Preparation method of electrostatic self-assembly carbon aerogel phase change material composite system based on pomelo peel

Abstract

The application discloses a preparation method of a static self-assembly carbon aerogel phase change material composite system based on pomelo peel, and overcomes the shortcomings of low thermal conductivity and long-period instability of the pomelo peel-based composite phase change material, so as to provide a preparation method of a static self-assembly pomelo peel aerogel skeleton composite phase change material with high thermal conductivity, high enthalpy and long-period stability. Compared with the prior art, the pomelo peel-based aerogel composite phase change material prepared by the application has high thermal conductivity, realizes the thermal conductivity of 1.18Wm ‑1 k ‑1 , the thermal conductivity of the composite phase change material is 3.48 times higher than that of the pure phase change material with the thermal conductivity of 0.25Wm ‑1 k ‑1 , the leakage loss rate of the phase change material is low, the performance is stable after 100 cycles, and the leakage rate is only 0.52%; the proportion of the carbon aerogel is low, and according to the reduction of the proportion of the carbon nanotube, the proportion of the carbon aerogel in the composite phase change material system is 10-20%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal energy storage, and particularly relates to a technology for constructing a pomelo peel aerogel framework composite phase change material through electrostatic self-assembly to improve thermal performance, and especially to the regulation and control of thermal conductivity and energy storage performance of the phase change material. BACKGROUND

[0002] In order to solve the technical problems of low thermal conductivity, easy leakage and poor cycle stability of pure phase change materials, researchers have developed a series of composite phase change materials by compounding porous carbon materials, metal particles and other functional carriers with phase change materials to improve the thermal conductivity, form stability and cycle durability of the phase change materials. Among them, the three-dimensional support network structure aerogel composite phase change material based on porous framework materials (such as porous carbon, metal organic framework, silicon dioxide, etc.) can effectively prevent the leakage of phase change and improve the stability of the overall performance of the composite phase change material, and is particularly significant in improving the performance of the phase change material. However, the existing porous aerogel still faces many practical problems, such as the difficulty in realizing high thermal conductivity while maximizing energy storage performance in the regulation of the pore structure of traditional carbon materials; the framework material prepared by the traditional high-temperature carbonization aerogel method has been shaped and cannot be well matched with the structure of the actual application container with different shapes, which seriously restricts its large-scale production and application; the high-performance materials such as metal organic framework have high cost, which is not conducive to environmental friendliness and commercial application, etc.

[0003] Porous carbon materials from biomass sources have the advantages of low cost, wide source, renewable and environmental friendly. Through pyrolysis and activation process, agricultural and forestry wastes can be efficiently converted into porous carbon materials with high specific surface area and adjustable pore structure for the preparation of composite phase change materials, which has attracted widespread attention in recent years. Through pyrolysis and activation process, agricultural and forestry wastes can be efficiently converted into porous carbon materials with high specific surface area and adjustable pore structure, and have the advantages of low cost, wide source, renewable and environmental friendly. Pomelo peel, as a biological waste produced during pomelo processing, has almost no economic value, but its annual output is huge. According to statistics, the annual output of pomelos in China is as high as 5 million tons, of which 40-50% is pomelo peel.

[0004] Although existing research has improved the loading capacity of pomelo peel-based composite phase change materials, there are still key technical bottlenecks in terms of thermal performance, stability and form retention. The first problem is the contradiction between thermal conductivity and energy storage capacity: increasing thermal conductivity requires increasing the proportion of the thermal conductive skeleton, which inevitably reduces the loading capacity of the phase change material, thereby reducing the energy storage capacity of the system; while increasing the loading capacity of the phase change material will weaken the continuity of the thermal conductive network, not only reducing the thermal conductivity, but also increasing the risk of leakage during the phase change. Secondly, in practical applications, the existing materials still have insufficient thermal conductivity, and there are stability problems during long-term cyclic use, which seriously restricts their engineering application. Therefore, how to break through this performance trade-off technical problem and achieve the synergistic optimization of thermal efficiency and energy storage capacity has become a key scientific problem to be solved in this field. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the low thermal conductivity and long-period instability of pomelo peel-based composite phase change materials, and to provide a preparation method of an electrostatic self-assembly pomelo peel aerogel skeleton composite phase change material with enhanced thermal conductivity, high enthalpy value and long-period stability.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application comprises the following steps:

