CN106497521A - Preparation method of ternary fatty acid-silicon dioxide composite shape-stabilized phase change material - Google Patents

Abstract

The invention relates to a preparation method of a ternary fatty acid-silicon dioxide composite qualitative phase change material. The fatty acid is used as a phase change core material, and the type of ternary eutectic fatty acid is selected according to the applicable temperature range, and the three-dimensional network structure is utilized. The silica is used as an inorganic carrier to encapsulate and bind the core material, so as to obtain a composite shape-setting phase change material with different phase transition temperatures and latent heat. The supporting role of the carrier can ensure the immobility and processability of the phase change material, and can ensure that it does not leak during the phase change process, so the entire composite material can still maintain its solid shape and performance, thus ensuring the composite Energy storage stability properties of shape-setting phase change materials. The composite shape-setting phase-change material of the present invention has high latent heat, adjustable phase-change temperature, and no obvious phase separation phenomenon, and can be widely used in the fields of building energy-saving materials, temperature-adjusting clothing, solar energy utilization, medical materials, waste heat recovery, and the like.

Description

A kind of preparation method of ternary fatty acid-silicon dioxide composite shape-setting phase change material

technical field

The invention relates to the interdisciplinary field of preparation technology of phase-change energy storage materials and porous matrix materials, and relates to a preparation method of ternary fatty acid-silicon dioxide composite shape-setting phase-change materials, in particular to the preparation of fatty acid eutectics by melting mixing and ultrasonic oscillation. And using a sol-gel process to uniformly disperse the liquid phase change material in the Si-O-Si inorganic network structure to further prepare a composite shape-setting phase change material.

Background technique

Fatty acid is the most widely used solid-liquid phase change material in nature. It has the advantages of large latent heat of phase change, non-toxicity, environmental protection and recyclable use, so it has a wider application field. However, the melting point of a single fatty acid is often high. According to the theory of the lowest eutectic point, two or more fatty acids can be mixed according to a certain ratio, so as to obtain a fatty acid eutectic product that is more suitable for the medium and low temperature field, which broadens its application range and Increased economic value. However, fatty acids are prone to leakage of liquid phase substances during the phase change process, which reduces the energy storage properties. Therefore, it can be loaded with a carrier material to prepare a composite phase change material, which not only limits the flow of liquid phase change materials, but also its mechanical properties. Performance and stability can be significantly improved.

At present, how to encapsulate and fix fatty acids is a subject of much concern in the research field of phase change energy storage materials. Therefore, the key to effective encapsulation and immobilization of fatty acids with appropriate carriers is the key to current research and development. The common shaping techniques mainly include melt mixing and ultrasonic vibration combination method, microcapsule method, sol-gel method and chemical grafting method, etc. The process of melting mixing and ultrasonic oscillation combination method is simple, but because the carrier and core material are only combined by simple physical adsorption, the packaging stability is average. The small particle size of the microencapsulation method can increase the overall heat dissipation area and has strong processability, but the process is complicated and the encapsulation efficiency is low. The chemical grafting method has good packaging stability but poor thermal conductivity and is not conducive to the rapid response of heat storage and heat release. The sol-gel method is a wet chemical method that is widely used and can achieve functional attachment at room temperature.

Contents of the invention

The object of the present invention is to provide a preparation method of a ternary fatty acid-silicon dioxide composite shape-setting phase change material in order to overcome the disadvantages of a single fatty acid phase transition temperature being too high and a narrow application range.

The technical scheme of the present invention is: a kind of preparation method of ternary fatty acid-silicon dioxide composite qualitative phase change material, and its specific steps are as follows:

⑴Weigh the three long-chain fatty acids into the container according to the calculated ratio, seal the rubber stopper tightly and heat it in a water bath at 50-60°C for 25-30min. Melt the fatty acid, then put it in the oven for later use;

(2) After mixing the precursor, absolute ethanol and deionized water in proportion, adjust the pH of the mixture to between 3 and 4, and stir evenly with a magnetic stirrer;

(3) Then adjust the pH of the reaction system to 6-8, mix in the molten ternary eutectic fatty acid, stir in a water bath, and then ultrasonically disperse again;

(4) Seal the above mixed solutions and place them in absolute ethanol for aging for 24-28 hours, the temperature is controlled at 48-50°C, and the solvent is replaced with n-hexane to replace the remaining part of the ethanol solvent;

(5) Add modifiers to modify the surface of the composite gel, and then place the gel in an oven to dry to constant weight, and finally obtain the ternary fatty acid-silica composite phase change material.

