Wide-temperature-range modified natural ester insulating oil and molecular structure design method thereof

Abstract

The invention relates to wide-temperature-range modified natural ester insulating oil and a molecular structure design method thereof, and the molecular structure of the wide-temperature-range modified natural ester insulating oil with different ester chain structures is obtained by converting natural ester into mixed fatty acid methyl ester with the chain length of C8-C18, then blending the proportion and introducing groups for molecular modification. According to the design method, natural ester insulating oil molecules with different ester chain structures are constructed, and the influence rule of the fatty acid methyl ester carbon chain length proportion, the C = C double bond number and the modification group on the flash point and pour point of the natural ester insulating oil is obtained; the obtained wide-temperature-range modified natural ester insulating oil not only keeps the high flash point of the natural ester insulating oil, but also has the characteristic of low pour point, so that the working temperature range of the natural ester insulating oil is widened, and the defect that a natural ester insulating oil transformer operates under high-altitude, cold regions and extreme weather conditions is overcome; the preparation process is simple, reaction conditions are mild, the environment is not polluted, and batch production is easy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of advanced insulating materials, and particularly relates to a wide-temperature-range modified natural ester insulating oil and a molecular structure design method thereof. BACKGROUND

[0002] As a newly emerging high-heat-resistant-grade and environmentally friendly liquid dielectric, natural ester insulating oil has been widely used in distribution transformers and has been preliminarily demonstrated in large power transformers. Natural ester insulating oil is mainly refined from soybean oil, rapeseed oil and the like, and is a mixture of dozens of triglycerides. The fatty acid branches of the molecular structure of the natural ester insulating oil mainly include straight-chain fatty acids containing an even number of carbon atoms. In addition to saturated fatty acids, these fatty acids also contain unsaturated fatty acids, which can be divided into monounsaturated fatty acids and polyunsaturated fatty acids according to the number of C=C double bonds. The molecular configuration of the natural ester insulating oil is a key factor affecting its intrinsic properties.

[0003] Chinese patent document CN 119684137 A discloses a natural ester insulating oil bifunctional antioxidant and its preparation and application, and relates to the technical field of insulating oil. The bifunctional antioxidant is obtained by introducing a hydroxyl group (-OH) and a tert-butyl group (-C(CH3)3) into the molecular structure of N-phenyl-alpha-naphthylamine. When the bifunctional antioxidant is added to natural ester insulating oil, the tert-butyl group in the molecular structure can effectively capture free radicals, and the hydroxyl group can improve the free radical scavenging efficiency and further improve the antioxidant effect. The hydroxyl group can also effectively absorb high-energy ultraviolet light, which helps to enhance the lightning impulse resistance of the insulating oil. The bifunctional antioxidant has a synergistic effect in improving the antioxidant capacity and lightning impulse resistance of the insulating oil, thereby prolonging the service life of the insulating oil and improving the operation safety of electrical equipment.

[0004] The existing natural ester has a relatively complex molecular composition, and has common problems such as a high pour point and difficulty in simultaneously improving the pour point and flash point, which leads to the need to further improve the low-temperature environmental applicability of natural ester insulating oil transformers. Therefore, it is necessary to balance the pour point and flash point of natural ester insulating oil by regulating the molecular chain length and the number of double bonds, so as to obtain a new type of insulating oil with a lower pour point on the basis of a high flash point of natural ester insulating oil.

[0005] The introduction of short straight-chain and odd-carbon-chain fatty acid methyl esters can reduce the pour point and viscosity. Fatty acid methyl esters with an appropriate number of unsaturated bonds can simultaneously improve the flash point and pour point of the modified natural ester. The unsaturated bonds are customized and tailored by means such as cyclization, branching and epoxidation, the symmetry of the molecular structure is reduced, the pour point and viscosity are optimized, and the biodegradability is improved.

[0006] In view of the structural characteristics of the modified natural ester, a small amount of unsaturated long straight-chain fatty acid methyl ester and branched chain are introduced through methyl ester exchange reaction and secondary ester exchange reaction to improve the flash point of the modified natural ester and reduce the pour point, so as to obtain a wide temperature range modified natural ester insulating oil molecular structure. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a wide temperature range modified natural ester insulating oil, wherein the molecular structure of the wide temperature range modified natural ester insulating oil has different ester chain structures, and the flash point of the modified natural ester can be improved and the pour point can be reduced.

