Composite low-temperature secondary refrigerant as well as preparation method and application thereof

Abstract

The invention provides a composite low-temperature secondary refrigerant and a preparation method and application thereof. The composite low-temperature secondary refrigerant comprises the following components in percentage by weight: 40%-50% of formate, 20%-30% of triethanolamine, 5%-15% of urea and the balance of deionized water. Through reasonable formula matching, the advantages of all the components are fully played, the comprehensive performance of the composite low-temperature secondary refrigerant is further improved, normal work under the temperature condition of-50 DEG C or below can be achieved, and the composite low-temperature secondary refrigerant is particularly suitable for refrigeration equipment and the like in the lithium hexafluorophosphate production process.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration technology, specifically relating to a composite low-temperature refrigerant, its preparation method, and its application. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is a commonly used electrolyte in lithium-ion batteries. Due to its excellent ionic conductivity and chemical stability, it has been widely applied in many fields. With the rapid development of electric vehicles, energy storage systems, and other fields, the market demand for LiPF6 is increasing daily. To meet these demands, the optimization and improvement of LiPF6 production processes are imperative. For example, by strictly controlling the production environment, improving separation and purification processes, or upgrading production equipment, the production efficiency and finished product quality of LiPF6 can be significantly improved.

[0003] The production process of lithium hexafluorophosphate is relatively complex and requires strict control of operating conditions and environmental parameters, such as reaction temperature, reaction time and reaction pressure. The regulation of the above parameters has an important impact on the purity and yield of lithium hexafluorophosphate. Through reasonable process design and optimization, not only can the purity and yield of the finished product be improved, but also the production cost can be reduced and the production efficiency can be improved. Among them, the preparation of lithium hexafluorophosphate needs to be carried out in a low temperature (e.g. 0℃~20℃) or ultra-low temperature (e.g. -60℃) environment. The refrigerant system achieves rapid cooling and constant temperature control of core equipment such as reactor and crystallization device through circulating medium to ensure reaction efficiency and the purity of the finished product. However, it still faces some challenges in the actual production process, mainly including the following two aspects: (1) Traditional refrigerant systems are insufficient in terms of environmental protection and energy efficiency, and are not highly compatible with existing refrigeration systems; (2) The purity of lithium hexafluorophosphate crystals decreases due to temperature fluctuations during the growth process, resulting in uneven crystal form.

[0004] Currently, commonly used refrigerants in the preparation of lithium hexafluorophosphate include dichloromethane, organic acid salts, or aqueous solutions of ethylene glycol. Specifically, dichloromethane has excellent thermal conductivity, but it is inherently toxic and has a high evaporation pressure, which may lead to high operating pressure in the refrigeration system, increasing energy consumption and failure rate of production equipment. Furthermore, the corrosiveness of dichloromethane can cause irreversible damage to the pipes and equipment of the refrigeration system. Organic acid salt refrigerants, compared to other traditional refrigerants, have higher thermal conductivity and environmental performance. However, they may crystallize at extremely low temperatures, thus affecting the refrigeration effect. Ethylene glycol, when used as a refrigerant, has advantages such as stability, a low freezing point, stable use at low temperatures, good miscibility with water, and a large heat capacity for efficient heat transfer. However, its disadvantages include a rapid increase in solution viscosity at low temperatures, leading to increased flow resistance. In addition, ethylene glycol is slightly toxic and corrosive to metals, requiring strict control of its concentration.

[0005] Therefore, there is an urgent need in this field to develop a refrigerant that has good thermodynamic properties, good fluidity, chemical stability and low corrosivity in low-temperature environments, so as to achieve efficient, reliable and safe operation of refrigeration systems and meet the production requirements of lithium hexafluorophosphate. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite low-temperature refrigerant, its preparation method, and its applications. This invention, through a rational formulation, fully leverages the advantages of each component, further improving the overall performance of the composite low-temperature refrigerant. It can operate normally at temperatures of -50°C and below, and is particularly suitable for refrigeration equipment in lithium hexafluorophosphate production processes.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite cryogenic refrigerant, which comprises the following components by weight percentage:

[0009] Formate 40%~50%

[0010] Triethanolamine 20%~30%

[0011] Urea 5%~15%

[0012] The remainder is deionized water.

