KR102197682B1 - Preparation method of fatty acid isoalkyl ester based vegetable insulating oil - Google Patents

Abstract

The present invention relates to a method for producing a fatty acid isoalkyl ester-based vegetable electrical insulating oil and to a vegetable electrical insulating oil prepared by the above method, wherein vegetable oils and branched alkyl alcohols are reacted under enzyme catalyst and anti-freeze treatment by the method according to the present invention. The prepared fatty acid isoalkyl ester vegetable electrical insulating oil has low viscosity and low pour point, improves low-temperature fluidity, improves the problem of sedimentation of some components, has a high dielectric breakdown voltage, and has similar insulating properties as conventional mineral oil-derived electrical insulating oils. As it can represent, it can be usefully used as an eco-friendly bio-insulating oil.

Description

Preparation method of fatty acid isoalkyl ester based vegetable insulating oil

The present invention relates to a method for preparing a fatty acid isoalkyl ester-based vegetable electrical insulating oil by reacting vegetable oils and branched alkyl alcohols under an enzyme catalyst, and to a vegetable electrical insulating oil prepared by the method.

Transformer-insulating oil is a fluid used to insulate electrical equipment, especially transformers. Electrical insulating oil is essential to reduce power loss when converting electrical energy from high voltage to low voltage when operating a transformer, and electrical insulating oil can prevent damage that may be caused by a large amount of heat. Therefore, electric insulating oil is used not only for power efficiency but also for the life and safety of the transformer. As industrial development increases, the demand for these electric insulating oils continues to increase.

The insulating oil that has been used the most up to now is mineral oil derived from petroleum resources. However, mineral oil is limited in supply due to the depletion of fossil fuels, has a low flash point, and poses a risk of explosion, and is not biodegradable and toxic, causing serious human hazard and environmental pollution. Leaks of tens of liters of transformer oil, currently used in thousands of transformers worldwide, can cause severe water and soil pollution.

In order to solve this problem, many studies have been conducted to replace the existing mineral oil-based insulating oil with a renewable and biodegradable vegetable oil-based oil. Vegetable oil is a renewable resource with high biodegradability, low toxicity and high flash point, but has electrical properties that can be used as insulating oil. For this reason, vegetable electrical insulating oils such as Envirotemp FR3® insulating oil and BIOTEMP® insulating oil have been developed and used commercially for about 20 years. However, since vegetable electrical insulating oil is composed of triglyceride esters of saturated or unsaturated fatty acids, vegetable oil-based insulating oil has a problem that its viscosity is high and its pour point is higher than that of mineral oil.Therefore, it is necessary to improve the low-temperature characteristics and fluidity of vegetable electrical insulating oil.

Accordingly, the present inventors synthesized a branched monoalkyl ester by causing a transesterification reaction using a branched alcohol and cottonseed oil as starting materials in the presence of an enzyme catalyst, and the prepared cottonseed oil-based branched monoalkyl ester has viscosity and low temperature fluidity properties. The present invention was completed by confirming this excellence and confirming that it can be used as a vegetable electrical insulating oil that can replace mineral oil.

Korean Patent Registration No. 10-1806750

An object of the present invention is to provide a method for producing a vegetable electrical insulating oil comprising the step of reacting vegetable oils and branched alkyl alcohols of C _3-5 under an enzyme catalyst to obtain a fatty acid isoalkyl ester-based electrical insulating oil (Step 1). Is to do.

Another object of the present invention is to obtain a fatty acid isoalkyl ester-based electric insulating oil by reacting vegetable oils and C _3-5 branched alkyl alcohols under an enzyme catalyst (step 1); And freezing the fatty acid isoalkyl ester-based electrical insulating oil obtained in step 1 (step 2) (step 2); to provide a method for producing vegetable electrical insulating oil comprising.

Another object of the present invention is to provide a vegetable electrical insulating oil prepared by the above method.

The present invention provides a method for preparing vegetable electrical insulating oil comprising a step of reacting vegetable oils and fats and branched alkyl alcohols of C _3-5 under an enzyme catalyst to obtain a fatty acid isoalkyl ester-based electrical insulating oil (step 1).

In addition, the present invention is a step of obtaining a fatty acid isoalkyl ester-based electric insulating oil by reacting a vegetable oil and a branched alkyl alcohol of C _3-5 under an enzyme catalyst (step 1); And freezing the fatty acid isoalkyl ester-based electrical insulating oil obtained in step 1 (winterization) (step 2). It provides a method for producing vegetable electrical insulating oil comprising a.

Furthermore, the present invention provides a vegetable electrical insulating oil prepared by the above method.

