Preparation method and application of octyl syringate

Abstract

The invention belongs to the technical field of insulating oil additives, and discloses a preparation method and application of octyl syringate. The preparation method of the octyl syringate comprises the following steps: (1) mixing syringic acid, n-caprylic alcohol and a first catalyst, and reacting; the first catalyst is at least one of phosphotungstic acid, boron tungstic acid, silicotungstic acid and molybdophosphoric acid; and (2) adding a molecular sieve and a second catalyst, and reacting again. The octyl syringate prepared by the preparation method disclosed by the invention can be used as an insulating oil additive to be applied to insulating oil, so that the insulating oil is effectively protected, the service life of the insulating oil is prolonged, the performance reduction caused by aging oxidation is reduced, the oxidation stability of the insulating oil is improved, the volatility of the insulating oil under a high-temperature condition is reduced, and the flash point of an oil product is improved; therefore, the insulating oil is not easy to cause fire or explosion accidents at high temperature, and meets the requirements of electrical equipment insulating oil with higher standards.

Description

Technical Field

[0001] The invention relates to the field of insulating oil additives, and in particular to a preparation method and application of octyl syringate. Background Art

[0002] Natural ester insulating oil is regarded as an ideal substitute for mineral insulating oil due to its excellent fire safety and environmental protection and non-toxicity. However, the unstable groups such as β-H and C=C contained in the molecular structure of natural ester insulating oil are easily attacked by oxygen molecules under high temperature or oxygen, thereby inducing oxidation reactions and generating oxidation products such as small molecular organic acids and aldehyde compounds. The accumulation of these oxidation products will not only reduce the dielectric properties and stability of the insulating oil, but also cause corrosion to the materials in the insulation system, significantly shorten the service life of electrical equipment, and increase the risk of failure.

[0003] In order to solve the problem of insufficient oxidation stability of natural ester insulating oil, commercial antioxidants such as 2,6-di-tert-butyl-p-cresol (BHT) and tert-butylhydroquinone (TBHQ) are usually used in the prior art to delay its oxidation process. These antioxidants reduce the oxidation reaction rate by capturing free radicals, inhibiting free radical chain reactions, and decomposing peroxides, thereby extending the service life of insulating oil and improving the operating reliability of power equipment.

[0004] However, although the commercial antioxidants currently used can delay the oxidation process of natural ester insulating oil, they also have some significant disadvantages. These antioxidants have certain biological toxicity, which will cause potential pollution to the environment and ecosystem during production and use, and their antioxidant effect will be significantly reduced under high temperature conditions, and they cannot effectively inhibit the oxidation reaction of natural ester insulating oil, resulting in the performance of insulating oil in high temperature environment. The decline, thus affecting the stable operation of power equipment. At the same time, due to the short validity period of commercial antioxidants, they need to be frequently replenished to maintain their performance, which not only increases maintenance costs, but also has an adverse effect on the normal operation of power equipment. In addition, commercial antioxidants will also have a negative impact on the dielectric and physicochemical properties of natural ester insulating oil, such as increasing dielectric loss, reducing insulation strength, etc., and changes in these properties of natural ester insulating oil will affect the electrical performance and safety of power equipment. Therefore, it is urgent to develop an efficient and environmentally friendly antioxidant that can maintain the excellent physicochemical and electrical properties of natural ester insulating oil while improving the oxidation stability of natural ester insulating oil, so as to meet the needs of modern power equipment for high-performance insulating oil. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a preparation method and application of octyl syringate.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing octyl syringate, comprising the following steps:

[0008] (1) mixing syringic acid, n-octanol and a first catalyst and reacting;

[0009] The first catalyst is at least one of phosphotungstic acid, borotungstic acid, silicotungstic acid, and molybdophosphoric acid;

[0010] The reaction temperature is 60°C-80°C and the pressure is 7kPa-10kPa;

[0011] (2) adding molecular sieve and second catalyst and reacting again;

[0012] The secondary reaction adopts a step-by-step temperature increase method; the pressure of the secondary reaction is 1.1 kPa-4 kPa.

[0013] In the preparation method of octyl syringate of the present invention, syringic acid and n-octanol are used to synthesize octyl syringate under the action of a special catalyst. The preparation method of the present invention reduces the reaction steps, greatly shortens the process time of octyl syringate, and the raw materials used are cheap and easy to obtain, the reaction conditions are mild, the process safety is good, the post-treatment operation is simple, the three wastes are generated less, and the environment is friendly, and it is suitable for green large-scale production.

