Modification method for reducing supercooling degree of sugar alcohol phase change material

Abstract

The invention discloses a modification method for reducing the supercooling degree of a sugar alcohol phase change material. The modification method for reducing the supercooling degree of the sugar alcohol phase change material comprises the following steps: (1) mixing the sugar alcohol phase change material, an amine substance and a benzene series, and carrying out azeotropic reflux reaction; (2) adding the mixture obtained in the step (1) into a benzene series solution containing an acylation reagent in a low-temperature environment, and reacting; and (3) carrying out suction filtration, drying and evaporation on the mixture after the reaction in the step (2), placing the mixture in an organic solvent to form a precipitate, and carrying out suction filtration and drying treatment to obtain the modified sugar alcohol phase change material. The sugar alcohol phase change material obtained by the modification method provided by the invention has the advantages of low supercooling degree, long service cycle, basically unchanged thermal property and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of phase change energy storage materials, and particularly relates to a modification method for reducing the supercooling degree of sugar alcohol phase change materials. Background Art

[0002] Sugar alcohols are polyols containing more than two hydroxyl groups. However, unlike polyols such as ethylene glycol, propylene glycol, and pentaerythritol synthesized from petrochemicals, sugar alcohols can be prepared from a wide range of corresponding sugar substances, that is, by reducing the aldehyde or ketone groups on the sugar molecules to hydroxyl groups to obtain the corresponding sugar alcohols. Common sugar alcohols include xylitol, sorbitol, erythritol, and D-mannitol. They can not only be used as food additives, but also have a high latent heat of phase change, are non-toxic, non-corrosive, and have no phase stratification. They have a large energy storage density in the entire working range and can achieve efficient energy utilization. They are excellent medium-temperature phase change materials (90°C to 200°C). However, compared with paraffin-based organic phase change materials, the supercooling problem of sugar alcohol phase change materials seriously restricts their large-scale promotion and use. The supercooling degree of some sugar alcohol phase change materials is as high as 60°C or above. Therefore, it is necessary to modify them to inhibit supercooling.

[0003] CN112126413A discloses a composite phase change material and its preparation method. 4g of erythritol and 0.2g of graphene oxide are placed in a beaker, dissolved in an ethanol-water solution, and ultrasonically treated for 6 hours to obtain a mixture. The mixture is then dried in an 80°C oven for 8 hours to obtain a dried mixture, which is then ground to obtain a composite phase change material. The liquid graphene oxide increases the surface area and acts as a nucleating agent, thereby reducing the supercooling of the composite phase change material. However, erythritol and graphene oxide are only bonded together by hydrogen bonds and van der Waals forces between functional groups. This leads to delamination over long-term use, causing the supercooling of the composite phase change material to gradually increase. Furthermore, the ratio of graphene oxide to erythritol must be precisely controlled. A too low ratio can easily lead to instability in the composite phase change material, while a too high ratio can easily cause cracking and other adverse phenomena, making it unsuitable for large-scale promotion and use. At the same time, graphene oxide itself has a high cost. After it is compounded with erythritol, it offsets the advantage of erythritol's high heat storage density to a certain extent, which is not worth the cost.

[0004] CN116970371A discloses an energy storage phase change material and its preparation and application. Sodium carboxymethyl cellulose is dissolved in water, and erythritol is added to the sodium carboxymethyl cellulose aqueous solution, followed by stirring at room temperature to obtain a homogeneous sugar alcohol polymer aqueous solution. The homogeneous sugar alcohol polymer aqueous solution is then dehydrated to obtain an energy storage phase change material. This method employs physical blending technology to induce crystallization through heterogeneous nucleation, thereby reducing the supercooling of erythritol. However, suppressing the supercooling of erythritol through the physical action of sodium carboxymethyl cellulose and an ionic crosslinker can easily result in an extension of the glass transition time of erythritol in the metastable phase of phase transition and a fundamental change in the phase transition properties. This means that the thermal properties of the composite energy storage phase change material will differ from those of the original phase change material, causing certain interference in its practical application. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a modification method for reducing the supercooling degree of a sugar alcohol phase change material. The sugar alcohol phase change material obtained by the modification method provided by the present invention has the advantages of low supercooling degree, long service life, and substantially unchanged thermal properties.

