Dielectric fluids

Abstract

The present invention relates to dielectric fluids and esters, particularly to ester compositions suitable for use in dielectric fluid compositions as well as to dielectric fluid compositions, methods of manufacturing ester compositions and dielectric fluid compositions, and to electrical apparatus containing the dielectric fluids.

Claims

1. An ester composition, wherein the ester composition comprises esters formed from the reaction of: (a) pentaerythritol; and (b) three or more C.sub.4 to C.sub.12 monocarboxylic acids, wherein only one of the three or more C.sub.4 to C.sub.12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of: (i) a branched C.sub.8 to C.sub.12 carboxylic acid wherein the branched C.sub.8 to C.sub.12 carboxylic acid comprises a backbone having no branching at the C2 position; and (ii) a branched C.sub.9 to C.sub.12 carboxylic acid wherein the branched C.sub.9 to C.sub.12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C.sub.4 to C.sub.12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

2. The ester composition of claim 1, wherein the linear chain carboxylic acids comprise a linear C.sub.10 carboxylic acid.

3. The ester composition of claim 1, wherein the ester composition comprises esters formed from the reaction of: (a) pentaerythritol; and (b) four C.sub.7 to C.sub.10 monocarboxylic acids wherein at least one of the four C.sub.7 to C.sub.10 monocarboxylic acids is a branched C.sub.8 to C.sub.10 carboxylic acid wherein the branched C.sub.8 to C.sub.10 carboxylic acid comprises a backbone having no branching at the C2 position.

4. The ester composition of claim 1, wherein the ester composition comprises esters formed from the reaction of: (a) pentaerythritol; and (b) heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid; and wherein the ester composition is prepared by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture: 60-70% heptanoic acid; 12-20% of a mixture of n-octanoic and n-decanoic acids; and 15-25% 3,5,5-trimethylhexanoic acid.

5. A dielectric fluid composition comprising: (I) an ester composition, wherein the ester composition comprises esters of: (a) pentaerythritol; and (b) three or more C.sub.4 to C.sub.12 monocarboxylic acids, wherein only one of the three or more C.sub.4 to C.sub.12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of: (i) a branched C.sub.8 to C.sub.12 carboxylic acid wherein the branched C.sub.8 to C.sub.12 carboxylic acid comprises a backbone having no branching at the C2 position; and (ii) a branched C.sub.9 to C.sub.12 carboxylic acid wherein the branched C.sub.9 to C.sub.12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C.sub.4 to C.sub.12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content; and (II) one or more additives.

6. The dielectric fluid composition of claim 5, wherein the one or more additives (II) are selected from the group consisting of antioxidants, metal deactivators and pour point depressants.

7. The dielectric fluid composition of claim 5, wherein the dielectric fluid composition comprises an antioxidant in an amount of at least 0.0001% by weight of the composition and/or a metal deactivator in an amount of at least 0.0001% by weight of the composition; wherein the antioxidant optionally comprises a sterically hindered phenolic antioxidant and/or wherein the metal deactivator comprises a tolutriazole derivative.

8. The dielectric fluid composition of claim 5, wherein the ester composition (I) comprises esters of: (a) pentaerythritol; and (b) heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid; and wherein the ester composition is prepared by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture: 60-70% heptanoic acid; 12-20% of a mixture of n-octanoic and n-decanoic acids; and 15-25% 3,5,5-trimethylhexanoic acid.

9. A method of manufacturing an ester composition, wherein the method comprises forming esters by reacting: (a) pentaerythritol; and (b) three or more C.sub.4 to C.sub.12 monocarboxylic acids, wherein only one of the three or more C.sub.4 to C.sub.12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of: (i) a branched C.sub.8 to C.sub.12 carboxylic acid wherein the branched C.sub.8 to C.sub.12 carboxylic acid comprises a backbone having no branching at the C2 position; and (ii) a branched C.sub.9 to C.sub.12 carboxylic acid wherein the branched C.sub.9 to C.sub.12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C.sub.4 to C.sub.12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

10. The method of claim 9, wherein the method comprises forming esters by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises: 50-70% of heptanoic acid as a molar percentage of the acid mixture; and 10-30% of a combination of C.sub.8 and C.sub.10 monocarboxylic acids as a molar percentage of the acid mixture and/or 10-30% of a C.sub.9 monocarboxylic acid as a molar percentage of the acid mixture.

