Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/20—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils

Definitions

• Dielectric Fluids Comprising Polyol Esters, Methods for Preparing M ixtu res of Polyol Esters, and Electrical Apparatuses Comprising
• Dielectric fluids comprising a mixture of polyol esters are provided, as are processes for preparing the mixtures of polyol esters, and electrical apparatuses comprising the dielectric fluids.
• dielectric fluids which are easily available and generally cost effective. Examples are mineral oil, silicone fluid, and synthetic hydrocarbon oils used in transformers, power cables and capacitors. Such fluids must be electrically insulating, resistant to degradation, and be able to act as a heat transfer medium so that heat generated in an electrical apparatus can be dissipated to the surrou nding environment.
• flu ids also have several deficiencies. Many of these flu ids are not considered to be biodegradable in a reasonable time frame. Some have electrical properties which render them less than optimal. In recent years regu latory agencies have become increasingly concerned about oil spills which can contaminate the ground soil and other areas. A biodegradable dielectric fluid would be desirable for electrical apparatus such as transformers used in populated or ecologically sensitive areas.
• United States Patent No. 6, 160, 144 relates to synthetic esters of alcohols and fatty acid mixtures contain ing at least 85% by weight of oleic acid and 0.5 to 2.5% by weight of stearic acid and to their use as lubricants and hydraulic oils and for cosmetic purposes.
• United States Patent No. 6,278,006 discloses oils containing a triacylglycerol polyol ester and a non-glycerol polyol ester, as well of methods of making such oils and methods for improving lubrication properties of a vegetable oil.
• United States Patent No. 7,048,875 relates to a high oleic oil composition useful as an electrical insulation fluid, to electrical insulation fluid compositions, and electrical apparatuses which comprise the same. Disclosed are the electrical properties of h igh oleic acid triglyceride compositions that comprise fatty acid components of at least 75% oleic acid, less than 10% diunsaturated fatty acid component; less than 3% triu nsatu rated fatty acid component; and less than 8% satu rated fatty acid component.
• the electrical insulation flu id comprises fatty acid components of: at least 75% oleic acid, less than 10% linoleic acid, less than 3% linolenic acid, less than 4% stearic acid, and less than 4% palmitic acid.
• biodegradable dielectric fluids having good oxidative stability There is a continuing need for biodegradable dielectric fluids having good oxidative stability. There is an ongoing need for electrical apparatuses which comprise a biodegradable dielectric fluid having good oxidative stability. There is a need for a process to prepare biodegradable dielectric flu ids having good oxidative stability.
• dielectric fluids comprising a mixture of polyol esters derived from the reaction of a polyol with a mixtu re of fatty acid esters derived from a high oleic soybean oil.
• the high oleic soybean oil has a C18: 1 content of greater than 65% of the fatty acid moieties in the oil; and a combined C18:2 and C18:3 content of less than 20% of the fatty acid moieties in the oil.
• the mixtures of polyol esters have electrical properties which make them well suited as insulation fluids in electrical apparatuses.
• electrical apparatuses comprising the dielectric fluids, a dielectric material impregnated with the dielectric fluid, and processes for making the mixtures of polyol esters of which the dielectric fluids are comprised.
• dielectric flu id is a mixture comprising polyol esters derived from a reaction of:
• a polyol comprising pentaerythritol, trimethylolpropane, neopentyl glycol, or combinations thereof;
• the dielectric fluid meets the criteria for "Ready Biodegradation" under the conditions of the 28-day C0 2 Evolution Test according to OECD Guideline 301 B.
• a process for preparing a mixture of polyol esters comprising the steps of a) providing a high oleic soybean oil comprising fatty acid moieties wherein the soybean oil comprises
• an electrical apparatus comprising a dielectric fluid wherein the dielectric fluid comprises a mixtu re comprising polyol esters derived from a reaction of: a) a polyol comprising pentaerythritol, trimethylolpropane, neopentyl glycol, or combinations thereof; and
• dielectric material comprising a cellulosic paper, a synthetic paper, or a nonwoven web; and the dielectric fluid comprising a mixtu re comprising polyol esters derived from a reaction of:
• compositions comprising, “comprising,” “includes,” “including, “ “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion .
