A phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof

Abstract

The application belongs to the technical field of thermal energy storage, and discloses a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof. A three-dimensional porous framework is constructed by polyvinyl alcohol, cellulose nanofiber and short fibers, the three-dimensional porous framework protects the phase change material, the phase change material takes nanosilica as a central core, octadecanol as an intermediate layer, and a mixture of polyvinyl alcohol and cellulose nanofiber as the outermost layer of protective shell, which not only ensures the integrity of the phase change material, but also prevents the leakage of high-temperature liquid phase change material. The preparation process is simple, can meet the needs of heat preservation and energy storage in a medium and low temperature environment, can be used for the interlayer of key equipment with a large temperature difference between the inside and outside environments, and the outer protective wall of important buildings, and has very high economic value and broad application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal energy storage, and more particularly relates to a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof. BACKGROUND

[0002] Fossil fuels have been the main heat energy source for a long time, and their limited reserves have become a bottleneck restricting sustainable development. Thermal energy storage technology is a key technology for sustainable energy utilization efficiency, and its importance is increasingly important in the development trend of global energy transformation. Thermal energy storage technology mainly includes three energy storage methods: latent heat storage, sensible heat storage and chemical heat storage. Among them, latent heat storage technology is simple to operate, safe and low in price, and is highly concerned. As the core part of latent heat storage technology, phase change energy storage materials play a crucial role in the process of thermal energy storage and release. Phase change energy storage materials can realize efficient conversion and storage of energy through the large amount of latent heat absorbed or released during phase change, which not only improves the overall efficiency of the energy system, but also provides strong support for stable supply and flexible scheduling of energy, and realizes sustainable green development. Among them, the phase change energy storage composite material of aerogel shows great application potential in many fields such as solar equipment, heat-insulating wearable fabrics, energy-saving buildings and heat preservation equipment in extremely cold areas.

[0003] However, phase change energy storage materials also face many challenges in practical application, the most prominent of which is the liquid leakage problem that may occur during phase change conversion, which directly affects its long-term stability and reliability. Chinese invention patent CN118667520A discloses a preparation method of an aerogel solid-liquid phase change composite foam material. First, a boron nitride sheet foam aerogel is prepared, and then a solid-liquid phase change material is filled into the pore network structure of the boron nitride sheet foam aerogel through melting or solution filling to obtain an aerogel solid-liquid phase change composite foam material. This method can fill the phase change material into the pore channel of the aerogel, but the phase change material will still leak in liquid state after softening.

[0004] Therefore, how to provide a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof is a technical problem that those skilled in the art need to solve. SUMMARY

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the application provides a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof. The process is simple, the phase change energy storage composite aerogel with a directional pore structure prepared has excellent mechanical properties, rich pore structure, good heat preservation performance and uniform distribution of phase change materials.

[0006] In order to achieve the above purpose, the application adopts the following technical solutions:

[0007] The phase change energy storage composite aerogel of the directional pore structure is characterized in that the raw materials include the following components in parts by weight: 0.5-2 parts of nano-silicon dioxide, 5-15 parts of octadecanol, 80-120 parts of polyvinyl alcohol aqueous solution, 0.1-0.2 parts of chopped fibers, 0.05-0.5 parts of modified boron nitride sheets, and 0.5-2 parts of cellulose nanofibers.

[0008] Preferably, the mass fraction of the polyvinyl alcohol aqueous solution is 10-40 wt%, and the cellulose nanofiber is a gel with a mass fraction of 1 wt%.

[0009] Preferably, the chopped fibers are selected from one or more of quartz fibers, carbon fibers, aramid fibers, and glass fibers, and the length of the chopped fibers is 0.2-2 mm.

[0010] Preferably, the modified boron nitride sheets are selected from one of hydroxylated, carboxylated, and aminated modified boron nitride sheets.

[0011] The application also provides a preparation method of the phase change energy storage composite aerogel of the directional pore structure.

