Sintered expanded graphite shaped molten salt energy storage material and preparation method thereof

Abstract

The application discloses sintered expanded graphite shaped molten salt energy storage material and a preparation method thereof. The energy storage material is mainly composed of sintered expanded graphite and molten salt, the sintered expanded graphite is a carrier of the molten salt, the mass of the sintered expanded graphite and the molten salt accounts for 35-45% and 55-65% of the total mass of the sintered expanded graphite shaped molten salt energy storage material respectively, the molten salt is a high-temperature molten salt, the high-temperature molten salt comprises one or more combinations of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride and potassium chloride, the sintered expanded graphite is mainly prepared from a mixture of pitch, a dispersing agent, expanded graphite and an adjusting component through drying, pressure forming, drying and sintering in sequence, and the adjusting component accounts for 1-5% of the total mass of the sintered expanded graphite shaped molten salt energy storage material. The sintered expanded graphite shaped molten salt energy storage material has good heat conduction performance, low heat loss, good corrosion resistance, high strength and can prevent molten salt leakage, and thus has good safety.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and to a sintered expanded graphite shaped molten salt energy storage material and its preparation method. Background Technology

[0002] Molten salt energy storage technology is a thermal energy storage technology that uses molten salt as the heat storage medium. This technology can effectively store and release large amounts of thermal energy and is widely used in solar thermal power generation, industrial waste heat recovery, and district heating systems. It has advantages such as high heat storage density, wide temperature range, low cost, long lifespan, and environmental friendliness. However, molten salts typically have disadvantages such as low thermal conductivity and strong corrosive properties at high temperatures.

[0003] Expanded graphite is a loose, porous, worm-like material with a large network of micropores. Its large specific surface area and high surface activity give it excellent adsorption, coating, and thermal conductivity properties, making it widely applicable in energy storage and other fields. However, expanded graphite exhibits phenomena such as sedimentation, segregation, and molten salt separation in phase change materials.

[0004] Compared to expanded graphite, porous graphite materials offer advantages such as lightweight, good thermal conductivity, excellent corrosion resistance, good heat resistance, and superior processability, leading to their wide application in the automotive, aerospace, energy storage, medical, electronics, and communications industries. However, existing technologies using bitumen as a binder in porous graphite products typically exhibit the following characteristics:

[0005] On the one hand, the role of asphalt binder comes from the residue after asphalt is calcined and carbonized, which binds the solid fillers together. During the sintering process, about 50% of the light components of asphalt volatilize, and the residue after asphalt is calcined is what plays the role of binding.

[0006] On the other hand, asphalt is prone to embrittlement at room temperature and has unstable bonding properties, resulting in porous graphite products with poor strength retention at room temperature. Summary of the Invention

[0007] To address the problems associated with existing expanded graphite, porous graphite, and high-temperature molten salt materials, this invention provides a sintered expanded graphite-shaped molten salt energy storage material and its preparation method. The preparation method of this invention uses pitch to shape and sinter expanded graphite, solving the problems of sedimentation, segregation, and molten salt separation during practical applications. By combining the molten salt with the sintered expanded graphite framework material, the sintered expanded graphite exhibits good strength retention at room temperature, resulting in a composite material with excellent overall strength and good thermal conductivity, while also preventing molten salt leakage.

[0008] To solve the above technical problems, the following technical solution is adopted:

[0009] I. A sintered expanded graphite shaped molten salt energy storage material

[0010] The sintered expanded graphite shaped molten salt energy storage material is mainly composed of sintered expanded graphite and molten salt, with the sintered expanded graphite serving as a carrier for the molten salt.

[0011] The sintered expanded graphite and molten salt account for 35-45% and 55-65% of the total mass of the sintered expanded graphite shaped molten salt energy storage material, respectively.

[0012] The molten salt is a high-temperature molten salt, which includes one or more of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride, and potassium chloride.

[0013] The sintered expanded graphite contains a modifier component, and the mass ratio of the modifier component to the sintered expanded graphite is 1–5:35–45, meaning the mass of the modifier component accounts for 1–5% of the total mass of the sintered expanded graphite shaped molten salt energy storage material. The modifier component is one or more of silicon carbide, chopped carbon fibers, and phenolic resin. The length of the chopped carbon fibers is 1–100 mm.

[0014] Furthermore, the sintered expanded graphite is mainly prepared by sequentially drying, pressing, drying and sintering a mixture of asphalt, dispersant, expanded graphite and adjusting components; the mass ratio of asphalt to dispersant is 2.5 to 3.5:1; the mass ratio of asphalt to expanded graphite is 5 to 20:1; and the mass ratio of expanded graphite to adjusting components is 1 to 15:1.

