A lithium chloride-based building facade cooling material and a method for producing the same

Abstract

This invention relates to the field of building materials technology, and particularly to a lithium chloride-based cooling material for building facades and its preparation method. The method includes the following steps: Step 1, surface activation and drying of expanded perlite; Step 2, preparation of a LiCl-MgCl2 eutectic salt aqueous solution; Step 3, vacuum impregnation loading; Step 4, solid-liquid separation and preliminary drying: obtaining LiCl-MgCl2 / expanded perlite composite particles. Using LiCl and expanded perlite as raw materials, activated expanded perlite and a LiCl-MgCl2 eutectic salt aqueous solution are constructed. Vacuum impregnation loading overcomes the problems of rapid LiCl dissolution and loss due to rainwater, and the easy shedding of crystalline salt after long-term cycling, thus obtaining a cooling material particularly suitable for surface cooling of exterior structures of civil buildings, industrial plants, etc.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a lithium chloride-based cooling material for building facades and its preparation method. Background Technology

[0002] In summer, buildings in cities experience significant internal temperature increases due to the large amount of heat absorbed by their surfaces, leading to excessive energy consumption and requiring urgent attention. Anhydrous lithium chloride (LiCl) is widely used as an adsorbent due to its excellent moisture absorption capacity, wide relative humidity range, outstanding chemical stability, and low cost. Porous matrices typically possess large pore volumes, high specific surface areas, and suitable pore sizes, providing mass transfer channels and loading hygroscopic salts. Expanded perlite, due to its porosity, is widely used for salt adsorption and is suitable for combined use with LiCl. However, the current application of LiCl on building facades has a significant drawback: LiCl has extremely high water solubility, meaning that rainwater can directly penetrate it when used outdoors. When LiCl is applied to the surface of a material, it dissolves rapidly and is lost with rainwater. Typically, after 1-2 heavy rains, the moisture absorption capacity decreases by 40%-60%, significantly reducing the cooling effect. When there are large temperature differences between day and night, LiCl dissolves after the material absorbs moisture. If the moisture evaporates too quickly during the drying process, LiCl will crystallize and precipitate on the surface of expanded perlite. After long-term circulation, the crystallized salt is prone to falling off, further aggravating LiCl loss. Typically, LiCl needs to be replenished every 3-6 months, resulting in high maintenance costs. The inventors have proposed a composite cooling material based on LiCl for passive cooling of buildings and its preparation method, which overcomes the above-mentioned significant drawbacks. It is especially suitable for surface cooling projects of exterior structures of civil buildings, industrial plants, etc., to reduce indoor heat load and lower energy consumption. Summary of the Invention

[0003] The purpose of this invention is to provide a lithium chloride-based cooling material for building facades and its preparation method, thereby solving the problems mentioned in the background art. The specific technical solution is as follows: The first objective of this invention is to provide a method for preparing a building facade cooling material based on lithium chloride, the method comprising the following steps: Step 1: Surface activation and drying of expanded perlite: Expanded perlite with a particle size of 2-4 mm was selected, soaked in a 0.5% silane coupling agent-ethanol solution for 1 hour, and then placed in a vacuum drying oven to remove moisture and complete surface activation, thus obtaining activated expanded perlite. Step 2: Prepare an aqueous solution of LiCl-MgCl2 eutectic salt. Weigh anhydrous LiCl and MgCl2 at a mass ratio of (1.5-5):1, add deionized water, and stir to prepare a eutectic salt aqueous solution with a mass concentration of 30%-35%, ensuring that the salts are completely dissolved. Step 3, Vacuum impregnation load: Impregnate in a continuous vacuum impregnation tank to allow the eutectic salt solution to fully penetrate into the pores of the expanded perlite; Step 4: Solid-liquid separation and preliminary drying: Expanded perlite and excess eutectic salt aqueous solution were separated by a continuous vacuum filter. Then, the expanded perlite loaded with eutectic salt was sent to a tunnel drying oven and dried at 60°C for 8 hours to obtain LiCl-MgCl2 / expanded perlite composite particles.

