A composite phase change thermal storage material and its preparation method

Abstract

This invention provides a composite phase change thermal energy storage material and its preparation method, belonging to the technical field of phase change thermal energy storage materials. This invention utilizes nitrogen quantum dot-doped porous carbon aerogel as a support carrier, acidified paraffin as a phase change thermal energy storage agent, and incorporates titanium dioxide-carbon nanotube composite materials to effectively improve the latent heat of phase change and thermal conductivity of the composite phase change thermal energy storage material, while ensuring good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of phase change thermal energy storage technology, specifically relating to a composite phase change thermal energy storage material and its preparation method. Background Technology

[0002] Phase change materials (PCMs) are capable of reversible phase transitions during isothermal phase transitions, absorbing and releasing large amounts of heat energy, thus slowing down the rate of temperature rise / fall due to thermal changes. PCMs store energy through phase transitions during heat exchange, absorbing or releasing large amounts of latent heat within a specific temperature range. This characteristic allows PCMs to effectively store and release heat energy, making them valuable in various fields such as building energy conservation, solar thermal utilization, electronic product heat dissipation, and transportation.

[0003] Chinese patent (publication number CN117025177A) discloses a composite phase change thermal storage material and its preparation method. This invention first uses directional freezing technology to prepare ordered copper / carbon nanotube aerogels as a support material. Then, sodium acetate / potassium acetate, uniformly mixed and dissolved in a specific ratio, is composited with the copper / carbon nanotube aerogels. The composite phase change thermal storage material prepared by this method exhibits low supercooling. The porous aerogel effectively inhibits phase separation and prevents leakage during solid-liquid circulation by adsorbing the phase change material. It also has a high thermal conductivity, reducing the need for large-area heat exchange tubes and lowering the size and cost of the phase change thermal storage device. However, this patented technology still does not solve the problems of low latent heat of phase change, low thermal conductivity, and poor cycle stability found in existing composite phase change thermal storage materials, thus limiting their application.

[0004] Therefore, how to modify the phase change thermal storage agent of composite phase change thermal storage materials, and introduce porous carriers and high thermal conductivity components to effectively improve the latent heat of phase change and thermal conductivity of the materials, while ensuring good cycle stability, has become a key area that needs to be tackled. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite phase change thermal storage material and its preparation method, thereby solving the problems of low latent heat of phase change, low thermal conductivity, and poor cycle stability of existing composite phase change thermal storage materials.

[0006] This invention uses nitrogen quantum dot-doped porous carbon aerogel as a support carrier, acidified paraffin as a phase change heat storage agent, and adds titanium dioxide-carbon nanotube composite material to work together to effectively improve the latent heat of phase change and thermal conductivity of the composite phase change heat storage material, while ensuring good cycle stability.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a composite phase change thermal storage material, comprising the following steps:

[0009] Step S1: By weight, 15-20 parts of carbon aerogel and 5-10 parts of carbon nanotubes are mixed evenly and placed into a vacuum heating furnace cavity. Heat treatment is carried out under a nitrogen atmosphere. After cooling, a carbon aerogel mixture is obtained.

[0010] Step S2: By weight, 20-30 parts of the carbon aerogel mixture are combined with 50-60 parts of the phase change thermal storage agent by vacuum impregnation to obtain a composite phase change thermal storage material.

[0011] The carbon aerogel is a nitrogen quantum dot-doped porous carbon aerogel.

[0012] The preparation method of the nitrogen quantum dot-doped porous carbon aerogel includes: adding 3-5 parts by weight of acetic acid to 180-200 parts of deionized water, mixing evenly, adding 1-3 parts of chitosan and stirring for 10-20 min, then adding 6-8 parts of graphene oxide and 2-4 parts of nitrogen quantum dots, stirring for 2-4 h to obtain a dispersion; freezing the dispersion at -4℃ for 20-24 h, and then freeze-drying to obtain nitrogen quantum dot-doped porous carbon aerogel.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] As a preferred technical solution of the present invention, the method for preparing nitrogen quantum dots includes: dissolving 2-4 parts by weight of 2-azidoimidazole in 12-16 parts by weight of tetrahydrofuran, then adding 3-4 parts by weight of polyethyleneimine, and reacting at 60-65°C for 20-24 hours; after the reaction is completed, adding 1-2 parts by weight of deionized water, evaporating the tetrahydrofuran by rotary evaporation, extracting with ethyl acetate, dialysis of the aqueous phase solution for 8-10 hours, filtering with a filter membrane, and freeze-drying the filtrate to obtain nitrogen quantum dots.