[0012] (1) Disperse the nano-silicon dioxide and octadecanol into an ethanol solution, continuously stir, then evaporate at 80℃ for 12 h, grind after cooling, and obtain SiO2@C18 phase change materials;

[0013] (2) Mix the polyvinyl alcohol aqueous solution and the SiO2@C18 phase change materials, stir at room temperature, then slowly add acetic acid under vigorous stirring, stir for 1.5 h, add chopped fibers to obtain a mixed solution, drop 0.1M sodium hydroxide solution, adjust the pH value of the mixed solution to 8, and continue to stir to obtain a PVA@SiO2@C18 solution;

[0014] (3) Add the modified boron nitride sheets and cellulose nanofibers into deionized water, ball mill for 3 h to obtain a CNF / BN suspension emulsion; add the CNF / BN suspension emulsion into the PVA@SiO2@C18 solution, and continue to stir for 4 h to obtain a high-thermal-conductivity phase change solution;

[0015] (4) Remove the bubbles in the high-thermal-conductivity phase change solution by vacuum drying at 0.5 MPa, and then perform freeze-drying to obtain the phase change energy storage composite aerogel.

[0016] Preferably, the temperature of the stirring in step (1) is 80℃, and the time is 1-3 h.

[0017] Preferably, the mass ratio of the polyvinyl alcohol aqueous solution to the SiO2@C18 phase change materials in step (2) is 100:3-10.

[0018] Preferably, the stirring rate in step (2) is 400 r / min.

[0019] Preferably, after adjusting the pH value of the mixed solution to 8 in step (2), the stirring is continued for 2-6 h.

[0020] Preferably, the mass ratio of the CNF / BN suspension emulsion and the PVA@SiO2@C18 solution in step (3) is 1:6.

[0021] Preferably, the specific operation of the freeze-drying in step (4) is: directional freeze-drying for 72 h through liquid nitrogen, or first freezing for 24 h in a refrigerator, and then drying for 72 h in a freeze dryer after complete freezing.

[0022] According to the technical solution described above, compared with the prior art, the present application provides a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof, and has the following beneficial effects:

[0023] 1. The present application constructs a three-dimensional porous framework by polyvinyl alcohol, cellulose nanofiber and short fibers, and prepares a porous thermal insulation aerogel. The three-dimensional porous framework protects the phase change material, the phase change material has a central core body of nanosilica, an intermediate layer of octadecanol, and an outermost protective shell of mixed raw materials of polyvinyl alcohol and cellulose nanofiber, which not only ensures the integrity of the phase change material, but also prevents the leakage of high-temperature liquid phase change material.

[0024] 2. The present application adds modified boron nitride sheets to the energy storage composite aerogel, which increases the thermal conductivity between the phase change materials without affecting the lightweight thermal insulation performance of the overall aerogel. Polyvinyl alcohol, cellulose nanofiber and short fibers together give the aerogel excellent compression resistance and compression resilience.

[0025] 3. The preparation process of the present application is simple, can meet the needs of thermal insulation and energy storage in medium and low temperature environments, and can be used for key equipment interlayers with large temperature differences between the inside and outside environments, as well as important building outer protective walls, and has very high economic value and broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0027] Figure 1 Fig. a and b are structural schematic diagrams of the phase change energy storage composite aerogel and a phase change material obtained in Example 4.

[0028] Figure 2 Microstructure of the phase change energy storage composite aerogel obtained in Example 4.

[0029] Figure 3 Physical image of the phase change energy storage composite aerogel obtained in Example 4.

[0030] Figure 4 50% strain compression strength of the phase change energy storage composite aerogel obtained in Example 4.

[0031] Figure 5 Thermal insulation performance of the phase change energy storage composite aerogel obtained in Example 4. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0033] The cellulose nanofiber of the present application is purchased from Hu Zhou Shensixin New Material Technology Co., Ltd.; the length of the chopped fiber is 0.2-2 mm.

[0034] Example 1

[0035] A preparation method of a phase change energy storage composite aerogel with a directional pore structure, comprising the following steps:

[0036] (1) 1 g of nanosilica and 5 g of octadecanol are dispersed into 50 ml of an ethanol solution, continuously stirred at 80°C for 1 h, and then evaporated at 80°C for 12 h to obtain a large amount of flocculation, which is ground after cooling to obtain a SiO2@C18 phase change material;

[0037] (2) 100 g (15 wt%) of a polyvinyl alcohol aqueous solution and 10 g of the SiO2@C18 phase change material are mixed, stirred at 400 r / min for 0.5 h at room temperature, then 100 μL of acetic acid is slowly added under vigorous stirring, stirred for 1.5 h, then 0.1 g of chopped quartz fiber is added for continuous stirring, and 0.1 M sodium hydroxide solution is added dropwise to adjust the pH value of the mixed solution to 8, and continue to stir for 2 h to obtain a PVA@SiO2@C18 solution;

