Carbon dioxide adsorbent as well as synthesis method and application thereof

Abstract

The invention discloses a carbon dioxide adsorbent as well as a synthesis method and application thereof. The adsorbent comprises zinc oxide, alkali metal salt, a 13X molecular sieve and a binder component, based on the mass of the adsorbent, the content of the zinc oxide is 10%-60%, the mass content of the alkali metal salt is 5%-50%, the mass content of the 13X molecular sieve is 10%-60%, and the mass content of the binder component is 0.05%-10%. The adsorbent disclosed by the invention can greatly improve the utilization rate of an active center in the process of adsorbing carbon dioxide, and shows relatively high activity, cyclic regeneration performance and stability.

Description

A carbon dioxide adsorbent, its synthesis method and application Technical Field

[0001] This invention relates to the field of carbon emission reduction technology, and specifically to a carbon dioxide adsorption material, its synthesis method, and its application. Background Technology

[0002] Carbon dioxide capture has long been considered a key technology for reducing carbon dioxide emissions from fossil fuel power generation and industrial processes. Compared with traditional solvent absorption processes, solid adsorbent treatment methods have attracted widespread attention due to their low energy consumption, low pollution, and simple processes. Based on their adsorption temperatures, they are classified into three categories: low-temperature, medium-temperature, and high-temperature. Low-temperature adsorbents mainly include zeolite molecular sieves, carbonates, metal-organic frameworks (MOFs), and carbonaceous materials, which can adsorb carbon dioxide at relatively low temperatures (<200℃).

[0003] CN102078796A discloses an absorbent using activated carbon and titanium dioxide as a composite support, with potassium carbonate loaded on the surface of the composite support. This enhances the regeneration performance of the absorbent compared to a single-support type. Sengupta et al. (Surajit Sengupta, Vinay Amte. Energy & Fuel. 2015) synthesized a 50 wt% loaded K2CO3 / Al2O3 adsorbent and compared the effects of single-step and multi-step impregnation methods on the decarbonization performance of the adsorbent. However, the simple impregnation method still limits the loading and dispersion of the active component, affecting the decarbonization performance and cycle stability of the adsorbent. CN109046258A discloses a method for modifying molecular sieves such as ZSM-5 and MCM-41 with organic amines, which exhibits a high adsorption capacity for CO2. However, due to the strong polarity of the molecular sieves, they readily absorb moisture, competing with CO2 molecules for adsorption, and regeneration energy consumption also increases.

[0004] For supported alkali metal salt adsorbents, in actual use, the solid adsorbent mainly undergoes a gas-solid reaction when it comes into contact with CO2-containing flue gas. Generally, they suffer from high mass transfer resistance and low utilization of active centers. Moreover, if the active components of the supported adsorbent are not precisely controlled, it will lead to poor dispersion and large particles, which will also reduce the utilization of active centers. Summary of the Invention

[0005] To address the problems of poor dispersibility of active sites and low utilization rate of gas-solid reactions in existing supported alkali metal adsorbents, this invention provides a carbon dioxide adsorbent, its synthesis method, and its applications. The adsorbent of this invention can significantly improve the utilization rate of active sites during carbon dioxide adsorption, exhibiting high activity, regeneration performance, and stability.

[0006] The first aspect of this invention provides a carbon dioxide adsorbent, comprising: zinc oxide, an alkali metal salt, 13X molecular sieve, and a binder component; based on the mass of the adsorbent, the zinc oxide content is 10% to 60%, preferably 20% to 45%; the alkali metal salt content is 5% to 50%, preferably 10% to 32%; the 13X molecular sieve content is 10% to 60%, preferably 20% to 45%; and the binder component content is 0.05% to 10%, preferably 0.1% to 5%.

[0007] Furthermore, the alkali metal salt is an alkali metal carbonate, selected from one or more of sodium carbonate and potassium carbonate.

[0008] Furthermore, the binder component is derived from a binder selected from one or more of silica sol, alumina sol, kaolin, sepiolite, diatomaceous earth, attapulgite, montmorillonite, and bentonite, preferably one or more of silica sol, kaolin, attapulgite, and bentonite.

