Molding method of magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation

Abstract

The invention discloses a forming method of a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation. The forming method comprises the following steps: calcining a magnesium-containing precursor to prepare porous magnesium oxide raw powder; the preparation method comprises the following steps: carrying out impregnation modification on magnesium oxide raw powder and an alkali metal salt solution to obtain wet mixed thick slurry, drying the slurry, and carrying out secondary calcination to obtain modified adsorbent raw powder; and mixing the raw powder with deionized water, a forming aid and the like to prepare a plastic wet material, and performing extrusion-spheronization balling, drying and calcining to obtain regular spherical adsorbent particles. The formed adsorbent prepared through the method has the advantages of being controllable in particle size, high in mechanical strength, good in adsorptive property after being formed, excellent in cycling stability and the like, can be used for CO2 chemical adsorption trapping of CO2-containing gas under the medium-temperature condition, and is good in CO2 adsorptive property, economical efficiency of the technological method and environmental protection performance, the process technology is easy to amplify, and the method is suitable for industrial production. The method is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide adsorption technology, and specifically relates to a molding method for a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation. Background Technology

[0002] With the deepening of industrialization, the large-scale use of fossil fuels has led to a sharp increase in emissions of greenhouse gases such as carbon dioxide. The resulting global climate change has become a major challenge facing human society in the 21st century, posing a serious threat to the ecological environment and sustainable development. As the most significant greenhouse gas, the reduction and control of carbon dioxide emissions has reached a global consensus. CO2 capture, utilization, and storage (CCUS) technology, as one of the key technologies for controlling carbon emissions, has received increasing attention in recent years.

[0003] Solid adsorbent materials, as one of the materials for CO2 capture, have become a current research hotspot. Magnesium oxide is favored due to its wide availability of raw materials and high theoretical adsorption capacity (22.3 mmol·g⁻¹). -1 With its excellent anti-sintering properties and significant economic benefits, it is regarded as an ideal material for medium-temperature CO2 capture and is suitable for various industrial scenarios such as flue gas from coal-fired power plants.

[0004] The adsorption mechanism of magnesium-based adsorbents for CO2 is as follows: In practical applications, the dense MgCO3 shell formed by the reaction of CO2 and MgO hinders CO2 gas diffusion, resulting in an actual adsorption capacity that is less than 10% of the theoretical value. Simultaneously, the high-temperature sintering effect during the adsorbent calcination and regeneration process leads to a decrease in the material's specific surface area and a rapid decline in the cyclic adsorption activity. More importantly, there is currently very little research on the molding and large-scale preparation processes of magnesium-based adsorbents. Compared to powder materials with the same active components, large-scale prepared molded CO2 adsorbents experience a further significant reduction in adsorption activity due to the deterioration of the pore structure.

[0005] Existing publicly available solutions primarily improve the adsorption performance of MgO-based CO2 adsorbent powder materials through modification, lacking suitable molding processes and materials for MgO-based CO2 adsorbents to meet the needs of industrial-scale preparation and application. The shortcomings of existing publicly available solutions include, but are not limited to, the following: 1) The preparation process of magnesium oxide precursor is complex, energy-intensive and costly: Some of the published schemes rely on multiple chemical reactions and multiple high-temperature calcination to prepare magnesium source precursors, which not only makes the process complex, but also leads to a significant increase in energy consumption and cost, which is not conducive to industrial scale-up preparation. 2) High cost of adsorbent modification formulation materials: The materials selected in the publicly available schemes for magnesium oxide modification are not entirely reasonable. Some schemes prefer to use lithium salts such as lithium nitrate to improve the performance of magnesium oxide, but the scarcity and high cost of lithium resources make it a significant bottleneck in industrial-scale application. 3) Poor environmental friendliness of the modification process: Some publicly available modification schemes rely on organic solvents such as methanol as media, which not only increases the cost of recycling and disposing of organic solvent media, but also poses potential safety hazards and environmental pollution. 4) Insufficient large-scale molding process and performance in loading and use: Regarding the molding of adsorbents, some existing publicly available solutions employ a process of high-pressure briquetting followed by crushing and screening. On the one hand, excessively high extrusion pressure not only consumes a lot of energy but also easily damages the microporous structure inside the adsorbent, reducing the CO2 adsorption reactivity. On the other hand, the irregular adsorbent particles obtained through crushing can easily increase the flow resistance of the adsorbent bed and increase the energy consumption of gas transport in fixed-bed or moving-bed adsorption reactors.