[0015] Preferably, the freeze-drying conditions are: freeze-drying temperature of -10℃ to -20℃ and freeze-drying time of 40 to 48 hours.

[0016] The porous structure of nitrogen quantum dot-doped porous carbon aerogel can effectively support phase change materials and prevent their loss in the molten state. At the same time, the doping of nitrogen quantum dots can change the microstructure of the phase change material, enhance the intermolecular interaction forces, and thus improve the overall stability of the material. In addition, nitrogen quantum dots can occupy vacancies or interstitial sites in the material, reduce defects, and thus increase cycle stability.

[0017] As a preferred embodiment of the present invention, the carbon nanotubes in step S1 are titanium dioxide-carbon nanotube composite materials; the preparation method of the titanium dioxide-carbon nanotube composite material includes: weighing 30-40 parts by weight of carbon nanotubes, 10-15 parts by weight of titanium dioxide, 8-10 parts by weight of methyltrioctylammonium chloride, 3-5 parts by weight of 2-methyl-2,4-pentanediol and 1-2 parts by weight of polyethylene glycol, mixing them evenly, and then ball milling and dispersing them for 28-30 hours to obtain a mixed slurry, and placing the mixed slurry in a nitrogen atmosphere. The mixture is treated in an atmospheric atmosphere at 780–800°C for 10–12 hours, cooled to room temperature, dried, pulverized, and ground to obtain a mixed powder. 80–100 parts of the mixed powder are added to 180–200 parts of deionized water and stirred for 1–2 hours. Then, 5–8 parts of 3-aminopropyltriethoxysilane are added and stirred for 1–2 hours. After the reaction is completed, the mixture is dried at 110–120°C for 12–14 hours and ground to obtain a titanium dioxide-carbon nanotube composite material.

[0018] Carbon nanotubes have very high thermal conductivity, which can enhance the thermal conductivity of composite materials, ensure uniform heat distribution during thermal storage, and reduce thermal hysteresis during thermal storage. At the same time, by introducing titanium dioxide through modification treatment, more heat conduction paths can be formed, improving the efficiency of heat transfer. The combined effect of carbon nanotubes and titanium dioxide effectively improves the thermal conductivity of composite phase change thermal storage materials.

[0019] Preferably, the heat treatment temperature in step S1 is 800–900°C, and the treatment time is 1–2 hours.

[0020] As a preferred technical solution of the present invention, the phase change heat storage agent in step S2 is paraffin wax; the paraffin wax is acidified paraffin wax; the preparation method of the acidified paraffin wax includes: adding 100-120 parts by weight of paraffin wax into a reaction vessel equipped with a stirrer and heating it to 170-175°C; then adding 20-25 parts of maleic anhydride and 10-15 parts of boric acid, stirring for 1-2 hours under nitrogen protection, then adding 8-10 parts of benzoyl peroxide, controlling the temperature at 175-180°C, reacting for 1-3 hours, and obtaining acidified paraffin wax after purification.

[0021] Acidification of paraffin can introduce polar groups such as carboxyl groups into the paraffin molecules. These polar groups can increase the intermolecular interaction forces, improve crystallinity and order, thereby increasing the latent heat of phase change in composite phase change thermal storage materials.

[0022] Preferably, the vacuum degree of the vacuum impregnation treatment in step S2 is 0.07-0.09 MPa, the temperature is 50-100℃, and the time is 2-4 h.

[0023] In a second aspect, the present invention provides a composite phase change thermal storage material prepared by the method described in the first aspect.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) This invention uses acidified paraffin as a phase change heat storage agent. The paraffin is modified by maleic anhydride and boric acid, and polar groups such as carboxyl groups are introduced. The polar groups increase the interaction force between paraffin molecules, improve the crystallinity and order, and effectively enhance the latent heat of phase change of the composite phase change heat storage material.