[0007] The first object of the present application is to provide a preparation method of an electrostatic self-assembly carbon aerogel phase change material composite system based on pomelo peel, comprising the following steps:

[0008] s1, preparing high specific surface area biochar: carbonizing white peel powder of pomelo peel inner layer at 450℃ for 1 hour under nitrogen atmosphere to obtain primary carbonization product; then stirring the product with potassium hydroxide at a mass ratio of 1:2 in 0.1 mol / L potassium hydroxide solution for 12 hours for pre-activation, after vacuum suction filtration and drying at 80℃ for 24 hours, then activating at 900℃ for 2 hours under nitrogen protection; washing the activated product with hydrochloric acid solution until neutral, and drying to obtain the final activated porous biochar.

[0009] S2, preparing hydrogel: ultrasonic dispersion of activated biochar and 1% sodium dodecyl sulfate in deionized water for 1 hour to obtain biochar dispersion, and ultrasonic dispersion of aminated carbon nanotubes and 1% polyvinylpyrrolidone in aqueous solution for 30 minutes to obtain carbon nanotube dispersion; in an ice acetic acid solution with a pH value of 4 to 5, chitosan and polyacrylamide are dissolved in a ratio of 10:10 and stirred for 30 minutes to form a colloid; then gradually add the above two dispersions to the chitosan polyacrylamide solution, strictly control the temperature below 30℃ during mixing, stir for 30 min, and ensure uniform mixing of the materials, and the biochar and carbon nanotubes are electrostatically self-adsorbed and remain stable. After mixing evenly, pour the prepared hydrogel into the mold, and place it in a 5-10℃ environment for 12-24 hours for gelation.

[0010] S3, preparing carbon aerogel skeleton: the obtained hydrogel is frozen at -70℃ for 5 hours, and then vacuum freeze-dried for 24 hours to obtain carbon aerogel.

[0011] S4, preparing aerogel skeleton composite phase change material: immerse the carbon aerogel in the molten phase change material under a vacuum environment of 0.08 MPa and keep for 30 minutes to ensure that the phase change material penetrates and fills the three-dimensional porous network structure of the carbon aerogel.

[0012] Further, the purity of the aminated carbon nanotubes is greater than 95%, and the amination degree is 0.45wt%.

[0013] Further, the mass ratio of the activated biochar to the aminated carbon nanotubes, chitosan to polyacrylamide is 55 to 80:0 to 25:10:10.

[0014] Further, the viscosity of the chitosan is 100 to 200 mPa·s, the molecular weight of the polyacrylamide is 5,000,000, and the molecular weight of the polyvinylpyrrolidone is 58,000.

[0015] Further, the preparation method and particle size requirements of the white peel powder of the inner layer of pomelo peel are as follows: the white peel of the inner layer of pomelo peel is peeled off, dried, mechanically pulverized and sieved, and the powder with a particle size of 26-74 μm (corresponding to 200-600 mesh) after sieving is taken; the particle size distribution of the pomelo peel powder is uniform, which is conducive to the formation of uniform pore structure in the subsequent carbonization process.

[0016] Further, the addition amount of the aminated carbon nanotubes is 0 to 25% of the carbon aerogel. Preferably, the addition amount of the aminated carbon nanotubes is 20% of the mass of the activated biochar.

[0017] Further, the phase change material is an organic phase change material with a phase change temperature of 0-100 DEG C. It includes but is not limited to alkanes, fatty acids, alcohols, lipids and other organic phase change materials with latent heat of phase change. Among them: 1) paraffin phase change material includes normal alkane, isomeric alkane and its mixture, the phase change enthalpy value range is 180-240J / g; 2) fatty acid phase change material includes lauric acid, myristic acid, palmitic acid, stearic acid and its ester derivatives, the phase change enthalpy value range is 150-200J / g; 3) alcohol phase change material includes normal alcohol, polyhydric alcohol and its derivatives, the phase change enthalpy value range is 120-180J / g; 4) lipid phase change material includes unsaturated fatty acids such as oleic acid, linoleic acid and glycerides, the phase change enthalpy value range is 140-190J / g.