[0008] In order to solve the above technical problems, the technical solution of the present application is that the molecular structure of the wide temperature range modified natural ester insulating oil comprises different ester chain structures, which is obtained by converting natural ester into mixed fatty acid methyl ester with a chain length of C8-C18, and then separating the mixed fatty acid methyl ester into fatty acid methyl ester with different chain lengths; and then adjusting the proportion of the mixed fatty acid methyl ester and introducing a group modification, so as to obtain a wide temperature range modified natural ester insulating oil with different ester chain molecular structures.

[0009] Preferably, the molecular formula of the wide temperature range modified natural ester insulating oil is C 54 H 96 O6, and the molecular structure is as follows:

[0010] .

[0011] By using the above technical solution, a small amount of unsaturated long straight-chain fatty acid methyl ester and branched chain are introduced through methyl ester exchange reaction and secondary ester exchange reaction, so that the low pour point characteristic is combined on the basis of the high flash point of the natural ester insulating oil, the working temperature range of the natural ester insulating oil is widened, the performance short board of the natural ester insulating oil transformer in high altitude, cold area and extreme climate conditions is made up, the flash point of the modified natural ester is improved, the pour point is reduced, a wide temperature range modified natural ester insulating oil molecular structure is obtained, and the demand for transformer operation can be met.

[0012] Preferably, when the mixed fatty acid methyl ester is adjusted according to the chain length ratio, the proportion of long-chain fatty acid methyl ester with a chain length of C14-C18 is 70-80%, and the proportion of short-chain fatty acid methyl ester with a chain length of C8-C12 is 20-30%. The long-chain fatty acid methyl ester comprises one or more of stearic acid methyl ester, oleic acid methyl ester and linoleic acid methyl ester; and the short-chain fatty acid methyl ester comprises caprylic acid methyl ester.

[0013] Preferably, when the mixed fatty acid methyl ester is adjusted according to the saturation ratio, the proportion of saturated fatty acid methyl ester is 80-90%, and the proportion of unsaturated fatty acid methyl ester is 10-20%.

[0014] Preferably, the mixed fatty acid methyl ester is formulated according to the unsaturated ratio, wherein the proportion of monounsaturated fatty acid methyl ester is 60-70%, and the proportion of polyunsaturated fatty acid methyl ester is 30-40%.

[0015] Preferably, the natural ester is coconut oil and soybean oil.

[0016] The technical problem to be solved by the present application is to provide a molecular structure design method of a wide-temperature-range modified natural ester insulating oil.

[0017] In order to solve the above technical problems, the technical scheme of the present application is as follows: the molecular structure design method of the wide-temperature-range modified natural ester insulating oil, that is, the preparation method of the wide-temperature-range modified natural ester insulating oil, comprises the following steps:

[0018] S1: a plurality of natural esters are weighed according to the proportion, and are mixed with methanol solution and NaOH solution respectively; after reaction, a mixed fatty acid methyl ester with a chain length of C8-C18 and a glycerol mixture are obtained, and then the mixed fatty acid methyl ester is separated;

[0019] S2: the mixed fatty acid methyl ester is separated into uniform fatty acid methyl esters with different chain lengths, and then the proportion of the fatty acid methyl ester is adjusted and mixed again to synthesize a modified natural ester;

[0020] S3: the molecular modification is performed by introducing a benzene ring, and a wide-temperature-range modified natural ester insulating oil with different ester chain structures is obtained after reaction. The wide-temperature-range modified natural ester insulating oil has a high flash point and a low frequency point.

[0021] Preferably, the molecular formula of the wide-temperature-range modified natural ester insulating oil is C54H96O6, and the molecular structure is as follows:

[0022] .

[0023] By using the above technical scheme, the natural ester insulating oil molecule with different ester chain structures is constructed to solve the problem that the flash point and the pour point of the natural ester insulating oil are difficult to improve simultaneously, and the influence law of the carbon chain length ratio of the fatty acid methyl ester, the number of C=C double bonds and the modification group on the flash point and the pour point of the natural ester insulating oil is obtained. The prepared new modified natural ester overcomes the problem that the traditional additive only improves a single performance and the improvement effect is limited. On the basis of maintaining the high flash point of the natural ester insulating oil, the low pour point characteristic is also possessed, the working temperature range of the natural ester insulating oil is widened, and the performance short board of the natural ester insulating oil transformer in high altitude, cold area and extreme climate conditions is made up. The preparation process is simple, the reaction condition is mild, the environment is not polluted, and batch production is easy. Therefore, the wide-temperature-range modified natural ester insulating oil prepared by the present application meets the green development concept.