[0013] This invention provides a composite low-temperature refrigerant suitable for lithium hexafluorophosphate production. It exhibits excellent fluidity at low temperatures, enabling continuous cooling and maintaining system stability while effectively reducing corrosion of equipment. This results in low viscosity, low corrosivity, and low-temperature stability, as detailed below:

[0014] (1) The present invention uses formate as the main cryogenic agent, which has higher thermal conductivity and environmental protection performance, thereby reducing the freezing point of the solution to -50°C and below.

[0015] (2) The appropriate amount of triethanolamine provided by the present invention can form a passivation film on the surface of metal equipment, inhibit electrochemical corrosion, and thus extend the service life of the production equipment. If the weight percentage of triethanolamine is low, the pH value of the system will be low, increasing the risk of acid corrosion.

[0016] (3) This invention introduces a specific amount of urea as a low-temperature synergist to form a ternary eutectic system with triethanolamine-formate, thereby disrupting the hydrogen bond network between water molecules, inhibiting ice crystal formation, and further synergistically lowering the freezing point of the solution, allowing the freezing point of the solution to break through to -50℃ and below. The urea-formate system has a certain pH buffering capacity. If the weight percentage of urea is low, this capacity will be weakened, resulting in an excessively low pH value of the system, which will cause the corrosivity of the entire system to increase sharply. If the weight percentage of urea is high, it will affect the eutectic point of the system. If the concentration exceeds the optimal freezing point, the solution will become supersaturated, leading to a tendency for solute to precipitate, which will cause the freezing point of the solution to rise. In addition, at low temperatures, excessive urea may crystallize and precipitate due to decreased solubility, further clogging the filter and pipeline.

[0017] (4) The composite low-temperature refrigerant provided by the present invention has the advantages of being non-flammable and low in toxicity, and meets the OECD 301 easy-degradable standard.

[0018] Specifically, the weight percentage of the formate can be, for example, 40%, 42%, 45%, 48%, or 50%; the weight percentage of the triethanolamine can be, for example, 20%, 22%, 25%, 28%, or 30%; and the weight percentage of the urea can be, for example, 5%, 8%, 10%, 12%, or 15%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0019] Preferably, the mass ratio of the formate to the triethanolamine is (1.5~2.5):1, for example, it can be 1.5:1, 1.8:1, 2:1, 2.2:1 or 2.5:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] This invention achieves a lower freezing point (-50°C and below) and reduces corrosion of production equipment by adjusting the mass ratio of formate to triethanolamine. Using a higher concentration of formate may lead to crystallization at extremely low temperatures, and the solution viscosity increases with concentration, resulting in poor flowability and affecting refrigeration performance. Conversely, using a higher concentration of triethanolamine increases the solution viscosity, reduces flowability, and causes excessive alkalinity, making the system more prone to side reactions.

[0021] Preferably, the formate comprises potassium formate.

[0022] Preferably, the composite cryogenic refrigerant further includes the following components by weight percentage: 0.01% to 0.13% additives, for example, 0.01%, 0.05%, 0.08%, 0.1%, 0.11%, 0.12% or 0.13%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] In this invention, by adjusting the content range of the additives, a synergistic effect is achieved in protecting the production equipment and further reducing the corrosion rate.

[0024] Preferably, the additive includes benzotriazole and / or sodium molybdate, more preferably benzotriazole and sodium molybdate. Benzotriazole can specifically adsorb onto the copper metal surface, effectively preventing pitting corrosion; sodium molybdate can generate MoO4. 2- A passivation layer is applied to protect the stainless steel metal.

[0025] This invention achieves the good effects of low viscosity, low corrosiveness and low temperature stability of composite low-temperature refrigerant through composite formulation optimization and synergistic modification of the above-mentioned additives.

[0026] In a second aspect, the present invention provides a method for preparing a composite low-temperature refrigerant as described in the first aspect, the method comprising the following steps:

[0027] The composite low-temperature refrigerant is obtained by mixing formate, triethanolamine, urea and deionized water according to the formula.

[0028] Preferably, before mixing formate, triethanolamine, urea and deionized water according to the formula, an additive is also added.

