A preparation method of high-purity heat-conducting energy-storage molten salt

Abstract

The present invention relates to the technical field of latent heat energy storage, and discloses a preparation method of a high-purity heat-conducting energy-storage molten salt. The preparation method of the high-purity heat-conducting energy-storage molten salt includes the following steps: Step (1) purifying a sodium chloride sample, a potassium chloride sample, and a sodium fluoride sample; Step (2) mixing the high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride prepared in Step (1), and melting them to obtain a composite molten salt; Step (3) mixing ethanol and an ammonia water solution, adding the load-modified composite molten salt, and then adding tetraethoxysilane to react to obtain a microencapsulated composite molten salt; Step (4) dispersing multi-walled carbon nanotubes, aluminum chloride, and an aqueous hydrochloric acid solution in ethanol, and reacting to obtain hydroxylated single-walled carbon nanotubes; Step (5) reacting erythritol, hydroxylated multi-walled carbon nanotubes, and the microencapsulated composite molten salt to obtain the high-purity heat-conducting energy-storage molten salt. The high-purity heat-conducting energy-storage molten salt obtained in the present invention has excellent heat-conducting performance and energy-storage performance.

Description

Technical Field

[0001] The present invention relates to the technical field of latent heat energy storage, and particularly to a preparation method of a high-purity heat-conducting energy-storage molten salt. Background Art

[0002] Vigorously developing and using new energy and improving energy utilization efficiency have become one of the important measures to solve the energy crisis problem in today's society. However, in the process of developing and utilizing new energy, there is a contradiction of spatio-temporal mismatch between energy supply and demand. In many fields such as industry and people's livelihood, there are problems of low efficiency in the process of energy conversion and utilization. To ensure the balance between energy input and output ends and improve energy utilization efficiency, the research and development of energy storage materials and energy storage technologies have increasingly become an important topic in the scientific and industrial circles.

[0003] As one of the energy storage materials widely used at present, molten salt has many advantages such as large heat storage density, heat storage and release temperature, and a wide range of use. The thermal properties such as specific heat capacity, latent heat of fusion, and thermal conductivity of molten salt will have a great impact on the performance and application range of molten salt. The latent heat of fusion of different molten salt materials is different, and most molten salts face the problem of low thermal conductivity. Therefore, it is necessary to provide a molten salt with good thermal conductivity and heat storage performance at the same time. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a preparation method of a high-purity heat-conducting energy-storage molten salt, including the following steps:

[0005] Step (1) Purification of single-component salts: Purify sodium chloride samples, potassium chloride samples, and sodium fluoride samples to obtain high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride;

[0006] Step (2) Preparation of composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride, and ball mill to obtain a mixed powder; under an argon atmosphere, melt the mixed powder, keep it warm, cool it, and grind it to obtain a composite molten salt;

[0007] Step (3) Preparation of microencapsulated composite molten salt: Mix ethanol and 28wt% ammonia water solution to obtain a mixed solution, add the loaded and modified composite molten salt to the mixed solution, then add tetraethoxysilane, heat and stir to react, wash, and centrifuge to obtain a microencapsulated composite molten salt;

[0008] In the above reaction process, under an alkaline environment, tetraethoxysilane hydrolyzes and condenses to form a silicon shell wrapped on the surface of the composite molten salt, and a microencapsulated composite molten salt is obtained.

[0009] Step (4) Preparation of hydroxylated multi-walled carbon nanotubes: Disperse multi-walled carbon nanotubes, aluminum chloride, and 0.51 mol / L hydrochloric acid aqueous solution in 80 wt% ethanol, apply microwave, wash, filter, and dry to obtain hydroxylated single-walled carbon nanotubes;

[0010] In the above reaction process, the multi-walled carbon nanotubes were oxidized by an acidic solution, and hydroxyl groups were introduced into the multi-walled carbon nanotubes under the action of metal chloride and alcohol solvent to obtain hydroxylated single-walled carbon nanotubes.

