A calcium-based thermal storage particle with an Al-supported core-shell structure and its preparation method

Abstract

This invention discloses an Al-supported core-shell structured calcium-based thermal storage particle and its preparation method, belonging to the field of thermal storage material technology. The thermal storage particle is cast using a mixture of manganese dioxide and graphite to form a hydrophobic surface, with the calcium-based raw material being inexpensive and readily available calcium hydroxide, and internally doped with different proportions of inert carrier aluminum nitrate. This invention regulates the absorbance of the core-shell structured calcium-based thermal storage material by changing the mass ratio of manganese dioxide and graphite in the hydrophobic surface, overcoming the poor absorbance of traditional calcium-based materials. Furthermore, by doping with different proportions of inert carrier, the thermal storage / release performance of the calcium-based material is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of thermal storage materials technology, specifically relating to an Al-supported shell-core structure calcium-based thermal storage particle and its preparation method. Background Technology

[0002] Faced with energy shortages and environmental problems, large-scale use of clean energy has become a trend in energy development. Concentrated solar power (CSP), as one of the main ways of utilizing solar energy, provides an effective solution to the global energy crisis. Thermal energy storage technology can address the intermittency and instability of CSP. Compared with sensible and latent heat energy storage, thermochemical energy storage (TCES) has high energy density, low energy loss, and long cycle life, showing broad application prospects.

[0003] Currently, among various thermochemical energy storage (TCES) technologies, calcium cycle (CaL) energy storage technology has attracted widespread attention due to its advantages of being widely available, non-toxic, and environmentally friendly. Calcium carbonate stands out among numerous thermochemical energy storage materials due to its low cost, easy availability, and high reaction kinetics. Poor light absorption characteristics are one of the main reasons why calcium-based thermal energy storage materials have not yet achieved large-scale application.

[0004] Currently, in the field of thermochemical thermal energy storage, scholars are focusing more on the heat storage / release stability during calcium cycling. Significant progress has been made in modifying calcium-based materials by adding inert supports and pore-forming agents, and in granulation molding of calcium-based thermal energy storage materials to reduce segregation during cycling. To address the low solar radiation absorptivity of calcium-based materials, uniform doping with light-absorbing components can effectively improve light absorption performance. However, this increase in absorbance comes at the cost of sacrificing the active CaO required for the reaction; reduced active components mean lower thermal energy storage density. To date, few scholars have proposed effective solutions to this problem. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a calcium-based thermal storage particle with an Al-supported core-shell structure constructed based on hydrophobic surfaces and its preparation method. The method includes the proportions of manganese dioxide and graphite, the ratio of active CaO to inert support, and a granulation process.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides an Al-supported core-shell structured calcium-based thermal storage material, "black on the outside and white on the inside": a dark outer shell formed by manganese and its oxides absorbs light, while the interior contains an aluminum-supported calcium-based material for heat storage / release reactions. The calcium-based material is calcium hydroxide, with Al(NO3)3·9H2O as the inert support, and the light-absorbing components are manganese and its oxides.

[0008] Furthermore, the hydrophobic surface components required for the preparation of the Al-supported core-shell structure calcium-based thermal storage material are manganese dioxide and graphite, and the mass ratio of manganese dioxide to graphite in the hydrophobic surface is 1:0-4. Preferably, the mass ratio of manganese dioxide to graphite in the hydrophobic surface is 1:0, 3:2, 1:2 or 1:4.

[0009] The calcium-based material includes CaO and Ca. 12 Al 14 O 33 The calcium-based material contains 92.5%-80% CaO. 12 Al 14 O 33 The content of [certain components] is 7.5%-20%; preferably, the calcium-based material contains CaO and Ca [components]. 12 Al 14 O 33 The contents were 92.5% and 7.5%, 84.5% and 15.5%, or 80% and 20%, respectively.

