EP2841539A1

EP2841539A1 - Esters as cooling and insulating fluids for transformers

Info

Publication number: EP2841539A1
Application number: EP13726667.2A
Authority: EP
Inventors: Jürgen O. METZGER; Rolf Luther; Angela ROBBEN; Gunther Kraft
Original assignee: Fuchs Petrolub SE
Current assignee: Fuchs SE
Priority date: 2012-04-26
Filing date: 2013-04-26
Publication date: 2015-03-04
Anticipated expiration: 2033-04-26
Also published as: CN104271716A; DE102012103701A1; AU2013252181A1; US9666328B2; AU2013252181B2; CA2869867C; JP2015521341A; WO2013159761A1; CN104271716B; US20150090944A1; JP6166354B2; EP2841539B1; CA2869867A1; BR112014026490A2; ES2656071T3; BR112014026490B1; NO2883278T3

Abstract

The invention relates to compositions including esters of polyvalent alcohols that are esterified with fatty acids, partially unsaturated, from plant oils, and to the use thereof as cooling and insulating fluids for transformers.

Description

Esters as cooling and insulating fluids for transformers

Field of the invention

The present invention relates to compositions containing esters of polyhydric alcohols esterified with fatty acids, partially unsaturated, from vegetable oils and their use as cooling and insulating fluids for transformers.

State of the art

Safe operation of transformers requires sufficient electrical insulation and dissipation of the heat released by the transformation of electrical voltages. It is known that certain liquids have insulating and heat-dissipating properties. Conventionally, mineral oils or silicones are used. However, these have a very poor biodegradability and thus pose a danger to humans and the environment in the event of leaks, leaks or other leakage from the transformer. The former also have a very low flash point of less than 150 ° C, i. a high fire hazard potential.

Therefore, biodegradable vegetable oils have been proposed for use as an insulating liquid in transformers. It is obvious,

To use vegetable oils as insulating liquid, since these biologically light and completely degradable and i.d.R. not endangering water (according to the German "Administrative Regulation on Water Hazardous Substances" - VwVwS) and having a flame and ignition point of more than 300 ° C (according to the Pensky-Martens process), all at low raw material costs, in addition they have a higher water absorption capacity in comparison mineral oil, which slows down the degradation of the transformer board's cellulose and increases the life of the transformer .. Vegetable oils had been used as insulating oils since the end of the 19th century, but their use soon receded as they were used in transformers The use of hermetically sealed transformers, which largely exclude the ingress of air, has changed the requirement profile in recent years.

CONFIRMATION COPY Oxidization sensitivity is still important, but not to the same extent as in old transformers, and is manageable in hermetically sealed transformers. On the other hand, environmental awareness has increased significantly worldwide. Accordingly, vegetable oils such as castor oil, sunflower oil, rapeseed oil, soybean oil, among others, have been proposed as transformer liquid in many cases, cf. WO 97/22977 A1 and US Pat. No. 6,340,658 B1.

In addition to the oxidation stability, other necessary properties of a transformer liquid came more and more into the foreground, including a high flame and focus, a low viscosity (for better heat convection), in particular a low pour point, low acid number, good dielectric stability and low sludge formation in the stability test according to DIN EN 61099 "Specifications for unused synthetic organic esters for electricity purposes" (see Table 1). In addition, good corrosion properties and seal compatibility are essential. Unfortunately, natural vegetable oils do not all meet these necessary or desired properties at the same time, especially in terms of viscosity and cold properties as well as oxidation stability they show weaknesses in one or more of the properties. Oxidative stability is generally minimized by the addition of antioxidants. In contrast, especially the cold properties can be improved only slightly by additives. The lowering of the viscosity by simple mixing of vegetable oils with proportions of other, significantly thinner base oils is impossible due to the requirements of high flame and foci. GB 1602092 discloses the use of trimethylolpropane esters of linear saturated fatty acids of 7 to 10 carbon atoms and their use as dielectric insulating liquid for transformers. From the examples, trimethylolpropane esters having a viscosity of 25 and 30 mm ² / s, respectively at 30 ° C. and a focal point of 277 ° C. or 293 ° C., are known. A similar disclosure content has WO 2005/1 18756 A1. However, this discloses broader linear or branched carboxylic acids having 6 to 12 carbon atoms. However, branched carboxylic acids are not natural fatty acids.

Summary of the invention

The present invention is characterized by the subject matter of the independent claims. Preferred embodiments are subject of the dependent claims or described below. The present invention relates to esters in the form of mixed esters and / or

Estermischungen,

with R, R and R ² or R, R to R ⁴ independently of each other and next to each other:

R is methyl, ethyl, propyl and / or isopropyl,

R = at least 30%, preferably at least 50%, of linear saturated acid groups having 6 to 12 C atoms, preferably having 8 to 10 C atoms, and

R ² = at least 30%, preferably at least 20%, of acid groups having 14 to 22 C atoms, preferably 18 C atoms, having one or more double bonds, preferably with cis-configured double bonds),

optionally marked as follows:

R ³ 0 to a maximum of 20%, preferably 1 to a maximum of 10%, linear saturated acid groups having 14 to 22 carbon atoms.

