Refrigerator oil and working fluid compositions

Abstract

The application relates to the technical field of refrigeration oil products, in particular to a refrigeration oil and a working fluid composition containing the refrigeration oil. The refrigeration oil comprises a base oil, and the base oil comprises a first polyol ester and a second polyol ester; the first polyol ester is a complex ester synthesized by esterification reaction of a pentaerythritol and a first carboxylic acid mixture, the first carboxylic acid mixture comprises at least one acid selected from C8-C9 monohydric fatty acids, C5 monohydric fatty acids and C4-C9 diacids; the second polyol ester is a mixed ester synthesized by esterification reaction of a dipentaerythritol and a second carboxylic acid mixture, the second carboxylic acid mixture comprises at least one acid of C8-C9 monohydric fatty acids and C5 monohydric fatty acids. The refrigeration oil of the application can be completely miscible with R32 refrigerant at a lower temperature, can maintain a higher working viscosity after being dissolved, has good lubricity and stability, and can be applied in a more harsh compressor working condition or a lower-temperature refrigeration environment.

Description

Technical Field

[0001] This application relates to the field of refrigeration oil products, and more specifically, to a refrigeration oil, and also to a working fluid composition comprising the refrigeration oil. Background Technology

[0002] With increasingly stringent environmental regulations, traditional hydrochlorofluorocarbon (HCFC) refrigerants are being phased out at an accelerated pace, and HFC refrigerants are about to be frozen at baseline levels. In the domestic market, HFCs are mainly used in household air conditioners, automotive air conditioners, industrial refrigeration, and refrigeration repair. Among them, HFC-R32 refrigerant is increasingly becoming the mainstream in the refrigeration market due to its environmental friendliness and high efficiency. However, the refrigeration oils widely used for HFC refrigerants have poor compatibility with R32. Poor compatibility between refrigeration oil and refrigerant causes a thick oil film to form on the inner surface of the heat exchanger, easily leading to increased thermal resistance and affecting heat exchange efficiency. Simultaneously, the oil remaining on the pipe walls is difficult to return to the compressor, resulting in insufficient lubrication of the compressor's moving friction pairs and causing reliability issues.

[0003] For refrigeration systems, especially large systems where the evaporator and condenser are far apart, the compatibility between lubricating oil and refrigerant is crucial for oil return. However, existing mineral oils, alkylbenzenes, and synthetic POE oils have poor compatibility with R32 refrigerant. Particularly in compressors of 3HP and above, large refrigeration systems, and in ultra-low temperature heating and low evaporation temperature conditions, the compatibility of the refrigeration oils used with R32 cannot meet the requirements for good miscibility. Therefore, the poor compatibility of refrigeration oils with R32 has, to some extent, hindered their application in high-horsepower refrigeration systems or limited them to certain application scenarios. To avoid this, developing refrigeration oil compositions with better compatibility with R32 refrigerant is of great significance.

[0004] On the other hand, to ensure the long-term, high-speed, and reliable operation of the refrigeration compressor, the lubricity and stability of the refrigeration oil and refrigerant also need to be improved. The lubricity of the refrigeration oil composition is particularly important for the reliable operation of the compressor, directly affecting the system's cooling performance. While good miscibility between the refrigeration oil and refrigerant facilitates oil return in the system, it can also lead to excessive dilution of the refrigeration oil by the refrigerant, thus affecting the working viscosity and lubrication performance of the refrigeration oil. Therefore, the miscibility of the refrigeration oil needs to balance its lubricity and stability to better address the compatibility issues and application requirements of refrigerant R32.

[0005] There are a number of technical solutions for synthetic ester refrigeration oils that can, to some extent, solve the problem of poor compatibility with R32 refrigerant. However, they still have shortcomings in balancing the lubricity, compatibility, and stability of synthetic esters. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a refrigeration oil that has good low-temperature compatibility and suitable solubility with HFCs refrigerants, especially R32 refrigerant, so as to ensure that the provided refrigeration oil can maintain a thick oil film and good stability even under harsh operating conditions.

[0007] To achieve the above objectives, according to the first aspect of this technical solution, this technical solution provides a refrigeration oil.

