A magnesium oxide carbon dioxide adsorbent, its preparation method and application

Abstract

The present invention provides a magnesium oxide carbon dioxide adsorbent, a preparation method thereof and an application thereof, belonging to the technical field of adsorption materials. The magnesium oxide carbon dioxide adsorbent provided by the present invention is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The morphological characteristics of the octahedral shape can expose the (111) crystal plane of magnesium oxide, thereby exposing the strong basic sites on its surface; moreover, the particle size of the embroidered ball-shaped powder is 20-40 μm, having a smaller particle size and a larger specific surface area. Therefore, the magnesium oxide carbon dioxide adsorbent provided by the present invention can expose more basic sites, and thus can effectively improve the adsorption capacity of magnesium oxide for CO2. The results of the examples show that the adsorption amount of CO2 by the magnesium oxide carbon dioxide adsorbent provided by the present invention is 4 times that of commercial magnesium oxide for CO2 adsorption.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption materials, and in particular to a magnesium oxide carbon dioxide adsorbent, a preparation method thereof, and an application thereof. Background Art

[0002] CO2 adsorption is crucial for reducing greenhouse gas emissions and addressing climate change. Currently, common CO2 adsorption methods include: chemical adsorption in which adsorbents such as alkali metal carbonates or amine compounds react with carbon dioxide; physical or chemical interaction adsorption of CO2 using adsorbents such as activated carbon, metal oxides, and metal-organic framework materials; and absorption and fixation of CO2 by organisms such as microorganisms or plants through their metabolic processes. Among them, the method of using adsorbents to adsorb CO2 has the characteristics of low energy consumption, simple operation, and can quickly adsorb and desorb CO2, enabling high-efficiency and low-cost CO2 separation, and thus has attracted much attention.

[0003] Magnesium oxide can react with CO2 through a chemical reaction, enabling CO2 molecules to be embedded in the crystal structure of magnesium oxide to achieve CO2 adsorption. Compared with other metal oxides, magnesium oxide is rich in resources, has a theoretical adsorption capacity of up to 1100 mg CO2 / g adsorbent, requires less energy during the regeneration process, has a low cost, is non-toxic, and can effectively adsorb CO2 in the range from room temperature to medium temperature, and is thus used for CO2 adsorption. However, due to insufficient surface basic sites or low quality of magnesium oxide, the contact and diffusion of CO2 molecules are restricted, resulting in the actual value of CO2 adsorption by magnesium oxide not reaching the theoretical value. To improve the actual adsorption amount of magnesium oxide for CO2, researchers have improved the CO2 adsorption capacity by adding modifiers such as molten salts. For example, using molten salts (such as NaNO3) to form NO 2+ on the surface of magnesium oxide, providing O 2- , this process increases the number of surface basic sites of magnesium oxide; and, the molten salt changes the original reaction path between magnesium oxide and CO2, forming oxygen vacancies by extracting lattice oxygen on the surface of magnesium oxide, promoting the rapid formation of O 2- , thereby enhancing the surface basic sites of magnesium oxide. Another example is to improve the CO2 capture ability of magnesium oxide by the method of amino-functionalization modification of magnesium oxide. The amino group has strong basicity and can form a stable chemical bond with CO2. By introducing amino groups on the surface of magnesium oxide, the number of surface basic sites can be increased, the selectivity and adsorption efficiency of the adsorbent can be improved, and CO2 molecules can be more easily captured.

[0004] However, whether it is molten salt modification or amination modification of magnesium oxide, both involve relatively high material and production costs, and the preparation process requires complex synthesis methods and precise process control. Otherwise, it is difficult to improve the quantity and quality of the basic sites of magnesium oxide, resulting in a relatively low actual CO2 adsorption capacity per gram of magnesium oxide.

[0005] Therefore, developing a magnesium oxide that can improve the quantity of basic sites without modification is of great significance for enhancing the CO2 adsorption capacity of magnesium oxide. Summary of the Invention

[0006] The purpose of the present invention is to provide a magnesium oxide carbon dioxide adsorbent, its preparation method and application. The magnesium oxide carbon dioxide adsorbent provided by the present invention can improve the quantity of basic sites of magnesium oxide.