[0011] Step (5) Preparation of high-purity thermally conductive energy storage molten salt: Add erythritol and hydroxylated multi-walled carbon nanotubes to deionized water, heat and stir, then add microencapsulated composite molten salt, continue stirring and reacting. After the reaction is completed, filter, wash, and dry to obtain high-purity thermally conductive energy storage molten salt.

[0012] In the above reaction process, the hydroxyl groups in erythritol and hydroxylated multi-walled carbon nanotubes cross-linked and reacted with the hydroxyl groups on the surface of the microcapsule structure of the microencapsulated composite molten salt to form a dense thermal conduction network on the microcapsule surface.

[0013] Preferably, in the step (1), the purification method of the single crystal salt:

[0014] S1: Dissolve the sodium chloride sample in pure water at 50 - 80 °C to obtain a sodium chloride solution; after cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate according to the volume ratio of tetrahydrofuran to the filtrate of 1 - 2:1, settle for 4 - 6 h, filter under vacuum, dissolve the filter residue in pure water, and filter through microfiltration and nanofiltration membranes in sequence to obtain a sodium chloride slurry; cool the sodium chloride slurry to -5 - 0 °C for crystallization, centrifugally dehydrate, and dry to obtain high-purity sodium chloride;

[0015] S2: Purify the potassium chloride sample and sodium fluoride sample in the same way as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

[0016] Preferably, in the step (2), the mass ratio between high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride is 0.44 - 0.52:0.32 - 0.40:0.12 - 0.20; ball milling time: 1 - 1.5 h, drying temperature: 90 - 110 °C.

[0017] Preferably, in the step (2), the melting conditions of the mixed powder: Heat the mixed powder at a heating rate of 1.5 - 2.5 °C / min to 520 - 600 °C under a pressure of 0.15 - 0.25 MPa until the salt is completely melted; heat preservation time: 4 - 5 h; cooling conditions: Cool to room temperature.

[0018] Preferably, in the step (3), the preparation method of the loaded and modified composite molten salt: Add 1-2 g of the composite molten salt to an ethanol solution of polyvinylpyrrolidone, stir at a rotation speed of 100-200 r / r / min at room temperature for 20-24 h, then centrifuge at a rotation speed of 3000-4000 r / min for 15-30 min, and wash the centrifuged product with ethanol; wherein, the ethanol solution of polyvinylpyrrolidone is obtained by mixing 1-2 g of polyvinylpyrrolidone and 40-80 mL of ethanol and stirring at a rotation speed of 100-200 r / min for 20-30 min.

[0019] Preferably, in the step (3), the dosage ratio among ethanol, 28 wt% aqueous ammonia solution, the loaded and modified composite molten salt, and tetraethoxysilane is 100-120 g∶4-5 g∶5.8-6.5 g∶9.3-12.5 mL; the heating and stirring reaction conditions are: reacting at a temperature of 25-35 °C and a stirring speed of 100-200 r / min for 1-1.5 h; the centrifugation conditions: centrifuging at a rotation speed of 3000-4000 r / min for 15-30 min.

[0020] Preferably, in the step (4), the dosage ratio among multi-walled carbon nanotubes, aluminum chloride, 0.51 mol / L hydrochloric acid aqueous solution, and 80 wt% ethanol is 0.1-0.7 g∶0.1-1.3 g∶1-2 mL∶20-30 mL; the microwave action time: 4-10 min; the washing conditions: repeatedly washing with deionized water until the pH of the system is neutral; the drying conditions: drying at 110-120 °C for 5-10 min.

[0021] Preferably, in the step (5), the dosage ratio among deionized water, erythritol, hydroxylated multi-walled carbon nanotubes, and microencapsulated composite molten salt is: 150-200 mL∶10-20 g∶0.5-5 g∶80-100 g.