[0008] According to an embodiment of this application, the refrigeration oil includes a base oil, characterized in that the base oil includes a first polyol ester and a second polyol ester;

[0009] The first polyol ester is a complex ester synthesized by esterification reaction of a mixture of pentaerythritol and a first carboxylic acid. The first carboxylic acid mixture includes at least one acid selected from C8-C9 monobasic fatty acids, a C5 monobasic fatty acid, and a C4-C9 dibasic acid.

[0010] The second polyol ester is a mixed ester synthesized by esterification of a mixture of dipentaerythritol and a second carboxylic acid, wherein the second carboxylic acid mixture includes at least one acid of C8-C9 monobasic fatty acid and a C5 monobasic fatty acid.

[0011] Furthermore, the C4-C9 dicarboxylic acids are selected from succinic acid, adipic acid, and octanoic acid.

[0012] Furthermore, the monobasic fatty acid of C5 is selected from valeric acid, 2-methylbutyric acid and 3-methylbutyric acid.

[0013] Furthermore, the C8-C9 monobasic fatty acids are selected from octanoic acid, 2-methylheptanoic acid, 3-methylheptanoic acid, 4-methylheptanoic acid, 5-methylheptanoic acid, nonanoic acid, 2-methyloctanoic acid, 3-methyloctanoic acid, 4-methyloctanoic acid, 5-methyloctanoic acid, 6-methyloctanoic acid, 2-ethylheptanoic acid, 3-ethylheptanoic acid, 4-ethylheptanoic acid, 2,3,4-trimethylhexanoic acid, 3,4,5-trimethylhexanoic acid, and 3,5,5-trimethylhexanoic acid.

[0014] Furthermore, the molar ratio of the pentaerythritol to the dipentaerythritol is (1-9):1.

[0015] Furthermore, the kinematic viscosity of the refrigeration oil at 40°C is 44-200 mm. 2The kinematic viscosity at 100℃ is 6.0 mm² / s. 2 / s or more.

[0016] Furthermore, the refrigeration oil also includes additives, which include at least one of anti-wear agents, antioxidants, anti-foaming agents, and acid scavengers.

[0017] Furthermore, the first polyol ester includes at least one of the structural units shown in formula [I].

[0018]

[0019] Among them, R1-R6 are independent C4-C8 hydrocarbon groups or 7≥m≥2.

[0020] To achieve the above objectives, according to a second aspect of this technical solution, this technical solution provides a working fluid composition comprising the refrigeration oil and R32 refrigerant provided in the first aspect of this technical solution.

[0021] Furthermore, the low-temperature two-phase separation temperature of the refrigeration oil and R32 refrigerant is not higher than -20°C.

[0022] Furthermore, the working fluid composition for the refrigeration machine has a solubility viscosity of not less than 2.0 cp at 110°C and 4.2 MPa.

[0023] The embodiments of this application have the following beneficial effects: By controlling the raw material ratio of polyols, diacids, and fatty acids to form a specific combination of polyol esters for refrigeration oil, a working fluid composition for refrigeration equipment that is completely miscible with R32 refrigerant at lower temperatures can be obtained. By controlling the feeding ratio of fatty acids and diacids with specific structures during synthesis, a refrigeration oil that maintains a high dissolution viscosity after dissolution can be obtained, thereby ensuring that the working fluid composition has sufficient oil film strength. Compared with existing refrigeration oils, the refrigeration oil of this invention is completely miscible with R32 refrigerant at lower temperatures, and maintains a high working viscosity after dissolution. Its lubricity and stability are excellent, enabling the product to be used in harsh compressor conditions or low-temperature refrigeration environments. Detailed Implementation

[0024] The following describes in detail the suitable implementation methods of this application.

[0025] The refrigeration oil provided in this application includes a base oil and suitable additives, wherein the additives include at least one selected from anti-wear agents, antioxidants, antifoaming agents, and acid scavengers. Preferably, the main components of the refrigeration oil may include:

[0026]

[0027] There are no specific restrictions on the types of additives used in the refrigeration oil in this application. Antioxidants may include hindered phenols, diarylamines, phenothiazines, organic sulfonates, etc.; acid scavengers may include glycidyl ester type epoxy compounds, glycidyl ether type epoxy compounds, and phenyl glycidyl ethers, etc.; anti-wear agents may include alkyl phosphates and alkyl phosphates, dialkyl dithiophosphates and phosphates, etc.; and antifoaming agents may include silicone-containing polydimethylsiloxanes or other non-silicone polyacrylates, etc.

