JP2015536549A - Blended oil compositions useful as dielectric fluid compositions and methods for their preparation - Google Patents

Abstract

In the present invention, compositions that are suitable for use as dielectric fluids are derived from renewable source oils and blends thereof. Synthetic esters of renewable sources as described herein are manufactured using ingredients that are derived from natural or biological raw materials that can be regenerated by conventional agricultural techniques. Dielectric fluids that can meet industry standards are obtained using a method that combines the appropriate percentage of ingredients selected from synthetic polyol esters, natural oils, and mineral oils to customize the properties of the resulting dielectric fluids . Some of the properties that can be manipulated in the practice of the present invention include electrical strength, resistivity, impulse strength, dissipation factor, dielectric constant, specific heat, thermal conductivity, chemical stability, gas absorption, pour point. , Viscosity, volatility, flash and combustion points, and biodegradability.

Description

  The present invention relates to dielectric fluid compositions suitable for use as transformer insulators and coolants.

  The electrical industry uses dielectric fluids to cool electrical equipment such as transformers, power cables, breakers, and capacitors. Typically these dielectric fluids are used in combination with solid insulators in liquid filled transformers. Examples include mineral oils, high molecular weight hydrocarbons (HMWH), silicone fluids, and synthetic hydrocarbon oils (polyalpha-olefins). Such fluids must be electrically insulating, resistant to decomposition, and can dissipate large amounts of heat generated by electrical devices to the surrounding environment, thereby making the solid insulation last longer. To work as a heat transfer medium.

  However, transformers with mineral oil are typically not used inside buildings due to concerns about safety, the environment, and the special containment considerations required.

  Standards have been developed to qualify dielectric fluids as suitable for use in various facilities. The American Society for Testing Materials has developed ASTM standards D3487-88 and D522292 that define specification limits for mineral-based and hydrocarbon high-burning point insulating oils. ASTM D6871-03 establishes specification limits for natural ester fluids used in electrical equipment, and International Electrotechnical Standard IEC 61699 establishes specification limits for synthetic ester fluids, IEC 60296 Edition 4 ( 4th edition) sets the specification limits for uninhibited mineral oil.

  Additives are often added to dielectric fluids to enhance fluid performance and thereby prolong distribution and power transformers. One common practice is the addition of antioxidant additives to oils without inhibitors. Another common practice is the addition of anti-gassing additives to fluids that have a positive gassing tendency. For example, a dielectric fluid used in a transformer can generate gas during the course of use, which can create pressure problems when used inside a closed vessel. The performance of the coolant can also be influenced by the presence of bubbles in the fluid. U.S. Patent Application Publication No. 2010 / 0279904A1 describes an electrical insulating oil that includes a heavy reforming oil as a gas evolution inhibitor.

  The use of conventional dielectric fluids is not without problems. In recent years, regulatory agencies have become increasingly concerned about oil spills that can contaminate ground soil and other areas. Many conventional fluids are not biodegradable within a reasonable time frame. Some have electrical properties that make them sub-optimal. Biodegradable dielectric fluids may be desirable for electrical devices such as transformers used in populated or ecologically sensitive areas.

Natural and synthetic esters can be used as dielectric fluids to replace mineral oil for safety and environmental reasons. Canadian Patent Application 2,492,565 discloses two or more specific chemical structures having at least a pour point of about −40 ° C. and alkyl groups having a chain length of C _{5 to} C _22. A dielectric coolant comprising a mixture of polyol esters is disclosed. U.S. Pat. No. 8,187,508 B2 describes a base reagent for electrical insulating oils mainly containing esterification products of glycerin and straight or branched fatty acids having 6 to 14 carbon atoms. ing.

  The oxidative stability of natural esters can be improved (1) by reducing the number of double bonds (unsaturation) by complete or partial hydrogenation and / or (2) by reducing polyunsaturation in the oil. Are known. However, both processes can increase the oxidative stability of natural oils, but such measures can increase the pour point of the oil and this result can be used for transformers that are exposed to low ambient temperatures. Undesirable for oil to be used.

  A biodegradable electrical coolant with good oxidative stability that is still fluid at low temperatures and remains stable at high temperatures or otherwise retains its desired properties at extreme temperatures Needed continuously. Furthermore, it may be desirable to obtain transformer dielectric coolant from renewable source materials.

  There is also a need for a method of controlling the properties of biodegradable electrical coolants that will ensure that they are still fluid under various temperatures and remain stable.

  In one aspect, the invention is a composition useful as a dielectric fluid, wherein the composition comprises (i) about 50 wt% to about 99 wt% mineral oil, based on the weight of the fluid, and (ii) About 1 wt.% To about 50 wt.% Of a first blend, wherein the first blend is (1) about 1 to about 99 wt.% Of renewable source synthesis, based on the weight of the first blend. A saturated line of polyol ester, wherein the polyol ester comprises (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) at least about 95 mol% of the carboxyl derivative contains 6 to 12 carbon atoms. A polyol ester which is a fully esterified reaction product obtained from a reaction mixture comprising a mixture of linear carboxyl derivatives; and (2) from about 1% to about 99% by weight of about 24 mole% Consisting essentially of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having less than about 75 mol% monounsaturation; the dielectric fluid composition comprises (a) components of a blend Compared with gassing tendency of (1)-without addition of aromatic gassing prevention additive-with reduced gassing tendency; (b) measured by ASTM D-97 below about -20 ° C It is a composition having such a pour point.

  In another aspect, the invention is a composition useful as a dielectric fluid, wherein the composition comprises (i) about 50 wt% to about 99 wt% mineral oil, based on the weight of the fluid (ii) ) About 1 wt.% To about 50 wt.% Of the first blend, wherein the first blend is (1) about 1 to about 99 wt.% Renewable source based on the weight of the first blend. A synthetic polyol ester, wherein the polyol ester comprises (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) at least about 95 mol% of the carboxyl derivative contains 6 to 12 carbon atoms. A polyol ester which is a fully esterified reaction product obtained from a reaction mixture comprising a mixture of linear carboxyl derivatives; and (2) from about 1% to about 99% by weight of about 75 moles Essentially consisting of a triacylglycerol natural oil obtained from a natural source, consisting essentially of a long chain fatty acid ester having super monounsaturation, the first blend being uninhibited, and a dielectric fluid composition comprising Compared to the gas generation tendency of component (1) of the dielectric fluid composition--without the addition of an aromatic gas generation prevention additive--a composition having a reduced gas generation tendency.

  In another aspect, the invention is a composition useful as a dielectric fluid, wherein the composition comprises (i) about 50 wt% to about 99 wt% mineral oil, based on the weight of the fluid; ii) from about 1% to about 50% by weight of a triacylglycerol natural oil derived from natural sources consisting essentially of a long chain fatty acid ester having greater than about 75 mol% monounsaturation; (iii) optional A blend comprising a selected additive; a composition having a reduced gassing tendency compared to the gassing tendency of component (i)-without added aromatic gassing prevention additive.

  In another aspect, the present invention is a composition useful as a dielectric fluid, wherein the composition comprises (i) from about 25 wt% to about 99 wt% mineral oil, based on the weight of the blend (ii) ) About 1% to about 75% by weight of a first blend, wherein the first blend is (1) about 1 to about 99% by weight of renewable source, based on the weight of the first blend. A synthetic polyol ester, wherein the polyol ester is (i) a glycerol oligomer component having at least 4 hydroxyl groups; and (ii) at least about 95 mol% of the carboxyl derivative comprises 6 to 12 carbon atoms. A polyol ester which is a fully esterified reaction product obtained from a reaction mixture consisting essentially of a mixture of a linear carboxyl derivative of: (2) from about 1 wt% to about 99 wt % Of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester; and (3) optionally comprising an additive, wherein the dielectric fluid composition comprises (a) a component of the blend Compared to the gassing tendency of (1)-without the addition of an aromatic gassing prevention additive-having a reduced gassing tendency; (b) a dielectric in the range of about 2.5 to less than about 4.5 (C) a composition comprising less than 3000 ppm of unreacted or partially reacted polyol.

  In another aspect, the present invention is a composition useful as a dielectric fluid, wherein the composition comprises (i) from about 25 wt% to about 99 wt% mineral oil, based on the weight of the blend (ii) ) About 1 wt.% To about 75 wt.% Of a first blend, wherein the first blend is (1) about 1 to about 99 wt.% Of less than 3000 ppm unreacted or partially reacted polyol. And a renewable source synthetic polyol ester further comprising a synthetic antioxidant, the polyol ester comprising: (i) a glycerol oligomer component having at least 4 hydroxyl groups; and (ii) at least one of the carboxyl derivatives A fully ester obtained from a reaction mixture consisting essentially of a mixture of saturated linear carboxyl derivatives, about 95 mol% containing 6 to 12 carbon atoms The reaction product polyol ester; and (2) optionally containing an additive; the dielectric fluid composition has a fragrance as compared to the gas evolution tendency of component (1) of the dielectric fluid composition A composition having a reduced tendency to generate gas-without the addition of a group gas generation prevention additive.

