Method for synthesizing LiCl-impregnated TpPa-1, an adsorbent.

Abstract

This invention belongs to the field of adsorption-based thermal management and water-collecting composite materials, and in particular provides a method for synthesizing LiCl@TpPa-1, an environmentally friendly adsorbent, and its use in heat exchanger coatings and for efficient adsorption and desorption of water vapor. [Solution] The present invention obtains a composite material, LiCl@TpPa-1, by impregnating a TpPa-1 skeletal material with LiCl through an impregnation treatment. Such a composite design cleverly combines the high porosity and structural stability of TpPa-1 with the strong hygroscopic properties of LiCl. When used as a surface coating for heat exchangers, it forms an adsorption coating structure with high water absorption, rapid regeneration, and long-term cycle stability, successfully avoiding deliquescence and structural degradation.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption-based heat management and water harvesting composite materials, and particularly relates to a synthesis method of LiCl@TpPa-1, an environmentally friendly adsorbent, and its use for coating heat exchangers and efficient adsorption / desorption of water vapor.

Background Art

[0002] Dehumidification of air is essential for maintaining thermal comfort, improving indoor air quality, and enhancing the energy efficiency of refrigeration systems, especially in hot and humid climates. There are mainly two methods for dehumidification: the condensation method and the adsorption method. The condensation method removes moisture by cooling air below the dew point, but this method is essentially energy-intensive and depends on the refrigeration cycle. On the other hand, the adsorption method captures moisture using a hygroscopic material, so cooling of the entire air is not required, and it is particularly suitable for the utilization of low-grade heat sources such as solar energy or industrial waste heat, realizing significant energy savings, reduction of operating costs and carbon emissions, and improvement of environmental sustainability.

[0003] A dehumidification system using a solid adsorbent, as an advanced form of adsorption technology, has become a promising alternative to vapor compression coolers. However, its performance still largely depends on the type of adsorbent. Conventional adsorbents such as silica gel, zeolite, and hygroscopic salts (e.g., lithium chloride) are widely used, but each has limitations. Silica gel has limited performance in a low-humidity environment due to its excessively high heat of adsorption. Zeolite shows high hygroscopicity in dry air, but its regeneration temperature exceeds 120°C and its thermal conductivity is also low. Hygroscopic salts such as lithium chloride show excellent water absorption, but are prone to deliquescence, corrosion, and salt migration, which affect the long-term stability of the system.

[0004] In recent years, advanced porous materials such as metal-organic frameworks (MOFs) have been frequently used for dehumidification applications. MOFs possess a tunable pore structure and high specific surface area, allowing for precise control of adsorption performance. However, most MOFs have low hydrolysis stability in humid environments, and their complex and energy-intensive preparation processes limit their large-scale application and practical use. For this reason, researchers are focusing on covalent organic frameworks (COFs), which are crystalline porous polymers in which light elements (C, H, O, N, B) are covalently bonded. Covalent organic frameworks offer advantages such as structural stability, high thermochemical stability, and tunable physicochemical properties. Furthermore, their photothermal regeneration capability makes them suitable for low-energy solar thermal dehumidification systems.

[0005] Among the reported COFs, TpPa-1 has attracted considerable attention due to its excellent stability under extreme chemical and thermal conditions. Its two-dimensional layered structure, linked by ketone-enamine bonds, is formed by a Schiff base condensation reaction between 1,3,5-trialdehydrophiloglobulusinol and p-phenylenediamine, followed by tautomerization. This structure exhibits high crystallinity, persistent porosity, and aligned mesopores with a diameter of 1-2 nm. TpPa-1 shows great potential for applications in fields such as gas storage, purification, and catalysis, and in recent years has demonstrated excellent performance in water vapor adsorption.

[0006] However, the water absorption capacity of conventional TpPa-1 (60%, 0.3-0.4 g / g at RH) is moderate and insufficient to meet the requirements of high-performance dehumidification. One effective way to improve performance is to impregnate COF with a hygroscopic salt such as lithium chloride (LiCl). LiCl not only significantly improves water absorption but also shifts adsorption to lower relative humidity ranges, making it particularly suitable for high-temperature, dry climates. However, the direct use of LiCl is limited by stability and handling issues. Therefore, by embedding LiCl in the porous framework of TpPa-1, it is possible to maintain high adsorption capacity while mitigating the drawbacks of free salts.