[0014] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the molar ratio of the syringic acid to the n-octanol is 1:(1-1.5).

[0015] Preferably, the molar ratio of the syringic acid to the n-octanol is any one of or both of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, and 1:1.5.

[0016] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the mass of the first catalyst is 0.5%-2% of the total mass of the syringic acid and the n-octanol.

[0017] Preferably, the mass of the first catalyst is in the range of any one of 0.5%, 1%, 1.5%, 2% or both of the total mass of the syringic acid and the n-octanol.

[0018] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the first catalyst is phosphotungstic acid.

[0019] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the mixing is carried out in a stirring manner; the stirring rate is 100 rpm-300 rpm.

[0020] Preferably, the stirring rate is any one of or both of 100 rpm, 150 rpm, 200 rpm, 250 rpm, and 300 rpm.

[0021] As a preferred embodiment of the method for preparing octyl syringate of the present invention, in step (1), the reaction time is 1 h to 3 h.

[0022] Preferably, the reaction time is within the range of 1 h, 2 h, 3 h or both.

[0023] As a preferred embodiment of the method for preparing octyl syringate of the present invention, in step (1), the reaction temperature is any one of 60°C, 70°C, 80°C or both, and the pressure is any one of 7kPa, 8kPa, 9kPa or 10kPa or both.

[0024] As a preferred embodiment of the method for preparing octyl syringate of the present invention, in step (2), the heating rate of the stepwise heating method is (8°C-11°C) / h, and the heating time is 2h-5h.

[0025] The preparation method of octyl syringate of the present invention adopts a step-by-step heating method. In the early stage of the chemical reaction, a lower starting temperature is used to reduce impurities generated by high temperature. Then, the reaction is carried out under relatively mild conditions by gradually increasing the temperature, thereby avoiding temperature runaway and product quality degradation caused by too fast a reaction.

[0026] Preferably, the heating rate of the step-by-step heating method is 10°C / h and the heating time is 4h.

[0027] As a preferred embodiment of the method for preparing octyl syringate of the present invention, in step (2), the pressure of the second reaction is in the range of any one or both of 1.1 kPa, 2 kPa, 3 kPa, and 4 kPa.

[0028] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the mass of the molecular sieve is 1%-2% of the total mass of the syringic acid and the n-octanol.

[0029] Preferably, the mass of the molecular sieve is in the range of 1%, 1.2%, 1.5%, 2% or both of the total mass of the syringic acid and the n-octanol.

[0030] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the molecular sieve is Molecular sieve.

[0031] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the second catalyst is a Lewis acid catalyst; the mass of the Lewis acid catalyst is 0.5%-2% of the total mass of the syringic acid and the n-octanol.

[0032] Preferably, the mass of the Lewis acid catalyst is in the range of any one of 0.5%, 1%, 1.5%, 2% or both of the total mass of the syringic acid and the n-octanol.

[0033] As a preferred embodiment of the method for preparing octyl syringate of the present invention, a non-polar solvent is further added to the reaction; the non-polar solvent is ethyl acetate and / or anhydrous ethanol.

[0034] In the preparation method of octyl syringate of the present invention, a non-polar solvent is used to further increase the solubility and miscibility of the reactants.

[0035] Preferably, the non-polar solvent is anhydrous ethanol.

[0036] As a preferred embodiment of the method for preparing octyl syringate of the present invention, the mass of the non-polar solvent is 1%-5% of the total mass of the syringic acid and the n-octanol.

[0037] Preferably, the mass of the non-polar solvent is in the range of 1%, 2%, 3%, 4%, 5% or any one of the two of the total mass of the syringic acid and the n-octanol.

[0038] In a second aspect, the present invention provides the use of octyl syringate obtained by the preparation method in preparing insulating oil for electrical equipment.

