Calcium-based co2 sorbent of porous structure, preparation method and application thereof

Abstract

This invention provides a porous calcium-based CO2 adsorbent, its preparation method, and its application. The preparation method includes: S1, adding a metal source (a calcium source and a second metal source, wherein the second metal in the second metal source includes one or a combination of aluminum, magnesium, titanium, zirconium, yttrium, cerium, lanthanum, neodymium, and ytterbium), ethylene glycol, citric acid, polyvinylpyrrolidone, and urea to deionized water, and stirring at room temperature to form a mixture; S2, placing the mixture into a hydrothermal reactor, allowing it to stand at 120–160°C for 18–30 h, cooling to room temperature, centrifuging, and washing to obtain a solid product; S3, drying and grinding the solid product to obtain a solid powder; S4, calcining the solid powder in air and cooling to obtain the calcium-based CO2 adsorbent. This invention uses a hydrothermal synthesis method to prepare a calcium-based CO2 adsorbent with nano-CaO particle size, uniform doping of structural stabilizers, and a porous framework, exhibiting high CO2 isothermal adsorption-desorption performance and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature carbon dioxide capture technology, and in particular relates to a porous calcium-based CO2 adsorbent, its preparation method and its application. Background Technology

[0002] The combustion of fossil fuels leads to massive CO2 emissions, causing a series of global climate change problems and seriously threatening the sustainable development of human society. Therefore, large-scale carbon emission reduction in the fossil energy industry is imperative. Based on resource endowment, coal-fired power plants are my country's most important large-scale stationary CO2 emission sources, characterized by large emissions, high emission temperatures, and low CO2 concentrations. Therefore, the development of efficient and low-cost high-temperature CO2 capture technology is of great significance.

[0003] Among existing technologies, calcium-based chemical chaining (CaL) is the most promising high-temperature CO2 capture technology due to the advantages of CaO, such as its wide availability, low price, environmental friendliness, and high high-temperature CO2 adsorption capacity. The reaction principle of CaL technology is as follows: CaO reacts with CO2 to generate CaCO3 (i.e., CaO carbonation or CO2 adsorption), and then CaCO3 is calcined and decomposed into CaO and CO2 (i.e., CaO regeneration or CO2 desorption). This reversible process is greatly affected by thermodynamic equilibrium. To achieve high CO2 capture capacity and good adsorbent regeneration, traditional CaL processes typically employ variable-temperature operation, for example, adsorption at 600–700℃ and desorption at 800–900℃. This leads to two serious problems: firstly, repeated variable-temperature operation greatly increases the energy consumption of CO2 capture and reduces the timeliness of CO2 treatment; secondly, CaCO3 has poor thermal stability and is prone to sintering during high-temperature calcination, causing the CO2 capture capacity of the adsorbent to decrease rapidly with increasing cycle number. These problems greatly limit the large-scale application of CaL technology. Developing a highly stable calcium-based CO2 adsorbent with isothermal adsorption-desorption properties is crucial for CaL technology.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a porous calcium-based CO2 adsorbent, its preparation method and its application, to solve the problems of increased energy consumption for CO2 capture and low timeliness of CO2 disposal caused by the use of variable temperature adsorption-desorption in the CaL process in the prior art, as well as the problems of poor anti-sintering ability and poor cycle stability of the calcium-based CO2 adsorbent in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a method for preparing a porous calcium-based CO2 adsorbent, the method comprising the following steps:

[0007] S1. Add the metal source, ethylene glycol, citric acid, polyvinylpyrrolidone and urea to deionized water and stir at room temperature to form a homogeneous mixture; wherein the metal source includes a calcium source and a second metal source, and the second metal in the second metal source includes one or a combination of aluminum, magnesium, titanium, zirconium, yttrium, cerium, lanthanum, neodymium and ytterbium.

[0008] S2. The mixture is placed in a hydrothermal reactor and left to stand in a constant temperature oven at 120-160°C for 18-30 hours. After cooling naturally to room temperature, it is then centrifuged and washed to obtain a solid product.

[0009] S3. The solid product is placed in a constant temperature oven to dry, and then ground to obtain solid powder;

[0010] S4. The solid powder is calcined in air and then cooled to obtain a calcium-based CO2 adsorbent.

[0011] Preferably, the calcium source in step S1 is one or a combination of calcium acetate and calcium nitrate; the second metal source is an acetate or nitrate of a second metal.

