Phase-change energy-storage composite aerogel with directional pore channel structure and preparation method of phase-change energy-storage composite aerogel

Abstract

The invention belongs to the technical field of heat energy storage, and discloses a phase change energy storage composite aerogel with a directional pore channel structure and a preparation method of the phase change energy storage composite aerogel. A three-dimensional porous skeleton is constructed by polyvinyl alcohol, cellulose nanofibers and chopped fibers, the phase change material is protected by the three-dimensional porous skeleton, and the phase change material takes nanosilicon dioxide as a central core body, octadecanol as a middle layer and a mixed raw material of polyvinyl alcohol and cellulose nanofibers as an outermost protective shell, so that the completeness of the phase change material is ensured, and the phase change material has a good phase change effect. And high-temperature liquid leakage of the phase change material is prevented. The preparation process is simple, can meet the requirements for heat preservation and energy storage in medium and low temperature environments, can be used for key equipment interlayers with large internal and external environment temperature difference and important building outer layer protection walls, and has very high economic value and wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal energy storage, and more specifically relates to a phase-change energy storage composite aerogel with a directional pore structure and a preparation method thereof. Background Art

[0002] As the main thermal energy source for a long time, the limited reserves of fossil fuels have become a bottleneck restricting sustainable development. As a key technology for sustainable energy utilization efficiency, thermal energy storage technology is becoming increasingly important in the development wave of global energy transformation. Thermal energy storage technology is mainly divided into three types of energy storage: latent heat storage, sensible heat storage and chemical heat storage. Among them, latent heat storage technology is simple to operate, highly safe and low-cost, and has attracted much attention. Phase change energy storage materials, as the core part of latent heat storage technology, play a vital role in the process of thermal energy storage and release. Phase change energy storage materials can realize efficient conversion and storage of energy by absorbing or releasing a large amount of latent heat during the phase change of the material. This process can not only improve the overall efficiency of the energy system, but also provide strong support for the stable supply and flexible scheduling of energy, and can achieve sustainable green development. Among them, aerogel phase change energy storage composite materials have shown great application potential in many fields such as solar energy equipment, thermal insulation wearable fabrics, energy-saving buildings and thermal insulation equipment in extremely cold areas.

[0003] However, phase change energy storage materials also face many challenges in practical applications, the most prominent of which is the liquid phase leakage problem that may occur during the phase change conversion process of the material, which directly affects its long-term stability and reliability. Chinese invention patent CN118667520A discloses a method for preparing an aerogel solid-liquid phase change composite foam material, first preparing a boron nitride sheet foam aerogel, and then by melt filling or solution filling, the solid-liquid phase change material enters the pores of the boron nitride sheet porous network structure of the boron nitride sheet foam aerogel to obtain an aerogel solid-liquid phase change composite foam material. This method can fill the phase change material into the aerogel pores, but the phase change material will still leak in a 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 technical personnel in this field urgently need to solve. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the present invention provides a phase change energy storage composite aerogel with a directional pore structure and a preparation method thereof. The process is simple, and the prepared phase change energy storage composite aerogel with a directional pore structure has excellent mechanical properties, rich pore structure, good thermal insulation performance, and uniformly distributed phase change materials.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

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

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

[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 to 2 mm.

[0010] Preferably, the modified boron nitride sheet is selected from boron nitride sheets modified by hydroxylation, carboxylation, and amination.

[0011] The present invention also provides a method for preparing the above-mentioned phase change energy storage composite aerogel with a directional pore structure, comprising the following steps:

[0012] (1) dispersing nano-silicon dioxide and octadecyl alcohol into an ethanol solution, stirring continuously, and then evaporating at 80° C. for 12 h, cooling and grinding to obtain a SiO2@C18 phase change material;

[0013] (2) The polyvinyl alcohol aqueous solution and the SiO2@C18 phase change material were mixed and stirred at room temperature, and then acetic acid was slowly added under vigorous stirring, and the mixture was stirred for 1.5 hours. Short-cut fibers were added to obtain a mixed solution, and 0.1 M sodium hydroxide solution was added dropwise. After the pH value of the mixed solution was adjusted to 8, the mixture was stirred continuously to obtain a PVA@SiO2@C18 solution.

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

[0015] (4) The high thermal conductivity phase change solution is passed through a vacuum drying oven at 0.5 MPa to remove bubbles in the solution, and then freeze-dried to obtain a phase change energy storage composite aerogel.

[0016] Preferably, the stirring temperature in step (1) is 80° C. and the stirring time is 1 to 3 hours.

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

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

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

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

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

[0022] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a phase-change energy storage composite aerogel with a directional pore structure and a preparation method thereof, which has the following beneficial effects:

[0023] 1. The present invention constructs a three-dimensional porous skeleton by polyvinyl alcohol, cellulose nanofibers and chopped fibers to prepare a porous thermal insulation aerogel. The three-dimensional porous skeleton protects the phase change material. The phase change material has nano-silicon dioxide as the central core, octadecyl alcohol as the middle layer, and polyvinyl alcohol and cellulose nanofiber mixed raw materials as the outermost protective shell, which not only ensures the integrity of the phase change material, but also prevents the high-temperature liquid leakage of the phase change material.