[0029] Preferably, the preparation method includes the following steps: first mixing urea aqueous solution and formate, then adding triethanolamine to adjust the pH of the system to 9-13, and finally adding additives to obtain the composite low-temperature refrigerant.

[0030] Specifically, the pH value of the adjustment system can be, for example, 9, 9.2, 10.5, 12.8 or 13, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] As a preferred technical solution of the present invention, the preparation method includes the following steps: first, urea and deionized water are mixed and stirred until completely dissolved to obtain a urea aqueous solution; then, formate is added to the urea aqueous solution, followed by triethanolamine, and the pH value of the system is adjusted to 9-13; finally, additives are added, and the mixture is stirred or ultrasonically dispersed to obtain the composite low-temperature refrigerant.

[0032] Thirdly, the present invention provides an application of a composite low-temperature refrigerant prepared by the preparation method described in the first aspect or the second aspect, wherein the composite low-temperature refrigerant is used in the preparation of lithium hexafluorophosphate.

[0033] The composite low-temperature refrigerant provided by this invention has advantages such as being non-flammable, low toxicity, biodegradable, safe, and improving the energy efficiency ratio of refrigeration systems, and is therefore suitable for the production of lithium hexafluorophosphate.

[0034] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention provides a composite low-temperature refrigerant that exhibits excellent fluidity at low temperatures. This not only enables continuous cooling and maintains stable system operation, but also effectively reduces corrosion to equipment, thus achieving low viscosity, low corrosivity, and low-temperature stability. Specifically, its performance is as follows:

[0037] (1) The present invention uses formate as the main cryogenic agent to lower the freezing point of the solution to -50°C and below.

[0038] (2) The appropriate amount of triethanolamine provided by the present invention can form a passivation film on the surface of metal equipment, inhibit electrochemical corrosion, and thus extend the service life of production equipment.

[0039] (3) This invention introduces a specific amount of urea as a low-temperature synergist to form a ternary eutectic system with triethanolamine-formate, thereby disrupting the hydrogen bond network between water molecules, inhibiting ice crystal formation, and further synergistically lowering the freezing point of the solution, so that the freezing point of the solution breaks through to -50°C and below.

[0040] (4) The composite low-temperature refrigerant provided by the present invention has the advantages of being non-flammable and low in toxicity, and meets the OECD 301 easy-degradable standard. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0042] Example 1

[0043] This embodiment provides a composite cryogenic refrigerant, which comprises the following components by weight percentage:

[0044] Potassium formate 45%

[0045] Triethanolamine 25%

[0046] 10% urea

[0047] Benzotriazole 0.02%

[0048] Sodium molybdate 0.06%

[0049] The remainder is deionized water.

[0050] The mass ratio of potassium formate to triethanolamine is 1.8:1.

[0051] This embodiment also provides a method for preparing the above-mentioned composite low-temperature refrigerant, the preparation method comprising the following steps:

[0052] According to the formula, urea and deionized water are first mixed and stirred at 40°C until completely dissolved to obtain a urea aqueous solution. Potassium formate is then added to the urea aqueous solution in three portions, with continuous stirring to avoid local supersaturation. Triethanolamine is then added and stirred evenly. The pH of the system is adjusted to 12. Finally, benzotriazole and sodium molybdate additives are added and stirred to obtain the composite low-temperature refrigerant.

[0053] Example 2

[0054] This embodiment provides a composite cryogenic refrigerant, which comprises the following components by weight percentage:

[0055] Potassium formate 45%

[0056] Triethanolamine 30%

[0057] 15% urea

[0058] Benzotriazole 0.03%

[0059] Sodium molybdate 0.1%

[0060] The remainder is deionized water.

[0061] The mass ratio of potassium formate to triethanolamine is 1.5:1.

[0062] This embodiment also provides a method for preparing the above-mentioned composite low-temperature refrigerant, the preparation method comprising the following steps:

[0063] According to the formula, urea and deionized water are first mixed and stirred at 40°C until completely dissolved to obtain a urea aqueous solution. Potassium formate is then added to the urea aqueous solution in three portions, with continuous stirring to avoid local supersaturation. Triethanolamine is then added and stirred evenly. The pH of the system is adjusted to 13. Finally, benzotriazole and sodium molybdate additives are added and stirred to obtain the composite low-temperature refrigerant.