[0026] (2) In the titanium dioxide-carbon nanotube composite material of the present invention, carbon nanotubes can ensure uniform heat distribution during the heat storage process and reduce thermal hysteresis during the heat storage process. Titanium dioxide can form more heat conduction paths and improve the efficiency of heat transfer. The two work together to effectively improve the thermal conductivity of the composite phase change heat storage material. At the same time, the boron element in the acidified paraffin combines with the nitrogen quantum dots in the nitrogen quantum doped porous carbon aerogel, further improving the thermal conductivity of the material.

[0027] (3) The nitrogen quantum dot-doped porous carbon aerogel of the present invention changes the microstructure of the phase change material by introducing nitrogen quantum dots, enhances the intermolecular interaction force, and at the same time, nitrogen quantum dots effectively occupy the interstitial positions in the material and reduce defects, thereby improving the cycle stability; in addition, the amino groups contained in the titanium dioxide-carbon nanotube composite material will combine with the groups in the acidified paraffin to form a network interconnection structure, further improving the cycle stability of the material.

[0028] (4) The carbon aerogel with micron-sized pores of the present invention is beneficial to the phase change process of the phase change heat storage agent. The carbon nanotubes have high thermal conductivity, which ensures uniform heat distribution during the heat storage process, while enhancing the strength and light absorption capacity of the composite material. The combination of carbon aerogel and carbon nanotubes can improve the thermal response speed of the phase change material and increase its thermal stability. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] The sources of some components in the examples and comparative examples are as follows:

[0031] Carbon aerogel, item number 002, purchased from Tianjin Deruifengkai New Material Technology Co., Ltd.

[0032] Carbon nanotubes, item number Pas1004, purchased from Hongna New Materials Technology Co., Ltd.

[0033] Paraffin wax, product number M5310, was purchased from Anhui Zesheng Technology Co., Ltd.

[0034] 2-Azide imidazole, CAS No. 56751-68-9, purchased from Tianjin Yankai Technology Co., Ltd.;

[0035] Tetrahydrofuran, CAS No. 109-99-9, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0036] Polyethyleneimine, product number E107079, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0037] Ethyl acetate, CAS No. 141-78-6, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0038] Acetic acid, CAS No. 64-19-7, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] Chitosan, product number KJT01, was purchased from Xi'an Shizeyuan Biotechnology Co., Ltd.

[0040] Graphene oxide, product number DN-20DY, purchased from Zhejiang Zhitai Nano-Micro New Materials Co., Ltd.

[0041] Titanium dioxide, product number R-996, purchased from Dongguan Wohai Trading Co., Ltd.

[0042] Methyltrioctylammonium chloride, CAS No. 5137-55-3, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0043] 2-Methyl-2,4-pentanediol, CAS No. 107-41-5, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] Polyethylene glycol, product number PA73288, was purchased from Shanghai Chuangsai Technology Co., Ltd.

[0045] 3-Aminopropyltriethoxysilane, CAS No. 919-30-2, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0046] Maleic anhydride, CAS No. 108-31-6, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0047] Boric acid, CAS No. 10043-35-3, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0048] Benzoyl peroxide, CAS No. 94-36-0, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0049] Preparation of nitrogen quantum dots: 4 parts by weight of 2-azidoimidazole were dissolved in 16 parts of tetrahydrofuran, and then 4 parts of polyethyleneimine were added. The mixture was reacted at 60°C for 24 h. After the reaction was completed, 2 parts of deionized water were added, the tetrahydrofuran was evaporated by rotary evaporation, and then extracted with ethyl acetate. The aqueous solution was dialyzed for 8-10 h, filtered through a filter membrane, and the filtrate was freeze-dried (freeze-drying temperature: -10°C, freeze-drying time: 48 h) to obtain nitrogen quantum dots.