[0006] Based on existing technologies, magnesium oxide-based solid adsorbent solutions for CO2 capture in industrial gases face technical bottlenecks that hinder both improved adsorption performance and large-scale industrial application. Existing processes primarily focus on enhancing adsorption potential through powder materials. The few existing solutions that disclose adsorbent molding processes have significant shortcomings; the commonly used high-pressure molding methods lead to decreased porosity and adsorption performance of the adsorbent material. Some processes also rely on expensive components such as organic solvents and Li metal salts, resulting in potential environmental safety risks and high costs for large-scale applications. Furthermore, the molded adsorbents obtained from existing technologies lack performance verification under harsh adsorption reaction conditions such as atmospheric pressure and low CO2 concentrations. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, such as significantly reduced adsorption capacity, poor cycle stability, and lack of industrial-scale production processes for molded adsorbents compared to powdered materials, this invention provides a molding method suitable for large-scale preparation of magnesium oxide-based carbon dioxide adsorbents. Porous magnesium oxide powder is prepared using a magnesium-containing precursor as the magnesium source, and a modification process is coupled with an extrusion-spheronization molding process to achieve large-scale preparation of adsorbent particles. Compared with existing technologies, the molded adsorbent obtained by this invention has the advantages of maintaining performance after molding, good cycle stability, and high particle strength.

[0008] The technical solution adopted by this invention to solve its technical problem is: A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Magnesium-containing precursors are calcined to obtain magnesium oxide powder with high specific surface area; wherein the calcination temperature is 450-550℃ and the calcination time is 2-6 h. 2) Magnesium oxide powder is impregnated in an alkali metal salt aqueous solution of a set concentration to prepare a wet mixed slurry; wherein, the mass fractions of magnesium oxide powder and alkali metal salt are x and y, where x+y=1 and x≠0, y>0; the mass fraction of the total amount of alkali metal salt in the alkali metal salt aqueous solution is 5%~40%; the liquid-solid ratio of the salt solution to magnesium oxide powder is 0.1~10 mL / g, so that the impregnated material is a thick slurry with no obvious free liquid; 3) The wet mixed slurry is continuously stirred at a stirring speed of 300-700 rpm and an impregnation temperature of 10-40 ℃ for 2-8 hours; 4) Allow the wet mixed slurry to air dry naturally for 6–12 h, then place it in a drying oven and dry at 100–125 ℃ for 3–15 h to obtain a dry solid sample. Then, pulverize the dried sample and place it in a resistance furnace and calcine at 450–550 ℃ for 2–4 h to obtain the modified magnesium-based adsorbent powder. 5) The modified magnesium-based adsorbent powder is mixed with deionized water and molding aid in an optimized mass ratio to obtain a bulk material; wherein the mass ratio of modified magnesium-based adsorbent powder to molding aid is 4:1 to 19:1, and the solid-liquid mass ratio is 1.5:1 to 5:1. The billet is placed in an extruder for extrusion and then broken into cylindrical particles. The cylindrical particles are placed in a spherical rolling machine for spherical rolling. After high-speed grinding and rolling, adsorbent sphere particles with good sphericity are formed. The obtained microspheres were air-dried at room temperature for 6–9 h, then placed in a drying oven and dried at 100–125 °C for 3–15 h. The dried microspheres were then calcined in an electric resistance furnace at 500–700 °C for 1–3 h to finally obtain magnesium-based adsorbent microspheres.

[0009] Further, in step 1), the magnesium-containing precursor is a magnesium-containing compound that can be converted into magnesium oxide through heat treatment, including one or a mixture of two or more of the following: natural minerals such as magnesite, magnesium oxides, carbonates, basic carbonates, hydroxides, or organic acid salts. Magnesium oxalate is preferred.

[0010] In step 2), the alkali metal salt is selected from one or a mixture of two or more of nitrates, carbonates, chlorides, and sulfates.

[0011] The preferred materials are sodium nitrate and sodium carbonate, with the mass fractions of magnesium oxide powder, sodium nitrate, and sodium carbonate being x, y, and z, where x + y + z = 1, x ≠ 0, and y + z > 0; preferably, 0.60 ≤ x ≤ 0.90, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and y + z > 0.

[0012] In step 5), the molding aid includes a binder and an extrusion aid, and the mass ratio of the binder and the extrusion aid is 1:1 to 3:1.

[0013] The binder is selected from one or a mixture of two of the following: boehmite and cement inorganic binder.

[0014] The extrusion aid is selected from one or a mixture of two of the following: guar gum powder, nitric acid, and lubricating oil.

