Long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single crystal phase change material and preparation method thereof

Abstract

The invention discloses a long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single-crystal phase change material and a preparation method thereof, ethylenediamine is used as an alkaline ligand, long-chain n-alkanoic acid is used as an acidic ligand, and the long-chain n-alkanoic acid is introduced to amino groups at two ends of ethylenediamine through a salt forming reaction to form the long-chain single-crystal phase change material with a sandwich layered structure. The structural formula of the material is [NH3 (CH2) 2NH3] < 2 + >. 2 [RCOO] <->, wherein R represents C11-C15 linear alkyl; the single crystal is regular in structure and belongs to a triclinic system and a P1 space group, and Z is equal to 1. The narrow phase change temperature zone and the phase change enthalpy of the material are averagely improved by more than 30% and can be maximally improved by more than 80% compared with corresponding long-chain n-alkanoic acid, and the material has good thermodynamic properties and is expected to be applied to the fields of industrial waste heat recovery, solar heat storage, aerospace thermal control systems and the like as an efficient phase change energy storage material.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change energy storage materials, and particularly relates to a single crystal phase change material with a "sandwich" layered structure prepared by a salt-forming reaction using ethylenediamine and long-chain normal alkanoic acid as ligands. Background Art

[0002] Phase change energy storage materials (PCMs) play an important role in solving energy shortages, improving energy utilization efficiency, etc., and are widely used in industrial waste heat recovery, solar energy heat storage, building energy conservation, aerospace thermal control and other fields. However, traditional phase change energy storage materials have significant defects: although organic materials (such as fatty acids, paraffins, etc.) have advantages such as good cycle stability and no phase separation, their phase change enthalpies are generally low; although inorganic materials (such as hydrated salts, molten salts, etc.) have higher phase change enthalpies, they face problems such as large supercooling degrees and serious phase separation. In addition, due to the difficulty of forming a long-range ordered structure in the molecular arrangement of long-chain organic materials, it is usually difficult to crystallize into single crystals, and accurate thermodynamic data cannot be obtained, resulting in limited phase change performance.

[0003] In recent years, researchers have improved the phase change enthalpy of phase change energy storage materials by modifying functional groups or extending carbon chains. For example, long-chain amine compounds are combined with short-chain strong acids to form salt materials. However, in the prior art, long-chain fatty acids are more often compounded with other materials to improve their thermodynamic properties, and the formed composites still have problems such as low crystallinity, wide phase change temperature range, and insufficient thermal stability. In addition, although the inorganic ammonium salts of long-chain fatty acids (such as di-n-alkylammonium tetrachlorometalate) have a layered structure, their synthesis conditions are harsh, and the influence law of carbon chain length on phase change performance has not been clarified. The development of layered materials such as di-n-alkylammonium tetrachlorometalate mainly realizes through solvothermal synthesis method (150 - 200 °C, nitrogen protection) or ion exchange method (such as the reaction of tetrachlorometalic acid with long-chain quaternary ammonium salt in DMF for 48 hours). By regulating the alkyl chain length (C8 - C 18 ) and the type of counter ion, the layer spacing (1.2 - 3.8 nm) can be adjusted. In terms of performance, short-chain (C8 - C 12 ) materials have relatively low phase change temperatures (-20 - 50 °C) and have fast ion conduction characteristics (10-3 S / cm), but their thermal stability is poor (decomposition temperature < 200 °C); long-chain (C 14 - C 18)The layered structure of the material is more stable, and the phase change enthalpy value is increased to 80 - 120 J / g, but the ionic mobility decreases by two orders of magnitude. However, these materials still face many problems: synthesis requires strict anhydrous and anaerobic conditions, and trace impurities are likely to cause lamellar defects; the carbon chain length has a non-linear relationship with the phase change performance (for example, the C16 material shows a performance inflection point due to chain entanglement), and there is a lack of a universal structure-activity model; the cycle stability is poor, and the layered structure is prone to collapse after high-temperature phase change (the enthalpy value decays by 40% after 20 cycles). Current research focuses on developing amphiphilic templating agents and gradient carbon chain composite strategies to break through the above bottlenecks (Chemistry of Materials, 2023, 35(8): 3205 - 3218; Journal of Materials Chemistry A, 2022, 10(12): 6589 - 6602). Therefore, developing a new single-crystal phase change material with both high phase change enthalpy and narrow phase change temperature range has important scientific significance and application value. Summary of the Invention

[0004] The object of the present invention is to solve the problems in the prior art that the long-chain fatty acid has low phase change enthalpy and is difficult to form single crystals, and to provide a long-chain ethylenediamine bis(n-alkanoic acid) diammonium salt phase change material with both high phase change enthalpy and narrow phase change temperature range, and to provide a preparation method for this material.