[0050] Preparation of titanium dioxide-carbon nanotube composite material: 40 parts by weight of carbon nanotubes, 15 parts by weight of titanium dioxide, 10 parts by weight of methyltrioctylammonium chloride, 5 parts by weight of 2-methyl-2,4-pentanediol and 2 parts by weight of polyethylene glycol were weighed and mixed evenly. The mixture was then ball-milled and dispersed for 30 hours to obtain a mixed slurry. The mixed slurry was placed in a nitrogen atmosphere and treated at 800°C for 10 hours. After cooling to room temperature, it was dried, pulverized and ground to obtain a mixed powder. 100 parts of the mixed powder were added to 200 parts of deionized water and stirred for 2 hours. Then, 8 parts of 3-aminopropyltriethoxysilane were added and stirred for 2 hours. After the reaction was completed, the mixture was dried at 120°C for 12 hours and ground to obtain the titanium dioxide-carbon nanotube composite material.

[0051] Preparation of acidified paraffin: 120 parts by weight of paraffin were added to a reaction vessel equipped with a stirrer and heated to 175°C; then 25 parts of maleic anhydride and 15 parts of boric acid were added, and the mixture was stirred for 2 hours under nitrogen protection. Then 10 parts of benzoyl peroxide were added, and the reaction was carried out at 180°C for 3 hours. After purification, acidified paraffin was obtained.

[0052] Example 1

[0053] This embodiment provides a method for preparing a composite phase change thermal storage material, including the following steps:

[0054] The preparation method of nitrogen quantum dot-doped porous carbon aerogel includes: adding 5 parts by weight of acetic acid to 200 parts of deionized water, mixing evenly, adding 3 parts of chitosan and stirring for 20 min, then adding 8 parts of graphene oxide and 4 parts of nitrogen quantum dots, stirring for 4 h to obtain a dispersion; freezing the dispersion at -4℃ for 24 h, and then freeze-drying to obtain nitrogen quantum dot-doped porous carbon aerogel.

[0055] Step S1: By weight, 20 parts of nitrogen quantum dot-doped porous carbon aerogel and 10 parts of titanium dioxide-carbon nanotube composite material are mixed evenly and placed in a vacuum heating furnace cavity for heat treatment in a nitrogen atmosphere (temperature is 900℃, time is 1h). After cooling, carbon aerogel mixture is obtained.

[0056] Step S2: By weight, 30 parts of the carbon aerogel mixture and 60 parts of acidified paraffin are combined by vacuum impregnation treatment (vacuum degree of 0.09MPa, temperature of 100℃, time of 2h) to obtain composite phase change thermal storage material.

[0057] Example 2

[0058] This embodiment provides a method for preparing a composite phase change thermal storage material, including the following steps:

[0059] The preparation method of nitrogen quantum dot-doped porous carbon aerogel includes: adding 3 parts by weight of acetic acid to 180 parts of deionized water, mixing evenly, adding 1 part of chitosan and stirring for 10 min, then adding 6 parts of graphene oxide and 2 parts of nitrogen quantum dots, stirring for 2 h to obtain a dispersion; freezing the dispersion at -4℃ for 20 h, and then freeze-drying to obtain nitrogen quantum dot-doped porous carbon aerogel.

[0060] Step S1: By weight, 15 parts of nitrogen quantum dot-doped porous carbon aerogel and 5 parts of titanium dioxide-carbon nanotube composite material are mixed evenly and placed in a vacuum heating furnace cavity for heat treatment in a nitrogen atmosphere (temperature is 800℃, time is 2h). After cooling, carbon aerogel mixture is obtained.

[0061] Step S2: By weight, 20 parts of the carbon aerogel mixture and 50 parts of acidified paraffin are combined by vacuum impregnation treatment (vacuum degree of 0.07MPa, temperature of 50℃, time of 4h) to obtain composite phase change thermal storage material.

[0062] Example 3

[0063] This embodiment provides a method for preparing a composite phase change thermal storage material, including the following steps:

[0064] The preparation method of nitrogen quantum dot-doped porous carbon aerogel includes: adding 4 parts by weight of acetic acid to 190 parts of deionized water, mixing evenly, adding 2 parts of chitosan and stirring for 15 min, then adding 7 parts of graphene oxide and 3 parts of nitrogen quantum dots, stirring for 3 h to obtain a dispersion; freezing the dispersion at -4℃ for 22 h, and then freeze-drying to obtain nitrogen quantum dot-doped porous carbon aerogel.

