A cold storage medium, a preparation method and application thereof

Abstract

The application discloses a cold storage medium and a preparation method and application thereof. The cold storage medium is prepared by mixing tetrahydrothiophene, a surfactant and a thickening agent in a solvent, or by mixing the tetrahydrothiophene, the surfactant and the thickening agent in the solvent and then introducing carbon dioxide. Compared with a traditional refrigerant hydrate, the application utilizes the stable emulsion formed by the environment-friendly medium tetrahydrothiophene, the surfactant and the thickening agent, further utilizes the solubilization of the tetrahydrothiophene to carbon dioxide, overcomes the shortcomings of long hydrate formation induction time, large supercooling degree and low hydrate rate caused by the immiscibility of the hydrate medium and water, improves the stability of the system under the action of the thickening agent, and improves the cold storage density.

Description

A cold storage medium, its preparation method and application Technical Field

[0001] This invention relates to the field of air conditioning cold storage applications, specifically to a method for cold storage of tetrahydrothiophene and low-pressure carbon dioxide hydrate slurry. Background Technology

[0002] With economic development and improved living standards, air conditioning is becoming increasingly widespread, leading to a surge in electricity consumption and contributing significantly to the widening peak-valley difference in my country's power grid. To mitigate the adverse impact of air conditioning on power supply, the concept of chilled water storage air conditioning has been proposed to achieve load-side peak shaving and reduce electricity consumption during peak hours. Chilled water storage air conditioning stores the cooling capacity generated by refrigeration equipment during off-peak periods and releases it during peak hours, thus reducing electricity consumption during these periods. This technology enables peak shaving and valley filling, thereby reducing investment in power generation and transmission equipment, lowering overall energy consumption, and reducing carbon dioxide emissions.

[0003] Currently used air conditioning cold storage media include water, ice, and eutectic salts. Compared to water's sensible heat storage, ice storage has the advantage of high cold storage density, making it the primary method for air conditioning cold storage. However, ice storage has a low cold storage temperature, resulting in high energy consumption.

[0004] Hydrate-based cold storage is a potential next-generation cold storage medium, primarily utilizing the formation of hydrates between refrigerants and water within the air conditioning temperature range for cold storage. Compared to ice-based cold storage, refrigerant hydrates typically have higher cold storage temperatures, reducing energy consumption. However, refrigerants are generally insoluble in water, making refrigerant hydrate formation difficult and resulting in low actual cold storage density, thus hindering the widespread application of hydrate-based cold storage technology. Furthermore, common cold storage hydrate media (such as R22 and R141b) are environmentally harmful and will be replaced. Therefore, it is necessary to address the environmental issues of hydrate media and the drawbacks of long induction time, slow growth rate, and low hydrate density, focusing on the rapid and high-density formation of cold storage materials and hydrates. Summary of the Invention

[0005] The purpose of this invention is to provide a refrigerant for cold storage that meets environmental protection requirements, has high cold storage capacity, and low pressure, so that the cold storage process of hydrates is fast and stable.

[0006] The present invention adopts the following technical solution:

[0007] A cold storage medium includes tetrahydrothiophene, a surfactant, and a thickener; further, it includes carbon dioxide.

[0008] This invention discloses a method for preparing the aforementioned cold storage medium, comprising the following steps: mixing tetrahydrothiophene, a surfactant, and a thickener in a solvent to obtain the cold storage medium; or mixing tetrahydrothiophene, a surfactant, and a thickener in a solvent and then introducing carbon dioxide to obtain the cold storage medium. Mixing can be performed using a conventional stirrer or ultrasonic stirring.

[0009] In this invention, the surfactant includes a biodegradable and environmentally friendly surfactant, which can be selected from one or more of sophorolipids, lignin sulfonates, isomeric alcohol polyoxyethylene ethers, and sucrose fatty acid esters. In actual use, it is a single surfactant or a mixture of surfactants.

[0010] In this invention, the thickener is an organic synthetic thickener, which can be selected from one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, and polyethylene glycol. In actual use, it is a single thickener or a mixture of thickeners.

[0011] In this invention, the solvent is water.

[0012] In this invention, the concentration of the surfactant in the cold storage medium is 0.1–3%, the concentration of the thickener is 0.1–2%, and the concentration of tetrahydrothiophene is 20–40%. Preferably, the concentration of the surfactant in the cold storage medium is 0.5–2%, the concentration of the thickener is 0.3–1%, and the concentration of tetrahydrothiophene is 25–35%. The concentrations are mass concentrations, based on the solvent, such as water.

[0013] In this invention, when the cold storage medium includes carbon dioxide, the pressure of the introduced carbon dioxide is 0.1 to 0.7 MPa, preferably 0.25 to 0.4 MPa.

[0014] The cold storage agent in this invention forms type II hydrates or a mixture of type I and type II hydrates. Through the complementary advantages of the hydrate substances, excellent cold storage thermophysical properties of the hydrates are obtained. The cold storage temperature of the hydrates is 3–10℃, and the phase change pressure is 0.1–0.7 MPa.

[0015] Compared with traditional refrigerant hydrates, this invention utilizes the environmentally friendly medium tetrahydrothiophene to form a stable emulsion with surfactants and thickeners. Furthermore, it leverages the solubilizing effect of tetrahydrothiophene on carbon dioxide to overcome the disadvantages of long hydrate formation induction time, high supercooling, and low hydration rate caused by the immiscibility of the hydrate medium with water. The stability of the system is improved by the thickener, thereby increasing the cold storage density. Detailed Implementation

[0016] This invention relates to a stable emulsion formed by tetrahydrothiophene or tetrahydrothiophene + carbon dioxide under the action of surfactants and thickeners, resulting in a cold storage medium. The surfactants include biodegradable and environmentally friendly surfactants such as sophorolipids, lignin sulfonates, isomeric alcohol polyoxyethylene ethers, and sucrose fatty acid esters; in practice, a single surfactant or a mixture of surfactants is used. The thickeners are organic synthetic thickeners such as sodium carboxymethyl cellulose, polyvinyl alcohol, and polyethylene glycol.