[0010] This invention also provides a method for preparing an Al-supported core-shell structured calcium-based thermal storage material, comprising the following steps:

[0011] Step 1: Prepare a hydrophobic surface using manganese dioxide and graphite, and place it at an angle;

[0012] Step 2: Mix deionized water, calcium hydroxide and aluminum nitrate, and stir to form a uniform wet mixture;

[0013] Step 3: The wet mixture obtained in Step 2 is titrated on an inclined hydrophobic surface using a combination of capillary tube and syringe to obtain wet Al-supported core-shell structured calcium-based thermal storage particles with uniform particle size.

[0014] Step 4: Dry the wet Al-supported core-shell structured calcium-based thermal storage particles obtained in Step 3.

[0015] Step 5: Calcining the particles obtained in step 4 yields the Al-supported core-shell structured calcium-based thermal storage particles.

[0016] Further, in step 1, the mass ratio of manganese dioxide to graphite is 1:0.6-4. Preferably, the mass ratio of manganese dioxide to graphite is 3:2-1:4, and more preferably, the mass ratio of manganese dioxide to graphite is 3:2, 1:2, or 1:4.

[0017] Further, in step 2, the mass ratio of calcium hydroxide to aluminum nitrate is 2.5-9:1; the mass-volume ratio of the total mass of calcium hydroxide and aluminum nitrate to deionized water is 3-3.1:5.

[0018] Furthermore, in step 4, the drying temperature is 65-85℃, and the drying time is 12-14 hours.

[0019] Further, in step 5, the calcination conditions are as follows: the temperature is increased to 900℃ at a heating rate of 10℃ / min, and held at that temperature for 90min. Calcination removes the stable substance Ca formed from graphite. 12 Al 14 O 33 .

[0020] The beneficial effects of this invention are as follows:

[0021] (1) The present invention uses a mixture of manganese dioxide and graphite to construct an Al-supported shell-core structure of calcium-based thermal storage particles with hydrophobic surface assistance, so that the calcium-based thermal storage material can achieve high light absorption characteristics without consuming the internal active CaO.

[0022] (2) By placing the light-absorbing component on the outer surface of the particles, this invention achieves the transformation of calcium-based materials from white to black and also solves the problem of the light-absorbing component consuming active CaO. This "black on the outside and white on the inside" shell-core structure calcium-based thermal storage particles can be used in thermochemical thermal storage systems to efficiently utilize solar radiation energy and have high energy storage density, thereby improving the utilization rate of solar energy.

[0023] (3) This invention regulates the light absorption of the core-shell structure calcium-based thermal storage material by changing the mass ratio of manganese dioxide and graphite in the hydrophobic surface, thus overcoming the shortcomings of poor light absorption performance of traditional calcium-based materials. Its calcium-based raw material is inexpensive and readily available calcium hydroxide, and it is doped with different proportions of inert carrier aluminum nitrate. By doping with different proportions of inert carrier, the heat storage / heat release performance of the calcium-based material is enhanced.

[0024] (4) The raw materials required for the thermal storage material described in this invention are inexpensive and readily available, the operation steps are simple, and it does not involve high temperature or chemical toxicity reactions, making it suitable for industrial-scale production. Attached Figure Description

[0025] Figure 1 The spectral absorbance of Comparative Example 1 and Examples 1-3;

[0026] Figure 2 The energy storage density calculated based on CaO is shown in Comparative Example 2 and Examples 3-5;

[0027] Figure 3 This is a schematic diagram of the structure of a combination tool consisting of a capillary tube and a syringe. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified in the examples, the procedures shall be performed in accordance with the techniques or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from the market.

[0030] Both the capillary tube and the syringe are purchased laboratory-grade materials. Simply attach the capillary tube to the syringe needle hole. Figure 3 As shown.

[0031] Example 1

[0032] Core-shell structured Al-supported calcium-based thermal storage particles

[0033] Based on the preparation process, specifically:

[0034] Step 1: The hydrophobic surface component is pure manganese dioxide, which is placed in a petri dish, compacted, and tilted.