[0012] Preferably, the metal ions in the metal source in step S1 include calcium ions and a second metal ion, and the molar ratio between the calcium ions and the second metal ions is 1:0.1 to 1:9.

[0013] Preferably, the molar ratio between ethylene glycol, citric acid and metal ions in the metal source in step S1 is (3-1):(3-1):1.

[0014] Preferably, the molar ratio between polyvinylpyrrolidone and metal ions in the metal source in step S1 is 1:1 to 9:1.

[0015] Preferably, the molar ratio between urea and metal ions in the metal source in step S1 is 0.5:1 to 3:1.

[0016] Preferably, in the mixture obtained in step S1, the total concentration of metal ions in the metal source is 0.1 to 0.5 mol / L.

[0017] Preferably, the washing in step S2 includes washing with deionized water and washing with anhydrous ethanol, wherein the washing with deionized water is performed at least once, and the washing with anhydrous ethanol is performed at least once.

[0018] Preferably, the drying temperature in step S3 is 60–100°C, and the drying time is 12–24 hours.

[0019] Preferably, the roasting process in step S4 includes a step of stepped heating and holding, specifically: first heating from room temperature to 150-180°C and holding for 30-60 minutes; then heating to 300-350°C and holding for 30-60 minutes; then heating to 500-550°C and holding for 30-120 minutes; and finally heating to 700-800°C.

[0020] Preferably, the heating rates for the first, second, third, and fourth heating cycles are all 1–5 °C / min.

[0021] The present invention also provides a porous calcium-based CO2 adsorbent, which is prepared by the above-described preparation method.

[0022] The present invention also provides an application of the porous calcium-based CO2 adsorbent prepared by the above-described preparation method, wherein the calcium-based CO2 adsorbent is applied to isothermal CO2 adsorption-desorption; wherein the isothermal CO2 adsorption-desorption temperature is 550-650°C, and the CO2 concentration during the isothermal CO2 adsorption-desorption ranges from 0.5 vol.% to 15 vol.%.

[0023] As described above, the porous calcium-based CO2 adsorbent, its preparation method, and its application of the present invention have the following beneficial effects:

[0024] This invention introduces ethylene glycol and citric acid to form an "ethylene glycol-citric acid-metal ion" chelate, promoting the homogeneous mixing of calcium ions and the second metal ion (structural stabilizer ion). The hydrolysis of urea is used to regulate the pH of the solution, improving the uniformity of the metal chelate. Polyvinylpyrrolidone (PVP) is a nonionic surfactant that protects the formed nanoparticles and prevents their aggregation. During the calcination step, PPVP is decomposed, burned, and removed, resulting in a rich porous structure. A calcium-based CO2 adsorbent with nano-CaO particle size, uniform doping of the second metal oxide (structural stabilizer), and a porous framework is prepared using a hydrothermal synthesis method. The synthesis method is simple and easy to operate, enabling industrial production.

[0025] In the porous calcium-based CO2 adsorbent prepared in this invention, the CaO crystal size is small, exhibiting a faster CO2 adsorption-desorption rate; the structural stabilizer is uniformly dispersed in the CaO framework at the nanoscale, effectively inhibiting the sintering of CaO particles; the abundant macropores in the framework provide sufficient space for the periodic deformation of the adsorbent during the CO2 adsorption-desorption process, further preventing structural collapse.

[0026] The porous calcium-based CO2 adsorbent prepared in this invention exhibits high CO2 isothermal adsorption-desorption performance and cycling stability, effectively solving the problems of high energy consumption and low efficiency in calcium-based chemical loop CO2 high-temperature capture technology, and has great industrialization value. It can achieve isothermal CO2 adsorption-desorption processes at relatively low temperatures (550–650℃) and over a wide CO2 concentration range (0.5–15 vol.%), and can be applied to most CO2 stationary emission sources. Furthermore, this calcium-based CO2 adsorbent combines high capture capacity and high cycling stability; the porous calcium-based adsorbent doped with the structural stabilizer MgO achieves a CO2 capture capacity of 0.568 g CO2 / g at 650℃ and a CO2 concentration of 15 vol.%. 吸附剂 After 50 isothermal adsorption-desorption cycles, the capture capacity still remains above 90% of the initial value. Attached Figure Description

[0027] Figure 1 The XRD patterns of the calcium-based CO2 adsorbents prepared in Example 1 and Comparative Examples 1 to 3 of this invention are shown.

[0028] Figure 2 The images shown are SEM images of the calcium-based CO2 adsorbents prepared in Examples 1 and 3 of the present invention.