[0024] Preferably, the natural ester in step S1 is coconut oil and soybean oil, and the specific steps are as follows:

[0025] S11: Coconut oil and soybean oil are mixed with methanol solution and NaOH aqueous solution, respectively, to obtain a mixed solution;

[0026] S12: The mixed solution is added to a water bath device connected with a reflux condenser, and magnetic stirring is performed until the mixed solution is clear; after stirring is completed, the solution is cooled to room temperature at room temperature;

[0027] S13: After cooling, HCl aqueous solution is added to neutralize the residual base, so that the pH of the solution is 7, to obtain a mixed fatty acid methyl ester and glycerol mixture;

[0028] S14: Petroleum ether is added, stirred and layered, to obtain a mixed fatty acid methyl ester in the upper layer of the solution, and dried.

[0029] Preferably, the specific steps of step S2 are:

[0030] S21: Gas chromatography (GC) analysis is performed on the mixed fatty acid methyl ester (FAME) after complete methyl esterification, and the percentage content of each type of fatty acid methyl ester in the mixed fatty acid methyl ester is calculated according to the peak area of the standard substance and the peak area of the obtained spectrum;

[0031] S22: Using a vacuum fractionation separation method, the pressure is -0.1 MPa, and a gradient heating method is used, with a heating rate of 10°C / h, to raise the temperature to 80-120°C, to separate uniform fatty acid methyl esters of different chain lengths, including long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester, and short-chain octanoic acid methyl ester;

[0032] S23: The long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester, and short-chain octanoic acid methyl ester are mixed with the calculated percentage content and added with p-toluenesulfonic acid catalyst; the temperature is raised to 120°C, the pressure is reduced to -0.1 mbar, and the reaction is stirred for 5 h to synthesize modified natural ester.

[0033] By adjusting the proportion of fatty acid methyl esters, the chain length, saturation ratio, and unsaturation ratio can be adjusted, so that the fatty acid methyl ester contains a high content of saturated fatty acid methyl ester (≥80%) and an appropriate amount of unsaturated fatty acid methyl ester (≤20%), thereby optimizing the flash point and pour point performance, and synthesizing a wide temperature range modified natural ester insulating oil with high flash point and low pour point.

[0034] Preferably, the specific step of introducing benzene ring for molecular modification in the step S3 is: mixing the modified natural ester with benzoic acid in proportion, adding 1% p-toluene sulfonic acid as catalyst, stirring and reacting at 120 DEG C under reduced pressure for 8h, so that the modified natural ester insulating oil with wide temperature range is obtained, and the pour point of the synthetic modified natural ester is-49~-55 DEG C, and the flash point is 300~320 DEG C. By introducing benzene ring into the modified natural ester molecule (benzene ring is introduced by the reaction of benzoic acid and synthetic natural ester), the intermolecular force and crystallization performance are regulated, so that the application temperature range of the modified natural ester is widened (such as low temperature fluidity and high temperature oxidation stability), and the modified natural ester structure with wide temperature range is obtained. By modifying the natural ester, when the content of benzene ring is about 0.3~0.5wt.% of the mass of the insulating oil, the pour point of the wide temperature range modified natural ester insulating oil can be as low as-50 DEG C or below, and the flash point is higher than 300 DEG C.

[0035] Preferably, the molar ratio of the total amount of various fatty acid methyl esters prepared from the natural ester to trihydroxymethyl propane in the step S23 is 3~6:1;

[0036] The molar ratio of long chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short chain octanoic acid methyl ester in the step S23 is 7~17:1:0.5~1:0.5~1;

[0037] The amount of the catalyst toluene sulfonic acid catalyst is 0.01% of the total mass of the methyl ester and trihydroxymethyl propane.

[0038] Preferably, the molar ratio of the total amount of various fatty acid methyl esters to trihydroxymethyl propane in the step S23 is 3.1:1;

[0039] Preferably, the molar ratio of the modified natural ester to benzoic acid in the step S3 is 1:0.3~0.5.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] (1) The present application constructs the molecular structure of the natural ester insulating oil with different ester chain structures, and obtains the influence law of the carbon chain length ratio of fatty acid methyl ester, the number of C=C double bonds and the modified group on the flash point and pour point of the natural ester insulating oil;