R ⁴ 0 to a maximum of 20%, preferably not more than 10%, other acid groups apart from R, R ² and optionally R ³

The ester is composed of the acid groups R ¹ to R ⁴ and the alcohol group

together. H ₂ C-O

The above percentages refer to the relative number of acid groups R ¹ , R ² , and so on, as far as they are related to the polyhydric alcohol (s) of the general formula whether they are bound as a mixture of esters (ester mixture), each having a uniform structure, such as or as a mixed ester in which the acid groups R ¹ and R ² or R ¹ to R ^{4 of} an alcohol radical are present in any distribution. The percentages add up to 100 in total.

The fatty acids according to acid group R ¹ or R ² and R ³ are preferably accessible from natural fats as a mixture, for example from natural sources such as sunflower oil or rapeseed oil, preferably their high oleic acid variants.

The acid groups R ² are accessible from fatty acids having a chain length of 6 to 12 C atoms, in particular 8 or 10 C atoms, for example as distillation cuts of vegetable oils such as coconut oil, palm kernel oil and the like.

Detailed illustration of the invention

Surprisingly, it was found that the above-mentioned mixed ester or

Ester mixtures meet and exceed the requirements of DIN EN 61099 (see Table 1), i. in particular at the same time have a low viscosity, a low pour point (DIN ISO 3016), a high flash point according to Pensky-Martens (DIN ES ISO 2719,> 250 ° C.) and a high focal point (DIN EN ISO 2592) as well as high oxidation stability Furthermore, the dielectric insulating liquid according to the invention, in particular largely, is produced on the basis of renewable raw materials, for example to over 80% by weight (based on the educts used for the synthesis).

Surprisingly, it was found that esters of polyhydric alcohols

such as in particular trimethylolpropane (R = ethyl) esterified one after the other and then mixed or together with two or more different fatty acids that meet the requirements described above outstanding. A first subject of the present application therefore relates to compositions containing the above esters of polyhydric alcohols according to formula V with three hydroxy groups, such as trimethylolpropane, with

a) linear acid groups with 6 to 12 C atoms and

b) fatty acids having 14 to 22 C atoms, preferably predominantly 18 C atoms, and one or more double bonds, preferably cis-configured,

or the above definition, in transformers or as transformer oil.

The acid radical b) is obtainable from natural vegetable oils such as sunflower oil, rapeseed oil and the like, preferably their high-acid-acid variants. In particular, a high proportion of b) of oleic acid guarantees good cold properties at the same time great aging stability.

The fatty acid residues a) having a chain length of 6 to 12 carbon atoms, in particular 8 or 10 carbon atoms, are either likewise obtainable from vegetable oils such as coconut oil (for example as a distillation cut) or wholly or partly from synthetic sources. The radicals R ² are linear and preferably have 8 and / or 10 C atoms. In a triester, all radicals R may be the same or only two radicals may be the same or different. Preferably, a distribution of the radicals R ¹ and R ^{2 is} such that the flash point or the focal point above, preferably as far above 250 ° C, and the viscosity is a value of <= or <35 mm ² / s at 40th ° C and the pour point has a value <-45 ° C. The low viscosity and in particular the low pour point can be achieved by selected acid components in the ester.

For a mixed ester 1 of trimethylolpropane (TMP) with R ¹ = oleic acid radical with 18 C atoms (purity greater than 95% by weight) and with more than 80% by weight of R ¹ having cis-configured double bond and a radical R ² with 8 and / or 10 C atoms, the following mixed esters 1 are accessible: Table 1

Properties of various mixed esters 1

^* calculated ^** kinematic viscosity

Table 2

Physical properties of the

Ester 2 (TMP plus oleic acid) and

Ester 3 (TMP plus n-C8 / C10 acid)

and Properties of Ester Blends of Ester 2 and Ester 3

^* calculated ^** kinematic viscosity The physical mixtures of the trimethylolpropane esters 2 and 3 can be used to adjust all intermediate viscosities and to lower the pour point. Surprisingly and unpredictably, however, it has been found in particular that the flash point exceeds the limit value of 250 ° C. required by DIN EN 61099 by physical mixing of esters 2 and 3 in a ratio of 1: 1 to 1: 2. It is important that by varying ratios of [R ¹ ]: [R ² ] according to Table 1 or of ester 2: ester 3 viscosity and pour point and flash point can be adjusted. It is also important that the viscosity of the mixed or mixed esters according to the invention is markedly lower than those of the pure trimethylolpropane ester 2 (TMP plus R ¹ = oleic acid radical) and the pour point is lower than that of the trimethylolpropane ester 3, which is already known as Insulating fluid has been proposed. Thus, the inventive mixed ester or ester mixture exceeds the performance of the ester 3 (compare Table 1 and Table 2)

