Calcium-based heat storage material based on hydrotalcite phase transition modification as well as preparation method and application of calcium-based heat storage material

Abstract

The invention discloses a hydrotalcite precursor calcium-based material as well as a preparation method and application thereof. The method comprises the following steps: taking calcium hydroxide and aluminum hydroxide as a calcium source and an aluminum source, and performing constant-temperature water bath and phase transformation in an alkaline environment created by sodium carbonate to obtain a hydrotalcite precursor material with a layered double hydroxide structure; the preparation method comprises the following steps: performing high-temperature calcination on a hydrotalcite precursor, performing phase transformation on the hydrotalcite precursor to form a composite structure containing active CaO and a mayenite skeleton phase, and introducing oxygen vacancies into the material to improve the COadsorption capacity and cycling stability to obtain the calcium-based material based on hydrotalcite phase transformation modification. The problems of high-temperature sintering and agglomeration of the calcium carbonate calcium-based heat storage material in multiple heat charging and discharging processes can be solved, and the service life of the material is prolonged. Meanwhile, oxygen deficiency is introduced into the material in the phase transformation process, the reaction cycle stability and the thermochemical heat storage efficiency are improved, and the material is suitable for the field of medium-high temperature thermochemical industrial energy storage.

Description

Technical Field

[0001] The present invention belongs to the field of material engineering and thermochemical energy storage technology, and relates to the performance optimization and preparation process of calcium-based heat storage materials. Specifically, it relates to a calcium-based heat storage material based on hydrotalcite phase transition modification and its preparation method and application. By introducing oxygen vacancy defects, the material's adsorption capacity for carbon dioxide is enhanced, and the cycle stability is improved, providing technical support for the long-term and efficient application of calcium-based heat storage materials. Background Art

[0002] Renewable energy sources such as solar energy and wind energy have significant volatility and randomness. Coupling them directly with the power system will inevitably increase the instability of the system. Heat storage equipment has become one of the core technologies to solve the problem of renewable energy grid connection because of its ability to efficiently transfer and dispatch energy in the time-space dimension. Coupling it with new energy electricity has become a general trend. Traditional thermal energy storage methods mainly include sensible heat storage, phase change heat storage and thermochemical heat storage. Compared with phase change heat storage and sensible heat storage, thermochemical heat storage technology realizes energy storage and release through reversible chemical reactions. It has the advantages of fast temperature range and theoretically infinite heat storage time and temperature. It is one of the key technologies to achieve long-term energy storage.

[0003] Among the many thermochemical heat storage materials, calcium-based heat storage materials have become a hot topic in thermochemical energy storage research in recent years due to their low cost, wide range of raw materials, good heat storage performance, and environmental friendliness and pollution-free. 3 Calcium looping (CaL) as a reaction medium can not only effectively capture carbon dioxide, but also as a thermochemical reaction that can achieve medium- and high-temperature heat storage, its related research has received extensive attention in recent years. The core reaction of the CaL cycle is the reaction of CaO and CO 2 The reversible reaction between CaCO 3 Decomposes into CaO and CO 2 and absorb heat; in the heat release process, CaO and CO 2 The reaction produces CaCO 3 This cyclic process of releasing heat makes the CaL system have broad application prospects in the field of medium and high temperature heat storage (600-1000°C).

[0004] However, despite the great potential shown in the field of thermochemical energy storage, the heat storage performance of calcium-based heat storage materials will decay sharply with the increase of the number of cycles. This is mainly manifested in the fact that calcium-based materials are prone to high-temperature sintering during multiple charging and discharging cycles, which leads to the agglomeration of material particles, the reduction of specific surface area and reaction activity, and thus significantly weakens the heat storage performance of the material, resulting in a decrease in cycle stability. Therefore, the heat storage material needs to be replaced regularly in the heat storage system to ensure its healthy life structure. This problem greatly increases the operating cost and safety of the unit and is the main factor limiting its large-scale application.

[0005] At present, there have been studies on methods such as doping modified calcium-based materials to hinder the high-temperature sintering of material reactions and slow down the decay of cycle performance. However, the commonly used calcium-based material doping methods mostly use inert doping, which is prone to problems such as a single function of the doping body structure and difficulty in efficiently improving the stability of the calcium cycle heat storage cycle. Taking the anti-sintering medium and high temperature thermochemical heat storage material based on a sandwich particle structure disclosed in Chinese invention patent CN116285914A as an example, it uses flaky inert doping materials to be dispersed layer by layer in a granular heat storage functional matrix material to form a multi-layer sandwich particle structure to alleviate the sintering problem of the material at high temperature. However, it mainly relies on the physical isolation effect of the flaky inert material, fails to effectively solve the problem of introducing oxygen vacancy defects inside the material, and has limited improvement in the cycle stability and carbon dioxide adsorption capacity of the calcium-based material.

