Pentaerythritol mixed fatty acid ester as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of pentaerythritol fatty acid ester synthesis, and particularly relates to pentaerythritol mixed fatty acid ester as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing pentaerythritol, fatty acid, a catalyst and a water-carrying agent, and carrying out esterification reaction to obtain esterification reaction liquid; carrying out purification treatment on the esterification reaction liquid to obtain pentaerythritol mixed fatty acid ester; the fatty acid comprises n-heptanoic acid, n-octanoic acid and 3, 5, 5-trimethyl hexanoic acid, and the molar ratio of the n-heptanoic acid to the n-octanoic acid to the 3, 5, 5-trimethyl hexanoic acid is (1-8): (1-8): 2. According to the invention, acid raw materials for esterification reaction are reasonably selected to react with pentaerythritol, and meanwhile, the molar ratio of three fatty acids is regulated and controlled, so that the obtained pentaerythritol mixed fatty acid ester has the characteristics of low viscosity and high ignition point, thereby having excellent low-temperature fluidity and high-temperature stability; meanwhile, the pentaerythritol mixed fatty acid ester provided by the invention also has excellent electrical performance.

Description

Technical Field

[0001] This invention belongs to the field of pentaerythritol fatty acid ester synthesis technology, specifically relating to a pentaerythritol mixed fatty acid ester, its preparation method, and its application. Background Technology

[0002] Insulating oil, also known as transformer oil, is an extremely important type of liquid dielectric. It is widely used in large power equipment such as power transformers, high-voltage bushings, circuit breakers, and capacitors, and is hailed as the "blood" of power equipment.

[0003] Early insulating oils were refined directly from petroleum, primarily consisting of naphthenic mineral oils. Due to their low cost, stable performance, and mature production processes, they quickly became the most widely used insulating oils globally. However, mineral oils are flammable and poorly biodegradable; leaks can easily cause fires and severe environmental pollution. As safety and environmental protection requirements have increased, the limitations of mineral oils have become increasingly apparent.

[0004] Ester-based insulating oils have gained widespread recognition as an excellent alternative to mineral oils. However, within the ester family, significant performance differences exist between natural esters derived from vegetable oils and chemically synthesized esters. While natural esters are highly regarded for their superior biodegradability and renewability, compared to synthetic esters, natural ester molecules, derived from vegetable oils, typically contain unsaturated double bonds, are easily oxidized, and contain long-chain fatty acids, resulting in poor low-temperature fluidity. Furthermore, the ester bonds in triglycerides are more prone to hydrolysis. Therefore, in many applications with stringent performance requirements, synthetic ester insulating oils demonstrate irreplaceable advantages and become the superior choice.

[0005] However, the low-temperature fluidity and high-temperature stability of synthetic ester insulating oils are currently poor and need to be further improved. Summary of the Invention

[0006] The purpose of this invention is to provide a pentaerythritol mixed fatty acid ester, its preparation method, and its application. The pentaerythritol mixed fatty acid ester provided by this invention has the characteristics of low viscosity and high flash point, thus exhibiting excellent low-temperature fluidity and high-temperature stability, and has wide application value as a base oil for ester-based insulating oils.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing pentaerythritol mixed fatty acid esters, comprising the following steps: Pentaerythritol, fatty acids, catalysts, and dehydrating agents are mixed and subjected to esterification to obtain an esterification reaction solution. The esterification reaction solution is then purified to obtain the pentaerythritol mixed fatty acid ester. The fatty acids include n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid, and the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is (1~8):(1~8):2.

[0008] Preferably, the molar ratio of the hydroxyl group of the pentaerythritol to the carboxyl group of the fatty acid is 1:1 to 1.05.

[0009] Preferably, the catalyst is a tin-based catalyst; the mass percentage of the catalyst relative to the total mass of the pentaerythritol and fatty acids is 0.1-0.2%.

[0010] Preferably, the tin-based catalyst is stannous oxalate.

[0011] Preferably, the water-removing agent includes one or more of toluene, xylene, and petroleum ether.

[0012] Preferably, the temperature of the esterification reaction is 180~200℃.

[0013] Preferably, the purification process includes: mixing the esterification reaction solution and activated carbon and then performing vacuum distillation; the vacuum distillation temperature is 180~200℃ and the vacuum pressure is -0.05~-0.09MPa.

[0014] The present invention provides a pentaerythritol mixed fatty acid ester prepared by the preparation method described in the above technical solution.