[0007] Recent studies have shown the potential of LiCl@TpPa-1 composites in water collection and adsorption refrigerators, but the complexity of the synthesis process still limits its practical application. Conventional TpPa-1 preparations use solvothermal methods, which require harsh conditions such as high temperatures (typically 120°C), long reaction times (up to 72 hours), and the use of toxic organic solvents such as mesitylene and dioxane. Such energy-intensive and environmentally unfriendly synthesis methods are difficult to scale up industrially and pose a major obstacle to large-scale commercial application of this material, especially in application scenarios requiring low-cost, sustainable large-scale production. [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention addresses the above-mentioned critical problems by providing an environmentally friendly and efficient method for synthesizing LiCl-impregnated TpPa-1 (LiCl@TpPa-1). Since the synthesis is carried out at room temperature and atmospheric pressure, the use of harmful solvents is avoided, offering significant advantages in terms of energy saving and environmental protection, while also enabling rapid and highly reproducible material preparation. In addition to the novel synthesis method, this invention forms an adsorption coating structure with high water absorption, rapid regeneration, and long-term cycle stability by coating the composite material onto the surface of a heat exchanger. Through this dual innovation in materials and processes, the technology of this invention provides a practical and sustainable solution for next-generation dehumidification systems and climate-adaptive cooling technologies. [Means for solving the problem]

[0009] The LiCl@TpPa-1, an environmentally friendly adsorbent of the present invention, is a LiCl-impregnated covalent organic skeleton composite material (LiCl@TpPa-1) that is synthesized by an environmentally friendly solvent method at room temperature. It solves the expansion and environmental problems of conventional high-temperature solvent-thermal COF synthesis and is particularly suitable for efficient air dehumidification in hot and humid climates.

[0010] The method for synthesizing LiCl@TpPa-1, an environmentally friendly adsorbent of the present invention, is as follows: (1) Preparation of TpPa-1 A DMF solution of 1,3,5-trial dehydrophiloglobulucinol TPG (Solution A) and a DMF solution of p-phenylenediamine PDA (Solution B) were prepared separately and sonicated for 10-20 minutes. Solution B was then slowly added to Solution A to obtain a mixed solution, and the mixture was stirred and reacted at room temperature for 5-20 hours. During the reaction, the color changed from pale yellow to bright red, indicating successful formation of the TpPa-1 covalent organic skeleton. The red precipitate was centrifuged, thoroughly washed with deionized water and ethanol, and dried at 50-100°C for 1-5 hours. (2) Preparation of LiCl-impregnated TpPa-1 (LiCl@TpPa-1) by post-synthesis salt loading method First, the TpPa-1 powder synthesized at room temperature is dried at 50-100°C. Deionized water was used to prepare an aqueous LiCl solution, with a concentration of 15-45 wt.%. Add the dried TpPa-1 powder to the LiCl aqueous solution and stir at room temperature for 4-8 hours to allow the LiCl to uniformly penetrate the porous framework of TpPa-1 by capillary infiltration and ion diffusion. Then, vacuum dry at 50-100°C for 9-15 hours to remove residual moisture, ensure complete salt embedding, and prevent premature moisture absorption. Store the final LiCl@TpPa-1 composite material in a desiccator. Includes.

[0011] The amount of LiCl supported in the resulting composite material LiCl@TpPa-1 is 15-45 wt.%.

[0012] In step (1), the concentration of solution A is 4.2 mg / mL, the concentration of solution B is 3.27 mg / mL, and the volume ratio of solution A to solution B in the mixed solution is 1:1.

[0013] The use of LiCl@TpPa-1, an environmentally friendly adsorbent prepared in this invention, as a coating material for heat exchanger surfaces is, specifically, (S1) LiCl@TpPa-1 powder is uniformly dispersed in deionized water, magnetically stirred, and then a polymer adhesive is added to obtain a coating solution. (S2) Before coating, the aluminum fins of the heat exchanger are ultrasonically cleaned with an acetic acid solution, then washed with a sodium hydroxide solution, and finally rinsed thoroughly with deionized water to improve surface cleanliness and wettability. (S3) The aluminum fins cleaned in step (2) are immersed in the coating solution of step (1), dried after immersion, and the immersion-drying cycle is repeated, or a coating is formed by methods such as spray coating or electrophoretic deposition. The drying process ensures thermal stability and curing of the adhesive, resulting in a composite coating with high mechanical strength and strong adhesive force. Includes.