[0006] In summary, although the CaL system shows broad application prospects in the field of thermochemical heat storage, its high-temperature sintering agglomeration, structural degradation and CO 2 Problems such as decreased adsorption capacity have seriously limited its practical application performance. Therefore, how to improve the cyclic stability of the CaL system, optimize the material morphology and structure, and enhance CO 2 Improving the adsorption capacity and inhibiting agglomeration to improve its applicability in industrial heat storage applications are technical problems that need to be solved urgently in the field of calcium-based heat storage materials. Summary of the invention

[0007] 1. Purpose of the invention In view of the above-mentioned defects and shortcomings of the prior art, the present invention aims to provide a calcium-based heat storage material based on hydrotalcite phase transformation modification and its preparation method and application. Through the controllable synthesis and phase transformation mechanism of the hydrotalcite precursor, an inert skeleton is constructed in the calcium aluminum mixed phase and oxygen vacancy defects are introduced, which effectively inhibits the agglomeration of calcium oxide particles and enhances the CO 2 The adsorption capacity of calcium carbonate based heat storage materials solves the problems of agglomeration, heat storage performance attenuation, mechanical stability decline and CO 2In addition, the present invention also adopts a porous molding process to prepare a calcium-based heat storage material with a porous structure, which optimizes the heat storage efficiency of the material and the adaptability to actual application scenarios.

[0008] (II) Technical solution In order to achieve the purpose of the invention and solve the technical problems, the present invention adopts the following technical solutions: The first invention object of the present invention is to provide a method for preparing a calcium-based heat storage material based on hydrotalcite phase transformation modification, which is used to improve the cycle stability of the calcium-based heat storage material, inhibit the high-temperature sintering agglomeration effect and enhance the CO 2 Adsorption capacity, the preparation method mainly includes the following implementation steps: SS1. Raw material mixing and grinding: A calcium source and an aluminum source are mixed according to a preset molar ratio, wherein the calcium source is calcium hydroxide and the aluminum source is aluminum hydroxide, and dispersed by grinding. During the grinding process, the raw materials are first dry-ground under solvent-free conditions, and then a proper amount of deionized water is added for wet grinding, and finally a uniformly dispersed mixed powder is formed; SS2. Synthesis of hydrotalcite phase precursor: The mixed powder obtained in step SS1 is mixed with a carbonate solution, and the mixture is continuously stirred in an alkaline environment to react in a constant temperature water bath to promote the formation of a layered structure of calcium aluminum double hydroxide to synthesize a precursor having a hydrotalcite crystal structure. After the reaction is completed, the obtained product is rinsed to neutrality with deionized water, and a solid precursor is obtained after filtering and drying; SS3. High temperature calcination and phase transformation: The solid precursor obtained in step SS2 is calcined in a high temperature environment and an oxidative atmosphere, and the hydrotalcite precursor is thermally decomposed and phase-transformed by controlling the heating rate and the holding time to generate a solid phase containing active calcium oxide (CaO) and a hydrotalcite phase (Ca 4 Al 2 O 6 CO 3 ), in which the hydrotalcite phase is distributed on the surface of the active CaO particles as an inert skeleton to inhibit grain boundary migration and particle sintering at high temperatures. At the same time, the lattice distortion introduces oxygen vacancy defects during the phase transformation process to increase CO 2 Adsorption activity, after calcination, the obtained product is cooled to room temperature to obtain a modified calcium-based heat storage material powder; SS4. Forming of porous materials: The product powder obtained in step SS3 is evenly sprayed with deionized water for wetting treatment, and a pore-forming agent is added in a preset proportion to adjust the pore structure and specific surface area. The obtained mixture is plastically formed and spheronized and then dried to obtain porous calcium-based heat storage material particles with enhanced cycle stability.

[0009] The second object of the present invention is to provide a calcium-based heat storage material, which is prepared using the above-mentioned method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite.

[0010] The third invention objective of the present invention is to provide an application of the above-mentioned calcium-based heat storage material in industrial heat storage. The calcium-based heat storage material is filled into a fixed bed reactor or a fluidized bed reactor, and heat absorption and release are achieved through a reversible decarbonization-carbonization process. The microstructure and porosity of the calcium-based heat storage material are optimized to improve its thermochemical stability and anti-sintering ability during the cyclic heat storage process, and reduce the attenuation of heat storage efficiency during long-term use. Realizing long-term storage of heat based on the above process is an important path to solve the instability of current new energy in time and space.