[0064] Example 3

[0065] This embodiment provides a composite cryogenic refrigerant, which comprises the following components by weight percentage:

[0066] Potassium formate 50%

[0067] Triethanolamine 20%

[0068] 5% urea

[0069] Benzotriazole 0.01%

[0070] Sodium molybdate 0.05%

[0071] The remainder is deionized water.

[0072] The mass ratio of potassium formate to triethanolamine is 2.5:1.

[0073] This embodiment also provides a method for preparing the above-mentioned composite low-temperature refrigerant, the preparation method comprising the following steps:

[0074] According to the formula, urea and deionized water are first mixed and stirred at 40°C until completely dissolved to obtain a urea aqueous solution. Potassium formate is then added to the urea aqueous solution in three portions, with continuous stirring to avoid local supersaturation. Triethanolamine is then added and stirred evenly. The pH of the system is adjusted to 11.5. Finally, benzotriazole and sodium molybdate additives are added and stirred to obtain the composite low-temperature refrigerant.

[0075] Example 4

[0076] This embodiment provides a composite cryogenic refrigerant, which comprises the following components by weight percentage:

[0077] Potassium formate 45%

[0078] Triethanolamine 25%

[0079] 10% urea

[0080] The remainder is deionized water.

[0081] The mass ratio of potassium formate to triethanolamine is 1.8:1.

[0082] This embodiment also provides a method for preparing the above-mentioned composite low-temperature refrigerant, the preparation method comprising the following steps:

[0083] According to the formula, urea and deionized water are first mixed and stirred at 40°C until completely dissolved to obtain a urea aqueous solution. Then, potassium formate is added to the above urea aqueous solution in three portions, and the mixture is stirred continuously to avoid local supersaturation. Triethanolamine is then added and stirred evenly. The pH of the system is adjusted to 12, and the composite low-temperature refrigerant is obtained.

[0084] Example 5

[0085] The difference between this embodiment and Embodiment 1 is that, by weight percentage, the composite cryogenic refrigerant comprises the following components:

[0086] Potassium formate 25%

[0087] Triethanolamine 25%

[0088] 10% urea

[0089] Benzotriazole 0.02%

[0090] Sodium molybdate 0.06%

[0091] The remainder is deionized water.

[0092] The mass ratio of potassium formate to triethanolamine was 1:1, and all other parameters were the same as in Example 1.

[0093] Example 6

[0094] The difference between this embodiment and Embodiment 1 is that, by weight percentage, the composite cryogenic refrigerant comprises the following components:

[0095] Potassium formate 45%

[0096] Triethanolamine 15%

[0097] 10% urea

[0098] Benzotriazole 0.02%

[0099] Sodium molybdate 0.06%

[0100] The remainder is deionized water.

[0101] The mass ratio of potassium formate to triethanolamine was 3:1, and all other parameters were the same as in Example 1.

[0102] Example 7

[0103] The difference between this embodiment and Embodiment 1 is that, by weight percentage, the composite cryogenic refrigerant comprises the following components:

[0104] Potassium formate 45%

[0105] Triethanolamine 35%

[0106] 10% urea

[0107] Benzotriazole 0.02%

[0108] Sodium molybdate 0.06%

[0109] The remainder is deionized water, and everything else is the same as in Example 1.

[0110] Example 8

[0111] The difference between this embodiment and Embodiment 1 is that, by weight percentage, the composite cryogenic refrigerant comprises the following components:

[0112] Potassium formate 45%

[0113] Triethanolamine 25%

[0114] 2% urea

[0115] Benzotriazole 0.02%

[0116] Sodium molybdate 0.06%

[0117] The remainder is deionized water, and everything else is the same as in Example 1.

[0118] Example 9

[0119] The difference between this embodiment and Embodiment 1 is that, by weight percentage, the composite cryogenic refrigerant comprises the following components:

[0120] Potassium formate 45%

[0121] Triethanolamine 25%

[0122] 20% urea

[0123] Benzotriazole 0.02%

[0124] Sodium molybdate 0.06%

[0125] The remainder is deionized water, and everything else is the same as in Example 1.

