Trimethylolpropane mixed fatty acid ester, and preparation method and application thereof

Abstract

This invention discloses a trimethylolpropane mixed fatty acid ester, its preparation method, and its applications. The mixed fatty acid ester is obtained by esterification of two or more fatty acids with trimethylolpropane. The fatty acids are selected from combinations of octanoic acid, decanoic acid, and oleic acid, or combinations of oleic acid with octanoic acid or decanoic acid. The mixed fatty acid ester of this invention possesses both a high flash point and a low pour point, while maintaining low viscosity at low temperatures. It also exhibits excellent dielectric properties, meeting the various requirements of electrical equipment for insulating media. Furthermore, this mixed fatty acid ester uses renewable fatty acids as raw materials, has good biodegradability, aligns with the trend of green and environmentally friendly development, and avoids the environmental pollution problems caused by traditional mineral insulating oils and some synthetic insulating oils. It has broad application prospects in power equipment such as transformers and capacitors.

Description

Technical Field

[0001] This invention relates to a mixed fatty acid ester, specifically to a trimethylolpropane mixed fatty acid ester, its preparation method, and its application. Background Technology

[0002] As the core insulating and cooling medium in power equipment, insulating oil's performance directly determines the equipment's insulation reliability, heat dissipation efficiency, and service life, becoming one of the key factors restricting the development of power equipment towards higher parameters and wider environmental adaptability.

[0003] Currently, insulating oils are mainly classified into three categories: mineral insulating oils, traditional synthetic insulating oils, and vegetable insulating oils. Mineral insulating oils still dominate in medium and low voltage power equipment due to their wide availability of raw materials, low cost, and excellent dielectric loss performance. However, their low ignition point makes them prone to combustion under fault conditions such as high temperature, overload, or partial discharge. Furthermore, their high pour point makes them susceptible to solidification or increased viscosity at low temperatures, leading to a significant decrease in equipment heat dissipation efficiency and deterioration of insulation performance. While traditional synthetic insulating oils, represented by alkylbenzenes, offer some improvement in ignition and pour point compared to mineral insulating oils, their raw materials rely on petrochemical derivatives. Their preparation requires complex catalytic polymerization and refining processes, and they are difficult to completely biodegrade, which does not meet the requirements of green power development. Natural ester insulating oils made from vegetable oils have advantages such as being renewable, biodegradable, and having a high ignition point. However, the molecular structure of natural vegetable oils contains a large number of unsaturated double bonds, which are prone to oxidative polymerization at high temperatures, leading to increased oil viscosity, increased acid value, and rapid deterioration of insulation performance. In addition, natural vegetable oils have a high content of high-carbon chain saturated fatty acids, resulting in a high pour point and poor low-temperature fluidity.

[0004] Therefore, given the difficulty of achieving a balance between ignition point, pour point, dielectric properties, and environmental friendliness in existing insulating oils, developing a plant-based synthetic ester insulating oil with a low pour point, high ignition point, excellent dielectric properties, and environmental friendliness is of significant practical importance and value.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a trimethylolpropane mixed fatty acid ester, its preparation method, and its application, which solves the problem that existing insulating oils are difficult to balance in terms of ignition point, pour point, dielectric properties, and environmental friendliness. The mixed fatty acid ester of this invention not only has a high ignition point, which can improve the safety of power equipment under fault conditions, but also has a low pour point, which ensures good fluidity in low-temperature environments and guarantees the heat dissipation efficiency and insulation performance of the equipment.

[0007] To achieve the above objectives, the present invention provides a trimethylolpropane mixed fatty acid ester, which is obtained by esterification of two or more fatty acids with trimethylolpropane; wherein the fatty acids are selected from a combination of octanoic acid, decanoic acid and oleic acid, or a combination of oleic acid with octanoic acid or decanoic acid.

[0008] This invention utilizes octanoic acid (C8), decanoic acid (C10), and oleic acid (C18), which are abundant in natural plants and have low extraction costs. By esterifying any two or more of these fatty acids with trimethylolpropane, a mixed fatty acid ester can be generated. By rationally adjusting the ratio of the three fatty acids, the mixed fatty acid ester can possess both a high flash point and a low pour point.