[0042] (2) The novel wide temperature range modified natural ester insulating oil with different lipid chain structures prepared by the present application overcomes the problem that the traditional additive only improves a single performance and the improvement effect is limited, and has low pour point characteristics on the basis of high flash point of the natural ester insulating oil, so that the working temperature range of the natural ester insulating oil is widened, and the performance short board of the natural ester insulating oil transformer in high altitude, cold area and extreme climate conditions is made up;

[0043] (3) The preparation process is simple, the reaction condition is mild, the environment is not polluted, and batch production is easy. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Device diagram used in the embodiment of the molecular structure design method of the wide-temperature-range modified natural ester insulating oil of the present application;

[0045] Figure 2 Wide-temperature-range modified natural ester insulating oil sample diagram obtained in Experimental Example 1 of the molecular structure design method of the wide-temperature-range modified natural ester insulating oil of the present application. DETAILED DESCRIPTION

[0046] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments but not all of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0047] In the present application, “and / or” includes any and all combinations of one or more of the listed associated items.

[0048] In the present application, “a plurality of” means two or more, that is, it includes two, three, four, five, etc.

[0049] It should be noted that in the present application, the terms “include”, “contain” or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitation, the element defined by the sentence “including a…” does not exclude the presence of another identical element in the process, method, article or device including the element.

[0050] In the present specification, certain embodiments can be disclosed in a format that is in a range. It should be understood that such “in a range” description is merely for convenience and brevity, and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered to have specifically disclosed all possible sub-ranges and independent digital values within the range. For example, the description of the range 1-6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5 and 6. The above rule applies regardless of the breadth of the range.

[0051] Room temperature as used herein refers to 25°C.

[0052] Embodiment: The molecular structure of the wide temperature range modified natural ester insulating oil comprises different ester chain structures, which is obtained by converting natural ester into mixed fatty acid methyl ester with chain length of C8~C18, separating the mixed fatty acid methyl ester into fatty acid methyl ester with different chain length, adjusting the proportion of the mixed fatty acid methyl ester, and introducing a group modification.

[0053] In some embodiments, the molecular formula of the wide temperature range modified natural ester insulating oil is C 54 H 96 O6, and the molecular structure is as follows:

[0054] .

[0055] In some embodiments, when the mixed fatty acid methyl ester is adjusted according to the chain length ratio, the long-chain fatty acid methyl ester with chain length of C14~C18 accounts for 70~80%, and the short-chain fatty acid methyl ester with chain length of C8~C12 accounts for 20~30%. The long-chain fatty acid methyl ester includes one or more of stearic acid methyl ester, oleic acid methyl ester, and linoleic acid methyl ester; and the short-chain fatty acid methyl ester includes octanoic acid methyl ester.

[0056] In some embodiments, when the mixed fatty acid methyl ester is adjusted according to the saturation ratio, the saturated fatty acid methyl ester accounts for 80~90%, and the unsaturated fatty acid methyl ester accounts for 10~20%.

[0057] In some embodiments, when the mixed fatty acid methyl ester is adjusted according to the unsaturation ratio, the mono-unsaturated fatty acid methyl ester accounts for 60~70%, and the poly-unsaturated fatty acid methyl ester accounts for 30~40%.

[0058] In some embodiments, the natural ester is coconut oil and soybean oil.

[0059] The molecular structure design method of the wide temperature range modified natural ester insulating oil comprises the following steps:

[0060] S1: A plurality of natural esters are weighed according to the proportion, and are mixed with methanol solution and NaOH solution respectively; after reaction, a mixture of mixed fatty acid methyl ester with chain length of C8~C18 and glycerol is obtained, and then the mixed fatty acid methyl ester is separated;

[0061] The natural ester in step S1 is coconut oil and soybean oil, and the specific steps are as follows:

[0062] S11: Coconut oil and soybean oil are mixed with methanol solution and NaOH aqueous solution respectively to obtain a mixed solution;

[0063] S12: The mixed solution is added to a water bath device connected with a reflux condenser, and magnetic stirring is performed until the mixed solution is clear; after stirring is completed, it is cooled to room temperature at room temperature;

[0064] S13: After cooling, HCl aqueous solution is added to neutralize the residual base, so that the pH of the solution is 7, and a mixed fatty acid methyl ester and glycerol mixture is obtained;

[0065] S14: Petroleum ether is added, stirred and layered, and a mixed fatty acid methyl ester in the upper layer of the solution is obtained and dried;

[0066] S2: The mixed fatty acid methyl ester is separated into uniform fatty acid methyl esters of different chain lengths, and the proportion of the fatty acid methyl ester is adjusted to re-mix the reaction to synthesize modified natural esters; the modified natural esters have high flash point and low pour point;