[0015] Furthermore, the porosity of the sintered expanded graphite is 50% to 70%, that is, the volume ratio of the sintered expanded graphite to the molten salt is 30 to 50: 50 to 70.

[0016] II. A method for preparing sintered expanded graphite shaped molten salt energy storage material

[0017] The preparation method includes the following steps:

[0018] 1) Mix asphalt particles, dispersant, expanded graphite, and adjusting components to obtain an expanded graphite-asphalt mixture. Specifically, step 1) involves: pre-passing the asphalt particles through a 100-mesh sieve, retaining fine particles; passing the expanded graphite through a 100-mesh sieve, retaining coarse particles; mixing the sieved asphalt particles and dispersant at a mass ratio of 2.5–3.5:1; then adding the sieved expanded graphite and adjusting components at a mass ratio of 5–20:1 (asphalt particles to expanded graphite) and 1–15:1 (expanded graphite to adjusting components); and stirring thoroughly at a speed of 100–150 r / min to obtain the expanded graphite-asphalt mixture. During this process, appropriately controlling the stirring rate helps prevent the agglomeration of the expanded graphite powder and adjusting components.

[0019] Specifically, the preparation process of the asphalt particles is as follows: after grinding the asphalt with a grinder, it is passed through a 100-mesh sieve to remove some coarse particles, thus obtaining asphalt particles.

[0020] Specifically, the asphalt is one or more of medium-temperature asphalt, modified asphalt, and high-temperature asphalt.

[0021] Specifically, the dispersant is made of one or more of ethanol, toluene, and quinoline.

[0022] 2) After drying the expanded graphite-asphalt mixture, it is transferred to a mold and pressurized to obtain a molded block. After drying the molded block, a preform is obtained. In step 2), the drying process is as follows: drying at 60℃~90℃ for 2~5h and then naturally cooling. Stirring is stopped during the drying and natural cooling stages. The pressure for pressurization is 10MPa. After pressurization, the strength of the preform increases, which helps the asphalt to bond together and form a heat-conducting network during sintering. The drying conditions are: drying at an ambient temperature of 50~100℃ for 1~2h.

[0023] 3) The preform is sintered to obtain sintered expanded graphite. The specific sintering process in step 3) is as follows: Under an inert gas atmosphere, the temperature is raised from 50℃ to 400℃ at a rate of 1.2–1.5℃ / h; held at 400℃ for 30 min; then raised from 400℃ to 900–1400℃ at a rate of 1.5–2℃ / min; after reaching the desired temperature, held for 2 h, and then cooled to 50–200℃ at a rate of 1.5–2℃ / min. During the sintering process, the rate of release of lightweight components within the asphalt is controlled by adjusting the heating and cooling rates, thereby meeting the structural requirements of the sintered expanded graphite.

[0024] In this step, the porosity of the sintered expanded graphite obtained by sintering is 50-70%.

[0025] 4) A eutectic salt is prepared using molten salt, and then composited onto sintered expanded graphite using a vacuum impregnation method to obtain the sintered expanded graphite shaped molten salt energy storage material. In step 4), the conditions for the vacuum impregnation method are: immersing the sintered expanded graphite in the molten eutectic salt, maintaining a vacuum pressure of -0.08 atm, and a temperature higher than the eutectic salt's eutectic melting point. A suitable vacuum level helps the molten eutectic salt fully fill the sintered expanded graphite, increasing the energy storage density.

[0026] Further, in step 4), the specific process of preparing the eutectic salt using molten salt material is as follows: after drying and grinding the molten salt material, the resulting powder is melted and cooled at a temperature above the eutectic point to obtain the eutectic salt. The molten salt is one or a combination of several of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride, and potassium chloride.

[0027] In this invention, "high-temperature molten salt" refers to an inorganic salt composed of halides of alkali metals and alkaline earth metals, nitrates, sulfates, etc., that can melt at a temperature of 300°C or above. In other words, "high-temperature molten salt" refers to molten salt with a working temperature of 300°C or higher.

[0028] In this invention, the inert gas is any one or a combination of two or more of nitrogen, helium, neon, argon, krypton, and radon.

[0029] The beneficial effects of this invention are as follows:

[0030] 1. The method of the present invention improves the problem of poor thermal conductivity of high-temperature molten salt energy storage materials. The 3D network porous structure formed by asphalt and expanded graphite after high-temperature sintering gives the energy storage material of the present invention better heat transfer performance, thus further improving the heat transfer efficiency and enhancing the application capability of high-temperature molten salt energy storage materials, thereby obtaining huge economic benefits.