[0004] Preferably, step 5 is also included: LiCl-MgCl2 / expanded perlite composite particles are mixed with rapid-hardening sulfoaluminate cement, poured into a custom mold, pressed under a pressure of 0.3-0.5MPa, and dried and cured at 60℃ for 6 hours to prepare paving blocks.

[0005] Preferably, the process also includes step 5: mixing LiCl-MgCl2 / expanded perlite composite particles, composite fibers, and adhesive to prepare a spraying material; Step 5.1: Add the adhesive to the mixing tank and stir at low speed at 30°C. Slowly add the composite fiber while stirring. Stir for 10 minutes to ensure that the composite fiber is evenly dispersed in the adhesive without agglomeration. Step 5.2: Add LiCl-MgCl2 / expanded perlite composite particles and stir to obtain composite fiber reinforced cooling material.

[0006] Preferably, the adhesive comprises an aqueous acrylate copolymer adhesive, and the composite fiber comprises polypropylene staple fiber.

[0007] Preferably, step 5 further includes step 5.2: adding a thickener to adjust the viscosity. Hydroxypropyl methylcellulose and deionized water were added to the composite fiber reinforced cooling material and stirred at 800 r / min for 20 min. During the stirring, the viscosity of the system was monitored with a viscometer to ensure that the viscosity of the system remained stable at 12000-15000 mPa·s.

[0008] The second objective of this invention is to provide a building facade cooling material based on lithium chloride, characterized in that the facade cooling material is prepared by the above-described preparation method.

[0009] A third objective of the present invention is to provide a building facade cooling structure based on lithium chloride, characterized in that it includes a functional layer constructed from the aforementioned facade cooling material and a moisture-permeable and waterproof layer, wherein the moisture-permeable and waterproof layer is laid on the surface of the functional layer, and the moisture-permeable and waterproof layer is used to block liquid water and allow water vapor in the air to diffuse into the functional layer.

[0010] Beneficial effects: This invention uses LiCl and expanded perlite as raw materials to construct an activated expanded perlite and LiCl-MgCl2 eutectic salt aqueous solution. By vacuum impregnation loading, it overcomes the problems of rapid dissolution and loss of LiCl caused by rainwater, and easy shedding of crystallized salt after long-term circulation, and obtains a cooling material that is particularly suitable for surface cooling of the facade structure of civil buildings, industrial plants and other buildings.

[0011] A sprayable raw material is prepared by mixing LiCl-MgCl2 / expanded perlite composite particles, composite fibers, and binders. It can be directly sprayed onto the exterior of buildings using spraying equipment, making it very suitable for large-area spraying and reducing project time. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This is an electron microscope image of the LiCl-MgCl2 / expanded perlite composite particles prepared in Example 1; Figure 2 This is the temperature curve corresponding to Table 2. Detailed Implementation

[0014] Example 1

[0015] A method for preparing a building facade cooling material based on lithium chloride, the process comprising the following steps: S1. Surface activation and drying of expanded perlite: Expanded perlite with a particle size of 2-4 mm was selected and soaked in a 0.5% silane coupling agent-ethanol solution for 1 hour. Then it was placed in a vacuum drying oven and dried for 4 hours at 80-100℃ and a vacuum of -0.1 MPa, combined with microwave-assisted drying at 300W, to remove moisture and complete surface activation, thus obtaining activated expanded perlite. Preparation of aqueous solution of S2, LiCl-MgCl2 eutectic salt: Weigh anhydrous LiCl and MgCl2 at a mass ratio of (1.5-5):1, add deionized water, and stir to prepare a eutectic salt aqueous solution with a mass concentration of 30%-35%, ensuring that the salts are completely dissolved. S3, Vacuum Impregnation Load: The activated expanded perlite and the eutectic salt solution were added to a continuous vacuum impregnation tank at a solid-liquid ratio of 1:3. The vacuum degree was controlled at -0.1MPa. The tank was stirred intermittently for 10 minutes every 2 hours at a speed of 200r / min for 12 hours to allow the eutectic salt solution to fully penetrate into the pores of the expanded perlite. S4. Solid-liquid separation and preliminary drying: After impregnation, the expanded perlite was separated from the excess eutectic salt aqueous solution using a continuous vacuum filter. The eutectic salt-loaded expanded perlite was then fed into a tunnel drying oven and dried at 60°C for 8 hours to obtain LiCl-MgCl2 / expanded perlite composite particles. Electron micrographs are shown below. Figure 1 As shown. Example 2