[0039] The octyl syringate obtained by the preparation method of the present invention has a stable molecular structure, and its moderate alkyl chain length gives the octyl syringate good and balanced dispersibility and mobility. At the same time, the octyl syringate obtained by the preparation method of the present invention has excellent antioxidant properties under high temperature environment and shows excellent solubility and dispersibility in oil phase environment. Natural ester insulating oil is processed by vegetable oil (such as soybean oil, rapeseed oil, palm oil, etc.), and its main component is triglyceride, which contains a large amount of unsaturated bonds in the molecule, has weaker oxidation stability, and needs to improve its antioxidant capacity. Therefore, the octyl syringate obtained by the preparation method of the present invention can be used as an insulating oil additive and applied to insulating oil, which can more effectively protect insulating oil, extend its service life, reduce the performance degradation caused by oxidation, and will not produce agglomeration and precipitation in insulating oil at the same time, and has a long effective period in insulating oil, reducing the demand for frequent addition. This is of great significance for the stable operation of electrical equipment and electrical systems. In addition, the octyl syringate prepared by the preparation method of the present invention has good compatibility with natural ester insulating oil, will not significantly affect other physical and chemical properties of the oil, and can increase surface tension through intermolecular hydrogen bonds or dipole interactions, reduce the volatility of the insulating oil under high temperature conditions, and increase the flash point of the oil, making the insulating oil less prone to fire or explosion accidents at high temperatures, which helps to improve the overall performance of the oil and meet higher standards for electrical equipment.

[0040] In a third aspect, the present invention provides an insulating oil for electrical equipment, comprising octyl syringate and natural ester insulating oil prepared by the preparation method of the present invention.

[0041] As a preferred embodiment of the insulating oil for electrical equipment of the present invention, the mass of the octyl syringate is 0.05%-0.5% of the mass of the natural ester insulating oil.

[0042] Preferably, the mass of the octyl syringate is in the range of any one or both of 0.05%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of the mass of the natural ester insulating oil.

[0043] As a preferred embodiment of the insulating oil for electrical equipment of the present invention, the method for preparing the insulating oil for electrical equipment comprises the following steps: mixing the octyl syringate and the natural ester insulating oil, and drying.

[0044] Preferably, the mixing is carried out by ultrasound; and the drying is carried out by vacuum drying.

[0045] Preferably, the drying temperature is 100° C. and the drying time is 48 hours.

[0046] Compared with the prior art, the invention has the following beneficial effects: firstly, the preparation method of octyl syringate of the invention reduces the reaction steps, greatly shortening the process time and production cycle of octyl syringate; secondly, the raw materials used in the synthesis method of the invention are cheap and easily available, and the amount of three wastes (waste gas, waste water and solid waste) generated in the whole process is small, which is environmentally friendly and suitable for green large-scale production; in addition, the octyl syringate prepared by the preparation method of the invention can be used as an insulating oil additive in insulating oil to more effectively protect the insulating oil, extend its service life, reduce the performance degradation caused by aging and oxidation, improve the oxidation stability of the insulating oil, reduce the volatility of the insulating oil under high temperature conditions, and improve the flash point of the oil product, so that the insulating oil is less likely to have fire or explosion accidents at high temperatures, and meet the requirements of insulating oil of higher standards for electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is the structural formula of octyl syringate of the present invention;

[0048] Figure 2 This is the infrared spectrum of octyl syringate synthesized in Example 1 of the present invention;

[0049] Figure 3 It is a schematic diagram of the DPPH radical scavenging rate of octyl syringate synthesized in Examples 1-7 of the present invention and Comparative Examples 1-7. DETAILED DESCRIPTION

[0050] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] The following is an elaboration in conjunction with specific embodiments to illustrate the practical effects of the solutions of the present invention.

[0052] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, equipment, etc. used, unless otherwise specified, can be obtained from commercial sources.

[0053] The raw materials used in the following examples and comparative examples are described as follows, but are not limited to these materials:

[0054] Table 1: Manufacturers and concentrations of reagents used in the examples and comparative examples of the present invention

[0055]

[0056] Example 1: Synthesis of Octyl Syringate

[0057] (I) Syringic acid and n-octanol are weighed in a ratio of 1:1.2, and phosphotungstic acid is selected as the first catalyst, and its amount is 1wt% of the total mass of syringic acid and n-octanol; anhydrous ethanol is used as a non-polar solvent, and its amount is 3wt% of the total mass of syringic acid and n-octanol. The whole reaction takes place in a three-necked flask, which is equipped with a sampling port and a condenser, and then the condenser is connected to a receiving bottle and a circulating water vacuum pump in sequence. The connection of each part of the device is sealed with high-temperature silicone grease. The reaction temperature and internal vacuum degree are controlled by an oil bath pot and a vacuum regulating valve, respectively.