[0015] In step 7), the optimized process of extrusion-rounding is as follows: extrusion speed 5-60 rpm, extrusion pressure 0.2-0.4 MPa, extrusion orifice diameter 0.1-6 mm, and rounding speed 300-3000 rpm.

[0016] The beneficial effects of this invention are mainly reflected in: 1) This invention prepares porous magnesium oxide raw powder using magnesium-containing precursors with stable sources and controllable costs. Magnesium oxide with a high specific surface area is obtained through simple calcination, avoiding the problems of complex precursor preparation steps and high costs in some existing routes, which make it difficult to promote industrially. It is suitable for large-scale preparation.

[0017] 2) This invention avoids using lithium salt modified material systems that are more sensitive to resource supply and cost fluctuations. By optimizing the range and loading of modified formulation materials, it achieves a synergistic improvement in the activity and cycle stability of adsorbent materials under non-lithium salt modification, thus better meeting the economic and sustainability requirements for large-scale CO2 capture industrial applications.

[0018] 3) The impregnation process of this invention preferably uses water as a solvent to prepare the salt solution and carry out the impregnation load, avoiding the use of organic solvent systems such as methanol, thereby reducing the environmental treatment burden caused by solvent recovery, reducing production costs and scale-up complexity, and effectively improving the industrial feasibility and long-term operational safety of the process.

[0019] 4) This invention proposes to spherically granulate magnesium-based adsorbent powder on a large scale, using an extrusion-spheronization process to prepare regular spherical particles, and to complete the shaping under low extrusion pressure, which helps to avoid densification of the pore structure and reduce performance loss.

[0020] 5) The integrated process of "precursor calcination - impregnation modification - low-pressure extrusion spheroidization" is adopted to replace conventional technologies such as high-pressure crushing, so as to realize the transformation of powder into regular spherical particles. At the same time, it takes into account the control of particle morphology regularity and the reduction of pore structure damage, reduces reactor pressure drop and gas transportation energy consumption, improves mechanical strength and ensures cycle stability in industrial operation, which is conducive to the large-scale, low-cost and stable production of magnesium oxide-based molded CO2 adsorbent materials. Attached Figure Description

[0021] Figure 1 A schematic diagram of a molding method for magnesium oxide-based carbon dioxide adsorbents suitable for large-scale preparation.

[0022] Figure 2 The CO2 concentration change of the NaNO3 and NaNO3 / Na2CO3 modified 3 mm MgO-based medium-temperature CO2 adsorption granules of Example 1 was tested during CO2 adsorption at normal pressure in a mixed gas atmosphere of "approximately 15% CO2 + the remainder N2".

[0023] Figure 3 The CO2 concentration change during the CO2 adsorption process of the NaNO3 and NaNO3 / Na2CO3 modified 3 mm MgO-based medium-temperature CO2 adsorption granules of Example 3 was tested under normal pressure and in a mixed gas atmosphere of "about 15% CO2 + the rest N2".

[0024] Figure 4 The CO2 concentration change during the CO2 adsorption process of the NaNO3 / Na2CO3 modified 3 mm MgO-based medium-temperature CO2 adsorption molded particles of Example 1 was tested (reaction conditions: atmospheric pressure, atmosphere of "approximately 15% CO2 + the rest N2" mixed gas).

[0025] Figure 5 The CO2 concentration change during the CO2 adsorption process of the NaNO3-modified 3 mm MgO-based medium-temperature CO2 adsorption shaped particles of Example 2 was tested (reaction conditions: atmospheric pressure, atmosphere of "approximately 15% CO2 + the rest N2" mixed gas).

[0026] Figure 6 CO2 adsorption process and adsorption capacity of 3 mm MgO-based medium-temperature adsorption granules modified with NaNO3 / Na2CO3 (Example 1) and NaNO3 (Example 2) (reaction conditions: atmospheric pressure, atmosphere is a mixed gas of "about 15% CO2 + the rest N2").

[0027] Figure 7 Cyclic adsorption performance of 3 mm MgO-based medium-temperature adsorption molded particles modified with NaNO3 / Na2CO3 (Example 1) and NaNO3 (Example 2) when adsorbing CO2 gas containing about 15% concentration (reaction conditions: atmospheric pressure, atmosphere is a mixed gas of "about 15% CO2 + the rest N2").

[0028] Figure 8 The MgO material modified by NaNO3 / Na2CO3 (Example 1) (Example 1).

[0029] Figure 9 NaNO3 modified MgO material (Example 2).

