A method for cyclically capturing low concentrations of carbon dioxide from air

Abstract

The present application belongs to the technical field of carbon dioxide capture in air, and relates to a method for cyclically capturing low-concentration carbon dioxide from air, comprising the following steps: S1, preparing a hydrotalcite or a hydrotalcite-like product, the hydrotalcite or the hydrotalcite-like product containing CO2 captured from air; S2, calcining the hydrotalcite product to obtain a calcined product; S3, stirring the calcined product in ultrapure water, performing open reaction, centrifugally separating the obtained solution after reaction, and drying to obtain a solid product; S4, sequentially repeating S2-S3 to obtain a multiple-cycle product, and realizing multiple capture of CO2 in air; in each calcination process, the solid product releases purified CO2, and the CO2 is collected by a corresponding pipeline collection system to realize collection and production of the CO2 product. The method solves the problems that high-efficiency capture of low-concentration CO2 in air in the process of mineral formation cannot be realized at present, and the quality of the formed minerals is guaranteed and the minerals can be cyclically applied.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture technology in the air, and specifically relates to a method for cyclically capturing low concentrations of carbon dioxide from the air. Background Technology

[0002] With industrialization, global warming has intensified, and CO2 produced by human activities is a major atmospheric emission, contributing significantly to global climate change. As global energy demand continues to grow, the burning of fossil fuels is also increasing. By the end of this century, CO2 emissions are projected to rise by 6.4%, indicating that global warming is ongoing. Therefore, reducing atmospheric CO2 levels has become a primary measure to mitigate climate change, and researchers are actively seeking optimal methods for CO2 fixation. From a long geological evolutionary perspective, geological CO2 sequestration has always been a crucial natural means of regulating atmospheric CO2 concentration. Geological CO2 sequestration is also an effective way to address the current global greenhouse effect. However, natural geological sequestration often requires millions of years, far from meeting today's rapid carbon sequestration needs. Therefore, the scientific community has begun to employ artificial intervention to promote mineral carbon sequestration. For example, using stable and high-performance minerals as adsorbents to rapidly adsorb carbon dioxide from the air or industrial emissions, or artificially promoting the rapid formation of secondary carbon-fixing minerals (minerals that absorb carbon dioxide and fix it within their structure during formation).

[0003] Existing research indicates that the efficiency of carbon dioxide fixation from the atmosphere during mineral formation is low, and the crystallization state of minerals cannot be adequately guaranteed at low CO2 concentration levels, resulting in unstable mineral formation quality. Furthermore, the mineralization time required for atmospheric carbon dioxide to participate in mineral formation and achieve carbon dioxide fixation often exceeds tens or even hundreds of years. The shortest reported mineralization cycle is for the formation of magnesite (MgCO3) minerals from carbon dioxide and magnesium ions, but this process still requires a long reaction time of 72 days. Therefore, the long reaction time cannot meet the current needs for geological sequestration of atmospheric carbon dioxide. Therefore, there is an urgent need to develop a new mineralogical method for the efficient, convenient, and short-time cyclic capture of low-concentration CO2 from the atmosphere. Summary of the Invention

[0004] The purpose of this invention is to provide a method for cyclically capturing low-concentration carbon dioxide from the air. By optimizing the reaction conditions, the amount of carbon dioxide captured from the air is increased, solving the current problem that it is impossible to simultaneously achieve efficient capture of low-concentration CO2 from the air during mineral formation in a short period of time, and to ensure the amount of minerals formed and their recycling.

[0005] This invention is achieved through the following technical solution:

[0006] A method for cyclically capturing low concentrations of carbon dioxide from the air includes the following steps:

[0007] S1. Prepare hydrotalcite or hydrotalcite-like products, wherein the hydrotalcite or hydrotalcite-like products contain carbon dioxide captured from the air;

[0008] S2. Calcining hydrotalcite or hydrotalcite-like products to obtain calcined product C-LDH-1;

[0009] S3. Place the calcined product C-LDH-1 into ultrapure water and stir. React in an open container. Centrifuge and dry the resulting solution to obtain the solid product R-LDH-1.

[0010] S4. Repeat S2-S3 sequentially to obtain multiple cyclic products, thereby achieving multiple captures of carbon dioxide from the air.

[0011] During each calcination process, the solid product releases purified carbon dioxide gas, which is collected by a suitable pipeline collection system to achieve the collection and production of carbon dioxide products.

[0012] Furthermore, in S1, the content of carbon dioxide captured from the air during the formation of hydrotalcite or hydrotalcite-like products is controlled by adjusting the reaction conditions and reaction elements, including the following steps:

[0013] Step 1: At a reaction temperature of 25-80℃, mix a mixed salt solution of divalent and trivalent metals with an alkaline solution, maintaining a constant pH of 6-10 during the mixing process to obtain a turbid reaction solution.