Fatty acid isoalkyl ester-based vegetable electrical insulating oil prepared by reacting and preventing freezing of vegetable oils and branched alkyl alcohols under enzyme catalyst by the method according to the present invention has low viscosity and pour point, improving low-temperature fluidity, and sedimentation of some components. Is improved, the dielectric breakdown voltage is high, and it can exhibit insulation properties similar to those of the existing mineral oil-derived electric insulation oil, so it can be usefully used as an eco-friendly bio insulation oil.

1 is a graph comparing the pour point (°C) of monoalkyl esters according to types of acyl acceptors; Dimethyl carbonate (DMC), methanol (methyl alcohol, MeOH), ethanol (ethyl alcohol, EtOH), isopropyl alcohol (2-propanol, isopropyl alcohol, IPA), isobutyl alcohol (IBA) and iso Isoamyl alcohol (IAA).
2 shows the relative yields (%) of fatty acid iso-propyl esters (FAPEs) according to the molar ratio of isopropyl alcohol and cottonseed oil (isopropanol/cotton seed oil ratio, mol/mol). This is the graph shown.
3 is a graph showing the relative yield (%) of fatty acid isopropyl esters (FAPEs) according to the water content (water content, %, v/v IPA) compared to isopropyl alcohol.
Figure 4 is a relative yield of fatty acid isopropyl esters (FAPEs) according to the amount of enzyme catalyst added (enzyme ratio, %, w/w oil) compared to the weight of cottonseed oil produced by reacting for 3 hours (black) or 12 hours (gray) ( %).
5 is a graph showing the change in the yield (g/g cotton seed oil) of fatty acid isopropyl esters (FAPEs) according to the reaction time and temperature of cottonseed oil and isopropyl alcohol.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method for producing a vegetable electrical insulating oil comprising a step of reacting vegetable oils and fats and branched alkyl alcohols of C _3-5 under an enzyme catalyst to obtain a fatty acid isoalkyl ester-based electrical insulating oil (Step 1).

In addition, the present invention is a step of obtaining a fatty acid isoalkyl ester-based electric insulating oil by reacting a vegetable oil and a branched alkyl alcohol of C _3-5 under an enzyme catalyst (step 1); And

It relates to a method for producing a vegetable electrical insulating oil comprising a step (winterization) the fatty acid isoalkyl ester-based electrical insulating oil obtained in step 1 (step 2);

Specifically, the step of reacting the vegetable fats and oils and C _3-5 branched alkyl alcohols under an enzyme catalyst is to produce fatty acid isoalkyl esters using vegetable fats and oils and C _3-5 branched alkyl alcohols as starting materials. It means the step of mixing with the enzyme catalyst. The reaction may be a transesterification reaction, and in this case, the branched alkyl alcohol of C _3-5 may simultaneously serve as a solvent in which the reaction occurs and a substrate participating as an acyl acceptor.

In the present invention, the term "insulating oil" is an oil used for electrical insulation of transformers, circuit breakers, capacitors, cables, and the like, and is also referred to as electrical insulating oil. Most of them are petroleum-based, but some are non-flammable synthetic insulating oils, such as diphenyl chloride, etc. are also used. Depending on the purpose, diphenyl chloride is also used, but in general, the bulk electrical resistance is large and the viscosity is low. The ones that are stable against are selected. In addition, "transformer" refers to a device that changes the value of an alternating voltage or current using an electromagnetic induction phenomenon.

In the method for producing vegetable electrical insulating oil according to the present invention, the vegetable oil in step 1 may be cottonseed oil.

In the present invention, the cottonseed oil refers to oil extracted from cottonseed as a raw material, and is mainly used as a raw material for margarine, organic canning, salad oil, mayonnaise, other edible oils, medicines, candles, hydrogenated oil, soap, etc. have. Cottonseed oil is an unsaturated fatty acid, consisting of oleic acid with one double bond and linoleic acid with two double bonds. It is rich in vitamin E, lowers cholesterol, improves heart disease, and increases polymorphic glioblastoma. It is known to have an effect such as inhibiting metastasis.

In the method for producing vegetable electrical insulating oil according to the present invention, the branched alkyl alcohol of C _3-5 in step 1 is isopropyl alcohol, isobutyl alcohol, and isoamyl alcohol. It may be one or more selected from the group consisting of. When using short-chain alkyl alcohols of C ₂ or less, there is a problem that low-temperature fluidity is very low due to a high pour point. In case of using a branched alkyl alcohol of C ₆ or more, the pour point is increased again and low-temperature fluidity is lowered. There is a problem that this becomes expensive. It may be preferable to use isopropyl alcohol among the isopropyl alcohol, isobutyl alcohol and isoamyl alcohol in terms of low temperature characteristics and economic efficiency. The isopropyl alcohol is also called 2-propanol, and is sometimes used as the term isopropanol.