• a composition , a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.
• wt% means weight percent.
• high oleic acid content soybean oils are used as starting materials for the production of mixtu res of polyol esters.
• the polyol ester mixtures have physical properties usefu l for electrical insu lation fluids, also referred to as dielectric fluids.
• dielectric fluids also referred to as dielectric fluids.
• mixtures of polyol esters having specific structural and physical characteristics and properties, methods of making such mixtures, dielectric fluids which comprise the mixtures of polyol esters, and electrical apparatuses which comprise the dielectric fluids.
• Vegetable oils usually have a high percentage of triglyceride esters of saturated and unsaturated organic acids.
• Oleic acid is a
• High oleic soybean (HOS) oil may be derived from high oleic soybean seeds which have been genetically modified to yield high oleic content, as disclosed in World Patent Publication WO 94/1 1 516, which is hereby incorporated in its entirety by reference.
• a h igh oleic soybean seed is a soybean seed wherein oleic acid accounts for greater than 65 percent of the fatty acid moieties in the oil and, preferably, greater than 75 percent of the fatty acid moieties in the oil.
• High oleic soybean oil may be derived from high oleic soybean seeds as disclosed in United States Patent No. 5,981 ,781 , which is hereby incorporated in its entirety by reference. High oleic soybean oil may be purified by such process steps as refining, bleaching, and deodorizing, as described in United States Patent No. 5,981 ,781 , to obtain refined, bleached, and deodorized high oleic soybean oil (RBD HOS oil). HOS Oil and/or RBD HOS oil may be used in the processes disclosed herein to prepare dielectric flu ids comprising a mixture of polyol esters. I n one embodiment, HOS oil may comprise refined, bleached, and deodorized high oleic soybean oil.
• a triglyceride composition is a glycerol backbone lin ked to th ree fatty acid molecules.
• Pure vegetable oils are triglycerides of certain fatty acids with a carbon chain generally ranging from 16 to 22 carbon atoms, although small amounts of shorter and/or longer carbon chains can also be present. If the carbon chain has no double bonds, it is a satu rated oil, and is designated Cn:0 where n is the number of carbon atoms.
• Carbon chains with one double bond are monounsaturated and are designated Cn: 1 ; those with two dou ble bonds are designated Cn:2, and those with th ree double bonds are designated Cn:3.
• palmitic acid is a C16:0 acid
• stearic acid is a C18: 0 acid
• oleic acid is a C18: 1 acid
• linoleic acid is a C18:2 acid
• linolenic acid is a C18:3 acid.
• the acids are in the combined state as triglycerides, and when the oils are hydrolyzed they are separated into the acid and glycerol components.
• High oleic soybean oil has a C18: 1 content of greater than 65% of the fatty acid moieties in the oil and a combined C18:2 and C18:3 content of less than 20% of the fatty acid moieties in the oil.
• the HOS oil has a C18: 1 content of greater than about 70% of the fatty acid moieties, and a combined 01 8:2 and 018:3 content of less than 15% of the fatty acid.
• the HOS oil further comprises a combined 016:0 and 01 8:0 content of less than 15% of the fatty acid moieties.
• the HOS oil has a 018: 1 content of greater than about 75% of the fatty acid moieties, and a combined 018:2 and 018:3 content of less than 10% of the fatty acid moieties. In one embodiment, the HOS oil has a 01 8: 1 content of greater than about 80% of the fatty acid moieties, and a combined 018:2 and 018: 3 content of less than 10% of the fatty acid.
• a mixture of polyol esters can be obtained in two synthesis steps from HOS oil.
• the HOS oil comprising fatty acid moieties is converted to glycerol and a mixture of fatty acid esters through base-catalyzed reaction with an alcohol.
• the mixture of fatty acid esters comprises the fatty acid moieties of the HOS oil.
• the first synthetic step is represented in Scheme I below, where the alcohol is shown as R 4 OH and R 1 , R 2 , and R 3 represent the same or different C 15 to C 2 i carbon chains of the fatty acid moieties in the triglyceride starting material and in the fatty acid ester products R 1 C0 2 R 4 , R 2 C0 2 R 4 , and R 3 C0 2 R 4 .