[0035] Step 2: Weigh 12.16g Ca(OH)2 and 2.94g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0036] Step 3, the obtained wet mixture is passed through a combination tool of capillary tube and syringe (e.g., Figure 3 As shown), uniform calcium-based thermal storage particles were obtained by titration on a hydrophobic surface.

[0037] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0038] Step 5: The dried particles are calcined at 900℃ for 90 minutes to obtain the core-shell structured Al-supported calcium-based thermal storage particles. These are labeled as Ca84.5 / Al15.5-Mn1 / CO.

[0039] Example 2

[0040] Core-shell structured Al-supported calcium-based thermal storage particles

[0041] Based on the preparation process, specifically:

[0042] Step 1: The hydrophobic surface is composed of 20 wt% manganese dioxide and 80 wt% graphite. At room temperature, manganese dioxide and graphite are stirred at 850 r / min to obtain the hydrophobic surface, which is then placed in a petri dish, compacted, and tilted.

[0043] Step 2: Weigh 12.16g Ca(OH)2 and 2.94g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0044] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniformly sized calcium-based heat storage particles by titration on a hydrophobic surface.

[0045] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0046] Step 5: The dried particles are calcined at 900℃ for 90 min to remove surface graphite, thus obtaining the core-shell structured Al-supported calcium-based thermal storage particles. They are labeled as Ca84.5 / Al15.5-Mn1 / C4.

[0047] Example 3

[0048] Core-shell structured Al-supported calcium-based thermal storage particles

[0049] Based on the preparation process, specifically:

[0050] Step 1: The hydrophobic surface component consists of 60 wt% manganese dioxide and 40 wt% graphite. It is placed in a petri dish, compacted, and tilted.

[0051] Step 2: Weigh 12.16g Ca(OH)2 and 2.94g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0052] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniformly sized calcium-based heat storage particles by titration on a hydrophobic surface.

[0053] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0054] Step 5: The dried particles are calcined at 900℃ for 90 min to remove surface graphite, thus obtaining the core-shell structured Al-supported calcium-based thermal storage particles. They are labeled as Ca84.5 / Al15.5-Mn3 / C2.

[0055] Example 4

[0056] Core-shell structured Al-supported calcium-based thermal storage particles

[0057] Based on the preparation process, specifically:

[0058] Step 1: The hydrophobic surface component consists of 60 wt% manganese dioxide and 40 wt% graphite. It is placed in a petri dish, compacted, and tilted.

[0059] Step 2: Weigh 10.16g Ca(OH)2 and 1.14g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0060] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniformly sized calcium-based heat storage particles by titration on a hydrophobic surface.

[0061] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0062] Step 5: The dried particles are calcined at 900℃ for 90 min to remove surface graphite, thus obtaining the core-shell structured Al-supported calcium-based thermal storage particles. They are labeled as Ca92.5 / Al7.5-Mn3 / C2.

[0063] Example 5

[0064] Core-shell structured Al-supported calcium-based thermal storage particles

[0065] Based on the preparation process, specifically:

[0066] Step 1: The hydrophobic surface component consists of 60 wt% manganese dioxide and 40 wt% graphite. It is placed in a petri dish, compacted, and tilted.

[0067] Step 2: Weigh 9.48g Ca(OH)2 and 3.03g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0068] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniformly sized calcium-based heat storage particles by titration on a hydrophobic surface.

[0069] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0070] Step 5: The dried particles are calcined at 900℃ for 90 min to remove surface graphite, thus obtaining the core-shell structured Al-supported calcium-based thermal storage particles. They are labeled as Ca80 / Al20-Mn3 / C2.

[0071] Comparative Example 1

[0072] Coreless Al-supported calcium-based thermal storage particles

[0073] Based on the preparation process, specifically:

[0074] Step 1: The hydrophobic surface component is pure graphite, which is placed in a petri dish, compacted, and tilted.

[0075] Step 2: Weigh 12.16g Ca(OH)2 and 2.94g Al(NO3)3 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0076] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniformly sized calcium-based heat storage particles by titration on a hydrophobic surface.