[0014] Step 2: Continue stirring the turbid reaction solution, and then allow it to stand and age at the reaction temperature;

[0015] Step 3: After aging, centrifuge the reaction solution to obtain a solid precipitate and a supernatant. Wash the solid precipitate until the pH of the supernatant is neutral to obtain the solid product.

[0016] Step 4: After drying the solid product, hydrotalcite or hydrotalcite-like products are obtained.

[0017] Furthermore, in step one, the pH is kept constant at 7-9.

[0018] Furthermore, in step one, the molar ratio of divalent metals to trivalent metals in the mixed salt solution is (1-4):1.

[0019] Furthermore, in step one, the mixed solution of divalent and trivalent metals is a magnesium-aluminum mixed solution, a zinc-aluminum mixed solution, a nickel-iron mixed solution, or a nickel-aluminum mixed solution.

[0020] Furthermore, in step one, the alkaline solution is a sodium hydroxide solution.

[0021] Furthermore, in step two, the aging time is 0 to 24 hours.

[0022] Furthermore, in S2, the calcination temperature is 300–500℃.

[0023] Furthermore, in S3, the drying method is oven drying, freeze drying, or natural drying; the drying temperature does not exceed 80℃.

[0024] Furthermore, after the recycled products lose their activity, they are dissolved in an acidic solution to form a bimetallic mixed solution, which is then mixed with an alkaline solution to resynthesize hydrotalcite or hydrotalcite-like minerals.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] This invention discloses a method for capturing low-concentration carbon dioxide from the air through circulation. Utilizing the characteristic that positively charged hydrotalcite and hydrotalcite-like minerals require anions as interlayer balancing ions during their formation, this invention attempts to introduce air during the formation process of hydrotalcite and hydrotalcite-like minerals, exploring the conversion of airborne carbon dioxide into interlayer balancing anions to achieve the goal of capturing airborne carbon dioxide. Current research is uncertain whether hydrotalcite and hydrotalcite-like minerals can effectively absorb low-concentration carbon dioxide from the air during their formation process, and the absorption efficiency of airborne carbon dioxide and its influencing factors are still unclear. Therefore, this invention focuses on adjusting the pH, temperature, and reaction time of the reaction solution to induce airborne carbon dioxide to enter the solution and be converted into carbonate or bicarbonate ions, which are then captured by the positively charged hydrotalcite and hydrotalcite-like mineral lamellar structures, thereby improving the capture efficiency of airborne carbon dioxide by hydrotalcite and hydrotalcite-like minerals during their formation process. Simultaneously, hydrotalcite and hydrotalcite-like minerals transform into bimetallic oxides during low-temperature calcination, and the resulting bimetallic oxides react with water to transform into hydrotalcite or hydrotalcite-like substances (a phenomenon known as the memory effect). At this point, by controlling the contact between the calcined bimetallic oxide and water and air, it is hoped that carbon dioxide in the air can be re-fixed. Accordingly, this invention utilizes the memory effect to potentially achieve the cyclic capture and production of carbon dioxide in the air: low-temperature calcination can release CO2 absorbed between layers of hydrotalcite or hydrotalcite-like oxides, thus achieving the purification and release of CO2 fixed in a single capture. The released CO2 can then be used for industrial production of CO2 products. The calcined product can then capture a large amount of CO2 from the air during subsequent reactions with water, thus achieving cyclic CO2 capture. Combining single capture and cyclic capture, the cyclic absorption and production of CO2 in the air can be achieved, reducing CO2 levels while simultaneously producing CO2 products. However, whether hydrotalcite and hydrotalcite-like oxides can continuously achieve this "structure destruction-structure restoration" cycle using the memory effect is currently unclear. Therefore, the feasibility of using this "structure destruction-structure restoration" cycle to achieve the cyclic capture of low-concentration carbon dioxide in the air, as well as the capture efficiency of cyclically fixing carbon dioxide and the factors affecting the capture efficiency, are also currently unclear. Therefore, this invention focuses on the effects of cycle number and calcination temperature on the structural memory effect of hydrotalcite and hydrotalcite-like materials, and particularly on how hydrotalcite and hydrotalcite-like materials achieve the effect of cyclically capturing low-concentration carbon dioxide from the air through a "structural destruction-structural restoration" cycle under the regulation of these factors. This invention focuses on the effect of the formation and structural reconstruction processes of hydrotalcite and hydrotalcite-like materials on the capture efficiency of low-concentration carbon dioxide from the air, and improves the carbon dioxide capture efficiency through optimized design of conditions.

[0027] This invention enables the direct acquisition of valuable materials, chemical reagents, or purified CO2 products after processing, thereby achieving multi-functional utilization of hydrotalcite and hydrotalcite-like minerals and reducing carbon capture costs. In other words, this processing method simultaneously satisfies the requirements for capturing CO2 from the air and industrial CO2 production. Furthermore, the solid products are easily recyclable and reusable, with low cost, simple and efficient processing, low energy consumption, and a short preparation cycle, making it suitable for large-scale production and possessing broad application prospects.