  In another aspect, the present invention is an electrical device comprising the dielectric fluid of the present invention.

  In another aspect, the present invention provides a method for preparing a dielectric fluid composition, the method comprising (a) (1) a renewable source synthetic saturated polyol ester, wherein the polyol ester comprises (i) Obtained from a reaction mixture comprising a polyhydroxyl component having at least 3 hydroxyl groups and (ii) a mixture of saturated linear carboxyl derivatives wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms. A polyol ester that is a fully esterified reaction product; (2) a trihydrate derived from a natural source consisting essentially of a long chain fatty acid ester having from about 24 mol% to less than about 75 mol% monounsaturated ester. An acylglycerol natural oil; (3) from a natural source consisting essentially of a long chain fatty acid ester having about 75 mol% or more of a monounsaturated ester (4) blending two or more components selected from the group consisting of mineral oils to obtain a dielectric fluid blend composition of at least about 95 to about 100 weight percent; and (b) ) The following characteristics: (i) burning point, (ii) power factor, (iii) volume resistivity, (iv) gas evolution tendency; and (v) measuring at least one of the pour points; (c) Adjust the percentages of ingredients as necessary to determine the following properties: at least 300 ° C. burning point; less than about −20 ° C. pour point; 40 ° C. less than about 30 centistokes; or measured according to ASTM D-2300 Having a gas generation tendency in the range of about −30 μL / min to about +30 μL / min and having at least one gas generation tendency without any added aromatic gas generation prevention additive. The method comprising the steps of: obtaining a command.

2 is a graph of oil stability index (OSI) versus percentage of high oleic soybean oil in a blended composition.

  In one embodiment, the present invention is a composition useful as a dielectric fluid comprising a synthetic, renewable source polyol ester. Synthetic esters can be used either alone or as a blend with other natural and / or mineral oils, such as triacylglycerol oils.

  The renewable source synthetic polyol ester fluids of the present invention are synthetic because they are obtained by esterification / transesterification ((trans) esterification) reactions or processes under controlled process conditions. The (trans) esterification reaction can be performed by any known conventional or non-conventional means, including the use of catalysts that can be acidic, basic, or enzymatic. In one embodiment, no added catalyst is required because the reaction can be autocatalytic under certain conditions.

  For example, it is well established that esterification of an alcohol can be accomplished by contacting the alcohol with a carboxylic acid, or derivative thereof, under conditions suitable to form a carboxylic acid ester. In some embodiments, when starting from a carboxylic acid, the process is well known in the chemical arts, such as acid catalysts-strong mineral acids such as hydrochloric acid, phosphoric acid, sulfuric acid, or p-toluenesulfonic acid. And other such strong protic acids which are customary can be catalyzed. Lewis acids may be suitable for esterification processes that can provide the synthetic oils of the present invention. Lewis acids such as aluminum, titanium and tin compounds (such as stannous (II) chloride dihydrate and dibutyltin oxide) are known and customary for such processes.

  In other embodiments, esterification of the alcohol can be accomplished without added catalyst using an excess of carboxylic acid to ensure complete esterification. Excess fatty acid can be completely removed under reduced pressure after the reaction. If not, residual acids present in the product can affect properties such as oxidative stability, hydrolytic stability, power factor and other properties, and therefore the quality of the product should be improved. is there. Oil purification can be effective to improve oil quality. This is particularly important when the reactive carboxylic acid is a short or medium chain fatty acid.

  In addition to carboxylic acids, the esters of the present invention can be obtained using carboxylic acid halides such as carboxylic acid derivatives such as carboxylic acid chlorides and bromides. Carboxylic anhydrides or esters can also be useful derivatives of carboxylic acids to produce the synthetic esters of the present invention. In another embodiment, natural oils and / or esters can be a suitable source of carboxyl groups (also referred to herein as “acyl” groups) of the synthetic esters of the present invention, or a conventional type known as transesterification. In the transesterification, the acyl groups of the starting ester are transferred to different hydroxyl-containing compounds to form different esters, and the transesterification reaction is catalyzed by a typical esterification catalyst.

  The carboxylic acid or derivative used in the practice of the invention to produce the synthetic ester of the invention contains 6 to 12 carbon atoms. Carboxylic acids or derivatives having 6 to 12 carbon atoms are referred to herein as medium chain acids or derivatives. For the purposes of the present invention, carboxylic acids and derivatives having 14 or more carbon chain lengths are considered long chain acyl compounds.

  The synthetic medium chain polyacyl esters of the present invention comprise or consist essentially of saturated fatty acid carbon chains. That is, there are essentially no carbon-carbon multiple bonds. For example, hexanoic acid, octanoic acid, decanoic acid, dodecanoic acid, derivatives thereof as set forth herein above, and mixtures of any of these may be suitable for use in the practice of the present invention. .

  It may be customary to refer to acids that are virtually found by their common names. For the avoidance of doubt, straight-chain saturated acids having 6 to 12 carbons and their derivatives are suitable for use herein regardless of the name used to describe them. For example, hexanoic acid is also known as caproic acid, octanoic acid is known as caprylic acid, decanoic acid is known as capric acid, and dodecanoic acid is also known as lauric acid. Caproic acid (C6) shall be considered a medium chain fatty acid for purposes of the present invention, along with caprylic acid (C8), capric acid (C10) and lauric acid (C12).

  The synthetic esters of the present invention are produced from renewable source materials. For example, renewable sources of medium chain carboxylic acids can be obtained from natural sources such as palm kernel oil or coconut oil, which necessarily contains a large proportion of medium chain fatty acids suitable for use herein. Oils obtained from palm kernels and coconuts can be hydrolyzed by conventional methods known to those skilled in the edible oil industry and fractionated by known methods such as distillation or separation based on molecular weight or polarity difference-i.e. The medium-chain carboxylic acid, separated from the higher chain acid, is used to produce the synthetic ester of the present invention from a suitable polyol.

  The synthetic ester of the present invention is produced by reacting a polyol with a mixture of medium chain fatty acids. The percentage of each medium chain fatty acid in the mixture can be adjusted to provide an ester of the desired properties, but any one of the individual medium chain fatty acids can be used in the mixture used to produce the synthetic ester. From about 5 to about 90%, provided that at least about 95% of the total ester linkages of the synthetic ester comprise medium chain esters and the remaining esters are short and / or long chain esters. In one embodiment, at least about 90% of the ester linkages of the synthetic ester comprise a mixture of caprylyl, capryl and / or lauryl esters.

  Compositions derived from carboxylic acids and their derivatives according to these parameters provide a balanced set of desired properties that enhance the performance of synthetic esters and their blends, especially when used as dielectric coolants. It has been discovered herein that it can.

  While the presence of carbon-carbon multiple bonds in the synthetic esters of the present invention is not preferred, it is outside the scope of the present invention that the synthetic esters of the present invention may not achieve 100% purity in this regard. Absent. Therefore, special consideration is given to the cost and utility of completely eliminating carbon-carbon multiple bonds, as well as other components that may be present in the claimed composition that may contain, in particular, unsaturated components. Thus, it is contemplated in the presently claimed invention that such functionality is kept to a minimum, taking into account factors such as the benefits gained from such means. The synthetic esters of the present invention comprise less than 5 mol%, preferably less than 3 mol%, more preferably less than 1 mol% of unsaturated esters.

  The synthetic esters of the present invention result from the reaction of a medium chain carboxyl component with a polyhydroxyl component that can include a polyhydroxy alcohol having at least 3 hydroxyl functional groups per molecule. For the purposes of the present invention, such polyhydroxyl alcohols may alternatively be referred to herein as “polyols”. The polyols of the present invention can be monomeric multifunctional alcohols such as glycerol or pentaerythritol (PE) or trimethylolpropane (TMP) or trimethylolethane (TME), or-for example diglycerol, triglycerol, ditrimethylolpropane, di- It can be an oligomeric alcohol such as pentaerythritol or a mixture thereof. The polyols of the present invention may contain naturally occurring compounds such as saccharides or saccharide alcohols, such as monosaccharides and disaccharides and / or their derivatives, as minor components. For example, sucrose, glucose, fructose, mannose, sorbitol, or starch and other cellulosic materials may be possible polyols suitable for use in the practice of the present invention. For the purposes of the present invention, there is no intended distinction between the terms “polyhydroxyl alcohol” and “polyol”, and these terms have the same meaning without any effect on the intended scope of the invention. Can be used. In one embodiment, the polyol is asymmetric and does not include hydrogen on the carbon adjacent to the hydroxyl-bearing carbon (ie, the β position), such as, for example, trimethylolpropane. In another embodiment, the polyol is diglycerol, triglycerol, tetraglycerol or mixtures thereof.

  In another embodiment, the synthetic ester composition of the present invention can be blended with natural oils. The blends of the present invention comprise a suitable triacylglycerol oil in a relative amount of from about 5 to about 90% by weight of the blend, and the renewable source synthetic ester can provide from about 10 to about 95% by weight of the blend. . Alternatively, the blend can include triacylglycerol in an amount of about 10 to about 80 wt%, or about 10 to about 70 wt%, or about 20 to about 50 wt%, or about 30 to 40 wt%. It may be critical that in some applications the composition of the blend is adjusted to provide a blend that can be classified as a K class fluid, and this relative amount of triacylglycerol component is a K class dielectric. In those applications that should be blended to provide a sex fluid, the actual percentage of triacylglycerol can be adjusted to achieve the desired balance of properties to meet that criterion.