[0009] Furthermore, in the adsorbent, the alkali metal salt is introduced into the adsorbent using ZIF-8 doped with a coordination compound as a template. The coordination compound is one or more of crown ethers and ethylenediaminetetraacetic acid, preferably crown ethers, and more preferably 18-crown ether-6.

[0010] Furthermore, the ratio of weak base centers to medium-strong base centers in the adsorbent is (1-10):1, preferably (4-8):1.

[0011] A second aspect of the present invention provides a method for synthesizing a carbon dioxide adsorbent, comprising the following steps:

[0012] (1) Imidazole organic ligands and zinc source are dissolved in alcohol solvents respectively. Then, the solution containing imidazole organic ligands is mixed with the solution containing zinc source. Then, coordination compound is added. After reaction and drying, coordination compound-doped ZIF-8 is obtained.

[0013] (2) The coordination compound-doped ZIF-8 obtained in step (1) is mixed with an alkali metal salt solution, and after coordination reaction, it is dried;

[0014] (3) Mix the material obtained in step (2) and 13X molecular sieve with slurry containing binder, shape and dry to obtain a shaped body;

[0015] (4) Activate the molded body obtained in step (3) to obtain the carbon dioxide adsorbent of the present invention.

[0016] Furthermore, in step (1), before the drying step after the reaction is completed, there may be conventional separation and washing steps.

[0017] Furthermore, in the method for synthesizing the carbon dioxide adsorbent, the imidazole organic ligand in step (1) is one or more of imidazole, 2-methylimidazolium, and benzimidazole, preferably 2-methylimidazolium.

[0018] Furthermore, in step (1), the zinc source is one or more of zinc nitrate, zinc chloride, and zinc sulfate.

[0019] Furthermore, the alcohol solvent in step (1) is one or more of methanol and ethanol.

[0020] Further, in step (1), the molar ratio of zinc source: 2-methylimidazole: alcohol is 1:(20-100):(500-2000).

[0021] Further, in step (1), the coordination compound is one or more of crown ethers and ethylenediaminetetraacetic acid, preferably a crown ether, more preferably 18-crown ether-6. The mass ratio of the coordination compound to the zinc source is 0.001 to 1:1, preferably 0.01 to 1:1.

[0022] Further, the reaction conditions in step (1) are as follows: temperature is 10℃-50℃, and time is 1-30h.

[0023] Further, the drying conditions in step (1) are as follows: the drying temperature is 60℃-200℃, preferably 80℃-140℃; the drying time is 1h-24h, preferably 4h-12h.

[0024] Further, in step (2), the preferred process includes: adding an alkali metal salt solution to the ZIF-8 doped with the coordination compound obtained in step (1) to carry out a coordination reaction, drying, and obtaining the metal-coordinated material. Further, before the drying step after the reaction, there may also be conventional separation and washing steps.

[0025] Further, in step (2), the alkali metal salt solution is an aqueous solution of an alkali metal carbonate, wherein the alkali metal carbonate is one or more of sodium carbonate and potassium carbonate. The alkali metal content in the alkali metal salt solution is 5%–40% by mass, preferably 10%–30%.

[0026] Further, in step (2), the coordination compound-doped ZIF-8 obtained in step (1) is mixed with an alkali metal salt solution, wherein the mass ratio of the coordination compound-doped ZIF-8 obtained in step (1) to the alkali metal salt is (0.1~10):1, preferably (0.5~5):1.

[0027] Further, the coordination reaction conditions in step (2) are as follows: the reaction temperature is 10-90℃, preferably 10-50℃; the reaction time is 0.5-12h, preferably 1-5h.

[0028] Furthermore, the drying conditions described in step (2) are as follows: the drying temperature is 80-120℃ and the drying time is 5-24h.

[0029] Furthermore, in step (3), by mass, the material in step (2) is: 13X molecular sieve = 1:(0.5~5).