[0028] Furthermore, the calcination temperature is 300–500℃. Temperatures above 500℃ are prone to producing other mineral phases that affect the recycling and capture performance, while temperatures below 300℃ make it difficult to release carbon dioxide between mineral layers. At the same time, the recycling and regeneration of minerals and the recycling and capture performance of carbon dioxide will be limited.

[0029] Furthermore, after these minerals lose their activity, they can be dissolved in acid to form a bimetallic mixed solution, which can then be mixed with an alkaline solution to resynthesize hydrotalcite-like minerals and hydrotalcite minerals, facilitating subsequent reuse. Attached Figure Description

[0030] Figure 1 These are the XRD patterns of the products from the system at different pH values ​​in Example 1;

[0031] Figure 2 These are the XRD patterns of the system products at different temperatures in Example 2;

[0032] Figure 3 These are the XRD patterns of the system products at different aging times in Example 3;

[0033] Figure 4 These are the XRD patterns of the products from the different metal systems that participated in the reaction in Example 4;

[0034] Figure 5 These are the XRD patterns of the system products under different magnesium-aluminum ratios in Example 5;

[0035] Figure 6 The XRD pattern of the product of the cyclic calcination system in Example 6;

[0036] Figure 7 The graph shows the performance of the hydrotalcite group minerals in Example 6 when calcined at 300℃, 400℃ and 500℃ respectively to fix CO2 in a cyclic manner. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0038] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0039] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0040] This invention discloses a method for cyclically capturing low concentrations of carbon dioxide from the air, wherein a single capture includes the following steps:

[0041] 1) At a certain temperature, a mixed salt solution of divalent and trivalent metals in a certain molar ratio is titrated with sodium hydroxide solution into ultrapure water. The pH is kept constant during the mixing process to obtain a turbid reaction solution for coprecipitation reaction.

[0042] 2) After mixing, the turbid solution was stirred for 2 hours, and then left to stand at room temperature for a certain period of time.

[0043] 3) After aging, the mixture is centrifuged to obtain solid precipitate and supernatant, and the concentration of metal ions in the supernatant is measured;

[0044] 4) Wash the obtained solid precipitate with water several times until the pH of the supernatant is close to neutral;

[0045] 5) Finally, the obtained solid is dried to obtain hydrotalcite or hydrotalcite-like minerals (collectively referred to as hydrotalcite group minerals, abbreviated as LDH).

[0046] Minerals composed of Mg and Al elements with carbonate as the balancing ion are called hydrotalcite. Minerals with the same structure but composed of other elements or with other anions as the balancing ion are called hydrotalcite-like minerals.

[0047] Cyclic capture includes the following steps:

[0048] Step 1: The target hydrotalcite obtained from the single capture is calcined at 500℃ to obtain the calcined product C-LDH-1-500℃;

[0049] Step 2: Under normal temperature and pressure, the calcined product is placed in ultrapure water and magnetically stirred. The reaction is carried out in an open environment for 12 hours. The resulting solution is centrifuged and freeze-dried to obtain the solid product R-LDH-1-500℃. This is the hydrotalcite or hydrotalcite-like product obtained in the first cycle.

[0050] Step 3: Take the target hydrotalcite R-LDH-1 obtained from the first cycle and calcine it again at a low temperature of 500℃ to obtain the calcined product C-LDH-2 at 500℃;

[0051] Step 4: Under normal temperature and pressure, the product after the second calcination is placed in ultrapure water and magnetically stirred. The reaction is carried out in an open container for 12 hours. The resulting solution is centrifuged and freeze-dried to obtain the solid product R-LDH-2-500℃, which is the hydrotalcite or hydrotalcite-like product obtained in the second cycle.

[0052] Step 5: Take the target hydrotalcite R-LDH-2 obtained from the second cycle and calcine it again at a low temperature of 500℃ to obtain the calcined product C-LDH-3 at 500℃;

[0053] Step 6: Under normal temperature and pressure, place the product after the third calcination into ultrapure water and stir magnetically. React in an open container for 12 hours. Centrifuge the resulting solution after the reaction, freeze-dry it, and obtain the solid product R-LDH-3-500℃. This is the hydrotalcite or hydrotalcite-like product obtained in the third cycle.

[0054] During each low-temperature calcination process, the pure CO2 gas released by calcination and decomposition is collected. At this time, with the help of a suitable pipeline collection system, the collection and production of carbon dioxide products can be realized, thus making it possible to realize the integration of CO2 enrichment and purification from the air to industrial production.

[0055] The invention will be further illustrated below with specific implementation examples:

[0056] Example 1:

[0057] A method for regulating the pH of hydrotalcite formation to control the amount of CO2 captured from the air, specifically including the following steps:

[0058] 1) Prepare 500 mL of a mixed salt solution containing 0.18 mol magnesium nitrate and 0.06 mol aluminum nitrate in a magnesium-aluminum molar ratio of 3:1, and simultaneously prepare 500 mL of a 2 mol / L NaOH solution.