[0067] The specific steps of step S2 are as follows:

[0068] S21: The mixed fatty acid methyl ester (FAME) after sufficient methyl esterification is subjected to gas chromatography (GC) analysis, and the percentage content of each type of fatty acid methyl ester in the mixed fatty acid methyl ester is calculated according to the peak area of the standard substance and the peak area of the obtained spectrum;

[0069] S22: A vacuum fractionation separation method is used, the pressure is -0.1 MPa, and a gradient heating method is used, the heating rate is 10°C / h, the temperature is raised to 80~120°C, and uniform fatty acid methyl esters of different chain lengths are separated; including long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester;

[0070] S23: The long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester are mixed with the percentage content calculated in step S21 and p-toluenesulfonic acid is added as a catalyst; after the temperature is raised to 120°C and the pressure is reduced to -0.1 mbar, stirring is performed for 5h to synthesize modified natural esters;

[0071] The molar ratio of the total amount of fatty acid methyl ester prepared from the natural ester to trihydroxymethyl propane in step S23 is 3~6:1;

[0072] The molar ratio of the long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester in step S23 is 7~17:1:0.5~1:0.5~1;

[0073] The amount of catalyst toluenesulfonic acid is 0.01% of the total mass of methyl ester and trihydroxymethyl propane;

[0074] In some embodiments, the molar ratio of the total amount of fatty acid methyl ester prepared from the natural ester to trihydroxymethyl propane in step S23 is 3.1:1;

[0075] S3: introducing benzene ring for molecular modification in the modified natural ester, and obtaining wide temperature range modified natural ester insulating oil with different lipid chain structure after reaction;

[0076] The specific steps of introducing benzene ring for molecular modification in the step S3 are: mixing the modified natural ester with benzoic acid in proportion, i.e. mixing according to the molar ratio of 1:0.3-0.5, adding 1% p-toluenesulfonic acid as catalyst, stirring and reacting at 120°C under reduced pressure for 8h, thereby obtaining wide temperature range modified natural ester insulating oil with different lipid chain structure, and the molecular structure is:

[0077] ;

[0078] The pour point of the synthesized wide temperature range modified natural ester insulating oil is -49--55°C, and the flash point is 300-320°C. By introducing benzene ring or benzoic acid into the modified natural ester molecule through molecular modification, the intermolecular force and crystallization performance thereof are regulated, thereby the molecular structure of the wide temperature range modified natural ester is designed. When the benzene ring content is about 0.3-0.5wt.% of the mass of the insulating oil, the pour point of the wide temperature range modified natural ester insulating oil can be as low as below -50°C, and the flash point is higher than 300°C.

[0079] Experimental Example 1: the molecular structure design method of the wide temperature range modified natural ester insulating oil, the natural ester is coconut oil and soybean oil, comprising the following steps:

[0080] S1: taking a plurality of natural esters according to the proportion, mixing with methanol solution and NaOH solution respectively, obtaining mixed fatty acid methyl ester and glycerol mixture with chain length of C8-C18 after reaction, and then separating to obtain mixed fatty acid methyl ester;

[0081] S11: taking 50g of coconut oil (chain length C8-C12) and 50g of soybean oil, mixing with 10g of NaOH and 500mL of methanol solution respectively to obtain mixed solution;

[0082] S12: pouring the solution mixture into a water bath device connected with a reflux condenser, stirring at 65°C for 60min at a stirring speed of 300r / min until the solution is clear; after stirring, standing at room temperature until room temperature;

[0083] S13: after cooling, adding a small amount of HCl aqueous solution to neutralize the residual alkali, until the solution pH=7, obtaining mixed fatty acid methyl ester and glycerol mixture;

[0084] S14: 5 mL of petroleum ether was added and stirred for 5 min and left to stand for layering, obtaining the mixed fatty acid methyl ester on the upper layer of the solution, and placing it in a vacuum drying box with a vacuum degree of -0.1 MPa, 60°C drying for 24 h;

[0085] S2: The mixed fatty acid methyl ester was separated into uniform fatty acid methyl esters of different chain lengths, and the proportion of the fatty acid methyl ester was adjusted to re-mix the reaction to synthesize modified natural ester;

[0086] S21: GC analysis was performed on the FAME after sufficient methyl esterification, and the percentage content of each type of fatty acid was calculated according to the peak area of the standard substance and the peak area of the obtained spectrum;