[0005] For the above object, the structural formula of the single-crystal phase change material of long-chain ethylenediamine bis(n-alkanoic acid) diammonium salt provided by the present invention is [NH3(CH2)2NH3] 2+ ·2[RCOO] - , where R represents a straight-chain alkyl group of C 11 ~C 15 ; this single-crystal phase change material belongs to the triclinic system, space group, Z = 1 (indicating that each unit cell contains one compound molecule).

[0006] The preparation method of the above single-crystal phase change material of long-chain ethylenediamine bis(n-alkanoic acid) diammonium salt is as follows:

[0007] Step 1: Completely dissolve the long-chain n-alkanoic acid in absolute ethanol, and then dropwise add ethylenediamine with a purity ≥ 90%. After ultrasonic dispersion, a precursor solution is obtained; the molar ratio of the long-chain n-alkanoic acid to ethylenediamine in the precursor solution is 2 - 5:1, and the mass ratio of the long-chain n-alkanoic acid to the volume of absolute ethanol is 1 g:150 - 400 mL; the long-chain n-alkanoic acid is selected from any one of n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, n-pentadecanoic acid, and n-hexadecanoic acid.

[0008] Step 2: Place the precursor solution in a rotary evaporator and perform rotary evaporation at 55 - 80 °C. Stop heating when the solution volume is reduced to 80% - 84% of the original volume, and let it stand for 10 - 12 hours to precipitate needle-shaped crystals. Recrystallize the precipitated needle-shaped crystals with absolute ethanol to obtain a long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single-crystal phase change material.

[0009] Further, in the above Step 1, it is preferred that the n-alkanoic acid is n-tetradecanoic acid.

[0010] Further, in the above Step 1, it is preferred that the molar ratio of the long-chain n-alkanoic acid to ethylenediamine in the precursor solution is 3:1.

[0011] Further, in the above Step 1, it is preferred that the mass ratio of the long-chain n-alkanoic acid to the volume of absolute ethanol is 1 g: 180 - 250 mL.

[0012] Further, in the above Step 2, when the long-chain n-alkanoic acid is n-dodecanoic acid, it is preferred that the rotary evaporation temperature is 60 ± 2 °C.

[0013] Further, in the above Step 2, when the long-chain n-alkanoic acid is n-tridecanoic acid or n-tetradecanoic acid, it is preferred that the rotary evaporation temperature is 65 ± 2 °C.

[0014] Further, in the above Step 2, when the long-chain n-alkanoic acid is n-pentadecanoic acid or n-hexadecanoic acid, it is preferred that the rotary evaporation temperature is 75 ± 2 °C.

[0015] Further, in the above Step 2, it is preferred that the number of recrystallizations with absolute ethanol is 3 - 6 times.

[0016] The beneficial effects of the present invention are as follows:

[0017] In the present invention, ethylenediamine is used as the basic ligand and long-chain n-alkanoic acid is used as the acidic ligand. By precisely controlling the molar ratio of the long-chain n-alkanoic acid to ethylenediamine (greater than 2:1), optimizing the solvent volume and temperature gradient, long-chain n-alkanoic acid is introduced onto the amino groups at both ends of ethylenediamine, successfully solving the technical problem that it is difficult for long-chain fatty acids to form single crystals. A series of ethylenediamine bis-n-alkanoic acid diammonium salt single-crystal phase change materials with a "sandwich" layered structure of "organic layer - inorganic layer - organic layer" (the organic layer refers to the long carbon chain, and the inorganic layer refers to the short carboxyl and ammonium groups) are prepared for the first time. This method combines rotary evaporation and static crystallization, and cooperates with the multiple recrystallization process, significantly improving the regularity and purity of the crystals, and finally obtaining high-quality single crystals. The single crystals of the obtained material have a regular structure, and its unique "organic layer - inorganic layer - organic layer" structure is connected by strong N-H···O hydrogen bonds, endowing the material with excellent thermodynamic properties, including narrow temperature range phase change (7.12 - 16.64 °C) and high phase change enthalpy (236.41 - 342.81 J·g -1) It is increased by more than 30% on average compared with the corresponding long-chain n-alkanoic acid. Among them, the phase change enthalpy of the single-crystal phase change material of long-chain ethylenediamine bis(n-tetradecanoate) is even increased by 80.43%. This breakthrough not only overcomes the bottleneck of the difficult crystallization of traditional long-chain organic materials, but also provides a new solution for the application of high-efficiency phase change energy storage materials in the fields of industrial waste heat recovery, solar energy heat storage, and aerospace thermal control systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the crystal cell structure diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-dodecanoate) obtained in Example 1.