[0022] Preferably, in the step (5), the heating temperature: 60-80 °C; the stirring conditions: stirring at a rotation speed of 100-200 r / min for 2-4 h; the continued stirring reaction time: 6-8 h; the washing liquid used for washing includes deionized water; the drying conditions: drying at 40-60 °C for 10-14 h.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. In the present invention, a molten salt system with a high melting enthalpy is formed by compounding sodium chloride, potassium chloride, and sodium fluoride. Before preparing the composite molten salt, the samples of sodium chloride, potassium chloride, and sodium fluoride are purified to reduce organic and inorganic impurities in the single salts, avoiding the influence of impurities in the samples of sodium chloride, potassium chloride, and sodium fluoride on the comprehensive performance of the composite molten salt, and also reducing the corrosion of production equipment during the reaction process and in the later use of the molten salt.

[0025] 2. In the present invention, through the microencapsulation treatment of the composite molten salt, a stable silicon shell structure is formed on the surface of the composite molten salt, which can improve the energy storage capacity and thermal conductivity of the molten salt; further, multi-walled carbon nanotubes with excellent thermal conductivity and thermal stability are hydroxylated, and the hydroxyl groups in the hydroxylated multi-walled carbon nanotubes react with the hydroxyl groups on the surface of the microcapsule structure of the microencapsulated composite molten salt and the hydroxyl groups in erythritol to form a dense thermal conduction network on the microcapsule surface, enhancing the thermal conductivity of the molten salt.

[0026] 3. In the present invention, while erythritol participates in the formation of the thermal conduction network on the microcapsule surface, it is also an organic phase change material, which combines with the inorganic phase change material molten salt, and the two cooperate to further enhance the energy storage capacity of the sodium chloride, potassium chloride, and sodium fluoride composite molten salt system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the process flow chart for the preparation of the high-purity thermal conduction and energy storage molten salt of the present invention;

[0028] Figure 2 is the purity test comparison chart of high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride in Examples 1-4 of the present invention;

[0029] Figure 3 is the thermal conductivity test comparison chart of the high-purity thermal conduction and energy storage molten salt in Examples 1-4 and Comparative Examples 1-4 of the present invention;

[0030] Figure 4 is the melting enthalpy test comparison chart of the high-purity thermal conduction and energy storage molten salt in Examples 1-4 and Comparative Examples 1-4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] Example 1

[0033] This embodiment discloses a preparation method of high-purity thermally conductive energy storage molten salt, which includes the following steps:

[0034] Step (1) Purification of single-component salts:

[0035] S1: Dissolve the sodium chloride sample in pure water at 50 °C to obtain a sodium chloride solution; after cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate according to the volume ratio of tetrahydrofuran to the filtrate of 1:1, sediment for 4 - 6 h, filter under vacuum, dissolve the filter residue in pure water, and filter successively through microfiltration and nanofiltration membrane to obtain a sodium chloride slurry; cool the sodium chloride slurry to -5 °C for crystallization, centrifugally dehydrate, and dry to obtain high-purity sodium chloride.

[0036] S2: Purify the potassium chloride sample and sodium fluoride sample in the same method as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

[0037] Step (2) Preparation of composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride according to the ratio of 0.44:0.32:0.12, ball mill for 1 h, dry at 90 °C to obtain a mixed powder; under an argon atmosphere, heat the mixed powder to 520 °C at a heating rate of 1.5 °C / min under a pressure of 0.15 MPa until the salt is completely melted, keep it warm for 4 h, cool to room temperature, and grind to obtain the composite molten salt.

[0038] Step (3) Preparation of microencapsulated composite molten salt: Mix 1 g of polyvinylpyrrolidone and 40 mL of ethanol, stir at a rotation speed of 100 r / min for 20 min to obtain an ethanol solution of polyvinylpyrrolidone; add 1 g of composite molten salt to the ethanol solution of polyvinylpyrrolidone, stir at a rotation speed of 100 r / min at room temperature for 20 h, then centrifuge at a rotation speed of 3000 r / min for 15 min, wash the centrifuged product with ethanol to obtain a loaded and modified composite molten salt; mix 100 g of ethanol and 4 g of 28 wt% ammonia water solution to obtain a mixed solution, add 5.8 g of the loaded and modified composite molten salt to the mixed solution, then add 9.3 mL of tetraethoxysilane, react at a temperature of 25 °C and a stirring speed of 100 r / min for 1 h, wash, and centrifuge at a rotation speed of 3000 r / min for 15 min to obtain the microencapsulated composite molten salt.