[0018] Further, the charge characteristics of each component in the electrostatic self-assembly process are: the activated biochar is negatively charged after modification by sodium dodecyl sulfate, and the amino-functionalized carbon nanotube is positively charged under acidic conditions with a pH value of 4-5; the negatively charged modified biochar and the positively charged amino-functionalized carbon nanotube generate strong electrostatic attraction.

[0019] Further, the mold in the S2 step is a container of any shape for macro-encapsulation of aerogel composite phase change material.

[0020] The beneficial effects of the present application are:

[0021] Efficient use of biomass waste: the high-value utilization of waste pomelo peel is realized, the preparation process is simple, the cost is low, it is suitable for large-scale commercial application, and it meets the green and sustainable development concept. The activated biochar realizes the porous structure, can adsorb more phase change materials, and effectively reduces the leakage risk in the melting process.

[0022] Innovative electrostatic self-assembly mechanism: the electrostatic self-assembly strategy based on surface charge regulation proposed in the present application can realize the directional self-assembly of surface negatively charged biochar and surface positively charged amino-functionalized carbon nanotube in gel solution to form a stable three-dimensional network structure.

[0023] Compared with the prior art, the pomelo peel-based aerogel composite phase change material prepared by the present application has high thermal conductivity, and realizes the thermal conductivity of 1.18Wm- 1 k- 1 , which is 3.48 times higher than that of pure phase change material with a thermal conductivity of 0.25Wm- 1 k- 1 ; the leakage loss rate of the phase change material is low, the performance is stable after 100 cycles, and the leakage rate is only 0.52%; the proportion of carbon aerogel is low, and according to the reduction of the proportion of carbon nanotubes, the proportion of carbon aerogel in the composite phase change material system is 10-20%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 SEM comparison of biochar aerogel phase change material, wherein Figure 1 (a) is a biochar prepared in step S1, Figure 1 (b)-(d) are SEM comparison of biochar aerogel of specific examples 1-3.

[0025] Figure 2 Leakage performance test comparison of example 1 and pure paraffin.

[0026] Figure 3 Thermal conductivity performance comparison of specific examples 1-3 and pure paraffin. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present application clearer, the following further describes the present application in combination with examples. The specific examples described herein are only used to explain the present application and do not limit the present application.

[0028] Example 1

[0029] S1 Preparation of high specific surface area biochar: white peel powder of pomelo inner layer is carbonized at 450℃ for 1 hour under nitrogen atmosphere to obtain a primary carbonization product; then the product is pre-activated with potassium hydroxide at a mass ratio of 1:2 in a 0.1 mol / L potassium hydroxide solution for 12 hours, and after vacuum filtration and drying at 80℃ for 24 hours, it is activated at 900℃ for 2 hours under nitrogen protection; the activated product is washed to neutral with hydrochloric acid solution, and after drying, the final activated porous biochar is obtained.

[0030] S2 Preparation of hydrogel: 1.2g of activated biochar is ultrasonically dispersed with 1% sodium dodecyl sulfate in 12g of deionized water for 1 hour, and 0.4g of aminated carbon nanotubes is ultrasonically dispersed with 1% polyvinylpyrrolidone in 5g of aqueous solution for 30 minutes; in an ice acetic acid solution with a pH value of 4 to 5, chitosan and polyacrylamide are dissolved in 10g of aqueous solution at a ratio of 0.2g:0.2g and stirred for 30 minutes to form a colloid; then the above two dispersions are gradually added to the chitosan-polyacrylamide solution, and the temperature is strictly controlled below 30℃ during the mixing process, and stirred for 30 minutes to ensure uniform mixing of the substances, and the biochar and carbon nanotubes achieve electrostatic self-adsorption and remain stable. After uniform mixing, it is placed in a 4℃ environment for 24 hours for gelation. In this example, the amount of carbon nanotubes is 20%, and the amount of biochar is 60%.