It is therefore to be noted that each of the "pure" types of esters 2 and 3 does not in itself fulfill the requirements for the target values of viscosity, cold behavior and flash point in its entirety, but rather special intra (Table 1) or intermolecular (Table 2) mixtures ,

The mixed ester or ester mixtures according to the invention thus show advantages over the prior art and represent an advance in the direction of the desired properties of a transformer oil. The class of mixed trimethylolpropane triesters complies with DIN EN 61099 and has been issued by the Commission in accordance with the Administrative Regulation on Water Polluting Substances (VwVwS) for the assessment of water pollutants (KBwS) classified as non-hazardous to water (NWG). Their natural degradability is significantly more than 60% after 28 days in the range of "readily biodegradable" according to Final Detergency Tests OECD 301. The compositions according to the invention exhibit good thermal properties and excellent dielectric properties.

In order to further improve the properties of the insulating liquid, it is possible and preferred to use antioxidants and / or metal deactivators and / or pour point depressants. In the further embodiment, the composition according to the invention additionally contains between 0.01 and 3% by weight, in particular 0.1 and 2.5% by weight, particularly preferably 1, 0 and 2.0% by weight, of at least one antioxidant and / or

0.01 and 1.0% by weight, preferably 0.02 and 0.08% by weight, of at least one metal deactivator and / or

From 0.1 to 5% by weight, in particular from 0.1 to 3% by weight and more preferably from 1.5 to 2.5% by weight, of at least one pour point depressant and / or

0.01 to 2% by weight, in particular 0.01 to 0.5% by weight and more preferably 0.01 to 0.08% by weight, of at least one defoamer, based in each case on the weight of the ester.

The antioxidants are preferably selected from the following substances and mixtures of the listed substances:

from the group of phenolic antioxidants, e.g. alkylated monophenols (e.g., 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-phenol, 2-

Tert-butyl-4,6-dimethylphenol and / or 2,6-di-tert-butyl-4-ethylphenol) and / or alkylated hydroquinones (eg 2,5-di-tert-butyl-hydroquinone and / or 2,6- Di-tert-butyl-4-methoxyphenol) and / or hydroxylated thiodiphenyl ethers (eg 2,2'-thio-bis (4-octylphenol) and / or alkylidene-bisphenols (eg 2,2'-methylene-bis (6- Tert-butyl-4-methylphenol) and / or benzyl compounds (eg, 1, 3,5-tri- (3,5-di-tert-butyl-4-hydroxybenzyl) -2,4,6, -tri-methylbenzene) and / or acylaminophenols (eg N- (3,5-di-tert-butyl-4-hydroxyphenol) -carbamic acid octyl ester) ®

from the group of aminic antioxidants: di-phenylamine,

octylated di-phenylamine and / or N-phenyl-1-naphthylamine®

Tocopherols and gallates

The metal deactivators are preferably selected from the following substances and mixtures of the listed substances: benzotriazoles and their derivatives, salicylaminoguanidine, toluene triazoles and their derivatives, 2-mercaptobenzothiazole, 2-mercaptobenzotriazole and / or salicylidene-propylenediamine and derivatives thereof.

The pour point depressants are preferably organic compounds such as diethylhexyl adipates, methacrylate polymers, polyvinyl acetates and their derivatives or / and mixtures of the listed substances. The antifoam additives are preferably compounds such as polyethylene glycol ethers, amino alcohols, and / or ester-based additives.

Another object of the invention is the use of the compositions according to the invention comprising the esters of general formula I according to the above definition (s) as a dielectric insulating liquid in aggregates of electric power engineering, such as transformers.

The transformers are power transformers, distribution transformers, pole transformers, on-load tap-changers or switches.

The invention is illustrated by the following experimental examples without being limited thereto. test Examples

Experimental Example 1 (mixed ester, acid catalyzed esterification of

Trimethylolpropane with the fatty acid mixture) 1, 03 mol fatty acid mixture (0.26 mol of oleic acid, 0.46 mol of caprylic acid and 0.31 mol of capric acid), 5 g of p-toluenesulfonic acid and 0.33 mol (40.7 g) of trimethylolpropane were mixed with 150 ml o-xylene refluxed on a water separator (3 h, 145 ° C) until no more water was separated off. Thereafter, the batch was washed in a separatory funnel with deionized water to neutrality of the aqueous phase. The o-xylene was separated by means of a rotary evaporator. Residues of the solvent and fatty acids were removed by short path distillation at 168 ° C. and ² × 10 -2 mbar, yielding 80%.