[0017] The cold storage medium of this invention is a mono- or binary mixed hydrate of tetrahydrothiophene or tetrahydrothiophene + carbon dioxide, which is an emulsion formed in a solvent by ultrasonication or high-speed stirring under the action of a surfactant and a thickener. The concentration of the surfactant is 0.5-2%, and the concentration of the thickener is 0.3-1%.

[0018] The present invention will be further described below with reference to specific embodiments. All raw materials used in the present invention are conventional products, and the specific preparation operations and performance testing are conventional techniques. The cold storage density of the cold storage hydrate was measured and calculated using the existing mixing calorimetry method.

[0019] Example 1

[0020] The hydrate-based cold storage system is a liquid mixture of tetrahydrothiophene, water, acidic sophorolipid, and sodium carboxymethyl cellulose. First, 0.5 g of sodium carboxymethyl cellulose was added to 100 g of water and allowed to stand for 8 hours. Then, 1.5 g of acidic sophorolipid and 28.6 g of tetrahydrothiophene were added, and the mixture was stirred using conventional ultrasonication to form a stable cold storage emulsion. The mass ratio of tetrahydrothiophene to water was 1:3.5. At 2°C, a hydrate was formed within 135 minutes. The cold storage density was determined to be 172 kJ / kg using the mixture calorimetry method.

[0021] Cyclic stability test procedure: A test tube containing the emulsion was placed in a constant-temperature water bath at 2°C. After hydrate formation, the test tube was placed in another constant-temperature water bath at 12°C until the hydrate decomposed. After the fluid temperature in the test tube stabilized, it was placed back into the 2°C constant-temperature water bath to form hydrate again. The stability of hydrate formation was analyzed through the hydrate formation / decomposition process. The hydrate could still stably form hydrate after 20 cycles, and no decrease in cold storage capacity was observed. This was mainly due to the good stability of the emulsion and the absence of stratification. Previous research by the inventors on the formation and stability of HCFC-141b hydrate in organic phase change emulsions found that it could only be cycled a maximum of 6 times. This invention uses environmentally friendly raw materials, which not only solves the problem of the non-environmental nature of existing cold storage materials, but also unexpectedly solves the problem of poor cyclic stability of existing cold storage hydrates.

[0022] Example 2

[0023] The hydrate-based cold storage system is a liquid mixture of tetrahydrothiophene, carbon dioxide, isotretinoin polyoxyethylene ether, and sodium carboxymethyl cellulose. First, 0.7 g of sodium carboxymethyl cellulose is added to 100 g of water and allowed to stand for 10 hours. Then, 1 g of isotretinoin polyoxyethylene ether and 28.6 g of tetrahydrothiophene are added. Carbon dioxide is then introduced into the cold storage tank, and the pressure reaches 0.35 MPa. The mixture is stirred using a stirrer to form a stable cold storage emulsion. The mass ratio of tetrahydrothiophene to water is 1:3.5. Under ambient conditions of 7.5℃, a mixed hydrate of type I and type II can be formed within 90 minutes for cold storage.

[0024] Example 3

[0025] The hydrate-based cold storage system is a liquid mixture of tetrahydrothiophene, water, acidic sophorolipid, and sodium carboxymethyl cellulose. First, 0.5g of sodium carboxymethyl cellulose was added to 100g of water and allowed to stand for 8 hours. Then, 1.5g of acidic sophorolipid and 30g of tetrahydrothiophene were added, and the mixture was stirred using conventional ultrasonication to form a stable cold storage emulsion.

[0026] Example 4

[0027] The hydrate-based cold storage system is a liquid mixture of tetrahydrothiophene, water, acidic sophorolipid, and sodium carboxymethyl cellulose. First, 0.5g of sodium carboxymethyl cellulose was added to 100g of water and allowed to stand for 10 hours. Then, 1.55g of acidic sophorolipid and 32g of tetrahydrothiophene were added, and the mixture was stirred using conventional ultrasonication to form a stable cold storage emulsion.

[0028] Example 5

[0029] The hydrate-based cold storage system is a liquid mixture of tetrahydrothiophene, water, acidic sophorolipid, and sodium carboxymethyl cellulose. First, 0.45g of sodium carboxymethyl cellulose was added to 100g of water and allowed to stand for 7 hours. Then, 1.4g of acidic sophorolipid and 26g of tetrahydrothiophene were added, and the mixture was stirred using conventional ultrasonication to form a stable cold storage emulsion.

Claims

1. A cold storage medium, characterized in that, It includes tetrahydrothiophene, a surfactant, a thickener, and carbon dioxide; the surfactant is sophorolipid; the thickener is selected from one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, and polyethylene glycol; in the cold storage medium, the concentration of the surfactant is 0.1-3%, the concentration of the thickener is 0.1-2%, and the concentration of tetrahydrothiophene is 20-40%; the pressure of the carbon dioxide introduced is 0.1-0.7 MPa.

2. The method for preparing the cold storage medium according to claim 1 includes the following steps: mixing tetrahydrothiophene, a surfactant, and a thickener in a solvent to obtain the cold storage medium; or mixing tetrahydrothiophene, a surfactant, and a thickener in a solvent and introducing carbon dioxide to obtain the cold storage medium.

3. The method for preparing the cold storage medium according to claim 2, characterized in that, The solvent is water.

4. The use of the cold storage medium according to claim 1 as an air conditioning cold storage agent or in the preparation of an air conditioning cold storage agent.