[0007] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a magnesium oxide carbon dioxide adsorbent, which is an embroidered ball-like powder formed by stacking octahedral magnesium oxide, and the particle size of the embroidered ball-like powder is 20 - 40 μm.

[0009] The present invention also provides a preparation method of the magnesium oxide carbon dioxide adsorbent described in the above technical solution, including the following steps:

[0010] (1) Mix a carbon source, a water-soluble magnesium salt, an alkali and water, and carry out a hydrothermal reaction to obtain magnesium carbonate;

[0011] (2) Calcinate the magnesium carbonate obtained in step (1), and after cooling to room temperature, obtain the magnesium oxide carbon dioxide adsorbent; the cooling rate is 20 - 200 °C / min.

[0012] Preferably, the carbon source in step (1) includes one or more of ascorbic acid, urea, potassium bicarbonate and sodium bicarbonate.

[0013] Preferably, the water-soluble magnesium salt in step (1) includes one or more of anhydrous magnesium sulfate, anhydrous magnesium chloride and magnesium acetate.

[0014] Preferably, the alkali in step (1) includes NaOH and / or KOH.

[0015] Preferably, the molar ratio of the carbon element of the carbon source to the magnesium element of the water-soluble magnesium salt in step (1) is (3 - 10):1.

[0016] Preferably, the temperature of the hydrothermal reaction in step (1) is 120 - 200 °C; the hydrothermal reaction time is 3 - 10 h.

[0017] Preferably, in the step (2), the calcination temperature is 650 - 900 °C; the calcination time is 1 - 3 h.

[0018] Preferably, in the step (2), the heating rate for heating to the calcination temperature is 5 - 35 °C / min.

[0019] The present invention also provides the use of the magnesium oxide carbon dioxide adsorbent described in the above technical solution or the magnesium oxide carbon dioxide adsorbent prepared by the preparation method described in the above technical solution as a CO2 adsorbent.

[0020] The present invention provides a magnesium oxide carbon dioxide adsorbent, which is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The particle size of the embroidered ball-shaped powder is 20 - 40 μm. The magnesium oxide carbon dioxide adsorbent provided by the present invention is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The octahedral morphological characteristics can expose the (111) crystal plane of magnesium oxide, thereby exposing the strong basic sites on its surface; moreover, the particle size of the embroidered ball-shaped powder is 20 - 40 μm, having a smaller particle size and a larger specific surface area. Therefore, the magnesium oxide carbon dioxide adsorbent provided by the present invention can expose more basic sites, and thus can effectively improve the adsorption capacity of magnesium oxide for CO2. The results of the examples show that the adsorption amount of CO2 by the magnesium oxide carbon dioxide adsorbent provided by the present invention is 4 times that of commercial magnesium oxide for CO2 adsorption. Description of the Drawings

[0021] Figure 1 SEM image of anhydrous magnesium carbonate prepared in Example 1 of the present invention;

[0022] Figure 2 SEM image of the magnesium oxide carbon dioxide adsorbent prepared in Example 1 of the present invention;

[0023] Figure 3 TEM image of the magnesium oxide carbon dioxide adsorbent prepared in Example 1 of the present invention;

[0024] Figure 4 CO2-TPD test result curve of the magnesium oxide carbon dioxide adsorbent prepared in Example 1 of the present invention and commercial magnesium oxide;

[0025] Figure 5 Curve of the magnesium oxide carbon dioxide adsorbent prepared in Example 1 of the present invention and commercial magnesium oxide adsorbing 100% CO2 gas at 50 °C for 4 h. Detailed Embodiments

[0026] The present invention provides a magnesium oxide carbon dioxide adsorbent, which is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide, and the particle size of the embroidered ball-shaped powder is 20 - 40 μm.

[0027] In the present invention, the magnesium oxide carbon dioxide adsorbent is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The morphological characteristics of the octahedral shape can expose the (111) crystal plane of magnesium oxide, thereby exposing the strong basic sites on its surface.

[0028] In the present invention, the particle size of the octahedral magnesium oxide is preferably 0.3 - 1 μm, more preferably 0.5 - 0.8 μm. In the magnesium oxide carbon dioxide adsorbent provided by the present invention, when the particle size of the octahedral magnesium oxide is within the above range, more basic sites can be exposed.

