Modified expanded graphite composite phase change material as well as preparation method and application thereof

Abstract

The invention discloses a modified expanded graphite composite phase change material as well as a preparation method and application thereof, and belongs to the technical field of phase change materials, the phase change material comprises modified sodium acetate trihydrate and modified expanded graphite, the modified sodium acetate trihydrate is used as a main body material of the phase change material, and the modified expanded graphite is used as a carrier material of the phase change material. The modified expanded graphite composite phase change material has the advantages of small supercooling degree, high thermal conductivity, good thermal reliability, simple preparation, low cost, safety and no toxicity in the whole preparation process, and suitableness for medium and low temperature industrial waste heat recovery application.

Description

Technical Field

[0001] The invention relates to the technical field of phase change materials, and in particular to a modified expanded graphite composite phase change material, a preparation method and application thereof. Background Art

[0002] Phase change material (PCM) is a material that can store energy through its own solid-liquid conversion, which can reuse energy to a certain extent. PCM can be divided into organic PCM and inorganic PCM. Compared with many organic PCMs, hydrated salt phase change materials in inorganic PCMs show obvious advantages, including high latent heat, non-toxicity, non-flammability and low cost, so they have great potential in energy storage applications. However, hydrated salt phase change materials have problems such as low thermal conductivity and easy leakage, which seriously limit their application. In order to overcome the above problems, high thermal conductivity particles or carbon materials can be introduced into phase change materials as modifiers and carriers.

[0003] Expanded graphite is one of the most popular carrier materials. On the one hand, expanded graphite is a loose and porous worm-like substance made from natural flake graphite, also called graphite worms, which has a rich porous structure and can adsorb phase change materials; on the other hand, expanded graphite has high thermal conductivity, and its thermal conductivity is about 2000 W / (m·K), which can shape and compound phase change materials while increasing thermal conductivity. However, the problem with expanded graphite as a carrier material is that it has poor hydrophilicity, while inorganic hydrated salt phase change materials have good hydrophilicity, and the compatibility of the two is poor. This leads to the need to use a large amount of expanded graphite to load inorganic phase change materials in order to meet reliable thermal stability. Therefore, it is necessary to improve the hydrophilicity of expanded graphite, so as to reduce the amount of expanded graphite used and achieve considerable thermal stability.

[0004] In order to solve the problem of poor hydrophilicity of expanded graphite and improve its compatibility with inorganic phase change materials, there are usually two solutions in the prior art: first, preparing oxidized expanded graphite with more hydrophilic groups by the Hummer method, however, the pore structure of the expanded graphite will be destroyed during the oxidation process. Second, using surfactants to improve the hydrophilicity of expanded graphite, for example, Zhou et al. used TritonX-100 surfactant to improve the hydrophilicity of expanded graphite, and compounded it with MgCl2·6H2O-NH4Al(SO4)2·12H2O. After 100 cycles, it showed good thermal stability. However, the surfactant and expanded graphite are physically combined, and this bond will break after the composite phase change material has been cycled many times.

[0005] The inorganic hydrated salt sodium acetate trihydrate is a very promising medium and low temperature phase change material because of its large phase change latent heat (285 J / g), suitable phase change temperature (58°C), stable chemical properties, and harmlessness. Although the thermal conductivity of sodium acetate trihydrate has certain advantages over organic phase change materials, it still does not meet the application requirements, and its leakage problem also limits its application. In the invention patent CN202011432592.6, hexadecyltrimethylammonium bromide is used to surface treat expanded graphite, and then sodium acetate trihydrate is adsorbed to obtain a composite phase change energy storage material, which has the characteristics of good thermal conductivity and no leakage. However, hexadecyltrimethylammonium bromide belongs to quaternary ammonium salt compounds and has certain toxicity; and the price is relatively high, which will increase production costs when used on a large scale. Summary of the invention

[0006] One of the purposes of the present invention is to provide a modified expanded graphite composite phase change material, which is used to solve the shortcomings of the expanded graphite composite phase change material in the prior art that the preparation price is too high and toxic materials are used in the preparation process.

[0007] The present invention is achieved through the following technical scheme: a modified expanded graphite composite phase change material, the phase change material comprises: modified sodium acetate trihydrate and modified expanded graphite, wherein the modified sodium acetate trihydrate is used as the main material of the phase change material, and the modified expanded graphite is used as the carrier material of the phase change material.