[0077] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0078] Step 5: The dried particles are calcined at 900℃ for 90 min to remove surface graphite, thus obtaining the coreless Al-supported calcium-based thermal storage particles. They are labeled as Ca84.5 / Al15.5-Mn0 / C1.

[0079] Comparative Example 2

[0080] Core-shell structured calcium-based thermal storage particles

[0081] Based on the preparation process, specifically:

[0082] Step 1: The hydrophobic surface component consists of 60 wt% manganese dioxide and 40 wt% graphite. It is placed in a petri dish, compacted, and tilted.

[0083] Step 2: Weigh 6g of Ca(OH)2 into a beaker, add an appropriate amount of deionized water and stir to form a uniform wet mixture;

[0084] Step 3: The obtained wet mixture is used as a combination of capillary tube and syringe to obtain uniform core-shell structured calcium-based thermal storage particles by titration on a hydrophobic surface;

[0085] Step 4: Dry the obtained wet granules at 70°C for 12 hours;

[0086] Step 5: The dried particles are calcined at 900℃ for 90 minutes to remove graphite, thus obtaining the core-shell structured calcium-based thermal storage particles. They are labeled as Ca100-Mn3 / C2.

[0087] Experimental Example 1

[0088] The light absorption characteristics of the samples from Examples 1-3 and Comparative Example 1 were investigated using a Carry 5000 Agilent Technologies UV / Vis / NIR spectrometer in the wavelength range of 300-2500 nm. Approximately 120 mg of particulate sample was placed in a circular measuring mold, and its reflectance was measured using the spectrometer. To quantitatively compare the solar absorptivity of different samples, the average solar absorptivity A was introduced. ave The average solar absorptivity is calculated by the weighted integral of the sample absorptivity and the standard solar spectrum AM1.5D, and the specific calculation formula is as follows:

[0089]

[0090] Where A(λ) is the solar absorptivity, λ is the wavelength, and I(λ) is the wavelength. AM1.5D The solar spectrum is under AM1.5D conditions.

[0091] With the same Al loading, the spectral absorbance of Al-loaded calcium-based thermal storage particles with different hydrophobic surface structures are as follows: Figure 1As shown. The shaded area in the background represents the standard AM1.5D solar spectrum corresponding to the Y-axis on the right. The study found that the spectral irradiance of AM1.5D is mainly concentrated in the wavelength range of 300-1350 nm. Within the 300-1350 nm range, Comparative Example 1 has the lowest average solar absorptivity at 19.36%, indicating that the coreless Al-supported calcium-based thermal storage particles have poor solar absorption capacity. The solar absorption capacity of the core-shell structured Al-supported calcium-based thermal storage particles gradually increases with the increase of the MnO2 mass ratio in the hydrophobic surface. The average solar absorptivity is arranged in the following order: Example 1 > Example 3 > Example 2 > Comparative Example 1. The trend of the average solar absorptivity is consistent with its color depth, with Example 1 having the highest absorptivity at 88.72%, which is more than 4.58 times that of Comparative Example 1. However, without graphite, the particles have adhesion problems due to the weak hydrophobicity of the hydrophobic surface during granulation; after adding graphite, the strong hydrophobic interaction between graphite and water allows the powder to adhere better to the surface. The thermal storage particles of this invention are used in a thermochemical energy storage and solar concentrating system. This system requires the particles to be in a fluidized state to absorb solar radiation. Particle adhesion reduces the sphericity of the particles and also hinders the heat conduction of solar radiation absorbed on the particle surface by the black outer shell into the particle interior.