[0039] Step (4) Preparation of hydroxylated multi-walled carbon nanotubes: Disperse 0.5 g of multi-walled carbon nanotubes, 0.1 g of aluminum chloride, and 1 mL of 0.51 mol / L hydrochloric acid aqueous solution in 20 mL of 80 wt% ethanol, apply microwave for 4 min, wash repeatedly with deionized water until the pH of the system is neutral, filter, and dry at 110 °C for 5 min to obtain hydroxylated single-walled carbon nanotubes.

[0040] Step (5) Preparation of high-purity thermal conductive energy storage molten salt: Add 10 g of erythritol and 0.1 g of hydroxylated multi-walled carbon nanotubes to 150 mL of deionized water, heat to 60 °C, stir at a speed of 100 r / min for 2 h, then add 80 g of microencapsulated composite molten salt, and continue to stir and react for 6 h. After the reaction is completed, filter, wash the filter residue with deionized water, and dry at 40 °C for 10 h to obtain high-purity thermal conductive energy storage molten salt.

[0041] Example 2

[0042] This example discloses a preparation method of high-purity thermal conductive energy storage molten salt, including the following steps:

[0043] Step (1) Purification of single crystal salts:

[0044] S1: Dissolve the sodium chloride sample in pure water at 80 °C to obtain a sodium chloride solution; after cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate according to the volume ratio of tetrahydrofuran to the filtrate of 2:1, sediment for 6 h, filter under vacuum, dissolve the filter residue in pure water, and filter successively through microfiltration and nanofiltration membrane to obtain a sodium chloride slurry; cool the sodium chloride slurry to 0 °C for crystallization, centrifugally dehydrate, and dry to obtain high-purity sodium chloride.

[0045] S2: Purify the potassium chloride sample and sodium fluoride sample in the same way as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

[0046] Step (2) Preparation of composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride according to the ratio of 0.52:0.40:0.20, ball mill for 1.5 h, dry at 110 °C to obtain a mixed powder; in an argon atmosphere, heat the mixed powder to 600 °C at a heating rate of 2.5 °C / min under a pressure of 0.25 MPa until the salt is completely melted, keep warm for 5 h, cool to room temperature, and grind to obtain a composite molten salt.

[0047] Step (3) Preparation of microencapsulated composite molten salt: Mix 2 g of polyvinylpyrrolidone and 80 mL of ethanol, stir at a rotation speed of 200 r / min for 30 min to obtain an ethanol solution of polyvinylpyrrolidone; add 2 g of composite molten salt to the ethanol solution of polyvinylpyrrolidone, stir at a rotation speed of 200 r / min at room temperature for 24 h, then centrifuge at a rotation speed of 4000 r / min for 30 min, and wash the centrifuged product with ethanol to obtain a loaded and modified composite molten salt; Mix 120 g of ethanol and 5 g of 28 wt% ammonia water solution to obtain a mixed solution, add 6.5 g of the loaded and modified composite molten salt to the mixed solution, then add 12.5 mL of tetraethoxysilane, react at a temperature of 35 °C and a stirring speed of 200 r / min for 1.5 h, wash, and centrifuge at a rotation speed of 4000 r / min for 30 min to obtain microencapsulated composite molten salt.

[0048] Step (4) Preparation of hydroxylated multi-walled carbon nanotubes: Disperse 5.0 g of multi-walled carbon nanotubes, 1.3 g of aluminum chloride, and 2 mL of 0.51 mol / L hydrochloric acid aqueous solution in 30 mL of 80 wt% ethanol, apply microwave for 10 min, wash repeatedly with deionized water until the pH of the system is neutral, filter, and dry at 120 °C for 10 min to obtain hydroxylated single-walled carbon nanotubes.

[0049] Step (5) Preparation of high-purity thermally conductive energy storage molten salt: Add 20 g of erythritol and 1 g of hydroxylated multi-walled carbon nanotubes to 200 mL of deionized water, heat to 80 °C, stir at a rotation speed of 200 r / min for 4 h, then add 100 g of microencapsulated composite molten salt, continue to stir and react for 8 h. After the reaction, filter, wash the filter residue with deionized water, and dry at 60 °C for 14 h to obtain high-purity thermally conductive energy storage molten salt.

