Preparation method of ionic liquid photo-thermal energy storage material based on water vapor adsorption

Abstract

The invention discloses an ionic liquid photo-thermal energy storage material based on water vapor adsorption. A composite film is prepared by taking polyvinyl alcohol as a matrix, hydrophilic ionic liquid as a water absorbent and graphene oxide as a photo-thermal conversion material. The preparation process comprises the following steps: mixing the ionic liquid with a polyvinyl alcohol aqueous solution; then graphene oxide is uniformly dispersed in the ionic gel precursor solution; and finally, the black flexible film is prepared by a freezing-freeze-drying method. The prepared ionic liquid photo-thermal energy storage material based on water vapor adsorption has high water absorption capacity, high enthalpy value and good photo-thermal conversion performance, can store more heat, can realize solar energy-heat energy conversion, and has important significance in the fields of clean energy utilization and heat storage.

Description

Technical Field

[0001] The present invention relates to the field of energy storage composite materials, and more specifically, to a preparation method of an ionic liquid photothermal energy storage material based on water vapor adsorption. Background Art

[0002] At present, the energy crisis and environmental problems are becoming increasingly prominent. To solve this problem, the use of clean energy and the improvement of the utilization efficiency of the energy system have become the research focus of scientific researchers. Solar energy has the disadvantages of intermittency, volatility, and unstable supply, which limit the utilization of solar clean energy. The water vapor adsorption heat storage technology mainly uses a water vapor adsorbent to adsorb heat and release heat, and desorb heat to store and release heat energy, so as to realize the storage and utilization of clean energy such as solar energy.

[0003] There are various types of adsorbents, and there are many materials commonly used for water vapor adsorption. For example, some traditional materials, such as silica gel and zeolite. However, these traditional materials have some inherent problems. The adsorption capacity of silica gel is relatively low, resulting in a low heat storage density. The desorption temperature of zeolite is high and the energy consumption is high. Therefore, a higher-grade heat energy is required to desorb the material. Metal-organic framework materials have also been studied for adsorption heat storage in recent years. Its advantage is its tunable properties. However, its high cost hinders its large-scale application. Inorganic hydrated salts are a cheap water vapor adsorbent, which is suitable for a relatively low relative humidity. When the relative humidity is high, the inorganic hydrated salts will dissolve, and the formation of the solution hinders the diffusion of water vapor, resulting in a decrease in the adsorption rate. Therefore, it is very necessary to find a material that can overcome the above disadvantages.

[0004] Ionic liquids have a high water absorption capacity and adsorption enthalpy, and have now begun to be used in fields such as adsorption heat pumps. However, it has some inherent problems, such as its liquid form and fluidity, which hinder its flexible application in devices. At the same time, due to its low light absorption, it cannot directly utilize solar energy and can only store heat using a heat transfer medium, resulting in a reduction in thermal efficiency. Therefore, the present invention provides an ionic liquid photothermal energy storage material based on water vapor adsorption, which combines the photothermal conversion material graphene oxide with an ionic liquid adsorbent, not only realizing the integration of photothermal-storage heat and the direct utilization of solar energy, but also due to the action of the polyvinyl alcohol medium, an ionic liquid solid film is prepared to prevent the leakage of the ionic liquid and expand the application of the ionic liquid adsorbent. It provides a practical way for the efficient utilization of solar energy and has important significance. Summary of the Invention

[0005] The present invention provides a preparation method of an ionic liquid photothermal energy storage material based on water vapor adsorption by compounding graphene oxide and ionic liquid gel. The purpose is to prepare a solid ionic liquid material, and a further purpose is to provide a method for preparing this product to achieve the integration of photothermal energy storage and efficient utilization of solar energy.

[0006] The first aspect of the present invention is to provide an ionic liquid photothermal energy storage material based on water vapor adsorption, which is prepared by dispersing graphene oxide in an ionic gel precursor, spreading it into a film with a glass rod, and then freeze-drying.