[0009] Preferably, the molar ratio of trimethylolpropane to octanoic acid, decanoic acid, and oleic acid is (0.5~6.5):(0~14.0):(0~1):(1~5), and the molar amounts of decanoic acid and octanoic acid cannot both be 0. More preferably, the molar ratio of trimethylolpropane to octanoic acid, decanoic acid, and oleic acid is (1.0~6.5):(2.0~14.0):(0~1):(1~5).

[0010] A second objective of this invention is to provide a method for preparing the aforementioned trimethylolpropane mixed fatty acid ester, the method comprising: Trimethylolpropane is reacted with two or more fatty acids in petroleum ether under the action of a catalyst and under heating conditions to undergo an esterification reaction, thereby obtaining a trimethylolpropane mixed fatty acid ester.

[0011] Preferably, the catalyst is selected from stannous oxalate; or / and, the amount of the catalyst is 0.1~0.2% of the total mass of the reaction raw materials; or / and, the boiling range of the petroleum ether is 90~120℃.

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

[0013] More preferably, the heating is carried out by first stirring at 90~110°C to completely dissolve the reactants, and then raising the temperature to 180~200°C to carry out the esterification reaction.

[0014] Preferably, after the esterification reaction is completed, activated carbon is added to the product for deacidification and color removal by vacuum distillation. After vacuum distillation, the product is filtered to obtain trimethylolpropane mixed fatty acid esters.

[0015] More preferably, the temperature of the vacuum distillation is 160~200℃, and the vacuum pressure of the vacuum distillation is -0.05~-0.09MPa. Vacuum distillation is used to remove unreacted fatty acids. The temperature range of 160~200℃ exceeds the boiling point of fatty acids, which can effectively remove excess fatty acids.

[0016] A third objective of this invention is to provide the application of the aforementioned trimethylolpropane mixed fatty acid ester in insulating oil.

[0017] A fourth objective of this invention is to provide a low pour point, high flash point insulating oil comprising: the aforementioned trimethylolpropane mixed fatty acid ester.

[0018] The trimethylolpropane mixed fatty acid ester, its preparation method, and its application of the present invention solve the problem that existing insulating oils are difficult to balance in terms of ignition point, pour point, dielectric properties, and environmental friendliness, and have the following advantages: (1) The mixed fatty acid ester of the present invention has both a high flash point and a low pour point, and can maintain a low viscosity under low temperature conditions. It also has excellent dielectric properties, which can meet the various requirements of power equipment for insulating media. In addition, the mixed fatty acid ester uses renewable fatty acids as raw materials, has good biodegradability, conforms to the development trend of green environmental protection, avoids the pollution problems caused by traditional mineral insulating oil and some synthetic insulating oil, and has broad application prospects in power equipment such as transformers and capacitors;

[0019] (2) The mixed fatty acid ester of the present invention has relatively environmentally friendly raw material sources, reasonable preparation process, and excellent dielectric properties of the resulting product, which meets the requirements of green power development for insulating oil. Attached Figure Description

[0020] Figure 1 The figure shows the liquid chromatography-mass spectrometry test results of the trimethylolpropane mixed fatty acid ester prepared in Example 1 of the present invention.

[0021] Figure 2 The figure shows the liquid chromatography-mass spectrometry test results of the trimethylolpropane mixed fatty acid ester prepared in Example 2 of the present invention.

[0022] Figure 3 The figure shows the liquid chromatography-mass spectrometry test results of the trimethylolpropane mixed fatty acid ester prepared in Example 3 of the present invention.

[0023] Figure 4 The figure shows the liquid chromatography-mass spectrometry test results of the trimethylolpropane mixed fatty acid ester prepared in Example 4 of the present invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that: Unless otherwise specified in the examples, conditions should be followed according to standard conditions or the manufacturer's recommendations. Instruments whose manufacturers are not specified are all commercially available products. Raw materials and reagents whose manufacturers are not specified are all commercially available goods or can be prepared using known methods.

[0026] In this invention, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are used only for simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0027] The features mentioned in this invention can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification, provided that there is no contradiction in the combination of these features. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0028] In the description of this invention, it should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] Example 1: A trimethylolpropane mixed fatty acid ester, the preparation method of which includes: The reaction mixture was prepared by reacting trimethylolpropane with octanoic acid, decanoic acid, and oleic acid in a molar ratio of 3.1:6.9:1:2. Specifically, 67.086 g (0.5 mol) of trimethylolpropane, 158.992 g (1.1 mol) of octanoic acid, 27.130 g (0.16 mol) of decanoic acid, 88.976 g (0.32 mol) of oleic acid, and 0.34 g of stannous oxalate 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, and the mixture was stirred at 100 °C and 600 r / min until the reactants were completely dissolved. The temperature was then raised to 180 °C for esterification.

