A method for preparing high enthalpy biomass-based shape-stabilized phase change materials

Abstract

A method for preparing a high-enthalpy biomass-based shaped-steady phase change material belongs to the technical field of phase change energy storage materials. This biomass-based phase change material is composed of a coordination cross-linking network compound and a hydrated salt solid-liquid phase change material; wherein, the coordination cross-linking network compound is composed of a polymer compound, metal ion coordination, and a mechanical strength enhancer. Utilizing a polymer containing a large number of hydrophilic groups such as carboxyl and hydroxyl groups, in-situ ionic cross-linking is achieved while fully adsorbing hydrated salts to form a high-enthalpy shaped-steady phase change material. The mechanical strength enhancer improves mechanical strength, making the system more stable. There is no liquid leakage during operation, and the cycle performance is good. The material has a simple synthesis process and is easy to apply. This biomass-based phase change material has a high latent heat of phase change, excellent shape-steady effect, and does not experience liquid leakage; it has broad application prospects in the field of thermal energy storage and management.

Description

Technical Field

[0001] This invention relates to a method for preparing a high enthalpy biomass-based shaped phase change material, which belongs to the technical field of phase change energy storage materials. Background Technology

[0002] Phase change energy storage materials are the main method of latent heat energy storage, which stores or releases heat through the phase change of a substance. The main materials used are phase change materials, which can be divided into solid-solid phase change materials, solid-liquid phase change materials, solid-gas phase change materials, etc. Among them, solid-liquid phase change materials have advantages such as small volume difference before and after phase change, and are the most commonly used phase change materials. However, solid-liquid phase change materials have the problem of leakage in the liquid state.

[0003] Solid-liquid phase change materials are classified into organic and inorganic phase change materials. Inorganic phase change materials are mostly hydrated salt phase change materials. Their main advantages over organic phase change materials are that they are non-flammable, have high thermal conductivity, and have a large phase change enthalpy. However, they have two problems: supercooling and phase separation.

[0004] The method of preparing shaped phase change materials by loading solid-liquid phase change materials (PLCs) onto porous materials can not only solve the leakage problem of PLCs, but also provide abundant nucleation sites to reduce supercooling, while eutectic hydrated salts can alleviate phase separation. Currently, inorganic materials are used as porous support materials, but to solve the leakage problem, large amounts of inorganic porous materials are used, resulting in low enthalpy values ​​of the composite PLCs. Organic support frameworks have adjustable pore surface areas and can effectively adsorb compatible organic solid-liquid PLCs when used as support materials, but due to poor compatibility with inorganic materials, it is difficult to load crystalline hydrated salt PLCs. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention prepares a high enthalpy biomass-based sturdy phase change material. It utilizes a polymer containing a large number of hydrophilic groups such as carboxyl and hydroxyl groups, which undergoes in-situ ionic cross-linking while fully adsorbing hydrated salts to form a high enthalpy sturdy phase change material. Furthermore, a mechanical strength enhancer improves the defect of poor mechanical strength, making the system more stable. It also exhibits no liquid leakage and good circulation performance during operation.

[0006] The technical solution adopted in this invention is: a high enthalpy biomass-based shape-stabilized phase change material, wherein the biomass-based shape-stabilized phase change material is composed of a hydrophilic coordination crosslinking network compound and a hydrated salt phase change compound; wherein the mass percentage is:

[0007] Hydrophilic coordination cross-linked network compounds: 1%~20%

[0008] Hydrated salt phase change materials: 80%~99%

[0009] Among them, the hydrophilic coordination cross-linking network compound is prepared from a polymer compound, metal ions and mechanical strength enhancer;

[0010] The polymeric compound is polyacrylic acid and its salts, carboxymethyl cellulose and its salts, sodium alginate or potassium alginate; the mechanical strength enhancer is one or more of cellulose nanocrystals, bacterial cellulose, and cellulose nanofibers.

[0011] The hydrophilic coordination crosslinking network compound is prepared by the following method: a polymeric compound with a mass ratio of (6-9):1 and a mechanical strength enhancer are dissolved in a solvent to prepare a homogeneous solution, a solution of metal ions is added, the mixture is stirred until a gel is formed, and the hydrophilic coordination crosslinking network compound is obtained by freeze drying.

[0012] The molecular weight of the polymer compound is 1,000 to 9,000,000.

[0013] The metal ions are calcium ions, magnesium ions, ferrous ions, ferric ions, zinc ions, aluminum ions, and copper ions.

[0014] The phase change material is one or more of the following: sodium acetate trihydrate, sodium thiosulfate pentahydrate, calcium chloride hexahydrate, barium hydroxide octahydrate, magnesium nitrate hexahydrate, sodium carbonate decahydrate, sodium sulfate decahydrate, and disodium hydrogen phosphate dodecahydrate.