[0030] Figure 10 XRD of the powder sample corresponding to pure MgO (Example 4) before granulation. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] Reference Figures 1-10 A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Magnesium-containing precursors are calcined to obtain magnesium oxide powder with high specific surface area; wherein the calcination temperature is 450-550℃ and the calcination time is 2-6 h. 2) Magnesium oxide powder is impregnated in an alkali metal salt aqueous solution of a set concentration to prepare a wet mixed slurry; wherein, the mass fractions of magnesium oxide powder and alkali metal salt are x and y, where x+y=1 and x≠0, y>0; the mass fraction of the total amount of alkali metal salt in the alkali metal salt solution is 5%~40%; the liquid-solid ratio of the salt solution to magnesium oxide powder is 0.1~10 mL / g, so that the impregnated material is a thick slurry with no obvious free liquid; 3) The wet mixed slurry is continuously stirred at a stirring speed of 300-700 rpm and an impregnation temperature of 10-40 ℃ for 2-8 hours; 4) Allow the wet mixed slurry to air dry naturally for 6–12 h, then place it in a drying oven and dry at 100–125 ℃ for 3–15 h to obtain a dry solid sample. Then, pulverize the dried sample and place it in a resistance furnace and calcine at 450–550 ℃ for 2–4 h to obtain the modified magnesium-based adsorbent powder. 5) The modified magnesium-based adsorbent powder is mixed with deionized water and molding aids (binders, extrusion aids) in an optimized mass ratio to obtain a bulk material; wherein the mass ratio of modified magnesium-based adsorbent powder to molding aids is 4:1 to 19:1, and the solid-liquid mass ratio is 1.5:1 to 5:1. 6) After the preform is placed in the extruder for extrusion, it is then broken into cylindrical particles. The extrusion speed is 5-60 rpm, the extrusion pressure is 0.2-0.4 MPa, the orifice diameter is 0.1-6 mm, and the rounding speed is 300-3000 rpm.

[0033] 7) The cylindrical particles are placed in a spherical rolling machine for spherical rolling. After high-speed grinding and rolling, adsorbent sphere particles with good sphericity are formed. 8) The obtained microspheres are air-dried at room temperature for 6-9 hours, then placed in a drying oven and dried at 100-125 °C for 3-15 hours. The dried microspheres are then placed in a resistance furnace and calcined at 500-700 °C for 1-3 hours to finally obtain magnesium-based adsorbent microspheres.

[0034] Example 1 A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Step 1: Magnesium oxalate was heated from room temperature to 500℃ in air at a rate of 10℃ / min, and calcined at 500℃ for 4 h to obtain magnesium oxide powder with high specific surface area. 3.1 kg of sodium nitrate powder and 1.9 kg of sodium carbonate powder were dissolved in 50 L of deionized water, mixed thoroughly, and placed in an enamel-lined reactor. 7.4 kg of MgO was then added to the reactor, and the mixture was continuously stirred at high speed at room temperature for 8 h. After standing, the slurry was removed, air-dried for 12 h, and then dried at 120℃ for 12 h to obtain a solid sample. The dried lumps were then ground into powder in a grinder and calcined in a resistance furnace at 500℃ for 2 h to obtain modified magnesium-based adsorbent powder loaded with alkali metal salts sodium nitrate and sodium carbonate. Step 2: Take 1 kg of the magnesium-based adsorbent raw powder and weigh it with the binder boehmite (PB) and the extrusion aid pure nitric acid (NA) in a ratio of 90 wt%, 5 wt%, and 5 wt%. Then, mix the mixed powder thoroughly with deionized water with a nitric acid mass fraction of 7.5 wt% (solid-liquid mass ratio of 1.5:1), and then knead the resulting mixture into a lumpy blank. Subsequently, the preform was extruded under conditions of a 3 mm orifice diameter, a screw speed of 50 rpm / min, and an extrusion pressure of 0.3 MPa to obtain strips. The strips were then broken into cylindrical particles with a length of 2–4 mm. These cylindrical particles were then placed in a spheroidizing machine for spheroidizing at a spheroidizing rate of 1200 rpm / min, spheroidizing in the forward direction for 3 minutes and in the reverse direction for 3 minutes. After high-speed grinding and rolling, adsorbent microspheres were formed. The obtained microspheres were air-dried at room temperature for 6 hours, then dried in a drying oven at 100 °C for 6 hours to remove surface moisture. Finally, they were calcined in a resistance furnace at 700 °C for 2 hours to obtain magnesium-based adsorbent microspheres. Microspheres with a particle size of approximately 3 mm were sieved out as samples for testing.