[0038] (3) 0.05 g of hydroxylated boron nitride sheet and 2 g (1 wt%) of cellulose nanofiber are added to 50 ml of deionized water, and ball-milled for 3 h to obtain a CNF / BN suspension emulsion; 10 g of the obtained CNF / BN suspension emulsion is added to 60 g of the PVA@SiO2@C18 solution, and continues to stir for 4 h to obtain a high-thermal-conductivity phase change solution;

[0039] (4) The high-thermal-conductivity phase change solution is first deaerated by vacuum drying oven at 0.5 MPa to remove bubbles, then frozen in a refrigerator for 24 h, and after complete freezing, freeze-dried by a freeze dryer for 72 h to obtain the phase change energy storage composite aerogel.

[0040] Example 2

[0041] A preparation method of a phase change energy storage composite aerogel with a directional pore structure, comprising the following steps:

[0042] (1) 1 g of nanosilica and 5 g of octadecanol are dispersed into 50 ml of an ethanol solution, continuously stirred at 80°C for 1 h, then evaporated at 80°C for 12 h, and after cooling, ground to obtain a SiO2@C18 phase change material;

[0043] (2) 100 g (15 wt%) of a polyvinyl alcohol aqueous solution and 10 g of the SiO2@C18 phase change material are mixed, stirred at 400 r / min at room temperature for 0.5 h, then 100 μL of acetic acid is slowly added under vigorous stirring, after stirring for 1.5 h, 0.15 g of short quartz fiber is added to continue stirring, and 0.1 M sodium hydroxide solution is added dropwise to adjust the pH value of the mixed solution to 8, and continue to stir for 2 h to obtain a PVA@SiO2@C18 solution;

[0044] (3) 0.05 g of hydroxylated boron nitride sheet and 2 g (1 wt%) of cellulose nanofiber are added to 50 ml of deionized water, and ball milled for 3 h to obtain a CNF / BN suspension emulsion; 10 g of the obtained CNF / BN suspension emulsion is added to 60 g of the PVA@SiO2@C18 solution, and continues to stir for 4 h to obtain a high-thermal-conductivity phase change solution;

[0045] (4) The high-thermal-conductivity phase change solution is deaerated by vacuum drying oven at 0.5 MPa to remove bubbles, and then subjected to directional freeze-drying in liquid nitrogen for 72 h to obtain the phase change energy storage composite aerogel with a directional pore structure.

[0046] Example 3

[0047] A preparation method of a phase change energy storage composite aerogel with a directional pore structure, comprising the following steps:

[0048] (1) 1 g of nanosilica and 10 g of octadecanol are dispersed into 50 ml of an ethanol solution, continuously stirred at 80°C for 1 h, then evaporated at 80°C for 12 h, and after cooling, ground to obtain a SiO2@C18 phase change material;

[0049] (2) 100 g (15 wt%) polyvinyl alcohol aqueous solution and 3 g SiO2@C18 phase change material were mixed, stirred at 400 r / min for 1 h at room temperature, then 100 μL acetic acid was slowly added under vigorous stirring, after stirring for 1.5 h, 0.2 g short quartz fiber was added, the pH value of the mixed solution was adjusted to 8 by dropwise adding 0.1 M sodium hydroxide solution, and stirring was continued for 4 h to obtain a PVA@SiO2@C18 solution;

[0050] (3) 0.1 g hydroxylated boron nitride sheet and 1 g (1 wt%) cellulose nanofiber were added to 50 ml deionized water, and ball milling was performed for 3 h to obtain a CNF / BN suspension emulsion, 10 g of the obtained CNF / BN suspension emulsion was added to 60 g of the PVA@SiO2@C18 solution, and stirring was continued for 4 h to obtain a high-thermal-conductivity phase change solution;

[0051] (4) The high-thermal-conductivity phase change solution was degassed by vacuumizing at 0.5 MPa in a vacuum oven, and then liquid nitrogen directional freeze-drying was performed for 72 h to obtain a phase change energy storage composite aerogel with a directional pore structure.