[0029] In the present invention, the particle size of the embroidered ball-shaped powder is 20 - 40 μm, preferably 25 - 35 μm. The embroidered ball-shaped powder of the magnesium oxide carbon dioxide adsorbent provided by the present invention has a smaller particle size and a larger specific surface area. Therefore, the magnesium oxide carbon dioxide adsorbent provided by the present invention can expose more basic sites, and thus can effectively improve the adsorption capacity and removal rate of magnesium oxide for CO2.

[0030] The present invention also provides a preparation method of the magnesium oxide carbon dioxide adsorbent described in the above technical solution, including the following steps:

[0031] (1) Mix a carbon source, a water-soluble magnesium salt, an alkali, and water, and carry out a hydrothermal reaction to obtain magnesium carbonate;

[0032] (2) Calcinate the magnesium carbonate obtained in step (1), and after cooling to room temperature, obtain the magnesium oxide carbon dioxide adsorbent; the cooling rate is 20 - 200 °C / min.

[0033] The present invention mixes a carbon source, a water-soluble magnesium salt, an alkali, and water, and carries out a hydrothermal reaction to obtain magnesium carbonate.

[0034] In the present invention, the carbon source preferably includes one or more of ascorbic acid, urea, potassium bicarbonate, and sodium bicarbonate, more preferably ascorbic acid or urea. The present invention uses the carbon source to provide CO2, which can combine with hydroxide ions to form carbonate ions, and the carbonate ions combine with magnesium ions in the solution to form magnesium carbonate. The above carbon sources used in the present invention are rich in sources and are easy to generate CO2.

[0035] In the present invention, the water-soluble magnesium salt preferably includes one or more of anhydrous magnesium sulfate, anhydrous magnesium chloride, and magnesium acetate, more preferably anhydrous magnesium sulfate. The present invention uses the water-soluble magnesium salt to provide magnesium ions to form magnesium carbonate with carbonate ions.

[0036] In the present invention, the molar ratio of the carbon element of the carbon source to the magnesium element of the water-soluble magnesium salt is preferably (3 to 10):1, more preferably (5 to 8):1. By controlling the molar ratio of the carbon element to the magnesium element within the above range, the present invention can not only fully convert the magnesium salt into magnesium carbonate, but also affect the crystallization process of magnesium carbonate, resulting in embroidered ball-shaped magnesium carbonate.

[0037] In the present invention, the base is preferably NaOH and / or KOH. By adding a base to the reaction system, the present invention provides hydroxide ions, which combine with the carbon dioxide generated by the carbon source to form carbonate ions, and then the carbonate ions react with the water-soluble magnesium salt to form magnesium carbonate. In the present invention, the base is preferably an alkali solution, and the concentration of the alkali solution is preferably 3 to 10 moL / L, more preferably 5 moL / L.

[0038] The present invention has no special limitation on the dosage of the base, as long as the pH value of the mixed solution formed by the carbon source, the water-soluble magnesium salt, the base and water is 8 to 12.5. By limiting the pH value of the above system within the above range, the present invention can make the system alkaline, which is more conducive to fully converting the carbon dioxide generated by the carbon source into carbonate ions.

[0039] In the present invention, the water serves as a reaction solvent. The present invention has no special limitation on the dosage of the water, as long as it can fully dissolve the carbon source, the water-soluble magnesium salt and the base and enable the hydrothermal reaction to proceed smoothly. In an embodiment of the present invention, when the anhydrous magnesium sulfate is 3.6110 g and the ascorbic acid is 7.0448 g, the volume of the water is 30 mL.

[0040] The present invention has no special limitation on the method of mixing the carbon source, the water-soluble magnesium salt, the base and water. A conventional mixing method can be adopted as long as the carbon source, the water-soluble magnesium salt and the base can be completely dissolved in water to form a mixed solution.