[0011] (III) Technical Effect Compared with the prior art, the calcium-based heat storage material based on hydrotalcite phase transition modification and its preparation method and application of the present invention have the following beneficial and significant technical effects: (1) The present invention utilizes the phase transition mechanism of hydrotalcite to achieve microstructural regulation of calcium-based thermal storage materials, effectively inhibiting the sintering and agglomeration of particles during high-temperature cycles and improving the cycle stability of calcium-based thermal storage materials. 3 After multiple high-temperature charging and discharging cycles, the heat storage system is prone to grain growth and particle sintering, resulting in a decrease in specific surface area and a decay of heat storage performance. The present invention forms a calcium aluminum mixed phase during the calcination process through the structural design of the hydrotalcite precursor. The inert skeleton is evenly distributed on the active CaO surface, effectively hindering grain boundary migration and reducing the sintering rate, thereby extending the service life of the material.

[0012] (2) The present invention introduces oxygen vacancy defects during the phase transition process, thereby enhancing the material's ability to adsorb carbon dioxide and comprehensively strengthening the heat storage and release characteristics of the calcium-based heat storage material. During the high-temperature calcination of the hydrotalcite precursor, the material undergoes thermal decomposition and lattice distortion, generating a large number of oxygen vacancies, which enhance the CO absorption of the CaO particles. 2 Chemical adsorption activity improves the reaction reversibility of the heat storage material, allowing it to maintain a high thermochemical conversion rate during long-term cyclic heat storage.

[0013] (3) The present invention improves the uniformity of the pore structure of the material, enhances the gas diffusion performance and reaction rate by optimizing the proportion of pore formers and the molding process. The porosity is regulated by using a specific proportion of pore formers, so that the resulting heat storage material has a high specific surface area and uniform pore size distribution, thereby reducing the heat and mass transfer resistance, improving the reaction kinetics during the heat storage and release process, and can meet most heat storage and release application scenarios of the material.

[0014] (4) The process involved in the present invention has low material cost, can form a product with strong stability and can be mass-produced, and the equipment and preparation process are simple, easy to remove impurities, and have high production efficiency. 2 and Al(OH) 3 As raw materials, combined with wet chemical synthesis, heat treatment and molding processes, it can achieve batch preparation. At the same time, the material is non-toxic and pollution-free, and is suitable for solar thermal power generation, industrial waste heat recovery and CO 2 In areas such as heat capture, it provides new solutions for efficient and long-term heat storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of a method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite provided in an embodiment of the present invention.

[0016] Figure 2 1 is an XRD image of a precursor (a) and a product (b) of a calcium-based heat storage material in an embodiment of the present invention; Figure 3 It is a schematic diagram of the heat storage reaction rate DN at different proportions of the calcium-based heat storage material modified by hydrotalcite phase transition provided in an embodiment of the present invention.

[0017] Figure 4 It is a schematic diagram of the powder material of the calcium-based heat storage material modified by the hydrotalcite phase transition provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention aims to provide a calcium-based heat storage material based on hydrotalcite phase transition modification and its preparation method and application. In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Embodiment 1: like Figure 1 As shown, the method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite provided in this embodiment mainly comprises the following steps during implementation: SS1. Raw material mixing and grinding: The calcium source and the aluminum source are mixed according to a preset molar ratio, wherein the calcium source is calcium hydroxide and the aluminum source is aluminum hydroxide, and dispersed by grinding. During the grinding process, the raw materials are first dry-ground under solvent-free conditions, and then an appropriate amount of deionized water is added for wet grinding, and finally a uniformly dispersed mixed powder is formed.

[0020] Preferably, the molar ratio of the calcium source to the aluminum source is Ca:Al=(5-9):2, wherein the molar ratio of the calcium source is greater than that of the hydrotalcite phase (Ca4 Al 2 O 6 CO 3 ) An excess ratio method is adopted, and the excess part of the calcium source is used as an active substance to participate in the subsequent calcium charging and releasing cycle. The aluminum source is used to form a hydrotalcite phase structure and generate a calcium aluminum mixed phase inert skeleton through phase transformation to provide structural support while ensuring the heat storage performance of the material, and the ratio of active components to inert skeletons is optimized by adjusting the molar ratio of the calcium source to the aluminum source.