[0052] Example 4

[0053] A method for preparing a phase change energy storage composite aerogel with a directional pore structure, comprising the following steps:

[0054] (1) 1 g nano-silicon dioxide and 9 g octadecanol were dispersed into 40 ml ethanol solution, and continuous stirring was performed at 80°C for 1 h, then evaporation was performed at 80°C for 12 h, and grinding was performed after cooling to obtain a SiO2@C18 phase change material;

[0055] (2) 100 g (15 wt%) polyvinyl alcohol aqueous solution and 3 g SiO2@C18 phase change material were mixed, stirred at 400 r / min for 1 h at room temperature, then 100 μL acetic acid was slowly added under vigorous stirring, after stirring for 1.5 h, 0.15 g short quartz fiber was added, the pH value of the mixed solution was adjusted to 8 by dropwise adding 0.1 M sodium hydroxide solution, and stirring was continued for 4 h to obtain a PVA@SiO2@C18 solution;

[0056] (3) 0.1 g hydroxylated boron nitride sheet and 0.5 g (1 wt%) cellulose nanofiber were added to 50 ml deionized water, and ball milling was performed for 3 h to obtain a CNF / BN suspension emulsion; 10 g of the obtained CNF / BN suspension emulsion was added to 60 g of the PVA@SiO2@C18 solution, and stirring was continued for 4 h to obtain a high-thermal-conductivity phase change solution;

[0057] (4) The high-thermal-conductivity phase change solution was degassed by vacuumizing at 0.5 MPa in a vacuum oven, and then liquid nitrogen directional freeze-drying was performed for 72 h to obtain a phase change energy storage composite aerogel with a directional pore structure.

[0058] Comparative Example 1

[0059] A preparation method of a phase change energy storage composite aerogel, comprising the following steps:

[0060] (1) 1g of nanosilica and 5g of octadecanol are dispersed into 50ml of an ethanol solution, continuously stirred at 80℃ for 1h, water-washed, ground, and SiO2@C18 phase change material is obtained;

[0061] (2) 100g (15wt%) of a polyvinyl alcohol aqueous solution and 10g of SiO2@C18 phase change material are mixed, stirred at 400r / min for 0.5h at room temperature, then 100ul of acetic acid is slowly added under vigorous stirring, stirred for 1.5h, then 0.1g of short quartz fiber is added to continue stirring, and 0.1M sodium hydroxide solution is added dropwise to adjust the pH value of the mixed solution to 8, and continue to stir for 2h, to obtain a PVA@SiO2@C18 solution;

[0062] (3) 0.05g of hydroxylated boron nitride sheet is added into 50ml of deionized water, and ball-milled for 3h to obtain a BN suspension emulsion, 10g of the obtained BN suspension emulsion is added into 60g of the PVA@SiO2@C18 solution, and continues to stir for 5h to obtain a high-thermal-conductivity phase change solution;

[0063] (4) the high-thermal-conductivity phase change solution is frozen in a refrigerator for 24h, and after complete freezing, freeze-drying is carried out by a freeze-drying machine for 72h to obtain a phase change energy storage composite aerogel.

[0064] As can be seen from the above examples, the energy storage composite aerogel material with a directional pore structure prepared by the present application uses polyvinyl alcohol, cellulose nanofiber and short fiber as a three-dimensional porous skeleton material, which ensures high specific surface area, high porosity and low density, and also endows the aerogel with good heat insulation performance. The three-dimensional porous skeleton protects the phase change material, and the phase change material has a center core body of nanosilica, an intermediate layer of octadecanol, and an outermost protective shell of a mixed raw material of polyvinyl alcohol and cellulose nanofiber. The phase change material is added into the three-dimensional aerogel structure, which ensures that the aerogel is light and heat-insulating, and achieves the purpose of constant-temperature energy storage.

[0065] Figure 1 Fig. a and Fig. b are a structure schematic diagram and a phase change material schematic diagram of the phase change energy storage composite aerogel obtained in Example 4, respectively, and the three-dimensional porous skeleton protects the phase change material, and constructs a three-dimensional porous aerogel structure. Figure 2 Fig. c is a micro-morphology diagram of the phase change energy storage composite aerogel obtained in Example 4, and it can be observed that the bubble-shaped phase change material is distributed in the aerogel. Figure 3 Fig. d is a physical diagram of the phase change energy storage composite aerogel obtained in Example 4, with a diameter of 30mm and a height of 30mm. Figure 4The phase change energy storage composite aerogel obtained in Example 4 was subjected to a 50% strain compression strength curve, indicating that the three-dimensional structure with polyvinyl alcohol, cellulose nanofiber and quartz fiber as the basic skeleton material has good compression resilience. Figure 5 After the phase change energy storage composite aerogel obtained in Example 4 was heated at 100°C for 15 min on a heating table, the temperature of the top of the aerogel was only 38.4°C, indicating that the aerogel has good heat preservation and energy storage effect.