[0029] Figure 3 The figure shows the change curve of the calcium-based CO2 adsorbent's CO2 capture capacity with the number of cycles during isothermal adsorption-desorption at 650°C and 15 vol.% CO2 concentration, as prepared in Example 1 and Comparative Examples 1 to 3 of the present invention.

[0030] Figure 4 The figures show the changes in CO2 capture capacity of the porous calcium-based CO2 adsorbent (CaMg-1) prepared in Example 1 of this invention with the number of cycles at 550°C and 15 vol.% CO2 concentration, and at 550°C and 0.5 vol.% CO2 concentration. Detailed Implementation

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] This invention provides a method for preparing a porous calcium-based CO2 adsorbent, the method comprising the following steps:

[0033] S1. Add the metal source, ethylene glycol, citric acid, polyvinylpyrrolidone and urea to deionized water and stir at room temperature to form a homogeneous mixture; wherein, the metal source includes a calcium source and a second metal source, and the second metal in the second metal source includes one or a combination of aluminum, magnesium, titanium, zirconium, yttrium, cerium, lanthanum, neodymium and ytterbium.

[0034] S2. The mixture is placed in a hydrothermal reactor and left to stand in a constant temperature oven at 120-160℃ (e.g., any value within the range of 120℃, 130℃, 140℃, 150℃, 160℃, etc.) for 18-30 hours (e.g., any value within the range of 18h, 21h, 24h, 27h, 30h, etc.). After that, it is naturally cooled to room temperature, then centrifuged and washed to obtain the solid product.

[0035] S3. Place the solid product in a constant temperature oven to dry, and then grind it to obtain solid powder;

[0036] S4. Place the solid powder in a muffle furnace and calcine it in an air atmosphere. After cooling, obtain a calcium-based CO2 adsorbent.

[0037] Specifically, the second metal source serves as a structural stabilizer source. The second metal oxides corresponding to the second metal (Al2O3, MgO, TiO2, ZrO2, Y2O3, CeO2, La2O3, Nd2O3, Yb2O3, etc.) are all heat-resistant. They are incorporated into the CaO matrix as structural stabilizers to enhance the anti-sintering ability of calcium-based adsorbents. However, the strengthening effect depends on whether the structural stabilizer can be uniformly distributed in the CaO framework at the nanoscale. In a specific embodiment of the present invention, ethylene glycol and citric acid are introduced to form an "ethylene glycol-citric acid-metal ion" chelate, which promotes the homogeneous mixing of calcium ions and the second metal ions. The pH of the solution is controlled by the hydrolysis of urea to improve the uniformity of the metal chelate, so that the structural stabilizer is uniformly dispersed in the CaO framework at the nanoscale, effectively inhibiting the sintering of CaO particles.

[0038] Specifically, in the porous calcium-based CO2 adsorbent prepared in the specific embodiments of the present invention, the CaO crystal size is less than 40 nm, exhibiting a relatively fast CO2 adsorption-desorption rate. The CaO crystal size is mainly related to the content of the structural stabilizer (second metal) and the amount of polyvinylpyrrolidone. Generally, increasing the content of the structural stabilizer in the adsorbent is beneficial to reducing the CaO crystal size, and increasing the amount of polyvinylpyrrolidone in the preparation process helps to obtain a smaller CaO particle size. In the preparation method, the molar ratio of calcium ions to second metal ions can be reduced, or the molar ratio of polyvinylpyrrolidone to metal ions in the metal source can be increased to control the particle size.

[0039] Meanwhile, since the molar volume of CaCO3 is much larger than that of CaO, the adsorbent inevitably undergoes periodic expansion and contraction during the CO2 cyclic adsorption-desorption process. This requires the prepared calcium-based CO2 adsorbent to have a certain level of porosity to cope with the structural collapse caused by periodic deformation. In the specific embodiment of the present invention, polyvinylpyrrolidone is added. As a nonionic surfactant, polyvinylpyrrolidone can protect the formed nanoparticles and prevent them from agglomerating. In the calcination step, polyvinylpyrrolidone will be decomposed, burned and removed, resulting in a rich pore structure. The abundant macropores in the framework provide sufficient space for the periodic deformation of the adsorbent during the CO2 adsorption-desorption process, further preventing structural collapse.

[0040] As an example, in step S1, the calcium source is one or a combination of calcium acetate and calcium nitrate; the second metal source is an acetate or nitrate of a second metal.