  The blends of the present invention can comprise a triacylglycerol oil comprising an ester of a carboxylic acid comprising or consisting essentially of a long chain acid. Glycerol long-chain acid esters can be obtained from natural or biological sources such as oil-producing crops including soy, canola, sunflower, palm, palm kernel, coconut, and other known sources of natural oils. The triacylglycerol oil component of the presently claimed composition can be a mixture of oils. In one embodiment, suitable triacylglycerol oils for use in the present invention have a high mono-unsaturated ester content, i.e., 60 mol% or more. For example, an oil with a high monounsaturated content is a soybean oil described in US Pat. No. 5,981,781, incorporated herein by reference as if fully described. And can be obtained from natural sources that provide high acyl oleate (oleyl) compositions. Such high oleic soybean (HOS) oils contain more than 75 mol% high oleyl (C18: 1) of acyl component, with less than 10 mol% total polyunsaturated esters (C18: 2 and C18: 3) Have quantity. Other natural oils with a high oleic acid content are, for example, sunflower oil, safflower oil, olive oil, and canola oil.

  In another embodiment, natural esters having a low to moderate monounsaturated acid content may be suitable for use herein. For example, an oil having from about 24 mole percent to less than about 75 mole percent—or alternatively from about 60 mole percent to less than about 75 mole percent monounsaturated acid—is believed to have low to moderate monounsaturation. Such oils include, for example, soybean oil, sunflower oil, safflower oil, and canola oil.

  In yet another aspect of the present invention, any renewable source saturated polyol ester having desirable low and high temperature properties can be blended with a natural ester such that the total unsaturation in the blend does not exceed an iodine number of 100. . Preferred renewable source synthetic polyol esters are selected from glycerol-based esters, trimethylolpropane-based esters, glycerol oligomer-based esters and mixtures thereof.

  The blends of the present invention can provide surprising synergies that cannot be easily predicted based on the properties of the individual components alone.

  In the present invention, renewable source saturated synthetic polyol esters as described herein are natural or biological raw materials that use fatty acid components derived from raw materials that can be regenerated by conventional agricultural techniques. Manufactured.

  Further, described herein are methodologies for obtaining various cooling liquid compositions, wherein the cooling liquid has properties that are customized or adjusted to meet the specific needs of the application. The

  Further described herein are electrical insulation systems that include dielectric coolants and solid electrical insulation materials that can be customized to meet specific needs in various electrical operating systems, and methods for customizing the insulation systems. .

Ideally, the dielectric coolant used in the transformer has a high dielectric strength, high volume resistivity (at least about 10 ¹¹ ohm cm at 25 ° C. as measured by ASTM D-1169), high impulse strength. , Low dissipation factor, low viscosity, high specific heat, high thermal conductivity, good chemical stability and gas absorption properties, good low temperature flow properties (low viscosity and low pour point), low volatility, high flash point and combustion It should have spot (nonflammability), non-toxicity, easy biodegradability, and low cost availability. Furthermore, it may be desirable for the coolant to have a dielectric constant (Dk) that is similar to a solid dielectric used in electrical equipment. It is difficult to provide a single base stock fluid with all of the desired properties. However, the fluid composition of the present invention provides an overall balance of desirable properties in a blended composition comprising a renewable source polyol ester.

  The dielectric coolants described herein may be referred to generically using a variety of alternative terms. For example, the terms “transformer oil”, “coolant”, “insulating fluid” may be used generically to refer to dielectric coolants, or may be characteristic of the presently claimed invention. Other terms referring to the composition may be used interchangeably in the text of the specification. The contextual use of such terms herein is where a term is intended to be generic or when it is specific for a given use or composition. It should be easily communicated to those skilled in the art.

  The physical properties of the synthetic esters and blends of the present invention make them particularly suitable for use as a dielectric fluid. The ester compositions of the present invention are desirable low temperature properties (eg, viscosity and pour point), high temperature properties (eg, flash point) that Applicants believe is critical to the performance of the synthetic ester compositions of the present invention. And combustion points), chemical stability (ie, thermal and oxidative stability) and electrical properties (eg, dissipation factor, dielectric constant) can be formulated to embody various properties. In addition, the gassing tendency of a dielectric fluid is a critical feature of any dielectric fluid because it is useful as a metering performance that indicates whether a suitable fluid is preferred under the conditions of use. is there.

  The low temperature properties of the compositions of the present invention are particularly useful in transformers that are generally exposed to variable atmospheric temperatures, such as temperature extremes. The dielectric coolant of the present invention has a pour point lower than about -20 ° C, as measured by ASTM D-97, alternatively about -30 ° C, or lower than about -40 ° C.

  Furthermore, in order for the coolants to be efficient in their ability as heat transfer fluids, the fluids must have low viscosity, high thermal conductivity, high specific heat, and-especially from temperatures below 0 ° C to above 100 ° C. It is desirable to have a high coefficient of expansion at the transformer operating temperature, which can range up to temperatures above. Of these properties, viscosity is considered to be a more influential property for heat transfer either by natural convection with smaller self-cooling transformers or forced convection with pumps in larger units. . The generally accepted trend is that the lower the kinematic viscosity, the higher the heat dissipation. Kinematic viscosity is the ratio of the dynamic viscosity of a liquid to its density.

  Again, providing an ideal dielectric fluid is not without problems. Low viscosity fluids generally tend to have low flash points and burn points and may not meet the less flammable K class criteria. On the other hand, fluids that meet the K class criteria typically have higher kinematic viscosities and are typically not effective in dissipating the heat generated by liquid transformers. This ineffective heat dissipation contributes to shortening the life of the transformer. The insulating coolant of the present invention has a kinematic viscosity at 40 ° C. of 40 cSt or less as measured by ASTM D-445, and can nevertheless meet the criteria for being a K-class fluid.

  Viscosity index (VI) is an empirical unitless number that indicates the effect of temperature changes on the kinematic viscosity of oil. The higher the VI of the oil, the lower its tendency to change viscosity with temperature. For example, lower VI dielectric coolants such as naphthenic mineral oils tend to be thinner at transformer operating temperatures and thus dissipate the heat generated very effectively, for example, saturated ester High VI fluids, such as natural ester oils containing, tend to have lower viscosity at low temperatures, so the fluid quickly reaches the expected use temperature during cold start. Natural vegetable oils generally have high viscosity index values (> 200) compared to synthetic esters and mineral oils.

  High temperature properties such as flash point and combustion point are critical properties of dielectric fluids. The flash point represents the temperature of the fluid that will result in the ignition of the fluid vapor, and the combustion point represents the temperature of the fluid at which combustion occurs when exposed to air and an ignition source. The dielectric coolant of the present invention meets the standards for less flammable liquids that qualify them as K-class materials, which are the highest combustion performance criteria for dielectric fluids. The coolant of the present invention has a combustion point of at least 300 ° C. as measured by ASTM D-92, which is the standard for K class materials.

  One other important desirable feature for dielectric fluids is good aging stability, mainly related to oxidative stability over time. Oxidation is a critical factor in the aging of dielectric fluids, which is particularly important for fluids used in free-breathing transformers versus those used in sealed transformers. Good oxidative stability minimizes sludge and acid formation, which improves electrical conduction, ensures acceptable heat transfer, and maintains system life.

  Fluids containing natural esters typically have higher oxidation rates than do mineral oils and will typically polymerize when exposed to air and heat. Therefore, the conventional practice is that natural ester fluids are not recommended for free breathing transformers. In the practice of the present invention, dielectric fluid coolants that are oxidatively stable compared to conventional fluids containing natural esters can be used to produce natural oils that have some degree of unsaturation as described in the present invention. Obtained by blending with a synthetic polyol ester of a renewable source that does not have

  In one embodiment of the present invention, an improved dielectric fluid composition comprising an unsaturated natural oil and a renewable source synthetic polyol ester contains components in a manner to control the iodine value of the blended composition. Obtained by blending, wherein the blended composition has an iodine number of 100 or less. An iodine number of less than 100 may indicate a coolant that is oxidatively stable under the conditions of use. The iodine value is an indicator of the degree of unsaturation present in the compositions described herein.

  Natural oils contain naturally occurring antioxidants such as tocopherols. However, natural antioxidants present in natural oils are typically not effective in stabilizing the oil compared to synthetic antioxidants. As a result, for example, 2,6-di-t-butyl-p-cresol (DBPC), also known as butylated hydroxytoluene (BHT); butylated hydroxyanisole (BHA); propyl gallate; or t-butyl It may be customary to add one or more synthetic antioxidants, such as hydroquinone (TBHQ), to the natural ester dielectric fluid to improve the oxidative stability of the fluid. However, in some applications it may be desirable to use a dielectric fluid that has no added synthetic antioxidants or only a trace amount of an inhibitor.