[0015] Preferably, the kinematic viscosity of the pentaerythritol mixed fatty acid ester at 40°C is <28.6 mm. 2 / s; Ignition point ≥310℃.

[0016] This invention provides the application of the pentaerythritol mixed fatty acid ester described in the above technical solution as a base oil for synthetic ester insulating oil.

[0017] This invention provides a method for preparing a pentaerythritol mixed fatty acid ester, comprising the following steps: mixing pentaerythritol, fatty acids, a catalyst and a dehydrating agent and then performing an esterification reaction to obtain an esterification reaction solution; purifying the esterification reaction solution to obtain the pentaerythritol mixed fatty acid ester; wherein the fatty acids include n-heptanoic acid, n-octanoic acid and 3,5,5-trimethylhexanoic acid, and the molar ratio of n-heptanoic acid, n-octanoic acid and 3,5,5-trimethylhexanoic acid is (1~8):(1~8):2. The preparation method provided by this invention uses pentaerythritol with heptanoic acid, octanoic acid, and 3,5,5-trimethylhexanoic acid as raw materials for esterification reaction. Simultaneously, the molar ratio of heptanoic acid, octanoic acid, and 3,5,5-trimethylhexanoic acid is optimized to (1~8):(1~8):2. By rationally selecting the acid raw materials for the esterification reaction and reacting with pentaerythritol, while simultaneously controlling the molar ratio of the three fatty acids, the resulting pentaerythritol mixed fatty acid ester exhibits low viscosity and a high flash point, thus possessing excellent low-temperature fluidity and high-temperature stability. Furthermore, the pentaerythritol mixed fatty acid ester provided by this invention also possesses excellent electrical properties. Compared with the existing Midel 7131, the pentaerythritol mixed fatty acid ester prepared by this invention has a lower kinematic viscosity and a higher flash point than Midel 7131, especially a higher breakdown voltage. Therefore, the pentaerythritol mixed fatty acid ester prepared by this invention has broad application value as a base oil for ester-based insulating oils.

[0018] Meanwhile, the preparation method provided by this invention has a simple process flow and high conversion rate, making it more suitable for industrial applications. Attached Figure Description

[0019] Figure 1 The flowchart illustrates the preparation process of pentaerythritol mixed fatty acid esters provided by this invention. Detailed Implementation

[0020] This invention provides a method for preparing pentaerythritol mixed fatty acid esters, comprising the following steps: Pentaerythritol, fatty acids, catalysts, and dehydrating agents are mixed and subjected to esterification to obtain an esterification reaction solution. The esterification reaction solution is then purified to obtain the pentaerythritol mixed fatty acid ester. The fatty acids include n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid, and the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is (1~8):(1~8):2.

[0021] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0022] In this invention, the catalyst is preferably a tin-based catalyst, and in the examples, it can be stannous oxalate. The dehydrating agent preferably includes one or more of toluene, xylene, and petroleum ether, and in the examples, it can be petroleum ether. The boiling range of the petroleum ether is 90~120℃.

[0023] In this invention, the molar ratio of the hydroxyl group of the pentaerythritol to the carboxyl group of the fatty acid is 1:1 to 1.05, and in the examples it can be 1:1.05.

[0024] In this invention, the molar ratio of n-heptanoic acid, n-octanoic acid and 3,5,5-trimethylhexanoic acid is (1~8):(1~8):2, preferably (2~8):(1~6):2, more preferably (5~8):(1~3):2, and even more preferably (5.5~8):(1~2.5):2. In the embodiments, it can be 2.9:1.1:1 (i.e., 5.8:2.2:2), 3:1:1 (i.e., 6:2:2), 7.7:1.33:2 or 7:1:2.

[0025] In this invention, the mass percentage of the catalyst relative to the total mass of the pentaerythritol and fatty acids is preferably 0.1-0.2%, and in the examples it can be 0.1%. This invention does not have special requirements regarding the amount of the dehydrating agent, as long as the reaction proceeds smoothly.

[0026] In this invention, the mixing preferably includes: sequentially loading pentaerythritol, fatty acid, catalyst, and dehydrating agent into a reaction apparatus, and then heating under stirring until the above-mentioned reactants are completely dissolved. The heating temperature is preferably 155~160℃. The stirring speed is preferably 500~700 r / min, and in the examples it can be 600 r / min.

[0027] In this invention, a water separator and a reflux condenser are used during the esterification reaction. The preferred temperature for the esterification reaction is 180-200°C, but in some embodiments it can be 190°C. The endpoint of the esterification reaction is determined by measuring the acid value of the resulting esterification solution. The esterification reaction is considered complete when the acid value of the esterification solution is ≤15 mg KOH / g.