[0050] Example 3

[0051] This example discloses a preparation method of high-purity thermally conductive energy storage molten salt, including the following steps:

[0052] Step (1) Purification of single crystal salt:

[0053] S1: Dissolve the sodium chloride sample in pure water at 60 °C to obtain a sodium chloride solution; after cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate according to the volume ratio of tetrahydrofuran to the filtrate of 1.3:1, settle for 4.5 h, filter under vacuum, dissolve the filter residue in pure water, and filter successively through microfiltration and nanofiltration membrane to obtain a sodium chloride slurry; cool the sodium chloride slurry to -3 °C for crystallization, centrifuge for dehydration, and dry to obtain high-purity sodium chloride.

[0054] S2: Purify potassium chloride samples and sodium fluoride samples in the same way as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

[0055] Step (2) Prepare the composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride in a ratio of 0.47∶0.35∶0.15, ball mill for 1.2 h, dry at 95 °C to obtain a mixed powder; under an argon atmosphere, heat the mixed powder to 550 °C at a heating rate of 1.8 °C / min under a pressure of 0.18 MPa until the salt is completely melted, keep warm for 4.3 h, cool to room temperature, and grind to obtain the composite molten salt.

[0056] Step (3) Prepare the microencapsulated composite molten salt: Mix 1.3 g of polyvinylpyrrolidone and 60 mL of ethanol, stir at a speed of 150 r / min for 25 min to obtain an ethanol solution of polyvinylpyrrolidone; add 1.3 g of the composite molten salt to the ethanol solution of polyvinylpyrrolidone, stir at a speed of 150 r / min at room temperature for 22 h, then centrifuge at a speed of 3500 r / min for 20 min, and wash the centrifuged product with ethanol to obtain the loaded and modified composite molten salt; mix 105 g of ethanol and 4.3 g of 28 wt% ammonia water solution to obtain a mixed solution, add 6.0 g of the loaded and modified composite molten salt to the mixed solution, then add 10.2 mL of tetraethoxysilane, react at a temperature of 28 °C and a stirring speed of 150 r / min for 1.2 h, wash, and centrifuge at a speed of 3400 r / min for 20 min to obtain the microencapsulated composite molten salt.

[0057] Step (4) Prepare hydroxylated multi-walled carbon nanotubes: Disperse 2.0 g of multi-walled carbon nanotubes, 0.5 g of aluminum chloride, and 1.3 mL of 0.51 mol / L hydrochloric acid aqueous solution in 25 mL of 80 wt% ethanol, apply microwave for 6 min, wash repeatedly with deionized water until the pH of the system is neutral, filter, and dry at 115 °C for 8 min to obtain hydroxylated single-walled carbon nanotubes.

[0058] Step (5) Prepare high-purity heat-conducting energy-storage molten salt: Add 3 g of erythritol and 0.4 g of hydroxylated multi-walled carbon nanotubes to 160 mL of deionized water, heat to 65 °C, stir at a speed of 150 r / min for 2.5 h, then add 86 g of the microencapsulated composite molten salt, continue to stir and react for 6.5 h. After the reaction, filter, wash the filter residue with deionized water, and dry at 45 °C for 12 h to obtain the high-purity heat-conducting energy-storage molten salt.

[0059] Example 4

[0060] This example discloses a preparation method of high-purity heat-conducting energy-storage molten salt, including the following steps:

[0061] Step (1) Purification of single-component salts:

[0062] S1: Dissolve the sodium chloride sample in pure water at 70 °C to obtain a sodium chloride solution; after cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate at a volume ratio of tetrahydrofuran to the filtrate of 1.6:1 and sediment for 5 h, perform vacuum filtration, dissolve the filter cake in pure water, and filter it successively through microfiltration and nanofiltration membranes to obtain a sodium chloride slurry; cool the sodium chloride slurry to -1 °C for crystallization, perform centrifugal dehydration and drying to obtain high-purity sodium chloride.