  The fluids of the present invention are shown by the oil stability index (OSI) in the substantial absence of synthetic antioxidants, i.e., even when no synthetic antioxidants are added to the fluid composition. Furthermore, it has excellent oxidation stability. The inhibitor-free coolant obtained according to the present invention can be used alone for use in both sealed and free-breathing electrical equipment or can be added to another inhibitor-free dielectric fluid. it can. For purposes of the present invention, excellent oxidative stability is at least 20 hours OSI induction time measured at 130 ° C. according to the method of the American Oil Chemistry Society (AOCS method 12b-92). Indicated by.

  Inhibitor-free dielectric fluid blends as described herein include renewable source saturated polyol esters and highly monounsaturated acid-based natural esters, and these dielectric coolants are synthesized oxidation Provides good chemical stability even when essentially free of inhibitor. In the practice of the present invention, the dielectric fluid is “no inhibitor” if it contains less than 0.08 wt% synthetic antioxidant, based on the weight of the fluid. However, if necessary, synthetic additives such as aromatic gas generation prevention additives, metal passivators, antifoaming agents, electrostatic charging tendency depressants, and pour point depressants are further enhanced in stability. Therefore, it can be added to a fluid without an inhibitor. A fluid of the present invention is said to be “preventive” if it contains greater than 0.08% by weight of antioxidant but does not contain a total of greater than 0.4% by weight of synthetic antioxidant. The inhibitored fluid can contain any effective amount of other synthetic additives.

  In one aspect of the present invention, an inhibitor-free blend of a synthetic ester of the present invention and at least one natural oil having a monounsaturated ester content of greater than or equal to about 75 mole% is measured from the OSI of the blend. Demonstrates surprising stability, as shown by the induction time longer than that of either of the separate components without inhibitor. The blend without inhibitor demonstrates the synergistic effect of blending the synthetic ester with the natural ester, thereby increasing OSI compared to either of the separate components. In particular, an inhibitor-free blend comprising 50% by weight, or in particular 70% by weight or more of a synthetic ester, or more particularly an inhibitor-free blend comprising about 80% by weight or more of a synthetic ester, or 90% by weight or more of a synthetic ester. An unexpectedly improved OSI can be obtained for the blends it contains.

  In another aspect of the present invention, a blend of synthetic ester and natural oil, wherein the synthetic ester is purified to an acid value of less than about 0.07 mg KOH / g ester before blending with natural oil, is improved. Demonstrated oxidative stability. Purifying or purifying the synthetic ester of the present invention prior to blending improves the properties of the blended composition, for example, lowering the power factor, and as a dielectric fluid, for example, volume resistivity When used, the performance of the blend can be increased. Treatment of synthetic esters to remove impurities such as unreacted hydroxyl compounds, unreacted acids, particularly unsaturated acids or esters, can improve the performance of synthetic esters and blends containing the esters.

  Synthetic esters suitable for use in the practice of the present invention have an acid number according to ASTM D-974 of less than about 0.05 mg KOH / gram, preferably an acid number of less than about 0.03, most preferably The acid value is about 0.01 mg KOH / gram or less. Commercially available synthetic esters having an acid number higher than the desired acid number can be processed to reduce the acid number to a level that provides a fluid that is useful as a dielectric fluid.

  Fluid purification can be performed by treating either individual components or blends thereof with silica gel, activated carbon, basic alumina—or any two or any combination of these three— The result is an improved dielectric fluid compared to the untreated fluid. The treatment of the synthetic ester can be supplemented by heating the fluid to a temperature of about 50 ° C. to about 150 ° C. during the treatment. In particular, the treated fluid of the present invention comprises a synthetic ester having less than 3000 ppm unreacted or partially reacted polyol, preferably less than 1500 ppm unreacted polyol, more preferably less than 500 ppm unreacted polyol. Most preferably, the synthetic ester useful in the practice of the present invention comprises from about 50 to about 0 ppm unreacted or partially reacted polyol.

The purified dielectric fluid of the present invention has a power factor as measured by ASTM D-924 of less than about 0.5% at 25 ° C and less than about 5% at 100 ° C. Furthermore, the purified dielectric fluid of the present invention has a volume resistivity, as measured by ASTM D-1169, greater than 10 ¹¹ ohm cm at 25 ° C.

  The tendency of the dielectric fluid to generate gas, ie its tendency to absorb or release gas under electrical stress, can affect the performance of liquid transformers, cables and capacitors. Gas evolution trends can be measured by ASTM D2300, where a decrease or increase in pressure indicates fluid behavior under this electrical stress. A fluid having a low gassing tendency tends to generate less gas and / or better absorb any evolved gas, which may be desirable, especially in closed systems, so low gassing performance is very Is desirable. The American Society for Testing Materials has developed ASTM standard D3487-00 that sets limits for gas evolution trends as measured by ASTM D2300-8 +30 μL / min for transformer coolant. The International Electrotechnical Commission (IEC) does not provide a standard for the gassing tendency of insulating fluids, but has proposed a maximum of +5 μL / min as measured by IEC 60628 for special applications.

  In one embodiment of the present invention, the dielectric fluid of the present invention is produced by ASTM D2300-8 by a process of blending at least one dielectric fluid having a positive gassing tendency with a natural ester having a negative gassing tendency. As measured, it is formulated to control the gas evolution tendency of the fluid such that the gas evolution tendency of the fluid is within the range of +30 to -30 μL / min. The gassing tendency of the blended dielectric fluid described herein is controlled without the use of an aromatic gassing prevention additive conventionally used to control the gassing behavior of the dielectric fluid. The

  The dissipation factor is a measure of dielectric loss in a fluid that in turn indicates the amount of energy dissipated as heat. The dissipation factor value should be as low as possible. Natural ester and synthetic ester insulating fluids typically have a higher dissipation factor than high temperature, especially non-polar mineral insulating oils. Typical values for the fluids of the present invention are less than about 0.5% at 25 ° C and less than about 5.0% at 100 ° C. If the unaged fluid exceeds these values indicating the presence of soluble polar contaminants, the fluid can be purified to eliminate or reduce the level of contaminants.

Dielectric constant (Dk) is defined as the amount of electrostatic energy that can be stored per unit volume per unit potential gradient, which can be measured for dielectric fluids by ASTM D924. Conventional mineral oil has a dielectric constant of about 2.2 and solid cellulose insulation has about 4.5. The dielectric constant of natural and polyol esters is higher than that of mineral oil and is in the range of about 2.5 to 4.5 at 25 ° C. Increasing the dielectric constant, Dk, of the liquid insulator in the transformer and matching them to that of the solid insulator balances the insulation system without increasing stress in the oil channel and improves the use of mixed dielectrics To do. In one aspect of the invention, the ratio of the dielectric constant of the coolant to the insulating solid material (Dk _r ) is designed to be greater than 0.5 or may be in the range of 0.5 to about 1.0. . The high Dk liquid insulation provides labor savings in transformer design and operation. Aspects of the present invention that the dielectric fluid of the present invention can be formulated so that the dielectric constant value of the dielectric fluid of the present invention is closer to a solid insulating material such as cellulose, Nomex® or cellulose-Nomex® blend. It is.

  In another embodiment of the invention, the synthetic polyol ester comprises a glycerol oligomer ester, wherein the ester is a product obtained after esterification of the glycerol oligomer or oligomer mixture thereof. Glycerol oligomers include for the purposes of the present invention diglycerol to hexaglycerol oligomers and mixtures thereof. One advantage of using di-, tri-, or higher glycerol oligomer esters (GOE) in the practice of this invention is that glycerol oligomer esters typically have a dielectric constant of about 3.1 over natural oils. Has a high dielectric constant (about 4.5). Therefore, it is an aspect of the present invention to provide a method for controlling or adjusting the dielectric constant of a dielectric fluid to a range where the fluid dielectric constant more closely matches that of solid insulating paper. The method includes mixing the GOE with a natural ester or other renewable source synthetic polyol ester or mineral oil, or a blend containing mineral oil. For the purposes of the present invention, the glycerol oligomer comprises 2 to 6 glycerol repeat units, preferably 2 or 3 glycerol repeat units, or mixtures thereof and has 4 to 8 hydroxyls. Preferably at least about 90% of the oligomer is diglycerol.