[0007] The second aspect of the present invention is to provide a preparation method of an ionic liquid photothermal energy storage material:

[0008] Specifically, the preparation method of the ionic liquid photothermal energy storage material includes the following steps:

[0009] (1) Prepare the ionic gel precursor. Prepare an aqueous solution of polyvinyl alcohol (PVA). Heat and stir the PVA powder to dissolve it in deionized water to form an aqueous PVA solution. Then add a certain mass of ionic liquid to the aqueous PVA solution;

[0010] (2) Prepare the graphene oxide ionic gel precursor. Add graphene oxide to the ionic liquid PVA aqueous solution, heat and stir until the graphene oxide is completely and uniformly dispersed in the ionic gel precursor;

[0011] (3) Prepare the graphene oxide ionic gel. Pour the graphene oxide ionic gel precursor onto a glass plate and use a glass rod to evenly coat the solution. After coating, place the material in the freezer of the refrigerator. After freezing and freeze-drying, then take it out and peel the black film from the glass plate to obtain the ionic liquid photothermal energy storage material based on water vapor adsorption.

[0012] In the step (1), the heating temperature for dissolving the PVA powder in deionized water is 80 - 90 °C, and the stirring time is more than 6 h.

[0013] In the step (1), the concentration of PVA in the aqueous solution is 0.05 - 0.1 g / mL.

[0014] In step (1), the ionic liquid should be an ionic liquid with a positive group of 1-ethyl-3-methylimidazole or 1-allyl-3-methylimidazole, and acetic acid or halide as the anion, including one or more of Emim Ac, Emim Cl, Emim Br, Amim Ac, and Amim Cl. Preferably, 1-ethyl-3-methylimidazole acetate (Emim Ac) is used. 1-ethyl-3-methylimidazole acetate (Emim Ac) has better water absorption compared to other ionic liquids of the same type. At room temperature and high humidity (85%), the water absorption capacity can reach 1.52 g / g, and it has a relatively high desorption heat, which can be as high as 2,868 J / g, and can effectively store heat.

[0015] In step (1), the mass of the ionic liquid should be less than 40% of the total mass of PVA, GO, and the ionic liquid. Preferably, the mass of the ionic liquid should be 40% of the total mass of PVA, GO, and the ionic liquid. Compared with other ratios, the ionic liquid loading is the largest and the ionic liquid in the material will not leak, with strong water absorption performance and high energy storage density.

[0016] In step (2), the mass ratio of GO to PVA is 1:1 - 4:1. Preferably, the mass ratio of GO to PVA is 2:1. The proportion of GO affects the ionic liquid loading of the composite material. Compared with other ratios, when GO:PVA = 2:1, the GO loading is large and the ionic liquid is not easily leaked.

[0017] The stirring in step (2) includes mechanical stirring and magnetic stirring, and the mixture is stirred at 70 - 80 °C for 3 - 4 h.

[0018] In step (3), the coating thickness of the graphene oxide ion gel on the glass plate is 0.2 mm - 2 mm.

[0019] In step (3), the freezing time is more than 2 h, the freeze-drying temperature is -60 - 50 °C, and the freeze-drying time is more than 12 h.

[0020] The ionic liquid photothermal energy storage material based on water vapor adsorption prepared by the present invention has high water absorption and high enthalpy value, and has good photothermal conversion performance. It can not only store more heat, but also realize solar - thermal energy conversion, which is of great significance in the field of clean energy utilization and thermal storage.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) The present invention uses ionic liquids as materials for adsorbing water vapor. Compared with traditional adsorption materials, ionic liquids have a higher water absorption capacity and adsorption enthalpy. The material, after being processed, has good flexibility, elasticity, and photothermal conversion performance. Compared with widely studied adsorbents such as MOF and inorganic hydrated salts, it is not prone to leakage and corrosion, can be used in high relative humidity environments, and is more suitable for use in the field of adsorption thermal energy storage.

[0023] (2) The present invention uses a method of thermal mixing - freeze - drying to prepare desorption temperature - controlled materials. The device is easy to obtain, the method is simple, and the operation is convenient. The product can be obtained in only two steps.

[0024] (3) The present invention uses graphene oxide as a photothermal conversion material. The raw material processing technology is mature, it has good thermal stability and light absorption effect, which improves the photothermal conversion efficiency of the ionic liquid material. At the same time, due to the addition of graphene oxide, the composite material graphene oxide becomes a stress concentration body, which improves the elastic modulus of the composite material.