[0041] Specifically, calcium acetate is preferably calcium acetate monohydrate, and calcium nitrate is preferably calcium nitrate tetrahydrate; the second metal includes one or a combination of aluminum, magnesium, titanium, zirconium, yttrium, cerium, lanthanum, neodymium, and ytterbium. When the second metal is magnesium, the corresponding second metal source is magnesium acetate or magnesium nitrate, wherein magnesium acetate is preferably magnesium acetate tetrahydrate, and magnesium nitrate is preferably magnesium nitrate hexahydrate.

[0042] As an example, the metal ions in the metal source in step S1 include calcium ions and second metal ions, and the molar ratio between calcium ions and second metal ions is 1:0.1 to 1:9.

[0043] Specifically, the molar ratio between calcium ions and the second metal ions can be any value within a range such as 1:0.1, 1:0.5, 1:1, 1:3, 1:5, 1:7, 1:9, etc., and can be adjusted according to actual conditions. The second metal oxide is doped into the CaO matrix as a structural stabilizer. The content of the second metal will affect the size of CaO in the adsorbent, the porosity of the adsorbent, and the trapping capacity of the adsorbent. Although increasing the content of the second metal is beneficial to reducing the CaO particle size and increasing the porosity, it will reduce its trapping capacity.

[0044] As an example, in step S1, the molar ratio between ethylene glycol, citric acid and metal ions in the metal source is (3-1):(3-1):1.

[0045] Specifically, the molar ratio between ethylene glycol, citric acid, and metal ions in the metal source can be any value within a range such as 3:3:1, 3:2:1, 3:1:1, 2:3:1, 2:2:1, 2:1:1, 1:3:1, 1:2:1, 1:1:1, etc. The introduction of ethylene glycol and citric acid forms an "ethylene glycol-citric acid-metal ion" chelate, which promotes the homogeneous mixing of calcium ions and the second metal ions in the structure stabilizer. The metal ions in the metal source include calcium ions and the second metal ions.

[0046] As an example, the molar ratio between polyvinylpyrrolidone (PVP) and metal ions in the metal source is 1:1 to 9:1.

[0047] Specifically, the molar ratio between polyvinylpyrrolidone and metal ions in the metal source can be any value within a range such as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc., and can be adjusted according to actual conditions. As a nonionic surfactant, polyvinylpyrrolidone can protect the formed nanoparticles, so that the structural stabilizer (second metal oxide) is uniformly dispersed in the CaO framework at the nanoscale, preventing its agglomeration.

[0048] As an example, the molar ratio between urea and metal ions in the metal source is 0.5:1 to 3:1.

[0049] Specifically, urea hydrolysis is used to regulate the pH of the solution and improve the uniformity of the "ethylene glycol-citric acid-metal ion" chelate. The molar ratio between urea and the metal ions in the metal source can be any value within the range of 0.5:1, 1:1, 2:1, 3:1, etc., and can be adjusted according to actual conditions.

[0050] As an example, in the mixture obtained in step S1, the total concentration of metal ions in the metal source is 0.1 to 0.5 mol / L.

[0051] Specifically, the metal ions in the metal source include calcium ions and second metal ions. In the mixed solution, the total concentration of metal ions in the metal source can be any value within a range such as 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc., and can be adjusted according to actual conditions.

[0052] As an example, the washing in step S2 includes washing with deionized water and washing with anhydrous ethanol, with the washing with deionized water performed at least once and the washing with anhydrous ethanol performed at least once.

[0053] Preferably, the product is washed three times with deionized water and then once with anhydrous ethanol.

[0054] As an example, the drying temperature in step S3 is 60–100°C, and the drying time is 12–24 hours.

[0055] Specifically, the drying temperature in step S3 can be any value within the range of 60℃, 70℃, 80℃, 90℃, 100℃, etc., and can be adjusted according to the actual situation; the drying time can be any value within the range of 12h, 15h, 18h, 21h, 24h, etc., and can be adjusted according to the actual situation.

[0056] As an example, the roasting procedure in step S4 includes a stepped heating and holding process, specifically: first, the temperature is raised from room temperature to 150–180°C (e.g., any value within the range of 150°C, 160°C, 170°C, 180°C, etc.), and held at that temperature for 30–60 minutes (e.g., any value within the range of 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc.); then, the temperature is raised a second time to 300–350°C (e.g., any value within the range of 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, etc.), and held at that temperature for 30–60 minutes (e.g., any value within the range of 300°C, 40 minutes, 50 minutes, 60 minutes, etc.). The temperature is raised to 500-550℃ (e.g., 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, etc.) and held for 30-120 minutes (e.g., 30min, 45min, 60min, 75min, 90min, 105min, 120min, etc.); finally, the temperature is raised to 700-800℃ (e.g., 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, etc.).