  In yet another embodiment, a blend of renewable source synthetic esters and mineral oil may be effective as a dielectric coolant. In certain embodiments, the mineral oil is a severely hydrotreated naphthenic oil or a severely hydrotreated isoparaffinic oil. “Severely hydrotreated” means that the mineral oil is (1) hydrocracked, (2) hydroisomerized, and (3) as described, for example, in US Pat. No. 6,790,386. ) Means to be subjected to a sequential process of hydrogenation. Mineral oil treated in this manner can be biodegradable. However, the blends of the present invention with mineral oils have aromatic gas generating additives to provide a dielectric fluid having a low or negative gassing tendency, ie, a gassing tendency of less than about +30 to about −30 μL / min. Need. The blend comprises at least about 25 wt%, or alternatively from about 50 wt% to about 99 wt%, or from about 75 to about 95 wt% mineral oil, the renewable source composition of the present invention and a high monounsaturated ester content. From about 1 to about 75% by weight of the renewable source composition of the present invention. Mineral oils are (1) natural oils or blends thereof, particularly those having a significant monounsaturated ester content, (2) synthetic polyol esters or blends thereof, or (3) natural oils as in (1) and (2 ) And any of the blends containing both synthetic oils. Mineral oil blends as described herein have improved oxidative stability, low pour point, low viscosity, low viscosity index and improved while potentially increasing cost effectiveness with non-mineral oil fluids. It can be formulated according to the method of the present invention to provide a blended insulating fluid having a desirable balance of properties such as gassing tendency. The blend of the present invention is a standard set to provide a fluid that is stable and effective in use as a dielectric fluid, but does not require a gas generant additive to meet the gas generative propensity criteria. Formulated to satisfy.

  Additives for improving the performance of the coolant described herein may be optional. In certain embodiments, the observed improvement is surprising given the absence of additives. For example, oxidative stability can be improved to an unexpected degree without the use of antioxidants by blending synthetic esters with natural oils. However, if necessary, additives can be used. Depending on the composition of the blend, the blended composition of the present invention may comprise an antioxidant, a pour point depressant, an antigassing aromatic agent, a metal passivator, an antifoam agent, and an electrostatic charge tendency depressant. It may not be necessary to add synthetic additives such as.

  For example, in one embodiment, the blended composition of the present invention comprises from about 51% to about 99% by weight of the blend of a renewable source saturated synthetic polyol ester as a major component and from about 1% by weight of the blend to About 49% by weight of natural oil as a minor component for use in an open respiration transformer, with additives added.

  In another embodiment, the blended composition of the present invention is used in a hermetic transformer with a renewable source synthetic polyol ester as a minor component from about 1% by weight of the blend to about 49% by weight of the blend. From about 51 to about 99% by weight of the blend of natural base esters as the main component, with additives added.

  In another embodiment, the blended composition of the present invention comprises from about 51% to about 99% by weight of the blend, either naphthenic or isoparaffinic mineral oil as the main component, and from about 1% to about 99% by weight of the blend. 49% by weight of minor components, including a blend of renewable source synthetic saturated polyol esters and high oleic acid based triglycerides for use in power transformers, with additives added.

  Where antioxidants are included, high molecular weight phenolic antioxidants such as IRGANOX® 259 can be included, or TBHQ can be added for blends containing mineral oil or BHT Can be added. It may be advantageous to match a specific antioxidant with a particular major component of the fluid blend for optimal results. For example, blends containing synthetic esters as the main component of the blend are clearly better stabilized by antioxidants such as IRGANOX® 259 than by TBHQ. Blends containing natural esters as the main component are clearly better stabilized by TBHQ. Surprisingly, the blend of synthetic antioxidants was not as effective in improving the stability of the blended fluid composition as when the appropriate major components of the fluid blend were matched to the individual antioxidants.

  For dielectric fluids categorized as bio-based fluids, the United States Department of Agriculture (USDA) states that 66% renewable carbon or bio-based carbon content and natural for synthetic polyol esters For esters, a minimum standard of 95% renewable or biobased carbon content is established. The composition of the present invention has a renewable carbon or biobased carbon content of greater than 66%.

  In one embodiment, the blend composition of the present invention comprises an insulating paper selected from regular kraft paper, thermally upgraded cellulose paper, Nomex® paper, and cellulose / Nomex® blended paper. Useful for liquid transformers.

Summary The following raw materials were used in the examples.
The following fatty acids: palmitic acid (6.5 wt%), stearic acid (4.15 wt%), oleic acid (73.9 wt%), linoleic acid (8.77 wt%), and linolenic acid (2. Purified, bleached and deodorized high oleic soybean oil (RBD HOS oil) containing 94% by weight) triglycerides was obtained according to US Pat. No. 5,981,781.
Commercial soybean oil was obtained from Homestead Farms, Des Moines, IA.
Type II mineral oil with inhibitor, Universal N 61B, was obtained from ExxonMobil, Fairfax, VA.
A mineral oil without inhibitor, Nytro Taurus, was obtained from Nynas.
A blend of capryl and caprin (C8 / C10) fatty acids was obtained from Acme Hardesty. Heptanoic acid (C7) was obtained from Alfa Aesar (Heysham, England).
Lauric acid (> 98%) was used as received from Alfa Aesar.
Glycerol and trimethylolpropane (97%) were obtained from Aldrich Company (Milwaukee, WI).
Diglycerol was obtained from Solvay Performance Chemicals (Houston, TX).
Glyceryl tricaprylate-caprate (GTCC) is sold under the trade name Grindsted® MCT 60 X by DuPont. Trimethylolpropane tricaprylate-Caprate (TTCC) (WAGLINOL 3/13480) and pentaerythritol tetracaprylate-Caprate (PTCC) (WAGLINOL 4/13680) are available from Industrial Quimica Lasem, S.A. A. Obtained from Barcelona, Spain.
Silica gel was obtained from EMD Chemicals.
Activated carbon (PWA powder) was obtained from Calgon.
Basic alumina (G250) was obtained from BASF Company.

  The iodine value of the natural ester was determined by quantifying the unsaturation using proton NMR.

  Turbidity measurements on the compositions were performed using a turbidimetric turbidimeter (MicroTPW, Model 20000, Scientific Inc. FT. Myers, FL) that monitors the light reflected from the suspended particles. The NTU (Nephelometric Turbidity Unit) number represents the transparency of the solution; the lower number represents the higher transparency.

  The color was measured as an APHA value (platinum-cobalt system) according to ASTM D-1209.

Comparative Examples 1-3
Commercially available synthetic saturated polyol esters (GTCC, TTCC and PTCC) were evaluated to determine their suitability as base stocks for use in transformers. These esters contain the same mixture of (C8 / C10) fatty acids but differ only in the identity of the polyols used to make the esters. The measured properties of these polyol esters are reported in Table 1.

  From the data shown in Table 1, none of the commercially available polyol ester fluids tested were desirable for dielectric fluids (for low viscosity, high dielectric constant, low pour point, flash point and burn point). (K class standard, low power factor, low gas generation tendency) combination. All three polyol esters exceeded the upper limit of positive gas evolution tendency of +30 μL / min as defined by ASTM D3487-00 and are therefore not suitable as a dielectric fluid for the practice of the present invention.

Comparative Example 4
Preparation of Trimethylolpropane Tricaprylate-Caprate (TTCC) Into a 1 L three-necked round bottom flask equipped with a Dean-Stark trap and condenser, magnetic stirrer, nitrogen inlet, thermocouple and external heating mantle, 1-trimethylolpropane (131.4 g, 0.98 mol) and a 60/40 C8 / C10 fatty acid blend (499.5 g, 3.21 mol) were added. The mixture was heated to 225 ° C. with stirring at 400 rpm and a nitrogen atmosphere. The pressure was reduced to 75 mmHg by approximately 100 mmHg over 5 hours and held for an additional 6 hours, during which time distillate was collected in the trap.

  The Dean-Stark trap was replaced with a condenser equipped with a collection flask and the nitrogen inlet to the headspace was replaced with a nitrogen purge. The reaction was heated to 225 ° C. at 5 mm Hg pressure with rapid nitrogen purge and stirring at 400 rpm, and the distillate was collected over 7 hours to produce trimethylolpropane tricaprylate-caprate (523.5 g, 98.3 %).

Example 1
Production of trimethylolpropane tricaprylate-caprate-laurate In a 1 L three-necked round bottom flask equipped with a Dean-Stark trap and condenser, magnetic stirrer, nitrogen inlet, thermocouple and external heating mantle, 1,1,1 -Trimethylolpropane (104.2 g, 0.8 mol), 60/40 C8 / C10 fatty acid blend (332.0 g, 2.1 mol) and C12 fatty acid (83.0 g, 0.4 mol) were added. . The mixture was heated to 225 ° C. with stirring at 400 rpm and a nitrogen atmosphere. The pressure was reduced to 75 mmHg by approximately 100 mmHg over 5 hours and held for an additional 6 hours, during which time distillate was collected in the trap. The Dean-Stark trap was replaced with a condenser equipped with a collection flask and the nitrogen inlet to the headspace was replaced with a nitrogen purge. The reaction was heated to 225 ° C. at 5 mm Hg pressure with a fast nitrogen purge and with stirring at 400 rpm, and the distillate was collected over 7 hours to produce the trimethylolpropane triester (429.9 g, 97.9%).

  The properties of this fluid were measured along with the same properties for a laboratory synthesized ester fluid from a C8 / C10 fatty acid blend (Comparative Example 4) and are provided in Table 2.