[0015] A method for preparing a high-enthalpy biomass-based shape-stabilized phase change material includes the following steps:

[0016] (1) A homogeneous solution is prepared by dissolving a polymer compound with a mass ratio of (6-9):1 and a mechanical strength enhancer in a solvent, wherein the mass fraction of the polymer compound in the solution is 2.4-2.6%;

[0017] (2) Add the solution of metal ions and stir until a gel is formed;

[0018] (3) The obtained gel was frozen for 10-20 hours; then freeze-dried for 30-40 hours to obtain a hydrophilic coordination cross-linked network compound;

[0019] (4) The hydrophilic coordination crosslinking network compound is immersed in the molten hydrated salt phase change material, and the excess phase change material is adsorbed with filter paper to obtain the biomass-based shaped phase change material.

[0020] Furthermore, the concentration of metal ions in step (2) is 1 mol / L.

[0021] The beneficial effects of this invention are as follows: The high-enthalpy biomass-based shape-stabilized phase change material provided by this invention consists of a hydrophilic coordination crosslinking network compound composed of a polymer compound, metal ion coordination, and a mechanical strength enhancer. Utilizing a polymer containing a large number of hydrophilic groups such as carboxyl and hydroxyl groups, in-situ ionic crosslinking is achieved while simultaneously adsorbing hydrated salts to form a high-enthalpy shape-stabilized phase change material. The superhydrophilic porous framework improves the loading rate, which can reduce supercooling in inorganic phase change materials and further suppress phase separation. The mechanical strength enhancer improves the defect of poor mechanical strength, making the system more stable, with good cycle performance, no leakage, and low raw material cost, thus having broad application prospects. Attached Figure Description

[0022] Figure 1 The image shows the DSC diagram of the high enthalpy biomass-based shape-stabilized phase change material prepared in Example 1 and the eutectic hydrated salts of sodium sulfate decahydrate and disodium hydrogen phosphate dodecahydrate. In the diagram, a represents the eutectic hydrated salt; b represents the shape-stabilized phase change material.

[0023] Figure 2 This is a photograph of the contact angle test of the sodium alginate-based aerogel prepared in Example 1.

[0024] Figure 3 The image shows the shaping effect of the high enthalpy value biomass-based shaped phase change material prepared in Example 1.

[0025] Where a is a eutectic hydrated salt and b is a shape-fixed phase change material.

[0026] Figure 4 This is a comparison of the compressive strength of the sodium alginate-based aerogel prepared in Example 1 and the sodium alginate aerogel without the addition of a mechanical strength enhancer.

[0027] Where a represents no mechanical strength enhancer added, and b represents the addition of mechanical strength enhancer.

[0028] Figure 5 Cyclic performance diagram of high enthalpy biomass-based shape-stabilized phase change material. Detailed Implementation

[0029] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but are not intended to limit the invention in any way. The implementation of the present invention is not limited thereto.

[0030] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Example

[0031] Weigh 0.78 g of sodium alginate and 0.086 g of cellulose nanocrystals (mass ratio 9:1), add 35 ml of water, and stir at 60 °C until completely dispersed and dissolved. After cooling, add 3 mL of 0.1 mol / L ferric chloride hexahydrate solution under mechanical stirring to form a gel. Freeze in a refrigerator for 12 h, then freeze-dry for 36 h to obtain a sodium alginate-based hydrophilic coordination crosslinking network compound. Subsequently, impregnate it in an excess of molten sodium sulfate decahydrate and disodium hydrogen phosphate dodecahydrate hydrate in a mass ratio of 2:8, place in a 50 °C oven for 2 h, remove it, and use filter paper to remove the hydrated salt phase change material that seeps out from the surface. Repeat several times until no water stains remain to obtain a biomass-based shaped phase change material, which contains 7.49 g of hydrated salt phase change material and 0.85 g of coordination crosslinking network polymer compound.

[0032] Figure 1 The images show the DSC diagrams of the shaped phase change material and the pure phase change material in Example 1, where: a) is the hydrated salt phase change material, and b) is the shaped composite phase change material. The phase change enthalpy of the pure hydrated salt phase change material is 221.7 J / g, while that of the shaped phase change material is 192.9 J / g. The enthalpy is retained at 87.0%, exhibiting a high phase change enthalpy, and the phase change temperature remains unchanged. The high enthalpy is attributed to the large number of carboxylic acid and hydroxyl groups in its sugar chains. These functional groups form numerous hydrogen bonds between hydroxyl and carboxyl groups in water. The sodium alginate-based hydrophilic coordination crosslinking network compound possesses the porous properties of an aerogel and the superhydrophilicity of sodium alginate, allowing it to adsorb large amounts of hydrated salt, forming a high-enthalpy shaped phase change material. Figure 2 As shown, in the contact angle test, the water droplet was completely absorbed within 0.2 seconds. Figure 3 In (b), the prepared shape-stabilized phase change material can maintain its shape stability in an environment of 60°C for 40 minutes, while Figure 3 The hydrated salt phase change material in (a) completely melted, indicating that the prepared high-enthalpy biomass-based phase change material has good shape retention and can avoid leakage. Due to the properties of sodium alginate, the prepared aerogel is brittle and not easy to store. Adding a mechanical strength enhancer allows the rod-shaped cellulose nanocrystals to form intermolecular hydrogen bonds with the sodium alginate matrix, providing support and making the system more stable. Figure 4 As shown in (b), the compressive strength was significantly improved to 0.98 MPa, while Figure 4 In (a), the compressive strength of sodium alginate aerogel without added mechanical strength enhancers is 0.46 MPa. Its cycling performance is good, such as... Figure 5 As shown, after 100 phase transition cycles, the phase transition enthalpy is 191.8 J / g, with no significant decrease, indicating that the system has good cycle performance.