[0008] Furthermore, the modified sodium acetate trihydrate is sodium acetate trihydrate modified by nano-silicon carbide.

[0009] Furthermore, the modified expanded graphite is expanded graphite modified by aluminum oxide.

[0010] Furthermore, the mass ratio of the modified sodium acetate trihydrate to the modified expanded graphite is 100:12 to 100:14.

[0011] Furthermore, the volume expansion multiple of the modified expanded graphite is 200 to 300 times.

[0012] Furthermore, the mass ratio of sodium acetate trihydrate to nano-silicon carbide is 100:1.

[0013] On the other hand, the present invention also provides a method for preparing a modified expanded graphite composite phase change material, which is used to prepare the modified expanded graphite composite phase change material shown above. It includes the following steps: S100, preparing a modified sodium acetate trihydrate main material, placing the sodium acetate trihydrate in an oven and heating it until it melts, then adding silicon carbide as a thermal conductivity enhancer to the melted sodium acetate trihydrate, and stirring for 30 to 40 minutes, and cooling to obtain silicon carbide modified sodium acetate trihydrate; S200, preparing alumina modified expanded graphite, dispersing the expanded graphite in a solvent, and standing at room temperature for 3 to 5 hours to obtain an expanded graphite mixed solution; using ammonia water to adjust the pH of the aluminum nitrate nonahydrate solution to obtain a white Al(OH)3 suspension, and The suspension is placed in an ultrasonic cleaning machine and shaken for 20 to 30 minutes; the expanded graphite mixed solution is heated to 80°C, and the suspension is added dropwise to the expanded graphite mixed solution within 5 minutes. After the addition is completed, the suspension is allowed to stand at room temperature for 12 to 24 hours to allow the expanded graphite to fully absorb Al(OH)3; after the standing is completed, the expanded graphite mixed solution is filtered, and the filtered product is washed 3 to 5 times. After the washing is completed, the suspension is dried at 70 to 80°C for 12 to 18 hours; and at the same time, the suspension is placed in a muffle furnace and calcined at 400 to 500°C for 2 hours to prepare alumina-modified expanded graphite.

[0014] Further, S300, the prepared modified sodium acetate trihydrate and alumina modified expanded graphite are mixed, stirred at 70-80°C for 3 min and kept warm for 30 min; the stirring and keeping warm steps are repeated three times to obtain a modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material.

[0015] Furthermore, adjusting the pH value of the aluminum nitrate nonahydrate solution includes: adjusting the pH value of the aluminum nitrate nonahydrate solution to pH = 6~7 using ammonia water.

[0016] On the other hand, the present invention also provides an application of a modified expanded graphite composite phase change material, and an application of the composite phase change material prepared according to the modified expanded graphite composite phase change material as described above, or the modified expanded graphite composite phase change material preparation method as described above, in medium and low temperature industrial waste heat recovery.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] 1. The modified expanded graphite composite phase change material provided by the present invention has small supercooling, large thermal conductivity, good thermal reliability, simple preparation, low cost, safe and non-toxic in the entire preparation process, and is suitable for medium and low temperature industrial waste heat recovery applications.

[0019] 2. The composite phase change material of the present invention is composed of expanded graphite modified by alumina, sodium acetate trihydrate, and nano-silicon carbide, and the supercooling is only 0.5-3.5°C.

[0020] 3. The expanded graphite in the composite phase change material of the present invention still maintains its original pore structure after modification; and the modified expanded graphite can significantly improve the compatibility between the expanded graphite and the inorganic hydrated salt phase change material, thereby improving the adsorption rate of the inorganic hydrated salt phase change material; in addition, the modified expanded graphite and the added nano-silicon carbide can significantly improve the thermal conductivity of the phase change material.

[0021] 4. The phase change enthalpy of the composite phase change material of the present invention is 213.90-254.10 kJ / kg, and the thermal conductivity is 3.6-5.4 W / (m·K), which fully meets the requirements for medium and low temperature industrial waste heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0023] Figure 1 This is a morphology image of the modified expanded graphite provided in Example 1 under a scanning electron microscope.

[0024] Figure 2 This is a morphology image of the modified expanded graphite provided in Example 1 under a transmission electron microscope.