[0059] The two solutions were added dropwise to a 2L beaker (with 200mL of ultrapure water added beforehand) using an automatic pH dispenser. During the addition, magnetic stirring was maintained and the pH was kept constant at 10 (i.e., the target reaction pH value is 10). The reaction temperature of the system was kept at 25℃ (room temperature).

[0060] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours for aging, and then centrifuge to obtain solid product.

[0061] 3) The solid product is washed with water to remove the hydroxide ions adsorbed on the surface. Then, the solid is freeze-dried to obtain the target hydrotalcite (a layered bimetallic hydroxide mineral composed of magnesium and aluminum, MgAl-LDH).

[0062] To obtain a higher carbon dioxide capture rate, the effect of reaction pH on the synthesis yield of MgAl-LDH and the amount of carbon dioxide captured from the air during the formation of MgAl-LDH was investigated. Based on Example 1, with other conditions kept constant, the effect of different reaction pH on the MgAl-LDH yield and the amount of carbon dioxide captured during the formation of the target hydrotalcite was investigated by changing the pH during the dropwise addition process to 6, 7, 8, and 9.

[0063] For Example 1 of the present invention, X-ray diffraction analysis was performed on the product obtained in Case 1 to identify the mineral phases of the product, and the results are as follows. Figure 1 As shown, the results indicate that adjusting the reaction pH (6–10) can regulate the crystallinity of the hydrotalcite mineral phase. Hydrotalcite crystallization is poor at lower pH levels (e.g., pH 6), while it crystallizes better at pH ≥ 7. Furthermore, the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed in the target hydrotalcite were measured. The utilization rates of Mg and Al ions and the amount of carbon dioxide fixed during hydrotalcite formation at different pH levels are shown in Table 1. The results show that the amount of carbon dioxide captured from the air during hydrotalcite formation can be controlled by the reaction pH. As the reaction pH increases from 6 to 10, the amount of carbon dioxide fixed first increases and then decreases, reaching a maximum of 13.34 mg / g. At pH 6, MgAl-LDH is not fully formed, resulting in a relatively low amount of carbon dioxide captured from the air (8.58 mg / g). When the pH increases to 7, MgAl-LDH is fully formed, and as the pH continues to increase, the amount of HCO3- in the system increases. - Turn into CO3 2- The CO2 fixation rate initially increases and then decreases. In this implementation case, under optimal conditions, producing one ton of MgAl-LDH can capture 13.34 kg of carbon dioxide from the air; in terms of raw materials, capturing one ton of carbon dioxide requires the input of 21.70 tons of Mg and 13.63 tons of Al. Therefore, the input consumption is relatively high. Subsequent cases will continue to optimize the process to achieve implementation conditions with lower inputs and higher carbon fixation.

[0064] Table 1. Amount of CO2 absorbed from the air during the formation of hydrotalcite at different reaction pH levels (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0065]

[0066] Example 2

[0067] A method for regulating the CO2 content captured from the air by controlling the formation temperature of hydrotalcite specifically includes the following steps:

[0068] 1) Prepare 500 mL of a mixed salt solution containing 0.18 mol magnesium nitrate and 0.06 mol aluminum nitrate in a magnesium-aluminum molar ratio of 3:1, and simultaneously prepare 500 mL of a 2 mol / L NaOH solution.

[0069] The two solutions were added dropwise to a 2L beaker (with 200mL of ultrapure water added beforehand) using an automatic pH dispenser. During the addition, magnetic stirring was maintained and the temperature was kept at 25℃, with the pH constant at 10 (i.e., the target reaction pH value is 10).

[0070] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours, and then centrifuge to obtain solid product.

[0071] 3) The solid product was washed with water to remove the adsorbed hydroxide ions on the surface. Subsequently, the solid was freeze-dried to obtain the target hydrotalcite (MgAl-LDH).

[0072] The solid obtained after drying was characterized and the product was identified and analyzed.

[0073] To obtain a higher carbon dioxide capture rate, the effects of reaction temperature during the formation of hydrotalcite on the yield of MgAl-LDH and the amount of carbon dioxide captured from the air during the formation of MgAl-LDH were investigated. Based on Example 2, with other conditions kept constant, the effects of different reaction temperatures on the yield of MgAl-LDH and the amount of carbon dioxide captured from the air during the formation of the target hydrotalcite were investigated by changing the reaction temperature during the formation of MgAl-LDH to 40°C, 60°C, and 80°C.

