A method for the preparation of a porous hydrated calcium silicate solid adsorbent for direct capture of co2 from the atmosphere

Abstract

The application discloses a preparation method of a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from atmosphere, and the method comprises the following steps: mixing a silicon solution and a calcium solution to form a precursor, stirring, solid-liquid separation, taking the solid, drying, putting into a liquid environment again, centrifugal separation and drying to obtain the solid. The adsorbent can be applied to CO2 capture in different CO2 concentration environments. Under the same conditions, compared with a traditional hydrated calcium silicate adsorbent, the adsorbent prepared by the method has refined pore size and higher specific surface area, can quickly capture CO2 in the early stage of adsorption, and especially enhances the ability of the hydrated calcium silicate to directly capture CO2 in the atmospheric environment. The preparation method can maintain the system pure, and has simple process and low cost. The preparation method of the porous hydrated calcium silicate can be theoretically extended to other inorganic substances which can obtain stable non-classical precursors.

Description

Technical Field

[0001] This invention belongs to the fields of inorganic non-metallic materials and environment, and particularly relates to a method for preparing a porous hydrated calcium silicate solid adsorbent that directly captures CO2 from the atmosphere. Background Technology

[0002] As of April 4, 2023, the concentration of CO2 in the atmosphere had reached 422.73 ppm, an increase of nearly 30 ppm compared to 2010. This has had a huge impact on the world environment, such as the greenhouse effect and glacial melting, and has had a great negative impact on the human world.

[0003] Traditional carbon capture methods typically involve capturing and storing CO2 at large point sources before or after combustion. This effectively prevents the concentration of CO2 in the atmosphere from increasing, but it relies on large power sources and can only mitigate carbon emissions, not directly remove CO2 from the air to reduce its concentration. Therefore, direct air capture (DAC) is highly anticipated. However, DAC places high demands on adsorbent materials. Commonly used amine-based liquid adsorbents have high CO2 adsorption capacity, but they corrode equipment and cause high energy consumption due to solvent evaporation during regeneration. Solid adsorbents, such as MOFs, suffer from poor gas selectivity and stability, making it difficult to accurately remove CO2 from the atmosphere. Their adsorption capacity is also low at atmospheric pressure, and only a limited number of functionalized MOFs can achieve DAC. Therefore, developing new and excellent solid adsorbents capable of directly capturing CO2 from the air is an urgent need to address the problem of excessive carbon emissions.

[0004] To address the aforementioned technical issues, liquid amine adsorbents are loaded into a porous framework through physical impregnation, silane linking, and in-situ polymerization. The resulting "solid amine" adsorbent has advantages such as high carbon absorption capacity, strong selectivity for CO2, and no corrosion to equipment. However, its process is complex and costly, making it difficult to apply on a large scale to DACs. Summary of the Invention

[0005] Objective of the Invention: This invention aims to provide a method for preparing a porous hydrated calcium silicate solid adsorbent that directly captures CO2 from the atmosphere. This method utilizes a hydrated calcium silicate precursor to refine the pore structure of this inexpensive calcium-silicon mineral, increasing the surface area in contact with air and achieving rapid CO2 absorption. The process is very simple and requires no additional templates or pore-forming agents.

[0006] Technical Solution: The present invention discloses a method for preparing a porous hydrated calcium silicate solid adsorbent that directly captures CO2 from the atmosphere. The porous hydrated calcium silicate solid adsorbent is prepared by the following method: a silicon solution and a calcium solution are mixed to form a precursor, which is then stirred, separated into solid and liquid components, and dried to obtain a dried CSH precursor. The dried CSH precursor is placed in a liquid environment, and the CSH precursor undergoes transformation using its own spherical precursor as a template. After the transformation is completed, the product is collected to obtain the porous hydrated calcium silicate solid adsorbent.