[0031] 2. The method of the present invention increases the specific surface area of ​​the raw materials by strictly controlling the fineness of the raw materials and strictly controlling the sintering temperature in multiple stages, so that the sintered expanded graphite has good porosity and excellent flexural strength, which further improves the safety performance of high-temperature molten salt energy storage materials during transportation and use.

[0032] 3. The sintered expanded graphite obtained by this invention has good environmental adaptability, excellent corrosion resistance, and a wide applicable temperature range, which expands the application scope of this sintered expanded graphite in high-temperature molten salt energy storage materials. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the preparation process of the sintered expanded graphite shaped molten salt energy storage material provided by the present invention;

[0034] Figure 2 These are microscopic morphology images of the sintered expanded graphite shaped molten salt energy storage materials obtained in Examples 1 to 3 of this invention;

[0035] Figure 3 These are physical images of Embodiment 1 and Comparative Example 2 before and after 100 cycles. Detailed Implementation

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0037] To keep the drawings simple, each drawing only schematically shows the parts relevant to the invention, and they do not represent the actual structure of the product.

[0038] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0039] The first aspect of this invention provides a sintered expanded graphite-shaped molten salt energy storage material. This energy storage material exhibits excellent thermal conductivity and good flexural strength at room temperature, thereby reducing heat loss during application and saving on usage costs. Furthermore, this sintered expanded graphite-shaped molten salt energy storage material possesses excellent corrosion resistance and good strength, preventing molten salt leakage and improving the safety of high-temperature molten salt applications. This invention involves fixing expanded graphite within a sintered pitch skeleton after high-temperature sintering. Using the prepared sintered expanded graphite as a substrate to prepare the sintered expanded graphite-shaped molten salt energy storage material further prevents molten salt leakage, ultimately overcoming the problems of sedimentation, segregation, and molten salt separation that occur with expanded graphite in practical applications.

[0040] A second aspect of this invention provides a method for preparing a sintered expanded graphite shaped molten salt energy storage material. Specific steps are as follows: Figure 1 As shown. The preparation method of this invention achieves an effective combination of sintered expanded graphite and high-temperature molten salt through a reaction process of high-temperature sintering and vacuum impregnation. The preparation method of this invention also provides an optimized raw material fineness and a stable sintering heating rate based on the above raw material combination.

[0041] The preparation method of this invention is simple, greatly saving equipment costs and significantly improving the cost-effectiveness of the product.

[0042] Specific embodiments of the present invention are as follows:

[0043] Example 1

[0044] In this embodiment, medium-temperature asphalt was pre-obtained as a binder, ethanol as a dispersant, phenolic resin as a modifier, and a high-temperature molten salt comprising 48 wt% sodium chloride and 52 wt% magnesium chloride (the eutectic point of this high-temperature molten salt is 450°C). Based on these materials, a sintered expanded graphite-shaped molten salt energy storage material was prepared. Figure 1 As shown, the preparation method includes the following steps:

[0045] 1) Grind medium-temperature asphalt using a grinder, and after passing it through a 100-mesh sieve, collect the fine particles to obtain asphalt granules. Pass expanded graphite through a 100-mesh sieve, retaining the coarse particles. Thoroughly mix the asphalt granules and ethanol at a mass ratio of 3:1. Then, add expanded graphite and adjust the composition according to a mass ratio of asphalt granules to expanded graphite of 10:1 and a mass ratio of expanded graphite to phenolic resin of 10:1. Mix thoroughly at a speed of 120 r / min to obtain an expanded graphite-asphalt mixture.

[0046] 2) After drying the expanded graphite-asphalt mixture at 70℃ for 3 hours, it is naturally cooled, transferred to a mold and pressed at 10 MPa. The molded block is removed from the mold and then transferred to an oven. After drying at 80℃ for 1 hour, the preform is obtained.

[0047] 3) The preform is sintered to obtain sintered expanded graphite. The specific sintering process is as follows: First, the temperature is raised from 50℃ to 400℃ at a rate of 1.2℃ / h; the temperature is held at 400℃ for 30 min; the temperature is raised from 400℃ to 1000℃ at a rate of 1.7℃ / min; after the temperature is raised to 1100℃, it is held for 2 h and then the temperature is lowered to 200℃ at a rate of 2℃ / min. The reaction environment is a nitrogen atmosphere.