[0057] As an example, the heating rates for the first, second, third, and fourth heating cycles are all 1–5 °C / min.

[0058] Specifically, the heating rates for the first, second, third, and fourth heating cycles can be any value within a range such as 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, and can be adjusted according to actual conditions.

[0059] In the specific embodiments of this invention, a stepped heating program is used to calcine the adsorbent in a gentler manner, so as to avoid the sintering of adsorbent particles caused by the violent decomposition of metal oxide precursors and polyvinylpyrrolidone, which would adversely affect the CO2 adsorption-desorption performance. Therefore, excessively rapid heating rate, excessively high calcine temperature, and excessively long isothermal time may all lead to larger adsorbent particles and reduced porosity, thereby reducing its CO2 adsorption-desorption performance and cycle stability.

[0060] This invention also provides a porous calcium-based CO2 adsorbent, which is prepared using the above-described preparation method. Furthermore, this invention provides an application of the porous calcium-based CO2 adsorbent, which is used for isothermal CO2 adsorption-desorption; wherein the isothermal CO2 adsorption-desorption temperature is 550–650°C, and the CO2 concentration during isothermal CO2 adsorption-desorption ranges from 0.5 vol.% to 15 vol.%.

[0061] Specifically, the porous calcium-based CO2 adsorbent of this invention can achieve isothermal CO2 adsorption-desorption processes at relatively low temperatures and over a wide range of CO2 concentrations, and can be applied to most CO2 stationary emission sources. The isothermal CO2 adsorption-desorption temperature can include any value within the range of 550℃, 570℃, 590℃, 600℃, 620℃, 640℃, 650℃, etc., and can be adjusted according to actual conditions. The CO2 concentration range during isothermal CO2 adsorption-desorption can include any value within the range of 0.5 vol.%, 1 vol.%, 5 vol.%, 10 vol.%, 15 vol.%, etc., and can be adjusted according to actual conditions.

[0062] To better understand the porous calcium-based CO2 adsorbent, its preparation method, and its application in this invention, specific embodiments are described below. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0063] Example 1

[0064] This embodiment provides a porous calcium-based CO2 adsorbent doped with MgO, and its preparation method includes the following steps:

[0065] S1. Add 2.64g calcium acetate monohydrate, 3.22g magnesium acetate tetrahydrate, 3.4mL ethylene glycol, 5.76g citric acid, 16.67g polyvinylpyrrolidone, and 4.5g urea to 120mL deionized water and stir at room temperature for 2 hours until a homogeneous mixture is formed; wherein, the polyvinylpyrrolidone used in this example is PVP10;

[0066] S2. The mixture is placed in a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. After standing in a constant temperature oven at 120°C for 24 hours, the hydrothermal reactor is removed and allowed to cool naturally to room temperature. The product is then collected by centrifugation using a high-speed centrifuge. The product is washed three times with deionized water and then once with anhydrous ethanol to obtain a solid product.

[0067] S3. Place the solid product in a constant temperature oven and dry it at 60°C for 18 hours, then grind it thoroughly to obtain solid powder;

[0068] S4. The solid powder is placed in a muffle furnace and calcined in air atmosphere (calcination procedure: from room temperature to 160℃ at a heating rate of 2℃ / min, and held at that temperature for 30min; then, at a heating rate of 2℃ / min, the temperature is increased to 320℃ and held at that temperature for 30min; then, at a heating rate of 2℃ / min, the temperature is increased to 500℃ and held at that temperature for 30min; finally, at a heating rate of 2℃ / min, the temperature is increased to 700℃). After cooling, a porous calcium-based CO2 adsorbent with doped structure stabilizer MgO is obtained (named CaMg-1).

[0069] Compare with Example 1

[0070] This comparative example provides a porous calcium-based CO2 adsorbent (named Ca-1) without a structure stabilizer. The preparation method differs from that in Example 1 in that magnesium acetate tetrahydrate is not added in step S1. Other methods and steps are the same as in Example 1 and will not be repeated here.

[0071] Compare with Example 2

[0072] This comparative example provides a calcium-based CO2 adsorbent doped with MgO, and its preparation method includes the following steps:

[0073] A1. Add 3.54g of calcium nitrate tetrahydrate and 3.85g of magnesium nitrate hexahydrate to 50mL of deionized water and stir at 60℃ to obtain a homogeneous mixture containing calcium and magnesium ions.

