Preparation method of composite phase change material for solving supercooling problem of sodium acetate trihydrate

Abstract

The application discloses a preparation method of a composite phase change material for solving the supercooling problem of sodium acetate trihydrate, and relates to the technical field of phase change material production, and comprises the following steps: S1, 30 g of natural crystalline bischofite is weighed, dried at 120 DEG C for 12 h, and then dissolved in 90 g of anhydrous ethanol to form a magnesium chloride solution; S2, the magnesium chloride solution is filtered by using a vacuum filtration bottle, and insoluble substances are separated; the ethanol component in the obtained solution after filtration is evaporated by using a rotary evaporator, and a precipitate, magnesium chloride hexahydrate MgCl2.6H2O, is obtained; S3, the magnesium chloride hexahydrate MgCl2.6H2O is combined with sodium acetate trihydrate SAT at an optimized mass ratio of 3:17; and S4, after complete melting and uniformity, 1% sodium polyacrylate PAAS is added as a thickening agent, and the mixture is packaged in expanded graphite EG. The method can realize effective utilization of the by-product bischofite of a salt lake, and simultaneously solve the supercooling problem of SAT.

Description

Technical Field

[0001] This invention relates to the field of phase change material production technology, specifically to a method for preparing composite phase change materials that solves the problem of supercooling of sodium acetate trihydrate. Background Technology

[0002] Sodium acetate trihydrate (SAT) has been extensively studied as a promising phase change material (PCM) for thermal energy storage applications, particularly in the mid-to-low temperature range of 40–70 °C, which is highly relevant to applications such as building heating, solar thermal systems, and electronic cooling. This hydrated salt possesses numerous significant advantages and has been a focus of PCM research for the past two decades. Its phase change temperature of approximately 58 °C aligns well with many practical applications, while its high latent heat capacity of 250–264 J / g enables efficient energy storage in compact systems. Compared to organic PCMs, SAT exhibits relatively high thermal conductivity, which helps accelerate heat transfer during charge-discharge cycles. The material is non-toxic, low-cost, and readily available, further enhancing its commercial viability.

[0003] However, despite these advantageous properties, pure SAT suffers from severe supercooling, typically between 15 and 25 °C, which is a major obstacle to its practical application. This supercooling, where the material remains liquid well below its crystallization temperature, leads to unpredictable energy release times and reduces system efficiency. Researchers have explored various improvement strategies to address this issue, including adding nucleating agents such as disodium hydrogen phosphate dodecahydrate, sodium tetraborate decahydrate, and carbon-based materials. Thickeners such as carboxymethyl cellulose and sodium polyacrylate have been used to prevent phase separation, while porous matrices including expanded graphite, metal foams, and carbon aerogels have been investigated for shape stabilization. However, neither the supercooling nor the high cost has been simultaneously resolved. Therefore, a comprehensive approach is needed that considers not only material composition but also microstructure and encapsulation technology. Summary of the Invention

[0004] To address the aforementioned technical problems, a method for preparing composite phase change materials that solves the problem of supercooling of sodium acetate trihydrate is provided. This technical solution resolves the aforementioned issues.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a composite phase change material that solves the problem of supercooling of sodium acetate trihydrate includes the following steps:

[0007] S1. Weigh 30 g of natural hydrated magnesium chloride, dry it at 120 ℃ for 12 h, and then dissolve it in 90 g of anhydrous ethanol to form a magnesium chloride solution.

[0008] S2. Filter the magnesium chloride solution using a vacuum filtration flask to separate the insoluble matter. Then, evaporate the ethanol component in the filtered solution using a rotary evaporator to obtain the precipitate magnesium chloride hexahydrate MgCl2·6H2O.

[0009] S3. Combine magnesium chloride hexahydrate MgCl2·6H2O with sodium acetate trihydrate SAT at an optimized mass ratio of 3:17;

[0010] S4. After complete melting and uniformity, add 1% sodium polyacrylate (PAAS) as a thickener and encapsulate it in expanded graphite (EG).

[0011] Preferably, step S3 specifically includes:

[0012] Weigh out SAT and MgCl2·6H2O phase change energy storage materials according to the ratio, put them into beakers and label them. Weigh out SAT and MgCl2·6H2O in the corresponding mass ratio of 85%:15%, place them in the beakers, heat them evenly, and add a 3.5 cm magnetic stirrer to stir them until they are fully melted.

[0013] Preferably, step S4 specifically includes:

[0014] S401. Place expandable graphite in a drying oven and dry it continuously at 103±2 ℃ for 12 h;

[0015] S402. Weigh 0.2-0.5 g of dried expandable graphite each time and place it in a 50 mL high-temperature ceramic crucible;

[0016] S403, the muffle furnace is preheated to 800 ℃. After the temperature stabilizes, the high-temperature ceramic crucible containing expandable graphite is heat-treated for 60 s and then taken out to prepare loose and porous EG.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The eutectic mixture significantly reduces supercooling to only 1.1 °C, which is almost negligible; PAAS effectively prevents phase separation during thermal cycling; EG encapsulation provides excellent shape stability and prevents leakage. The resulting composite material exhibits stable thermal properties in repeated experiments, with high latent heat retention, and operates reliably within the designed temperature range.

[0019] 2. This study enables the effective utilization of magnesium chloride, a byproduct of salt lakes. It not only provides a practical solution for utilizing magnesium chloride from salt lakes, but also offers a general method for developing low-subcooling eutectic hydrated salts (PCMs) suitable for various thermal energy storage applications.