[0024] 2. The modified boron nitride sheet is added to the energy storage composite aerogel of the present invention, which increases the heat conduction between the phase change materials without affecting the lightweight thermal insulation performance of the overall aerogel. Polyvinyl alcohol, cellulose nanofibers, and short-cut fibers together give the aerogel excellent compression resistance and compression resilience.

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

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 In the figure, a and b are respectively a schematic diagram of the structure of the phase change energy storage composite aerogel obtained in Example 4 and a schematic diagram of the phase change material.

[0028] Figure 2 This is a microscopic morphology of the phase change energy storage composite aerogel obtained in Example 4.

[0029] Figure 3 This is a physical picture of the phase change energy storage composite aerogel obtained in Example 4.

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

[0031] Figure 5 The 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 invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The cellulose nanofibers of the present invention are purchased from Huzhou Shansi New Material Technology Co., Ltd.; the length of the short-cut fibers is 0.2 to 2 mm.

[0034] Example 1

[0035] A method for preparing a phase-change energy storage composite aerogel with a directional pore structure comprises the following steps:

[0036] (1) Dispersing 1 g of nano-silicon dioxide and 5 g of octadecyl alcohol in 50 ml of ethanol solution, stirring continuously at 80 ° C for 1 h, and then evaporating at 80 ° C for 12 h to obtain a large amount of floccules, which were ground after cooling to obtain SiO2@C18 phase change material;

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

[0038] (3) 0.05 g of hydroxylated boron nitride sheets and 2 g (1 wt%) of cellulose nanofibers were 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 was added to 60 g of PVA@SiO2@C18 solution and stirred for 4 h to obtain a high thermal conductivity phase change solution;

[0039] (4) The high thermal conductivity phase change solution was first evacuated in a vacuum oven at 0.5 MPa to remove bubbles, then frozen in a refrigerator for 24 hours. After being completely frozen, it was freeze-dried in a freeze dryer for 72 hours to obtain a phase change energy storage composite aerogel.

[0040] Example 2

[0041] A method for preparing a phase-change energy storage composite aerogel with a directional pore structure comprises the following steps:

[0042] (1) 1 g of nano-silicon dioxide and 5 g of octadecyl alcohol were dispersed in 50 ml of ethanol solution, stirred continuously at 80 ° C for 1 h, then evaporated at 80 ° C for 12 h, cooled and ground to obtain SiO2@C18 phase change material;

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

[0044] (3) 0.05 g of hydroxylated boron nitride sheets and 2 g (1 wt%) of cellulose nanofibers were 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 was added to 60 g of PVA@SiO2@C18 solution and stirred for 4 h to obtain a high thermal conductivity phase change solution;

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

[0046] Example 3

[0047] A method for preparing a phase-change energy storage composite aerogel with a directional pore structure comprises the following steps:

[0048] (1) 1 g of nano-silicon dioxide and 10 g of octadecyl alcohol were dispersed in 50 ml of ethanol solution, stirred continuously at 80 ° C for 1 h, then evaporated at 80 ° C for 12 h, cooled and ground to obtain 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 room temperature for 1 h at 400 r / min, and then 100 μL acetic acid was slowly added under vigorous stirring. After stirring for 1.5 h, 0.2 g chopped quartz fiber was added, and 0.1 M sodium hydroxide solution was added dropwise to adjust the pH value of the mixed solution to 8. Stirring was continued for 4 h to obtain PVA@SiO2@C18 solution;

[0050] (3) 0.1 g of hydroxylated boron nitride sheets and 1 g (1 wt%) of cellulose nanofibers were added to 50 ml of deionized water and ball-milled for 3 h to obtain a CNF / BN suspension. 10 g of the obtained CNF / BN suspension was added to 60 g of PVA@SiO2@C18 solution and stirred for 4 h to obtain a high thermal conductivity phase change solution.

[0051] (4) The high thermal conductivity phase change solution was passed through a vacuum oven at 0.5 MPa to evacuate bubbles, and then subjected to liquid nitrogen directional freeze-drying 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 comprises the following steps:

[0054] (1) 1 g of nano-silicon dioxide and 9 g of octadecyl alcohol were dispersed in 40 ml of ethanol solution, stirred continuously at 80 ° C for 1 h, then evaporated at 80 ° C for 12 h, cooled and ground to obtain 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 and stirred at room temperature for 1 h at 400 r / min, and then 100 μL acetic acid was slowly added under vigorous stirring. After stirring for 1.5 h, 0.15 g chopped quartz fiber was added, and the pH value of the mixed solution was adjusted to 8 by dropping 0.1 M sodium hydroxide solution. Stirring was continued for 4 h to obtain PVA@SiO2@C18 solution;