[0092] Experimental Example 2

[0093] Cyclic energy storage / release experiments were performed on samples from Examples 3-5 and Comparative Example 2 using a Jupiter-STA449F5 thermogravimetric analyzer (TGA). Approximately 20 mg of sample was placed in an alumina crucible, and cyclic energy storage / release experiments were conducted under alternating CO2 and N2 atmospheres for 40 cycles. The samples were calcined at 750°C and 100 ml / min N2 atmosphere for 15 minutes, and then carbonized at 850°C and a mixed atmosphere of 100 ml / min CO2 and 10 ml / min N2 for 15 minutes, with N2 acting as a protective gas. The CO2 absorption capacity per unit mass of the sample (C) was used to determine the energy storage / release. n (gCO2 / g calcined sample) and energy storage density calculated based on CaO (E g,n The heat storage / heat release performance of the sample was evaluated using the (MJ / kg) method.

[0094]

[0095] In the formula, n is the number of iterations; m car,n and m cal,n ΔH represents the mass of the sample after n carbonation and calcination cycles, respectively; ΔH is the enthalpy of reaction, 178 kJ / mol.

[0096] Calcium-based thermal storage particles with different proportions of Al-supported core-shell structures were constructed using a composition of 60wt% MnO2 and 40wt% graphite hydrophobic surfaces. The energy storage density based on CaO was calculated for Comparative Example 2 and Examples 3-5 as follows: Figure 2As shown, all embodiments exhibited relatively stable and reliable thermal energy storage / release capabilities. This is mainly due to the formation of an inert support, Ca12Al14O33, by doping with Al(NO3)3, a framework structure that enables stable heat storage / release of the thermal energy particles. However, when the Al doping ratio exceeds a certain value, the energy storage density calculated based on CaO in the samples actually decreases. Example 3 exhibited the highest energy storage density calculated based on CaO after 40 cycles, with Eg,n at 1.71 MJ / kg, approximately 1.15 times that of Comparative Example 2.

[0097] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. An Al-supported core-shell structured calcium-based thermal storage material, characterized in that, It comprises an outer shell formed of manganese dioxide and graphite, and a core of aluminum-supported calcium-based material; said calcium-based material includes CaO and Ca2+. 12 Al 14 O 33 The calcium-based material contains 92.5%-80% CaO. 12 Al 14 O 33 The content is 7.5%-20%; the mass ratio of manganese dioxide to graphite is 1:0.6-4.

2. A method for preparing an Al-supported core-shell structured calcium-based thermal storage material as described in claim 1, characterized in that, Includes the following steps: Step 1: Prepare a hydrophobic surface using manganese dioxide and graphite, and place it at an angle; Step 2: Mix deionized water, calcium hydroxide and aluminum nitrate, and stir to form a uniform wet mixture; Step 3: The wet mixture obtained in Step 2 is titrated on an inclined hydrophobic surface using a combination of capillary tube and syringe to obtain wet Al-supported core-shell structured calcium-based thermal storage particles with uniform particle size. Step 4: Dry the wet Al-supported core-shell structured calcium-based thermal storage particles obtained in Step 3. Step 5: Calcining the particles obtained in step 4 yields the Al-supported core-shell structured calcium-based thermal storage particles. In step 1, the mass ratio of manganese dioxide to graphite is 1:0.6-4.

3. The method for preparing an Al-supported core-shell structured calcium-based thermal storage material according to claim 2, characterized in that, The mass ratio of manganese dioxide to graphite is 3:2, 1:2, or 1:

4.

4. The method for preparing an Al-supported core-shell structured calcium-based thermal storage material according to claim 2, characterized in that, In step 2, the mass ratio of calcium hydroxide to aluminum nitrate is 2.5-9:1; the mass-volume ratio of the total mass of calcium hydroxide and aluminum nitrate to deionized water is 3-3.1:

5.

5. The method for preparing an Al-supported core-shell structured calcium-based thermal storage material according to claim 2, characterized in that, In step 4, the drying temperature is 65-85℃ and the drying time is 12-14 hours.

6. The method for preparing an Al-supported core-shell structured calcium-based thermal storage material according to claim 2, characterized in that, In step 5, the calcination conditions are as follows: heat to 900℃ at a heating rate of 10℃ / min, and maintain the temperature for 90min.

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