[0019] Figure 2 It is the TG / DSC thermal analysis diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-dodecanoate) obtained in Example 1.

[0020] Figure 3 It is the crystal cell structure diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-tridecanoate) obtained in Example 2.

[0021] Figure 4 It is the TG / DSC thermal analysis diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-tridecanoate) obtained in Example 2.

[0022] Figure 5 It is the crystal cell structure diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-tetradecanoate) obtained in Example 3.

[0023] Figure 6 It is the TG / DSC thermal analysis diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-tetradecanoate) obtained in Example 3.

[0024] Figure 7 It is the crystal cell structure diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-pentadecanoate) obtained in Example 4.

[0025] Figure 8 It is the TG / DSC thermal analysis diagram of the single-crystal phase change material of long-chain ethylenediamine bis(n-pentadecanoate) obtained in Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be further described in detail below in conjunction with the drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0027] Example 1

[0028] Step 1: Weigh 1.202 g (6 mmol) of dodecanoic acid and add it to 240 mL of absolute ethanol. Stir at room temperature until completely dissolved to form a transparent solution; then weigh 0.204 g (2 mmol) of ethylenediamine with a purity of more than 90%, and add it dropwise to the above transparent solution. Ultrasonically disperse it evenly to obtain a precursor solution.

[0029] Step 2: Place the precursor solution from Step 1 in a rotary evaporator and rotate it at 60 °C. When the volume of the solution has evaporated to 200 mL, turn off the power of the rotary evaporator and let it stand at room temperature for 12 hours. Needle-like crystals will precipitate from the solution. Recrystallize the precipitated needle-like crystals 5 times with absolute ethanol to obtain white transparent crystals, namely the single crystal phase change material of long-chain ethylenediamine bis-n-dodecanoate diammonium salt (denoted as 2C12), and its structural formula is [NH3(CH2)2NH3] 2+ ·2[C 11 H 23 COO] - , and the relative molar mass is 460.73 g·mol -1 .

[0030] Tested by an X-ray single crystal diffractometer and analyzed and confirmed by professional single crystal analysis software, the 2C12 crystal belongs to the triclinic system, space group, unit cell parameters: α = 93.69(3)°, β = 91.61(3)°, γ = 101.50(3)°. Figure 1 Figure 2C12 shows the unit cell structure diagram, indicating that its single unit cell contains one 2C12 molecule (i.e., Z = 1). The ethylenediamine cation and the n-dodecanoate anion are connected by strong N-H···O hydrogen bonds, forming a layered "sandwich" structure of "organic layer - inorganic layer - organic layer". Figure 2 The TG / DSC test results show that the melting starting point of 2C12 is 82.48 °C, the melting end point is 97.12 °C, the phase change temperature range is 16.64 °C, and the phase change enthalpy is 245.70 J·g -1 . During the heating process, an endothermic peak appears at 87.23 °C and 94.12 °C respectively, indicating that the solid-solid phase change and solid-liquid phase change temperatures are close, showing good phase change characteristics.

[0031] Example 2

[0032] Step 1: Weigh 0.643 g (3 mmol) of n-tridecanoic acid and add it to 230 mL of absolute ethanol. Stir at room temperature until completely dissolved to form a transparent solution. Then weigh 0.102 g (1 mmol) of ethylenediamine with a purity of over 90% and add it dropwise to the above transparent solution. Ultrasonically disperse it evenly to obtain a precursor solution.

[0033] Step 2: Place the precursor solution from Step 1 in a rotary evaporator and rotate and evaporate it at 65 °C. When the volume of the solution has evaporated to 190 mL, turn off the power of the rotary evaporator and let it stand at room temperature for 10 hours. Needle-shaped crystals will precipitate in the solution. Recrystallize the precipitated needle-shaped crystals 5 times with absolute ethanol to obtain white transparent crystals, namely the single-crystal phase change material of long-chain ethylenediamine bis-n-tridecanoate diammonium salt (denoted as 2C13), and its structural formula is [NH3(CH2)2NH3] 2+ ·2[C 12 H 25 COO] - , and the relative molar mass is 488.78 g·mol -1 .

