Preparation method and application of molten salt modified magnesite-derived MgO-based CO2 adsorbent material

Abstract

This invention relates to the field of carbon dioxide adsorption technology, specifically to a method for preparing and applying a molten salt modified magnesite-derived MgO-based CO2 adsorbent. The method includes: Step 1, using magnesite as a magnesium source, obtaining magnesite-derived MgO through a high-temperature two-step calcination pore-forming process in air; Step 2, adding the magnesite-derived MgO to a molten salt aqueous solution, mixing, and then drying to obtain hydrated magnesite-derived MgO; Step 3, calcining the hydrated magnesite-derived MgO in air and naturally cooling to room temperature to obtain the molten salt modified magnesite-derived MgO-based CO2 adsorbent. This invention achieves low-cost, easily industrialized preparation of the adsorbent through stepwise calcination and molten salt calcination modification, while significantly improving its CO2 adsorption performance and regeneration performance.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide adsorption technology, specifically to a method for preparing and applying a molten salt modified magnesite-derived MgO-based CO2 adsorption material. Background Technology

[0002] As a major greenhouse gas, carbon dioxide's excessive emissions have led to global warming, a critical challenge hindering sustainable development. Developing efficient, stable, and economical CO2 capture technologies is of significant practical importance for achieving the "dual carbon" goal (carbon reduction and emission reduction). Magnesium oxide, as the core active component of magnesium-based adsorbents, has its microstructure, surface properties, and adsorption performance directly determined by its raw materials and synthesis process, thus influencing the technology's industrial application prospects.

[0003] Currently, the raw materials for preparing MgO adsorbents are mainly divided into two categories: chemical reagents and natural minerals. Using chemical reagents such as magnesium acetate and urea as precursors, nanoscale MgO with specific morphology and pore structure can be prepared by hydrothermal method. These adsorbents have shown good performance regulation potential in laboratory-scale CO2 adsorption tests. However, chemical reagents are expensive, and the hydrothermal method requires precise control of parameters such as reaction temperature, time, and pH under high pressure. It also requires multiple washing, drying, and calcination processes, making the process complex and requiring large equipment investment, which is difficult to meet the needs of large-scale industrial production. For example, CN117443339B discloses a method for preparing molten salt modified magnesium oxide adsorbent particles for carbon dioxide capture and its application. Using magnesium chloride as the magnesium source, and magnesium chloride, which is abundant and low in cost, is used to synthesize light basic magnesium carbonate by reacting with sodium bicarbonate. Then, a microporous magnesium oxide precursor is prepared by two-step calcination. The microporous magnesium oxide is impregnated with a mixed salt composed of nitrate and carbonate to obtain molten salt modified magnesium oxide powder. Then, a binder is added to the powder and it is extruded into granular adsorbent.

[0004] However, the chemical reactivity and environmental toxicity of magnesium chloride increase the difficulty and ecological cost of its use and storage. In contrast, preparing MgO adsorbents from natural magnesite (mainly MgCO3) offers significant cost and technological advantages. Magnesite, as a abundant and bulk magnesium mineral, can be directly purchased as powdered raw material, eliminating pretreatment processes. Its mining and raw material acquisition costs are low, and it can be continuously produced using existing calcining kilns in the metallurgical and building materials industries, exhibiting strong equipment compatibility and excellent industrial adaptability. However, current technologies for preparing magnesite-derived MgO often employ single-temperature calcination, resulting in products with uneven pore structures, low specific surface areas, and insufficient utilization of trace impurities in the raw materials. Furthermore, the lack of effective activation and modification methods leads to poor adsorbent activity and cycling stability. Currently, there are no reports on methods to fully utilize the characteristics of magnesite raw materials, supplemented by effective modification techniques, to prepare MgO-based CO2 adsorbents with rich pore structures and excellent activity, thereby synergistically enhancing adsorption capacity and cycling stability. Summary of the Invention

[0005] To address the problems of complex preparation processes, high costs, low adsorption capacity, and poor cycle stability of existing MgO-based adsorbents, this invention provides a method for preparing and applying molten salt modified magnesite-derived MgO-based CO2 adsorbents. By using stepwise calcination and molten salt hydrocracking modification, the adsorbent can be prepared at low cost and easily on an industrial scale, while significantly improving its CO2 adsorption performance and regeneration performance.