[0028] In this invention, the purification process preferably includes: mixing the esterification reaction solution and activated carbon, followed by vacuum distillation. The percentage of activated carbon by mass relative to the total mass of pentaerythritol and fatty acids is preferably 1-5%, more preferably 2-3%. The vacuum distillation temperature is preferably 180-200°C, and the vacuum pressure is preferably -0.05 to -0.09 MPa. The vacuum distillation time is preferably 10-12 hours. After vacuum distillation, this invention preferably further includes solid-liquid separation of the reaction solution obtained from vacuum distillation to obtain the pentaerythritol mixed fatty acid ester. The solid-liquid separation is preferably filtration.

[0029] The present invention provides a pentaerythritol mixed fatty acid ester prepared by the preparation method described in the above technical solution.

[0030] The pentaerythritol mixed fatty acid ester has the following structure: ; Where R1, R2, R3, and R4 are independent: , or .

[0031] In this invention, the kinematic viscosity of the pentaerythritol mixed fatty acid ester at 40°C is preferably <28.6 mm. 2 / s, more preferably 26.8~28.6mm 2 / s, which can be 28.09mm in the example. 2 / s, 28.57mm 2 / s, 26.80mm 2 / s or 27.66mm 2 / s.

[0032] In this invention, the flash point of the pentaerythritol mixed fatty acid ester is preferably ≥310℃, more preferably 311~314℃, and in the examples it can be 311℃, 314℃ or 312℃.

[0033] In this invention, the pour point of the pentaerythritol mixed fatty acid ester is preferably ≤-54℃, more preferably -54~-57℃.

[0034] In this invention, the breakdown voltage of the pentaerythritol mixed fatty acid ester is preferably ≥89kV, more preferably 89~97kV, and in the examples it can be 91.4kV, 89.6kV, 97.0kV or 93.7kV.

[0035] This invention provides the application of the pentaerythritol mixed fatty acid ester described in the above technical solution as a base oil for synthetic ester insulating oil.

[0036] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1 68.073 g pentaerythritol, 164.033 g n-heptanoic acid, 60.569 g n-octanoic acid, 66.460 g 3,5,5-trimethylhexanoic acid (the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is 3:1:1) and 0.359 g stannous oxalate (the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used) were added sequentially to a three-necked flask. 14 mL of petroleum ether with a boiling range of 90-120 °C was added. A water separator and a reflux condenser were installed. The mixture was stirred at 160 °C at a speed of 600 r / min until the reactants were completely dissolved. The temperature was then increased to 190 °C to carry out the esterification reaction (the esterification reaction was considered complete when the acid value of the product obtained after the esterification reaction was ≤15 mg KOH / g). After the reaction, the product is purified. First, 10 grams of activated carbon is added to the product of the esterification reaction and vacuum distillation is carried out (the temperature of vacuum distillation is preferably 200℃, the vacuum pressure is preferably -0.08MPa, and the time is 12h) to remove acid and decolorize. After distillation, the product is filtered to obtain pentaerythritol mixed fatty acid ester.

[0038] Example 2 68.073 g pentaerythritol, 158.565 g n-heptanoic acid, 66.625 g n-octanoic acid, 66.460 g 3,5,5-trimethylhexanoic acid (the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid was 2.9:1.1:1) and 0.360 g stannous oxalate (the mass of stannous oxalate was 0.1% of the total mass of pentaerythritol and the fatty acids used) were added sequentially to a three-necked flask. 14 mL of petroleum ether with a boiling range of 90-120 °C was added. A water separator and a reflux condenser were installed. The mixture was stirred at 160 °C at a speed of 600 r / min until the reactants were completely dissolved. The temperature was then increased to 190 °C to carry out the esterification reaction (the esterification reaction was considered complete when the acid value of the product obtained after the esterification reaction was ≤15 mg KOH / g). After the reaction, the product is purified. First, 10 grams of activated carbon is added to the product of the esterification reaction and vacuum distillation is carried out (the temperature of vacuum distillation is preferably 200℃, the vacuum pressure is preferably -0.08MPa, and the time is 12h) to remove acid and decolorize. After distillation, the product is filtered to obtain pentaerythritol mixed fatty acid ester.