[0035] Example 2 A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Step 1: Magnesium oxalate was heated from room temperature to 500 °C in air at a rate of 10 °C / min, and calcined at 500 °C for 4 h to obtain magnesium oxide powder with high specific surface area. 2 kg of sodium nitrate powder was dissolved in 20 L of deionized water, mixed thoroughly, and placed in an enamel-lined reactor. 8 kg of MgO was then added to the reactor, and the mixture was continuously stirred at high speed at room temperature for 8 h. After standing, the suspension was removed, air-dried naturally for 12 h, and then dried at 120 °C for 12 h to obtain a solid sample. The dried lumps were then ground into powder in a grinder and calcined in a resistance furnace at 500 °C for 2 h to obtain modified magnesium-based adsorbent powder loaded with alkali metal salt sodium nitrate. Step 2: Take 1 kg of the magnesium-based adsorbent raw powder and weigh it with the binder boehmite (PB) and the extrusion aid pure nitric acid (NA) in a ratio of 90 wt%, 5 wt%, and 5 wt%. Then, mix the mixed powder thoroughly with deionized water with a nitric acid mass fraction of 7.5 wt% (solid-liquid mass ratio of 1.5:1), and then knead the resulting mixture into a lumpy blank. Subsequently, the preform was extruded under conditions of a 3 mm orifice diameter, a screw speed of 50 rpm / min, and an extrusion pressure of 0.3 MPa to obtain strips. The strips were then broken into cylindrical particles with a length of 2–4 mm. These cylindrical particles were then placed in a spheroidizing machine for spheroidizing at a spheroidizing rate of 1200 rpm / min, spheroidizing in the forward direction for 3 minutes and in the reverse direction for 3 minutes. After high-speed grinding and rolling, adsorbent microspheres were formed. The obtained microspheres were air-dried at room temperature for 6 hours, then dried in a drying oven at 100 °C for 6 hours to remove surface moisture. Finally, they were calcined in a resistance furnace at 700 °C for 2 hours to obtain magnesium-based adsorbent microspheres. Microspheres with a particle size of approximately 3 mm were sieved out as samples for testing.

[0036] Example 3 A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Step 1: Magnesium oxalate was heated from room temperature to 500℃ in air at a rate of 10℃ / min and calcined at 500℃ for 4 hours to obtain magnesium oxide powder with high specific surface area. 3.1 kg of sodium nitrate powder and 1.9 kg of sodium carbonate powder were dissolved in 50 L of deionized water, mixed thoroughly, and placed in an enamel-lined reactor. 7.4 kg of MgO was then added to the reactor, and the mixture was continuously stirred at high speed at room temperature for 8 hours. After standing, the slurry was removed, air-dried for 12 hours, and then dried at 120℃ for 12 hours to obtain a solid sample. The dried lumps were then ground into powder in a grinder and calcined in a muffle furnace at 500℃ for 2 hours to obtain modified magnesium-based adsorbent powder loaded with alkali metal salts sodium nitrate and sodium carbonate. Step 2: Take 1 kg of the magnesium-based adsorbent powder and weigh it together with the binder boehmite (PB) and the extrusion aid pure nitric acid (NA) in a ratio of 90 wt%, 5 wt%, and 5 wt%. Then, thoroughly mix the powder with deionized water containing 1.25 wt% nitric acid (solid-liquid mass ratio of 1:4), and knead the resulting mixture into a lumpy blank. Subsequently, the preform was extruded under conditions of a 3 mm orifice diameter, a screw speed of 50 rpm / min, and an extrusion pressure of 0.3 MPa to obtain strips. The strips were then broken into cylindrical particles with a length of 2–4 mm. These cylindrical particles were then placed in a spheroidizing machine for spheroidizing at a spheroidizing rate of 1200 rpm / min, spheroidizing in the forward direction for 3 minutes and in the reverse direction for 3 minutes. After high-speed grinding and rolling, adsorbent microspheres were formed. The obtained microspheres were air-dried at room temperature for 6 hours, then dried in a drying oven at 100 °C for 6 hours to remove surface moisture. Finally, they were calcined in a resistance furnace at 700 °C for 2 hours to obtain magnesium-based adsorbent microspheres. Microspheres with a particle size of approximately 3 mm were sieved out as samples for testing.