Preferably, the long-chain fatty acid described in step (1) is a ternary system, and the specific ratio is as follows: the mass ratio of capric acid-lauric acid-myristic acid is 1: (0.5-0.6): (0.3-0.4), capric acid The mass ratio of acid-lauric acid-palmitic acid is 1:(0.5-0.6):(0.1-0.2), and the mass ratio of capric acid-myristic acid-palmitic acid is 1:(0.3-0.4):(0.2-0.25 ), the mass ratio of lauric acid-myristic acid-palmitic acid is 1:(0.6-0.7):(0.3-0.4).

The precursor described in the preferred step (2) is tetraethyl orthosilicate; Precursor: dehydrated alcohol: deionized water is mixed according to the mass ratio of 1: (4～6): (6～8); Magnetic stirrer The rotating speed is 350-400r/min, and the stirring time is 28-30min.

Preferably, the temperature of the water bath described in step (3) is 55-60° C., and the stirring time is 55-60 min.

Preferably, the dosage of the ternary fatty acid system in step (3) is 40-65% of the mass of the phase change material.

Preferably, the modification temperature in step (5) is 48-50°C, and the modification time is 10-12h; the oven temperature is 55-60°C.

Preferably, the modifying agent is one of trimethylchlorosilane or n-hexane, and the amount of the modifying agent added is 10-15% of the mass of the composite gel.

Beneficial effect:

(1) Long-chain fatty acids used as phase change core materials have the advantages of low cost, non-toxicity, good thermal stability, no supercooling and phase separation during the phase change process, high latent heat of phase change, and wide and easy access to sources. Different types can be selected in actual use Fatty acids are compounded according to different mass ratios to obtain a ternary fatty acid mixture with adjustable phase transition temperature and more suitable for application requirements in the field of normal temperature. In addition, the preparation process of the ternary fatty acid eutectic is simple, safe, time-saving and easy to obtain.

(2) Schroeder's formula is more accurate for the composition ratio and thermophysical property prediction of the ternary phase change system (the deviation between the estimated value of the four groups of ternary fatty acid eutectics in the present invention and the DSC test value, the latent heat of phase change <20J/g, phase transition temperature <5°C), since the appropriate phase transition temperature must be selected according to the application field, it has a certain reference effect on the preparation and application of fatty acid eutectics in practice.

(3) Silica, as a three-dimensional structure carrier with large specific surface area and porosity, can evenly and firmly embed the phase change core material inside its skeleton, effectively alleviating the leakage of solid-liquid phase change materials during the phase change process.

(4) The hydrophobically treated silica gel structure has good hydrophobic function, which ensures the complete structure of the carrier and its firm binding to the organic fatty acids of the core material.

(5) The ternary fatty acid/silicon dioxide composite shape-setting phase change material of the present invention has high phase change latent heat and good thermal stability, and its phase change temperature can be regulated by changing the type and mass ratio of the phase change core material to meet the application conditions of composite materials.

Description of drawings

Fig. 1 is the physical figure of the LA-MA-PA/silicon dioxide composite phase-change material of the embodiment of the present invention 1;

Fig. 2 is the SEM picture of the LA-MA-PA/silicon dioxide composite phase change material of embodiment 1 of the present invention;

Fig. 3 is a DSC diagram of the LA-MA-PA/silica composite phase change material of Example 1 of the present invention.

detailed description

The present invention is further illustrated below by way of examples.

Example 1

First, use an electronic balance to weigh lauric acid (LA), myristic acid (MA) and palmitic acid (PA) according to the eutectic quality of 1:0.7:0.38, add them to the test tube and cover with a rubber stopper to seal the mixture After complete melt mixing, heat in a 60°C water bath for 25 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, absolute ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:5:7, and hydrochloric acid was added to adjust the pH of the solution to 3. /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 7, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 60°C for 58 minutes, and then ultrasonically dispersed again. The mixed solutions were respectively sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 24 hours at a temperature of 48° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding trimethylchlorosilane accounting for 10% of the composite gel mass, wherein the modification temperature and time were 50° C. and 10 h, respectively. The gel was baked in an oven at 60°C to constant weight to obtain a LA-MA-PA/silica composite phase change material with a phase transition temperature of 30.0°C and a latent heat of 99.3 J/g.