[0041] In the present invention, the temperature of the hydrothermal reaction is preferably 120 to 200 °C, more preferably 150 to 180 °C; the time of the hydrothermal reaction is preferably 3 to 10 h, more preferably 3 to 6 h. The present invention has no special limitation on the device for the hydrothermal reaction, and any conventional hydrothermal reaction device can be used. In the present invention, the device for the hydrothermal reaction is preferably a reaction kettle with a polytetrafluoroethylene lining. In the present invention, the device for the hydrothermal reaction is preferably placed in a homogeneous reactor for the hydrothermal reaction. In the present invention, the homogeneous reactor can promote mass transfer and enable the uniform reaction of each material. In an embodiment of the present invention, the power of the homogeneous reactor is preferably 5 Hz.

[0042] Preferably, after the hydrothermal reaction, the reaction system is cooled to room temperature, and then the solid product obtained from the hydrothermal reaction is washed, filtered, and dried in sequence to obtain magnesium carbonate. The present invention places no special limitation on the operation methods of the washing, filtering, and drying, as long as the impurities on the surface of the magnesium carbonate can be sufficiently removed and it can be dried.

[0043] After obtaining the magnesium carbonate, the present invention calcines the magnesium carbonate and, after cooling to room temperature, obtains a magnesium oxide carbon dioxide adsorbent; the cooling rate is 20 - 200 °C / min.

[0044] In the present invention, the calcination temperature is preferably 650 - 900 °C, more preferably 650 - 800 °C; the calcination time is preferably 1 - 3 h, more preferably 2 - 3 h. By performing calcination at the above temperature and time, the present invention can cause the magnesium carbonate to lose weight and generate magnesium oxide and CO2. The present invention places no special limitation on the calcination device, and any conventional calcination device can be used. In an embodiment of the present invention, the calcination device is a muffle furnace.

[0045] The present invention preferably grinds the magnesium carbonate into powder before calcination. By grinding, the present invention can disperse the agglomerated magnesium carbonate, which is more conducive to the full conversion of magnesium carbonate into magnesium oxide. The present invention places no special limitation on the particle size of the ground magnesium carbonate powder, as long as the agglomerated magnesium carbonate particles can be dispersed.

[0046] In the present invention, the heating rate for raising the temperature to the calcination temperature is preferably 5 - 35 °C / min, more preferably 20 - 25 °C / min. By raising the temperature at the above heating rate, the present invention is more conducive to the transformation of the morphology of magnesium oxide into an octagonal pyramid shape.

[0047] In the present invention, the cooling rate is 20 - 200 °C / min, preferably 100 - 150 °C / min. By cooling at the above rate, the present invention has a relatively fast cooling rate, which can fully expose the (111) crystal plane of magnesium oxide.

[0048] The method provided by the present invention does not require the addition of molten salt or ionic liquid and directly calcines in air. The required equipment is simple and easy to operate; moreover, by a simple calcination method, the present invention greatly exposes the (111) crystal plane of magnesium oxide, thereby exposing the strong basic sites on its surface, and further effectively improving the carbon dioxide adsorption capacity and removal rate of magnesium oxide.

[0049] The present invention also provides the application of the magnesium oxide carbon dioxide adsorbent described in the above technical solution as a CO2 adsorbent.

[0050] The present invention has no special limitation on the application method of the magnesium oxide carbon dioxide adsorbent as a CO2 adsorbent, and a conventional method for adsorbing CO2 by an adsorbent can be adopted.

[0051] Since the magnesium oxide carbon dioxide adsorbent provided by the present invention greatly exposes the (111) crystal plane of magnesium oxide and exposes the strong basic sites on its surface, it can thus be used as a CO2 adsorbent and effectively improve the adsorption capacity and removal rate of magnesium oxide for carbon dioxide.

[0052] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0053] Example 1

[0054] A magnesium oxide carbon dioxide adsorbent, which is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide, the particle size of the octahedral magnesium oxide is 0.5 - 0.8 μm, and the particle size of the embroidered ball-shaped powder is 30 μm.