[0030] Further, in step (3), the binder is one or more of silica sol, alumina sol, kaolin, sepiolite, diatomaceous earth, attapulgite, montmorillonite, and bentonite, preferably one or more of silica sol, kaolin, attapulgite, and bentonite.

[0031] Furthermore, in step (3), the mass ratio of the binder to water in the slurry containing the binder is 1:2 to 10.

[0032] Furthermore, the properties of the 13X molecular sieve described in step (3) are as follows: specific surface area of ​​300–600 m². 2 / g, preferably 350-500m 2 / g; average pore size is 5-15nm, preferably 8-12nm.

[0033] Further, in step (3), the mass ratio of the material obtained in step (2) to the 13X molecular sieve and the binder is 1:(0.5~5):(0.01~0.5), preferably 1:(0.8~2.2):(0.05~0.1).

[0034] Furthermore, the molding method described in step (3) is one or more of extrusion molding, ball forming, and spray molding, and is operated in accordance with methods known in the art.

[0035] Furthermore, the drying conditions described in step (3) are as follows: the drying temperature is 80-120℃ and the drying time is 5-24h.

[0036] Furthermore, the activation method described in step (4) includes three-stage activation:

[0037] First stage activation: The molded body obtained in step (3) is first pretreated at high temperature in an inert atmosphere, at a temperature of 300-1000℃, preferably 500-800℃. The inert atmosphere is one or more of nitrogen, argon, and helium, preferably nitrogen, and the volume hourly space velocity of the inert atmosphere is 100-1000 h⁻¹. -1 The processing time is 1 to 24 hours, preferably 6 to 12 hours;

[0038] Second stage activation: Then switch to CO2 atmosphere for treatment, the treatment temperature is 400-900℃, preferably 700-800℃, the CO2 atmosphere is a mixture of CO2 and an inert atmosphere (preferably selected from at least one of nitrogen, argon and helium, preferably nitrogen), the volume content of CO2 in the mixture is 1%-80%, preferably 10%-50%, the treatment time is 1-24h, preferably 6-12h;

[0039] The third stage of activation: Finally, activation is carried out in a mixed atmosphere of CO2 and water vapor at a temperature of 40-300°C, preferably 50-100°C. The volume content of CO2 in the mixed atmosphere of CO2 and water vapor is 5%-8%, and the treatment time is 1-24 hours, preferably 6-12 hours.

[0040] The third aspect of the present invention provides the application of the above-mentioned carbon dioxide adsorbent in solid adsorption carbon capture.

[0041] Furthermore, the application includes: contacting carbon dioxide-containing gas with the carbon dioxide adsorbent for adsorption to obtain purified gas.

[0042] Furthermore, the application employs a fixed-bed reactor or a fluidized-bed reactor.

[0043] Furthermore, in the aforementioned application, the carbon dioxide-containing gaseous raw material is flue gas, and its main components by volume are CO2 (5%–20%), water vapor (3%–15%), and nitrogen (60%–80%).

[0044] Furthermore, in the aforementioned application, the adsorption conditions include: a temperature of 50–100°C, a pressure of 0.1–5 MPa, and a volume hourly space velocity of 50–1000 h⁻¹. -1 .

[0045] Furthermore, the adsorbent after adsorption saturation can be regenerated under an N2 atmosphere at a regeneration reaction temperature of 100–300°C.

[0046] Compared with the prior art, the carbon dioxide adsorbent and its synthesis method provided by the present invention have the following advantages:

[0047] 1. The carbon dioxide adsorbent provided by this invention uses a method of coupling coordination compounds with metal-organic porous materials to anchor alkali metals in the porous materials, thereby achieving high dispersion of active centers and improving the utilization rate of active centers. In addition, a multi-step activation method is preferably used to eliminate the metal-organic porous materials and coordination compounds, thereby retaining a well-developed pore structure inside the adsorbent, reducing the mass transfer resistance of reactant gas molecules inside, and improving the reaction efficiency.