• the second synthesis step the mixtu re of fatty acid esters R 1 C0 2 R 4 , R 2 C0 2 R 4 , and R 3 C0 2 R 4 is reacted with a polyol other than glycerol to produce a mixture of polyol esters, which comprises the fatty acid moieties of the HOS oil.
• the process for preparing a mixtu re of polyol esters can be performed as follows.
• An HOS oil is reacted with an aliphatic monoalcohol having a chain length of from 1 to 5 carbons in the presence of a first base catalyst to produce a reaction mixture comprising glycerol and a mixture of the fatty acid esters corresponding to the fatty acid moieties of the HOS oil.
• the monoalcohol is shown as R 4 OH, where R 4 represents an alkyl grou p containing from 1 to 5 carbons.
• Th is transesterification reaction can be driven to completion by (1 ) the use of excess monoalcohol (about 25 to 50 weight % based on HOS oil) and (2) separating and removing the glycerol that is formed during the transesterification of the fatty acid moieties of the HOS oil.
• the glycerol may be separated, for example, by cooling the reaction mixtu re and allowing a bottom glycerol layer to form, due to glycerol having a higher density than the reaction mixture.
• Other conventional means of separation can be used such as liquid/liquid extraction, solvent extraction, salting out, or other separation methods that would not resu lt in destruction of the esterified product.
• the glycerol bottom layer can be physically removed by any conventional method known in the art.
• the monoalcohol comprises methanol, ethanol, a propanol isomer, a butanol isomer, a pentanol isomer, or combinations thereof.
• the monoalcohol comprises methanol.
• the first base catalyst can comprise sodium carbonate, potassiu m carbonate, lithium carbonate, sodiu m hydroxide, potassium hydroxide, lithium hydroxide, sodiu m methoxide, or combinations thereof.
• Other base catalysts known to one of ordinary skill can be used to obtain the same result, and any such catalyst can be useful in the practice of this invention.
• the amount of the first base catalyst used is typically from about 0.1 wt% to about 1.0 wt%, for example from about 0.1 wt% to about 0.5 wt%, based on the amount of HOS oil used. A larger amount of base can be used, but may not be necessary or economical.
• the first base catalyst comprises sodiu m carbonate.
• the first base catalyst comprises potassiu m carbonate. Transesterification of vegetable oil to the corresponding methyl esters is well-known and widely used to man ufacture biodiesel, see for example [J. Braz. Chem. Soc , 1998, 9, 199-210].
• Suitable reaction conditions for reacting HOS oil with an aliphatic monoalcohol include a reaction temperature from about 25 °C to about 150 °C, for example from about 50 °C to about 100 °C, and a reaction time from about 30 minutes to about 4 hours. I n one embodiment, the reaction can be carried out under atmospheric pressure and refluxing conditions for about 3 or more hours.
• reacting the HOS oil with an aliphatic monoalcohol can be repeated more than once in a multi-stage process.
• the first stage is performed as described herein above.
• the bottom layer of glycerol byproduct is separated and removed, more methanol and base catalyst are added to the mixture comprising triglycerides and fatty acid esters, and heating of the reaction mixture is continued to produce a second reaction mixture comprising glycerol and a mixture of fatty acid esters.
• the removal of glycerol, addition of more methanol and base, and heating steps are repeated until the triglycerides contained in the HOS oil have been transesterified to fatty acid esters.
• the reaction of HOS oil with the aliphatic monoalcohol is performed in two stages. I n a two stage process, a total about 30 weight % of the monoalcohol and a total of about 0.1 wt% to about 1 .0 wt %, for example about 0.1 wt% to about 0.5 wt%, of the base catalyst are used, based on the amou nt of HOS oil used.
• the resulting mixture of fatty acid esters can be used in the next step of the process without fu rther treatment.
• the yield of this transesterification reaction is almost quantitative.
• the mixture of fatty acid esters obtained can have some remaining glycerol and/or glycerol esters (triglycerides). In one embodiment there is less than 10% of glycerol and/or glycerol esters present in the mixture. I n another embodiment there is less than 5%, or less than 3%, or less than 1 % of glycerol and/or glycerol esters in the fatty acid ester mixtu re.