[0025] Figure 3 This is a contact angle diagram between the modified expanded graphite and water provided in Example 1.

[0026] Figure 4 This is a diagram of the initial state of the leakage test sample block provided in Example 1.

[0027] Figure 5 This is a filter paper image of the leakage test sample block provided in Example 1 after being heated at 70°C for 1 hour.

[0028] Figure 6 This is a differential scanning calorimetry curve provided for Example 1.

[0029] Figure 7 This is the temperature change curve after 50 cycles provided in Example 1.

[0030] Figure 8 Thermal conductivity diagram provided for Example 1.

[0031] Fig. 9 The contact angle diagram of unmodified expanded graphite and water provided for comparative example.

[0032] Fig.10 Differential scanning calorimetry graph provided for comparative example. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art in the art of the present invention. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail. Regarding the "comprising", "including", "having", "containing" and the like used herein, they are all open-ended terms, that is, they mean including but not limited to. Unless the context clearly indicates otherwise, the expressions "a" and "one" used herein include plural references. The term "about" used herein means a range of ±20% of the value thereafter. In some embodiments, the term "about" means a range of ±10% of the value thereafter. In some embodiments, the term "about" means a range of ±5% of the value thereafter.

[0035] Embodiment 1,

[0036] This embodiment provides a method for preparing a modified expanded graphite composite phase change material, which specifically comprises the following steps:

[0037] 1) 20 g of sodium acetate trihydrate was placed in an oven and heated to 80°C to melt, and then 0.2 g of silicon carbide was added to the melted sodium acetate trihydrate as a thermal conductivity enhancer, and the mixture was transferred to an oil bath and heated at the same temperature while stirring for 30 minutes to obtain a modified sodium acetate trihydrate phase change material.

[0038] 2) Take 4.8g of expanded graphite with a volume expansion ratio of 200 to 300 times and disperse it in 200mL of 20% ethanol aqueous solution by mass, let it stand at room temperature for 3h to obtain an expanded graphite mixture; use ammonia water to adjust 40mL of 0.2 mol / L aluminum nitrate nonahydrate solution to pH = 6 to obtain a white suspension, and ultrasonically vibrate for 20 min; heat the expanded graphite mixture to 80℃, then add the white suspension dropwise to the expanded graphite mixture within 5min, and let it stand at room temperature for 24h; filter and wash the expanded graphite attached with Al(OH)3 3 times, and dry it at 80℃ for 12h; place it in a muffle furnace and calcine it at 500℃ for 2h to obtain alumina-modified expanded graphite.

[0039] It should be noted that in step 2), the pH of the aluminum nitrate nonahydrate solution is adjusted to 6 in order to precipitate aluminum ions in the form of aluminum hydroxide, thereby forming an Al(OH)3 modification layer on the surface of the expanded graphite, thereby preparing conditions for the subsequent drying and calcination processes.

[0040] 3) 20.2 g of modified sodium acetate trihydrate and 2.4 g of alumina-modified expanded graphite were mixed, stirred at 80°C for 3 min and kept warm for 30 min; the stirring and warming steps were repeated three times to obtain a modified sodium acetate trihydrate / alumina-modified expanded graphite composite phase change material.

[0041] The performance of the composite phase change material prepared by the preparation method in this embodiment is tested. The modified expanded graphite prepared in step 2) of this embodiment is scanned under a scanning electron microscope (SEM) to obtain the following morphology: Figure 1 As shown, from Figure 1 It can be seen that the modified expanded graphite still maintains a porous structure, and alumina does not block the pores of the expanded graphite.

[0042] The morphology of the modified expanded graphite in step 2) of this embodiment under a transmission electron microscope (TEM) is as follows: Figure 2 As shown, from Figure 2 It can be seen that there is an obvious Al2O3 film attached to the surface of the expanded graphite. Figure 3 The contact angle between the modified expanded graphite and water in step 2) of this embodiment is shown. Figure 3 It can be seen that the contact angle between modified expanded graphite and water is 56°.

