Inorganic phase change material special for cold chain and industrial cold storage and preparation method thereof

Abstract

The application discloses a kind of cold chain and industry special inorganic phase change material and its preparation method, the material is composed of inorganic hydrated salt matrix, composite nucleating agent and prevent phase separation thickening network;Among them, composite nucleating agent utilizes the nano-pore of silica aerogel to limit domain encapsulation to zinc borate crystal nucleus, and is coated with graphene heat conduction layer on surface;Prevent phase separation thickening network utilizes the long chain cooperation of polyacrylic acid sodium and xanthan gum with amphiphilic nano-silica node to construct three-dimensional skeleton.The application also discloses the method for preparing the microcapsule material with core-shell structure by gradient temperature control spray granulation.The application effectively solves the problem that the existing inorganic phase change material has large supercooling degree, is easy to separate and has low heat conduction efficiency in 2-22 DEG C temperature range, realizes the stability of thousands of cycles with extremely low supercooling degree within 0.5 DEG C, and has cold chain health safety and industrial cold storage durability.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage and phase change materials technology, and in particular to an inorganic phase change material for cold chain and industrial cold storage and its preparation method. Background Technology

[0002] Phase change energy storage materials are widely used in cold chain logistics and industrial waste heat recovery due to their advantages such as high energy density and constant temperature during phase change. Among them, 2-22℃ is the core temperature range for fresh food cold chain storage (usually requiring 2-10℃) and industrial central air conditioning cold storage (usually requiring 6-22℃).

[0003] However, existing general-purpose inorganic phase change materials (such as single hydrated salt systems) generally suffer from the following technical drawbacks when applied in this temperature range: Traditional hydrated salts need to overcome a huge nucleation barrier during crystallization, resulting in actual crystallization temperatures that are much lower than theoretical phase transition temperatures (supercooling is often greater than 3°C). This makes it difficult to meet high standards for cold chain temperature control (such as pharmaceuticals or high-end fresh produce). During long-term melting-crystallization cycles, inorganic salts and water of crystallization are prone to density stratification, which leads to a rapid decay of the material's energy storage capacity. This makes it unable to meet the durability requirements of thousands of cycles required for industrial cold storage scenarios. Inorganic salts themselves have low thermal conductivity, resulting in slow cold storage and release rates, which cannot meet the rapid thermal response requirements of industrial scenarios.

[0004] While existing technologies attempt to address these issues by adding thickeners or nucleating agents, it is often difficult to achieve both simultaneously. For example, excessive thickener addition can reduce latent heat, while ordinary nucleating agents tend to agglomerate and fail during repeated cycles. Furthermore, cold chain scenarios have stringent requirements for the non-toxicity and hygiene safety of materials, while industrial scenarios prioritize mechanical strength and cycle life. Existing technologies struggle to meet both standards simultaneously with a single material system. Therefore, there is an urgent need for an inorganic phase change material specifically designed for cold chain and industrial cold storage, along with its preparation method. Summary of the Invention

[0005] The present invention aims to solve the technical problems of existing inorganic phase change materials in the temperature range of 2-22℃, such as large supercooling, easy phase separation, poor thermal conductivity, and inability to balance food-grade safety and industrial-grade durability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An inorganic phase change material for cold chain and industrial cold storage, the inorganic phase change material comprising an inorganic hydrated salt matrix, a composite nucleating agent dispersed in the inorganic hydrated salt matrix, and a phase separation prevention thickening network distributed throughout the inorganic hydrated salt matrix; The inorganic hydrated salt matrix includes at least one of sodium sulfate decahydrate, calcium chloride hexahydrate, sodium acetate trihydrate, sodium carbonate decahydrate, or disodium hydrogen phosphate dodecahydrate. The composite nucleating agent includes a porous carrier framework, inorganic salt nuclei filling the pores of the porous carrier framework, and a carbon-based thermally conductive layer covering the outer surface of the porous carrier framework. The anti-phase separation thickening network includes a polymer backbone and inorganic nanoparticle nodes grafted onto the polymer backbone. The inorganic nanoparticle nodes form a three-dimensional support framework in the inorganic hydrated salt matrix.