[0014] In step (S1), the concentration of LiCl@TpPa-1 in the coating solution is 100 mg / 5 mL, and the mass fraction of the polymer adhesive is 5% to 20%. The polymer adhesive is hydroxyethylcellulose, polyvinyl alcohol, or sodium polyacrylate.

[0015] In process (S2), the concentration of the acetic acid solution is 0.3 M, the ultrasonic cleaning time is 5 minutes, the concentration of the sodium hydroxide solution is 1 M, and the cleaning time is 5 minutes.

[0016] In process (S3), the immersion time each time is 5-10 minutes, the drying temperature each time is 80°C, and the drying time is 1 hour. In process (S3), the coating thickness is 0.05 mm to 0.2 mm. [Effects of the Invention]

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) The backbone material of TpPa-1 is known for its excellent thermal and chemical stability. In this invention, this material is synthesized at room temperature and impregnated with lithium chloride at an optimal content of 15 - 45 wt.%. Such a composite design not only significantly improves the water vapor adsorption performance by skillfully combining the porosity / structural stability of TpP-1 and the strong hygroscopicity of LiCl, but also avoids the problems of deliquescence and structural degradation.

[0019] (2) This invention innovatively developed the coating process of the LiCl@TpPa-1 composite material on the aluminum heat exchange fins of the HVAC system. By using polymer adhesives such as sodium polyacrylate, mechanical stability, uniform coating distribution, and maintenance of adsorption performance are ensured. The finally coated fins are assembled into a functional fin-tube heat exchanger and evaluated under actual weather conditions.

[0020] According to the test results, the dehumidification capacity of the heat exchanger with the LiCl@TpPa-1 coating is more than three times that of the conventional silica gel system, and the coefficient of performance (COP) is improved by more than 2.5 times. This composite material also has a low-temperature regeneration capacity (about 70 °C), so it is suitable for the utilization of renewable or low-grade waste heat and shows excellent cycle stability in multiple adsorption / desorption cycles.

[0021] (3) This invention is the first to successfully integrate a COF-based adsorbent into a practical heat exchanger system, providing an expandable high-performance air dehumidification solution and promoting the practical application of advanced porous materials in energy-saving and environmentally friendly climate control technologies.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic diagram of an environmentally friendly synthesis process of TpPa-1 and LiCl@TpPa-1 at normal temperature and atmospheric pressure. [Figure 2] In Figure 2, (a) is the XRD pattern of TpPa-1 synthesized at room temperature, and (b) is a schematic diagram of the two-dimensional laminated structure of TpPa-1. [Figure 3] Figure 3(a) shows the effect of synthesis temperature on the XRD pattern of TpPa-1, and (b) shows the effect of synthesis temperature on the water absorption performance of TpPa-1. [Figure 4] In Figure 4, (a) shows the effect of different LiCl content on the water absorption capacity of synthesized TpPa-1 at 20°C and 75%RH; (b) shows the thermal stability of the original TpPa-1 and LiCl(30wt%)@TpPa-1; (c) shows the nitrogen gas adsorption isotherms of the original TpPa-1 and LiCl(30wt%)@TpPa-1; (d) shows the XRD patterns of the original TpPa-1 and LiCl(30wt%)@TpPa-1 in dry and wet conditions; (e) shows the particle morphology of the original TpPa-1; and (f) shows the particle morphology of LiCl(30wt%)@TpPa-1. [Figure 5] In Figure 5, (a) shows the water adsorption isotherms of LiCl@TpPa-1 composite materials with different LiCl contents, and (b) shows the relationship between the partial pressure of water vapor and the amount of water absorbed by LiCl(30wt%)@TpPa-1 at different temperatures. [Figure 6] Figure 6(a) shows the effect of adhesive type and content on the water absorption performance of the LiCl (30 wt%) @ TpPa-1 coating, and (b) shows the effect of sodium polyacrylate content on the mechanical stability of the coating under severe vibration (100 Hz, amplitude 4 mm). [Figure 7] Figure 7 shows a real-world example of a LiCl (30 wt%) @ TpPa-1 coated fin tube heat exchanger and a schematic diagram of its adsorption and desorption processes. [Figure 8]Figure 8 shows (a) the temperature curves for air outlet, water outlet, and water inlet of a heat exchanger coated with LiCl(30wt%)@TpPa-1 during performance testing, (b) a comparison of the inlet and outlet air humidity ratio curves for heat exchangers coated with LiCl(30wt%)@TpPa-1 and silica gel, (c) a comparison of the average moisture content reduction rate during half-cycle dehumidification of heat exchangers with two types of coatings, LiCl(30wt%)@TpPa-1 and silica gel, (d) a comparison of the coefficient of performance (COP) of heat exchangers coated with LiCl(30wt%)@TpPa-1 and silica gel, and (e) the cycle stability of the heat exchanger coated with LiCl(30wt%)@TpPa-1 over multiple dehumidification and regeneration cycles. [Modes for carrying out the invention]