[0016] The LiCl-MgCl2 / expanded perlite composite particles prepared in Example 1 were mixed with rapid-hardening sulfoaluminate cement, poured into a custom mold, pressed under a pressure of 0.3-0.5 MPa, and dried and cured at 60°C for 6 hours to prepare a block that can be laid. Example 3

[0017] The LiCl-MgCl2 / expanded perlite composite particles, composite fibers, and binder prepared in Example 1 were mixed to prepare a spraying material: Water-based acrylic copolymer adhesive was added to a mixing tank and stirred at low speed (300 r / min) at 30°C. Polypropylene short fibers were slowly added while stirring (the speed was increased to 500 r / min) for 10 min to ensure that the fibers were uniformly dispersed in the adhesive without agglomeration. Then, LiCl-MgCl2 / expanded perlite composite particles prepared in Example 1 were added, along with hydroxypropyl methylcellulose and deionized water. The mixture was stirred at 800 r / min for 20 min, and the viscosity was monitored with a viscometer to ensure that the viscosity of the system was stable at 12000-15000 mPa·s. The composite fiber reinforced cooling material was obtained. The composite fiber reinforced cooling material can be coated normally or sprayed directly onto the exterior of buildings using a spraying device. Example 4

[0018] A lithium chloride-based building facade cooling structure includes a functional layer and a moisture-permeable and waterproof layer constructed from facade cooling materials prepared in Example 1, Example 2, or Example 3. Generally, the moisture-permeable and waterproof layer is made of expanded polytetrafluoroethylene / polyvinylidene fluoride microporous membrane or moisture-permeable and waterproof roll material. The moisture-permeable and waterproof layer is laid on the surface of the functional layer, or the moisture-permeable and waterproof layer completely covers the functional layer. It is used to block liquid water and allow water vapor in the air to diffuse to the functional layer. In rainy weather, it blocks liquid water to reduce the loss of LiCl and further improves the performance.

[0019] Comparative Example 1 Expanded perlite and LiCl aqueous solution were added to a continuous vacuum impregnation tank at a solid-liquid ratio of 1:3. The vacuum degree was controlled at -0.1MPa. The tank was stirred intermittently for 10 minutes every 2 hours at a speed of 200r / min for 12 hours to allow the eutectic salt aqueous solution to fully penetrate into the pores of the expanded perlite. After impregnation, expanded perlite and LiCl aqueous solution were separated by a continuous vacuum filter. Then, the LiCl-loaded expanded perlite was sent to a tunnel drying oven and dried at 60°C for 8 hours to obtain LiCl / expanded perlite composite particles.