[0063] S2: Purify the potassium chloride sample and sodium fluoride sample in the same method as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

[0064] Step (2) Preparation of composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride in a ratio of 0.50:0.37:0.17, perform ball milling for 1.3 h, and dry at 105 °C to obtain a mixed powder; under an argon atmosphere, heat the mixed powder at a pressure of 0.22 MPa and a heating rate of 2.2 °C / min to 580 °C until the salt is completely melted, keep it warm for 4.6 h, cool it to room temperature, and grind to obtain a composite molten salt.

[0065] Step (3) Preparation of microencapsulated composite molten salt: Mix 1.6 g of polyvinylpyrrolidone and 70 mL of ethanol, stir at a rotation speed of 180 r / min for 25 min to obtain an ethanol solution of polyvinylpyrrolidone; add 1.6 g of composite molten salt to the ethanol solution of polyvinylpyrrolidone, stir at a rotation speed of 180 r / min at room temperature for 23 h, then centrifuge at a rotation speed of 3700 r / min for 25 min, and wash the centrifuged product with ethanol to obtain a loaded and modified composite molten salt; mix 110 g of ethanol and 4.6 g of 28 wt% ammonia water solution to obtain a mixed solution, add 6.2 g of the loaded and modified composite molten salt to the mixed solution, then add 11.3 mL of tetraethoxysilane, react at a temperature of 30 °C and a stirring speed of 180 r / min for 1.3 h, wash, and centrifuge at a rotation speed of 3600 r / min for 25 min to obtain a microencapsulated composite molten salt.

[0066] Step (4) Preparation of hydroxylated multi-walled carbon nanotubes: Disperse 3.5 g of multi-walled carbon nanotubes, 0.9 g of aluminum chloride, and 1.6 mL of 0.51 mol / L hydrochloric acid aqueous solution in 25 mL of 80 wt% ethanol, apply microwave for 8 min, wash repeatedly with deionized water until the pH of the system is neutral, filter, and dry at 118 °C for 6 min to obtain hydroxylated single-walled carbon nanotubes.

[0067] Step (5) Preparation of high-purity heat-conducting energy-storage molten salt: Add 16 g of erythritol and 0.7 g of hydroxylated multi-walled carbon nanotubes to 180 mL of deionized water, heat to 70 °C, stir at a speed of 180 r / min for 3 h, then add 93 g of microencapsulated composite molten salt, and continue stirring and reacting for 7 h. After the reaction is completed, filter, wash the filter residue with deionized water, and dry at 50 °C for 13 h to obtain high-purity heat-conducting energy-storage molten salt.

[0068] Comparative Example 1

[0069] Compared with Example 3, in Comparative Example 1, the composite molten salt was not microencapsulated. In the step of preparing high-purity heat-conducting energy-storage molten salt, the composite molten salt was used instead of the microencapsulated composite molten salt, and other conditions remained unchanged.

[0070] Comparative Example 2

[0071] Compared with Example 3, in Comparative Example 2, erythritol was not added in the step of preparing high-purity heat-conducting energy-storage molten salt, and other conditions remained unchanged.

[0072] Comparative Example 3

[0073] Compared with Example 3, in Comparative Example 3, hydroxylated multi-walled carbon nanotubes were not added in the step of preparing high-purity heat-conducting energy-storage molten salt, and other conditions remained unchanged.

[0074] Comparative Example 4

[0075] Compared with Example 3, in Comparative Example 4, sodium chloride sample, potassium chloride sample, and sodium fluoride sample were used instead of high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride in the step of preparing the composite molten salt, and other conditions remained unchanged.