[0087] S22: Using a vacuum fractionation separation method, the pressure was -0.1 MPa, and a gradient heating method was used, with a heating rate of 10°C / h, the temperature was raised to 80~120°C, and uniform fatty acid methyl esters of different chain lengths were separated, including long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester;

[0088] S23: The long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester were mixed in a molar ratio of 7:1:1:1, the total amount of each type of fatty acid methyl ester and the molar ratio of trihydroxymethyl propane was 3.1:1, and a catalyst p-toluene sulfonic acid was slowly added, the amount was 0.01% of the total mass of methyl ester and trihydroxymethyl propane; the temperature was raised to 120°C, the pressure was reduced to -0.1 mbar, the stirring reaction was carried out for 5 h, the stirring speed was 300 r / min, and the modified natural ester was synthesized;

[0089] S3: The molecular structure of the wide temperature range modified natural ester insulating oil with different ester chain structures was obtained by introducing a benzene ring, specifically: the modified natural ester was mixed with benzoic acid in a molar ratio of 1:0.3, 1% p-toluene sulfonic acid was added as a catalyst, and the wide temperature range modified natural ester insulating oil with different fatty chain structures was designed by vacuum distillation stirring reaction at 120°C, -0.1 MPa for 8 h, with a stirring speed of 300 r / min, the pour point was -55°C, the flash point was 318°C, the molecular formula was C 54 H 96 O6, and the molecular structure was:

[0090] .

[0091] Comparative Example 1: The molecular structure design method of the wide temperature range modified natural ester insulating oil includes the following steps:

[0092] S1: 50 g of coconut oil (chain length C8~C12) and 50 g of soybean oil were weighed out and mixed with 10 g of NaOH and 500 mL of a methanol solution, respectively, to obtain a mixed solution;

[0093] Then, the solution mixture was poured into a water bath device connected with a reflux condenser, and magnetic stirring was performed at 65°C for 60 min at a stirring speed of 300 r / min until the solution was clear.

[0094] After stirring, the solution was left to stand at room temperature. After cooling, a small amount of aqueous HCl was added to neutralize the residual base until the pH of the solution was 7, to obtain a mixed fatty acid methyl ester and glycerol mixture.

[0095] Next, 5 mL of petroleum ether was added, stirred for 5 min, and left to stand to separate the layers, to obtain the mixed fatty acid methyl ester in the upper layer of the solution, which was placed in a vacuum drying oven at a vacuum degree of -0.1 MPa and dried at 60°C for 24 h.

[0096] S2: Next, GC analysis was performed on the FAME after complete methyl esterification, and the percentage content of each type of fatty acid was calculated based on the peak area of the standard substance and the peak area of the obtained spectrum.

[0097] Using a vacuum fractionation separation method at a pressure of -0.1 MPa and a gradient temperature rise method with a temperature rise rate of 10°C / h, the temperature was raised to 80~120°C, and uniform fatty acid methyl esters of different chain lengths, including long-chain methyl stearate, methyl oleate, methyl linoleate, and short-chain methyl octanoate, were separated.

[0098] The long-chain methyl stearate, methyl oleate, methyl linoleate, and short-chain methyl octanoate were mixed in a molar ratio of 8:1:0.5:0.5, the molar ratio of methyl ester to trihydroxymethyl propane was 3.1:1, and a small amount of p-toluenesulfonic acid catalyst was slowly added, with the amount being 0.01% of the total mass of the methyl ester and trihydroxymethyl propane. The temperature was raised to 150°C, the pressure was reduced to 0.2 mbar, and stirring was performed for 5 h to synthesize modified natural ester.

[0099] S3: The modified natural ester was mixed with benzoic acid in a molar ratio of 1:0.3, 1% p-toluenesulfonic acid was added as a catalyst, and vacuum distillation stirring was performed at 120°C and -0.1 MPa for 8 h to obtain a wide temperature range modified natural ester insulating oil with a different lipid chain structure, which had a pour point of -52°C and a flash point of 310°C.