Experimental Example 2 (mixed ester, alkaline transesterification of TMP trioleyl ester and C8 / C10 TMP triester)

300 g of a dried mixture of trimethylolpropane trioleyl ester and C8 / C10 trimethylolpropane triester in a ratio of 1: 2 was subjected to multiple acid treatment under oxygen-free nitrogen, and after heating to 60 ° C., 2 g of sodium methoxide were added. After a reaction time of 2 hours, the batch was taken up in 500 ml of tert-butyl methyl ether. After adding dilute HCl to neutralize the sodium methoxide, the batch was washed with deionized water until neutral to the aqueous phase.

The tert-butyl methyl ether was separated by means of a rotary evaporator. Residues of the solvent and free fatty acids were removed by short path distillation at 168 ° C and 2 ^* 10-2 mbar. The yield was 87%.

Claims

claims

1. Compositions comprising or consisting of esters of the general formula I,

With

R is methyl, ethyl, propyl and / or isopropyl

R ¹ = at least 30% of linear saturated acid groups having 6 to 12 C atoms, R ² = at least 30% of acid groups having 14 to 22 C atoms having one or more double bonds, and optionally

R ³ 0 to a maximum of 20% linear saturated acid groups with 14 to 22 C

Atoms.

2. Ester compositions according to claim 1, wherein the ester composition simultaneously has a viscosity of <35 mm ² / s at 40 ° C, a pour point of below -50 ° C and a flash point of greater than 250 ° C and additionally in particular a focal point have greater than 250 ° C.

3. Compositions according to at least one of the preceding claims, wherein the radicals R ² to more than 90%, in particular more than 95%, 18 C atoms and have a double bond.

4. Compositions according to at least one of the preceding claims, wherein the radicals R ² to more than 80% have at least one c / s-configured double bond.

5. Compositions according to at least one of the preceding claims, wherein the radicals R ^{2 are} linear saturated acid groups having 8 and / or 10 C-atoms.

6. Compositions according to at least one of the preceding claims, wherein the esters mixtures of esters a) with R ¹ with R ² and optionally R ³ , b) with R ¹ with R ² and optionally R ⁴ or c) esters R ¹ with R ² and optionally R ³ and R ⁴ are.

7. Compositions according to at least one of the preceding claims, wherein the composition further contains

0.01% and 3% by weight of at least one antioxidant and / or

0.01 and 1.0% by weight of at least one metal deactivator and / or

0.1 to 5% by weight of at least one pour point depressant and / or

0.01 to 2% by weight of at least one antifoam,

each based on the / the ester.

The composition of claim 7, wherein the antioxidant (s) are selected from one or more members of the group comprising phenolic antioxidants, aminic antioxidants, tocopherols, and gallates.

The composition of claim 7, wherein the metal deactivator (s) are selected from one or more members of the group comprising

Benzotriazoles and their derivatives, salicylaminoguanidine, toluene triazoles and their derivatives, 2-mercaptobenzothiazole, 2-mercaptobenzotriazole and / or salicylidene-propylenediamine and derivatives thereof.

A composition according to claim 7, wherein the pour point (s) are selected from one or more members of the group comprising diethylhexyl adipates, methacrylate polymers, polyvinyl acetates and their derivatives.

1 1. The composition of claim 7, wherein the antifoam compound (s) are selected from one or more members of the group comprising polyalkylene glycol ethers, aminoalcohols, and ester based additives.

12. The composition according to at least one of the preceding claims, wherein the composition to greater than 70 wt.%, Preferably greater than 85 wt.%, In particular greater than 95 wt.%, And particularly preferably greater than 98 wt.% Exclusively of esters according to one of claims 1 to 6.

13. The composition according to at least one of the preceding claims, wherein the radicals R ¹ and R ^{2 are} in a numerical ratio of R ¹ to R ² of 1 to 1 to 5 to 1, in particular 1 to 1 to 3 to 1 and particularly preferably 1 to 1 to 2 to 1.

14. Compositions according to at least one of the preceding claims, with independent from each other

R is ethyl, and / or

R ¹ = at least 50% of linear saturated acid groups having 6 to 12 C atoms, and / or

R ² = at least 20% of acid groups having 14 to 22 C atoms, preferably 18 C atoms, having one or more double bonds, and / or

R ³ 1 to a maximum of 10%, linear saturated acid groups having 14 to 22 C atoms, and / or

R ⁴ 0 to a maximum of 10%, other acid groups apart from R ¹ , R ² and optionally R ³ .

15. Use of the composition according to at least one of the preceding claims as a dielectric insulating liquid in aggregates of electric power engineering.

16. Use according to claim 15, wherein the units are power transformers, distribution transformers, pole transformers, current and voltage transformers and on-load tap changers.