[0037] Example 4 A method for molding a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation includes the following steps: Step 1: Weigh 1 kg of commercial pure MgO raw powder, binder boehmite (PB), and extrusion aid pure nitric acid (NA) in a ratio of 90 wt%, 5 wt%, and 5 wt%, respectively. Then, thoroughly mix the powder with deionized water containing 7.5 wt% nitric acid (solid-liquid mass ratio of 1.5:1) and knead the resulting mixture into a lumpy blank. Subsequently, the preform was extruded using an extruder at an extrusion speed of 50 rpm / min to obtain strips. The strips were then broken into cylindrical particles with a length of 2–4 mm. These cylindrical particles were then placed in a spheroidizing machine for spheroidizing at a spheroidizing speed of 1200 rpm / min, spheroidizing in the forward direction for 3 minutes and in the reverse direction for 3 minutes. After high-speed grinding and rolling, adsorbent microspheres were formed. The obtained microspheres were air-dried at room temperature for 6 hours, then dried in a drying oven at 100 ℃ for 6 hours to remove surface moisture. Finally, they were calcined in a resistance furnace at 700 ℃ for 2 hours to obtain magnesium-based adsorbent microspheres. Microspheres with a particle size of approximately 3 mm were sieved out as samples for testing.

[0038] Step 2, Comparison of Adsorbent Molding and Granulation: Compared to Example 3, Example 1 produces more regular spherical particles with relatively uniform particle size and intact particles; while in Example 3, with a relatively small solid-liquid ratio, the particles become more moist during molding, resulting in particle adhesion and relatively poor particle integrity. Therefore, compared to Example 3, Example 1 is more advantageous for obtaining molded particles with regular shape, higher integrity, and more uniform particle size distribution.

[0039] The adsorbent performance test results are as follows: (1) Mechanical strength test: A DS2-500N digital display pressure tester from Taiwan Yi Nuo Electronics Co., Ltd. was used. During the test, the tester was held at a uniform height and pressed naturally until the particles were crushed. The pressure value displayed by the tester was recorded, which is the mechanical strength of the particles. Table 1 shows a comparison of the mechanical strength of different MgO medium-temperature adsorption shaped particles (Examples 1, 2, and 4).

[0040] Table 1. Mechanical strength of pure MgO, NaNO3 modified adsorbent, and NaNO3 / Na2CO3 modified adsorbent particles;

[0041] Based on the compressive strength data, the strengths of pure MgO microspheres, NaNO3-modified microspheres, and NaNO3 / Na2CO3 co-modified microspheres measured in five tests were approximately 1.24, 2.44, and 3.3 N, respectively. Overall, the modified adsorption-molded microspheres obtained by the "precursor calcination—impregnation modification—low-pressure extrusion spheronization" molding process of this invention all showed improved strength.

[0042] (2) Adsorption cycle test: An atmospheric pressure gas mixture was used, with the gas composition being approximately: 85 vol% N2 / 15 vol% CO 2，Magnesium-based adsorbent spheres were placed in an adsorption experimental setup. The CO2 adsorption experiment was conducted in a fixed-bed reactor. 1 g of adsorbent spheres were weighed and placed in the reactor, then heated to 450 °C in a nitrogen flow of 100 mL / min and held for 30 min to remove adsorbed impurities. The temperature was then lowered to 100 °C, stabilized for 5 minutes, and then 500 mL / min of simulated flue gas (85 vol% N2 / 15 vol% CO2) was introduced to raise the temperature to 300 °C for adsorption, which lasted for 120 min. After adsorption, desorption began, maintaining a pure N2 atmosphere at 500 mL / min (consistent with the simulated flue gas flow rate). The temperature was raised to the desorption temperature (450 °C) for 30 min; this constituted one cycle. The temperature was then lowered to 100 °C, stabilized for 5 minutes, and then 500 mL / min of simulated flue gas was introduced to raise the temperature, and multiple cycles were performed. The CO2 concentration curve recorded by a gas analyzer was used to calculate the adsorption capacity using an integral method. The formula for calculating the amount of CO2 adsorbed is as follows: ; Among them, Q t The adsorption capacity at time t is expressed in g / g. C0 represents the instantaneous carbon dioxide concentration in the gas before entering the reaction zone (initial carbon dioxide concentration), expressed as a percentage. t q represents the instantaneous carbon dioxide concentration at the outlet at time t, expressed as a percentage. t The gas flow rate at time t is expressed in mL / min. In the formula, 22.4 represents the molar volume of the ideal gas in L / mol. M0 represents the mass of the adsorbent added to the reactor in g.