[0007] Furthermore, the porous carrier framework is silica aerogel particles, the inorganic salt crystal nuclei are zinc borate crystals that are in situ crystallized inside the nanopores of the silica aerogel particles; the carbon-based thermally conductive layer is a graphene sheet that is adsorbed and fixed on the outer surface of the silica aerogel particles by van der Waals forces; and the particle size of the zinc borate crystals is limited to the pore size range of the nanopores.

[0008] Furthermore, the polymer backbone in the anti-phase separation thickening network is formed by the interaction of sodium polyacrylate molecular chains and xanthan gum molecular chains through hydrogen bonding and intermolecular physical entanglement; the inorganic nanoparticle nodes include hydrophilic nano-silica and hydrophobic nano-silica, the hydrophobic nano-silica is adsorbed on the surface of the carbon-based thermally conductive layer of the composite nucleating agent, and is connected to the hydrophilic nano-silica distributed in the liquid phase through the polymer backbone.

[0009] This invention also provides a method for preparing the above-mentioned inorganic phase change material for cold chain and industrial cold storage, which adopts a low-temperature eutectic synthesis-spray granulation integrated process, including: constructing a matrix precursor liquid containing an anti-phase separation network; preparing a composite nucleating agent loaded with crystal nuclei; mixing slurry; and molding in a spray granulation tower with a temperature gradient field (hot air zone 50-60℃, cold air zone 2-10℃) to form microcapsule particles with a core-shell structure.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: The composite nucleating agent constructed in this invention utilizes the confinement effect of aerogel nanopores to force zinc borate crystal nuclei to maintain directional alignment, stably controlling the supercooling within 0.5℃ (superior to the existing 1-3℃), ensuring stable phase transition performance across the entire temperature range of 2-22℃. By introducing an anti-phase separation thickening network, the relative positions of the matrix and nucleating agent are locked at the microscale using the physical entanglement of polymer long chains and the anchoring effect of inorganic nanonodes, endowing the material with industrial-grade durability resistant to melting-crystallization cycles.

[0011] Through microcapsule design, the outer dense hard shell is composed of inorganic salts and graphene, which not only builds an efficient heat-conducting network to improve the cold storage rate, but also realizes the physical encapsulation of the phase change core material, meeting the non-toxic and hygienic requirements of cold chain scenarios. The innovative gradient temperature-controlled spray granulation process utilizes the material's own phase change characteristics to directly complete the shell densification and nucleus crystallization during the granulation process. The process flow is short and easy to industrialize and mass-produce. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0013] Figure 1 This is a schematic diagram of the microstructure of the inorganic phase change material microcapsule particles for cold chain and industrial cold storage provided in an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of the composite nucleating agent in an embodiment of the present invention; Figure 3 This is a process flow diagram of the preparation method provided in the embodiments of the present invention.