[0074] For Example 2 of the present invention, X-ray diffraction analysis was performed on the product obtained in Case 2 to identify the mineral phases of the product, and the results are as follows. Figure 2 As shown, the results indicate that adjusting the reaction temperature (40℃, 60℃, 80℃) can regulate the degree of crystallinity of the hydrotalcite mineral, thereby regulating the amount of carbon dioxide captured (Table 2). Figure 2As shown, the higher the temperature, the better the crystallinity of LDH. Furthermore, the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed in the target hydrotalcite were measured, yielding the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed during hydrotalcite formation at different temperatures, as shown in Table 2. As the reaction temperature increased from room temperature to 80℃, the amount of carbon dioxide captured from the air during hydrotalcite formation generally increased synchronously (from 8.16 to 13.77 mg / g). At 80℃, LDH formation achieved the highest capture rate of CO2 from the air. Although higher temperatures resulted in less dissolved CO2 in the solution, higher temperatures led to better LDH crystallization, thus improving the CO2 capture efficiency in the liquid phase. This indicates that adjusting the reaction temperature can control the CO2 capture efficiency during hydrotalcite formation. In this implementation case, under optimal conditions, producing one ton of MgAl-LDH can capture 13.77 kg of carbon dioxide from the air; based on raw materials, capturing one ton of carbon dioxide requires 14.92 tons of Mg and 5.60 tons of Al. Table 2. Amount of CO2 absorbed from the air during the formation of hydrotalcite at different reaction temperatures (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0075]

[0076] Example 3

[0077] A method for capturing CO2 from the air during the formation of hydrotalcite at different aging times specifically includes the following steps:

[0078] 1) Prepare 500 mL of a mixed salt solution containing 0.18 mol magnesium nitrate and 0.06 mol aluminum nitrate in a magnesium-aluminum molar ratio of 3:1, and simultaneously prepare 500 mL of a 2 mol / L NaOH solution.

[0079] The two solutions were added dropwise to a 2L beaker (with 200mL of ultrapure water pre-added) using an automatic pH dispenser. During the addition, magnetic stirring was maintained and the pH was kept constant at 10 (i.e., the target reaction pH value is 10).

[0080] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours, and then centrifuge to obtain solid product.

[0081] 3) The solid product was washed with water to remove the adsorbed hydroxide ions on the surface. Subsequently, the solid was freeze-dried to obtain the target hydrotalcite (MgAl-LDH).

[0082] The solid obtained after drying was characterized and the product was identified and analyzed.

[0083] To investigate the effects of aging time on the LDH synthesis yield and the amount of carbon dioxide fixed in the target mineral, based on Example 3, with other conditions kept constant, the aging time at room temperature was changed to 0h, 2h, 4h, 6h, 12h, and 24h. That is, a synthesis experiment was conducted at each of the above aging times to explore the effects of different aging times on the MgAl-LDH synthesis yield and the amount of carbon dioxide fixed in the target hydrotalcite.

[0084] For Example 3 of the present invention, X-ray diffraction analysis was performed on the product obtained in Example 3, and the mineral phase identification results of the product are as follows: Figure 3 As shown, the results indicate that hydrotalcite mineral phases can be formed at different aging times, and the longer the aging time, the better the crystallinity of LDH. The utilization rates of Mg and Al ions and the amount of carbon dioxide fixed in the target hydrotalcite were measured, and the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed during hydrotalcite formation at different temperatures were obtained, as shown in Table 3. With the extension of time, the CO3 adsorbed at the beginning of aging... 2- As the carbon dioxide is released, the amount absorbed gradually decreases. The above results indicate that hydrotalcite can absorb CO2 from the air during its formation process at different aging times, with hydrotalcite aged for 0 hours absorbing the most CO2. In this implementation case, under optimal conditions, producing one ton of MgAl-LDH can capture 16.31 kg of carbon dioxide from the air; based on raw materials, capturing one ton of carbon dioxide requires the input of 14.61 tons of Mg and 5.52 tons of Al.

[0085] Table 3. Amount of CO2 absorbed from the air during LDH formation at different aging times (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0086]

[0087] Example 4

[0088] A method for regulating the capture of CO2 from the air during the formation of hydrotalcite-like materials by adjusting the metal composition specifically includes the following steps:

[0089] 1) Prepare 500 mL of a mixed salt solution containing a certain proportion of magnesium nitrate and aluminum nitrate, and at the same time prepare 500 mL of a 2 mol / L NaOH solution.

[0090] The two solutions were added dropwise to a 2L beaker (with 200mL of ultrapure water pre-added) using an automatic pH dispenser. During the addition, magnetic stirring was maintained and the pH was kept constant at 10 (i.e., the target reaction pH value is 10).

[0091] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours, and then centrifuge to obtain solid product.

[0092] 3) The solid product is washed with water to remove the adsorbed hydroxide ions on the surface. Subsequently, the solid is freeze-dried to obtain the target hydrotalcite or hydrotalcite-like material.

[0093] The solid obtained after drying was characterized and the product was identified and analyzed.

[0094] To investigate the influence of the structural composition of hydrotalcite and hydrotalcite-like materials on the amount of carbon dioxide captured from the air during their formation, based on Example 4, other conditions were kept constant, except that the divalent metal nitrate (i.e., magnesium nitrate) added in step 1) was changed to nickel nitrate or zinc nitrate, and the trivalent metal nitrate was kept to be aluminum nitrate or changed to iron nitrate. Finally, MgAl-LDH, NiAl-LDH, ZnAl-LDH, and NiFe-LDH were synthesized under fixed conditions, respectively, to explore the influence of different metal types on the LDH synthesis yield and the amount of carbon dioxide fixed in the target LDH.