[0076] Experimental Example

[0077] Test 1. Purity of single-component salt: The purity of high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride prepared by the single-component salt purification method disclosed in Examples 1-4 was tested respectively according to GB 1266-1986, GB 6549-2011, and GB 4293-1984. The test results are shown in Table 1:

[0078] Table 1

[0079] sample Example 1 Example 2 Example 3 Example 4 Sodium chloride purity / % 99.0 99.85 99.90 99.86 99.88 Potassium chloride purity / % 99.0 99.78 99.83 99.80 99.81 Sodium fluoride purity / % 98.0 98.76 99.53 98.99 99.24

[0080] It can be seen from the data in Table 1 that the high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride prepared in Examples 1-4 of the present invention have higher purity compared with the sodium chloride sample, potassium chloride sample, and sodium fluoride sample.

[0081] Test 2. Thermal conductivity: The thermal diffusivity of the high-purity heat-conducting energy-storage molten salts prepared in Examples 1-4 and Comparative Examples 1-4 was measured and analyzed by a laser thermal conductivity meter (LFA457). Platinum-rhodium was used as the sample container. During the measurement, high-purity nitrogen was used as the protective gas and purge gas, with the flow rate controlled at 50 mL / min and the heating rate at 10 °C / min. Each sample was measured three times, and the average value was taken to ensure the accuracy of the thermal conductivity measurement.

[0082] Test 3. Melting enthalpy: The melting enthalpy of the high-purity heat-conducting energy-storage molten salts prepared in Examples 1-4 and Comparative Examples 1-4 was measured using a Netzsch DSC-404F3 differential scanning calorimeter. Before the sample test, the temperature and sensitivity of the DSC were calibrated with a metal standard sample to ensure the reliability of the test equipment used. During the test, first, the sample was ground into powder, then about 10 mg of molten salt powder was accurately weighed with an analytical balance. Next, the weighed molten salt was placed in a graphite crucible, covered with a graphite crucible lid, and finally placed on the sample pan of the DSC and heated for testing. The purge gas used for the test was argon, with a gas flow rate of 50 mL / min and a heating rate of 10 °C / min. Each test was performed with three heating and cooling cycles to ensure the accuracy and repeatability of the experiment. The test results are shown in Table 2:

[0083] Table 2

[0084]

[0085] From the test results in Table 2, it can be seen that the thermal conductivity of the high-purity heat-conducting energy-storage molten salts prepared in Examples 1-4 of the present invention has been greatly improved compared with conventional molten salts; at the same time, the high-purity heat-conducting energy-storage molten salts prepared in Examples 1-4 of the present invention have good heat storage capacity, and the melting enthalpy is up to 421.1 J / g at most.

[0086] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of high-purity heat-conducting energy-storing molten salt, characterized in that Including the following steps: Step (1) Purification of single-component salts: Purify sodium chloride sample, potassium chloride sample, and sodium fluoride sample to obtain high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride; Step (2) Preparation of composite molten salt: Mix high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride, and ball-mill to obtain a mixed powder; Under an argon atmosphere, melt the mixed powder, keep it warm, cool it, and grind it to obtain a composite molten salt; The mass ratio among high-purity sodium chloride, high-purity potassium chloride, and high-purity sodium fluoride is 0.44 - 0.52:0.32 - 0.40:0.12 - 0.20; Step (3) Preparation of microencapsulated composite molten salt: Mix ethanol and 28wt% ammonia water solution to obtain a mixed solution, add the loaded and modified composite molten salt to the mixed solution, then add tetraethoxysilane, heat and stir for reaction, wash, and centrifuge to obtain microencapsulated composite molten salt; The preparation method of the loaded and modified composite molten salt: Add 1 - 2 g of composite molten salt to an ethanol solution of polyvinylpyrrolidone, stir at a speed of 100 - 200 r / min at room temperature for 20 - 24 h, then centrifuge at a speed of 3000 - 4000 r / min for 15 - 30 min, and wash the centrifuged product with ethanol; Among them, the ethanol solution of polyvinylpyrrolidone is obtained by mixing 1 - 2 g of polyvinylpyrrolidone and 40 - 80 mL of ethanol and stirring at a speed of 100 - 200 r / min for 20 - 30 min; Step (5) Preparation of hydroxylated multi-walled carbon nanotubes: Disperse multi-walled carbon nanotubes, aluminum chloride, and 0.51 mol / L hydrochloric acid aqueous solution in 80wt% ethanol, under microwave action, wash, filter, and dry to obtain hydroxylated single-walled carbon nanotubes; Step (6) Preparation of high-purity thermally conductive energy storage molten salt: Add erythritol and hydroxylated multi-walled carbon nanotubes to deionized water, heat, stir, then add microencapsulated composite molten salt, continue to stir for reaction, after the reaction ends, filter, wash, and dry to obtain high-purity thermally conductive energy storage molten salt.