[0048] In the sintered expanded graphite obtained in this embodiment, the mass ratio of sintered expanded graphite to the adjusting components is 45:1.

[0049] 4) Sodium chloride and anhydrous magnesium chloride were dried in an oven at 130℃ for 2 hours and then ground in a mortar for 30 minutes. The dried mixed powder was placed in a reaction vessel under nitrogen protection at a pressure of 2.5 MPa and heated to 580℃ at a heating rate of 4℃ / min, and held at that temperature for 4 hours. Finally, it was allowed to cool naturally to room temperature to form a sodium chloride-magnesium chloride eutectic salt. Sintered expanded graphite was immersed in the molten eutectic salt, and the eutectic salt was composited onto the sintered expanded graphite matrix by vacuum impregnation at -0.08 atm and 525℃ to obtain an expanded graphite shaped molten salt energy storage material.

[0050] Example 2

[0051] In this embodiment, except for the following differences, all other steps and conditions are the same as in Example 1: In this embodiment, modified asphalt is used as a binder, and a combination of chopped carbon fibers and phenolic resin is used as an adjusting component. In step 1), the mass ratio of asphalt particles to expanded graphite is 5:1, the ratio of expanded graphite to chopped carbon fibers is 15:1, and the mass ratio of expanded graphite to phenolic resin is 5:1.

[0052] In this embodiment, the mass ratio of sintered expanded graphite to the adjusting components is 35:1.3.

[0053] Example 3

[0054] In this embodiment, except for the following differences, all other steps and conditions are the same as in Example 1: This embodiment uses a combination of medium-temperature asphalt and high-temperature asphalt as the binder, with a mass ratio of 3:1 between the two. A combination of chopped carbon fibers and phenolic resin is used as the adjusting component. In step 1), the mass ratio of asphalt particles to expanded graphite is 5:1, the ratio of expanded graphite to chopped carbon fibers is 15:1, and the mass ratio of expanded graphite to phenolic resin is 5:1.

[0055] In the sintered expanded graphite obtained in this embodiment, the mass ratio of sintered expanded graphite to the adjusting components is 35:1.

[0056] Comparative Example 1

[0057] This comparative example prepared a sodium chloride-magnesium chloride eutectic salt via the following process: Sodium chloride and anhydrous magnesium chloride were dried separately in an oven at 130°C for 2 hours, then mixed at a mass ratio of 48:52 and ground in a mortar for 30 minutes. The dried mixed powder was placed in a reaction vessel under nitrogen protection at a pressure of 2.5 MPa, heated to 580°C at a heating rate of 4°C / min, and held at that temperature for 4 hours. Finally, it was allowed to cool naturally to room temperature to form the sodium chloride-magnesium chloride eutectic salt.

[0058] Comparative Example 2

[0059] This comparative example prepared a composite phase change material of expanded graphite and sodium chloride-magnesium chloride eutectic salt through the following process: Sodium chloride and anhydrous magnesium chloride were dried separately in an oven at 130℃ for 2 h, then mixed at a mass ratio of 48:52 and ground in a mortar for 30 min. The dried mixed powder was placed in a reaction vessel under nitrogen protection at a pressure of 2.5 MPa, heated to 580℃ at a heating rate of 4℃ / min, and held at that temperature for 4 h. Finally, it was naturally cooled to room temperature to form sodium chloride-magnesium chloride eutectic salt.

[0060] The volume ratio of expanded graphite to high-temperature molten salt is 43:57 (set according to the porosity of the material obtained in Example 1, so that the volume ratio of expanded graphite to high-temperature molten salt in this comparative example is equal to the volume ratio of sintered expanded graphite to high-temperature molten salt in Example 1). The high-temperature molten salt is composited into the expanded graphite by vacuum impregnation under the conditions of -0.08 atm and 525°C.

[0061] The thermal conductivity and flexural strength of the products obtained in the comparative examples and embodiments of the present invention, as well as the porosity of the sintered expanded graphite obtained in each embodiment, are shown in the table below:

[0062]

[0063] As shown in the table above, the sintered expanded graphite obtained by the method of this invention has stable and good porosity. Compared with the eutectic salt obtained in Comparative Example 1, the energy storage material obtained by the method of this invention has higher thermal conductivity and stronger flexural strength. Compared with the material obtained in Comparative Example 2, the flexural strength of the energy storage material obtained by the method of this invention is significantly increased.