[0039] Example 3 68.073 g pentaerythritol, 191.372 g n-heptanoic acid, 36.341 g n-octanoic acid, 59.814 g 3,5,5-trimethylhexanoic acid (the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid was 7.7:1.33:2) and 0.356 g stannous oxalate (the mass of stannous oxalate was 0.1% of the total mass of pentaerythritol and the fatty acids used) were added sequentially to a three-necked flask. 14 mL of petroleum ether with a boiling range of 90-120 °C was added. A water separator and a reflux condenser were installed. The mixture was stirred at 160 °C at a speed of 600 r / min until the reactants were completely dissolved. The temperature was then increased to 190 °C to carry out the esterification reaction (the esterification reaction was considered complete when the acid value of the product obtained after the esterification reaction was ≤15 mg KOH / g). After the reaction, the product is purified. First, 10 grams of activated carbon is added to the product of the esterification reaction and vacuum distillation is carried out (the temperature of vacuum distillation is preferably 200℃, the vacuum pressure is preferably -0.08MPa, and the time is 12h) to remove acid and decolorize. After distillation, the product is filtered to obtain pentaerythritol mixed fatty acid ester.

[0040] Example 4 68.073 g pentaerythritol, 191.372 g n-heptanoic acid, 30.284 g n-octanoic acid, 66.460 g 3,5,5-trimethylhexanoic acid (the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid was 7:1:2) and 0.356 g stannous oxalate (the mass of stannous oxalate was 0.1% of the total mass of pentaerythritol and the fatty acids used) were added sequentially to a three-necked flask. 14 mL of petroleum ether with a boiling range of 90-120 °C was added. A water separator and a reflux condenser were installed. The mixture was stirred at 160 °C at a speed of 600 r / min until the reactants were completely dissolved. The temperature was then increased to 190 °C to carry out the esterification reaction (the esterification reaction was considered complete when the acid value of the product obtained after the esterification reaction was ≤15 mg KOH / g). After the reaction is completed, the product is purified. First, 10 grams of activated carbon is added to the product of the esterification reaction and vacuum distillation is carried out (the temperature of vacuum distillation is preferably 200℃, the vacuum pressure is preferably -0.08MPa, and the time is 12h) to remove acid and decolorize. After the distillation and decolorization are completed, the product is filtered to obtain pentaerythritol mixed fatty acid ester.

[0041] Comparative Example 1 Synthetic ester insulating oil Midel 7131.

[0042] Comparative Example 2 (3,5,5-trimethylhexanoic acid omitted compared to Example 1) The preparation method is basically the same as that in Example 1, except that 68.073 g of pentaerythritol, 191.372 g of n-heptanoic acid, 90.852 g of n-octanoic acid and stannous oxalate (the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used) are added sequentially to a three-necked flask.

[0043] Comparative Example 3 (octanoic acid omitted compared to Example 1) The preparation method is basically the same as that in Example 1, except that 68.073 g of pentaerythritol, 191.372 g of n-heptanoic acid, 99.69 g of 3,5,5-trimethylhexanoic acid and stannous oxalate (the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used) are added sequentially to a three-necked flask.

[0044] Comparative Example 4 (n-heptanoic acid omitted compared to Example 1) The preparation method is basically the same as that in Example 1, except that 68.073 g of pentaerythritol, 211.99 g of octanoic acid, 99.69 g of 3,5,5-trimethylhexanoic acid and stannous oxalate (the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used) are added sequentially to a three-necked flask.

[0045] Comparative Example 5 The preparation method is basically the same as that in Example 1, except that: 66.460 g of 3,5,5-trimethylhexanoic acid in Example 1 is replaced with 66.460 g of n-nonyl, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and fatty acids used.

[0046] Comparative Example 6 The preparation method is basically the same as that in Example 1, except that 164.033 g of n-heptanoic acid in Example 1 is replaced with 146.359 g of n-hexanoic acid, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and fatty acids used.

[0047] Comparative Example 7 The preparation method is basically the same as that in Example 1, except that 60.569 g of octanoic acid in Example 1 is replaced with 48.786 g of hexanoic acid, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and fatty acids used.

[0048] Comparative Example 8 The preparation method is basically the same as that in Example 1, except that 66.460 g of 3,5,5-trimethylhexanoic acid in Example 1 is replaced with 48.786 g of n-hexanoic acid, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and fatty acids used.

[0049] Comparative Example 9 The preparation method is basically the same as that in Example 1, except that: the mass of n-heptanoic acid is 164.033 g, the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is 3:3:14, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used.