[0021] In addition, a high-energy ball mill is selected to achieve uniform mixing and dispersion of powder materials, wherein dry grinding and wet grinding are performed for multiple cycles, each cycle includes grinding and intermittent stages, and the amount of deionized water added during wet grinding is controlled to be 20% to 30% of the total mass of the mixed powder to ensure sufficient mixing and uniform dispersion of the calcium source and the aluminum source, and finally the obtained mixed powder reaches a submicron particle size. Furthermore, the deionized water added in the wet grinding stage is pre-dissolved with 0.1 to 0.5 wt.% of a dispersant, and the dispersant is sodium polyacrylate or sodium hexametaphosphate; the absolute value of the Zeta potential of the mixed powder is ≥30 mV, and the particle agglomeration index (CI value) is ≤15%.

[0022] SS2. Synthesis of hydrotalcite phase precursor: The mixed powder obtained in step SS1 is mixed with a carbonate solution, and the mixture is reacted in a constant temperature water bath with continuous stirring under an alkaline environment to promote the formation of a layered structure of calcium aluminum double hydroxide to synthesize a precursor having a hydrotalcite crystal structure. After the reaction is completed, the obtained product is rinsed to neutrality with deionized water, and a solid precursor is obtained after filtration and drying.

[0023] Preferably, the carbonate solution is sodium carbonate decahydrate (Na 2 CO 3 10H 2 O) aqueous solution, the addition amount is 50%~60% of the molar amount of aluminum hydroxide, the water bath temperature is maintained at 75~85°C, the stirring rate is 200~400rpm, the reaction time is 6~10 hours, the standard of rinsing the material to neutrality is that the pH value of the filtrate is stable at 6.5~7.5, and the number of rinsing times is ≥5 times, the hydrotalcite phase precursor generated by the reaction is filtered by vacuum filtration to remove residual solvent and unreacted ions, and dried under preset temperature conditions to prevent the material from cracking or uneven structural changes due to rapid dehydration.

[0024] The drying process is preferably carried out in a vacuum drying oven at a drying temperature of 90-110°C for 10-14 hours. The moisture content of the precursor powder after drying is ≤5%. The specific surface area of ​​the solid precursor is 20-40 m 2 / g, and its XRD spectrum shows that the half-peak width of the characteristic peaks of layered double hydroxides (LDHs) (2θ=11.3°, 22.8°, 34.5°) is ≤0.5°.

[0025] SS3. High temperature calcination and phase transformation: The solid precursor obtained in step SS2 is calcined in a high temperature environment and an oxidative atmosphere, and the hydrotalcite precursor is thermally decomposed and phase-transformed by controlling the heating rate and the holding time to generate a solid phase containing active calcium oxide (CaO) and a hydrotalcite phase (Ca 4 Al 2 O 6 CO 3 ), in which the hydrotalcite phase is distributed on the surface of the active CaO particles as an inert skeleton to inhibit grain boundary migration and particle sintering at high temperatures. At the same time, the lattice distortion introduces oxygen vacancy defects during the phase transformation process to increase CO 2 Adsorption activity, after calcination is completed, the obtained product is cooled to room temperature to obtain modified calcium-based heat storage material powder.

[0026] Preferably, the calcination temperature in the high temperature environment is 850-950°C, the heating rate is 5-10°C / min, and the holding time is 80-100 minutes, so that the hydrotalcite precursor is completely decomposed and phase-transformed to form the desired composite powder; the oxidizing atmosphere is air or a mixed gas with an oxygen volume fraction of ≥21%; after calcination, programmed cooling is adopted, and the cooling rate is 2-5°C / min to avoid cracking of the calcium aluminum mixed phase due to thermal stress caused by rapid cooling.

[0027] The calcination process preferably adopts a staged heating method, including initial heating to the medium temperature range to remove surface adsorbed water and weakly bonded water molecules, and then further heating to the target temperature range to achieve complete decomposition of the hydrotalcite structure and introduction of oxygen defects. During the calcination process, an oxidizing atmosphere is introduced to optimize the specific surface area and surface chemical activity of the material, and to ensure the uniform distribution of oxygen defects, thereby increasing its CO 2 Adsorption capacity.

[0028] Preferably, the hydrotalcite phase (Ca 4 Al 2 O 6 CO 3 The mass proportion of ) is controlled at 15%~30%, and the grain size is 50~200nm; the concentration of the oxygen vacancy defect is regulated by the calcination temperature and the holding time, and the EPR test signal intensity is similar to that of CO 2 The adsorption capacity showed a linear positive correlation.