[0020] Experimental verification of the products prepared in Examples 1-3 and Comparative Example 1: Multiple 20cm x 20cm sealed enclosure structures were constructed as models for performance verification. Temperature sensors were installed on the top of the sealed enclosures, and a 1200W / m² temperature sensor was placed 1 meter above the enclosures. 2 A solar simulator was used to irradiate the top of a sealed box. In control group 1, no material was placed on the top of the sealed box. In control group 2, a 1cm thick layer of expanded perlite particles was laid on the top of the sealed box. In experimental group 1, a 1cm thick layer of LiCl-MgCl2 / expanded perlite composite particles prepared in Example 1 was laid on the top of the sealed box. In experimental group 2, a 1cm thick block prepared in Example 2 was laid on the top of the sealed box. In experimental group 3, the top of the sealed box was sprayed with composite fiber-reinforced cooling material prepared in Example 3. Before the experiment, a constant temperature and humidity machine was used to generate gas with 80% relative humidity and 20°C above the sealed box to simulate the temperature and humidity of a summer night. The LiCl-MgCl2 / expanded perlite composite particles were allowed to absorb water naturally for 8 hours. During the natural water absorption process, the quality of the material laid on top was also tested, and the water absorption data was obtained. The water absorption data is shown in Table 1. Subsequently, 6 hours of continuous simulated light irradiation was performed, and the values ​​detected by the temperature sensor were read. The temperature curve was exported. Figure 2 As shown, the data read is in seconds, and the results after conversion to hours are shown in Table 2. Table 1 Table 2 The results show that: Comparing blank group 1 and blank group 2, it can be seen that compared with no laying, laying expanded perlite particles can delay the temperature rise of the top of the sealed box. This is because expanded perlite particles themselves have a certain heat insulation and water retention capacity. Comparing the blank group 2 and the experimental group 1, it can be seen that the LiCl-MgCl2 / expanded perlite composite particles prepared in Example 1 have a better effect in delaying the temperature rise. This is because the LiCl-MgCl2 eutectic salt structure can passively absorb moisture in the air. After being irradiated by the solar simulator, the moisture is converted into gas and absorbs heat, thereby delaying the temperature rise of the top of the sealed box. The material prepared in Example 1 has a cooling advantage of 2°C after 30 minutes and a cooling advantage of nearly 3°C after 6 hours. Comparing experimental groups 1-3, it can be seen that experimental group 2 has a slightly lower cooling capacity than experimental group 1, while experimental group 3 has a stronger cooling capacity than experimental group 1. This is because after experimental group 2 is compressed into a block, the density increases, the space available for air circulation decreases, and the ability to absorb moisture from the air decreases. The water-based acrylic copolymer adhesive and polypropylene short fibers added to experimental group 3 also have water absorption capacity, and because they are spray-coated, the space available for air circulation is not compressed, so the water absorption capacity is not weakened. Therefore, the temperature remains relatively stable during the period of 3-7.5 hours.