[0031] S3 Preparation of carbon aerogel skeleton: the obtained hydrogel is frozen at -70℃ for 5 hours, and then vacuum freeze-dried for 24 hours to obtain a carbon aerogel.

[0032] S4 Preparation of aerogel skeleton composite phase change material: under the vacuum environment of 0.08 MPa, immerse the carbon aerogel into the molten phase change material and keep for 30 minutes to ensure that the phase change material fully penetrates and fills the three-dimensional porous network structure of the carbon aerogel, and the carbon aerogel skeleton phase change material is prepared.

[0033] Further, in order to compare with Example 1, different proportions of carbon aerogel composite phase change materials are prepared for comparison. In the specific implementation, only the step S2 is different. In the subsequent examples, only the step S2 is changed, and the remaining steps are unchanged, which will not be described here.

[0034] Example 2

[0035] S2 Preparation of hydrogel: 1.4g activated biochar and 1% sodium dodecyl sulfate are ultrasonically dispersed in 14g deionized water for 1 hour, and 0.2g amino carbon nanotube and 1% polyvinylpyrrolidone are ultrasonically dispersed in 5g aqueous solution for 30 minutes; chitosan and polyacrylamide are dissolved in 10g aqueous solution in a ratio of 0.2g:0.2g in an ice acetic acid solution with a pH value of 4 to 5, and stirred for 30 minutes to form a colloid; then gradually add the above two dispersions to the chitosan polyacrylamide solution, strictly control the temperature below 30℃ during mixing, stir for 30min to ensure uniform mixing of the substances, and the biochar and carbon nanotube realize electrostatic self-adsorption and remain stable. After uniform mixing, place it in a 4℃ environment for 24 hours for gelation. In this example, the amount of carbon nanotube is 10%, and the proportion of biochar is 70%.

[0036] Example 3

[0037] S2 Preparation of hydrogel: 1.6g activated biochar and 1% sodium dodecyl sulfate of 1% activated biochar are ultrasonically dispersed in 16g deionized water for 1 hour; chitosan and polyacrylamide are dissolved in 10g in a ratio of 0.2g:0.2g in an ice acetic acid solution with a pH value of 4 to 5, and stirred for 30 minutes to form a colloid; then gradually add the above biochar solution to the chitosan polyacrylamide solution, strictly control the temperature below 30℃ during mixing, stir for 30min to ensure uniform mixing of the substances. After uniform mixing, place it in a 4℃ environment for 12 hours for gelation. In this example, the amount of carbon nanotube is 0%, and the proportion of biochar is 80%. This example will be used as a comparative example for comparison with Example 1 and Example 2.

[0038] 1、SEM characterization analysis

[0039] Figure 1 SEM images of carbon aerogels prepared in Example 1 and Example 2, wherein Figure 1(a) The characterization results of the activated biochar obtained according to the preparation step S1 show that a large number of uniform mesopores are formed on the surface of the biochar powder after KOH activation, which helps the capillary adsorption of the PCM; Figure 1 (b)-(d) are the SEM characterization results of the biochar aerogels of Examples 1-3, respectively. It is obvious that the electrostatic adsorption between the carbon nanotubes and the biochar can make the carbon aerogel form a more uniform three-dimensional network structure, which plays a key role in the formation of the overall heat conduction path. Comparative Example 3 does not add amino-functionalized carbon nanotubes, and the carbon aerogel has a disordered pore structure without the electrostatic self-assembly effect, so it cannot form an effective heat conduction path.

[0040] 2. Leakage performance of the composite phase change material

[0041] Figure 2 The leakage performance test of Example 1 and pure phase change material shows that after 1 hour of high-temperature baking, the pure paraffin completely melts in 25 minutes, while the aerogel phase change material of Example 1 has stable performance, with a leakage rate of only 0.18%, and no obvious change in appearance before and after heating. The 100-cycle test shows good experimental data repeatability.

