Fused salt heat storage material based on lithium nitrate and sodium stearate modified graphene and preparation method thereof

Abstract

The invention discloses a fused salt heat storage material based on lithium nitrate and sodium stearate modified graphene. The fused salt heat storage material comprises the following components in parts by mass: 20-35 parts of sodium nitrate, 25-40 parts of potassium nitrate, 10-20 parts of lithium nitrate, 10-25 parts of halogenated metal salt, 0.5-2 parts of sodium stearate modified graphene and 0.5-1 part of an antioxidant, the sodium stearate modified graphene is prepared by the following steps: dispersing graphene in absolute ethyl alcohol, adding sodium stearate, and performing ultrasonic treatment to obtain the sodium stearate modified graphene. The fused salt heat storage material is low in melting point, high in heat stability, phase change latent heat, specific heat capacity and heat conductivity and low in viscosity.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of molten salt heat storage materials, in particular to a molten salt heat storage material based on lithium nitrate and sodium stearate modified graphene and a preparation method thereof. BACKGROUND

[0002] The molten salt heat storage material refers to a functional fluid composed of inorganic salts or eutectic mixtures thereof, which realizes high-density heat energy reversible storage through a solid-liquid phase change and a sensible heat cooperative mechanism. The material has key strategic value in the fields of concentrated solar thermal power generation, valley electricity peak regulation, and high-temperature industrial waste heat recovery. The existing commercial system generally adopts an alkali / alkaline earth metal nitrate or carbonate eutectic formula, which has the advantages of low cost, low vapor pressure and high thermal decomposition threshold. However, the system has the problem of high melting point, which becomes a core bottleneck restricting its development.

[0003] The specific heat capacity of the current commercial molten salt heat storage material is not high, and even after multi-component compounding, the specific heat capacity is only 1.8 J / (g•℃), which still cannot meet the requirement of solar thermal power generation on the specific heat capacity of heat transfer fluid (greater than 2.25 J / (g•℃)). The existing technology compensates for the above problems by increasing the amount of alkali / alkaline earth metal salt or multi-component compounding, but has the disadvantages of high viscosity, low flowability and increased pumping energy consumption. SUMMARY

[0004] The application aims to solve the technical defects of low specific heat capacity, large heat storage system volume and low energy efficiency of the molten salt heat storage material in the prior art, and provides a molten salt heat storage material based on lithium nitrate and sodium stearate modified graphene and a preparation method thereof.

[0005] The technical scheme adopted to achieve the purpose of the application is as follows: A molten salt heat storage material based on lithium nitrate and sodium stearate modified graphene comprises the following components in mass fraction: 20-35 parts of sodium nitrate, 25-40 parts of potassium nitrate, 10-20 parts of lithium nitrate, 10-25 parts of halogenated metal salt, 0.5-2 parts of sodium stearate modified graphene, and 0.5-1 part of antioxidant. The sodium stearate modified graphene is prepared by the following steps: dispersing graphene in anhydrous ethanol, adding sodium stearate and ultrasonicating to obtain sodium stearate modified graphene.

[0006] This invention lowers the melting point and increases the specific heat capacity of molten salt thermal storage materials through the synergistic effect of nitrates, metal halide salts, and sodium stearate-modified graphene. Specifically, lithium nitrate disrupts the crystal structure due to its ionic properties, while the metal halide salt further modulates the eutectic system. Together, these factors significantly reduce the melting point of the molten salt, effectively solving the problem of traditional molten salts easily solidifying and clogging pipes at low temperatures, thus greatly reducing the need for insulation and heat tracing. Simultaneously, the high molar heat capacity of lithium nitrate effectively improves the thermal storage performance of the molten salt thermal storage material. Sodium stearate-modified graphene, by constructing a thermally conductive network and enhancing the freedom of ion vibration, synergistically improves the thermal storage and heat transfer capabilities of the molten salt, further enhancing the material's thermal storage efficiency in medium- and high-temperature scenarios.

[0007] In addition, the molten salt thermal storage material provided by the present invention inhibits the thermal decomposition of a single salt through halide metal salts and nitrates. At the same time, sodium stearate modified graphene can be uniformly dispersed in the molten salt thermal storage material to form a thermally conductive network, which improves the thermal conductivity and slows down the oxidation rate of the molten salt thermal storage material.