[0055] The preparation method of the above-mentioned magnesium oxide carbon dioxide adsorbent is as follows:

[0056] (1) Using ascorbic acid as the carbon source, anhydrous magnesium sulfate as the water-soluble magnesium salt, and a 5 moL / L NaOH solution as the alkali solution; wherein, the molar ratio of the carbon element of the carbon source to the magnesium element of the water-soluble magnesium salt is 8:1, denoted as n(C):n(Mg) = 8:1;

[0057] Dissolve 7.0448 g of the carbon source, 3.6110 g of the water-soluble magnesium salt, and the alkali solution in 30 mL of water to obtain a mixed solution. The pH value of the mixed solution is 12.5. Place the mixed solution in a 100 mL polytetrafluoroethylene inner liner, put it into a reaction kettle, and then place it in a homogeneous reactor. Adjust the frequency of the homogeneous reactor to 5 Hz, and keep it at 180 °C for 3 h for hydrothermal reaction; after the hydrothermal reaction, cool the system to room temperature, wash and filter, and then place the obtained solid powder in a drying oven and dry it for 24 h to obtain anhydrous magnesium carbonate;

[0058] (2) Grind the anhydrous magnesium carbonate obtained in step (1) into powder and place it in a boron nitride crucible, and calcine it in a muffle furnace. Set the initial temperature to 20 °C, increase the temperature to 650 °C at a heating rate of 25 °C / min, calcine for 2 h, and after the end, place the crucible in cold water and cool it to room temperature at a cooling rate of 150 °C / min to obtain the magnesium oxide carbon dioxide adsorbent.

[0059] Example 2

[0060] A magnesium oxide carbon dioxide adsorbent, which is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The particle size of the octahedral magnesium oxide is 0.3 - 1 μm, and the particle size of the embroidered ball-shaped powder is 30 μm.

[0061] The preparation method of the above magnesium oxide carbon dioxide adsorbent is as follows:

[0062] (1) Using ascorbic acid as the carbon source, anhydrous magnesium sulfate as the water-soluble magnesium salt, and a 5 moL / L NaOH solution as the alkali solution; wherein, n(C):n(Mg) = 8:1;

[0063] Dissolve 7.0448 g of the carbon source, 3.6110 g of the water-soluble magnesium salt, and the alkali solution in 30 mL of water to obtain a mixed solution with a pH value of 12.5; place the mixed solution in a 100 mL polytetrafluoroethylene inner liner, put it into a reaction kettle, and then place it in a homogeneous reactor. Adjust the frequency of the homogeneous reactor to 5 Hz, keep it at 180 °C for 3 h for hydrothermal reaction; after the hydrothermal reaction, cool the system to room temperature, wash and filter by suction, and then place the obtained solid powder in a drying oven and dry it for 24 h to obtain anhydrous magnesium carbonate;

[0064] (2) Grind the anhydrous magnesium carbonate obtained in step (1) into powder and place it in a boron nitride crucible, calcine it in a muffle furnace, set the initial temperature to 20 °C, heat it to 800 °C at a heating rate of 25 °C / min, calcine for 2 h, and after completion, place the crucible in cold water and cool it to room temperature at a cooling rate of 150 °C / min to obtain the magnesium oxide carbon dioxide adsorbent.

[0065] Test Example 1

[0066] The SEM image of the anhydrous magnesium carbonate prepared in Example 1 is as Figure 1 shown, Figure 1 The upper right corner of Figure 1 is the SEM image at high magnification. It can be seen from

[0067] that the surface of the anhydrous magnesium carbonate prepared in Example 1 is an embroidered ball shape composed of spheres with an average diameter of about 0.05 nm, and the diameter of the embroidered ball-shaped powder is about 30 μm. This indicates that the anhydrous magnesium carbonate prepared in Example 1 is an embroidered ball-shaped magnesium carbonate powder with a particle size of Figure 2 shown, Figure 2 The upper right corner of Figure 2It can be seen that the magnesium oxide carbon dioxide adsorbent prepared in Example 1 is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide. The particle size of the octahedral magnesium oxide is about 0.3 - 1 μm, and the particle size of the embroidered ball-shaped powder is about 20 - 40 μm.

[0068] The TEM image of the magnesium oxide carbon dioxide adsorbent prepared in Example 1 is as Figure 3 shown, where (a) is the transmission image, (b) is the high-resolution image, and (c) is the selected area electron diffraction pattern (SAED). In Figure 3 it, Figure (a) confirms that the magnesium oxide in the magnesium oxide carbon dioxide adsorbent prepared in Example 1 is in an octahedral form. From Figure 3 (b) and (c), it can be seen that the quadrilateral contour of the appropriately arranged isolated particles and the related selected area electron diffraction (SAED) pattern indicate that the (111) crystal plane is exposed on the surface of the magnesium oxide particles. Conventional commercially available magnesium oxide particles often appear as polydisperse aggregates rather than isolated octahedral crystals. This shows that the crystal structure of the magnesium oxide carbon dioxide adsorbent provided by the present invention is different from that of conventional commercially available magnesium oxide.