[0034] Tested by an X-ray single crystal diffractometer and analyzed and confirmed with professional single crystal analysis software, the 2C13 crystal belongs to the triclinic system, space group, unit cell parameters: α = 87.202(3)°, β = 86.531(3)°, γ = 78.500(2)°. Figure 3 Figure is the unit cell structure diagram of 2C13, showing that its single unit cell contains one 2C13 molecule (i.e., Z = 1). The ethylenediamine cation and the n-dodecanoate anion are connected by strong N-H···O hydrogen bonds to form a layered "sandwich" structure of "organic layer - inorganic layer - organic layer". Figure 4 The TG / DSC test results show that the melting starting point of 2C13 is 91.79 °C, the melting end point is 101.10 °C, the phase change temperature range is 9.31 °C, and the phase change enthalpy is 236.41 J·g -1 . During the heating process, an endothermic peak appears at 96.85 °C, indicating that the solid-liquid phase change temperature is relatively concentrated, showing good phase change characteristics.

[0035] Example 3

[0036] Step 1: Weigh 1.370 g (6 mmol) of n-tetradecanoic acid and add it to 250 mL of absolute ethanol. Stir at room temperature until completely dissolved to form a transparent solution. Then weigh 0.204 g (2 mmol) of ethylenediamine with a purity of over 90% and add it dropwise to the above transparent solution. Ultrasonically disperse it evenly to obtain a precursor solution.

[0037] Step 2: Place the precursor solution from Step 1 in a rotary evaporator and rotate and evaporate it at 65 °C. When the volume of the solution has evaporated to 200 mL, turn off the power of the rotary evaporator and let it stand at room temperature for 10 hours. Needle-shaped crystals will precipitate in the solution. Recrystallize the precipitated needle-shaped crystals 5 times with absolute ethanol to obtain white transparent crystals, namely the single-crystal phase change material of long-chain ethylenediamine bis-n-tetradecanoate diammonium salt (denoted as 2C14), and its structural formula is [NH3(CH2)2NH3]2+ ·2[C 13 H 27 COO] - , with a relative molar mass of 516.83 g·mol -1 .

[0038] Tested by an X-ray single crystal diffractometer and analyzed and confirmed with professional single crystal analysis software, the 2C14 crystal belongs to the triclinic system, space group, unit cell parameters: α = 91.105(2)°, β = 93.210(2)°, γ = 100.733(9)°. Figure 5 Figure 1 is the unit cell structure diagram of 2C14, showing that its single unit cell contains one 2C14 molecule (i.e., Z = 1), and the ethylenediamine cation and the n-dodecanoic acid anion are connected by strong N-H···O hydrogen bonds to form a layered "sandwich" structure of "organic layer - inorganic layer - organic layer". Figure 6 The TG / DSC test results of Figure 2 show that the melting starting point of 2C14 is 91.72 °C, the melting end point is 100.15 °C, the phase change temperature range is 8.43 °C, and the phase change enthalpy is 342.18 J·g -1 . During the heating process, an endothermic peak appears at 96.85 °C, indicating that the solid-liquid phase change temperature is relatively concentrated, showing good phase change characteristics.

[0039] Example 4

[0040] Step 1: Weigh 0.635 g (3 mmol) of n-hexadecanoic acid and add it to 250 mL of absolute ethanol. Stir at room temperature until completely dissolved to form a transparent solution; then weigh 0.102 g (1 mmol) of ethylenediamine with a purity of over 90%, and add it dropwise to the above transparent solution. Ultrasonically disperse it evenly to obtain a precursor solution.

[0041] Step 2: Place the precursor solution from Step 1 in a rotary evaporator and rotate and evaporate at 75 °C. Turn off the power of the rotary evaporator when the solution volume has evaporated to 200 mL, and let it stand at room temperature for 12 hours. Needle-like crystals precipitate out in the solution; recrystallize the precipitated needle-like crystals 5 times with absolute ethanol to obtain white transparent crystals, namely the single crystal phase change material of long-chain ethylenediamine bis(n-hexadecanoate) diammonium salt (denoted as 2C16), and its structural formula is [NH3(CH2)2NH3] 2+ ·2[C 15 H 31 COO] - , with a relative molar mass of 516.83 g·mol -1 .

[0042] Tested by an X-ray single crystal diffractometer and analyzed and confirmed with professional single crystal analysis software, the 2C16 crystal belongs to the triclinic system, Space group, unit cell parameters: α = 91.105(5)°, β = 93.210(5)°, γ = 100.733(2)°. Figure 7 This is the crystal cell structure diagram of 2C16, showing that its single crystal cell contains one 2C16 molecule (i.e., Z = 1). The ethylenediamine cation and the dodecanoic acid anion are connected by strong N-H···O hydrogen bonds to form a layered "sandwich" structure of "organic layer - inorganic layer - organic layer". Figure 8 The TG / DSC test results of [substance] show that the melting starting point of 2C16 is 98.46 °C, the melting end point is 105.58 °C, the phase change temperature range is 7.12 °C, and the phase change enthalpy is 262.32 J·g -1 . During the heating process, an endothermic peak appears at 102.48 °C, indicating that the solid-liquid phase change temperature is relatively concentrated, showing good phase change characteristics.