[0025] (4) The ionic liquid photothermal storage material prepared by the present invention is used for photothermal conversion and thermal storage. Compared with solid - liquid phase change materials, it has a higher energy storage density. The higher water absorption capacity promotes the application of ionic liquid materials in solar thermal energy storage, and has good prospects and application value. Description of the Drawings

[0026] Attached Figure 1 is the ionic liquid photothermal energy storage material for water vapor adsorption prepared in Example 1 of the present invention Attached Figure 2 is the water absorption performance curve of the ionic liquid photothermal energy storage material for water vapor adsorption prepared in Example 1 of the present invention at 25 °C and RH80% Detailed Embodiments

[0027] The following combines specific embodiments to further illustrate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0028] Example 1

[0029] (1) Take 10 g of PVA powder and add it to 100 mL of deionized water, and mechanically stir it in an oil bath at 90 °C for 6 h to obtain a 0.1 g / mL PVA solution. Take 5 mL of the PVA aqueous solution and pour it into a small beaker, and add 0.5 g of the ionic liquid Emim Ac to obtain an ionic gel precursor solution.

[0030] (2) Take 0.25 g of graphene oxide powder and add it to the ionic gel precursor solution, so that the mass ratio of PVA to GO is 2:1. Magnetically stir it in an oil bath at 70 °C for 4 hours. The solution in the small beaker turns black, and the graphene oxide is evenly dispersed without precipitation.

[0031] (3) Pour the hot graphene oxide ionic gel precursor rapidly onto a glass plate. Use a glass rod with tape wrapped around both ends to evenly spread the liquid on the glass plate. The gap between the glass rod and the glass plate can adjust the thickness of the sample. After spreading evenly, place the glass plate with the sample on its surface into a refrigerator at -15°C and freeze for 2 h. Subsequently, place it into a freeze dryer at -50°C and about 10 Pa and freeze-dry for 12 h to obtain the ionic liquid photothermal energy storage film.

[0032] (4) Product measurement: Use a thermostatic and humidistatic chamber and an electronic analytical balance to measure the leakage performance and water absorption performance of the ionic liquid photothermal energy storage material; Use a SUPERSCAN SSX-550 electron microscope (Japan) to observe the morphology of the final product. The working pressure of the scanning electron microscope is 20 kV; Use a xenon lamp to simulate natural light to measure the photothermal conversion performance of the ionic liquid photothermal energy storage material; Use a permanent comprehensive thermal analyzer to measure the desorption latent heat of the ionic liquid photothermal energy storage material. All measurements are carried out in a nitrogen environment, and the heating or cooling rate is 5°C / min respectively. About 5 mg of the ionic liquid photothermal energy storage material is placed in an open porcelain crucible and heated from room temperature 25°C to 120°C for 19 min, and the water vapor is completely desorbed and evaporated. Finally, after measurement, the loading amount of the ionic liquid in the composite material is 40 wt%, in an environment of 25°C and RH80%, it can adsorb 0.58 g / g of water vapor within 3 h, the heat storage density is 1668 J / g, and the liquid will not leak out of the membrane material within 24 h. Under simulated natural light of 250 kW / m 2 After 10 min, the desorption conversion rate reaches 80%.

[0033] Example 2

[0034] The process and conditions are the same as those in Example 1, except that in step (1) of Example 1, the addition amount of the ionic liquid Emim Ac is changed to 0.225 g, and in step (2), the addition amount of the graphene oxide powder is changed to 0.25 g, so that the mass ratio of PVA to GO is 2:1, and the ionic liquid accounts for 30% of the total mass. The rest are the same as those in Example 1 to obtain the ionic liquid photothermal energy storage material. Among them, the loading amount of the ionic liquid in the composite material is 30 wt%, in an environment of 25°C and RH80%, it can adsorb 0.45 g / g of water vapor within 3 h, the heat storage density is 1260 J / g, and the liquid will not leak out of the membrane material within 24 h. Under simulated natural light of 250 kW / m 2 After 10 min, the desorption conversion rate reaches 87%.

[0035] Example 3

[0036] The process and conditions are the same as those in Example 1, except that the addition amount of ionic liquid Emim Ac in step (1) of Example 1 is changed to 0.667 g, and the addition amount of graphene oxide powder in step (2) is changed to 0.5 g, so that the mass ratio of PVA to GO is 1:1, and the ionic liquid accounts for 40% of the total mass. The rest are the same as those in Example 1, and an ionic liquid photothermal energy storage material is obtained. The loading amount of the ionic liquid in the composite material is 40 wt%, and in an environment of 25 °C and RH80%, 0.55 g / g of water vapor can be adsorbed within 3 h, the heat storage density is 1504 J / g, and the liquid will not leak out of the membrane material within 24 h. After 10 min under simulated natural light of 250 kW / m 2 The desorption conversion rate reaches 83%.