[0048] 2. The components of the adsorbent of this invention have good dispersibility and suitable alkalinity. During the adsorption of carbon dioxide in the raw gas, the utilization rate of the active center can be greatly improved, exhibiting high activity, regeneration performance and stability. Attached Figure Description

[0049] Figure 1 shows the CO2-TPD of the adsorbent molded body obtained in Example 1 of the present invention;

[0050] Figure 2 shows the CO2-TPD of the adsorbent molded body obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0051] The adsorbent of the present invention, its preparation method and application are further illustrated by the following examples, but it should not be considered that the present invention is limited to the following examples.

[0052] In this invention, the basicity of the sample was tested using a Mack AutoChem II chemisorption analyzer. 0.1 g of the sample (20-40 mesh) was accurately weighed and loaded onto the sample. The sample was heated to 550°C under a helium atmosphere, activated, and then cooled to 60°C. Carbon dioxide was fully adsorbed at this temperature, followed by helium purging. After 90 minutes, the sample was heated to 600°C, during which the catalyst desorbed. The desorption process was detected using a thermal conductivity detector (TCD). The obtained data were plotted, and the characteristic peaks were integrated. Peaks in the temperature range of 100°C–250°C were identified as weak base peaks, and those in the range of 250°C–400°C were identified as medium-strong base peaks. The ratio of their peak areas represents the ratio of the base content of the weak base to the strong base center.

[0053] Example 1

[0054] First, zinc nitrate and 2-methylimidazole were dissolved separately in methanol solution. The zinc nitrate solution was then added to the 2-methylimidazole solution and mixed thoroughly. The molar ratio of Zn:2-methylimidazole:methanol was 1:60:1200. Simultaneously, 18-crown ether-6 was added to the mixture at a mass ratio of 0.08:1 to zinc nitrate. The mixture was stirred at 20°C for 24 hours. After conventional centrifugation, washing, and drying (at 100°C for 10 hours), complex-doped ZIF-8 was obtained. At a mass ratio of 3:1 between the coordination compound-doped ZIF-8 and the alkali metal salt, 10 g of the complex-doped ZIF-8 was mixed with 30 wt% potassium carbonate solution and reacted at 30°C for 4 hours. After separation, washing, and drying (at 100°C for 10 hours), the loaded material was obtained. This material was then mixed with 13X molecular sieve powder (specific surface area 4500 m²). 2The mixture of 13X (with an average pore size of 10 nm) and silica sol (with a SiO2 mass content of 30%) as a binder, wherein the mass ratio of materials 13X to SiO2 is 1:0.8:0.1, is extruded and then dried (drying at 100℃ for 10 h) to obtain the shaped adsorbent.

[0055] The obtained shaped adsorbent was activated. First, it was activated under a nitrogen atmosphere for 500 h. -1 The adsorbent was pretreated at 600℃ for 6 hours using a space velocity of 600℃; then treated with 20% CO2 gas (the remainder being nitrogen) at 700℃ for 6 hours; finally, treated with a mixed gas of 8% CO2 (the remainder being water vapor) at 60℃ for 6 hours to obtain the target adsorbent.

[0056] The adsorbent contained 31% potassium carbonate, 40% 13X molecular sieve, 24% zinc oxide, and 5% binder by weight. The base ratio of the weak base to the medium-strong base centers in the adsorbent was 5:1. The CO2-TPD characterization results are shown in Figure 1.

[0057] The adsorbent material was used in a fixed-bed low-temperature CO2 adsorption experiment at a space velocity of 400 h⁻¹. -1 The adsorbent was adsorbed under a mixture of CO2, water vapor, and N2 gas at 70℃ and 0.1 MPa, with water vapor concentration of 6%, CO2 concentration of 12%, and the remainder being N2. The adsorbent was then regenerated by heating to 180℃ under a nitrogen atmosphere, completing one cycle. The CO2 adsorption capacity of the adsorbent was 2.8 mmol / g. After 10 cycles, the CO2 adsorption capacity remained at 2.7 mmol / g.