[0043] Then, a leakage test was conducted on the modified expanded graphite composite phase change material prepared in this embodiment. Figure 4 shows the initial state of the sample block, Figure 5 The filter paper after heating at 70°C for 1 hour is shown. As can be seen from the figure, the composite phase change material is pressed into a cylinder with a height of 2.5 cm and a diameter of 3 cm, and heated at 70°C for 1 hour. No liquid appears on the filter paper of the sample block, indicating that the alumina-modified expanded graphite is well loaded with the modified sodium acetate trihydrate phase change material and will not cause leakage of the phase change material.

[0044] Figure 6 The differential scanning calorimetry (DSC) curve of the composite phase change material prepared in this embodiment is shown. It can be seen from the figure that after 50 cycles, the phase change latent heat of the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material prepared in the embodiment remains at 235.33 J / g, which is only 4.57 J / g lower than that without cycles. The phase change temperature of the composite phase change material is about 58.3°C, which meets the requirements of industrial waste heat recovery, has high latent heat, does not have leakage, and has good application prospects.

[0045] The composite phase change material prepared in this embodiment is heated until it melts. During the cooling process, the temperature of the phase change material is recorded every 5 seconds to obtain a temperature change curve, such as: Figure 7 As shown in the figure, it can be seen that the supercooling degree of the composite phase change material prepared in this embodiment is only 3.5°C after 50 cycles, and the heat absorption and heat release platforms of the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material are relatively long, indicating that this solution solves the problem of large supercooling degree of sodium acetate trihydrate.

[0046] The thermal conductivity of the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material prepared in this embodiment is as follows: Figure 8 As shown. Figure 8 It can be seen that the thermal conductivity of sodium acetate trihydrate is only 0.432 W / (m·K), while the thermal conductivity increases to 3.607 W / (m·K) after adding 12% modified expanded graphite and 1% nano-silicon carbide.

[0047] Embodiment 2,

[0048] This embodiment provides a method for preparing a modified expanded graphite composite phase change material, which specifically comprises the following steps:

[0049] 1) 20 g of sodium acetate trihydrate was placed in an oven and heated to 75 °C to melt, and then 0.2 g of silicon carbide was added to the melted sodium acetate trihydrate as a thermal conductivity enhancer, and the mixture was transferred to an oil bath and heated at the same temperature while stirring for 40 min to obtain a modified sodium acetate trihydrate phase change material.

[0050] 2) Take 4.8 g of expanded graphite with a volume expansion ratio of 200 to 300 times and disperse it in 200 mL of 20% ethanol aqueous solution, let it stand at room temperature for 5 hours to obtain an expanded graphite mixture; use ammonia water to adjust 30 mL of 0.2 mol / L aluminum nitrate nonahydrate solution to pH = 6 to obtain a white suspension, and ultrasonically vibrate for 30 minutes; heat the expanded graphite mixture to 80°C, then add the white suspension dropwise to the expanded graphite mixture within 5 minutes, and let it stand at room temperature for 12 hours; filter and wash the expanded graphite attached with Al(OH)3 3 times, and dry it at 70°C for 18 hours; place it in a muffle furnace and calcine it at 500°C for 1.5 hours to obtain alumina-modified expanded graphite.

[0051] 3) 20.2 g of modified sodium acetate trihydrate and 1.6 g of alumina-modified expanded graphite were mixed, stirred at 80°C for 5 min and kept warm for 20 min; the stirring and keeping warm steps were repeated three times to obtain a modified sodium acetate trihydrate / alumina-modified expanded graphite composite phase change material.

[0052] According to tests, the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material of this embodiment has a phase change temperature of 59.93° C. and a phase change enthalpy of 254.10 J / g.

[0053] Embodiment 3,

[0054] This embodiment provides a method for preparing a modified expanded graphite composite phase change material, which specifically comprises the following steps:

[0055] 1) 20 g of sodium acetate trihydrate was placed in an oven and heated to 80°C to melt, and then 0.2 g of silicon carbide was added to the melted sodium acetate trihydrate as a thermal conductivity enhancer, and the mixture was transferred to an oil bath and heated at the same temperature while stirring for 40 minutes to obtain a modified sodium acetate trihydrate phase change material.