[0028] The base oil of the refrigeration oil includes a first polyol ester and a second polyol ester. The first polyol ester is a complex ester synthesized by esterification of a mixture of pentaerythritol and a first carboxylic acid, wherein the first carboxylic acid mixture includes at least one acid selected from C8-C9 monobasic fatty acids, a C5 monobasic fatty acid, and a C4-C9 dibasic acid. The second polyol ester is a mixed ester synthesized by esterification of a mixture of dipentaerythritol and a second carboxylic acid, wherein the second carboxylic acid mixture includes at least one acid from C8-C9 monobasic fatty acids and a C5 monobasic fatty acid.

[0029] In the refrigeration oil, the C4-C9 dicarboxylic acid accounts for 2 mol%-20 mol% of the total amount of the first carboxylic acid mixture, preferably 3 mol%-15 mol% of the total amount of the first carboxylic acid mixture, and more preferably 5 mol%-10 mol% of the first carboxylic acid mixture.

[0030] The monobasic fatty acid of C5 in the second carboxylic acid mixture is preferably n-valeric acid, which accounts for more than 25 mol% of the total amount of the second carboxylic acid mixture, and more preferably 75 mol%-95 mol% of the total amount of the second carboxylic acid mixture.

[0031] In the base oil raw materials of refrigeration oil, dipentaerythritol accounts for 10 mol%-50 mol% of the total organic alcohol raw materials, preferably 15 mol%-45 mol% of the total organic alcohol raw materials, and more preferably 20 mol%-40 mol% of the total organic alcohol raw materials.

[0032] Optionally, from the perspective of obtaining the structural stability of the first polyol ester, the C4-C9 dicarboxylic acid is selected from succinic acid, adipic acid and octanoic acid, more preferably adipic acid.

[0033] Optionally, the monobasic fatty acid of C5 is selected from valeric acid, 2-methylbutyric acid, and 3-methylbutyric acid. From a compatibility perspective, 2-methylbutyric acid or 3-methylbutyric acid, which have better performance, are preferred as the monobasic fatty acid of C5.

[0034] Optionally, the C8-C9 monobasic fatty acids are selected from octanoic acid, 2-methylheptanoic acid, 3-methylheptanoic acid, 4-methylheptanoic acid, 5-methylheptanoic acid, 2-ethylhexanoic acid, nonanoic acid, 2-methyloctanoic acid, 3-methyloctanoic acid, 4-methyloctanoic acid, 5-methyloctanoic acid, 6-methyloctanoic acid, 2-ethylheptanoic acid, 3-ethylheptanoic acid, 4-ethylheptanoic acid, 2,3,4-trimethylhexanoic acid, 3,4,5-trimethylhexanoic acid, and 3,5,5-trimethylhexanoic acid. Preferably, 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid are preferred due to their better stability.

[0035] Optionally, the molar ratio of the pentaerythritol to the dipentaerythritol is (1-9):1.

[0036] Optionally, the kinematic viscosity of the refrigeration oil at 40°C is 44-200 mm. 2 The kinematic viscosity at 100℃ is 6.0 mm² / s. 2 / s or more.

[0037] In some embodiments, the first polyol ester includes at least one of the structural units represented by formula [I].

[0038]

[0039] Among them, R1-R6 are independent C4-C8 hydrocarbon groups or 7≥m≥2.

[0040] The refrigeration oil provided in this application embodiment can be mixed with R32 refrigerant to form a working fluid composition for refrigeration machines. The low-temperature two-phase separation temperature of the refrigeration oil and R32 refrigerant is not higher than -20°C. Simultaneously, the solubility viscosity of the working fluid composition for refrigeration machines at 110°C and 4.2 MPa is not less than 2.0 cp.

[0041] The refrigeration oil provided in this invention is a composite ester refrigeration oil with a specific combination formed by controlling the raw material ratio of polyols, diacids, and fatty acids. This allows for a refrigeration working fluid composition that remains completely miscible with R32 refrigerant at lower temperatures. By controlling the feeding ratio of fatty acids and diacids with specific structures during synthesis, a refrigeration oil that maintains a high viscosity after dissolution can be obtained, thus ensuring sufficient oil film strength in the working fluid composition. Compared to existing refrigeration oils, the refrigeration oil of this invention remains completely miscible with R32 refrigerant at lower temperatures and maintains a high working viscosity after dissolution. Its good lubricity and stability allow the product to be used in harsh compressor conditions or low-temperature refrigeration environments.