[0030] After the reaction was completed, the product was purified. First, 7 g of activated carbon was added to the product, and the product was subjected to reduced pressure distillation to remove acid and decolorize at a temperature of 160℃ and a vacuum pressure of -0.05MPa. After distillation, the product was filtered to obtain trimethylolpropane mixed fatty acid esters.

[0031] like Figure 1 The figure shows the liquid chromatography-mass spectrometry (LC-MS) results of the trimethylolpropane mixed fatty acid esters prepared in Example 1 of this invention. In the figure, RT 7.82 represents trimethylolpropane trioctanoate, RT 9.60 represents trimethylolpropane dioctanoate-decanoate, RT 11.54 represents trimethylolpropane dioctanoate-decanoate, RT 14.04 and RT 15.90 represent trimethylolpropane dioctanoate-oleic acid, RT 17.95 represents trimethylolpropane dioctanoate-decanoate-oleic acid, RT 19.90 represents trimethylolpropane dioctanoate-oleic acid, RT 21.94 and RT 23.64 represent trimethylolpropane dioctanoate-oleic acid, RT 25.18 represents trimethylolpropane dioctanoate-oleic acid, and RT 28.22 and RT 29.67 represent trimethylolpropane trioleic acid.

[0032] Example 2: A trimethylolpropane mixed fatty acid ester is prepared by a method basically the same as that in Example 1, except that: The molar ratio of the three acids used, trimethylolpropane: octanoic acid: decanoic acid: oleic acid, is 6.3: 13.9: 1: 4.9. Specifically, the amounts of the three acids used are 158.992 g (1.1 mol) of octanoic acid, 13.565 g (0.079 mol) of decanoic acid, and 111.22 g (0.39 mol) of oleic acid.

[0033] like Figure 2The figure shows the liquid chromatography-mass spectrometry (LC-MS) results of the trimethylolpropane mixed fatty acid esters prepared in Example 2 of this invention. In the figure, RT 6.69 represents trimethylolpropane trioctanoate, RT 8.53 represents trimethylolpropane dioctanoate-decanoate, RT 10.22 represents trimethylolpropane dioctanoate-decanoate, RT 13.27 and RT 15.32 represent trimethylolpropane dioctanoate-oleic acid, RT 17.44 represents trimethylolpropane dioctanoate-decanoate-oleic acid, RT 19.41 represents trimethylolpropane dioctanoate-oleic acid, RT 21.64 and RT 23.39 represent trimethylolpropane dioctanoate-oleic acid, RT 25.34 and RT 26.95 represent trimethylolpropane dioctanoate-oleic acid, and RT 28.13 and RT 29.50 represent trimethylolpropane trioleic acid.

[0034] Example 3: A trimethylolpropane mixed fatty acid ester is prepared by a method basically the same as that in Example 1, except that: Two acids were used, with a molar ratio of trimethylolpropane: octanoic acid: oleic acid of 1.1: 2.3: 1. Specifically, the amounts of the two acids used were 158.992 g (1.1 mol) of octanoic acid and 133.612 g (0.47 mol) of oleic acid.

[0035] like Figure 3 The figure shows the liquid chromatography-mass spectrometry test results of the trimethylolpropane mixed fatty acid esters prepared in Example 3 of the present invention. In the figure, RT 6.70 represents trimethylolpropane trioctanoate, RT 13.17 and RT 15.34 represent dioctanoic acid-oleic acid-trimethylolpropane, RT 21.63, RT 23.43 and RT 25.47 represent dioctanoic acid-oleic acid-trimethylolpropane, and RT 28.12 and RT 29.58 represent trimethylolpropane trioleate.

[0036] Example 4: A trimethylolpropane mixed fatty acid ester is prepared by a method basically the same as that in Example 1, except that: The molar ratio of the three acids used, trimethylolpropane: octanoic acid: decanoic acid: oleic acid, is 1.6: 2.9: 1:1.1. Specifically, the amounts of the three acids used are 136.278 g (0.94 mol) of octanoic acid, 54.284 g (0.32 mol) of decanoic acid, and 95.526 g (0.34 mol) of oleic acid.