[0058] (II) In a reaction vessel, a mixture of syringic acid, n-octanol and phosphotungstic acid was added and reacted under magnetic stirring at a stirring rate of 200 rpm. In the initial stage of the reaction, the temperature of the reaction system was set to 70° C. and the vacuum pressure was set to 8 kPa.

[0059] (III) After reacting for 2 h under the above conditions, a desiccant of 1.2 wt% of the total mass of syringic acid and n-octanol was added to the reactants. 1 wt% of Lewis acid catalyst (zinc chloride, ZnCl2) based on the total mass of molecular sieve, syringic acid and n-octanol promotes the further reaction.

[0060] (IV) Subsequently, the vacuum pressure of the reaction system was reduced to 3 kPa, and the temperature was gradually increased to 110°C at a rate of 10°C per hour. The reaction was considered complete when no obvious bubbles were generated in the reaction vessel, and the total reaction time was 6 h.

[0061] (V) Subsequently, the reaction mixture is cooled to room temperature. The mixture is washed with deionized water and distilled water for multiple times to remove residual acid catalyst and other byproducts. The washed mixture is subjected to a reverse osmosis membrane to further remove moisture and impurities in the reaction process to obtain octyl syringate.

[0062] Verification example:

[0063] The crude octyl syringate prepared in Example 1 was extracted with ether as an organic solvent to separate octyl syringate. Then, it was subjected to reduced pressure distillation to obtain further purified octyl syringate, and its infrared spectrum was as follows: Figure 2 shown.

[0064] from Figure 2 From the figure: 3420cm -1 The characteristic peak at 1680 cm is the vibration peak of the phenolic hydroxyl group in octyl syringate. -1 The vibration peak of carbon group is 1152cm -1 The vibration peak of COC is at .

[0065] Example 2: Synthesis of Octyl Syringate

[0066] The only difference between the preparation method of octyl syringate in this embodiment and that in Embodiment 1 is that in step (I), borotungstic acid is selected as the first catalyst.

[0067] Example 3: Synthesis of Octyl Syringate

[0068] The only difference between the preparation method of octyl syringate in this embodiment and that in Embodiment 1 is that in step (I), silicotungstic acid is selected as the first catalyst.

[0069] Example 4: Synthesis of Octyl Syringate

[0070] The only difference between the preparation method of octyl syringate in this embodiment and that in Example 1 is that in step (I), molybdophosphoric acid is selected as the first catalyst.

[0071] Example 5: Synthesis of Octyl Syringate

[0072] The only difference between the preparation method of octyl syringate in this embodiment and that in embodiment 1 is that in step (I), the amount of phosphotungstic acid used is 0.5 wt % of the total mass of syringic acid and n-octanol.

[0073] Example 6: Synthesis of Octyl Syringate

[0074] The only difference between the preparation method of octyl syringate in this embodiment and that in embodiment 1 is that in step (I), the amount of phosphotungstic acid used is 2 wt % of the total mass of syringic acid and n-octanol.

[0075] Example 7: Synthesis of Octyl Syringate

[0076] The only difference between the preparation method of octyl syringate in this example and that in Example 1 is that in step (I), the non-polar solvent is ethyl acetate.

[0077] Comparative Example 1: Synthesis of Octyl Syringate

[0078] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that in step (I), p-toluenesulfonic acid is selected as the first catalyst.

[0079] Comparative Example 2: Synthesis of Octyl Syringate

[0080] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that in step (III), no Molecular sieve.

[0081] Comparative Example 3: Synthesis of Octyl Syringate

[0082] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that the vacuum pressure is kept at 3 kPa during the entire reaction process.

[0083] Comparative Example 4: Synthesis of Octyl Syringate

[0084] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that the stepwise temperature increase method is not adopted in the overall reaction process, and the reaction temperature is always 110°C.

[0085] Comparative Example 5: Synthesis of Octyl Syringate

[0086] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that the stepwise temperature increase method is not adopted in the overall reaction process, and the reaction temperature is always 70°C.

[0087] Comparative Example 6: Synthesis of Octyl Syringate

[0088] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that the vacuum pressure is kept at 8 kPa during the entire reaction process.

[0089] Comparative Example 7: Synthesis of Octyl Syringate

[0090] The only difference between the preparation method of octyl syringate in this comparative example and that in Example 1 is that in step (I), the amount of phosphotungstic acid used is 5 wt % of the total mass of syringic acid and n-octanol.