[0065] Step S1: By weight, 18 parts of nitrogen quantum dot-doped porous carbon aerogel and 6 parts of titanium dioxide-carbon nanotube composite material are mixed evenly and placed in a vacuum heating furnace cavity for heat treatment under nitrogen atmosphere (temperature 850℃, time 2h). After cooling, carbon aerogel mixture is obtained.

[0066] Step S2: By weight, 25 parts of the carbon aerogel mixture and 55 parts of acidified paraffin are combined by vacuum impregnation treatment (vacuum degree of 0.08MPa, temperature of 80℃, time of 3h) to obtain composite phase change thermal storage material.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon aerogel is used instead of nitrogen quantum dot-doped porous carbon aerogel, commercially available carbon nanotubes are used instead of titanium dioxide-carbon nanotube composite material, and commercially available paraffin wax is used instead of acidified paraffin wax.

[0069] Comparative Example 2

[0070] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon nanotubes are used instead of titanium dioxide-carbon nanotube composite materials, and commercially available paraffin wax is used instead of acidified paraffin wax.

[0071] Comparative Example 3

[0072] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon aerogel is used instead of nitrogen quantum dot-doped porous carbon aerogel, and commercially available paraffin wax is used instead of acidified paraffin wax.

[0073] Comparative Example 4

[0074] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon aerogel is used instead of nitrogen quantum dot-doped porous carbon aerogel, and commercially available carbon nanotubes are used instead of titanium dioxide-carbon nanotube composite materials.

[0075] Comparative Example 5

[0076] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon aerogel is used instead of nitrogen quantum dot-doped porous carbon aerogel.

[0077] Comparative Example 6

[0078] This comparative example provides a method for preparing a composite phase change thermal storage material. The difference from Example 1 is that commercially available carbon nanotubes are used instead of the titanium dioxide-carbon nanotube composite material.

[0079] Comparative Example 7

[0080] This comparative example provides a method for preparing a composite phase change thermal storage material, which differs from Example 1 in that commercially available paraffin wax is used instead of acidified paraffin wax.

[0081] The properties of the composite phase change thermal storage materials prepared in the above embodiments and comparative examples were tested as follows:

[0082] Phase change latent heat test: The test was conducted using a synchronous thermal analyzer (TGA / DSC 3+ type, Mettler Toledo GmbH, Switzerland). 10 mg of the composite phase change heat storage material prepared in the examples and comparative examples was placed in a crucible and linearly heated / cooled at a rate of 2 °C / min under a nitrogen atmosphere with a flow rate of 5 mL / min. The temperature range was 30–120 °C. DSC curves were obtained and the latent heat of phase change was calculated using the built-in formula of the instrument.

[0083] Thermal conductivity test: The test was conducted using a thermal constant analyzer (TPS2500, Hot Disk GmbH, Sweden). 0.5g of the composite phase change thermal storage material prepared in the examples and comparative examples was pressed into a disc with a diameter of 12.7mm and a thickness of 5mm under a pressure of 8MPa using a tablet press. The probe was clamped in the middle of the phase change material disc at room temperature. The probe model was 5501. The test time was set to 20s and the power was set to 20mW. The thermal conductivity was obtained after measurement.

[0084] Cyclic stability test: The composite phase change thermal storage materials prepared in the examples and comparative examples were used as samples before the cyclic test. The composite phase change thermal storage materials prepared in the examples and comparative examples were placed in a 90℃ constant temperature drying oven and heated for 2 hours. After being taken out, they were naturally cooled to room temperature. The above operation process was repeated 100 times to obtain the samples after the cyclic test. The samples before the cyclic test and the samples after the cyclic test were tested using a synchronous thermal analyzer (TGA / DSC 3+ type, Mettler Toledo GmbH, Switzerland). The phase change enthalpy change rate was obtained by comparing the curves of the two tests.