[0074] A2. Add 9.43g of ammonium carbonate to 50mL of deionized water and stir at room temperature until fully dissolved to obtain the second solution;

[0075] A3. Under stirring conditions, the second solution is added dropwise to the mixed solution containing calcium and magnesium ions, and the mixture is stirred continuously at 60°C for 2 hours.

[0076] A4. After step A3, the product is collected by vacuum filtration and washed three times with deionized water and then once with anhydrous ethanol to obtain a solid product.

[0077] A5. Place the solid product in a constant temperature oven and dry it at 60°C for 18 hours. Then grind it thoroughly to obtain a solid powder.

[0078] A6. The solid powder was placed in a muffle furnace and calcined in an air atmosphere (calcination procedure: heating from room temperature to 160℃ at a heating rate of 2℃ / min and holding for 30min; then heating to 320℃ at a heating rate of 2℃ / min and holding for 30min; then heating to 500℃ at a heating rate of 2℃ / min and holding for 30min; finally, heating to 700℃ at a heating rate of 2℃ / min). After cooling, a calcium-based CO2 adsorbent doped with the structural stabilizer MgO was obtained (named CaMg-2).

[0079] Compare with Example 3

[0080] This comparative example provides a calcium-based CO2 adsorbent without doping with a structure stabilizer, the preparation method of which includes the following steps:

[0081] B1. Add 12.6g of calcium nitrate tetrahydrate to 50mL of deionized water and stir at 60℃ to obtain a homogeneous calcium ion solution.

[0082] B2. Add 16.8g of ammonium carbonate to 50mL of deionized water and stir at room temperature until fully dissolved to obtain the second solution;

[0083] B3. Under stirring conditions, the second solution is added dropwise to the calcium ion solution, and the mixture is stirred continuously at 60°C for 2 hours.

[0084] B4. After step B3, the product is collected by vacuum filtration and washed three times with deionized water and then once with anhydrous ethanol to obtain a solid product.

[0085] B5. Place the solid product in a constant temperature oven and dry it at 60°C for 18 hours, then grind it thoroughly to obtain a solid powder.

[0086] B6. The solid powder was placed in a muffle furnace and calcined in air atmosphere (calcination procedure: heating from room temperature to 160℃ at a heating rate of 2℃ / min and holding for 30 min; then heating to 320℃ at a heating rate of 2℃ / min and holding for 30 min; then heating to 500℃ at a heating rate of 2℃ / min and holding for 30 min; finally, heating to 700℃ at a heating rate of 2℃ / min). After cooling, a calcium-based CO2 adsorbent without structure stabilizer was obtained (named Ca-2).

[0087] See Figure 1The XRD patterns of the calcium-based CO2 adsorbents prepared in Examples 1 and Comparative Examples 1-3 are shown. Analysis of the patterns shows that the calcium-based CO2 adsorbents (Ca-1 and Ca-2) without structural stabilizers in Comparative Examples 1 and 3 are composed of CaCO3 and CaO. The calcium-based CO2 adsorbents (CaMg-1 and CaMg-2) with MgO doped with structural stabilizer prepared in Examples 1 and 2 are composed of CaCO3, CaO, and MgO. The porous calcium-based CO2 adsorbent (CaMg-1) with MgO doped with structural stabilizer prepared in Example 1 has grain sizes of 30 nm, 28 nm, and 17 nm for CaCO3, CaO, and MgO, respectively, estimated based on the XRD characteristic peaks of each crystal phase.

[0088] See Figure 2 The images show SEM images of the calcium-based CO2 adsorbents prepared in Examples 1 and Comparative Examples 1-3. Analysis of the images shows that the calcium-based CO2 adsorbents (CaMg-2 and Ca-2) prepared in Comparative Examples 2 and 3 exhibit a bulky and dense morphology, while the calcium-based CO2 adsorbents (CaMg-1 and Ca-1) prepared in Examples 1 and Comparative Examples 1 have obvious channels. Among them, the porous calcium-based CO2 adsorbent (CaMg-1) doped with the structural stabilizer MgO has abundant and uniform macropores.