In the method for producing vegetable electrical insulating oil according to the present invention, the enzyme catalyst in step 1 may be a lipase. In one embodiment of the present invention, Lypozyme 435 was purchased and used as a lipase enzyme catalyst.

In the method for producing a vegetable electric insulating oil according to the present invention, the molar ratio of the vegetable oil and the branched alkyl alcohol of C _3-5 in Step 1 may be 1:3.5 to 1:7. If the molar ratio of the branched alkyl alcohol of C _3-5 to vegetable oil is lower than 3.5, the total reaction volume is not sufficient and the enzyme and substrate are not completely blended, resulting in a decrease in reaction efficiency. Conversely, the molar ratio is higher than 1:7. In some cases, the component is over-diluted and effective collisions are reduced, resulting in a lower conversion. The molar ratio may be preferably 1:4 to 1:5, more preferably 1:4.3 to 1:4.7.

In the method for producing a vegetable electrical insulating oil according to the present invention, the vegetable oil of step 1 and the branched alkyl alcohol of C _3-5 may be reacted at a temperature of 40 to 60° C. for 60 to 180 minutes. The reaction to produce oil through the transesterification process is best done at high temperatures, and the high reaction temperature lowers the viscosity of the vegetable oil and increases the reaction rate. However, at a high temperature of 60°C or higher, the enzyme catalyst is deactivated and activity is lost, so if the temperature is too high, the oil yield may decrease, and at a temperature of 40°C or less, the yield of the fatty acid isoalkyl ester may decrease. Preferably, the vegetable oil of step 1 and the branched alkyl alcohol of C _3-5 may be reacted for 90 to 180 minutes at a temperature of 50 to 60°C.

In the method for producing vegetable electrical insulating oil according to the present invention, the water content in step 1 may be 0 to 0.3% (v/v) relative to the volume of the branched alkyl alcohol of C _3-5 . Preferably, it may be 0 to 0.25% (v/v), more preferably 0 to 0.2% (v/v). When the transesterification reaction proceeds using a lipase immobilized in a non-aqueous medium, the water added to the reaction solution maintains the activity of the lipase, and in the aqueous medium, the lipase serves as a catalyst for the hydrolysis reaction to occur in the fatty acid alkyl ester. Thus, excess water reduces the conversion of vegetable oils to fatty acid esters in the transesterification reaction. Accordingly, in an embodiment of the present invention, as a result of confirming the conversion rate of fatty acid isopropyl ester according to the moisture content, It was confirmed that it is preferable to set the moisture content to 0.3% (v/v) or less relative to the volume of isopropyl alcohol.

In the method for preparing vegetable electrical insulating oil according to the present invention, the enzyme catalyst in step 1 may be added 2 to 6% (w/w) based on the total weight of the vegetable fat, preferably 2.5 to 5.5% (w /w) may be added, more preferably 3 to 5% (w/w) may be added. When added below the above range, the yield of the fatty acid isoalkyl ester decreases, and when added above the above range, the cost of using the enzyme is high compared to the reaction efficiency.

In the method for producing vegetable electrical insulating oil according to the present invention, in the antifreeze treatment in step 2, the fatty acid isoalkyl ester-based electrical insulating oil obtained in step 1 is cooled for 20 to 30 hours at a temperature of -15 to 15°C, and then the precipitate is It may be to remove. Preferably, it may be cooled for 22 to 26 hours at a temperature of -2 to 5°C. The flash point and the pour point are similarly inversely proportional to each other, and when outside the above range, a problem of greatly deteriorating the physical properties of the flash point or the pour point may occur. For example, in the case of antifreezing treatment at a temperature higher than the above range, the pour point may be lowered but the flash point may be weakened.

In addition, the present invention provides a vegetable electrical insulating oil prepared by the above method.

The vegetable electrical insulating oil according to the present invention can be manufactured in an environmentally friendly manner using cottonseed oil, IPA and lipase, and has low viscosity and pour point, high dielectric breakdown voltage, and other insulating properties at the same level as mineral oil. Can be maintained, it can be usefully used as an electrical insulating oil of a transformer.

Hereinafter, the present invention will be described in more detail by the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

< Example 1> According to the type of solvent Monoalkyl Ester oil manufacturers

In order to prepare the monoalkyl ester, an transesterification reaction was carried out in a 500 ml three-necked reactor.