[0056] (3) 0.1 g of hydroxylated boron nitride sheets and 0.5 g (1 wt%) of cellulose nanofibers were 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 was added to 60 g of PVA@SiO2@C18 solution and stirred for 4 h to obtain a high thermal conductivity phase change solution;

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

[0058] Comparative Example 1

[0059] A method for preparing a phase-change energy storage composite aerogel comprises the following steps:

[0060] (1) Dispersing 1 g of nano-silicon dioxide and 5 g of octadecyl alcohol in 50 ml of ethanol solution, stirring continuously at 80° C. for 1 h, filtering and washing with water, and grinding to obtain SiO2@C18 phase change material;

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

[0062] (3) 0.05 g of hydroxylated boron nitride flakes were added to 50 ml of deionized water and ball-milled for 3 h to obtain a BN suspension emulsion. 10 g of the obtained BN suspension emulsion was added to 60 g of PVA@SiO2@C18 solution and stirred for 5 h to obtain a high thermal conductivity phase change solution.

[0063] (4) The high thermal conductivity phase change solution is frozen in a refrigerator for 24 hours. After being completely frozen, it is freeze-dried in a freeze dryer for 72 hours to obtain a phase change energy storage composite aerogel.

[0064] It can be seen from the above embodiments that the energy storage composite aerogel material with a directional pore structure prepared by the present invention uses polyvinyl alcohol, cellulose nanofibers, and chopped fibers as three-dimensional porous skeleton materials, which ensures its high specific surface area, high porosity, and low density, and also gives the aerogel good thermal insulation properties. The three-dimensional porous skeleton protects the phase change material, and the phase change material has nano-silicon dioxide as the central core, octadecyl alcohol as the middle layer, and polyvinyl alcohol and cellulose nanofiber mixed raw materials as the outermost protective shell. The phase change material is added to the three-dimensional aerogel structure to ensure that the aerogel is lightweight and heat-insulating, and achieves the purpose of constant temperature energy storage.

[0065] Figure 1 In the figure, a and b are respectively a schematic diagram of the structure of the phase change energy storage composite aerogel obtained in Example 4 and a schematic diagram of the phase change material. The three-dimensional porous skeleton protects the phase change material to construct a three-dimensional porous aerogel structure. Figure 2 This is a microscopic morphology of the phase change energy storage composite aerogel obtained in Example 4. It can be observed that the vesicular phase change material is distributed in the aerogel. Figure 3 This is a physical picture of the phase change energy storage composite aerogel obtained in Example 4, with a diameter of 30 mm and a height of 30 mm. Figure 4The 50% strain compression strength curve of the phase change energy storage composite aerogel obtained in Example 4 shows that the three-dimensional structure with polyvinyl alcohol, cellulose nanofibers and quartz fibers as basic skeleton materials has good compression resilience. Figure 5 After the phase change energy storage composite aerogel obtained in Example 4 was heated on a 100° C. heating table for 15 minutes, the temperature of the top of the aerogel was only 38.4° C., indicating that the aerogel has a good thermal insulation and energy storage effect.

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

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

[0068]

[0069] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to 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 invention comprises the following raw materials in parts by weight: 0.5-2 parts of nano silicon dioxide, 5-15 parts of octadecyl alcohol, 80-120 parts of polyvinyl alcohol aqueous solution, 0.1-0.2 parts of short-cut fibers, 0.05-0.5 parts of modified boron nitride sheets and 0.5-2 parts of cellulose nanofibers.

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

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 hydroxylated, carboxylated and aminated 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 to 4, characterized in that: The following steps are involved: (1) dispersing nano-silicon dioxide and octadecyl alcohol into an ethanol solution, stirring continuously, and then evaporating at 80° C. for 12 h, cooling and grinding to obtain a SiO2@C18 phase change material; (2) The polyvinyl alcohol aqueous solution and the SiO2@C18 phase change material were mixed and stirred at room temperature, and then acetic acid was slowly added under vigorous stirring, and the mixture was stirred for 1.5 hours. Short-cut fibers were added to obtain a mixed solution, and 0.1 M sodium hydroxide solution was added dropwise. After the pH value of the mixed solution was adjusted to 8, the mixture was stirred continuously to obtain a PVA@SiO2@C18 solution. (3) Adding the modified boron nitride sheets and cellulose nanofibers into deionized water and ball milling for 3 h to obtain a CNF / BN suspension emulsion; adding the CNF / BN suspension emulsion into the PVA@SiO2@C18 solution and continuing to stir for 4 h to obtain a high thermal conductivity phase change solution; (4) The high thermal conductivity phase change solution is passed through a vacuum drying oven at 0.5 MPa to remove bubbles in the solution, and then freeze-dried to obtain a 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 to the SiO2@C18 phase change material in step (2) is 100:3-10.

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 value of the mixed solution to 8 in step (2), stirring is continued 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 the CNF / BN suspension and the PVA@SiO2@C18 solution in step (3) is 1:6.

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