• the mixture of fatty acid esters is essentially free of glycerol and/or glycerol esters.
• the composition of the fatty acid moieties in the mixture of fatty acid esters corresponds to the composition of the fatty acid moieties of the HOS oil.
• the fatty acid esters are then reacted with a polyol in the presence of a second base catalyst to produce a reaction mixture comprising the aliphatic monoalcohol used in the first synthesis step and a mixtu re of polyol esters containing the fatty acid moieties of the HOS oil.
• the second base catalyst can be selected from the same group of catalysts as the first catalyst, and can be the same as the first catalyst or different from the first catalyst.
• the polyol comprises pentaerythritol, trimethylolpropane, neopentyl glycol, or combinations thereof.
• This transesterification reaction can be driven to higher conversion by the use of a slight excess of the fatty acid esters of the HOS oil, for example from about 1 .15 to about 1.5 equivalents in relation to the total hydroxyl groups of the polyol, and by the removal of the monoalcohol formed during the transesterification with the polyol.
• unreacted fatty acid esters can be removed by distillation.
• the polyol comprises pentaerythritol
• the second synthetic step can be represented as shown in Scheme II below,
• catalyst comprises potassiu m hydroxide.
• temperatu re is slowly increased as the conversion to polyol esters
• Suitable reaction conditions for reacting the fatty acid esters with the polyol include a reaction temperature from about 50 °C to about 200 °C and a reaction time from about 5 hours to about 150 hou rs under a vacuum in the range of 5 torr to about 100 torr.
• the preparation of pentaerythritol esters in high conversion may requ ire h igher temperature and longer reaction time.
• the mixture of polyol esters can be separated from any h igher-boiling by-products, for example by centrifuging the mixture and passing it through a th in layer of silica gel.
• the mixtu re of polyol esters can then be dried on full vacuum (0.5 torr or lower) at 1 10°C, typically for about 1 hour, to provide the final mixture of polyol esters.
• a mixture of polyol esters can be obtained from other vegetable oils, for example including but not limited to sunflower oil, canola oil, safflower oil, rapeseed oil, corn oil, olive oil, coconut oil, palm oil, castor oil, commodity soybean oil, high oleic sunflower oil, high oleic canola oil, and mixtures thereof.
• the characteristics of the mixture of polyol esters for example the content of unsaturated and saturated moieties such as C18: 1 , C18:2, C13: 3, C16:0, and C18:0 moieties, can reflect the composition of the vegetable oil(s) from which they are derived.
• a mixture of polyol esters can be refined, for example by distillation, to separate one or more polyol esters from the mixtu re, or to enrich or deplete the mixture with respect to one or more of the polyol esters.
• the process for preparing a mixtu re of polyol esters further comprises providing at least one vegetable oil other than h igh oleic soybean oil in addition to the high oleic soybean oil.
• I MC-130 Canola oil available from Cargill, Inc. , has an oleic acid content of about 75% and a polyunsatu rated fatty acid content (C18:2 and C18: 3) of about 14%.
• United States Patent No. 5,767,338 describes plants and seeds of IMC-130. See also United States Patent No. 5,861 , 187.
• United States Patent No. 4,627, 192 describes h igh oleic acid sunflower oils.
• the mixtu re of polyol esters derived from reaction of a polyol comprising pentaerythritol, trimethylolpropane, neopentyl glycol, or combinations thereof and a mixture of fatty acid esters derived from HOS oil can be used as a dielectric fluid.
• the dielectric fluid comprises at least about 30 wt%, or at least about 50 wt%, or at least about 70 weight percent, or at least about 80 wt%, or at least about 90 wt% to about 1 00 wt%, of the mixture of polyol esters comprising the fatty acid moieties of the HOS oil.
• the dielectric fluid may further comprise from about 1 wt% to about 70 wt%, for example from about 1 wt% to about 50 wt%, or from about 1 wt% to about 30 wt%, or from about 1 wt% to about 20 wt%, or from about 1 wt% to about 10 wt% of a blending component comprising other dielectric fluids such as vegetable oils, vegetable oil based fluids, algal oils, one or more polyol esters derived from a vegetable oil other than HOS oil, mineral oils, synthetic esters, silicon fluids, poly alpha olefins, or mixtures thereof based on the total weight of the dielectric fluid.