[0043] Figure 4 and Figure 5The CO2 adsorption process of the modified MgO-based CO2 adsorbent molding materials in Examples 1 and 2 is presented. The complete experimental process of the modified 3mm molding adsorbent from pretreatment to adsorption and desorption is described. First, the molding material undergoes a high-temperature N2 pretreatment stage, with the temperature increased to 450 °C at a rate of 10 °C / min, and maintained at a pure N2 atmosphere for 30 minutes, with the outlet CO2 concentration maintained at zero baseline. Subsequently, the temperature of the reaction device is lowered to 100 °C, and the atmosphere is switched to simulated flue gas (15% CO2, 85% N2). The CO2 concentration rises and stabilizes at the inlet concentration, indicating that the gas in the pipeline and reaction device has reached equilibrium. Then, the programmed temperature rise stage begins. While keeping the simulated flue gas inlet constant, the temperature of the fixed-bed adsorption reactor is increased from 100 °C to 300 °C at a rate of 10 °C / min. During this non-isothermal process, the core adsorption reaction stage begins, and adsorption is maintained at a constant temperature of 300 °C for 120 minutes. From the start of the programmed temperature rise phase, the CO2 concentration at the outlet of the fixed-bed adsorption reactor decreases due to the adsorption and capture effect of the shaped CO2 adsorbent. Finally, after the isothermal adsorption phase, the fixed-bed adsorption reactor enters the shaped CO2 adsorbent desorption and regeneration phase. The gas inside the reactor is switched back to pure N2, and the temperature is programmed to rise from 300 ℃ to 450 ℃. After isothermal desorption for 30 min, the outlet CO2 concentration rapidly drops to zero as N2 is purged, and the shaped CO2 adsorbent is regenerated.

[0044] Figure 6 CO2 concentration-time breakthrough curves for two modified MgO-based adsorbents (Examples 1 and 2) at representative stages of CO2 capture are presented. As shown in the figures, after introducing simulated flue gas containing a low concentration of CO2, the real-time CO2 concentration in the adsorption curves of both modified samples began to decrease, indicating the adsorbent's CO2 capture effect. The NaNO3-modified MgO sample (Example 2) showed a more significant decrease in CO2 concentration and a more pronounced trend in the initial stage of the reaction, indicating that the NaNO3-modified MgO sample (Example 1) had a stronger adsorption effect in the initial stage. In contrast, the NaNO3+Na2CO3-modified MgO sample showed a relatively smaller decrease in CO2 concentration in the initial stage, exhibiting milder initial kinetics, but its long-term CO2 adsorption capacity was better. The different performance characteristics of the two modified samples are related to the following factors: molten nitrate can provide a more efficient reaction / mass transfer channel at the gas-liquid-solid three-phase interface and help alleviate the hindrance of the dense MgCO3 product layer to subsequent reactions; the introduction of carbonate may increase CO3 concentration. 2- Nucleation and diffusion conditions enhance the degree of available reaction, thereby helping to extend the effective adsorption phase.

[0045] on the whole, Figures 4-6The data results show that the 3 mm NaNO3 / Na2CO3 modified particles of Example 1 and the 3 mm NaNO3 modified particles of Example 2 exhibited adsorption capacities of 0.158 and 0.147 kg / kg, respectively, in a fixed-bed adsorption reactor. Compared with the adsorption capacities of 0.01–0.02 kg / kg for pure magnesium oxide molded materials reported in published literature and 0.0108 kg / kg for the pure magnesium oxide molded material of Example 4 of this invention, the CO2 adsorption performance of the modified adsorption molded materials obtained in Examples 1 and 2 of this invention is significantly improved.

[0046] Furthermore, Figure 7 The results showed that after five cycles, the adsorption capacity of the adsorbent particles in Examples 1 and 2 decreased slightly, but gradually stabilized, indicating that the material experienced structural or effective adsorption site loss in the initial cycling stage, and then entered a relatively stable adsorption state. In the fifth cycle, the modified adsorbent particles in Examples 1 and 2 maintained CO2 adsorption performance of 0.123 and 0.118 kg / kg, respectively. Comparatively, the CO2 adsorption capacity of the NaNO3 / Na2CO3 co-doped sample was consistently higher than that of the NaNO3-modified sample in each cycle, and the decrease with each cycle was slightly smaller, indicating that NaNO3 and Na2CO3 co-doping modification is more conducive to maintaining higher effective adsorption capacity and cycling stability under shaped particle conditions. Furthermore, the CO2 adsorption performance of the adsorbent particles in Examples 1 and 2 after five cycles was still significantly higher than that reported in the literature and the performance of the pure MgO shaped material in Example 4. Therefore, the modified particle material used in this invention exhibits good cyclic adsorption performance in a low-concentration CO2 gas atmosphere containing 15%.