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Figure 1 is a schematic diagram of an environmentally friendly synthesis process for TpPa-1 and LiCl@TpPa-1 under room temperature and atmospheric pressure. [Examples]

[0025] The synthesis method for the environmentally friendly adsorbent LiCl@TpPa-1 is as follows:

[0026] (1) Reaction synthesis of TpPa-1 at room temperature 1,3,5-Trialdehydrophiloglobulinol TPG (63 mg dissolved in 15 mL of DMF) and p-phenylenediamine PDA (49 mg dissolved in 15 mL of DMF) were each dissolved by sonication for 15 minutes. Then, the PDA solution was slowly added to the TPG solution, and the mixture was stirred and reacted at room temperature for 12 hours. During the reaction, the color changed from pale yellow to bright red, indicating successful formation of the TpPa-1 covalent organic skeleton. The red precipitate was centrifuged, thoroughly washed with deionized water and ethanol, and dried at 80°C for 3 hours.

[0027] (2) Preparation of LiCl@TpPa-1 by post-synthesis salt loading method First, TpPa-1 powder synthesized at room temperature was dried at 80°C and accurately weighed. Then, a LiCl aqueous solution of the target concentration of 15-45 wt.% was added using deionized water. Dried TpPa-1 powder was added to a LiCl solution and stirred at room temperature for 6 hours, allowing LiCl to uniformly penetrate the porous framework via capillary infiltration and ion diffusion. Residual moisture was removed, and the material was vacuum-dried at 80°C for 12 hours to ensure complete embedding of the salt. The final composite material, LiCl@TpPa-1, was stored in a desiccator to prevent premature moisture absorption.

[0028] The use of the prepared LiCl@TpPa-1 for coating the heat exchanger surface specifically includes the following steps:

[0029] LiCl@TpPa-1 powder was uniformly dispersed in deionized water (100 mg / 5 mL), and the mixture was magnetically stirred. To enhance the adhesion between the adsorbent and the aluminum substrate, three types of polymer adhesives—hydroxyethylcellulose, polyvinyl alcohol, and sodium polyacrylate—were added to prepare the coating solution. The mass fractions of the polymer adhesives were 0%, 5%, 10%, 15%, and 20%, and their effects on coating performance and water absorption capacity were systematically investigated.

[0030] Before coating, the aluminum fins are first ultrasonically cleaned with 0.3M acetic acid for 5 minutes, then washed with 1M sodium hydroxide for 5 minutes, and finally rinsed thoroughly with deionized water to improve surface cleanliness and wettability.

[0031] The cleaned aluminum fins were immersed in a LiCl@TpPa-1 coating solution and dried at 80°C for 1 hour. This immersion-drying cycle was repeated until the coating thickness reached approximately 0.1 mm. Other methods such as spray coating or electrophoretic deposition can also be used. The drying process ensured thermal stability and adhesive curing, resulting in a composite coating with high mechanical strength and strong adhesive properties.

[0032] Figure 2(a) shows a comparison of the XRD patterns of TpPa-1 synthesized at room temperature in this example and TpPa-1 synthesized by the solvothermal method at 120°C for 3 days in the literature. S. Kandambeth, et al., (J Am Chem Soc, 2012, 134, 19524-19527). and Y. Wang et al. (eScience, 2023, 3, 4, 100154). As shown in the figure, the crystallinity of TpPa-1 synthesized at room temperature was confirmed by powder X-ray diffraction (XRD), showing characteristic peaks at 4.8°, 8.5°, 12.5°, and 27°, which is consistent with TpPa-1 synthesized by the conventional solvothermal method (120°C, 72 hours). At the same time, the 4.8° peak corresponds to the reflection from the (100) plane, and the 27° peak corresponds to the (001) interlayer stacking, confirming the formation of a two-dimensional layered structure. Figure 2(b) is a schematic diagram of the two-dimensional stacked structure of TpPa-1, where characteristic lattice spacings of 1.8 nm and 0.33 nm were clearly observed.