11. The method of claim 9, wherein the method comprises forming esters by reacting: (a) pentaerythritol; and (b) four C.sub.7 to C.sub.10 monocarboxylic acids wherein one of the four C.sub.7 to C.sub.10 monocarboxylic acids is a branched C.sub.8 to C.sub.10 carboxylic acid wherein the branched C.sub.8 to C.sub.10 carboxylic acid comprises a backbone having no branching at the C2 position and the remaining carboxylic acids are each independently linear chain carboxylic acids.

12. The method of claim 11, wherein the method comprises forming esters by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture: 60-70% heptanoic acid; 12-20% of a mixture of n-octanoic and n-decanoic acids; and 15-25% 3,5,5-trimethylhexanoic acid.

13. A method of manufacturing a dielectric fluid composition comprising an ester composition, wherein the method comprises combining ester composition (I) with one or more additives (II) wherein ester composition (I) comprises an ester of: (a) pentaerythritol; and (b) three or more C.sub.4 to C.sub.12 monocarboxylic acids, wherein only one of the three or more C.sub.4 to C.sub.12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of: (i) a branched C.sub.8 to C.sub.12 carboxylic acid wherein the branched C.sub.8 to C.sub.12 carboxylic acid comprises a backbone having no branching at the C2 position; and (ii) a branched C.sub.9 to C.sub.12 carboxylic acid wherein the branched C.sub.9 to C.sub.12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C.sub.4 to C.sub.12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

14. An electrical apparatus comprising the ester composition of claim 1.

15. The electrical apparatus of claim 14, wherein the electrical apparatus is a transformer.

16. A method of using the ester composition of claim 1, comprising preparing a dielectric fluid comprising the ester composition of claim 1 and one or more additives, and introducing the dielectric fluid into an electrical apparatus.

17. The method of claim 16, wherein the electrical apparatus is a transformer.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) The present invention will now be illustrated by way of example.

Example 1

(2) An ester composition suitable for use as a dielectric fluid was prepared by forming esters by reacting pentaerythritol with a mixture of heptanoic acid (C.sub.7), 3,5,5-trimethylhexanoic acid (isononanoic acid) (iC.sub.9) and a mixture of octanoic acid and decanoic acid (C.sub.8/C.sub.10).

(3) The mixture of octanoic acid and decanoic acid (C.sub.8/C.sub.10) used in the method comprised a commercially available mixed acid described as having the composition as set out in Table 1.

(4) TABLE-US-00001 TABLE 1 Component Proportion (% w/w) C.sub.6 <3 C.sub.8 50-65 C.sub.10 35-50 C.sub.12 <3 Other <1

(5) Approximately 900 g of ester composition was prepared according to the following method:

(6) 200 g pentaerythritol was combined with 650 g heptanoic acid (C.sub.7), 243 g 3,5,5-trimethylhexanoic acid (isononanoic acid) (iC.sub.9) and 179 g of a mixture of n-octanoic acid and n-decanoic acid (C.sub.8/C.sub.10). The amounts of acids and alcohol were selected such that the acid mixture was present in 30 molar % excess relative to the alcohol and such that the acids were present relative to one another in the molar percentages set out in Table 2.

(7) TABLE-US-00002 TABLE 2 Acid Molar % C.sub.7 65 iC.sub.9 20 C.sub.8/C.sub.10 mixture 15

(8) Esters were then prepared by refluxing pentaerythritol and the acid mixture at between 248-252 C. under a nitrogen atmosphere for 2.5 hours to produce an ester composition. Water was removed as it was formed using Dean-Stark apparatus.

(9) Following completion of the reflux stage excess acid was removed by vacuum distillation, and the acid value, hydroxyl value and colour of the ester composition was determined. The results are presented in Table 4.

(10) The ester composition was then processed further to prepare a dielectric fluid composition.

(11) The ester composition was then stirred at 80 C. for one hour in the presence of Alumina in an amount of 1 g Alumina for every 0.01 mg KOH/g required to neutralise the reaction mixture to remove any residual acid. As well as Fullers' earth powders F160 (0.45% w/w) and F115FF (0.112% w/w) to clean the sample, and sterically hindered phenolic antioxidant (0.25% w/w).

(12) The composition was then filtered.

(13) A tolutriazole derivative metal deactivator, Irgamet 39, was added to the composition in an amount of 0.005% w/w.

(14) The composition was then degassed for approximately thirty minutes until the moisture content of the composition was below 80 ppm.

(15) Electrical and physical testing was performed on the composition according to the test methods given in Table 3. The results are presented in Table 4.