[0085] The test data is shown in Table 1:

[0086] Table 1 Performance Test Results

[0087] Latent heat of phase transition (kJ / kg) Thermal conductivity (W / (m·K)) Phase transition enthalpy change rate (%) Example 1 223.88 28.75 2.38 Example 2 221.75 28.69 2.51 Example 3 222.82 28.71 2.44 Comparative Example 1 206.03 21.28 5.51 Comparative Example 2 208.45 21.32 4.12 Comparative Example 3 209.41 24.55 5.34 Comparative Example 4 219.72 21.28 5.28 Comparative Example 5 219.85 24.58 4.13 Comparative Example 6 219.93 24.61 4.11 Comparative Example 7 210.08 24.59 4.12

[0088] As can be seen from the above, the present invention uses nitrogen quantum dot-doped porous carbon aerogel as a support, acidified paraffin as a phase change heat storage agent, and adds titanium dioxide-carbon nanotube composite material to obtain composite phase change heat storage material (Examples 1 to 3). Its latent heat of phase change is 221.75 to 223.88 kJ / kg, thermal conductivity is 28.69 to 28.75 W / (m·K), and phase change enthalpy change rate is 2.38 to 2.51%.

[0089] Compared to Example 1, using commercially available carbon aerogel instead of nitrogen quantum dot-doped porous carbon aerogel, using commercially available carbon nanotubes instead of titanium dioxide-carbon nanotube composite material, and using commercially available paraffin wax instead of acidified paraffin wax resulted in a decrease in latent heat of phase change, a decrease in thermal conductivity, and a increase in the rate of change of enthalpy of phase change (Comparative Example 1); compared to Example 1, using commercially available carbon nanotubes instead of titanium dioxide-carbon nanotube composite material and using commercially available paraffin wax instead of acidified paraffin wax resulted in a decrease in latent heat of phase change, a decrease in thermal conductivity, and a increase in the rate of change of enthalpy of phase change (Comparative Example 2); compared to Example 1, using commercially available carbon aerogel instead of nitrogen quantum dot-doped porous carbon aerogel and using commercially available paraffin wax instead of acidified paraffin wax resulted in a decrease in latent heat of phase change, a decrease in thermal conductivity, and a increase in the rate of change of enthalpy of phase change (Comparative Example 2); compared to Example 1, using commercially available carbon aerogel instead of nitrogen quantum dot-doped porous carbon aerogel and using commercially available paraffin wax instead of acidified paraffin wax resulted in a decrease in latent heat of phase change, a decrease in thermal conductivity, and a increase in the rate of change of enthalpy of phase change (Comparative Example 2). Comparative Example 3); Compared with Example 1, using commercially available carbon aerogel instead of nitrogen quantum dot-doped porous carbon aerogel and using commercially available carbon nanotubes instead of titanium dioxide-carbon nanotube composite material resulted in a decrease in thermal conductivity and an increase in the rate of change of enthalpy of phase transition (Comparative Example 4); Compared with Example 1, using commercially available carbon aerogel instead of nitrogen quantum dot-doped porous carbon aerogel resulted in a decrease in thermal conductivity and an increase in the rate of change of enthalpy of phase transition (Comparative Example 5); Compared with Example 1, using commercially available carbon nanotubes instead of titanium dioxide-carbon nanotube composite material resulted in a decrease in thermal conductivity and an increase in the rate of change of enthalpy of phase transition (Comparative Example 6); Compared with Example 1, using commercially available paraffin instead of acidified paraffin resulted in a decrease in latent heat of phase transition, a decrease in thermal conductivity, and an increase in the rate of change of enthalpy of phase transition (Comparative Example 7).

[0090] In summary, this invention effectively improves the latent heat of phase change and thermal conductivity of composite phase change thermal storage materials by using nitrogen quantum dot-doped porous carbon aerogel as a support, acidified paraffin as a phase change heat storage agent, and adding titanium dioxide-carbon nanotube composite materials, while ensuring good cycle stability.

[0091] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention fall within the protection and disclosure scope of this invention.