[0006] A first aspect of the present invention provides a modification method for reducing the supercooling degree of a sugar alcohol phase change material, comprising the following steps:

[0007] (1) mixing a sugar alcohol phase change material, an amine substance and a benzene series substance, and performing an azeotropic reflux reaction;

[0008] (2) adding a benzene series solution containing an acylating agent to the mixture obtained in step (1) in a low temperature environment to carry out a reaction;

[0009] (3) The mixture after the reaction in step (2) is filtered, dried and evaporated, and then placed in an organic solvent to form a precipitate, and then filtered and dried to obtain the modified sugar alcohol phase change material.

[0010] Furthermore, in step (1), the sugar alcohol phase change material is selected from at least one of xylitol, sorbitol, erythritol and D-mannitol.

[0011] Furthermore, in step (1), the amine substance is selected from one or more of N,N-dimethylformamide, melamine and triethanolamine, preferably N,N-dimethylformamide.

[0012] Furthermore, in step (1), the benzene series compound is selected from one or more of benzene, toluene and xylene, preferably toluene.

[0013] Furthermore, in step (1), the mass ratio of the sugar alcohol phase change material, the amine substance and the benzene series is 1: (0.09-0.43): (7-60), preferably 1: (0.14-0.27): (10-45).

[0014] Furthermore, in step (1), the reaction temperature is 100°C to 178°C, preferably 109°C to 150°C.

[0015] Furthermore, in step (1), the azeotropic reflux reaction time is 0.5h to 12h, preferably 2.5h to 6.5h.

[0016] Furthermore, in step (2), the low-temperature water bath environment temperature is -15°C to 10°C, preferably -3.4°C to 5.7°C.

[0017] Furthermore, in step (2), the acylating agent is selected from one or more of acetyl bromide, propionyl bromide and acryloyl bromide, preferably acryloyl bromide.

[0018] Furthermore, in step (2), the benzene series compound is selected from one or more of benzene, toluene and xylene, preferably toluene.

[0019] Furthermore, in step (2), the mass ratio of the acylating agent to the benzene series is 1:(17-60), preferably 1:(26-43).

[0020] Furthermore, in step (2), the mass ratio of the sugar alcohol phase change material to the acylating agent is 1:(0.05-0.37), preferably 1:(0.09-0.21).

[0021] Furthermore, in step (2), the adding method is preferably a dropwise addition method, wherein the dropping speed of the benzene series solution containing the acylating agent is (2.9 g / min to 6.7 g / min): 50 g of sugar alcohol phase change material, preferably (3.5 g / min to 5.6 g / min): 50 g of sugar alcohol phase change material; in step (2), the stirring speed when the acylating agent benzene series solution is added dropwise is 1000 rpm to 3000 rpm, preferably 1400 rpm to 1900 rpm.

[0022] Furthermore, in step (2), after the addition is completed, the temperature is raised to 18°C ​​to 60°C, preferably 27°C to 56°C.

[0023] Furthermore, in step (2), after the addition is completed, the reaction is continued to be stirred at a speed of 500 rpm to 1300 rpm, preferably 800 rpm to 1100 rpm, for 10 h to 40 h, preferably 16 h to 33 h.

[0024] Furthermore, in step (3), the desiccant used for the drying is selected from any one of color-changing silica gel, 5A molecular sieve and calcium chloride.

[0025] Furthermore, in step (3), the evaporation is preferably rotary evaporation, the evaporation speed is 45 rpm to 165 rpm, preferably 50 rpm to 130 rpm, the temperature is 50°C to 150°C, preferably 70°C to 130°C, and the time is 20 min to 180 min, preferably 50 min to 100 min.

[0026] Furthermore, in step (3), the organic solvent is selected from one or more of petroleum ether, acetone and chloroform, preferably petroleum ether.

[0027] Furthermore, in step (3), the drying temperature of the drying treatment is 40° C. to 60° C., and the drying time is 20 h to 30 h.

[0028] The second aspect of the present invention provides a modified sugar alcohol phase change material obtained by the above modification method.

[0029] Furthermore, the modified sugar alcohol phase change material has a phase change temperature of 90°C to 200°C, a phase change latent heat of 230J / g to 350J / g, and a supercooling degree of 7°C to 15°C.