• a blending component comprising other dielectric fluids such as vegetable oils, vegetable oil based fluids, algal oils, one or more polyol esters derived from a vegetable oil other than HOS oil, mineral oils, synthetic esters, silicon fluids, poly alpha olefins, or mixtures thereof based on the total
• the dielectric fluid fu rther comprises a blending component selected from the group consisting of vegetable oil, algal oil, one or more polyol esters derived from a vegetable oil other than HOS oil, mineral oil, silicone fluids, synthetic esters, poly alpha olefins, or mixtures thereof.
• vegetable oil based fluids that can be used are Envirotemp® FR3TM fluid (Cooper Industries, I nc.) and BIOTEMP® Biodegradable Dielectric
• algal oil refers to the lipid components, including triacylglycerols, produced by microalgal cells such as Chlorella, Parachlorella, Dunaliella, and others, for example as disclosed in published patent application US 2010/0303957.
• An example of a high fire point hydrocarbon oil that can be used is R-Temp® hydrocarbon oil (Cooper I ndustries, I nc.).
• Examples of synthetic esters include polyol esters which contain fatty acid moieties of less than about 10 carbon atoms in chain length. Commercially available synthetic esters that can be used include those sold under the trade names M idel® 7131 (The Micanite and Insulators Co. , Manchester UK), REOLEC® 138 fluid (FMC, Manchester, UK), and ENVIROTEMP 200 fire-resistant fluid (Cooper Power Fluid Systems).
• the dielectric fluids can contain other useful additives, for example oxidation in hibitors, metal deactivators, in particular copper deactivators, corrosion inhibitors, flame retardants, thermal stabilizers, viscosity modifiers, pour point depressants, anti-foaming agents, acid-base indicators, and dyes, provided that the additives are soluble in the compositions, are thermally stable at high temperatures, and do not deleteriously affect the electrical properties of the dielectric fluid.
• the dielectric fluid further comprises at least one additive selected from the group consisting of oxidation inhibitors, corrosion inhibitors, metal deactivators, and pour point depressants.
• dielectric breakdown voltage low dissipation factor
• high specific heat high thermal conductivity
• low coefficient of expansion low viscosity
• low sensitivity of viscosity to temperature low pour point temperatures
• low volatility high flash point
• low moisture content low moisture content.
• the dielectric fluids of the present invention possess a wide variety of these desirable properties, as well as good oxidative stability. Oxidative stability is related to the degree of unsaturation in the dielectric fluid and can be measured, for example by using a standard method for determin ing an oil stability index.
• the high oleic acid content of the soybean oil used to prepare polyol esters of the present invention helps to provide good oxidative stability to the disclosed dielectric fluids.
• dielectric fluids disclosed herein are expected to be biodegradable as they are derived from a vegetable oil which is readily biodegradable.
• a dielectric fluid comprising a mixture of TMP esters derived from the fatty acids of crude HOS oil has been found to meet the criteria for "Ready Biodegradation" under the conditions of the 28-day C0 2 Evolution test according to OECD Guideline 301 B.
• Published Canadian Patent Application CA 2594765 discloses a biodegradability (28d BOD/COD) of 72% for the trioleate ester of trimethylolpropane.
• the dielectric fluids disclosed herein are suitable for use in any application requiring electrical insulation fluids having the properties of the fluids disclosed herein, such as liquid-filled power transformers, distribution transformers, traction transformers, reactors, and their accessory equipment such as switches and tap changers, all of which are fluid-filled.
• the combination of fluid and solid insulation such as kraft paper, kraft board, aramid paper, cotton paper, aramid board, or composites (i.e., fiber glass/epoxy, nylon, polyester), provides electrical insulation for the electrical apparatus.
• the fluid serves as a heat transfer maxim m to aid in cooling electrical devices.
• the electrical apparatus comprising the dielectric fluid disclosed herein is an electrical transformer, an electrical capacitor, a fluid-filled transmission line, an electrical power cable, an electrical inductor, or a high voltage switch.