[0037] Example 4

[0038] The process and conditions are the same as those in Example 1, except that the addition amount of ionic liquid Emim Ac in step (1) of Example 1 is changed to 0.445 g, and the addition amount of graphene oxide powder in step (2) is changed to 0.167 g, so that the mass ratio of PVA to GO is 3:1, and the ionic liquid accounts for 40% of the total mass. The rest are the same as those in Example 1, and an ionic liquid photothermal energy storage material is obtained. The loading amount of the ionic liquid in the composite material is 40 wt%, and in an environment of 25 °C and RH80%, 0.58 g / g of water vapor can be adsorbed within 3 h, the heat storage density is 1624 J / g, and the liquid will not leak out of the membrane material within 24 h. After 10 min under simulated natural light of 250 kW / m 2 The desorption conversion rate reaches 85%.

Claims

1. A preparation method of an ionic liquid photothermal energy storage membrane material based on water vapor adsorption, characterized in that, It includes the following steps: (1) Prepare an ionic gel precursor. Prepare an aqueous solution of polyvinyl alcohol (PVA). Heat and stir the PVA powder to dissolve it in water to form an aqueous PVA solution. Then add a certain mass of ionic liquid to the aqueous PVA solution; (2) Prepare a graphene oxide ionic gel precursor. Add graphene oxide (GO) to the ionic liquid PVA aqueous solution, heat and stir until the graphene oxide is uniformly dispersed in the ionic gel precursor; (3) Prepare a graphene oxide ionic gel. Pour the graphene oxide ionic gel precursor onto a flat plate, uniformly coat the solution. After coating, freeze the material and then perform freeze-drying. After freeze-drying, take out the film and peel it off the flat plate to obtain an ionic liquid photothermal energy storage film material.

2. The preparation method according to claim 1, characterized in that: In step (1), the heating temperature for dissolving the PVA powder in water is 80 - 90 °C (preferably 85 - 90 °C, more preferably 88 - 90 °C), the stirring time is more than 6 h (preferably 6 - 8 h, more preferably 6 - 7 h), and the concentration of PVA in the aqueous solution is 0.05 - 0.1 g / mL (preferably 0.08 - 0.1 g / mL, more preferably 0.95 - 0.1 g / mL).

3. The preparation method according to claim 1, characterized in that: In step (1), the ionic liquid should be an ionic liquid with one or two of the positive groups of 1-ethyl-3-methylimidazole or 1-allyl-3-methylimidazole, and one or more of acetate or halide ions as anions. Specifically, it includes one or more of 1-ethyl-3-methylimidazole acetate (Emim Ac), 1-ethyl-3-methylimidazole chloride (Emim Cl), 1-ethyl-3-methylimidazole bromide (Emim Br), 1-allyl-3-methylimidazole acetate (Amim Ac), and 1-allyl-3-methylimidazole chloride (Amim Cl). Preferably, Emim Ac is used. The mass of the ionic liquid should account for less than 40% of the total mass of PVA, GO, and the ionic liquid (preferably 20% - 40%, more preferably 35 - 40%).

4. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of GO to PVA is 1:1 - 4:1 (preferably 1:1 - 2:1, more preferably 2:1), and it is stirred at 70 - 80 °C (preferably 70 - 75 °C, more preferably 70 - 72 °C) for 3 - 4 h (preferably 3.5 - 4 h, more preferably 3.75 - 4 h).

5. The preparation method according to claim 1, characterized in that: In step (3), the freezing time for freeze-drying is more than 2 h, and the freezing temperature is -10—-30 °C; the freeze-drying temperature is -60—-50 °C, and the freeze-drying time is more than 12 h; The film thickness is 0.2 mm - 2 mm.

6. A water vapor adsorption ionic liquid photothermal energy storage membrane material prepared by the preparation method according to any one of claims 1-5.

7. An application of the water vapor adsorption ionic liquid photothermal energy storage membrane material according to claim 6 as an adsorption heat storage material or a water absorption and dehumidification material.

8. The application according to claim 7, characterized in that: The film is prepared with polyvinyl alcohol as the matrix, a hydrophilic ionic liquid as the water absorbent, and graphene oxide as the photothermal conversion material. Among them, PVA can fix the ionic liquid to avoid the fluidity of the ionic liquid; it can spontaneously absorb water vapor in the air, and after the composite material is saturated with moisture, it can desorb under sunlight and has photothermal conversion and heat storage effects.

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