[0030] Furthermore, after the modified sugar alcohol phase change material continuously absorbs and releases heat 500 times, its phase change temperature is basically unchanged compared with before the continuous absorption and release of heat 500 times, the phase change latent heat value changes by no more than 5% compared with before the continuous absorption and release of heat 500 times, and the supercooling degree is no more than 15% compared with before the continuous absorption and release of heat 500 times.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) The present invention introduces acyl compounds into the sugar alcohol phase change material through chemical modification. Unlike physical modification methods involving the simple addition of nucleating agents, the modified sugar alcohol phase change material prepared by the present invention has stable physical and chemical properties. The modification process does not substantially affect the thermal properties of the sugar alcohol phase change material, i.e., the phase transition temperature of the sugar alcohol phase change material remains essentially unchanged before and after modification. Furthermore, the introduction of the acyl compounds increases the latent heat of phase change of the modified sugar alcohol phase change material.

[0033] (2) The inventors discovered that the supercooling phenomenon of sugar alcohol phase change materials is mainly caused by the mutual hydrogen bonding between the hydroxyl functional groups. Excessive hydrogen bonding easily constrains and limits the mobility and molecular order of the melted sugar alcohol phase change material molecules, thus causing a more serious supercooling problem. The present invention successfully replaces part of the hydroxyl functional group structure by introducing acyl compounds, appropriately reducing the strength of hydrogen bonding in the sugar alcohol phase change material. Therefore, the supercooling degree of the modified sugar alcohol phase change material is significantly reduced and it is not easy to reciprocate.

[0034] (3) The modification method of the present invention is simple, and the obtained product has stable thermal properties, low supercooling, strong repeatability, and is suitable for industrial batch production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the SEM picture of erythritol before modification;

[0036] Figure 2 This is a SEM photo of the modified erythritol prepared in Example 1;

[0037] Figure 3 This is a SEM photo of the modified erythritol prepared in Comparative Example 4;

[0038] Figure 4 This is a SEM photograph of the modified erythritol prepared in Comparative Example 6;

[0039] Figure 5 500 consecutive DSC endothermic-exothermic curves of erythritol before modification;

[0040] Figure 6 500 consecutive DSC endothermic-exothermic curves of the modified erythritol prepared in Example 1;

[0041] Figure 7 500 consecutive DSC endothermic-exothermic curves of the modified erythritol prepared in Comparative Example 4;

[0042] Figure 8 500 consecutive DSC endothermic-exothermic curves of the modified erythritol prepared in Comparative Example 6. DETAILED DESCRIPTION

[0043] The following examples further illustrate the modification method and effect of the modified sugar alcohol phase change material of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples.

[0044] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0045] In the present invention, a DSC-60Plus differential scanning calorimeter produced by Shimadzu Corporation of Japan is used to test the phase change temperature, phase change latent heat and supercooling of the sugar alcohol phase change material before and after modification.

[0046] In the present invention, a FlexSEM1000II scanning electron microscope produced by Hitachi, Japan, was used to observe the surface morphology of the sugar alcohol phase change material before and after modification.

[0047] Example 1

[0048] 50g of erythritol, 10g of N,N-dimethylformamide, and 1500g of toluene were placed in a round-bottom flask and azeotropically refluxed in an oil bath at 132°C for 4 hours. The mixture was then cooled naturally to 25°C. The round-bottom flask was transferred to a -1.6°C water bath and stirred at 1670 rpm while adding 206.4g of a toluene solution of 6.4g of acryloyl bromide and 200g of toluene dropwise at a rate of 4.2g / min. After the addition was complete, the water bath temperature was raised to 37°C and stirring continued at 970 rpm for 26 hours. The resulting mixture was filtered, and the paste-like filter cake was passed through 5A molecular sieves and then rotary evaporated at 110 rpm, 96°C, and evaporation for 75 minutes. The resulting product was precipitated in petroleum ether, filtered, and dried at 50°C for 25 hours to obtain the modified sugar alcohol phase change material.

[0049] Example 2

[0050] 50g of erythritol, 7g of N,N-dimethylformamide, and 1150g of toluene were placed in a round-bottom flask and azeotropically refluxed in an oil bath at 132°C for 4 hours. The mixture was then cooled naturally to 25°C. The round-bottom flask was then transferred to a -1.6°C water bath and stirred at 1670 rpm while 121.5g of a toluene solution of 4.5g acryloyl bromide and 117g toluene was added dropwise at a rate of 4.2g / min. After the addition was complete, the water bath temperature was raised to 37°C and stirring continued at 970 rpm for 26 hours. The resulting mixture was filtered, and the thin paste filter cake was passed through 5A molecular sieves and then rotary evaporated at 110 rpm, 96°C, and evaporation for 75 minutes. The resulting product was precipitated in petroleum ether, filtered, and dried at 50°C for 25 hours to obtain the modified sugar alcohol phase change material.