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a molten salt modified magnesite-derived MgO-based CO2 adsorbent material, comprising: Step 1: Using magnesite as the magnesium source, magnesite-derived MgO is obtained by high-temperature two-step calcination and pore-forming process in air atmosphere. Step 2: Add magnesite-derived MgO to a molten salt aqueous solution, mix and dry to obtain hydrated magnesite-derived MgO; Step 3: Calcine hydrated magnesite-derived MgO in air atmosphere and cool naturally to room temperature to obtain molten salt modified magnesite-derived MgO-based CO2 adsorbent material.

[0007] Preferably, in step 1, the high-temperature two-step calcination pore-forming process includes: The first step is to raise the temperature from room temperature to 385-405 ℃ at a rate of 8-15 ℃ / min and maintain the temperature for 1.5-2.5 h; The second step is to continue raising the temperature to 650-715 ℃ at a rate of 3-6 ℃ / min and hold it for 3.5-6.5 h.

[0008] Preferably, in step 2, the concentration of the molten salt aqueous solution is 0.10~0.25 g / mL.

[0009] Preferably, in step 2, the molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2.

[0010] Preferably, in step 2, the solid-liquid ratio of magnesite-derived MgO to the molten salt aqueous solution is 0.4~5.0 g / mL.

[0011] Preferably, in step 3, the calcination temperature is 425~480 ℃ and the time is 3.5~5.5 h.

[0012] Secondly, the present invention provides a molten salt modified magnesite-derived MgO-based CO2 adsorbent material, which, by mass percentage, consists of 78.8%~95.0% MgO, 4.7%~18.0% molten salt, and 0.3%~3.2% impurities. The molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2, and the impurities are one or more of SiO2, Fe2O3, and CaO.

[0013] Thirdly, the present invention provides an application of a molten salt modified magnesite-derived MgO-based CO2 adsorbent material, which captures CO2 in the range of 255~415 °C.

[0014] Preferably, the total CO2 adsorption capacity of the adsorbent material is 4.52~11.9 mmol / g, and the CO2 adsorption rate is 88.6%~94.1% within 10~15 min.

[0015] Preferably, after 10 adsorption-desorption cycles, the capacity retention rate of the adsorbent material is higher than 89%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing molten salt modified magnesite-derived MgO-based CO2 adsorbent material. Using natural magnesite as raw material, it is readily available and inexpensive. A stepwise calcination pore-forming process replaces the traditional single-temperature calcination. The first step is rapid heating calcination, which utilizes rapid heating and short-term holding to promote rapid decomposition and vigorous gas release of magnesite, generating a large number of micropores in situ, achieving efficient pore formation. The second step is slow heating calcination, which ensures complete decomposition of magnesium carbonate through slow heating and long-term holding, while stabilizing the pore structure and avoiding excessive sintering of grains, ultimately obtaining a MgO body with a large specific surface area, interconnected pores, and sufficient activity.

[0017] This invention utilizes a stepped heating process to achieve gradual decomposition and orderly gas release of magnesite, constructing a controllable interconnected pore structure. This increases the specific surface area and pore volume, providing ample channels and active sites for CO2 diffusion and adsorption. Simultaneously, it inhibits grain growth and structural sintering, enabling low-cost, large-scale preparation of highly active MgO matrices and solving the problems of high cost, complex processes, and difficulty in industrialization associated with chemical reagent methods. Compared to existing MgO adsorbent materials prepared by single-temperature calcination, the MgO adsorbent material prepared by this invention exhibits a richer pore structure, higher adsorption capacity, and more stable recycling and regeneration capabilities.

[0018] The one-step method of preparing molten salt-modified MgO-based adsorbents by simultaneously hydrating and incorporating molten salt into MgO after stepwise calcination in an aqueous solution containing molten salt, followed by a single calcination, can significantly shorten the process flow, reduce washing and multiple drying / calcination steps, and significantly reduce energy consumption and preparation costs. At the same time, it can achieve more uniform dispersion of molten salt in the MgO matrix and pores, avoid molten salt loss and pore structure blockage, and reduce MgO grain growth caused by high-temperature heat treatment, thereby endowing the material with richer pore structure, higher active sites and better cycle stability.