[0042] The present application will now be described in more detail through preferred embodiments and comparative examples, but the present application is not limited to any of the embodiments described below.

[0043] In each embodiment and comparative example, under necessary catalytic conditions, esterification was carried out with a raw material ratio of 1:1.1 for hydroxyl and carboxyl groups to obtain the corresponding components, thereby achieving a complete esterification reaction. (A-1)-(A-18) are the first polyol esters, and (B-1)-(B-8) are the second polyol esters.

[0044] [First Polyol Ester]

[0045] (A-1) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 3-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 3:80:17.

[0046] The viscosity at 40℃ is 61.25 mm. 2 / s, kinematic viscosity at 100℃: 7.964 mm³ / s 2 / s, viscosity index 95.

[0047] (A-2) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 3-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 3:85:12.

[0048] The viscosity at 40℃ is 58.78 mm. 2 / s, kinematic viscosity at 100℃: 7.709 mm³ / s 2 / s, viscosity index 93.

[0049] (A-3) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 5:45:50.

[0050] The viscosity at 40℃ is 69.91 mm. 2 / s, kinematic viscosity at 100℃: 8.672 mm³ / s 2 / s, viscosity index 95.

[0051] (A-4) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 5:50:45.

[0052] The viscosity at 40℃ is 45.86 mm. 2 / s, kinematic viscosity at 100℃: 6.625 mm³ / s 2 ( / s, viscosity index 94).

[0053] (A-5) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 5:65:30.

[0054] The viscosity at 40℃ is 42.29 mm. 2 / s, kinematic viscosity at 100℃: 42.29 mm³ / s 2 / s, viscosity index 92.

[0055] (A-6) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 5:75:20.

[0056] The viscosity at 40℃ is 49.79 mm. 2 / s, kinematic viscosity at 100℃: 6.869 mm² / s 2 / s, viscosity index 91.

[0057] (A-7) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 5:75:20.

[0058] The viscosity at 40℃ is 41.68 mm. 2 / s, kinematic viscosity at 100℃: 6.133 mm³ / s 2 / s, viscosity index 90.

[0059] (A-8) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 5:85:10.

[0060] The viscosity at 40℃ is 43.16 mm. 2 / s, kinematic viscosity at 100℃: 43.16 mm² 2 / s, viscosity index 98.

[0061] (A-9) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 10:70:20.

[0062] The viscosity at 40℃ is 61.72 mm. 2 / s, kinematic viscosity at 100℃: 8.237 mm³ / s 2 / s, viscosity index 103.

[0063] (A-10) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 10:75:15.

[0064] The viscosity at 40℃ is 52.67 mm. 2 / s, kinematic viscosity at 100℃: 7.426 mm³ / s 2 / s, viscosity index 102.

[0065] (A-11) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 12:65:23.

[0066] The viscosity at 40℃ is 75.84 mm. 2 / s, kinematic viscosity at 100℃: 9.568 mm³ / s 2 / s, viscosity index 104.

[0067] (A-12) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 12:70:18.

[0068] The viscosity at 40℃ is 73.47 mm. 2 / s, kinematic viscosity at 100℃: 9.279 mm² / s 2 / s, viscosity index 102.

[0069] (A-13) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 15:80:5.

[0070] The viscosity at 40℃ is 77.16 mm. 2 / s, kinematic viscosity at 100℃: 9.737 mm³ / s 2 / s, viscosity index 105.

[0071] (A-14) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 15:80:5.

[0072] The viscosity at 40℃ is 64.80 mm. 2 / s, kinematic viscosity at 100℃: 8.601 mm³ / s 2 / s, viscosity index 104.

[0073] (A-15) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 2:50:48.

[0074] The viscosity at 40℃ is 64.71 mm. 2 / s, kinematic viscosity at 100℃: 7.973 mm³ / s 2 / s, viscosity index 86.

[0075] (A-16) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 20:75:5.

[0076] The viscosity at 40℃ is 108.28 mm. 2 / s, kinematic viscosity at 100℃: 12.79 mm² / s 2 / s, viscosity index 112.

[0077] (A-17) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 15:40:45.