[0058] Example 2

[0059] First, zinc chloride and 2-methylimidazole were dissolved separately in methanol solution. The zinc chloride solution was then added to the 2-methylimidazole solution and mixed thoroughly. The molar ratio of Zn:2-methylimidazole:methanol was 1:80:1500. Simultaneously, 18-crown ether-6 was added to the mixture at a mass ratio of 0.2:1 to zinc chloride. The mixture was stirred at 20°C for 24 hours. After conventional centrifugation, washing, and drying (at 100°C for 10 hours), complex-doped ZIF-8 was obtained. At a mass ratio of 3:1 between the coordination compound-doped ZIF-8 and the alkali metal salt, 10 g of the complex-doped ZIF-8 was mixed with a 25 wt% potassium carbonate aqueous solution and reacted at 30°C for 4 hours. After separation, washing, and drying (at 100°C for 10 hours), the loaded material was obtained. This material was then mixed with 13X molecular sieve powder (specific surface area 4500 m²). 2The mixture consists of 13X (with an average pore size of 10 nm) and silica sol (with a SiO2 mass content of 20%) as a binder, wherein the mass ratio of materials 13X to SiO2 is 1:1:0.1. After extrusion, the mixture is dried (at 120°C for 12 hours) to obtain the shaped adsorbent.

[0060] The obtained shaped adsorbent was activated. First, it was activated under a nitrogen atmosphere for 800 h. -1 The adsorbent was pretreated at 600℃ for 8 hours using a space velocity of 600℃; then treated with 10% CO2 gas (the remainder being nitrogen) at 700℃ for 6 hours; finally, the target adsorbent was obtained by treating with a 6% CO2 mixed gas (the remainder being water vapor) at 60℃ for 6 hours.

[0061] The adsorbent contains 33% potassium carbonate, 48% 13X molecular sieve, 15% zinc oxide, and 4% binder by weight. The ratio of weak base to medium-strong base centers in the adsorbent is 6.5:1.

[0062] The adsorbent material was used in a fixed-bed low-temperature CO2 adsorption experiment at a space velocity of 400 h⁻¹. -1 The adsorbent was adsorbed under a mixture of CO2, water vapor, and N2 gas at 70℃ and 0.1 MPa, with water vapor concentration of 6%, CO2 concentration of 12%, and the remainder being N2. The adsorbent was then regenerated by heating to 180℃ under a nitrogen atmosphere, completing one cycle. The CO2 adsorption capacity of the adsorbent was 2.5 mmol / g. After 10 cycles, the CO2 adsorption capacity remained at 2.3 mmol / g.

[0063] Example 3

[0064] First, zinc chloride and 2-methylimidazole were dissolved separately in methanol solution. The zinc chloride solution was then added to the 2-methylimidazole solution and mixed thoroughly. The molar ratio of Zn:2-methylimidazole:methanol was 1:40:1500. Simultaneously, 18-crown ether-6 was added to the mixture at a mass ratio of 0.4:1 to zinc chloride. The mixture was stirred at 20°C for 24 hours. After conventional centrifugation, washing, and drying (at 100°C for 10 hours), complex-doped ZIF-8 was obtained. At a mass ratio of 4:1 between the coordination compound-doped ZIF-8 and the alkali metal salt, 10 g of the complex-doped ZIF-8 was mixed with a 30 wt% potassium carbonate aqueous solution and reacted at 30°C for 4 hours. After separation, washing, and drying (at 100°C for 10 hours), the loaded material was obtained. This material was then mixed with 13X molecular sieve powder (specific surface area 4500 m²). 2 / g, with an average pore size of 10nm), bentonite and water were mixed as a binder, wherein the mass ratio of the loading material 13X: bentonite: water was 1:1:0.2:0.8. After extrusion, the mixture was dried (drying at 120℃ for 12h) to obtain a shaped adsorbent.