[0100] The molecular structure design method of the wide temperature range modified natural ester insulating oil of Comparative Example 2 includes the following steps:

[0101] S1: 50 g of coconut oil (chain length C8~C12) and 50 g of soybean oil were weighed out and mixed with 10 g of NaOH and 500 mL of a methanol solution, respectively. Then, the solution mixture was poured into a water bath device connected with a reflux condenser, and stirred at 65°C for 60 min at a stirring speed of 300 r / min until the solution was clear. After stirring, the solution was left to stand at room temperature until it reached room temperature;

[0102] After cooling, a small amount of aqueous HCl was added to neutralize the residual base until the solution pH=7, obtaining a mixture of mixed fatty acid methyl esters and glycerol;

[0103] Then, 5 mL of petroleum ether was added, stirred for 5 min and left to stand to separate the layers, obtaining the fatty acid methyl esters in the upper layer of the solution, which was placed in a vacuum drying oven and dried at 60°C for 24 h;

[0104] S2: Then, the FAME after sufficient methyl esterification was subjected to GC analysis, and the percentage content of each type of fatty acid was calculated according to the peak area of the standard substance and the peak area of the obtained spectrum;

[0105] Using a reduced pressure fractionation separation method, the pressure was-0.1 MPa, and a gradient heating method was used, with a heating rate of 10°C / h, and the temperature was raised to 80~120°C, obtaining uniform fatty acid methyl esters of different chain lengths, including long-chain methyl stearate, methyl oleate, methyl linoleate and short-chain methyl octanoate;

[0106] The long-chain methyl stearate, methyl oleate, methyl linoleate and short-chain methyl octanoate were mixed with trihydroxymethyl propane at a molar ratio of 8.5:0.5:0.5:0.5, the molar ratio of methyl ester to trihydroxymethyl propane was 3.1:1, and a small amount of p-toluenesulfonic acid catalyst was added, the amount of which was 0.01% of the total mass of methyl ester and trihydroxymethyl propane; the temperature was raised to 120°C, the pressure was reduced to-0.1 mbar, and the stirring reaction was carried out for 5 h at a stirring speed of 300 r / min, to synthesize modified natural ester;

[0107] S3: The modified natural ester was mixed with benzoic acid at a molar ratio of 1:0.3, 1% p-toluenesulfonic acid was added as a catalyst, and the reduced pressure distillation stirring reaction was carried out at 120°C and-0.1 MPa for 8 h, to obtain a wide temperature range modified natural ester insulating oil with different lipid chain structures, the pour point of which was-49°C and the flash point was 300°C.

[0108] For those skilled in the art, the specific embodiments are only exemplary descriptions of the present application, and it is obvious that the specific implementation of the present application is not limited by the above method. Any non-essential improvement or direct application of the concept and technical solution of the present application to other occasions is within the protection scope of the present application.

Claims

1. A wide temperature range modified natural ester insulating oil characterized in that, The molecular structure of the wide-temperature-range modified natural ester insulating oil comprises different ester chain structures, which is obtained by converting natural ester into mixed fatty acid methyl ester with chain length of C8-C18, separating the mixed fatty acid methyl ester into fatty acid methyl ester with different chain lengths, adjusting the proportion of the mixed fatty acid methyl ester, and introducing a group for modification.

2. The wide temperature range modified natural ester insulating oil according to claim 1, characterized in that, The molecular formula of the wide-temperature-range modified natural ester insulating oil is C 54 H 96 O6, and the molecular structure is: 。 3. The wide temperature range modified natural ester insulating oil according to claim 1, characterized in that, When the mixed fatty acid methyl ester is adjusted according to the chain length ratio, the long-chain fatty acid methyl ester with chain length of C14-C18 accounts for 70-80%, and the short-chain fatty acid methyl ester with chain length of C8-C12 accounts for 20-30%.

4. The wide temperature range modified natural ester insulating oil of claim 1, wherein, When the mixed fatty acid methyl ester is adjusted according to the saturation ratio, the saturated fatty acid methyl ester accounts for 80-90%, and the unsaturated fatty acid methyl ester accounts for 10-20%.

5. The wide temperature range modified natural ester insulating oil of claim 1, wherein, When the mixed fatty acid methyl ester is adjusted according to the unsaturation ratio, the mono-unsaturated fatty acid methyl ester accounts for 60-70%, and the poly-unsaturated fatty acid methyl ester accounts for 30-40%.

6. A method for designing a molecular structure of a wide-temperature-range modified natural ester insulating oil, characterized by comprising: The method comprises the following steps: S1: a plurality of natural esters are weighed according to the proportion, mixed with methanol solution and NaOH solution respectively, and after reaction, a mixed fatty acid methyl ester with chain length of C8-C18 and a glycerol mixture are obtained, and then the mixed fatty acid methyl ester is separated to obtain the mixed fatty acid methyl ester; S2: the mixed fatty acid methyl ester is separated into uniform fatty acid methyl ester with different chain lengths, and then the proportion of the fatty acid methyl ester is adjusted and mixed for reaction to synthesize modified natural ester; S3: the molecular structure of the wide-temperature-range modified natural ester insulating oil with different ester chain structures is obtained by introducing a benzene ring for molecular modification.