[0043] The single crystal phase change material prepared in the above example was compared with the data of long-chain n-alkanoic acids reported in the literature, and the results are shown in Table 1.

[0044] Table 1

[0045]

[0046] Note: The performance data of lauric acid, myristic acid, and palmitic acid in Table 1 are from the literature "Al-Ahmed A, Mazumder M AJ, Salhi B, et al. Effects of carbon-based fillers on thermal properties of fatty acids and their eutectics as phase change materials used for thermal energy storage: A Review[J]. Journal of Energy Storage, 2021, 35: 102329.".

[0047] As can be seen from Table 1, through the bridging effect of ethylenediamine in the present invention, both the carbon chain and the functional group of the long-chain n-alkanoic acid are doubled, thereby significantly improving the thermal properties of the long-chain n-alkanoic acid. It should be noted that there seems to be a small error in the original text where "262.32J·g " in ID=8 is incomplete. I've translated it as best as possible based on the context. Also, the "substance" in ID=8 is a placeholder as the original text doesn't clearly define what the TG / DSC test is for.

Claims

1. A long-chain ethylenediamine diammonium salt single crystal phase change material, characterized in that: The structural formula of the single crystal phase change material is [NH3(CH2)2NH3] 2+ ·2[RCOO] - , where R represents C 11 ~C 15 The single crystal phase change material belongs to the triclinic system, the P1 space group, and Z=1.

2. A method for preparing the long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single crystal phase change material according to claim 1, characterized in that It consists of the following steps: Step 1: completely dissolving a long-chain n-alkanoic acid in anhydrous ethanol, then adding ethylenediamine with a purity of ≥90% dropwise, and obtaining a precursor solution after uniform ultrasonic dispersion; the molar ratio of the long-chain n-alkanoic acid to ethylenediamine in the precursor solution is 2-5:1, and the volume ratio of the mass of the long-chain n-alkanoic acid to the anhydrous ethanol is 1 g:150-400 mL; the long-chain n-alkanoic acid is selected from any one of n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, n-pentadecanoic acid, and n-hexadecanoic acid; Step 2: Place the precursor solution in a rotary evaporator and perform rotary evaporation at 55-80° C., stop heating when the solution volume is reduced to 80%-84% of the original volume, and let it stand for 10-12 hours to precipitate needle-shaped crystals; recrystallize the precipitated needle-shaped crystals with anhydrous ethanol to obtain a single crystal phase change material of long-chain ethylenediamine diammonium bis-n-alkanoate.

3. The method for preparing the long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single crystal phase change material according to claim 2, characterized in that: In step 1, the long-chain n-alkanoic acid is n-tetradecanoic acid.

4. The method for preparing the long-chain ethylenediamine bis-normal-alkanoic acid diammonium salt single crystal phase change material according to claim 2 or 3, characterized in that: In step 1, the molar ratio of long-chain n-alkanoic acid to ethylenediamine in the precursor solution is 3:

1.

5. The method for preparing the long-chain ethylenediamine bis-normal-alkanoic acid diammonium salt single crystal phase change material according to claim 2 or 3, characterized in that: In step 1, the mass ratio of the long-chain n-alkanoic acid to the volume of anhydrous ethanol is 1 g:180-250 mL.

6. The method for preparing the long-chain ethylenediamine bis-normal-alkanoic acid diammonium salt single crystal phase change material according to claim 2, characterized in that: In step 2, when the long-chain n-alkanoic acid is n-dodecanoic acid, the rotary evaporation temperature is 60±2°C.

7. The method for preparing the long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single crystal phase change material according to claim 2, characterized in that: In step 2, when the long-chain n-alkanoic acid is n-tridecanoic acid or n-tetradecanoic acid, the rotary evaporation temperature is 65±2°C.

8. The method for preparing the long-chain ethylenediamine bis-n-alkanoic acid diammonium salt single crystal phase change material according to claim 2, characterized in that: In step 2, when the long-chain n-alkanoic acid is n-pentadecanoic acid or n-hexadecanoic acid, the rotary evaporation temperature is 75±2°C.

9. The method for preparing the long-chain ethylenediamine bis-normal-alkanoic acid diammonium salt single crystal phase change material according to claim 2, characterized in that: In step 2, the recrystallization with anhydrous ethanol is performed 3 to 6 times.

Images