[0014] In the figure: 20: composite nucleating agent; 21: porous carrier framework; 22: inorganic salt crystal nucleus; 23: carbon-based thermally conductive layer; 30: anti-phase separation thickening network; 40: crystalline core layer; 50: dense outer shell layer. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] The raw materials and reagents used in the embodiments of this invention are all commercially available products, and their specific specifications are as follows: Sodium sulfate decahydrate: analytical grade (AR, ≥99.0%), CAS No.: 7727-73-3, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Disodium hydrogen phosphate dodecahydrate: analytical grade (AR, ≥99%), CAS No.: 10039-32-4, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Calcium chloride hexahydrate: analytical grade (AR, ≥97%), CAS No.: 7774-34-7, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Zinc borate: analytical grade (anhydrous), CAS No.: 1332-07-6, purchased from Shanghai Haohong Biomedical Technology Co., Ltd. (Leyan). Silica aerogel particles: industrial grade, porosity >90%, pore size 10-50nm, purchased from Guangzhou People's Chemical Plant; Graphene sheets: Single or few-layer graphene, sheet diameter 1-5 micrometers, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd. Sodium polyacrylate: chemically pure, molecular weight (Mw) 3 million-5 million, CAS number: 9003-04-7, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (in this example, the high-viscosity flocculant grade product from this manufacturer is used, rather than the low molecular weight dispersant grade product). Xanthan gum: USP grade (pharmaceutical grade), CAS No.: 11138-66-2, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Hydrophilic nano-silica: analytical grade, particle size 15nm-30nm, specific surface area 200±25m² 2 / g, CAS No.: 7631-86-9, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; Hydrophobic nano-silica: modified with dimethyldichlorosilane, particle size 15nm, specific surface area 300±50m² 2 / g, CAS No.: 68611-44-9, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Example 1 An inorganic phase change material for cold chain and industrial cold storage is disclosed, which is in the form of microcapsule particles with a core-shell structure. The core-shell structure includes an inner crystalline core layer 40 and an outer dense outer shell layer 50, the thickness of which is 5 micrometers to 15 micrometers. The inorganic phase change material is composed of an inorganic hydrated salt matrix, a composite nucleating agent, and a phase separation-preventing thickening network.

[0017] In this embodiment, the mass percentage ratio of each component is as follows: inorganic hydrated salt matrix 85-92%, composite nucleating agent 3-8%, and anti-phase separation thickening network material 2-5%. Among them, the mass ratio of sodium polyacrylate to xanthan gum in the anti-phase separation thickening network material is approximately 1:1.

[0018] The inorganic hydrated salt matrix is ​​a binary eutectic system of sodium sulfate decahydrate and disodium hydrogen phosphate dodecahydrate in a mass ratio of 4:6, with a eutectic phase transition temperature of 5.5 degrees Celsius. The composite nucleating agent is uniformly dispersed in the inorganic hydrated salt matrix.

[0019] The composite nucleating agent 20 has a ternary heterostructure, such as Figure 2 As shown: the porous carrier framework 21 consists of silica aerogel particles with pore sizes ranging from 10 nm to 50 nm; the inorganic salt crystal nuclei 22 are zinc borate crystals, which are crystallized in situ and fill the nanopores of the porous carrier framework 21, with a mass ratio of zinc borate crystals to silica aerogel particles of 1:5; the carbon-based thermally conductive layer 23 is a graphene sheet, which is adsorbed onto the outer surface of the porous carrier framework 21 by van der Waals forces.

[0020] A phase-separation thickening network 30 is distributed throughout the inorganic hydrated salt matrix. This network consists of a polymer backbone and inorganic nanoparticle nodes. The polymer backbone is formed by hydrogen bonding and intermolecular physical entanglement between sodium polyacrylate molecular chains with a molecular weight of 3-5 million and xanthan gum molecular chains. It should be noted that this invention utilizes the long-chain entanglement effect of sodium polyacrylate to construct the gel network; therefore, high molecular weight sodium polyacrylate with a molecular weight greater than 3 million must be selected to distinguish it from low molecular weight (Mw<10000) sodium polyacrylate commonly used as a dispersant, which cannot form an effective viscoelastic support framework in this system.

[0021] The inorganic nanoparticle nodes include hydrophilic nano-silica and hydrophobic nano-silica, with the hydrophilic nano-silica dispersed in the liquid phase region of the inorganic hydrated salt matrix and connected to the polymer backbone; Hydrophobic nano-silica is adsorbed onto the carbon-based thermally conductive layer 23 on the surface of the composite nucleating agent 20, and is connected to the hydrophilic nano-silica through the polymer backbone to form a three-dimensional support framework anchoring the composite nucleating agent and the inorganic hydrated salt matrix.