[0021] The products prepared in Example 1 and Comparative Example 1 were then subjected to anti-bleeding tests: Experimental group 4 was constructed. The top of the sealed chamber in experimental group 4 was covered with a 1 cm thick layer of LiCl / expanded perlite composite particles prepared in Comparative Example 1. A spray device was installed above experimental groups 1 and 4, using deionized water at a pressure of 0.2 MPa and a rainfall rate of 50 mm / h. The samples were continuously sprayed for 2 hours, equivalent to 1-2 heavy rainstorms. The spraying was repeated, and the leachate was collected separately after each spraying, equivalent to a long-term rainy season. After each spraying, the samples were dried at 60℃ to constant weight, and the chloride ion concentration in the leachate was determined by titration. The content of LiCl was measured to determine the degree of LiCl loss. Specifically, the leachate was collected, diluted to 1L, and 25.00mL was transferred to a 250mL Erlenmeyer flask. 5mL of phosphate buffer solution was added to adjust the pH to 7.5. 1mL of 5% K2CrO4 indicator was added and the solution was shaken well. The solution was then slowly titrated with 0.1mol / L AgNO3 standard solution while shaking. The titration endpoint was reached when a stable brick-red precipitate appeared and did not fade within 30s. The volume of AgNO3 standard solution consumed was recorded. The results are shown in Table 3. Table 3 The volume of AgNO3 standard solution consumed indicates that the LiCl / expanded perlite composite particles, formed by directly fixing expanded perlite and LiCl aqueous solution in a continuous vacuum impregnation tank, showed significant dissolution and loss of LiCl into the leachate after the first three sprays. By the 30th spray, the LiCl flow rate was almost exhausted, resulting in only 0.18 ml of AgNO3 solution being consumed during titration. In contrast, the LiCl-MgCl2 / expanded perlite composite particles constructed in Example 1 maintained a stable loss rate even after 30 sprays, demonstrating their excellent resistance to flow rate fluctuations. This result indicates that the introduction of MgCl2 as a synergistic fixative effectively enhances the retention capacity of LiCl on the expanded perlite carrier and significantly inhibits its dissolution behavior in a water-laden environment. Compared to a single LiCl-supported structure, the LiCl-MgCl2 dual-salt system may enhance the physical adsorption and chemical interaction between the salt and the porous carrier, forming a more stable composite solid structure and thus maintaining good stability under long-term water contact conditions.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for producing a lithium chloride-based building facade cooling material, characterized by, The method includes the following steps: S1. Surface activation and drying of expanded perlite: Expanded perlite with a particle size of 2-4 mm was selected and soaked in a 0.5% silane coupling agent-ethanol solution for 1 hour. Then it was placed in a vacuum drying oven and dried for 4 hours at 80-100℃ and a vacuum of -0.1 MPa, combined with microwave-assisted drying at 300W, to remove moisture and complete surface activation, thus obtaining activated expanded perlite. Preparation of aqueous solution of S2, LiCl-MgCl2 eutectic salt: Weigh anhydrous LiCl and MgCl2 at a mass ratio of (1.5-5):1, add deionized water, and stir to prepare a eutectic salt aqueous solution with a mass concentration of 30%-35%, ensuring that the salts are completely dissolved. S3, Vacuum Impregnation Load: The activated expanded perlite and the eutectic salt solution were added to a continuous vacuum impregnation tank at a solid-liquid ratio of 1:

3. The vacuum degree was controlled at -0.1MPa. The tank was stirred intermittently for 10 minutes every 2 hours at a speed of 200r / min for 12 hours to allow the eutectic salt solution to fully penetrate into the pores of the expanded perlite. S4. Solid-liquid separation and preliminary drying: After impregnation, the expanded perlite and excess eutectic salt aqueous solution were separated by a continuous vacuum filter. Then, the expanded perlite loaded with eutectic salt was sent into a tunnel drying oven and dried at 60°C for 8 hours to obtain LiCl-MgCl2 / expanded perlite composite particles. Step 5: Preparation of composite fiber reinforced spray material: Add water-based acrylic copolymer adhesive to a mixing tank and stir at 300 r / min at 30°C. Slowly add polypropylene short fibers while stirring, and increase the speed to 500 r / min. Stir for 10 min to ensure that the polypropylene short fibers are uniformly dispersed in the adhesive without agglomeration. Then add the LiCl-MgCl2 / expanded perlite composite particles and stir. Subsequently, add hydroxypropyl methylcellulose and deionized water and stir at 800 r / min for 20 min. During this period, monitor with a viscometer to ensure that the viscosity of the system is stable at 12000-15000 mPa·s to obtain the composite fiber reinforced cooling material. The composite fiber reinforced cooling material can be coated normally or directly sprayed onto the exterior of buildings using spraying equipment.

2. A lithium chloride-based building facade cooling material, characterized by, It is prepared by the preparation method described in claim 1.

3. A building facade cooling structure based on lithium chloride, characterized in that, It includes a functional layer constructed from the exterior cooling material as described in claim 2 and a moisture-permeable and waterproof layer, wherein the moisture-permeable and waterproof layer is laid on the surface of the functional layer or completely covers the functional layer, and the moisture-permeable and waterproof layer is used to block liquid water and allow water vapor in the air to diffuse into the functional layer.

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