[0007] Preferably, the silicon solution is a sodium metasilicate solution with a concentration of less than or equal to 0.1 mol / L; more preferably, the concentration of the sodium metasilicate solution is 0.05 mol / L to 0.1 mol / L. When the concentration is higher than 0.1 mol / L, the hydrated calcium silicate forms flakes before separation, and after drying, the nano-sized flakes of hydrated calcium silicate agglomerate, reducing the specific surface area.

[0008] Preferably, the calcium solution is a calcium nitrate solution or a calcium chloride solution.

[0009] Preferably, after mixing the silicon solution and the calcium solution, the molar ratio of calcium to silicon is 0.8 to 1.5. When the molar ratio of calcium to silicon is less than 0.8, the mass of hydrated calcium silicate obtained is too small; when the molar ratio is greater than 1.5, impurities such as calcium hydroxide will be generated, affecting the purity and structure of hydrated calcium silicate.

[0010] Preferably, after mixing the silicon solution and the calcium solution, the reaction is carried out for 10–60 seconds, followed by solid-liquid separation. Solid-liquid separation is performed immediately after mixing the silicon solution and the calcium solution. If the reaction time is too long, the hydrated calcium silicate will form flakes before separation, and after drying, it will agglomerate, reducing the specific surface area.

[0011] Preferably, the solid-liquid separation method is a vacuum filtration method. The solid-liquid separation employs vacuum filtration, and the solid precipitate is washed with water and ethanol, respectively.

[0012] Preferably, after vacuum filtration, the obtained hydrated calcium silicate is washed and then vacuum dried at 25 to 60°C for 3 to 7 days to obtain the dried CSH precursor. The vacuum drying temperature is 25-60°C. Drying efficiency is too low when the drying temperature is below 25°C; and the nanostructure of the hydrated calcium silicate will be damaged when the drying temperature is above 60°C.

[0013] Preferably, the liquid environment is water, calcium nitrate solution, or sodium hydroxide solution, with a liquid-to-solid mass ratio of 200:1. The hydrated calcium silicate precursor grows into a sheet-like structure in the liquid environment. The solid framework of the precursor itself prevents stacking between the converted hydrated calcium silicate nanosheets, greatly refining the pore structure and increasing the specific surface area.

[0014] Preferably, the dried CSH precursor is placed in a liquid environment for 12 to 24 hours. The dried precursor is then placed in a liquid environment for several hours to a day. If the precursor is placed in too short a time, it will not have been converted into flake-like hydrated calcium silicate; if it is placed in too long a time, the hydrated calcium silicate will carbonize, producing impurities such as calcium carbonate and silica gel.

[0015] Preferably, the method for collecting the product is centrifugation, with a centrifugation speed of 5000-12000 rpm.

[0016] Calcium silicate hydrate is an amorphous nanomaterial whose nanoscale layered structure provides a large number of intrinsic pores, resulting in a high specific surface area (10-200 m²). 2 / g, depending on synthesis conditions). The adsorption mechanism of CO2 by hydrated calcium silicate is that calcium in the structure combines with CO2 to form calcium carbonate precipitate. The nanoscale size, porous structure formed by its own precursor as a framework, and huge specific surface area of ​​the hydrated calcium silicate we prepared enable CO2 to react rapidly with hydrated calcium silicate even at very low partial pressures (such as in the atmosphere).

[0017] This invention utilizes a precursor of hydrated calcium silicate as a framework and completes the transformation of the precursor into sheet-like hydrated calcium silicate in a liquid environment, forming a honeycomb structure. This solves the problem of layer stacking in hydrated calcium silicate, releasing the internal closed pores and surfaces, and enabling porous hydrated calcium silicate to absorb atmospheric CO2. This preparation method requires no templates, pore-forming agents, or the addition of any other substances during the synthesis of hydrated calcium silicate, ensuring system purity, simple process, and no increase in cost, while also accelerating the CO2 absorption capacity of hydrated calcium silicate. Furthermore, this strategy of using a precursor as a framework for transformation may be applicable to other materials.