Example 2
Purification of Commercial Synthetic Polyol Ester (TTCC) Trimethylolpropane tricaprylate / caprate (3005.9 g, Waglinol 3/13480) was added to a 5 L 3-neck round bottom flask equipped with a nitrogen purge, thermocouple, heater and magnetic stirrer. , Activated carbon (30.0 g, Calgon, PWA powder) and basic alumina (30.0 g, BASF, G250) were added. The system was heated to 130 ° C. with nitrogen passing through the headspace while stirring at 250 rpm for 90 minutes. Allow the fluid to cool and coarsely layer 1/2 inch Celite 545 (approximately 30 g, EDM) on 1/2 inch silica gel 60 (approximately 30 g, Alfa Aesar) using reduced pressure and nitrogen atmosphere. Passed through a fritted funnel to produce purified trimethylolpropane triester (2793.0 g, 92.9%). The properties of the purified triester compared to the as received commercial ester are reported in Table 3.

  Purification of the commercial product as received improved the quality of the product and its electrical properties. A significant power factor decrease and volume resistivity increase was observed for the purified product. The oxidative stability of the fluid was improved by the purification procedure.

Example 3
Preparation of diglycerol ester or glycerol oligomer ester (GOE) A 22 L reaction flask was equipped with an overhead stirrer, thermocouple, inlet for blowing nitrogen into the liquid, and a distillation column and condenser. The flask is flushed with nitrogen and diglycerol (3.1 Kg), heptanoic acid (1.2 Kg), octanoic acid (6.8 Kg), and decanoic acid (4.0 Kg) are charged into the flask and nitrogen is added to the mixture. Infused into. The reaction was heated slowly to 150 ° C., heated for 4 hours, then heated at 150 ° C. to 224 ° C. for another 11 hours. A total of about 1.25 L of water was collected. After cooling the reaction mixture to room temperature, the distillation column was removed and the distillation head was connected directly to the flask. The reaction mixture was distilled at 1 torr pressure until the pot temperature reached 217 ° C., at which temperature unreacted acid (694 g) was recovered. After cooling to room temperature, the reaction mixture was diluted with hexane (7 L) and transferred to a 30 L bottom valved resin kettle. The material was then washed with a mixture of saturated NaCl (1 L), NaOH solution (10%, 2 L) and DI water (3 L), NaOH (10%, 3 × 2 L), and DI water (5 × 3 L). . The hexane solvent was removed on a rotary evaporator to form a crude product. The crude product was passed through thin (3/4 inch) silica gel and the filtrate was dried in vacuo at 110 ° C. for 1 hour to give an oil (11.8 Kg). The oil sample was treated with activated carbon (2%) at 110 ° C. under 1 torr vacuum for 1 hour. After cooling to room temperature, the activated carbon was removed by filtration through a silica gel bed to give an almost colorless oil. About 3.2 L of filtrate was passed through a 10 inch silica gel column and about 3 L of eluent was collected. FAME analysis showed the following contents: heptanoic acid (8.6%), octanoic acid (55.2%), decanoic acid (35.9%), and lauric acid (0.2%).

FAME analysis was performed as described below.
FAME profile test

Stock Preparation For this test, several stock solutions were first prepared.
Analytical oil: 30 mg / ml in toluene.
Cool the stock acid-methanol (50 mL) and slowly add acetyl chloride (5 mL).
Stock salt-1M aqueous sodium chloride.
Stock internal standard-5 mg / mL in toluene, internal standard is triglyceride, which is less than 100% conversion of all oils to methyl esters because the internal standard reaction rate should be close to that of the oil Will react with the oil sample to form methyl esters there. An internal standard that is tripentadecanoin (C15: 0) is Nu-Chek Prep, Inc. Purchased from catalog code T-145.

Sample Experiment In a 20 mL vial with a small stir bar, combine stock oil (100 μL), stock internal standard (100 μL), and stock acid (1 mL). The vial is heated to 80 ° C. with stirring for 1 hour; as soon as it cools, the vial is opened and stock aqueous sodium chloride (1 mL) and hexane (300 μL) are added. Mix well and pipette the entire solution into a small vial (approximately 3 mL) to allow easier layer separation. About 300 μL of organic liquid (top layer) is pipetted into a GC vial with an insert.

GC Method Specification Established method to confirm retention time using a GLC-461 reference standard mixture of 32 different methyl esters C4: 0 to C24: 1. Column: Supelco 24152 Omegawax 320 30 m long, diameter 320 μm, film thickness 0.30 μm. Oven lamp: initial temperature 160 ° C. remains for 5 minutes, then increases to 220 ° C. at 2 ° C./minute, remains for 10 minutes, then increases to 240 ° C. at 20 ° C./minute, remains for 5 minutes is there. The carrier gas is helium. Inlet pressure 250 ° C. at 11.55 psi; split ratio 50: 1 split flow rate: 77.8 mL / min; total flow rate: 82.3 mL / min. Initial flow rate 1.6 ml / min at 11.56 psi. Flame ionization detector used set at 270 ° C., hydrogen flow rate 35 mL / min; air flow rate 400 mL / min; mode constant column + makeup flow; combined flow 32.0, makeup gas is helium.

Calculation data analysis explanation example
Calculate the methyl ester relative weight percent for the methyl ester from the oil. Three replicates are performed for each of the currently processed samples using the same stock oil solution. From each of these samples, a FAME profile is established and the average for the three replicates is calculated for each methyl ester present with standard deviation.

Fluid Oxidative Stability Comparative Examples 5-8: Two neat synthetic polyol ester fluids (Comparative Examples 5 and 6) in the absence of added antioxidants and high oleic soybean oil (HOS) and commercial soybean oil (Soy) ) And other natural ester fluids (Comparative Examples 7 and 8) were evaluated by the oil stability index (OSI). The OSI measurement was performed at 130 ° C. using an Oxidative Stability Instrument (Omion, Inc, Rockland, Mass.) Using the official AOCS method (AOCS Method Cd 12b-97). Samples were tested in duplicate, and the average value for each fluid is shown in Table 5.

  Examples 4-7: Blends were prepared by mixing the purified TTCC fluid of Example 2 with high oleic soybean oil in a weight ratio ranging from 10-50% by weight.

  Example 8: A separate blend was prepared by separately mixing 90 wt% of the GOE of Example 3 with 10 wt% high oleic soybean oil.

  Example 9: A blend was prepared by mixing 90 wt% GOE of Example 3 with 10 wt% commercial soybean oil.

  The oxidative stability of the blend in the absence of synthetic antioxidants was evaluated by OSI and compared to neat fluid in Table 5. The amount of unsaturation in high oleic soybean oil and commercial soybean oil is determined from NMR, and the unsaturation in the blend is calculated based on the amount of natural ester present and is reported as the iodine number.

  Saturated polyol esters demonstrated a higher degree of OSI induction time compared to natural esters, and genetically modified high oleic soybean oil had a longer induction time when compared to conventional commercial soybean oil.

  The effect of high oleic soybean oil content in the blend consisting of TTCC on OSI induction time is shown in FIG. The highest oxidative stability of the fluid blend is reached with about 10 wt% HOS oil, and the blend fluid stability gradually decreases with increasing HOS oil, and the stability of neat polyol esters with about 50 wt% HOS oil. Reached sex.

Gas evolution tendency of fluids The gas evolution tendency of neat high oleic soybean oil and commercial soybean oil (Comparative Examples 7 and 8) and two synthetic polyol ester fluids (Comparative Examples 2 and 6) under electrical stress is determined by ASTM. Tested in the Double Laboratories according to D2300 and their values are reported in Table 6. Under electrical stress, natural vegetable oils have a tendency to gas absorption (negative gas generation), and synthetic saturated polyol esters have a tendency to outgas (positive gas generation).

Examples 10-12
As shown in Table 6, blends were prepared by mixing renewable source synthetic saturated polyol ester fluids with natural esters without the addition of any additives, and testing the gassing tendency of these blends, Compared to neat ester fluid.

  Addition of natural ester fluids such as high oleic soybean (HOS) oil or commercial soybean oil (Soy) to saturated TMP based triesters (TTCC) or glycerol oligomer based esters (GOE) as shown in Table 6 Unexpectedly changed the properties of the synthetic saturated fluid from outgassing to gas absorption (Comparative Examples 2 and 6 and Examples 10-12).

  The effect of synthetic antioxidant additives on the gas evolution tendency of neat and blend fluids was studied. As shown in Table 7, the additive had no effect on either the negative gassing propensity fluid (Comparative Examples 8 and 9) or the positive gassing propensity fluid (Comparative Example 2). Surprisingly, the additive showed a notable effect on the blend. Non-linear effects of a reduced gassing tendency were also evident for the blends (Examples 13, 14, 16).

  When the addition was reversed, i.e., when a small amount of saturated polyol ester was added to the natural ester, the negative gassing tendency rate decreased slightly from -39.1 to -36.2 (Example 18), The effect is not as significant as the addition of natural esters to polyol esters.

Mixed ester and mineral oil blends:
The gas evolution tendency of mineral oil with inhibitor, Univolt N61B (Comparative Example 10) and mineral oil without inhibitor, Nytro Taurus (Comparative Example 11) was tested and found to be within acceptable limits. Nevertheless, the gassing tendency of these fluids is determined by the addition of high oleic soybean oil (Examples 22 and 23) or blends of synthetic esters and high oleic soybean oil without the addition of antigassing additives (Examples 22 and 23). Improved by either addition of Example 24). Again, a reduced positive gassing trend was observed for the blend fluid in the presence of antioxidant additives, as shown in Example 25 of Table 8.