[0008] In the above technical solution, the ratio of graphene to anhydrous ethanol is 1g:(500~1000)mL, and the mass ratio of graphene to sodium stearate is 1:(1~3).

[0009] In the above technical solution, the power of the ultrasound is 50~100W, the frequency is 20~40kHz, and the duration is 30~60min; the ultrasound is performed in an ice water bath.

[0010] In the above technical solution, the halide metal salt is sodium chloride or potassium chloride.

[0011] In the above technical solution, the antioxidant is ferric oxide or magnesium oxide.

[0012] Another aspect of the present invention includes a method for preparing the molten salt thermal storage material, comprising the following steps: Step S1: Sodium nitrate, potassium nitrate, lithium nitrate and halide metal salt are mixed and dissolved in deionized water to form an inorganic molten salt solution; Step S2: The inorganic molten salt solution, antioxidant and sodium stearate modified graphene are mixed and dried to obtain a mixed powder; Step S3: Heat the mixed powder until it melts, and after cooling, obtain molten salt thermal storage material.

[0013] The preparation method provided by this invention achieves uniform molecular-level dispersion of each component through solution mixing, avoiding graphene agglomeration and ensuring that the prepared molten salt thermal storage material has a dense structure and uniform performance. Furthermore, the preparation method provided by this invention has good repeatability and is suitable for large-scale production.

[0014] In the above technical solution, in step S1, sodium nitrate, potassium nitrate, lithium nitrate and halide metal salt are mixed and then dissolved in deionized water under stirring conditions. The stirring temperature is 60~80℃, the stirring time is 1~2h, and the stirring speed is 100~200r / min.

[0015] In the above technical solution, in step S2, the drying is vacuum drying, and the temperature of the vacuum drying is 80~100℃, and the time is 12~24h.

[0016] In the above technical solution, in step S3, the melting is carried out in an inert atmosphere, which is a nitrogen atmosphere or an argon atmosphere; the heating rate to melt is 5~10℃ / min.

[0017] In the above technical solution, after heating to the point of melting in step S3, the process further includes heat preservation, the heat preservation time being 0.5~1h, and the cooling rate being 1~5℃ / min.

[0018] Compared with the prior art, the beneficial effects of the present invention are: The molten salt thermal storage material provided by this invention utilizes lithium nitrate, which, due to its small ionic radius, can effectively disrupt the ordered lattice arrangement and lower the melting point of the molten salt when forming a molten salt thermal storage material system with other components. The halide metal salt, through synergistic regulation of the eutectic point, enables the molten salt thermal storage material system to maintain liquid fluidity at low temperatures. Sodium stearate-modified graphene is dispersed at the nanoscale through ultrasonic treatment. The thermally conductive network it constructs not only improves the heat transfer efficiency but also enhances the interaction with molten salt ions through surface polar groups, significantly increasing the specific heat capacity of the system. The antioxidant forms a stable protective layer in a high-temperature environment, inhibiting the decomposition and oxidation of the molten salt and extending the service life of the material. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] Example 1 This embodiment provides a molten salt thermal storage material: The molten salt thermal storage material comprises the following components in parts by weight: 20 parts sodium nitrate, 25 parts potassium nitrate, 10 parts lithium nitrate, 10 parts potassium chloride, 0.5 parts sodium stearate-modified graphene, and 0.5 parts ferric oxide.

[0021] The preparation method of the sodium stearate modified graphene includes the following steps: 1g of graphene was dispersed in 500mL of anhydrous ethanol, and 1g of sodium stearate was added. The mixture was then sonicated in an ice-water bath to obtain sodium stearate-modified graphene. The sonication power was 50W, the frequency was 20kHz, and the duration was 30min.