[0095] X-ray diffraction analysis was performed on Example 4 of the present invention to identify the mineral phase of the product, and the results are as follows. Figure 4 The results showed that various metal reactions could form the hydrotalcite mineral phase, with ZnAl-LDH exhibiting the best crystallinity. The utilization rate of metal ions and the amount of carbon dioxide fixed in the target hydrotalcite were measured. Table 4 shows the utilization rate of Mg and Al ions and the amount of carbon dioxide fixed during LDH synthesis with different metal participation. The results indicate that various metals can capture CO2 from the air during LDH formation. Adjusting the structural composition of hydrotalcite or hydrotalcite-like minerals can improve the carbon dioxide capture to some extent. For example, replacing Mg in MgAl-LDH with Zn or Ni can increase the carbon dioxide capture from 8.16 mg / g to 12.67 or 12.78 mg / g. In this implementation case, using ZnAl-LDH, producing 1 ton of ZnAl-LDH can capture 12.67 kg of carbon dioxide from the air; based on raw materials, capturing 1 ton of carbon dioxide requires 12.45 tons of Zn and 4.68 tons of Al. Based on NiAl-LDH, capturing 1 ton of carbon dioxide requires the input of 12.55 tons of Ni and 4.71 tons of Al.

[0096] Table 4. Amount of CO2 absorbed from the air during LDH formation with different metals (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0097]

[0098] Example 5

[0099] A method for controlling the capture of CO2 from the air during the formation of hydrotalcite by adjusting the element ratio specifically includes the following steps:

[0100] 1) Prepare 500 mL of a mixed salt solution containing magnesium and aluminum in a molar ratio of 3:1, and simultaneously prepare 500 mL of a 2 mol / L NaOH solution.

[0101] The two solutions were added dropwise to a 2L beaker (with 200mL of ultrapure water pre-added) using an automatic pH dispenser. During the addition, magnetic stirring was maintained and the pH was kept constant at 10 (i.e., the target reaction pH value is 10).

[0102] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours, and then centrifuge to obtain solid product.

[0103] 3) The solid product was washed with water to remove the adsorbed hydroxide ions on the surface. Subsequently, the solid was freeze-dried to obtain the target hydrotalcite (MgAl-LDH).

[0104] The solid obtained after drying was characterized and the product was identified and analyzed.

[0105] To investigate the effects of different magnesium-aluminum ratios on LDH synthesis yield and carbon dioxide fixation in the target mineral, based on Example 5, other conditions were kept constant. The magnesium-aluminum molar ratios were changed to 1:1, 2:1, 3:1, and 4:1, respectively, to synthesize Mg1Al1-LDH, Mg2Al1-LDH, Mg3Al1-LDH, and Mg4Al1-LDH under fixed conditions. The effects of different magnesium-aluminum ratios on LDH synthesis yield and carbon dioxide fixation were explored.

[0106] For Example 5 of the present invention, X-ray diffraction analysis was performed on the product obtained in Example 5 to identify the mineral phases of the product, and the results are as follows. Figure 5 As shown, the results indicate that adjusting different metal ratios can regulate the degree of exothermic crystallization of the hydrotalcite mineral phase; the higher the magnesium-aluminum molar ratio, the better the crystallinity of LDH.

[0107] Furthermore, the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed in the target hydrotalcite were measured. Table 5 shows the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed during LDH synthesis under different metal ratios. The results indicate that as the Mg / Al molar ratio increased from 1:1 to 4:1, the CO2 content captured from the air during LDH formation decreased from 19.58 mg / g to a minimum of 8.16 mg / g, indicating that the amount of carbon dioxide fixed can be controlled by adjusting the molar ratio of Mg and Al added during hydrotalcite formation. In this implementation case, under optimal conditions, producing one ton of MgAl-LDH can capture 19.58 kg of carbon dioxide from the air; based on optimal raw materials, capturing one ton of carbon dioxide requires the input of 19.01 tons of Mg and 7.52 tons of Al.

[0108] Table 5. Amount of CO2 absorbed from the air during LDH formation under different magnesium-aluminum ratios (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0109]

[0110]

[0111] Example 6

[0112] A method for regulating the destruction and reconstruction process of hydrotalcite structure to achieve the cyclic capture of carbon dioxide in the air, specifically including the following steps:

[0113] 1) Take 10g of the target mineral obtained at pH=10 in Example 1, calcine it in a muffle furnace at 500℃ for 3 hours, cool it to room temperature, and weigh it to determine the mass of the calcined product CLDH-1-500℃.

[0114] 2) The solid was then poured into a beaker containing 200 mL of ultrapure water and magnetically stirred at room temperature and pressure. The mixture was then left open for 12 h to react. After centrifugation and freeze-drying, the mass of the total product R-LDH-1 at 500℃ was determined using a balance.