[0022] When the ambient temperature drops below the phase transition point, the zinc borate crystals located in the nanopores of the silica aerogel particles are affected by the confined domain effect, and the lattice maintains its directional arrangement, inducing heterogeneous nucleation of the inorganic hydrated salt matrix coated on the outside.

[0023] When the ambient temperature rises above the phase transition point, the inorganic hydrated salt matrix melts. The anti-phase separation thickening network utilizes the viscoelasticity of the polymer backbone and the anchoring effect of the inorganic nanoparticle nodes to restrict the relative displacement between the inorganic hydrated salt matrix and the composite nucleating agent.

[0024] Example 2 like Figure 3 As shown, a method for preparing an inorganic phase change material specifically for cold chain and industrial cold storage includes the following steps: Step 1: Add 40 kg of sodium sulfate decahydrate and 60 kg of disodium hydrogen phosphate dodecahydrate to a constant temperature reactor and heat to 45 degrees Celsius to completely melt them, forming an inorganic hydrated salt eutectic solution; then add 1.5 kg of sodium polyacrylate powder, 1.5 kg of xanthan gum powder and 0.5 kg of hydrophilic nano silica to the solution in sequence, start a shear emulsifier, and shear mix at 2000 rpm for 30 minutes to construct a stable anti-phase separation thickening network and obtain the matrix precursor liquid; Step 2: Place 0.8 kg of silica aerogel particles in a vacuum container, evacuate to -0.08 MPa, and draw in a saturated zinc borate solution. After restoring to normal pressure, dry the particles with the solution adsorbed under vacuum at 60 degrees Celsius, allowing zinc borate to nucleate in situ within the pores of the silica aerogel particles, thus obtaining a porous support framework loaded with the inorganic salt nuclei (at this point, the mass ratio of zinc borate nuclei to silica aerogel framework is approximately 1:5). Step 3: The porous carrier framework (1-1.2 kg) prepared in Step 2 is premixed with 0.5 kg of graphene sheets and 0.2 kg of hydrophobic nano-silica. Since the hydrophobic nano-silica has an affinity for graphene, it is preferentially adsorbed on the graphene surface. Then, the premixed mixture is added to the matrix precursor solution prepared in Step 1. Step 4: Pump the mixed slurry into the atomizer of the spray granulation tower. The atomized slurry droplets first enter the hot air drying zone at 55 degrees Celsius, where surface moisture evaporates and inorganic salts and graphene precipitate to form a dense, hard shell. Subsequently, the droplets settle into the cold air crystallization zone at 5 degrees Celsius, where the inorganic hydrated salt matrix inside the droplets undergoes cryogenic crystallization under the induction of the composite nucleating agent, solidifying to form the inorganic phase change material.

[0025] Example 3 This embodiment uses the same preparation method as Example 2, the difference being the adjustment of process parameters: the inorganic hydrated salt matrix is ​​calcium chloride hexahydrate; the mass ratio of zinc borate crystals to silica aerogel particles is adjusted to 1:4; the thickness of the dense outer shell layer is controlled to 20 micrometers. To achieve this thickness, the feed pump pressure is adjusted to 1.5 MPa (lower than 2-4 MPa in Example 2), and the atomizing nozzle orifice diameter is increased to increase the atomized droplet size, thereby increasing the total amount of material precipitated on the surface to form the shell layer.

[0026] The temperature of the hot air drying zone of the spray granulation tower was set to 60 degrees Celsius, and the temperature of the cold air crystallization zone was set to 2 degrees Celsius. Under these parameters, the zinc borate crystals inside the microcapsule particles were always confined within the silica aerogel channels during the cyclic test from 2 degrees Celsius to 22 degrees Celsius, without agglomeration or detachment.

[0027] The anti-phase separation thickening network anchors the composite nucleating agent in the matrix through hydrophobic nano-silica nodes. After 1000 melting and crystallization cycles, the supercooling of the material remains below 0.5 degrees Celsius, and the latent heat of phase change decay rate is less than 3%.