[0051] Example 3

[0052] Compared with Example 1, the difference is that melamine and xylene are used instead of N,N-dimethylformamide and toluene respectively, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0053] Example 4

[0054] Compared with Example 1, the difference is that the amount of N,N-dimethylformamide in "10g N,N-dimethylformamide and 1500g toluene placed in a round-bottom flask" is increased to 13.5g, and the amount of toluene is reduced to 500g. Other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0055] Example 5

[0056] Compared with Example 1, the difference is that the oil bath ambient temperature is lowered to 109°C, the azeotropic reflux reaction time is extended to 12 h, the low-temperature water bath ambient temperature is raised to 10°C, and the stirring speed is reduced to 1000 rpm when the acylating agent benzene series solution is added dropwise. The other reaction conditions and material composition remain unchanged to obtain a modified sugar alcohol phase change material.

[0057] Example 6

[0058] Compared with Example 1, the difference is that acetyl bromide, benzene and acetone are used instead of acryloyl bromide, toluene and petroleum ether respectively, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0059] Example 7

[0060] Compared with Example 1, the difference is that the amount of acryloyl bromide in "6.4 g of acryloyl bromide and 200 g of toluene" is increased to 18.5 g, the amount of toluene is increased to 314.5 g, and the dripping rate of the acylating agent benzene series solution is increased to 6.7 g / min. The other reaction conditions and material composition remain unchanged to obtain a modified sugar alcohol phase change material.

[0061] Example 8

[0062] Compared with Example 1, the difference is that the water bath temperature in "after the addition is completed, the water bath temperature is increased to 37°C" is increased by 56°C, the stirring reaction speed is reduced to 500 rpm, the time is shortened to 10 h, the rotary evaporation speed is reduced to 50 rpm, the temperature is increased to 130°C, and the time is shortened to 20 min. The other reaction conditions and material composition remain unchanged to obtain a modified sugar alcohol phase change material.

[0063] Comparative Example 1

[0064] Compared with Example 1, the difference is that N,N-dimethylformamide is omitted, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0065] Comparative Example 2

[0066] Compared with Example 1, the difference is that anhydrous methanol is used instead of toluene, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0067] Comparative Example 3

[0068] Compared with Example 1, the difference is that after erythritol, N,N-dimethylformamide and toluene are placed in a round-bottom flask, a heating and stirring reaction at 132° C. is adopted instead of an azeotropic reflux reaction in an oil bath environment. Other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0069] Comparative Example 4

[0070] Compared with Example 1, the difference is that the water bath temperature is 20° C. instead of the low-temperature water bath environment, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0071] Comparative Example 5

[0072] Compared with Example 1, the difference is that the rotary evaporation process is omitted, and other reaction conditions and material compositions remain unchanged to obtain a modified sugar alcohol phase change material.

[0073] Comparative Example 6

[0074] Following the method described in CN112126413A, 4g of erythritol and 0.2g of 300nm graphene oxide were placed in a beaker and dissolved in an ethanol-water solution with a volume ratio of 6:1. The mixture was then ultrasonically treated at 200Hz for 6 hours to produce a mixture. The mixture was then dried in an 80°C oven for 8 hours and ground to produce a composite phase-change material with a particle size of 400nm.

[0075] Comparative Example 7

[0076] Following the method described in CN116970371A, 0.3 g of sodium carboxymethyl cellulose (500 mPa·s viscosity) was dissolved in 30 mL of water. 1.2 g of erythritol was added to the mixed solution and stirred at room temperature for 2 hours to form a homogeneous aqueous solution of the sugar alcohol polymer. This solution was then dried at 80°C under normal pressure for 16 hours to obtain a composite phase change material.

[0077] Test Example 1

[0078] The thermal properties of the sugar alcohol phase change materials before and after modification in Examples 1-8 and Comparative Examples 1-7 were measured. The specific results are shown in Table 1.