[0078] The viscosity at 40℃ is 95.94 mm. 2 / s, kinematic viscosity at 100℃: 11.58 mm³ / s 2 / s, viscosity index 109.

[0079] (A-18) An ester obtained by esterification of pentaerythritol with a mixture of adipic acid, 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 2:88:10.

[0080] The viscosity at 40℃ is 31.07 mm. 2 / s, kinematic viscosity at 100℃: 5.077 mm³ / s 2 / s, viscosity index 85.

[0081] [Second Polyol Ester]

[0082] (B-1) An ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 75:25.

[0083] The viscosity at 40℃ is 78.58 mm. 2 / s, kinematic viscosity at 100℃: 10.78 mm³ / s 2 / s, viscosity index 124.

[0084] (B-2) An ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 85:15.

[0085] The viscosity at 40℃ is 82.99 mm. 2 / s, kinematic viscosity at 100℃: 11.28 mm³ / s 2 / s, viscosity index 125.

[0086] (B-3) An ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 95:5.

[0087] The viscosity at 40℃ is 64.17 mm. 2 / s, kinematic viscosity at 100℃: 9.594 mm³ / s 2 / s, viscosity index 131.

[0088] (B-4) An ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 95:5.

[0089] The viscosity at 40℃ is 63.59 mm. 2 / s, kinematic viscosity at 100℃: 9.475 mm³ / s 2 / s, viscosity index 129.

[0090] (B-5) An ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 35:65.

[0091] The viscosity at 40℃ is 117.85 mm. 2 / s, kinematic viscosity at 100℃: 13.09 mm² / s 2 / s, viscosity index 105.

[0092] (B-6) is an ester obtained by esterification of dipentaerythritol with a mixture of valeric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 25:75.

[0093] The viscosity at 40℃ is 284.35 mm. 2 / s, kinematic viscosity at 100℃ 20.17mm 2 / s, viscosity index 81.

[0094] (B-7) An ester obtained by esterification of dipentaerythritol with a mixture of 2-methylbutyric acid and 3,5,5-trimethylhexanoic acid in a carboxyl molar ratio of 45:55.

[0095] The viscosity at 40℃ is 172.57 mm. 2 / s, kinematic viscosity at 100℃: 15.73 mm³ / s 2 / s, viscosity index 93.

[0096] (B-8) is an ester obtained by esterification of dipentaerythritol with a mixture of 3-methylbutyric acid and 2-ethylhexanoic acid in a carboxyl molar ratio of 55:45.

[0097] The viscosity at 40℃ is 123.64 mm.2 / s, kinematic viscosity at 100℃: 13.09 mm² / s 2 / s, viscosity index 99.

[0098] The first polyol ester and the second polyol ester were mixed in a molar ratio of 9:1 to obtain Examples 1-8 and Comparative Examples 9-24, i.e., the molar ratio of pentaerythritol to dipentaerythritol was 9:1; the first polyol ester and the second polyol ester were mixed in a molar ratio of 1:1 to obtain Examples 9-16 and Comparative Examples 1-8, i.e., the molar ratio of pentaerythritol to dipentaerythritol was 1:1. The types and specific compositions of the first and second polyol esters used in each example and comparative example are shown in Tables 1-5.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103] Table 3

[0104]

[0105] Table 4

[0106]

[0107] Table 5

[0108]

[0109] Referring to SH / T 0699-2000 "Test Method for Compatibility of Refrigeration Oil and Refrigerant": A certain mass of test oil and refrigerant is charged into a test tube, and heated to room temperature or in a water bath until the test oil and refrigerant become a homogeneous and transparent solution. Then, the test tube is cooled in a cold bath. The mixture of refrigeration oil and refrigerant with an oil content of 5%-50% is slowly cooled from 45℃ to -40℃. The temperature at which phase separation or white turbidity occurs is taken as the two-phase separation temperature at the oil content. Two-phase separation curves are plotted using the two-phase separation temperature data for different oil contents. The highest measured temperature on the curve is the two-phase separation temperature of the test oil and refrigerant. The lower the two-phase separation temperature, the better the compatibility between the refrigeration oil and refrigerant. It should be noted that "immiscible" means that no two-phase separation and persistent turbidity were observed within the measured temperature range of this test, that is, two-phase separation or turbidity occurred in the refrigeration oil at room temperature (25℃). The refrigerant used in the test is R32.

