; fresh adsorbent in a humid atmosphere of 75% RH, followed by regeneration in a humid atmosphere of 75% RH. Figure 5 The figures show the concentration change curves of the adsorbent in Example 1 under regeneration cycle breakthrough test in a humid atmosphere of 75% RH and rapid desorption of CO2 released under Ar purging at 25°C and 20 ml / min. Figure 6 The image shows the weight change curve of the adsorbent in Example 1 after a penetration test in a humid atmosphere of 75% RH, during which it rapidly desorbs and releases CO2 at 25°C and 0.05 bar.

[0027] Figure 7 The graph shows the CO2 adsorption diffusion rate of Example 1 after the adsorbent in Example 1 is saturated with water vapor in a humid Ar atmosphere of 75% RH. Specific Implementation

[0028] The present invention will be described in detail below through some representative examples. It should be understood that the following examples are merely illustrative and should not be construed as limiting the protection of this invention. Any technical solutions implemented based on the content described in this invention should be covered within the protection scope of this invention.

[0029] ① Moisture promotes the synthesis of carbonaceous adsorbents for low-concentration CO2 adsorption:

[0030] Nitrogen-based amine ligands were dissolved in a solvent, and formaldehyde aqueous solution was added. After thorough mixing, the mixture was poured into a reactor for a coordination reaction for 12 hours. The resulting product was then centrifuged and dried at 80°C for 12 hours to obtain a nitrogen-containing Schiff base polymer. The nitrogen-containing Schiff base polymer was then subjected to high-temperature carbonization under inert gases (Ar, N2, etc.). The carbonization process involved passing the polymer at room temperature through a process at 2°C for 1 minute. -1 Heat to 80℃ and hold for 1 hour, then pass through a 5℃ filter for 5 minutes. -1 The carbon adsorbent was heated to the carbonization temperature and held for 4 hours, followed by drying at 80°C for 12 hours to obtain a polar carbon adsorbent. The nitrogen source amine ligand included one or more of hexamethylenediamine, aniline, p-phenylenediamine, or o-phenylenediamine. The solvent included one or more of water, ethanol, methanol, or dimethylformamide. The specific experimental conditions in each example are shown in Table 1.

[0031] Nitrogen-based nitrile ligands were uniformly mixed with a solvent, and azobisisobutyronitrile (AIBN) initiator was added. After thorough mixing, the solution was poured into a reactor for a coordination reaction for 12 hours. Following centrifugation and drying at 80°C for 12 hours, a nitrogen-containing polyacrylonitrile polymer was obtained. This nitrogen-containing polyacrylonitrile polymer was then subjected to high-temperature carbonization under inert gases (Ar, N2, etc.). The carbonization process involved passing the carbon at room temperature through a process at 2°C for 1 minute. -1 Heat to 80℃ and hold for 1 hour, then pass through a 5℃ filter for 5 minutes. -1 The carbon adsorbent was heated to the carbonization temperature and held for 4 hours, followed by drying at 80°C for 12 hours to obtain a polar carbon adsorbent. The nitrogen source nitrile ligands included one or more of acrylonitrile, ethylene acetonitrile, and styrene nitrile; the solvents included one or more of water, ethanol, methanol, acetone, acetonitrile, and tetrahydrofuran. Specific experimental conditions for each example are shown in Table 2.

[0032] ② Adsorbent adsorption performance test

[0033] Breakthrough test: The adsorbent, activated for 5 hours under vacuum conditions at 200℃ and an absolute pressure below 0.01 bar, was filled into the adsorption column, and CO volume fraction was increased. 2: A mixture of N2 (0.3 / 99.7, CO2 3000 ppm) was introduced into the adsorption column. The adsorption column size was 100 mm * 80 mm. A gas chromatograph-mass spectrometer was connected to the end of the adsorption column to detect the composition of the gas passing through the adsorption column, and finally the adsorption capacity and separation time were calculated. After adsorbing low concentrations of CO2, the adsorbent was regenerated by purging with Ar at 20 ml / min for 40 min at atmospheric pressure (1 bar) at 25 °C for 10 min, or by regenerating under vacuum conditions of 0.05 bar at 25 °C for 10 min, which desorbed all CO2 and restored the adsorption performance. Specific test results are as follows. Figure 4 , Figure 5 and Figure 6 As shown.

[0034] ③ Static isotherm and pore size distribution test of adsorbent

[0035] Weigh 50±2 mg of adsorbent and place it into a sample tube of a VSTAR gas adsorption analyzer (vapor adsorption capacity method). Activate and degas at 200℃ for 5 h. Place the sample tube in a constant temperature water bath or thermal insulation jacket. Introduce high-purity CO2, N2, or H2O gas into the sample tube and measure the gas adsorption amount under different equilibrium pressures. Obtain the adsorption isotherm and pore size distribution. Figure 1 , 2 As shown in Figure 3. Specific aperture test results are shown in Table 1 or Table 2.

[0036] ④ CO2 diffusion rate test of adsorbent

[0037] 50±2 mg of adsorbent was weighed and placed into a sample tube of the IGA (Intelligent Gas Quality Analyzer). The tube was activated and degassed at 200℃ for 5 hours. The sample tube was then placed in a constant temperature water bath or in an insulated jacket, and CO2 gas was introduced into the tube. The amount of gas adsorbed at different time points was measured to obtain the adsorption rate curve. Specific test results are as follows: Figure 5 As shown.