[0042] 3. Thermal conductivity of the composite phase change material

[0043] The thermal conductivity test of the aerogel composite phase change materials of Examples 1-3 shows that the thermal conductivity of the composite aerogel phase change materials of Examples 1-3 is increased by 386% and 34.8% compared with that of pure paraffin, respectively. This shows that the electrostatic self-assembly aerogel prepared can realize effective heat conduction path and improve the overall thermal conductivity of the composite phase change material. Comparative Example 3 does not perform electrostatic self-assembly of biochar and carbon nanotubes, so the thermal conductivity is limitedly improved, and the thermal performance is poor.

[0044] The technical solutions of the present application are not limited to the above specific examples, and any technical variations made according to the technical solutions of the present application fall within the scope of protection of the present application.

Claims

1. A method for preparing an electrostatically self-assembled carbon aerogel phase change material composite system based on grapefruit peel, characterized in that, Includes the following steps: S1. Preparation of high specific surface area biochar: The white peel powder of the inner layer of grapefruit peel was carbonized at 450℃ for 1 hour under nitrogen atmosphere to obtain primary carbonization product; then the product was pre-activated by stirring in 0.1mol / L potassium hydroxide solution at a mass ratio of 1:2 for 12 hours. After vacuum filtration and drying at 80℃ for 24 hours, it was activated at 900℃ for 2 hours under nitrogen protection. The activated product was washed with hydrochloric acid solution until neutral, and then dried to obtain the final activated porous biochar. S2. Preparation of hydrogel: Activated biochar and 1% sodium dodecyl sulfate were ultrasonically dispersed in deionized water for 1 hour to obtain a biochar dispersion. Simultaneously, aminated carbon nanotubes and 1% polyvinylpyrrolidone were ultrasonically dispersed in an aqueous solution for 30 minutes to obtain a carbon nanotube dispersion. Chitosan and polyacrylamide were dissolved in a 1:1 ratio in a glacial acetic acid solution with a pH of 4 to 5 and stirred for 30 minutes to form a colloid. Then, the above two dispersions were gradually added to the chitosan-polyacrylamide solution. During the mixing process, the temperature was strictly controlled below 30°C, and the mixture was stirred for 30 minutes to ensure uniform mixing. The biochar and carbon nanotubes achieved electrostatic self-adsorption and remained stable. After uniform mixing, the mixture was placed in an environment of 5-10°C and allowed to stand for 12-24 hours to gel. S3. Preparation of carbon aerogel framework: The obtained hydrogel was frozen at -70℃ for 5 hours, and then freeze-dried under vacuum for 24 hours to obtain carbon aerogel; S4. Preparation of composite phase change materials: Under a vacuum of 0.08 MPa, carbon aerogel was immersed in molten phase change material and kept for 30 minutes to ensure that the phase change material fully penetrated and filled the three-dimensional porous network structure of carbon aerogel.

2. The preparation method of the electrostatic self-assembled carbon aerogel phase change material composite system based on grapefruit peel according to claim 1, characterized in that, The aminated carbon nanotubes have a purity greater than 95% and an amination degree of 0.45 wt%.

3. The preparation method of the electrostatic self-assembled carbon aerogel phase change material composite system based on grapefruit peel according to claim 1, characterized in that, The mass ratio of activated biochar to aminated carbon nanotubes, chitosan, and polyacrylamide is 55-80:0-25:10:

10.

4. The preparation method of the electrostatic self-assembled carbon aerogel phase change material composite system based on grapefruit peel according to claim 1, characterized in that, The chitosan has a viscosity of 100 to 200 mPa·s, the polyacrylamide has a molecular weight of 5,000,000, and the polyvinylpyrrolidone has a molecular weight of 58,000.

5. The preparation method of the electrostatic self-assembled carbon aerogel phase change material composite system based on grapefruit peel according to claim 1, characterized in that, The amount of aminated carbon nanotubes added is 0 to 25% of the mass of activated biochar.

6. The preparation method of the electrostatic self-assembled carbon aerogel phase change material composite system based on grapefruit peel according to claim 1, characterized in that, The phase change material is an organic phase change material with a phase change temperature of 0-100℃.

7. A self-assembled carbon aerogel / phase change material composite system based on grapefruit peel, characterized in that: The electrostatic self-assembled carbon aerogel / phase change material composite system based on grapefruit peel prepared by the method according to any one of claims 1 to 5.

Images