[0056] 2) Take 4.8g of expanded graphite with a volume expansion ratio of 200 to 300 times and disperse it in 200mL of 20% ethanol aqueous solution by mass, let it stand at room temperature for 4h to obtain an expanded graphite mixture; use ammonia water to adjust 50mL of 0.2 mol / L aluminum nitrate nonahydrate solution to pH = 7 to obtain a white suspension, and ultrasonically vibrate for 30 min; heat the expanded graphite mixture to 80℃, then add the white suspension dropwise to the expanded graphite mixture within 5min, and let it stand at room temperature for 20h; filter and wash the expanded graphite attached with Al(OH)3 3 times, and dry it at 80℃ for 12h; place it in a muffle furnace and calcine it at 400℃ for 2h to obtain alumina-modified expanded graphite.

[0057] 3) 20.2 g of modified sodium acetate trihydrate and 2.0 g of alumina-modified expanded graphite were mixed, stirred at 70 °C for 3 min and kept warm for 30 min; the stirring and keeping warm steps were repeated three times to obtain a modified sodium acetate trihydrate / alumina-modified expanded graphite composite phase change material.

[0058] According to the test, the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material of this embodiment has a phase change temperature of 59.63° C. and a phase change enthalpy of 243.40 J / g.

[0059] Embodiment 4,

[0060] This embodiment provides a method for preparing a modified expanded graphite composite phase change material, which specifically comprises the following steps:

[0061] 1) 20 g of sodium acetate trihydrate was placed in an oven and heated to 80 °C to melt, and then 0.2 g of silicon carbide was added to the melted sodium acetate trihydrate as a thermal conductivity enhancer, and the mixture was transferred to an oil bath and heated at the same temperature while stirring for 35 min to obtain a modified sodium acetate trihydrate phase change material.

[0062] 2) Take 4.8g of expanded graphite with a volume expansion ratio of 200 to 300 times and disperse it in 200mL of 20% ethanol aqueous solution, let it stand at room temperature for 3h to obtain an expanded graphite mixture; use ammonia water to adjust 40mL of 0.2 mol / L aluminum nitrate nonahydrate solution to pH=7 to obtain a white suspension, and ultrasonically vibrate for 20min; heat the expanded graphite mixture to 80℃, then add the white suspension dropwise to the expanded graphite mixture within 5min, and let it stand at room temperature for 24h; filter and wash the expanded graphite attached with Al(OH)3 3 times, and dry it at 80℃ for 12h; place it in a muffle furnace and calcine it at 500℃ for 2h to obtain alumina-modified expanded graphite.

[0063] 3) 20.2 g of modified sodium acetate trihydrate and 2.8 g of alumina-modified expanded graphite were mixed, stirred at 80°C for 3 min and kept warm for 30 min; the stirring and keeping warm steps were repeated three times to obtain a modified sodium acetate trihydrate / alumina-modified expanded graphite composite phase change material.

[0064] According to tests, the modified sodium acetate trihydrate / alumina modified expanded graphite composite phase change material of this embodiment has a phase change temperature of 58.92° C. and a phase change enthalpy of 213.90 J / g.

[0065] Comparative ratio,

[0066] This comparative example comprises the following steps:

[0067] 1) 20 g of sodium acetate trihydrate was placed in an oven and heated to 80°C to melt, and then 0.2 g of silicon carbide was added to the melted sodium acetate trihydrate as a thermal conductivity enhancer, and the mixture was transferred to an oil bath and heated at the same temperature while stirring for 30 minutes to obtain a modified sodium acetate trihydrate phase change material.

[0068] 2) Take 4.8 g of expanded graphite with a volume expansion ratio of 200 to 300 times and disperse it in 200 mL of 20% ethanol aqueous solution by mass, let it stand at room temperature for 3 hours to obtain an expanded graphite mixed solution; filter and wash, and dry it at 80°C for 12 hours to obtain dispersed expanded graphite.

[0069] 3) 20.2 g of modified sodium acetate trihydrate and 2.4 g of expanded graphite were mixed, stirred at 80° C. for 3 min and kept warm for 30 min; the stirring and keeping warm steps were repeated three times to obtain a modified sodium acetate trihydrate / expanded graphite composite phase change material.

[0070] The contact angle between the unmodified expanded graphite and water in step 2) of this comparative example is 85°. Fig. 9 shown.

[0071] The phase change temperature of the composite phase change material finally prepared in this comparative example is 58.50 °C, and the phase change enthalpy is 227.73 J / g; after 50 cycles, the phase change temperature is 58.15 °C, and the phase change enthalpy is 123.26 J / g. Fig.10 shown.