[0065] The obtained shaped adsorbent was activated. First, it was activated under a helium atmosphere for 800 h. -1 The adsorbent was pretreated at 650℃ for 7 hours using a space velocity of 650 h; then treated with 10% CO2 gas (the remainder being nitrogen) at 750℃ for 6 hours; finally, the target adsorbent was obtained by treating with a 6% CO2 mixed gas (the remainder being water vapor) at 50℃ for 10 hours.

[0066] The adsorbent contains 22% carbonate by weight, 48% 13X molecular sieve by weight, 22% zinc oxide by weight, and 8% binder by weight. The ratio of weak base to medium-strong base centers in the adsorbent is 6:1.

[0067] The adsorbent material was used in a fixed-bed low-temperature CO2 adsorption experiment at a space velocity of 600 h⁻¹. -1 The adsorbent was adsorbed under a mixture of CO2, water vapor, and N2 gas at 70℃ and 0.1 MPa, with water vapor concentration of 8%, CO2 concentration of 10%, and the remainder being N2. Then, the adsorbent was regenerated by heating to 160℃ under a nitrogen atmosphere, completing one cycle. The CO2 adsorption capacity of the adsorbent was 2.8 mmol / g. After 10 cycles, the CO2 adsorption capacity remained at 2.6 mmol / g.

[0068] Example 4

[0069] First, zinc nitrate and 2-methylimidazole were dissolved separately in methanol solution. The zinc nitrate solution was then added to the 2-methylimidazole solution and mixed thoroughly. The molar ratio of Zn:2-methylimidazole:methanol was 1:40:1500. Simultaneously, 18-crown ether-6 was added to the mixture at a mass ratio of 0.4:1 to zinc chloride. The mixture was stirred at 20°C for 24 hours. After conventional centrifugation, washing, and drying (at 100°C for 10 hours), complex-doped ZIF-8 was obtained. At a mass ratio of 3:1 between the coordination compound-doped ZIF-8 and the alkali metal salt, 10 g of the complex-doped ZIF-8 was mixed with a 20 wt% potassium carbonate aqueous solution and reacted at 30°C for 4 hours. After separation, washing, and drying (at 100°C for 10 hours), the loaded material was obtained. This material was then mixed with 13X molecular sieve powder (specific surface area 4500 m²). 2 / g, with an average pore size of 10nm), bentonite and water were mixed as a binder, wherein the mass ratio of the loading material 13X: bentonite: water was 1:1:0.15:1. After extrusion, the mixture was dried (drying at 120℃ for 12h) to obtain a shaped adsorbent.

[0070] The obtained shaped adsorbent was activated. First, it was activated under a helium atmosphere for 900 h. -1 The adsorbent was pretreated at 700℃ for 8 hours using a space velocity of 10%; then treated with 10% CO2 gas (the remainder being nitrogen) at 700℃ for 6 hours; finally, the target adsorbent was obtained by treating with a 6% CO2 mixed gas (the remainder being water vapor) at 80℃ for 6 hours.

[0071] The adsorbent contains 32% carbonate by weight, 45% 13X molecular sieve by weight, 16% zinc oxide by weight, and 7% binder by weight. The ratio of weak base to medium-strong base centers in the adsorbent is 7:1.

[0072] The adsorbent material was used in a fixed-bed low-temperature CO2 adsorption experiment at a space velocity of 600 h⁻¹. -1 The adsorbent was adsorbed under a mixture of CO2, water vapor, and N2 gas at 70℃ and 0.1 MPa, with water vapor concentration of 8%, CO2 concentration of 10%, and the remainder being N2. The adsorbent was then regenerated by heating to 160℃ under a nitrogen atmosphere, completing one cycle. The CO2 adsorption capacity of the adsorbent was 2.8 mmol / g. After 10 cycles, the CO2 adsorption capacity remained at 2.5 mmol / g.

[0073] Comparative Example 1

[0074] The only difference between Comparative Example 1 and Example 1 is the adsorbent used. Specifically, the only difference between Comparative Example 1 and Example 1 is that 18-crown ether-6 was not added during the adsorbent preparation process.