[0091] Test Example 1: DPPH free radical scavenging test

[0092] This test example tests the antioxidant properties of octyl syringate synthesized in Examples 1-7 and Comparative Examples 1-7.

[0093] The specific steps are as follows: 3 ml of 0.2 mM DPPH solution was mixed with 3 mL of octyl syringate synthesized in Example 1-7 and Comparative Example 1-7, respectively, and the mixture was placed in a dark place at room temperature for 30 min, and then the absorbance A was measured. 样品 3 ml of anhydrous ethanol plus 3 ml of 0.2 mM DPPH solution was used as a blank control group and placed at room temperature and away from light for 30 minutes, and then its absorbance A was measured. 空白 .

[0094] The calculation formula of DPPH free radical scavenging ability is as follows:

[0095] Clearance rate (%) = (A 空白 -A 样品 ) / A 空白 ×100%

[0096] like Figure 3As shown, the octyl syringate product obtained by the preparation method of octyl syringate of the present invention exhibits extremely high antioxidant performance in the DPPH free radical scavenging experiment, and its DPPH free radical scavenging rate reaches 96% or higher, which indicates that the preparation method more effectively retains and enhances the antioxidant activity of octyl syringate.

[0097] Application example 1: Insulating oil

[0098] The octyl syringate synthesized in Example 1 was added to the natural ester insulating oil at 0.1 wt % of the total mass of the natural ester insulating oil, and the oil sample was ultrasonically dispersed using an ultrasonic oscillator until the solution was clear and transparent to ensure that the octyl syringate was fully dissolved.

[0099] Application example 2: Insulating oil

[0100] The only difference between this application example and application example 1 is that the addition amount of octyl syringate is 0.2wt% of the total mass of the natural ester insulating oil.

[0101] Application example 3: Insulating oil

[0102] The only difference between this application example and application example 1 is that the addition amount of octyl syringate is 0.3wt% of the total mass of the natural ester insulating oil.

[0103] Application example 4: Insulating oil

[0104] The only difference between this application example and application example 1 is that the addition amount of octyl syringate is 0.4wt% of the total mass of the natural ester insulating oil.

[0105] Application example 5: Insulating oil

[0106] The only difference between this application example and application example 1 is that the addition amount of octyl syringate is 0.5wt% of the total mass of the natural ester insulating oil.

[0107] Application Example 1: Insulating Oil

[0108] The only difference between this comparative example and Example 1 is that octyl syringate is replaced by 2,6-di-tert-butyl-p-cresol (BHT).

[0109] Application Example 2: Insulating Oil

[0110] The only difference between this comparative example and application example 1 is that the addition amount of octyl syringate is 0.6wt% of the total mass of the natural ester insulating oil.

[0111] Application Example 3: Insulating Oil

[0112] The only difference between this comparative example and application example 1 is that octyl syringate is replaced by syringic acid.

[0113] Application Example 4: Insulating Oil

[0114] The only difference between this comparative example and application example 1 is that octyl syringate is replaced by methyl syringate.

[0115] Application Example 5: Insulating Oil

[0116] The only difference between this comparative example and application example 1 is that octyl syringate is replaced by ethyl syringate.

[0117] Application Example 6: Insulating Oil

[0118] The only difference between this comparative example and application example 1 is that eugenol is used to replace octyl syringate.

[0119] Application Example 7: Insulating Oil

[0120] The only difference between this comparative example and application example 1 is that the addition amount of octyl syringate is 0.05wt% of the total mass of the natural ester insulating oil.

[0121] Application Example 8: Insulating Oil

[0122] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 1 is used.

[0123] Application Example 9: Insulating Oil

[0124] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 2 is used.

[0125] Application Example 10: Insulating Oil

[0126] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 3 is used.

[0127] Application Example 11: Insulating Oil

[0128] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 4 is used.

[0129] Application Example 12: Insulating Oil

[0130] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 5 is used.

[0131] Application Example 13: Insulating Oil

[0132] The only difference between this comparative example and application example 1 is that the octyl syringate synthesized in comparative example 6 is used. Test example 2: Thermal oxidative aging test and flash point test of insulating oil

[0133] This test example tests the acid value and dielectric loss factor of the insulating oils of application examples 1-5 and application comparison examples 1-13 during the aging process to characterize their antioxidant effects; and tests the flash point of the ester insulating oil to analyze the effect of antioxidants on the flash point of the natural ester insulating oil.