[0028] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An inorganic phase change material specifically for cold chain and industrial cold storage, characterized in that, The inorganic phase change material comprises an inorganic hydrated salt matrix, a composite nucleating agent dispersed in the inorganic hydrated salt matrix, and a phase separation-preventing thickening network distributed throughout the inorganic hydrated salt matrix; the inorganic hydrated salt matrix comprises at least one of sodium sulfate decahydrate, calcium chloride hexahydrate, sodium acetate trihydrate, sodium carbonate decahydrate, or disodium hydrogen phosphate dodecahydrate; the composite nucleating agent comprises a porous carrier framework, inorganic salt nuclei filling the pores of the porous carrier framework, and a carbon-based thermally conductive layer coating the outer surface of the porous carrier framework; the phase separation-preventing thickening network comprises a polymer backbone and inorganic nanoparticle nodes grafted onto the polymer backbone, the inorganic nanoparticle nodes forming a three-dimensional support framework in the inorganic hydrated salt matrix.

2. The inorganic phase change material for cold chain and industrial cold storage as described in claim 1, characterized in that, The porous carrier framework is silica aerogel particles, and the inorganic salt nuclei are zinc borate crystals that are in situ crystallized inside the nanopores of the silica aerogel particles; the carbon-based thermally conductive layer is a graphene sheet that is adsorbed and fixed on the outer surface of the silica aerogel particles by van der Waals forces; the particle size of the zinc borate crystals is limited to the pore size range of the nanopores, and the mass ratio of the zinc borate crystals to the silica aerogel particles is 1:8 to 1:

4.

3. The inorganic phase change material for cold chain and industrial cold storage as described in claim 1, characterized in that, The polymer backbone in the anti-phase separation thickening network is formed by the interaction of sodium polyacrylate molecular chains and xanthan gum molecular chains through hydrogen bonding and intermolecular physical entanglement; the inorganic nanoparticle nodes include hydrophilic nano-silica and hydrophobic nano-silica, the hydrophilic nano-silica is distributed in the liquid phase region of the inorganic hydrated salt matrix, the hydrophobic nano-silica is adsorbed on the surface of the carbon-based thermally conductive layer of the composite nucleating agent, and the hydrophilic nano-silica and the hydrophobic nano-silica are connected by the polymer backbone.

4. The inorganic phase change material for cold chain and industrial cold storage as described in claim 1, characterized in that, The inorganic phase change material is in the form of microcapsule particles, and the microcapsule particles have a core-shell structure; the core-shell structure includes a crystalline core layer composed of the inorganic hydrated salt matrix and a dense outer shell layer formed by the aggregation of dehydrated inorganic salt and the composite nucleating agent; the thickness of the dense outer shell layer is 1 micrometer to 20 micrometers.

5. A method for preparing an inorganic phase change material for cold chain and industrial cold storage as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: Step 1: Prepare an inorganic hydrated salt eutectic solution in a constant temperature reactor, add polymer backbone raw materials and hydrophilic nano silica, and obtain the matrix precursor solution by shearing and mixing. Step 2: Prepare the porous carrier framework loaded with the inorganic salt crystal nuclei, mix it with the carbon-based thermally conductive layer material and hydrophobic nano-silica, and then add it to the matrix precursor liquid and homogeneously disperse it to obtain a mixed slurry. Step 3: Pump the mixed slurry into a spray granulation tower with a temperature gradient field; Step 4: Pass the atomized slurry droplets sequentially through a hot air drying zone at a temperature of 50°C to 60°C and a cold air crystallization zone at a temperature of 2°C to 10°C. A dense hard shell is formed on the surface of the droplets, and crystallization is completed inside. The inorganic phase change material is then collected.

6. The preparation method according to claim 5, characterized in that, In step two, the porous support framework loaded with the inorganic salt crystal nuclei is prepared by pressing a saturated zinc borate solution into the pores of silica aerogel using a negative pressure impregnation method, and inducing in-situ nucleation of zinc borate within the pores under vacuum drying conditions.

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