[0066] At the same time, the compression resistance of the aerogel is also a key factor in the actual application scenario of the aerogel. Table 1 is the compression strength of the phase change energy storage composite aerogel under 50% strain. The compression strength of the energy storage composite aerogel gradually increases, which can better play the supporting role of the mixed fibers on the three-dimensional structure.

[0067] Table 1 Compression strength of phase change energy storage composite aerogel under 50% strain

[0068]

[0069] The above description of the disclosed embodiments enables one skilled in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A phase change energy storage composite aerogel with a directional pore structure, characterized in that, The raw materials include the following parts by weight: 0.5-2 parts nano silica, 5-15 parts octadecyl alcohol, 80-120 parts polyvinyl alcohol aqueous solution, 0.1-0.2 parts chopped fibers, 0.05-0.5 parts modified boron nitride sheets, and 0.5-2 parts cellulose nanofibers.

2. The phase change energy storage composite aerogel with a directional pore structure according to claim 1, characterized in that, The polyvinyl alcohol aqueous solution has a mass fraction of 10-40 wt%, and the cellulose nanofibers are a gel with a mass fraction of 1 wt%.

3. The phase change energy storage composite aerogel with a directional pore structure according to claim 1, characterized in that, The chopped fibers are selected from one or more of quartz fibers, carbon fibers, aramid fibers, and glass fibers, and the length of the chopped fibers is 0.2 to 2 mm.

4. The phase change energy storage composite aerogel with a directional pore structure according to claim 1, characterized in that, The modified boron nitride sheet is selected from one of the following: hydroxylated, carboxylated, or aminolated modified boron nitride sheets.

5. A method for preparing a phase change energy storage composite aerogel with a directional pore structure according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Disperse nano-silica and octadecyl alcohol in an ethanol solution, stir continuously, then evaporate at 80°C for 12 h, cool and grind to obtain SiO2@C18 phase change material; (2) Mix polyvinyl alcohol aqueous solution and SiO2@C18 phase change material, stir at room temperature, then slowly add acetic acid under vigorous stirring, stir for 1.5h, add short chopped fibers to obtain a mixed solution, add 0.1M sodium hydroxide solution dropwise, adjust the pH of the mixed solution to 8, and continue stirring to obtain PVA@SiO2@C18 solution; (3) Modified boron nitride sheets and cellulose nanofibers were added to deionized water and ball-milled for 3 hours to obtain CNF / BN suspension; CNF / BN suspension was added to PVA@SiO2@C18 solution and stirred for 4 hours to obtain high thermal conductivity phase change solution; (4) The high thermal conductivity phase change solution is vacuumed in a vacuum drying oven at 0.5 MPa to remove air bubbles, and then freeze-dried to obtain phase change energy storage composite aerogel.

6. The method for preparing a phase change energy storage composite aerogel with a directional pore structure according to claim 5, characterized in that, The stirring temperature in step (1) is 80°C and the stirring time is 1 to 3 hours.

7. The method for preparing a phase change energy storage composite aerogel with a directional pore structure according to claim 5, characterized in that, The mass ratio of the polyvinyl alcohol aqueous solution and the SiO2@C18 phase change material in step (2) is 100:3 to 10.

8. The method for preparing a phase change energy storage composite aerogel with a directional pore structure according to claim 5, characterized in that, The stirring rate at room temperature in step (2) is 400 r / min.

9. The method for preparing a phase change energy storage composite aerogel with a directional pore structure according to claim 5, characterized in that, After adjusting the pH of the mixed solution to 8 in step (2), continue stirring for 2 to 6 hours.

10. The method for preparing a phase change energy storage composite aerogel with a directional pore structure according to claim 5, characterized in that, The mass ratio of CNF / BN suspension emulsion to PVA@SiO2@C18 solution in step (3) is 1:6.

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