[0019] The naturally occurring quartz, calcite, dolomite, and hematite gangue minerals in magnesite can act as in-situ inert dopant and physical barriers during the stepwise calcination and one-step hydration molten salt modification processes. These impurities inhibit MgO grain sintering, stabilize the pore structure, and promote uniform dispersion of the molten salt, thereby simultaneously improving the CO2 capture performance and cycle stability of the adsorbent. Overall, these natural impurities do not require additional addition or increase costs, yet they synergize with stepwise calcination and one-step hydration molten salt modification to simultaneously improve the material's CO2 capture capacity and cycle life. Further incorporation of molten salt forms a uniform liquid / semi-liquid coating layer on the MgO surface, significantly reducing the reaction energy barrier between CO2 and MgO, accelerating carbonation kinetics, and increasing adsorption capacity. Simultaneously, the molten salt covers the active crystal faces of MgO, inhibiting grain agglomeration and sintering during high-temperature adsorption-desorption cycles, protecting the pore structure from collapse, and thus significantly improving cycle stability.

[0020] The adsorbent material prepared by modification with hydrated molten salt has excellent CO2 capture performance. Its adsorption capacity, adsorption rate and carbonation conversion rate are relatively fast. After 10 adsorption-desorption cycles, the capacity retention rate is still at a high level. Its comprehensive performance is far superior to that of commercial MgO. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the magnesite-derived MgO adsorbent material prepared in step 1 of Example 1; Figure 2 This is a scanning electron microscope image of the molten salt modified magnesite-derived MgO adsorbent material prepared in Example 1. Detailed Implementation

[0022] The following specific embodiments 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.

[0023] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0024] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0025] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0026] This invention discloses a method for preparing a molten salt modified magnesite-derived MgO-based CO2 adsorbent, comprising: Step 1: Using magnesite as the magnesium source, magnesite-derived MgO is obtained by high-temperature two-step calcination and pore-forming process in air atmosphere.

[0027] The high-temperature two-step calcination pore-forming process includes: The first step is to raise the temperature from room temperature to 385-405 ℃ at a rate of 8-15 ℃ / min and maintain the temperature for 1.5-2.5 h; The second step is to continue raising the temperature to 650-715 ℃ at a rate of 3-6 ℃ / min and hold it for 3.5-6.5 h.

[0028] Step 2: Add the magnesite-derived MgO to the molten salt solution, mix, and then place in a 90°C constant temperature drying oven to dry until the water evaporates, thus obtaining hydrated magnesite-derived MgO.

[0029] The solid-liquid ratio of magnesite-derived MgO to molten salt aqueous solution is 0.4~5.0 g / mL.

[0030] The molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2.

[0031] Step 3: Calcine hydrated magnesite-derived MgO at 425~480 ℃ for 3.5~5.5 h in air atmosphere, and then naturally cool to room temperature to obtain molten salt modified magnesite-derived MgO-based CO2 adsorbent material.

[0032] The present invention also discloses a molten salt modified magnesite-derived MgO-based CO2 adsorbent material, which, by mass percentage, consists of 78.8%~95.0% MgO, 4.7%~18.0% molten salt, and 0.3%~3.2% impurities. The molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2, and the impurities are one or more of SiO2, Fe2O3, and CaO.

[0033] This invention discloses the application of a molten salt modified magnesite-derived MgO-based CO2 adsorbent, which captures CO2 in the temperature range of 255–415 °C. The total CO2 adsorption capacity of this adsorbent is 4.52–11.9 mmol / g, and the adsorption rate is extremely fast, with a CO2 adsorption rate of 88.6%–94.1% within 10–15 min. After 10 adsorption-desorption cycles, the adsorbent retains a capacity retention rate of over 89%.

[0034] Example 1 Step 1: Using natural magnesite as raw material, 1.0 g of magnesite powder was placed in a high-temperature tube furnace and calcined in air using a high-temperature calcination process. The high-temperature calcination process consisted of two steps: the first step involved raising the temperature from room temperature to 400 °C at a rate of 10 °C / min and holding for 2 hours; the second step involved raising the temperature further at a rate of 3 °C / min to 700 °C and holding for 5 hours. After calcination, the temperature was naturally cooled to room temperature to obtain magnesite-derived MgO.