[0069] Test Example 2

[0070] To verify the distribution of basic sites on the surface of the magnesium oxide carbon dioxide adsorbent prepared in Example 1, temperature-programmed desorption of CO2 (CO2-TPD) was used to test the material. The test instrument used was a Micromeritics ChemiSorb 2750 type reactor from Micromeritics Instrument Corporation, USA. Weigh 70 mg of MgO and under an argon atmosphere, raise the temperature from room temperature to 300 °C at a flow rate of 50 mL·min -1 at a rate of 10 °C·min -1 , and then maintain it at this temperature for 2 h to remove the surface-adsorbed impurities. Then, after reducing the temperature to 50 °C under an argon atmosphere at a flow rate of 50 mL·min -1 , introduce CO2 at a flow rate of 50 mL·min -1 and maintain it for 3.5 h. Finally, after purging the sample with argon at a flow rate of 50 mL·min -1 for 1.5 h, raise the temperature to 850 °C at a rate of 10 °C·min -1 to obtain the corresponding CO2 temperature-programmed desorption curve.

[0071] Figure 4 are the CO2-TPD test result curves of commercial magnesium oxide (Adamas Beta Chemical Reagent Co., Ltd.) and the magnesium oxide carbon dioxide adsorbent prepared in Example 1. In Figure 4Among them, the characteristic peak of the desorption temperature indicates the basic strength of the adsorbent, and the area under the distribution curve indicates the number of basic sites in the adsorbent. From Figure 4 it can be seen that three main peaks appear at temperatures below 200 °C, 300 - 500 °C, and 700 - 900 °C respectively, which indicate the weak basic sites, medium basic sites, and strong basic sites of magnesium oxide. However, commercial magnesium oxide only exposes some medium basic sites, and the number is much smaller than that of the magnesium oxide carbon dioxide adsorbent prepared in this experiment. This shows that the magnesium oxide carbon dioxide adsorbent provided by the present invention can improve the number of basic sites of magnesium oxide.

[0072] Test Example 3

[0073] In order to verify the actual CO₂ adsorption capacity of the octahedral MgO adsorbent, the MgO carbon dioxide adsorbent prepared in Example 1 and the commercial MgO carbon dioxide adsorbent were tested using a thermogravimetric analyzer (TGA). Calculate the mass change of the MgO adsorbent before and after introducing high-purity CO₂ gas, and then calculate the difference to obtain the saturated CO₂ adsorption capacity of the MgO adsorbent material. Weigh a sample with a mass of about 10 mg and heat it to 600 °C (heating rate 20 °C·min -1 ) under a 100% high-purity nitrogen gas flow (gas flow rate 20 mL·min -1 ) and hold for 1 h to avoid the influence of moisture and carbon dioxide in the air on the sample. After pretreatment, lower the temperature to 150 °C and hold for 1 h, and continue to introduce high-purity N₂ as a protective gas during the cooling process. After the system stabilizes, introduce high-purity CO₂ gas (gas flow rate 60 mL·min -1 ), and the adsorption test process lasts for 4 h. The calculation formula for the CO₂ adsorption capacity of the adsorbent material is shown in Equation (I):

[0074] CO₂ adsorption capacity (mmol·g -1 ) = (m t - m0) × 1000 / (m0 × M (CO2) ) Equation (I)

[0075] In Equation (I), m t is the mass of the sample at time t, m0 is the initial mass of the sample before adsorption, and M (CO2) is the molar molecular weight of CO₂ (44 g·mol -1 ).

[0076] Figure 5 are the curves of commercial magnesium oxide (Adamas Beta Chemical Reagent Co., Ltd.) and the magnesium oxide carbon dioxide adsorbent prepared in Example 1 for adsorbing 100% CO₂ gas at 50 °C for 4 h. From Figure 5 it can be seen that the CO₂ adsorption performance of commercial magnesium oxide is about 0.1 mmol g -1, while the CO2 adsorption performance of the magnesium oxide carbon dioxide adsorbent prepared in this experiment is about 0.4 mmol g -1 , which is 4 times that of commercial magnesium oxide.