[0033] By changing the ratio of polymer matrix to cellulose nanocrystals to 8:1, 7:1, and 6:1, while keeping the other conditions the same as in Example 1, shape-stabilizing phase change materials with different proportions of mechanical strength enhancers were obtained. The prepared materials have good mechanical properties and shape-stabilizing effect.

[0034] By replacing the mechanical strength enhancer cellulose nanocrystals with bacterial cellulose, and keeping the other conditions the same as in Examples 1-4, shape-stabilizing phase change materials with different proportions of mechanical strength enhancer were obtained. The prepared materials have good mechanical properties and shape-stabilizing effect.

[0035] By replacing the mechanical strength enhancer with cellulose nanofibers, and keeping the other conditions the same as in Examples 1-4, shape-stabilized phase change materials with different proportions of mechanical strength enhancer were obtained. The prepared materials have good mechanical properties and shape-stabilizing effect.

[0036] By changing the polymer compounds to sodium polyacrylate, potassium polyacrylate, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose, and keeping the other conditions the same as in Example 1, shape-stabilized phase change materials with different polymer coordination frameworks were obtained. The prepared materials have good mechanical properties and shape-stabilizing effects.

[0037] The metal ion solution was changed to calcium ion solution, magnesium ion solution, ferrous ion solution, zinc ion solution, aluminum ion solution, and ferrous copper ion solution, while the other conditions were the same as in Example 1, to obtain shape-stabilized phase change materials with different ion coordination. The prepared materials have good mechanical properties and shape-stabilizing effect.

[0038] The hydrated phase change materials were replaced with sodium acetate trihydrate, sodium thiosulfate pentahydrate, calcium chloride hexahydrate, sodium carbonate decahydrate, disodium hydrogen phosphate dodecahydrate, sodium sulfate decahydrate, barium hydroxide octahydrate, and magnesium nitrate hexahydrate, respectively. All other conditions remained the same as in Example 1, resulting in an inorganic sturdy phase change material. The prepared material exhibited good mechanical properties and sturdy design.

Claims

1. A high-enthalpy biomass-based shape-stabilized phase change material, characterized in that: The biomass-based shape-stabilized phase change material is composed of a hydrophilic coordination cross-linked network compound and a hydrated salt phase change; wherein, by mass percentage, it is: Hydrophilic coordination cross-linked network compounds: 1%~20% Hydrated salt phase change materials: 80%~99% Among them, the hydrophilic coordination cross-linking network compound is prepared from a polymer compound, metal ions and mechanical strength enhancer; The polymeric compound is polyacrylic acid and its salts, carboxymethyl cellulose and its salts, sodium alginate or potassium alginate; the mechanical strength enhancer is one or more of cellulose nanocrystals, bacterial cellulose, and cellulose nanofibers. The hydrophilic coordination crosslinking network compound is prepared by the following method: A homogeneous solution was prepared by dissolving a polymeric compound with a mass ratio of (6-9):1 and a mechanical strength enhancer in a solvent. A metal ion solution was added, and the mixture was stirred until a gel was formed. The hydrophilic coordination crosslinking network compound was obtained by freeze-drying. The metal ions are calcium ions, magnesium ions, ferrous ions, ferric ions, zinc ions, aluminum ions, and copper ions.

2. The high enthalpy biomass-based shape-stabilized phase change material according to claim 1, characterized in that: The molecular weight of the polymer compound is 1,000 to 9,000,000.

3. The high enthalpy biomass-based shape-stabilized phase change material according to claim 1, characterized in that, The phase change material is one or more of the following: sodium acetate trihydrate, sodium thiosulfate pentahydrate, calcium chloride hexahydrate, barium hydroxide octahydrate, magnesium nitrate hexahydrate, sodium carbonate decahydrate, sodium sulfate decahydrate, and disodium hydrogen phosphate dodecahydrate.

4. A method for preparing a high-enthalpy biomass-based shape-stabilized phase change material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) A homogeneous solution is prepared by dissolving a polymer compound with a mass ratio of (6-9):1 and a mechanical strength enhancer in a solvent, wherein the mass fraction of the polymer compound in the solution is 2.4-2.6%; (2) Add the solution of metal ions and stir until a gel is formed; (3) The obtained gel was frozen for 10-20 hours; then freeze-dried for 30-40 hours to obtain a hydrophilic coordination cross-linked network compound; (4) The hydrophilic coordination crosslinking network compound is immersed in the molten hydrated salt phase change material, and the phase change material that has seeped out is removed and adsorbed with filter paper to obtain the biomass-based shaped phase change material.

5. The method for preparing a high enthalpy biomass-based shape-stabilized phase change material according to claim 4, characterized in that: The concentration of metal ions in the metal ion solution in step (2) is 0.1 mol / L.

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