[0018] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention proposes a method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere; without the addition of any other substances, the specific surface area of ​​hydrated calcium silicate is increased by >400%, and in the application of directly capturing CO2 from the atmosphere, compared with ordinary hydrated calcium silicate adsorbents, the absorption of CO2 is accelerated by 432.2% within 1 hour. This preparation method can maintain the purity of the system, while the process is simple and low in cost; theoretically, the porous hydrated calcium silicate preparation method proposed in this invention can be extended to other inorganic substances that can obtain stable non-classical precursors. Attached Figure Description

[0019] Figure 1 Schematic diagram of the preparation method of porous hydrated calcium silicate solid adsorbent;

[0020] Figure 2 A schematic diagram of the preparation method of conventional hydrated calcium silicate solid adsorbent;

[0021] Figure 3 Aperture distribution of the examples and comparative examples;

[0022] Figure 4 SEM images of Examples 1 and 2;

[0023] Figure 5 SEM images from Examples 3 and 4;

[0024] Figure 6 SEM images from Examples 5 and 6;

[0025] Figure 7 SEM images for comparison examples 1 and 2. Detailed Implementation

[0026] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a porous hydrated calcium silicate solid adsorbent that directly captures CO2 from the atmosphere. The method involves mixing a silicon solution and a calcium solution to form a precursor, stirring, separating the solid from the liquid, drying the solid, and then placing it in a liquid environment for conversion. The precursor is then centrifuged and dried to obtain the final product.

[0027] The present invention will be further described in conjunction with the embodiments.

[0028] Example 1

[0029] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in pure water at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours.

[0030] Example 2

[0031] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in pure water at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 5% to adsorb CO2 for 96 hours.

[0032] Example 3

[0033] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in 0.20 mol / L calcium nitrate solution at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours.

[0034] Example 4

[0035] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in 0.20 mol / L calcium nitrate solution at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 5% to adsorb CO2 for 96 hours.

[0036] Example 5

[0037] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in a 0.20 mol / L sodium hydroxide solution at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours.

[0038] Example 6

[0039] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution to form a precursor. Immediately after 30 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried to constant weight in an oven at 45°C. Subsequently, the dried precursor powder was placed in a 0.20 mol / L sodium hydroxide solution at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried to constant weight in an oven at 45°C. The dried powder was then placed in an environment with a CO2 concentration of 5% to adsorb CO2 for 96 hours.

[0040] Example 7

[0041] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.04 mol / L sodium silicate solution to form a precursor. Immediately after a 10-second reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried in an oven at 25°C for 7 days until constant weight. Subsequently, the dried precursor powder was placed in pure water at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the powder was again dried in an oven at 25°C until constant weight. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours.

[0042] Example 8

[0043] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.075 mol / L sodium silicate solution to form a precursor. Immediately after 60 seconds of reaction, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried in a 60°C oven for three days until constant weight. Subsequently, the dried precursor powder was placed in pure water at a liquid-to-solid ratio of 200:1 and reacted for 12 hours. After centrifugation, the powder was again dried in a 60°C oven until constant weight. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours.

[0044] like Figure 2 As shown, Comparative Examples 1-2 are calcium silicate hydrates prepared using conventional synthesis methods.

[0045] Comparative Example 1

[0046] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution. After reacting for 24 h, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried in an oven at 45 °C to constant weight. The dried powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 h.

[0047] Comparative Example 2

[0048] 100 mL of 0.05 mol / L calcium nitrate solution was mixed with an equal volume of 0.05 mol / L sodium silicate solution. After reacting for 24 h, the mixture was vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried in an oven at 45 °C to constant weight. The dried powder was then placed in an environment with a CO2 concentration of 5% to adsorb CO2 for 96 h.