Specifically, 100g of cottonseed oil (Daejeonghwa Geum Co., Ltd.) and acyl acceptor candidates for methanol (methyl alcohol, MeOH; Daejeonghwa) in a 3-neck reactor (3-neck beaker type reactor, Labmarket) Gold Co., Ltd.), ethanol (ethyl alcohol, EtOH; Daejung Hwa-Kum Co., Ltd.), dimethyl carbonate (DMC; Acros organics), isopropyl alcohol (IPA; Daejung Hwa-Gum Co., Ltd.), Isobutyl alcohol (IBA; Daejunghwakeum Co., Ltd.) and isoamyl alcohol (IAA; Daejunghwakeum Co., Ltd.) were added respectively. At this time, the cottonseed oil and the acyl receptor were used as substrates, and the acyl receptor was also used as a reaction solvent. The mixture of the cottonseed oil and the acyl receptor in a molar ratio of 1:4.5 was stirred at 250 rpm using a mechanical stirrer, and in order to initiate the reaction, an enzyme catalyst, Lipase (Lipozyme 435, Novozymes) was added 5% (w/ The addition amount of w) was injected during stirring to induce an ester exchange reaction. The reaction mixture was filtered to separate the enzyme, and the filtrate was evaporated using a rotary evaporator. Finally, the supernatant containing the ester and the low glycerol was separated using a separatory funnel to obtain the monoalkyl esters (fatty acid methyl esters) of Examples 1-1 to 1-6.

Example 1-1 1-2 1-3 1-4 1-5 1-6 Types of acyl receptors DMC MeOH EtOH IPA IBA IAA Cottonseed oil: acyl receptor molar ratio 1:4.5 1:4.5 1:4.5 1:4.5 1:4.5 1:4.5 Moisture content (% (v/v) based on the volume of the acyl receptor) 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% Enzyme added amount (% by weight of cottonseed oil (w/w)) 5% 5% 5% 5% 5% 5% Reaction temperature, time 50℃, 12h 50℃, 12h 50℃, 12h 50℃, 12h 50℃, 12h 50℃, 12h

< Experimental example 1> According to the type of alcohol Monoalkyl Pour point analysis of ester

In order to improve the low-temperature fluidity of cottonseed oil, the pour point of the monoalkyl esters of Examples 1-1 to 1-6 prepared by an enzymatic transesterification reaction using various types of alcohols as acyl acceptors ) Compared. The pour point was measured according to the method of KS M ISO 3016 (2014).

Methanol and ethanol were used as short-chain alcohols, and methanol and ethanol were solvents used to synthesize vegetable oil-based alkyl esters used as fossil-derived diesel substitutes. DMC is an environmentally friendly solvent capable of converting from triglycerides to methyl esters and at the same time converting the resulting glycerol by-products to glycerol carbonate. Isopropyl alcohol (IPA), isobutyl alcohol (IBA) and isoamyl alcohol (IAA) were used as branched alcohols.

1 is a graph comparing the pour point (°C) of monoalkyl esters according to types of acyl acceptors; Dimethyl carbonate (DMC), methanol (methyl alcohol, MeOH), ethanol (ethyl alcohol, EtOH), isopropyl alcohol (2-propanol, isopropyl alcohol, IPA), isobutyl alcohol (IBA) and iso Isoamyl alcohol (IAA).

As a result, the pour point of the monoalkyl ester produced using MeOH and DMC was found to be similar to that of the cottonseed oil-based biodiesel -4 to 0°C. In contrast, the pour point of monoalkyl esters in which IPA and IAA were used as acyl acceptors decreased from -9°C to -12°C. As a result, it was found that the pour point of the monoalkyl ester using the branched alcohol is lower than that of the monoalkyl ester using the linear alcohol, which is why the branched alcohol decomposes the crystal structure of the cottonseed oil-based monoester oil at low temperature. It can be expected because it delays solidification and maintains fluidity at low temperatures.

As the number of carbons increases, the hydrophobicity increases, and the conversion rate may decrease by inhibiting the activity of enzymes.If the conversion rate decreases, the components remaining without reaction may decrease the insulation properties and low-temperature fluidity, and the number of carbons increases and the overall chain length becomes longer. It loses the low viscosity characteristics that can be obtained by converting to the ground linear structure. In addition, IPA can be purchased at relatively low prices such as chemical solvents and detergents, and IBA and IAA are used as alternative fuels, chemical solvents, and raw materials for the synthesis of food additives, so the price is relatively high.

Therefore, as a result of considering economic and experimental efficiency among branched alcohols IPA, IBA and IAA, which showed a low pour point, it was confirmed that IPA with the lowest carbon number of 3 among branched alcohols was most suitable for preparing insulating oil. IPA was used.