[0075] The CO2 adsorption capacity of the obtained adsorbent was 1.8 mmol / g. After 10 cycles, the CO2 adsorption capacity decreased to 0.6 mmol / g.

[0076] Comparative Example 2

[0077] The only difference between Comparative Example 2 and Example 1 is the adsorbent used. Specifically, the only difference in the adsorbent preparation process compared to Example 1 is that 13X molecular sieve was not added during the adsorbent synthesis process in Comparative Example 2. The CO2-TPD diagram of the obtained adsorbent is shown in Figure 2.

[0078] The CO2 adsorption capacity of the obtained adsorbent was 1.1 mmol / g. After 10 cycles, the CO2 adsorption capacity was 1.0 mmol / g.

[0079] Comparative Example 3

[0080] The only difference from Example 1 is that the resulting adsorbent was not activated.

[0081] The CO2 adsorption capacity of the obtained adsorbent was 0.8 mmol / g. After 10 cycles, the CO2 adsorption capacity was 0.6 mmol / g.

[0082] Comparative Example 4

[0083] The only difference compared to Example 1 is that the resulting adsorbent underwent only the first stage of activation.

[0084] The CO2 adsorption capacity of the obtained adsorbent was 1.0 mmol / g. After 10 cycles, the CO2 adsorption capacity was 0.8 mmol / g.

Claims

1. A carbon dioxide adsorbent, comprising: The adsorbent comprises zinc oxide, alkali metal salt, 13X molecular sieve, and binder components; based on the mass of the adsorbent, the zinc oxide content is 10%–60%, preferably 20%–45%; the alkali metal salt content is 5%–50%, preferably 10%–32%; the 13X molecular sieve content is 10%–60%, preferably 20%–45%; and the binder component content is 0.05%–10%, preferably 0.1%–5%.

2. The adsorbent according to claim 1, characterized in that, The alkali metal salt is an alkali metal carbonate, selected from one or more of sodium carbonate and potassium carbonate.

3. The adsorbent according to claim 1, characterized in that, In the adsorbent, the alkali metal salt is introduced into the adsorbent using ZIF-8 doped with a coordination compound as a template; wherein the coordination compound is one or more of crown ethers and ethylenediaminetetraacetic acid, preferably crown ethers, and more preferably 18-crown ether-6.

4. The adsorbent according to claim 1, characterized in that, The ratio of weak base centers to medium-strong base centers in the adsorbent is (1-10):1, preferably (4-8):

1.

5. A method for synthesizing a carbon dioxide adsorbent, comprising the following steps: (1) dissolving an imidazole organic ligand and a zinc source in an alcohol solvent, then mixing the solution containing the imidazole organic ligand with the solution containing the zinc source evenly, adding a coordination compound, reacting, and drying to obtain a coordination compound-doped ZIF-8; (2) mixing the coordination compound-doped ZIF-8 obtained in step (1) with an alkali metal salt solution, reacting, and drying; (3) mixing the material obtained in step (2) and 13X molecular sieve with a slurry containing a binder, molding, and drying to obtain a molded body; (4) activating the molded body obtained in step (3) to obtain the carbon dioxide adsorbent.

6. The method according to claim 5, characterized in that, In step (1), the imidazole organic ligand is one or more of imidazole, 2-methylimidazolium, and benzimidazole, preferably 2-methylimidazolium; and / or, the zinc source is one or more of zinc nitrate, zinc chloride, and zinc sulfate; and / or, the alcohol solvent is one or more of methanol and ethanol; and / or, in molar amounts, zinc source: 2-methylimidazolium: alcohol = 1:(20-100):(500-2000).

7. The method according to claim 5, characterized in that, In step (1), the coordination compound is one or more of crown ethers and ethylenediaminetetraacetic acid, preferably crown ethers, more preferably 18-crown ether-6; and / or, the mass ratio of the coordination compound to the zinc source is 0.001 to 1:1, preferably 0.01 to 1:1; and / or, the drying conditions in step (1) are as follows: the drying temperature is 60℃-200℃, preferably 80℃-140℃; the drying time is 1h-24h, preferably 4h-12h.