[0035] Step 2: Using the hydration molten salt modification process, 1.0 g of magnesite-derived MgO powder was added to a beaker containing 5 mL of NaNO3 aqueous solution, wherein the concentration of NaNO3 was 0.25 g / mL. The beaker was placed in a vacuum drying oven and kept at 90 ℃ for 12 h to obtain hydrated magnesite-derived MgO. Step 3: Using a calcination process, 1.0 g of hydrated magnesite-derived MgO is placed in a high-temperature tube furnace and heated to 450°C. It is then calcined in air for 4 h. After calcination, it is naturally cooled to room temperature to obtain NaNO3-modified magnesite-derived MgO-based CO2 adsorbent, which is the final molten salt-modified magnesite-derived MgO-based CO2 adsorbent.

[0036] See Figure 1The scanning electron microscope image of the magnesite-derived MgO adsorbent material prepared in Example 1 shows that the magnesite-derived MgO adsorbent material obtained after calcination of magnesite has a porous block structure formed by the aggregation of nanoparticles. There are abundant pores between the particles. This structure provides sufficient sites for subsequent molten salt loading.

[0037] See Figure 2 The scanning electron microscope image of the NaNO3-modified magnesite-derived MgO-based CO2 adsorbent material prepared in Example 1 shows that the hydrated magnesite-derived MgO still maintains a porous structure after being loaded with NaNO3, but the pores between particles are slightly reduced and the surface becomes smoother. This indicates that the molten salt magnesite-derived MgO surface has achieved uniform coating and no obvious agglomeration or phase separation has occurred.

[0038] The NaNO3-modified magnesite-derived MgO-based CO2 adsorbent material obtained in Example 1 was subjected to CO2 adsorption performance testing using a thermogravimetric analyzer. The total CO2 adsorption capacity was measured to be 11.9 mmol / g; the CO2 adsorption rate reached 92.7% within 10 min; and the capacity retention rate was higher than 89.3% after 10 adsorption-desorption cycles.

[0039] Example 2 Step 1: Using natural magnesite as raw material, 1.5 g of magnesite powder was placed in a high-temperature tube furnace and calcined in air using a high-temperature calcination process. The high-temperature calcination process consisted of two steps: the first step involved heating from room temperature to 400 °C at a rate of 15 °C / min and holding at that temperature for 2.5 h; the second step involved further heating at a rate of 5 °C / min to 700 °C and holding at that temperature for 5.5 h. After calcination, the mixture was naturally cooled to room temperature to obtain magnesite-derived MgO.

[0040] Step 2: Using the hydration molten salt modification process, 1.5 g of magnesite-derived MgO powder was added to a beaker containing 5 mL of NaNO2 aqueous solution, wherein the concentration of NaNO2 was 0.2 g / mL. The beaker was placed in a vacuum drying oven and kept at 90 ℃ for 12 h to obtain hydrated magnesite-derived MgO. Step 3: Using a calcination process, 1.5 g of hydrated magnesite-derived MgO was placed in a high-temperature tube furnace and heated to 480℃ and calcined in air atmosphere for 5 h. After calcination, it was naturally cooled to room temperature to obtain NaNO2-modified magnesite-derived MgO-based CO2 adsorbent material.

[0041] The adsorbent material obtained in Example 2 was subjected to CO2 adsorption performance testing using a thermogravimetric analyzer: its total CO2 adsorption capacity was measured to be 7.85 mmol / g; the CO2 adsorption rate reached 91.4% within 15 min; and the capacity retention rate was higher than 94.6% after 10 adsorption-desorption cycles.

[0042] Example 3 Step 1: Using natural magnesite as raw material, 2.0 g of magnesite powder was placed in a high-temperature tube furnace and calcined in air using a high-temperature calcination process. The high-temperature calcination process consisted of two steps: the first step involved raising the temperature from room temperature to 405 °C at a rate of 10 °C / min and holding for 2 hours; the second step involved raising the temperature further at a rate of 6 °C / min to 700 °C and holding for 4.5 hours. After calcination, the temperature was naturally cooled to room temperature to obtain magnesite-derived MgO.