[0038] Table 1. Preparation conditions and properties of carbon adsorbents using nitrogen-containing Schiff base polymers as carbon sources.

[0039]

[0040] Table 2. Preparation conditions and properties of carbon adsorbents using nitrogen-containing polyacrylonitrile polymers as carbon sources.

[0041]

[0042] Table 3 Adsorption performance of carbonaceous adsorbents in each example

[0043]

[0044] The prepared adsorbents—the activated adsorbent of Example 1 and the adsorbent of Example 1 after adsorbing water vapor in a humid Ar atmosphere of 75% RH—were characterized. Table 4 shows that the adsorbent of Example 1 had nitrogen and oxygen atom contents of 10.3 at.% and 12.6 at.%, respectively, and its forms were mainly pyridine-N and carboxyl groups. Figure 1 It can be seen that the adsorbent in Example 1 has a strong water vapor adsorption capacity, proving that the adsorbent forms a polar carbonaceous surface. Figure 2 It can be seen that the N2 adsorption isotherm after the adsorbent adsorbs water vapor in Example 1 is a Type I isotherm, indicating that the adsorbed water vapor does not occupy the micropores. Figure 3 It can be seen that after adsorbing water vapor, the distribution of micropores at 0.35 nm and 0.50 nm in Example 1 is more abundant and concentrated, which is beneficial to the adsorption of low-pressure CO2. Figure 4It can be seen that under a humid atmosphere, the CO2 breakthrough time of Example 1 is increased by 70% and the breakthrough rate is significantly improved, increasing the utilization rate of the fixed bed and achieving water vapor-promoted adsorption of low-concentration CO2. Furthermore, its performance remains stable after regeneration, demonstrating long-term cyclic operation capability. Figure 5 and Figure 6 It can be seen that the adsorbent has stable performance and can be rapidly regenerated under simple conditions, completely desorbing CO2. From Figure 7 It can be seen that H2O entering the pores increases the overall CO2 diffusion rate, which is beneficial to the rapid adsorption of CO2.

[0045] Table 4 Elemental distribution of the adsorbent in Example 1

[0046]

Claims

1. An application of a polar carbon adsorbent in enhanced CO2 capture in the presence of water vapor, characterized in that: The polar carbon adsorbent has a nitrogen atom content of 5-15 at.%, an oxygen atom content of 5-15 at.%, and a micropore size concentratedly distributed in 0.30-0.70 nm; and the preparation method of the polar carbon adsorbent comprises using a nitrogen-containing organic coordination polymer as a carbon source, and performing carbonization and drying at 400-800 o C to obtain; and the type of the polymer is a nitrogen-containing Schiff base polymer or a nitrogen-containing polyacrylonitrile polymer.

2. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that: It is suitable for humid conditions with a humidity range of 10-90%RH.

3. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that: The method for preparing the nitrogen-containing Schiff base polymer includes dissolving a nitrogen-source amine ligand in a solvent, adding an aqueous formaldehyde solution, mixing thoroughly and uniformly, pouring the mixture into a reactor for a coordination reaction, and obtaining the nitrogen-containing Schiff base polymer by centrifugation and drying. The nitrogen-source amine ligand includes one or more of hexamethylenediamine, aniline, p-phenylenediamine, and o-phenylenediamine. The solvent includes one or more of water, ethanol, methanol, and dimethylformamide. The molar ratio of nitrogen-source amine ligand:solvent:formaldehyde is (0.5-5):(1-3):(1-10).

4. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that: The method for preparing the nitrogen-containing polyacrylonitrile polymer includes uniformly mixing a nitrogen-source nitrile ligand with a solvent, adding an azobisisobutyronitrile initiator, mixing thoroughly, pouring into a reactor for coordination reaction, and obtaining the nitrogen-containing polyacrylonitrile polymer by centrifugation and drying; the nitrogen-source nitrile ligand includes one or more of acrylonitrile, ethylene acetonitrile, and styrene acrylonitrile; the solvent includes one or more of water, ethanol, methanol, acetone, acetonitrile, and tetrahydrofuran; the molar ratio of nitrogen-source nitrile ligand:solvent:initiator is (0.5-5):(1-2):(1-10).

5. The application of a polar carbon adsorbent as described in claim 3 or 4 in enhanced CO2 capture in the presence of water vapor, characterized in that: The coordination reaction temperature is 10-100 ℃, and the coordination reaction time is 1-40 h.

6. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that, It is used for the adsorption and capture of low concentrations of CO2 in confined spaces.

7. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that: Adsorption temperature is 0-50°C o C, adsorption pressure is 1-8 bar; the volume ratio of CO2 and N2 in the treated gas is (0.04-3):(99.96-97).

8. The application of the polar carbon adsorbent as described in claim 1 in enhanced CO2 capture in the presence of water vapor, characterized in that: The regeneration method of the polar carbon adsorbent includes the following steps: regenerating by purging with inert gas for 0.5-5 h at atmospheric pressure at 20-50 ℃ or under vacuum conditions at 20-50 ℃ with an absolute pressure equal to or lower than 0.05 bar for 0.5-5 h.

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