(16) TABLE-US-00003 TABLE 3 Property Test Method Water content IEC 60814 Acid Value Modified IEC 62021-2 Hydroxyl value IR spectrometer Colour ISO 2211 Tan delta at 90 C. IEC 60247 VR at 90 C. IEC 60247 Breakdown voltage IEC 60156 Viscosity at 40 C. Brookfield DV-I Prime Viscometer Density at 20 C. ISO 3675 COC flash point ISO 2592 COC fire point ISO 2592 PMCC flash point ISO 2719 Pour point Modified ISO 3016

(17) TABLE-US-00004 TABLE 4 Physical and electrical properties Value Water content (ppm) 28 Acid Value (mgKOH/g) 0.013 Hydroxyl (mgKOH/g) 0.8 Colour (HU) 65 Tan delta at 90 C. 0.008 VR at 90 C. (Gm) 32 Breakdown (kV) 79.4 Viscosity at 40 C. (cP) 26.9 Density at 20 C. (g/cm.sup.3) 0.969 COC flash point ( C.) 290 COC Fire 322 point ( C.) PMCC Flash point ( C.) 266 Pour point ( C.) 55

(18) As can be seen from the above the dielectric fluid composition of Example 1 has physical and electrical properties rendering it suitable for use as a dielectric fluid.

Examples 2 to 5

(19) The method of Example 1 was repeated using different ratios of acids. Esters were thus formed by reacting pentaerythritol with a mixture of heptanoic acid (C.sub.7), 3,5,5-trimethyl hexanoic acid (isononanoic acid) (iC.sub.9) and a mixture of octanoic acid and decanoic acid (C.sub.8/C.sub.10). Again, the mixture of octanoic acid and decanoic acid (C.sub.8/C.sub.10) used in the method had the composition as set out in Table 1.

(20) In each example approximately 900 g of ester composition was prepared according to the following method:

(21) Pentaerythritol was combined with heptanoic acid (C.sub.7), 3,5,5-trimethyl hexanoic acid (isononanoic acid) (iC.sub.9) and a mixture of octanoic acid and decanoic acid (C.sub.8/C.sub.10). The amounts of acids and alcohol were selected such that the acid mixture was present in 30 molar % excess relative to the alcohol and such that the acids were present relative to one another in the molar percentages set out in Table 5

(22) TABLE-US-00005 TABLE 5 Example 1 2 3 4 5 Acid Molar % C.sub.7 65 70 60 55 60 iC.sub.9 20 20 20 20 25 C.sub.8/C.sub.10 15 10 20 25 15

(23) In each example esters were then prepared by refluxing pentaerythritol and the acid mixture at between 248-252 C. under a nitrogen atmosphere for between 2 and 3 hours to produce an ester composition. Water was removed as it was formed using Dean-Stark apparatus.

(24) Following completion of the reflux stage the ester composition was processed and tested as described in relation to Example 1. The results are presented in Table 6 together with the results of Example 1.

(25) TABLE-US-00006 TABLE 6 Example 1 2 3 4 5 Acid Ratio C.sub.7 65 70 60 55 60 iC.sub.9 20 20 20 20 25 C.sub.8/C.sub.10 15 10 20 25 15 Physical and electrical properties Water content 28 42 69 68 55 (ppm) Acid Value 0.013 0.015 0.02 0.013 0.024 (mgKOH/g) Hydroxyl 0.8 0.2 <0.5 1.7 2.8 (mgKOH/g) Colour (HU) 65 58 49 68 92 Tan delta at 0.008 0.0084 0.0076 0.0178 90 C. VR at 90 C. 32 32 36.4 15.2 (Gm) Breakdown 79.4 65 71 79 (kV) Viscosity at 26.9 26 26.9 27.8 27.4 40 C. (cP) Density at 0.969 0.967 0.967 0.969 0.968 20 C. (g/cm.sup.3) COC flash 290 274 278 270 282 point ( C.) COC Fire 322 320 320 328 320 point ( C.) PMCC Flash 266 266 261 268 264 point ( C.) Pour point 55 52.5 54 50 54 (C)

(26) It will be appreciated that preferred embodiments of ester compositions according to the present invention may have physical and electrical properties making them suitable for use in dielectric fluid compositions in electrical apparatus such as for example transformers.

(27) It will be appreciated that preferred embodiments of dielectric fluid compositions according to the present invention may have a viscosity at 40 C. which compares favourably to known dielectric fluid compositions.

(28) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(29) All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

(30) Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(31) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.