[0089] Application Example 1

[0090] This application example provides an application of a calcium-based CO2 adsorbent. The calcium-based CO2 adsorbents prepared in Example 1 and Comparative Examples 1-3 were applied to isothermal CO2 adsorption-desorption, and their isothermal CO2 adsorption-desorption performance and cycle stability were tested. The specific method is as follows: 5 mg of calcium-based CO2 adsorbent was placed in a thermogravimetric analyzer (TGA), and the temperature was increased from room temperature to 700°C at a rate of 10°C / min under an Ar atmosphere of 100 ml / min. After holding at this temperature for 5 min, the temperature was then lowered to the target temperature (T). t Then, under constant temperature conditions, the atmosphere is cyclically switched. The adsorption is carried out at 100 ml / min in a z vol.% CO2 / N2 atmosphere for x min until adsorption saturation, and then desorbed at 100 ml / min in an Ar atmosphere for y min until desorption is complete.

[0091] The specific combinations of test conditions and test results for different experimental purposes are shown in Table 1 below:

[0092] Table 1. Test conditions and results of isothermal CO2 adsorption-desorption performance and cyclic stability of the calcium-based CO2 adsorbents prepared in Example 1 and Comparative Examples 1-3 in Application Example 1.

[0093] Example 1 (CaMg-1) 650℃ 15 6 6 Compare with Example 1 (Ca-1) 650℃ 15 6 18 Compare with Example 2 (CaMg-2) 650℃ 15 6 20 Compare with Example 3 (Ca-2) 650℃ 15 6 20

[0094] As can be seen from the data comparison in Table 1 above, CaMg-1 in Example 1 exhibits higher CO2 adsorption-desorption performance, especially with a significant increase in the CO2 desorption rate; additionally, refer to Figure 3 The graph shows the CO2 capture capacity of the calcium-based CO2 adsorbents prepared in Examples 1 and Comparative Examples 1 to 3 at 650°C and a CO2 concentration of 15 vol.% as a function of cycle number. As can be seen from the graph, without the addition of a structural stabilizer, the cycle stability of Ca-1 is significantly higher than that of Ca-2. After adding the structural stabilizer MgO, the cycle stability of CaMg-2 did not improve; conversely, the cycle stability of CaMg-1 was significantly improved, with an initial CO2 capture capacity reaching 0.568 g CO2 / g. 吸附剂 (Explanation: Each gram of calcium-based CO2 adsorbent has a CO2 capture capacity of 0.568 g), and after 50 isothermal cycles, the capture capacity is 0.517 g CO2 / g. 吸附剂 Its capture capacity decreased by only 9%.

[0095] Application Example 2

[0096] This application example provides an application of a calcium-based CO2 adsorbent. The porous calcium-based CO2 adsorbent (CaMg-1) with doped structural stabilizer MgO prepared in Example 1 is applied to isothermal CO2 adsorption-desorption at a low temperature and low CO2 concentration. Its isothermal CO2 adsorption-desorption performance and cycle stability are tested. The specific method is the same as that in Application Example 1, and will not be repeated here.

[0097] The specific test conditions and corresponding test results are as follows:

[0098] When T t At 550℃ and z=15, the measured values ​​are x=20 and y=60.

[0099] When T t At 550℃ and z=0.5, the values ​​of x and y were found to be 60 and 60, respectively.

[0100] See Figure 4 The graph shows the variation of CO2 capture capacity of the porous calcium-based CO2 adsorbent (CaMg-1) prepared in Example 1 (with MgO doped as a stabilizer) with the number of cycles at low temperatures and low CO2 concentrations. As can be seen from the graph, at 550℃ and 0.5 vol.% CO2 concentration, this calcium-based CO2 adsorbent (CaMg-1) can still achieve isothermal CO2 adsorption-desorption, with an initial CO2 capture capacity of 0.518 g CO2 / g. 吸附剂 After 10 cycles, the capture capacity was 0.484 g CO2 / g 吸附剂 Its capture capacity decreased by only 7%.