Example 2

First, use an electronic balance to weigh lauric acid (LA), myristic acid (MA) and palmitic acid (PA) according to the eutectic quality of 1:0.64:0.35, add them to the test tube, cover the rubber stopper and seal the mixture After complete melt mixing, heat in a 60°C water bath for 25 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, absolute ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:5:7, and hydrochloric acid was added to adjust the pH of the solution to 3. /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 7, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 60°C for 58 minutes, and then ultrasonically dispersed again. The mixed solutions were respectively sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 24 hours at a temperature of 48° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding n-hexane accounting for 10% of the composite gel mass, wherein the modification temperature and time were 50° C. and 10 h, respectively. The gel was baked in an oven at 60°C to constant weight to obtain a LA-MA-PA/silica composite phase change material with a phase transition temperature of 25.0°C and a latent heat of 98.2 J/g.

Example 3

First, use an electronic balance to weigh capric acid (CA), lauric acid (LA) and myristic acid (MA) according to the eutectic quality of 1:0.60:0.33, add them to the test tube and cover with a rubber stopper to seal the mixture After complete melt mixing, heat in a 55°C water bath for 28min and then ultrasonically disperse. Tetraethyl orthosilicate, absolute ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:6:7, and hydrochloric acid was added to adjust the pH of the solution to 4. /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 6, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 55°C for 58 minutes, and then ultrasonically dispersed again. The mixed solutions were sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 27 hours each at a temperature of 50° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding trimethylchlorosilane accounting for 12% of the composite gel mass, wherein the modification temperature and time were 48° C. and 11 h, respectively. The gel was baked in an oven at 58° C. to a constant weight to obtain a CA-LA-MA/silica composite phase change material with a phase transition temperature of 14.5° C. and a latent heat of 75.2 J/g.

Example 4

First, use an electronic balance to weigh capric acid (CA), lauric acid (LA) and myristic acid (MA) according to the eutectic quality of 1:0.55:0.36, add them to the test tube and cover with a rubber stopper to seal the mixture After complete melt mixing, heat in a 55°C water bath for 28min and then ultrasonically disperse. Tetraethyl orthosilicate, dehydrated ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:6:7, and hydrochloric acid was added to adjust the pH of the solution to 4, and the /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 6, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 55°C for 58 minutes, and then ultrasonically dispersed again. The mixed solutions were respectively sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 27 hours each, the aging temperature was 50°C, and the solvent was replaced with n-hexane to replace the remaining ethanol solvent. The surface of the composite gel was modified by adding n-hexane accounting for 12% of the composite gel mass, wherein the modification temperature and time were 48° C. and 11 h, respectively. The gel was baked in an oven at 58° C. to a constant weight to obtain a CA-LA-MA/silica composite phase change material with a phase transition temperature of 13.5° C. and a latent heat of 76.1 J/g.

Example 5

First, use an electronic balance to weigh capric acid (CA), lauric acid (LA) and palmitic acid (PA) according to the eutectic quality of 1:0.60:0.15, add them to the test tube and cover with a rubber stopper to seal the mixture completely. After melt mixing, heat in a water bath at 55°C for 30 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, dehydrated ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:5:8, and hydrochloric acid was added to adjust the pH of the solution to 4, and the /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 6, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 59°C for 60 minutes, and then ultrasonically dispersed again. The mixed solutions were sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 28 hours each at a temperature of 48° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding trimethylchlorosilane accounting for 15% of the composite gel mass, wherein the modification temperature and time were 49° C. and 12 h, respectively. The gel was baked in an oven at 60°C to constant weight to obtain a CA-LA-PA/silica composite phase change material with a phase transition temperature of 16.3°C and a latent heat of 69.3 J/g.

Example 6

First, use an electronic balance to weigh capric acid (CA), lauric acid (LA) and palmitic acid (PA) according to the eutectic quality of 1:0.55:0.2, add them to the test tube, cover the rubber stopper and seal it until the mixture is completely After melt mixing, heat in a water bath at 55°C for 30 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, dehydrated ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:5:8, and hydrochloric acid was added to adjust the pH of the solution to 4, and the /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 6, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 59°C for 60 minutes, and then ultrasonically dispersed again. The mixed solutions were sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 28 hours each at a temperature of 48° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding n-hexane accounting for 15% of the composite gel mass, wherein the modification temperature and time were 49° C. and 12 h, respectively. The gel was baked in an oven at 60°C to constant weight to obtain a CA-LA-PA/silica composite phase change material with a phase transition temperature of 15.7°C and a latent heat of 70.2 J/g.