[0043] Step 2: Using the hydrated molten salt modification process, 1.0 g of magnesite-derived MgO powder was added to a beaker containing 5 mL of KNO3 aqueous solution, wherein the concentration of KNO3 was 0.1 g / mL. The beaker was placed in a vacuum drying oven and kept at 90 ℃ for 12 h to obtain hydrated magnesite-derived MgO. Step 3: Using a calcination process, 1.0 g of hydrated magnesite-derived MgO was placed in a high-temperature tube furnace and heated to 450℃ and calcined in air atmosphere for 4.5 h. After calcination, it was naturally cooled to room temperature to obtain KNO3-modified magnesite-derived MgO-based CO2 adsorbent material.

[0044] The adsorbent material obtained in Example 3 was subjected to CO2 adsorption performance testing under a thermogravimetric analyzer: its total CO2 adsorption capacity was measured to be 4.52 mmol / g, the CO2 adsorption rate reached 90.7% within 15 min, and the capacity retention rate was higher than 93.8% after 10 adsorption-desorption cycles.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for preparing a molten salt modified magnesite-derived MgO-based CO2 adsorbent, characterized in that, include: Step 1: Using magnesite as the magnesium source, magnesite-derived MgO is obtained by high-temperature two-step calcination and pore-forming process in air atmosphere. Step 2: Add magnesite-derived MgO to a molten salt aqueous solution, mix and dry to obtain hydrated magnesite-derived MgO; Step 3: Calcine hydrated magnesite-derived MgO in air atmosphere and cool naturally to room temperature to obtain molten salt modified magnesite-derived MgO-based CO2 adsorbent material.

2. The preparation method of the molten salt modified magnesite-derived MgO-based CO2 adsorbent material according to claim 1, characterized in that, In step 1, the high-temperature two-step calcination pore-forming process includes: The first step is to raise the temperature from room temperature to 385-405 ℃ at a rate of 8-15 ℃ / min and maintain the temperature for 1.5-2.5 h; The second step is to continue raising the temperature to 650-715 ℃ at a rate of 3-6 ℃ / min and hold it for 3.5-6.5 h.

3. The preparation method of the molten salt modified magnesite-derived MgO-based CO2 adsorbent material according to claim 1, characterized in that, In step 2, the concentration of the molten salt aqueous solution is 0.10~0.25 g / mL.

4. The preparation method of the molten salt modified magnesite-derived MgO-based CO2 adsorbent material according to claim 1, characterized in that, In step 2, the molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2.

5. The preparation method of the molten salt modified magnesite-derived MgO-based CO2 adsorbent material according to claim 1, characterized in that, In step 2, the solid-liquid ratio of magnesite-derived MgO to molten salt aqueous solution is 0.4~5.0 g / mL.

6. The method for preparing the molten salt modified magnesite-derived MgO-based CO2 adsorbent material according to claim 1, characterized in that, In step 3, the calcination temperature is 425~480 ℃ and the time is 3.5~5.5 h.

7. An adsorbent obtained by the preparation method of the molten salt modified magnesite-derived MgO-based CO2 adsorbent according to any one of claims 1 to 6, characterized in that, The adsorbent comprises, by mass percentage, 78.8%–95.0% MgO, 4.7%–18.0% molten salt, and 0.3%–3.2% impurities, wherein the molten salt is one or more of NaNO3, NaNO2, KNO3, and KNO2, and the impurities are one or more of SiO2, Fe2O3, and CaO.

8. The application of the molten salt modified magnesite-derived MgO-based CO2 adsorbent material as described in claim 7, characterized in that, The adsorbent material captures CO2 in the range of 255~415 °C.

9. The application according to claim 8, characterized in that, The total CO2 adsorption capacity of this adsorbent material is 4.52~11.9 mmol / g, and the CO2 adsorption rate is 88.6%~94.1% within 10~15 min.

10. The application according to claim 8, characterized in that, After 10 adsorption-desorption cycles, the capacity retention rate of the adsorbent material is higher than 89%.

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