[0029] SS4. Forming of porous materials: The product powder obtained in step SS3 is evenly sprayed with deionized water for wetting treatment, and a pore-forming agent is added in a preset proportion to adjust the pore structure and specific surface area. The obtained mixture is plastically formed and spheronized and then dried to obtain porous calcium-based heat storage material particles with enhanced cycle stability.

[0030] Preferably, the addition ratio of the pore former is set according to the target porosity grade: when the addition amount of the pore former is 5%-15%, the porosity of the porous particles is 40%-50%; when the addition amount is 15%-30%, the porosity is increased to 50%-60%; and the pores include a composite structure of mesopores (2-50nm) and macropores (>50nm) to meet the CO 2 The need for coordinated regulation of diffusion and volume expansion stress.

[0031] Preferably, the plastic forming method is selected from extrusion forming, compression molding or spray granulation, wherein extrusion forming is suitable for columnar or flaky particles, compression molding is suitable for block materials, and spray granulation is suitable for spherical particles, and is combined with spheronization to form a particle structure with uniform morphology, wherein the particle size distribution is controlled between 0.5 mm and 5 mm to optimize the packing density and thermochemical reaction characteristics of the material.

[0032] Preferably, the porous particles are pre-calcined at 300-500°C for 1-2 hours to remove the residual pore-forming agent and stabilize the pore structure; the CO 2 The adsorption capacity is ≥8mmol / g, and the capacity retention rate is ≥85% after 50 decarbonization / carbonization cycles.

[0033] Embodiment 2: On the basis of the above-mentioned embodiment 1, as a more preferred example, the preparation method of the calcium-based heat storage material based on the phase transition modification of hydrotalcite provided in this embodiment 2 mainly comprises the following steps: Calcium hydroxide and aluminum hydroxide are added to a planetary high-energy ball mill in a molar ratio of 5:2. The ball mill speed is set to 500r / min, and one cycle is 4min of work and 6min of rest. Dry grinding and wet grinding are 12 and 15 cycles respectively. Then the mixture is placed in a three-forked flask, and sodium carbonate decahydrate crystals with half a molar amount of aluminum hydroxide are added. After rinsing to neutrality in a constant temperature water bath, the precursor filter cake is obtained after filtration and dried, and then calcined in a tubular furnace to obtain a calcium-based heat storage material.

[0034] Select an appropriate amount of precursor product powder, spray deionized water evenly to wet it and mix it evenly, and add the pore-forming agent in a certain proportion, and then plasticize and extrude it into strips in the high-pressure cavity of the extruder. Transfer the strip mixture to a rolling cylinder for high-speed centrifugation, roll it into balls, dry it, and then calcine it to obtain porous formed particles.

[0035] Embodiment 3: On the basis of the above-mentioned embodiment 1, as a more preferred example, the preparation method of the calcium-based heat storage material based on the phase transition modification of hydrotalcite provided in this embodiment 3 mainly comprises the following steps: Calcium hydroxide and aluminum hydroxide are added to a planetary high-energy ball mill in a molar ratio of 6:2. The ball mill speed is set to 500r / min, and one cycle is 4min of work and 6min of rest. Dry grinding and wet grinding are 12 and 15 cycles respectively. Then the mixture is placed in a three-forked flask, and sodium carbonate decahydrate crystals with half a molar amount of aluminum hydroxide are added. After rinsing to neutrality in a constant temperature water bath, the precursor filter cake is obtained after filtration and dried, and then calcined in a tubular furnace to obtain a calcium-based heat storage material.

[0036] Select an appropriate amount of precursor product powder, spray deionized water evenly to wet it and mix it evenly, add a pore-forming agent in a certain proportion, and plasticize and extrude it into strips in the high-pressure cavity of the extruder. Transfer the strip mixture to a rolling cylinder for high-speed centrifugation, roll it into balls, dry it, and then calcine it to obtain porous formed particles.

[0037] Embodiment 4: On the basis of the above-mentioned embodiment 1, as a more preferred example, the preparation method of the calcium-based heat storage material based on the phase transition modification of hydrotalcite provided in this embodiment 4 mainly comprises the following steps: Calcium hydroxide and aluminum hydroxide are added to a planetary high-energy ball mill in a molar ratio of 7:2. The ball mill speed is set to 500r / min, and one cycle is 4min of work and 6min of rest. Dry grinding and wet grinding are 12 and 15 cycles respectively. Then the mixture is placed in a three-forked flask, and sodium carbonate decahydrate crystals with half a molar amount of aluminum hydroxide are added. After rinsing to neutrality in a constant temperature water bath, the precursor filter cake is obtained after filtration and dried, and then calcined in a tubular furnace to obtain a calcium-based heat storage material.