[0033] Compared to the solvothermal method, TpPa-1(001) synthesized by the room-temperature method exhibits stronger orientation and higher intensity of the 27° peak, indicating that the low-temperature process induces different crystal growth orientations.

[0034] As shown in Figure 3, the effects of synthesis temperature (-40°C, 20°C, 80°C) on crystal orientation (see Figure 3(a)) and water absorption performance (see Figure 3(b)) were further analyzed. XRD data showed that in-plane growth of (100) was promoted at high temperatures, while (001) stacking was promoted at low temperatures. In water absorption tests at 20°C and 75% relative humidity, the adsorption capacity increased with increasing temperature, but comparable performance was maintained even with room temperature samples, demonstrating a good balance between adsorption efficiency, material integrity, and synthesis sustainability.

[0035] Exposure of LiCl@TpPa-1 composite material:

[0036] To improve the water absorption capacity of TpPa-1 synthesized at room temperature, the COF skeleton was impregnated with LiCl, a highly hygroscopic salt, at different loading amounts (0%, 15%, 30%, 45%).

[0037] As shown in Figure 4(a), an increase in LiCl content and an improvement in LiCl@TpPa-1 water absorption were detected under conditions of 20°C and 75% RH, reaching an optimal value at 30 wt.%. Above this concentration, particularly at 45 wt.%, water absorption decreased due to pore blockage and salt accumulation. Notably, unlike many polymer adsorbents, LiCl@TpPa-1 did not exhibit deliquescence or structural deformation during adsorption, demonstrating the excellent moisture resistance and rigidity of the COF structure.

[0038] As shown in Figure 4(b), thermogravimetric analysis (TGA) revealed that the thermal decomposition curves for the original TpPa-1 and LiCl (30 wt.%)@TpPa-1 were nearly identical, indicating that the introduction of LiCl did not affect the thermal stability of the framework. Water decomposition and adsorption occurred below 150°C, but significant decomposition of the framework occurred between 330 and 500°C. Furthermore, the sample with added LiCl showed a high residual mass after decomposition, confirming the material's stability in applications involving salt retention and repeated regeneration during dehumidification.

[0039] Figure 4(c) shows the isotherms of nitrogen gas adsorption and desorption, and the BET specific surface area of ​​the material is 10⁵ m² from the original TpPa⁻¹. 2 From / g, the sample supporting 30 wt.% LiCl was 28m 2 The decrease in / g is due to partial filling or blockage of pores by LiCl. Notably, despite the decrease in specific surface area, the composite material maintains high water absorption, indicating that the adsorption mechanism is driven primarily by the hydration of LiCl, rather than by physical adsorption to the inner surface of the COF material.

[0040] Figure 4(d) shows the XRD patterns of the original TpPa-1 and LiCl (30 wt%)@TpPa-1 in dry and wet conditions. This confirms that the crystal structure of TpPa-1 is not damaged even after the introduction of LiCl, and that no peak shift or broadening is observed after moisture absorption even when exposed to a humid environment, indicating that the COF framework maintains structural stability through multiple adsorption and desorption cycles.

[0041] Figure 4(f) shows a scanning electron microscope (SEM) image of LiCl (30 wt%) @ TpPa-1, demonstrating that the characteristic lamellar structure of TpPa-1 is not impaired even after salt loading, and the surface is slightly rough due to the uniform dispersion of LiCl particles. Importantly, the absence of particle aggregation or structural breakdown further supports the material's stability and potential for practical application.

[0042] In summary, LiCl@TpPa-1 composite materials possess high water absorption capacity, thermal structural stability, and periodic moisture resistance, making them ideal materials for adsorption-type thermal management and air dehumidification.

[0043] Water absorption behavior of LiCl@TpPa-1

[0044] Figure 5(a) shows the isotherms of water vapor adsorption at 30°C, with all LiCl samples from 0–45 wt.% exhibiting V-shaped isotherm characteristics. Typically, adsorption is weak in the low relative humidity (RH) region, but increases sharply above approximately 60% RH, which is consistent with the properties of adsorbents where hydration is dominant. The original TpPa-1 showed low adsorption across the entire RH range, which reflects its inherently limited hydrophilicity. In contrast, the introduction of LiCl significantly improved water adsorption capacity (reaching 80% and 0.62 g / g at RH), which is mainly due to chemiadsorption by hydration of LiCl.