[0077] It can be seen from the above experimental results that the CO2 adsorption performance of the magnesium oxide carbon dioxide adsorbent prepared in the present invention is much higher than that of commercial magnesium oxide. This is because the magnesium oxide carbon dioxide adsorbent prepared in the present invention is an embroidered spherical powder formed by stacking octagonal pyramid-shaped magnesium oxides, and has a smaller particle size. This octagonal pyramid-shaped morphological feature can expose the (111) crystal plane of magnesium oxide, thereby exposing the strong basic sites on its surface. Therefore, the magnesium oxide carbon dioxide adsorbent provided by the present invention can expose more basic sites, and thus can effectively improve the adsorption capacity of magnesium oxide for CO2.

[0078] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A magnesium oxide carbon dioxide adsorbent, wherein the magnesium oxide carbon dioxide adsorbent is an embroidered ball-shaped powder formed by stacking octahedral magnesium oxide, and the particle size of the embroidered ball-shaped powder is 20 - 40 μm; the particle size of the octahedral magnesium oxide is 0.3 - 1 μm; The preparation method of the magnesium oxide carbon dioxide adsorbent comprises the following steps: (1) Mix a carbon source, a water-soluble magnesium salt, an alkali, and water, and carry out a hydrothermal reaction to obtain magnesium carbonate; the pH value of the mixed solution formed by mixing the carbon source, the water-soluble magnesium salt, the alkali, and water is 8 - 12.5; the device for the hydrothermal reaction is placed in a homogeneous reactor; (2) Calcinate the magnesium carbonate obtained in step (1), and after cooling to room temperature, obtain the magnesium oxide carbon dioxide adsorbent; the cooling rate is 20 - 200 °C / min; The carbon source in step (1) includes one or more of ascorbic acid, urea, potassium bicarbonate, and sodium bicarbonate; The molar ratio of the carbon element of the carbon source to the magnesium element of the water-soluble magnesium salt in step (1) is (3 - 10):1; The alkali in step (1) includes NaOH and / or KOH; The temperature of the hydrothermal reaction in step (1) is 120 - 200 °C; the hydrothermal reaction time is 3 - 10 h; The calcination temperature in step (2) is 650 - 900 °C; the calcination time is 1 - 3 h.

2. The preparation method of the magnesium oxide carbon dioxide adsorbent according to claim 1, comprising the following steps: (1) Mix a carbon source, a water-soluble magnesium salt, an alkali, and water, and carry out a hydrothermal reaction to obtain magnesium carbonate; the pH value of the mixed solution formed by mixing the carbon source, the water-soluble magnesium salt, the alkali, and water is 8 - 12.5; (2) Calcinate the magnesium carbonate obtained in step (1), and after cooling to room temperature, obtain the magnesium oxide carbon dioxide adsorbent; the cooling rate is 20 - 200 °C / min; The carbon source in step (1) includes one or more of ascorbic acid, urea, potassium bicarbonate, and sodium bicarbonate; The molar ratio of the carbon element of the carbon source to the magnesium element of the water-soluble magnesium salt in step (1) is (3 - 10):1; The alkali in step (1) includes NaOH and / or KOH; The temperature of the hydrothermal reaction in step (1) is 120 - 200 °C; the hydrothermal reaction time is 3 - 10 h; The calcination temperature in step (2) is 650 - 900 °C; the calcination time is 1 - 3 h.

3. The preparation method according to claim 2, wherein, The water-soluble magnesium salt in step (1) includes one or more of anhydrous magnesium sulfate, anhydrous magnesium chloride, and magnesium acetate.

4. The preparation method according to claim 2, characterized in that, The heating rate for raising the temperature to the calcination temperature in step (2) is 5 - 35 °C / min.

5. The application of the magnesium oxide carbon dioxide adsorbent according to claim 1 or the magnesium oxide carbon dioxide adsorbent prepared by the preparation method according to any one of claims 2 - 4 as a CO2 adsorbent.

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