[0038] Select an appropriate amount of precursor product powder, spray deionized water evenly to wet it and mix it evenly, add a pore-forming agent in a certain proportion, and plasticize and extrude it into strips in the high-pressure cavity of the extruder. Transfer the strip mixture to a rolling cylinder for high-speed centrifugation, roll it into balls, dry it, and then calcine it to obtain porous formed particles.

[0039] Embodiment 5: On the basis of the above-mentioned embodiment 1, as a more preferred example, the preparation method of the calcium-based heat storage material based on the phase transition modification of hydrotalcite provided in this embodiment 5 mainly comprises the following steps: Calcium hydroxide and aluminum hydroxide are added to a planetary high-energy ball mill in a molar ratio of 8:2. The ball mill speed is set to 500r / min, and one cycle is 4min of work and 6min of rest. Dry grinding and wet grinding are 12 and 15 cycles respectively. Then the mixture is placed in a three-forked flask, and sodium carbonate decahydrate crystals with half a molar amount of aluminum hydroxide are added. After rinsing to neutrality in a constant temperature water bath, the precursor filter cake is obtained after filtration and dried, and then calcined in a tubular furnace to obtain a calcium-based heat storage material.

[0040] Select an appropriate amount of precursor product powder, spray deionized water evenly to wet it and mix it evenly, add a pore-forming agent in a certain proportion, and plasticize and extrude it into strips in the high-pressure cavity of the extruder. Transfer the strip mixture to a rolling cylinder for high-speed centrifugation, roll it into balls, dry it, and then calcine it to obtain porous formed particles.

[0041] Embodiment 6: Based on the above-mentioned embodiment 1, as a more preferred example, the preparation method of the calcium-based heat storage material based on the phase transition modification of hydrotalcite provided in this embodiment 6 mainly comprises the following steps: Calcium hydroxide and aluminum hydroxide are added to a planetary high-energy ball mill in a molar ratio of 9:2. The ball mill speed is set to 500r / min, and one cycle is 4min of work and 6min of rest. Dry grinding and wet grinding are 12 and 15 cycles respectively. Then the mixture is placed in a three-forked flask, and sodium carbonate decahydrate crystals with half a molar amount of aluminum hydroxide are added. After rinsing to neutrality in a constant temperature water bath, the precursor filter cake is obtained after filtration and dried, and then calcined in a tubular furnace to obtain a calcium-based heat storage material.

[0042] Select an appropriate amount of precursor product powder, spray deionized water evenly to wet it and mix it evenly, add a pore-forming agent in a certain proportion, and plasticize and extrude it into strips in the high-pressure cavity of the extruder. Transfer the strip mixture to a rolling cylinder for high-speed centrifugation, roll it into balls, dry it, and then calcine it to obtain porous formed particles.

[0043] Example 7: Test results Figure 2 Figure 2 shows the XRD images of the precursor (a) and product (b) of the calcium-based thermal storage material in the embodiment of the present invention, wherein (a) shows the crystal structure characteristics of the hydrotalcite phase precursor synthesized under different Ca / Al molar ratios. As the Ca / Al molar ratio increases from 5:2 to 9:2, the intensity of the characteristic diffraction peak of the hydrotalcite phase gradually decreases, indicating that excessive calcium source will affect the crystallinity of the hydrotalcite phase; (b) is the XRD spectrum of the calcined product, wherein "◇" is marked as the characteristic peak of CaO and "○" is marked as the characteristic peak of Ca 4 Al 2 O 6 CO 3Characteristic peaks. It can be seen that with the increase of Ca / Al ratio, the diffraction peak intensity of the active component CaO is significantly enhanced, while the calcium aluminum mixed phase Ca 4 Al 2 O 6 CO 3 The diffraction peak intensity of is relatively weakened, which corresponds to the content change trend of the hydrotalcite phase in the precursor. Therefore, the optimal balance between the active components and the inert skeleton of calcium-based thermal storage materials can be achieved by optimizing the Ca / Al ratio.