[0020] 3. The preparation method is simple and inexpensive, and it is a novel and effective method for preparing composite phase change materials. Attached Figure Description

[0021] Figure 1 The supercooling curves of three repeated experiments of SAT and MgCl2·6H2O at a ratio of 85%:15% after adding 1% PAAS thickener;

[0022] Figure 2 The enthalpy curve of SAT and MgCl2·6H2O at a ratio of 85%:15% after adding 1% PAAS thickener and 2.5% EG. Detailed Implementation

[0023] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0024] Reference Figure 1 As shown, a method for preparing a composite phase change material that solves the problem of supercooling of sodium acetate trihydrate includes the following steps:

[0025] S1. Weigh 30 g of natural hydrated magnesium chloride, dry it at 120 ℃ for 12 h, and then dissolve it in 90 g of anhydrous ethanol to form a magnesium chloride solution.

[0026] S2. Filter the magnesium chloride solution using a vacuum filtration flask to separate the insoluble matter. Then, evaporate the ethanol component in the filtered solution using a rotary evaporator to obtain the precipitate magnesium chloride hexahydrate MgCl2·6H2O.

[0027] S3. Combine magnesium chloride hexahydrate MgCl2·6H2O with sodium acetate trihydrate SAT at an optimized mass ratio of 3:17;

[0028] S4. After complete melting and uniformity, add 1% sodium polyacrylate (PAAS) as a thickener and encapsulate it in expanded graphite (EG).

[0029] Step S3 specifically includes:

[0030] Weigh out SAT and MgCl2·6H2O phase change energy storage materials according to the ratio, put them into beakers and label them. Weigh out SAT and MgCl2·6H2O in the corresponding mass ratio of 85%:15%, place them in the beakers, heat them evenly, and add a 3.5 cm magnetic stirrer to stir them until they are fully melted.

[0031] Step S4 specifically includes:

[0032] S401. Place expandable graphite in a drying oven and dry it continuously at 103±2 ℃ for 12 h;

[0033] S402. Weigh 0.2-0.5 g of dried expandable graphite each time and place it in a 50 mL high-temperature ceramic crucible;

[0034] S403, the muffle furnace is preheated to 800 ℃. After the temperature stabilizes, the high-temperature ceramic crucible containing expandable graphite is heat-treated for 60 s and then taken out to prepare loose and porous EG.

[0035] After complete fusion, the sample was collected in a test tube, connected to a temperature recorder, and placed in a water bath for cooling. The cooling curve was then measured. After the sample solidified, it was sent for DSC testing. The temperature range was set to 20–70 °C, the heating rate was 5 °C / min, and the protective gas was nitrogen.

[0036] Step cooling results as follows Figure 1 As shown, the supercooling degrees in the three experimental groups were 0.7 ℃, 1.8 ℃, and 0.9 ℃, respectively, with an average supercooling degree of 1.1 ℃. DSC results show that at this ratio, the composite phase change material still has a high enthalpy value, reaching 187.94 J / g.

[0037] The process of using this invention is as follows: purified magnesium chloride (MgCl2·6H2O) is combined with SAT at an optimized mass ratio of 3:17, 1% PAAS is added as a thickener and then encapsulated in EG to complete the preparation of the material and reduce the supercooling of SAT.

[0038] In summary, the advantages of this invention are: first, the eutectic mixture significantly reduces the supercooling to only 1.1 °C, which is almost negligible; second, PAAS effectively prevents phase separation during thermal cycling; and third, EG encapsulation provides excellent shape stability and prevents leakage. The resulting composite material exhibits stable thermal properties in repeated experiments, with high latent heat retention, and operates reliably within the designed temperature range. This research not only provides a practical solution for utilizing magnesium chloride from salt lakes but also offers a general method for developing low-supercooling eutectic hydrated salt PCMs suitable for various thermal energy storage applications.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for preparing a composite phase change material that solves the problem of supercooling of sodium acetate trihydrate, characterized in that, Includes the following steps: S1. Weigh 30 g of natural hydrated magnesium chloride, dry it at 120 ℃ for 12 h, and then dissolve it in 90 g of anhydrous ethanol to form a magnesium chloride solution. S2. Filter the magnesium chloride solution using a vacuum filtration flask to separate the insoluble matter. Then, evaporate the ethanol component in the filtered solution using a rotary evaporator to obtain the precipitate magnesium chloride hexahydrate MgCl2·6H2O. S3. Magnesium chloride hexahydrate MgCl2·6H2O and sodium acetate trihydrate SAT are combined at an optimized mass ratio of 3:

17. S4. After complete melting and uniformity, add 1% sodium polyacrylate (PAAS) as a thickener and encapsulate it in expanded graphite (EG).

2. The method for preparing a composite phase change material to solve the problem of supercooling of sodium acetate trihydrate according to claim 1, characterized in that, Step S3 specifically includes: Weigh out SAT and MgCl2·6H2O phase change energy storage materials according to the ratio, put them into beakers and label them. Weigh out SAT and MgCl2·6H2O in the corresponding mass ratio of 85%:15%, place them in the beakers, heat them evenly, and add a 3.5 cm magnetic stirrer to stir them until they are fully melted.

3. The method for preparing a composite phase change material to solve the problem of supercooling of sodium acetate trihydrate according to claim 1, characterized in that, Step S4 specifically includes: S401. Place expandable graphite in a drying oven and dry it continuously at 103±2 ℃ for 12 h; S402. Weigh 0.2-0.5 g of dried expandable graphite each time and place it in a 50 mL high-temperature ceramic crucible; S403, the muffle furnace is preheated to 800 ℃. After the temperature stabilizes, the high-temperature ceramic crucible containing expandable graphite is heat-treated for 60 s and then taken out to prepare loose and porous EG.

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