Claims

1. A method for preparing a composite phase change thermal storage material, characterized in that, Includes the following steps: Step S1: By weight, mix 15-20 parts of carbon aerogel and 5-10 parts of carbon nanotubes evenly and place them into a vacuum heating furnace cavity. Heat treat them under a nitrogen atmosphere and obtain a carbon aerogel mixture after cooling. Step S2: By weight, 20-30 parts of the carbon aerogel mixture are combined with 50-60 parts of the phase change thermal storage agent by vacuum impregnation to obtain a composite phase change thermal storage material. The carbon aerogel is a nitrogen quantum dot-doped porous carbon aerogel. The preparation method of the nitrogen quantum dot-doped porous carbon aerogel includes: adding 3-5 parts by weight of acetic acid to 180-200 parts of deionized water, mixing evenly, adding 1-3 parts of chitosan and stirring for 10-20 min, then adding 6-8 parts of graphene oxide and 2-4 parts of nitrogen quantum dots, stirring for 2-4 h to obtain a dispersion; freezing the dispersion at -4℃ for 20-24 h, and then freeze-drying to obtain nitrogen quantum dot-doped porous carbon aerogel; The carbon nanotubes are titanium dioxide-carbon nanotube composite materials. The preparation method of the titanium dioxide-carbon nanotube composite material includes: weighing 30-40 parts by weight of carbon nanotubes, 10-15 parts by weight of titanium dioxide, 8-10 parts by weight of methyltrioctylammonium chloride, 3-5 parts by weight of 2-methyl-2,4-pentanediol and 1-2 parts by weight of polyethylene glycol, mixing them evenly, and then ball milling and dispersing them for 28-30 hours to obtain a mixed slurry. The mixed slurry is placed in a nitrogen atmosphere and treated at 780-800℃ for 10-12 hours. After cooling to room temperature, it is dried, pulverized and ground to obtain a mixed powder. 80-100 parts of the mixed powder are added to 180-200 parts of deionized water and stirred for 1-2 hours. Then 5-8 parts of 3-aminopropyltriethoxysilane are added and stirred for 1-2 hours. After the reaction is completed, it is dried at 110-120℃ for 12-14 hours and ground to obtain the titanium dioxide-carbon nanotube composite material. The phase change heat storage agent is paraffin wax; the paraffin wax is acidified paraffin wax; the preparation method of the acidified paraffin wax includes: adding 100-120 parts by weight of paraffin wax into a reaction vessel equipped with a stirrer and heating it to 170-175°C; then adding 20-25 parts of maleic anhydride and 10-15 parts of boric acid, stirring for 1-2 hours under nitrogen protection, then adding 8-10 parts of benzoyl peroxide, controlling the temperature at 175-180°C, reacting for 1-3 hours, and obtaining acidified paraffin wax after purification.

2. The method for preparing the composite phase change thermal storage material according to claim 1, characterized in that, The method for preparing the nitrogen quantum dots includes: dissolving 2-4 parts by weight of 2-azidoimidazole in 12-16 parts by weight of tetrahydrofuran, then adding 3-4 parts by weight of polyethyleneimine, and reacting at 60-65°C for 20-24 hours; after the reaction is completed, adding 1-2 parts by weight of deionized water, evaporating the tetrahydrofuran by rotary evaporator, extracting with ethyl acetate, dialysis of the aqueous phase solution for 8-10 hours, filtering with a filter membrane, and freeze-drying the filtrate to obtain nitrogen quantum dots.

3. The method for preparing the composite phase change thermal storage material according to claim 2, characterized in that, The freeze-drying conditions are as follows: freeze-drying temperature is -10℃ to -20℃, and freeze-drying time is 40 to 48 hours.

4. The method for preparing the composite phase change thermal storage material according to claim 1, characterized in that, The heat treatment in step S1 is carried out at a temperature of 800~900℃ for 1~2 hours.

5. The method for preparing the composite phase change thermal storage material according to claim 1, characterized in that, The vacuum degree of the vacuum impregnation treatment in step S2 is 0.07~0.09MPa, the temperature is 50~100℃, and the time is 2~4h.

6. A composite phase change thermal storage material, characterized in that, Prepared by the method according to any one of claims 1 to 5.