[0101] In summary, this invention introduces ethylene glycol and citric acid to form an "ethylene glycol-citric acid-metal ion" chelate, promoting the homogeneous mixing of calcium ions and the second metal ion (structural stabilizer ion). The hydrolysis of urea is used to regulate the pH of the solution, improving the uniformity of the metal chelate. Polyvinylpyrrolidone (PVP), a nonionic surfactant, protects the formed nanoparticles and prevents their aggregation. During the calcination step, PPVP is decomposed, burned, and removed, resulting in a rich porous structure. A calcium-based CO2 adsorbent with nano-sized CaO particles, uniform doping of the second metal oxide (structural stabilizer), and a porous framework is prepared using a hydrothermal synthesis method. The synthesis method is simple and easy to operate, enabling industrial production. In the porous calcium-based CO2 adsorbent prepared in this invention, the small crystal size of CaO results in a faster CO2 adsorption-desorption rate. The structural stabilizer (second metal oxide) is uniformly distributed at the nanoscale. The adsorbent is dispersed within the CaO framework, effectively inhibiting CaO particle sintering. The abundant macropores in the framework provide ample space for the periodic deformation of the adsorbent during CO2 adsorption-desorption, further preventing structural collapse. The porous calcium-based CO2 adsorbent prepared in this invention exhibits high CO2 isothermal adsorption-desorption performance and cycling stability, effectively solving the problems of high energy consumption and low efficiency in calcium-based chemical chaining CO2 high-temperature capture technology, and has significant industrialization value. It can achieve isothermal CO2 adsorption-desorption processes at relatively low temperatures (550–650℃) and a wide CO2 concentration range (0.5–15 vol.%), and can be applied to most CO2 stationary emission sources. Furthermore, this calcium-based CO2 adsorbent combines high capture capacity and high cycling stability; the porous calcium-based adsorbent doped with the structural stabilizer MgO achieves a CO2 capture capacity of 0.568 g CO2 / g at 650℃ and a CO2 concentration of 15 vol.%. 吸附剂 After 50 isothermal adsorption-desorption cycles, the trapping capacity still retains more than 90% of the initial value. Therefore, this invention effectively overcomes the various shortcomings of the prior art and thus has high industrial application value.

[0102] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a porous structured calcium-based CO2 adsorbent, characterized in that, The preparation method includes the following steps: S1. Add the metal source, ethylene glycol, citric acid, polyvinylpyrrolidone, and urea to deionized water and stir at room temperature to form a homogeneous mixture; wherein the metal source includes a calcium source and a second metal source, and the second metal in the second metal source includes one or a combination of aluminum, magnesium, titanium, zirconium, yttrium, cerium, lanthanum, neodymium, and ytterbium; the molar ratio between the urea and the metal ions in the metal source is 0.5:1 to 3:1; S2. The mixture is placed in a hydrothermal reactor and left to stand in a constant temperature oven at 120~160℃ for 18~30h. After cooling naturally to room temperature, it is then centrifuged and washed to obtain a solid product. S3. The solid product is placed in a constant temperature oven to dry, and then ground to obtain solid powder; S4. The solid powder is calcined in air and then cooled to obtain a calcium-based CO2 adsorbent. The calcination process includes a step-by-step heating and holding process, specifically: heating from room temperature to 150-180°C for the first time and holding for 30-60 minutes; then heating to 300-350°C for the second time and holding for 30-60 minutes; then heating to 500-550°C for the third time and holding for 30-120 minutes; and finally heating to 700-800°C for the fourth time.

2. The method of claim 1, wherein: The calcium source mentioned in step S1 is one or a combination of calcium acetate and calcium nitrate; the second metal source is an acetate or nitrate of a second metal.

3. The method of claim 1, wherein: Step S1 includes one or a combination of the following conditions: The metal ions in the metal source include calcium ions and second metal ions, and the molar ratio between the calcium ions and the second metal ions is 1:0.1 to 1:

9. The molar ratio between the ethylene glycol, citric acid and the metal ions in the metal source is (3~1):(3~1):1; The molar ratio between the polyvinylpyrrolidone and the metal ions in the metal source is 1:1 to 9:

1.

4. The method of claim 1, wherein: In the mixture obtained in step S1, the total concentration of metal ions in the metal source is 0.1~0.5 mol / L.

5. The method of claim 1, wherein: The washing process in step S2 includes washing with deionized water and washing with anhydrous ethanol. The washing with deionized water is performed at least once, and the washing with anhydrous ethanol is performed at least once.

6. The method of claim 1, wherein: The drying temperature in step S3 is 60~100℃, and the drying time is 12~24h.

7. The method of claim 1, wherein: The heating rates for the first, second, third, and fourth heating cycles are all 1~5℃ / min.

8. A porous structured calcium-based CO2 adsorbent characterized by: The calcium-based CO2 adsorbent is prepared by any one of the preparation methods described in claims 1 to 7.

9. Use of a porous structured calcium-based CO2 sorbent produced by a method according to any one of claims 1 to 7, characterized in that, The calcium-based CO2 adsorbent is applied to isothermal CO2 adsorption-desorption; wherein the isothermal CO2 adsorption-desorption temperature is 550~650℃, and the CO2 concentration range during isothermal CO2 adsorption-desorption is 0.5 vol.%~15 vol.%.

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