• a dielectric material is impregnated with at least 10 weight percent of a dielectric fluid, wherein the dielectric material comprises a cellulosic paper, a synthetic paper, or a nonwoven web; and the dielectric fluid comprises comprises a cellulosic paper, a synthetic paper, or a nonwoven web; and the dielectric fluid comprises a mixture comprising polyol esters derived from a reaction of: a) a polyol comprising pentaerythritol, trimethylolpropane, neopentyl glycol, or combinations thereof; and b) a mixture of fatty acid esters derived from a high oleic soybean oil comprising fatty acid moieties, wherein the high oleic soybean oil has i) a C18: 1 content of greater than 65% of the fatty acid moieties in the oil; and ii) a combined C18:2 and C18: 3 content of less than 20% of the fatty acid moieties in the
• the dielectric material can be impregnated with at least about 5 weight percent, or at least about 10 weight percent, or at least about 15 weight percent, or at least about 20 weight percent of a dielectric fluid.
• the dielectric material can be impregnated with the dielectric fluid such that it is satu rated with the dielectric fluid.
• synthetic paper refers to any non-cellulose or cloth paper, for example an aramid-based paper.
• the dielectric fluids disclosed herein provide new alternatives to mineral oil and petroleum-based synthetic esters contain ing fatty acid moieties of less than about 10 carbon atoms in chain length - alternatives which are derived from a renewable starting material, high oleic soybean oil, and wh ich have desired properties, including a high fire point and a low pour point. They also provide superior low temperatu re performance over vegetable oil-based fluids.
• the dielectric fluid comprising a mixture of polyol esters has a flash point of greater than about 280 °C.
• the dielectric fluid has a flash point of greater than about 310 °C. In one embodiment, the dielectric fluid has a flash point of greater than about 320 °C.
• the dielectric fluid has a pour point of less than about -10 °C. In one embodiment, the dielectric flu id has a pour point of less than about -30 °C. I n one embodiment, the dielectric fluid has a flash point of greater than about 280 °C and a pour point of less than about -10 °C. I n one embodiment, the dielectric flu id has a fire point of greater than about 325 °C. I n one embodiment, the dielectric fluid has a fire point of greater than about 370 °C. I n one embodiment, the dielectric fluid has a fire point of greater than about 325 °C and a pour point of less than about -10 °C.
• the dielectric fluid has a fire point of greater than about 325 °C and a pour point of less than about -30 °C.
• the dielectric fluid has a viscosity of less than about 45 cST at 40 °C and less than about 14 cST at 100 °C.
• the dielectric fluid has a viscosity of less than about 25 cST at 40 °C and less than about 10 cST at 100 °C.
• the dielectric fluid has a power factor of less than about 0.15% at 25 °C and less than about 5% at 100 °C.
• the dielectric fluid has a power factor of less than about 0.03% at 25 °C and less than about 3% at 100 °C. In one embodiment, the dielectric fluid has a dielectric breakdown voltage of greater than about 35 KV when measured across a 1 mm gap at 25 °C. I n one embodiment, the dielectric fluid has an oil stability index of at least about 8 hours at 1 1 0 °C. I n one embodiment, the dielectric fluid has an oil stability index of at least about 14 hours at 1 1 0 °C. In one embodiment, the dielectric flu id has an oil stability index of at least about 25 hours at 1 10 °C.
• Also disclosed herein is a method of using an electrical apparatus, the method comprising employing in the apparatus a dielectric fluid comprising a mixtu re comprising polyol esters derived from a reaction of a) a polyol comprising pentaeryth ritol, trimethylolpropane, neopentyl glycol, or combinations thereof, and b) a mixtu re of fatty acid esters derived from a high oleic soybean oil comprising fatty acid moieties, wherein the high oleic soybean oil has i) a C18: 1 content of greater than 65% of the fatty acid moieties in the oil, and ii) a combined C18:2 and C18:3 content of less than 20% of the fatty acid moieties in the oil.
• dielectric fluids disclosed herein may be used to retrofill existing electrical equ ipment that incorporates other, less desirable dielectric flu ids. These other fluids may be replaced with dielectric flu id comprising a mixtu re of polyol esters as disclosed herein using any suitable method known in the art.
• the following materials were used in the examples. All commercial reagents were used as received.