[0037] like Figure 4The figure shows the liquid chromatography-mass spectrometry (LC-MS) results of the trimethylolpropane mixed fatty acid esters prepared in Example 4 of this invention. In the figure, RT 8.93 represents trimethylolpropane trioctanoate, RT 11.29 represents trimethylolpropane dioctanoate-decanoate, RT 13.68 represents trimethylolpropane dioctanoate-decanoate, RT 16.53 represents trimethylolpropane tridecanoate, RT 18.63 represents trimethylolpropane dioctanoate-oleic acid, RT 20.72 represents trimethylolpropane dioctanoate-decanoate-oleic acid, RT 22.60 represents trimethylolpropane didecanoate-oleic acid, RT 24.09 and RT 26.31 represent trimethylolpropane dioleate-octanoate, RT 27.74 and RT 29.21 represent trimethylolpropane dioleate-decanoate, and RT 30.91 and RT 40.93 represent trimethylolpropane dioleate-octanoate. 32.82 represents trimethylolpropane trioleate.

[0038] The esterification reaction of trimethylolpropane with octanoic acid, decanoic acid, and oleic acid theoretically produces 10 fatty acid esters. (See [link to relevant documentation]) Figures 1-4 Analysis of Examples 1-4 by liquid chromatography-mass spectrometry showed that Examples 1 and 2 contained 9 fatty acid esters, but lacked the characteristic peak of tridecanoate. This was because n-decanoic acid accounted for only 10% and 5% in Examples 1 and 2, respectively, and due to the influence of chemical activity and steric hindrance, the content of the generated tridecanoate was too low, below the detection limit, and therefore undetectable. In Example 4, n-decanoic acid accounted for 20%, and 10 fatty acid esters were detected in the product, consistent with the theoretical value. Example 3 contained 4 fatty acid esters, consistent with the theoretical value.

[0039] Comparative Example 1: The purchased synthetic ester insulating oil Midel 7131 was used as a comparison.

[0040] Comparative Example 2: This comparative example is the trimethylolpropane fatty acid ester insulating oil disclosed in Example 1 of Chinese patent application CN115872861A.

[0041] Comparative Example 3: This comparative example is the trimethylolpropane fatty acid ester insulating oil disclosed in Example 1 of Chinese patent application CN107735484A.

[0042] Comparative Example 4: This comparative example is the trimethylolpropane fatty acid ester insulating oil disclosed in Example 1 of Chinese patent application CN117660091A.

[0043] Comparative Example 5: A trimethylolpropane mixed fatty acid ester is prepared by a method basically the same as that in Example 1, except that: Two acids were used, with a molar ratio of trimethylolpropane: octanoic acid: decanoic acid of 1.1: 2.3: 1, specifically 158.992 g (1.1 mol) of octanoic acid and 79.69 g (0.47 mol) of decanoic acid.

[0044] Comparative Example 6: A trimethylolpropane mixed fatty acid ester is prepared by a method basically the same as that in Example 1, except that: Two acids were used, with a molar ratio of trimethylolpropane: octanoic acid: decanoic acid of 0.8:1.5:1, specifically 136.99 g (0.95 mol) of octanoic acid and 108.524 g (0.63 mol) of decanoic acid.

[0045] The fatty acid esters obtained in Examples 1-4 and Comparative Examples 1-6 were subjected to relevant tests. The kinematic viscosity (40°C) was determined according to NB / SH / T 0870-2020, the pour point was determined according to GB / T 3535-2006, the open flash point and ignition point were determined according to GB / T3536-2008, and the breakdown voltage was determined according to GB / T 507.

[0046] The kinematic viscosity, pour point, and flash point of the mixed fatty acid esters were measured to evaluate whether the products obtained by the method of the present invention meet the physical, chemical, and electrical performance requirements for synthetic ester insulating oils. The kinematic viscosity, pour point, flash point, and flash point values ​​of the products from Examples 1-4 and Comparative Examples 1-6 are shown in Table 1.

[0047] Table 1 Performance test results of oil samples from Examples 1-4 and Comparative Examples 1-6 ; Note: "-" indicates that this performance was not tested.