[0022] The preparation method of the molten salt thermal storage material includes the following steps: S1. Sodium nitrate, potassium nitrate, lithium nitrate and potassium chloride are mixed and stirred at 100 r / min and 60℃ for 1 h to dissolve in deionized water to form an inorganic molten salt solution. S2. The inorganic molten salt solution, ferric oxide and sodium stearate modified graphene are mixed and then vacuum dried at 80°C for 12 hours to obtain a mixed powder. S3. The mixed powder is heated to 150°C at a heating rate of 5°C / min, held at that temperature for 0.5h, and then cooled to room temperature at a cooling rate of 1°C / min to obtain molten salt thermal storage material.

[0023] Example 2 This embodiment provides a molten salt thermal storage material: The molten salt thermal storage material comprises the following components in parts by weight: 35 parts sodium nitrate, 40 parts potassium nitrate, 20 parts lithium nitrate, 25 parts sodium chloride, 2 parts sodium stearate-modified graphene, and 1 part magnesium oxide.

[0024] The preparation method of the sodium stearate modified graphene includes the following steps: 1g of graphene was dispersed in 1000mL of anhydrous ethanol, and 3g of sodium stearate was added. The mixture was then sonicated in an ice-water bath to obtain sodium stearate-modified graphene. The sonication power was 100W, the frequency was 40kHz, and the duration was 60min.

[0025] The preparation method of the molten salt thermal storage material includes the following steps: S1. Sodium nitrate, potassium nitrate, lithium nitrate and sodium chloride are mixed and stirred at 200 r / min and 80℃ for 2 h to dissolve in deionized water to form an inorganic molten salt solution. S2. The inorganic molten salt solution, magnesium oxide and sodium stearate modified graphene are mixed and then vacuum dried at 100°C for 24 hours to obtain a mixed powder. S3. The mixed powder is heated to 200°C at a heating rate of 10°C / min, held at that temperature for 1 hour, and then cooled to room temperature at a cooling rate of 5°C / min to obtain molten salt thermal storage material.

[0026] Example 3 This embodiment provides a molten salt thermal storage material: The molten salt thermal storage material comprises the following components in parts by mass: 27 parts sodium nitrate, 32 parts potassium nitrate, 15 parts lithium nitrate, 18 parts potassium chloride, 1 part sodium stearate-modified graphene, and 0.7 parts ferric oxide.

[0027] The preparation method of the sodium stearate modified graphene includes the following steps: 1g of graphene was dispersed in 750mL of anhydrous ethanol, and 2g of sodium stearate was added. The mixture was then sonicated in an ice-water bath to obtain sodium stearate-modified graphene. The sonication power was 75W, the frequency was 30kHz, and the duration was 45min.

[0028] The preparation method of the molten salt thermal storage material includes the following steps: S1. Sodium nitrate, potassium nitrate, lithium nitrate and potassium chloride are mixed and stirred at 150 r / min and 70℃ for 1.5 h to dissolve in deionized water to form an inorganic molten salt solution. S2. The inorganic molten salt solution, ferric oxide and sodium stearate modified graphene are mixed and then vacuum dried at 90°C for 18 hours to obtain a mixed powder. S3. The mixed powder is heated to 175°C at a heating rate of 7°C / min, held at that temperature for 0.75h, and then cooled to room temperature at a cooling rate of 3°C to obtain molten salt thermal storage material.

[0029] Comparative Example 1 This comparative example provides a molten salt thermal storage material: The molten salt thermal storage material comprises the following components in parts by weight: 27 parts sodium nitrate, 32 parts potassium nitrate, and 15 parts lithium nitrate.

[0030] The preparation method of the molten salt thermal storage material includes the following steps: S1. Sodium nitrate, potassium nitrate and lithium nitrate are mixed and stirred at 150 r / min and 70℃ for 1.5 h to dissolve in deionized water to form an inorganic molten salt solution. S2. The inorganic molten salt solution is vacuum dried at 90°C for 18 hours, then heated to 175°C at a heating rate of 7°C / min, held at that temperature for 0.75 hours, and then cooled to room temperature at a cooling rate of 3°C to obtain the molten salt thermal storage material.

[0031] Comparative Example 2 This comparative example provides a molten salt thermal storage material: The molten salt thermal storage material comprises the following components in parts by mass: 27 parts sodium nitrate, 32 parts potassium nitrate, 15 parts lithium nitrate, 18 parts potassium chloride, and 0.7 parts ferric oxide.