[0110] Referring to SH / T 0699-2000 "Test Method for Compatibility of Refrigeration Oil and Refrigerant": A certain mass of test oil and refrigerant were filled into an explosion-proof autoclave. An online viscometer and related accessories were connected and sealed. A vacuum pump was used to evacuate the autoclave. The initial temperature of the heater was set to 30℃. The viscosity of the mixture under certain temperature and pressure conditions was measured, with a temperature gradient interval of 10℃. The pressure inside the autoclave was controlled by switching valves to control the refrigerant content. A platinum resistance pressure sensor and a temperature sensor and related accessories were connected, and the temperature and pressure were monitored in real time. After the temperature inside the autoclave stabilized, the pressure inside the autoclave was observed and recorded approximately every 10 minutes. The online viscometer could directly read the viscosity of the mixed solution, which is the solubility viscosity (dynamic viscosity) under specific conditions. The lower the solubility viscosity, the lower the lubricating film strength and the poorer the anti-wear lubrication performance of the combination of refrigeration oil and refrigerant; the higher the solubility viscosity, the higher the lubricating film strength and the better the anti-wear lubrication performance of the combination of refrigeration oil and refrigerant. The refrigerant used in the test was R32.

[0111] A primary objective of the refrigeration oil implemented in this invention is to enable its application in low-temperature or extremely low-temperature conditions; therefore, the low-temperature fluidity of the refrigeration oil needs to be considered. Tables 1-5 show that the structural form of the C5 monobasic fatty acid in the second polyol ester directly affects the low-temperature fluidity of the refrigeration oil. When the selected second polyol ester contains branched C5 monobasic fatty acids, such as Comparative Examples 17-24, the pour point of the refrigeration oil in Table 5 is in the higher range of -32°C to -1°C, resulting in poor low-temperature fluidity. Conversely, when the selected second polyol ester uses valeric acid instead of branched C5 fatty acids, such as Examples 1-16 and Comparative Examples 1-16, the pour point of the refrigeration oil in Tables 1-4 is in the lower range than that of Comparative Examples 17-24, resulting in better low-temperature fluidity. Therefore, valeric acid is preferably used in the second carboxylic acid mixture as a raw material for the second polyol ester, rather than branched C5 fatty acids.

[0112] By comparing the examples and comparative examples in Tables 1-4, it was found that the compatibility between refrigeration oil and refrigerant is affected by both the amount of dicarboxylic acid in the first carboxylic acid mixture and the amount of n-valeric acid in the second carboxylic acid mixture. When the proportion of adipic acid in the total amount of the first carboxylic acid ring mixture reaches or exceeds 15 mol%, it easily leads to the refrigeration oil and R32 refrigerant becoming immiscible or having very poor compatibility, as seen in Comparative Examples 4-7 and 15-16. In particular, when the proportion of adipic acid in the total amount of the first carboxylic acid ring mixture reaches or exceeds 20 mol%, the compatibility between the synthesized refrigeration oil and R32 refrigerant is even worse. The experimental data also show that a higher proportion of n-valeric acid in the total amount of the second carboxylic acid ring mixture is more beneficial to the compatibility between refrigeration oil and R32 refrigerant. When the proportion of n-valeric acid in the total amount of the second carboxylic acid ring mixture is less than or equal to 35 mol%, the compatibility between refrigeration oil and R32 refrigerant is relatively poor, as seen in Comparative Examples 2, 3, 5, 7, and 13-16. Furthermore, by increasing the proportion of valeric acid in the total amount of the second carboxylic acid ring mixture, the problem of poor compatibility between the refrigeration oil and R32 refrigerant caused by the excessive proportion of adipic acid in the first carboxylic acid ring mixture can be compensated. Specifically, refer to Examples 13 and 14. Although the proportion of adipic acid in the total amount of the first carboxylic acid ring mixture reaches 15 mol%, the proportions of valeric acid in the total amount of the second carboxylic acid ring mixture reach 95 mol% and 85 mol%, respectively, and the proportion of the second polyol ester reaches 50 mol% of the total amount of the first and second polyol esters. The overall proportion of valeric acid is relatively high, ensuring that the compatibility between the obtained refrigeration oil and R32 refrigerant remains at a good level. Therefore, in order to improve the working fluid properties of the base oil and refrigerant composition, the amounts of adipic acid and valeric acid must be limited to balance their solubility, viscosity, and compatibility.