[0048] The physicochemical properties of insulating oil include key indicators such as kinematic viscosity, pour point, flash point, ignition point, and breakdown voltage. Kinematic viscosity reflects the flow properties of the oil sample at a specific temperature. Lower kinematic viscosity helps improve the flowability of insulating oil in low-temperature environments, ensuring that equipment can still operate normally under cold conditions. Pour point is directly related to the low-temperature operating limit of the oil sample. The lower the pour point, the stronger the ability of the oil sample to maintain a flowing state in low-temperature environments, and the wider its applicable range. Flash point and ignition point are important parameters for measuring the safety of insulating oil. Higher flash point and ignition point can effectively reduce the risk of fire and ensure the safe operation of equipment. Breakdown voltage reflects the dielectric properties of insulating oil. The higher the breakdown voltage, the stronger the breakdown resistance of the oil sample, which can effectively prevent equipment failure due to the breakdown of the insulating medium. As shown in Table 1 above, the trimethylolpropane mixed fatty acid esters prepared in Examples 1-4 of this invention exhibit significant advantages in key performance indicators such as kinematic viscosity, pour point, ignition point, and breakdown voltage. Compared to the commercially available synthetic ester insulating oil Midel 7131 (Comparative Example 1), the kinematic viscosity of Example 1 is lower than that of Comparative Example 1, while its open flash point (279°C) and ignition point (311°C) are both higher. Its breakdown voltage (87.9 kV) is also significantly higher than the 75 kV of Comparative Example 1. Compared to Comparative Examples 2-6, the breakdown voltage of this invention is much higher than that of Comparative Examples 2-6. In summary, by optimizing the types and ratios of fatty acids, this invention effectively improves the ignition point and breakdown voltage of the trimethylolpropane mixed fatty acid ester while maintaining a low pour point. It exhibits good low-temperature flow properties and excellent thermal stability and electrical insulation properties, fully meeting the physicochemical and electrical performance requirements of synthetic ester insulating oils in practical applications.

[0049] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A trimethylolpropane mixed fatty acid ester, characterized in that, This mixed fatty acid ester is obtained by esterification of two or more fatty acids with trimethylolpropane. The fatty acid is selected from a combination of octanoic acid, capric acid and oleic acid, or a combination of oleic acid with octanoic acid or capric acid.

2. The trimethylolpropane mixed fatty acid ester according to claim 1, characterized in that, The molar ratio of trimethylolpropane to octanoic acid, decanoic acid and oleic acid is (0.5~6.5):(0~14.0):(0~1):(1~5), and the molar amounts of decanoic acid and octanoic acid cannot both be 0.

3. The method for preparing trimethylolpropane mixed fatty acid esters as described in claim 1 or 2, characterized in that, The method includes: Trimethylolpropane is reacted with two or more fatty acids in petroleum ether under the action of a catalyst and under heating conditions to undergo an esterification reaction, thereby obtaining a trimethylolpropane mixed fatty acid ester.

4. The preparation method according to claim 3, characterized in that, The catalyst is selected from stannous oxalate; Or / and, the amount of the catalyst used is 0.1~0.2% of the total mass of the reaction raw materials; Or / and, the boiling range of the petroleum ether is 90~120℃.

5. The preparation method according to claim 3, characterized in that, The esterification reaction is carried out at a temperature of 180~200℃.

6. The preparation method according to claim 5, characterized in that, The heating process involves first stirring at 90-110°C to completely dissolve the reactants, then raising the temperature to 180-200°C to carry out the esterification reaction.

7. The preparation method according to any one of claims 3 to 6, characterized in that, After the esterification reaction is completed, activated carbon is added to the product for deacidification and color removal by vacuum distillation. After vacuum distillation, the product is filtered to obtain trimethylolpropane mixed fatty acid esters.

8. The preparation method according to claim 7, characterized in that, The temperature of the vacuum distillation is 160~200℃, and the vacuum pressure of the vacuum distillation is -0.05~-0.09MPa.

9. The application of the trimethylolpropane mixed fatty acid ester as described in claim 1 or 2 in insulating oil.

10. A low pour point, high flash point insulating oil, characterized in that, The insulating oil comprises: a trimethylolpropane mixed fatty acid ester as described in claim 1 or 2.

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