[0115] 3) Subsequently, 8g of product R-LDH-1-500℃ was taken and calcined in a muffle furnace at 500℃ for 3 hours. After cooling to room temperature, the mass of the calcined product CLDH-2-500℃ was determined by weighing.

[0116] 4) The solid was then poured into a beaker containing 200 mL of ultrapure water and magnetically stirred at room temperature and pressure. The mixture was left open for 12 h to react. After centrifugation and freeze-drying, the mass of the total product R-LDH-2-500℃ was determined using a balance.

[0117] 5) Then take 6g of product R-LDH-2-500℃, calcine it in a muffle furnace at 500℃ for 3 hours, cool it to room temperature, and weigh it to determine the mass of the calcined product CLDH-3-500℃.

[0118] 6) The solid was then poured into a beaker containing 200 mL of ultrapure water and magnetically stirred at room temperature and pressure. The mixture was left open for 12 hours, then centrifuged, freeze-dried, and the mass of the total product R-LDH-3-500℃ was determined using a balance. This process was repeated three times.

[0119] To investigate whether the "structural destruction-structural reconstruction" cycle of hydrotalcite can effectively capture carbon dioxide from the air, and to practice controlling the carbon dioxide capture content in this process, this case study explored the effect of calcination temperature based on the relevant experiments at 500℃. The above-mentioned cycle experiments were repeated at 300℃ and 400℃. The calcination system products after three cycles at 300℃ were R-LDH-1-300℃, R-LDH-2-300℃, and R-LDH-3-300℃; the cycle system products were C-LDH-1-300℃, C-LDH-2-300℃, and C-LDH-3-300℃.

[0120] The products of the calcination system after three cycles at 400℃ are R-LDH-1-400℃, R-LDH-2-400℃, and R-LDH-3-400℃; the products of the cycle system are C-LDH-1-400℃, C-LDH-2-400℃, and C-LDH-3-400℃.

[0121] The calcined and recycled products were characterized, and the carbon content and XRD analysis were performed on the products. The products of the hydrotalcite calcination system are referred to as "R-LDH-nT" (n represents the number of cycles and T represents the calcination temperature), and the products of the recycled system are referred to as "C-LDH-nT" (n represents the number of cycles and T represents the calcination temperature).

[0122] The XRD characterization results of the system products at 500℃ are as follows: Figure 6 As shown, the results indicate that the peak shapes of the hydrotalcite products after multiple calcination cycles are consistent with the standard peaks, suggesting that hydrotalcite has the potential to undergo multiple "structural destruction-structural reconstruction" cycles. Furthermore, the effects of calcination temperature and the number of cycles on the capture of carbon dioxide from the air were investigated, and the results are shown below. Figure 7 As shown. Figure 7The results show that the carbon fixation capacity of LDH (hydrotalcite) was significantly improved after calcination at 300℃, 400℃, and 500℃, with each cycle significantly increasing the amount of carbon dioxide fixed. Therefore, adjusting the number of "structure destruction-structure reconstruction" cycles can regulate the amount of carbon dioxide captured. Furthermore, experiments at different calcination temperatures showed that the total carbon fixation after three cycles at 300℃, 400℃, and 500℃ reached 170.8, 216.55, and 160.02 mg / g, respectively, indicating that the amount of carbon dioxide captured from the air during the structure reconstruction process of LDH can be controlled by the calcination temperature.

[0123] In this implementation case, based on three cycles of capture at 400℃, producing 1 ton of MgAl-LDH can cumulatively capture 216.55 kg of carbon dioxide from the air; in terms of raw materials, capturing 1 ton of carbon dioxide requires the input of 1.11 tons of Mg and 0.42 tons of Al. Furthermore, from... Figure 7 It is evident that increasing the number of cycles can significantly increase the amount of carbon dioxide fixed, thereby reducing input costs.

[0124] Example 7

[0125] A method for controlling the capture of CO2 content in the air during the formation of hydrotalcite by adjusting the air contact mode, specifically including the following steps:

[0126] 1) Prepare 500 mL of a mixed salt solution containing 0.18 mol magnesium nitrate and 0.06 mol aluminum nitrate in a magnesium-aluminum molar ratio of 3:1, and simultaneously prepare 500 mL of a 2 mol / L NaOH solution.

[0127] The two solutions were added dropwise to a 2L beaker (pre-filled with 200mL of ultrapure water) using an automatic pH dispenser. Magnetic stirring was maintained during the addition, and the pH was kept constant at 10 (i.e., the target reaction pH was 10). Air was pumped in during the reaction to increase the contact area between the system and the air.

[0128] 2) After mixing, react for 2 hours with continuous stirring, then let stand at room temperature for 12 hours, and then centrifuge to obtain solid product.

[0129] 3) The solid product was washed with water to remove the adsorbed hydroxide ions on the surface. Subsequently, the solid was freeze-dried to obtain the target hydrotalcite (MgAl-LDH).