[0032] The preparation method of the molten salt thermal storage material includes the following steps: S1. Sodium nitrate, potassium nitrate, lithium nitrate and potassium chloride are mixed and stirred at 150 r / min and 70℃ for 1.5 h to dissolve in deionized water to form an inorganic molten salt solution. S2. The inorganic molten salt solution and ferric oxide are mixed and then vacuum dried at 90°C for 18 hours to obtain a mixed powder. S3. The mixed powder is heated to 175°C at a heating rate of 7°C / min, held at that temperature for 0.75h, and then cooled to room temperature at a cooling rate of 3°C to obtain molten salt thermal storage material.

[0033] The performance of the molten salt thermal storage materials in Examples 1-3 and Comparative Examples 1-2 of this invention was tested. The test parameters included melting point, decomposition point, latent heat of phase change, specific heat capacity, thermal conductivity, and viscosity. The test results are shown in Table 1. The melting point, decomposition point, and latent heat of phase change were determined by differential scanning calorimetry and thermogravimetric analysis. The specific heat capacity was measured using a simultaneous thermal analyzer, the thermal conductivity was measured using a thermal conductivity meter, and the viscosity was measured using a rheometer.

[0034] Table 1 Performance test results of molten salt thermal storage materials As can be seen from Table 1, the melting point of the molten salt thermal storage material provided in Examples 1-3 of the present invention is significantly lower than that of the comparative example, and the thermal stability, latent heat of phase change, specific heat capacity and thermal conductivity are significantly improved. The viscosity is also optimized, which meets the requirements of solar thermal power generation for the specific heat capacity of heat transfer fluid.

[0035] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene, characterized in that, It includes the following components in parts by weight: 20-35 parts sodium nitrate, 25-40 parts potassium nitrate, 10-20 parts lithium nitrate, 10-25 parts metal halide salt, 0.5-2 parts sodium stearate-modified graphene, and 0.5-1 part antioxidant. The sodium stearate modified graphene is prepared by the following steps: dispersing graphene in anhydrous ethanol, adding sodium stearate, and then sonicating to obtain sodium stearate modified graphene.

2. The molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 1, characterized in that, The ratio of graphene to anhydrous ethanol is 1 g: (500~1000) mL, and the mass ratio of graphene to sodium stearate is 1: (1~3).

3. The molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 1, characterized in that, The ultrasound has a power of 50~100W, a frequency of 20~40kHz, and a duration of 30~60min; the ultrasound is performed in an ice-water bath.

4. The molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 1, characterized in that, The halide metal salt is sodium chloride or potassium chloride.

5. The molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 1, characterized in that, The antioxidant is ferric oxide or magnesium oxide.

6. The preparation method of the molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 1, characterized in that, Includes the following steps: Step S1: Sodium nitrate, potassium nitrate, lithium nitrate and halide metal salt are mixed and dissolved in deionized water to form an inorganic molten salt solution; Step S2: The inorganic molten salt solution, antioxidant and sodium stearate modified graphene are mixed and dried to obtain a mixed powder; Step S3: Heat the mixed powder until it melts, and after cooling, obtain molten salt thermal storage material.

7. The preparation method of the molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 6, characterized in that, In step S1, sodium nitrate, potassium nitrate, lithium nitrate and halide metal salt are mixed and then dissolved in deionized water under stirring conditions. The stirring temperature is 60~80℃, the stirring time is 1~2h, and the stirring speed is 100~200r / min.

8. The method for preparing molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 6, characterized in that, In step S2, the drying is vacuum drying, and the temperature of the vacuum drying is 80~100℃, and the time is 12~24h.

9. The preparation method of the molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 6, characterized in that, In step S3, the melting is carried out in an inert atmosphere, which is either a nitrogen atmosphere or an argon atmosphere; the heating rate to melt is 5~10℃ / min.

10. The method for preparing molten salt thermal storage material based on lithium nitrate and sodium stearate modified graphene as described in claim 6, characterized in that, In step S3, after heating to the point of melting, the process further includes heat preservation for 0.5 to 1 hour and cooling at a rate of 1 to 5 °C / min.

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