[0047] (3) XRD testing: The crystal structure of the bifunctional composite material was characterized and analyzed using a PANalytical X'Pert PRO X-ray diffractometer. The operating voltage was 40 kV and the operating current was 40 mA. The scanning range was 10-80° and the scanning step size was 0.026°. The final results were obtained by Jade software analysis.

[0048] Figure 8 , Figure 9 and Figure 10The XRD patterns are shown for NaNO3 / Na2CO3 modified MgO, NaNO3 modified MgO, and pure MgO powders before granulation with medium-temperature adsorbents (Examples 1, 2, and 4). The XRD results show that the pure MgO sample exhibits only the characteristic diffraction peaks of MgO, with sharp peaks and high intensity, indicating that the sample is dominated by a single, well-crystallized MgO main phase without any obvious impurities. The modified MgO sample retains the characteristic peaks of MgO while showing diffraction peaks corresponding to NaNO3 and Na2CO3, indicating that the alkali metal salts have been loaded into the MgO system. Furthermore, the position of the MgO main peak remains essentially unchanged, suggesting that the modification process did not alter the main crystalline phase of MgO.

[0049] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A molding method for a magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation, characterized in that, The method includes the following steps: Magnesium-containing precursors are calcined to obtain magnesium oxide powder with high specific surface area; wherein the calcination temperature is 450-550 ℃ and the calcination time is 2-6 h. Magnesium oxide powder is impregnated in an alkali metal salt aqueous solution of a set concentration to prepare a wet mixed slurry; wherein, the mass fractions of magnesium oxide powder and alkali metal salt are x and y, where x+y=1 and x≠0, y>0; the mass fraction of the total alkali metal salt in the alkali metal salt aqueous solution is 5%~40%; the liquid-solid ratio of the salt solution to magnesium oxide powder is 0.1~10 mL / g, so that the impregnated material is a thick slurry with no obvious free liquid; 3) Stir the wet mixed slurry continuously at a stirring speed of 300-700 rpm and an impregnation temperature of 10-40 ℃ for 2-8 hours; 4) Allow the wet mixed slurry to air dry naturally for 6–12 h, then place it in a drying oven and dry at 100–125 ℃ for 3–15 h to obtain a dry solid sample. Then, pulverize the dried sample and place it in a resistance furnace and calcine at 450–550 ℃ for 2–4 h to obtain the modified magnesium-based adsorbent powder. 5) The modified magnesium-based adsorbent powder is mixed with deionized water and molding aid in an optimized mass ratio to obtain a bulk material; wherein the mass ratio of modified magnesium-based adsorbent powder to molding aid is 4:1 to 19:1, and the solid-liquid mass ratio is 1.5:1 to 5:

1. 6) After the billet is placed in the extruder for extrusion, it is then broken into cylindrical particles; 7) The cylindrical particles are placed in a spherical rolling machine for spherical rolling. After high-speed grinding and rolling, adsorbent sphere particles with good sphericity are formed. 8) The obtained microspheres were air-dried at room temperature for 6-9 hours, then placed in a drying oven at 100-125 °C for 3-15 hours. The dried microspheres were then calcined in an electric resistance furnace at 500-700 °C for 1-3 hours to finally obtain magnesium-based adsorbent microspheres.

2. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 1, characterized in that, In the first part, the magnesium-containing precursor is a magnesium-containing compound that can be converted into magnesium oxide by heat treatment, including one or a mixture of two or more of the following: magnesite natural mineral, magnesium oxide, carbonate, basic carbonate, hydroxide or organic acid salt.

3. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 1, characterized in that, In step 2), the alkali metal salt is selected from one or a mixture of two or more of nitrates, carbonates, chlorides, and sulfates.

4. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 1, characterized in that, In step 5), the molding aid includes a binder and an extrusion aid, and the mass ratio of the binder and the extrusion aid is 1:1 to 3:

1.

5. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 4, characterized in that, The binder is selected from one or a mixture of two of the following: boehmite and cement inorganic binder.

6. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 4, characterized in that, The extrusion aid is selected from one or a mixture of two of nitric acid, lubricating oil, and fennel powder.

7. The molding method for the magnesium oxide-based carbon dioxide adsorbent suitable for large-scale preparation as described in claim 1, characterized in that, In step 7), the optimized process of extrusion-rounding is as follows: extrusion speed 5-60 rpm, extrusion pressure 0.2-0.4 MPa, extrusion orifice diameter 0.1-6 mm, and rounding speed 300-3000 rpm.

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