[0130] The solid obtained after drying was characterized and the product was identified and analyzed.

[0131] To investigate the effects of air contact mode on LDH yield and the amount of carbon dioxide captured from the air during LDH mineral formation, based on Example 7, other conditions were kept constant. A synthesis experiment was conducted by adding air pump to the reaction process, that is, under air pump conditions, the aging time was 0h, 12h, and 24h, respectively, to explore the effect of air pump blowing on the synthesis yield of MgAl-LDH and the amount of carbon dioxide fixed in the target hydrotalcite.

[0132] In Example 7 of this invention, the utilization rates of Mg and Al ions and the amount of carbon dioxide fixed in the target hydrotalcite formed under different aging times under air pump conditions were measured. The utilization rates of Mg and Al ions and the amount of carbon dioxide fixed during LDH synthesis under different aging times under air pump conditions are shown in Table 6. The results show that the amount of carbon dioxide fixed from the air is significantly increased during LDH formation under air pump conditions. Looking at the two sets of experiments with aging times of 12 and 24 hours, the natural gas (air)-liquid contact mode resulted in relatively low carbon dioxide capture from the air (8.16 and 7.89 mg / g), which may be because the gas-liquid exchange process is relatively slow under natural conditions, while the hydrotalcite formation process is relatively fast. However, after air was introduced, the amount of carbon dioxide captured increased significantly, reaching 20.07 and 15.36 mg / g, respectively. This is because the addition of air pumps increases the contact between the system and carbon dioxide in the air. These results indicate that the amount of carbon dioxide captured can be controlled by adjusting the contact mode between air and the reaction liquid during hydrotalcite formation.

[0133] In this implementation case, under optimal conditions, producing one ton of MgAl-LDH can capture 20.07 kg of carbon dioxide from the air; under optimal raw material conditions, capturing one ton of carbon dioxide requires the input of 11.93 tons of Mg and 4.48 tons of Al.

[0134] Table 6 shows the amount of CO2 absorbed from the air during the formation of LDH at different aging times before and after air pump blowing (unit: mg / g, representing the mass of reactants consumed and carbon dioxide absorbed to form 1g of hydrotalcite).

[0135]

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for cyclically capturing low concentrations of carbon dioxide from the air, characterized in that, Includes the following steps: S1. Prepare hydrotalcite or hydrotalcite-like products, wherein the hydrotalcite or hydrotalcite-like products contain carbon dioxide captured from the air; S2. Calcining hydrotalcite or hydrotalcite-like products to obtain calcined product C-LDH-1; S3. The calcined product C-LDH-1 is placed in ultrapure water and stirred. The reaction is carried out in an open environment. The resulting solution is centrifuged and dried to obtain the solid product R-LDH-1. In S3, the open environment reaction allows the calcined product to capture carbon dioxide from the air as an interlayer equilibrium anion during the hydration and reconstruction of the hydrotalcite structure. S4. Repeat S2-S3 sequentially to obtain multiple cyclic products, thereby achieving multiple captures of carbon dioxide from the air. During each calcination process, the solid product releases purified carbon dioxide gas. The carbon dioxide gas is collected by a suitable pipeline collection system to achieve the collection and production of carbon dioxide products. In S1, the content of carbon dioxide captured from the air during the formation of hydrotalcite or hydrotalcite-like products is controlled by adjusting the reaction conditions and reaction elements, including the following steps: Step 1: At a reaction temperature of 25-80℃, a mixed salt solution of divalent and trivalent metals is mixed with an alkaline solution. During the mixing process, the pH is kept constant at 6-10 to obtain a turbid reaction solution. In Step 1, the mixed solution of divalent and trivalent metals can be a magnesium-aluminum mixed solution, a zinc-aluminum mixed solution, a nickel-iron mixed solution, or a nickel-aluminum mixed solution. Step 2: Continue stirring the turbid reaction solution, and then allow it to stand and age at the reaction temperature; Step 3: After aging, centrifuge the reaction solution to obtain a solid precipitate and a supernatant. Wash the solid precipitate until the pH of the supernatant is neutral to obtain the solid product. Step 4: After drying the solid product, hydrotalcite or hydrotalcite-like products are obtained.

2. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In step one, the pH is kept constant at 7-9.

3. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In step one, the molar ratio of divalent metal to trivalent metal in the mixed salt solution is (1-4):

1.

4. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In step one, the alkaline solution is a sodium hydroxide solution.

5. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In step two, the aging time is 0 to 24 hours.

6. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In S2, the calcination temperature is 300~500℃.

7. The method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, In S3, the drying method is oven drying, freeze drying, or natural drying; the drying temperature does not exceed 80℃.

8. A method for cyclically capturing low-concentration carbon dioxide from the air according to claim 1, characterized in that, After the recycled products lose their activity, they are dissolved in an acidic solution to form a bimetallic mixed solution, which is then mixed with an alkaline solution to resynthesize hydrotalcite or hydrotalcite-like minerals.

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