[0079] Table 1 Thermal properties of sugar alcohol phase change materials before and after modification prepared in Examples and Comparative Examples

[0080]

[0081]

[0082] As can be seen from Table 1, the modified sugar alcohol phase change material prepared by the method of the present invention has good thermal properties. The latent heat of phase change and supercooling of the sample in Example 1 are 340.5 J / g and 7.0°C, respectively. After 500 consecutive endothermic-exothermic cycles, the latent heat of phase change and supercooling of the sample in Example 1 are maintained at 338.7 J / g and 7.3°C, respectively. The latent heat of phase change of the samples in Comparative Example 6 and Comparative Example 7 are both lower than 230 J / g, and their supercooling are both over 20°C, which is significantly different from the samples in the examples. Figure 1 and Figure 2 It can be seen that the microscopic morphology of the sample in Example 1 is not much different from that of the raw material erythritol, that is, the modification method of the present invention does not produce surface structure destruction effect on the raw material erythritol. Figure 3 and Figure 4 It can be seen that the microscopic morphology of the samples of Comparative Examples 4 and 6 has changed to a certain extent. In particular, after the addition of graphene oxide to Comparative Example 6, the microscopic morphology of the composite phase change material has changed significantly, with obvious delamination and peeling, which is not conducive to the long-term use of the material. Figure 5-Figure 8 It can be seen that after 500 consecutive endothermic-exothermic experiments, the thermal stability of the sample in Example 1 was good, and no significant change in supercooling occurred; while the sample in Comparative Example 6 showed an obvious increase in supercooling, and a new phase transition characteristic peak appeared in its DSC melting curve. This is because the addition of graphene oxide brought adverse factors to erythritol itself.

Claims

1. A modification method for reducing the supercooling degree of a sugar alcohol phase change material, comprising the following steps: (1) mixing a sugar alcohol phase change material, an amine substance, and a benzene series substance, and performing an azeotropic reflux reaction; (2) adding a benzene series solution containing an acylating agent to the mixture obtained in step (1) in a low temperature environment to carry out a reaction; (3) The mixture after the reaction in step (2) is filtered, dried and evaporated, and then placed in an organic solvent to form a precipitate, and then filtered and dried to obtain the modified sugar alcohol phase change material.

2. The modification method according to claim 1, characterized in that In step (1), the sugar alcohol phase change material is selected from at least one of xylitol, sorbitol, erythritol and D-mannitol; And / or, in step (1), the amine substance is selected from one or more of N,N-dimethylformamide, melamine and triethanolamine; And / or, in step (1), the benzene series compound is selected from one or more of benzene, toluene and xylene.

3. The modification method according to claim 1, characterized in that In step (1), the mass ratio of the sugar alcohol phase change material, the amine substance and the benzene series is 1: (0.09-0.43): (7-60); and / or, in step (1), the reaction temperature is 100° C. to 178° C.; And / or, in step (1), the azeotropic reflux reaction time is 0.5h to 12h.

4. The modification method according to claim 1, characterized in that In step (2), the acylating agent is selected from one or more of acetyl bromide, propionyl bromide and acryloyl bromide; And / or, in step (2), the benzene series compound is selected from one or more of benzene, toluene and xylene, preferably toluene.

5. The modification method according to claim 1, characterized in that In step (2), the mass ratio of the acylating agent to the benzene series is 1:(17-60); And / or, in step (2), the mass ratio of the sugar alcohol phase change material to the acylating agent is 1:(0.05-0.37).

6. The modification method according to claim 1, characterized in that In step (2), the low-temperature water bath environment temperature is -15°C to 10°C; And / or, in step (2), after the addition is completed, the temperature is raised to 18° C. to 60° C.; And / or, in step (2), after the addition is completed, the reaction is continued to be stirred at a speed of 500 rpm to 1300 rpm for 10 h to 40 h.

7. The modification method according to claim 1, characterized in that The evaporation is preferably rotary evaporation, the evaporation speed is 45 rpm to 165 rpm, the temperature is 50° C. to 150° C., and the time is 20 min to 180 min; And / or, in step (3), the organic solvent is selected from one or more of petroleum ether, acetone and chloroform.

8. A modified sugar alcohol phase change material obtained by the modification method according to any one of claims 1 to 7.

9. The modified sugar alcohol phase change material according to claim 8, characterized in that: The modified sugar alcohol phase change material has a phase change temperature of 90° C. to 200° C., a phase change latent heat value of 230 J / g to 350 J / g, and a supercooling degree of 7° C. to 15° C.

10. The modified sugar alcohol phase change material according to claim 8, characterized in that: After the modified sugar alcohol phase change material continuously absorbs and releases heat 500 times, its phase change temperature is basically unchanged compared with before the continuous absorption and release of heat 500 times, the phase change latent heat value changes by no more than 5% compared with before the continuous absorption and release of heat 500 times, and the supercooling degree is no more than 15% compared with before the continuous absorption and release of heat 500 times.

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