• the silica gel was dried in a vacuum oven at 200°C for 3 days under about 200 torr vacuum before use.
• Refined, bleached, and deodorized high oleic soybean oil (RBD HOS oil) containing triglycerides of 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 linolen ic acid (2.94 wt%) was obtained according to United States Patent No. 5,981 ,781 .
• Methanol 99.8%, sodium carbonate (99.5%), potassium hydroxide (>85%), hexanes (99.9%), silica gel 60 and potassium carbonate (99.9%) were obtained from EMD Chemicals Inc. (Gibbstown, NJ).
• Neopentyl glycol 99%, trimethylolpropane (97%), and pentaerythritol (98%) were obtained from Aldrich Company (Milwaukee, Wl).
• GC gas chromatography
• C is Celsius
• mm is millimeter
• mL is milliliter
• L is liter
• min is minute
• cm centimeter
• G is gram(s)
• mg is milligrams
• h is hour(s)
• temp or "T” is temperature
• I Comparative Example
• I D is internal diameter
• NPG is neopentyl glycol
• TMP trimethylolpropane
• PE is pentaerythritol.
• ASTM stands for American Society for Testing and Materials which provides standard protocols for material evaluation .
• AOCS stands for American Oil Chemists' Society which provides standard methods for material evaluation.
• OECD stands for Organization for Economic Co-operation and Development.
• Methyl esters were analyzed using an Agilent 6890 Series GC with a OmegawaxTM 320 column , 30m long, diameter 320 ⁇ , film th ickness 0.30 ⁇ .
• Oven ramp I nitial temp 1 60 C holds for 5 minutes, then increase at 2°C/min to 220°C and hold for 10 minutes, then increase at 20°C/min to 240°C and hold for 5 minutes.
• the carrier gas was helium.
• I nitial flow rate 1.6 ml/min with 1 1.56 psi.
• a 20-liter, jacketed, Pyrex® reactor equipped with mechanical stirring, reflux condenser, internal thermocouple, nitrogen inlet, and a drain was dried by sweeping with n itrogen overn ight.
• the reactor was charged with crude HOS oil (1 2.0 kg), methanol (3.0 kg) and potassiu m carbonate (45 g). The mixture was heated to reflux under nitrogen for 3 hours. The reaction mixture was cooled to 25°C. The bottom layer contain ing glycerol (1 .9 kg) was removed via the drain .
• the reactor, containing the top layer, was charged with methanol (400 g) and potassium carbonate (2.0 g). The mixture was heated to reflux for 2 hours.
• the distillation residue was centrifuged and the resulting liquid was passed th rough a silica gel column [2" (OD) X 4"] to give a mixture of NPG esters as the product (732.6 g).
• the solid from the centrifuge was extracted with hexanes (2 X 150 mL).
• the silica gel colu mn was washed with the combined hexane extracts and additional hexanes (300 mL).
• the combined hexane washes were concentrated and dried under vacuum to give an additional amount of the NPG esters as product (93.5 g).
• the solid from the centrifuge was extracted with hexanes (2 X 150 mL).
• the silica gel column was washed with the combined hexane extracts and additional hexanes (300 mL).
• the combined hexane washes were concentrated and dried under vacuu m to give an additional amount of the NPG esters product (170 g).
• 1 H NMR analysis of the product confirmed its identify as a mixture of esters comprising neopentyl glycol and fatty acid moieties of crude HOS oil.
• the composition was found to comprise 2% NPG monoesters, 93% NPG diesters, and 5% triglycerides (HOS oil).
• the su itability of using the product as a dielectric fluid was evaluated by measuring its electrical and physical properties using the methods listed in Table 1. Results are given in Table 2.
• trimethylolpropane 140 g was heated under 10 torr to 95 °C over 6 hours, then to 1 54 °C over an additional 4.5 hours. Additional KOH (0.47 g) was added and the mixture was heated under 0.8 torr at 123 - 150 °C for 8 hou rs more. During the heating period, the temperature gradually increased while the boiling slowed down. A total about 86.2 g of MeOH was recovered from the liquid nitrogen trap. The reaction mixture was distilled under 45 m torr vacu um up to 239 °C. The unreacted methyl esters were collected as distillate (57.8 g).