< Example 2> Preparation of fatty acid isopropyl ester

Fatty acid iso-propyl esters (FAPEs), which can be used as electrical insulating oil, were synthesized through transesterification using IPA and cottonseed oil identified as the optimal solvents in Experimental Example 1.

At this time, the transesterification reaction was performed in the same manner as in Example 1, but 1 mmol (0.860 g) of cottonseed oil, various amounts of IPA (molar ratio to cottonseed oil), lipase enzyme (w/w based on the weight of cottonseed oil), and It was performed in a screw-cap glass vial containing water (%, v/v based on IPA volume). During the reaction, the temperature was maintained using an oil bath. After the reaction was completed, each reaction medium was filtered using a syringe filter having a pore size of 45 μm to obtain fatty acid isopropyl ester from the filtrate.

< Experimental example 2> Optimization of transesterification conditions for synthesis of fatty acid isopropyl ester

In synthesizing the fatty acid isopropyl ester using IPA and cottonseed oil of Example 2, the molar ratio of IPA and cottonseed oil, water content, enzyme addition ratio, reaction temperature and reaction time conditions were optimized.

In order to optimize the reaction conditions, the filtrate obtained by the method of Example 2, that is, fatty acid isopropyl esters (FAPEs), was analyzed by gas chromatography (GC) to measure the oil conversion rate and composition from vegetable oil to electric insulating oil.

GC analysis was performed using an HP-INNOWAX column (polyethylene glycol capillary tube, length 30m×diameter 0.53mm, film thickness 0.5µm) and a GC system (M600D, Young Lin Instrument, Korea) equipped with a flame ionization detector. The temperature of the capillary column was initially maintained at 150° C. for 8 minutes, increased to 240° C. at a rate of 10° C. per minute, and maintained for 10 minutes. All procedures were repeated 3 times.

2-1. Cottonseed Oil and IPA Molar ratio Yield analysis of fatty acid isopropyl ester according to

In a solvent-free system without using a solvent, isopropyl alcohol (IPA) plays an important role in determining the reaction efficiency because isopropyl alcohol (IPA) plays a role as a solvent in which the reaction occurs and a substrate that participates as an acyl receptor. have.

Accordingly, after fixing the reaction conditions at 1 mmol of cottonseed oil, the moisture content based on the total volume of IPA was 0.2%, the amount of lipase (lypozyme 435) added based on the total weight of the cottonseed oil was 10%, the reaction temperature was 50°C, and the reaction time was 3 hours, cottonseed oil and IPA The transesterification reaction of Example 2 was performed by varying the molar ratio of. The relative yield (%) of fatty acid isopropyl esters (FABEs) synthesized from cottonseed oil was measured and shown in FIG. 2.

Figure 2 shows the relative yields (%) of fatty acid iso-propyl esters (FAPEs) according to the molar ratio of isopropyl alcohol and cottonseed oil (isopropanol/cotton seed oil ratio, mol/mol). This is the graph shown.

As shown in FIG. 2, as the molar ratio of IPA and cottonseed oil increased from 1:1 to 4.5:1, the relative conversion rate of FAPEs increased, and as the molar ratio increased to 4.5:1 or more, the conversion rate decreased again, and FAPEs The yield was found to be the highest at a 4.5:1 molar ratio. Therefore, it was confirmed that the optimum molar ratio of IPA and cottonseed oil was 4.5:1.

2-2. Yield analysis of fatty acid isopropyl ester according to water content relative to IPA volume

In order to compare the change in FAPEs conversion with increasing moisture content, the molar ratio of 1 mmol of cottonseed oil, IPA and cottonseed oil was 4.5:1, the amount of lipase (lypozyme 435) added based on the total weight of cottonseed oil was 10%, the reaction temperature was 50°C, and the reaction time was 3 hours. After fixing the reaction conditions with, the transesterification reaction of Example 2 was performed by varying the moisture content (%) by adding 0 to 0.4% of water relative to the volume of IPA serving as a substrate and a reaction solvent to the reaction solution. The relative yield (%) of fatty acid isopropyl esters (FABEs) synthesized from cottonseed oil was measured and shown in FIG. 3.

3 is a graph showing the relative yield (%) of fatty acid isopropyl esters (FAPEs) according to the water content (water content, %, v/v IPA) compared to isopropyl alcohol.

As a result, when the amount of water added increases from 0 to 0.2% relative to the total volume of IPA, the relative yield of fatty acid isopropyl ester is maintained at 90% or more, but hydrolysis of fatty ester occurs when the moisture content is 0.4% or more. The conversion of the isopropyl ester was reduced to 63.8%. Accordingly, it was confirmed that it is preferable to set the moisture content to 0.3% (v/v) or less relative to the volume of isopropyl alcohol.