[0064] The microstructure images of the sintered expanded graphite shaped molten salt energy storage materials obtained in Examples 1 to 3 of this invention are as follows: Figure 2 As shown, the sintered expanded graphite shaped molten salt energy storage material obtained by the method of the present invention exhibits good adhesion between the high-temperature molten salt particles, the adjusted composition, and the sintered expanded graphite framework.

[0065] Cyclic tests were conducted on the materials obtained in Embodiment 1 and Comparative Example 2 of this invention. In each cycle of the cyclic test, the temperature control program was to raise the temperature from room temperature to 500°C at a rate of 20°C / min, and then stop heating and cool the furnace to room temperature after reaching 500°C. The results are as follows: Figure 3 As shown. By Figure 3 It is evident that the sintered expanded graphite material of the present invention overcomes the problems of sedimentation, segregation, and molten salt separation that occur during long-term use of expanded graphite compared to the expanded graphite used in Comparative Example 2.

[0066] It should be noted that the present invention is not limited to the specific technical solutions of the above embodiments. In addition to the above embodiments, the present invention may have other implementation schemes. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A sintered expanded graphite shaped molten salt energy storage material, characterized in that: The sintered expanded graphite shaped molten salt energy storage material is mainly composed of sintered expanded graphite and molten salt, with the sintered expanded graphite serving as a carrier for the molten salt. The sintered expanded graphite contains a modifying component, and the mass ratio of the modifying component to the sintered expanded graphite is 1~5:35~45. The modifying component is one or more of silicon carbide, chopped carbon fiber and phenolic resin. The sintered expanded graphite is mainly prepared by sequentially drying, pressing, drying and sintering a mixture of asphalt, dispersant, expanded graphite and adjusting components; the mass ratio of asphalt to dispersant is 2.5~3.5:1; the mass ratio of asphalt to expanded graphite is 5~20:1; the mass ratio of expanded graphite to adjusting components is 1~15:

1.

2. The sintered expanded graphite shaped molten salt energy storage material according to claim 1, characterized in that: The sintered expanded graphite and molten salt account for 35-45% and 55-65% of the total mass of the sintered expanded graphite shaped molten salt energy storage material, respectively.

3. The sintered expanded graphite shaped molten salt energy storage material according to claim 1, characterized in that: The molten salt is a high-temperature molten salt, which includes one or more combinations of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride and potassium chloride; and / or, the porosity of the sintered expanded graphite is 50% to 70%.

4. A method for preparing a sintered expanded graphite shaped molten salt energy storage material as described in any one of claims 1 to 3, characterized in that: Includes the following steps: 1) Mix asphalt particles, dispersant, expanded graphite, and adjusting components to obtain an expanded graphite-asphalt mixture; 2) After drying the expanded graphite-asphalt mixture, it is transferred to a mold and pressed to obtain a molded block. After drying the molded block, a preform is obtained. 3) The preform is sintered to obtain sintered expanded graphite; 4) A eutectic salt is prepared using molten salt, and the eutectic salt is composited onto sintered expanded graphite using a vacuum impregnation method to obtain the sintered expanded graphite shaped molten salt energy storage material.

5. The preparation method according to claim 4, characterized in that: Step 1) specifically involves: passing asphalt particles through a 100-mesh sieve and retaining fine particles, passing expanded graphite through a 100-mesh sieve and retaining coarse particles, mixing asphalt particles and dispersant at a mass ratio of 2.5 to 3.5:1, adding expanded graphite and adjusting components at a mass ratio of 5 to 20:1 for asphalt particles and 1 to 15:1 for expanded graphite and adjusting components, and stirring thoroughly at a speed of 100 to 150 r / min to obtain the expanded graphite-asphalt mixture.

6. The preparation method according to claim 4, characterized in that: In step 2), the drying process is as follows: drying at 60℃~90℃ for 2~5 hours and then naturally cooling; the pressure for pressing is 10MPa; the drying conditions are: drying at an ambient temperature of 50~100℃ for 1~2 hours.

7. The preparation method according to claim 4, characterized in that: In step 3), the sintering process is as follows: under an inert gas atmosphere, the temperature is raised from 50°C to 400°C at a rate of 1.2~1.5°C / h; the temperature is held at 400°C for 30 min; the temperature is then raised from 400°C to 900~1400°C at a rate of 1.5~2°C / min. Keep warm for 2 hours, then cool down to 50~200℃ at a rate of 1.5~2℃ / min.

8. The preparation method according to claim 4, characterized in that: In step 4), the conditions for vacuum impregnation are: vacuum pressure of -0.08 atm and temperature greater than the eutectic salt's melting point.

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