• the distillation residue was centrifuged and the resulting liquid was passed through a silica gel column (-14 g) to give a mixture of TMP esters as the product (970 g).
• the solid from the centrifuge was extracted with hexanes.
• the silica gel column was washed with the combined hexane extracts and additional hexanes (300 ml_). The combined hexane washes were concentrated and dried under vacuum to give an additional amount of the mixture of TMP esters product (75 g).
• a portion of the product obtained (847 g) was mixed with bleaching clay grade F-1 15FF (from BASF, 8.8 g), and Celite (2.2 g), and stirred at room temperature under vacuum (1 torr) for 1 hour, then heated to 1 10 °C for 1 hour under 0.5 torr.
• the mixture was cooled to room temperatu re and passed through a 1/2" silica gel column (ID 1.5").
• the collected product was heated to 1 10 °C for 1 hou r u nder 0.1 torr before it was evaluated.
• 1 H NMR analysis of the product confirmed its identify as a mixture of esters comprising trimethylolpropane and fatty acid moieties of RBD HOS oil.
• the composition was found to comprise 2% TMP diesters, 90% TMP triesters, and 8% triglycerides (HOS oil).
• trimethylolpropane (156 g) was heated under 10 torr to 103 °C over 2 hours. Then the pressure was reduced to 15 torr and the reaction mixture was heated to193 °C over 7.5 hour. The reaction mixture was then distilled under 40 mTorr vacuum to recover the unreacted methyl esters as distillate. The distillation residue was centrifuged and the resulting liquid was passed through a silica gel column (18 g silica gel) to give an oil which was further dried under 30 mTorr at 1 10 °C for 1 hour to give a mixture of TMP esters as the product (962 g). The solid from the centrifuge was extracted with hexanes.
• the silica gel column was washed with the combined hexane extracts and additional hexanes. The combined hexane washes were concentrated and dried to give an additional amount of product (108 g).
• 1 H NMR analysis of the product confirmed its identify as a mixture of esters comprising trimethylolpropane and fatty acid moieties of crude HOS oil.
• the composition was found to comprise 1.4% TMP diesters, 97.4% TMP triesters, and 1 .2% triglycerides (HOS oil).
• the distillation residue was centrifuged and the resulting liqu id was passed through a silica gel column (14 g), then dried at 1 10 °C under 0.1 torr vacuu m for 1 hou r to give a mixture of PE esters as the product (930 g).
• 1 H NMR analysis of the product confirmed its identify as a mixture of esters comprising pentaerythritol and fatty acid moieties of crude HOS oil.
• the composition was found to comprise 4% PE triesters, 90% PE tetraesters, and 6% triglycerides (HOS oil).
• Example 4 The polyol ester mixtures obtained in Example 4, Example 5, Example 6, Example 8, and Comparative Example B were evaluated using the methods listed in Table 1 .
• Samples of Envirotemp® FR3TM fluid (Cooper Industries, I nc.), which is a vegetable oil-based fluid formulated from commodity soybean oil, and Midel® 71 31 (The Micanite and Insulators Co. , Manchester UK), which is a synthetic ester composition of linear and branched C 5 to Ci 0 fatty acids as mixed esters with pentaerythritol, were also evaluated using the same methods. The data are presented in Table 2.
• Table 2 Summary of Dielectric Fluid Properties Measured
• the data in Table 2 show that the mixtures of polyol esters of the Examples have desirable properties for use as dielectric fluids.
• the flash points and fire points of the fluids of the Examples are suitably high, and significantly higher than those of the synthetic ester composition Midel® 7131 . They also have significantly lower moisture content than Midel® 7131 and the vegetable oil-based Envirotemp® FR3TM.
• the analogous polyol esters of Example 5 (derived from the reaction of trimethylolpropane and the mixture of methyl esters of fatty acid moieties derived from high oleic soybean oil) show better electrical properties in terms of the power factor, both when measured at 25 °C and when measured at 1 00 °C.
• the extremely high power factors of the flu id of Comparative Example B would preclude its use as a dielectric fluid. I n contrast, the characteristics of the flu id of Example 5 show that it is su itable for use as a dielectric flu id.

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