2-3. Yield analysis of fatty acid isopropyl ester according to the amount of enzyme catalyst added to the weight of cottonseed oil

In order to compare the change in the conversion rate of FAPEs according to the increase in the amount of enzyme added, the molar ratio of 1 mmol of cottonseed oil, IPA and cottonseed oil is 4.5:1, the moisture content based on the total volume of IPA is 0%, the reaction temperature is 50°C, and the reaction time is 3 hours or 12 hours. After fixing the reaction conditions as, the transesterification reaction of Example 2 was performed by varying the amount of lipase (lypozyme 435) added to 0.5 to 10% (w/w) based on the total weight of cottonseed oil. The relative yield (%) of fatty acid isopropyl esters (FABEs) synthesized from cottonseed oil was measured and shown in FIG. 4.

4 is a relative yield of fatty acid isopropyl esters (FAPEs) according to the amount of enzyme catalyst added (enzyme ratio, %, w/w oil) compared to the weight of cottonseed oil produced by reacting for 3 hours (black) or 12 hours (gray) %).

As a result, when the reaction time was fixed at 3 hours (black), the yield of FAPEs increased to a maximum conversion rate of 90% when the catalyst changed from 0.5% (w/w) to 10% (w/w) relative to the weight of cottonseed oil. , The highest efficiency was observed when 5% (w/w) of the enzyme was used. It was found that the conversion rate increased dramatically in the range of 0.5 to 3% (w/w), and in the case of a reaction to maximize the conversion rate in a short time, it was confirmed that at least 2% (w/w) of the enzyme should be added relative to the weight of cottonseed oil. It was confirmed that it is preferable to add 2 to 6% (w/w), and in particular, adding 5% (w/w) of the lipase enzyme is the most optimal enzyme addition amount.

On the other hand, when the reaction time was fixed at 12 hours (gray), as a result of comparing the conversion efficiency of FAPEs, the change in the yield of insulating oil according to the amount of enzyme added was similar to the trend when the reaction time was fixed at 3 hours. When a small amount of enzyme was used, the amount of FAPEs produced increased significantly as the reaction time increased, but when a sufficient amount of catalyst was used, there was no significant difference in the yield according to the time increase, and the amount of catalyst added was 10% (w/w). The further increase resulted in a decrease in the yield due to the decomposition reaction. These results show that when performing the transesterification reaction using cottonseed oil and IPA using lipase, a high conversion rate is displayed in a short time.

2-4. Analysis of production of fatty acid isopropyl ester according to reaction temperature and time

In order to compare the change in the conversion rate of FAPEs according to the reaction temperature and time, the molar ratio of 1 mmol of cottonseed oil, IPA and cottonseed oil was 4.5:1, the moisture content based on the total volume of IPA was 0%, and the amount of lipase (lypozyme 435) added based on the total weight of the cottonseed oil. After fixing the reaction conditions to 5% (w/w), the transesterification reaction of Example 2 was carried out at various temperatures of 40, 50 and 60° C., and fatty acid isopropyl from cottonseed oil according to an increase in reaction time of 0 to 180 minutes. The production rate (g/g) of ester (FABEs) was measured and shown in FIG. 5.

5 is a graph showing the change in the yield (g/g cotton seed oil) of fatty acid isopropyl esters (FAPEs) according to the reaction time and temperature of cottonseed oil and isopropyl alcohol.

As a result, the initial reaction rate was found to be faster as the reaction temperature increased from 40°C to 60°C. The amount of FAPEs synthesized relative to 1 g of cottonseed oil was saturated to a maximum of 92.7% (w/w) at a reaction time of 90 minutes at a reaction temperature of 50°C or a reaction time of 60 minutes at a reaction temperature of 60°C. When the reaction temperature was fixed at 40° C., the conversion rate of FAPEs was lower than 70% even after reaction for 180 minutes. From these results, it was confirmed that it was preferable to react for 90 to 180 minutes at a temperature of 50 to 60°C in consideration of the conversion rate and thermal efficiency, and in particular, it was confirmed that the optimum synthesis temperature was 50°C.

The productivity of the electric insulating oil was 567.8 g/L/h under optimal conditions.