[0045] Among the tested composite materials, the sample loaded with 30 wt.% LiCl showed optimal adsorption performance, demonstrating an optimal balance between pore accessibility and hygroscopic salt content. When the loading amount was increased to 45 wt.%, partial pore blockage occurred (BET surface area was 28M). 2 The overall performance actually decreased due to the reduction in / g.

[0046] As shown in Table 1, under 80% RH conditions, LiCl(30wt%)@TpPa-1 exhibits superior performance compared to many COF and MOF-based adsorbents reported to date (adsorption capacity increased by 35-50%), highlighting its superiority as a high-performance water absorbent.

[0047] [Table 1] TIFF0007866345000003.tif63170

[0048] Figure 5(b) shows the relationship between the partial pressure of water vapor and the amount of water absorbed by LiCl(30wt%)@TpPa-1 at different temperatures. As shown in Figure 5(b), the thermodynamic analysis of the water absorption behavior of the material was performed by measuring the adsorption isotherms at 30°C, 45°C, and 60°C. The isothermal heat of adsorption was calculated using the Clausius-Clapeyron equation, and the average value was approximately 2308 kJ / kg, which is slightly lower than the latent heat of vaporization of water (approximately 2400 kJ / kg). This indicates high energy efficiency in the adsorption process and low renewable energy consumption, making it suitable for adsorption-type water collection systems or efficient air dehumidification systems.

[0049] (Examples of application) Use of LiCl@TpPa-1 adsorption coating for dehumidifying heat exchangers

[0050] In this study, in order to realize the practical application of adsorption coating of LiCl (30 wt%) @ TpPa-1 to heat exchangers, we developed an innovative composite coating using a polymer adhesive to improve adhesion to aluminum substrates.

[0051] Although LiCl@TpPa-1 powder exhibits excellent water absorption (1.44 g / g at 80% RH), its poor adhesion to metal substrates and mechanical compatibility severely limit its practical application as a coating in heat exchanger systems. Therefore, the effectiveness of three water-dispersible adhesives—hydroxyethylcellulose, sodium polyacrylate, and polyvinyl alcohol—in improving the adhesion and stability of the coating was investigated.

[0052] The addition of these adhesives to the LiCl@TpPa-1 slurry affects the water absorption performance of the composite material. Specifically, increasing the adhesive content significantly reduces the water absorption rate in all formulations (Figure 6(a)), mainly because effective water adsorption is inhibited due to pore blockage and reduced access of water vapor to the active LiCl adsorption sites.

[0053] However, among the adhesives tested, sodium polyacrylate showed the best performance due to its superior rheological and coating properties. Sodium polyacrylate is highly suitable for dip coating processes because it offers high slurry viscosity and excellent dispersion stability. Furthermore, this adhesive can improve the uniformity and film thickness control of the coating film.

[0054] mechanical stability The mechanical integrity of the coating film was evaluated by a vibration test at 100 Hz with an amplitude of 4 mm. Increasing the adhesive content significantly improved the mechanical strength and reduced the mass loss after vibration (Figure 6(b)). Such improvements are mainly due to the formation of a more cohesive polymer network that firmly fixes the composite particles to the substrate surface.

[0055] Optimized formula Considering both hygroscopicity and mechanical durability, a formulation containing 20 wt.% sodium polyacrylate was ultimately determined to be the optimal solution. This formulation offers a good balance of coating strength, adhesion, and water absorption capacity, making it suitable for long-term practical use of coated heat exchangers.

[0056] LiCl (30 wt%) @ TpPa-1 coating and a commercially available silica gel coating as a baseline were prepared using an optimized slurry formulation. The two coatings were applied to the surface of a fin-tube heat exchanger using a controlled dip coating method (see Figure 7).

[0057] To evaluate practical performance, the adsorption performance and thermal efficiency of two types of coated heat exchangers were tested under conditions simulating dehumidification of high-temperature, high-humidity air, and the adsorption performance and thermal efficiency of the novel LiCl-based composite material were directly compared with conventional silica gel desiccants.