8. The method according to claim 5, characterized in that, Step (2) includes: adding an alkali metal salt solution to the coordination compound-doped ZIF-8 obtained in step (1), carrying out a coordination reaction, drying, and obtaining a metal-coordinated material; preferably, the mass ratio of the coordination compound-doped ZIF-8 obtained in step (1) to the alkali metal salt is (0.1-10):1, more preferably (0.5-5):

1.

9. The method according to claim 5, characterized in that, In step (2), the alkali metal salt solution is an aqueous solution of alkali metal carbonate, wherein the alkali metal carbonate is one or more of sodium carbonate and potassium carbonate; the mass content of the alkali metal in the alkali metal salt solution is 5% to 40%, preferably 10% to 30%.

10. The method according to claim 5, characterized in that, The coordination reaction conditions in step (2) are as follows: the reaction temperature is 10-90℃, preferably 10-50℃; the reaction time is 0.5-12h, preferably 1-5h; and / or the drying conditions in step (2) are as follows: the drying temperature is 80-120℃, and the drying time is 5-24h.

11. The method according to claim 5, characterized in that, In step (3), the binder is one or more of silica sol, alumina sol, kaolin, sepiolite, diatomaceous earth, palygorskite, montmorillonite, and bentonite, preferably one or more of silica sol, kaolin, palygorskite, and bentonite; and / or, in the slurry containing the binder in step (3), the mass ratio of the binder to water is 1:2 to 10; and / or, the properties of the 13X molecular sieve described in step (3) are as follows: specific surface area of ​​300 to 600 m². 2 / g, preferably 350-500m 2 / g; average pore size of 5-15nm, preferably 8-12nm; and / or, in step (3), the mass ratio of the material obtained in step (2) to 13X molecular sieve and binder is 1:(0.5-5):(0.01-0.5), preferably 1:(0.8-2.2):(0.05-0.1). and / or, the drying conditions in step (3) are as follows: drying temperature of 80-120℃, drying time of 5-24h.

12. The method according to claim 5, characterized in that, The activation method described in step (4) includes three stages of activation: First stage activation: The molded body obtained in step (3) is first pretreated at high temperature in an inert atmosphere, at a temperature of 300-1000℃, preferably 500-800℃. The inert atmosphere is one or more of nitrogen, argon, and helium, preferably nitrogen, and the volume hourly space velocity of the inert atmosphere is 100-1000 h⁻¹. -1 The first stage of activation involves a treatment time of 1–24 hours, preferably 6–12 hours. The second stage involves switching to a CO2 atmosphere for treatment at a temperature of 400–900°C, preferably 700–800°C. The CO2 atmosphere is a mixture of CO2 and an inert atmosphere (preferably selected from at least one of nitrogen, argon, and helium, with nitrogen being the preferred choice). The volume content of CO2 in the mixture is 1%–80%, preferably 10%–50%, and the treatment time is 1–24 hours, preferably 6–12 hours. The third stage involves activation in a mixture of CO2 and water vapor at a temperature of 40–300°C, preferably 50–100°C. The volume content of CO2 in the mixture is 5%–8%, and the treatment time is 1–24 hours, preferably 6–12 hours.

13. The application of the carbon dioxide adsorbent according to any one of claims 1-4 or the carbon dioxide adsorbent prepared by any one of claims 5-12 in solid adsorption carbon capture.

14. The application according to claim 13, characterized in that, The application includes: contacting carbon dioxide-containing gas with the carbon dioxide adsorbent for adsorption to obtain purified gas; preferably, the application uses a fixed-bed reactor or a fluidized bed reactor; preferably, in the application, the carbon dioxide-containing gas feedstock is flue gas, comprising, by volume, 5%–20% CO2, 3%–15% water vapor, and 60%–80% nitrogen; preferably, in the application, the adsorption conditions include: a temperature of 50–100°C, a pressure of 0.1–5 MPa, and a volume hourly space velocity of 50–1000 h⁻¹. -1 .

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