< Example 3> Preparation of freeze-protected fatty acid isopropyl ester

In the process of synthesizing FAPEs from vegetable oil through transesterification using IPA and cottonseed oil as substrates, the reaction produces 3 molecules of fatty acid monoalkyl esters and 1 molecule of glycerol by-product from triglycerides. When IPA and glycerol by-products are completely separated from the synthesized monoalkyl ester, the precipitation of steryl glyceride contained in cottonseed oil may occur. This precipitation occurs when the saturated alkyl ester crystallizes at a melting point higher than room temperature, and may interfere with the low-temperature fluidity and electrical properties of the electric insulating oil.

In order to prevent the problem of formation of a precipitate, winterization was performed to remove steryl glycerides and some saturated alkyl esters through cooling and precipitation. Since excessive removal of the saturated alkylester can reduce the flash point, crystallization was carried out in a narrow temperature range around room temperature.

Specifically, using cottonseed oil and IPA, the molar ratio of IPA and cottonseed oil, which are the optimal conditions identified in Example 2 and Experimental Example 2, was 4.5:1, the moisture content based on the total volume of IPA was 0%, and lipase based on the total weight of the cottonseed oil (lypozyme 435). The lipase enzyme was filtered off after transesterification reaction was carried out under the conditions of an addition amount of 5% (w/w), a reaction temperature of 50°C, and a reaction time of 6 hours or longer.

After extracting the oil with hexane to the reaction solution filtered lipase, the oil was concentrated to evaporate the solvent, and cooled at 15°C or -15°C for 24 hours as shown in Table 2 below, and then at the same temperature. The solidified oil was removed by centrifuge. Thereafter, the fatty acid isopropyl ester (electrical insulating oil) of Examples 3-1 and 3-2 was obtained by filtration using a 0.45 μm pore size filter in a reduced pressure filter.

Meanwhile, the reaction solution obtained by filtering the lipase was not subjected to a hexane extraction process, and cooled at 2° C. for 24 hours as shown in Table 2 below, and then centrifuged at the same temperature to remove the solidified oil. Thereafter, the fatty acid isopropyl ester (electrical insulating oil) of Example 3-3 was obtained by filtration using a 0.45 μm pore size filter in a reduced pressure filter without a concentration process.

Example 3-1 Example 3-2 Example 3-3 Precipitation Concentrate after oil extraction with hexane Concentrate after oil extraction with hexane Simple separation without extraction Cooling 15℃, 24h -15℃, 24h 2℃, 24h

< Experimental example 3> Characterization of freeze-protected fatty acid isopropyl ester

In order to confirm the optimal anti-freeze treatment conditions, for each of the anti-freeze-treated fatty acid isopropyl esters of Examples 3-1 to 3-3, solidification was observed at room temperature for 2 days or more, and the flash point and pour point were measured. .

The flash point and pour point were confirmed by requesting analysis from the Korea Petroleum Institute (FSCEs), and the flash point was measured based on KS M 2010 and the pour point based on the KS M 2014 test analysis method.

In addition, before the cryoprotection treatment was performed by the method of Example 3, the precipitates generated from fatty acid isopropyl esters (FAPEs) that were not cryoprotected were confirmed to be solidified at room temperature for 2 days or more and the composition through GC/MS analysis. GC/MS analysis was confirmed with a GC-MS system (Agilent 7890B GC combined with Agilent 5977B MS detector) using HP-5ms column (5% phenyl-methyl polysiloxane capillary, 30 m long × 0.25 mm diameter, 0.1 μm thick). And helium was used as the carrier gas. The temperature of the oven was maintained at 140° C. for 1 minute, increased to 190° C. at a rate of 15° C. per minute, increased to 260° C. at a rate of 7° C. per minute, and maintained at 20° C. per minute up to 300° C. for 10 minutes.

Example 3-1 Example 3-2 Example 3-3 Flash point (℃) N/A 58.0 128.5 Pour point (℃) * -9 -9 * Sediment occurs at room temperature

As a result, when the cooling treatment was not performed, solidified precipitates occurred within 12 hours. When the precipitate was separated and analyzed by GC/MS, other components other than wax and mono/di-glyceride were not detected, and the precipitate was judged as solidified fat. Fatty acid isopropyl ester without antifreeze treatment was found to be unable to analyze electrical properties and pour point due to a large amount of precipitates.

As shown in Table 3, it was found that the fatty acid isopropyl ester treated for freezing by the method of Example 3-1 generated a precipitate even after repeated two or more times. The fatty acid isopropyl ester treated with antifreeze by the method including the hexane extraction process of Example 3-2 was found to have a flash point lower than the reference value (130°C) according to the insulating oil management standard. On the other hand, the fatty acid isopropyl ester treated for freezing by the method of Example 3-3 recovered the flash point, which had fallen significantly during the freezing prevention treatment by the method of Example 3-2, to near the lowest reference value, and it was found that the low pour point was maintained. .