[0058] Dehumidification performance of LiCl@TpPa-1 coated heat exchangers The LiCl@TpPa-1 composite material combines the structural stability of the TpPa-1 covalent organic skeleton with the strong hygroscopic properties of LiCl, resulting in significantly improved water absorption performance (see Figure 7).

[0059] LiCl (30 wt%) @ TpPa-1 and a commercially available silica gel coating were prepared in an optimized formulation and uniformly coated onto the surface of a fin tube heat exchanger. Air dehumidification conditions in a tropical environment were simulated, and the moisture absorption performance and energy efficiency of the novel composite material were directly compared with conventional adsorbents.

[0060] During the test, the air-filled conditions were 33±0.3℃ and 65±2%RH. In the dehumidification phase, cooling water at 32±1℃ circulated through the heat exchanger tubes, and in the regeneration phase, it switched to hot water at 70±2℃, with the circulation switching every 5 minutes (see Figure 8(a)).

[0061] The LiCl(30wt%)@TpPa-1 coated heat exchanger exhibited excellent circulating dehumidification performance. During the dehumidification phase, the moisture content in the outlet air rapidly decreased, demonstrating a significant moisture absorption effect (Figure 8(b)). During the regeneration phase, the outlet humidity ratio rapidly increased, confirming rapid and reversible adsorption and desorption characteristics.

[0062] Compared to a silica gel-coated heat exchanger under the same conditions, the LiCl(30wt%)@TpPa-1 system showed more than three times the dehumidification capacity (Figure 8(c)) and more than 2.5 times the coefficient of performance (COP) (Figure 8(d)).

[0063] In the long-term cycle test (Figure 8(e)), no performance degradation was observed, and no salt precipitation, structural degradation, or peeling was seen with the LiCl(30wt%)@TpPa-1 coating, confirming the system's cycle durability, structural robustness, and long-term applicability in practical dehumidification and energy recovery applications.

[0064] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to these embodiments, and obvious improvements, substitutions, or modifications that can be made by those skilled in the art without departing from the essence of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for synthesizing LiCl-impregnated TpPa-1, which is an adsorbent, (1) Preparation of TpPa-1 In the formulation of solution A, the DMF solution of 1,3,5-trial dehydrofloroglucinol TPG is ultrasonically dissolved. In the formulation of solution B, the DMF solution of p-phenylenediamine PDA is ultrasonically dissolved, Then, solution B was slowly added to solution A to obtain a mixed solution, and the reaction was continued at room temperature while stirring. During the reaction, the color changed from pale yellow to bright red, indicating the successful formation of the TpPa-1 covalent organic skeleton. The red precipitate was centrifuged, thoroughly washed with deionized water and ethanol, and dried. (2) Preparation of LiCl-impregnated TpPa-1 by post-synthesis salt loading method First, the TpPa-1 powder synthesized at room temperature was dried. A LiCl aqueous solution is prepared using deionized water. Dried TpPa-1 powder is added to an aqueous LiCl solution and stirred at room temperature. The LiCl penetrates the porous framework of TpPa-1 through capillary infiltration and ion diffusion. The mixture is then vacuum-dried to remove residual moisture and ensure complete salt embedding. The final LiCl-impregnated TpPa-1 composite material is stored in a desiccator. A synthesis method characterized by including the following.

2. The synthesis method according to claim 1, characterized in that in step (1), the concentration of solution A is 4.2 mg / mL, the concentration of solution B is 3.27 mg / mL, and the volume ratio of solution A to solution B in the mixed solution is 1:

1.

3. In process (1), The ultrasonic dissolution time is 10 to 20 minutes. The reaction time at room temperature is 5 to 20 hours. The drying temperature is 50-100°C, and the drying time is 1-5 hours. The synthesis method according to claim 1, characterized in that

4. The synthesis method according to claim 1, characterized in that in step (2), the drying temperature of the TpPa-1 powder is 50 to 100°C and the concentration of the LiCl aqueous solution is 15 to 45 wt.%.

5. The synthesis method according to claim 1, characterized in that in step (2), the stirring time at room temperature is 4 to 8 hours, the vacuum drying temperature is 50 to 100°C, and the time is 9 to 15 hours.

6. The synthesis method according to claim 1, characterized in that in step (2), the amount of LiCl supported in the LiCl-impregnated TpPa-1 of the obtained composite material is 15 to 45 wt.%.

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