[0044] Figure 3 The figure shows the heat storage reaction rate DN of the calcium-based heat storage material modified by hydrotalcite phase transition provided in the embodiment of the present invention at different Ca / Al ratios. The figure reflects the heat storage reaction rate DN of the material under CO 2 Reaction kinetics under atmosphere. As can be seen from the figure, all samples experienced obvious changes in reaction rate within the same time range, and all showed a characteristic curve of first decreasing and then recovering, indicating that the material has typical reversible reaction characteristics in the process of heat storage and heat release. When the Ca / Al molar ratio is low (such as 5Ca-2Al, 6Ca-2Al), the maximum reaction rate of the material is higher, indicating that it has a faster CO 2 Adsorption and release kinetics. However, with the increase of the Ca / Al molar ratio (7Ca-2Al, 8Ca-2Al, 9Ca-2Al), the decrease in the reaction rate decreased, and the position of the lowest point was relatively delayed, indicating that the introduction of excess calcium source reduced the reactivity of the material to a certain extent. Further analysis found that the sample with Ca / Al=7:2 had the optimal reaction rate curve, indicating that the calcium-based heat storage material at this ratio maintained good reactivity and balance during the heat storage and release process. It also shows that by regulating the Ca / Al ratio, the microstructure and heat storage performance of the material can be effectively optimized.

[0045] Figure 4 Schematic diagram of the cycle performance of the calcium-based heat storage material based on the hydrotalcite phase transformation modification provided in the embodiment of the present invention. Figure 4 It can be seen that with the increase of the number of cycles, the carbon conversion rate and heat storage density of materials with different molar ratios show a downward trend. This is mainly due to the sintering and particle agglomeration of the materials during the high-temperature cycle, which leads to a decrease in specific surface area and CO 2 The adsorption capacity decreases. However, there are significant differences in the extent of the decrease in materials with different molar ratios, indicating that the Ca / Al ratio has an important influence on the cyclic stability of the material. Specifically, the carbon conversion rate of the unmodified CaO (black curve) decreases rapidly after just a few cycles, accompanied by a serious attenuation of the heat storage density, indicating that its sintering resistance is extremely poor and it is difficult to meet the needs of long-term heat storage applications. In contrast, the modified calcium-based heat storage material of the present invention that introduces a hydrotalcite phase transition exhibits better cyclic stability. In addition, Figure 4 The analysis results show that an appropriate Ca / Al molar ratio can effectively improve the cyclic stability of calcium-based thermal storage materials, optimize their thermal storage density, and reduce performance degradation during long-term use, providing a more reliable material choice for industrial-grade thermochemical energy storage applications.

[0046] So far, the technical solution of the present invention has been described in conjunction with the contents of the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to the above specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite, characterized in that: The preparation method mainly comprises the following implementation steps: SS1. A calcium source and an aluminum source are mixed according to a preset molar ratio, wherein the calcium source is calcium hydroxide and the aluminum source is aluminum hydroxide, and the mixture is dispersed by grinding. During the grinding process, the raw materials are first dry-ground under solvent-free conditions, and then wet-ground by adding an appropriate amount of deionized water to form a uniformly dispersed mixed powder; SS2. The mixed powder obtained in step SS1 is mixed with a carbonate solution, and the mixture is reacted in a constant temperature water bath under constant stirring in an alkaline environment to promote the formation of a layered structure of calcium aluminum double hydroxide to synthesize a precursor having a hydrotalcite crystal structure. After the reaction is completed, the obtained product is rinsed with deionized water to neutrality, and then filtered and dried to obtain a solid precursor; SS3. The solid precursor obtained in step SS2 is calcined in a high temperature environment and an oxidizing atmosphere. By controlling the heating rate and the holding time, the hydrotalcite precursor undergoes thermal decomposition and phase transformation to generate a composite powder comprising active calcium oxide (CaO) and a hydrotalcite phase (Ca4Al2O6CO3), wherein the hydrotalcite phase is distributed on the surface of the active CaO particles as an inert skeleton to inhibit grain boundary migration and particle sintering at high temperatures. At the same time, during the phase transformation process, lattice distortion introduces oxygen vacancy defects to enhance CO2 adsorption activity. After the calcination is completed, the obtained product is cooled to room temperature to obtain a modified calcium-based heat storage material powder; SS4. The product powder obtained in step SS3 is uniformly sprayed with deionized water for wetting treatment, and a pore-forming agent is added in a preset proportion to adjust the pore structure and specific surface area. The obtained mixture is plastically formed and spheronized and then dried to obtain porous calcium-based heat storage material particles with enhanced cycle stability.

2. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 1, characterized in that: In the above step SS1, the molar ratio of the calcium source to the aluminum source is Ca:Al=(5~9):2, wherein the molar ratio of the calcium source is in excess of the hydrotalcite phase (Ca4Al2O6CO3) formed in the subsequent step, and the excess calcium source participates in the subsequent calcium charging and releasing cycle as an active substance, and the aluminum source is used to form a hydrotalcite phase structure and generate a calcium aluminum mixed phase inert skeleton through phase transformation, so as to provide structural support while ensuring the heat storage performance of the material, and optimize the ratio of active components to inert skeletons by regulating the molar ratio of the calcium source to the aluminum source.

3. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 1, characterized in that: In the above step SS1, a high-energy ball mill is selected to achieve uniform mixing and dispersion of the powder materials, wherein dry grinding and wet grinding are performed for multiple cycles, each cycle includes grinding and intermittent stages, and the amount of deionized water added during the wet grinding process is controlled to be 20% to 30% of the total mass of the mixed powder to ensure sufficient mixing and uniform dispersion of the calcium source and the aluminum source, and ultimately to make the obtained mixed powder reach a submicron particle size.

4. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 3, characterized in that: The deionized water added in the wet grinding stage is pre-dissolved with 0.1-0.5wt.% of a dispersant, and the dispersant is sodium polyacrylate or sodium hexametaphosphate; the absolute value of the Zeta potential of the mixed powder is ≥30mV, and the particle agglomeration index (CI value) is ≤15%.

5. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 1, characterized in that: The carbonate solution is a sodium carbonate decahydrate (Na2CO3·10H2O) aqueous solution, the addition amount of which is 50% to 60% of the molar amount of aluminum hydroxide, the water bath temperature is maintained at 75 to 85°C, the stirring rate is 200 to 400 rpm, the reaction time is 6 to 10 hours, the standard for rinsing the material to neutrality is that the pH value of the filtrate is stable at 6.5 to 7.5, and the number of rinsing times is ≥5 times, the hydrotalcite phase precursor generated by the reaction is filtered by vacuum filtration to remove residual solvent and unreacted ions, and is dried under preset temperature conditions to prevent the material from cracking or uneven structural changes due to rapid dehydration.

6. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 5, characterized in that: The drying process is carried out in a vacuum drying oven at a drying temperature of 90-110°C for 10-14 hours. The moisture content of the precursor powder after drying is ≤5%. The specific surface area of ​​the solid precursor is 20-40 m 2 / g, and its XRD spectrum shows that the half-peak width of the characteristic peaks of layered double hydroxides (LDHs) (2θ=11.3°, 22.8°, 34.5°) is ≤0.5°.

7. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 1, characterized in that: In the above step SS3, the calcination temperature in the high temperature environment is 850~950℃, the heating rate is 5~10℃ / min, and the holding time is 80~100 minutes, so that the hydrotalcite precursor is completely decomposed and phase transformed to form the required composite powder; the oxidizing atmosphere is air or a mixed gas with an oxygen volume fraction of ≥21%; after calcination, a programmed cooling method is adopted, and the cooling rate is 2~5℃ / min to avoid cracking of the calcium aluminum mixed phase due to thermal stress caused by rapid cooling.

8. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 7, characterized in that: The calcination process adopts a staged heating method, including initial heating to the medium temperature range to remove surface adsorbed water and weakly bonded water molecules, and then further heating to the target temperature range to achieve complete decomposition of the hydrotalcite structure and introduction of oxygen defects. At the same time, an oxidizing atmosphere is introduced during the calcination process to optimize the specific surface area and surface chemical activity of the material, ensure the uniform distribution of oxygen defects, and improve its CO2 adsorption capacity.

9. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 8, characterized in that: The mass proportion of the hydrotalcite phase (Ca4Al2O6CO3) is 15%~30%, and its grain size is 50~200nm; the concentration of the oxygen vacancy defect is regulated by the calcination temperature and the insulation time, and its EPR test signal intensity is linearly positively correlated with the CO2 adsorption capacity.

10. The method for preparing a calcium-based heat storage material based on phase transition modification of hydrotalcite according to claim 1, characterized in that: In the above step SS4, the added pore-forming agent includes one or more of methyl cellulose, starch, polyvinyl alcohol, and microcrystalline cellulose, and the addition ratio is 5wt.%, 10wt.%, 15wt.%, 20wt.% or 30wt.%, and the addition ratio is regulated according to the target porosity and specific surface area requirements, and is controlled to decompose during the subsequent heat treatment process to ensure that the obtained heat storage material particles have high porosity and excellent gas-solid reaction diffusion properties.

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