2. The preparation method of the high-purity heat-conducting energy storage molten salt according to claim 1, characterized in that, In the said step (1), the purification method of single-component salts: S1: Dissolve the sodium chloride sample in pure water at 50 - 80°C to obtain a sodium chloride solution; After cooling the sodium chloride solution to room temperature, filter it through a nanofiltration membrane, add tetrahydrofuran to the filtrate according to the volume ratio of tetrahydrofuran to the filtrate of 1 - 2:1 and settle for 4 - 6 h, filter under vacuum, dissolve the filter residue in pure water, and filter successively through microfiltration and nanofiltration membrane to obtain a sodium chloride slurry; Cool the sodium chloride slurry to -5 - 0°C for crystallization, centrifuge for dehydration, and dry to obtain high-purity sodium chloride; S2: Purify the potassium chloride sample and sodium fluoride sample in the same method as in S1 to obtain high-purity potassium chloride and high-purity sodium fluoride.

3. The preparation method of the high-purity heat-conducting energy storage molten salt according to claim 1, characterized in that, In the said step (2), the ball-milling time: 1 - 1.5 h, the drying temperature: 90 - 110°C.

4. The preparation method of the high-purity heat-conducting energy-storing molten salt according to claim 1, characterized in that, In the step (2), the melting conditions of the mixed powder are as follows: the mixed powder is heated to 520 - 600 °C at a heating rate of 1.5 - 2.5 °C / min under a pressure of 0.15 - 0.25 MPa until the salt is completely melted; the heat preservation time is 4 - 5 h; the cooling condition is to cool to room temperature.

5. The preparation method of the high-purity heat-conducting energy-storing molten salt according to claim 1, characterized in that, In the step (3), the dosage ratio of ethanol, 28 wt% ammonia aqueous solution, the composite molten salt with load modification, and tetraethoxysilane is 100 - 120 g : 4 - 5 g : 5.8 - 6.5 g : 9.3 - 12.5 mL; the heating and stirring reaction conditions are as follows: reacting for 1 - 1.5 h under the conditions of a temperature of 25 - 35 °C and a stirring speed of 100 - 200 r / min; the centrifugation condition is to centrifuge at a rotational speed of 3000 - 4000 r / min for 15 - 30 min.

6. The preparation method of the high-purity heat-conducting energy-storing molten salt according to claim 1, wherein, In the step (4), the dosage ratio of multi-walled carbon nanotubes, aluminum chloride, 0.51 mol / L hydrochloric acid aqueous solution, and 80 wt% ethanol is 0.1 - 0.7 g : 0.1 - 1.3 g : 1 - 2 mL : 20 - 30 mL; the microwave action time is 4 - 10 min; the washing condition is to wash repeatedly with deionized water until the pH of the system is neutral; the drying condition is to dry at 110 - 120 °C for 5 - 10 min.

7. The preparation method of the high-purity heat-conducting energy-storing molten salt according to claim 1, wherein, In the step (5), the dosage ratio of deionized water, erythritol, hydroxylated multi-walled carbon nanotubes, and microencapsulated composite molten salt is 150 - 200 mL : 10 - 20 g : 0.5 - 5 g : 80 - 100 g.

8. The preparation method of the high-purity heat-conducting energy-storing molten salt according to claim 1, wherein, In the step (5), the heating temperature is 60 - 80 °C; the stirring condition is to stir at a rotational speed of 100 - 200 r / min for 2 - 4 h; the continuous stirring reaction time is 6 - 8 h; the washing liquid used for washing includes deionized water; the drying condition is to dry at 40 - 60 °C for 10 - 14 h.

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