7. The method of designing the molecular structure of a wide-temperature-range modified natural ester insulating oil according to claim 6, characterized in that, The natural ester in the step S1 is coconut oil and soybean oil, and the specific steps are as follows: S11: the coconut oil and the soybean oil are mixed with methanol solution and NaOH aqueous solution respectively to obtain a mixed solution; S12: the mixed solution is added into a water bath device connected with a reflux condenser, and magnetic stirring is performed until the mixed solution is clear; after the stirring is completed, the solution is cooled to room temperature at room temperature; S13: after cooling, HCl aqueous solution is added for neutralization of residual alkali, so that the pH of the solution is 7, and a mixed fatty acid methyl ester and glycerol mixture is obtained; S14: petroleum ether is added for stirring and separation, and the mixed fatty acid methyl ester in the upper layer of the solution is obtained and dried.

8. The method of designing the molecular structure of a wide-temperature-range modified natural ester insulating oil according to claim 6, characterized in that, The specific steps of the step S2 are as follows: S21: gas chromatography (GC) analysis is performed on the mixed fatty acid methyl ester after methyl esterification, and the percentage content of each type of fatty acid methyl ester in the mixed fatty acid methyl ester is calculated according to the peak area of the standard substance and the peak area of the obtained spectrum; S22: a vacuum fractionation separation method is adopted, the pressure is-0.1 MPa, and a gradient heating method is adopted, the temperature is raised to 80-120°C at a heating rate of 10°C / h, and uniform fatty acid methyl ester with different chain lengths is separated, including long-chain stearic acid methyl ester, oleic acid methyl ester, linoleic acid methyl ester and short-chain octanoic acid methyl ester; S23: long chain of stearic acid methyl ester, methyl oleate, methyl linoleate and short chain of methyl octanoate according to the percentage of the calculated content and the mixture of trihydroxy methyl propane in step S21, and add p-toluene sulfonic acid as catalyst; after the temperature rises to 120°C, the pressure is reduced to-0.1mbar, stirring for 5h, synthesis of modified natural ester.

9. The method of designing the molecular structure of a wide-temperature-range modified natural ester insulating oil according to claim 8, characterized in that, The specific steps of introducing benzene ring for molecular modification in the step S3 are: mixing modified natural ester with benzoic acid in proportion, adding p-toluene sulfonic acid as catalyst, 120°C under reduced pressure distillation stirring reaction 8h, so as to obtain wide temperature range modified natural ester insulating oil with different lipid chain structure, and the pour point of the wide temperature range modified natural ester insulating oil obtained by synthesis is-49~-55°C, and the flash point is 300~320°C.

10. The method of designing the molecular structure of a wide-temperature-range modified natural ester insulating oil according to claim 9, characterized in that, The molar ratio of the total amount of fatty acid methyl ester prepared by the step S23 to trihydroxy methyl propane is 3~6:1; The molar ratio of the long chain of stearic acid methyl ester, methyl oleate, methyl linoleate and short chain of methyl octanoate is 7~17:1:0.5~1:0.5~1; The amount of the catalyst toluene sulfonic acid is 0.01% of the total mass of fatty acid methyl ester and trihydroxy methyl propane; The molar ratio of the modified natural ester to benzoic acid in the step S3 is 1:0.3~0.

5. The specific steps of introducing benzene ring for molecular modification in the step S3 are: mixing modified natural ester with benzoic acid in proportion, adding p-toluene sulfonic acid as catalyst, 120°C under reduced pressure distillation stirring reaction 8h, so as to obtain wide temperature range modified natural ester insulating oil with different lipid chain structure, and the pour point of the wide temperature range modified natural ester insulating oil obtained by synthesis is-49~-55°C, and the flash point is 300~320°C. The molar ratio of the total amount of fatty acid methyl ester prepared by the step S23 to trihydroxy methyl propane is 3~6:1; The molar ratio of the long chain of stearic acid methyl ester, methyl oleate, methyl linoleate and short chain of methyl octanoate is 7~17:1:0.5~1:0.5~1; The amount of the catalyst toluene sulfonic acid is 0.01% of the total mass of fatty acid methyl ester and trihydroxy methyl propane; The molar ratio of the modified natural ester to benzoic acid in the step S3 is 1:0.3~0.5.

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