  Therefore, the fluid of the present invention is tailored to have good chemical stability with respect to oxidative and electrical stress by blending a synthetic polyol ester fluid with an appropriate amount of natural ester, especially high oleic soybean oil. can do.

Synthetic polyol ester and natural ester blend of renewable sources Example 26
An inhibitor-free blend fluid was formulated by mixing only 90 wt% TTCC and 10 wt% HOS oil, and this fluid was an aromatic gas generation additive, synthetic antioxidant, passive Essentially free of synthetic additives such as agents and pour point depressants. The properties of the blended fluid are shown in Table 9.

Examples 27-28
A fluid formulation with inhibitors was also prepared by blending a renewable source synthetic polyol ester (purified TTCC) as the main basestock and a natural ester (HOS) as a minor (additive) component. The resulting fluid has excellent balanced properties as shown in Table 9 and is suitable as an insulating fluid for use in transformers, particularly in open breathing power transformers.

  The data in Table 9 shows the flexibility of changing the properties of fluids by blending renewable source synthetic esters with natural esters, thereby changing their performance as dielectric fluids.

Comparative Example 12
A commercially available dielectric fluid based on natural ester oil was tested and the properties of this fluid are reported in Table 10. As the data shows, this fluid did not meet the desired properties of viscosity, pour point, oxidation stability and gassing tendency.

Example 29
A fluid formulation with an inhibitor of improved properties, natural ester soybean oil as the main component, a mixture of two synthetic polyol esters (TTCC and GTCC) as minor components, 0.2% antioxidant and Prepared by blending 1.0% pour point depressant. As shown in Table 10, this fluid had excellent oxidative stability, low gas generation tendency, excellent low temperature fluid properties compared to commercial fluids, and met the K fire safety class. Again, it was found that oxidatively stable fluids also have a low tendency to outgas. This fluid is useful in both sealed and open distribution and power transformers.

  The formulations of the present invention are not limited to the described compositions, and further optimization of the formulations can be performed to improve fluid performance.

Example 30
Inhibitor-free dielectric fluid, severely hydrogenated inhibitor-free insulating material oil (80 wt%, Nytro Taurus), 16 wt% polyol ester (trimethylolpropane tricaprylate / caprate), and 4 wt% Of high oleic soybean oil. No synthetic additives were added to the fluid. The properties of the dielectric fluid blend without inhibitor were tested and compared with neat mineral oil (Comparative Example 13) in Table 11.

  As can be seen in Table 11, the addition of 20 wt% mixed ester to mineral oil did not significantly change the properties of the mineral oil. Nevertheless, the addition of a polar, stable ester fluid blend to a non-polar mineral oil ensures the reliability, sustainability of power transformers due to the excellent stability of the solid insulator in the dielectric fluid of the present invention. Potential and may increase lifetime. Upon aging, this fluid may have more resistance to moisture and thermal and electrical stress when compared to neat mineral oil, keeping the solid insulating paper dry and lower sludge Maintains formation and lower acid generation. Furthermore, the biodegradability of this fluid will be higher than that of mineral oil.

  Table 12 reports the oxidative stability of ester blends in the presence of antioxidants and compares to neat ester fluids.

Example 31
Diglyceride Impurities and Power Factor (Pf) Reduction in Commercial MCT60X Samples 1H NMR analysis on an “as received” MCT60X sample indicated it contained approximately 3800 ppm diglyceride. After silica gel treatment (see Example 2), purified MCT60X showed that its diglyceride impurity decreased below the detection limit based on 1H NMR analysis. Therefore, the Pf of the sample was significantly reduced (see Table 13).

  Another aspect of the present invention may be as follows.
[1] A composition useful as a dielectric fluid, wherein the composition comprises (i) about 50% to about 99% by weight mineral oil and (ii) about 1% by weight, based on the weight of the fluid. About 50% by weight of the first blend, the first blend comprising:
  (1) about 1 to about 99% by weight of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a polyhydroxyl having at least 3 hydroxyl groups A fully esterified reaction product obtained from a reaction mixture comprising a component and (ii) a mixture of saturated linear carboxyl derivatives wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms. A polyol ester; and
  (2) Triacylglycerol natural oils obtained from natural sources consisting essentially of about 1 wt% to about 99 wt% of long chain fatty acid esters having monounsaturation of about 24 mol% to less than about 75 mol%
Consists essentially of;
  The dielectric fluid composition comprises
  (A) having a reduced gassing tendency without the addition of an aromatic gassing prevention additive compared to the gassing tendency of component (1) of the blend;
  (B) A composition having a pour point as measured by ASTM D-97 below about -20 ° C.
[2] The composition according to [1], wherein the first blend contains about 10 to about 80% by weight of triacylglycerol.
[3] The composition according to [2], wherein the first blend contains about 10 to about 70% by weight of triacylglycerol.
[4] The composition according to [3], wherein the first blend contains about 30 to about 40% by weight of triacylglycerol.
[5] The composition of [1], wherein the synthetic polyol ester comprises an unreacted or partially reacted polyol having an acid value of less than about 0.07 mg KOH / gram and less than about 3000 ppm.
[6] A composition useful as a dielectric fluid, the composition comprising: (i) about 50 wt% to about 99 wt% mineral oil and (ii) about 1 wt% based on the weight of the fluid About 50% by weight of the first blend, the first blend comprising:
  (1) about 1 to about 99% by weight of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a polyhydroxyl having at least 3 hydroxyl groups A fully esterified reaction product obtained from a reaction mixture comprising a component and (ii) a mixture of saturated linear carboxyl derivatives wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms. A polyol ester; and
  (2) about 1% to about 99% by weight of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having greater than about 75 mol% monounsaturation
Essentially consists of
  The first blend is without an inhibitor, and
  A composition wherein the dielectric fluid composition has a reduced tendency to gas generation without the addition of an aromatic gas generation additive as compared to the gas evolution tendency of component (1) of the dielectric fluid composition.
[7] The polyhydroxyl component is selected from the group consisting of glycerol, trimethylolpropane (TMP), trimethyloloethane (TME), pentaerythritol (PE), ditrimethylolpropane, dipentaerythritol, and mixtures thereof. The composition according to any one of [1] to [6], which is selected.
[8] A composition useful as a dielectric fluid, wherein the composition comprises (i) about 50 wt% to about 99 wt% mineral oil, based on the weight of the fluid; (ii) about 1 wt% % To about 50% by weight of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having monounsaturation greater than about 75 mol%; (iii) optional additives; A blend comprising
  A composition in which the blend has a reduced gassing tendency compared to the gassing tendency of component (i) without the additive aromatic gas generation prevention additive.
[9] A composition useful as a dielectric fluid, wherein the composition comprises (i) about 25% to about 99% by weight mineral oil and (ii) about 1% to About 75% by weight of a first blend, said first blend comprising:
  (1) about 1 to about 99 wt% of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a glycerol oligomer having at least 4 hydroxyl groups A fully esterified product obtained from a reaction mixture consisting essentially of: and (ii) a mixture of saturated linear carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms Polyol ester which is a reaction product;
  (2) about 1% to about 99% by weight of a triacylglycerol natural oil obtained from natural sources consisting essentially of long chain fatty acid esters; and
  (3) Optional additives
Including
  The dielectric fluid composition comprises
  (A) having a reduced gassing tendency without the addition of an aromatic gassing prevention additive compared to the gassing tendency of component (1) of the blend;
  (B) having a dielectric constant in the range of about 2.5 to less than about 4.5;
  (C) Contains less than 3000 ppm unreacted or partially reacted polyol
Composition.
[10] A composition useful as a dielectric fluid, wherein the composition comprises (i) about 50 wt% to about 99 wt% mineral oil and (ii) about 1 wt% based on the weight of the fluid. About 50% by weight of the first blend, the first blend comprising:
  (1) A renewable source synthetic polyol ester having from about 1 to about 99% by weight of less than 3000 ppm unreacted or partially reacted polyol and further comprising a synthetic antioxidant, said polyol ester Essentially from a mixture of saturated linear carboxyl derivatives, wherein (i) a glycerol oligomer component having at least 4 hydroxyl groups; and (ii) at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms A polyol ester which is a fully esterified reaction product obtained from the resulting reaction mixture;
  (2) about 1% to about 99% by weight of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester; and
  (3) Optional additives
Essentially consists of
  A composition wherein the dielectric fluid composition has a reduced tendency to gas generation without the addition of an aromatic gas generation additive as compared to the gas evolution tendency of component (1) of the dielectric fluid composition.
[11] The composition according to any one of [1] to [10], wherein the mineral oil is a severely hydrotreated isoparaffinic oil or a severely hydrotreated naphthenic oil.
[12] The composition comprises
  (A) contacting the synthetic polyol ester or blend thereof with activated carbon and basic alumina at a temperature of about 50 ° C to about 150 ° C; and
  (B) filtering the mixture.
It is a composition as described in any one of said [1]-[11] processed by, Comprising:
The composition thus obtained is
  (1) having a power factor as measured by ASTM D-924 at 25 ° C. of less than about 0.5%;
  (2) having a dielectric constant (Dk) in the range of about 2.5 to about 4.5;
  (3) has a pour point, as measured by ASTM D-97, below about -20 ° C.
Composition.
[13] The composition according to any one of [1] to [12], wherein the pour point is about −40 ° C. or lower.
[14] An electric device including the dielectric fluid according to any one of [1] to [13].
[15] A method for preparing a dielectric fluid composition, the method comprising:
  (A) (1) Synthetic saturated polyol ester of a renewable source, wherein the polyol ester comprises (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) at least about 95 mol% of the carboxyl derivative. A polyol ester which is a fully esterified reaction product obtained from a reaction mixture comprising a mixture of saturated carboxyl derivatives containing 6 to 12 carbon atoms;
(2) a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having from about 24 mol% to less than about 75 mol% monounsaturated ester;
(3) a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having about 75 mol% or more of a monounsaturated ester; and
(4) Mineral oil
Blending two or more ingredients selected from the group consisting of
Obtaining at least about 95 to about 100 weight percent of a dielectric fluid blend composition;
  (B) The following characteristics:
(I) combustion point, (ii) power factor, (iii) volume resistivity, (iv) gas evolution tendency; and (v) pour point.
Measuring at least one of:
  (C) Adjust the percentages of the ingredients as necessary to obtain the following properties: a combustion point of at least 300 ° C; a pour point of less than about -20 ° C; a viscosity of less than about 30 centistokes at 40 ° C; or ASTM D- Obtaining a blend having at least one gassing tendency ranging from about −30 μL / min to about +30 μL / min as measured according to 2300 and free of any added aromatic gassing prevention additives included;
Including methods.