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that the concentration of the sodium silicate solution is higher than 0.1 mol / L. The specific steps are as follows:

[0051] 100 mL of 0.12 mol / L calcium nitrate solution was mixed with an equal volume of 0.12 mol / L sodium silicate solution. After reacting for 30 seconds, the mixture was immediately vacuum filtered to separate the solid from the liquid. The obtained solid was washed three times each with water and ethanol, and then dried in an oven at 45°C to constant weight. Note that because the concentration of the sodium silicate solution was higher than 0.1 mol / L, the reaction between the calcium nitrate solution and the sodium silicate solution was too rapid. Although the solid and liquid were separated immediately after 30 seconds, the precursor formed by the sodium silicate solution and the sodium silicate solution did not have time to separate before being converted into lamellar hydrated calcium silicate.

[0052] Subsequently, the dried, layered calcium silicate hydrate was placed in pure water at a liquid-to-solid ratio of 200:1 and reacted for 24 hours. After centrifugation, the product was dried again in an oven at 45°C until constant weight. The dried calcium silicate hydrate powder was then placed in an environment with a CO2 concentration of 0.023% to adsorb CO2 for 336 hours. The microstructure of the product was the same as that of Comparative Example 1, and the final adsorption effect was also the same as that of Comparative Example 1.

[0053] The examples are porous hydrated calcium silicate prepared by the method proposed in this invention, while the comparative examples are hydrated calcium silicate prepared using conventional synthesis methods. The specific surface area and pore size distribution of the products in each example were determined using the N2 adsorption method, the microstructure of the products was observed using scanning electron microscopy (SEM), and the CO2 adsorption capacity was determined using the rate of change of mass and TG. The preparation methods and performance of each example are summarized in the table below.

[0054] Table 1

[0055]

[0056] It can be seen that the porous hydrated calcium silicate prepared by this invention has a honeycomb morphology, unlike the layered hydrated calcium silicate prepared by conventional methods. Under atmospheric conditions (CO2 concentration of 0.023%) and accelerated carbonization conditions (CO2 concentration of 5%), the hydrated calcium silicate prepared by our new strategy can adsorb CO2 more rapidly than conventionally prepared hydrated calcium silicate. Without the addition of other modifying substances, the pore size of the hydrated calcium silicate is significantly refined, and the specific surface area is increased by >400%. In applications of direct atmospheric CO2 capture, compared with ordinary hydrated calcium silicate adsorbents, the absorption of CO2 is accelerated by 432.2% within 1 hour.

Claims

1. A method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere, characterized in that, The porous hydrated calcium silicate solid adsorbent is prepared by the following method: a silicon solution and a calcium solution are mixed to form a precursor; the mixture is stirred for 10-60 seconds, followed by solid-liquid separation, and then vacuum dried at 25°C to 60°C for 3-7 days to obtain a dried CSH precursor; the dried CSH precursor is placed in a liquid environment for 12-24 hours, and the CSH precursor undergoes transformation using its own spherical precursor as a template. After the transformation is complete, the product is collected, thus obtaining a honeycomb-structured porous hydrated calcium silicate solid adsorbent; the silicon solution is a sodium metasilicate solution, and the concentration of the sodium metasilicate solution should be less than or equal to 0.1 mol / L; after mixing the silicon solution and the calcium solution, the calcium content is: The molar ratio of silicon is 0.8 to 1.5; the liquid environment is water, calcium nitrate solution, or sodium hydroxide solution.

2. The method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere according to claim 1, characterized in that, The calcium solution is either calcium nitrate solution or calcium chloride solution.

3. The method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere according to claim 1, characterized in that, The solid-liquid separation method is vacuum filtration.

4. The method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere according to claim 3, characterized in that, After vacuum filtration, the obtained hydrated calcium silicate is washed and then dried to obtain the dried CSH precursor.

5. The method for preparing a porous hydrated calcium silicate solid adsorbent for directly capturing CO2 from the atmosphere according to claim 1, characterized in that, The method for collecting the product is centrifugation, with a centrifugation speed of 5000-12000 rpm.

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