[0050] Comparative Example 10 The preparation method is basically the same as that in Example 1, except that: the mass of n-heptanoic acid is 164.033 g, the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is 14:14:3, and the mass of stannous oxalate is 0.1% of the total mass of pentaerythritol and the fatty acids used.

[0051] Test case The kinematic viscosity, pour point, flash point, and breakdown voltage of the purified pentaerythritol mixed fatty acid esters were measured to evaluate whether the products obtained by the method of the present invention meet the physicochemical and electrical performance requirements for synthetic ester insulating oils. The kinematic viscosity, pour point, flash point, and breakdown voltage values ​​of the products of Examples 1-4 and Comparative Examples 1-10 are shown in Table 1.

[0052] Table 1 Performance test results of oil samples from Examples 1-4 and Comparative Examples 1-10

[0053] Analysis of the data from Examples 1-4 revealed that the kinematic viscosity of the pentaerythritol mixed fatty acid esters prepared in this invention is lower than that of Comparative Example 1, Midel 7131, while the ignition point is higher. In particular, the breakdown voltage is significantly higher than that of Comparative Example 1, Midel 7131. This indicates that the pentaerythritol mixed fatty acid esters prepared in this invention possess excellent physicochemical and electrical properties. Analysis of the data from Comparative Examples 2-10 revealed that after adjusting the types and proportions of fatty acids, the kinematic viscosity, pour point, ignition point, and breakdown voltage of the pentaerythritol mixed fatty acid ester products did not meet the standards of Examples 1-4.

[0054] As can be seen from the above embodiments, the preparation method provided by the present invention uses pentaerythritol with n-heptanoic acid, n-octanoic acid and 3,5,5-trimethylhexanoic acid as raw materials for esterification reaction, and optimizes the molar ratio of n-heptanoic acid, n-octanoic acid and 3,5,5-trimethylhexanoic acid to (1~8):(1~8):2. By rationally selecting the acid raw materials for esterification reaction and reacting with pentaerythritol, and simultaneously controlling the molar ratio of the three fatty acids, the pentaerythritol mixed fatty acid ester obtained by the present invention has the characteristics of low viscosity and high flash point, thus exhibiting excellent low-temperature fluidity and high-temperature stability. At the same time, the pentaerythritol mixed fatty acid ester provided by the present invention also has excellent electrical properties. Compared with the prior art Midel 7131, the kinematic viscosity of the pentaerythritol mixed fatty acid ester prepared by the present invention is lower than that of Midel 7131, the flash point is higher than that of Midel 7131, and especially the breakdown voltage is higher than that of Midel 7131. Therefore, the pentaerythritol mixed fatty acid ester prepared by the present invention has broad application value as a base oil for ester-based insulating oils.

[0055] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a pentaerythritol mixed fatty acid ester, characterized in that, Includes the following steps: Pentaerythritol, fatty acids, catalysts, and dehydrating agents are mixed and subjected to esterification to obtain an esterification reaction solution. The esterification reaction solution is then purified to obtain the pentaerythritol mixed fatty acid ester. The fatty acids include n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid, and the molar ratio of n-heptanoic acid, n-octanoic acid, and 3,5,5-trimethylhexanoic acid is (1~8):(1~8):

2.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the hydroxyl group of the pentaerythritol to the carboxyl group of the fatty acid is 1:1 to 1.

05.

3. The preparation method according to claim 1, characterized in that, The catalyst is a tin-based catalyst; the mass percentage of the catalyst relative to the total mass of the pentaerythritol and fatty acids is 0.1-0.2%.

4. The preparation method according to claim 3, characterized in that, The tin-based catalyst is stannous oxalate.

5. The preparation method according to claim 1, characterized in that, The water-removing agent includes one or more of toluene, xylene, and petroleum ether.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The esterification reaction is carried out at a temperature of 180~200℃.

7. The preparation method according to claim 1, characterized in that, The purification process includes: mixing the esterification reaction solution and activated carbon and then performing vacuum distillation; the vacuum distillation temperature is 180~200℃ and the vacuum negative pressure is -0.05~-0.09MPa.

8. The pentaerythritol mixed fatty acid ester prepared by the preparation method according to any one of claims 1 to 7.

9. The pentaerythritol mixed fatty acid ester according to claim 8, characterized in that, The kinematic viscosity of the pentaerythritol mixed fatty acid ester at 40°C is <28.6 mm. 2 / s; Ignition point ≥310℃.

10. The use of the pentaerythritol mixed fatty acid ester as described in claim 8 or 9 as a base oil for synthetic ester insulating oil.

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