Example 7

First, use an electronic balance to weigh capric acid (CA), myristic acid (MA) and palmitic acid (PA) according to the eutectic quality of 1:0.32:0.25, add them to the test tube and cover with a rubber stopper to seal the mixture After complete melt mixing, heat in a 60°C water bath for 30 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, dehydrated ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:4:8, and hydrochloric acid was added to adjust the pH of the solution to 3, and the /min) Stir evenly for 30min. Dilute ammonia water was added to adjust the pH of the reaction system to 7, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 55°C for 60 minutes, and then ultrasonically dispersed again. The mixed solutions were sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 24 hours each at a temperature of 50° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding trimethylchlorosilane accounting for 15% of the composite gel mass, wherein the modification temperature and time were 49° C. and 12 h, respectively. The gel was baked in an oven at 60° C. to a constant weight to obtain a CA-MA-PA/silica composite phase change material with a phase transition temperature of 18.2° C. and a latent heat of 58.0 J/g.

Example 8

First, use an electronic balance to weigh capric acid (CA), myristic acid (MA) and palmitic acid (PA) according to the eutectic quality of 1:0.4:0.2, add them to the test tube, cover the rubber stopper and seal the mixture After complete melt mixing, heat in a 60°C water bath for 30 minutes and then ultrasonically disperse. Tetraethyl orthosilicate, dehydrated ethanol and deionized water were mixed according to the ratio of TEOS:H ₂ O:EtOH=1:4:8, and hydrochloric acid was added to adjust the pH of the solution to 3, and the /min) Stir evenly for 28min. Dilute ammonia water was added to adjust the pH of the reaction system to 7, and the molten LA-MA-PA ternary eutectic fatty acid was mixed in, stirred in a water bath at 55°C for 60 minutes, and then ultrasonically dispersed again. The mixed solutions were respectively sealed and placed in tetraethyl orthosilicate/absolute ethanol mixed solution for aging for 24 hours at a temperature of 50° C., and the solvent was replaced with n-hexane to replace the residual ethanol solvent. The surface of the composite gel was modified by adding n-hexane accounting for 15% of the composite gel mass, wherein the modification temperature and time were 49° C. and 12 h, respectively. The gel was baked in an oven at 60° C. to a constant weight to obtain a CA-MA-PA/silica composite phase change material with a phase transition temperature of 18.0° C. and a latent heat of 60.0 J/g.

The relevant parameters and test results are shown in Table 1.

Claims (7)

1. a preparation method of ternary fatty acid-silicon dioxide composite qualitative phase change material, its concrete steps are as follows: ⑴Weigh the three long-chain fatty acids into the container according to the calculated ratio, seal the rubber stopper tightly and heat it in a water bath at 50-60°C for 25-30min. Melt the fatty acid, then put it in the oven for later use; (2) After mixing the precursor, absolute ethanol and deionized water in proportion, adjust the pH of the mixture to between 3 and 4, and stir evenly with a magnetic stirrer; (3) Then adjust the pH of the reaction system to 6-8, mix in the molten ternary eutectic fatty acid, stir in a water bath and then ultrasonically disperse again; (4) Seal the above mixed solutions and place them in absolute ethanol for aging for 24-28 hours, the temperature is controlled at 48-50°C, and the solvent is replaced with n-hexane; (5) Add modifiers to modify the surface of the composite gel, and then place the gel in an oven to dry to constant weight, and finally obtain the ternary fatty acid-silica composite phase change material. 2. The preparation method according to claim 1, characterized in that the long-chain fatty acid described in step (1) is a ternary system, and the specific proportioning is as follows: the mass ratio of capric acid-lauric acid-myristic acid is 1 :(0.5-0.6):(0.3-0.4), the mass ratio of capric acid-lauric acid-palmitic acid is 1:(0.5-0.6):(0.1-0.2), the mass ratio of capric acid-myristic acid-palmitic acid The ratio is 1:(0.3-0.4):(0.2-0.25), and the mass ratio of lauric acid-myristic acid-palmitic acid is 1:(0.6-0.7):(0.3-0.4). 3. the preparation method according to claim 1, is characterized in that the precursor described in step (2) is tetraethyl orthosilicate; Precursor: dehydrated alcohol: deionized water according to 1:(4～6 ): (6-8) mass ratio mixing; the magnetic stirrer speed is 350-400r/min, and the stirring time is 28-30min. 4. The preparation method according to claim 1, characterized in that the temperature of the water bath in step (3) is 55-60° C., and the stirring time is 55-60 min. 5. The preparation method according to claim 1, characterized in that in the step (3), the dosage of the tribasic fatty acid system is 40-65% of the quality of the phase change material. 6. The preparation method according to claim 1, characterized in that the modification temperature described in step (5) is 48-50°C, and the modification time is 10-12h; the oven temperature is 55-60°C . 7. The preparation method according to claim 1, characterized in that the modifying agent is one of trimethylchlorosilane or n-hexane, and the amount of modifying agent incorporated is 10 to 15% of the composite gel mass .