[0113] According to the petrochemical industry standard SH / T 0189-92 "Determination of Anti-wear Performance of Lubricating Oils", the anti-wear performance of the oils was determined, and the quality of their anti-wear performance was evaluated by comparing the average wear scar diameter. Table 1 shows that the oils in Examples 1-5 showed no significant difference in compatibility with R32 refrigerant, and the average wear scar diameter decreased accordingly with the reduction of the amount of C5 monobasic fatty acid in the base oil components. Furthermore, when the oils showed good compatibility with R32 refrigerant, as shown in Comparative Examples 9-12 in Table 4, the compatibility "improved" with the increase of the proportion of valeric acid in the base oil. However, under conditions of 110℃ and 4.2MPa, the viscosity of the base oil in relation to R32 refrigerant was adversely affected, and the anti-wear lubrication effect significantly deteriorated. The experimental results of Example 9 and Comparative Example 1 also indicate that the addition of dipentaerythritol mixed esters played a crucial role in balancing the lubrication effect and compatibility of the oils. Of course, to achieve better anti-wear and lubrication effects, necessary anti-wear additives can also be added to refrigeration oil.

[0114] As can be seen from the test data in Table 1-2, under the actual operating conditions of the compressor (110℃, 4.2MPa), the dissolved viscosity is above 2.0cp, which ensures a sufficiently thick oil film between the friction pairs of the compressor pump body parts, thereby improving the wear resistance of the working fluid composition and enhancing the reliability of compressor operation. Therefore, the refrigeration oil described herein balances low-temperature compatibility, lubricity, and high-temperature stability.

[0115] Some embodiments in this specification are described in a progressive or parallel manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0116] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A refrigeration oil, comprising a base oil, characterized in that, The base oil includes a first polyol ester and a second polyol ester; The first polyol ester is a composite ester synthesized by esterification reaction of pentaerythritol and a mixture of the first carboxylic acid. The first carboxylic acid mixture includes at least one acid selected from C8-C9 monobasic fatty acids, a C5 monobasic fatty acid, and adipic acid. Adipic acid accounts for 5 mol%-10 mol% of the total amount of the first carboxylic acid mixture. The C8-C9 monobasic fatty acid in the first carboxylic acid mixture is 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid, and the C5 monobasic fatty acid is 3-methylbutyric acid or 2-methylbutyric acid. The second polyol ester is a mixed ester synthesized by esterification reaction of a mixture of dipentaerythritol and a second carboxylic acid. The second carboxylic acid mixture includes at least one acid of a C8-C9 monobasic fatty acid and n-valeric acid, with n-valeric acid accounting for 75 mol%-95 mol% of the total amount of the second carboxylic acid mixture. The C8-C9 monobasic fatty acid in the second carboxylic acid mixture is 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid.

2. The refrigeration oil according to claim 1, characterized in that, The molar ratio of the pentaerythritol to the dipentaerythritol is (1-9):

1.

3. The refrigeration oil according to claim 1, characterized in that, The kinematic viscosity of the refrigeration oil at 40°C is 44-200 mm. 2 The kinematic viscosity at 100℃ is 6.0 mm² / s. 2 / s or more.

4. The refrigeration oil according to claim 1, characterized in that, It also includes additives, which include at least one of anti-wear agents, antioxidants, anti-foaming agents and acid scavengers.

5. The refrigeration oil according to claim 1, characterized in that, The first polyol ester includes at least one of the structural units shown in formula [I]. 【I】 Wherein, R1-R6 are independent C4 hydrocarbon groups, C7-C8 hydrocarbon groups, or... m=4.

6. A working fluid composition for a refrigeration unit, characterized in that, Includes the refrigeration oil and R32 refrigerant as described in any one of claims 1-5.

7. The working fluid composition for a refrigeration unit according to claim 6, characterized in that, The low-temperature two-phase separation temperature of the refrigeration oil and R32 refrigerant is not higher than -20℃.

8. The working fluid composition for a refrigeration unit according to claim 6, characterized in that, The working fluid composition for the refrigeration machine has a solubility viscosity of not less than 2.0 cp at 110°C and 4.2 MPa.

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