Accordingly, it was confirmed that simple separation without cooling at 2° C. for 24 hours and extraction of hexane is an optimal condition for the antifreeze treatment of fatty acid isopropyl ester.

< Experimental example 4> Insulation characteristics of electric insulating oil derived from cottonseed oil produced under optimal conditions

The characteristics of the fatty acid isopropyl ester produced under the optimum conditions identified in Experimental Example 2 and Experimental Example 3 as an electrical insulating oil were obtained by the Korea Petroleum Institute (FSCEs) based on KS (Korean Industrial Standard) and ASTM (American Society for Testing and Materials). It was evaluated according to the method. Specifically, viscosity (viscocity) was measured based on KS M ISO 3104 (2008), and the pour point was measured according to KS M ISO 3016 (2014). The dielectric breakdown voltage was measured according to KS C IEC 60156 (2013), the water content was measured according to KS M ISO 12937 (2003), and the oxidation stability was measured according to KS C 2101. (2006). Density was measured according to ASTM D4052-15.

The physical properties and electrical properties measured by the above method for the electric insulating oil (fatty acid isopropyl ester) applicable to the transformer produced under optimal conditions are shown in Table 4 below in comparison with mineral oil.

characteristic unit Mineral oil Cottonseed oil-based electrical insulating oil
(Fatty acid isopropyl ester) density g/cm ³ <0.91 0.879 Viscosity 40℃ mm ² /s <13.0 6.063 100℃ <4.0 2.161 Pour point ℃ <-27.5 -9 Insulation breakdown voltage kV > 40 75.9 Moisture content (m/m)% <0.003 0.04 Oxidation stability Sludge % - 0.03 Acid value mg KOH/g <0.40 0.03

The density of cottonseed oil-based insulating oil was 0.879 g/cm ^{3, which} was similar to that before transesterification, but was lower than the mineral oil standard value of 0.91 g/cm ³ . The viscosity of cottonseed oil-based insulating oil was 6.06 mm ² /s at 40°C and 2.161 mm ² /s at 100°C, which was lower than that of mineral oil at each temperature. Since the low density and low viscosity can increase the fluidity of the synthetic oil and improve the cooling efficiency, these results indicate that the insulating oil based on cottonseed oil according to the present invention has improved insulating properties than mineral oil. The dielectric breakdown voltage of the cottonseed oil-based insulating oil was 75.9 kV, which was higher than 40 kV, the lowest reference point of the mineral oil, and it was confirmed that the electrical characteristics of the cottonseed oil-based insulating oil according to the present invention are sufficient to be used in a transformer. As a result of measuring low-temperature fluidity as a pour point, the pour point of the cottonseed oil-based insulating oil produced through the transesterification according to the present invention was -9℃, which was higher than -13℃ in terms of mineral oil, but the conventional cottonseed oil methyl ester (estimated 0℃) Since it was lower, it was confirmed that it has a lower temperature fluidity than the soybean oil-based insulating oil composed of methyl ester with a pour point of 0°. Other insulating properties and physical and chemical properties were similar to those of mineral oil.

Based on these results, cottonseed oil-based fatty acid isopropyl ester according to the present invention can be prepared in an environment-friendly manner using cottonseed oil, IPA and lipase, and has low viscosity and pour point, high dielectric breakdown voltage, and other insulating properties. It has been confirmed that it can be used as an electrical insulating oil for a transformer because it can maintain the same level of characteristics as mineral oil.

So far, the present invention has been looked at around its preferred embodiments. Those of ordinary skill in the art to which the present invention pertains will be able to understand that the present invention may be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative point of view rather than a limiting point of view. The scope of the present invention is not shown in the foregoing description, but in the claims, and all differences within the scope should be construed as being included in the present invention.

Claims (13)

A mixture of cottonseed oil and isobutyl alcohol (IBA) 1:4 to 1:5 molar ratio was reacted with 10% by weight of lipase based on the total weight of the cottonseed oil at a temperature of 40 to 60°C for 60 to 180 minutes, Obtaining a fatty acid isoalkyl ester-based electrical insulating oil (step 1); And
It characterized in that it is produced, comprising a freeze protection (winterization) step (step 2) of removing the precipitate by centrifugation after cooling for 22 to 26 hours at a temperature of -2 to 5 ℃, vegetable electric insulating oil.
delete delete delete delete delete The method of claim 1,
The molar ratio of the cottonseed oil and isobutyl alcohol (IBA) is 1:4.3 to 1:4.7, characterized in that, vegetable electrical insulating oil. delete delete delete delete delete delete

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