Claims (15)

A composition useful as a dielectric fluid comprising: (i) from about 50 wt% to about 99 wt% mineral oil and (ii) from about 1 wt% to about 50, based on the weight of the fluid. And a first blend, wherein the first blend comprises:
(1) about 1 to about 99% by weight of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a polyhydroxyl having at least 3 hydroxyl groups A fully esterified reaction product obtained from a reaction mixture comprising a component and (ii) a mixture of saturated linear carboxyl derivatives wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms. A polyol ester; and (2) from a natural source consisting essentially of from about 1% to about 99% by weight of a long chain fatty acid ester having from about 24 mol% to less than about 75 mol% monounsaturation Consisting essentially of a triacylglycerol natural oil;
The dielectric fluid composition comprises
(A) having a reduced gassing tendency without the addition of an aromatic gassing prevention additive compared to the gassing tendency of component (1) of the blend;
(B) A composition having a pour point as measured by ASTM D-97 below about -20 ° C.   The composition of claim 1, wherein the first blend comprises from about 10 to about 80 wt% triacylglycerol.   The composition of claim 2, wherein the first blend comprises from about 10 to about 70 weight percent triacylglycerol.   4. The composition of claim 3, wherein the first blend comprises about 30 to about 40 weight percent triacylglycerol.   The composition of claim 1, wherein the synthetic polyol ester comprises an unreacted or partially reacted polyol having an acid number of less than about 0.07 mg KOH / gram and less than about 3000 ppm. A composition useful as a dielectric fluid comprising: (i) from about 50 wt% to about 99 wt% mineral oil and (ii) from about 1 wt% to about 50, based on the weight of the fluid. And a first blend, wherein the first blend comprises:
(1) about 1 to about 99% by weight of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a polyhydroxyl having at least 3 hydroxyl groups A fully esterified reaction product obtained from a reaction mixture comprising a component and (ii) a mixture of saturated linear carboxyl derivatives wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms. A polyol ester; and (2) a triacylglycerol natural oil obtained from a natural source consisting essentially of from about 1% to about 99% by weight of a long chain fatty acid ester having greater than about 75 mole% monounsaturation Essentially consists of
The first blend is without an inhibitor, and the dielectric fluid composition has no addition of an aromatic gas generation additive as compared to the gassing tendency of component (1) of the dielectric fluid composition. And a composition having a reduced tendency to generate gas.   The polyhydroxyl component is selected from the group consisting of glycerol, trimethylolpropane (TMP), trimethyloloethane (TME), pentaerythritol (PE), ditrimethylolpropane, dipentaerythritol and mixtures thereof. The composition as described in any one of Claims 1-6. A composition useful as a dielectric fluid comprising: (i) from about 50 wt% to about 99 wt% mineral oil, based on the weight of the fluid; (ii) from about 1 wt% to about A blend comprising 50% by weight of a triacylglycerol natural oil derived from a natural source consisting essentially of a long chain fatty acid ester having greater than about 75 mol% monounsaturation; and (iii) optional additives Is;
A composition in which the blend has a reduced gassing tendency compared to the gassing tendency of component (i) without the additive aromatic gas generation prevention additive. A composition useful as a dielectric fluid comprising: (i) from about 25% to about 99% by weight mineral oil and (ii) from about 1% to about 75% by weight, based on the weight of the blend. % Of the first blend, the first blend comprising:
(1) about 1 to about 99 wt% of a synthetic polyol ester of renewable source, based on the weight of the first blend, wherein the polyol ester is (i) a glycerol oligomer having at least 4 hydroxyl groups A fully esterified product obtained from a reaction mixture consisting essentially of: and (ii) a mixture of saturated linear carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms Polyol ester which is a reaction product;
(2) about 1% to about 99% by weight of a triacylglycerol natural oil obtained from natural sources consisting essentially of long chain fatty acid esters; and (3) optionally containing additives;
The dielectric fluid composition comprises
(A) having a reduced gassing tendency without the addition of an aromatic gassing prevention additive compared to the gassing tendency of component (1) of the blend;
(B) having a dielectric constant in the range of about 2.5 to less than about 4.5;
(C) A composition comprising less than 3000 ppm unreacted or partially reacted polyol. A composition useful as a dielectric fluid comprising: (i) from about 50 wt% to about 99 wt% mineral oil and (ii) from about 1 wt% to about 50, based on the weight of the fluid. And a first blend, wherein the first blend comprises:
(1) A renewable source synthetic polyol ester having from about 1 to about 99% by weight of less than 3000 ppm unreacted or partially reacted polyol and further comprising a synthetic antioxidant, said polyol ester Essentially from a mixture of saturated linear carboxyl derivatives, wherein (i) a glycerol oligomer component having at least 4 hydroxyl groups; and (ii) at least about 95 mol% of the carboxyl derivatives contain 6 to 12 carbon atoms A polyol ester which is a fully esterified reaction product obtained from the resulting reaction mixture;
(2) about 1% to about 99% by weight of a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester; and (3) consisting essentially of optional additives;
A composition wherein the dielectric fluid composition has a reduced tendency to gas generation without the addition of an aromatic gas generation additive as compared to the gas evolution tendency of component (1) of the dielectric fluid composition.   The composition according to any one of claims 1 to 10, wherein the mineral oil is a severely hydrotreated isoparaffinic oil or a severely hydrotreated naphthenic oil. The composition is
2. Treated by contacting (a) the synthetic polyol ester or blend thereof with activated carbon and basic alumina at a temperature of about 50 ° C. to about 150 ° C., and (b) filtering the mixture. 11. The composition according to any one of 11
The composition thus obtained is
(1) having a power factor as measured by ASTM D-924 at 25 ° C. of less than about 0.5%;
(2) having a dielectric constant (Dk) in the range of about 2.5 to about 4.5;
(3) A composition having a pour point, as measured by ASTM D-97, less than about -20 ° C.   The composition according to any one of claims 1 to 12, wherein the pour point is about -40 ° C or lower.   An electrical device comprising the dielectric fluid according to claim 1. A method of preparing a dielectric fluid composition, the method comprising:
(A) (1) Synthetic saturated polyol ester of a renewable source, wherein the polyol ester comprises (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) at least about 95 mol% of the carboxyl derivative. A polyol ester which is a fully esterified reaction product obtained from a reaction mixture comprising a mixture of saturated carboxyl derivatives containing 6 to 12 carbon atoms;
(2) a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having from about 24 mol% to less than about 75 mol% monounsaturated ester;
(3) a triacylglycerol natural oil obtained from a natural source consisting essentially of a long chain fatty acid ester having about 75 mol% or more of a monounsaturated ester; and (4) two selected from the group consisting of mineral oils Blending the above components to obtain a dielectric fluid blend composition of at least about 95 to about 100 weight percent;
(B) The following characteristics:
Measuring at least one of (i) a combustion point, (ii) power factor, (iii) volume resistivity, (iv) gas evolution tendency; and (v) a pour point;
(C) Adjust the percentages of the ingredients as necessary to obtain the following properties: a combustion point of at least 300 ° C; a pour point of less than about -20 ° C; a viscosity of less than about 30 centistokes at 40 ° C; or ASTM D- Obtaining a blend having at least one gassing tendency ranging from about −30 μL / min to about +30 μL / min as measured according to 2300 and free of any added aromatic gassing prevention additives included; Including methods.