[0134] The insulating oils of application examples 1-5 and comparative application examples 1-13 were placed in a vacuum drying oven at 100° C. and dried for 48 hours under vacuum conditions. After drying, the samples were taken out of the vacuum drying oven and allowed to cool to room temperature.

[0135] (1) Use a flash point tester (SYD-261 closed cup flash point tester) to test the flash point of each sample.

[0136] (2) The dried samples were placed in an aging box (DHG-9240A electric heating blast drying box), the aging temperature was set to 130°C, and they were placed in the aging box for 15 days, during which the temperature was kept constant; before and after the aging experiment, the dielectric loss factor of each sample was tested using a JDC-1 dielectric loss & resistivity tester, and the acid value of each sample was tested by manual titration.

[0137] Table 1: Flash point, acid value and dielectric loss factor of the insulating oil of Test Example 2 before and after aging

[0138]

[0139]

[0140] As shown in Table 1, compared with Application Example 1, when the addition amount of eugenol is 0.6wt% of the natural ester insulating oil, its antioxidant effect is weakened. This shows that the antioxidant effect of eugenol is not infinitely improved with the increase of the addition amount, but there is a saturation effect. After exceeding this content, its antioxidant effect in natural ester insulating oil will decrease with the increase of the addition amount. In addition, the results of Application Comparative Example 2 show that the addition of eugenol increases the content of acidic and polar substances in the insulating oil, resulting in an increase in the acid value and dielectric loss factor, thereby accelerating the decomposition and oxidation reaction of the insulating oil, and promoting the accumulation of thermal oxidation aging byproducts, resulting in a decrease in the overall performance of the insulating oil.

[0141] In summary, among all antioxidants, the oil sample to which octyl syringate prepared by the present invention is added exhibits the best antioxidant effect, and its acid value and dielectric loss factor have the smallest increase, showing stronger antioxidant capacity and better electrical performance retention, which is crucial for ensuring the reliability and safety of power equipment in long-term operation. At the same time, octyl syringate can significantly increase the flash point of natural ester insulating oil, which means that it can only cause combustion at a higher temperature, thereby improving the safety of insulating oil.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing octyl syringate, characterized in that: The following steps are involved: (1) mixing syringic acid, n-octanol and a first catalyst and reacting; The first catalyst is at least one of phosphotungstic acid, borotungstic acid, silicotungstic acid, and molybdophosphoric acid; The reaction temperature is 60°C-80°C and the pressure is 7kPa-10kPa; (2) adding molecular sieve and second catalyst and reacting again; The secondary reaction adopts a step-by-step temperature increase method; the pressure of the secondary reaction is 1.1 kPa-4 kPa.

2. The method for preparing octyl syringate as claimed in claim 1, wherein The mass of the first catalyst is 0.5%-2% of the total mass of the syringic acid and the n-octanol.

3. The method for preparing octyl syringate as claimed in claim 1, wherein In step (1), the reaction time is 1 h-3 h.

4. The method for preparing octyl syringate as claimed in claim 1, wherein In step (2), the heating rate of the step-by-step heating method is (8°C-15°C) / h, and the heating time is 2h-5h.

5. The method for preparing octyl syringate as claimed in claim 1, wherein The mass of the molecular sieve is 1%-2% of the total mass of the syringic acid and the n-octanol.

6. The method for preparing octyl syringate as claimed in claim 1, characterized in that In step (1), a non-polar solvent is further added to the reaction; the non-polar solvent is ethyl acetate and / or anhydrous ethanol.

7. The method for preparing octyl syringate as claimed in claim 6, wherein: The mass of the non-polar solvent is 1%-5% of the total mass of the syringic acid and the n-octanol.

8. Use of octyl syringate obtained by the preparation method according to any one of claims 1 to 7 in preparing insulating oil for electrical equipment.

9. An insulating oil for electrical equipment, characterized in that: The invention comprises octyl syringate and natural ester insulating oil prepared by the preparation method according to any one of claims 1 to 7.

10. The insulating oil for electric equipment according to claim 9, characterized in that: The mass of the octyl syringate is 0.05%-0.5% of the mass of the natural ester insulating oil.

Images