[0126] Comparative Example 1

[0127] This comparative example provides a dichloromethane refrigerant.

[0128] Comparative Example 2

[0129] The difference between this comparative example and Example 1 is that the composite low-temperature refrigerant does not contain urea, benzotriazole, or sodium molybdate additives, and the content of deionized water is adaptively adjusted to meet the total weight percentage of the system to 100%. All other aspects are the same as in Example 1.

[0130] Comparative Example 3

[0131] This comparative example provides an aqueous solution of ethylene glycol as a refrigerant, wherein the weight percentage of ethylene glycol is 50%.

[0132] Comparative Example 4

[0133] This comparative example provides an aqueous solution of potassium formate as a refrigerant, wherein the weight percentage of potassium formate is 50%.

[0134] Test conditions

[0135] The refrigerants provided in the above embodiments and comparative examples were subjected to performance tests under the following conditions:

[0136] (1) Freezing point: The freezing point of the refrigerant is tested using a freezing point meter.

[0137] (2) Viscosity: The viscosity of the refrigerant was tested using a rotational rheometer.

[0138] (3) Thermal conductivity: Tested according to ISO 22007-2 standard.

[0139] (4) Corrosion rate of stainless steel: The corrosion rate of the sample was determined according to the standard GB / T 10124-1988.

[0140] (5) Flammability: Tested according to ASTM D4206.

[0141] (6) Toxicity: Tested according to the standard of LD50 oral.

[0142] (7) Biodegradability: Tested according to OECD 301 standards.

[0143] The test results are shown in Table 1:

[0144] Table 1

[0145]

[0146]

[0147] As shown in Table 1, compared to the conventional refrigerants used in Comparative Examples 1-4, the composite low-temperature refrigerants prepared in Examples 1-4 of this invention, through the reasonable combination of formate, triethanolamine, and urea content ranges, enable them to operate stably in a temperature range of -50℃ or even lower, and exhibit good fluidity. Furthermore, the composite low-temperature refrigerant provided by this invention has the advantages of being non-flammable and low in toxicity, and meets the OECD 301 biodegradable standard.

[0148] Triethanolamine, as a powerful corrosion inhibitor, combined with the corrosion-inhibiting properties of formate and the use of deionized water, forms a comprehensive anti-corrosion system, providing excellent protection for common metals such as carbon steel, copper, and stainless steel. Furthermore, the main components of formate and triethanolamine are less toxic than ethylene glycol, are non-flammable, making them safer to use, and formate is highly biodegradable, resulting in a low environmental impact.

[0149] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite cryogenic refrigerant, characterized in that, The composite cryogenic refrigerant comprises the following components by weight percentage: Formate 40%~50% Triethanolamine 20%~30% Urea 5%~15% The remainder is deionized water.

2. The composite cryogenic refrigerant according to claim 1, characterized in that, The mass ratio of the formate to the triethanolamine is (1.5~2.5):

1.

3. The composite cryogenic refrigerant according to claim 1 or 2, characterized in that, The formate includes potassium formate.

4. The composite cryogenic refrigerant according to claim 1, characterized in that, The composite cryogenic refrigerant also includes the following components by weight percentage: Additives: 0.01%~0.13%.

5. The composite cryogenic refrigerant according to claim 4, characterized in that, The additives include benzotriazole and / or sodium molybdate.

6. The composite cryogenic refrigerant according to claim 5, characterized in that, The additives include benzotriazole and sodium molybdate.

7. A method for preparing a composite cryogenic refrigerant as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: The composite low-temperature refrigerant is obtained by mixing formate, triethanolamine, urea and deionized water according to the formula.

8. The preparation method according to claim 7, characterized in that, Before mixing formate, triethanolamine, urea and deionized water according to the formula, additives are also added.

9. The preparation method according to claim 8, characterized in that, The preparation method includes the following steps: first, mixing urea aqueous solution and formate, then adding triethanolamine, adjusting the pH of the system to 9-13, and finally adding additives to obtain the composite low-temperature refrigerant.

10. The application of a composite cryogenic refrigerant prepared by any one of claims 1-6 or any one of claims 7-9, characterized in that, The composite low-temperature refrigerant is used in the preparation of lithium hexafluorophosphate.

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