[0072] By comparing this comparative example with Example 1, it can be found that: the supporting material of this comparative example is unmodified expanded graphite, because its compatibility with the modified sodium acetate trihydrate phase change material matrix is ​​general, and its ability to load the phase change material is limited. After the cycle, the phase change enthalpy value is significantly reduced; while the supporting material of Example 1 is expanded graphite modified with alumina, and its compatibility with the modified sodium acetate trihydrate phase change material matrix is ​​improved, and the phase change enthalpy value is not significantly reduced after the cycle.

[0073] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modified expanded graphite composite phase change material, characterized in that: The composite phase change material comprises: Modified sodium acetate trihydrate and modified expanded graphite, wherein: Modified sodium acetate trihydrate is used as the main material of the phase change material, and modified expanded graphite is used as the carrier material of the phase change material.

2. The modified expanded graphite composite phase change material according to claim 1, characterized in that: The modified sodium acetate trihydrate is sodium acetate trihydrate modified by nano silicon carbide.

3. The modified expanded graphite composite phase change material according to claim 1, characterized in that: The modified expanded graphite is expanded graphite modified by aluminum oxide.

4. The modified expanded graphite composite phase change material according to claim 1, characterized in that: The mass ratio of the modified sodium acetate trihydrate to the modified expanded graphite is 100:12 to 100:

14.

5. The modified expanded graphite composite phase change material according to claim 1, characterized in that: The volume expansion multiple of the modified expanded graphite is 200 to 300 times.

6. The modified expanded graphite composite phase change material according to claim 2, characterized in that: The mass ratio of the sodium acetate trihydrate to the nano-silicon carbide is 100:

1.

7. A method for preparing a modified expanded graphite composite phase change material, characterized in that: The method for preparing the modified expanded graphite composite phase change material according to any one of claims 1 to 6 comprises the following steps: S100, preparing a modified sodium acetate trihydrate main material, placing the sodium acetate trihydrate in an oven and heating it until it melts, then adding silicon carbide as a thermal conductivity enhancer to the melted sodium acetate trihydrate, stirring for 30 to 40 minutes, and cooling to obtain silicon carbide modified sodium acetate trihydrate; S200, preparing alumina modified expanded graphite, dispersing the expanded graphite in a solvent, and standing at room temperature for 3-5 hours to obtain an expanded graphite mixed solution, Then, the pH value of the aluminum nitrate nonahydrate solution was adjusted to obtain an Al(OH)3 suspension, and the suspension was placed in an ultrasonic cleaning machine for 20 to 30 minutes. The expanded graphite mixed solution is heated to 80° C., and the suspension is added dropwise to the expanded graphite mixed solution within 5 minutes. After the addition is completed, the mixture is allowed to stand at room temperature for 12 to 24 hours to allow the expanded graphite to fully absorb Al(OH)3; After standing, the expanded graphite mixture is filtered, and the filtered product is washed 3 to 5 times. After washing, it is dried at 70 to 80° C. for 12 to 18 hours; at the same time, it is placed in a muffle furnace and calcined at 400 to 500° C. for 2 hours to prepare alumina-modified expanded graphite.

8. The method for preparing the modified expanded graphite composite phase change material according to claim 7, characterized in that: The preparation method further comprises: S300, mixing the prepared modified sodium acetate trihydrate and alumina modified expanded graphite, stirring at 70-80° C. for 3 min and keeping the mixture warm for 30 min; The stirring and heat preservation steps were repeated three times to obtain a modified sodium acetate trihydrate / aluminum oxide modified expanded graphite composite phase change material.

9. The method for preparing the modified expanded graphite composite phase change material according to claim 7, characterized in that: The step of adjusting the pH value of the aluminum nitrate nonahydrate solution comprises: adjusting the pH value of the aluminum nitrate nonahydrate solution to pH = 6-7 using aqueous ammonia.

10. An application of a modified expanded graphite composite phase change material, characterized in that: Application of the composite phase change material prepared by the modified expanded graphite composite phase change material according to any one of claims 1 to 6 or the modified expanded graphite composite phase change material preparation method according to any one of claims 7 to 9 in medium and low temperature industrial waste heat recovery.

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